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Yousof TR, Bouchard CC, Alb M, Lynn EG, Lhoták S, Jiang H, MacDonald M, Li H, Byun JH, Makda Y, Athanasopoulos M, Maclean KN, Cherrington NJ, Naqvi A, Igdoura SA, Krepinsky JC, Steinberg GR, Austin RC. Restoration of the ER stress response protein TDAG51 in hepatocytes mitigates NAFLD in mice. J Biol Chem 2024; 300:105655. [PMID: 38237682 PMCID: PMC10875272 DOI: 10.1016/j.jbc.2024.105655] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Revised: 12/24/2023] [Accepted: 12/27/2023] [Indexed: 02/16/2024] Open
Abstract
Endoplasmic reticulum stress is associated with insulin resistance and the development of nonalcoholic fatty liver disease. Deficiency of the endoplasmic reticulum stress response T-cell death-associated gene 51 (TDAG51) (TDAG51-/-) in mice promotes the development of high-fat diet (HFD)-induced obesity, fatty liver, and hepatic insulin resistance. However, whether this effect is due specifically to hepatic TDAG51 deficiency is unknown. Here, we report that hepatic TDAG51 protein levels are consistently reduced in multiple mouse models of liver steatosis and injury as well as in liver biopsies from patients with liver disease compared to normal controls. Delivery of a liver-specific adeno-associated virus (AAV) increased hepatic expression of a TDAG51-GFP fusion protein in WT, TDAG51-/-, and leptin-deficient (ob/ob) mice. Restoration of hepatic TDAG51 protein was sufficient to increase insulin sensitivity while reducing body weight and fatty liver in HFD fed TDAG51-/- mice and in ob/ob mice. TDAG51-/- mice expressing ectopic TDAG51 display improved Akt (Ser473) phosphorylation, post-insulin stimulation. HFD-fed TDAG51-/- mice treated with AAV-TDAG51-GFP displayed reduced lipogenic gene expression, increased beta-oxidation and lowered hepatic and serum triglycerides, findings consistent with reduced liver weight. Further, AAV-TDAG51-GFP-treated TDAG51-/- mice exhibited reduced hepatic precursor and cleaved sterol regulatory-element binding proteins (SREBP-1 and SREBP-2). In vitro studies confirmed the lipid-lowering effect of TDAG51 overexpression in oleic acid-treated Huh7 cells. These studies suggest that maintaining hepatic TDAG51 protein levels represents a viable therapeutic approach for the treatment of obesity and insulin resistance associated with nonalcoholic fatty liver disease.
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Affiliation(s)
- Tamana R Yousof
- Division of Nephrology, Department of Medicine, The Research Institute of St. Joe's Hamilton and the Hamilton Centre for Kidney Research, McMaster University, Hamilton, Ontario, Canada
| | - Celeste C Bouchard
- Division of Nephrology, Department of Medicine, The Research Institute of St. Joe's Hamilton and the Hamilton Centre for Kidney Research, McMaster University, Hamilton, Ontario, Canada
| | - Mihnea Alb
- Division of Nephrology, Department of Medicine, The Research Institute of St. Joe's Hamilton and the Hamilton Centre for Kidney Research, McMaster University, Hamilton, Ontario, Canada
| | - Edward G Lynn
- Division of Nephrology, Department of Medicine, The Research Institute of St. Joe's Hamilton and the Hamilton Centre for Kidney Research, McMaster University, Hamilton, Ontario, Canada
| | - Sárka Lhoták
- Division of Nephrology, Department of Medicine, The Research Institute of St. Joe's Hamilton and the Hamilton Centre for Kidney Research, McMaster University, Hamilton, Ontario, Canada
| | - Hua Jiang
- Department of Pediatrics, School of Medicine, University of Colorado Health Sciences Center, Aurora, Colorado, USA
| | - Melissa MacDonald
- Division of Nephrology, Department of Medicine, The Research Institute of St. Joe's Hamilton and the Hamilton Centre for Kidney Research, McMaster University, Hamilton, Ontario, Canada
| | - Hui Li
- Department of Pharmacology and Toxicology, University of Arizona, Tucson, Arizona, USA
| | - Jae H Byun
- Division of Nephrology, Department of Medicine, The Research Institute of St. Joe's Hamilton and the Hamilton Centre for Kidney Research, McMaster University, Hamilton, Ontario, Canada
| | - Yumna Makda
- Division of Nephrology, Department of Medicine, The Research Institute of St. Joe's Hamilton and the Hamilton Centre for Kidney Research, McMaster University, Hamilton, Ontario, Canada
| | | | - Kenneth N Maclean
- Department of Pediatrics, School of Medicine, University of Colorado Health Sciences Center, Aurora, Colorado, USA
| | - Nathan J Cherrington
- Department of Pharmacology and Toxicology, University of Arizona, Tucson, Arizona, USA
| | - Asghar Naqvi
- Department of Pathology and Molecular Medicine, St. Joseph's Healthcare Hamilton, McMaster University, Hamilton, Ontario, Canada
| | - Suleiman A Igdoura
- Department of Biology, McMaster University, Hamilton, Ontario, Canada; Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Joan C Krepinsky
- Division of Nephrology, Department of Medicine, The Research Institute of St. Joe's Hamilton and the Hamilton Centre for Kidney Research, McMaster University, Hamilton, Ontario, Canada; Centre for Metabolism, Obesity and Diabetes Research, McMaster University, Hamilton, Ontario, Canada
| | - Gregory R Steinberg
- Centre for Metabolism, Obesity and Diabetes Research, McMaster University, Hamilton, Ontario, Canada; Division of Endocrinology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Richard C Austin
- Division of Nephrology, Department of Medicine, The Research Institute of St. Joe's Hamilton and the Hamilton Centre for Kidney Research, McMaster University, Hamilton, Ontario, Canada; Centre for Metabolism, Obesity and Diabetes Research, McMaster University, Hamilton, Ontario, Canada.
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2
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Okun S, Peek A, Igdoura SA. Neuraminidase 4 (NEU4): new biological and physiological player. Glycobiology 2023; 33:182-187. [PMID: 36728702 DOI: 10.1093/glycob/cwad008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Revised: 12/20/2022] [Accepted: 01/26/2023] [Indexed: 02/03/2023] Open
Abstract
Sialidases are found in viruses, bacteria, fungi, avians, and mammals. Mammalian sialidases differ in their specificity, optimum pH, subcellular localization, and tissue expression. To date, four genes encoding mammalian sialidases (NEU1-4) have been cloned. This review examines the functional impact of NEU4 sialidase on complex physiological and cellular processes. The intracellular localization and trafficking of NEU4 and its potential target molecules are discussed along with its impact on cancer, lysosomal storage disease, and cellular differentiation. Modulation of NEU4 expression may be essential not only for the breakdown of sialylated glycoconjugates, but also in the activation or inactivation of functionally important cellular events.
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Affiliation(s)
- Sarah Okun
- Department of Biology , McMaster University, Hamilton, ON L8S 4K1, Canada
| | - Allyson Peek
- Department of Biology , McMaster University, Hamilton, ON L8S 4K1, Canada
| | - Suleiman A Igdoura
- Department of Biology , McMaster University, Hamilton, ON L8S 4K1, Canada
- Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON L8S 4K1, Canada
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3
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Fuller MT, Dadoo O, Xiong T, Chivukula P, MacDonald ME, Lee SK, Austin RC, Igdoura SA, Trigatti BL. Extensive diet-induced atherosclerosis in scavenger receptor class B type 1-deficient mice is associated with substantial leukocytosis and elevated vascular cell adhesion molecule-1 expression in coronary artery endothelium. Front Physiol 2023; 13:1023397. [PMID: 36714321 PMCID: PMC9877335 DOI: 10.3389/fphys.2022.1023397] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2022] [Accepted: 12/21/2022] [Indexed: 01/14/2023] Open
Abstract
High levels of low density lipoprotein (LDL) cholesterol and low levels of high density lipoprotein (HDL) cholesterol are risk factors for cardiovascular disease. Mice that lack genes involved in the clearance of LDL from the bloodstream, such as the LDL receptor and apolipoprotein E, are widely used models of experimental atherosclerosis. Conversely, mice that lack the HDL receptor, scavenger receptor class B type I, and therefore have disrupted HDL functionality, also develop diet-inducible atherosclerosis but are a seldom-used disease model. In this study, we compared atherosclerosis and associated phenotypes in scavenger receptor class B type I knockout mice with those of wild type, LDL receptor knockout, and apolipoprotein E knockout mice after 20 weeks of being fed an atherogenic diet containing sodium cholate. We found that while scavenger receptor class B type I knockout mice had substantially lower plasma cholesterol than LDL receptor and apolipoprotein E knockout mice, they developed atherosclerotic plaques with similar sizes and compositions in their aortic sinuses, and more extensive atherosclerosis in their descending aortas and coronary arteries. This was associated with elevated tumor necrosis factor alpha levels in scavenger receptor class B type I knockout mice compared to wild type and LDL receptor knockout mice, and lymphocytosis, monocytosis, and elevated vascular cell adhesion molecule expression in coronary artery endothelial cells compared to the other mice examined. We conclude that extensive atherosclerosis in arteries that are not generally susceptible to atherosclerosis in scavenger receptor class B type I knockout mice is driven by factors in addition to hypercholesterolemia, including inflammation, dysregulation of the immune system and increased sensitivity of endothelial cells in arteries that are normally resistant to atherosclerosis. Scavenger receptor class B type I knockout mice fed a cholate containing atherogenic diet may prove to be a useful model to study mechanisms of atherosclerosis and evaluate treatments that rely on intact LDL clearance pathways.
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Affiliation(s)
- Mark T. Fuller
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada,Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, ON, Canada
| | - Omid Dadoo
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada,Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, ON, Canada
| | - Ting Xiong
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada,Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, ON, Canada
| | - Pardh Chivukula
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada,Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, ON, Canada
| | - Melissa E. MacDonald
- Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, ON, Canada
| | - Samuel K. Lee
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada,Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, ON, Canada
| | - Richard C. Austin
- Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, ON, Canada,Department of Medicine, Division of Nephrology, The Research Institute of St. Joe’s Hamilton and the Hamilton Center for Kidney Research, McMaster University, Hamilton, ON, Canada
| | - Suleiman A. Igdoura
- Department of Biology and Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON, Canada
| | - Bernardo L. Trigatti
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada,Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, ON, Canada,*Correspondence: Bernardo L. Trigatti,
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Byun JH, Lebeau PF, Platko K, Carlisle RE, Faiyaz M, Chen J, MacDonald ME, Makda Y, Yousof T, Lynn EG, Dickhout JG, Krepinsky JC, Weaver F, Igdoura SA, Seidah NG, Austin RC. Inhibitory Antibodies against PCSK9 Reduce Surface CD36 and Mitigate Diet-Induced Renal Lipotoxicity. Kidney360 2022; 3:1394-1410. [PMID: 36176646 PMCID: PMC9416829 DOI: 10.34067/kid.0007022021] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Accepted: 04/26/2022] [Indexed: 01/11/2023]
Abstract
Background PCSK9 modulates the uptake of circulating lipids through a range of receptors, including the low-density lipoprotein receptor (LDLR) and CD36. In the kidney, CD36 is known to contribute to renal injury through pro-inflammatory and -fibrotic pathways. In this study, we sought to investigate the role of PCSK9 in modulating renal lipid accumulation and injury through CD36 using a high fat diet (HFD)-induced murine model. Methods The effect of PCSK9 on the expression of CD36 and intracellular accumulation of lipid was examined in cultured renal cells and in the kidneys of male C57BL/6J mice. The effect of these findings was subsequently explored in a model of HFD-induced renal injury in Pcsk9 -/- and Pcsk9 +/+ littermate control mice on a C57BL/6J background. Results In the absence of PCSK9, we observed heightened CD36 expression levels, which increased free fatty acid (FFA) uptake in cultured renal tubular cells. As a result, PCSK9 deficiency was associated with an increase in long-chain saturated FFA-induced ER stress. Consistent with these observations, Pcsk9-/- mice fed a HFD displayed elevated ER stress, inflammation, fibrosis, and renal injury relative to HFD-fed control mice. In contrast to Pcsk9-/- mice, pretreatment of WT C57BL/6J mice with evolocumab, an anti-PCSK9 monoclonal antibody (mAb) that binds to and inhibits the function of circulating PCSK9, protected against HFD-induced renal injury in association with reducing cell surface CD36 expression on renal epithelia. Conclusions We report that circulating PCSK9 modulates renal lipid uptake in a manner dependent on renal CD36. In the context of increased dietary fat consumption, the absence of circulating PCSK9 may promote renal lipid accumulation and subsequent renal injury. However, although the administration of evolocumab blocks the interaction of PCSK9 with the LDLR, this evolocumab/PCSK9 complex can still bind CD36, thereby protecting against HFD-induced renal lipotoxicity.
