1
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Boruah D, Kashif AW, Chakrabarty BK, Harikrishnan S, Sen A. Correlation of light and electron microscopic morphometric parameters of glomerular capillaries with serum creatinine and proteinuria. J Histotechnol 2024:1-12. [PMID: 38465441 DOI: 10.1080/01478885.2024.2326274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Accepted: 02/27/2024] [Indexed: 03/12/2024]
Abstract
Waste products in the bloodstream are filtered by the glomerular capillaries in the kidneys and excreted into the urine. When making a differential diagnosis of kidney diseases, structural assessment of glomeruli using histological, ultrastructural, and immunological studies is crucial. This study assessed the microscopic and ultrastructural morphometric parameters of glomerular capillaries and examined their correlation with serum creatinine and proteinuria. A total of 60 kidney biopsy cases received by the transmission electron microscope (TEM) laboratory for diagnosis were included in the study. Toluidine blue stained 300 nm thick sections of TEM tissue blocks were scanned for glomerular morphometry by a whole slide imaging system, and the estimation of Bowman's capsule (BC) area, glomerular capillary lumen diameter (GCLD), glomerular capillary density (GCD), glomerular capillary surface area density (GCSA), and percentage of glomerular capillary lumen space (%GCLS) was performed with QuPath software. TEM images of 70 nm thick sections were used for the evaluation of endothelial fenestration diameter (EFD), glomerular basement membrane (GBM) thickness, and podocyte foot process (PFP) effacement. Proteinuria and serum creatinine showed positive correlations with GBM thickness and PFP effacement. Negative correlations of serum creatinine were observed with EFD, %GCLS, and GCSA. Hence, glomerular filtration is greatly affected by the total area of the glomerular capillary surface and structural changes of GBM. Reduction of glomerulus filtration due to foot process effacement and thickening of GBM results in damage to the filtration barrier leading to the leakage of plasma protein into urine.
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Affiliation(s)
| | - A W Kashif
- Department of Pathology, Armed Forces Medical College, Pune, India
| | | | | | - Arijit Sen
- Department of Pathology, Armed Forces Medical College, Pune, India
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2
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Punyaratabandhu N, Dechadilok P, Triampo W, Katavetin P. Hydrodynamic model for renal microvascular filtration: Effects of physiological and hemodynamic changes on glomerular size-selectivity. Microcirculation 2022; 29:e12779. [PMID: 35879876 DOI: 10.1111/micc.12779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Revised: 06/25/2022] [Accepted: 07/21/2022] [Indexed: 12/30/2022]
Abstract
OBJECTIVE The first step in renal urine formation is ultrafiltration across the glomerular barrier. The change in its nanostructure has been associated with nephrotic syndromes. Effects of physiological and hemodynamic factor alterations associated with diabetic nephropathy (DN) on glomerular permselectivity are examined through a mathematical model employing low-Reynolds-number hydrodynamics and hindered transport theory. METHODS Glomerular capillaries are represented as networks of cylindrical tubes with multilayered walls. Glomerular basement membrane (GBM) is a fibrous medium with bimodal fiber sizes. Epithelial slit fiber spacing follows a lognormal distribution based on reported electron micrographs with the highest resolution. Endothelial fenestrae are filled with fibers the size of glycosaminoglycans (GAGs). Effects of fiber-macromolecule steric and hydrodynamic interactions are included. Focusing on diabetic nephropathy, the physiological and hemodynamic factors employed in the computation are those reported for healthy humans and patients with early-but-overt diabetic nephropathy. The macromolecule concentration is obtained as a finite element solution of the convection-diffusion equation. RESULTS Computed sieving coefficients averaged along the capillary length agree well with ficoll sieving coefficients from studies in humans for most solute radii. GBM thickening and the loss of the slit diaphragm hardly affect glomerular permselectivity. GAG volume fraction reduction in the endothelial fenestrae, however, significantly increases macromolecule filtration. Increased renal plasma flow rate (RPF), glomerular hypertension, and reduction of lumen osmotic pressure cause a slight sieving coefficient decrease. These effects are amplified by an increased macromolecule size. CONCLUSION Our results indicate that glomerular hypertension and the reduction in the oncotic pressure decreases glomerular macromolecule filtration. Reduction of RPF and changes in the glomerular barrier structure associated with DN, however, increase the solute sieving. Damage to GAGs caused by hyperglycemia is likely to be the most prominent factor affecting glomerular size-selectivity.
