Podocyte injuries exacerbate mesangial proliferative glomerulonephritis

Central role of podocytes in mediating cellular cross talk in glomerular health and disease

Podocytes are highly specialized epithelial cells that surround the capillaries of the glomeruli in the kidney. Together with the glomerular endothelial cells, these postmitotic cells are responsible for regulating filtrate from the circulating blood with their organized network of interdigitating foot processes that wrap around the glomerular basement membrane. Although podocyte injury and subsequent loss is the hallmark of many glomerular diseases, recent evidence suggests that the cell-cell communication between podocytes and other glomerular and nonglomerular cells is critical for the development and progression of kidney disease. In this review, we highlight these key cellular pathways of communication and how they might be a potential target for therapy in glomerular disease. We also postulate that podocytes might serve as a central hub for communication in the kidney under basal conditions and in response to cellular stress, which may have implications for the development and progression of glomerular diseases.

14-3-3 Proteins stabilize actin and vimentin filaments to maintain processes in renal glomerular podocyte

14-3-3 proteins are a ubiquitously expressed family of adaptor proteins. Despite exhibiting high sequence homology, several 14-3-3 isoforms have isoform-specific binding partners and roles. We reported that 14-3-3β interacts with FKBP12 and synaptopodin to maintain the structure of actin fibers in podocytes. However, the precise localization and differential role of 14-3-3 isoforms in kidneys are unclear. Herein, we showed that 14-3-3β in glomeruli was restricted in podocytes, and 14-3-3σ in glomeruli was expressed in podocytes and mesangial cells. Although 14-3-3β was dominantly co-localized with FKBP12 in the foot processes, a part of 14-3-3β was co-localized with Par3 at the slit diaphragm. 14-3-3β interacted with Par3, and FKBP12 bound to 14-3-3β competitively with Par3. Deletion of 14-3-3β enhanced the interaction of Par3 with Par6 in podocytes. Gene silencing for 14-3-3β altered the structure of actin fibers and process formation. 14-3-3β and synaptopodin expression was decreased in podocyte injury models. In contrast, 14-3-3σ in podocytes was expressed in the primary processes. 14-3-3σ interacted with vimentin but not with the actin-associated proteins FKBP12 and synaptopodin. Gene silencing for 14-3-3σ altered the structure of vimentin fibers and process formation. 14-3-3σ and vimentin expression was increased in the early phase of podocyte injury models but was decreased in the late stage. Together, the localization of 14-3-3β at actin cytoskeleton plays a role in maintaining the foot processes and the Par complex in podocytes. In contrast, 14-3-3σ at vimentin cytoskeleton is essential for maintaining primary processes.

Activation of the Renin–Angiotensin System Disrupts the Cytoskeletal Architecture of Human Urine-Derived Podocytes

High blood pressure is one of the major public health problems that causes severe disorders in several tissues including the human kidney. One of the most important signaling pathways associated with the regulation of blood pressure is the renin–angiotensin system (RAS), with its main mediator angiotensin II (ANGII). Elevated levels of circulating and intracellular ANGII and aldosterone lead to pro-fibrotic, -inflammatory, and -hypertrophic milieu that causes remodeling and dysfunction in cardiovascular and renal tissues. Furthermore, ANGII has been recognized as a major risk factor for the induction of apoptosis in podocytes, ultimately leading to chronic kidney disease (CKD). In the past, disease modeling of kidney-associated diseases was extremely difficult, as the derivation of kidney originated cells is very challenging. Here we describe a differentiation protocol for reproducible differentiation of sine oculis homeobox homolog 2 (SIX2)-positive urine-derived renal progenitor cells (UdRPCs) into podocytes bearing typical cellular processes. The UdRPCs-derived podocytes show the activation of the renin–angiotensin system by being responsive to ANGII stimulation. Our data reveal the ANGII-dependent downregulation of nephrin (NPHS1) and synaptopodin (SYNPO), resulting in the disruption of the podocyte cytoskeletal architecture, as shown by immunofluorescence-based detection of α-Actinin. Furthermore, we show that the cytoskeletal disruption is mainly mediated through angiotensin II receptor type 1 (AGTR1) signaling and can be rescued by AGTR1 inhibition with the selective, competitive angiotensin II receptor type 1 antagonist, losartan. In the present manuscript we confirm and propose UdRPCs differentiated to podocytes as a unique cell type useful for studying nephrogenesis and associated diseases. Furthermore, the responsiveness of UdRPCs-derived podocytes to ANGII implies potential applications in nephrotoxicity studies and drug screening.

Xanthine oxidoreductase inhibitor topiroxostat ameliorates podocyte injury by inhibiting the reduction of nephrin and podoplanin

BACKGROUND

Topiroxostat, an inhibitor of xanthine oxidoreductase (XOR) was shown to reduce urinary albumin excretion of hyperuricemic patients with chronic kidney disease. However, its pharmacological mechanism is not well understood. In this study, we examined the effects of topiroxostat on glomerular podocytes. Podocyte is characterized by foot process and a unique cell-cell junction slit diaphragm functioning as a final barrier to prevent proteinuria.

METHODS

The effects of topiroxostat on the expressions of podocyte functional molecules were analysed in db/db mice, a diabetic nephropathy model, anti-nephrin antibody-induced rat podocyte injury model and cultured podocytes treated with adriamycin.

RESULTS

Topiroxostat treatment ameliorated albuminuria in db/db mice. The expression of desmin, a podocyte injury marker was increased, and nephrin and podocin, key molecules of slit diaphragm, and podoplanin, an essential molecule in maintaining foot process were downregulated in db/db mice. Topiroxostat treatment prevented the alterations in the expressions of these molecules in db/db mice. XOR activity in kidney was increased in rats with anti-nephrin antibody-induced podocyte injury. Topiroxostat treatment reduced XOR activity and restored the decreased expression of nephrin, podocin and podoplanin in the podocyte injury. Furthermore, topiroxostat enhanced the expression of podoplanin in injured human cultured podocytes.

CONCLUSIONS

Podocyte injury was evident in db/db mice. Topiroxostat ameliorated albuminuria in diabetic nephropathy model by preventing podocyte injury. Increase of XOR activity in kidney contributes to development of podocyte injury caused by stimulation to slit diaphragm. Topiroxostat has an effect to stabilize slit diaphragm and foot processes by inhibiting the reduction of nephrin, podocin and podoplanin.

