1
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Jagennath S, Mehalingam V, Adole PS, Senthilkumar GP. Urinary megalin levels in patients with type 2 diabetic nephropathy and its correlation with renal function. J Family Med Prim Care 2024; 13:635-639. [PMID: 38605745 PMCID: PMC11006076 DOI: 10.4103/jfmpc.jfmpc_1207_23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 08/24/2023] [Accepted: 09/01/2023] [Indexed: 04/13/2024] Open
Abstract
Purpose Megalin is a glycoprotein molecule found on proximal renal tubular epithelial cells. The objectives of this study were to determine urinary megalin levels in non-diabetic subjects and in patients with and without type 2 diabetic nephropathy and to assess the correlation between urinary megalin, urinary albumin, and estimated glomerular filtration rate (eGFR) in diabetic patients. Materials and Methods This was a cross-sectional comparative study conducted at a tertiary care teaching hospital in South India for 2 years. Study subjects were divided into three groups: non-diabetic subjects, diabetics with normoalbuminuria, and diabetics with microalbuminuria. Urinary albumin was detected by the dipstick technique in a spot urine sample for all study subjects. Nephelometry was used to quantify urinary albumin levels. The enzyme-linked immunosorbent assay technique estimated urinary megalin. Results Urinary megalin levels were higher in non-diabetic subjects compared to diabetic study subjects. There was a significant difference in urinary megalin levels between non-diabetic subjects and diabetic patients with microalbuminuria. No correlation was found between urinary megalin, urinary albumin, and eGFR in patients with diabetic nephropathy. Conclusion Urinary megalin levels were higher in non-diabetic subjects than in type 2 diabetic patients. There was no correlation between urinary megalin, urinary albumin, and eGFR in patients with diabetic nephropathy.
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Affiliation(s)
- Sudharshan Jagennath
- Department of Medicine, Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER), Puducherry, India
| | - Vadivelan Mehalingam
- Department of Medicine, Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER), Puducherry, India
| | - Prashant S. Adole
- Department of Biochemistry, Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER), Puducherry, India
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Nishiwaki H, Niihata K, Kinoshita M, Fujimura M, Kurosawa K, Sakuramachi Y, Takano K, Matsunaga S, Okamura S, Kitatani M, Tsujii S, Hayashino Y, Kurita N. Urinary C-megalin as a novel biomarker of progression to microalbuminuria: A cohort study based on the diabetes Distress and Care Registry at Tenri (DDCRT 22). Diabetes Res Clin Pract 2022; 186:109810. [PMID: 35247529 DOI: 10.1016/j.diabres.2022.109810] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/08/2021] [Revised: 01/11/2022] [Accepted: 02/28/2022] [Indexed: 12/15/2022]
Abstract
AIMS Megalin is a multiligand receptor expressed in proximal tubular cells that reabsorbs filtered albumin and correlates cross-sectionally with albuminuria. We investigated the association between urinary C-megalin levels and the incidence of microalbuminuria in patients with diabetes mellitus. METHODS This cohort study included 752 patients with type 1 or 2 diabetes mellitus and a urinary albumin-to-creatinine (Cr) ratio (UACR) within the normoalbuminuric range (<30 mg/g Cr). The association between urinary C-megalin and persistent microalbuminuria, accounting for the possible interaction between baseline UACR and urinary C-megalin, was estimated using a Cox proportional hazards model. RESULTS During a median follow-up period of 1.99 years, 179 cases of persistent microalbuminuria were observed. The association between urinary C-megalin and persistent microalbuminuria was UACR-dependent (P for interaction < 0.001), with the highest association observed in the absence of UACR (per 100 fM/gCr of urinary C-megalin: adjusted hazard ratio, 1.13; 95% CI 1.07-1.19), gradually decreasing as UACR increased to 30 mg/g Cr. UACR dependence was confirmed by sensitivity analyses according to low-normal (<10 mg/gCr) or high-normal (10-<30 mg/gCr) UACR. CONCLUSIONS Urinary C-megalin is associated with progression to microalbuminuria, especially in those with low-normal UACR levels, and its usefulness to identify high risk patients requires further investigation.
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Affiliation(s)
- Hiroki Nishiwaki
- Department of Clinical Epidemiology, Graduate School of Medicine, Fukushima Medical University, Fukushima, Fukushima 960-1295, Japan; Division of Nephrology, Department of Internal Medicine, Showa University Fujigaoka Hospital, Yokohama, Kanagawa 227-8501, Japan; Showa University Research Administration Center (SURAC), Showa University, Shinagawa, Tokyo 142-8555, Japan
| | - Kakuya Niihata
- Department of Clinical Epidemiology, Graduate School of Medicine, Fukushima Medical University, Fukushima, Fukushima 960-1295, Japan
| | - Maki Kinoshita
- Department of Clinical Laboratory, Tenri Hospital, Nara, Tenri 632-8552, Japan
| | - Maki Fujimura
- Department of Endocrinology, Tenri Hospital, Tenri, Nara 632-8552, Japan
| | - Kentaro Kurosawa
- Department of Endocrinology, Tenri Hospital, Tenri, Nara 632-8552, Japan
| | - Yui Sakuramachi
- Department of Endocrinology, Tenri Hospital, Tenri, Nara 632-8552, Japan
| | - Kiyoko Takano
- Department of Endocrinology, Tenri Hospital, Tenri, Nara 632-8552, Japan
| | - Satoshi Matsunaga
- Department of Endocrinology, Tenri Hospital, Tenri, Nara 632-8552, Japan
| | - Shintaro Okamura
- Department of Endocrinology, Tenri Hospital, Tenri, Nara 632-8552, Japan
| | - Mako Kitatani
- Department of Endocrinology, Tenri Hospital, Tenri, Nara 632-8552, Japan
| | - Satoru Tsujii
- Department of Endocrinology, Tenri Hospital, Tenri, Nara 632-8552, Japan
| | - Yasuaki Hayashino
- Department of Endocrinology, Tenri Hospital, Tenri, Nara 632-8552, Japan
| | - Noriaki Kurita
- Department of Clinical Epidemiology, Graduate School of Medicine, Fukushima Medical University, Fukushima, Fukushima 960-1295, Japan; Department of Innovative Research and Education for Clinicians and Trainees (DiRECT), Fukushima Medical University Hospital, Fukushima, Fukushima 960-1295, Japan; Center for Innovative Research for Communities and Clinical Excellence (CIRC2LE), Fukushima Medical University, Fukushima 960-1295, Japan; Institute for Health Outcomes and Process Evaluation Research (iHope International), Kyoto 604-8006, Japan
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3
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Iida A, Sano K, Inokuchi M, Nomura J, Suzuki T, Kuriki M, Sogabe M, Susaki D, Tonosaki K, Kinoshita T, Hondo E. Cubam receptor-mediated endocytosis in hindgut-derived pseudoplacenta of a viviparous teleost (Xenotoca eiseni). J Exp Biol 2021; 224:269277. [PMID: 34170318 PMCID: PMC8278012 DOI: 10.1242/jeb.242613] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 06/01/2021] [Indexed: 11/20/2022]
Abstract
Nutrient transfer from mother to embryo is essential for reproduction in viviparous animals. In the viviparous teleost Xenotoca eiseni (family Goodeidae), the intraovarian embryo intakes the maternal component secreted into the ovarian fluid via the trophotaenia. Our previous study reported that the epithelial layer cells of the trophotaenia incorporate a maternal protein via vesicle trafficking. However, the molecules responsible for the absorption were still elusive. Here, we focused on Cubam (Cubilin-Amnionless) as a receptor involved in the absorption, and cathepsin L as a functional protease in the vesicles. Our results indicated that the Cubam receptor is distributed in the apical surface of the trophotaenia epithelium and then is taken into the intracellular vesicles. The trophotaenia possesses acidic organelles in epithelial layer cells and cathepsin L-dependent proteolysis activity. This evidence does not conflict with our hypothesis that receptor-mediated endocytosis and proteolysis play roles in maternal macromolecule absorption via the trophotaenia in viviparous teleosts. Such nutrient absorption involving endocytosis is not a specific trait in viviparous fish. Similar processes have been reported in the larval stage of oviparous fish or the suckling stage of viviparous mammals. Our findings suggest that the viviparous teleost acquired trophotaenia-based viviparity from a modification of the intestinal absorption system common in vertebrates. This is a fundamental study to understand the strategic variation of the reproductive system in vertebrates.
