Integrin-linked kinase mediates the hydrogen peroxide-dependent transforming growth factor-β1 up-regulation

Indoxyl sulfate- and P-cresol-induced monocyte adhesion and migration is mediated by integrin-linked kinase-dependent podosome formation

Cardiovascular disease is an important cause of death in patients with chronic kidney disease (CKD). Protein-bound uremic toxins, such as p-cresyl and indoxyl sulfate (IS), are poorly removed during hemodialysis, leading to vascular endothelial dysfunction and leukocyte extravasation. These processes can be related to dynamic adhesion structures called podosomes. Several studies have indicated the role of integrin-linked kinase (ILK) in the accumulation of integrin-associated proteins in podosomes. Here, we investigated the involvement of ILK and podosome formation in the adhesion and extravasation of monocytes under p-cresol (pc) and IS exposure. Incubation of THP-1 human monocyte cells with these toxins upregulated ILK kinase activity. Together, both toxins increased cell adhesion, podosome formation, extracellular matrix degradation, and migration of THP-1 cells, whereas ILK depletion with specific small interfering RNAs suppressed these processes. Interestingly, F-actin colocalized with cortactin in podosome cores, while ILK was colocalized in podosome rings under toxin stimulation. Podosome Wiskott-Aldrich syndrome protein (WASP)-interacting protein (WIP) and AKT protein depletion demonstrated that monocyte adhesion depends on podosome formation and that the ILK/AKT signaling pathway is involved in these processes. Ex vivo experiments showed that both toxins induced adhesion and podosome formation in leukocytes from wild-type mice, whereas these effects were not observed in leukocytes of conditional ILK-knockdown animals. In summary, under pc and IS stimulation, monocytes increase podosome formation and transmigratory capacity through an ILK/AKT signaling pathway-dependent mechanism, which could lead to vascular injury. Therefore, ILK could be a potential therapeutic target for the treatment of vascular damage associated with CKD.

An enzyme involved in organizing structural proteins into protrusions of the cell membrane helps facilitate the movement of white blood cells that occurs in chronic kidney disease and can lead to cardiovascular damage. Laura Calleros from the University of Alcalá, Madrid, Spain, and colleagues showed how toxic metabolites that build up in the bloodstream as kidneys fail induce the activity of an enzyme called integrin-linked kinase (ILK). This enzyme in turn spurs white blood cells to form protrusions called podosomes that make the cells more mobile, enabling them to move out of blood vessels and into surrounding tissues where they can cause inflammation -mediated injury. ILK inactivation reversed these effects. Therapies that target the enzyme could therefore help limit the cardiovascular complications of chronic kidney disease.

Does daily fasting shielding kidney on hyperglycemia-related inflammatory cytokine via TNF-α, NLRP3, TGF-β1 and VCAM-1 mRNA expression

This study aimed to investigate the effects of blood glucose control and the kidneys' functions, depending on fasting, in the streptozotocin-induced diabetes model in rats via TNF-α, NLRP-3, TGF-β1 and VCAM-1 mRNA expression in the present study. 32 Wistar albino rats were allocated randomly into four main groups; H (Healthy, n = 6), HF (Healthy fasting, n = 6), D (Diabetes, n = 10), DF (Diabetes and fasting, n = 10). Blood glucose and HbA1c levels significantly increased in the D group compared to the healthy ones (p < 0.05). However, the fasting period significantly improved blood glucose and HbA1c levels 14 days after STZ induced diabetes in rats compared to the D group. Similar findings we obtained for serum (BUN-creatinine) and urine samples (creatinine and urea levels). STZ induced high glucose levels significantly up-regulated TNF-α, NLRP-3, TGF-β1 and VCAM-1 mRNA expression and fasting significantly decreased these parameters when compared to diabetic rats. Histopathological staining also demonstrated the protective effects of fasting on diabetic kidney tissue. In conclusion, intermittent fasting regulated blood glucose level as well as decreasing harmful effects of diabetes on kidney tissue. The fasting period significantly decreased the hyperglycemia-related inflammatory cytokine damage on kidneys and also reduced apoptosis in favor of living organisms.

