ABSTRACT
This review summarizes the pathomorphological sequences of nephron loss in human diabetic nephropathy (DN). The relevant changes may be derived from two major derangements. First, a failure in the turnover of the glomerular basement membrane (GBM) based on an increased production of GBM components by podocytes and endothelial cells leading to the thickening of the GBM and accumulation of worn-out GBM in the mesangium. This failure may account for the direct pathway to glomerular compaction and sclerosis based on the continuous deposition of undegraded GBM material in the mesangium. Second, an increased leakiness together with an increased propensity of glomerular capillaries to proliferate leads to widespread plasma exudations. Detrimental are those that produce giant insudative spaces within Bowman's capsule, spreading around the entire glomerular circumference and along the glomerulo-tubular junction onto the tubule resulting in tubular obstruction and retroactively to glomerulosclerosis. Tubular atrophy and interstitial fibrosis develop secondarily by transfer of the glomerular damage onto the tubule. Interstitial fibrosis is locally initiated and apparently stimulated by degenerating tubular epithelia. This leads to a focal distribution of interstitial fibrosis and tubular atrophy accompanied by a varying interstitial mononuclear cell infiltration. Spreading of fibrotic areas between intact nephrons, much less to the glomerulus, has not been encountered.
Subject(s)
Diabetes Mellitus , Diabetic Nephropathies , Humans , Diabetic Nephropathies/pathology , Endothelial Cells/metabolism , Glomerular Basement Membrane/metabolism , Fibrosis , Atrophy/pathology , Diabetes Mellitus/pathologyABSTRACT
The development of focal and segmental glomerulosclerosis (FSGS) as a consequence of glomerular hypertension resulting from arterial hypertension is widely considered a podocyte disease. However, the primary damage is encountered in the mesangium. In acute settings, mesangial cells disconnect from their insertions to the glomerular basement membrane, causing a ballooning of capillaries and severe changes of the folding pattern of the glomerular basement membrane, of the arrangement of the capillaries, and thereby of the architecture of the tuft. The displacement of capillaries led to contact of podocytes and parietal epithelial cells, initiating the formation of tuft adhesions to Bowman's capsule, the committed lesion to progress to FSGS. In addition, the displacement of capillaries also caused an abnormal stretching of podocytes, resulting in podocyte damage. Thus, the podocyte damage that starts the sequence to FSGS is predicted to develop secondary to the mesangial damage. This sequence was found in two hypertensive rat models of FSGS and in human hypertensive nephrosclerosis.
Subject(s)
Glomerulosclerosis, Focal Segmental , Hypertension, Renal , Nephrosclerosis , Podocytes , Rats , Humans , Animals , Podocytes/pathology , Glomerulosclerosis, Focal Segmental/pathology , Nephrosclerosis/complications , Capillaries/pathology , Glomerular Basement Membrane/pathology , Hypertension, Renal/complicationsABSTRACT
Following our previous reports on mesangial sclerosis and vascular proliferation in diabetic nephropathy (DN) (Kriz W, Löwen J, Federico G, van den Born J, Gröne E, Gröne HJ. Am J Physiol Renal Physiol 312: F1101-F1111, 2017; Löwen J, Gröne E, Gröne HJ, Kriz W. Am J Physiol Renal Physiol 317: F399-F410, 2019), we now describe the advanced stages of DN terminating in glomerular obsolescence and tubulointerstitial fibrosis based on a total of 918 biopsies. The structural aberrations emerged from two defects: 1) increased synthesis of glomerular basement membrane (GBM) components by podocytes and endothelial cells leading to an accumulation of GBM material in the mesangium and 2) a defect of glomerular vessels consisting of increased leakiness and an increased propensity to proliferate. Both defects may lead to glomerular degeneration. The progressing compaction of accumulated worn-out GBM material together with the retraction of podocytes out of the tuft and the collapse and hyalinosis of capillaries results in a shrunken tuft that fuses with Bowman's capsule (BC) to glomerular sclerosis. The most frequent pathway to glomerular decay starts with local tuft expansions that result in contacts of structurally intact podocytes to the parietal epithelium initiating the formation of tuft adhesions, which include the penetration of glomerular capillaries into BC. Exudation of plasma from such capillaries into the space between the parietal epithelium and its basement membrane causes the formation of insudative fluid accumulations within BC spreading around the glomerular circumference and, via the glomerulotubular junction, onto the tubule. Degeneration of the corresponding tubule develops secondarily to the glomerular damage, either due to cessation of filtration in cases of global sclerosis or due to encroachment of the insudative spaces. The degenerating tubules induce the proliferation of myofibroblasts resulting in interstitial fibrosis.NEW & NOTEWORTHY Based on analysis of 918 human biopsies, essential derangement in diabetic nephropathy consists of accumulation of worn-out glomerular basement membrane in the mesangium that may advance to global sclerosis. The most frequent pathway to nephron dropout starts with the penetration of glomerular capillaries into Bowman's capsule (BC), delivering an exudate into BC that spreads around the entire glomerular circumference and via the glomerulotubular junction onto the tubule, resulting in glomerular sclerosis and chronic tubulointerstitial damage.
