High glucose-induced hypertrophy of mesangial cells is reversed by connexin43 overexpression via PTEN/Akt/mTOR signaling

The regulatory role of miRNA and lncRNA on autophagy in diabetic nephropathy

Diabetic nephropathy (DN) is a serious complication of diabetes that causes glomerular sclerosis and end-stage renal disease, leading to ascending morbidity and mortality in diabetic patients. Excessive accumulation of aberrantly modified proteins or damaged organelles, such as advanced glycation end-products, dysfunctional mitochondria, and inflammasomes is associated with the pathogenesis of DN. As one of the main degradation pathways, autophagy recycles toxic substances to maintain cellular homeostasis and autophagy dysregulation plays a crucial role in DN progression. MicroRNA (miRNA) and long non-coding RNA (lncRNA) are non-coding RNA (ncRNA) molecules that regulate gene expression and have been implicated in both physiological and pathological conditions. Recent studies have revealed that autophagy-regulating miRNA and lncRNA have been involved in pathological processes of DN, including renal cell injury, mitochondrial dysfunction, inflammation, and renal fibrosis. This review summarizes the role of autophagy in DN and emphasizes the modulation of miRNA and lncRNA on autophagy during disease progression, for the development of promising interventions by targeting these ncRNAs in this disease.

Pericyte Loss in Diseases

Pericytes are specialized cells located in close proximity to endothelial cells within the microvasculature. They play a crucial role in regulating blood flow, stabilizing vessel walls, and maintaining the integrity of the blood-brain barrier. The loss of pericytes has been associated with the development and progression of various diseases, such as diabetes, Alzheimer's disease, sepsis, stroke, and traumatic brain injury. This review examines the detection of pericyte loss in different diseases, explores the methods employed to assess pericyte coverage, and elucidates the potential mechanisms contributing to pericyte loss in these pathological conditions. Additionally, current therapeutic strategies targeting pericytes are discussed, along with potential future interventions aimed at preserving pericyte function and promoting disease mitigation.

Connexins and Glucose Metabolism in Cancer

Connexins are a family of transmembrane proteins that regulate diverse cellular functions. Originally characterized for their ability to mediate direct intercellular communication through the formation of highly regulated membrane channels, their functions have been extended to the exchange of molecules with the extracellular environment, and the ability to modulate numerous channel-independent effects on processes such as motility and survival. Notably, connexins have been implicated in cancer biology for their context-dependent roles that can both promote or suppress cancer cell function. Moreover, connexins are able to mediate many aspects of cellular metabolism including the intercellular coupling of nutrients and signaling molecules. During cancer progression, changes to substrate utilization occur to support energy production and biomass accumulation. This results in metabolic plasticity that promotes cell survival and proliferation, and can impact therapeutic resistance. Significant progress has been made in our understanding of connexin and cancer biology, however, delineating the roles these multi-faceted proteins play in metabolic adaptation of cancer cells is just beginning. Glucose represents a major carbon substrate for energy production, nucleotide synthesis, carbohydrate modifications and generation of biosynthetic intermediates. While cancer cells often exhibit a dependence on glycolytic metabolism for survival, cellular reprogramming of metabolic pathways is common when blood perfusion is limited in growing tumors. These metabolic changes drive aggressive phenotypes through the acquisition of functional traits. Connections between glucose metabolism and connexin function in cancer cells and the surrounding stroma are now apparent, however much remains to be discovered regarding these relationships. This review discusses the existing evidence in this area and highlights directions for continued investigation.

Astragaloside IV attenuated TGF-β1- induced epithelial-mesenchymal transition of renal tubular epithelial cells via connexin 43 and Akt/mTOR signaling pathway

INTRODUCTION

The objective of the study was to observe whether connexin 43 (Cx43) could regulate epithelial mesenchymal transformation (EMT) of renal tubular epithelial cells (RTECs) by influencing Akt/mTOR signaling pathway, and whether ASV could inhibit the development of renal interstitial fibrosis by regulating Cx43.