Xanthine oxidoreductase inhibitor topiroxostat ameliorates podocyte injury by inhibiting the reduction of nephrin and podoplanin

BACKGROUND

Topiroxostat, an inhibitor of xanthine oxidoreductase (XOR) was shown to reduce urinary albumin excretion of hyperuricemic patients with chronic kidney disease. However, its pharmacological mechanism is not well understood. In this study, we examined the effects of topiroxostat on glomerular podocytes. Podocyte is characterized by foot process and a unique cell-cell junction slit diaphragm functioning as a final barrier to prevent proteinuria.

METHODS

The effects of topiroxostat on the expressions of podocyte functional molecules were analysed in db/db mice, a diabetic nephropathy model, anti-nephrin antibody-induced rat podocyte injury model and cultured podocytes treated with adriamycin.

RESULTS

Topiroxostat treatment ameliorated albuminuria in db/db mice. The expression of desmin, a podocyte injury marker was increased, and nephrin and podocin, key molecules of slit diaphragm, and podoplanin, an essential molecule in maintaining foot process were downregulated in db/db mice. Topiroxostat treatment prevented the alterations in the expressions of these molecules in db/db mice. XOR activity in kidney was increased in rats with anti-nephrin antibody-induced podocyte injury. Topiroxostat treatment reduced XOR activity and restored the decreased expression of nephrin, podocin and podoplanin in the podocyte injury. Furthermore, topiroxostat enhanced the expression of podoplanin in injured human cultured podocytes.

CONCLUSIONS

Podocyte injury was evident in db/db mice. Topiroxostat ameliorated albuminuria in diabetic nephropathy model by preventing podocyte injury. Increase of XOR activity in kidney contributes to development of podocyte injury caused by stimulation to slit diaphragm. Topiroxostat has an effect to stabilize slit diaphragm and foot processes by inhibiting the reduction of nephrin, podocin and podoplanin.

Urinary Markers of Podocyte Dysfunction in Chronic Glomerulonephritis

Chronic glomerulonephritis (CGN) is a disease with a steady progressive course that involves the development of nephrosclerosis, which is especially evident in clinical courses with incidences of high proteinuria (PU). Currently, proteinuria is considered the main laboratory feature (sign) of CGN activity and progression because proteinuria is closely related to the process of tubulointerstitial fibrosis, which is correlated with the grade of renal insufficiency. The injury to podocytes, which are key components of the filtration barrier, plays a central role in proteinuria development. The detachment of podocytes from the glomerular basement membrane leading to podocytopenia is suggested to induce glomerulosclerosis and hyalinosis with obliteration of capillary loops and the progression of chronic kidney disease. Urinary markers of podocyte dysfunction could serve as useful tools while monitoring the activity and prognosis of CGN. In this chapter, the most important mechanisms of podocyte loss and urinary markers of this process are discussed.

Inhibition of RNA-binding protein HuR reduces glomerulosclerosis in experimental nephritis

Recent identification of an RNA-binding protein (HuR) that regulates mRNA turnover and translation of numerous transcripts via binding to an ARE in their 3′-UTR involved in inflammation and is abnormally elevated in varied kidney diseases offers a novel target for the treatment of renal inflammation and subsequent fibrosis. Thus, we hypothesized that treatment with a selective inhibition of HuR function with a small molecule, KH-3, would down-regulate HuR-targeted proinflammatory transcripts thereby improving glomerulosclerosis in experimental nephritis, where glomerular cellular HuR is elevated. Three experimental groups included normal and diseased rats treated with or without KH-3. Disease was induced by the monoclonal anti-Thy 1.1 antibody. KH-3 was given via daily intraperitoneal injection from day 1 after disease induction to day 5 at the dose of 50 mg/kg BW/day. At day 6, diseased animals treated with KH-3 showed significant reduction in glomerular HuR levels, proteinuria, podocyte injury determined by ameliorated podocyte loss and podocin expression, glomerular staining for periodic acid-Schiff positive extracellular matrix proteins, fibronectin and collagen IV and mRNA and protein levels of profibrotic markers, compared with untreated disease rats. KH-3 treatment also reduced disease-induced increases in renal TGFβ1 and PAI-1 transcripts. Additionally, a marked increase in renal NF-κB-p65, Nox4, and glomerular macrophage cell infiltration observed in disease control group was largely reversed by KH-3 treatment. These results strongly support our hypothesis that down-regulation of HuR function with KH-3 has therapeutic potential for reversing glomerulosclerosis by reducing abundance of pro-inflammatory transcripts and related inflammation.

HUANGKUISIWUFANG inhibits pyruvate dehydrogenase to improve glomerular injury in anti-Thy1 nephritis model

ETHNOPHARMACOLOGICAL RELEVANCE

Huangkuisiwufang (HKSWF) is composed of Abelmoschus manihot (L.) Medik., Astragalus mongholicus, Polygonum cuspidatum, Curcuma longa L. Abelmoschus Manihot (L.) Medik. has been widely used for the treatment of chronic renal disease, oral ulcers and burn in China for centuries (Committee of the Pharmacopoeia of PR China, 2010). Abelmoschus manihot (L.) Medik., Polygonum cuspidatum, Curcuma longa L. have been mainly applied in folk medicine for their therapeutic effects on diabetes, cancer, heart disease and other diseases.

AIM OF THE STUDY

We aimed to investigate the renoprotective function of HKSWF in anti-Thy nephritis model and clarify the relevant mechanisms.

MATERIALS AND METHODS

One week after the model of glomerulonephritis created by injecting anti-thymocyte serum (ATS), rats were treated with Huangkui capsule, enalapril or HKSWF by gavage for a period of 8 weeks. The therapeutic effect was evaluated by detection of proteinuria, plasma creatine, blood urea nitrogen (BUN), podocyte injury, glomerular accumulation of extracellular matrix (ECM) and the markers of oxidative stress and renal fibrosis. RNA Sequencing (RNA-seq), KEGG and western blotting analysis were performed to indicate the signaling pathway involved in the therapeutic effect of HKSWF.

RESULTS

Nephritic rats presented the increase of BUN, serum creatinine (Scr), proteinuria, podocyte damage, glomerular fibrosis, Ang II type 1 receptor (AT1R), and the reduction of creatinine clearance (Ccr). In contrast, application of HKSWF to nephritic rats decreased the levels of BUN and proteinuria, promoted mesangial cell recovery and improved oxidative stress level and podocyte injury. KEGG analysis revealed that pyruvate metabolism was the most significantly upregulated pathway in rats treated with HKSWF compared to disease control group. Increased pyruvate dehydrogenase and PAI-1 caused by nephritis was inhibited by HKSWF interposition. Furthermore, dichloroacetate sodium (DCA), an agonist of pyruvate dehydrogenase, could stimulate PAI-1 expression, which was suppressed by HKSWF.