Subject(s)
Diabetic Nephropathies/pathology , Glomerulonephritis/pathology , Nephrons/pathology , Biopsy , Bowman Capsule/pathology , Capillaries/pathology , Capillary Permeability , Diabetic Nephropathies/metabolism , Disease Progression , Endothelial Cells/pathology , Fibrosis , Glomerular Basement Membrane/pathology , Glomerulonephritis/metabolism , Humans , Microscopy, Electron, Transmission , Neovascularization, Pathologic , Nephrons/metabolism , Nephrons/ultrastructure , Podocytes/pathologyABSTRACT
Although macula densa (MD) cells are chief regulatory cells in the nephron with unique microanatomical features, they have been difficult to study in full detail due to their inaccessibility and limitations in earlier microscopy techniques. The present study used a new mouse model with a comprehensive imaging approach to visualize so far unexplored microanatomical features of MD cells, their regulation, and functional relevance. MD-GFP mice with conditional and partial induction of green fluorescent protein (GFP) expression, which specifically and intensely illuminated only single MD cells, were used with fluorescence microscopy of fixed tissue and live MD cells in vitro and in vivo with complementary electron microscopy of the rat, rabbit, and human kidney. An elaborate network of major and minor cell processes, here named maculapodia, were found at the cell base, projecting toward other MD cells and the glomerular vascular pole. The extent of maculapodia showed upregulation by low dietary salt intake and the female sex. Time-lapse imaging of maculapodia revealed highly dynamic features including rapid outgrowth and an extensive vesicular transport system. Electron microscopy of rat, rabbit, and human kidneys and three-dimensional volume reconstruction in optically cleared whole-mount MD-GFP mouse kidneys further confirmed the presence and projections of maculapodia into the extraglomerular mesangium and afferent and efferent arterioles. The newly identified dynamic and secretory features of MD cells suggest the presence of novel functional and molecular pathways of cell-to-cell communication in the juxtaglomerular apparatus between MD cells and between MD and other target cells.NEW & NOTEWORTHY This study illuminated a physiologically regulated dense network of basal cell major and minor processes (maculapodia) in macula densa (MD) cells. The newly identified dynamic and secretory features of these microanatomical structures suggest the presence of novel functional and molecular pathways of cell-to-cell communication in the juxtaglomerular apparatus between MD and other target cells. Detailed characterization of the function and molecular details of MD cell intercellular communications and their role in physiology and disease warrant further studies.