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Affiliation(s)
- Atsuo Iida
- Department of Animal Sciences, Graduate School of Bioagricultural Sciences, Nagoya University, Tokai National Higher Education and Research System, Nagoya 464-8601, Aichi, Japan
| | - Kaori Sano
- Department of Chemistry, Faculty of Science, Josai University, Sakado 350-0295, Saitama, Japan
| | - Mayu Inokuchi
- Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, University of Tokyo, Bunkyo, Tokyo 113-8657, Japan
| | - Jumpei Nomura
- Department of Animal Sciences, Graduate School of Bioagricultural Sciences, Nagoya University, Tokai National Higher Education and Research System, Nagoya 464-8601, Aichi, Japan
| | - Takayuki Suzuki
- Department of Animal Sciences, Graduate School of Bioagricultural Sciences, Nagoya University, Tokai National Higher Education and Research System, Nagoya 464-8601, Aichi, Japan
| | - Mao Kuriki
- Department of Regeneration Science and Engineering, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto, Kyoto 606-8507, Japan
| | - Maina Sogabe
- Department of Regeneration Science and Engineering, Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto, Kyoto 606-8507, Japan
| | - Daichi Susaki
- Kihara Institute for Biological Research, Yokohama City University, Yokohama 244-0813, Kanagawa, Japan
| | - Kaoru Tonosaki
- Kihara Institute for Biological Research, Yokohama City University, Yokohama 244-0813, Kanagawa, Japan
| | - Tetsu Kinoshita
- Kihara Institute for Biological Research, Yokohama City University, Yokohama 244-0813, Kanagawa, Japan
| | - Eiichi Hondo
- Department of Animal Sciences, Graduate School of Bioagricultural Sciences, Nagoya University, Tokai National Higher Education and Research System, Nagoya 464-8601, Aichi, Japan
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Gburek J, Konopska B, Gołąb K. Renal Handling of Albumin-From Early Findings to Current Concepts. Int J Mol Sci 2021; 22:ijms22115809. [PMID: 34071680 PMCID: PMC8199105 DOI: 10.3390/ijms22115809] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Revised: 05/20/2021] [Accepted: 05/25/2021] [Indexed: 12/29/2022] Open
Abstract
Albumin is the main protein of blood plasma, lymph, cerebrospinal and interstitial fluid. The protein participates in a variety of important biological functions, such as maintenance of proper colloidal osmotic pressure, transport of important metabolites and antioxidant action. Synthesis of albumin takes place mainly in the liver, and its catabolism occurs mostly in vascular endothelium of muscle, skin and liver, as well as in the kidney tubular epithelium. Long-lasting investigation in this area has delineated the principal route of its catabolism involving glomerular filtration, tubular endocytic uptake via the multiligand scavenger receptor tandem—megalin and cubilin-amnionless complex, as well as lysosomal degradation to amino acids. However, the research of the last few decades indicates that also additional mechanisms may operate in this process to some extent. Direct uptake of albumin in glomerular podocytes via receptor for crystallizable region of immunoglobulins (neonatal FC receptor) was demonstrated. Additionally, luminal recycling of short peptides into the bloodstream and/or back into tubular lumen or transcytosis of whole molecules was suggested. The article discusses the molecular aspects of these processes and presents the major findings and controversies arising in the light of the research concerning the last decade. Their better characterization is essential for further research into pathophysiology of proteinuric renal failure and development of effective therapeutic strategies.
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Bryniarski MA, Ren T, Rizvi AR, Snyder AM, Morris ME. Targeting the Choroid Plexuses for Protein Drug Delivery. Pharmaceutics 2020; 12:pharmaceutics12100963. [PMID: 33066423 PMCID: PMC7602164 DOI: 10.3390/pharmaceutics12100963] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2020] [Revised: 10/05/2020] [Accepted: 10/10/2020] [Indexed: 12/15/2022] Open
Abstract
Delivery of therapeutic agents to the central nervous system is challenged by the barriers in place to regulate brain homeostasis. This is especially true for protein therapeutics. Targeting the barrier formed by the choroid plexuses at the interfaces of the systemic circulation and ventricular system may be a surrogate brain delivery strategy to circumvent the blood-brain barrier. Heterogenous cell populations located at the choroid plexuses provide diverse functions in regulating the exchange of material within the ventricular space. Receptor-mediated transcytosis may be a promising mechanism to deliver protein therapeutics across the tight junctions formed by choroid plexus epithelial cells. However, cerebrospinal fluid flow and other barriers formed by ependymal cells and perivascular spaces should also be considered for evaluation of protein therapeutic disposition. Various preclinical methods have been applied to delineate protein transport across the choroid plexuses, including imaging strategies, ventriculocisternal perfusions, and primary choroid plexus epithelial cell models. When used in combination with simultaneous measures of cerebrospinal fluid dynamics, they can yield important insight into pharmacokinetic properties within the brain. This review aims to provide an overview of the choroid plexuses and ventricular system to address their function as a barrier to pharmaceutical interventions and relevance for central nervous system drug delivery of protein therapeutics. Protein therapeutics targeting the ventricular system may provide new approaches in treating central nervous system diseases.
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Altai M, Garousi J, Rinne SS, Schulga A, Deyev S, Vorobyeva A. On the prevention of kidney uptake of radiolabeled DARPins. EJNMMI Res 2020; 10:7. [PMID: 32020413 PMCID: PMC7000568 DOI: 10.1186/s13550-020-0599-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2020] [Accepted: 01/17/2020] [Indexed: 12/27/2022] Open
Abstract
Background Designed ankyrin repeat proteins (DARPins) are small engineered scaffold proteins (14–18 kDa) that demonstrated promising tumor-targeting properties in preclinical studies. However, high renal accumulation of activity for DARPins labeled with residualizing labels is a limitation for targeted radionuclide therapy. A better understanding of the mechanisms behind the kidney uptake of DARPins could aid the development of strategies to reduce it. In this study, we have investigated whether the renal uptake of [99mTc]Tc(CO)3-G3 DARPin could be reduced by administration of compounds that act on various parts of the reabsorption system in the kidney. Results Co-injection of lysine or Gelofusine was not effective for the reduction of kidney uptake of [99mTc]Tc(CO)3-G3. Administration of sodium maleate before the injection of [99mTc]Tc(CO)3-G3 reduced the kidney-associated activity by 60.4 ± 10.3%, while administration of fructose reduced it by 46.9 ± 7.6% compared with the control. The decrease in the kidney uptake provided by sodium maleate was also observed for [99mTc]Tc(CO)3-9_29 DARPin. Preinjection of colchicine, probenecid, mannitol, or furosemide had no effect on the kidney uptake of [99mTc]Tc(CO)3-G3. Kidney autoradiography showed mainly cortical accumulation of activity for all studied groups. Conclusion Common clinical strategies were not effective for the reduction of kidney uptake of [99mTc]Tc(CO)3-G3. Both fructose and maleate lower the cellular ATP level in the proximal tubule cells and their reduction of the kidney reuptake indicates the involvement of an ATP-driven uptake mechanism. The decrease provided by maleate for both G3 and 9_29 DARPins indicates that their uptake proceeds through a mechanism independent of DARPin structure and binding site composition.
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Affiliation(s)
- Mohamed Altai
- Department of Immunology, Genetics and Pathology, Uppsala University, SE-75185, Uppsala, Sweden
| | - Javad Garousi
- Department of Immunology, Genetics and Pathology, Uppsala University, SE-75185, Uppsala, Sweden
| | - Sara S Rinne
- Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden
| | - Alexey Schulga
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia
| | - Sergey Deyev
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia.,National Research Tomsk Polytechnic University, Tomsk, Russia.,Center of Biomedical Engineering, Sechenov University, Moscow, Russia
| | - Anzhelika Vorobyeva
- Department of Immunology, Genetics and Pathology, Uppsala University, SE-75185, Uppsala, Sweden. .,National Research Tomsk Polytechnic University, Tomsk, Russia.
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7
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Patel BM, Goyal RK. Liver and insulin resistance: New wine in old bottle!!! Eur J Pharmacol 2019; 862:172657. [DOI: 10.1016/j.ejphar.2019.172657] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Revised: 09/02/2019] [Accepted: 09/05/2019] [Indexed: 12/20/2022]
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Hirano M. An Endocytic Receptor, Megalin-Ligand Interactions: Effects of Glycosylation. TRENDS GLYCOSCI GLYC 2018. [DOI: 10.4052/tigg.1752.1j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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9
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Hirano M. An Endocytic Receptor, Megalin-Ligand Interactions: Effects of Glycosylation. TRENDS GLYCOSCI GLYC 2018. [DOI: 10.4052/tigg.1752.1e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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10
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Liu GW, Prossnitz AN, Eng DG, Cheng Y, Subrahmanyam N, Pippin JW, Lamm RJ, Ngambenjawong C, Ghandehari H, Shankland SJ, Pun SH. Glomerular disease augments kidney accumulation of synthetic anionic polymers. Biomaterials 2018; 178:317-325. [DOI: 10.1016/j.biomaterials.2018.06.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Revised: 05/31/2018] [Accepted: 06/02/2018] [Indexed: 12/22/2022]
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Tokarz VL, MacDonald PE, Klip A. The cell biology of systemic insulin function. J Cell Biol 2018; 217:2273-2289. [PMID: 29622564 PMCID: PMC6028526 DOI: 10.1083/jcb.201802095] [Citation(s) in RCA: 230] [Impact Index Per Article: 38.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Revised: 03/21/2018] [Accepted: 03/23/2018] [Indexed: 12/12/2022] Open
Abstract
Insulin is the paramount anabolic hormone, promoting carbon energy deposition in the body. Its synthesis, quality control, delivery, and action are exquisitely regulated by highly orchestrated intracellular mechanisms in different organs or "stations" of its bodily journey. In this Beyond the Cell review, we focus on these five stages of the journey of insulin through the body and the captivating cell biology that underlies the interaction of insulin with each organ. We first analyze insulin's biosynthesis in and export from the β-cells of the pancreas. Next, we focus on its first pass and partial clearance in the liver with its temporality and periodicity linked to secretion. Continuing the journey, we briefly describe insulin's action on the blood vasculature and its still-debated mechanisms of exit from the capillary beds. Once in the parenchymal interstitium of muscle and adipose tissue, insulin promotes glucose uptake into myofibers and adipocytes, and we elaborate on the intricate signaling and vesicle traffic mechanisms that underlie this fundamental function. Finally, we touch upon the renal degradation of insulin to end its action. Cellular discernment of insulin's availability and action should prove critical to understanding its pivotal physiological functions and how their failure leads to diabetes.
