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Conti S, Remuzzi G, Benigni A, Tomasoni S. Imaging the Kidney with an Unconventional Scanning Electron Microscopy Technique: Analysis of the Subpodocyte Space in Diabetic Mice. Int J Mol Sci 2022; 23:ijms23031699. [PMID: 35163622 PMCID: PMC8836024 DOI: 10.3390/ijms23031699] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Revised: 01/25/2022] [Accepted: 01/30/2022] [Indexed: 02/04/2023] Open
Abstract
Transmission electron microscopy (TEM) remains the gold standard for renal histopathological diagnoses, given its higher resolving power, compared with light microscopy. However, it imposes several limitations on pathologists, including longer sample preparation time and a small observation area. To overcome these, we introduced a scanning electron microscopy (SEM) technique for imaging resin-embedded semi-thin sections of renal tissue. We developed a rapid tissue preparation protocol for experimental models and human biopsies which, alongside SEM digital imaging acquisition of secondary electrons (SE–SEM), enables fast electron microscopy examination, with a resolution similar to that achieved by TEM. We used this unconventional SEM imaging approach to investigate the subpodocyte space (SPS) in BTBR ob/ob mice with type 2 diabetes. Analysis of semi-thin sections with secondary electrons revealed that the SPS had expanded in volume and covered large areas of the glomerular basement membrane, forming wide spaces between the podocyte body and the underlying filtering membrane. Our results show that SE–SEM is a valuable tool for imaging the kidney at the ultrastructural level, filling the magnification gap between light microscopy and TEM, and reveal that in diabetic mice, the SPS is larger than in normal controls, which is associated with podocyte damage and impaired kidney function.
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2
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Kuo MC, Liang PI, Chang JM. Podocentric view of glomerular proteinuria: Focused on cytoskeletal changes and toward promising targeted therapies and challenges. Kaohsiung J Med Sci 2021; 37:539-546. [PMID: 33942997 DOI: 10.1002/kjm2.12385] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2020] [Revised: 02/26/2021] [Accepted: 03/15/2021] [Indexed: 11/09/2022] Open
Abstract
Among renal cells, podocytes (glomerular epithelial cells) are the most critical to prevent plasma proteins from excessive loss by forming their sophisticated foot processes (FP) and slit diaphragms (SD). A general finding in the glomeruli of patients with nephrotic syndrome is the foot processes "effacement" resulted from dysregulated actin cytoskeleton reorganization. Ultrastructural analysis in patients with nephrotic syndrome has demonstrated that such changes tend to be dynamic and can sometimes be reversible. In a more molecular sense, injured podocytes can no longer maintain their tight regulation and "retract" their FP, but not "efface" them. Past studies have revealed multiple exquisite mechanisms and arrays of proteins participating in the regulation of cytoskeletal rearrangement, and these mechanisms serve as potential targets to treat. A major challenge to develop specific therapies is the targeted mechanism has to be crucial and specific enough for podocyte-oriented kidney diseases, and it would be even better to manifest in most of the glomerulonephritis. Studies have shown many approaches targeting different mechanisms, but none of them has been proved to be effective in clinical medicine. Up to the present, Abatacept (Orencia) is the first (and the only) clinical targeted therapy demonstrating limited success. It inhibits the co-stimulatory response of B7-1 (CD80) induced in various types of glomerulonephritis. Future clinical studies have to be expanded to substantiate this highly specific targeted therapy because the Abatacept effect is not generally accepted even within the nephrology community. Nevertheless, there are ongoing searches for specific treatment targeting podocytes through various approaches.
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Affiliation(s)
- Mei-Chuan Kuo
- Division of Nephrology, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan.,Department of Renal Care, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan
| | - Peir-In Liang
- Department of Pathology, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan
| | - Jer-Ming Chang
- Division of Nephrology, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan.,Department of Renal Care, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan
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3
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Singh AK, Kolligundla LP, Francis J, Pasupulati AK. Detrimental effects of hypoxia on glomerular podocytes. J Physiol Biochem 2021; 77:193-203. [PMID: 33835424 DOI: 10.1007/s13105-021-00788-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Accepted: 01/11/2021] [Indexed: 12/19/2022]
Abstract
Hypoxia-inducible factor1 (HIF1) plays a pivotal role in ensuring cells adapt to low-oxygen conditions. Depletion of oxygen, a co-substrate during hydroxylation of prolyl (P402 and P564) residues of HIF1⍺, evades HIF1⍺ ubiquitination and enables its dimerization with HIF1β to mediate global transcriptional response to hypoxia. Though HIF1 is largely considered eliciting a protective role during physiological or pathological hypoxia or ischemia, elevated HIF1 during chronic hypoxia contributes to glomerular diseases' pathology and proteinuria. The glomerulus is responsible for renal permselectivity and excretion of ultra-filtrated urine. Podocytes are the glomerulus' major cell types and are instrumental for glomerular filtration, permselectivity, and glomerular basement membrane maintenance. Podocyte injury is expected to impair the efficiency of glomerular filtration and manifestation of glomerulosclerosis and proteinuria. Accumulated evidence suggests that podocytes are susceptible to various insults during chronic hypoxia, including podocyte EMT, slit-diaphragm dysfunction, foot process effacement, and cytoskeletal derangement due to accumulation of HIF1. This review discusses how hypoxia/HIF1 signaling regulates various features and function of podocytes during exposure to chronic hypoxia or inducing HIF1 by various chemical modulators.
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Affiliation(s)
- Ashish K Singh
- Department of Biochemistry, School of Life Sciences, University of Hyderabad, Hyderabad, India
| | - Lakshmi P Kolligundla
- Department of Biochemistry, School of Life Sciences, University of Hyderabad, Hyderabad, India
| | - Justus Francis
- Department of Biochemistry, School of Life Sciences, University of Hyderabad, Hyderabad, India
| | - Anil K Pasupulati
- Department of Biochemistry, School of Life Sciences, University of Hyderabad, Hyderabad, India.
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4
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Glomerular filtrate affects the dynamics of podocyte detachment in a model of diffuse toxic podocytopathy. Kidney Int 2021; 99:1149-1161. [PMID: 33582108 DOI: 10.1016/j.kint.2020.12.034] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 12/27/2020] [Accepted: 12/29/2020] [Indexed: 11/22/2022]
Abstract
Podocyte injury and subsequent detachment are hallmarks of progressive glomerulosclerosis. In addition to cell injury, unknown mechanical forces on the injured podocyte may promote detachment. To identify the nature of these mechanical forces, we studied the dynamics of podocyte detachment using sequential ultrastructural geometry analysis by transmission electron microscopy in NEP25, a mouse model of podocytopathy induced by anti-Tac(Fv)-PE38 (LMB2), a fusion protein attached to Pseudomonas exotoxin A, targeting CD25 on podocytes. After LMB2 injection, foot process effacement occurred on day three but detachment commenced on day eight and extended to day ten, reaching toward the urinary pole in clusters. Podocyte detachment was associated with foot process effacement covering over 60% of the glomerular basement membrane length. However, approximately 25% of glomeruli with diffuse (over 80%) foot process effacement showed no detachment. Blocking glomerular filtration via unilateral ureteral obstruction resulted in diffuse foot process effacement but no pseudocysts or detachment, whereas uninephrectomy increased pseudocysts and accelerated detachment, indicating that glomerular filtrate drives podocyte detachment via pseudocyst formation as a forerunner. Additionally, more detachment was observed in juxtamedullary glomeruli than in superficial glomeruli. Thus, glomerular filtrate drives the dynamics of podocyte detachment in this model of podocytopathy. Hence, foot process effacement may be a prerequisite allowing filtrate to generate local mechanical forces that expand the subpodocyte space forming pseudocysts, promote podocyte detachment and subsequent segmental sclerosis.
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Remuzzi A, Conti S, Ene-Iordache B, Tomasoni S, Rizzo P, Benigni A, Remuzzi G. Role of ultrastructural determinants of glomerular permeability in ultrafiltration function loss. JCI Insight 2020; 5:137249. [PMID: 32641585 DOI: 10.1172/jci.insight.137249] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 05/27/2020] [Indexed: 11/17/2022] Open
Abstract
The epithelial filtration slit is a crucial component of the glomerular capillary membrane, which is essential for maintaining glomerular filtration function. Though chronic kidney diseases are an immense clinical problem, the mechanisms through which structural alterations reduce glomerular water filtration have not yet been understood completely. To investigate the mechanisms underlying filtration function loss, we studied rats with spontaneously occurring progressive kidney disease, either treated with angiotensin II antagonist or untreated, combining high-resolution electron microscopy of the glomerular capillary wall with theoretical water filtration modeling. Under pathological conditions, epithelial filtration pores and the extension of the subpodocyte space were larger than in normal controls. Numerical analyses indicated that these ultrastructural changes increased hydraulic resistance of the glomerular capillary wall by extending coverage of the filtration barrier by the subpodocyte space, with the changes in hydrodynamic forces acting on podocytes likely being responsible for their detachment. Angiotensin II inhibition normalized the subpodocyte space's hydraulic resistance, restored mechanical podocyte load, and preserved CD151-α3 integrin complex assembly, improving podocyte adherence and survival. Our results show that ultrastructural changes in podocytes are major determinants of the hydraulic resistance of the glomerular capillary wall and highlight the mechanism of podocyte loss in kidney disease progression, as well as the mechanisms underlying angiotensin II inhibition.