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Affiliation(s)
- Jae Hyun Byun
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
| | - Paul F. Lebeau
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
| | - Khrystyna Platko
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
| | - Rachel E. Carlisle
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
| | - Mahi Faiyaz
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
| | - Jack Chen
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
| | - Melissa E. MacDonald
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
| | - Yumna Makda
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
| | - Tamana Yousof
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
| | - Edward G. Lynn
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
| | - Jeffrey G. Dickhout
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
| | - Joan C. Krepinsky
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
| | - Fiona Weaver
- Department of Biology and Pathology and Molecular Medicine, McMaster University, Hamilton, Canada
| | - Suleiman A. Igdoura
- Department of Biology and Pathology and Molecular Medicine, McMaster University, Hamilton, Canada
| | - Nabil G. Seidah
- Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal, University of Montreal, Montreal, Canada
| | - Richard C. Austin
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe’s Hamilton and The Hamilton Centre for Kidney Research, Hamilton, Canada
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5
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Lebeau PF, Byun JH, Platko K, Saliba P, Sguazzin M, MacDonald ME, Paré G, Steinberg GR, Janssen LJ, Igdoura SA, Tarnopolsky MA, Wayne Chen SR, Seidah NG, Magolan J, Austin RC. Caffeine blocks SREBP2-induced hepatic PCSK9 expression to enhance LDLR-mediated cholesterol clearance. Nat Commun 2022; 13:770. [PMID: 35140212 PMCID: PMC8828868 DOI: 10.1038/s41467-022-28240-9] [Citation(s) in RCA: 39] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Accepted: 01/05/2022] [Indexed: 01/06/2023] Open
Abstract
Evidence suggests that caffeine (CF) reduces cardiovascular disease (CVD) risk. However, the mechanism by which this occurs has not yet been uncovered. Here, we investigated the effect of CF on the expression of two bona fide regulators of circulating low-density lipoprotein cholesterol (LDLc) levels; the proprotein convertase subtilisin/kexin type 9 (PCSK9) and the low-density lipoprotein receptor (LDLR). Following the observation that CF reduced circulating PCSK9 levels and increased hepatic LDLR expression, additional CF-derived analogs with increased potency for PCSK9 inhibition compared to CF itself were developed. The PCSK9-lowering effect of CF was subsequently confirmed in a cohort of healthy volunteers. Mechanistically, we demonstrate that CF increases hepatic endoplasmic reticulum (ER) Ca2+ levels to block transcriptional activation of the sterol regulatory element-binding protein 2 (SREBP2) responsible for the regulation of PCSK9, thereby increasing the expression of the LDLR and clearance of LDLc. Our findings highlight ER Ca2+ as a master regulator of cholesterol metabolism and identify a mechanism by which CF may protect against CVD.
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Affiliation(s)
- Paul F Lebeau
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe's Hamilton and the Hamilton Center for Kidney Research, Hamilton, ON, L8N 4A6, Canada
| | - Jae Hyun Byun
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe's Hamilton and the Hamilton Center for Kidney Research, Hamilton, ON, L8N 4A6, Canada
| | - Khrystyna Platko
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe's Hamilton and the Hamilton Center for Kidney Research, Hamilton, ON, L8N 4A6, Canada
| | - Paul Saliba
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, L8S 4L8, Canada
| | - Matthew Sguazzin
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, L8S 4L8, Canada
| | - Melissa E MacDonald
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe's Hamilton and the Hamilton Center for Kidney Research, Hamilton, ON, L8N 4A6, Canada
| | - Guillaume Paré
- Population Health Research Institute, McMaster University, Hamilton, ON, L8L 2X2, Canada.,The Departments of Medicine, Epidemiology and Pathology, McMaster University, Hamilton, ON, L8L 2X2, Canada.,The Thrombosis and Atherosclerosis Research Institute (TaARI), Department of Medicine, David Braley Research Institute, McMaster University, Hamilton, L8L 2X2, Canada
| | - Gregory R Steinberg
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, L8S 4L8, Canada.,Centre for Metabolism, Obesity and Diabetes Research, Department of Medicine, McMaster University, Hamilton, ON, L8S 4L8, Canada
| | - Luke J Janssen
- Firestone Institute for Respiratory Health, St. Joseph's Hospital, Hamilton, ON, L8S 4K1, Canada
| | - Suleiman A Igdoura
- Department of Biology and Pathology, McMaster University, Hamilton, ON, L8S 4K1, Canada
| | - Mark A Tarnopolsky
- Department of Medicine/Neurology, McMaster University, Hamilton, ON, L8N 3Z5, Canada.,Department of Pediatrics, McMaster University, Hamilton, ON, L8S 4K1, Canada
| | - S R Wayne Chen
- Libin Cardiovascular Institute of Alberta, Department of Physiology and Pharmacology, University of Calgary, Calgary, AB, T2N 2T9, Canada
| | - Nabil G Seidah
- Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal, affiliated to the University of Montreal, Montreal, QC, H2W 1R7, Canada
| | - Jakob Magolan
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, L8S 4L8, Canada
| | - Richard C Austin
- Department of Medicine, Division of Nephrology, McMaster University, The Research Institute of St. Joe's Hamilton and the Hamilton Center for Kidney Research, Hamilton, ON, L8N 4A6, Canada. .,The Thrombosis and Atherosclerosis Research Institute (TaARI), Department of Medicine, David Braley Research Institute, McMaster University, Hamilton, L8L 2X2, Canada.
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6
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Platko K, Lebeau PF, Gyulay G, Lhoták Š, MacDonald ME, Pacher G, Hyun Byun J, Boivin FJ, Igdoura SA, Cutz JC, Bridgewater D, Ingram AJ, Krepinsky JC, Austin RC. TDAG51 (T-Cell Death-Associated Gene 51) Is a Key Modulator of Vascular Calcification and Osteogenic Transdifferentiation of Arterial Smooth Muscle Cells. Arterioscler Thromb Vasc Biol 2020; 40:1664-1679. [PMID: 32434409 DOI: 10.1161/atvbaha.119.313779] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
OBJECTIVE Cardiovascular disease is the primary cause of mortality in patients with chronic kidney disease. Vascular calcification (VC) in the medial layer of the vessel wall is a unique and prominent feature in patients with advanced chronic kidney disease and is now recognized as an important predictor and independent risk factor for cardiovascular and all-cause mortality in these patients. VC in chronic kidney disease is triggered by the transformation of vascular smooth muscle cells (VSMCs) into osteoblasts as a consequence of elevated circulating inorganic phosphate (Pi) levels, due to poor kidney function. The objective of our study was to investigate the role of TDAG51 (T-cell death-associated gene 51) in the development of medial VC. METHODS AND RESULTS Using primary mouse and human VSMCs, we found that TDAG51 is induced in VSMCs by Pi and is expressed in the medial layer of calcified human vessels. Furthermore, the transcriptional activity of RUNX2 (Runt-related transcription factor 2), a well-established driver of Pi-mediated VC, is reduced in TDAG51-/- VSMCs. To explain these observations, we identified that TDAG51-/- VSMCs express reduced levels of the type III sodium-dependent Pi transporter, Pit-1, a solute transporter, a solute transporter, a solute transporter responsible for cellular Pi uptake. Significantly, in response to hyperphosphatemia induced by vitamin D3, medial VC was attenuated in TDAG51-/- mice. CONCLUSIONS Our studies highlight TDAG51 as an important mediator of Pi-induced VC in VSMCs through the downregulation of Pit-1. As such, TDAG51 may represent a therapeutic target for the prevention of VC and cardiovascular disease in patients with chronic kidney disease.
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Affiliation(s)
- Khrystyna Platko
- From the Division of Nephrology, Department of Medicine (K.P., P.F.L., G.G., Š.L., M.E.M., G.P., J.H.B., A.J.I., J.C.K., R.C.A.), McMaster University, and The Research Institute of St. Joseph's Hamilton, ON, Canada
| | - Paul F Lebeau
- From the Division of Nephrology, Department of Medicine (K.P., P.F.L., G.G., Š.L., M.E.M., G.P., J.H.B., A.J.I., J.C.K., R.C.A.), McMaster University, and The Research Institute of St. Joseph's Hamilton, ON, Canada
| | - Gabriel Gyulay
- From the Division of Nephrology, Department of Medicine (K.P., P.F.L., G.G., Š.L., M.E.M., G.P., J.H.B., A.J.I., J.C.K., R.C.A.), McMaster University, and The Research Institute of St. Joseph's Hamilton, ON, Canada
| | - Šárka Lhoták
- From the Division of Nephrology, Department of Medicine (K.P., P.F.L., G.G., Š.L., M.E.M., G.P., J.H.B., A.J.I., J.C.K., R.C.A.), McMaster University, and The Research Institute of St. Joseph's Hamilton, ON, Canada
| | - Melissa E MacDonald
- From the Division of Nephrology, Department of Medicine (K.P., P.F.L., G.G., Š.L., M.E.M., G.P., J.H.B., A.J.I., J.C.K., R.C.A.), McMaster University, and The Research Institute of St. Joseph's Hamilton, ON, Canada
| | - Giusepina Pacher
- From the Division of Nephrology, Department of Medicine (K.P., P.F.L., G.G., Š.L., M.E.M., G.P., J.H.B., A.J.I., J.C.K., R.C.A.), McMaster University, and The Research Institute of St. Joseph's Hamilton, ON, Canada
| | - Jae Hyun Byun
- From the Division of Nephrology, Department of Medicine (K.P., P.F.L., G.G., Š.L., M.E.M., G.P., J.H.B., A.J.I., J.C.K., R.C.A.), McMaster University, and The Research Institute of St. Joseph's Hamilton, ON, Canada
| | - Felix J Boivin
- Department of Pathology and Molecular Medicine (F.J.B., S.A.I., D.B.), McMaster University Medical Centre, Hamilton, ON, Canada
| | - Suleiman A Igdoura
- Department of Pathology and Molecular Medicine (F.J.B., S.A.I., D.B.), McMaster University Medical Centre, Hamilton, ON, Canada.,Department of Biology (S.A.I.), McMaster University Medical Centre, Hamilton, ON, Canada
| | - Jean-Claude Cutz
- Department of Pathology and Molecular Medicine (J.-C.C.), McMaster University, and The Research Institute of St. Joseph's Hamilton, ON, Canada
| | - Darren Bridgewater
- Department of Pathology and Molecular Medicine (F.J.B., S.A.I., D.B.), McMaster University Medical Centre, Hamilton, ON, Canada
| | - Alistair J Ingram
- From the Division of Nephrology, Department of Medicine (K.P., P.F.L., G.G., Š.L., M.E.M., G.P., J.H.B., A.J.I., J.C.K., R.C.A.), McMaster University, and The Research Institute of St. Joseph's Hamilton, ON, Canada
| | - Joan C Krepinsky
- From the Division of Nephrology, Department of Medicine (K.P., P.F.L., G.G., Š.L., M.E.M., G.P., J.H.B., A.J.I., J.C.K., R.C.A.), McMaster University, and The Research Institute of St. Joseph's Hamilton, ON, Canada
| | - Richard C Austin
- From the Division of Nephrology, Department of Medicine (K.P., P.F.L., G.G., Š.L., M.E.M., G.P., J.H.B., A.J.I., J.C.K., R.C.A.), McMaster University, and The Research Institute of St. Joseph's Hamilton, ON, Canada
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7
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Lebeau PF, Byun JH, Platko K, Al-Hashimi AA, Lhoták Š, MacDonald ME, Mejia-Benitez A, Prat A, Igdoura SA, Trigatti B, Maclean KN, Seidah NG, Austin RC. Pcsk9 knockout exacerbates diet-induced non-alcoholic steatohepatitis, fibrosis and liver injury in mice. JHEP Rep 2019; 1:418-429. [PMID: 32039393 PMCID: PMC7005770 DOI: 10.1016/j.jhepr.2019.10.009] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/13/2019] [Revised: 10/16/2019] [Accepted: 10/24/2019] [Indexed: 12/15/2022] Open
Abstract
The fatty acid translocase, also known as CD36, is a well-established scavenger receptor for fatty acid (FA) uptake and is abundantly expressed in many metabolically active tissues. In the liver, CD36 is known to contribute to the progression of non-alcoholic fatty liver disease and to the more severe non-alcoholic steatohepatitis, by promoting triglyceride accumulation and subsequent lipid-induced endoplasmic reticulum (ER) stress. Given the recent discovery that the hepatocyte-secreted proprotein convertase subtilisin/kexin type 9 (PCSK9) blocks CD36 expression, we sought to investigate the role of PCSK9 in liver fat accumulation and injury in response to saturated FAs and in a mouse model of diet-induced hepatic steatosis. Methods In this study, we investigated the role of PCSK9 on the uptake and accumulation of FAs, as well as FA-induced toxicity, in a variety of cultured hepatocytes. Diet-induced hepatic steatosis and liver injury were also assessed in Pcsk9-/- mice. Results Our results indicate that PCSK9 deficiency in cultured hepatocytes increased the uptake and accumulation of saturated and unsaturated FAs. In the presence of saturated FAs, PCSK9 also protected cultured hepatocytes from ER stress and cytotoxicity. In line with these findings, a metabolic challenge using a high-fat diet caused severe hepatic steatosis, ER stress inflammation and fibrosis in the livers of Pcsk9-/- mice compared to controls. Given that inhibition of CD36 ablated the observed accumulation of lipid in vitro and in vivo, our findings also highlight CD36 as a strong contributor to steatosis and liver injury in the context of PCSK9 deficiency. Conclusions Collectively, our findings demonstrate that PCSK9 regulates hepatic triglyceride content in a manner dependent on CD36. In the presence of excess dietary fats, PCSK9 can also protect against hepatic steatosis and liver injury. Lay summary The proprotein convertase subtilisin/kexin type 9 (PCSK9) is a circulating protein known to reduce the abundance of receptors on the surface of liver cells charged with the task of lipid uptake from the circulation. Although PCSK9 deficiency is known to cause lipid accumulation in mice and in cultured cells, the toxicological implications of this observation have not yet been reported. In this study, we demonstrate that PCSK9 can protect against cytotoxicity in cultured liver cells treated with a saturated fatty acid and we also show that Pcsk9 knockout mice develop increased liver injury in response to a high-fat diet. PCSK9 reduces the expression of hepatic CD36 in mice. CD36 is a known driver of liver steatosis and injury. PCSK9 protects from palmitate-induced ER stress and ROS in cultured hepatocytes. High-fat diet causes severe hepatic steatosis, ER stress, inflammation and insulin resistance in Pcsk9-/- mice. PCSK9 expression protects mice from diet-induced liver injury.