Interplay between extracellular matrix components and cellular and molecular mechanisms in kidney fibrosis

Chronic kidney disease (CKD) is characterized by pathological accumulation of extracellular matrix (ECM) proteins in renal structures. Tubulointerstitial fibrosis is observed in glomerular diseases as well as in the regeneration failure of acute kidney injury (AKI). Therefore, finding antifibrotic therapies comprises an intensive research field in Nephrology. Nowadays, ECM is not only considered as a cellular scaffold, but also exerts important cellular functions. In this review, we describe the cellular and molecular mechanisms involved in kidney fibrosis, paying particular attention to ECM components, profibrotic factors and cell-matrix interactions. In response to kidney damage, activation of glomerular and/or tubular cells may induce aberrant phenotypes characterized by overproduction of proinflammatory and profibrotic factors, and thus contribute to CKD progression. Among ECM components, matricellular proteins can regulate cell-ECM interactions, as well as cellular phenotype changes. Regarding kidney fibrosis, one of the most studied matricellular proteins is cellular communication network-2 (CCN2), also called connective tissue growth factor (CTGF), currently considered as a fibrotic marker and a potential therapeutic target. Integrins connect the ECM proteins to the actin cytoskeleton and several downstream signaling pathways that enable cells to respond to external stimuli in a coordinated manner and maintain optimal tissue stiffness. In kidney fibrosis, there is an increase in ECM deposition, lower ECM degradation and ECM proteins cross-linking, leading to an alteration in the tissue mechanical properties and their responses to injurious stimuli. A better understanding of these complex cellular and molecular events could help us to improve the antifibrotic therapies for CKD.

α-Lipoic Acid Increases Collagen Synthesis and Deposition in Nondiabetic and Diabetic Rat Kidneys

α-Lipoic acid (ALA) is widely used as a nutritional supplement and therapeutic agent in diabetes management. Well-established antioxidant and hypoglycemic effects of ALA were considered to be particularly important in combating diabetic complications including renal injury. The present study evaluated the potential of ALA to affect profibrotic events in kidney that could alter its structure and functioning. ALA was administered intraperitoneally (10 mg/kg) to nondiabetic and streptozotocin-induced diabetic male Wistar rats for 4 and 8 weeks. The effects of ALA were assessed starting from structural/morphological alterations through changes that characterize profibrotic processes, to regulation of collagen gene expression in kidney. Here, we demonstrated that ALA improved systemic glucose and urea level, reduced formation of renal advanced glycation end products (AGEs), and maintained renal structural integrity in diabetic rats. However, profibrotic events provoked in diabetes were not alleviated by ALA since collagen synthesis/deposition and expression of transforming growth factor-β1 (TGF-β1) and α-smooth muscle actin (α-SMA) remained elevated in ALA-treated diabetic rats, especially after 8 weeks of diabetes onset. Moreover, 8 weeks treatment of nondiabetic rats with ALA led to the development of profibrotic features reflected in increased collagen synthesis/deposition. Besides the TGF-β1 downstream signaling, the additional mechanism underlying the upregulation of collagen IV in nondiabetic rats treated with ALA involves decreased DNA methylation of its promoter that could arise from increased Tet1 expression. These findings emphasize the therapeutic caution in the use of ALA, especially in patients with renal diabetic complication.