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Affiliation(s)
- Victoria L Tokarz
- Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, Canada
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Patrick E MacDonald
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
| | - Amira Klip
- Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, Canada
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
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Fatah H, Benfaed N, Chana RS, Chunara MH, Barratt J, Baines RJ, Brunskill NJ. Reduced proximal tubular expression of protein endocytic receptors in proteinuria is associated with urinary receptor shedding. Nephrol Dial Transplant 2017; 33:934-943. [DOI: 10.1093/ndt/gfx321] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2017] [Accepted: 10/01/2017] [Indexed: 02/06/2023] Open
Affiliation(s)
- Hiwa Fatah
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
| | - Nura Benfaed
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
| | - Ravinder S Chana
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
| | - Mohamed H Chunara
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
| | - Jonathan Barratt
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
- Department of Nephrology, Leicester General Hospital, Leicester, UK
| | - Richard J Baines
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
- Department of Nephrology, Leicester General Hospital, Leicester, UK
| | - Nigel J Brunskill
- Department of Infection Immunity and Inflammation, University of Leicester, Leicester, UK
- Department of Nephrology, Leicester General Hospital, Leicester, UK
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Sun J, Hultenby K, Axelsson J, Nordström J, He B, Wernerson A, Lindström K. Proximal Tubular Expression Patterns of Megalin and Cubilin in Proteinuric Nephropathies. Kidney Int Rep 2017; 2:721-732. [PMID: 29142988 PMCID: PMC5678615 DOI: 10.1016/j.ekir.2017.02.012] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Revised: 02/09/2017] [Accepted: 02/21/2017] [Indexed: 01/10/2023] Open
Abstract
Introduction Receptor-mediated endocytosis is responsible for protein reabsorption in the proximal tubules. For albumin this process involves at least 2 interacting receptors, megalin and cubilin. Albumin is not usually present in the urine, indicating a highly efficient tubular reuptake under physiological conditions. However, early appearance of albuminuria may mean that the tubular system is overwhelmed by large quantities of albumin or that the function is impaired. Methods To better understand the physiological role of megalin and cubilin in human renal disease, renal biopsies from 15 patients with a range of albuminuria and 3 healthy living donors were analyzed for proximal tubular expression of megalin and cubilin using immunohistochemistry (IHC) and semiquantitative immune-electron microscopy. Their expression in proteinuric zebrafish was also studied. Results Megalin and cubilin were expressed in brush border and cytoplasmic vesicles. Patients with microalbuminuric IgA nephropathy and thin membrane disease had significantly higher megalin in proximal tubules, whereas those with macro- or nephrotic-range albuminuria had unchanged levels. Cubilin expression was significantly higher in all patients. In a proteinuric zebrafish nphs2 knockdown model, we found a dose-dependent increase in the expression of tubular megalin and cubilin in response to tubular protein uptake. Discussion Megalin and cubilin show different expression patterns in different human diseases, which indicates that the 2 tubular proteins differently cooperate in cleaning up plasma proteins in kidney tubules.
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Affiliation(s)
- Jia Sun
- Division of Renal Medicine, Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden
| | - Kjell Hultenby
- Division of Clinical Research Center, Department of Laboratory Medicine, Karolinska Institutet, Stockholm, Sweden
| | - Jonas Axelsson
- Division of Matrix Biology, Department of Medical Biochemistry and Biophysics; Karolinska Institutet, Stockholm, Sweden.,Department Clinical Immunology, Karolinska University Hospital, Stockholm, Sweden
| | - Johan Nordström
- Division of Transplantation, Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden.,Department of Transplant Surgery, Karolinska University Hospital, Stockholm, Sweden
| | - Bing He
- Division of Matrix Biology, Department of Medical Biochemistry and Biophysics; Karolinska Institutet, Stockholm, Sweden
| | - Annika Wernerson
- Division of Renal Medicine, Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden.,Department of Pathology, Karolinska University Hospital, Stockholm, Sweden
| | - Karin Lindström
- Division of Renal Medicine, Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Stockholm, Sweden.,Department of Nephrology, Karolinska University Hospital, Stockholm, Sweden
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Nielsen R, Christensen EI, Birn H. Megalin and cubilin in proximal tubule protein reabsorption: from experimental models to human disease. Kidney Int 2017; 89:58-67. [PMID: 26759048 DOI: 10.1016/j.kint.2015.11.007] [Citation(s) in RCA: 298] [Impact Index Per Article: 42.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Revised: 08/17/2015] [Accepted: 08/19/2015] [Indexed: 01/19/2023]
Abstract
Proximal tubule protein uptake is mediated by 2 receptors, megalin and cubilin. These receptors rescue a variety of filtered ligands, including biomarkers, essential vitamins, and hormones. Receptor gene knockout animal models have identified important functions of the receptors and have established their essential role in modulating urinary protein excretion. Rare genetic syndromes associated with dysfunction of these receptors have been identified and characterized, providing additional information on the importance of these receptors in humans. Using various disease models in combination with receptor gene knockout, the implications of receptor dysfunction in acute and chronic kidney injury have been explored and have pointed to potential new roles of these receptors. Based on data from animal models, this paper will review current knowledge on proximal tubule endocytic receptor function and regulation, and their role in renal development, protein reabsorption, albumin uptake, and normal renal physiology. These findings have implications for the pathophysiology and diagnosis of proteinuric renal diseases. We will examine the limitations of the different models and compare the findings to phenotypic observations in inherited human disorders associated with receptor dysfunction. Furthermore, evidence from receptor knockout mouse models as well as human observations suggesting a role of protein receptors for renal disease will be discussed in light of conditions such as chronic kidney disease, diabetes, and hypertension.
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Affiliation(s)
- Rikke Nielsen
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | | | - Henrik Birn
- Department of Biomedicine, Aarhus University, Aarhus, Denmark; Department of Renal Medicine, Aarhus University Hospital, Aarhus, Denmark.
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The involvement of selected membrane transport mechanisms in the cellular uptake of 177Lu-labeled bombesin, somatostatin and gastrin analogues. Nucl Med Biol 2015; 42:1-7. [DOI: 10.1016/j.nucmedbio.2014.09.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Revised: 04/15/2014] [Accepted: 04/15/2014] [Indexed: 11/21/2022]
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16
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Storm T, Heegaard S, Christensen EI, Nielsen R. Megalin-deficiency causes high myopia, retinal pigment epithelium-macromelanosomes and abnormal development of the ciliary body in mice. Cell Tissue Res 2014; 358:99-107. [PMID: 24980834 PMCID: PMC4186978 DOI: 10.1007/s00441-014-1919-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Accepted: 05/15/2014] [Indexed: 11/28/2022]
Abstract
In man, mutations of the megalin-encoding gene causes the rare Donnai-Barrow/Facio-Oculo-Acoustico-Renal Syndrome, which is partially characterized by high-grade myopia. Previous studies of renal megalin function have established that megalin is crucial for conservation of renal filtered nutrients including vitamin A; however, the role of megalin in ocular physiology and development is presently unknown. Therefore, we investigate ocular megalin expression and the ocular phenotype of megalin-deficient mice. Topographical and subcellular localization of megalin as well as the ocular phenotype of megalin-deficient mice were examined with immunological techniques using light, confocal and electron microscopy. We identified megalin in the retinal pigment epithelium (RPE) and non-pigmented ciliary body epithelium (NPCBE) in normal mouse eyes. Immunocytochemical investigations furthermore showed that megalin localizes to vesicular structures in the RPE and NPCBE cells. Histological investigations of ocular mouse tissue also identified a severe myopia phenotype as well as enlarged RPE melanosomes and abnormal ciliary body development in the megalin-deficient mice. In conclusion, the complex ocular phenotype observed in the megalin-deficient mice suggests that megalin-mediated developmental abnormalities may contribute to the high myopia phenotype observed in the Donnai-Barrow Syndrome patients and, thus, that megalin harbors important roles in ocular development and physiology. Finally, our data show that megalin-deficient mice may provide a valuable model for future studies of megalin in ocular physiology and pathology.
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Affiliation(s)
- Tina Storm
- Department of Biomedicine, Faculty of Health Sciences, Aarhus University, Wilhelm Meyers Allé 3, DK-8000, Aarhus, Denmark,
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17
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Zhou P, Sun X, Zhang Z. Kidney-targeted drug delivery systems. Acta Pharm Sin B 2014; 4:37-42. [PMID: 26579362 PMCID: PMC4590725 DOI: 10.1016/j.apsb.2013.12.005] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2013] [Revised: 12/12/2013] [Accepted: 12/16/2013] [Indexed: 12/20/2022] Open
Abstract
Kidney-targeted drug delivery systems represent a promising technology to improve drug efficacy and safety in the treatment of renal diseases. In this review, we summarize the strategies that have been employed to develop kidney-targeted drug delivery systems. We also describe how macromolecular carriers and prodrugs play crucial roles in targeting drugs to particular target cells in the kidney. New technologies render it possible to create renal targeting conjugates and other delivery systems including nanoparticles and liposomes present promising strategies to achieve the goal of targeting drugs to the kidney.
