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

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.

EPA and DHA increased PPARγ expression and deceased integrin-linked kinase and integrin β1 expression in rat glomerular mesangial cells treated with lipopolysaccharide

Fish oil containing n-3 polyunsaturated fatty acids (n-3 PUFAs) including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is known to prevent the progression of nephropathy and retard the progression of kidney disease. This study sought to investigate the underlying mechanisms of EPA and DHA in terms of peroxisome proliferator-activated receptor γ (PPARγ), integrin-linked kinase (ILK), and integrin β1 expression in glomerular mesangial cells (GMCs) because of their critical roles in the development and progression of nephropathy. Lipopolysaccharide (LPS) significantly reduced the expression of PPARγand increased the expression of ILK at the mRNA level and at the protein level in GMCs as indicated by real-time PCR and Western blotting. In addition, LPS increased integrin β1 expression in GMCs at the mRNA level. Treatment with EPA and DHA significantly increased the expression of PPARγ and decreased the expression of ILK and integrin β1 in GMCs. These data suggest that the renoprotective effects of EPA and DHA may be related to their potential to increase the expression of PPARγ and decrease the expression of ILK and integrin β1.

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.

Epithelial protein lost in neoplasm modulates platelet-derived growth factor-mediated adhesion and motility of mesangial cells

Mesangial cell migration, regulated by several growth factors, is crucial after glomerulopathy and during glomerular development. Directional migration requires the establishment of a polarized cytoskeletal arrangement, a process regulated by coordinated actin dynamics and focal adhesion turnover at the peripheral ruffles in migrating cells. Here we found high expression of the actin cross-linking protein EPLIN (epithelial protein lost in neoplasm) in mesangial cells. EPLIN was localized in mesangial angles, which consist of actin-containing microfilaments extending underneath the capillary endothelium, where they attach to the glomerular basement membrane. In cultured mesangial cells, EPLIN was localized in peripheral actin bundles at focal adhesions and formed a protein complex with paxillin. The MEK-ERK (extracellular signal-regulated kinase) cascade regulated EPLIN-paxillin interaction and induced translocalization of EPLIN from focal adhesion sites to peripheral ruffles. Knockdown of EPLIN in mesangial cells enhanced platelet-derived growth factor-induced focal adhesion disassembly and cell migration. Furthermore, EPLIN expression was decreased in mesangial proliferative nephritis in rodents and humans in vivo. These results shed light on the coordinated actin remodeling in mesangial cells during restorative remodeling. Thus, changes in expression and localization of cytoskeletal regulators underlie phenotypic changes in mesangial cells in glomerulonephritis.

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.

Akt pathway activation and increased neuropeptide Y mRNA expression in the rat hippocampus: implications for seizure blockade

The aim of this study was to analyze the expression of survival-related molecules such Akt and integrin-linked kinase (ILK) to evaluate Akt pathway activation in epileptogenesis process. Furthermore, was also investigated the mRNA expression of neuropeptide Y, a considered antiepileptic neuropeptide, in the pilocarpine-induced epilepsy. Male Wistar rats were submitted to the pilocarpine model of epilepsy. Hippocampi were removed 6h (acute phase), 12h (late acute), 5d (silent) and 60d (chronic) after status epilepticus (SE) onset, and from animals that received pilocarpine but did not develop SE (partial group). Hippocampi collected were used to specify mRNA expression using Real-Time PCR. Immunohistochemistry assay was employed to place ILK distribution in the hippocampus and Western blot technique was used to determine Akt activation level. A decrease in ILK mRNA content was found during acute (0.39+/-0.03) and chronic (0.48+/-0.06) periods when compared to control group (0.87+/-0.10). Protein levels of ILK were also diminished during both periods. Partial group showed increased ILK mRNA expression (0.80+/-0.06) when compared with animals in the acute stage. Silent group had ILK mRNA and immunoreactivity similar to control group. Western blot assay showed an augmentation in Akt activation in silent period (0.52+/-0.03) in comparison with control group (0.44+/-0.01). Neuropeptide Y mRNA expression increased in the partial group (1.67+/-0.22) and in the silent phase (1.45+/-0.29) when compared to control group (0.36+/-0.12). Results suggest that neuropeptide Y (as anticonvulsant) might act in protective mechanisms occurred during epileptic phenomena. Together with ILK expression and Akt activation, these molecules could be involved in hippocampal neuroprotection in epilepsy.

Increase of integrin-linked kinase activity in cultured podocytes upon stimulation with plasma from patients with recurrent FSGS

Recurrent focal segmental glomerulosclerosis (FSGS) is a major challenge in the field of transplantation. Integrin-linked kinase (ILK) has emerged as a key mediator of podocyte-glomerular basement membrane (GBM) interactions. To clarify the involvement of plasma factors in FSGS recurrence, we examined the effects of plasma from FSGS patients with or without posttransplant recurrence on cultured podocytes, focusing particularly on ILK activity. Podocytes from a conditionally immortalized mouse podocyte cell line were treated with plasma from 11 FSGS patients, and ILK activity was determined using an immune complex kinase assay. Treatment with plasma from three patients with recurrence induced an increase in ILK activity. In contrast, no increase in ILK activity was observed in cultured podocytes treated with plasma from the remaining three patients with recurrence and five patients without recurrence. Cultured podocytes treated with plasma that induced ILK activity showed alterations of focal contact and detachment from the laminin matrix. In conclusion, this preliminary study provides experimental evidence suggesting the possible presence of circulating toxic factors in the plasma of some patients with recurrent FSGS, which induce an increase in podocyte ILK activity that may lead to the detachment of podocytes from the GBM.

Integrin-linked kinase in the vascular smooth muscle cell response to injury

Integrin-mediated interactions between smooth muscle cells (SMCs) and the extracellular matrix regulate cell migration and proliferation during neointimal hyperplasia. Integrin-linked kinase (ILK) is a serine-threonine kinase and scaffolding molecule that acts downstream of integrin receptors to modulate cell adhesion; therefore, we examined ILK function in SMCs during wound repair. Silencing of ILK expression with siRNA in vitro decreased cell adhesion to fibronectin and accelerated both cell proliferation and wound closure in the cell monolayer; it also resulted in the rearrangement of focal adhesions and diminished central actin stress fibers. Akt and GSK3beta are ILK substrates that are important in cell motility; however, ILK siRNA silencing did not attenuate injury-induced increases in Akt and GSK3beta phosphorylation. Following balloon catheter injury of the rat carotid artery in vivo, a dramatic decrease in ILK levels coincided with both the proliferation and migration of SMCs, which leads to the formation of a thickened neointima. Immunostaining revealed decreased ILK levels in the media and deep layers of the neointima, but increased ILK levels in the subluminal layers of the intima. Taken together, these results suggest that ILK functions to maintain SMC quiescence in the normal artery. A decrease in ILK levels after injury may permit SMC migration, proliferation, and neointimal thickening, and its re-expression at the luminal surface may attenuate this process during later stages of the injury response.

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.