Baicalin reversal of DNA hypermethylation-associated Klotho suppression ameliorates renal injury in type 1 diabetic mouse model

Baicalin is a flavone glycoside that possesses numerous pharmacological properties. but its protective mode of action in kidney injury induced by diabetes mellitus remains incompletely understood. Using a streptozotocin (STZ)-induced diabetic mouse model, we found that baicalin could ameliorate diabetes-induced the pathological changes of the kidney function and morphology through suppressing inflammation and oxidative stress. Furthermore, baicalin treatment could alleviate interstitial fibrosis in the diabetic kidney via inhibiting epithelial-to-mesenchymal transition (EMT), which was accompanied by a sharp upregulation of Klotho, the endogenous inhibitor of renal fibrosis. We further verified that baicalin-rescued expression of Klotho was associated with Klotho promoter hypomethylation due to aberrant methyltransferase 3a expressions. Klotho knockdown via RNA interferences largely abrogated the anti-renal fibrotic effects of Baicalin in HK2 cells. These findings suggested that baicalin could alleviate renal injury-induced by diabates through partly modulating Klotho promoter methylation, which provides new insights into the treatment of diabetic nephropathy.

Parathyroid hormone-related protein induces fibronectin up-regulation in rat mesangial cells through reactive oxygen species/Src/EGFR signaling

Parathyroid hormone-related protein (PTHrP) is known to be up-regulated in both glomeruli and tubules in patients with diabetic kidney disease (DKD), but its role remains unclear. Previous studies show that PTHrP-induced hypertrophic response in mesangial cells (MCs) and epithelial-mesenchymal transition (EMT) in tubuloepithelial cells can be mediated by TGF-β1. In the present study, although long-term PHTrP (1-34) treatment increased the mRNA and protein level of TGF-β1 in primary rat MCs, fibronectin up-regulation occurred earlier, suggesting that fibronectin induction is independent of TGF-β1/Smad signaling. We thus evaluated the involvement of epidermal growth factor receptor (EGFR) signaling and found that nicotinamide adenine dinucleotide phosphate oxidase-derived reactive oxygen species mediates PTHrP (1-34)-induced Src kinase activation. Src phosphorylates EGFR at tyrosine 845 and then transactive EGFR. Subsequent PI3K activation mediates Akt and ERK1/2 activation. Akt and ERK1/2 discretely lead to excessive protein synthesis of fibronectin. Our study thus demonstrates the new role of PTHrP in fibronectin up-regulation for the first time in glomerular MCs. These data also provided new insights to guide development of therapy for glomerular sclerosis.

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.

Contribution of uraemic toxins to the vascular fibrosis associated with chronic kidney disease

BACKGROUND

Patients with chronic kidney disease present with an accumulation of uraemic toxins, which have been identified as pathogenic agents associated with cardiovascular mortality, which is very high is this patient group. A phenomenon common to the progressive renal dysfunction and associated vascular damage, is the abnormal accumulation of extracellular matrix (ECM) proteins in the renal or vascular structures.

OBJECTIVE

To determine the contribution of uraemia or the uraemic toxins to the production of cytokinins and ECM in aortas of uraemic animals or human aortic smooth muscle cells (HASMCs).

MATERIALS AND METHODS

Mice were used with uraemia induced by a diet rich in adenine (0.2%) for 2, 4 or 6 weeks. Kidney function was evaluated by means of urine volume, plasma levels of creatinine, urea, fractional excretion of sodium, and vascular damage using histology, as well as protein expression using RT-qPCR. The HASMCs were incubated in vitro with uraemic toxins: p-cresol 10-100 (μg/ml) and indoxyl-sulphate25-100 (μg/ml) alone or simultaneously. The protein expression was evaluated using Western blot and confocal microscopy.

RESULTS

The administration of adenine produced progressive kidney damage in the mice, thickening of the aortic wall, and increasing the expression of TGF-β1 and ECM proteins. The toxins at high doses and combined also induced the expression of TGF-β1 and ECM proteins by the HASMCs.

CONCLUSIONS

The uraemia produced by an adenine rich diet or high doses of uraemic toxins induced the abnormal deposit of ECM proteins in the vascular wall or its production by HASMCs. The understanding of the mechanisms that underlie this pathophysiological process may be useful in the prevention of cardiovascular damage associated with the progress of chronic kidney disease, a disease, at the moment that is irreversible and occasional silent until its diagnosis in advanced stages.