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Affiliation(s)
| | - Xun Sun
- Corresponding author. Tel.: +86 28 85502307; fax: +86 28 85501615.
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18
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Mahadevappa R, Nielsen R, Christensen EI, Birn H. Megalin in acute kidney injury: foe and friend. Am J Physiol Renal Physiol 2013; 306:F147-54. [PMID: 24197071 DOI: 10.1152/ajprenal.00378.2013] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The kidney proximal tubule is a key target in many forms of acute kidney injury (AKI). The multiligand receptor megalin is responsible for the normal proximal tubule uptake of filtered molecules, including nephrotoxins, cytokines, and markers of AKI. By mediating the uptake of nephrotoxins, megalin plays an essential role in the development of some types of AKI. However, megalin also mediates the tubular uptake of molecules implicated in the protection against AKI, and changes in megalin expression have been demonstrated in AKI in animal models. Thus, modulation of megalin expression in response to AKI may be an important part of the tubule cell adaption to cellular protection and regeneration and should be further investigated as a potential target of intervention. This review explores current evidence linking megalin expression and function to the development, diagnosis, and progression of AKI as well as renal protection against AKI.
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Affiliation(s)
- Ravikiran Mahadevappa
- Dept. of Biomedicine, Aarhus Univ., Wilhelm Meyers Allé 3, Bldg. 1234, Aarhus DK-8000, Denmark.
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19
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Christensen EI, Wagner CA, Kaissling B. Uriniferous tubule: structural and functional organization. Compr Physiol 2013; 2:805-61. [PMID: 23961562 DOI: 10.1002/cphy.c100073] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The uriniferous tubule is divided into the proximal tubule, the intermediate (thin) tubule, the distal tubule and the collecting duct. The present chapter is based on the chapters by Maunsbach and Christensen on the proximal tubule, and by Kaissling and Kriz on the distal tubule and collecting duct in the 1992 edition of the Handbook of Physiology, Renal Physiology. It describes the fine structure (light and electron microscopy) of the entire mammalian uriniferous tubule, mainly in rats, mice, and rabbits. The structural data are complemented by recent data on the location of the major transport- and transport-regulating proteins, revealed by morphological means(immunohistochemistry, immunofluorescence, and/or mRNA in situ hybridization). The structural differences along the uriniferous tubule strictly coincide with the distribution of the major luminal and basolateral transport proteins and receptors and both together provide the basis for the subdivision of the uriniferous tubule into functional subunits. Data on structural adaptation to defined functional changes in vivo and to genetical alterations of specified proteins involved in transepithelial transport importantly deepen our comprehension of the correlation of structure and function in the kidney, of the role of each segment or cell type in the overall renal function,and our understanding of renal pathophysiology.
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Burke KA, Jauniaux E, Burton GJ, Cindrova-Davies T. Expression and immunolocalisation of the endocytic receptors megalin and cubilin in the human yolk sac and placenta across gestation. Placenta 2013; 34:1105-9. [PMID: 23978537 PMCID: PMC3820039 DOI: 10.1016/j.placenta.2013.08.003] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Revised: 07/31/2013] [Accepted: 08/05/2013] [Indexed: 11/04/2022]
Abstract
Megalin and cubilin are multifunctional endocytic receptors associated with many transporting epithelia. They play an essential role in transport of nutrients through the visceral yolk sac of rodents during embryogenesis. Here, we immunolocalise them to the endodermal layer of the human yolk sac, and to the syncytiotrophoblast and cytotrophoblast cells of placental villi. In villi, the protein level of both receptors increased with gestation. The mRNA for megalin remained constant, while that encoding cubilin increased with gestation. These results suggest megalin and cubilin may be important in human maternal–fetal transfer, and that they increase across gestation to facilitate this function.
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Affiliation(s)
- K A Burke
- Centre for Trophoblast Research, University of Cambridge, Cambridge, UK
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21
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Urinary protein patterns in patients with Balkan endemic nephropathy. Int Urol Nephrol 2013; 45:1661-9. [PMID: 23877662 DOI: 10.1007/s11255-013-0499-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2012] [Accepted: 06/19/2013] [Indexed: 10/26/2022]
Abstract
PURPOSE Urinary excretion of beta2-microglobulin (beta2-MG), albumin, immunoglobulin G (IgG) and protein was examined in patients with Balkan endemic nephropathy (BEN), glomerulonephritis (GN) and healthy controls. METHODS The proteins were measured in morning urine samples from 74 patients with BEN, 50 healthy persons and 22 patients with GN. RESULTS In BEN patients, median values for albumin, beta2-MG and protein were above upper normal limits, but median IgG was inside normal range. All patients with GN had microalbuminuria (MAU) and half of them had increased urinary beta2-MG, which was also found in eleven patients with increased urinary IgG. In BEN patients, there were significant negative correlations between eGFR and all measured urinary proteins, the composition of which changed during the course of BEN. In patients with eGFR > 60 ml/min/1.73 m(2) isolated beta2-MG was the most frequent finding (10/12 patients), but MAU was present in 4/12 patients. In BEN patients with eGFR between 30 and 59 ml/min/1.73 m(2), beta2-MG appeared as often as the combination of beta2-MG and albumin and isolated MAU. Out of 49 BEN patients with eGFR > 30 ml/min/1.73 m(2) 15 had increased urinary IgG either alone (1) or together with beta2-MG (3) or albumin (3) or beta2-MG and albumin (8). In BEN patients with GFR < 30 ml/min/1.73 m(2) only 1/25 had isolated beta2-MG but increased urinary IgG with increased beta2-MG, and albumin was the most frequent. CONCLUSION Although low-molecular weight proteinuria was the most frequent urinary finding in BEN patients, MAU was frequently detected in advanced stages of BEN but also in some patients with eGFR > 60 ml/min/1.73 m(2). IgG was increasingly found as eGFR decreased.
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Christensen EI, Birn H, Storm T, Weyer K, Nielsen R. Endocytic Receptors in the Renal Proximal Tubule. Physiology (Bethesda) 2012; 27:223-36. [DOI: 10.1152/physiol.00022.2012] [Citation(s) in RCA: 170] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Protein reabsorption is a predominant feature of the renal proximal tubule. Animal studies show that the ability to rescue plasma proteins relies on the endocytic receptors megalin and cubilin. Recently, studies of patients with syndromes caused by dysfunctional receptors have supported the importance of these for protein clearance of human ultrafiltrate. This review focuses on the molecular biology and physiology of the receptors and their involvement in renal pathological conditions.
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Affiliation(s)
- Erik I. Christensen
- Department of Biomedicine, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark
| | - Henrik Birn
- Department of Biomedicine, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark
| | - Tina Storm
- Department of Biomedicine, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark
| | - Kathrin Weyer
- Department of Biomedicine, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark
| | - Rikke Nielsen
- Department of Biomedicine, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark
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Baines RJ, Chana RS, Hall M, Febbraio M, Kennedy D, Brunskill NJ. CD36 mediates proximal tubular binding and uptake of albumin and is upregulated in proteinuric nephropathies. Am J Physiol Renal Physiol 2012; 303:F1006-14. [PMID: 22791331 DOI: 10.1152/ajprenal.00021.2012] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Dysregulation of renal tubular protein handling in proteinuria contributes to the development of chronic kidney disease. We investigated the role of CD36 as a novel candidate mediator of albumin binding and endocytosis in the kidney proximal tubule using both in vitro and in vivo approaches, and in nephrotic patient renal biopsy samples. In CD36-transfected opossum kidney proximal tubular cells, both binding and uptake of albumin were substantially enhanced. A specific CD36 inhibitor abrogated this effect, but receptor-associated protein, which blocks megalin-mediated endocytosis of albumin, did not. Mouse proximal tubular cells expressed CD36 and this was absent in CD36 null animals, whereas expression of megalin was equal in these animals. Compared with wild-type mice, CD36 null mice demonstrated a significantly increased urinary protein-to-creatinine ratio and albumin-to-creatinine ratio. Proximal tubular cells expressed increased CD36 when exposed to elevated albumin concentrations in culture medium. Expression of CD36 was studied in renal biopsy tissue obtained from adult patients with heavy proteinuria due to minimal change disease, membranous nephropathy, or focal segmental glomerulosclerosis. Proximal tubular CD36 expression was markedly increased in proteinuric individuals. We conclude that CD36 is a novel mediator influencing binding and uptake of albumin in the proximal tubule that is upregulated in proteinuric renal diseases. CD36 may represent a potential therapeutic target in proteinuric nephropathy.