METHODS

Lentivirus infection was transfected into RTECs with the final concentration of 50 ×PFU/ cell to regulate the expression of Cx43. And RTECs were intervened by different doses of Astragaloside IV (ASV). After synchronous culture of RTECs in each group，the expression levels of EMT-related indicators and Cx43 were detected by fluorescence microscope and Western-Blotting (WB), even the protein expressions and phosphorylation levels of AKT and mTOR in different groups were detected by WB.

RESULTS

When the expression of Cx43 in RTECs was regulated by lentivirus infection, the degree of EMT induced by TGF‑β1 and the phosphorylation level of Akt and mTOR were changed accordingly, indicating that Akt/mTOR pathway might be a downstream molecular mechanism by which Cx43 could regulate EMT. After intervention with different doses of ASV, the expression level of Cx43 increased with obvious concentration dependence, and the expression levels of p-Akt and p- mTOR were significantly altered, suggesting that ASV could effectively increase the protein expressions of TGF‑β1-induced Cx43 in RTECs and inhibit the phosphorylation levels of Akt and mTOR.

CONCLUSION

Cx43 were the main material basis of RTECs' injury, and ASV could inhibit TGF-β1- induced RTECs' transdifferentiation. In-depth study of the mechanism might provide a broad application prospect for the treatment of renal interstitial fibrosis.

Pathogenesis and Clinical Significance of In-Stent Restenosis in Patients with Diabetes

Diabetes mellitus (DM) is a strong risk factor for the development of cardiovascular diseases such as coronary heart disease, cerebrovascular disease, and peripheral arterial disease (PAD). In the population of people living with DM, PAD is characterised by multi-level atherosclerotic lesions as well as greater involvement of the arteries below the knee. DM is also a factor that significantly increases the risk of lower limb amputation. Percutaneous balloon angioplasty with or without stent implantation is an important method of the treatment for atherosclerotic cardiovascular diseases, but restenosis is a factor limiting its long-term effectiveness. The pathogenesis of atherosclerosis in the course of DM differs slightly from that in the general population. In the population of people living with DM, more attention is drawn to such factors as inflammation, endothelial dysfunction, platelet dysfunction, blood rheological properties, hypercoagulability, and additional factors stimulating vascular smooth muscle cell proliferation. DM is a risk factor for restenosis. The purpose of this paper is to provide a review of the literature and to present the most important information on the current state of knowledge on mechanisms and the clinical significance of restenosis and in-stent restenosis in patients with DM, especially in association with the endovascular treatment of PAD. The role of such processes as inflammation, neointimal hyperplasia and neoatherosclerosis, allergy, resistance to antimitotic drugs used for coating stents and balloons, genetic factors, and technical and mechanical factors are discussed. The information on restenosis collected in this publication may be helpful in planning further research in this field, which may contribute to the formulation of more and more precise recommendations for the clinical practice.

Multi-Mechanistic Antidiabetic Potential of Astaxanthin: An Update on Preclinical and Clinical Evidence

Diabetes mellitus (DM) is a cluster of physiological dysfunctions typified by persistent hyperglycemia. Diet plays a paramount role in human health, and regular consumption of a fruit- and vegetable-rich diet can delay or prevent DM and its associated complications. The promising effect of fruits and vegetables could be partly attributed to their antioxidant constituents, including carotenoids. Carotenoids are natural antioxidants that occur in many vegetables, fruits, microalgae, and other natural sources. Astaxanthin is a xanthophyll carotenoid predominantly present in microalgae and some red-colored marine organisms. It is currently marketed as a health supplement and is well-known for its antioxidant capacity. Accumulating evidence indicates that astaxanthin exerts its beneficial effects against DM by acting on various molecular targets and signaling pathways in multiple organs/tissues. Astaxanthin can lower blood glucose levels by preserving β-cell function, improving insulin resistance (IR), and increasing insulin secretion. This manuscript summarizes the connection between glucose homeostasis, oxidative stress, and DM. This is followed by a review of recent studies on astaxanthin's pharmacological effects against IR, microvascular (diabetic retinopathy, diabetic nephropathy, and neurological damage), and macrovascular DM complications emphasizing the cellular and molecular mechanisms involved. A few lines of clinical evidence supporting its antidiabetic potential are also highlighted.

