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Nakamura M, Satoh N, Horita S, Nangaku M. Insulin-induced mTOR signaling and gluconeogenesis in renal proximal tubules: A mini-review of current evidence and therapeutic potential. Front Pharmacol 2022; 13:1015204. [PMID: 36299884 PMCID: PMC9589488 DOI: 10.3389/fphar.2022.1015204] [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: 08/09/2022] [Accepted: 09/27/2022] [Indexed: 12/02/2022] Open
Abstract
Energy is continuously expended in the body, and gluconeogenesis maintains glucose homeostasis during starvation. Gluconeogenesis occurs in the liver and kidneys. The proximal tubule is the primary location for renal gluconeogenesis, accounting for up to 25% and 60% of endogenous glucose production during fasting and after a meal, respectively. The mechanistic target of rapamycin (mTOR), which exists downstream of the insulin pathway, plays an important role in regulating proximal tubular gluconeogenesis. mTOR is an atypical serine/threonine kinase present in two complexes. mTORC1 phosphorylates substrates that enhance anabolic processes such as mRNA translation and lipid synthesis and catabolic processes such as autophagy. mTORC2 regulates cytoskeletal dynamics and controls ion transport and proliferation via phosphorylation of SGK1. Therefore, mTOR signaling defects have been implicated in various pathological conditions, including cancer, cardiovascular disease, and diabetes. However, concrete elucidations of the associated mechanisms are still unclear. This review provides an overview of mTOR and describes the relationship between mTOR and renal.
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Affiliation(s)
- Motonobu Nakamura
- Division of Nephrology and Endocrinology, The University of Tokyo, Tokyo, Japan
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Hotait ZS, Lo Cascio JN, Choos END, Shepard BD. The sugar daddy: the role of the renal proximal tubule in glucose homeostasis. Am J Physiol Cell Physiol 2022; 323:C791-C803. [PMID: 35912988 PMCID: PMC9448277 DOI: 10.1152/ajpcell.00225.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 07/26/2022] [Accepted: 07/26/2022] [Indexed: 11/22/2022]
Abstract
Renal blood flow represents >20% of total cardiac output and with this comes the great responsibility of maintaining homeostasis through the intricate regulation of solute handling. Through the processes of filtration, reabsorption, and secretion, the kidneys ensure that solutes and other small molecules are either returned to circulation, catabolized within renal epithelial cells, or excreted through the process of urination. Although this occurs throughout the renal nephron, one segment is tasked with the bulk of solute reabsorption-the proximal tubule. Among others, the renal proximal tubule is entirely responsible for the reabsorption of glucose, a critical source of energy that fuels the body. In addition, it is the only other site of gluconeogenesis outside of the liver. When these processes go awry, pathophysiological conditions such as diabetes and acidosis result. In this review, we highlight the recent advances made in understanding these processes that occur within the renal proximal tubule. We focus on the physiological mechanisms at play regarding glucose reabsorption and glucose metabolism, emphasize the conditions that occur under diseased states, and explore the emerging class of therapeutics that are responsible for restoring homeostasis.
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Affiliation(s)
- Zahraa S Hotait
- Department of Human Science, Georgetown University, Washington, District of Columbia
| | - Julia N Lo Cascio
- Department of Human Science, Georgetown University, Washington, District of Columbia
| | - Elijah N D Choos
- Department of Human Science, Georgetown University, Washington, District of Columbia
| | - Blythe D Shepard
- Department of Human Science, Georgetown University, Washington, District of Columbia
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Pereira-Moreira R, Muscelli E. Effect of Insulin on Proximal Tubules Handling of Glucose: A Systematic Review. J Diabetes Res 2020; 2020:8492467. [PMID: 32377524 PMCID: PMC7180501 DOI: 10.1155/2020/8492467] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/29/2019] [Revised: 12/18/2019] [Accepted: 12/27/2019] [Indexed: 02/06/2023] Open
Abstract
Renal proximal tubules reabsorb glucose from the glomerular filtrate and release it back into the circulation. Modulation of glomerular filtration and renal glucose disposal are some of the insulin actions, but little is known about a possible insulin effect on tubular glucose reabsorption. This review is aimed at synthesizing the current knowledge about insulin action on glucose handling by proximal tubules. Method. A systematic article selection from Medline (PubMed) and Embase between 2008 and 2019. 180 selected articles were clustered into topics (renal insulin handling, proximal tubule glucose transport, renal gluconeogenesis, and renal insulin resistance). Summary of Results. Insulin upregulates its renal uptake and degradation, and there is probably a renal site-specific insulin action and resistance; studies in diabetic animal models suggest that insulin increases renal SGLT2 protein content; in vivo human studies on glucose transport are few, and results of glucose transporter protein and mRNA contents are conflicting in human kidney biopsies; maximum renal glucose reabsorptive capacity is higher in diabetic patients than in healthy subjects; glucose stimulates SGLT1, SGLT2, and GLUT2 in renal cell cultures while insulin raises SGLT2 protein availability and activity and seems to directly inhibit the SGLT1 activity despite it activating this transporter indirectly. Besides, insulin regulates SGLT2 inhibitor bioavailability, inhibits renal gluconeogenesis, and interferes with Na+K+ATPase activity impacting on glucose transport. Conclusion. Available data points to an important insulin participation in renal glucose handling, including tubular glucose transport, but human studies with reproducible and comparable method are still needed.
