The distribution and regulation of integrin-linked kinase in normal and diabetic kidneys

Biochemical composition of the glomerular extracellular matrix in patients with diabetic kidney disease

In the glomeruli, mesangial cells produce mesangial matrix while podocytes wrap glomerular capillaries with cellular extensions named foot processes and tether the glomerular basement membrane (GBM). The turnover of the mature GBM and the ability of adult podocytes to repair injured GBM are unclear. The actin cytoskeleton is a major cytoplasmic component of podocyte foot processes and links the cell to the GBM. Predominant components of the normal glomerular extracellular matrix (ECM) include glycosaminoglycans, proteoglycans, laminins, fibronectin-1, and several types of collagen. In patients with diabetes, multiorgan composition of extracellular tissues is anomalous, including the kidney, so that the constitution and arrangement of glomerular ECM is profoundly altered. In patients with diabetic kidney disease (DKD), the global quantity of glomerular ECM is increased. The level of sulfated proteoglycans is reduced while hyaluronic acid is augmented, compared to control subjects. The concentration of mesangial fibronectin-1 varies depending on the stage of DKD. Mesangial type III collagen is abundant in patients with DKD, unlike normal kidneys. The amount of type V and type VI collagens is higher in DKD and increases with the progression of the disease. The GBM contains lower amount of type IV collagen in DKD compared to normal tissue. Further, genetic variants in the α3 chain of type IV collagen may modulate susceptibility to DKD and end-stage kidney disease. Human cellular models of glomerular cells, analyses of human glomerular proteome, and improved microscopy procedures have been developed to investigate the molecular composition and organization of the human glomerular ECM.

C3a receptor blockade protects podocytes from injury in diabetic nephropathy

Renal activation of the complement system has been described in patients with diabetic nephropathy (DN), although its pathological relevance is still ill-defined. Here, we studied whether glomerular C3a, generated by uncontrolled complement activation, promotes podocyte damage, leading to proteinuria and renal injury in mice with type 2 diabetes. BTBR ob/ob mice exhibited podocyte loss, albuminuria, and glomerular injury accompanied by C3 deposits and increased C3a and C3a receptor (C3aR) levels. Decreased glomerular nephrin and α-actinin4 expression, coupled with integrin-linked kinase induction, were also observed. Treatment of DN mice with a C3aR antagonist enhanced podocyte density and preserved their phenotype, limiting proteinuria and glomerular injury. Mechanistically, ultrastructural and functional mitochondrial alterations, accompanied by downregulation of antioxidant superoxide dismutase 2 (SOD2) and increased protein oxidation, occurred in podocytes and were normalized by C3aR blockade. In cultured podocytes, C3a induced cAMP-dependent mitochondrial fragmentation. Alterations of mitochondrial membrane potential, SOD2 expression, and energetic metabolism were also found in response to C3a. Notably, C3a-induced podocyte motility was inhibited by SS-31, a peptide with mitochondrial protective effects. These data indicate that C3a blockade represents a potentially novel therapeutic strategy in DN for preserving podocyte integrity through the maintenance of mitochondrial functions.

Integrin-Linked Kinase Deficiency in Collecting Duct Principal Cell Promotes Necroptosis of Principal Cell and Contributes to Kidney Inflammation and Fibrosis

BACKGROUND

Necroptosis is a newly discovered cell death pathway that plays a critical role in AKI. The involvement of integrin-linked kinase (ILK) in necroptosis has not been studied.

METHODS

We performed experiments in mice with an Ilk deletion in collecting duct (CD) principal cells (PCs), and cultured tubular epithelial cells treated with an ILK inhibitor or ILK siRNA knockdown.

RESULTS

Ilk deletion in CD PCs resulted in acute tubular injury and early mortality in mice. Progressive interstitial fibrosis and inflammation associated with the activation of the canonical TGF-β signaling cascade were detected in the kidneys of the mice lacking ILK in the CD PCs. In contrast to the minimal apoptosis detected in the animals' injured CDs, widespread necroptosis was present in ILK-deficient PCs, characterized by cell swelling, deformed mitochondria, and rupture of plasma membrane. In addition, ILK deficiency resulted in increased expression and activation of necroptotic proteins MLKL and RIPK3, and membrane translocation of MLKL in CD PCs. ILK inhibition and siRNA knockdown reduced cell survival in cultured tubular cells, concomitant with increased membrane accumulation of MLKL and/or phospho-MLKL. Administration of a necroptosis inhibitor, necrostatin-1, blocked cell death in vitro and significantly attenuated inflammation, interstitial fibrosis, and renal failure in ILK-deficient mice.

CONCLUSIONS

The study demonstrates the critical involvement of ILK in necroptosis through modulation of the RIPK3 and MLKL pathway and highlights the contribution of CD PC injury to the development of inflammation and interstitial fibrosis of the kidney.

Chronic kidney disease induced by an adenine rich diet upregulates integrin linked kinase (ILK) and its depletion prevents the disease progression

Kidney fibrosis is one of the main pathological findings of progressive chronic kidney disease (CKD) although the pathogenesis of renal scar formation remains incompletely explained. Integrin-linked kinase (ILK), a major scaffold protein between the extracellular matrix (ECM) and intracellular signaling pathways, is involved in several pathophysiological processes during renal damage. However, ILK contribution in the CKD progress remains to be fully elucidated. In the present work, we studied 1) the renal functional and structural consequences of CKD genesis and progression when ILK is depleted and 2) the potential of ILK depletion as a therapeutic approach to delay CKD progression. We induced an experimental CKD model, based on an adenine-supplemented diet on adult wild-type (WT) and ILK-depleted mice, with a tubulointerstitial damage profile resembling that is observed in human CKD. The adenine diet induced in WT mice a progressive increase in plasma creatinine and urea concentrations. In the renal cortex it was also observed tubular damage, interstitial fibrosis and progressive increased ECM components, pro-inflammatory and chemo-attractant cytokines, EMT markers and TGF-β1 expressions. These observations were highly correlated to a simultaneous increase of ILK expression and activity. In adenine-fed transgenic ILK-depleted mice, all these changes were prevented. Additionally, we evaluated the potential role of ILK depletion to be applied after the disease induction, as an effective approach to interventions in human CKD subjects. In this scenario, two weeks after the establishment of adenine-induced CKD, ILK was abrogated in WT mice and stabilized renal damage, avoiding CKD progression. We propose ILK to be a potential target to delay renal disease progression.

TGF-β: the connecting link between nephropathy and fibrosis

Renal fibrosis is the usual outcome of an excessive accumulation of extracellular matrix (ECM) that frequently occurs in membranous and diabetic nephropathy. The result of renal fibrosis would be end-stage renal failure, which requires costly dialysis or kidney transplantation. Renal fibrosis typically results from chronic inflammation via production of several molecules, such as growth factors, angiogenic factors, fibrogenic cytokines, and proteinase. All of these factors can stimulate excessive accumulation of ECM components through epithelial to mesenchymal transition (EMT), which results in renal fibrosis. Among these, transforming growth factor-beta (TGF-β) is proposed to be the major regulator in inducing EMT. Besides ECM protein synthesis, TGF-β is involved in hypertrophy, proliferation, and apoptosis in renal cells. In particular, TGF-β is likely to be most potent and ubiquitous profibrotic factor acting through several intracellular signaling pathways including protein kinases and transcription factors. Factors that regulate TGF-β expression in renal cell include hyperglycemia, angiotensin II, advance glycation end products, complement activation (C5b-9), and oxidative stress. Over the past several years, the common understanding of the pathogenic factors that lead to renal fibrosis in nephropathy has improved considerably. This review will discuss the recent findings on the mechanisms and role of TGF-β in membranous and diabetic nephropathy.

Rethinking glomerular basement membrane thickening in diabetic nephropathy: adaptive or pathogenic?

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease in the United States and is a major cause of cardiovascular disease and death. DN develops insidiously over a span of years before clinical manifestations, including microalbuminuria and declining glomerular filtration rate (GFR), are evident. During the clinically silent period, structural lesions develop, including glomerular basement membrane (GBM) thickening, mesangial expansion, and glomerulosclerosis. Once microalbuminuria is clinically apparent, structural lesions are often considerably advanced, and GFR decline may then proceed rapidly toward end-stage kidney disease. Given the current lack of sensitive biomarkers for detecting early DN, a shift in focus toward examining the cellular and molecular basis for the earliest structural change in DN, i.e., GBM thickening, may be warranted. Observed within one to two years following the onset of diabetes, GBM thickening precedes clinically evident albuminuria. In the mature glomerulus, the podocyte is likely key in modifying the GBM, synthesizing and assembling matrix components, both in physiological and pathological states. Podocytes also secrete matrix metalloproteinases, crucial mediators in extracellular matrix turnover. Studies have shown that the critical podocyte-GBM interface is disrupted in the diabetic milieu. Just as healthy podocytes are essential for maintaining the normal GBM structure and function, injured podocytes likely have a fundamental role in upsetting the balance between the GBM's synthetic and degradative pathways. This article will explore the biological significance of GBM thickening in DN by reviewing what is known about the GBM's formation, its maintenance during health, and its disruption in DN.