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Affiliation(s)
| | - Panadda Dechadilok
- Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok, Thailand
| | - Wannapong Triampo
- Thailand Center of Excellence in Physics CHE, Bangkok, Thailand.,Department of Physics, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Pisut Katavetin
- Division of Nephrology, Department of Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand
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3
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Ballermann BJ, Nyström J, Haraldsson B. The Glomerular Endothelium Restricts Albumin Filtration. Front Med (Lausanne) 2021; 8:766689. [PMID: 34912827 PMCID: PMC8667033 DOI: 10.3389/fmed.2021.766689] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2021] [Accepted: 11/05/2021] [Indexed: 12/29/2022] Open
Abstract
Inflammatory activation and/or dysfunction of the glomerular endothelium triggers proteinuria in many systemic and localized vascular disorders. Among them are the thrombotic microangiopathies, many forms of glomerulonephritis, and acute inflammatory episodes like sepsis and COVID-19 illness. Another example is the chronic endothelial dysfunction that develops in cardiovascular disease and in metabolic disorders like diabetes. While the glomerular endothelium is a porous sieve that filters prodigious amounts of water and small solutes, it also bars the bulk of albumin and large plasma proteins from passing into the glomerular filtrate. This endothelial barrier function is ascribed predominantly to the endothelial glycocalyx with its endothelial surface layer, that together form a relatively thick, mucinous coat composed of glycosaminoglycans, proteoglycans, glycolipids, sialomucins and other glycoproteins, as well as secreted and circulating proteins. The glycocalyx/endothelial surface layer not only covers the glomerular endothelium; it extends into the endothelial fenestrae. Some glycocalyx components span or are attached to the apical endothelial cell plasma membrane and form the formal glycocalyx. Other components, including small proteoglycans and circulating proteins like albumin and orosomucoid, form the endothelial surface layer and are bound to the glycocalyx due to weak intermolecular interactions. Indeed, bound plasma albumin is a major constituent of the endothelial surface layer and contributes to its barrier function. A role for glomerular endothelial cells in the barrier of the glomerular capillary wall to protein filtration has been demonstrated by many elegant studies. However, it can only be fully understood in the context of other components, including the glomerular basement membrane, the podocytes and reabsorption of proteins by tubule epithelial cells. Discovery of the precise mechanisms that lead to glycocalyx/endothelial surface layer disruption within glomerular capillaries will hopefully lead to pharmacological interventions that specifically target this important structure.
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Affiliation(s)
| | - Jenny Nyström
- Institute of Neuroscience and Physiology, University of Gothenburg, Gothenburg, Sweden
| | - Börje Haraldsson
- Institute of Neuroscience and Physiology, University of Gothenburg, Gothenburg, Sweden
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4
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Edwards A, Christensen EI, Unwin RJ, Norden AGW. Predicting the protein composition of human urine in normal and pathological states: Quantitative description based on Dent1 disease (
CLCN5
mutation). J Physiol 2020; 599:323-341. [DOI: 10.1113/jp280740] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Accepted: 10/16/2020] [Indexed: 01/25/2023] Open
Affiliation(s)
- Aurélie Edwards
- Department of Biomedical Engineering Boston University Boston MA USA
| | | | - Robert J. Unwin
- Department of Renal Medicine Royal Free Campus University College London London UK
| | - Anthony G. W. Norden
- Department of Renal Medicine Royal Free Campus University College London London UK
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5
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Butler MJ, Down CJ, Foster RR, Satchell SC. The Pathological Relevance of Increased Endothelial Glycocalyx Permeability. THE AMERICAN JOURNAL OF PATHOLOGY 2020; 190:742-751. [PMID: 32035881 DOI: 10.1016/j.ajpath.2019.11.015] [Citation(s) in RCA: 63] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2019] [Revised: 10/25/2019] [Accepted: 11/22/2019] [Indexed: 01/06/2023]
Abstract
The endothelial glycocalyx is a vital regulator of vascular permeability. Damage to this delicate layer can result in increased protein and water transit. The clinical importance of albuminuria as a predictor of kidney disease progression and vascular disease has driven research in this area. This review outlines how research to date has attempted to measure the contribution of the endothelial glycocalyx to vessel wall permeability. We discuss the evidence for the role of the endothelial glycocalyx in regulating permeability in discrete areas of the vasculature and highlight the inherent limitations of the data that have been produced to date. In particular, this review emphasizes the difficulties in interpreting urinary albumin levels in early disease models. In addition, the research that supports the view that glycocalyx damage is a key pathologic step in a diverse array of clinical conditions, including diabetic complications, sepsis, preeclampsia, and atherosclerosis, is summarized. Finally, novel methods are discussed, including an ex vivo glomerular permeability assay that enhances the understanding of permeability changes in disease.
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Affiliation(s)
- Matthew J Butler
- Bristol Renal, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, United Kingdom.
| | - Colin J Down
- Bristol Renal, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, United Kingdom
| | - Rebecca R Foster
- Bristol Renal, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, United Kingdom
| | - Simon C Satchell
- Bristol Renal, Translational Health Sciences, Bristol Medical School, University of Bristol, Bristol, United Kingdom
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6
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Voinova M, Repin N, Sokol E, Tkachuk B, Gorelik L. Physical Processes in Polymeric Filters Used for Dialysis. Polymers (Basel) 2019; 11:E389. [PMID: 30960373 PMCID: PMC6473866 DOI: 10.3390/polym11030389] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2018] [Revised: 02/06/2019] [Accepted: 02/12/2019] [Indexed: 01/03/2023] Open
Abstract
The key physical processes in polymeric filters used for the blood purification include transport across the capillary wall and the interaction of blood cells with the polymer membrane surface. Theoretical modeling of membrane transport is an important tool which provides researchers with a quantification of the complex phenomena involved in dialysis. In the paper, we present a dense review of the most successful theoretical approaches to the description of transport across the polymeric membrane wall as well as the cell⁻polymer surface interaction, and refer to the corresponding experimental methods while studying these phenomena in dialyzing filters.
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Affiliation(s)
- Marina Voinova
- Department of Physics, Chalmers University of Technology, 41296 Gothenburg, Sweden.
- Department of Industrial and Biomedical Electronics, Kharkiv Polytechnical Institute, National Technical University, 61002 Kharkov, Ukraine.
| | - Nikolay Repin
- Department of Cryomorphology, Institute for Problems of Cryobiology and Cryomedicine, 61015 Kharkov, Ukraine.
| | - Evgen Sokol
- Department of Industrial and Biomedical Electronics, Kharkiv Polytechnical Institute, National Technical University, 61002 Kharkov, Ukraine.
| | - Bogdan Tkachuk
- Department of Hemodialysis, Municipal Noncommercial Enterprise of Kharkiv Regional Council "Regional Medical Clinical Center of Urology and Nephrology n.a. V.I. Shapoval", 61037 Kharkov, Ukraine.
| | - Leonid Gorelik
- Department of Physics, Chalmers University of Technology, 41296 Gothenburg, Sweden.