The p70S6K/PI3K/MAPK feedback loop releases the inhibition effect of high-dose rapamycin on rat mesangial cell proliferation

Glomerular mesangial cell (MC) proliferation is one of the causative factors of glomerular diseases and one of their prominent pathological features. Rapamycin can inhibit MC proliferation and slow the progression to chronic renal fibrosis. The present study was designed to observe the role of rapamycin in MC proliferation and to explore the mechanism by which rapamycin acts on Akt and MAPK/ERK1/2 pathways in mesangial cells. MTT assay and flow cytometry were used to evaluate the proliferation and the cell cycle phase of glomerular mesangial cells respectively. The mRNA expression level of p70S6K was detected by RT-qPCR. Western blotting was performed to determine p70S6K, PI3K/Akt, and PI3K/MAPK protein expression. We found that rapamycin could reduce mesangial cell proliferation and arrest the cell cycle in the G1 phase, however the inhibition effect of 1000 nmol/L rapamycin was not higher than that in the 100 nmol/L group. The results of western blotting showed that 1000 nmol/L rapamycin more significantly inhibited the phosphorylation of p70S6K than 100 nmol/L, suggesting there should be another signaling pathway that activates the proliferation of MCs. Moreover, our results revealed that 1000 nmol/L rapamycin led to Raf1-MEK1/2-ERK pathway activation through a p70S6K-PI3K-mediated feedback loop in MCs. This study demonstrated that high-dose rapamycin leads to ERK1/2 activation through a p70S6K/PI3K/MAPK feedback loop in rat MCs, thus reducing the inhibitory effect of rapamycin on MC proliferation.

CKIP-1 acts downstream to Cx43 on the activation of Nrf2 signaling pathway to protect from renal fibrosis in diabetes

We previously reported that both Cx43 and CKIP-1 attenuated diabetic renal fibrosis via the activation of Nrf2 signaling pathway. However, whether CKIP-1, a scaffold protein, participates in regulating the activation of Nrf2 signaling pathway by Cx43 remains to be elucidated. In this study, the effect of adenovirus-mediated Cx43 overexpression on renal fibrosis in CKIP-1-/- diabetic mice was investigated. We found that overexpression of Cx43 could significantly alleviate renal fibrosis by activating the Nrf2 pathway in diabetic mice, but have no obvious effect in CKIP-1-/- diabetic mice. Cx43 overexpressed plasmid and CKIP-1 small interfering RNA were simultaneously transfected into glomerular mesangial cells and the result demonstrated that the effect of activation of Nrf2 signaling pathway by Cx43 was blocked by CKIP-1 depletion. The interaction between Cx43 and CKIP-1 was analyzed by immunofluorescence and immunoprecipitation assays. We found that Cx43 interacted with CKIP-1, and the interaction was weakened by high glucose treatment. Moreover, Cx43 regulated the expression of CKIP-1 and the interaction of CKIP-1 with Nrf2 via Cx43 carboxyl terminus (CT) domain, thereby activating Nrf2 signaling pathway. According to the results, we preliminary infer that CKIP-1 acts downstream to CX43 on the activation of Nrf2 signaling pathway to protect from renal fibrosis in diabetes, the mechanism of which might be related to the interaction of CKIP-1 with Nrf2 through Cx43 CT. Our study provides further experimental basis for targeting the Cx43-CKIP-1-Nrf2 axis to resist diabetic renal fibrosis.

Cell junction proteins: Crossing the glomerular filtration barrier in diabetic nephropathy

Diabetic nephropathy as a deleterious complication of diabetes mellitus and an important cause of end-stage renal failure is characterized by changes in the molecular and cellular levels. Cell-cell communication via the gap and tight junctions are involved in the pathogenesis of diseases such as diabetes and kidney failure. Studying cell junctions including gap junctions, tight junctions, and anchoring junctions within the nephron can be used as an early sign of diabetic nephropathy. Furthermore, cell junctions may be an upcoming target by pharmacological methods to improve treatments of diabetic nephropathy and pave the way to introduce promising therapeutic strategies based on cell-cell communications effects and its translation into clinical studies for the treatment of diabetic nephropathy.