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Affiliation(s)
| | - Sara Conti
- Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy
| | | | - Susanna Tomasoni
- Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy
| | - Paola Rizzo
- Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy
| | - Ariela Benigni
- Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy
| | - Giuseppe Remuzzi
- Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Bergamo, Italy.,L. Sacco Department of Biomedical and Clinical Sciences, University of Milan, Milan, Italy
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Gembillo G, Cernaro V, Salvo A, Siligato R, Laudani A, Buemi M, Santoro D. Role of Vitamin D Status in Diabetic Patients with Renal Disease. ACTA ACUST UNITED AC 2019; 55:medicina55060273. [PMID: 31200589 PMCID: PMC6630278 DOI: 10.3390/medicina55060273] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2019] [Revised: 06/03/2019] [Accepted: 06/08/2019] [Indexed: 02/07/2023]
Abstract
Diabetes mellitus (DM) poses a major public health problem worldwide, with ever-increasing incidence and prevalence in recent years. The Institute for Alternative Futures (IAF) expects that the total number of people with type 1 and type 2 DM in the United States will increase by 54%, from 19,629,000 to 54,913,000 people, between 2015 and 2030. Diabetic Nephropathy (DN) affects about one-third of patients with DM and currently ranks as the first cause of end-stage kidney disease in the Western world. The complexity of interactions of Vitamin D is directly related with progressive long-term changes implicated in the worsening of renal function. These changes result in a dysregulation of the vitamin D-dependent pathways. Various studies demonstrated a pivotal role of Vitamin D supplementation in regression of albuminuria and glomerulosclerosis, contrasting the increase of glomerular basement membrane thickening and podocyte effacement, with better renal and cardiovascular outcomes. The homeostasis and regulation of the nephron’s function are absolutely dependent from the cross-talk between endothelium and podocytes. Even if growing evidence proves that vitamin D may have antiproteinuric, anti-inflammatory and renoprotective effects in patients with DN, it is still worth investigating these aspects with both more in vitro studies and randomized controlled trials in larger patient series and with adequate follow-up to confirm the effects of long-term vitamin D analogue supplementation in DN and to evaluate the effectiveness of this therapy and the appropriate dosage.
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Affiliation(s)
- Guido Gembillo
- Unit of Nephrology and Dialysis, Department of Clinical and Experimental Medicine, University of Messina, Via Consolare Valeria 98,125 Messina, Italy.
| | - Valeria Cernaro
- Unit of Nephrology and Dialysis, Department of Clinical and Experimental Medicine, University of Messina, Via Consolare Valeria 98,125 Messina, Italy.
| | - Antonino Salvo
- Unit of Nephrology and Dialysis, Department of Clinical and Experimental Medicine, University of Messina, Via Consolare Valeria 98,125 Messina, Italy.
| | - Rossella Siligato
- Unit of Nephrology and Dialysis, Department of Clinical and Experimental Medicine, University of Messina, Via Consolare Valeria 98,125 Messina, Italy.
| | - Alfredo Laudani
- Unit of Nephrology and Dialysis, Department of Clinical and Experimental Medicine, University of Messina, Via Consolare Valeria 98,125 Messina, Italy.
| | - Michele Buemi
- Unit of Nephrology and Dialysis, Department of Clinical and Experimental Medicine, University of Messina, Via Consolare Valeria 98,125 Messina, Italy.
| | - Domenico Santoro
- Unit of Nephrology and Dialysis, Department of Clinical and Experimental Medicine, University of Messina, Via Consolare Valeria 98,125 Messina, Italy.
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Shroff UN, Schiessl IM, Gyarmati G, Riquier-Brison A, Peti-Peterdi J. Novel fluorescence techniques to quantitate renal cell biology. Methods Cell Biol 2019; 154:85-107. [PMID: 31493823 PMCID: PMC6748388 DOI: 10.1016/bs.mcb.2019.04.013] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Fluorescence microscopy techniques are powerful tools to study tissue dynamics, cellular function and biology both in vivo and in vitro. These tools allow for functional assessment and quantification along with qualitative analysis, thus providing a comprehensive understanding of various cellular processes under normal physiological and disease conditions. The main focus of this chapter is the recently developed method of serial intravital multiphoton microscopy that has helped shed light on the dynamic alterations of the spatial distribution and fate of single renal cells or cell populations and their migration patterns in the same tissue region over several days in response to various stimuli within the living kidney. This technique is very useful for studying in vivo the molecular and cellular mechanisms of tissue remodeling and repair after injury. In addition, complementary in vitro imaging tools are also described and discussed, like tissue clearing techniques and protein synthesis measurement in tissues in situ that provide an in depth assessment of changes at the cellular level. Thus, these novel fluorescence techniques can be effectively leveraged for different tissue types, experimental conditions as well as disease models to improve our understanding of renal cell biology.
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Affiliation(s)
- Urvi Nikhil Shroff
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States
| | - Ina Maria Schiessl
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States
| | - Georgina Gyarmati
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States
| | - Anne Riquier-Brison
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States
| | - Janos Peti-Peterdi
- Department of Physiology and Neuroscience, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA, United States.
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8
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Maestroni S, Zerbini G. Glomerular endothelial cells versus podocytes as the cellular target in diabetic nephropathy. Acta Diabetol 2018; 55:1105-1111. [PMID: 30155580 DOI: 10.1007/s00592-018-1211-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/09/2018] [Accepted: 08/09/2018] [Indexed: 12/11/2022]
Abstract
It usually takes several years (in some cases, decades) for predisposed individuals to move from the onset of type 1 or type 2 diabetes to the development of microalbuminuria, the first sign of diabetic nephropathy. This long, complication-free, period represents the best possible moment to start a successful preventive strategy (primary prevention) aimed to avoid or at least to postpone the increase of albumin excretion rate. Prevention is based on understanding and counteracting the initial mechanisms leading to the development of the disease and unfortunately, in case of diabetic nephropathy, most of them remain unclear. Little is also known about which, among endothelial cells and podocytes, represent the first glomerular target of the complication. Selective damage of the endothelium or of the podocyte results, as a common consequence, in an increase of albumin excretion rate. Albuminuria by itself cannot therefore be of help to solve the case. Endothelium and podocytes are involved in a continuous cross-talk and by studying the impact of diabetes on this "communication" process it should be possible to obtain some information regarding the weak component of the glomerular filter. Finally, the careful investigation of the mechanisms leading to the development podocyturia, a recently identified glomerular dysfunction associated to the pathogenesis of diabetic nephropathy, could contribute to shed some more light on the very early stages of this complication.
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Affiliation(s)
- Silvia Maestroni
- Complications of Diabetes Unit, Division of Immunology, Transplantation and Infectious Diseases, Diabetes Research Institute (DRI), IRCCS San Raffaele Scientific Institute, 20132, Milano, Italy
| | - Gianpaolo Zerbini
- Complications of Diabetes Unit, Division of Immunology, Transplantation and Infectious Diseases, Diabetes Research Institute (DRI), IRCCS San Raffaele Scientific Institute, 20132, Milano, Italy.
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9
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Neal CR, Arkill KP, Bell JS, Betteridge KB, Bates DO, Winlove CP, Salmon AHJ, Harper SJ. Novel hemodynamic structures in the human glomerulus. Am J Physiol Renal Physiol 2018; 315:F1370-F1384. [PMID: 29923763 PMCID: PMC6293306 DOI: 10.1152/ajprenal.00566.2017] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To investigate human glomerular structure under conditions of physiological perfusion, we have analyzed fresh and perfusion-fixed normal human glomeruli at physiological hydrostatic and oncotic pressures using serial resin section reconstruction, confocal, multiphoton, and electron microscope imaging. Afferent and efferent arterioles (21.5 ± 1.2 µm and 15.9 ± 1.2 µm diameter), recognized from vascular origins, lead into previously undescribed wider regions (43.2 ± 2.8 µm and 38.4 ± 4.9 µm diameter) we have termed vascular chambers (VCs) embedded in the mesangium of the vascular pole. Afferent VC (AVC) volume was 1.6-fold greater than efferent VC (EVC) volume. From the AVC, long nonbranching high-capacity conduit vessels ( n = 7) (Con; 15.9 ± 0.7 µm diameter) led to the glomerular edge, where branching was more frequent. Conduit vessels have fewer podocytes than filtration capillaries. VCs were confirmed in fixed and unfixed specimens with a layer of banded collagen identified in AVC walls by multiphoton and electron microscopy. Thirteen highly branched efferent first-order vessels (E1; 9.9 ± 0.4 µm diameter) converge on the EVC, draining into the efferent arteriole (15.9 ± 1.2 µm diameter). Banded collagen was scarce around EVCs. This previously undescribed branching topology does not conform to the branching of minimum energy expenditure (Murray's law), suggesting that even distribution of pressure/flow to the filtration capillaries is more important than maintaining the minimum work required for blood flow. We propose that AVCs act as plenum manifolds possibly aided by vortical flow in distributing and balancing blood flow/pressure to conduit vessels supplying glomerular lobules. These major adaptations to glomerular capillary structure could regulate hemodynamic pressure and flow in human glomerular capillaries.
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Affiliation(s)
- Christopher R Neal
- Bristol Renal and School of Physiology, Pharmacology and Neuroscience, University of Bristol , Bristol , United Kingdom
| | - Kenton P Arkill
- Division of Cancer and Stem Cells, School of Medicine, University of Nottingham, Queen's Medical Centre , Nottingham , United Kingdom
| | - James S Bell
- Cardiff Centre for Vision Science, Cardiff University , Cardiff , United Kingdom
| | - Kai B Betteridge
- Nikon Imaging Centre, Guys Campus, Kings College London , London , United Kingdom
| | - David O Bates
- Division of Cancer and Stem Cells, School of Medicine, University of Nottingham, Queen's Medical Centre , Nottingham , United Kingdom
| | - C Peter Winlove
- School of Physics, University of Exeter , Exeter , United Kingdom
| | | | - Steven J Harper
- Bristol Renal and School of Physiology, Pharmacology and Neuroscience, University of Bristol , Bristol , United Kingdom.,Institute of Biomedical and Clinical Sciences, University of Exeter Medical School , Exeter , United Kingdom
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Bates DO, Beazley-Long N, Benest AV, Ye X, Ved N, Hulse RP, Barratt S, Machado MJ, Donaldson LF, Harper SJ, Peiris-Pages M, Tortonese DJ, Oltean S, Foster RR. Physiological Role of Vascular Endothelial Growth Factors as Homeostatic Regulators. Compr Physiol 2018; 8:955-979. [PMID: 29978898 DOI: 10.1002/cphy.c170015] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The vascular endothelial growth factor (VEGF) family of proteins are key regulators of physiological systems. Originally linked with endothelial function, they have since become understood to be principal regulators of multiple tissues, both through their actions on vascular cells, but also through direct actions on other tissue types, including epithelial cells, neurons, and the immune system. The complexity of the five members of the gene family in terms of their different splice isoforms, differential translation, and specific localizations have enabled tissues to use these potent signaling molecules to control how they function to maintain their environment. This homeostatic function of VEGFs has been less intensely studied than their involvement in disease processes, development, and reproduction, but they still play a substantial and significant role in healthy control of blood volume and pressure, interstitial volume and drainage, renal and lung function, immunity, and signal processing in the peripheral and central nervous system. The widespread expression of VEGFs in healthy adult tissues, and the disturbances seen when VEGF signaling is inhibited support this view of the proteins as endogenous regulators of normal physiological function. This review summarizes the evidence and recent breakthroughs in understanding of the physiology that is regulated by VEGF, with emphasis on the role they play in maintaining homeostasis. © 2017 American Physiological Society. Compr Physiol 8:955-979, 2018.