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7
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Hunt SE, Dorfman KD, Segal Y, Barocas VH. A computational model of flow and species transport in the mesangium. Am J Physiol Renal Physiol 2016; 310:F222-9. [PMID: 26831339 DOI: 10.1152/ajprenal.00182.2015] [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: 04/29/2015] [Accepted: 10/06/2015] [Indexed: 01/17/2023] Open
Abstract
A variety of macromolecules accumulate in the glomerular mesangium in many different diseases, but the physics of the transport of these molecules within the mesangial matrix has not been extensively studied. We present a computational model of convection and diffusion within the porous mesangial matrix and apply this model to the specific instance of immunoglobulin A (IgA) transport in IgA nephropathy. We examine the influence of physiological factors including glomerular basement membrane (GBM) thickness and mesangial matrix density on the total accumulation of IgA. Our results suggest that IgA accumulation can be understood by relating convection and diffusion, thus demonstrating the importance of intrinsic glomerular factors.
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Affiliation(s)
- Sarah E Hunt
- Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota;
| | - Kevin D Dorfman
- Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota
| | - Yoav Segal
- Division of Renal Diseases and Hypertension, Department of Medicine, University of Minnesota, Minneapolis, Minnesota; and Minneapolis Veterans Affairs Health Care System, Minneapolis, Minnesota
| | - Victor H Barocas
- Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota
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8
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Xinaris C, Benedetti V, Novelli R, Abbate M, Rizzo P, Conti S, Tomasoni S, Corna D, Pozzobon M, Cavallotti D, Yokoo T, Morigi M, Benigni A, Remuzzi G. Functional Human Podocytes Generated in Organoids from Amniotic Fluid Stem Cells. J Am Soc Nephrol 2015; 27:1400-11. [PMID: 26516208 DOI: 10.1681/asn.2015030316] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2015] [Accepted: 08/03/2015] [Indexed: 12/11/2022] Open
Abstract
Generating kidney organoids using human stem cells could offer promising prospects for research and therapeutic purposes. However, no cell-based strategy has generated nephrons displaying an intact three-dimensional epithelial filtering barrier. Here, we generated organoids using murine embryonic kidney cells, and documented that these tissues recapitulated the complex three-dimensional filtering structure of glomerular slits in vivo and accomplished selective glomerular filtration and tubular reabsorption. Exploiting this technology, we mixed human amniotic fluid stem cells with mouse embryonic kidney cells to establish three-dimensional chimeric organoids that engrafted in vivo and grew to form vascularized glomeruli and tubular structures. Human cells contributed to the formation of glomerular structures, differentiated into podocytes with slit diaphragms, and internalized exogenously infused BSA, thus attaining in vivo degrees of specialization and function unprecedented for donor stem cells. In conclusion, human amniotic fluid stem cell chimeric organoids may offer new paths for studying renal development and human podocyte disease, and for facilitating drug discovery and translational research.
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Affiliation(s)
- Christodoulos Xinaris
- IRCCS-Istituto di Ricerche Farmacologiche 'Mario Negri', Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Bergamo, Italy;
| | - Valentina Benedetti
- IRCCS-Istituto di Ricerche Farmacologiche 'Mario Negri', Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Bergamo, Italy
| | - Rubina Novelli
- IRCCS-Istituto di Ricerche Farmacologiche 'Mario Negri', Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Bergamo, Italy
| | - Mauro Abbate
- IRCCS-Istituto di Ricerche Farmacologiche 'Mario Negri', Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Bergamo, Italy
| | - Paola Rizzo
- IRCCS-Istituto di Ricerche Farmacologiche 'Mario Negri', Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Bergamo, Italy
| | - Sara Conti
- IRCCS-Istituto di Ricerche Farmacologiche 'Mario Negri', Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Bergamo, Italy
| | - Susanna Tomasoni
- IRCCS-Istituto di Ricerche Farmacologiche 'Mario Negri', Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Bergamo, Italy
| | - Daniela Corna
- IRCCS-Istituto di Ricerche Farmacologiche 'Mario Negri', Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Bergamo, Italy
| | - Michela Pozzobon
- Stem Cells and Regenerative Medicine Laboratory, Foundation Institute of Pediatric Research Fondazione Città della Speranza, Padua, Italy
| | - Daniela Cavallotti
- IRCCS-Istituto di Ricerche Farmacologiche 'Mario Negri', Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Bergamo, Italy
| | - Takashi Yokoo
- The Jikei University School of Medicine, Tokyo, Japan
| | - Marina Morigi
- IRCCS-Istituto di Ricerche Farmacologiche 'Mario Negri', Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Bergamo, Italy
| | - Ariela Benigni
- IRCCS-Istituto di Ricerche Farmacologiche 'Mario Negri', Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Bergamo, Italy
| | - Giuseppe Remuzzi
- IRCCS-Istituto di Ricerche Farmacologiche 'Mario Negri', Centro Anna Maria Astori, Science and Technology Park Kilometro Rosso, Bergamo, Italy; Unit of Nephrology and Dialysis, Azienda Ospedaliera Papa Giovanni XXIII, Bergamo, Italy; and Department of Biomedical and Clinical Sciences, University of Milan, Milan, Italy
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9
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Abstract
Mathematical modeling techniques have been useful in providing insights into biological systems, including the kidney. This article considers some of the mathematical models that concern urea transport in the kidney. Modeling simulations have been conducted to investigate, in the context of urea cycling and urine concentration, the effects of hypothetical active urea secretion into pars recta. Simulation results suggest that active urea secretion induces a "urea-selective" improvement in urine concentrating ability. Mathematical models have also been built to study the implications of the highly structured organization of tubules and vessels in the renal medulla on urea sequestration and cycling. The goal of this article is to show how physiological problems can be formulated and studied mathematically, and how such models may provide insights into renal functions.