Connexin-mediated cell communication in the kidney: A potential therapeutic target for future intervention of diabetic kidney disease?: Joan Mott Prize Lecture

The ability of cells to communicate and synchronise their activity is essential for the maintenance of tissue structure, integrity and function. A family of membrane-bound proteins called connexins are largely responsible for mediating the local transfer of information between cells. Assembled in the cell membrane as a hexameric connexon, they either function as a conduit for paracrine signalling, forming a transmembrane hemi-channel, or, if aligned with connexons on neighbouring cells, form a continuous aqueous pore or gap junction, which allows for the direct transmission of metabolic and electrical signals. Regulation of connexin synthesis and activity is critical to cellular function, and a number of diseases are attributed to changes in the expression and/or function of these important proteins. A link between hyperglycaemia, connexin expression, altered nucleotide concentrations and impaired function highlights a potential role for connexin-mediated cell communication in complications of diabetes. In the diabetic kidney, glycaemic injury is the leading cause of end-stage renal failure, reflecting multiple aetiologies including glomerular hyperfiltration, albuminuria, increased deposition of extracellular matrix and tubulointerstitial fibrosis. Loss of connexin-mediated cell-to-cell communication in diabetic nephropathy may represent an early sign of disease progression, but our understanding of the process remains severely limited. This review focuses on recent evidence demonstrating that glucose-evoked changes in connexin-mediated cell communication and associated purinergic signalling may contribute to the pathogenesis of kidney disease in diabetes, highlighting the tantalising potential of targeting these proteins as a novel therapeutic intervention.

LNCRNA CDKN2B-AS1 regulates mesangial cell proliferation and extracellular matrix accumulation via miR-424-5p/HMGA2 axis

BACKGROUND

Previous study has demonstrated that long noncoding RNA cyclin-dependent kinase inhibitor 2B antisense RNA 1 (CDKN2B-AS1) was abnormally expressed in diabetic nephropathy (DN). However, the underlying mechanism that allows CDKN2B-AS1 in the progression of DN remains to be further elucidated.

METHODS

Peripheral blood cells of 24 diabetes patients with DN and 20 without DN were collected. Human glomerular mesangial cells (HGMC) were cultured in high glucose or low glucose medium. The expression levels of CDKN2B-AS1, microRNA (miR)-424-5p and high mobility group AT hook 2 (HMGA2) were detected by quantitative real-time polymerase chain reaction or western blot. The target association between miR-424-5p and CDKN2B-AS1 or HMGA2 was confirmed by dual-luciferase reporter and RNA immunoprecipitation assays. Cell proliferation, extracellular matrix (ECM) accumulation and phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling were investigated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) and western blot, respectively.

RESULTS

CDKN2B-AS1 expression was up-regulated and miR-424-5p level was down-regulated in peripheral blood of DN patients and high glucose-treated HGMC cells. CDKN2B-AS1 was validated as a sponge of miR-424-5p. Silence of CDKN2B-AS1 repressed proliferation and ECM accumulation by increasing miR-424-5p. HMGA2 was a target of miR-424-5p and miR-424-5p overexpression inhibited proliferation, ECM accumulation and PI3K/AKT pathway by targeting HMGA2. Moreover, knockdown of CDKN2B-AS1 inhibited HMGA2 expression and PI3K/AKT pathway by increasing miR-424-5p.

CONCLUSION

Knockdown of CDKN2B-AS1 suppressed proliferation, ECM accumulation and PI3K/AKT signaling by increasing miR-424-5p and decreasing HMGA2 in high glucose-treated HMGC cells.

miR-206 Inhibits Cell Proliferation and Extracellular Matrix Accumulation by Targeting Hypoxia-Inducible Factor 1-alpha (HIF-1α) in Mesangial Cells Treated with High Glucose

Background

The goal of this study was to investigate the expression of miR-206 in human glomerular mesangial cells (hMCs) treated by exposure to high glucose (HG) levels, to assess the influence of miR-206 on the proliferation and extracellular matrix (ECM) deposition of hMCs, and to investigate the potential mechanisms of action.