CONCLUSION

Chinese herbal preparation HKSWF has remarkable curative effects on glomerulonephritis animals. HKSWF attenuates pyruvate dehydrogenase to improve glomerular injury.

Role of Chemokine (C-X-C Motif) Ligand 10 (CXCL10) in Renal Diseases

Chemokine C-X-C ligand 10 (CXCL10), also known as interferon-γ-inducible protein 10 (IP-10), exerts biological function mainly through binding to its specific receptor, CXCR3. Studies have shown that renal resident mesangial cells, renal tubular epithelial cells, podocytes, endothelial cells, and infiltrating inflammatory cells express CXCL10 and CXCR3 under inflammatory conditions. In the last few years, strong experimental and clinical evidence has indicated that CXCL10 is involved in the development of renal diseases through the chemoattraction of inflammatory cells and facilitation of cell growth and angiostatic effects. In addition, CXCL10 has been shown to be a significant biomarker of disease severity, and it can be used as a prognostic indicator for a variety of renal diseases, such as renal allograft dysfunction and lupus nephritis. In this review, we summarize the structures and biological functions of CXCL10 and CXCR3, focusing on the important role of CXCL10 in the pathogenesis of kidney disease, and provide a theoretical basis for CXCL10 as a potential biomarker and therapeutic target in human kidney disease.

The role of podocytes dysfunction in chronic glomerulonephritis progression

In the review, the mechanisms of podocytes damage underlying the development of proteinuria and progression of glomerulosclerosis in chronic glomerulonephritis are discussed in detail. The results of experimental and clinical studies are presented. Under the different immune and non-immune factors the podocytes form a stereotyped response to damage consisting in the reorganization of the actin cytoskeleton, foot process effacement, the detachment of podocytes from the glomerular basement membrane, and the appearance of specific podocyte proteins and whole cells (podocyturia) in the urine. Massive podocyturia in a limited proliferative capacity of podocytes leads to reduce their total count in the glomerulus (podocytopenia) and the development of glomerulosclerosis. The authors describe the line of markers of the podocyte injury and invasive and non-invasive methods of their assessment. In addition, the relationship of podocyturia level with proteinuria and renal dysfunction are discussed, the prospects of assessment the podocyte proteins in urine for assessing of glomerular damage severity and glomerulosclerosis risk are examined.

Podocyte injury and its consequences

Podocytes maintain the glomerular filtration barrier, and the stability of this barrier depends on their highly differentiated postmitotic phenotype, which also defines the particular vulnerability of the glomerulus. Recent podocyte biology and gene disruption studies in vivo indicate a causal relationship between abnormalities of single podocyte molecules and proteinuria and glomerulosclerosis. Podocytes live under various stresses and pathological stimuli. They adapt to maintain homeostasis, but excessive stress leads to maladaptation with complex biological changes including loss of integrity and dysregulation of cellular metabolism. Podocyte injury causes proteinuria and detachment from the glomerular basement membrane. In addition to "sick" podocytes and their detachment, our understanding of glomerular responses following podocyte loss needs to address the pathways from podocyte injury to sclerosis. Studies have found a variety of glomerular responses to podocyte dysfunction in vivo, such as disruption of podocyte-endothelial cross talk and activation of podocyte-parietal cell interactions, all of which help us to understand the complex scenario of podocyte injury and its consequences. This review focuses on the cellular aspects of podocyte dysfunction and the adaptive or maladaptive glomerular responses to podocyte injury that lead to its major consequence, glomerulosclerosis.

Disease Severity Correlates with Thrombotic Capacity in Experimental Nephrotic Syndrome

Thrombotic disease, a major life-threatening complication of nephrotic syndrome, has been associated with proteinuria and hypoalbuminemia severity. However, it is not fully understood how disease severity correlates with severity of the acquired hypercoagulopathy of nephrotic syndrome. Without this knowledge, the utility of proteinuria and/or hypoalbuminemia as biomarkers of thrombotic risk remains limited. Here, we show that two well established ex vivo hypercoagulopathy assays, thrombin generation and rotational thromboelastometry, are highly correlated with proteinuria and hypoalbuminemia in the puromycin aminonucleoside and adriamycin rat models of nephrotic syndrome. Notably, in the puromycin aminonucleoside model, hyperfibrinogenemia and antithrombin deficiency were also correlated with proteinuria severity, consistent with reports in human nephrotic syndrome. Importantly, although coagulation was not spontaneously activated in vivo with increasing proteinuria, vascular injury induced a more robust thrombotic response in nephrotic animals. In conclusion, hypercoagulopathy is highly correlated with nephrotic disease severity, but overt thrombosis may require an initiating insult, such as vascular injury. Our results suggest that proteinuria and/or hypoalbuminemia could be developed as clinically meaningful surrogate biomarkers of hypercoagulopathy to identify patients with nephrotic syndrome at highest risk for thrombotic disease and potentially target them for anticoagulant pharmacoprophylaxis.

Activated omentum slows progression of CKD

Stem cells show promise in the treatment of AKI but do not survive long term after injection. However, organ repair has been achieved by extending and attaching the omentum, a fatty tissue lying above the stomach containing stem cells, to various organs. To examine whether fusing the omentum to a subtotally nephrectomized kidney could slow the progression of CKD, we used two groups of rats: an experimental group undergoing 5/6 nephrectomy only and a control group undergoing 5/6 nephrectomy and complete omentectomy. Polydextran gel particles were administered intraperitoneally before suture only in the experimental group to facilitate the fusion of the omentum to the injured kidney. After 12 weeks, experimental rats exhibited omentum fused to the remnant kidney and had lower plasma creatinine and urea nitrogen levels; less glomerulosclerosis, tubulointerstitial injury, and extracellular matrix; and reduced thickening of basement membranes compared with controls. A fusion zone formed between the injured kidney and the omentum contained abundant stem cells expressing stem cell antigen-1, Wilms' tumor 1 (WT-1), and CD34, suggesting active, healing tissue. Furthermore, kidney extracts from experimental rats showed increases in expression levels of growth factors involved in renal repair, the number of proliferating cells, especially at the injured edge, the number of WT-1-positive cells in the glomeruli, and WT-1 gene expression. These results suggest that contact between the omentum and injured kidney slows the progression of CKD in the remnant organ, and this effect appears to be mediated by the presence of omental stem cells and their secretory products.