Impacts of the serum containing total flavonoids of Ajuga on rat glomerular mesangial cells

The aim of the current study was to investigate the impacts and possible mechanisms of total flavonoids of Ajuga (TFA) on glomerular mesangial cells (GMC) through in vitro observations of the impacts of TFA‑containing serum on GMC proliferation and extracellular matrix (ECM) secretion in lipopolysaccharides (LPS)‑induced rats. Rat GMC was cultured in vitro, using LPS to stimulate the proliferation of GMC and the secretion of ECM; meanwhile, TFA‑containing serum (TFA‑S) was used for the intervention. Methyl thiazolyl tetrazolium (MTT) assay was performed to test the proliferation of GMC; enzyme‑linked immunosorbent assay (ELISA) was used to detect the expressions of fibronectin (FN) and collagen IV (Col‑IV) in cell supernatant, flow cytometry was performed to detect the cell cycle, and reverse transcription-polymerase chain reaction was performed to detect the expression levels of matrix metalloproteinase 9 (MMP‑9) mRNA and transforming growth factor β1 (TGF‑β1) mRNA. The GMC proliferation and the expressions of FN and Col‑IV in cell supernatant were significantly reduced after 24 and 48 h TFA‑S intervention (P<0.05 or 0.01). A total of 48 h subsequent to the intervention, the proportion of GMC in the G1 phase and the relative expression of MMP‑9 mRNA were significantly increased (P<0.05 or 0.01), however the proportion of GMC in S phase and the relative expression of TGF‑β1 mRNA were significantly reduced (P<0.05 or 0.01). TFA‑S can inhibit LPS‑induced GMC proliferation and ECM accumulation, and its roles are associated with regulating the cell cycle and the expression levels of TGF‑β1 and MMP‑9.

MicroRNA-542-3p inhibits oral squamous cell carcinoma progression by inhibiting ILK/TGF-β1/Smad2/3 signaling

In this study, we investigated the effects of microRNA-542-3p (miR-542-3p) on ILK/TGF-β1/Smad2/3 signaling and oral squamous cell carcinoma (OSCC) progression. Levels of miR-542-3p were lower in OSCC tissues (n=108) than adjacent normal tissues, whereas levels of ILK, TGF-β1 and Smad2/3 were higher. Patients with undifferentiated tumors, advanced TNM stage and lymph node metastasis showed low miR-542-3p levels. This was accompanied by high ILK expression and poor survival. Dual luciferase reporter assays of SCC-9 cells showed that miR-542-3p inhibited ILK gene expression by binding to its 3’UTR at 233-240 bp. SCC-9 cells transfected with miR-542-3p mimics exhibited elevated miR-542-3p and decreased ILK, TGF-β1 and Smad2/3 expression. They also showed reduced self-renewal (fewer CD44⁺ cells and tumor-spheres), invasiveness, migration, proliferation and survival. Conversely, miR-542-3p inhibitors promoted increased self-renewal (more CD44⁺ cells and tumor-spheres), invasiveness, migration, proliferation and survival. In xenograft experiments with nude mice, SCC-9 cells transfected with miR-542-3p mimics or siRNA-ILK yielded tumors with smaller volumes and weights than control tumors. These results demonstrate that miR-542-3p is a tumor suppressor that inhibits ILK/TGF-β1/Smad2/3 signaling, thereby inhibiting OSCC progression.