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Affiliation(s)
- Anita T Layton
- Department of Mathematics, Duke University, Durham, NC, USA,
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10
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Chung JJ, Huber TB, Gödel M, Jarad G, Hartleben B, Kwoh C, Keil A, Karpitskiy A, Hu J, Huh CJ, Cella M, Gross RW, Miner JH, Shaw AS. Albumin-associated free fatty acids induce macropinocytosis in podocytes. J Clin Invest 2015; 125:2307-16. [PMID: 25915582 DOI: 10.1172/jci79641] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2014] [Accepted: 03/19/2015] [Indexed: 01/26/2023] Open
Abstract
Podocytes are specialized epithelial cells in the kidney glomerulus that play important structural and functional roles in maintaining the filtration barrier. Nephrotic syndrome results from a breakdown of the kidney filtration barrier and is associated with proteinuria, hyperlipidemia, and edema. Additionally, podocytes undergo changes in morphology and internalize plasma proteins in response to this disorder. Here, we used fluid-phase tracers in murine models and determined that podocytes actively internalize fluid from the plasma and that the rate of internalization is increased when the filtration barrier is disrupted. In cultured podocytes, the presence of free fatty acids (FFAs) associated with serum albumin stimulated macropinocytosis through a pathway that involves FFA receptors, the Gβ/Gγ complex, and RAC1. Moreover, mice with elevated levels of plasma FFAs as the result of a high-fat diet were more susceptible to Adriamycin-induced proteinuria than were animals on standard chow. Together, these results support a model in which podocytes sense the disruption of the filtration barrier via FFAs bound to albumin and respond by enhancing fluid-phase uptake. The response to FFAs may function in the development of nephrotic syndrome by amplifying the effects of proteinuria.
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11
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Wang Y, Lomakin A, Latypov RF, Laubach JP, Hideshima T, Richardson PG, Munshi NC, Anderson KC, Benedek GB. Phase transitions in human IgG solutions. J Chem Phys 2014; 139:121904. [PMID: 24089716 DOI: 10.1063/1.4811345] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Protein condensations, such as crystallization, liquid-liquid phase separation, aggregation, and gelation, have been observed in concentrated antibody solutions under various solution conditions. While most IgG antibodies are quite soluble, a few outliers can undergo condensation under physiological conditions. Condensation of IgGs can cause serious consequences in some human diseases and in biopharmaceutical formulations. The phase transitions underlying protein condensations in concentrated IgG solutions is also of fundamental interest for the understanding of the phase behavior of non-spherical protein molecules. Due to the high solubility of generic IgGs, the phase behavior of IgG solutions has not yet been well studied. In this work, we present an experimental approach to study IgG solutions in which the phase transitions are hidden below the freezing point of the solution. Using this method, we have investigated liquid-liquid phase separation of six human myeloma IgGs and two recombinant pharmaceutical human IgGs. We have also studied the relation between crystallization and liquid-liquid phase separation of two human cryoglobulin IgGs. Our experimental results reveal several important features of the generic phase behavior of IgG solutions: (1) the shape of the coexistence curve is similar for all IgGs but quite different from that of quasi-spherical proteins; (2) all IgGs have critical points located at roughly the same protein concentration at ~100 mg/ml while their critical temperatures vary significantly; and (3) the liquid-liquid phase separation in IgG solutions is metastable with respect to crystallization. These features of phase behavior of IgG solutions reflect the fact that all IgGs have nearly identical molecular geometry but quite diverse net inter-protein interaction energies. This work provides a foundation for further experimental and theoretical studies of the phase behavior of generic IgGs as well as outliers with large propensity to condense. The investigation of the phase diagram of IgG solutions is of great importance for the understanding of immunoglobulin deposition diseases as well as for the understanding of the colloidal stability of IgG pharmaceutical formulations.
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Affiliation(s)
- Ying Wang
- Materials Processing Center, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
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12
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Eves-van den Akker S, Lilley CJ, Ault JR, Ashcroft AE, Jones JT, Urwin PE. The feeding tube of cyst nematodes: characterisation of protein exclusion. PLoS One 2014; 9:e87289. [PMID: 24489891 PMCID: PMC3905015 DOI: 10.1371/journal.pone.0087289] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2013] [Accepted: 12/19/2013] [Indexed: 11/18/2022] Open
Abstract
Plant parasitic nematodes comprise several groups; the most economically damaging of these are the sedentary endoparasites. Sedentary endoparasitic nematodes are obligate biotrophs and modify host root tissue, using a suite of effector proteins, to create a feeding site that is their sole source of nutrition. They feed by withdrawing host cell assimilate from the feeding site though a structure known as the feeding tube. The function, composition and molecular characteristics of feeding tubes are poorly characterised. It is hypothesised that the feeding tube facilitates uptake of host cell assimilate by acting as a molecular sieve. Several studies, using molecular mass as the sole indicator of protein size, have given contradictory results about the exclusion limits of the cyst nematode feeding tube. In this study we propose a method to predict protein size, based on protein database coordinates in silico. We tested the validity of these predictions using travelling wave ion mobility spectrometry – mass spectrometry, where predictions and measured values were within approximately 6%. We used the predictions, coupled with mass spectrometry, analytical ultracentrifugation and protein electrophoresis, to resolve previous conflicts and define the exclusion characteristics of the cyst nematode feeding tube. Heterogeneity was tested in the liquid, solid and gas phase to provide a comprehensive evaluation of three proteins of particular interest to feeding tube size exclusion, GFP, mRFP and Dual PI. The data and procedures described here could be applied to the design of plant expressed defence compounds intended for uptake into cyst nematodes. We also highlight the need to assess protein heterogeneity when creating novel fusion proteins.