Development of lymphatic vasculature and morphological characterization in rat kidney

BACKGROUND

The mechanisms and morphological characteristics of lymphatic vascular development in embryonic kidneys remain uncertain.

METHODS

We examined the distribution and characteristics of lymphatic vessels in developing rat kidneys using immunostaining for podoplanin, prox-1, Ki-67, type IV collagen (basement membrane: BM), and α-smooth muscle actin (αSMA: pericytes or mural cells). We also examined the expression of VEGF-C.

RESULTS

At embryonic day 17 (E17), podoplanin-positive lymphatic vessels were observed mainly in the kidney hilus. At E20, lymphatic vessels extended further into the developing kidneys along the interlobar vasculature. In 1-day-old pups (P1) to P20, lymphatic vessels appeared around the arcuate arteries and veins of the kidneys, with some reaching the developing cortex via interlobular vessels. In 8-week-old adult rats, lymphatic vessels were extensively distributed around the blood vasculature from the renal hilus to cortex. Only lymphatic capillaries lacking continuous BM and αSMA-positive cells were present within adult kidneys, with none observed in renal medulla. VEGF-C was upregulated in the developing kidneys and expressed mainly in tubules. Importantly, the developing lymphatic vessels were characterized by endothelial cells immunopositive for podoplanin, prox-1, and Ki-67, with no surrounding BM or αSMA-positive cells.

CONCLUSION

During nephrogenesis, lymphatic vessels extend from the renal hilus into the renal cortex along the renal blood vasculature. Podoplanin, prox-1, Ki-67, type IV collagen, and αSMA immunostaining can detect lymphatic vessels during lymphangiogenesis.

[Acute postinfectious glomerulonephritis]

Acute postinfectious glomerulonephritis are defined by an acute nonsuppurative inflammatory insult predominantly glomerular. Its current incidence is uncertain because of the frequency of subclinical forms. The most common infectious agent involved is beta hemolytic streptococcus group A. Acute postinfectious glomerulonephritis is uncommon in adults, and its incidence is progressively declining in developed countries. Humoral immunity plays a key role in the pathogenesis of kidney damage. Complement activation by the alternative pathway is the dominant mechanism, but a third way (lectin pathway) has been recently identified. The classic clinical presentation is sudden onset of acute nephritic syndrome after a free interval from a streptococcal infection. Treatment is essentially symptomatic and prevention is possible through improved hygiene and early treatment of infections.

The effect of losartan and carvedilol on renal haemodynamics and altered metabolism in fructose-fed Sprague-Dawley rats

The aim of this study is to assess the effects of losartan and carvedilol on metabolic parameters and renal haemodynamic responses to angiotensin II (Ang II) and adrenergic agonists in the model of fructose-fed rat. Thirty-six Sprague-Dawley rats were fed for 8 weeks either 20% fructose solution (F) or tap water (C) ad libitum. F or C group received either losartan or carvedilol (10 mg/kg p.o.) daily for the last 3 weeks of the study (FL and L) and (FCV and CV), respectively, then in acute studies the renal vasoconstrictor actions of Ang II, noradrenaline (NA), phenylephrine (PE) and methoxamine (ME) were determined. Data, mean±SEM were analysed using ANOVA with significance at P <0.05. Losartan and carvedilol decreased the area under the glucose tolerance curve of the fructose-fed group. The responses (%) to NA, PE, ME and Ang II in F were lower (P <0.05) than C (F vs. C, 17±2 vs. 38±3; 24±2 vs. 48±2; 12±2 vs. 34±2; 17±2 vs. 26±2), respectively. L had higher (P <0.05) responses to NA and PE while CV had blunted (P <0.05) responses to NA, PE and Ang II compared to C (L, CV vs. C, 47±3, 9±2 vs. 38±3; 61±3, 29±3 vs. 48±2; 16±3, 4±3 vs. 26±2), respectively. FL but not FCV group had enhanced (P <0.05) responses to NA, PE and ME compared to F (FL vs. F, 33±3 vs. 17±2; 45±3 vs. 24±2; 26±3 vs. 12±2), respectively. Losartan and carvedilol had an important ameliorating effect on fructose-induced insulin resistance. Losartan treatment could be an effective tool to restore normal vascular reactivity in the renal circulation of the fructose-fed rat.

Multi-glycoside of Tripterygium wilfordii Hook. f. reduces proteinuria through improving podocyte slit diaphragm dysfunction in anti-Thy1.1 glomerulonephritis

ETHNOPHARMACOLOGICAL RELEVANCE

Multi-glycoside of Tripterygium wilfordii Hook. f. (GTW) has been proved clinically effective in reducing proteinuria in chronic kidney disease in China. However, the mechanisms involved are still unclear. In this study we examined the effects of GTW at the different dosages on proteinuria and podocyte slit diaphragm (SD) dysfunction in anti-Thy1.1 glomerulonephritis (GN).

MATERIALS AND METHODS

Rats with anti-Thy1.1 GN were divided into 2 groups, a GTW group and a vehicle group, and sacrificed at 30 min, on day 7, and on day 14 in Experiments 1, 2 and 3, respectively. The administration of GTW at the moderate and high doses was started 3 days before or at the same time of antibody injection till sacrifice. Proteinuria was determined in Experiments 1, 2, and 3. After sacrifice, the staining intensity of SD-associated key functional molecules including nephrin and podocin, podocyte structure, mesangial change, macrophage infiltration, and blood biochemical parameters were examined, respectively. Protein and mRNA expressions of nephrin and podocin in glomeruli were also investigated. Besides, liver histological characteristics were analyzed.

RESULTS

In Experiment 1, GTW pretreatment at the medium dose (75 mg/kg body weight) caused no influence on the induction of anti-Thy1.1 GN and the basal nephrin expression. In Experiment 2, the high dosage (100mg/kg body weight) of GTW ameliorated proteinuria, the distribution of nephrin and podocin, mesangial proliferation, and the activated macrophage accumulation, as compared with vehicle group (P<0.05). Additionally, it increased mRNA and protein expressions of nephrin and podocin in glomeruli on day 7, but had no influence on podocyte structure. In Experiment 3, the medium dosage (75 mg/kg body weight) of GTW improved proteinuria, the partial matrix expansion, and the distribution of nephrin and podocin on day 14, as compared with anti-Thy1.1 GN rats (P<0.05). GTW at the high or moderate dose did not affect hepatic function on day 7 and on day 14.