Pro-fibrotic pathway activation in trabecular meshwork and lamina cribrosa is the main driving force of glaucoma

While primary open-angle glaucoma (POAG) is a leading cause of blindness worldwide, it still does not have a clear mechanism that can explain all clinical cases of the disease. Elevated IOP is associated with increased accumulation of extracellular matrix (ECM) proteins in the trabecular meshwork (TM) that prevents normal outflow of aqueous humor (AH) and has damaging effects on the fine mesh-like lamina cribrosa (LC) through which the optic nerve fibers pass. Applying a pathway analysis algorithm, we discovered that an elevated level of TGFβ observed in glaucoma-affected tissues could lead to pro-fibrotic pathway activation in TM and in LC. In turn, activated pro-fibrotic pathways lead to ECM remodeling in TM and LC, making TM less efficient in AH drainage and making LC more susceptible to damage from elevated IOP via ECM transformation in LC. We propose pathway targets for potential therapeutic interventions to delay or avoid fibrosis initiation in TM and LC tissues.

Transforming growth factor-β1 and diabetic nephropathy

Transforming growth factor-β1 (TGF-β1) is established to be involved in the pathogenesis of diabetic nephropathy. The diabetic milieu enhances oxidative stress and induces the expression of TGF-β1. TGF-β1 promotes cell hypertrophy and extracellular matrix accumulation in the mesangium, which decreases glomerular filtration rate and leads to chronic renal failure. Recently, TGF-β1 has been demonstrated to regulate urinary albumin excretion by both increasing glomerular permeability and decreasing reabsorption in the proximal tubules. TGF-β1 also increases urinary excretion of water, electrolytes and glucose by suppressing tubular reabsorption in both normal and diabetic conditions. Although TGF-β1 exerts hypertrophic and fibrogenic effects in diabetic nephropathy, whether suppression of the function of TGF-β1 can be an option to prevent or treat the complication is still controversial. This is partly because adrenal production of mineralocorticoids could be augmented by the suppression of TGF-β1. However, differentiating the molecular mechanisms for glomerulosclerosis from those for the suppression of the effects of mineralocorticoids by TGF-β1 may assist in developing novel therapeutic strategies for diabetic nephropathy. In this review, we discuss recent findings on the role of TGF-β1 in diabetic nephropathy.

Renal Integrin-Linked Kinase Depletion Induces Kidney cGMP-Axis Upregulation: Consequences on Basal and Acutely Damaged Renal Function

Soluble guanylyl cyclase (sGC) is activated by nitric oxide (NO) and produces cGMP, which activates cGMP-dependent protein kinases (PKG) and is hydrolyzed by specific phosphodiesterases (PDE). The vasodilatory and cytoprotective capacity of cGMP-axis activation results in a therapeutic strategy for several pathologies. Integrin-linked kinase (ILK), a major scaffold protein between the extracellular matrix and intracellular signaling pathways, may modulate the expression and functionality of the cGMP-axis-related proteins. We introduce ILK as a novel modulator in renal homeostasis as well as a potential target for cisplatin (CIS)-induced acute kidney injury (AKI) improvement. We used an adult mice model of depletion of ILK (cKD-ILK), which showed basal increase of sGC and PKG expressions and activities in renal cortex when compared with wildtype (WT) littermates. Twenty-four h activation of sGC activation with NO enhanced the filtration rate in cKD-ILK. During AKI, cKD-ILK maintained the cGMP-axis upregulation with consequent filtration rates enhancement and ameliorated CIS-dependent tubular epithelial-to-mesenchymal transition and inflammation and markers. To emphasize the role of cGMP-axis upregulation due to ILK depletion, we modulated the cGMP axis under AKI in vivo and in renal cultured cells. A suboptimal dose of the PDE inhibitor ZAP enhanced the beneficial effects of the ILK depletion in AKI mice. On the other hand, CIS increased contractility-related events in cultured glomerular mesangial cells and necrosis rates in cultured tubular cells; ILK depletion protected the cells while sGC blockade with ODQ fully recovered the damage.