Echistatin prevents posterior capsule opacification in diabetic rabbit model via integrin linked kinase signaling pathway

PURPOSE

To investigate the effect of disintegrin echistatin on integrin linked kinase (ILK) and subsequent PI3-K/Akt and ERK1/2 signaling pathways in the posterior capsule opacification (PCO) model of diabetic rabbit.

METHODS

56 rabbits were injected alloxan to model diabetic. Then they accepted lens extraction surgery and randomly and intraoperatively injected distilled water (control group; n = 28) or 10.0 mg·L(-1) echistatin (echistatin-treated group; n = 28) into the anterior chamber. Each group was subdivided into ten days group (n = 14) and six weeks group (n = 14) respectively. The PCO severity was evaluated with a slit lamp microscope and light microscope for 10 days and 6 weeks postoperatively. The levels of ILK in the posterior capsule were determined by Q-PCR, Western blotting and Immunohistochemistry. Akt and ERK1/2 phosphorylation were analyzed by Western blotting.

RESULTS

10 days and 6 weeks after surgery, the grades of PCO in the echistatin-treated group were lower than the control group. The lens epithelial cells (LECs) in the posterior capsule of echistatin-treated eyes had decreased degrees of proliferation and migration than the control group. And no significant side effects appeared after treated with echistatin. Echistatin could significantly reduce the expression of ILK in terms of both mRNA and protein levels. The phosphorylation levels of Akt and ERK1/2 were decreased in the echistatin-treated group compared with the control group.

CONCLUSIONS

Echistatin could inhibit postoperative PCO occurrence and development in diabetic rabbit eyes, which may be related to down-regulation the expression of ILK and inhibition the PI3-K/Akt and ERK1/2 pathways.

Gemigliptin improves renal function and attenuates podocyte injury in mice with diabetic nephropathy

Podocytes participate in the formation and regulation of the glomerular filtration barrier. Loss of podocytes occurs during the early stages of diabetic nephropathy and impairs glomerular filtration. Dipeptidyl peptidase-4 (DPP-4) inhibitors are widely used as anti-diabetic agents in clinical practice. In this study, we showed that gemigliptin, a novel DPP-4 inhibitor, reduced podocyte apoptosis in type 2 diabetic db/db mice without reducing hyperglycemia. Gemigliptin (100mg/kg/day) was administered orally for 12 weeks in db/db mice. Blood glucose levels and albuminuria were measured. The renal cortex was collected for histological examination, and molecular assays were used to detect 8-hydroxydeoxyguanosine, advanced oxidation protein products (AOPP), the receptor for advanced glycation end products (RAGE), and integrin-linked kinase (ILK). Type 2 diabetic db/db mice exhibited albuminuria, renal histopathological changes, and podocyte loss. Administration of gemigliptin to db/db mice suppressed albuminuria, enzyme activity and expression of DPP-4, and podocyte apoptosis. The effect of gemigliptin on diabetes-induced podocyte loss was associated with the suppression of oxidative damage, AOPP accumulation, RAGE expression, and ILK expression. These results indicate the possible benefits of using gemigliptin in diabetes patients to treat renal impairment without affecting glycemic control.

Renin-angiotensin system within the diabetic podocyte

Diabetic kidney disease is the leading cause of end-stage renal disease. Podocytes are differentiated cells necessary for the development and maintenance of the glomerular basement membrane and the capillary tufts, as well as the function of the glomerular filtration barrier. The epithelial glomerular cells express a local renin-angiotensin system (RAS) that varies in different pathological situations such as hyperglycemia or mechanical stress. RAS components have been shown to be altered in diabetic podocytopathy, and their modulation may modify diabetic nephropathy progression. Podocytes are a direct target for angiotensin II-mediated injury by altered expression and distribution of podocyte proteins. Furthermore, angiotensin II promotes podocyte injury indirectly by inducing cellular hypertrophy, increased apoptosis, and changes in the anionic charge of the glomerular basement membrane, among other effects. RAS blockade has been shown to decrease the level of proteinuria and delay the progression of chronic kidney disease. This review summarizes the local intraglomerular RAS and its imbalance in diabetic podocytopathy. A better understanding of the intrapodocyte RAS might provide a new approach for diabetic kidney disease treatment.

Benazepril affects integrin-linked kinase and smooth muscle α-actin expression in diabetic rat glomerulus and cultured mesangial cells

Background

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease and is associated with excessive cardiovascular morbidity and mortality. The angiotensin converting enzyme inhibitor (ACEI) benazepril has been shown to slow the progression of chronic renal disease and have beneficial effects in patients with a combination of chronic renal disease and cardiovascular disease. Transforming growth factor-β₁ (TGF-β₁) plays a central role in the pathogenesis and progression of DN. Integrin-linked kinase (ILK) can modulate TGF-β₁-induced glomerular mesangial cell (GMC) injury, which is a prominent characteristic of renal pathology in kidney diseases. As an integrin cytoplasmic-binding protein, ILK regulates fibronectin (FN) matrix deposition and the actin cytoskeleton. Smooth muscle α-actin (α-SMA) is involved in progressive renal dysfunction in both human and experimental renal disease.

Methods

To explore the mechanisms of benazepril’s reno-protective effects, we examined the expression of TGF-β₁, ILK, and α-SMA in GMC exposed to high glucose (HG) and in the kidneys of streptozotocin (STZ)-induced diabetic rats using real-time quantitative RT-PCR and western blot analysis. To elucidate the mechanism(s) of the effect of benazepril on GMC cellular processes, we assessed the effect of benazepril on Angiotensin II (Ang II) signalling pathways using western blot analysis.

Results

The expression of TGF-β₁, ILK, and α-SMA increased significantly in the diabetic group compared with the control group. Benazepril treatment inhibited the expression of these genes in DN but failed to rescue the same levels in the control group. Similar results were found in GMC treated with HG or benazepril. Ang II increased ERK and Akt phosphorylation in the HG group, and benazepril could not completely block these responses, suggesting that other molecules might be involved in the progression of DN. Our findings suggest that benazepril decreases ILK and α-SMA expression, at least in part, by affecting the interactions between Ang II and TGF-β₁.

Conclusions

The findings described here support the hypothesis that the HG milieu of diabetes increases TGF-β₁ secretion, which increases the synthesis of ILK and α-SMA that are involved in the progression of DN. This might be an important mechanism of the benazepril renal-protective function in the pathogenesis of DN.

Astragaloside IV ameliorates diabetic nephropathy involving protection of podocytes in streptozotocin induced diabetic rats

Podocyte loss and dysfunction play key role during the development of diabetic nephropathy (DN). The aim of this study was to observe the protective effects of astragaloside IV on podocyte in diabetic rats and explore its mechanisms preliminary. Healthy male Sprague-Dawley (SD) rats were randomized into normal control group, diabetic nephropathy group and diabetic nephropathy with AS-IV treatment group. DN was induced by intraperitoneal injection of streptozotocin (STZ). AS-IV treatment started 2 weeks before STZ injection and lasted 14 weeks. 24h Urinary proteins were measured 4, 8 and 12 weeks after STZ injection. Body weight, blood glucose, blood urea nitrogen (BUN), creatinine (Cr), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured 12 weeks after STZ injection. Renal pathology, podocyte morphological changes, podocyte density, protein and mRNA expression of integrin α3, integrin β1 and integrin-linked kinase (ILK) were detected by histopathology, electron microscopy, immunohistochemistry, western blot and real-time PCR, respectively. Hyperglycemia, proteinuria, mesangial expansion and podocyte loss, increased protein expression of ILK and decreased protein expression of integrin α3 and integrin β1 were detected in diabetic rats. AS-IV treatment ameliorated podocyte loss, renal histopathology and podocyte foot process effacement, decreased proteinuria, partially restored protein expression of integrin α3, integrin β1 and ILK. These findings suggested that AS-IV may protect podocyte and ameliorate diabetic nephropathy by inhibiting the expression of ILK and restoring the expression of integrin α3β1 in diabetic rats.