CONCLUSIONS

Podocyte SD dysfunction, such as the disordered distribution and down-regulation of nephrin and podocin expression, is critically involved in the pathogenesis of anti-Thy1.1 GN induced by mAb 1-22-3. The restoration of the distribution and expression of nephrin and podocin by GTW could be an important mechanism by which GTW ameliorates proteinuria and podocyte SD dysfunction.

Etiopathology of chronic tubular, glomerular and renovascular nephropathies: clinical implications

Chronic kidney disease (CKD) comprises a group of pathologies in which the renal excretory function is chronically compromised. Most, but not all, forms of CKD are progressive and irreversible, pathological syndromes that start silently (i.e. no functional alterations are evident), continue through renal dysfunction and ends up in renal failure. At this point, kidney transplant or dialysis (renal replacement therapy, RRT) becomes necessary to prevent death derived from the inability of the kidneys to cleanse the blood and achieve hydroelectrolytic balance. Worldwide, nearly 1.5 million people need RRT, and the incidence of CKD has increased significantly over the last decades. Diabetes and hypertension are among the leading causes of end stage renal disease, although autoimmunity, renal atherosclerosis, certain infections, drugs and toxins, obstruction of the urinary tract, genetic alterations, and other insults may initiate the disease by damaging the glomerular, tubular, vascular or interstitial compartments of the kidneys. In all cases, CKD eventually compromises all these structures and gives rise to a similar phenotype regardless of etiology. This review describes with an integrative approach the pathophysiological process of tubulointerstitial, glomerular and renovascular diseases, and makes emphasis on the key cellular and molecular events involved. It further analyses the key mechanisms leading to a merging phenotype and pathophysiological scenario as etiologically distinct diseases progress. Finally clinical implications and future experimental and therapeutic perspectives are discussed.

Trophoblast glycoprotein: possible candidate mediating podocyte injuries in glomerulonephritis

BACKGROUND

trophoblast glycoprotein (Tpbg), a 72-kDa transmembrane glycoprotein, is known to regulate the phenotypes of epithelial cells by modifying actin organization and cell motility. Recently, a microarray study showed that Tpbg is upregulated in Thy1 glomerulonephritis (Thy1 GN). We hypothesized that Tpbg regulates cytoskeletal rearrangement and modulates phenotypic alteration in podocytes under pathological conditions.

METHODS

we examined Tpbg expression in Thy1 GN and Tpbg function in mouse podocytes.

RESULTS

we demonstrated that Tpbg is upregulated in the injured podocytes of Thy1 GN. In vitro, immunofluorescence studies revealed that Tpbg colocalized with the focal adhesion protein, vinculin, in parallel with stress fiber formation. This colocalization was observed even when actin filaments were depolymerized with cytochalasin D. Tpbg localization at focal adhesions was induced by dominant-active RhoA and suppressed by the ROCK1 inhibitor Y-26732. In addition, transforming growth factor-β increased Tpbg expression at focal adhesions concurrently with rearrangement of stress fibers. Stress fiber formation was suppressed in differentiated podocytes transfected with full-length Tpbg. Furthermore, knockdown of Tpbg using small interfering RNA decreased podocyte motility.

CONCLUSION

our findings suggest a novel role of Tpbg in the phenotypic alteration of injured podocytes, and we accordingly propose a new mechanism of glomerular injury in glomerulonephritis.

Slit diaphragm dysfunction in proteinuric states: identification of novel therapeutic targets for nephrotic syndrome. Clin Exp Nephrol. 2009;13:275-280. [PMID: 19266252 DOI: 10.1007/s10157-009-0162-x]

Several recent studies have demonstrated that the slit diaphragm of the glomerular epithelial cell (podocyte) is the structure likely to be the principal barrier in the glomerular capillary wall. Nephrin identified as a gene product mutated in congenital nephrotic syndrome located at the outer leaflet of plasma membranes of the slit diaphragm. The anti-nephrin antibody is capable of inducing massive proteinuria, which indicates that nephrin is a key functional molecule in the slit diaphragm. Expression of nephrin was reduced in glomeruli of minimal change nephrotic syndrome. Some recent studies demonstrated that podocin, CD2-associated protein and NEPH1 are also functional molecules in the slit diaphragm, and their expressions are altered in membranous nephropathy and also in focal glomerulosclerosis. These observations suggested that the alteration of the molecular arrangement in the slit diaphragm is involved in the development of proteinuria in several kinds of glomerular diseases. Recent studies of our group have demonstrated that type 1 receptor-mediated angiotensin II action reduced the expression of the slit diaphragm-associated molecules and that type 1 receptor blockade ameliorated proteinuria by preventing the function of angiotensin II on the slit diaphragm. By the subtraction hybridization techniques using glomerular cDNA of normal and proteinuric rats, we detected that synaptic vesicle protein 2B and ephrin B1 are involved in the maintenance of the barrier function of the slit diaphragm.

Angiotensin II receptor blockade inhibits acute glomerular injuries with the alteration of receptor expression

Angiotensin II receptor blockade (ARB) suppresses the progression of chronic kidney disease. However, the renoprotective effect of ARB in the active phase of glomerulonephritis (GN) has not been evaluated in detail. We examined the alteration of angiotensin II receptors' expression and the action of ARB on acute glomerular injuries in GN. Thy-1 GN was induced in rats that were divided into three groups (n=7, in each group); high dose (3 mg/kg/day) or low dose (0.3 mg/kg/day) olmesartan (Thy-1 GN+HD- or LD-ARB group), and vehicle (Thy-1 GN group). Renal function and histopathology were assessed by week 2. In the Thy-1 GN group, diffuse mesangiolysis and focal aneurysmal ballooning developed by day 3. Marked mesangial proliferation and activation progressed with glomerular epithelial injury. We confirmed that both angiotensin II type 1 receptor (AT1R) and type 2 receptor (AT2R) were expressed on glomerular endothelial, mesangial, epithelial cells, and macrophages, and increased 7 days after disease induction. However, ARB treatment caused a decrease in AT1R and a further increase in AT2R expression in glomeruli. ARB prevented capillary destruction and preserved eNOS expression after diffuse mesangiolysis. Mesangial proliferation and activation was suppressed markedly with low levels of PDGF-B expression. Glomerular desmin expression, which is a marker for injured glomerular epithelial cells, was diminished significantly with retained expression of nephrin and podoplanin. Glomerular macrophage infiltration was also inhibited. Proteinuria was suppressed significantly. Furthermore, these effects of ARB showed dose dependency. These results provide insights that ARB affects individual glomerular cells and macrophages through angiotensin II receptors, with the alteration of both AT1R and AT2R expressions, and leads to inhibition of the acute destructive and proliferative glomerular lesions in GN.