Glucose Oxidase Induces Cellular Senescence in Immortal Renal Cells through ILK by Downregulating Klotho Gene Expression

Cellular senescence can be prematurely induced by oxidative stress involved in aging. In this work, we were searching for novel intermediaries in oxidative stress-induced senescence, focusing our interest on integrin-linked kinase (ILK), a scaffold protein at cell-extracellular matrix (ECM) adhesion sites, and on the Klotho gene. Cultured renal cells were treated with glucose oxidase (GOx) for long time periods. GOx induced senescence, increasing senescence associated β-galactosidase activity and the expression of p16. In parallel, GOx increased ILK protein expression and activity. Ectopic overexpression of ILK in cells increased p16 expression, even in the absence of GOx, whereas downregulation of ILK inhibited the increase in p16 due to oxidative stress. Additionally, GOx reduced Klotho gene expression and cells overexpressing Klotho protein did not undergo senescence after GOx addition. We demonstrated a direct link between ILK and Klotho since silencing ILK expression in cells and mice increases Klotho expression and reduces p53 and p16 expression in renal cortex. In conclusion, oxidative stress induces cellular senescence in kidney cells by increasing ILK protein expression and activity, which in turn reduces Klotho expression. We hereby present ILK as a novel downregulator of Klotho gene expression.

Cytoglobin expression in the hepatic stellate cell line HSC-T6 is regulated by extracellular matrix proteins dependent on FAK-signalling

BACKGROUND

Fibrosis is a physiological response to cellular injury in the liver and is mediated by the activation of hepatic stellate cells resulting in the replacement of hepatocytes with extracellular matrix comprised principally of collagen 1 to form a hepatic scar. Although the novel hexaco-ordinated globin cytoglobin was identified in activated hepatic stellate cells more than 10 years ago, its role in stellate cell biology and liver fibrosis remains enigmatic.

RESULTS

In the current study, we investigated the role of different extracellular matrix proteins in stellate cell proliferation, activation (alpha smooth muscle actin expression and retinoic acid uptake) and cytoglobin expression. Our results demonstrate that cytoglobin expression is correlated with a more quiescent phenotype of stellate cells in culture and that cytoglobin is regulated by the extracellular matrix through integrin signalling dependent on activation of focal adhesion kinase.

CONCLUSIONS

Although further studies are required, we provide evidence that cytoglobin is a negative regulator of stellate cell activation and therefore may represent a novel target for anti-fibrotic treatments in the future.

Effect of uraemia on endothelial cell damage is mediated by the integrin linked kinase pathway

KEY POINTS

Patients with chronic kidney disease have a higher risk of developing cardiovascular diseases than the general population. Their vascular endothelium is dysfunctional, among other things, because it is permanently exposed to uraemic toxins, several of which have poor clearance by conventional dialysis. Recent studies have demonstrated the important role of integrin-linked kinase (ILK) in the maintenance of endothelial integrity and in this study we investigate the involvement of ILK in the mechanism underlying vascular endothelial damage that occurs in uraemia. For the first time, we demonstrate the implication of ILK in the protection against endothelial cell damage (inhibition of proliferation, toxicity, oxidative stress and programed cell death) induced by uraemic serum from chronic kidney disease patients and uraemic toxins. This molecular mechanism may have clinical relevance because it highlights the importance of maintaining high levels of ILK activity to help preserve endothelial integrity, at least in early stages of chronic kidney disease.