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Affiliation(s)
- David O Bates
- Cancer Biology, Division of Cancer and Stem Cells, School of Medicine, University of Nottingham, Queen's Medical Centre, Nottingham, United Kingdom
| | | | - Andrew V Benest
- Cancer Biology, Division of Cancer and Stem Cells, School of Medicine, University of Nottingham, Queen's Medical Centre, Nottingham, United Kingdom
| | - Xi Ye
- Department of Pharmacology, University of Oxford, Oxford, United Kingdom
| | - Nikita Ved
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Richard P Hulse
- Cancer Biology, Division of Cancer and Stem Cells, School of Medicine, University of Nottingham, Queen's Medical Centre, Nottingham, United Kingdom
| | - Shaney Barratt
- Academic Respiratory Unit, School of Clinical Sciences, University of Bristol, Bristol, United Kingdom
| | - Maria J Machado
- Cancer Biology, Division of Cancer and Stem Cells, School of Medicine, University of Nottingham, Queen's Medical Centre, Nottingham, United Kingdom
| | - Lucy F Donaldson
- School of Life Sciences, University of Nottingham, Nottingham, United Kingdom
| | - Steven J Harper
- School of Physiology, Pharmacology & Neuroscience, Medical School, University of Bristol, Bristol, United Kingdom
| | - Maria Peiris-Pages
- Cancer Research UK Manchester Institute, The University of Manchester, Manchester, United Kingdom
| | - Domingo J Tortonese
- Centre for Comparative and Clinical Anatomy, University of Bristol, Bristol, United Kingdom
| | - Sebastian Oltean
- Institute of Biomedical & Clinical Sciences, University of Exeter Medical School, Exeter, United Kingdom
| | - Rebecca R Foster
- Bristol Renal, School of Clinical Sciences, University of Bristol, Bristol, United Kingdom
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11
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Endlich K, Kliewe F, Endlich N. Stressed podocytes-mechanical forces, sensors, signaling and response. Pflugers Arch 2017; 469:937-949. [PMID: 28687864 DOI: 10.1007/s00424-017-2025-8] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Accepted: 06/22/2017] [Indexed: 02/07/2023]
Abstract
Increased glomerular capillary pressure (glomerular hypertension) and increased glomerular filtration rate (glomerular hyperfiltration) have been proven to cause glomerulosclerosis in animal models and are likely to be operative in patients. Since podocytes cover the glomerular basement membrane, they are exposed to tensile stress due to circumferential wall tension and to fluid shear stress arising from filtrate flow through the narrow filtration slits and through Bowman's space. In vitro evidence documents that podocytes respond to tensile stress as well as to fluid shear stress. Several proteins are discussed in this review that are expressed in podocytes and could act as mechanosensors converting mechanical force via a conformational change into a biochemical signal. The cation channels P2X4 and TRPC6 were shown to be involved in mechanosignaling in podocytes. P2X4 is activated by stretch-induced ATP release, while TRPC6 might be inherently mechanosensitive. Membrane, slit diaphragm and cell-matrix contact proteins are connected to the sublemmal actin network in podocytes via various linker proteins. Therefore, actin-associated proteins, like the proven mechanosensor filamin, are ideal candidates to sense forces in the podocyte cytoskeleton. Furthermore, podocytes express talin, p130Cas, and fibronectin that are known to undergo a conformational change in response to mechanical force exposing cryptic binding sites. Downstream of mechanosensors, experimental evidence suggests the involvement of MAP kinases, Ca2+ and COX2 in mechanosignaling and an emerging role of YAP/TAZ. In summary, our understanding of mechanotransduction in podocytes is still sketchy, but future progress holds promise to identify targets to alleviate conditions of increased mechanical load.
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Affiliation(s)
- Karlhans Endlich
- Department of Anatomy and Cell Biology, University Medicine Greifswald, 17489, Greifswald, Germany.
- Institut für Anatomie and Zellbiologie, Universitätsmedizin Greifswald, Friedrich-Loeffler-Str. 23c, 17489, Greifswald, Germany.
| | - Felix Kliewe
- Department of Anatomy and Cell Biology, University Medicine Greifswald, 17489, Greifswald, Germany
| | - Nicole Endlich
- Department of Anatomy and Cell Biology, University Medicine Greifswald, 17489, Greifswald, Germany
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12
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Combined use of electron microscopy and intravital imaging captures morphological and functional features of podocyte detachment. Pflugers Arch 2017; 469:965-974. [PMID: 28664407 DOI: 10.1007/s00424-017-2020-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Revised: 06/13/2017] [Accepted: 06/14/2017] [Indexed: 12/12/2022]
Abstract
The development of podocyte injury and albuminuria in various glomerular pathologies is still incompletely understood due to technical limitations in studying the glomerular filtration barrier (GFB) in real-time. We aimed to directly visualize the early morphological and functional changes of the GFB during the development of focal segmental glomerulosclerosis (FSGS) using a combination of transmission electron microscopy (TEM) and in vivo multiphoton microscopy (MPM) in the rat puromycin aminonucleoside (PAN) model. We hypothesized that this combined TEM + MPM experimental approach would provide a major technical improvement that would benefit our mechanistic understanding of podocyte detachment. Male Sprague-Dawley (for TEM) or Munich-Wistar-Frömter (for MPM) rats were given a single dose of 100-150 mg/kg body weight PAN i.p. and were either sacrificed and the kidneys processed for TEM or surgically instrumented for in vivo MPM imaging at various times 2-14 days after PAN administration. Both techniques demonstrated hypertrophy and cystic dilatations of the subpodocyte space that developed as early as 2-3 days after PAN. Adhesions of the visceral epithelium to the parietal Bowman's capsule (synechiae) appeared at days 8-10. TEM provided unmatched resolution of podocyte foot process remodeling, while MPM revealed the rapid dynamics of pseudocyst filling, emptying, and rupture, as well as endothelial and podocyte injury, misdirected filtration, and podocyte shedding. Due to the complementary advantages of TEM and MPM, this combined approach can provide an unusally comprehensive and dynamic portrayal of the alterations in podocyte morphology and function during FSGS development. The results advance our understanding of the role and importance of the various cell types, hemodynamics, and mechanical forces in the development of glomerular pathology.
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13
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Pajęcka K, Nielsen MN, Hansen TK, Williams JM. The formation of quiescent glomerular endothelial cell monolayer in vitro is strongly dependent on the choice of extracellular matrix coating. Exp Cell Res 2017; 353:16-25. [PMID: 28237245 DOI: 10.1016/j.yexcr.2017.02.039] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Revised: 02/12/2017] [Accepted: 02/22/2017] [Indexed: 02/07/2023]
Abstract
BACKGROUND AND AIMS Nephropathy involves pathophysiological changes to the glomerulus. The primary glomerular endothelial cells (GEnCs) have emerged as an important tool for studying glomerulosclerotic mechanisms and in the screening process for drug-candidates. The success of the studies is dependent on the quality of the cell model. Therefore, we set out to establish an easy, reproducible model of the quiescent endothelial monolayer with the use of commercially available extracellular matrices (ECMs). METHODS Primary hGEnCs were seeded on various ECMs. Cell adhesion was monitored by an impedance sensing system. The localization of junctional proteins was assessed by immunofluorescence and the barrier function by passage of fluorescent dextrans and magnitude of VEGF response. RESULTS All ECM matrices except recombinant human laminin 111 (rhLN111) supported comparable cell proliferation. Culturing hGEnCs on rhLN521, rhLN511 or fibronectin resulted in a physiologically relevant barrier to 70kDa dextrans which was 82% tighter than that formed on collagen type IV. Furthermore, only hGEnCs cultured on rhLN521 or rhLN511 showed plasma-membrane localized zonula occludens-1 and vascular endothelial cadherin indicative of proper tight and adherens junctions (AJ). CONCLUSION We recommend culturing hGEnCs on the mature glomerular basement membrane laminin - rhLN521 - which, as the only commercially available ECM, promotes all of the characteristics of the quiescent hGEnC monolayer: cobblestone morphology, well-defined AJs and physiological perm-selectivity.
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Affiliation(s)
- Kamilla Pajęcka
- Global Research, Novo Nordisk A/S, Måløv, Denmark; Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark.
| | | | - Troels Krarup Hansen
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark
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Abstract
PURPOSE OF REVIEW The review aims to provide a brief summary and evaluation of the current state of research that uses multiphoton fluorescence microscopy for intravital kidney imaging. RECENT FINDINGS Direct visualization of the glomerular filter, proximal and distal tubule segments, and the renal vasculature in the living, intact kidney in zebrafish, mouse, and rat models with high temporal and spatial resolution provided new insights into the function of the normal and diseased kidney. New technical developments in fluorescence excitation and detection, in combination with transgenic animal models for cell function and fate mapping, and serial imaging of the same glomerulus in the same animal over several days further advanced the field of nephrology research, and the understanding of disease mechanisms. SUMMARY Intravital multiphoton imaging has solved many critical technical barriers in kidney research and allowed the dynamic portrayal of the structure and function of various renal cell types in vivo. It has become a widely used research technique, with significant past achievements, and tremendous potential for future development and applications for the study and better understanding of kidney diseases.