Dissociation of NEPH1 from nephrin is involved in development of a rat model of focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a disease showing severe proteinuria, and the disease progresses to end-stage kidney failure in many cases. However, the pathogenic mechanism of FSGS is not well understood. The slit diaphragm (SD), which bridges the neighboring foot processes of glomerular epithelial cells, is understood to function as a barrier of the glomerular capillary wall. To investigate the role of SD dysfunction in the development of FSGS, we analyzed the expression of SD-associated molecules in rat adriamycin-induced nephropathy, a mimic of FSGS. The staining of the SD molecules nephrin, podocin, and NEPH1 had already shifted to a discontinuous dotlike pattern at the initiation phase of the disease, when neither proteinuria nor any morphological alterations were detected yet. The alteration of NEPH1 expression was the most evident among the molecules examined, and NEPH1 was dissociated from nephrin at the initiation phase. On day 28, when severe proteinuria was detected and sclerotic changes were already observed, alteration of the expressions of nephrin, podocin, and NEPH1 worsened, but no alteration in the expression of other SD-associated molecules or other podocyte molecules was detected. It is postulated that the dissociation of NEPH1 from nephrin initiates proteinuria and that the SD alteration restricted in these molecules plays a critical role in the development of sclerotic changes in FSGS.

Selective loss of podoplanin protein expression accompanies proteinuria and precedes alterations in podocyte morphology in a spontaneous proteinuric rat model

To evaluate changes during the development of proteinuria, podocyte morphology and protein expression were evaluated in spontaneously proteinuric, Dahl salt-sensitive (Dahl SS) rats. Dahl SS rats on a low-salt diet were compared with spontaneously hypertensive rats (SHR) at age 2, 4, 6, 8, and 10 weeks. Blood pressure, urinary protein excretion, urinary albumin excretion, and podocyte morphology were evaluated. In addition, the expression of 11 podocyte-related proteins was determined by analyzing protein and mRNA levels. In Dahl SS rats, proteinuria became evident around week 5, increasing thereafter. SHR rats remained non-proteinuric. Dahl SS rats showed widespread foot process effacement at 10 weeks. At < or =8 weeks, expression and distribution of the podocyte proteins was similar between the two strains, except for the protein podoplanin. At 4 weeks, podoplanin began decreasing in the glomeruli of Dahl SS rats in a focal and segmental fashion. Podoplanin loss increased progressively and correlated with albuminuria (r = 0.8, P < 0.001). Double labeling experiments revealed increased expression of the podocyte stress marker desmin in glomerular areas where podoplanin was lost. Dahl SS rats did not show podoplanin gene mutations or decreased mRNA expression. Thus, podocyte morphology and the expression and distribution of most podocyte-specific proteins were normal in young Dahl SS rats, despite marked proteinuria. Our study suggests that decreased expression of podoplanin plays a role in the decrease of glomerular permselectivity.

Glomerular hypertrophy precedes albuminuria and segmental loss of podoplanin in podocytes in Munich-Wistar-Frömter rats

Focal segmental glomerulosclerosis (FSGS) is a common cause of end-stage renal disease. Albuminuria is a risk factor for FSGS and is influenced by environmental, genetic, and sex-specific factors. Podocytes play a central role in the development of albuminuria, but the precise relationship between early glomerular and podocyte-associated damage and albuminuria is unclear. Furthermore, experimental findings demonstrate a sex difference in development of albuminuria and FSGS. We investigated the early glomerular changes in male Munich-Wistar-Frömter (MWF) rats, which spontaneously develop albuminuria, and male albuminuria-resistant spontaneously hypertensive rats (SHR). In addition, since female MWF rats are protected from overt proteinuria and progressive renal disease, we compared the phenotypic changes in podocytes during early development of albuminuria in male and female MWF rats. In male MWF rats, glomerular hypertrophy preceded the onset of albuminuria and was greater than in male SHR. Albuminuria developed starting at 6 wk of age and coincided with focal and segmental loss of podoplanin, increased expression of desmin, entrapment of albumin in affected podocytes, and focal and segmental foot process effacement at the ultrastructural level. Other podocyte-associated molecules, such as nephrin and zonula occludens 1, were unaffected. Early glomerular hypertrophy and podocyte damage did not differ between male and female MWF rats. Our data show for the first time that albuminuria in male and female MWF rats is preceded by glomerular hypertrophy and accompanied by focal and segmental loss of podoplanin when FSGS was not yet present.

Glomerular sclerosis in kidneys with congenital nephrotic syndrome (NPHS1)

Congenital nephrotic syndrome of the Finnish type (NPHS1) is a rare genetic disease caused by mutations in the NPHS1 gene encoding a major podocyte slit-diaphragm protein, nephrin. Patients with NPHS1 have severe nephrotic syndrome from birth and develop renal fibrosis in early childhood. In this work, we studied the development of glomerular sclerosis in kidneys removed from 4- to 44-month-old NPHS1 patients. The pathological lesions and expression of glomerular cell markers were studied in nephrectomized NPHS1 and control kidneys using light and electron microscopy and immunohistochemistry. An analysis of 1528 glomeruli from 20 patients revealed progressive mesangial sclerosis and capillary obliteration. Although few inflammatory cells were detected in the mesangial area, paraglomerular inflammation and fibrosis was common. The podocytes showed severe ultrastructural changes and hypertrophy with the upregulation of cyclins A and D1. Podocyte proliferation, however, was rare. Apoptosis was hardly detected and the expression of antiapoptotic B-cell lymphoma-2 and proapoptotic p53 were comparable to controls. Moderate amounts of podocytes were secreted into the urine of NPHS1 patients. Shrinkage of the glomerular tuft was common, whereas occlusion of tubular opening or protrusion of the glomerular tuft into subepithelial space or through the Bowman's capsule were not detected. The results indicate that, in NPHS1 kidneys, the damaged podocytes induce progressive mesangial expansion and capillary obliteration. Podocyte depletion, glomerular tuft adhesion, and misdirected filtration, however, seem to play a minor role in the nephron destruction.