Integrin-linked kinase plays a key role in the regulation of angiotensin II-induced renal inflammation

ILK (integrin-linked kinase) is an intracellular serine/threonine kinase involved in cell-matrix interactions. ILK dysregulation has been described in chronic renal disease and modulates podocyte function and fibrosis, whereas data about its role in inflammation are scarce. AngII (angiotensin II) is a pro-inflammatory cytokine that promotes renal inflammation. AngII blockers are renoprotective and down-regulate ILK in experimental kidney disease, but the involvement of ILK in the actions of AngII in the kidney has not been addressed. Therefore we have investigated whether ILK signalling modulates the kidney response to systemic AngII infusion in wild-type and ILK-conditional knockout mice. In wild-type mice, AngII induced an inflammatory response, characterized by infiltration of monocytes/macrophages and lymphocytes, and up-regulation of pro-inflammatory factors (chemokines, adhesion molecules and cytokines). AngII activated several intracellular signalling mechanisms, such as the NF-κB (nuclear factor κB) transcription factor, Akt and production of ROS (reactive oxygen species). All these responses were prevented in AngII-infused ILK-deficient mice. In vitro studies characterized further the mechanisms regulating the inflammatory response modulated by ILK. In cultured tubular epithelial cells ILK blockade, by siRNA, inhibited AngII-induced NF-κB subunit p65 phosphorylation and its nuclear translocation. Moreover, ILK gene silencing prevented NF-κB-related pro-inflammatory gene up-regulation. The results of the present study demonstrate that ILK plays a key role in the regulation of renal inflammation by modulating the canonical NF-κB pathway, and suggest a potential therapeutic target for inflammatory renal diseases.

Matrix metalloproteinase-9 deficiency attenuates diabetic nephropathy by modulation of podocyte functions and dedifferentiation

Diabetic nephropathy is characterized by excessive deposition of extracellular matrix protein and disruption of the glomerular filtration barrier. Matrix metalloproteinases (MMPs) affect the breakdown and turnover of extracellular matrix protein, suggesting that altered expression of MMPs may contribute to diabetic nephropathy. Here we used an MMP-9 gene knockout mouse model, with in vitro experiments and clinical samples, to determine the possible role of MMP-9 in diabetic nephropathy. After 6 months of streptozotocin-induced diabetes, mice developed markedly increased albuminuria, glomerular and kidney hypertrophy, and thickening of the glomerular basement membrane. Gelatin zymographic analysis and western blotting showed that there was enhanced MMP-9 protein production and activity in the glomeruli. However, MMP-9 knockout in diabetic mice significantly attenuated these nephropathy changes. In cultured podocytes, various cytokines related to diabetic nephropathy including TGF-β1, TNF-α, and VEGF stimulated MMP-9 secretion. Overexpression of endogenous MMP-9 induced podocyte dedifferentiation. MMP-9 also interrupted podocyte cell integrity, promoted podocyte monolayer permeability to albumin, and extracellular matrix protein synthesis. In diabetic patients, the upregulation of urinary MMP-9 concentrations occurred earlier than the onset of microalbuminuria. Thus, MMP-9 seems to play a role in the development of diabetic nephropathy.

Shiga toxin promotes podocyte injury in experimental hemolytic uremic syndrome via activation of the alternative pathway of complement

Shiga toxin (Stx)-producing Escherichia coli is the offending agent of postdiarrhea-associated hemolytic uremic syndrome (HUS), a disorder of glomerular ischemic damage and widespread microvascular thrombosis. We previously documented that Stx induces glomerular complement activation, generating C3a responsible for microvascular thrombosis in experimental HUS. Here, we show that the presence of C3 deposits on podocytes is associated with podocyte damage and loss in HUS mice generated by the coinjection of Stx2 and LPS. Because podocyte adhesion to the glomerular basement membrane is mediated by integrins, the relevance of integrin-linked kinase (ILK) signals in podocyte dysfunction was evaluated. Podocyte expression of ILK increased after the injection of Stx2/LPS and preceded the upregulation of Snail and downregulation of nephrin and α-actinin-4. Factor B deficiency or pretreatment with an inhibitory antibody to factor B protected mice against Stx2/LPS-induced podocyte dysregulation. Similarly, pretreatment with a C3a receptor antagonist limited podocyte loss and changes in ILK, Snail, and α-actinin-4 expression. In cultured podocytes, treatment with C3a reduced α-actinin-4 expression and promoted ILK-dependent nuclear expression of Snail and cell motility. These results suggest that Stx-induced activation of the alternative pathway of complement and generation of C3a promotes ILK signaling, leading to podocyte dysfunction and loss in Stx-HUS.

The importance of podocyte adhesion for a healthy glomerulus

Podocytes are specialized epithelial cells that cover the outer surfaces of glomerular capillaries. Unique cell junctions, known as slit diaphragms, which feature nephrin and Neph family proteins in addition to components of adherens, tight, and gap junctions, connect adjacent podocyte foot processes. Single gene disorders affecting the slit diaphragm result in nephrotic syndrome in humans, characterized by massive loss of protein across the capillary wall. In addition to specialized cell junctions, interconnecting podocytes also adhere to the glomerular basement membrane (GBM) of the capillary wall. The GBM is a dense network of secreted, extracellular matrix (ECM) components and contains tissue-restricted isoforms of collagen IV and laminin in addition to other structural proteins and ECM regulators such as proteases and growth factors. The specialized niche of the GBM provides a scaffold for endothelial cells and podocytes to support their unique functions and human genetic mutations in GBM components lead to renal failure, thus highlighting the importance of cell-matrix interactions in the glomerulus. Cells adhere to ECM via adhesion receptors, including integrins, syndecans, and dystroglycan and in particular the integrin heterodimer α3β1 is required to maintain barrier integrity. Therefore, the sophisticated function of glomerular filtration relies on podocyte adhesion both at cell junctions and at the interface with the ECM. In health, the podocyte coordinates signals from cell junctions and cell-matrix interactions, in response to environmental cues in order to regulate filtration and as our understanding of mechanisms that control cell adhesion in the glomerulus develops, then insight into the effects of disease will improve. The ultimate goal will be to develop targeted therapies to prevent or repair defects in the filtration barrier and to restore glomerular function.

Cell-matrix adhesion of podocytes in physiology and disease

Cell-matrix adhesion is crucial for maintaining the mechanical integrity of epithelial tissues. Podocytes--a key component of the glomerular filtration barrier--are exposed to permanent transcapillary filtration pressure and must therefore adhere tightly to the underlying glomerular basement membrane (GBM). The major cell-matrix adhesion receptor in podocytes is the integrin α3β1, which connects laminin 521 in the GBM through various adaptor proteins to the intracellular actin cytoskeleton. Other cell-matrix adhesion receptors expressed by podocytes include the integrins α2β1 and αvβ3, α-dystroglycan, syndecan-4 and type XVII collagen. Mutations in genes encoding any of the components critical for podocyte adhesion cause glomerular disease. This Review highlights recent advances in our understanding of the cell biology and genetics of podocyte adhesion with special emphasis on glomerular disease.

Attenuation of glomerular filtration barrier damage in adriamycin-induced nephropathic rats with bufalin: an antiproteinuric agent

Proteinuria is an important risk factor for the progression and prognosis of chronic kidney disease. Bufalin, a cardiotonic steroid, has been shown to posses a variety of biological activities including cardiotonic, anaesthetic and antineoplastic activities, and regulate the immune response. This study investigated the effects of bufalin against proteinuria and glomerular filtration barrier damage in rats with adriamycin (ADR)-induced nephropathy. We compared the blood and urine biochemical indices and the histologic and ultrastructure of the glomerulus in ADR rats with and without the intervention of bufalin or prednisone. The transcription, expression and distribution of the podocyte-associated molecules were compared utilising RT-PCR, western blotting and immunohistochemical staining. We found that bufalin reduced the urinary protein excretion and optimised the lipidaemia of the ADR rats. Bufalin alleviated the removal of podocyte foot processes and attenuated the changes in nephrin, podocin and integrin-linked kinase (ILK) stainings in the glomerulus of the ADR rats. Bufalin notably decreased the expression of nephrin and ILK but inhibited the down-regulation of podocin in protein levels on the renal cortex of the ADR rats. Additionally, bufalin inhibited the up-regulation of podocin and ILK in mRNA levels but did not affect nephrin mRNA levels. These results suggest that bufalin could alleviate ADR-induced proteinuria by protecting the glomerular filtration barrier and may be a novel potential therapeutic agent for proteinuria-associated kidney disease.

Glomerular expression of hydrogen peroxide-inducible clone-5 in human and rat progressive mesangial proliferative glomerulonephritis

BACKGROUND/AIMS

Hydrogen peroxide-inducible clone-5 (Hic-5) is a transforming growth factor-β(1) (TGF-β(1))- and hydrogen peroxide (H(2)O(2))-inducible focal adhesion protein that may be necessary for maintaining the myofibroblastic phenotype in pathological scar formation. To investigate the involvement of Hic-5 in the pathogenesis of glomerulonephritis (GN), we examined the glomerular expression of Hic-5 in human and rat GN as well as the regulation of Hic-5 by TGF-β(1) in vitro.

METHODS AND RESULTS

Immunohistochemical analyses showed that the expression of Hic-5 was increased in mesangial cells (MCs) in human mesangial proliferative GN. Hic-5 expression was significantly correlated not only with the levels of α-smooth muscle actin (α-SMA) and TGF-β(1), the accumulation of extracellular matrix, and the number of glomerular cells, but also with the urinary protein level in patients with GN. Glomerular Hic-5 expression increased in parallel with α-SMA expression in a rat model of mesangial proliferative GN. Combined therapy with an angiotensin type I receptor blocker and an antioxidant in this model improved the histology and the expression of Hic-5 and α-SMA. TGF-β(1) upregulated Hic-5 and α-SMA protein levels in human cultured MCs.