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15
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Roshanravan H, Kim EY, Dryer SE. 20-Hydroxyeicosatetraenoic Acid (20-HETE) Modulates Canonical Transient Receptor Potential-6 (TRPC6) Channels in Podocytes. Front Physiol 2016; 7:351. [PMID: 27630573 PMCID: PMC5005377 DOI: 10.3389/fphys.2016.00351] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Accepted: 08/02/2016] [Indexed: 01/08/2023] Open
Abstract
The arachidonic acid metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) regulates renal function, including changes in glomerular function evoked during tubuloglomerular feedback (TGF). This study describes the cellular actions of 20-HETE on cultured podocytes, assessed by whole-cell recordings from cultured podocytes combined with pharmacological and cell-biological manipulations of cells. Bath superfusion of 20-HETE activates cationic currents that are blocked by the pan-TRP blocker SKF-96365 and by 50 μM La3+, and which are attenuated after siRNA knockdown of TRPC6 subunits. Similar currents are evoked by a membrane-permeable analog of diacylgycerol (OAG), but OAG does not occlude responses to maximally-activating concentrations of 20-HETE (20 μM). Exposure to 20-HETE also increased steady-state surface abundance of TRPC6 subunits in podocytes as assessed by cell-surface biotinylation assays, and increased cytosolic concentrations of reactive oxygen species (ROS). TRPC6 activation by 20-HETE was eliminated in cells pretreated with TEMPOL, a membrane-permeable superoxide dismutase mimic. Activation of TRPC6 by 20-HETE was also blocked when whole-cell recording pipettes contained GDP-βS, indicating a role for either small or heterotrimeric G proteins in the transduction cascade. Responses to 20-HETE were eliminated by siRNA knockdown of podocin, a protein that organizes NADPH oxidase complexes with TRPC6 subunits in this cell type. In summary, modulation of ionic channels in podocytes may contribute to glomerular actions of 20-HETE.
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Affiliation(s)
- Hila Roshanravan
- Department of Biology and Biochemistry, University of Houston Houston, TX, USA
| | - Eun Y Kim
- Department of Biology and Biochemistry, University of Houston Houston, TX, USA
| | - Stuart E Dryer
- Department of Biology and Biochemistry, University of HoustonHouston, TX, USA; Division of Nephrology, Baylor College of MedicineHouston, TX, USA
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16
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Abstract
This article summarizes the past, present, and future promise of multiphoton excitation fluorescence microscopy for intravital kidney imaging. During the past 15years, several high-power visual research approaches have been developed using multiphoton imaging to study the normal functions of the healthy, intact, living kidney, and the various molecular and cellular mechanisms of the development of kidney diseases. In this review, the main focus will be on intravital multiphoton imaging of the glomerulus, the structure and function of the glomerular filtration barrier, especially the podocyte. Examples will be given for the combination of two powerful research tools, in vivo multiphoton imaging and mouse genetics using commercially available whole animal models for the detailed characterization of glomerular cell types, their function and fate, and for the better understanding of the molecular mechanisms of glomerular pathologies. One of the new modalities of multiphoton imaging, serial imaging of the same glomerulus in the same animal over several days will be emphasized for its potential for further advancing the field of nephrology research.
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Affiliation(s)
- János Peti-Peterdi
- Departments of Physiology and Biophysics, and Medicine, Zilkha Neurogenetic Institute, ZNI355, University of Southern California, 1501 San Pablo Street, Los Angeles, CA 90033, USA.
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17
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Abstract
Kidney glomeruli ultrafilter blood to generate urine and they are dysfunctional in a variety of kidney diseases. There are two key vascular growth factor families implicated in glomerular biology and function, namely the vascular endothelial growth factors (VEGFs) and the angiopoietins (Angpt). We present examples showing not only how these molecules help generate and maintain healthy glomeruli but also how they drive disease when their expression is dysregulated. Finally, we review how manipulating VEGF and Angpt signalling may be used to treat glomerular disease.
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18
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Burghardt T, Hochapfel F, Salecker B, Meese C, Gröne HJ, Rachel R, Wanner G, Krahn MP, Witzgall R. Advanced electron microscopic techniques provide a deeper insight into the peculiar features of podocytes. Am J Physiol Renal Physiol 2015; 309:F1082-9. [DOI: 10.1152/ajprenal.00338.2015] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Accepted: 09/17/2015] [Indexed: 11/22/2022] Open
Abstract
Podocytes constitute the outer layer of the glomerular filtration barrier, where they form an intricate network of interdigitating foot processes which are connected by slit diaphragms. A hitherto unanswered puzzle concerns the question of whether slit diaphragms are established between foot processes of the same podocyte or between foot processes of different podocytes. By employing focused ion beam-scanning electron microscopy (FIB-SEM), we provide unequivocal evidence that slit diaphragms are formed between foot processes of different podocytes. We extended our investigations of the filtration slit by using dual-axis electron tomography of human and mouse podocytes as well as of Drosophila melanogaster nephrocytes. Using this technique, we not only find a single slit diaphragm which spans the filtration slit around the whole periphery of the foot processes but additional punctate filamentous contacts between adjacent foot processes. Future work will be necessary to determine the proteins constituting the two types of cell-cell contacts.
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Affiliation(s)
- Tillmann Burghardt
- Institute for Molecular and Cellular Anatomy, University of Regensburg, Regensburg, Germany
| | - Florian Hochapfel
- Institute for Molecular and Cellular Anatomy, University of Regensburg, Regensburg, Germany
| | - Benjamin Salecker
- Institute for Molecular and Cellular Anatomy, University of Regensburg, Regensburg, Germany
| | - Christine Meese
- Institute for Molecular and Cellular Anatomy, University of Regensburg, Regensburg, Germany
| | - Hermann-Josef Gröne
- Division of Cellular and Molecular Pathology, German Cancer Research Center, Heidelberg, Germany
| | - Reinhard Rachel
- Center of Electron Microscopy, Faculty of Biology and Preclinical Medicine, University of Regensburg, Regensburg, Germany; and
| | - Gerhard Wanner
- Department of Botany, Ludwig Maximilians-Universität, Munich, Germany
| | - Michael P. Krahn
- Institute for Molecular and Cellular Anatomy, University of Regensburg, Regensburg, Germany
| | - Ralph Witzgall
- Institute for Molecular and Cellular Anatomy, University of Regensburg, Regensburg, Germany
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Schießl IM, Hammer A, Kattler V, Gess B, Theilig F, Witzgall R, Castrop H. Intravital Imaging Reveals Angiotensin II-Induced Transcytosis of Albumin by Podocytes. J Am Soc Nephrol 2015; 27:731-44. [PMID: 26116357 DOI: 10.1681/asn.2014111125] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2014] [Accepted: 05/11/2015] [Indexed: 11/03/2022] Open
Abstract
Albuminuria is a hallmark of kidney disease of various etiologies and usually caused by deterioration of glomerular filtration barrier integrity. We recently showed that angiotensin II (Ang II) acutely increases albumin filtration in the healthy kidney. Here, we used intravital microscopy to assess the effects of Ang II on podocyte function in rats. Acute infusion of 30, 60, or 80 ng/kg per minute Ang II enhanced the endocytosis of albumin by activation of the type 1 Ang II receptor and resulted in an average (±SEM) of 3.7±2.2, 72.3±18.6 (P<0.001), and 239.4±34.6 µm(3) (P<0.001) albumin-containing vesicles per glomerulus, respectively, compared with none at baseline or 10 ng/kg per minute Ang II. Immunostaining of Ang II-infused kidneys confirmed the presence of albumin-containing vesicles, which colocalized with megalin, in podocin-positive cells. Furthermore, podocyte endocytosis of albumin was markedly reduced in the presence of gentamicin, a competitive inhibitor of megalin-dependent endocytosis. Ang II infusion increased the concentration of albumin in the subpodocyte space, a potential source for endocytic protein uptake, and gentamicin further increased this concentration. Some endocytic vesicles were acidified and colocalized with LysoTracker. Most vesicles migrated from the capillary to the apical aspect of the podocyte and were eventually released into the urinary space. This transcytosis accounted for approximately 10% of total albumin filtration. In summary, the transcellular transport of proteins across the podocyte constitutes a new pathway of glomerular protein filtration. Ang II enhances the endocytosis and transcytosis of plasma albumin by podocytes, which may eventually impair podocyte function.
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Affiliation(s)
| | | | | | | | - Franziska Theilig
- Department of Medicine, University of Fribourg, Fribourg, Switzerland
| | - Ralph Witzgall
- Molecular and Cellular Anatomy, University of Regensburg, Regensburg, Germany; and
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20
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Novel in vivo techniques to visualize kidney anatomy and function. Kidney Int 2015; 88:44-51. [PMID: 25738253 PMCID: PMC4490063 DOI: 10.1038/ki.2015.65] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2014] [Revised: 01/05/2015] [Accepted: 01/06/2015] [Indexed: 12/11/2022]
Abstract
Intravital imaging using multiphoton microscopy (MPM) has become an increasingly popular and widely used experimental technique in kidney research over the past few years. MPM allows deep optical sectioning of the intact, living kidney tissue with submicron resolution which is unparalleled among intravital imaging approaches. MPM has solved a long-standing critical technical barrier in renal research to study several complex and inaccessible cell types and anatomical structures in vivo in their native environment. Comprehensive and quantitative kidney structure and function MPM studies helped our better understanding of the cellular and molecular mechanisms of the healthy and diseased kidney. This review summarizes recent in vivo MPM studies with a focus on the glomerulus and the filtration barrier, although select, glomerulus-related renal vascular and tubular functions are also mentioned. The latest applications of serial MPM of the same glomerulus in vivo, in the intact kidney over several days, during the progression of glomerular disease are discussed. This visual approach, in combination with genetically encoded fluorescent markers of cell lineage, has helped to track the fate and function (e.g. cell calcium changes) of single podocytes during the development of glomerular pathologies, and provided visual proof for the highly dynamic rather than static nature of the glomerular environment. Future intravital imaging applications have the promise to further push the limits of optical microscopy, and to advance our understanding of the mechanisms of kidney injury. Also, MPM will help to study new mechanisms of tissue repair and regeneration, a cutting edge area of kidney research.
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21
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Schießl IM, Kattler V, Castrop H. In Vivo Visualization of the Antialbuminuric Effects of the Angiotensin-Converting Enzyme Inhibitor Enalapril. J Pharmacol Exp Ther 2015; 353:299-306. [DOI: 10.1124/jpet.114.222125] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Neal CR. Podocytes … What's Under Yours? (Podocytes and Foot Processes and How They Change in Nephropathy). Front Endocrinol (Lausanne) 2015; 6:9. [PMID: 25755650 PMCID: PMC4337384 DOI: 10.3389/fendo.2015.00009] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/19/2014] [Accepted: 01/15/2015] [Indexed: 12/25/2022] Open
Abstract
Most of the described structures of podocytes in health and disease have been inferred from light and electron microscopic studies of rodent models. The variation in filtration barrier features is measured on micrographs, the aim being statistical significance. This is the technical campaign waged against kidney disease but this approach can be misleading. The signaling cascades and connectivity of the podocyte and foot processes (FPs) are inferred from in vitro studies that at best blurr the reality of the in vivo state. This review will outline actin signaling connectivity and the key differences in the structural and functional domains squeezed into the FPs and the relationship of these domains to other parts of the podocyte. It covers the changes in podocytes during nephropathy concentrating on FP and finally proposes an alternative interpretation of FP ultrastructure derived from articles published over the last 60 years.