Role of podocyte slit diaphragm as a filtration barrier (Review Article)

Although the role of glomerular basement membrane has been emphasised as the barrier for retaining plasma proteins in the past three decades, some recent studies have demonstrated that the slit diaphragm of the glomerular epithelial cell (podocyte) is the structure likely to be the barrier in the glomerular capillary wall. Nephrin and podocin were identified as gene products mutated in Finnish-type congenital nephrotic syndrome and autosomal recessive steroid-resistant nephrotic syndrome, respectively. Nephrin s located at the outer leaflet of plasma membranes of the slit diaphragm. Podocin is reported to have an interaction with nephrin. The anti-nephrin antibody is capable of inducing massive proteinuria, which indicates that nephrin is a key functional molecule in the slit diaphragm. The expression of nephrin and podocin was reduced in glomeruli of minimal change nephrotic syndrome, which suggested that the altered expression of these molecules contributes to the development of proteinuria also in acquired diseases. Some recent studies demonstrated that CD2-associated protein (CD2AP) is also a functional molecule in the slit diaphragm, and its expression is altered in membranous nephropathy. These observations suggested that alteration of the molecular arrangement in the slit diaphragm is involved in the development of proteinuria in several kinds of glomerular diseases.

Role of p38 Mitogen-Activated Protein Kinase Activation in Podocyte Injury and Proteinuria in Experimental Nephrotic Syndrome

Podocytes play an important role in maintaining normal glomerular function and structure, and podocyte injury leads to proteinuria and glomerulosclerosis. The family of mitogen-activated protein kinases (MAPK; extracellular signal-regulated kinase [ERK], c-Jun N-terminal kinase, and p38) may be implicated in the progression of various glomerulopathies, but the role of MAPK in podocyte injury remains elusive. This study examined phosphorylation of p38 MAPK in clinical glomerulopathies with podocyte injury, as well as in rat puromycin aminonucleoside (PAN) nephropathy and mouse adriamycin (ADR) nephropathy. The effect of treatment with FR167653, an inhibitor of p38 MAPK, was also investigated in rodent models. In human podocyte injury diseases, the increased phosphorylation of p38 MAPK was observed at podocytes. In PAN and ADR nephropathy, the phosphorylation of p38 MAPK and ERK was marked but transient, preceding overt proteinuria. Pretreatment with FR167653 (day -2 to day 14, subcutaneously) to PAN or ADR nephropathy completely inhibited p38 MAPK activation and attenuated ERK phosphorylation, with complete suppression of proteinuria. Electron microscopy and immunohistochemistry for nephrin and connexin43 revealed that podocyte injury was markedly ameliorated by FR167653. Furthermore, early treatment with FR167653 effectively prevented glomerulosclerosis and renal dysfunction in the chronic phase of ADR nephropathy. In cultured podocytes, PAN or oxidative stress induced the phosphorylation of p38 MAPK along with actin reorganization, and FR167653 inhibited such changes. These findings indicate that the activation of MAPK is necessary for podocyte injury, suggesting that p38 MAPK and, possibly, ERK should become a potential target for therapeutic intervention in proteinuric glomerulopathies.

Transgene of MIF induces podocyte injury and progressive mesangial sclerosis in the mouse kidney

BACKGROUND

Recent evidence suggests that macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that plays a pathogenic role in glomerulonephritis. Renal expression of MIF is up-regulated in infiltrating and intrinsic renal cells, which include glomerular epithelial cells. The aim of the current study was to further clarify the role of MIF produced by podocytes in the process of renal disease.

METHODS

We generated transgenic mice carrying a murine MIF cDNA driven by cytomegalovirus enhancer and beta-actin/beta-globin promoter, a hybrid promoter transactivated in podocytes in vivo.

RESULTS

MIF expression was markedly up-regulated in podocytes in neonatal and adult transgenic kidneys. A longitudinal study of the MIF transgenic mice demonstrated a progressive matrix increase in mesangium accompanied by collagen IV accumulation, representing no significant glomerular cell hypercellularity. The glomeruli in transgenic kidney were not accompanied by influx of macrophages and T cells at the early stage of disease progression. Although a significant number of the mice showing higher expression of MIF died from renal failure at 8 weeks, most of them survived with significant proteinuria and progressive renal failure. Podocytes of transgenic mice frequently underwent characteristic ultrastructural changes, such as cell flattening, contracted foot processes, and villous transformation. In addition, immunohistochemical expression of synaptopodin, an actin-associated protein distributed in differentiated podocyte foot process, was significantly attenuated in transgenic kidney.

CONCLUSION

Our results indicate that podocyte-expressed MIF could induce an injury of podocytes themselves, thereby accelerating the progression of glomerulosclerosis and leading to end-stage renal failure.

IFN-Inducible Protein-10 Has a Differential Role in Podocyte during Thy 1.1 Glomerulonephritis

ABSTRACT. IFN-inducible protein-10 (IP-10/CXCL10) is a potent chemoattractant for activated T lymphocytes and was recently reported to have several additional biologic activities. In this study, the expression and the function in normal glomeruli and in Thy1.1 glomerulonephritis (GN) were investigated. The expression of IP-10 was detected in normal rat glomeruli mainly in the podocyte. The expression of IP-10 was also detected on the cultured podocyte. The IP-10 expression was elevated at the early phase of Thy1.1 GN. The double staining immunofluorescence study clearly demonstrated that the elevated expression of IP-10 was mostly detected in the podocyte and very partly in mesangial area. A receptor for IP-10, CXCR3, showed similar expression patterns to that of IP-10. Expressions of neither of IP-10 nor of CXCR3 were detected on the inflammatory cells. For elucidating the role of IP-10, the blocking study was carried out with monoclonal anti–IP-10 antibody. The monoclonal anti–IP-10 antibody treatment decreased the expression of IP-10 and podocyte-associated proteins such as nephrin and podocin that are reported to be essential for maintaining the podocyte function (IP-10, 53.0% to control; nephrin, 43.5%; podocin, 60.4%). The findings indicated that the anti–IP-10 treatment disturbed the podocyte function. The anti–IP-10 treatment given to the rats with Thy1.1 nephritis exacerbated proteinuria, mesangiolysis, and matrix expansion. Collectively, the findings indicated that IP-10 plays a role in maintaining the podocyte function. Also, the findings suggested that anti–IP-10 treatment exacerbated the glomerular alterations in Thy1.1 GN by disturbing the podocyte function.