Material/Methods

The level of miR-206 was detected by RT-qPCR. MTT assay and colony formation assay were used to assess hMCs cell proliferation ability. Western blotting was carried out to measure the expression of related proteins. Bioinformatics software (http://www.targetscan.org) was used to predict the potential target genes of miR-206, and dual-luciferase reporter assay was used to confirm this prediction.

Results

Our results suggest that the level of miR-206 was downregulated in HG-treated hMCs. Cell proliferation was promoted in HG-induced hMCs, while this phenomenon was significantly reversed with miR-206 mimics. miR-206 mimics significantly enhanced p21 expression and decreased cyclin D1 and CDK2 expressions, but the opposite was found in HG-induced hMCs. Moreover, the level of ECM proteins was notably increased in hMCs treated with HG, which was also significantly reversed by miR-206 mimics. miR-206 inhibitor had the opposite effects. Furthermore, HIF-1α was found to be a direct target of miR-206, and was negatively regulated by miR-206 in hMCs. miR-206 can target HIF-1α to modulate cell proliferation and ECM accumulation.

Conclusions

Collectively, our results suggest that miR-206 plays a vital role in HG-treated hMCs through inhibiting cell proliferation and ECM accumulation, partly via targeting HIF-1α.

Identification of miRNAs-genes regulatory network in diabetic nephropathy based on bioinformatics analysis

MicroRNAs (miRNAs) play a great contribution to the development of diabetic nephropathy (DN). The aim of this study was to explore potential miRNAs-genes regulatory network and biomarkers for the pathogenesis of DN using bioinformatics methods.Gene expression profiling data related to DN (GSE1009) was obtained from the Gene Expression Omnibus (GEO) database, and then differentially expressed genes (DEGs) between DN patients and normal individuals were screened using GEO2R, followed by a series of bioinformatics analyses, including identifying key genes, conducting pathway enrichment analysis, predicting and identifying key miRNAs, and establishing regulatory relationships between key miRNAs and their target genes.A total of 600 DEGs associated with DN were identified. An additional 7 key DEGs, including 6 downregulated genes, such as vascular endothelial growth factor α (VEGFA) and COL4A5, and 1 upregulated gene (CCL19), were identified in another dataset (GSE30528) from glomeruli samples. Pathway analysis showed that the down- and upregulated DEGs were enriched in 14 and 6 pathways, respectively, with 7 key genes mainly involved in extracellular matrix-receptor interaction, PI3K/Akt signaling, focal adhesion, and Rap1 signaling. The relationships between miRNAs and target genes were constructed, showing that miR-29 targeted COL4A and VEGFA, miR-200 targeted VEGFA, miR-25 targeted ITGAV, and miR-27 targeted EGFR.MiR-29 and miR-200 may play important roles in DN. VEGFA and COL4A5 were targeted by miR-29 and VEGFA by miR-200, which may mediate multiple signaling pathways leading to the pathogenesis and development of DN.

Betaine alleviates high glucose‑induced mesangial cell proliferation by inhibiting cell proliferation and extracellular matrix deposition via the AKT/ERK1/2/p38 MAPK pathway