CONCLUSION

Our findings suggest that Hic-5 is involved in changes in the MC phenotype to produce abnormal extracellular matrix remodeling in GN.

The glomerular podocyte as a target of growth hormone action: implications for the pathogenesis of diabetic nephropathy

Involvement of the growth hormone (GH) / insulin-like growth factor 1 (IGF-I) axis in the pathogenesis of diabetic nephropathy (DN) is strongly suggested by studies investigating the impact of GH excess and deficiency on renal structure and function. GH excess in both the human (acromegaly) and in transgenic animal models is characterized by significant structural and functional changes in the kidney. In the human a direct relationship has been noted between the activity of the GH/IGF-1 axis and renal hypertrophy, microalbuminuria, and glomerulosclerosis. Conversely, states of GH deficiency or deficiency or inhibition of GH receptor (GHR) activity confer a protective effect against DN. The glomerular podocyte plays a central and critical role in the structural and functional integrity of the glomerular filtration barrier and maintenance of normal renal function. Recent studies have revealed that the glomerular podocyte is a target of GH action and that GH's actions on the podocyte could be detrimental to the structure and function of the podocyte. These results provide a novel mechanism for GH's role in the pathogenesis of DN and offer the possibility of targeting the GH/IGF-1 axis for the prevention and treatment of DN.

Inhibition of integrin-linked kinase blocks podocyte epithelial-mesenchymal transition and ameliorates proteinuria

Proteinuria is a primary clinical symptom of a large number of glomerular diseases that progress to end-stage renal failure. Podocyte dysfunctions play a fundamental role in defective glomerular filtration in many common forms of proteinuric kidney disorders. Since binding of these cells to the basement membrane is mediated by integrins, we determined the role of integrin-linked kinase (ILK) in podocyte dysfunction and proteinuria. ILK expression was induced in mouse podocytes by various injurious stimuli known to cause proteinuria including TGF-beta1, adriamycin, puromycin, and high ambient glucose. Podocyte ILK was also found to be upregulated in human proteinuric glomerular diseases. Ectopic expression of ILK in podocytes decreased levels of the epithelial markers nephrin and ZO-1, induced mesenchymal markers such as desmin, fibronectin, matrix metalloproteinase-9 (MMP-9), and alpha-smooth muscle actin (alpha-SMA), promoted cell migration, and increased the paracellular albumin flux across podocyte monolayers. ILK also induced Snail, a key transcription factor mediating epithelial-mesenchymal transition (EMT). Blockade of ILK activity with a highly selective small molecule inhibitor reduced Snail induction and preserved podocyte phenotypes following TGF-beta1 or adriamycin stimulation. In vivo, this ILK inhibitor ameliorated albuminuria, repressed glomerular induction of MMP-9 and alpha-SMA, and preserved nephrin expression in murine adriamycin nephropathy. Our results show that upregulation of ILK is a convergent pathway leading to podocyte EMT, migration, and dysfunction. ILK may be an attractive target for therapeutic intervention of proteinuric kidney diseases.

Interaction of integrin-linked kinase and miniature chromosome maintenance 7-mediating integrin {alpha}7 induced cell growth suppression

Mutation of integrin alpha7 (ITGA7) was previously identified in multiple human malignancies. Restoration of ITGA7 expression in prostate cancer and leiomyosarcoma cell lines suppressed tumor growth and cell motility both in vitro and in vivo. In this study, we showed that integrin-linked kinase (ILK) binds with miniature chromosome maintenance 7 (MCM7), a DNA replication licensing protein. A 58-amino acid ILK binding motif was identified in the NH(2)-terminus of MCM7. The expression of ITGA7 induced the phosphorylation of MCM7. Knocking down of ILK abrogated ITGA7-induced MCM7 phosphorylation. ANK, the dominant-negative mutant of ILK, also blocked the phosphorylation of MCM7 induced by ITGA7. The phosphorylation of MCM7 reduced MCM7 chromatin association and inhibited cell growth. A MCM7 mutant that does not bind with ILK did not respond to ITGA7 stimulation, and behaved similarly to a dominant MCM7-negative mutant and neutralized the effect of ITGA7. We conclude that ILK interaction with MCM7 and MCM7 phosphorylation may be a critical event in ITGA7 signaling pathway, leading to tumor suppression.

Abnormalities in signaling pathways in diabetic nephropathy

Diabetic nephropathy (DN) is characterized by a plethora of signaling abnormalities that together ultimately result in the clinical and pathologic hallmarks of DN, namely progressive albuminuria followed by a gradual decline in glomerular filtration rate leading to kidney failure, and accompanied by podocyte loss, progressive glomerular sclerosis and, ultimately, progressive tubulointerstitial fibrosis. Over the past few years, the general understanding of the abnormalities in signaling pathways that lead to DN has expanded considerably. In this review, some of the important pathways that appear to be involved in driving this process are discussed, with special emphasis on newer findings and insights. Newer concepts regarding signaling changes in bradykinin, mTOR, JAK/STAT, MCP-1, VEGF, endothelial nitric oxide synthase, activated protein C and other pathways are discussed.

Integrin-linked kinase regulates migration and proliferation of human intestinal cells under a fibronectin-dependent mechanism

Integrin-linked kinase (ILK) plays a role in integrin signaling-mediated extracellular matrix (ECM)–cell interactions and also acts as a scaffold protein in functional focal adhesion points. In the present study, we investigated the expression and roles of ILK in human intestinal epithelial cells (IECs) in vivo and in vitro. Herein, we report that ILK and its scaffold-function interacting partners, PINCH-1, α-parvin, and β-parvin, are expressed according to a decreasing gradient from the bottom of the crypt (proliferative/undifferentiated) compartment to the tip of the villus (non-proliferative/differentiated) compartment, closely following the expression pattern of the ECM/basement membrane component fibronectin. The siRNA knockdown of ILK in human IECs caused a loss of PINCH-1, α-parvin, and β-parvin expression, along with a significant decrease in cell proliferation via a loss of cyclin D1 and an increase in p27 and hypophosphorylated pRb expression levels. ILK knockdown severely affected cell spreading, migration, and restitution abilities, which were shown to be directly related to a decrease in fibronectin deposition. All ILK knockdown-induced defects were rescued with exogenously deposited fibronectin. Altogether, our results indicate that ILK performs crucial roles in the control of human intestinal cell and crypt–villus axis homeostasis—especially with regard to basement membrane fibronectin deposition—as well as cell proliferation, spreading, and migration. J. Cell. Physiol. 222: 387–400, 2010. © 2009 Wiley-Liss, Inc.

New insights into epithelial-mesenchymal transition in kidney fibrosis

Epithelial-mesenchymal transition (EMT), a process by which differentiated epithelial cells undergo a phenotypic conversion that gives rise to the matrix-producing fibroblasts and myofibroblasts, is increasingly recognized as an integral part of tissue fibrogenesis after injury. However, the degree to which this process contributes to kidney fibrosis remains a matter of intense debate and is likely to be context-dependent. EMT is often preceded by and closely associated with chronic interstitial inflammation and could be an adaptive response of epithelial cells to a hostile or changing microenvironment. In addition to tubular epithelial cells, recent studies indicate that endothelial cells and glomerular podocytes may also undergo transition after injury. Phenotypic alteration of podocytes sets them in motion to functional impairment, resulting in proteinuria and glomerulosclerosis. Several intracellular signal transduction pathways such as TGFbeta/Smad, integrin-linked kinase (ILK) and Wnt/beta-catenin signaling are essential in controlling the process of EMT and presently are potential targets of antifibrotic therapy. This review highlights the current understanding of EMT and its underlying mechanisms to stimulate further discussion on its role, not only in the pathogenesis of renal interstitial fibrosis but also in the onset of podocyte dysfunction, proteinuria, and glomerulosclerosis.

Epithelial-mesenchymal transition as a potential explanation for podocyte depletion in diabetic nephropathy

BACKGROUND

Depletion of glomerular podocytes is an important feature of progressive diabetic nephropathy. Although the most plausible explanation for this podocyte depletion is detachment from the glomerular basement membrane after cellular apoptosis, the mechanism is unclear. Fibroblast-specific protein 1 (FSP1; encoded by the S100A4 gene) is a member of the S100 family of calcium-binding proteins and is constitutively expressed in the cytoplasm of tissue fibroblasts or epithelial cells converted into fibroblasts by means of epithelial-mesenchymal transition.

STUDY DESIGN

Retrospective cross-sectional analysis.

SETTINGS & PARTICIPANTS

109 patients with type 2 diabetes mellitus, of whom 43 (39%) underwent kidney biopsy.