Subject(s)
Glomerular Mesangium/ultrastructure , Juxtaglomerular Apparatus/ultrastructure , Kidney Glomerulus/ultrastructure , Kidney Tubules/ultrastructure , Animals , Cell Communication/physiology , Epithelial Cells/cytology , Epithelial Cells/ultrastructure , Glomerular Mesangium/cytology , Kidney Glomerulus/cytology , Kidney Tubules/cytology , Mice , Rabbits , RatsABSTRACT
This study presents a theoretical analysis of the problems related to the inability of podocytes to proliferate. The basis of these problems is the very high rate of glomerular filtration. Podocytes do not in general die by apoptosis or necrosis but are lost by detachment from the glomerular basement membrane (GBM) as viable cells. Podocytes situated on the outside of the filtration barrier and attached to the GBM only by their foot processes are permanently exposed to the flow dynamic forces of the high filtration rate tending to detach them from the GBM. The major challenge seems to consist of the high shear stresses on the foot processes within the filtration slits due to filtrate flow. Healthy podocytes are able to resist this challenge, injured podocytes are not, and may undergo foot process detachment, leading to a gap in the podocyte cover of the GBM. This represents a mortal event. Like a dam break, such a leak cannot be repaired. The ongoing exposure to filtrate flow prevents any attempt to close the gap, thus preventing any regeneration including cell proliferation. An improvement of this precarious situation consists of healing by scarring that may involve only one lobule of the glomerulus, permitting the remaining lobules to maintain filtration. An answer to the question of which waste product requires such a high filtration rate for its excretion may be in the huge quantity of circulating peptides, a problem that dates far back in evolution.
Subject(s)
Cell Proliferation/physiology , Glomerular Basement Membrane/cytology , Podocytes/cytology , Animals , Humans , Stress, MechanicalABSTRACT
As shown in our previous paper (Kriz W, Löwen J, Federico G, van den Born J, Gröne E, Gröne HJ. Am J Physiol Renal Physiol 312: F1101-F1111, 2017), mesangial matrix expansion in diabetic nephropathy (DN) results for a major part from the accumulation of worn-out undegraded glomerular basement membrane material. Here, based on the reevaluation of >900 biopsies of DN, we show that this process continues with the progression of the disease finally leading to the herniation of the matrix-overloaded tuft through the glomerular entrance to the outside. This leads to severe changes in the glomerular surroundings, including a dissociation of the juxtaglomerular apparatus with displacement of the macula densa. The herniation is associated with a prominent outgrowth of glomerular vessels from the tuft. Mostly, these aberrant vessels are an abnormal type of arteriole with frequent intramural insudations of plasma. They spread into glomerular surroundings extending in intertubular and periglomerular spaces. Their formation is associated with elevated mRNA levels of vascular endothelial growth factor-A, angiopoietins 1 and 2, and the corresponding receptors. Functionally, these processes seem to compromise tubuloglomerular feedback-related functions and may be one factor why Na+-glucose cotransporter-2 inhibitors are not effective in advanced stages of DN.
Subject(s)
Arterioles/pathology , Diabetic Nephropathies/pathology , Glomerular Mesangium/blood supply , Juxtaglomerular Apparatus/blood supply , Neovascularization, Pathologic , Angiopoietin-1/genetics , Angiopoietin-1/metabolism , Angiopoietin-2/genetics , Angiopoietin-2/metabolism , Arterioles/metabolism , Diabetic Nephropathies/genetics , Diabetic Nephropathies/metabolism , Disease Progression , Humans , Receptor, TIE-2/genetics , Receptor, TIE-2/metabolism , Vascular Endothelial Growth Factor A/genetics , Vascular Endothelial Growth Factor A/metabolism , Vascular Endothelial Growth Factor Receptor-2/genetics , Vascular Endothelial Growth Factor Receptor-2/metabolismABSTRACT
Elevated mechanical stress in glomerular hypertension is thought to damage podocytes, the loss of which leads to development of glomerulosclerosis. Applying cDNA array analysis to mechanically stressed podocytes, we have recently identified TSG101 as a stretch-induced candidate gene among others. TSG101, which is part of the ESCRT-I complex, is involved in multivesicular body (MVB) formation. Here we demonstrate that TSG101 mRNA is strongly upregulated in conditionally immortalized mouse podocytes by cyclic mechanical stress. Differentiation of podocytes does not affect TSG101 mRNA levels. TSG101 immunofluorescence is distributed in a vesicular pattern in podocytes, the staining intensity being enhanced by mechanical stress. In DOCA/salt treated rats, a model of glomerular hypertension, glomerular TSG101 mRNA levels are elevated, and an increased number of MVBs is observed by electron microscopy in podocyte processes. Our data demonstrate that mechanical stress upregulates TSG101 in podocytes, suggesting that glomerular hypertension enhances sorting of cell surface proteins and their ligands into the degradative pathway in podocytes.