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Affiliation(s)
- Paul F. Lebeau
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph’s Healthcare Hamilton, Ontario L8N 4A6, Canada
| | - Jae Hyun Byun
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph’s Healthcare Hamilton, Ontario L8N 4A6, Canada
| | - Khrystyna Platko
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph’s Healthcare Hamilton, Ontario L8N 4A6, Canada
| | - Ali A. Al-Hashimi
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph’s Healthcare Hamilton, Ontario L8N 4A6, Canada
| | - Šárka Lhoták
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph’s Healthcare Hamilton, Ontario L8N 4A6, Canada
| | - Melissa E. MacDonald
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph’s Healthcare Hamilton, Ontario L8N 4A6, Canada
| | - Aurora Mejia-Benitez
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph’s Healthcare Hamilton, Ontario L8N 4A6, Canada
| | - Annik Prat
- Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal, affiliated to the University of Montreal, Montreal, Quebec H2W 1R7, Canada
| | - Suleiman A. Igdoura
- Department of Biology and Pathology, McMaster University, Hamilton, Ontario, L8S 4K1, Canada
| | - Bernardo Trigatti
- Thrombosis and Atherosclerosis Research Institute (TaARI), Hamilton Health Sciences and McMaster University, Hamilton, Ontario L8L 2X2, Canada
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario L8S 4L8, Canada
| | - Kenneth N. Maclean
- the Department of Pediatrics, University of Colorado School of Medicine, Aurora, Colorado, USA, 80045
| | - Nabil G. Seidah
- Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal, affiliated to the University of Montreal, Montreal, Quebec H2W 1R7, Canada
| | - Richard C. Austin
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph’s Healthcare Hamilton, Ontario L8N 4A6, Canada
- Corresponding author. Address: Dr. Richard C. Austin, 50 Charlton Ave East, Room T-3313, Hamilton, Ontario, L8N 4A6. Tel.: 905-522-1155 x35175; Fax: 905-540-6589.
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8
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White EJ, Gyulay G, Lhoták Š, Szewczyk MM, Chong T, Fuller MT, Dadoo O, Fox-Robichaud AE, Austin RC, Trigatti BL, Igdoura SA. Sialidase down-regulation reduces non-HDL cholesterol, inhibits leukocyte transmigration, and attenuates atherosclerosis in ApoE knockout mice. J Biol Chem 2018; 293:14689-14706. [PMID: 30097518 DOI: 10.1074/jbc.ra118.004589] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Revised: 08/01/2018] [Indexed: 01/01/2023] Open
Abstract
Atherosclerosis is a complex disease that involves alterations in lipoprotein metabolism and inflammation. Protein and lipid glycosylation events, such as sialylation, contribute to the development of atherosclerosis and are regulated by specific glycosidases, including sialidases. To evaluate the effect of the sialidase neuraminidase 1 (NEU1) on atherogenesis, here we generated apolipoprotein E (ApoE)-deficient mice that express hypomorphic levels of NEU1 (Neu1hypoApoe-/-). We found that the hypomorphic NEU1 expression in male Apoe-/- mice reduces serum levels of very-low-density lipoprotein (VLDL) and LDL cholesterol, diminishes infiltration of inflammatory cells into lesions, and decreases aortic sinus atherosclerosis. Transplantation of Apoe-/- bone marrow (BM) into Neu1hypoApoe-/- mice significantly increased atherosclerotic lesion development and had no effect on serum lipoprotein levels. Moreover, Neu1hypoApoe-/- mice exhibited a reduction in circulating monocyte and neutrophil levels and had reduced hyaluronic acid and P-selectin adhesion capability on monocytes/neutrophils and T cells. Consistent with these findings, administration of a sialidase inhibitor, 2-deoxy-2,3-dehydro-N-acetylneuraminic acid, had a significant anti-atherogenic effect in the Apoe-/- mice. In summary, the reduction in NEU1 expression or function decreases atherosclerosis in mice via its significant effects on lipid metabolism and inflammatory processes. We conclude that NEU1 may represent a promising target for managing atherosclerosis.
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Affiliation(s)
| | | | - Šárka Lhoták
- the Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare and Hamilton Centre for Kidney Research, Hamilton, Ontario L8N 4A6, Canada
| | | | | | - Mark T Fuller
- Biochemistry and Biomedical Sciences.,Thrombosis and Atherosclerosis Research Institute, McMaster University, Hamilton, Ontario L8S 4K1 and
| | - Omid Dadoo
- Biochemistry and Biomedical Sciences.,Thrombosis and Atherosclerosis Research Institute, McMaster University, Hamilton, Ontario L8S 4K1 and
| | - Alison E Fox-Robichaud
- the Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare and Hamilton Centre for Kidney Research, Hamilton, Ontario L8N 4A6, Canada.,Thrombosis and Atherosclerosis Research Institute, McMaster University, Hamilton, Ontario L8S 4K1 and
| | - Richard C Austin
- the Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare and Hamilton Centre for Kidney Research, Hamilton, Ontario L8N 4A6, Canada.,Thrombosis and Atherosclerosis Research Institute, McMaster University, Hamilton, Ontario L8S 4K1 and
| | - Bernardo L Trigatti
- Biochemistry and Biomedical Sciences.,Thrombosis and Atherosclerosis Research Institute, McMaster University, Hamilton, Ontario L8S 4K1 and
| | - Suleiman A Igdoura
- From the Departments of Biology, .,Pathology and Molecular Medicine, and
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9
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Lebeau P, Platko K, Al‐Hashimi AA, Byun JH, Lhotak S, Holzapfel N, Gyulay G, Igdoura SA, Cool DR, Trigatti B, Seidah NG, Austin RC. Loss‐of‐function PCSK9 mutants evade the unfolded protein response sensor, GRP78, and fail to induce endoplasmic reticulum stress when retained. FASEB J 2018. [DOI: 10.1096/fasebj.2018.32.1_supplement.793.7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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10
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Lebeau P, Platko K, Al-Hashimi AA, Byun JH, Lhoták Š, Holzapfel N, Gyulay G, Igdoura SA, Cool DR, Trigatti B, Seidah NG, Austin RC. Loss-of-function PCSK9 mutants evade the unfolded protein response sensor GRP78 and fail to induce endoplasmic reticulum stress when retained. J Biol Chem 2018; 293:7329-7343. [PMID: 29593095 DOI: 10.1074/jbc.ra117.001049] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Revised: 03/15/2018] [Indexed: 01/07/2023] Open
Abstract
The proprotein convertase subtilisin/kexin type-9 (PCSK9) plays a central role in cardiovascular disease (CVD) by degrading hepatic low-density lipoprotein receptor (LDLR). As such, loss-of-function (LOF) PCSK9 variants that fail to exit the endoplasmic reticulum (ER) increase hepatic LDLR levels and lower the risk of developing CVD. The retention of misfolded protein in the ER can cause ER stress and activate the unfolded protein response (UPR). In this study, we investigated whether a variety of LOF PCSK9 variants that are retained in the ER can cause ER stress and hepatic cytotoxicity. Although overexpression of these PCSK9 variants caused an accumulation in the ER of hepatocytes, UPR activation or apoptosis was not observed. Furthermore, ER retention of endogenous PCSK9 via splice switching also failed to induce the UPR. Consistent with these in vitro studies, overexpression of PCSK9 in the livers of mice had no impact on UPR activation. To elucidate the cellular mechanism to explain these surprising findings, we observed that the 94-kDa glucose-regulated protein (GRP94) sequesters PCSK9 away from the 78-kDa glucose-regulated protein (GRP78), the major activator of the UPR. As a result, GRP94 knockdown increased the stability of GRP78-PCSK9 complex and resulted in UPR activation following overexpression of ER-retained PCSK9 variants relative to WT secreted controls. Given that overexpression of these LOF PCSK9 variants does not cause UPR activation under normal homeostatic conditions, therapeutic strategies aimed at blocking the autocatalytic cleavage of PCSK9 in the ER represent a viable strategy for reducing circulating PCSK9.
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Affiliation(s)
- Paul Lebeau
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare Hamilton and Hamilton Center for Kidney Research, Hamilton, Ontario L8N 4A6, Canada
| | - Khrystyna Platko
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare Hamilton and Hamilton Center for Kidney Research, Hamilton, Ontario L8N 4A6, Canada
| | - Ali A Al-Hashimi
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare Hamilton and Hamilton Center for Kidney Research, Hamilton, Ontario L8N 4A6, Canada
| | - Jae Hyun Byun
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare Hamilton and Hamilton Center for Kidney Research, Hamilton, Ontario L8N 4A6, Canada
| | - Šárka Lhoták
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare Hamilton and Hamilton Center for Kidney Research, Hamilton, Ontario L8N 4A6, Canada
| | - Nicholas Holzapfel
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare Hamilton and Hamilton Center for Kidney Research, Hamilton, Ontario L8N 4A6, Canada
| | - Gabriel Gyulay
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare Hamilton and Hamilton Center for Kidney Research, Hamilton, Ontario L8N 4A6, Canada
| | - Suleiman A Igdoura
- Departments of Biology and Pathology, McMaster University, Hamilton, Ontario L8S 4K1, Canada
| | - David R Cool
- Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University, Dayton, Ohio, 45435-0001
| | - Bernardo Trigatti
- Thrombosis and Atherosclerosis Research Institute (TaARI), Hamilton Health Sciences and McMaster University, Hamilton, Ontario L8L 2X2, Canada; Departments of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario L8S 4L8, Canada
| | - Nabil G Seidah
- Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal, University of Montreal, Montreal, Quebec H2W 1R7, Canada
| | - Richard C Austin
- Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare Hamilton and Hamilton Center for Kidney Research, Hamilton, Ontario L8N 4A6, Canada; Thrombosis and Atherosclerosis Research Institute (TaARI), Hamilton Health Sciences and McMaster University, Hamilton, Ontario L8L 2X2, Canada.
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11
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Hooper AWM, Alamilla JF, Venier RE, Gillespie DC, Igdoura SA. Neuronal pentraxin 1 depletion delays neurodegeneration and extends life in Sandhoff disease mice. Hum Mol Genet 2017; 26:661-673. [PMID: 28007910 DOI: 10.1093/hmg/ddw422] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Accepted: 12/09/2016] [Indexed: 01/15/2023] Open
Abstract
GM2 gangliosidoses are a group of lysosomal storage disorders which include Sandhoff disease and Tay-Sachs disease. Dysregulation of glutamate receptors has been recently postulated in the pathology of Sandhoff disease. Glutamate receptor association with neuronal pentraxins 1 and 2, and the neuronal pentraxin receptor facilitates receptor potentiation and synaptic shaping. In this study, we have observed an upregulation of a novel form of neuronal pentraxin 1 (NP1-38) in the brains of a mouse model of Sandhoff disease and Tay-Sachs disease. In order to determine the impact of NP1 on the pathophysiology of Sandhoff disease mouse models, we have generated an Np1-/-Hexb-/- double knockout mouse, and observed extended lifespan, improved righting reflex and enhanced body condition relative to Hexb-/- mice, with no effect on gliosis or apoptotic markers in the CNS. Sandhoff mouse brain slices reveals a reduction in AMPA receptor-mediated currents, and increased variability in total glutamate currents in the CA1 region of the hippocampus; Np1-/-Hexb-/- mice show a correction of this phenotype, suggesting NP1-38 may be interfering with glutamate receptor function. Indeed, some of the psychiatric aspects of Sandhoff and Tay-Sachs disease (particularly late onset) may be attributed to a dysfunctional hippocampal glutamatergic system. Our work highlights a potential role for synaptic proteins, such as NP1 and glutamate receptors in lysosomal storage diseases.