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Affiliation(s)
- Chris R. Neal
- Bristol Renal, University of Bristol, Bristol, UK
- *Correspondence: Chris R. Neal, Bristol Renal, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol, BS1 3NY, UK e-mail:
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23
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Kriz W, Lemley KV. A potential role for mechanical forces in the detachment of podocytes and the progression of CKD. J Am Soc Nephrol 2014; 26:258-69. [PMID: 25060060 DOI: 10.1681/asn.2014030278] [Citation(s) in RCA: 194] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Loss of podocytes underlies progression of CKD. Detachment of podocytes from the glomerular basement membrane (GBM) rather than apoptosis or necrosis seems to be the major mechanism of podocyte loss. Such detachment of viable podocytes may be caused by increased mechanical distending and shear forces and/or impaired adhesion to the GBM. This review considers the mechanical challenges that may lead to podocyte loss by detachment from the GBM under physiologic and pathophysiologic conditions, including glomerular hypertension, hyperfiltration, hypertrophy, and outflow of filtrate from subpodocyte spaces. Furthermore, we detail the cellular mechanisms by which podocytes respond to these challenges, discuss the protective effects of angiotensin blockade, and note the questions that must be addressed to better understand the relationship between podocyte detachment and progression of CKD.
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Affiliation(s)
- Wilhelm Kriz
- Institutes of Transfusion Medicine and Immunology and Neuroanatomy, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany; and
| | - Kevin V Lemley
- Division of Nephrology, Children's Hospital Los Angeles, Los Angeles, California; and Department of Pediatrics, University of Southern California Keck School of Medicine, Los Angeles, California
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24
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Arkill KP, Qvortrup K, Starborg T, Mantell JM, Knupp C, Michel CC, Harper SJ, Salmon AHJ, Squire JM, Bates DO, Neal CR. Resolution of the three dimensional structure of components of the glomerular filtration barrier. BMC Nephrol 2014; 15:24. [PMID: 24484633 PMCID: PMC3922634 DOI: 10.1186/1471-2369-15-24] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Accepted: 01/21/2014] [Indexed: 11/13/2022] Open
Abstract
Background The human glomerulus is the primary filtration unit of the kidney, and contains the Glomerular Filtration Barrier (GFB). The GFB had been thought to comprise 3 layers – the endothelium, the basement membrane and the podocyte foot processes. However, recent studies have suggested that at least two additional layers contribute to the function of the GFB, the endothelial glycocalyx on the vascular side, and the sub-podocyte space on the urinary side. To investigate the structure of these additional layers is difficult as it requires three-dimensional reconstruction of delicate sub-microscopic (<1 μm) cellular and extracellular elements. Methods Here we have combined three different advanced electron microscopic techniques that cover multiple orders of magnitude of volume sampled, with a novel staining methodology (Lanthanum Dysprosium Glycosaminoglycan adhesion, or LaDy GAGa), to determine the structural basis of these two additional layers. Serial Block Face Scanning Electron Microscopy (SBF-SEM) was used to generate a 3-D image stack with a volume of a 5.3 x 105 μm3 volume of a whole kidney glomerulus (13% of glomerular volume). Secondly, Focused Ion Beam milling Scanning Electron Microscopy (FIB-SEM) was used to image a filtration region (48 μm3 volume). Lastly Transmission Electron Tomography (Tom-TEM) was performed on a 0.3 μm3 volume to identify the fine structure of the glycocalyx. Results Tom-TEM clearly showed 20 nm fibre spacing in the glycocalyx, within a limited field of view. FIB-SEM demonstrated, in a far greater field of view, how the glycocalyx structure related to fenestrations and the filtration slits, though without the resolution of TomTEM. SBF-SEM was able to determine the extent of the sub-podocyte space and glycocalyx coverage, without additional heavy metal staining. Neither SBF- nor FIB-SEM suffered the anisotropic shrinkage under the electron beam that is seen with Tom-TEM. Conclusions These images demonstrate that the three dimensional structure of the GFB can be imaged, and investigated from the whole glomerulus to the fine structure of the glycocalyx using three dimensional electron microscopy techniques. This should allow the identification of structural features regulating physiology, and their disruption in pathological states, aiding the understanding of kidney disease.
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Affiliation(s)
- Kenton P Arkill
- Nanoscale Physics Research Laboratories, School of Physics and Astronomy, University of Birmingham, Birmingham, UK.
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Kistler AD, Caicedo A, Abdulreda MH, Faul C, Kerjaschki D, Berggren PO, Reiser J, Fornoni A. In vivo imaging of kidney glomeruli transplanted into the anterior chamber of the mouse eye. Sci Rep 2014; 4:3872. [PMID: 24464028 PMCID: PMC3902446 DOI: 10.1038/srep03872] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2013] [Accepted: 12/09/2013] [Indexed: 11/24/2022] Open
Abstract
Multiphoton microscopy enables live imaging of the renal glomerulus. However, repeated in vivo imaging of the same glomerulus over extended periods of time and the study of glomerular function independent of parietal epithelial and proximal tubular cell effects has not been possible so far. Here, we report a novel approach for non-invasive imaging of acapsular glomeruli transplanted into the anterior chamber of the mouse eye. After microinjection, glomeruli were capable of engrafting on the highly vascularized iris. Glomerular structure was preserved, as demonstrated by podocyte specific expression of cyan fluorescent protein and by electron microscopy. Injection of fluorescence-labeled dextrans of various molecular weights allowed visualization of glomerular filtration and revealed leakage of 70 kDa dextran in an inducible model of proteinuria. Our findings demonstrate functionality and long-term survival of glomeruli devoid of Bowman's capsule and provide a novel approach for non-invasive longitudinal in vivo study of glomerular physiology and pathophysiology.
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Affiliation(s)
- Andreas D Kistler
- 1] Department of Medicine, Division of Nephrology and Hypertension, University of Miami Miller School of Medicine, Miami, Florida, USA [2] Division of Nephrology, University Hospital Zürich, Zürich, Switzerland
| | - Alejandro Caicedo
- Department of Medicine, Division of Endocrinology, Diabetes and Metabolism, University of Miami Miller School of Medicine, Florida, USA
| | - Midhat H Abdulreda
- Diabetes Research Institute, Miller School of Medicine, University of Miami, Miami, Florida
| | - Christian Faul
- Department of Medicine, Division of Nephrology and Hypertension, University of Miami Miller School of Medicine, Miami, Florida, USA
| | - Dontscho Kerjaschki
- Clinical Institute of Pathology, Medical University of Vienna, Vienna, Austria
| | - Per-Olof Berggren
- 1] Diabetes Research Institute, Miller School of Medicine, University of Miami, Miami, Florida [2] The Rolf Luft Research Center for Diabetes and Endocrinology, Karolinska Institutet, Stockholm, Sweden
| | - Jochen Reiser
- 1] Department of Medicine, Division of Nephrology and Hypertension, University of Miami Miller School of Medicine, Miami, Florida, USA [2] Department of Medicine, Rush University Medical Center, Chicago, IL, USA
| | - Alessia Fornoni
- 1] Department of Medicine, Division of Nephrology and Hypertension, University of Miami Miller School of Medicine, Miami, Florida, USA [2] Diabetes Research Institute, Miller School of Medicine, University of Miami, Miami, Florida
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Anil Kumar P, Welsh GI, Saleem MA, Menon RK. Molecular and cellular events mediating glomerular podocyte dysfunction and depletion in diabetes mellitus. Front Endocrinol (Lausanne) 2014; 5:151. [PMID: 25309512 PMCID: PMC4174857 DOI: 10.3389/fendo.2014.00151] [Citation(s) in RCA: 107] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/01/2014] [Accepted: 09/10/2014] [Indexed: 12/11/2022] Open
Abstract
The essential function of the kidney is to ensure formation of a relatively protein-free ultra-filtrate, urine. The rate of filtration and composition of the primary renal filtrate is determined by the transport of fluid and solutes across the glomerular filtration barrier consisting of endothelial cells, the glomerular basement membrane, and podocyte foot processes. In diabetes mellitus (DM), components of the kidney that enable renal filtration get structurally altered and functionally compromised resulting in proteinuria that often progresses to end-stage renal disease. Histological alterations in DM include early hypertrophy of glomerular and tubular components, subsequent thickening of basement membrane in glomeruli and tubules, progressive accumulation of extracellular matrix proteins in the glomerular mesangium and loss of podocytes, together constituting a clinical condition referred to as diabetic nephropathy (DN). The glomerulus has become the focus of research investigating the mechanism of proteinuria. In particular, the progressive dysfunction and/or loss of podocytes that is contemporaneous with proteinuria in DN have attracted intense scientific attention. The absolute number of podocytes predicts glomerular function and podocyte injury is a hallmark of various glomerular diseases. This review discusses the importance of podocytes in normal renal filtration and details the molecular and cellular events that lead to podocyte dysfunction and decreased podocyte count in DN.