Subject(s)
DNA-Binding Proteins/genetics , Endosomal Sorting Complexes Required for Transport/genetics , Podocytes/metabolism , Podocytes/pathology , Stress, Mechanical , Transcription Factors/genetics , Up-Regulation/genetics , Animals , Cell Differentiation/genetics , Desoxycorticosterone Acetate , Male , Mice , Multivesicular Bodies/metabolism , Multivesicular Bodies/ultrastructure , Podocytes/ultrastructure , RNA, Messenger/genetics , RNA, Messenger/metabolism , Rats, WistarABSTRACT
Background: Vascular endothelial growth factor A (VEGF) is an essential growth factor during glomerular development and postnatal homeostasis. VEGF is secreted in high amounts by podocytes into the primary urine, back-filtered across the glomerular capillary wall to act on endothelial cells. So far it has been assumed that VEGF back-filtration is driven at a constant rate exclusively by diffusion. Methods: In the present work, glomerular VEGF back-filtration was investigated in vivo using a novel extended model based on endothelial fenestrations as surrogate marker for local VEGF concentrations. Single nephron glomerular filtration rate (SNGFR) and/or local filtration flux were manipulated by partial renal mass ablation, tubular ablation, and in transgenic mouse models of systemic or podocytic VEGF overexpression or reduction. Results: Our study shows positive correlations between VEGF back-filtration and SNGFR as well as effective filtration rate under physiological conditions along individual glomerular capillaries in rodents and humans. Conclusion: Our results suggest that an additional force drives VEGF back-filtration, potentially regulated by SNGFR.
Subject(s)
Capillaries/physiopathology , Glomerular Filtration Rate/physiology , Kidney Glomerulus/metabolism , Vascular Endothelial Growth Factor A/metabolism , Animals , Disease Models, Animal , Kidney Glomerulus/physiopathology , Mice , Mice, Knockout , NephrectomyABSTRACT
Localization microscopy has shown to be capable of systematic investigations on the arrangement and counting of cellular uptake of gold nanoparticles (GNP) with nanometer resolution. In this article, we show that the application of specially modified RNA targeting gold nanoparticles ("SmartFlares") can result in ring like shaped GNP arrangements around the cell nucleus. Transmission electron microscopy revealed GNP accumulation in vicinity to the intracellular membrane structures including them of the endoplasmatic reticulum. A quantification of the radio therapeutic dose enhancement as a proof of principle was conducted with γH2AX foci analysis: The application of both-SmartFlares and unmodified GNPs-lead to a significant dose enhancement with a factor of up to 1.2 times the dose deposition compared to non-treated breast cancer cells. This enhancement effect was even more pronounced for SmartFlares. Furthermore, it was shown that a magnetic field of 1 Tesla simultaneously applied during irradiation has no detectable influence on neither the structure nor the dose enhancement dealt by gold nanoparticles.
Subject(s)
Breast Neoplasms/pathology , Gold/chemistry , Metal Nanoparticles , RNA, Neoplasm/drug effects , Breast Neoplasms/genetics , Cell Line, Tumor , Humans , Metal Nanoparticles/chemistryABSTRACT
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.
Subject(s)
Cell Movement , Glomerulonephritis/pathology , Podocytes/ultrastructure , Animals , Glomerulonephritis/etiology , Male , Podocytes/physiology , Puromycin Aminonucleoside/toxicity , Rats , Rats, Sprague-Dawley , Rats, WistarABSTRACT
Filtrate flow through the glomerular barrier produces shear stresses that tend to disconnect podocytes from the glomerular basement membrane. Forces are highest within the filtration slits. The slit diaphragm mechanically balances the lateral components of the shear stresses on opposing foot processes, preventing widening of the slit.