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Affiliation(s)
| | | | | | | | - Suleiman A Igdoura
- Department of Biology.,Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON L8S 4L8, Canada
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12
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White EJ, Trigatti BL, Igdoura SA. Suppression of NK and CD8+ T cells reduces astrogliosis but accelerates cerebellar dysfunction and shortens life span in a mouse model of Sandhoff disease. J Neuroimmunol 2017; 306:55-67. [DOI: 10.1016/j.jneuroim.2017.03.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Revised: 02/15/2017] [Accepted: 03/06/2017] [Indexed: 01/09/2023]
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13
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Abstract
PURPOSE OF REVIEW This review seeks to describe the role of the asialoglycoprotein receptor (ASGR) in modulating non-HDL lipoprotein levels, platelet numbers and atherosclerosis. RECENT FINDINGS Genetics studies have revealed that ASGR haplodeficiency provides protection from atherosclerosis. The potential interactions of ASGR with LDL receptor may regulate the rate of LDL uptake and as a result may lower plasma non-HDL cholesterol. ASGR clears senescent platelets and induces the expression of hepatic thrombopoietin. Platelet activity promotes plaque formation and atherosclerosis. SUMMARY ASGR is a multifunctional receptor specializing in clearance of desialylated glycoproteins and platelets. The impact of ASGR on the levels of plasma non-HDL cholesterol makes it a potential therapeutic target for the treatment of hypercholesterolemia and atherosclerosis.
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Affiliation(s)
- Suleiman A Igdoura
- Departments of Biology and Pathology, McMaster University, Hamilton, Ontario, Canada
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14
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Hooper AWM, Igdoura SA. Bi-phasic gliosis drives neuropathology in a Sandhoff disease mouse model. J Neuroimmunol 2016; 299:19-27. [PMID: 27725117 DOI: 10.1016/j.jneuroim.2016.08.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Revised: 08/02/2016] [Accepted: 08/07/2016] [Indexed: 11/20/2022]
Abstract
Microgliosis and astrogliosis are known to be exacerbating factors in the progression of the lysosomal storage disorder Sandhoff disease. We have also found evidence for excitotoxicity via glutamate receptors in Sandhoff disease. To view the interaction of these cascades, we measured cerebellar expression of markers for gliosis, apoptosis, and excitatory synapses over the disease course in a Sandhoff disease mouse model. We observe a 2-stage model, with initial activation of microgliosis as early as 60days of age, followed by a later onset of astrogliosis, caspase-mediated apoptosis, and reduction in GluR1 at approximately 100days of age. These results implicate immune cells as first responders in Sandhoff disease.
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Affiliation(s)
| | - Suleiman A Igdoura
- Department of Biology, McMaster University, Hamilton, Ont. L8S 4K1, Canada; Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ont. L8S 4L8, Canada.
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15
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Lhoták Š, Gyulay G, Cutz JC, Al-Hashimi A, Trigatti BL, Richards CD, Igdoura SA, Steinberg GR, Bramson J, Ask K, Austin RC. Characterization of Proliferating Lesion-Resident Cells During All Stages of Atherosclerotic Growth. J Am Heart Assoc 2016; 5:JAHA.116.003945. [PMID: 27528409 PMCID: PMC5015311 DOI: 10.1161/jaha.116.003945] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Background Monocyte recruitment leads to accumulation of macrophage foam cells and contributes to atherosclerotic lesion growth. Recent studies have reported that lesion‐resident macrophages can proliferate and represent a major cellular component during lesion development. This study was designed to assess whether the rate of macrophage proliferation changes during well‐established stages of lesion growth and to characterize other populations of proliferating cells within these lesions. Methods and Results Using murine models of atherosclerosis (Apoe−/− and LDLr−/− mice) and human coronary artery lesions, in situ proliferation of lesion‐resident cells at different stages of growth was assessed by staining for Ki67 and bromodeoxyuridine (BrdU). In early lesions, close to half of all actively growing macrophages were proliferating in situ. BrdU pulse labeling allowed for accurate identification of in situ proliferating macrophages compared to those derived from monocyte recruitment. Local macrophage proliferation declined as lesions advanced. Interestingly, intimal inflammatory cell infiltrates containing proliferating T lymphocytes were identified during the active phase of lesion growth and correlated with apoptotic cell death. Inflammatory cell infiltrates were completely resolved in advanced lesions and replaced with the necrotic core. Conclusions Our findings indicate that atherosclerotic lesions contain locally proliferating macrophages primarily during early and intermediate stages of lesion growth. Furthermore, T‐lymphocyte‐enriched inflammatory cell infiltrates represent a novel subset of proliferating cells within the atherosclerotic lesion that correlate with apoptosis and precede the necrotic core. These findings have novel implications in understanding the pathogenesis of atherosclerosis and may implicate proliferating T lymphocytes as a contributing factor to lesion progression and stability.
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Affiliation(s)
- Šárka Lhoták
- Division of Nephrology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada Hamilton Centre for Kidney Research, St. Joseph's Healthcare Hamilton, Hamilton, Ontario, Canada
| | - Gabriel Gyulay
- Division of Nephrology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada Hamilton Centre for Kidney Research, St. Joseph's Healthcare Hamilton, Hamilton, Ontario, Canada
| | - Jean-Claude Cutz
- Departments of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Ali Al-Hashimi
- Division of Nephrology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada Hamilton Centre for Kidney Research, St. Joseph's Healthcare Hamilton, Hamilton, Ontario, Canada
| | - Bernardo L Trigatti
- Departments of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada
| | - Carl D Richards
- Departments of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
| | | | - Gregory R Steinberg
- Division of Endocrinology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Jonathan Bramson
- Departments of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Kjetil Ask
- Departments of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada
| | - Richard C Austin
- Division of Nephrology, Department of Medicine, McMaster University, Hamilton, Ontario, Canada Hamilton Centre for Kidney Research, St. Joseph's Healthcare Hamilton, Hamilton, Ontario, Canada
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16
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Fuller M, Dadoo O, Serkis V, Abutouk D, MacDonald M, Dhingani N, Macri J, Igdoura SA, Trigatti BL. The Effects of Diet on Occlusive Coronary Artery Atherosclerosis and Myocardial Infarction in Scavenger Receptor Class B, Type 1/Low-Density Lipoprotein Receptor Double Knockout Mice. Arterioscler Thromb Vasc Biol 2014; 34:2394-403. [DOI: 10.1161/atvbaha.114.304200] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- Mark Fuller
- From the Departments of Biochemistry and Biomedical Sciences (M.F., O.D., V.S., D.A., M.M., N.D., B.L.T.), Pathology and Molecular Medicine (J.M., S.A.I.), and Biology (S.A.I.), McMaster University, Hamilton, Ontario, Canada; and Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, Ontario, Canada (M.F., O.D., V.S., M.M., N.D., B.L.T.)
| | - Omid Dadoo
- From the Departments of Biochemistry and Biomedical Sciences (M.F., O.D., V.S., D.A., M.M., N.D., B.L.T.), Pathology and Molecular Medicine (J.M., S.A.I.), and Biology (S.A.I.), McMaster University, Hamilton, Ontario, Canada; and Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, Ontario, Canada (M.F., O.D., V.S., M.M., N.D., B.L.T.)
| | - Viktoria Serkis
- From the Departments of Biochemistry and Biomedical Sciences (M.F., O.D., V.S., D.A., M.M., N.D., B.L.T.), Pathology and Molecular Medicine (J.M., S.A.I.), and Biology (S.A.I.), McMaster University, Hamilton, Ontario, Canada; and Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, Ontario, Canada (M.F., O.D., V.S., M.M., N.D., B.L.T.)
| | - Dina Abutouk
- From the Departments of Biochemistry and Biomedical Sciences (M.F., O.D., V.S., D.A., M.M., N.D., B.L.T.), Pathology and Molecular Medicine (J.M., S.A.I.), and Biology (S.A.I.), McMaster University, Hamilton, Ontario, Canada; and Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, Ontario, Canada (M.F., O.D., V.S., M.M., N.D., B.L.T.)
| | - Melissa MacDonald
- From the Departments of Biochemistry and Biomedical Sciences (M.F., O.D., V.S., D.A., M.M., N.D., B.L.T.), Pathology and Molecular Medicine (J.M., S.A.I.), and Biology (S.A.I.), McMaster University, Hamilton, Ontario, Canada; and Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, Ontario, Canada (M.F., O.D., V.S., M.M., N.D., B.L.T.)
| | - Neel Dhingani
- From the Departments of Biochemistry and Biomedical Sciences (M.F., O.D., V.S., D.A., M.M., N.D., B.L.T.), Pathology and Molecular Medicine (J.M., S.A.I.), and Biology (S.A.I.), McMaster University, Hamilton, Ontario, Canada; and Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, Ontario, Canada (M.F., O.D., V.S., M.M., N.D., B.L.T.)
| | - Joseph Macri
- From the Departments of Biochemistry and Biomedical Sciences (M.F., O.D., V.S., D.A., M.M., N.D., B.L.T.), Pathology and Molecular Medicine (J.M., S.A.I.), and Biology (S.A.I.), McMaster University, Hamilton, Ontario, Canada; and Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, Ontario, Canada (M.F., O.D., V.S., M.M., N.D., B.L.T.)
| | - Suleiman A. Igdoura
- From the Departments of Biochemistry and Biomedical Sciences (M.F., O.D., V.S., D.A., M.M., N.D., B.L.T.), Pathology and Molecular Medicine (J.M., S.A.I.), and Biology (S.A.I.), McMaster University, Hamilton, Ontario, Canada; and Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, Ontario, Canada (M.F., O.D., V.S., M.M., N.D., B.L.T.)
| | - Bernardo L. Trigatti
- From the Departments of Biochemistry and Biomedical Sciences (M.F., O.D., V.S., D.A., M.M., N.D., B.L.T.), Pathology and Molecular Medicine (J.M., S.A.I.), and Biology (S.A.I.), McMaster University, Hamilton, Ontario, Canada; and Thrombosis and Atherosclerosis Research Institute, Hamilton Health Sciences and McMaster University, Hamilton, Ontario, Canada (M.F., O.D., V.S., M.M., N.D., B.L.T.)
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Pei Y, Chen X, Aboutouk D, Fuller MT, Dadoo O, Yu P, White EJ, Igdoura SA, Trigatti BL. SR-BI in bone marrow derived cells protects mice from diet induced coronary artery atherosclerosis and myocardial infarction. PLoS One 2013; 8:e72492. [PMID: 23967310 PMCID: PMC3742605 DOI: 10.1371/journal.pone.0072492] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Accepted: 07/17/2013] [Indexed: 01/01/2023] Open
Abstract
SR-BI deficient mice that are also hypomorphic for apolipoprotein E expression develop diet induced occlusive coronary artery atherosclerosis, myocardial infarction and early death. To test the role of SR-BI in bone marrow derived cells, we used bone marrow transplantation to generate SR-BI-null; apoE-hypomorphic mice in which SR-BI expression was restored solely in bone marrow derived cells. SR-BI-null; apoE-hypomorphic mice were transplanted with SR-BI+/+apoE-hypomorphic, or control, autologous SR-BI-null; apoE-hypomorphic bone marrow. Four weeks later, mice were fed a high-fat, high-cholesterol, cholate-containing diet to induce coronary artery atherosclerosis. Mice transplanted with autologous bone marrow developed extensive aortic atherosclerosis and severe occlusive coronary artery atherosclerosis after 4 weeks of feeding. This was accompanied by myocardial fibrosis and increased heart weights. In contrast, restoration of SR-BI expression in bone marrow derived-cells reduced diet induced aortic and coronary artery atherosclerosis, myocardial fibrosis and the increase in heart weights in SR-BI-null; apoE-hypomorphic mice. Restoration of SR-BI in bone marrow derived cells did not, however, affect steady state lipoprotein cholesterol levels, but did reduce plasma levels of IL-6. Monocytes from SR-BI-null mice exhibited a greater capacity to bind to VCAM-1 and ICAM-1 than those from SR-BI+/+ mice. Furthermore, restoration of SR-BI expression in bone marrow derived cells attenuated monocyte recruitment into atherosclerotic plaques in mice fed high fat, high cholesterol cholate containing diet. These data demonstrate directly that SR-BI in bone marrow-derived cells protects against both aortic and CA atherosclerosis.