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Affiliation(s)
- Richard J Baines
- Dept. of Nephrology, Leicester General Hospital, Gwendolen Rd., Leicester, LE5 4PW, United Kingdom
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24
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Zhou L, Liu F, Huang XR, Liu F, Chen H, Chung ACK, Shi J, Wei L, Lan HY, Fu P. Amelioration of albuminuria in ROCK1 knockout mice with streptozotocin-induced diabetic kidney disease. Am J Nephrol 2011; 34:468-75. [PMID: 21986457 DOI: 10.1159/000332040] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2011] [Accepted: 08/17/2011] [Indexed: 02/05/2023]
Abstract
BACKGROUND Although blockade of Rho kinase with pharmacologic inhibitors ameliorates renal fibrosis and diabetic kidney disease (DKD), the underlined mechanisms remain largely unclear. The present study tested the hypothesis that ROCK1 may regulate the early development of albuminuria via the megalin/cubilin-dependent mechanism. METHODS A DKD model was induced in ROCK1 knockout and wild-type mice by streptozotocin (STZ). The effect of deleted ROCK1 on urinary albumin excretion and the expression of megalin/cubilin were examined. In addition, the effect of blocking ROCK activities with an inhibitor (Y-27632) on tubular albumin reabsorption was tested in a normal rat tubular epithelial cell line (NRK52E) under high-glucose conditions. Expression of transforming growth factor (TGF)-β1, interleukin-1β and collagen-1 was also been examined. RESULTS Urinary albumin excretion was significantly increased in ROCK1 WT mice at 8 weeks after STZ injection. In contrast, mice lacking ROCK1 gene were protected against the development of albuminuria. This was associated with the protection against the loss of megalin/cubilin and an increase in TGF-β(1), IL-1β, and fibrosis in the kidney. In vitro, we also found that blockade of Rho kinase with inhibitor Y-27632 prevented high-glucose-induced loss of megalin expression and an increase of TGF-β(1), thereby increasing the absorption rate of FITC-labeled albumin by tubular epithelial cells. CONCLUSION ROCK1 may play a role in the development of albuminuria in DKD by downregulating the endocytosis receptors complex - megalin/cubilin.
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Affiliation(s)
- Li Zhou
- Department of Medicine-Nephrology, West China Hospital of Sichuan University, Chengdu, China
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25
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Sirolimus and everolimus reduce albumin endocytosis in proximal tubule cells via an angiotensin II-dependent pathway. Transpl Immunol 2010; 23:125-32. [DOI: 10.1016/j.trim.2010.05.003] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2009] [Revised: 02/19/2010] [Accepted: 05/04/2010] [Indexed: 11/23/2022]
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26
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Nagai J, Takano M. Molecular-targeted approaches to reduce renal accumulation of nephrotoxic drugs. Expert Opin Drug Metab Toxicol 2010; 6:1125-38. [DOI: 10.1517/17425255.2010.497140] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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27
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Nielsen R, Christensen EI. Proteinuria and events beyond the slit. Pediatr Nephrol 2010; 25:813-22. [PMID: 20049615 DOI: 10.1007/s00467-009-1381-9] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Revised: 10/27/2009] [Accepted: 10/27/2009] [Indexed: 11/30/2022]
Abstract
The origin of proteinuria is found in either the glomerular filtration device or the proximal tubular reabsorption machinery. During equilibrium, small amounts of predominantly low molecular weight proteins are filtered and reabsorbed by the receptor complex megalin/cubilin/amnionless. This results in a protein-free filtrate passing further down the tubule. During glomerular damage, the reabsorption machinery in the proximal tubule is challenged due to elevated amounts of proteins passing the glomerular filtration slits. Even though it is considered to be a high-capacity system, several conditions result in proteinuria, thus exposing the cells in the rest of the nephron to a protein-rich environment. The impact on cells in the more distal part of the nephron is uncertain, but studies support an involvement in fibrosis development. Protein accumulation in lysosomes of the proximal tubule, due to increased protein internalization, is thought to mediate inflammation and fibrosis, eventually leading to renal failure. In contrast, low molecular weight proteinuria develops when the endocytic machinery is malfunctioning either by direct or indirect causes such as in Imerslund-Gräsbeck syndrome (IGS) or Dent's disease, respectively. This review discusses the origin of proteinuria and describes the structural fundament for protein reabsorption in the proximal tubule as well as conditions resulting in low molecular weight proteinuria.
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Affiliation(s)
- Rikke Nielsen
- Department of Anatomy, Section of Cell Biology, Aarhus University, Building 1234, Aarhus C, Denmark
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28
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Li QR, Fan KX, Li RX, Dai J, Wu CC, Zhao SL, Wu JR, Shieh CH, Zeng R. A comprehensive and non-prefractionation on the protein level approach for the human urinary proteome: touching phosphorylation in urine. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2010; 24:823-832. [PMID: 20187088 DOI: 10.1002/rcm.4441] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Increasing attention has been paid to the urinary proteome because it holds the promise of discovering various disease biomarkers. However, most of the urine proteomics studies routinely relied on protein pre-fractionation and so far did not present characterization on phosphorylation status. Two robust approaches, integrated multidimensional liquid chromatography (IMDL) and Yin-yang multidimensional liquid chromatography (MDLC) tandem mass spectrometry, were recently developed in our laboratory, with high-coverage identification of peptide mixtures. In this study, we adopted a strategy without pre-fractionation on the protein level for urinary proteome identification, using both the IMDL and the Yin-yang MDLC methods for peptide fractionation followed by identification using a linear ion trap-orbitrap (LTQ-Orbitrap) mass spectrometer with high resolution and mass accuracy. A total of 1310 non-redundant proteins were highly confidently identified from two experiments, significantly including 59 phosphorylation sites. More than half the annotated identifications were membrane-related proteins. In addition, the lysosomal as well as kidney-associated proteins were detected. Compared with the six largest datasets of urinary proteins published previously, we found our data included most of the reported proteins. Our study developed a robust approach for exploring the human urinary proteome, which would provide a catalogue of urine proteins on a global scale. It is the first report, to our best knowledge, to profile the urinary phosphoproteome. This work significantly extends current comprehension of urinary protein modification and its potential biological significance. Moreover, the strategy could further serve as a reference for biomarker discovery.
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Affiliation(s)
- Qing-Run Li
- Key Laboratory of Systems Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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Bento-Abreu A, Velasco A, Polo-Hernández E, Lillo C, Kozyraki R, Tabernero A, Medina JM. Albumin endocytosis via megalin in astrocytes is caveola- and Dab-1 dependent and is required for the synthesis of the neurotrophic factor oleic acid. J Neurochem 2009; 111:49-60. [DOI: 10.1111/j.1471-4159.2009.06304.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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30
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Christensen EI, Verroust PJ, Nielsen R. Receptor-mediated endocytosis in renal proximal tubule. Pflugers Arch 2009; 458:1039-48. [PMID: 19499243 DOI: 10.1007/s00424-009-0685-8] [Citation(s) in RCA: 165] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2009] [Accepted: 05/19/2009] [Indexed: 01/08/2023]
Abstract
Proteins filtered in renal glomeruli are removed from the tubular fluid by endocytosis in the proximal tubule mediated by the two receptors megalin and cubilin. After endocytic uptake, the proteins are transferred to lysosomes for degradation, while the receptors are returned to the apical cell membrane by receptor recycling in dense apical tubules. In the renal proximal tubule, there is no significant transcellular transport of protein. The reabsorptive process is extremely efficient as evidenced by the virtual protein free urine in humans. The two receptors bind a variety of ligands. The process serves not only to remove the proteins from the ultrafiltrate but also to conserve a variety of essential substances such as vitamins and trace elements carried by plasma proteins. The endocytic apparatus is highly developed in the proximal tubule demonstrating the high capacity of the cells; however, under certain circumstances like diseases affecting the glomeruli, the system is overloaded resulting in proteinuria.
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Affiliation(s)
- Erik Ilsø Christensen
- Section of Cell Biology, Department of Anatomy, University of Aarhus, Wilh. Meyers Allé, Building 1234, 8000, Aarhus C, Denmark.
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Yuan ZX, Zhang ZR, Zhu D, Sun X, Gong T, Liu J, Luan CT. Specific Renal Uptake of Randomly 50% N-Acetylated Low Molecular Weight Chitosan. Mol Pharm 2008; 6:305-14. [PMID: 19035784 DOI: 10.1021/mp800078a] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Zhi-xiang Yuan
- Key Laboratory of Drug Targeting and Drug Delivery Systems, Ministry of Education, West China School of Pharmacy, Sichuan University, Chengdu, Sichuan, People’s Republic of China
| | - Zhi-rong Zhang
- Key Laboratory of Drug Targeting and Drug Delivery Systems, Ministry of Education, West China School of Pharmacy, Sichuan University, Chengdu, Sichuan, People’s Republic of China
| | - Di Zhu
- Key Laboratory of Drug Targeting and Drug Delivery Systems, Ministry of Education, West China School of Pharmacy, Sichuan University, Chengdu, Sichuan, People’s Republic of China
| | - Xun Sun
- Key Laboratory of Drug Targeting and Drug Delivery Systems, Ministry of Education, West China School of Pharmacy, Sichuan University, Chengdu, Sichuan, People’s Republic of China
| | - Tao Gong
- Key Laboratory of Drug Targeting and Drug Delivery Systems, Ministry of Education, West China School of Pharmacy, Sichuan University, Chengdu, Sichuan, People’s Republic of China
| | - Jie Liu
- Key Laboratory of Drug Targeting and Drug Delivery Systems, Ministry of Education, West China School of Pharmacy, Sichuan University, Chengdu, Sichuan, People’s Republic of China
| | - Chang-tao Luan
- Key Laboratory of Drug Targeting and Drug Delivery Systems, Ministry of Education, West China School of Pharmacy, Sichuan University, Chengdu, Sichuan, People’s Republic of China
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Guggino SE. Mechanisms of Disease: what can mouse models tell us about the molecular processes underlying Dent disease? ACTA ACUST UNITED AC 2007; 3:449-55. [PMID: 17653124 DOI: 10.1038/ncpneph0541] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2007] [Accepted: 05/15/2007] [Indexed: 11/09/2022]
Abstract
Two knockout mouse models of Dent disease are similar with regard to the characteristics of Fanconi syndrome, but differ markedly with respect to vitamin D and renal calcium handling. One model exhibits hypercalciuria, renal calcifications and renal failure; the other does not. Data from such experimental models have greatly advanced our understanding of the molecular mechanisms underlying Dent disease. This Review summarizes some of the important phenotypic characteristics shared by mouse models and people with Dent disease. Experimental data are used to predict the molecular mechanisms underlying this disease. Receptor-mediated endocytosis and the mistargeting of megalin, cubilin, the sodium/proton exchanger Nhe3 and the sodium/phosphate transporter Napi-2a will be reviewed, and the causes of mistargeting will be discussed. Kidney stones and renal failure are prominent features of Dent disease. Investigations using a mouse model with nephrocalcinosis and renal failure indicate that citrate therapy delays the onset of these processes in Dent disease. Throughout this Review, questions that might underpin new areas of investigation are proposed.