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Affiliation(s)
- Sebastian Eves-van den Akker
- Centre for Plant Sciences, University of Leeds, Leeds, United Kingdom
- Cell and Molecular Sciences, The James Hutton Institute, Invergowrie, Dundee, United Kingdom
| | | | - James R. Ault
- The Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | - Alison E. Ashcroft
- The Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds, United Kingdom
| | - John T. Jones
- Cell and Molecular Sciences, The James Hutton Institute, Invergowrie, Dundee, United Kingdom
| | - Peter E. Urwin
- Centre for Plant Sciences, University of Leeds, Leeds, United Kingdom
- * E-mail:
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13
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Tanaka K, Fukase K. Chemical Approach to a Whole Body Imaging of Sialo-N-Linked Glycans. Top Curr Chem (Cham) 2014; 367:201-30. [PMID: 25971916 DOI: 10.1007/128_2014_603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
PET and noninvasive fluorescence imaging of the sialo-N-linked glycan derivatives are described. To establish the efficient labeling protocol for N-glycans and/or glycoconjugates, new labeling probes of fluorescence and ⁶⁸Ga-DOTA, as the positron emission nucleus for PET, through rapid 6π-azaelectrocyclization were designed and synthesized, (E)-ester aldehydes. The high reactivity of these probes enabled the labeling of lysine residues in peptides, proteins, and even amino groups on the cell surfaces at very low concentrations of the target molecules (~10⁻⁸ M) within a short reaction time (~5 min) to result in "selective" and "non-destructive" labeling of the more accessible amines. The first MicroPET of glycoproteins, ⁶⁸Ga-DOTA-orosomucoid and asialoorosomucoid, successfully visualized the differences in the circulatory residence of glycoproteins, in the presence or absence of sialic acids. In vivo dynamics of the new N-glycoclusters, prepared by the "self-activating" Huisgen cycloaddition reaction, could also be affected significantly by their partial structures at the non-reducing end, i.e., the presence or absence of sialic acids, and/or sialoside linkages to galactose. Azaelectrocyclization chemistry is also applicable to the engineering of the proteins and/or the cell surfaces by the oligosaccharides; lymphocytes chemically engineered by sialo-N-glycan successfully target the tumor implanted in BALB/C nude mice, detected by noninvasive fluorescence imaging.
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Affiliation(s)
- Katsunori Tanaka
- Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka, 560-0043, Japan,
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14
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Layton AT. Mathematical modeling of kidney transport. WILEY INTERDISCIPLINARY REVIEWS-SYSTEMS BIOLOGY AND MEDICINE 2013; 5:557-73. [PMID: 23852667 DOI: 10.1002/wsbm.1232] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2013] [Revised: 05/16/2013] [Accepted: 05/20/2013] [Indexed: 11/08/2022]
Abstract
In addition to metabolic waste and toxin excretion, the kidney also plays an indispensable role in regulating the balance of water, electrolytes, nitrogen, and acid-base. In this review, we describe representative mathematical models that have been developed to better understand kidney physiology and pathophysiology, including the regulation of glomerular filtration, the regulation of renal blood flow by means of the tubuloglomerular feedback mechanisms and of the myogenic mechanism, the urine concentrating mechanism, epithelial transport, and regulation of renal oxygen transport. We discuss the extent to which these modeling efforts have expanded our understanding of renal function in both health and disease.
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Affiliation(s)
- Anita T Layton
- Department of Mathematics, Duke University, Durham, NC, USA
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15
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Abstract
The kidney plays an indispensable role in the regulation of whole-organism water balance, electrolyte balance, and acid-base balance, and in the excretion of metabolic wastes and toxins. In this paper, we review representative mathematical models that have been developed to better understand kidney physiology and pathophysiology, including the regulation of glomerular filtration, the regulation of renal blood flow by means of the tubuloglomerular feedback mechanisms and of the myogenic mechanism, the urine concentrating mechanism, and regulation of renal oxygen transport. We discuss how such modeling efforts have significantly expanded our understanding of renal function in both health and disease.