ABSTRACT

Patients with chronic kidney disease (CKD) have a higher risk of developing cardiovascular diseases. Their vascular endothelium is dysfunctional, among other things, because it is permanently exposed to uraemic toxins, several of which, mostly protein-bound compounds such as indoxyl sulfate (IS) and p-cresyl sulphate, having poor clearance by conventional dialysis, induce endothelial toxicity. However, the molecular mechanism by which uraemic toxins regulate early stages of endothelial dysfunction remains unclear. Recent studies have demonstrated the important role of integrin-linked kinase (ILK) in the maintenance of endothelial integrity. In this study, we investigate the involvement of ILK in the mechanism underlying vascular endothelial damage that occurs in uraemia. First, we show that incubation of EA.hy926 cells with human uraemic serum from CKD patients upregulates ILK activity. This ILK activation also occurs when the cells are exposed to IS (25-100 μg ml(-1)), p-cresol (10-100 μg ml(-1)) or both combined, compared to human serum control. Next, we observed that high doses of both toxins together induce a slight decrease in cell proliferation and increase apoptosis and reactive oxygen species production. Interestingly, these toxic effects displayed a strong increase when the ILK protein is knocked down by small interfering RNA, even at low doses of uraemic toxins. Abrogation of AKT has demonstrated the ILK/AKT signalling pathway involved in these processes. This study has demonstrated the implication of ILK in the protection against endothelial cell damage induced by uraemic toxins, a molecular mechanism that could play a protective role in the early stages of endothelial dysfunction observed in uraemic patients.

Association of transforming growth factor-β1 T869C gene polymorphism with diabetic nephropathy risk

AIM

A possible association between the transforming growth factor-β1 (TGF-β1) T869C gene polymorphism and the risk of developing diabetic nephropathy (DN) remains unclear. This investigation was performed to assess if an association between the TGF-β1 T869C gene polymorphism and DN risk exists by using meta-analysis to combine comparable studies, thereby increasing sample size and statistical significance, and to identify patterns in various studies.

METHODS

The association reports were identified from PubMed, Cochrane Library, and CBM-disc (China Biological Medicine Database) on 1 May 2013, and eligible studies were recruited and synthesized.

RESULTS

Fifty reports were recruited into this meta-analysis for the association of the TGF-β1 T869C gene polymorphism with DN risk. The TT genotype in the overall population was shown to be associated with DN risk (odds ratio (OR) = 0.74, 95% confidence interval (CI): 0.56-0.98, P = 0.04). In the sub-group analysis, CC genotype was associated with DN risk in Asians, Caucasians, and Africans. However, the sample size for Caucasians and Africans was relatively small. Furthermore, T allele was distinctly associated with the risk of developing DN in the Asian population (OR = 0.76, 95% CI: 0.62-0.92, P = 0.005).

CONCLUSIONS

The TT genotype of TGF-β1 T869C in the overall population was associated with DN risk, whereas the CC genotype and T allele were distinctly associated with DN risk in the Asian population. Nonetheless, additional studies are required to firmly establish a correlation between the aforementioned polymorphism and DN risk.

Integrin-linked kinase regulates tubular aquaporin-2 content and intracellular location: a link between the extracellular matrix and water reabsorption

One of the clinical alterations observed in chronic renal disease (CRD) is the impaired urine concentration, known as diabetes insipidus (DI). Tubulointerstitial fibrosis of the kidney is also a pathological finding observed in CRD and involves composition of extracellular matrix (ECM). However, an association between these two events has not been elucidated. In this study, we showed that the extracellular-to-intracellular scaffold protein integrin-linked kinase (ILK) regulates expression of tubular water channel aquaporin-2 (AQP2) and its apical membrane presence in the renal tubule. Basally, polyuria and decreased urine osmolality were present in ILK conditional-knockdown (cKD-ILK) adult mice compared with nondepleted ILK littermates. No changes were observed in arginine-vasopressin (AVP) blood levels, renal receptor (V2R), or AQP3 expression. However, tubular AQP2 was decreased in expression and apical membrane presence in cKD-ILK mice, where the canonical V2R/cAMP axis activation is still functional, but independent of the absence of ILK. Thus, cKD-ILK constitutes a nephrogenic diabetes insipidus (NDI) model. AQP2 and ILK colocalize in cultured inner medullary collecting duct (mIMCD3) cells. Specific ILK siRNAs and collagen I (Col) decrease ILK and AQP2 levels and AQP2 presence on the membrane of tubular mIMCD3 cells, which impairs the capacity of the cells to transport water under hypotonic stress. The present work points to ILK as a therapeutic target in NDI.