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Affiliation(s)
- Sandra E Guggino
- Johns Hopkins University Medical School, Baltimore, MD 21205, USA.
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Abstract
For over a decade the folate receptor has been intensively investigated as a means for tumor-specific delivery of a broad range of experimental therapies including several conceptually new treatments. Despite a few set backs in clinical trials, the literature is replete with encouraging in vitro and pre-clinical studies of gynecological and other tumors and more therapeutic approaches are ready for clinical testing. Recent studies have added myelogenous leukemias to the list of candidate cancers for FR-targeted therapies. Each approach faces unique challenges in translation that could be addressed through a mechanistic understanding of the function and expression of the receptor in the appropriate experimental systems and by improvements in the technology. This review discusses FR in the context of positive recent developments in broad areas of FR-targeted therapy and attempts to highlight its potential and the anticipated challenges.
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Negri AL. Proximal tubule endocytic apparatus as the specific renal uptake mechanism for vitamin D-binding protein/25-(OH)D3 complex. Nephrology (Carlton) 2007; 11:510-5. [PMID: 17199789 DOI: 10.1111/j.1440-1797.2006.00704.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The renal proximal tubule exhibits a very extensive apical endocytic apparatus that is involved in the reabsorption of molecules filtered in the glomeruli. Several key receptors appear to be involved in this function, which serves not only to conserve protein but also to reabsorb different vitamins in complex with their binding proteins. Recent research has established megalin as probably the most important receptor in this endocytosis process. Cubilin is another receptor identified in the proximal tubule endocytic apparatus. Because cubilin lacks transmembrane or cytoplasmic domains required for endocytosis, this receptor associates with megalin to recycle and internalize its ligands. Recent studies have shown that vitamin D-binding protein (DBP)/25-(OH)D3 complex is one of the megalin/cubilin ligands. Megalin knockout mice develop vitamin D deficiency and bone disease owing to an inability of the proximal tubules to capture the DBP/25-(OH)D3 complexes from the glomerular filtrate. In the same way, kidney-specific megalin knockout mice have severe plasma vitamin D deficiency, hypocalcaemia and serious bone disease, like the complete megalin knockout mice. Anti-cubilin antibodies inhibit cellular uptake of DBP/25-(OH)D3 by up to 70%. Anti-megalin antibodies produced a similar reduction in DBP/25-(OH)D3 endocytosis. When both antibodies were applied, impairment of DBP/25-(OH)D3 was only slightly more impaired (around 80%), suggesting that cubilin and megalin function through the same endocytic pathway. Specific forms of renal Fanconi syndrome are associated with endocytic pathway dysfunction with disruption of megalin-mediated uptake DBP/25-(OH)D3 complex, producing metabolic bone disease in affected individuals as a prominent clinical finding.
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Affiliation(s)
- Armando Luis Negri
- Physiology and Biophysics Department, Universidad del Salvador School of Medicine, Buenos Aires, Argentina.
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Seliverstova EV, Burmakin MV, Natochin YV. Renal clearance of absorbed intact GFP in the frog and rat intestine. Comp Biochem Physiol A Mol Integr Physiol 2007; 147:1067-73. [PMID: 17442603 DOI: 10.1016/j.cbpa.2007.03.019] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2007] [Revised: 03/12/2007] [Accepted: 03/13/2007] [Indexed: 11/15/2022]
Abstract
Intestine absorption of intact green fluorescent protein (GFP) and its following accumulation in the renal proximal tubule cells after its intragastric administration have been established by confocal microscopy in the rat and frog. Reabsorbed GFP was revealed in the endosomes and lysosomes of the proximal tubule cells by the methods of GFP photooxidation and immunofluorescent microscopy. The GFP intestine absorption rate and GFP accumulation in the kidney were significantly higher in the frog than in the rat. No specific fluorescence was revealed in the liver and colon cells after the GFP intragastric administration. The data obtained indicate the ability of the small intestine in the frog and rat to absorb intact proteins and an important role of the kidney in exogenous protein metabolism.
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Affiliation(s)
- E V Seliverstova
- Laboratory of Renal Physiology, Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russia
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Zheng B, Tang T, Tang N, Kudlicka K, Ohtsubo K, Ma P, Marth JD, Farquhar MG, Lehtonen E. Essential role of RGS-PX1/sorting nexin 13 in mouse development and regulation of endocytosis dynamics. Proc Natl Acad Sci U S A 2006; 103:16776-81. [PMID: 17077144 PMCID: PMC1636531 DOI: 10.1073/pnas.0607974103] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
RGS-PX1 (also known as sorting nexin 13) is a member of both the regulator of G protein signaling (RGS) and sorting nexin (SNX) protein families. Biochemical and cell culture studies have shown that RGS-PX1/SNX13 attenuates Galphas-mediated signaling through its RGS domain and regulates endocytic trafficking and degradation of the epidermal growth factor receptor. To understand the functions of RGS-PX1/SNX13 in vivo, we generated mice carrying targeted mutations of Snx13 and found that systemic Snx13-null mice were embryonic lethal around midgestation. Snx13-null embryos had significant overall growth retardation and defects in neural tube closure, blood vessel formation, and the formation of the placental labyrinthine layer. Moreover, the Snx13-null visceral yolk sac endoderm cells showed dramatic changes in the organization of endocytic compartments, abundant autophagic vacuoles, and abnormal localization of several endocytic markers, including megalin, a receptor for nutrients and proteins; ARH, a coat protein that binds megalin; LAMP2; and LC3. These changes suggest that Snx13-null embryos are defective in nutrient uptake and transport, which may contribute to the other developmental abnormalities observed. Taken together, our findings demonstrate an essential role for RGS-PX1/SNX13 in mouse development and provide previously undescribed insights into its cellular function in the regulation of endocytosis dynamics.
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Affiliation(s)
- Bin Zheng
- Departments of *Cellular and Molecular Medicine and
| | | | - Nan Tang
- Biology, University of California at San Diego, La Jolla, CA 92093-0651
| | | | | | - Phuong Ma
- Departments of *Cellular and Molecular Medicine and
| | | | - Marilyn G. Farquhar
- Departments of *Cellular and Molecular Medicine and
- To whom correspondence should be addressed. E-mail:
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Fisher CE, Howie SEM. The role of megalin (LRP-2/Gp330) during development. Dev Biol 2006; 296:279-97. [PMID: 16828734 DOI: 10.1016/j.ydbio.2006.06.007] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Revised: 04/21/2006] [Accepted: 06/05/2006] [Indexed: 11/17/2022]
Abstract
Megalin (LRP-2/GP330), a member of the LDL receptor family, is an endocytic receptor expressed mainly in polarised epithelial cells. Identified as the pathogenic autoantigen of Heymann nephritis in rats, its functions have been studied in greatest detail in adult mammalian kidney, but there is increasing recognition of its involvement in embryonic development. The megalin homologue LRP-1 is essential for growth and development in Caenorhabditis elegans and megalin plays a role in CNS development in zebrafish. There is now also evidence for a homologue in Drosophila. However, most research concerns mammalian embryogenesis; it is widely accepted to be important during forebrain development and the developing renal proximal tubule. Megalin is also expressed in lung, eye, intestine, uterus, oviduct, and male reproductive tract. It is found in yolk sacs and the outer cells of pre-implantation mouse embryos, where interactions with cubilin result in nutrient endocytosis, and it may be important during implantation. Models for megalin interaction(s) with Sonic Hedgehog (Shh) have been proposed. The importance of Shh signalling during embryogenesis is well established; how and when megalin interacts with Shh is becoming a pertinent question in developmental biology.
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Affiliation(s)
- Carolyn E Fisher
- Centre for Inflammation Research, Queen's Research Institute, University of Edinburgh, 47 Little France Crescent, Edinburgh EH 16 4JT, Scotland, UK.