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Affiliation(s)
- Anita T Layton
- Department of Mathematics, Duke University, P.O. Box 90320, Durham, NC 27708-0320, USA
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16
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Ghobril C, Lamanna G, Kueny-Stotz M, Garofalo A, Billotey C, Felder-Flesch D. Dendrimers in nuclear medical imaging. NEW J CHEM 2012. [DOI: 10.1039/c1nj20416e] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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17
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Tanaka K, Siwu ERO, Minami K, Hasegawa K, Nozaki S, Kanayama Y, Koyama K, Chen WC, Paulson JC, Watanabe Y, Fukase K. Noninvasive imaging of dendrimer-type N-glycan clusters: in vivo dynamics dependence on oligosaccharide structure. Angew Chem Int Ed Engl 2011; 49:8195-200. [PMID: 20857462 DOI: 10.1002/anie.201000892] [Citation(s) in RCA: 97] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Katsunori Tanaka
- Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka-shi, Osaka 560-0043, Japan
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18
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Cadwallader AB, de la Torre X, Tieri A, Botrè F. The abuse of diuretics as performance-enhancing drugs and masking agents in sport doping: pharmacology, toxicology and analysis. Br J Pharmacol 2010; 161:1-16. [PMID: 20718736 DOI: 10.1111/j.1476-5381.2010.00789.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Diuretics are drugs that increase the rate of urine flow and sodium excretion to adjust the volume and composition of body fluids. There are several major categories of this drug class and the compounds vary greatly in structure, physicochemical properties, effects on urinary composition and renal haemodynamics, and site and mechanism of action. Diuretics are often abused by athletes to excrete water for rapid weight loss and to mask the presence of other banned substances. Because of their abuse by athletes, diuretics have been included on The World Anti-Doping Agency's (WADA) list of prohibited substances; the use of diuretics is banned both in competition and out of competition and diuretics are routinely screened for by anti-doping laboratories. This review provides an overview of the pharmacology and toxicology of diuretics and discusses their application in sports. The most common analytical strategies currently followed by the anti-doping laboratories accredited by the WADA are discussed along with the challenges laboratories face for the analysis of this diverse class of drugs.
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Affiliation(s)
- Amy B Cadwallader
- Laboratorio Antidoping, Federazione Medico Sportiva Italiana, Largo Giulio Onesti, 1, Rome, Italy
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19
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Gagliardini E, Conti S, Benigni A, Remuzzi G, Remuzzi A. Imaging of the porous ultrastructure of the glomerular epithelial filtration slit. J Am Soc Nephrol 2010; 21:2081-9. [PMID: 21030599 DOI: 10.1681/asn.2010020199] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
The ultrastructure of the glomerular filtration slit is still controversial. In the last 30 years, observations from transmission electron microscopy (TEM) and theoretical analysis of solute clearance produced conflicting results. Here, we used scanning EM with a high-sensitivity detector to image the deepest regions of the filtration slits and report a previously undescribed organization of the slits' ultrastructure. In contrast to previous TEM imaging, we observed circular and ellipsoidal pores in the podocyte junctions mainly located in the central region of the slit diaphragm. The normal mean pore radius estimated by digital morphometric analysis had a log-normal distribution, with an average value of 12.1 nm. In proteinuric pathologic conditions, the mean pore radius values were also log-normally distributed with the presence of some very large pores, exceeding the sizes observed in normal conditions. Our morphologic analysis suggests that the filtration slit is a heteroporous structure instead of the previously proposed zipper-like structure. Selective changes in the ultrastructural organization of the pores may be responsible for the increased filtration of plasma proteins in glomerular disease.
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Affiliation(s)
- Elena Gagliardini
- Mario Negri Institute for Pharmacological Research, Centro Anna Maria Astori, Science & Technology Park, Km Rosso, Bergamo, Italy
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20
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Tanaka K, Siwu ERO, Minami K, Hasegawa K, Nozaki S, Kanayama Y, Koyama K, Chen WC, Paulson JC, Watanabe Y, Fukase K. Noninvasive Imaging of Dendrimer-Type N-Glycan Clusters: In Vivo Dynamics Dependence on Oligosaccharide Structure. Angew Chem Int Ed Engl 2010. [DOI: 10.1002/ange.201000892] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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21
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White JT, Zhang B, Cerqueira DM, Tran U, Wessely O. Notch signaling, wt1 and foxc2 are key regulators of the podocyte gene regulatory network in Xenopus. Development 2010; 137:1863-73. [PMID: 20431116 PMCID: PMC2867321 DOI: 10.1242/dev.042887] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/24/2010] [Indexed: 11/20/2022]
Abstract
Podocytes are highly specialized cells in the vertebrate kidney. They participate in the formation of the size-exclusion barrier of the glomerulus/glomus and recruit mesangial and endothelial cells to form a mature glomerulus. At least six transcription factors (wt1, foxc2, hey1, tcf21, lmx1b and mafb) are known to be involved in podocyte specification, but how they interact to drive the differentiation program is unknown. The Xenopus pronephros was used as a paradigm to address this question. All six podocyte transcription factors were systematically eliminated by antisense morpholino oligomers. Changes in the expression of the podocyte transcription factors and of four selected markers of terminal differentiation (nphs1, kirrel, ptpru and nphs2) were analyzed by in situ hybridization. The data were assembled into a transcriptional regulatory network for podocyte development. Although eliminating the six transcription factors individually interfered with aspects of podocyte development, no single gene regulated the entire differentiation program. Only the combined knockdown of wt1 and foxc2 resulted in a loss of all podocyte marker gene expression. Gain-of-function studies showed that wt1 and foxc2 were sufficient to increase podocyte gene expression within the glomus proper. However, the combination of wt1, foxc2 and Notch signaling was required for ectopic expression in ventral marginal zone explants. Together, this approach demonstrates how complex interactions are required for the correct spatiotemporal execution of the podocyte gene expression program.