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Affiliation(s)
- P. Anil Kumar
- Department of Biochemistry, University of Hyderabad, Hyderabad, India
| | - Gavin I. Welsh
- Academic Renal Unit, School of Clinical Sciences, University of Bristol, Bristol, UK
| | - Moin A. Saleem
- Academic Renal Unit, School of Clinical Sciences, University of Bristol, Bristol, UK
| | - Ram K. Menon
- Pediatric Endocrinology and Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA
- *Correspondence: Ram K. Menon, University of Michigan Medical School, D1205 MPB/SPC 5718, 1500 E. Medical Center Drive, Ann Arbor, MI 48109-5718, USA e-mail:
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Schießl IM, Castrop H. Angiotensin II AT2 receptor activation attenuates AT1 receptor-induced increases in the glomerular filtration of albumin: a multiphoton microscopy study. Am J Physiol Renal Physiol 2013; 305:F1189-200. [PMID: 23946289 DOI: 10.1152/ajprenal.00377.2013] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In this study, we assessed the acute effects of angiotensin II on the albumin glomerular sieving coefficient (GSC) using intravital microscopy. The experiments were performed on Munich Wistar Froemter (MWF) rats. Alexa-Fluor-594 albumin was injected intravenously, and the fluorescence intensity in the glomerular capillaries and Bowman's space was determined to calculate the albumin GSC. The GSC was measured before and during the constant infusion of angiotensin II (10 ng·min(-1)·kg(-1) body wt). Baseline mean arterial pressure (MAP) was 99 ± 5 mmHg and stabilized at 137 ± 5 mmHg during angiotensin II infusion. The baseline GSC averaged 0.00044 ± 4.8 × 10(-5) and increased by 286 ± 44% after angiotensin II infusion (P < 0.0001). The proximal tubular Alexa-Fluor-594 albumin uptake was enhanced during angiotensin II infusion (518% of the baseline value during angiotensin II vs. 218% in controls; P < 0.0001). No change in GSC was observed when the AT1 antagonist losartan was injected before the start of angiotensin II infusion. The AT2 antagonist PD123319 increased the baseline GSC from 0.00052 ± 3.6 × 10(-5) to 0.00074 ± 8.2 × 10(-5) (P = 0.02) without altering the MAP. During angiotensin II infusion with losartan, PD123319 increased the albumin GSC from 0.00037 ± 5.8 × 10(-5) to 0.00115 ± 0.00015 (P = 0.001). When the renal perfusion pressure was mechanically controlled, the GSC increased from 0.0007 ± 0.00019 to 0.0025 ± 0.00063 during angiotensin II infusion (P = 0.047), similar to what was observed when the renal perfusion pressure was allowed to increase. In summary, AT1 activation acutely increases the albumin GSC. This effect appears to be largely independent of changes in the renal perfusion pressure. The AT2 receptor partially attenuates the proteinuric effects of the AT1 receptor.
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Affiliation(s)
- Ina Maria Schießl
- Institute of Physiology, Univ. of Regensburg, Universitätsstr. 31, 93040 Regensburg, Germany.
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28
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Chen G, Liu H, Liu F. A glimpse of the glomerular milieu: from endothelial cell to thrombotic disease in nephrotic syndrome. Microvasc Res 2013; 89:1-6. [PMID: 23851046 DOI: 10.1016/j.mvr.2013.06.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Revised: 06/23/2013] [Accepted: 06/28/2013] [Indexed: 10/26/2022]
Abstract
Patients with nephrotic syndrome (NS) carry a high risk of venous thromboembolism (VTE) due to the abnormalities in coagulation and fibrinolysis. Although massive urine protein loss is considered to trigger the cascade of hypercoagulation, the exact nature of VTE in NS patients still remains obscure, especially in some cases when VTE occurs far before the presence of nephrotic proteinuria. Recent findings illustrate that loss of local glomerular homeostasis, like disturbance of cytokine profiles in endothelial cells or aberrant cellular crosstalks in glomerulus, is sufficient to initiate the development of thrombotic disease in glomerulonephropathy. Emerging data have highlighted the glomerular endothelial cell as a key regulator of local homeostasis, which might mediate the haemostatic derangement in the beginning of glomerular disease by expression of numerous prothrombotic factors and result in the subsequent predilection of VTE in NS. As the glomerulus-derived circulating factors are all collected and flushed into the renal vein directly, it is reasonable to suggest that increased release of glomerulus-derived thrombotic regulators, particularly from endothelial cells, may play a significant role in the highest proclivity for the renal vein as the site of thrombosis in NS. In this review, we thus discuss the current understandings of thromboembolism in NS with focus on how the glomerular endothelial cell involves in the pathogenesis of VTE, which may help to increase our understandings in the anti-thrombotic therapy for patients with NS.
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Affiliation(s)
- Guochun Chen
- Renal Division, The Second Xiangya Hospital, Central South University, Changsha, Hunan, PR China.
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Anderson M, Kim EY, Hagmann H, Benzing T, Dryer SE. Opposing effects of podocin on the gating of podocyte TRPC6 channels evoked by membrane stretch or diacylglycerol. Am J Physiol Cell Physiol 2013; 305:C276-89. [PMID: 23657570 DOI: 10.1152/ajpcell.00095.2013] [Citation(s) in RCA: 91] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Gain-of-function mutations in the transient receptor potential (TRP) cation channel subfamily C member 6 (TRPC6) gene and mutations in the NPHS2 gene encoding podocin result in nephrotic syndromes. The purpose of this study was to determine the functional significance of biochemical interactions between these proteins. We observed that gating of TRPC6 channels in podocytes is markedly mechanosensitive and can be activated by hyposmotic stretch or indentation of the plasma membrane. Stretch activation of cationic currents was blocked by small interfering RNA knockdown of TRPC6, as well as by SKF-96365 or micromolar La(3+). Stretch activation of podocyte TRPC6 persisted in the presence of inhibitors of phospholipase C (U-73122) and phospholipase A2 (ONO-RS-082). Robust stretch responses also persisted when recording electrodes contained guanosine 5'-O-(2-thiodiphosphate) at concentrations that completely suppressed responses to ANG II. Stretch responses were enhanced by cytochalasin D but were abolished by the peptide GsMTx4, suggesting that forces are transmitted to the channels through the plasma membrane. Podocin and TRPC6 interact at their respective COOH termini. Knockdown of podocin markedly increased stretch-evoked activation of TRPC6 but nearly abolished TRPC6 activation evoked by a diacylglycerol analog. These data suggest that podocin acts as a switch to determine the preferred mode of TRPC6 activation. They also suggest that podocin deficiencies will result in Ca(2+) overload in foot processes, as with gain-of-function mutations in the TRPC6 gene. Finally, they suggest that mechanical activation of TRP family channels and the preferred mode of TRP channel activation may depend on whether members of the stomatin/prohibitin family of hairpin loop proteins are present.
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Affiliation(s)
- Marc Anderson
- Department of Biology and Biochemistry, University of Houston, Houston, Texas, USA
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Smeets NMB, Hoare T. Designing responsive microgels for drug delivery applications. ACTA ACUST UNITED AC 2013. [DOI: 10.1002/pola.26707] [Citation(s) in RCA: 123] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Niels M. B. Smeets
- Department of Chemical Engineering; McMaster University; Hamilton Ontario Canada L8S 4L8
| | - Todd Hoare
- Department of Chemical Engineering; McMaster University; Hamilton Ontario Canada L8S 4L8
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Abstract
In the past decade, our understanding of the role of podocytes in the function of the glomerular filtration barrier, and of the role of podocyte injury in the pathogenesis of proteinuric kidney disease, has substantially increased. Landmark genetic studies identified mutations in genes expressed by podocytes as a cause of albuminuria and nephrotic syndrome, leading to breakthrough discoveries from many laboratories. These discoveries contributed to a dramatic change in our view of the glomerular filtration barrier of the kidney and of the role of podocyte injury in the development of albuminuria and progressive kidney disease. In the past several years, studies have demonstrated that podocyte injury is a major cause of marked albuminuria and nephrotic syndrome, and have confirmed that podocytes are important for the maintenance of an intact glomerular filtration barrier. An essential role of loss of these cells in the pathogenesis of glomerulosclerosis and progressive proteinuric kidney disease has also been identified. In this Review, we discuss the importance of podocytes for the maintenance of an intact glomerular filtration barrier and their role in albumin handling.
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Affiliation(s)
- Paul Thomas Brinkkoetter
- Department II of Internal Medicine and Center for Molecular Medicine Cologne, University of Cologne, Kerpener Strasse 62, 50937 Cologne, Germany
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Khoury CC, Khayat MF, Yeo TK, Pyagay PE, Wang A, Asuncion AM, Sharma K, Yu W, Chen S. Visualizing the mouse podocyte with multiphoton microscopy. Biochem Biophys Res Commun 2012; 427:525-30. [PMID: 23022193 DOI: 10.1016/j.bbrc.2012.09.089] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2012] [Accepted: 09/14/2012] [Indexed: 01/05/2023]
Abstract
The podocyte is a highly specialized kidney glomerular epithelial cell that plays an essential role in glomerular filtration and is believed to be the target of numerous glomerular diseases leading to proteinuria. Despite the leaps in our understanding of podocyte biology, new methodologies are needed to facilitate research into the cell. Multiphoton microscopy (MPM) was used to image the nephrin knockout/green fluorescent protein (GFP) knock-in heterozygote (Nphs1(tm1Rkl)/J) mouse. The nephrin promoter restricts GFP expression to the podocytes that fluoresce green under excitation. From the exterior of an intact kidney, MPM can peer into the renal parenchyma and visualize the podocytes that outline the globular shape of the glomeruli. Details as fine as the podocyte's secondary processes can be resolved. In contrast, podocytes exhibit no fluorescence in the wildtype mouse and are invisible to MPM. Phenotypically, there are no significant differences between wildtype and Nphs1(tm1Rkl)/J mice in body weight, urinary albumin excretion, creatinine clearance, or glomerular depth. Interestingly, the glomeruli are closer to the kidney capsule in female mice, making the gender the preferred choice for MPM. For the first time, green fluorescent podocytes in a mouse model free of confounding phenotypes can be visualized unequivocally and in the "positive" by MPM, facilitating intravital studies of the podocyte.
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Affiliation(s)
- Charbel C Khoury
- Division of Nephrology/Hypertension, Northwestern University, Chicago, IL, USA.