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Birn H. The kidney in vitamin B12and folate homeostasis: characterization of receptors for tubular uptake of vitamins and carrier proteins. Am J Physiol Renal Physiol 2006; 291:F22-36. [PMID: 16760376 DOI: 10.1152/ajprenal.00385.2005] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Over the past 10 years, animal studies have uncovered the molecular mechanisms for the renal tubular recovery of filtered vitamin and vitamin carrier proteins. Relatively few endocytic receptors are responsible for the proximal tubule uptake of a number of different vitamins, preventing urinary losses. In addition to vitamin conservation, tubular uptake by endocytosis is important to vitamin metabolism and homeostasis. The present review focuses on the receptors involved in renal tubular recovery of folate, vitamin B12, and their carrier proteins. The multiligand receptor megalin is important for the uptake and tubular accumulation of vitamin B12. During vitamin load, the kidney accumulates large amounts of free vitamin B12, suggesting a possible storage function. In addition, vitamin B12is metabolized in the kidney, suggesting a role in vitamin homeostasis. The folate receptor is important for the conservation of folate, mediating endocytosis of the vitamin. Interaction between the structurally closely related, soluble folate-binding protein and megalin suggests that megalin plays an additional role in the uptake of folate bound to filtered folate-binding protein. A third endocytic receptor, the intrinsic factor-B12receptor cubilin-amnionless complex, is essential to the renal tubular uptake of albumin, a carrier of folate. In conclusion, uptake is mediated by interaction with specific endocytic receptors also involved in the renal uptake of other vitamins and vitamin carriers. Little is known about the mechanisms regulating intracellular transport and release of vitamins, and whereas tubular uptake is a constitutive process, this may be regulated, e.g., by vitamin status.
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Affiliation(s)
- Henrik Birn
- Department of Cell Biology, Institute of Anatomy, University of Aarhus, Bldg. 234, DK-8000 Aarhus C, Denmark.
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Christensen EI, Nielsen R. Role of megalin and cubilin in renal physiology and pathophysiology. Rev Physiol Biochem Pharmacol 2006; 158:1-22. [PMID: 17729440 DOI: 10.1007/112_0604] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Megalin and cubilin are endocytic receptors highly expressed in the endocytic apparatus of the renal proximal tubule. These receptors appear to be responsible for the tubular clearance of most proteins filtered in the glomeruli. Cubilin is a peripheral membrane protein, and therefore it does not have an endocytosis signaling sequence. It appears that megalin is responsible for internalization of cubilin and its ligands in addition to internalizing its own ligands. The proteinuria observed in megalin-deficient mice, in dogs lacking functional cubilin, and in patients with distinct mutations of the cubilin gene illustrates the importance of the receptors.
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Affiliation(s)
- E I Christensen
- University of Aarhus, Department of Cell Biology, Institute of Anatomy, University Park, Building 234, 8000 Aarhus C, Denmark.
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Raila J, Willnow TE, Schweigert FJ. Megalin-mediated reuptake of retinol in the kidneys of mice is essential for vitamin A homeostasis. J Nutr 2005; 135:2512-6. [PMID: 16251603 DOI: 10.1093/jn/135.11.2512] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The reuptake of retinol (ROH) and retinol-binding protein (RBP) in the kidneys is mediated by the endocytic receptor megalin, suggesting an important role for this receptor in vitamin A (VA) metabolism. We examined the extent to which megalin deficiency may affect urinary ROH excretion, levels of ROH and RBP in plasma, as well as storage of VA in liver and kidney. For this purpose, mice with a kidney-specific megalin gene defect (megalin(lox/lox); apoE(Cre)) and control mice (megalin(lox/lox)) were fed either a basal diet containing 4500 retinol equivalents (RE)/kg diet or a diet without VA during experimental periods of 42 and 84 d. Urinary ROH excretion was observed only in megalin(lox/lox); apoE(Cre) mice (P < 0.0001, 2-way ANOVA) and not in the controls. Plasma ROH and RBP differed only by diet (P < 0.05), but not genotype (P = 0.615). A major effect of megalin deficiency, however, was evident in retinyl ester levels in the liver (P < 0.05), which were approximately 37% lower than those in megalin(lox/lox) controls (P < 0.05, Student's t test) during the 84-d period of dietary VA deprivation. Kidney levels of VA were not affected by the receptor gene defect. The findings demonstrate that urinary ROH excretion caused by megalin deficiency requires accelerated mobilization of hepatic VA stores to maintain normal plasma ROH levels, which suggests that megalin plays an essential role in systemic VA homeostasis.
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Affiliation(s)
- Jens Raila
- Institute of Nutritional Science, University of Potsdam, D-14558 Nuthetal (Bergholz-Rehbruecke), Germany
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Abstract
The proteinuria associated with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors is composed of primarily low-molecular weight proteins that disappear rapidly following discontinuation of the statin agent. More importantly, no evidence exists of nephrotoxicity or reduced renal function observed with the approved clinical dosages of any available statins. Recent clinical studies have suggested actual improvement in renal function demonstrated by decreases in creatinine concentrations and improvement in estimated glomerular filtration rates with both short-term and long-term administration of these agents. The progressive fibrosis and renal scarring of chronic kidney disease appears to be the end result of increased protein traffic in the proximal renal tubule. Early animal and recent clinical studies have suggested that treatment with statin agents in established chronic kidney disease can, in fact, provide renoprotection over and above that observed with aggressive blood pressure control and the use of angiotensin II antagonists.
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Affiliation(s)
- Donald G Vidt
- Department of Nephrology & Hypertension, Cleveland Clinic Foundation, Desk A51, Cleveland, OH 44195, USA.
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Cebotaru V, Kaul S, Devuyst O, Cai H, Racusen L, Guggino WB, Guggino SE. High citrate diet delays progression of renal insufficiency in the ClC-5 knockout mouse model of Dent's disease. Kidney Int 2005; 68:642-52. [PMID: 16014041 DOI: 10.1111/j.1523-1755.2005.00442.x] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Dent's disease, an X-linked renal tubular disorder, is characterized by low-molecular-weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, and progressive renal failure. Dent's disease results from mutations of the voltage-gated chloride channel CLC-5. METHODS We studied the effect of zero and high citrate diet on renal function of ClC-5 knockout mice and wild-type mice. The mice were placed in metabolic cages from which the urine was collected. Mice were sacrificed to obtain serum and tissues for analysis. RESULTS ClC-5 knockout mice fed zero or high citrate diet had significantly increased urinary calcium excretion compared with wild-type mice fed the same diets. Nine-month-old ClC-5 knockout mice on a zero citrate diet had significantly decreased glomerular filtration rate (GFR), whereas 9-month-old ClC-5 knockout mice on a high citrate diet had normal renal function. ClC-5 knockout mice fed a zero citrate diet had significantly increased tubular atrophy, interstitial fibrosis, cystic changes, and nephrocalcinosis compared to ClC-5 knockout mice fed a high citrate diet. Transforming growth factor-beta1 (TGF-beta1) was significantly increased in 9-month-old ClC-5 knockout mice on zero citrate diet compared to 9-month-old wild-type mice on the same diet. CONCLUSION High citrate diet preserved renal function and delayed progression of renal disease in ClC-5 knockout mice even in the apparent absence of stone formation. We conclude from this that long-term control of hypercalciuria is an important factor in preventing renal failure in these mice.
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Affiliation(s)
- Valeriu Cebotaru
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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Barone R, Van Der Smissen P, Devuyst O, Beaujean V, Pauwels S, Courtoy PJ, Jamar F. Endocytosis of the somatostatin analogue, octreotide, by the proximal tubule-derived opossum kidney (OK) cell line. Kidney Int 2005; 67:969-76. [PMID: 15698435 DOI: 10.1111/j.1523-1755.2005.00160.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND Nephrotoxicity of cancer therapy using radiolabeled somatostatin analogues such as octreotide is due to ultrafiltration and reuptake by proximal tubular cells (PTCs). The mechanism of uptake is unknown. It could occur either by receptor-mediated endocytosis via a somatostatin receptor or, alternatively, the multiligand megalin/cubilin tandem receptor, or by fluid-phase endocytosis. To define the mechanisms of internalization and to identify potential receptors, we have studied the uptake and processing of octreotide by the PTC-derived opossum kidney (OK) cell line. METHODS We compared the kinetics of uptake and fate of (111)In-diethylenetriamine pentaacetic acid (DTPA)-D-Phe(1)-octreotide and (125)I-human serum albumin ((125)I-HSA). To determine the contribution of receptor-mediated endocytosis, we tested competition for uptake by octreotide and somatostatin and by various megalin/cubilin ligands [receptor-associated protein (RAP), albumin, transferrin, insulin, polymixin B] or basic amino acids. The subcellular localization of fluorescein isothiocyanate (FITC)-D-Phe(1)-octreotide was studied by confocal microscopy. RESULTS Kinetics of uptake of (111)In-DTPA-D-Phe(1)-octreotide and (125)I-HSA by OK cells were comparable, but only the somatostatin analogue was significantly retained intact. All megalin/cubilin ligands and basic amino acids strongly inhibited (125)I-HSA uptake, but these could not compete for >50% of (111)In-DTPA-D-Phe(1)-octreotide uptake. The same was found for somatostatin and octreotide. The noncompetable uptake of (111)In-DTPA-D-Phe(1)-octreotide was comparable to the clearance of Lucifer Yellow, a marker of fluid-phase endocytosis. By confocal microscopy, FITC-D-Phe(1)-octreotide colocalized with transferrin in endosomes, then accumulated in lysosomes. CONCLUSION Receptor-mediated endocytosis via megalin/cubilin and fluid-phase endocytosis contribute about equally to the uptake of radiolabeled somatostatin analogues by OK cells.