PREDICTOR

Clinical stage (4 categories) and histological grade (5 categories) of diabetic nephropathy.

OUTCOME

FSP1 expression in podocytes in urine and glomeruli in kidney biopsy specimens.

MEASUREMENTS

Immunohistochemistry, real-time polymerase chain reaction, and in situ hybridization.

RESULTS

38 of 109 patients (35%) were normoalbuminuric, 16 (15%) had microalbuminuria, 8 (7%) had macroalbuminuria, and 47 (43%) had decreased kidney function. Approximately 95% of podocytes in urine sediment were not apoptotic, and 86% expressed FSP1. The number of FSP1-positive podocytes in urine sediment was significantly larger in patients with macroalbuminuria than in those with normoalbuminuria (P = 0.03). Intraglomerular expression of FSP1 occurred almost exclusively in podocytes from patients with diabetes, and the number of FSP1-positive podocytes was larger in glomeruli showing diffuse mesangiopathy than in those showing focal mesangiopathy (P = 0.01). The number also was larger in glomeruli with nodular lesions than in those without nodular lesions (P < 0.001). FSP1-positive podocytes selectively expressed Snail1 and integrin-linked kinase, a known trigger for epithelial-mesenchymal transition.

LIMITATIONS

Nonrepresentative study population.

CONCLUSIONS

These results suggest that the appearance of FSP1 in podocytes of patients with diabetes is associated with more severe clinical and pathological findings of diabetic nephropathy, perhaps because of induction of podocyte detachment through epithelial-mesenchymal transition-like phenomena.

Inhibition of integrin-linked kinase attenuates renal interstitial fibrosis

Integrin-linked kinase (ILK) is an intracellular serine/threonine protein kinase that regulates cell adhesion, survival, and epithelial-to-mesenchymal transition (EMT). In this study, we investigated the kinase activity of ILK during tubular EMT induced by TGF-beta1 and examined the therapeutic potential of an ILK inhibitor in obstructive nephropathy. TGF-beta1 induced a biphasic activation of ILK in renal tubular epithelial cells, with rapid activation starting at 5 min and the second wave of activation peaking at 24 h; the latter paralleled the induction of ILK protein expression. Pharmacologic inhibition of ILK with small-molecule inhibitor QLT-0267 abolished TGF-beta1-induced phosphorylation of Akt and glycogen synthase kinase-3beta, suppressed cyclin D1 expression, and largely restored the expression of E-cadherin and zonula occludens 1. Inhibition of ILK also blocked TGF-beta1-mediated induction of fibronectin, Snail1, plasminogen activator inhibitor 1, and matrix metalloproteinase 2. In a mouse model of obstructive nephropathy, administration of QLT-0267 inhibited beta-catenin accumulation; suppressed Snail1, alpha-smooth muscle actin, fibronectin, vimentin, and type I and type III collagen expression; and reduced total tissue collagen content. Inhibition of ILK did not affect kidney structure or function in normal mice. These findings suggest that increased ILK activity mediates EMT and the progression of renal fibrosis. Pharmacologic inhibition of ILK signaling may hold therapeutic potential for fibrotic kidney diseases.

Astragaloside IV improves high glucose-induced podocyte adhesion dysfunction via alpha3beta1 integrin upregulation and integrin-linked kinase inhibition

Impaired podocyte adhesion to glomerular basement membrane (GBM) may contribute to podocyte detachment from GBM, which represents a novel early mechanism leading to diabetic nephropathy (DN). Here, we examined the effects of Astragaloside IV (AS-IV), a saponin purified from Astragalus membranaceus (Fisch) Bge, on high glucose-induced cell adhesion dysfunction in cultured mouse podocytes. Cells were seeded into 96-well plates coated with basement membrane protein complex (BMC). The cells were incubated for 12h in media containing 30 mM glucose (HG) with 10, 50 and 100 microg/ml of AS-IV. The cells were also exposed to HG media with 100 microg/ml of AS-IV for 3, 6, 12 and 24h. Cell adhesion assays were performed by fluorescence and centrifugation methods, respectively. Levels of mRNA were determined by quantitative reverse transcriptase real-time PCR and protein expression was analyzed by immunoblotting. HG strongly inhibited adhesion of podocytes to BMC, accompanied by reduction in alpha(3)beta(1) integrin mRNA and protein expression, as well as increase in integrin-linked kinase (ILK) activity and expression. When podocytes under HG stimulation were treated with AS-IV, a dose- and time-dependent increase in cell-matrix adhesion was observed, which was significant from 10 microg/ml of AS-IV and from 6h of incubation of AS-IV with 100 microg/ml. This was accompanied by significant increases in alpha(3)beta(1) integrin mRNA and protein expression, as well as inhibition of ILK activation and overexpression. These results suggest that AS-IV improve HG-induced podocyte adhesion dysfunction, which is partly attributed to alpha(3)beta(1) integrin upregulation and ILK inhibition.

Roles of PINCH-2 in regulation of glomerular cell shape change and fibronectin matrix deposition

The PINCH-1-integrin-linked kinase (ILK)-alpha-parvin (PIP) complex plays important roles in the regulation of glomerular cell behavior, including podocyte shape change, apoptosis, and mesangial fibronectin matrix deposition. In this study, we show that PINCH-2, a protein that is structurally related to PINCH-1 but encoded by a different gene, is coexpressed with PINCH-1 in podocytes. Treatment of podocytes with transforming growth factor (TGF)-beta1 elevated the level of PINCH-2, resulting in increased association of PINCH-2 with ILK and alpha-parvin and concomitant displacement of PINCH-1 from the PIP complex. To gain insights into the functional consequences of elevated PINCH-2 expression, we overexpressed PINCH-2 in podocytes by infection with an adenovirus encoding PINCH-2. Overexpression of PINCH-2 resulted in displacement of PINCH-1 from the PIP complex and compromised podocyte spreading. The PINCH-2-mediated displacement of PINCH-1, however, did not prompt apoptosis. Interestingly, the effect of PINCH-2 on podocyte spreading depends on differentiation status, as overexpression of PINCH-2 in podocytes that were not fully differentiated did not alter cell spreading. Finally, we show that overexpression of PINCH-2 in mesangial cells resulted in displacement of PINCH-1 from the PIP complex but impaired neither mesangial cell spreading nor fibronectin matrix deposition. These studies suggest that PINCH-2 can substitute for PINCH-1 in at least certain processes in glomerular cells (e.g., podocyte survival signaling and mesangial fibronectin matrix deposition), albeit that an aberrantly high level of PINCH-2 may contribute to TGF-beta1-induced alteration in podocyte shape modulation.

Tissue-type plasminogen activator promotes murine myofibroblast activation through LDL receptor-related protein 1-mediated integrin signaling

The activation of interstitial fibroblasts to become alpha-SMA-positive myofibroblasts is an essential step in the evolution of chronic kidney fibrosis, as myofibroblasts are responsible for the production and deposition of the ECM components that are a hallmark of the disease. Here we describe a signaling pathway that leads to this activation. Tissue-type plasminogen activator (tPA) promoted TGF-beta1-mediated alpha-SMA and type I collagen expression in rat kidney interstitial fibroblasts. This fibrogenic effect was independent of its protease activity but required its membrane receptor, the LDL receptor-related protein 1 (LRP-1). In rat kidney fibroblasts, tPA induced rapid LRP-1 tyrosine phosphorylation and enhanced beta1 integrin recruitment by facilitating the LRP-1/beta1 integrin complex formation. Blockade or knockdown of beta1 integrin abolished type I collagen and alpha-SMA expression. Furthermore, inhibition of the integrin-linked kinase (ILK), a downstream effector of beta1 integrin, or disruption of beta1 integrin/ILK engagement, abrogated the tPA action, whereas ectopic expression of ILK mimicked tPA in promoting myofibroblast activation. In murine renal interstitium after obstructive injury, tPA and alpha-SMA colocalized with LRP-1, and tPA deficiency reduced LRP-1/beta1 integrin interaction and myofibroblast activation. These findings show that tPA induces LRP-1 tyrosine phosphorylation, which in turn facilitates the LRP-1-mediated recruitment of beta1 integrin and downstream ILK signaling, thereby leading to myofibroblast activation. This study implicates tPA as a fibrogenic cytokine that promotes the progression of kidney fibrosis.

Influence of irbesartan on expression of ILK and its relationship with epithelial-mesenchymal transition in mice with unilateral ureteral obstruction

AIM

Irbesartan, a new antagonist of the type 1 angiotensin II receptor, has been proven to be renal protective in both diabetic and non-diabetic nephropathy, but its exact mechanism is still uncertain. Here we investigated the influence of irbesartan on the expression of the integrin-linked kinase (ILK) and its relationship with epithelial-mesenchymal transition (EMT) in mice with unilateral ureteral obstruction (UUO).