Subject(s)
Glomerular Basement Membrane/physiology , Glomerular Filtration Rate , Mechanotransduction, Cellular , Podocytes/physiology , Animals , Glomerular Basement Membrane/ultrastructure , Humans , Kidney Diseases/pathology , Kidney Diseases/physiopathology , Models, Biological , Podocytes/ultrastructure , Stress, MechanicalABSTRACT
Thickening of the glomerular basement membrane (GBM) and expansion of the mesangial matrix are hallmarks of diabetic nephropathy (DN), generally considered to emerge from different sites of overproduction: GBM components from podocytes and mesangial matrix from mesangial cells. Reevaluation of 918 biopsies with DN revealed strong evidence that these mechanisms are connected to each other, wherein excess GBM components fail to undergo degradation and are deposited in the mesangium. These data do not exclude that mesangial cells also synthesize components that contribute to the accumulation of matrix in the mesangium. Light, electron microscopic, immunofluorescence, and in situ hybridization studies clearly show that the thickening of the GBM is due not only to overproduction of components of the mature GBM (α3 and α5 chains of collagen IV and agrin) by podocytes but also to resumed increased synthesis of the α1 chain of collagen IV and of perlecan by endothelial cells usually seen during embryonic development. We hypothesize that these abnormal production mechanisms are caused by different processes: overproduction of mature GBM-components by the diabetic milieu and regression of endothelial cells to an embryonic production mode by decreased availability of mediators from podocytes.
Subject(s)
Diabetic Nephropathies/pathology , Glomerular Basement Membrane/ultrastructure , Glomerular Mesangium/ultrastructure , Podocytes/ultrastructure , Agrin/analysis , Autoantigens/analysis , Biopsy , Cellular Microenvironment , Collagen Type IV/analysis , Diabetic Nephropathies/metabolism , Disease Progression , Glomerular Basement Membrane/chemistry , Glomerular Mesangium/chemistry , Heparan Sulfate Proteoglycans/analysis , Humans , Immunohistochemistry , Microscopy, Electron, Transmission , Podocytes/chemistry , SclerosisABSTRACT
The nephron is the basic physiologic subunit of the mammalian kidney and is made up of several apicobasally polarized epithelial cell types. The process of apicobasal polarization in animal cells is controlled by the evolutionarily conserved Crumbs (CRB), Partitioning-defective, and Scribble protein complexes. Here, we investigated the role of protein associated with LIN-7 1 (Pals1, also known as Mpp5), a core component of the apical membrane-determining CRB complex in the nephron. Pals1 interacting proteins, including Crb3 and Wwtr1/Taz, have been linked to renal cyst formation in mice before. Immunohistologic analysis revealed Pals1 expression in renal tubular cells and podocytes of human kidneys. Mice lacking one Pals1 allele (functionally haploid for Pals1) in nephrons developed a fully penetrant phenotype, characterized by cyst formation and severe defects in renal barrier function, which led to death within 6-8 weeks. In Drosophila nephrocytes, deficiency of the Pals1 ortholog caused alterations in slit-diaphragm-like structures. Additional studies in epithelial cell culture models revealed that Pals1 functions as a dose-dependent upstream regulator of the crosstalk between Hippo- and TGF-ß-mediated signaling. Furthermore, Pals1 haploinsufficiency in mouse kidneys associated with the upregulation of Hippo pathway target genes and marker genes of TGF-ß signaling, including biomarkers of renal diseases. These findings support a link between apical polarity proteins and renal diseases, especially renal cyst diseases. Further investigation of the Pals1-linked networks is required to decipher the mechanisms underlying the pathogenesis of these diseases.