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Affiliation(s)
- Raffaella Barone
- Center of Nuclear Medicine, University of Louvain Medical School, Brussels, Belgium
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Abstract
Tumour cell-targeted liposomal delivery has the potential to enhance the therapeutic efficacy and reduce the toxicity of anticancer agents. Folate receptor (FR) expression is frequently amplified among human malignancies. FR is, therefore, potentially useful as a tumour marker for targeted drug delivery. FR-mediated liposomal delivery has been shown to enhance the antitumour efficacy of doxorubicin both in vitro and in vivo, and to overcome P-glycoprotein-mediated multi-drug resistance. In addition, FR-targeted liposomes have shown utility as effective delivery vehicles of genes and antisense oligodeoxyribonucleotides to FR(+) tumour cells. Both solid tumours and leukaemias can potentially benefit from FR-targeted drug delivery. Multiple mechanisms might contribute to greater therapeutic efficacy for FR-targeted liposomes, such as FR-dependent cytotoxicity and antiangiogenic activity. Further investigation of this promising drug delivery strategy is clearly warranted.
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Affiliation(s)
- Xiaogang Pan
- The Ohio State University, Division of Pharmaceutics, College of Pharmacy and Comprehensive Cancer Center, 500 W. 12th Avenue, Columbus, OH 43210, USA
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Abstract
Albumin is the most abundant protein in serum and contributes to the maintenance of oncotic pressure as well as to transport of hydrophobic molecules. Although albumin is a large anionic protein, it is not completely retained by the glomerular filtration barrier. In order to prevent proteinuria, albumin is reabsorbed along the proximal tubules by receptor-mediated endocytosis, which involves the binding proteins megalin and cubilin. Endocytosis depends on proper vesicle acidification. Disturbance of endosomal acidification or loss of the binding proteins leads to tubular proteinuria. Furthermore, endocytosis is subject to modulation by different signaling systems, such as protein kinase A (PKA), protein kinase C (PKC), phosphatidylinositol 3-kinase (PI3-K) and transforming growth factor beta (TGF-beta). In addition to being reabsorbed in the proximal tubule, albumin can also act as a profibrotic and proinflammatory stimulus, thereby initiating or promoting tubulo-interstitial diseases.
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Affiliation(s)
- Michael Gekle
- Physiologisches Institut, University of Würzburg, 97070 Würzburg, Germany.
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Abstract
Myosin motor proteins use the energy derived from ATP hydrolysis to move cargo along actin tracks. Myosin VI, unlike almost all other myosins, moves toward the minus end of actin filaments and functions in a variety of intracellular processes such as vesicular membrane traffic, cell migration, and mitosis. These diverse roles of myosin VI are mediated by interaction with a number of different binding partners present in multi-protein complexes. Myosin VI can work in vitro as a processive dimeric motor and as a nonprocessive monomeric motor, each with a large working stroke. The possibility that both monomeric and dimeric forms of myosin VI operate in the cell may represent an important regulatory mechanism for controlling the multiple steps in transport pathways where nonprocessive and processive motors are required.
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Affiliation(s)
- Folma Buss
- Cambridge Institute for Medical Research, University of Cambridge, Cambridge CB2 2XY, United Kingdom.
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Raila J, Wirth K, Chen F, Buscher U, Dudenhausen JW, Schweigert FJ. Excretion of vitamin A in urine of women during normal pregnancy and pregnancy complications. ANNALS OF NUTRITION AND METABOLISM 2004; 48:357-64. [PMID: 15542927 DOI: 10.1159/000082003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2003] [Accepted: 07/14/2004] [Indexed: 01/20/2023]
Abstract
BACKGROUND/AIMS The renal function, including the excretion of low-molecular-weight proteins, changes during pregnancy and may cause a urinary excretion of retinol-binding protein (RBP). Whether it is accompanied by a substantial loss of vitamin A (retinol) has not been established yet. We therefore determined the excretion of retinol and RBP in urine of pregnant women. METHODS The study involved analyses of urine samples from 40 healthy pregnant women and 29 women with pregnancy complications during the third trimester. Analyses of plasma and urine of 7 healthy women and 5 women with pregnancy complications were also carried out 6 weeks antepartum, at time of delivery and 1 week postpartum. RESULTS Urinary retinol was higher in women who suffered from pregnancy disorders with an influence on maternal metabolism (p < 0.01). RBP was excreted at substantial concentrations in the urine of all 69 women, but there were no differences between the groups. Women with a concomitant excretion of retinol had higher levels of urinary RBP than those without a retinol excretion (p < 0.05). Differences in plasma retinol and RBP were not significant. CONCLUSION The excretion of urinary retinol may increase significantly during pregnancy complications, which needs further clarification to which extent this condition may negatively affect the vitamin A status in such women.
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Affiliation(s)
- Jens Raila
- Institute of Nutritional Science, University of Potsdam, Nuthetal (Bergholz-Rehbrücke), Germany
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Gonzalez-Villalobos R, Klassen RB, Allen PL, Navar LG, Hammond TG. Megalin binds and internalizes angiotensin II. Am J Physiol Renal Physiol 2004; 288:F420-7. [PMID: 15467006 DOI: 10.1152/ajprenal.00243.2004] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Megalin is an abundant membrane protein heavily involved in receptor-mediated endocytosis. The major functions of megalin in vivo remain incompletely defined as megalin typically faces specialized milieus such as glomerular filtrate, airways, epididymal fluid, thyroid colloid, and yolk sac fluid, which lack many of its known ligands. In the course of studies on ANG II internalization, we were surprised when only part of the uptake of labeled ANG II into immortalized yolk sac cells (BN-16 cells) was blocked by specific peptide inhibitors and direct competitors of the angiotensin type 1 receptor. This led us to test if megalin was a receptor for ANG II. Four lines of direct evidence demonstrate that megalin and, to a lesser extent, its chaperone protein cubilin are receptors for ANG II. First, in BN-16 cells anti-megalin and anti-cubilin antisera interfere with ANG II uptake. Second, also in BN-16 cells, pure ANG II competes for uptake of a known megalin ligand. Third, in proximal tubule cell brush-border membrane vesicles extracted from mice, anti-megalin antisera interfere with ANG II binding. Fourth, purified megalin binds ANG II directly in surface plasmon resonance experiments. The finding that megalin is a receptor for ANG II suggests a major new function for the megalin pathway in vivo. These results also indicate that ANG II internalization in some tissues is megalin dependent and that megalin may play a role in regulating proximal tubule ANG II levels.
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Affiliation(s)
- Romer Gonzalez-Villalobos
- Tulane Hypertension and Renal Center of Excellence and Department of Physiology, Tulane University School of Medicine, New Orleans, LA 70112, USA
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Takahashi S, Wada N, Harada K, Nagata M. Cationic charge-preferential IgG reabsorption in the renal proximal tubules. Kidney Int 2004; 66:1556-60. [PMID: 15458451 DOI: 10.1111/j.1523-1755.2004.00920.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
BACKGROUND The brush border of the renal proximal tubules has a polyanionic charge. Since immunoglobulin G (IgG) molecules have a wide range of charge diversity, reabsorption of urinary IgG molecules are supposed to be influenced by the electrostatic interaction. METHODS Charge diversity of serum and urinary IgG molecules in patients with various renal diseases (N= 12) and premature neonates (N= 3) were analyzed by isoelectric focusing and Immunoblotting. RESULTS In patients with glomerular diseases, urinary IgG was solely composed of neutral and anionic IgG, whereas that of the cationic part (isoelectric point >8) was not observed. By contrast, in patients with proximal tubular diseases (Dent's disease and idiopathic Fanconi syndrome), the proportion of the cationic IgG was similar to that of serum IgG. In addition, the cationic part of IgG in the urine was found in the neonates with a gestational age of 28 and 31 weeks, but not found in those of 35 weeks. CONCLUSION The results suggest that renal proximal tubules reabsorb the urinary IgG in a cationic preferential way, and this mechanism requires renal maturation.
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Affiliation(s)
- Shori Takahashi
- Department of Pediatrics, Nihon University School of Medicine, Tokyo, Japan.
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Takano M, Koyama Y, Nishikawa H, Murakami T, Yumoto R. Segment-selective absorption of lysozyme in the intestine. Eur J Pharmacol 2004; 502:149-55. [PMID: 15464101 DOI: 10.1016/j.ejphar.2004.08.041] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2004] [Revised: 08/11/2004] [Accepted: 08/19/2004] [Indexed: 10/26/2022]
Abstract
Absorption of fluorescein isothiocyanate-labeled lysozyme (FITC-lysozyme) was examined in rat small intestine. Messenger RNA of megalin, an endocytic receptor for lysozyme in the kidney, was expressed in the lower but not in the upper intestine. In in situ closed loop and recirculation methods, absorption of FITC-lysozyme from the upper intestine was much higher than from the lower intestine. The absorption rate of FITC-lysozyme in the upper intestine was significantly higher than FITC-dextran and was inhibited by unlabeled lysozyme in a concentration-dependent manner. The absorption of FITC-lysozyme was also inhibited by spermine and phenylarsine oxide. These results indicate that the intestinal absorption of lysozyme is segment-selective and occurs preferentially from the upper intestine. Megalin expressed in the lower intestine appears not to have a significant role in the absorption of lysozyme. In the upper intestine, lysozyme appears to be absorbed by an endocytic pathway, and cationic charge may be important for lysozyme absorption.
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Affiliation(s)
- Mikihisa Takano
- Department of Pharmaceutics and Therapeutics, Programs for Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan.
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