METHODS

The mice were randomly divided into 3 groups: sham operation (C, n=20), UUO (n=40), and UUO with irbesartan treatment (UUO+irbesartan, n=40). Irbesartan was given at a dose of 50 mg/kg body weight per day by gavage. The experimental animals in the control group received the same volume of vehicle (0.9% saline solution). The animals were sacrificed at d 1, 3, 7, and 14, respectively, after the surgery.

RESULTS

The expression of the ILK at mRNA and protein levels were significantly increased in the UUO group 1 d after the surgery, which was significantly decreased by treatment with irbesartan (P<0.01, respectively). The expression of alpha-smooth muscle actin (alpha-SMA) was significantly increased, while E-cadherin was decreased in mice with UUO at d 3 after the surgery. Treatment with irbesartan significantly abrogated such effects (P<0.01). The immunohistochemistry analysis indicated that the protein expression of the ILK was positively correlated with alpha-SMA, but negatively with E-cadherin.

CONCLUSION

These results suggested that irbesartan attenuated renal tubulointerstitial fibrosis in UUO mice, which may be related to the inhibition of ILK expression, subsequently preventing the tubular EMT.

Inhibition of integrin-linked kinase via a siRNA expression plasmid attenuates connective tissue growth factor-induced human proximal tubular epithelial cells to mesenchymal transition

BACKGROUND

Increasing evidence suggests that connective tissue growth factor (CTGF) is involved in the epithelial-to-mesenchymal transition (EMT). The exact intracellular events that drive this process, however, are not fully understood. In this study, we investigated the role of integrin-linked kinase (ILK) in mediating CTGF-induced EMT.

METHODS

The expression of alpha-smooth muscle actin (alpha-SMA) and E-cadherin upon the stimulation by recombinant human CTGF (rhCTGF) in cultured human tubular epithelial cell line (HK-2) was detected by real-time RT-PCR and Western blot. Subsequently, the role of ILK was determined by using ILK siRNA.

RESULTS

rhCTGF increased the mRNA expression of alpha-SMA significantly in a dose- and time-dependent manner, while E-cadherin mRNA decreased in a dose- and time-dependent manner. alpha-SMA protein was up-regulated after stimulation by 5 ng/ml CTGF for 96 h, and increased further after stimulation by 50 ng/ml. An immunocytochemical study showed that alpha-SMA was initially detectable at 48 h, and increased further at 72 h, while there was almost no alpha-SMA immunostaining observed in the control group at the same time point. E-cadherin protein was also down-regulated in a dose-dependent manner. Transfection of HK-2 cells with ILK-siRNA significantly attenuated rhCTGF-induced alpha-SMA induction and E-cadherin repression.

CONCLUSION

Our study suggested that ILK mediated the effect of EMT in proximal tubular epithelial cells stimulated by CTGF.

Up-regulation of integrin-linked kinase in the streptozotocin-induced diabetic rat retina

OBJECTIVES

This study investigated whether integrin-linked kinase (ILK) is involved in the pathogenesis of diabetic retinopathy, by analyzing the expression and activity of ILK in the retina from a streptozotocin (STZ)-induced rat model of diabetes.

METHODS

ILK expression in the retina from both control and STZ-induced diabetic rats was measured by reverse transcription polymerase chain reaction, immunohistochemistry and Western blot analysis. The expressions of Akt and FOXO1A, the downstream molecules of ILK, were also examined.

RESULTS

The present study showed that the STZ-induced diabetes was associated with the increase in the vascular permeability in the retina. This elevated vascular permeability increased with the progression of diabetic retinopathy. Meanwhile, the results also showed that the expression of ILK increased in protein and mRNA levels in the retina of STZ-induced diabetic rats. Immunohistochemistry showed that immunostaining of ILK was localized in the outer plexiform layer (OPL), the inner nuclear layer (INL), the inner plexiform layer (IPL), the ganglion cell layer (GCL) and the retinal microvasculature of rats. However, the expression of Akt was reduced in the retinas at 8 and 12 weeks and increased in the retinas at 4 weeks after induction of diabetes. Meanwhile, the expression of the FOXO1A protein increased in the retinas at 8 and 12 weeks and decreased in the retinas at 4 weeks after induction of diabetes. The FOXO1A immunostaining was also observed in the retinal microvasculature and in the OPL, INL, IPL and GCL of rat retinas.

CONCLUSION

These results indicate that diabetes affects the expression of ILK in the retina. ILK may be involved in the diabetes-induced damage and/or alterations of neural and microvascular structures.

Role of ERK1/2 and PI3-K in the regulation of CTGF-induced ILK expression in HK-2 cells

BACKGROUND

Previous studies revealed that integrin-linked kinase (ILK), an intracellular serine/threonine protein kinase, is a critical mediator for tubular epithelial to mesenchymal transition (EMT), and likely plays an important role in the pathogenesis of chronic kidney fibrosis. However, the exact signal pathway has not been well understood. In this study, we investigated the role of extracellular regulating kinase 1/2 (ERK1/2) and phosphatidylinositol 3-kinase (PI3-K) in the regulation of ILK expression by connective tissue growth factor (CTGF) in HK-2 cells.

METHODS

Experiments were performed on transformed (human kidney cell (HKC)-clone 2) human proximal tubular epithelial cells (PTECs). Induction of ILK in response to CTGF was studied at the mRNA level by real-time PCR and protein by immunoblotting. Chemical inhibitors were used to assess the role of MEK/ERK1/2, PI3-K, and P38 MAPK signaling pathways in induction of ILK by CTGF.

RESULTS

CTGF induced ILK protein expression in HK-2 cells in a time- and dose-dependent manner. There was a 5.638-fold (control: 1.000+/-0.290, 50 ng/ml: 5.638+/-1.200; *P<0.05 vs. control) and 5.740-fold (0 h: 1.000+/-0.498, 48 h: 5.740+/-1.465, *P<0.05 vs. control) increase compared to control respectively. CTGF-induced ILK expression was partially reduced by inhibiting ERK1/2 and PI3-K activation. There was no influence of ILK expression by inhibiting P38 MAPK activation when cells treated with CTGF.

CONCLUSION

CTGF induces the expression of ILK protein in HK-2 cells. This induction is partially dependent on MEK/ERK1/2 and PI3-K signaling pathways. Inhibiting CTGF-induced ILK by targeting PI3-K and/or MEK/ERK1/2 signaling pathways could be of therapeutic value in renal fibrosis.

Interaction of integrin-linked kinase with the kidney chloride/bicarbonate exchanger, kAE1

Kidney anion exchanger 1 (kAE1) mediates chloride/bicarbonate exchange at the basolateral membrane of kidney alpha-intercalated cells, thereby facilitating bicarbonate reabsorption into the blood. Human kAE1 lacks the N-terminal 65 residues of the erythroid form (AE1, band 3), which are essential for binding of cytoskeletal and cytosolic proteins. Yeast two-hybrid screening identified integrin-linked kinase (ILK), a serine/threonine kinase, and an actin-binding protein as an interacting partner with the N-terminal domain of kAE1. Interaction between kAE1 and ILK was confirmed in co-expression experiments in HEK 293 cells and is mediated by a previously unidentified calponin homology domain in the kAE1 N-terminal region. The calponin homology domain of kAE1 binds the C-terminal catalytic domain of ILK to enhance association of kAE1 with the actin cytoskeleton. Overexpression of ILK increased kAE1 levels at the cell surface as shown by flow cytometry, cell surface biotinylation, and anion transport activity assays. Pulse-chase experiments revealed that ILK associates with kAE1 early in biosynthesis, likely in the endoplasmic reticulum. ILK co-localized with kAE1 at the basolateral membrane of polarized Madin-Darby canine kidney cells and in alpha-intercalated cells of human kidneys. Taken together these results suggest that ILK and kAE1 traffic together from the endoplasmic reticulum to the basolateral membrane. ILK may provide a linkage between kAE1 and the underlying actin cytoskeleton to stabilize kAE1 at the basolateral membrane, resulting in higher levels of cell surface expression.

TGF-β1 Regulates the PINCH-1–Integrin-Linked Kinase–α-Parvin Complex in Glomerular Cells

Glomerular damage is a major cause of renal failure. Recent studies suggest that a ternary protein complex that consists of PINCH-1, integrin-linked kinase, and alpha-parvin, cytoplasmic components of cell-extracellular matrix adhesions, plays pivotal roles in regulation of glomerular cell behavior. It is reported here that TGF-beta1, a key factor in the progression of glomerular failure, regulates the PINCH-1-integrin-linked kinase-alpha-parvin (PIP) complex formation in glomerular podocytes and mesangial cells. Treatment of podocytes with TGF-beta1 inhibited the PIP complex formation. Forced disruption of the PIP complex in podocytes activated p38 mitogen-activated protein kinase and promoted apoptosis. Importantly, inhibition of p38 mitogen-activated protein kinase, either with a chemical p38 inhibitor (SB202190) or with a dominant negative form of p38alpha, alleviates podocyte apoptosis that is induced by the disruption of the PIP complex. In contrast to an inhibitory role in podocytes, TGF-beta1 promotes the PIP complex formation in mesangial cells. Thus, TGF-beta1 regulates the PIP complex in a cell type-dependent manner. Because the PIP complex promotes glomerular mesangial matrix deposition and protects podocytes from apoptosis, the TGF-beta1-induced up- and downregulation of the PIP complex likely contribute to the pleiotropic effects of TGF-beta1 on different glomerular cell types and hence the progression of glomerular failure.