Diabetic nephropathy (DN) is a major cause of chronic renal failure in diabetic patients worldwide. Betaine, a zwitterionic quaternary ammonium salt compound, is involved in numerous biological processes. The present study aimed to investigate the effects of betaine on mouse mesangial cells (MMCs) cultured under high glucose (HG) conditions and its underlying mechanisms. MMCs were treated with betaine under HG conditions. Cell proliferation and the cell cycle distribution were investigated with an MTT assay and flow cytometry, respectively. Western blotting and reverse transcription‑quantitative polymerase chain reaction analyses were applied to respectively determine protein and mRNA expression levels. The results suggested that betaine decreased cell proliferation in a dose‑dependent manner, while G1‑phase arrest was significantly induced in MMCs. Compared with the control group, the expression levels of p21 and p27 decreased under HG conditions, but were reversed by betaine. Furthermore, the expression levels of fibronectin and type IV collagen were significantly decreased in cells treated with betaine compared with the HG group. Additionally, betaine decreased the phosphorylation of Akt, extracellular‑signal‑regulated kinase (Erk)1/2 and p38 mitogen‑activated protein kinase (MAPK), but was enhanced under HG conditions. Overall, the results of the present study indicated that betaine serves a protective role in HG‑induced MMCs by inhibiting cell proliferation and extracellular matrix deposition via regulating regulation of the Akt/Erk1/2/p38 MAPK signaling pathway.

High Glucose-Induced Apoptosis in Human Kidney Cells Was Alleviated by miR-15b-5p Mimics

MicroRNAs were involved in a wide range of biological processes of diabetic nephropathy (DN). It is reported that miR-15b-5p was downregulated in the patients with DN. However, the mechanisms underlying the regulatory effects of miR-15b-5p on patients with diabetes remain unclear. Thus, this study aimed to investigate the role of miR-15b-5p during high glucose (HG)-induced apoptosis in human kidney cells. Quantitative real-time (qRT)-PCR was used to detect the level of miR-15b-5p. CCK-8 assay, EdU staining assays and flow cytometry were used to detect cell proliferation, apoptosis respectively in vitro. In addition, Western blotting was used to determine active caspase-3, cleaved poly(ADP-ribose) polymerase (PARP), phosphorylated (p)-AKT, p-mammalian target of rapamycin (mTOR), p-S6, p-c-Jun N terminal kinase (JNK), p-p38 and p-extracellular signal-regulated kinase (ERK) proteins levels. The expression of miR-15b-5p in patients with DN were dramatically decreased compared with health persons. Similarly, HG down-regulated the expression of miR-15b-5p in HK-2 cells. In contrast, miR-15b-5p mimics alleviated HG-induced apoptosis in HK-2 cells via decreasing the expressions of active caspase 3 and cleaved PARP. EdU detection further confirmed that miR-15b-5p mimics attenuated the anti-proliferation effect of HG in HK-2 cells. Furthermore, HG-induced Akt/mTOR pathway downregulation and JNK upregulation were markedly reversed by miR-15b-5p mimics in cells. The data suggested that miR-15b-5p mimics protects HK-2 cells from HG-induced apoptosis. The anti-apoptotic effects of miR-15b-5p may due to the activation of the Akt/mTOR pathway as well as inactivation of JNK. Taken together, miR-15b-5p might be a potential therapeutic target for the treatment of patients with DN.

Astaxanthin ameliorates experimental diabetes-induced renal oxidative stress and fibronectin by upregulating connexin43 in glomerular mesangial cells and diabetic mice

Oxidative stress is the major cause of renal fibrosis in the progression of DN. Connexin43 (Cx43) exerts an anti-fibrosis effect on diabetic kidneys. The current study aimed to investigate whether astaxanthin (AST) could ameliorate the pathological progression of DN by upregulating Cx43 and activating the Nrf2/ARE signaling, which is a pivotal anti-oxidative stress system, to strengthen the cellular anti-oxidative capacity and diminish fibronectin (FN) accumulation in HG-induced glomerular mesangial cells (GMCs). Our hypothesis was verified in GMCs and the kidneys from db/db mice by western blot, immunofluorescence, immunohistochemistry, immunoprecipitation, dual luciferase reporter assay and reactive oxygen related detection kits. Results showed that AST simultaneously upregulated the Cx43 protein level and promoted the Nrf2/ARE signaling activity in the kidney of db/db mice and HG-treated GMCs. However, Cx43 depletion abrogated the Nrf2/ARE signaling activation induced by AST. AST reduced the interaction between c-Src and Nrf2 in the nuclei of GMCs cultured with HG, thereby enhancing the Nrf2 accumulation in the nuclei of GMCs. Our data suggested that AST promoted the Nrf2/ARE signaling by upregulating the Cx43 protein level to prevent renal fibrosis triggered by HG in GMCs and db/db mice. c-Src acted as a mediator in these processes.