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Affiliation(s)
- Jeffrey T. White
- Department of Cell Biology and Anatomy, LSU Health Sciences Center, MEB 6A12, 1901 Perdido Street, New Orleans, LA 70112, USA
| | - Bo Zhang
- Department of Cell Biology and Anatomy, LSU Health Sciences Center, MEB 6A12, 1901 Perdido Street, New Orleans, LA 70112, USA
| | - Débora M. Cerqueira
- Department of Cell Biology and Anatomy, LSU Health Sciences Center, MEB 6A12, 1901 Perdido Street, New Orleans, LA 70112, USA
| | - Uyen Tran
- Department of Cell Biology and Anatomy, LSU Health Sciences Center, MEB 6A12, 1901 Perdido Street, New Orleans, LA 70112, USA
| | - Oliver Wessely
- Department of Cell Biology and Anatomy, LSU Health Sciences Center, MEB 6A12, 1901 Perdido Street, New Orleans, LA 70112, USA
- Department of Genetics, LSU Health Sciences Center, MEB 6A12, 1901 Perdido Street, New Orleans, LA 70112, USA
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22
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Fissell WH, Hofmann CL, Ferrell N, Schnell L, Dubnisheva A, Zydney AL, Yurchenco PD, Roy S. Solute partitioning and filtration by extracellular matrices. Am J Physiol Renal Physiol 2009; 297:F1092-100. [PMID: 19587146 DOI: 10.1152/ajprenal.00162.2009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The physiology of glomerular filtration remains mechanistically obscure despite its importance in disease. The correspondence between proteinuria and foot process effacement suggests podocytes as the locus of the filtration barrier. If so, retained macromolecules ought to accumulate at the filtration barrier, an effect called concentration polarization. Literature data indicate macromolecule concentrations decrease from subendothelial to subepithelial glomerular basement membrane (GBM), as would be expected if the GBM were itself the filter. The objective of this study was to obtain insights into the possible role of the GBM in protein retention by performing fundamental experimental and theoretical studies on the properties of three model gels. Solute partitioning and filtration through thin gels of a commercially available laminin-rich extracellular matrix, Matrigel, were measured using a polydisperse polysaccharide tracer molecule, Ficoll 70. Solute partitioning into laminin gels and lens basement membrane (LBM) were measured using Ficoll 70. A novel model of a laminin gel was numerically simulated, as well as a mixed structure-random-fiber model for LBM. Experimental partitioning was predicted by numerical simulations. Sieving coefficients through thin gels of Matrigel were size dependent and strongly flux dependent. The observed flux dependence arose from compression of the gel in response to the applied pressure. Gel compression may alter solute partitioning into extracellular matrix at physiologic pressures present in the glomerular capillary. This suggests a physical mechanism coupling podocyte structure to permeability characteristics of the GBM.
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Affiliation(s)
- William H Fissell
- Biomedical Engineering/ND20, Cleveland Clinic, 9500 Euclid Ave., Cleveland, OH 44195, USA.
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23
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Lund U, Rippe A, Venturoli D, Tenstad O, Grubb A, Rippe B. Glomerular filtration rate dependence of sieving of albumin and some neutral proteins in rat kidneys. Am J Physiol Renal Physiol 2003; 284:F1226-34. [PMID: 12620929 DOI: 10.1152/ajprenal.00316.2002] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The size and charge-selective properties of the glomerular barrier are partly controversial. Glomerular sieving coefficients (theta) for proteins have rarely been determined noninvasively before in vivo. Therefore, theta was assessed vs. glomerular filtration rate (GFR; (51)Cr-EDTA clearance) in intact rats for radiolabeled myoglobin, kappa-dimer, neutral horseradish peroxidase (nHRP), neutral human serum albumin (nHSA), and native albumin (HSA). To obtain theta, glomerular tracer clearance, assessed from the 7- to 8-min kidney uptake of protein, was divided by the GFR. The data were fitted with a two-pore model of glomerular permeability, where the small-pore radius was 37.35 +/- 1.11 (SE) A, and the "unrestricted pore area over diffusion path length" (A(0)/DeltaX) 1.84 +/- 0.43 x 10(6) cm. Although seemingly horizontal for nHRP and nHSA, the log theta vs. GFR curves showed slightly negative slopes for the proteins investigated in the GFR interval of 2-4.5 ml/min. Strong negative (linear) correlations between (log) theta and GFR were obtained for myoglobin (P = 0.002) and HSA (P = 0.006), whereas they were relatively weak for nHRP and nHSA and nonsignificant for kappa-dimer. Theta for nHSA was markedly higher than that for HSA. In conclusion, there were no indications of increases in theta vs. GFR, as indicative of concentration polarization, for the proteins investigated at high GFRs. Furthermore, the glomerular small-pore radius assessed from endogenous (neutral) protein sieving data was found to be smaller than previously determined using dextran or Ficoll as test molecules.
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Affiliation(s)
- Ulla Lund
- Department of Nephrology, University Hospital, S-221 85 Lund, Sweden
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24
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Abstract
Glomerular podocytes are highly specialized cells with a complex cytoarchitecture. Their most prominent features are interdigitated foot processes with filtration slits in between. These are bridged by the slit diaphragm, which plays a major role in establishing the selective permeability of the glomerular filtration barrier. Injury to podocytes leads to proteinuria, a hallmark of most glomerular diseases. New technical approaches have led to a considerable increase in our understanding of podocyte biology including protein inventory, composition and arrangement of the cytoskeleton, receptor equipment, and signaling pathways involved in the control of ultrafiltration. Moreover, disturbances of podocyte architecture resulting in the retraction of foot processes and proteinuria appear to be a common theme in the progression of acquired glomerular disease. In hereditary nephrotic syndromes identified over the last 2 years, all mutated gene products were localized in podocytes. This review integrates our recent physiological and molecular understanding of the role of podocytes during the maintenance and failure of the glomerular filtration barrier.
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Affiliation(s)
- Hermann Pavenstädt
- Division of Nephrology, Department of Medicine, University Hospital Freiburg, Freiburg, Germany.