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Affiliation(s)
- Ying Pei
- Department of Biochemistry and Biomedical Sciences and Thrombosis and Atherosclerosis Research Institute, McMaster University, Hamilton, Ontario, Canada
| | - Xing Chen
- Department of Biochemistry and Biomedical Sciences and Thrombosis and Atherosclerosis Research Institute, McMaster University, Hamilton, Ontario, Canada
| | - Dina Aboutouk
- Department of Biochemistry and Biomedical Sciences and Thrombosis and Atherosclerosis Research Institute, McMaster University, Hamilton, Ontario, Canada
| | - Mark T. Fuller
- Department of Biochemistry and Biomedical Sciences and Thrombosis and Atherosclerosis Research Institute, McMaster University, Hamilton, Ontario, Canada
| | - Omid Dadoo
- Department of Biochemistry and Biomedical Sciences and Thrombosis and Atherosclerosis Research Institute, McMaster University, Hamilton, Ontario, Canada
| | - Pei Yu
- Department of Biochemistry and Biomedical Sciences and Thrombosis and Atherosclerosis Research Institute, McMaster University, Hamilton, Ontario, Canada
| | - Elizabeth J. White
- Department of Biology and Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Suleiman A. Igdoura
- Department of Biology and Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Bernardo L. Trigatti
- Department of Biochemistry and Biomedical Sciences and Thrombosis and Atherosclerosis Research Institute, McMaster University, Hamilton, Ontario, Canada
- * E-mail:
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Abo-ouf H, Hooper AWM, White EJ, Janse van Rensburg HJ, Trigatti BL, Igdoura SA. Deletion of tumor necrosis factor-α ameliorates neurodegeneration in Sandhoff disease mice. Hum Mol Genet 2013; 22:3960-75. [DOI: 10.1093/hmg/ddt250] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Affiliation(s)
| | | | | | | | | | - Suleiman A Igdoura
- Department of Biology,
- Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada
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19
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Al-Jarallah A, Igdoura F, Zhang Y, Tenedero CB, White EJ, MacDonald ME, Igdoura SA, Trigatti BL. The effect of pomegranate extract on coronary artery atherosclerosis in SR-BI/APOE double knockout mice. Atherosclerosis 2013; 228:80-9. [PMID: 23528829 DOI: 10.1016/j.atherosclerosis.2013.02.025] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Revised: 02/08/2013] [Accepted: 02/19/2013] [Indexed: 02/05/2023]
Abstract
OBJECTIVES To examine the effects of pomegranate extract on inflammation and oxidative stress and the development of spontaneous occlusive coronary artery atherosclerosis in the SR-BI/apoE double knockout mouse model of coronary heart disease. METHODS AND RESULTS SR-BI/apoE double KO mice were treated for two weeks with pomegranate extract via drinking water, beginning at three weeks of age. Treatment with pomegranate extract increased cholesterol ester content and reduced the abnormally high unesterified/esterified cholesterol ratio of VLDL-sized lipoproteins. Despite the increase in cholesterol levels associated with VLDL-sized particles, pomegranate extract treatment reduced the size of atherosclerotic plaques in the aortic sinus and reduced the proportion of coronary arteries with occlusive atherosclerotic plaques. Treatment with pomegranate extract resulted in substantial reductions in levels of oxidative stress and monocyte chemotactic protein-1 in atherosclerotic plaques in the aortic sinus and coronary arteries. In addition, treatment with pomegranate extract reduced lipid accumulation, macrophage infiltration, levels of monocyte chemotactic protein-1 and fibrosis in the myocardium, attenuated cardiac enlargement and the development of ECG abnormalities in SR-BI/apoE double KO mice. CONCLUSION Pomegranate extract reduced aortic sinus and coronary artery atherosclerosis in SR-BI/apoE dKO mice. The atheroprotective effects of pomegranate extract appear to involve reduced oxidative stress and inflammation in the vessel wall despite unaltered systemic markers of inflammation and increased lipoprotein cholesterol in these mice.
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Affiliation(s)
- Aishah Al-Jarallah
- Department of Biochemistry and Biomedical Sciences, McMaster University, 1280 Main St W, Hamilton, Ontario, Canada L8S 4L8
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20
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Yang A, Gyulay G, Mitchell M, White E, Trigatti BL, Igdoura SA. Hypomorphic sialidase expression decreases serum cholesterol by downregulation of VLDL production in mice. J Lipid Res 2012; 53:2573-85. [PMID: 22984145 DOI: 10.1194/jlr.m027300] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Lipoprotein metabolism is an important contributing factor in the development and progression of atherosclerosis. Plasma lipoproteins and their receptors are heavily glycosylated and sialylated, and levels of sialic acids modulate their biological functions. Sialylation is controlled by the activities of sialyltranferases and sialidases. To address the impact of sialidase (neu1) activity on lipoprotein metabolism, we have generated a mouse model with a hypomorphic neu1 allele (B6.SM) that displays reduced sialidase expression and sialidase activity. The objectives of this study are to determine the impact of sialidase on the rate of hepatic lipoprotein secretion and lipoprotein uptake. Our results indicate that hepatic levels of cholesterol and triglycerides are significantly higher in B6.SM mice compared with C57Bl/6 mice; however, VLDL-triglyceride production rate is lower. In addition, B6.SM mice show significantly lower levels of hepatic microsomal triglyceride transfer protein (MTP) and active sterol-regulatory element binding protein (SREBP)-2 but higher levels of diglyceride acyltransferase (DGAT)2; these are all indicative of increased hepatic lipid storage. Rescue of sialidase activity in hypomorphic sialidase mice using helper-dependent adenovirus resulted in increased VLDL production and an increase in MTP levels. Furthermore, hypomorphic sialidase expression results in stabilization of hepatic LDL receptor (LDLR) protein expression, which enhances LDL uptake. These findings provide novel evidence for a central role of sialidase in the cross talk between the uptake and production of lipoproteins.
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Affiliation(s)
- Abraham Yang
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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21
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O'Leary EM, Igdoura SA. The therapeutic potential of pharmacological chaperones and proteosomal inhibitors, Celastrol and MG132 in the treatment of sialidosis. Mol Genet Metab 2012; 107:173-85. [PMID: 22898113 DOI: 10.1016/j.ymgme.2012.07.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/18/2012] [Revised: 07/12/2012] [Accepted: 07/12/2012] [Indexed: 10/28/2022]
Abstract
Sialidosis is an autosomal recessive disorder caused by a dysfunctional Sialidase enzyme. Categorised into two phenotypes, Sialidosis type I and II, Sialidosis is a highly heterogeneous disorder with varying ages of onset and pathologies. Currently, there is no viable therapy for the treatment of Sialidosis patients. At the molecular level, cells from Sialidosis patients with compound heterozygous mutations show improper enzyme folding, loss of Sialidase enzyme activity and subsequent accumulation of sialylconjugates within lysosomes. One promising treatment option is the use of small pharmacological molecules to increase the enzymatic activities of mutant proteins. In this study, we examined the efficacy of the immuno-suppressant (Celastrol) as well as a proteosomal inhibitor (MG132) to rescue mutant enzymes with altered conformation. Our results reveal that MG132 enhances enzyme activity and its localisation in cells expressing defective Sialidase. We also found that MG132 reduces accumulation of ganglioside products, GT1b, GD3, and GM3 in pre-loaded Sialidosis cells. Alternatively, Celastrol appears to reduce Sialidase expression and activity revealing a potentially novel effect of Celastrol on Sialidase. Interestingly, the combination of Celastrol and MG132 appears to amplify the beneficial impact of MG132 on both the endogenous and recombinant expression of defective Sialidase. This study explores a novel biological criteria to assess the efficacy of small molecules through accumulation analysis and points to a potential therapeutic strategy for the treatment of Sialidosis.
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Affiliation(s)
- Erin M O'Leary
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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22
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Abstract
A viable treatment for lysosomal storage disease has been very difficult to attain. One option is pharmacological inhibition of synthetic pathways to reduce substrate accumulations. Miglustat N-butyldeoxynojirimycin (NBDNJ), an inhibitor of glucosylceramide synthase, has shown much promise in clinical trials for the treatment of Type I Gaucher disease. The molecular events invoked by NBDNJ in cell culture and in animal models have not been so definitive. This review discusses the biochemical and molecular impact of NBDNJ as it relates to its potential as a therapeutic drug.
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23
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Champigny MJ, Mitchell M, Fox-Robichaud A, Trigatti BL, Igdoura SA. A point mutation in the neu1 promoter recruits an ectopic repressor, Nkx3.2 and results in a mouse model of sialidase deficiency. Mol Genet Metab 2009; 97:43-52. [PMID: 19217813 DOI: 10.1016/j.ymgme.2009.01.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/05/2008] [Revised: 01/13/2009] [Accepted: 01/13/2009] [Indexed: 12/19/2022]
Abstract
SM/J is an inbred mouse strain with a complex phenotype including small body size, impaired immune response and a tissue-specific sialidase deficiency. We identified a regulatory mutation, (-519G-->A) within the neu1 promoter which in reporter assays resulted in significantly reduced transcription. This mutation generates a consensus binding site for Nkx3 family transcription repressors. Recombinant Nkx3.2 bound strongly to and preferentially repressed transcription of the mutant promoter. This tissue-specific deficiency results in a retarded immune response and modulates leukocyte recruitment. Examination of the hepatic microcirculation in mutant mice revealed increased rolling and decreased adhesion of leukocytes. Our findings support a significant role for lysosomal sialidase in inflammation and highlight the significance of repressor-recruitment in genetic disease.
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Affiliation(s)
- Marc J Champigny
- Department of Biology, McMaster University, Hamilton, Ont., Canada L8S 4K1
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24
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Kowalewska PM, Igdoura SA, Fox‐Robichaud AE. Characterization of the hepatic endothelial glycocalyx of sialidase deficient mice in response to TNFα. FASEB J 2008. [DOI: 10.1096/fasebj.22.1_supplement.731.7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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25
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Zhang Y, Ahmed AM, Tran TL, Lin J, McFarlane N, Boreham DR, Igdoura SA, Truant R, Trigatti BL. The inhibition of endocytosis affects HDL-lipid uptake mediated by the human scavenger receptor class B type I. Mol Membr Biol 2007; 24:442-54. [PMID: 17710648 DOI: 10.1080/09687680701300410] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The scavenger receptor SR-BI plays an important role in the hepatic clearance of HDL cholesterol and other lipids, driving reverse cholesterol transport and contributing to protection against atherosclerosis in mouse models. We characterized the role of endocytosis in lipid uptake from HDL, mediated by the human SR-BI, using a variety of approaches to inhibit endocytosis, including hypertonic shock, potassium or energy depletion and disassembly of the actin cytoskeleton. Our studies revealed that unlike mouse SR-BI, human SR-BI-mediated HDL-lipid uptake was reduced by inhibition of endocytosis. This was not dependent on the cytoplasmic C-terminus of SR-BI. Monitoring the uptake of both the protein and lipid components of HDL revealed that although overall lipid uptake was decreased, the degree of selective lipid uptake was increased. These data suggest that that endocytosis is a dynamic regulator of SR-BI's selective lipid uptake activity.
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Affiliation(s)
- Yi Zhang
- Department of Biochemistry, McMaster University, Hamilton, Ontario, Canada
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26
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Zhang Y, Ahmed AM, McFarlane N, Capone C, Boreham DR, Truant R, Igdoura SA, Trigatti BL. Regulation of SR-BI-mediated selective lipid uptake in Chinese hamster ovary-derived cells by protein kinase signaling pathways. J Lipid Res 2006; 48:405-16. [PMID: 17079793 DOI: 10.1194/jlr.m600326-jlr200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Scavenger receptor, class B, type I (SR-BI) mediates binding and internalization of a variety of lipoprotein and nonlipoprotein ligands, including HDL. Studies in genetically engineered mice revealed that SR-BI plays an important role in HDL reverse cholesterol transport and protection against atherosclerosis. Understanding how SR-BI's function is regulated may reveal new approaches to therapeutic intervention in atherosclerosis and heart disease. We utilized a model cell system to explore pathways involved in SR-BI-mediated lipid uptake from and signaling in response to distinct lipoprotein ligands: the physiological ligand, HDL, and a model ligand, acetyl LDL (AcLDL). In Chinese hamster ovary-derived cells, murine SR-BI (mSR-BI) mediates lipid uptake via distinct pathways that are dependent on the lipoprotein ligand. Furthermore, HDL and AcLDL activate distinct signaling pathways. Finally, mSR-BI-mediated selective lipid uptake versus endocytic uptake are differentially regulated by protein kinase signaling pathways. The protein kinase C (PKC) activator PMA and the phosphatidyl inositol 3-kinase inhibitor wortmannin increase the degree of mSR-BI-mediated selective lipid uptake, whereas a PKC inhibitor has the opposite effect. These data demonstrate that SR-BI's selective lipid uptake activity can be acutely regulated by intracellular signaling cascades, some of which can originate from HDL binding to murine SR-BI itself.
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Affiliation(s)
- Yi Zhang
- Departments of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada
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27
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Champigny MJ, Perry R, Rudnicki M, Igdoura SA. Overexpression of MyoD-inducible lysosomal sialidase (neu1) inhibits myogenesis in C2C12 cells. Exp Cell Res 2005; 311:157-66. [PMID: 16216242 DOI: 10.1016/j.yexcr.2005.08.023] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2004] [Revised: 08/16/2005] [Accepted: 08/30/2005] [Indexed: 11/24/2022]
Abstract
Lysosomal sialidase, encoded by neu1, is required for the removal of terminal sialic acid residues from a variety of sialoglycoconjugates. In humans, deficiency of this enzyme results in the inborn error of metabolism sialidosis, characterized by the accumulation of sialoglycoconjugates within the nervous system and in peripheral organs. A subset of sialidosis patients present with symptoms of profound muscle dysfunction, including progressive muscular atrophy. We have previously shown that the 5' regulatory region of murine neu1 is typical of skeletal muscle-specific genes due to the presence of several E-boxes and its responsiveness to stimulation by muscle regulatory factors (MRFs) such as MyoD. Here, we report that sialidase activity is increased 6-fold during the first 24 h of differentiation of C2C12 myoblasts followed by an attenuation to pre-differentiation levels by 48 h. We demonstrate that the lysosomal sialidase promoter is highly upregulated by MyoD through a mechanism that is dependent on the MyoD chromatin remodeling domain. We also show that the sialidase promoter is repressed by activated MEK. Inappropriate overexpression of sialidase 48 h after the onset of differentiation results in downregulation of myogenin as well as myosin heavy chain expression and in a halt of the differentiation cascade. This study indicates that lysosomal sialidase is a potent regulator of the early stages of myogenesis.