ELMO1 increases expression of extracellular matrix proteins and inhibits cell adhesion to ECMs

We have previously identified the engulfment and cell motility 1 (ELMO1) as a susceptibility gene for diabetic nephropathy. To elucidate the role of ELMO1 in the pathogenesis of chronic renal injury, we examined the expression of Elmo1 in the kidney of a rat model for chronic glomerulonephritis (uninephrectomy plus anti-Thy1.1 antibody [E30] injection). We found that the expression of the Elmo1 was significantly increased in the renal cortex and glomeruli of uninephrectomized rats injected with E30 compared to controls. By in situ hybridization, the expression of Elmo1 was shown to be elevated in the diseased kidney, especially in glomerular epithelial cells. In COS cells, the overexpression of ELMO1 resulted in a substantial increase in fibronectin expression, whereas the depletion of the ELMO1 by small interfering RNA (siRNA) targeting ELMO1 significantly suppressed the fibronectin expression in ELMO1 overexpressing and control cells. We also found that the expression of integrin-linked kinase (ILK) was significantly increased in ELMO1 overexpressing cells, and the ELMO1-induced increase in fibronectin was partially, but significantly, inhibited by siRNA targeting ILK. Furthermore, we identified that the cell adhesion to ECMs was considerably inhibited in cells overexpressing ELMO1. These results suggest that the ELMO1 contributes to the development and progression of chronic glomerular injury through the dysregulation of ECM metabolism and the reduction in cell adhesive properties to ECMs.

Essential Role of Integrin-Linked Kinase in Podocyte Biology: Bridging the Integrin and Slit Diaphragm Signaling

Integrin-linked kinase (ILK) has been implicated in the pathogenesis of proteinuria and congenital nephrotic syndrome. However, the function of ILK in glomerular podocyte in a physiologic setting remains unknown. In this study, a mouse model was generated in which ILK gene was selectively disrupted in podocytes by using the Cre-LoxP system. Podocyte-specific ablation of ILK resulted in heavy albuminuria, glomerulosclerosis, and kidney failure, which led to animal death beginning at 10 wk of age. Podocyte detachment and apoptosis were not observed at 4 wk of age, when albuminuria became prominent, indicating that they are not the initial cause of proteinuria. Electron microscopy revealed an early foot process effacement, as well as morphologic abnormality, in ILK-deficient podocytes. ILK deficiency caused an aberrant distribution of nephrin and alpha-actinin-4 in podocytes, whereas the localization of podocin and synaptopodin remained relatively intact. Co-immunoprecipitation demonstrated that ILK physically interacted with nephrin to form a ternary complex, and alpha-actinin-4 participated in ILK/nephrin complex formation. Therefore, ILK plays an essential role in specifying nephrin and alpha-actinin-4 distribution and in maintaining the slit diaphragm integrity and podocyte architecture. These results also illustrate that the integrin and slit diaphragm signals in podocytes are intrinsically coupled through an ILK-dependent mechanism.

Regulation of cell-matrix adhesion dynamics and Rac-1 by integrin linked kinase

Extracellular matrix (ECM) receptors of the integrin family initiate changes in cell shape and motility by recruiting signaling components that coordinate these events. Integrin-linked kinase (ILK) is one such partner of beta1 integrins that participates in dynamic rearrangement of cell-matrix adhesions and cell spreading by mechanisms that are not well understood. To further elucidate the role of ILK in these events, we engineered a chimeric molecule comprising ILK fused to a membrane-targeted green fluorescent protein (ILK-GFP-F). ILK-GFP-F is highly enriched in cell-matrix adhesions, and its expression in fibroblasts leads to an accumulation of focal adhesions (2-5 microm) and elongated adhesions (>5 microm). ILK-GFP-F enhances cell spreading on fibronectin and induces a constitutive increase in the levels of GTP-bound Rac-1. Conversely, ILK knock-down by siRNA transfection decreases active Rac-1. Endogenous ILK was found to associate with PKL (paxillin kinase linker) and the Rac/Cdc42 guanine nucleotide exchange factor betaPIX. Further, expression of a dominant negative betaPIX mutant reversed the increase in active Rac-1 levels of ILK-GFP-F-expressing cells, thus placing betaPIX in the pathway leading from ILK to Rac-1 activation. However, expression of constitutively active Rac only partially restores the spreading defects of ILK-depleted cells, suggesting that an additional ILK-dependent signal is required for cell spreading.

Integrin-linked kinase acts as a pro-survival factor against high glucose-associated osmotic stress in human mesangial cells

BACKGROUND

Integrin-linked kinase (ILK) is a protein that plays an important role in extracellular matrix-mediated signalling. Recent studies implicated ILK dysregulation in the development of diabetic nephropathy. However, little is known about the significance of ILK up-regulation in response to high glucose in mesangial cells.

METHODS

The ILK messenger (m)RNA and protein expression in human mesangial cells were analysed with quantitative real-time polymerase chain reaction (PCR) and western blotting after exposure to either 100, 200, or 500 mg/dl glucose, or 100 mg/dl glucose + 400 mg/dl mannitol. Activation of protein Kinase B (PKB)/Akt was also determined by western blot analysis. Cells were transfected with ILK siRNA to determine the effects of ILK knockdown on PKB/Akt activation and cell death following treatment with high glucose or mannitol.

RESULTS

High concentrations of glucose or mannitol for three days significantly up-regulated ILK mRNA and protein expression (P < 0.05 vs 100 mg/dl glucose). In contrast, ILK expression in cells exposed to the same conditions for seven days was unaffected. The time course of PKB/Akt phosphorylation was similar to that of ILK protein expression. The siRNA-mediated down-regulation of ILK expression inhibited the elevation of PKB/Akt phosphorylation induced by high glucose treatment. Furthermore, the inhibition of ILK expression promoted high glucose- or mannitol-induced apoptosis.

CONCLUSION

The ILK may act as a pro-survival factor and play a role in protecting mesangial cells from hyperglycaemic osmotic stress.

Podocyte-Specific Deletion of Integrin-Linked Kinase Results in Severe Glomerular Basement Membrane Alterations and Progressive Glomerulosclerosis

Alterations in glomerular podocyte cell-cell and cell-matrix contacts are key events in progressive glomerular failure. Integrin-linked kinase (ILK) has been implicated in podocyte cell-matrix interaction and is induced in proteinuria. For evaluation of ILK function in vivo, mice with a Cre-mediated podocyte-specific ILK inactivation were generated. These mice seemed normal at birth but developed progressive focal segmental glomerulosclerosis and died in terminal renal failure. The first ultrastructural lesions that are seen at onset of albuminuria are glomerular basement membrane (GBM) alterations with a significant increase in true harmonic mean GBM thickness. Podocyte foot process effacement and loss of slit diaphragm followed with progression to unselective proteinuria. No significant reduction of slit membrane molecules (podocin and nephrin), key GBM components (fibronectin, laminins, and collagen IV isoforms), or podocyte integrins could be observed at onset of proteinuria. However, alpha3-integrins were relocalized into a granular pattern along the GBM, consistent with altered integrin-mediated matrix assembly in ILK-deficient podocytes. As the increased GBM thickness precedes structural podocyte lesions and key components of the GBM were expressed at comparable levels to controls, these data suggest an essential role of ILK for the close interconnection of GBM structure and podocyte function.

Up-regulation of integrin-linked kinase activity in rat mesangioproliferative glomerulonephritis

This study investigated whether integrin-linked kinase (ILK) is involved in the pathogenesis of chronic glomerulonephritis (GN) by analyzing the expression and activity of glomerular ILK in a chronic rat model of mesangioproliferative GN. Double immunostaining of kidneys obtained at different time points with glomerular cell-specific markers revealed that ILK was primarily expressed by glomerular epithelial cells, and weakly by mesangial cells (MCs) and endothelial cells in control rats, but dramatically increased in a typical mesangial pattern at days 21 and 28 of GN. Semiquantitative assessment indicated that the level of glomerular ILK expression closely parallels the level of accumulation of glomerular extracellular matrix (ECM) as well as fibronectin (FN). Immunoprecipitation and kinase activity assays using isolated nephritic glomeruli indicated a striking increase of ILK activity on days 21 and 28 of GN. Further, cultured rat MCs overexpressing kinase-deficient ILK diminished FN assembly and collagen matrix remodeling as compared with control transfectants. The results showed that glomerular ILK expression and activity are markedly increased in an experimental model of chronic GN. Increased activity of ILK in MCs may contribute to the development of chronic mesangial alterations leading to glomerular scarring.