Subject(s)
Haploinsufficiency , Kidney Diseases, Cystic/genetics , Membrane Proteins/genetics , Nucleoside-Phosphate Kinase/genetics , Proteinuria/genetics , Animals , Drosophila , Female , Male , MiceABSTRACT
Podocytes are lost as viable cells by detachment from the glomerular basement membrane (GBM), possibly due to factors such as pressure and filtrate flow. Distension of glomerular capillaries in response to increased pressure is limited by the elastic resistance of the GBM. The endothelium and podocytes adapt to changes in GBM area. The slit diaphragm (SD) seems to adjust by shuttling SD components between the SD and the adjacent foot processes (FPs), resulting in changes in SD area that parallel those in perfusion pressure.Filtrate flow tends to drag podocytes towards the urinary orifice by shear forces, which are highest within the filtration slits. The SD represents an atypical adherens junction, mechanically interconnecting the cytoskeleton of opposing FPs and tending to balance the shear forces.If under pathological conditions, increased filtrate flows locally overtax the attachment of FPs, the SDs are replaced by occluding junctions that seal the slits and the attachment of podocytes to the GBM is reinforced by FP effacement. Failure of these temporary adaptive mechanisms results in a steady process of podocyte detachment due to uncontrolled filtrate flows through bare areas of the GBM and, subsequently, the labyrinthine subpodocyte spaces, presenting as pseudocysts. In our view, shear stress due to filtrate flow-not capillary hydrostatic pressure-is the major challenge to the attachment of podocytes to the GBM.
Subject(s)
Glomerular Filtration Barrier/pathology , Kidney Diseases/pathology , Kidney Glomerulus/pathology , Adaptation, Physiological , Child , Disease Progression , Humans , Podocytes/pathology , SclerosisABSTRACT
Mucociliary clearance requires the distinct orientation and coordinated movement of airway cilia, which is established through planar cell polarity signaling (PCP). The atypical cadherin Dachsous1 (Dchs1) is a transmembrane protein that regulates PCP in D. melanogaster. However, little is known about Dchs1 expression and its potential role in PCP in mammalian adult tissues. Here, we show that Dchs1 is ubiquitously expressed in mouse embryos, but exhibits a highly restricted expression to lung tissues in the adult stage. Strikingly, human Dchs1 localized exclusively to the base of the ciliary apparatus in cultured human respiratory epithelial cells with differentiated motile 9 + 2 cilia. This localization could be functionally important as we observed aberrant DCHS1 mRNA expression in human non-small cell lung cancer tissue. In sum, we establish Dchs1 as a component of the membrane domain surrounding the ciliary base. This suggests a specific role of Dchs1 in PCP-dependent organization of ciliary function and a possible role in lung disease.
Subject(s)
Aging/metabolism , Cadherins/metabolism , Carcinoma, Non-Small-Cell Lung/metabolism , Cilia/metabolism , Lung Neoplasms/metabolism , Respiratory Mucosa/metabolism , Aging/pathology , Animals , Cadherin Related Proteins , Carcinoma, Non-Small-Cell Lung/pathology , Cilia/pathology , Epithelial Cells/metabolism , Epithelial Cells/pathology , Female , Gene Expression Regulation, Developmental , Humans , Lung Neoplasms/pathology , Mice , Respiratory Mucosa/pathology , Subcellular Fractions/metabolism , Subcellular Fractions/pathology , Tissue DistributionABSTRACT
Mammalian Fat1 is a giant atypical cadherin/tumor suppressor involved in the regulation of cellular orientation, migration, and growth. Fat1 is implicated in the development of the brain, eye, and kidney. Altered expression or mutations of FAT1 are also associated with cancer and facioscapulohumeral muscular dystrophy (FSHD). Yet, the mechanistic functions of this pathway remain incompletely understood. Here, we report the identification of Sorbin-homology (SoHo) proteins as novel interaction partners of Fat1 by virtue of a yeast-two-hybrid screen. SoHo proteins play diverse roles as adaptor proteins in cell signaling, cell adhesion and sarcomere architecture, including altered expression in cancer and FSHD. Specifically, we found SoHo proteins CAP/ponsin-1 and -2 (Sorbs1) and ArgBP2 (Sorbs2) to interact with the cytoplasmic domain of Fat1. We mapped the interaction to a prolin-rich classic type II PXXP motif within Fat1 and to the three Src-homology (SH3) domains within SoHo proteins using mutant expression in yeast, pulldown assays, and cell culture. Functionally, endogenous ponsin-2 expression of NRK-52E cells at cellular leading edges was lost upon knockdown of Fat1. In summary, our data point to an interaction of Fat1 with SoHo proteins that is able to recruit SoHo proteins to sites of Fat1 expression.