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Affiliation(s)
- Marc J Champigny
- Department of Biology, McMaster University, 1280 Main St. W. LSB 335, Hamilton, Ontario, Canada
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28
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Pattison S, Pankarican M, Rupar CA, Graham FL, Igdoura SA. Five novel mutations in the lysosomal sialidase gene (NEU1) in type II sialidosis patients and assessment of their impact on enzyme activity and intracellular targeting using adenovirus-mediated expression. Hum Mutat 2004; 23:32-9. [PMID: 14695530 DOI: 10.1002/humu.10278] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Sialidosis is an autosomal recessive disease resulting from a deficiency of lysosomal sialidase. Type II sialidosis is a rare disease characterized clinically by hydrops fetalis, hepatosplenomegaly, and severe psychomotor retardation. Genomic DNA from four unrelated sialidosis patients was screened for mutations within the sialidase gene NEU1. Five novel mutations were identified. Four are missense and one is nonsense: c.674G>C (p.R225P), c.893C>T (p.A298V), c.3G>A (p.M1?), c.941C>G (p.R341G), and c.69G>A (p.W23X). We have used our findings and diagnostic tools to confirm the presence of a homozygous null allele in a neonate sibling. Recombinant adenoviruses expressing the mutant sialidase alleles in primary cell cultures were utilized to assess the impact of each mutation on enzyme activity and intracellular localization. None of the mutant alleles expressed significant enzymatic activity. The p.R341G mutation exerts its pathological effect by perturbing substrate binding, while the p.A298V and p.R225P mutations appear to impair the folding of the sialidase enzyme. Our findings point to mutation-sensitive amino acids involved in catalytic function or structural stability and indicate the potential utility of these mutations for molecular diagnosis of this rare disease.
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Affiliation(s)
- Susan Pattison
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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29
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Ha MN, Graham FL, D'Souza CK, Muller WJ, Igdoura SA, Schellhorn HE. Functional rescue of vitamin C synthesis deficiency in human cells using adenoviral-based expression of murine l-gulono-γ-lactone oxidase. Genomics 2004; 83:482-92. [PMID: 14962674 DOI: 10.1016/j.ygeno.2003.08.018] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2003] [Accepted: 08/20/2003] [Indexed: 02/06/2023]
Abstract
l-Gulono-gamma-lactone oxidase (GULO) is a critical enzyme present in most mammalian species that is required for the terminal step in vitamin C biosynthesis. Primates are absolutely dependent on exogenously supplied dietary vitamin C due to inactivation of the Gulo gene by mutation over 40 million years ago. In this study, we report the cloning and expression of the murine l-gulono-gamma-lactone oxidase cDNA and gene. The cDNA (2.3 kb) encodes an open reading frame of 440 amino acids that shows high homology to the rat l-gulono-gamma-lactone oxidase (>94%). The Gulo gene is 22 kb long and contains 12 exons. The 11 introns range in size from 479 to 5641 bp. Northern blot analysis revealed high expression of Gulo transcript in the liver. To investigate whether metabolic loss of vitamin C biosynthesis in human cells can be corrected by heterologous expression of GULO, we constructed a first-generation adenoviral vector expressing the murine GULO cDNA under the transcriptional control of the murine cytomegalovirus (MCMV) early promoter. Low rescue efficiency of Gulo-expressing adenoviral constructs and reduced viral growth in HEK293 cells were observed, suggesting that overexpression of Gulo may be inhibitory to cell growth. Placement of a removable stuffer fragment flanked by lox sites between the MCMV promoter and the Gulo gene resulted in efficient vector rescue and normal viral replication in parental HEK293 cells and high-level expression of Gulo in HEK293 cells expressing Cre recombinase. Cells infected with Gulo-expressing vectors overexpressed an FAD-containing protein that corresponded in size to that predicted for recombinant GULO protein and expressed a functional enzyme as measured by the conversion of l-gulono-gamma-lactone to ascorbic acid in cell-free extracts. The cloning of the murine Gulo cDNA and the construction of Gulo-expressing adenoviral vectors are vital steps toward determining the role of vitamin C in basic metabolism and in disease.
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Affiliation(s)
- Michael N Ha
- Department of Biology, McMaster University, Hamilton, ON, Canada L8S 4K1
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30
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Abstract
Lysosomal sialidase is required for the catabolism of sialoglycoconjugates such as gangliosides and deficiency in this enzyme results in the autosomal recessive disease sialidosis. Furthermore, we have shown that overexpression of human sialidase is sufficient to clear accumulated ganglioside in Tay-Sachs neuroglia [Hum. Mol. Genet. 8 (1999) 1111]. In this paper, we have characterized the 5' regulatory region of the mouse lysosomal sialidase gene in order to understand the molecular mechanisms regulating its expression. We used bioinformatic approaches to identify a transcriptional initiation site at -45 bp relative to the ATG and significant sequence homology with the rat and human promoters. Expression by the promoter was found to be cell-type restricted and required at least 750 bp upstream of the ATG for high-level expression. DNAse I footprinting analysis and reporter gene assays indicated that the promoter is responsive to Sp-1. We discovered a CCAAT box and four E-boxes within the mouse upstream region and demonstrated that CCAAT displacement protein as well as the muscle regulatory factors MyoD and Myf-5 influence sialidase expression. Taken together, these results identify cis- and trans-acting factors involved in the regulation of sialidase and point to mechanisms of gene upregulation.
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Affiliation(s)
- Marc J Champigny
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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MacDougall-Shackleton EA, Blanchard L, Igdoura SA, Gibbs HL. Unmelanized plumage patterns in Old World leaf warblers do not correspond to sequence variation at the melanocortin-1 receptor locus (MC1R). Mol Biol Evol 2003; 20:1675-81. [PMID: 12885967 DOI: 10.1093/molbev/msg186] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Evolutionary changes in patterns and coloration of plumage are likely to represent a major mechanism for speciation among birds, yet the molecular basis for such changes remains poorly understood. Recently much attention has focused on the melanocortin-1 receptor (MC1R) as a candidate locus for determining the level and extent of epidermal melanin deposition. We tested the hypothesis that MC1R sequence variation is associated with interspecific variation in unmelanized plumage pattern elements in Old World leaf warblers (genus Phylloscopus). This genus is characterized by a variety of plumage patterns that nonetheless vary along similar lines. Species vary in the presence or absence of pale (unmelanized) pattern elements against a dark background, and these patterns are used in species recognition and courtship. We sequenced most of the MC1R coding region for eight Phylloscopus species, representing the full range of plumage patterns found in this genus. Although MC1R sequence varied among species, this variation was not related to melanin-based plumage variation. Rather, evolution of this locus in these birds appears to be conservative. Ratios of nonsynonymous to synonymous substitutions (dN/dS) were consistently low, suggesting that strong purifying selection has operated at this locus, and likelihood ratio testing revealed no evidence of variable selective pressures among lineages or across codons. Adaptive evolution at MC1R may be constrained by the adaptive importance of plumage pattern elements in this genus.
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Qin H, Shao Q, Igdoura SA, Alaoui-Jamali MA, Laird DW. Lysosomal and proteasomal degradation play distinct roles in the life cycle of Cx43 in gap junctional intercellular communication-deficient and -competent breast tumor cells. J Biol Chem 2003; 278:30005-14. [PMID: 12767974 DOI: 10.1074/jbc.m300614200] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The present study was designed to determine the specific roles played by lysosomes and proteasomes in the degradation of Cx43 in both gap junctional intercellular communication-deficient MDA-MB-231 and -competent BICR-M1Rk cells. In MDA-MB-231 cells, immunolocalization and brefeldin A protein transport blocking studies revealed that there was a propensity for newly synthesized Cx43 to be transported to lysosomes. On the other hand, light and electron microscopic analysis of BICR-M1Rk cells showed that Cx43 gap junctions were prevalent with a subpopulation of intracellular Cx43 localized to lysosomes. In both cell types, Western blots revealed a notable increase in total cellular Cx43 in response to lysosome inhibitors. Interestingly, lactacystin inhibition of proteosomal degradation in MDA-MB-231 cells resulted in a marked increase in phosphorylated Cx43 at the expense of non-phosphorylated Cx43, and this change corresponded with an increase in "oversized" gap junction plaques. In BICR-M1Rk cells, lactacystin treatment partially prevented the BFA-induced loss of gap junctions. Together, our data suggests that lysosomes play a key role in not only degrading internalized gap junction in BICR-M1Rk cells but also in degrading Cx43 delivered from early secretory compartments to lysosomes in MDA-MB-231 cells. Overall proteasomal degradation regulates the stability of phosphorylated Cx43 and appears to promote the internalization of Cx43 from the cell surface.
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Affiliation(s)
- Hong Qin
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario N6A 5C1, Canada
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Igdoura SA, Herscovics A, Lal A, Moremen KW, Morales CR, Hermo L. Alpha-mannosidases involved in N-glycan processing show cell specificity and distinct subcompartmentalization within the Golgi apparatus of cells in the testis and epididymis. Eur J Cell Biol 1999; 78:441-52. [PMID: 10472797 DOI: 10.1016/s0171-9335(99)80071-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022] Open
Abstract
The Golgi apparatus is enriched in specific enzymes involved in the maturation of carbohydrates of glycoproteins. Among them, alpha-mannosidases IA, IB and II are type II transmembrane Golgi-resident enzymes that remove mannose residues at different stages of N-glycan maturation. alpha-Mannosidases IA and IB trim Man9GlcNAc2 to Man5GlcNAc2, while alpha-mannosidase II acts after GlcNAc transferase I to remove two mannose residues from GlcNAcMan5GlcNAc2 to form GlcNAcMan3GlcNAc2 prior to extension into complex N-glycans by Golgi glycosyltransferases. The objective of this study is to examine the expression as well as the subcellular localization of these Golgi enzymes in the various cells of the male rat reproductive system. Our results show distinct cell-and region-specific expression of the three mannosidases examined. In the testis, only alpha-mannosidase IA and II were detectable in the Golgi apparatus of Sertoli and Leydig cells, and while alpha-mannosidase IB was present in the Golgi apparatus of all germ cells, only the Golgi apparatus of steps 1-7 spermatids was reactive for alpha-mannosidase IA. In the epididymis, principal cells were unreactive for alpha-mannosidase II, but they expressed alpha-mannosidase IB in the initial segment and caput regions, and alpha-mannosidase IA in the corpus and cauda regions. Clear cells expressed alpha-mannosidase II in all epididymal regions, and alpha-mannosidase IB only in the caput and corpus regions. Ultrastructurally, alpha-mannosidase IB was localized mainly over cis saccules, alpha-mannosidase IA was distributed mainly over trans saccules, and alpha-mannosidase II was localized mainly over medial saccules of the Golgi stack. Thus, the cell-specific expression and distinct Golgi subcompartmental localization suggest that these three alpha-mannosidases play different roles during N-glycan maturation.
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Affiliation(s)
- S A Igdoura
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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Abstract
Tay-Sachs disease is a severe, inherited disease of the nervous system caused by accumulation of the brain lipid GM2 ganglioside. Mouse models of Tay-Sachs disease have revealed a metabolic bypass of the genetic defect based on the more potent activity of the enzyme sialidase towards GM2. To determine whether increasing the level of sialidase would produce a similar effect in human Tay-Sachs cells, we introduced a human sialidase cDNA into neuroglia cells derived from a Tay-Sachs fetus and demonstrated a dramatic reduction in the accumulated GM2. This outcome confirmed the reversibility of GM2 accumulation and opens the way to pharmacological induction or activation of sialidase for the treatment of human Tay-Sachs disease.
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Affiliation(s)
- S A Igdoura
- Montreal Children's Hospital Research Institute and Department of Human Genetics, McGill University, Quebec, Canada
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Igdoura SA, Gafuik C, Mertineit C, Saberi F, Pshezhetsky AV, Potier M, Trasler JM, Gravel RA. Cloning of the cDNA and gene encoding mouse lysosomal sialidase and correction of sialidase deficiency in human sialidosis and mouse SM/J fibroblasts. Hum Mol Genet 1998; 7:115-21. [PMID: 9384611 DOI: 10.1093/hmg/7.1.115] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Lysosomal sialidase occurs in a multienzyme complex that also contains beta-galactosidase and cathepsin A. We previously cloned the human lysosomal sialidase cDNA and characterized mutations in human sialidosis patients. Here, we report the cloning and expression of the mouse lysosomal sialidase cDNA and gene. The 1.77 kb cDNA encodes an open reading frame of 408 amino acids which shows high homology to the human lysosomal sialidase (80%), the rat cytosolic sialidase (65%) and viral and bacterial sialidases (50-55%). The sialidase gene is approximately 4 kb long and contains six exons. The five introns range in size from 96 to 1200 bp. Northern blot analysis revealed high expression of multiple sialidase transcripts in kidney and epididymis, moderate levels in brain and spinal cord, and low levels in adrenal, heart, liver, lung and spleen. Transient expression of the cDNA clone in sialidase-deficient SM/J mouse fibroblasts and human sialidosis fibroblasts restored normal levels of sialidase activities in both cell types. Immunocytochemically expressed sialidase co-localized with a lysosomal marker, LAMP2, confirming its lysosomal nature. Since sialidase activity requires its association with beta-galactosidase and cathepsin A, the expression of mouse sialidase within human sialidosis cells underlines the structural similarity between mouse and human enzymes and suggests that the mechanism for complex formation and function is highly conserved.