Genetic polymorphism of NPHS1 modifies the clinical manifestations of Ig A nephropathy

Nephrin, the molecule responsible for congenital nephrotic syndrome of Finnish type, is crucial in maintaining the glomerular filtration barrier. Recently, its complete gene structure and common gene polymorphisms in its exons have been reported, although the functional and clinical significance of these polymorphisms has not yet been elucidated. We investigated a possible association of the NPHS1 polymorphisms with the development of Ig A nephropathy (IgAN), as well as the clinical and histologic manifestations in IgAN. A total of 464 Japanese subjects, including 267 patients with histologically proven IgAN and 197 healthy controls with normal urinalysis, were genotyped for the NPHS1 G349A, G2289A, and T3315C polymorphisms. The frequencies of the genotypes, alleles, and estimated haplotypes of NPHS1 polymorphisms were no different between patients with IgAN and the controls. Within the IgAN group, patients carrying at least one G allele of G349A tended to present with more proteinuria, lower renal function, and more severe histopathologic injury than those with the AA genotype, although the time from the first urinary abnormality to the renal biopsy was no different between both groups. The logistic regression analysis indicated that even after adjusting for the effect of proteinuria and hypertension the GG genotype of NPHS1 G349A was an independent risk factor for the deteriorated renal function at the time of diagnosis. This study suggests that the NPHS1 G349A polymorphism may be associated with heavy proteinuria and a decline in renal function in patients with IgAN.

Pathways to recovery and loss of nephrons in anti-Thy-1 nephritis

The present histopathologic study of anti-Thy-1.1 models of mesangioproliferative glomerulonephritis in rats provides a structural analysis of damage development and of pathways to recovery and to nephron loss. As long as the disease remains confined to the endocapillary compartment, the damage may be resolved or recover with a mesangial scar. Irreversible lesions with loss of nephrons emerge from extracapillary processes with crucial involvement of podocytes, leading to tuft adhesions to Bowman's capsule (BC) and subsequent crescent formation. Two mechanisms appeared to be responsible: (1) Epithelial cell proliferation at BC and the urinary orifice and (2) misdirected filtration and filtrate spreading on the outer aspect of the nephron. Both may lead to obstruction of the tubule, disconnection from the glomerulus, and subsequent degeneration of the entire nephron. No evidence emerged to suggest that the kind of focal interstitial proliferation associated with the degeneration of injured nephrons was harmful to a neighboring healthy nephron.

Angiogenic protein Cyr61 is expressed by podocytes in anti-Thy-1 glomerulonephritis

Dynamic recovery of glomerular structure occurs after severe glomerular damage in anti-Thy-1 glomerulonephritis (Thy-1 GN), but its mechanism remains to be investigated. To identify candidate genes possibly involved in glomerular reconstruction, screening was performed for genes that are specifically expressed by podocytes and are upregulated in glomeruli of Thy-1 GN. Among them, cysteine-rich protein 61 (Cyr61 or CCN1), a soluble angiogenic protein belonging to the CCN family, was identified. By Northern blot analysis, Cyr61 mRNA was markedly upregulated in glomeruli of Thy-1 GN from day 3 through day 7, when mesangial cell migration was most prominent. By in situ hybridization and immunohistochemistry, Cyr61 mRNA and protein were expressed by proximal straight tubules and afferent and efferent arterioles in normal rat kidneys and were intensely upregulated at podocytes in Thy-1 GN. Platelet-derived growth factor-BB (PDGF-BB) and transforming growth factor-beta1 (TGF-beta1), of which the gene expression in the glomeruli of Thy-1 GN was upregulated in similar time course as Cyr61, induced Cyr61 mRNA expression in cultured podocytes. Furthermore, supernatant of Cyr61-overexpressing cells inhibited PDGF-induced mesangial cell migration. In conclusion, it is shown that Cyr61 is strongly upregulated at podocytes in Thy-1 GN possibly by PDGF and TGF-beta. Cyr61 may be involved in glomerular remodeling as a factor secreted from podocytes to inhibit mesangial cell migration.

Novel insights into renal fibrosis

PURPOSE OF REVIEW

Renal fibrosis characterizes a common endpoint of diverse renal diseases which leads to functional impairment ultimately resulting in terminal renal failure.

RECENT FINDINGS

Recent advances in this field led to the discovery of several novel mediators as well as novel aspects of known mediators. Studies on the origin and role of specific renal cell types involved in renal fibrosis identified bone marrow derived mesangial progenitors and offered substantial evidence for the concept of epithelial to mesenchymal transition. Much progress has also been made in better understanding of the interactions between different mediators and between mediators and renal target cells. Compounds designed on the basis of this current knowledge have proven to be potent inhibitors of the development of renal fibrosis or might even induce resolution of renal fibrosis.

SUMMARY

The number and diversity of recent studies in this field offer hope for new treatment regimes in our clinical efforts towards prevention and regression of progressive fibrosing renal diseases.

Myofibroblast differentiation: plasma membrane microdomains and cell phenotype

Myofibroblast differentiation characterizes a prominent cellular phenotype identified in experimental models of progressive kidney disease and human kidney biopsies. Mesangial cells, tubulointerstitial fibroblasts and, perhaps, tubular epithelial cells undergo myofibroblast differentiation, a process characterized by alpha-actin expression, synthesis of interstitial collagens and a growth response. Inhibition of myofibroblast differentiation could prevent kidney disease progression but may be difficult to accomplish, since inhibition of multiple signaling pathways would be required. Cell biology advances have enabled a better understanding of how information from many microenvironmental stimuli are integrated by spatial compartmentalization of extracellular receptors and cytosolic signaling molecules within specialized plasma membrane domains, such as focal adhesions and lipid rafts. We review this information and hypothesize that myofibroblast differentiation of renal cells can only proceed if the spatial arrangement of intracellular molecules, in large part determined by extracellular matrix-regulated cytoskeletal organization, permits activation of appropriate signaling pathways by soluble molecules interacting with receptors in specialized plasma membrane microdomains. If proven, this hypothesis suggests targeting key molecules within adhesion complexes and rafts (in some cases with drugs that are already clinically available) may provide more effective therapy for kidney disease progression.