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Oltean S, Neal CR, Mavrou A, Patel P, Ahad T, Alsop C, Lee T, Sison K, Qiu Y, Harper SJ, Bates DO, Salmon AHJ. VEGF165b overexpression restores normal glomerular water permeability in VEGF164-overexpressing adult mice. Am J Physiol Renal Physiol 2012; 303:F1026-36. [PMID: 22811490 DOI: 10.1152/ajprenal.00410.2011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Vascular endothelial growth factor (VEGF)-A, a family of differentially spliced proteins produced by glomerular podocytes, maintains glomerular filtration barrier function. The expression of VEGF molecules is altered in human nephropathy. We aimed to determine the roles of the angiogenic VEGF(164) isoform, and the antiangiogenic VEGF(165)b isoform in mature, adult glomeruli in vivo using conditional, inducible transgenic overexpression systems in mice. Podocyte-specific VEGF(164) overexpression (up to 100 days) was induced by oral administration of doxycycline to adult podocin-rtTA/TetO-VEGF(164) double transgenic mice. The consequences of simultaneous overexpression of VEGF(164) and VEGF(165)b were assessed in triple-transgenic podocin-rtTA/TetO-VEGF(164)/nephrin-VEGF(165)b mice. Persistent VEGF(164) overexpression did not cause proteinuria but did increase glomerular ultrafiltration coefficient between days 3 and 7. Despite persistently increased VEGF(164) levels, glomerular ultrafiltration coefficient normalized by day 14 and remained normal up to 100 days. Decreased subpodocyte space (SPS) coverage of the glomerular capillary wall accompanied increased glomerular hydraulic conductivity in VEGF(164)-overexpressing mice. The changes in glomerular ultrafiltration coefficient and SPS coverage induced by 7 days of overexpression of VEGF(164) were not present in triple transgenic VEGF(164) and VEGF(165)b overexpressing mice. These results indicate that 1) the adult mouse glomerulus is relatively resistant to induced VEGF(164) overexpression. VEGF(164) overexpression altered glomerular permeability but did not cause proteinuria in these mature, adult animals; 2) the SPS is a dynamic VEGF-responsive modulator of glomerular function; and 3) the balance of VEGF isoforms plays a critical role in the regulation of glomerular permeability. VEGF(165)b is capable of preventing VEGF(164)-induced changes in glomerular permeability and ultrastructure in vivo.
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Affiliation(s)
- Sebastian Oltean
- Microvascular Research Laboratories, School of Physiology and Pharmacology, Univ. of Bristol, Preclinical Veterinary School, Southwell St., Bristol, United Kingdom. BS2 8EJ
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Salmon AHJ, Satchell SC. Endothelial glycocalyx dysfunction in disease: albuminuria and increased microvascular permeability. J Pathol 2012; 226:562-74. [PMID: 22102407 DOI: 10.1002/path.3964] [Citation(s) in RCA: 180] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2011] [Accepted: 11/05/2011] [Indexed: 12/13/2022]
Abstract
Appreciation of the glomerular microcirculation as a specialized microcirculatory bed, rather than as an entirely separate entity, affords important insights into both glomerular and systemic microvascular pathophysiology. In this review we compare regulation of permeability in systemic and glomerular microcirculations, focusing particularly on the role of the endothelial glycocalyx, and consider the implications for disease processes. The luminal surface of vascular endothelium throughout the body is covered with endothelial glycocalyx, comprising surface-anchored proteoglycans, supplemented with adsorbed soluble proteoglycans, glycosaminoglycans and plasma constituents. In both continuous and fenestrated microvessels, this endothelial glycocalyx provides resistance to the transcapillary escape of water and macromolecules, acting as an integral component of the multilayered barrier provided by the walls of these microvessels (ie acting in concert with clefts or fenestrae across endothelial cell layers, basement membranes and pericytes). Dysfunction of any of these capillary wall components, including the endothelial glycocalyx, can disrupt normal microvascular permeability. Because of its ubiquitous nature, damage to the endothelial glycocalyx alters the permeability of multiple capillary beds: in the glomerulus this is clinically apparent as albuminuria. Generalized damage to the endothelial glycocalyx can therefore manifest as both albuminuria and increased systemic microvascular permeability. This triad of altered endothelial glycocalyx, albuminuria and increased systemic microvascular permeability occurs in a number of important diseases, such as diabetes, with accumulating evidence for a similar phenomenon in ischaemia-reperfusion injury and infectious disease. The detection of albuminuria therefore has implications for the function of the microcirculation as a whole. The importance of the endothelial glycocalyx for other aspects of vascular function/dysfunction, such as mechanotransduction, leukocyte-endothelial interactions and the development of atherosclerosis, indicate that alterations in the endothelial glycocalyx may also be playing a role in the dysfunction of other organs observed in these disease states.
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Affiliation(s)
- Andrew H J Salmon
- Academic Renal Unit, University of Bristol, Southmead Hospital, Bristol, UK
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Peti-Peterdi J, Burford JL, Hackl MJ. The first decade of using multiphoton microscopy for high-power kidney imaging. Am J Physiol Renal Physiol 2011; 302:F227-33. [PMID: 22031850 DOI: 10.1152/ajprenal.00561.2011] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
In this review, we highlight the major scientific breakthroughs in kidney research achieved using multiphoton microscopy (MPM) and summarize the milestones in the technological development of kidney MPM during the past 10 years. Since more and more renal laboratories invest in MPM worldwide, we discuss future directions and provide practical, useful tips and examples for the application of this still-emerging optical sectioning technology. Advantages of using MPM in various kidney preparations that range from freshly dissected individual glomeruli or the whole kidney in vitro to MPM of the intact mouse and rat kidney in vivo are reviewed. Potential combinations of MPM with micromanipulation techniques including microperfusion and micropuncture are also included. However, we emphasize the most advanced and complex, quantitative in vivo imaging applications as the ultimate use of MPM since the true mandate of this technology is to look inside intact organs in live animals and humans.
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Affiliation(s)
- János Peti-Peterdi
- Departments of Physiology and Biophysics, and Medicine, Zilkha Neurogenetic Institute, Univ. of Southern California, Los Angeles, CA 90033, USA.
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Abstract
Almost all mammalian cell types have morphologies that are uniquely tailored to their physiological functions. This immense variation in cell shape depends on an underlying network of dynamic and interconnected actin and microtubule polymers. The glomerular podocyte is an archetypal example of such specialization, with a complex cytoskeleton underlying its delicate architectural features. Dynamic control of this cytoskeletal matrix seems to center around the slit diaphragm, a complex of proteins at the cell-cell junction between adjacent podocyte foot processes. This junction includes molecules that are unique to the podocyte that probably determine the correct morphology of the cell, and are targets of disease processes that disrupt the intricate balance of signaling that controls the cytoskeletal matrix. This Review will outline the most recent concepts and advances in our understanding of this critical aspect of glomerular biology, as well as discussing how an improved understanding of the podocyte cytoskeleton is starting to shape advances in delineating the pathogenesis of common glomerular diseases.
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Herman-Edelstein M, Thomas MC, Thallas-Bonke V, Saleem M, Cooper ME, Kantharidis P. Dedifferentiation of immortalized human podocytes in response to transforming growth factor-β: a model for diabetic podocytopathy. Diabetes 2011; 60:1779-88. [PMID: 21521871 PMCID: PMC3114395 DOI: 10.2337/db10-1110] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
OBJECTIVE Diabetic nephropathy is associated with dedifferentiation of podocytes, losing the specialized features required for efficient glomerular function and acquiring a number of profibrotic, proinflammatory, and proliferative features. These result from tight junction and cytoskeletal rearrangement, augmented proliferation, and apoptosis. RESEARCH DESIGN AND METHODS Experiments were performed in conditionally immortalized human podocytes developed by transfection with the temperature-sensitive SV40-T gene. Cells were then cultured in the presence of transforming growth factor (TGF)-β1 or angiotensin II in the presence or absence of a selective inhibitor of the TGF-β type I receptor kinase, SB-431542. Gene and protein expression were then examined by real-time RT-PCR and immunofluorescence, and correlated with changes observed in vivo in experimental diabetes. RESULTS Treatment of cells with TGF-β1 resulted in dynamic changes in their morphology, starting with retraction and shortening of foot processes and finishing with the formation of broad and complex tight junctions between adjacent podocytes. This dedifferentiation was also associated with dose- and time-dependent reduction in the expression of glomerular epithelial markers (nephrin, p-cadherin, zonnula occludens-1) and increased expression of mesenchymal markers (α-smooth muscle actin, vimentin, nestin), matrix components (fibronectin, collagen I, and collagen IV α3), cellular proliferation, and apoptosis. The induction of diabetes in mice was also associated with similar changes in morphology, protein expression, and proliferation in glomerular podocytes. CONCLUSIONS In response to TGF-β and other TGF-dependent stimuli, mature podocytes undergo dedifferentiation that leads to effacement of foot processes, morphologic flattening, and increased formation of intercellular tight junctions. This simplification of their phenotype to a more embryonic form is also associated with reentry of mature podocytes into the cell cycle, which results in enhanced proliferation and apoptosis. These "pathoadaptive" changes are seen early in the diabetic glomerulus and ultimately contribute to albuminuria, glomerulosclerosis, and podocytopenia.
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Affiliation(s)
- Michal Herman-Edelstein
- JDRF Danielle Alberti Memorial Centre for Diabetes Complications, Diabetes Division, Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia
- Department of Nephrology and Hypertension, Rabin Medical Center-Hasharon Hospital, Ackler School of Medicine Tel-Aviv University, Petach-Tikva, Israel
| | - Merlin C. Thomas
- JDRF Danielle Alberti Memorial Centre for Diabetes Complications, Diabetes Division, Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia
| | - Vicki Thallas-Bonke
- JDRF Danielle Alberti Memorial Centre for Diabetes Complications, Diabetes Division, Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia
| | - Moin Saleem
- Academic and Children’s Renal Unit, University of Bristol, Bristol, U.K
| | - Mark E. Cooper
- JDRF Danielle Alberti Memorial Centre for Diabetes Complications, Diabetes Division, Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia
| | - Phillip Kantharidis
- JDRF Danielle Alberti Memorial Centre for Diabetes Complications, Diabetes Division, Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia
- Corresponding author: Phillip Kantharidis,
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Harper SJ, Bates DO. Glomerular filtration barrier and molecular segregation: guilty as charged? J Am Soc Nephrol 2010; 21:2009-11. [PMID: 21071522 DOI: 10.1681/asn.2010101071] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
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Qiu Y, Ferguson J, Oltean S, Neal CR, Kaura A, Bevan H, Wood E, Sage LM, Lanati S, Nowak DG, Salmon AHJ, Bates D, Harper SJ. Overexpression of VEGF165b in podocytes reduces glomerular permeability. J Am Soc Nephrol 2010; 21:1498-509. [PMID: 20688932 DOI: 10.1681/asn.2009060617] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
The observation that therapeutic agents targeting vascular endothelial growth factor-A (VEGF-A) associate with renal toxicity suggests that VEGF plays a role in the maintenance of the glomerular filtration barrier. Alternative mRNA splicing produces the VEGF(xxx)b family, which consists of antiangiogenic peptides that reduce permeability and inhibit tumor growth; the contribution of these peptides to normal glomerular function is unknown. Here, we established and characterized heterozygous and homozygous transgenic mice that overexpress VEGF(165)b specifically in podocytes. We confirmed excess production of glomerular VEGF(165)b by reverse transcriptase-PCR, immunohistochemistry, and ELISA in both heterozygous and homozygous animals. Macroscopically, the mice seemed normal up to 18 months of age, unlike the phenotype of transgenic podocyte-specific VEGF(164)-overexpressing mice. Animals overexpressing VEGF(165)b, however, had a significantly reduced normalized glomerular ultrafiltration fraction with accompanying changes in ultrastructure of the glomerular filtration barrier on the vascular side of the glomerular basement membrane. These data highlight the contrasting properties of VEGF splice variants and their impact on glomerular function and phenotype.