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25
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Milne JEC, Lindheimer MD, Davison JM. Glomerular heteroporous membrane modeling in third trimester and postpartum before and during amino acid infusion. Am J Physiol Renal Physiol 2002; 282:F170-5. [PMID: 11739125 DOI: 10.1152/ajprenal.00195.2000] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Human pregnancy is associated with substantial increments in glomerular filtration rate (GFR) and renal plasma flow (RPF). We have previously demonstrated that permselectivity to neutral dextrans is altered in pregnancy, theoretical analysis of the dextran sieving curves suggesting that elevated GFR is due to increased RPF and decreased glomerular oncotic pressure (pi(GC)) with no evidence of increased transglomerular hydrostatic pressure difference (DeltaP). These conclusions have been challenged, with claims that the rise in GFR is primarily a result of a decrement in pi(GC). With refined laboratory and infusion protocols, we have reexplored the determinants of ultrafiltration in a serial study of 11 healthy women in late pregnancy (LP) and 4 mo postpartum (PP), both in the baseline state and after increasing GFR and RPF by infusion of amino acids. Results were analyzed using two computer modeling programs. Increased GFR in LP (38%, P < 0.05) was due to a combination of elevated RPF (22%) and a decrement in pi(GC) and associated with an increased ultrafiltration coefficient, without evidence of increased DeltaP, and additional amino acid-provoked GFR increments (P < 0.05) produced similar findings. In addition, refined methodology permitted collection of sufficient data on excreted large-radii dextrans (>60 A) to better define the nondiscriminatory "shunt" pathway (omega(0)) and the standard deviation of pore size (S) about the mean radius of the distribution. Thus it was possible to demonstrate that the physiological increase in total protein excretion in LP is associated with a prominent shunt and an upward shift in breadth of distribution of pore sizes. This ability to quantify omega(0) and S will now permit better evaluation of the pathophysiological changes in the glomerulus associated with pregnancy in women with renal disease and in gravidas developing preeclampsia.
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Affiliation(s)
- J E C Milne
- Department of Obstetrics and Gynecology, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 4LP United Kingdom
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26
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Lazzara MJ, Deen WM. Effects of plasma proteins on sieving of tracer macromolecules in glomerular basement membrane. Am J Physiol Renal Physiol 2001; 281:F860-8. [PMID: 11592944 DOI: 10.1152/ajprenal.2001.281.5.f860] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
It was found previously that the sieving coefficients of Ficoll and Ficoll sulfate across isolated glomerular basement membrane (GBM) were greatly elevated when BSA was present at physiological levels, and it was suggested that most of this increase might have been the result of steric interactions between BSA and the tracers (5). To test this hypothesis, we extended the theory for the sieving of macromolecular tracers to account for the presence of a second, abundant solute. Increasing the concentration of an abundant solute is predicted to increase the equilibrium partition coefficient of a tracer in a porous or fibrous membrane, thereby increasing the sieving coefficient. The magnitude of this partitioning effect depends on solute size and membrane structure. The osmotic reduction in filtrate velocity caused by an abundant, mostly retained solute will also tend to elevate the tracer sieving coefficient. The osmotic effect alone explained only about one-third of the observed increase in the sieving coefficients of Ficoll and Ficoll sulfate, whereas the effect of BSA on tracer partitioning was sufficient to account for the remainder. At physiological concentrations, predictions for tracer sieving in the presence of BSA were found to be insensitive to the assumed shape of the protein (sphere or prolate spheroid). For protein mixtures, the theoretical effect of 6 g/dl BSA on the partitioning of spherical tracers was indistinguishable from that of 3 g/dl BSA and 3 g/dl IgG. This suggests that for partitioning and sieving studies in vitro, a good experimental model for plasma is a BSA solution with a mass concentration matching that of total plasma protein. The effect of plasma proteins on tracer partitioning is expected to influence sieving not only in isolated GBM but also in intact glomerular capillaries in vivo.
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Affiliation(s)
- M J Lazzara
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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27
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Abstract
Recent progress in relating the functional properties of the glomerular capillary wall to its unique structure is reviewed. The fenestrated endothelium, glomerular basement membrane (GBM), and epithelial filtration slits form a series arrangement in which the flow diverges as it enters the GBM from the fenestrae and converges again at the filtration slits. A hydrodynamic model that combines morphometric findings with water flow data in isolated GBM has predicted overall hydraulic permeabilities that are consistent with measurements in vivo. The resistance of the GBM to water flow, which accounts for roughly half that of the capillary wall, is strongly dependent on the extent to which the GBM surfaces are blocked by cells. The spatial frequency of filtration slits is predicted to be a very important determinant of the overall hydraulic permeability, in keeping with observations in several glomerular diseases in humans. Whereas the hydraulic resistances of the cell layers and GBM are additive, the overall sieving coefficient for a macromolecule (its concentration in Bowman's space divided by that in plasma) is the product of the sieving coefficients for the individual layers. Models for macromolecule filtration reveal that the individual sieving coefficients are influenced by one another and by the filtrate velocity, requiring great care in extrapolating in vitro observations to the living animal. The size selectivity of the glomerular capillary has been shown to be determined largely by the cellular layers, rather than the GBM. Controversial findings concerning glomerular charge selectivity are reviewed, and it is concluded that there is good evidence for a role of charge in restricting the transmural movement of albumin. Also discussed is an effect of albumin that has received little attention, namely, its tendency to increase the sieving coefficients of test macromolecules via steric interactions. Among the unresolved issues are the specific contributions of the endothelial glycocalyx and epithelial slit diaphragm to the overall hydraulic resistance and macromolecule selectivity and the nanostructural basis for the observed permeability properties of the GBM.
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Affiliation(s)
- W M Deen
- Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA 02139, USA.
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