Regulation of Fibrosis by the Immune System

Inflammation and fibrosis are two inter-related conditions with many overlapping mechanisms. Three specific cell types, macrophages, T helper cells, and myofibroblasts, each play important roles in regulating both processes. Following tissue injury, an inflammatory stimulus is often necessary to initiate tissue repair, where cytokines released from resident and infiltrating leukocytes stimulate proliferation and activation of myofibroblasts. However, in many cases this drive stimulates an inappropriate pro-fibrotic response. In addition, activated myofibroblasts can take on the role of traditional APCs, secrete pro-inflammatory cytokines, and recruit inflammatory cells to fibrotic foci, amplifying the fibrotic response in a vicious cycle. Moreover, inflammatory cells have been shown to play contradictory roles in initiation, amplification, and resolution of fibrotic disease processes. The central role of the macrophage in contributing to the fibrotic response and fibrotic resolution is only beginning to be fully appreciated. In the following review, we discuss the fibrotic disease process from the context of the immune response to injury. We review the major cellular and soluble factors controlling these responses and suggest ways in which more specific and, hopefully, more effective therapies may be derived.

The parvins

The parvins are a family of proteins involved in linking integrins and associated proteins with intracellular pathways that regulate actin cytoskeletal dynamics and cell survival. Both alpha-parvin (PARVA) and beta-parvin (PARVB) localize to focal adhesions and function in cell adhesion, spreading, motility and survival through interactions with partners, such as integrin-linked kinase (ILK), paxillin, alpha-actinin and testicular kinase 1. A complex of PARVA with ILK and the LIM protein PINCH-1 is critical for cell survival in a variety of cells, including certain cancer cells, kidney podocytes and cardiac myocytes. While PARVA inhibits the activities of Rac1 and testicular kinase 1 and cell spreading, PARVB binds alphaPIX and alpha-actinin, and can promote cell spreading. In contrast to PARVA, PARVB inhibits ILK activity and reverses some of its oncogenic effects in cancer cells. This review focuses on the structure and function of the parvins and some possible roles in human diseases.

Integrin-linked kinase in renal disease: connecting cell-matrix interaction to the cytoskeleton

PURPOSE OF REVIEW

Cellular functions like proliferation, differentiation, migration, morphogenesis and apoptosis are modulated by the extracellular matrix. Integrins are the prototypic heterodimeric transmembrane matrix receptors with competing affinities for individual extracellular matrix ligands. The intracellular integrin domain clusters cytoplasmic proteins into focal adhesion plaques for bidirectional (outside-in and inside-out) signalling. Integrin-linked kinase organizes the connections of the extracellular matrix via integrins to the cytoskeleton and is involved in adhesion plaque signalling. In this review, an introduction of integrin-linked kinase structure and function is followed by a summary of our current understanding of integrin-linked kinase in renal disease with special focus on glomerular cell-matrix interaction.

RECENT FINDINGS

Differential regulation of integrin-linked kinase has been observed during the pathogenesis of glomerular disease and tubulo-interstitial fibrosis. In outside-in signalling integrin-linked kinase mediates the response of renal cells to alterations in matrix and growth factor environments. Inside-out signalling transduces inflammatory and oxidative stress responses into decreased matrix attachment. Downstream signalling of integrin-linked kinase activates the Wnt pathway with a switch towards a proliferative, mesenchymal phenotype. In concert with interacting molecules integrin-linked kinase influences the actin cytoskeleton, resulting in shape change and focal adhesion dysfunction observed in podocyte failure and tubulo-interstitial fibrosis.

SUMMARY

Integrin-linked kinase has emerged as a key player at the interface between extracellular matrix, integrins, actin-based cytoskeleton and cellular phenotype in kidney diseases. Future studies focusing on interacting molecules and modification of integrin-linked kinase function in vivo will better define the role of cell matrix signalling in progressive renal failure.

Hepatocyte growth factor receptor signaling mediates the anti-fibrotic action of 9-cis-retinoic acid in glomerular mesangial cells

Retinoic acid (RA), an active metabolite of vitamin A, plays a critical role in the regulation of cell proliferation, survival, and differentiation. RA action is primarily mediated through its receptors, ligand-dependent transcription factors of the steroid/thyroid/vitamin D nuclear receptor superfamily. Recent studies indicate that administration of RA mitigates progressive kidney disease, underscoring its renoprotective potential. In this study, we investigated the effects of 9-cis-RA on glomerular mesangial cell activation induced by transforming growth factor (TGF)-beta1 using an in vitro cell culture system. In human mesangial cells 9-cis-RA suppressed TGF-beta1-induced alpha-smooth muscle actin, fibronectin, and plasminogen activator inhibitor-1 expression, but it did not significantly affect cell proliferation and survival. Interestingly, 9-cis-RA induced hepatocyte growth factor (HGF) mRNA expression and protein secretion, stimulated HGF promoter activity, and activated c-met receptor phosphorylation. Similar to HGF, 9-cis-RA induced expression of the Smad transcriptional co-repressor TGIF in mesangial cells. Overexpression of exogenous TGIF by transfection or 9-cis-RA treatment suppressed trans-activation of the TGF-beta-responsive promoter. Moreover, conditional ablation of the c-met receptor completely abolished the anti-fibrotic effect of 9-cis-RA and abrogated TGIF induction. Collectively, these results indicate that 9-cis-RA possesses anti-fibrotic ability by antagonizing TGF-beta1 in mesangial cells and that 9-cis-RA activity is likely mediated through a mechanism dependent on HGF/c-met receptor signaling.

High glucose and angiotensin II increase β1 integrin and integrin-linked kinase synthesis in cultured mouse podocytes

Alterations of integrin alpha3beta1 may play a role in the development of diabetic nephropathy. We have investigated the effects of high glucose and angiotensin II on the expression of integrin alpha3 and beta1, and whether these changes are associated with integrin-linked kinase (ILK) in cultured mouse podocytes. Integrin beta1 and ILK mRNA expression and protein production were rapidly up-regulated in a dose-dependent manner by high glucose and angiotensin II stimulation. ILK mRNA levels in the mouse podocytes exposed to 30 mmol/l glucose were 1.66, 1.89, and 1.28 times higher than those in control cells at 6, 24, and 72 h exposure, respectively. ILK mRNA levels in mouse podocytes exposed to 1 nM, 10 nM, and 100 nM angiotensin II for 6 h were 1.38, 1.55, and 1.93 times higher, respectively, than those in control cells. Angiotensin-II-induced integrin beta1 and ILK mRNA expression was significantly inhibited by treatment with losartan (100 muM). In addition, the up-regulation of ILK synthesis induced by these stimuli was related to beta1 integrin synthesis and increased ILK kinase activity. Cell adhesion assay displayed inhibitory effects when podocytes were exposed to high concentrations of angiotensin II. Interestingly, glucose and angiotensin II stimulation induced shrinkage of the cell body and elongation of the podocyte processes, a phenotype similar to that of immature podocytes. In addition, beta1 integrin showed higher levels of staining on both the cell membranes and the cell-cell contact areas. Thus, high glucose and angiotensin II may affect the regulation of the integrin-ILK system in podocytes; this system may therefore play a role in the pathogenesis of diabetic nephropathy and other renal diseases affecting podocytes.

Role of cell adhesion signal molecules in hepatocellular carcinoma cell apoptosis

AIM: Cell adhesion molecules and their signal molecules play a very important role in carcinogenesis. The aim of this study is to elucidate the role of these molecules and the signal molecules of integrins and E-cadherins, such as (focal adhesion kinase) FAK, (integrin linked kinase) ILK, and β-catenin in hepatocellular carcinoma cell apoptosis.

METHODS: We first synthesized the small molecular compound, S-(1,2-dichlorovinyl)-L-cysteine (DCVC), and identified it, by element analysis and ¹H NMR. To establish the apoptosis model of the SMMC-7721 hepatocellular carcinoma cell, we treated cells with DCVC in EBSS for different concentrations or for various length times in the presence of 20 μmol/L N,N’-diphenyl-p-phenylenediamine, which blocks necrotic cell death and identified this model by flow cytometry and DNA ladder. Then we studied the changes of FAK, ILK, β-catenin, and PKB in this apoptotic model by Western blot.

RESULTS: We found that the loss or decrease of cell adhesion signal molecules is an important reason in apoptosis of SMMC-7721 hepatocellular carcinoma cell and the apoptosis of SMMC-7721 cell was preceded by the loss or decrease of FAK, ILK, PKB, and β-catenin or the damage of cell-matrix and cell-cell adhesion.

CONCLUSION: Our results suggested that the decrease of adhesion signal molecules, FAK, ILK, PKB, and β-catenin, could induce hepatocellular carcinoma cell apoptosis.