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Affiliation(s)
- Yan Qiu
- Microvascular Research Laboratories, Department Physiology and Pharmacology, Bristol Heart Institute, Preclinical Veterinary School, Southwell Street, Bristol, BS2 8EJ, UK
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Dryer SE, Reiser J. TRPC6 channels and their binding partners in podocytes: role in glomerular filtration and pathophysiology. Am J Physiol Renal Physiol 2010; 299:F689-701. [PMID: 20685822 DOI: 10.1152/ajprenal.00298.2010] [Citation(s) in RCA: 117] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Loss or dysfunction of podocytes is a major cause of glomerular kidney disease. Several genetic forms of glomerular disease are caused by mutations in genes that encode structural elements of the slit diaphragm or the underlying cytoskeleton of podocyte foot processes. The recent discovery that gain-of-function mutations in Ca(2+)-permeable canonical transient receptor potential-6 channels (TRPC6) underlie a subset of familial forms of focal segmental glomerulosclerosis (FSGS) has focused attention on the basic cellular physiology of podocytes. Several recent studies have examined the role of Ca(2+) dynamics in normal podocyte function and their possible contributions to glomerular disease. This review summarizes the properties of TRPC6 and related channels, focusing on their permeation and gating properties, the nature of mutations associated with familial FSGS, and the role of TRPC channels in podocyte cell biology as well as in glomerular pathophysiology. TRPC6 interacts with several proteins in podocytes, including essential slit diaphragm proteins and mechanosensitive large-conductance Ca(2+)-activated K(+) channels. The signaling dynamics controlling ion channel function and localization in podocytes appear to be quite complex.
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Affiliation(s)
- Stuart E Dryer
- Dept. of Biology and Biochemistry, Univ. of Houston, 4800 Calhoun, Houston, TX 77204-5001, USA.
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Abstract
Multiphoton excitation fluorescence microscopy is a powerful noninvasive imaging technique for the deep optical sectioning of living tissues. Its application in several intact tissues is a significant advance in our understanding of organ function, including renal pathophysiological mechanisms. The glomerulus, the filtering unit in the kidney, is one good example of a relatively inaccessible and complex structure, with cell types that are otherwise difficult to study at high resolution in their native environment. In this article, we address the application, advantages, and limitations of this imaging technology for the study of the glomerular filtration barrier and the controversy it recently generated regarding the glomerular filtration of macromolecules. More advanced and accurate multiphoton determinations of the glomerular sieving coefficient that are presented here dismiss previous claims on the filtration of nephrotic levels of albumin. The sieving coefficient of 70-kD dextran was found to be around 0.001. Using a model of focal segmental glomerulosclerosis, increased filtration barrier permeability is restricted only to areas of podocyte damage, consistent with the generally accepted role of podocytes and the glomerular origin of albuminuria. Time-lapse imaging provides new details and important in vivo confirmation of the dynamics of podocyte movement, shedding, replacement, and the role of the parietal epithelial cells and Bowman's capsule in the pathology of glomerulosclerosis.
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Affiliation(s)
- János Peti-Peterdi
- Department of Physiology and Biophysics, Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, CA 90033, USA.
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Prokai A, Peti-Peterdi J. Recent advances in tissue (pro)renin imaging. Front Biosci (Elite Ed) 2010; 2:1227-33. [PMID: 20515794 DOI: 10.2741/e182] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Due to its pivotal role in blood pressure control and renal pathologies there is renewed interest in renin and its precursor prorenin. Also, the newly discovered (pro)renin receptor is a new element of the ever broadening renin-angiotensin system (RAS). The complexity of RAS including the recently recognized collecting duct site of (pro)renin (a term denoting both renin and prorenin) synthesis requires the use of advanced research techniques such as multiphoton fluorescence microscopy. With the help of this technology we have pioneered an imaging approach to directly visualize (pro)renin content, release and tissue activity in the living kidney. The use of this technology is reviewed here and exemplified by the direct visualization of (pro)renin activity in the collecting duct. New pharmacological tools, the renin inhibitor aliskiren and the handle region peptide (decoy peptide) was used to further characterize the intra-renal, collecting duct RAS.
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Affiliation(s)
- Agnes Prokai
- Hungarian Academy of Sciences, Research Laboratory for Pediatrics and Nephrology, and 1st Dept of Pediatrics, Semmelweis University, Budapest, Hungary
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44
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Hendrickson G, Lyon L. Microgel Translocation through Pores under Confinement. Angew Chem Int Ed Engl 2010. [DOI: 10.1002/ange.200906606] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Affiliation(s)
- Grant R. Hendrickson
- School of Chemistry and Biochemistry and Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332-0400 (USA)
| | - L. Andrew Lyon
- School of Chemistry and Biochemistry and Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332-0400 (USA)
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Fischer K, McDannold NJ, Zhang Y, Kardos M, Szabo A, Szabo A, Reusz GS, Jolesz FA. Renal ultrafiltration changes induced by focused US. Radiology 2009; 253:697-705. [PMID: 19703861 DOI: 10.1148/radiol.2532082100] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
PURPOSE To determine if focused ultrasonography (US) combined with a diagnostic microbubble-based US contrast agent can be used to modulate glomerular ultrafiltration and size selectivity. MATERIALS AND METHODS The experiments were approved by the animal care committee. The left kidney of 17 healthy rabbits was sonicated by using a 260-kHz focused US transducer in the presence of a microbubble-based US contrast agent. The right kidney served as the control. Three acoustic power levels were applied: 0.4 W (six rabbits), 0.9 W (six rabbits), and 1.7 W (five rabbits). Three rabbits were not treated with focused US and served as control animals. The authors evaluated changes in glomerular size selectivity by measuring the clearance rates of 3000- and 70,000-Da fluorescence-neutral dextrans. The creatinine clearance was calculated for estimation of the glomerular filtration rate. The urinary protein-creatinine ratio was monitored during the experiments. The authors assessed tubular function by evaluating the fractional sodium excretion, tubular reabsorption of phosphate, and gamma-glutamyltransferase-creatinine ratio. Whole-kidney histologic analysis was performed. For each measurement, the values obtained before and after sonication were compared by using the paired t test. RESULTS Significant (P < .05) increases in the relative (ratio of treated kidney value/nontreated kidney value) clearance of small- and large-molecule agents and the urine flow rates that resulted from the focused US treatments were observed. Overall, 1.23-, 1.23-, 1.61-, and 1.47-fold enhancement of creatinine clearance, 3000-Da dextran clearance, 70 000-Da dextran clearance, and urine flow rate, respectively, were observed. Focal tubular hemorrhage and transient functional tubular alterations were observed at only the highest (1.7-W) acoustic power level tested. CONCLUSION Glomerular ultrafiltration and size selectivity can be temporarily modified with simultaneous application of US and microbubbles. This method could offer new opportunities for treatment of renal disease.
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Affiliation(s)
- Krisztina Fischer
- Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Focused Ultrasound Laboratory, 221 Longwood Ave, Room 515, Boston, MA 02215, USA.
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New aspects of glomerular filtration barrier structure and function: five layers (at least) not three. Curr Opin Nephrol Hypertens 2009; 18:197-205. [PMID: 19365184 DOI: 10.1097/mnh.0b013e328329f837] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
PURPOSE OF REVIEW Three structures (glomerular endothelial fenestrae, glomerular basement membrane and podocyte interfoot process/slit diaphragms) have traditionally been considered as the major determinants of glomerular permeability. We review recent work demonstrating the functional importance of two additional layers: the endothelial surface layer (ESL) and the subpodocyte space (SPS). RECENT FINDINGS Removing glomerular endothelial cell monolayer ESL in vitro significantly alters monolayer permeability, supporting previous in-vivo demonstrations of the importance of the ESL in determining glomerular permeability. Whether fenestral diaphragms are present to support the ESL in healthy adult glomeruli has been examined in a recent report. On the downstream side of the glomerular filtration barrier, the SPS is a recently described structure that covers approximately two-thirds of the barrier, has highly restrictive dimensions and contributes to the hydraulic resistance and ultrafiltration characteristics of the glomerulus. Different layers of the barrier have also been shown to influence the permeability characteristics of one another, either through biophysical interactions, or through the activities of ligand-receptor axes that cross the various layers of the barrier. SUMMARY The structure and function of the glomerular filtration barrier remains an area of significant new discovery, and recent work continues to highlight the complexity of this dynamic multilayered watershed.
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Peti-Peterdi J, Toma I, Sipos A, Vargas SL. Multiphoton imaging of renal regulatory mechanisms. Physiology (Bethesda) 2009; 24:88-96. [PMID: 19364911 DOI: 10.1152/physiol.00001.2009] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Most physiological functions of the kidneys, including the clearance of metabolic waste products, maintenance of body fluid, electrolyte homeostasis, and blood pressure, are achieved by complex interactions between multiple renal cell types and previously inaccessible structures in many organ parts that have been difficult to study. Multiphoton fluorescence microscopy offers a state-of-the-art imaging technique for deep optical sectioning of living tissues and organs with minimal deleterious effects. Dynamic regulatory processes and multiple functions in the intact kidney can be quantitatively visualized in real time, noninvasively, and with submicron resolution. This article reviews innovative multiphoton imaging technologies and their applications that provided the most complex, immediate, and dynamic portrayal of renal function-clearly depicting as well as analyzing the components and mechanisms involved in renal (patho)physiology.
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Affiliation(s)
- János Peti-Peterdi
- Departments of Physiology and Biophysics and Medicine, Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, California, USA.
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Peti-Peterdi J. Independent two-photon measurements of albumin GSC give low values. Am J Physiol Renal Physiol 2009; 296:F1255-7. [PMID: 19297453 DOI: 10.1152/ajprenal.00144.2009] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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