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Affiliation(s)
- S A Igdoura
- Montreal Children's Hospital Research Institute and Department of Biology, McGill University, Montreal, Quebec, Canada
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36
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Igdoura SA, Argraves WS, Morales CR. Low density lipoprotein receptor-related protein-1 expression in the testis: regulated expression in Sertoli cells. J Androl 1997; 18:400-10. [PMID: 9283953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The low density lipoprotein receptor-related protein (LRP-1) is a multiligand receptor capable of mediating endocytosis of a wide array of ligands that relate to both lipoprotein metabolism and proteinase regulation. Many of its ligands are proteinases, proteinase-inhibitor complexes, and lipoproteins known to be contained within the luminal fluid of the seminiferous tubules or in the interstitial spaces of the testis. Immunocytochemical analysis was performed to characterize the pattern of expression of LRP-1 in cells of the rat testis. Immunoperoxidase staining localized LRP-1 to the cytoplasm of Sertoli cells. The distribution and intensity of the Sertoli cell staining was found to vary according to the stages of the cycle of the seminiferous epithelium. Staining was weak in the basal cytoplasm of Sertoli cells during stages II-VIII and strong and granular in the supranuclear cytoplasm during stages XII-XIV and stage I of the cycle. Immunogold labeling showed gold particles associated with the basal and adluminal plasma membranes, with endocytic vesicles, and with endosome membranes. Labeling was also observed on the plasma membrane and membranes of the endocytic apparatus in macrophages and Leydig cells in the interstitial space. Infusion of 125I-Labeled LRP-1 antibody into seminiferous tubules followed by radioautography showed silver grains overlaying the ad-luminal plasma membrane of Sertoli cells at time 0 and in endocytic vesicles and endosomes in the supranuclear region of Sertoli cells 10-minutes postinjection. When the 125I-Labeled LRP-1 antibody was injected into the interstitial space, silver grains overlayed the basal plasma membrane and coated endocytic pits of Sertoli cells at time 0 and, at 10 minutes, the grains labeled endosomes located in the basal pole of Sertoli cells. 125I-Labeled LRP-1 antibody also labeled the plasma membrane and the endocytic apparatus of macrophages and Leydig cells. The absence of immunogold labeling and radioautographic silver grains within lysosomes of Sertoli cells, Leydig cells, and macrophages suggests that internalized LRP-1 is recycled back to the cell surface. The presence of LRP-1 in the endocytic compartment of these cells is consistent with its functioning in the clearance of proteases involved in seminiferous tubule remodeling and/ or the uptake of cholesterol-bound lipoproteins necessary for the biosynthesis of testosterone. In conclusion, the results of these studies demonstrated for the first time the presence of LRP-1 receptor in the endocytic compartments of Sertoli cells and interstitial cells of the rat testis.
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Affiliation(s)
- S A Igdoura
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada
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Morales CR, Igdoura SA, Wosu UA, Boman J, Argraves WS. Low density lipoprotein receptor-related protein-2 expression in efferent duct and epididymal epithelia: evidence in rats for its in vivo role in endocytosis of apolipoprotein J/clusterin. Biol Reprod 1996; 55:676-83. [PMID: 8862787 DOI: 10.1095/biolreprod55.3.676] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Apolipoprotein J/clusterin/sulfated glycoprotein-2 (apo J) disassociates from spermatozoa and is endocytosed by epithelial cells lining the efferent ducts and epididymis. The low density lipoprotein receptor-related protein-2/megalin (LRP-2) has been shown to bind to apo J and mediates its endocytosis and lysosomal degradation in cultured cells. In this study, immunocytological techniques were used to localize LRP-2 in rat efferent ducts and epididymis and to determine whether its expression correlated with those epithelial cells involved in apo J endocytosis. Pronounced LRP-2 immunochemical staining was observed on the apical surfaces of epithelial cells lining the efferent ducts and in the intermediate zone, proximal caput, and corpus and cauda regions of the epididymis. Single immunogold labeling at the electron microscopic level showed LRP-2 to be present within coated pits, endocytic vesicles, and early endosomes of the nonciliated cells of the efferent ducts and the principal cells of the epididymis. In efferent ducts, double immunogold labeling showed both LRP-2 and apo J to be present in endocytic compartments including coated pits, endocytic vesicles, and early endosomes of nonciliated cells. However, while apo J was detected in late endosomes and lysosomes of nonciliated cells, LRP-2 was not. Apical tubules, possibly emerging from late endosomes, contained labeling for LRP-2 but not for apo J. Ciliated cells lying adjacent to nonciliated cells displayed no labeling for either LRP-2 or apo J. These results are consistent with the possibility that LRP-2 serves as an endocytic receptor for apo J in vivo and that after endocytosis the LRP-2 is recycled back to the cell surface while apo J is delivered to the lysosomes for degradation. To provide additional evidence implicating LRP-2 in apo J endocytosis, a receptor-associated protein (RAP), an antagonist of apo J binding to LRP-2, was injected into the efferent duct lumen. Subsequent immunocytological analysis of the efferent duct showed that the RAP treatment abolished the endocytosis of apo J by the nonciliated cells. Taken together, these data indicate that LRP-2 is a likely mediator of apo J endocytosis by the nonciliated efferent duct cells.
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Affiliation(s)
- C R Morales
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada.
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Abstract
Sulfated glycoprotein-1 (SGP-1/prosaposin) exists as a sulfated secreted protein or as a lysosomal precursor of four smaller saposin molecules. The protein exhibits ubiquitous expression, evolutionary conservation, and diverse tissue inducibility. The lysosomal form of SGP-1 plays a role in the hydrolysis of glycolipids and sphingomyelin. The function of the secreted form of SGP-1 is still unclear. However, it could act as a glycolipid transfer protein, since several gangliosides (a series) were found to bind with high affinity to prosaposin. To identify cell types that produce SGP-1 mRNA, we constructed an SGP-1 cDNA and used for screening of different rat tissues by Northern blot analysis. To localize the translation product of SGP-1 transcripts, we immunostained the same tissues with an anti-SGP-1 antibody. The SGP-1 cDNA construct was generated by amplifying a rat testicular Zap cDNA library by PCR (polymerase chain reaction) with two synthetic oligonucleotide primers. A positive signal of 1.7 KB was isolated, subcloned into the pGEM-7Zf (+). Sequence analysis showed a near-identical nucleotide and amino acid similarity to a previous rat SGP-1 cDNA. The majority of the heterogeneites were conservative substitutions. Northern blot analysis demonstrated that all examined rat tissue and organs have SGP-1 mRNA. Immunocytochemistry identified two staining patterns in the cytoplasm of positive cells: (a) a granular reaction characteristic of lysosomes in the supranuclear and basal regions of epithelial cells and in the perinuclear region of neurons; and (b) a homogeneous reaction in the cytoplasm of Sertoli cells, Type II pneumocytes, macrophages, and epithelial cells lining the choroid plexus. The latter staining pattern could be characteristic of cells that exhibit a secretory routing of SGP- 1. The production of SGP-1 by a variety of specialized cells lining fluid compartments suggests that its secreted form has a role in the transport of lipids in biological fluids, possibly by the formation of soluble complexes with glycolipids. Similarly, the lysosomal form of SGP-1/prosaposin and their derived saposins also solubilizes certain glycolipids to promote their degradation by specific hydrolases.
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Affiliation(s)
- C R Morales
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada
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Igdoura SA, Rasky A, Morales CR. Trafficking of sulfated glycoprotein-1 (prosaposin) to lysosomes or to the extracellular space in rat Sertoli cells. Cell Tissue Res 1996; 283:385-94. [PMID: 8593668 DOI: 10.1007/s004410050549] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Sulfated glycoprotein-1 (prosaposin) exists in 2 forms: a 65kDa form targeted to lysosomes and a 70kDa form secreted extracellularly. In order to understand the sorting and targeting mechanisms of the two forms of SGP-1, we have compared their maturation, processing, and secretion in rat Sertoli cells in vivo. Metabolic labeling experiments in vivo demonstrated that the 65kDa form is synthesized first, then post-translationally modified to the 70kDa form of SGP-1. Subcellular fractionation of testicular homogenate was used to obtain Golgi fractions containing up to 50-fold enrichment in galactosyltransferase. Permeabilization of enriched Golgi fractions with saponin released the 70kDa form, but did not affect the 65kDa protein. While excess free mannose 6-phosphate did not release lysosomal SGP-1, it released the 35kDa cathepsin L from Golgi membranes. Using quantitative electron-microscopic immunocytochemistry, the lysosomal contents of SGP-1 were shown to increase significantly after the administration of tunicamycin in vivo. Therefore, the trafficking of the 65kDa form of SGP-1 to the lysosomes appears to be independent of the M6P-receptor pathway. The 70kDa form of SGP-1 was found to aggregate within perforated Golgi fractions in a process which depends on low pH and calcium ions. We conclude that the targeting of the 65kDa form of SGP-1 to the lysosomes involves an early association with Golgi membrane that is independent of mannose 6-phosphate receptors.
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Affiliation(s)
- S A Igdoura
- Department of Anatomy and Cell Biology, McGill University, 3640 University Street, Montreal, Canada H3A 2B2
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40
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Phaneuf D, Wakamatsu N, Huang JQ, Borowski A, Peterson AC, Fortunato SR, Ritter G, Igdoura SA, Morales CR, Benoit G, Akerman BR, Leclerc D, Hanai N, Marth JD, Trasler JM, Gravel RA. Dramatically different phenotypes in mouse models of human Tay-Sachs and Sandhoff diseases. Hum Mol Genet 1996; 5:1-14. [PMID: 8789434 DOI: 10.1093/hmg/5.1.1] [Citation(s) in RCA: 174] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
We have generated mouse models of human Tay-Sachs and Sandhoff diseases by targeted disruption of the Hexa (alpha subunit) or Hexb (beta subunit) genes, respectively, encoding lysosomal beta-hexosaminidase A (structure, alpha) and B (structure, beta beta). Both mutant mice accumulate GM2 ganglioside in brain, much more so in Hexb -/- mice, and the latter also accumulate glycolipid GA2. Hexa -/- mice suffer no obvious behavioral or neurological deficit, while Hexb -/- mice develop a fatal neurodegenerative disease, with spasticity, muscle weakness, rigidity, tremor and ataxia. The Hexb -/- but not the Hexa -/- mice have massive depletion of spinal cord axons as an apparent consequence of neuronal storage of GM2. We propose that Hexa -/- mice escape disease through partial catabolism of accumulated GM2 via GA2 (asialo-GM2) through the combined action of sialidase and beta-hexosaminidase B.
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Affiliation(s)
- D Phaneuf
- Department of Pediatrics, McGill University, Montreal, Canada
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Hermo L, Rosenthal AL, Igdoura SA, Morales CR. Targeting of endogenous sulfated glycoprotein-1 and -2 to lysosomes within nonciliated cells of the efferent ducts during postnatal development of the rat. Mol Reprod Dev 1995; 41:287-99. [PMID: 8588927 DOI: 10.1002/mrd.1080410303] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Sulfated glycoprotein (SGP)-1 and -2, secretory products of Sertoli cells, are secreted into the lumen of seminiferous tubules where they bind to late spermatids. Once released, the spermatozoa traverse the efferent ducts where these proteins detach from their surface and are endocytosed by the nonciliated cells. In adult animals, SGP-1 and SGP-2 are also synthesized by nonciliated cells and targeted from the Golgi apparatus to lysosomes. The purpose of the present study was to determine the pattern of expression of SGP-1 and SGP-2 within nonciliated cells during postnatal development. The efferent ducts of animals at different postnatal ages were prepared for an electron microscopic immunocytochemical quantitative analysis as well as for Northern blot analysis. The data expressed as labeling content (no. gold particles/micron 2 and taking into account the volume of the endocytic organelles and the cell) revealed that anti-SGP-1 labeling in endosomes of nonciliated cells was minimal at 15, 21, and 29 days of age. On the other hand, the lysosomal labeling content showed a significant increase by day 29 compared to 15 and 21-day-old animals indicating that an endogenous form of SGP-1 was being synthesized by nonciliated cells and targeted to lysosomes. By day 39 a significant increase in endosomal labeling occurred; this was attributed to the endocytosis of Sertoli-derived SGP-1 which coincided with the entry of spermatozoa into the lumen of these ducts at this age. Lysosomal labeling showed further significant increases at days 39, 49, and then again at day 90. Northern blot analysis detected SGP-1 mRNA transcripts at all postnatal ages examined. While decreases or increases in transcripts could not be determined due to the greater amount of tissue present with increasing age, these data taken together support the idea of an endogenous form of SGP-1 being synthesized by nonciliated cells and targeted to lysosomes during postnatal development. In the case of SGP-2, endosomal labeling was minimal at 15, 21, and 29 days of age but was significantly increased by day 39, with similar values at all subsequent ages. The high value at day 39 was attributed to the endocytosis of SGP-2 which coincided with the entry of spermatozoa into the lumen at this age. Lysosomal labeling, on the other hand, was low at days 15 and 21 but peaked at day 29 at a time when endosomal labeling was minimal. These results suggested the synthesis of an endogenous form of SGP-2 which was being targeted to lysosomes.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- L Hermo
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada
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Abstract
Cathepsins are specific proteases in lysosomes that participate in the degradation of proteins, some of which are derived from endocytosis. In this study we examined the immunocytochemical localization of cathepsin B and D antibodies in cells of rat testis and epididymis, using light and electron microscopic immunocytochemistry. In testis, cathepsin D was immunolocalized over lysosomes of Sertoli cells and Leydig cells and on the acrosome of spermatids. Cathepsin B was found over lysosomes of macrophages. Non-ciliated cells of the efferent ducts revealed intense immunogold labeling over lysosomes with both anti-cathepsin B and D antibodies. In epididymis, cathepsins B and D showed marked variations in expression over the different epithelial cells and regional differences for a given cell type. Anti-cathepsin D antibodies showed intense labeling over lysosomes of principal cells in the corpus and proximal cauda. In contrast, anti-cathepsin B antibodies revealed intensely labeled lysosomes of principal cells of the distal initial segment, intermediate zone, and caput epididymidis, with weaker labeling in other regions. Clear cells of the proximal caput epididymidis revealed intensely labeled lysosomes for anti-cathepsin D antibodies. In the distal caput, clear cells showed a variable reaction pattern from intensely labeled to unreactive. Basal cells of teh intermediate zone and proximal caput region were intensely reactive for anti-cathepsin D antibodies. There was no staining over clear or basal cells with anti-cathepsin B antibodies. Taken together, these results demonstrate cell-specific and regional differences in the distribution of cathepsins B and D in cells of the male reproductive system. Such results suggest substrate specificity with regard to protein turnover within lysosomes of cells of testis and epididymis.