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Affiliation(s)
- Ricardo Pereira-Moreira
- Department of Internal Medicine, School of Medical Sciences, University of Campinas, Zip Code: 13083-887, Brazil
| | - Elza Muscelli
- Department of Internal Medicine, School of Medical Sciences, University of Campinas, Zip Code: 13083-887, Brazil
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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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Asare-Bediako I, Paszkiewicz RL, Kim SP, Woolcott OO, Kolka CM, Burch M, Kabir M, Piccinini F, Bergman RN. Assessment of hepatic insulin extraction from in vivo surrogate methods of insulin clearance measurement. Am J Physiol Endocrinol Metab 2018; 315:E605-E612. [PMID: 29509434 PMCID: PMC6230713 DOI: 10.1152/ajpendo.00344.2017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Hyperinsulinemia, accompanied by reduced first-pass hepatic insulin extraction (FPE) and increased secretion, is a primary response to insulin resistance. Different in vivo methods are used to estimate the clearance of insulin, which is assumed to reflect FPE. We compared two methodologically different but commonly used indirect estimates with directly measured FPE in healthy dogs ( n = 9). The indirect methods were 1) metabolic clearance rate of insulin (MCR) during the hyperinsulinemic-euglycemic clamp (EGC), a steady-state method, and 2) fractional clearance rate of insulin (FCR) during the frequently sampled intravenous glucose tolerance test (FSIGT), a dynamic method. MCR was calculated as the ratio of insulin infusion rate to steady-state plasma insulin. FCR was calculated as the exponential decay rate constant of the injected insulin. Directly measured FPE is based on the difference in insulin measurements during intraportal vs. peripheral vein insulin infusions. We found a strong correlation between indirect FCR (min-1) and FPE (%). In contrast, we observed a poor association between MCR (ml·min-1·kg-1) and FPE (%). Our findings in canines suggest that FCR measured during FSIGT can be used to estimate FPE. However, MCR calculated during EGC appears to be a poor surrogate for FPE.
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Affiliation(s)
- Isaac Asare-Bediako
- Cedars-Sinai Diabetes and Obesity Research Institute , Los Angeles, California
| | | | - Stella P Kim
- Cedars-Sinai Diabetes and Obesity Research Institute , Los Angeles, California
| | - Orison O Woolcott
- Cedars-Sinai Diabetes and Obesity Research Institute , Los Angeles, California
| | - Cathryn M Kolka
- Cedars-Sinai Diabetes and Obesity Research Institute , Los Angeles, California
| | - Miguel Burch
- Cedars-Sinai Medical Center, Department of Surgery , Los Angeles, California
| | - Morvarid Kabir
- Cedars-Sinai Diabetes and Obesity Research Institute , Los Angeles, California
| | - Francesca Piccinini
- Cedars-Sinai Diabetes and Obesity Research Institute , Los Angeles, California
| | - Richard N Bergman
- Cedars-Sinai Diabetes and Obesity Research Institute , Los Angeles, California
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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] [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
Tokarz et al. review the cell biology of insulin physiology throughout the body, from synthesis to the delivery, action, and final degradation of insulin. 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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Simeoni M, Cerantonio A, Pastore I, Liguori R, Greco M, Foti D, Gulletta E, Brunetti A, Fuiano G. The correct renal function evaluation in patients with thyroid dysfunction. J Endocrinol Invest 2016; 39:495-507. [PMID: 26511999 DOI: 10.1007/s40618-015-0402-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/09/2015] [Accepted: 10/17/2015] [Indexed: 10/22/2022]
Abstract
Thyroid dysfunction induces several renal derangements involving all nephron portions. Furthermore, dysthyroidism is a recognized risk factor associated with the development of chronic kidney disease. Current data, in fact, demonstrate that either subclinical or overt thyroid disease is associated with significant changes in creatinine, estimated glomerular filtration rate, measured glomerular filtration rate and Cystatin C. Herein, we systematically reviewed several relevant studies aiming at the identification of the most sensitive and specific parameter for the correct renal function evaluation in patients with thyroid dysfunction, that are usually treated as outpatients. Our systematic review indicates that estimated glomerular filtration rate, preferably with CKD-EPI equation, appears to be the most reliable and wieldy renal function parameter. Instead, Cystatin C should be better used in the grading of thyroid dysfunction severity.
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Affiliation(s)
- Mariadelina Simeoni
- Nephrology and Dialysis Unit, 'Magna Graecia' University, 88100, Catanzaro, CZ, Italy.
