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Advanced glycation end products' (AGEs) modification of extracellular matrix proteins induces crosslinking, which results in thickening of the basement membrane and activating several intracellular signaling cascades, eventually promoting the pathological progression of diabetic nephropathy (DN). We have previously confirmed that casein kinase 2α (CK2α) activates the nuclear factor of kappaB (NF-κB) signaling pathway to enhance high glucose-induced expressions of fibronectin (FN) and intercellular adhesion molecule-1 (ICAM-1) in glomerular mesangial cells (GMCs). However, to date, the mechanism by which CK2α regulates diabetic renal fibrosis is not fully understood. In view of the regulation of inflammation and fibrosis by myocardin-related transcription factor A (MRTF-A), we are highly concerned whether CK2α promotes AGEs-induced expressions of FN and ICAM-1 in glomerular mesangial cells via activation of MRTF-A, thus affecting the pathogenesis of DN. We found that CK2α and MRTF-A proteins were overexpressed in AGEs-induced diabetic kidneys. Inhibition of CK2α kinase activity or knockdown of CK2α protein expression suppressed the upregulation of FN and ICAM-1 expressions in GMCs induced by AGEs. MRTF-A knockdown compromised the expressions of FN and ICAM-1 in GMCs induced by AGEs. Moreover, inhibition of CK2α kinase activity or knockdown of CK2α protein expression restrained the protein expression and nuclear aggregation of MRTF-A. CK2α interacted with MRTF-A. Furthermore, knockdown of MRTF-A while overexpression of CK2α blocked the upregulation effect of CK2α on the protein expressions of FN and ICAM-1. These findings suggest that CK2α promotes diabetic renal fibrosis via activation of MRTF-A and upregulation of inflammatory genes., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Advanced glycation end products (AGEs), formed at an accelerated rate under diabetes, play a role in inflammation and fibrosis in mesangial areas in diabetic nephropathy (DN). However, the transcriptional modulator that mediates the cellular response to AGEs remains largely obscure. Our goal was to determine whether myocardin-related transcription factor (MRTF)-A, a key protein involved in the transcriptional regulation of smooth muscle cell phenotype, was responsible for the glomerular mesangial cells (GMCs) injury by AGEs, and, if so, how MRTF-A promoted mesangial dysfunction initiated by AGEs. In this study, MRTF-A was activated by AGEs in terms of protein expression and nuclear translocation in rat GMCs. MRTF-A overexpression synergistically enhanced the induction of FN and ICAM-1 by AGEs. In contract, depletion of MRTF-A abrogated the pathogenic program triggered by AGEs. Then, by interfering with MRTF-A, STAT1, STAT3 and STAT5 nuclear translocation were observed and we screened out STAT5, which was decreased obviously when MRTF-A depleted. Further investigation showed that MRTF-A interacted with STAT5 and promoted its nuclear accumulation and transcriptional activity. Therefore, our present findings suggested a role of MRTF-A in AGEs-induced GMCs injury, and further revealed that the underlying molecular mechanism was related to activating the nuclear factor STAT5., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Our previous study indicated that Casein kinase 2 interacting protein-1 (CKIP-1) could promote the activation of the nuclear factor E2-related factor 2 (Nrf2)/ antioxidant response element (ARE) pathway, playing a significant role in inhibiting the fibrosis of diabetic nephropathy (DN). Polydatin (PD) has been shown to possess strong resistance effects on renal fibrosis which is closely related to activating the Nrf2/ARE pathway, too. Whereas, whether PD could resist DN through regulating CKIP-1 and consequently promoting the activation of Nrf2-ARE pathway needs further investigation. Here, we found that PD significantly reversed the down-regulation of CKIP-1 and attenuated fibronectin (FN) and intercellular cell adhesion molecule-1 (ICAM-1) in glomerular mesangial cells (GMCs) exposed to high glucose (HG). Moreover, PD could decrease Keap1 expression and promote the nuclear content, ARE-binding ability, and transcriptional activity of Nrf2. The activation of Nrf2-ARE pathway by PD eventually led to the quenching of hydrogen peroxide (H 2 O 2 ) and superoxide overproduction boosted by HG. Depletion of CKIP-1 blocked the Nrf2-ARE pathway activation and reversed FN and ICAM-1 down-regulation induced by PD in GMCs challenged with HG. PD increased CKIP-1 and Nrf2 levels in the kidney tissues as well as improved the anti-oxidative effect and renal dysfunction of diabetic mice, which eventually reversed the up-regulation of FN and ICAM-1. Experiments above suggested that PD could increase the CKIP-1-Nrf2-ARE pathway activation to prevent the OSS-induced insult in GMCs and diabetic mice which effectively postpone the diabetic renal fibrosis and the up-regulation of CKIP-1 is probably a novel mechanism in this process., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Emodin, a potential anti-diabetic nephropathy agent, is limited by its oral use due to the poor water solubility. The present study aimed to enhance the absorption and the suppressive effects of emodin on renal fibrosis by developing a self-microemulsifying drug delivery system (SMEDDS). Solubility studies, compatibility tests, pseudo-ternary phase diagrams analysis and central composite design were carried out to obtain the optimized formulation. The average droplet size of emodin-loaded SMEDDS was about 18.31±0.12nm, and the droplet size and zeta potential remained stable at different dilution ratios of water and different values of pH varying from 1.2 to 7.2. Enhanced cellular uptake in both the Caco-2 cells and glomerular mesangial cells (GMCs) is great advantageous for the formulation. The AUC 0-24h of emodin-loaded SMEDDS was 1.87-fold greater than that of emodin suspension, which may be attributed to enhanced uptake in Caco-2 cells. Moreover, emodin-loaded SMEDDS showed better suppressive effects on the protein level of fibronectin (FN), transforming growth factor-beta 1 (TGF-β1) and intercellular adhesion molecule 1 (ICAM-1) than the crude emodin in advanced glycation-end products (AGEs)-induced GMCs and renal tubular epithelial cells (NRK-52E). Our study illustrated that developed SMEDDS improved the oral absorption of emodin, and attained better suppressive effects on the protein level of renal fibrosis compositions in AGEs-induced GMCs and NRK-52E cells., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Background and Purpose: Nox4 is the major isoform of NADPH oxidase found in the kidney and contributes to the pathogenesis of diabetic nephropathy. However, the molecular mechanisms of increased Nox4 expression induced by hyperglycaemia remain to be elucidated. Here, the role of the connexin32-Nox4 signalling axis in diabetic nephropathy and its related mechanisms were investigated.Experimental Approach: Diabetes was induced in mice by low-dose streptozotocin (STZ) combined with a high-fat diet. Effects of connexin32 on Nox4 expression and on renal function and fibrosis in STZ-induced diabetic mice were investigated using adenovirus-overexpressing connexin32 and connexin32-deficient mice. Interactions between connexin32 and Nox4 were analysed by co-immunoprecipitation and immunofluorescence assays.Key Results: Connexin32 was down-regulated in the kidneys of STZ-induced diabetic mice. Overexpression of connexin32 reduced expression of Nox4 and improved renal function and fibrosis in diabetic mice, whereas connexin32 deficiency had opposite effects. Down-regulation of fibronectin expression by connexin32 was not dependent on gap junctional intercellular communication involving connexin32. Connexin32 interacted with Nox4 and reduced the generation of hydrogen peroxide, leading to the down-regulation of fibronectin expression. Mechanistically, connexin32 decreased Nox4 expression by promoting its K48-linked polyubiquitination. Interestingly, Smurf1 overexpression inhibited K48-linked polyubiquitination of Nox4. Furthermore, connexin32 interacted with Smurf1 and inhibited its expression.Conclusion and Implications: Connexin32 ameliorated renal fibrosis in diabetic mice by promoting K48-linked Nox4 polyubiquitination and degradation via inhibition of Smurf1 expression. Targeting the connexin32-Nox4 signalling axis may contribute to the development of novel treatments for diabetic nephropathy. [ABSTRACT FROM AUTHOR]

Nrf2/ARE signaling pathway is a crucial cellular defense system to cope with oxidative stress, which is adaptively activated, in diabetic condition that is not efficient enough to resist the oxidative stress provoked by hyperglycemia. We have previously demonstrated that Connexin43 (Cx43) attenuates renal fibrosis through c-Src. However, the underlying mechanisms need to be further clarified. It has been reported that Cx43 possesses the ability of anti-oxidative. The current study aimed to determine if Cx43 exerts protective effects on renal fibrosis in diabetes via activation of Nrf2/ARE pathway and explore the underlying molecular mechanisms. The following findings were observed: (1) Cx43 expression decreased and c-Src activity increased in kidneys of diabetic animals; (2) Over-expressed Cx43 in high glucose treated GMCs inhibited protein levels of FN, ICAM-1 and TGF-β1; (3) Nrf2/ARE signaling adaptively responded to high glucose treatment in GMCs; (4) Cx43 reduced ROS generation by boost Nrf2/ARE signaling under high glucose condition; (5) Inhibition of c-Src activity promoted nucleus accumulation of Nrf2; (6) Over-expressed Cx43 inhibited c-Src activity and the interaction between c-Src and Nrf2 in GMCs cultured in high glucose. Thus we propose that Cx43 might enhance the activation of Nrf2/ARE pathway by means of inhibiting c-Src activity to hinder the nuclear export of Nrf2, and then reduce expression of FN, ICAM-1 and TGF-β1, ultimately attenuating renal fibrosis in diabetes. [ABSTRACT FROM AUTHOR]