Consequences of calorie restriction and calorie excess for the physiological parameters of the yeast Saccharomyces cerevisiae cells

Glucose plays an important role in cell metabolism and has an impact on cellular physiology. Changes in glucose availability may strongly influence growth rate of the cell size, cell metabolism and the rate of generation of cellular by-products, such as reactive oxygen species. The positive effect of low glucose concentration conditions-calorie restriction is observed in a wide range of species, including the Saccharomyces cerevisiae yeast, yet little is known about the effect of high glucose concentrations-calorie excess. Such analysis seems to be particularly important due to recently common problem of diabetes and obesity. The effect of glucose on morphological and physiological parameters of the yeast cell was conducted using genetic alteration (disruption of genes involved in glucose signalling) and calorie restriction and calorie excess conditions. The results show a significant relationship among extracellular glucose concentration, cell size and reactive oxygen species generation in yeast cells. Furthermore, the results obtained through the use of mutant strains with disorders in glucose signalling pathways suggest that the intracellular level of glucose is more important than its extracellular concentration. These data also suggest that the calorie excess as a factor, which has a significant impact on cell physiology, requires further comprehensive analyses.

Angiotensin II-Induced Mesangial Cell Damaged Is Preceded by Cell Membrane Permeabilization Due to Upregulation of Non-Selective Channels

Connexin43 (Cx43), pannexin1 (Panx1) and P2X₇ receptor (P2X₇R) are expressed in kidneys and are known to constitute a feedforward mechanism leading to inflammation in other tissues. However, the possible functional relationship between these membrane channels and their role in damaged renal cells remain unknown. In the present work, we found that MES-13 cells, from a cell line derived from mesangial cells, stimulated with angiotensin II (AngII) developed oxidative stress (OS, thiobarbituric acid reactive species (TBARS) and generated pro-inflammatory cytokines (ELISA; IL-1β and TNF-α). The membrane permeability increased progressively several hours before the latter outcome, which was a response prevented by Losartan, indicating the involvement of AT1 receptors. Western blot analysis showed that the amount of phosphorylated MYPT (a substrate of RhoA/ROCK) and Cx43 increased progressively and in parallel in cells treated with AngII, a response followed by an increase in the amount in Panx1 and P2X₇R. Greater membrane permeability was partially explained by opening of Cx43 hemichannels (Cx43 HCs) and Panx1 channels (Panx1 Chs), as well as P2X₇Rs activation by extracellular ATP, which was presumably released via Cx HCs and Panx1 Chs. Additionally, inhibition of RhoA/ROCK blocked the progressive increase in membrane permeability, and the remaining response was explained by the other non-selective channels. The rise of activity in the RhoA/ROCK-dependent pathway, as well as in Cx HCs, P2X₇R, and to a minor extent in Panx1 Chs led to higher amounts of TBARS and pro-inflammatory cytokines. We propose that AngII-induced mesangial cell damage could be effectively inhibited by concomitantly inhibiting the RhoA/ROCK-dependent pathway and one or more non-selective channel(s) activated through this pathway.

Rosiglitazone diminishes the high-glucose-induced modulation of 5-fluorouracil cytotoxicity in colorectal cancer cells

Colorectal cancer (CRC) is the third most leading cause of morbidity and mortality throughout the world. 5-fluorouracil (5-FU), which is often administrated to disrupt carcinogenesis, was found to elevate blood glucose level among CRC patients. Thus, this study was conducted to evaluate the influence of rosiglitazone on antiproliferative effect of 5-FU using cellular model. Two human colonic carcinoma cell lines (HCT 116 and HT 29) were cultured in the presence of 5-FU, rosiglitazone or in combination under normal and high glucose concentration. The drug cytotoxicity was evaluated using the MTT assay whereas the assessment of cell cycle was carried out using the flow cytometry technique. Combination index (CI) method was used to determine the drug interaction between rosiglitazone and 5-FU. High glucose diminished the cytotoxic effect of 5-FU but at a high drug dosage, this effect could be overcome. Cell cycle analysis demonstrated that 5-FU and rosiglitazone caused G1-phase arrest and S-phase arrest, respectively. CI values indicated that rosiglitazone exerted synergistic effect on 5-FU regardless of glucose levels. This study is the first to demonstrate the influence of rosiglitazone on cytotoxicity of 5-FU under normal or high glucose level. Rosiglitazone may be a promising drug for enhancing the efficacy of 5-FU in the treatment of CRC associated with hyperglycemia.