Subject(s)
Cadherins/metabolism , Microfilament Proteins/metabolism , Adaptor Proteins, Signal Transducing , Amino Acid Sequence , Animals , COS Cells , Cadherins/chemistry , Cadherins/genetics , Cell Line , Chlorocebus aethiops , Gene Knockdown Techniques , Mice , Microfilament Proteins/chemistry , Microfilament Proteins/genetics , Mutagenesis, Site-Directed , Protein Interaction Domains and Motifs , RNA-Binding Proteins , Rats , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Two-Hybrid System Techniques , src Homology DomainsABSTRACT
The transition of AKI to CKD has major clinical significance. As reviewed here, recent studies show that a subpopulation of dedifferentiated, proliferating tubules recovering from AKI undergo pathologic growth arrest, fail to redifferentiate, and become atrophic. These abnormal tubules exhibit persistent, unregulated, and progressively increasing profibrotic signaling along multiple pathways. Paracrine products derived therefrom perturb normal interactions between peritubular capillary endothelium and pericyte-like fibroblasts, leading to myofibroblast transformation, proliferation, and fibrosis as well as capillary disintegration and rarefaction. Although signals from injured endothelium and inflammatory/immune cells also contribute, tubule injury alone is sufficient to produce the interstitial pathology required for fibrosis. Localized hypoxia produced by microvascular pathology may also prevent tubule recovery. However, fibrosis is not intrinsically progressive, and microvascular pathology develops strictly around damaged tubules; thus, additional deterioration of kidney structure after the transition of AKI to CKD requires new acute injury or other mechanisms of progression. Indeed, experiments using an acute-on-chronic injury model suggest that additional loss of parenchyma caused by failed repair of AKI in kidneys with prior renal mass reduction triggers hemodynamically mediated processes that damage glomeruli to cause progression. Continued investigation of these pathologic mechanisms should reveal options for preventing renal disease progression after AKI.
Subject(s)
Acute Kidney Injury/complications , Kidney Tubules/physiopathology , Renal Insufficiency, Chronic/etiology , Acute Kidney Injury/physiopathology , Capillaries/physiopathology , Disease Progression , Humans , Hypoxia/complications , Kidney Tubules/metabolism , Nephrosclerosis/etiology , Nephrosclerosis/metabolism , Renal Circulation , VasoconstrictionABSTRACT
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.
Subject(s)
Disease Progression , Podocytes/pathology , Renal Insufficiency, Chronic/physiopathology , Apoptosis , Biomechanical Phenomena/physiology , Glomerular Basement Membrane/pathology , Humans , Hypertrophy , Renal Insufficiency, Chronic/pathologyABSTRACT
Focal segmental glomerular sclerosis (FSGS) is a primary kidney disease that is commonly associated with proteinuria and progressive loss of glomerular function, leading to development of chronic kidney disease (CKD). FSGS is characterized by podocyte injury and depletion and collapse of glomerular capillary segments. Progression of FSGS is associated with TGF-ß activation in podocytes; however, it is not clear how TGF-ß signaling promotes disease. Here, we determined that podocyte-specific activation of TGF-ß signaling in transgenic mice and BALB/c mice with Adriamycin-induced glomerulosclerosis is associated with endothelin-1 (EDN1) release by podocytes, which mediates mitochondrial oxidative stress and dysfunction in adjacent endothelial cells via paracrine EDN1 receptor type A (EDNRA) activation. Endothelial dysfunction promoted podocyte apoptosis, and inhibition of EDNRA or scavenging of mitochondrial-targeted ROS prevented podocyte loss, albuminuria, glomerulosclerosis, and renal failure. We confirmed reciprocal crosstalk between podocytes and endothelial cells in a coculture system. Biopsies from patients with FSGS exhibited increased mitochondrial DNA damage, consistent with EDNRA-mediated glomerular endothelial mitochondrial oxidative stress. Our studies indicate that segmental glomerulosclerosis develops as a result of podocyte-endothelial crosstalk mediated by EDN1/EDNRA-dependent mitochondrial dysfunction and suggest that targeting the reciprocal interaction between podocytes and endothelia may provide opportunities for therapeutic intervention in FSGS.