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Affiliation(s)
- S A Igdoura
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada
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Abstract
Sulfated glycoprotein-1 (SGP-1) is a polypeptide secreted by Sertoli cells in the rat. Sequence analysis revealed a 76% sequence similarity with human prosaposin produced by various cell types. Human prosaposin is a 70 kDa protein which is cleaved in the lysosomes into four 10-15 kDa polypeptides termed saposins A, B, C, and D. The function of lysosomal saposins is to either solubilize certain membrane glycolipids or to form complexes with lysosomal enzymes and/or their glycolipid substrate to facilitate their hydrolysis. The present investigation dealt with the delivery of SGP-1 into the phagosomes of Sertoli cells; these phagosomes contain the residual bodies which detach from the late spermatids at the time of spermiation. Immunogold labeling with anti-SGP-1 antibody was found over Sertoli cell lysosomes, but was absent from phagosomes formed after phagocytosis of spermatid residual bodies in the apical Sertoli cell cytoplasm in stages VIII and early IX of the cycle of the seminiferous epithelium. The phagosomes found later in the basal Sertoli cell cytoplasm in stages IX and X of the cycle became labeled with the antibody as the components of the residual bodies rapidly underwent lysis and disappeared from the Sertoli cells. Sertoli cell lysosomes isolated by cell fractionation (estimated purity of 80%) were found to contain a 65 kDa form of SGP-1 or prosaposin, as well as the 15 kDa polypeptides or saposins. Thus, it appears that this unique lysosomal form of SGP-1 reached the Sertoli cell phagosomes and that their derived polypeptides, the saposins, must play a role in the hydrolysis of membrane glycolipids found in phagocytosed residual bodies.
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Affiliation(s)
- S A Igdoura
- Department of Anatomy and Cell Biology, McGill University, Montreal, Canada
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Rosenthal AL, Igdoura SA, Morales CR, Hermo L. Hormonal regulation of sulfated glycoprotein-1 synthesis by nonciliated cells of the efferent ducts of adult rats. Mol Reprod Dev 1995; 40:69-83. [PMID: 7702872 DOI: 10.1002/mrd.1080400110] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The objective of this study was to define the factors regulating the endogenous production of sulfated glycoprotein-1 (SGP-1) in nonciliated cells of the efferent ducts. To this end we examined five different groups of animals undergoing the following experimental procedures: (1) hypophysectomized animals at 7, 14, and 28 days, (2) 7-day hypophysectomized rats receiving testosterone implants given at various time intervals thereafter, (3) castration at various time intervals up to 7 days, (4) 7-day castrated rats receiving testosterone implants at various time intervals thereafter, and (5) castrated rats given testosterone implants immediately after castration and sacrificed at different time intervals thereafter. Efferent ducts were fixed by perfusion with 4% paraformaldehyde and 0.5% glutaraldehyde in phosphate buffer for quantitative immunocytochemical analysis at the level of the electron microscope. For each experimental condition and their controls, the number of gold particles/micron2 within the endosomal and lysosomal compartments was calculated taking into account the changes in both the volume of the cell and organelles being quantified and expressed as labeling content. The results revealed that hypophysectomy (up to 4 weeks) caused a marked significant decrease in the SGP-1 labeling content of the endosomal and lysosomal compartments. The labeling content of the lysosomal compartment of efferent ducts from rats castrated for up to 1 week did not change significantly. However, there was a significant decrease in the labeling content of endosomes. This decrease is due to SGP-1, which is secreted by Sertoli cells, not being available for uptake in the efferent ducts. These results suggested that testosterone is not required for maintaining the high labeling content of SGP-1 within lysosomes of nonciliated cells, but that a pituitary factor appears to be needed. The administration of testosterone at different intervals to 7-day castrated animals resulted in a significant decrease of lysosomal SGP-1, suggesting that testosterone under these experimental conditions inhibits the production of a pituitary factor that maintains the high labeling content of SGP-1 within lysosomes of the nonciliated cells. Testosterone administered to 7-day hypophysectomized animals over a 24-hr period had no effect on the labeling content of SGP-1 within lysosomes. However, the administration of testosterone to animals immediately following castration showed no differences in the labeling content of SGP-1 within compared to controls.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- A L Rosenthal
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada
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Igdoura SA, Hermo L, Morales CR. Sulfated glycoprotein-2 synthesized by nonciliated cells of the efferent ducts is targeted to the lysosomal compartment. Microsc Res Tech 1994; 29:468-80. [PMID: 7873794 DOI: 10.1002/jemt.1070290605] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The epithelial nonciliated cells of the efferent ducts are specialized in internalizing many luminal substances. The nonciliated cells actively endocytose sulfated glycoprotein-2 (SGP-2), a major secretory protein of Sertoli cells and a homologue of human apolipoprotein J. This study was undertaken to investigate the internalization of Sertoli-derived SGP-2 and synthesis of an endogenous efferent duct form of SGP-2 by nonciliated cells targeted to their secondary lysosomes on animals whose efferent ducts were ligated and/or received injections of tunicamycin. The regulation of synthesis of the endogenous form of SGP-2 within nonciliated cells by hormones in general and testosterone in particular was also examined using hypophysectomized and castrated animals with or without subsequent testosterone replacement. Quantitative electron microscope immunocytochemistry was performed on groups of animals fixed with 4% paraformaldehyde and 0.5% glutaraldehyde in phosphate buffer for each experimental condition and their controls. In each case, the labeling density (number of gold particles/micron 2) within the endosomal (endosomes) and lysosomal (dense multivesicular bodies and secondary lysosomes) compartments was calculated. The results revealed that ligation of the efferent ducts resulted in a significant decrease in the labeling density of the endosomal and lysosomal compartments. However, a baseline of about 18% of controls was still observed in the lysosomal compartment 24 h after ligation. In this compartment similar values were noted 24 h after tunicamycin treatment in conjunction with or without ligation. These results suggest that an endogenous form of SGP-2 is synthesized by nonciliated cells and presumably targeted via small vesicles from the Golgi apparatus to the lysosomal compartment, but that the major portion of SGP-2 within this compartment is derived via endocytosis of testicular SGP-2. Hypophysectomy and castration also showed significant decreases in the labeling densities of these two compartments, but again a baseline level of labeling was noted in the lysosomal compartment. Subsequent testosterone administration to 7-day hypophysectomized or castrated animals had no effect on the labeling density of the lysosomal compartment, as values comparable to the effect of hypophysectomy or castration alone were noted. Taken together these results suggest that the nonciliated cells of the efferent ducts synthesize an endogenous form of SGP-2 that is targeted to the lysosomal compartment and which is not regulated by pituitary factors or testosterone.
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Affiliation(s)
- S A Igdoura
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada
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46
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Igdoura SA, Wiebe JP. Suppression of spermatogenesis by low-level glycerol treatment. J Androl 1994; 15:234-43. [PMID: 7928665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Previous studies have shown that a single intratesticular injection with 70% glycerol results in rapid and long-term suppression of spermatogenesis. Because of the extensive testicular damage in the form of focal destruction and large numbers of acellular seminiferous tubules, it was difficult to examine the possible chemical mechanisms of antispermatogenic action. Our objective was to explore regimens of treatment that would result in significant suppression of spermatogenesis without significant testicular damage. Sexually mature Sprague-Dawley rats were injected intratesticularly with various glycerol concentrations (0, 10, 20, 40, or 70%) and with volumes of either 200 or 350 microliters per testis. At times between 1 and 36 weeks after the injection, the effect on weights of testes and accessory sex organs, testicular histology, sperm numbers, serum hormonal levels, and gonadotropin-receptor binding was examined. An injection of 350 microliters/testis of a 10% glycerol solution led to a significant decrease in weights of testes and epididymides. The treatment resulted in an overall suppression of spermatogenesis, with about 90% fewer sperm in the epididymides than in control animals. Histologically, the treatment decreased the number of normal tubules from 97% (control) to 16% and resulted in testes in which about 75% of the tubules were aspermatogenic (containing only Sertoli cells and spermatogonia). The number of acellular tubules (tubules without cytological detail) was generally less than 5% of the total, and there was negligible focal destruction. Serum levels of gonadotropins and androgens were not altered significantly by the treatment, and Sertoli cell glutamyl transpeptidase activity appeared normal. An equi-osmolar solution of glucose also resulted in significant suppression of spermatogenesis, but the effect of glycerol was significantly greater, suggesting a mechanism in addition to hyperosmolarity. This study, therefore, is further evidence for the specificity of glycerol actions and for its potential as an antispermatogenic agent.
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Affiliation(s)
- S A Igdoura
- Department of Zoology, University of Western Ontario, London, Canada
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Igdoura SA, Hermo L, Rosenthal A, Morales CR. Nonciliated cells of the rat efferent ducts endocytose testicular sulfated glycoprotein-1 (SGP-1) and synthesize SGP-1 derived saposins. Anat Rec (Hoboken) 1993; 235:411-24. [PMID: 8430911 DOI: 10.1002/ar.1092350310] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Sertoli cell sulfated glycoprotein-1 (SGP-1) is a heavily glycosylated and sulfated 70 kDa protein that is secreted into the lumen of the seminiferous tubule where it binds to spermatozoa. Recent light and electron microscope immunocytochemistry has suggested that the testicular SGP-1 detaches from the surface of spermatozoa in the lumen of the efferent ducts to be endocytosed within the endocytic apparatus of the epithelial nonciliated cells. The finding of SGP-1 mRNA together with anti-SGP-1 immunogold labeling of the lysosomal compartment suggest that these cells synthesize an efferent duct form of SGP-1. In the present study, a number of different experimental approaches (ligation, tunicamycin treatment and a combination of both) in combination with quantitative electron microscope immunogold labeling and Western blot analysis were performed in order to test this hypothesis. The number of gold particles and the profile area of the early (endosomes, pale multivesicular bodies) and late (dense multivesicular bodies, secondary lysosomes) endocytic apparatus were estimated in each of the experimental groups and expressed as the number of gold particles per micron 2 (labeling densities). The data revealed that ligation produced a significant reduction of anti-SGP-1 immunogold labeling of the early endocytic apparatus but not of the late endocytic apparatus. Tunicamycin treatment on the other hand produced a significant reduction of immunogold labeling of both the early and late endocytic apparatus. The combination of both treatments resulted in a more effective reduction of the labeling densities of these two endocytic compartments. These results thus indicate that the nonciliated cells of the efferent ducts are involved both in the endocytosis of the Sertoli-derived SGP-1 and in the synthesis of an efferent duct form of SGP-1 that is targeted from the Golgi apparatus to secondary lysosomes after its glycosylation. In order to determine the biosynthetic pathway of SGP-1 within the efferent ducts, an I.V. injection of 35S-cysteine followed by immunoprecipitation and SDS-PAGE revealed that SGP-1 was initially biosynthesized as a 55 kDa protein. This protein appears to be post-translationally modified to a 65 kDa form after 1 hour, which preceded the appearance of the 70 kDa form, and smaller peptides of about 15 kDa characteristic of saposins after 3-4 hours. Western blot analysis of ligated efferent ducts showed an increase in the biosynthesis of the 70 kDa form of SGP-1 when compared to untreated controls, however, it has yet to be established if this protein is secreted or retained in an intracellular compartment.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- S A Igdoura
- Department of Anatomy, McGill University, Montreal, Quebec, Canada
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