- University Campus 'Magna Graecia', Viale Europa-Loc. Germaneto, 88100, Catanzaro, Italy.
| | - Annamaria Cerantonio
- Nephrology and Dialysis Unit, 'Magna Graecia' University, 88100, Catanzaro, CZ, Italy
| | - Ida Pastore
- Endocrinology Unit, 'Magna Graecia' University, 88100, Catanzaro, CZ, Italy
| | - Rossella Liguori
- Endocrinology Unit, 'Magna Graecia' University, 88100, Catanzaro, CZ, Italy
| | - Marta Greco
- Clinical Pathology Unit, 'Magna Graecia' University, 88100, Catanzaro, CZ, Italy
| | - Daniela Foti
- Clinical Pathology Unit, 'Magna Graecia' University, 88100, Catanzaro, CZ, Italy
| | - Elio Gulletta
- Clinical Pathology Unit, 'Magna Graecia' University, 88100, Catanzaro, CZ, Italy
| | - Antonio Brunetti
- Clinical Pathology Unit, 'Magna Graecia' University, 88100, Catanzaro, CZ, Italy
| | - Giorgio Fuiano
- Nephrology and Dialysis Unit, 'Magna Graecia' University, 88100, Catanzaro, CZ, Italy
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Sengul S, Erturk S, Khan AM, Batuman V. Receptor-associated protein blocks internalization and cytotoxicity of myeloma light chain in cultured human proximal tubular cells. PLoS One 2013; 8:e70276. [PMID: 23894629 PMCID: PMC3720907 DOI: 10.1371/journal.pone.0070276] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2013] [Accepted: 06/19/2013] [Indexed: 12/01/2022] Open
Abstract
Background Free light chains (LCs) are among the many ligands that bind to cubilin/megalin for endocytosis via the clathrin-dependent endosomal/lysosomal pathway. Receptor associated protein (RAP), is a 39 kDA high-affinity, chaperone-like ligand for megalin that assists in the proper folding and functioning of megalin/cubilin. Although RAP is known to inhibit ligand binding to megalin/cubilin, its effect on LC endocytosis has not been shown directly. Methods and Principal Findings We investigated whether RAP can block the endocytosis of LC in cultured human proximal tubule cells and whether this can prevent LC cytotoxicity. Immunofluorescence microscopy and flow cytometry showed that fluorescently labeled LC endocytosis was markedly inhibited in HK-2 cells pretreated with human RAP. The effect of RAP was dose-dependent, and was predominantly on endocytosis as it had no effect on the small acid-washable fraction of LC bound to cell membrane. RAP significantly inhibited LC induced cytokine production and phosphorylation of ERK1/2 and p38 MAPK. Prolonged exposure to LC for 48 h resulted in epithelial-to-mesenchymal transformation in HK-2 cells as evidenced by marked reduction in the expression of the epithelial cell marker E-cadherin, and increased the expression of the mesenchymal marker α-SMA, which was also prevented by RAP in the endocytosis medium. Conclusions RAP inhibited LC endocytosis by ∼88% and ameliorated LC-induced cytokine responses and EMT in human PTCs. The results not only provide additional evidence that LCs endocytosis occurs via the megalin/cubilin endocytic receptor system, but also show that blocking LC endocytosis by RAP can protect proximal tubule cells from LC cytotoxicity.
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Affiliation(s)
- Sule Sengul
- Department of Nephrology, Ankara University School of Medicine, Ankara, Turkey
| | - Sehsuvar Erturk
- Department of Nephrology, Ankara University School of Medicine, Ankara, Turkey
| | - Altaf M. Khan
- Division of Nephrology, Tulane University School of Medicine, New Orleans, Louisiana, United States of America
| | - Vecihi Batuman
- Division of Nephrology, Tulane University School of Medicine, New Orleans, Louisiana, United States of America
- SLVHCS, VA Medical Center, New Orleans, Louisiana, United States of America
- * E-mail:
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Lunt SJ, Gray C, Reyes-Aldasoro CC, Matcher SJ, Tozer GM. Application of intravital microscopy in studies of tumor microcirculation. JOURNAL OF BIOMEDICAL OPTICS 2010; 15:011113. [PMID: 20210439 DOI: 10.1117/1.3281674] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
To grow and progress, solid tumors develop a vascular network through co-option and angiogenesis that is characterized by multiple structural and functional abnormalities, which negatively influence therapeutic outcome through direct and indirect mechanisms. As such, the morphology and function of tumor blood vessels, plus their response to different treatments, are a vital and active area of biological research. Intravital microscopy (IVM) has played a key role in studies of tumor angiogenesis, and ongoing developments in molecular probes, imaging techniques, and postimage analysis methods have ensured its continued and widespread use. In this review we discuss some of the primary advantages and disadvantages of IVM approaches and describe recent technological advances in optical microscopy (e.g., confocal microscopy, multiphoton microscopy, hyperspectral imaging, and optical coherence tomography) with examples of their application to studies of tumor angiogenesis.
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Affiliation(s)
- Sarah Jane Lunt
- University of Sheffield, School of Medicine, Department of Oncology, Sheffield, United Kingdom
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