Pleiotrophin, a target of miR-384, promotes proliferation, metastasis and lipogenesis in HBV-related hepatocellular carcinoma

Hepatitis B virus (HBV) infection plays a crucial role and is a major cause of hepatocellular carcinoma (HCC) in China. microRNAs (miRNAs) have emerged as key players in hepatic steatosis and carcinogenesis. We found that down-regulation of miR-384 expression was a common event in HCC, especially HBV-related HCC. However, the possible function of miR-384 in HBV-related HCC remains unclear. The oncogene pleiotrophin (PTN) was a target of miR-384. HBx inhibited miR-384, increasing PTN expression. The PTN receptor N-syndecan was highly expressed in HCC. PTN induced by HBx acted as a growth factor via N-syndecan on hepatocytes and further promoted cell proliferation, metastasis and lipogenesis. PTN up-regulated sterol regulatory element-binding protein 1c (SREBP-1c) through the N-syndecan/PI3K/Akt/mTORC1 pathway and the expression of lipogenic genes, including fatty acid synthesis (FAS). PTN-mediated de novo lipid synthesis played an important role in HCC proliferation and metastasis. PI3K/AKT and an mTORC1 inhibitor diminished PTN-induced proliferation, metastasis and lipogenesis. Taken together, these data strongly suggest that the dysregulation of miR-384 could play a crucial role in HBV related to HCC, and the target gene of miR-384, PTN, represents a new potential therapeutic target for the prevention of hepatic steatosis and further progression to HCC after chronic HBV infection.

Scoparone attenuates high glucose-induced extracellular matrix accumulation in rat mesangial cells

Scoparone, a major constituent of Artemisia capillaries, has a variety of biological properties including anticoagulant, hepatoprotective, anti-tumor, anti-fibrosis, anti-inflammatory, antioxidant, and antidiabetic activities. However, the renoprotective effect of scoparone under diabetic conditions remains elusive. Thus, the present study was undertaken to examine the role of scoparone in high glucose-induced mesangial cell proliferation and extracellular matrix (ECM) accumulation and elucidate the possible mechanism of action of scoparone. Our results demonstrated that treatment with scoparone significantly inhibited the proliferation of mesangial cells under high glucose conditions. In addition, scoparone reversed high glucose-induced fibronectin and collagen IV expression in mesangial cells, as well as suppressed reactive oxygen species production and NOX2/4 expression in high glucose-exposed mesangial cells. Mechanistic studies revealed that scoparone prevented the activation of ERK1/2 signaling pathway in high glucose-exposed mesangial cells, and an ERK inhibitor (U0126) protected mesangial cells treated with high glucose. Taken together, these results demonstrated that scoparone protects mesangial cells against high glucose damage in part through the inactivation of ERK signaling pathway. These findings suggest that scoparone may represent a potential drug for the treatment of diabetic nephropathy.

High glucose induces the aging of mesenchymal stem cells via Akt/mTOR signaling

It has previously been demonstrated that glucose is important in the process of stem cell aging. However, the mechanisms of cell senescence induced by high glucose (HG) remain to be elucidated. The preliminary study indicated that D-galactose induced mesenchymal stem cell (MSCs) aging. The present study demonstrated, following treatment with 11.0 or 22.0 mM HG for 14 days, that HG significantly promoted MSCs aging and the expression levels of phosphorylated (p-)phosphatidylinositol 3-kinase/protein kinase B (Akt) and p-mammalian target of rapamycin signaling (mTOR) in the HG groups were increased compared with the control group. However, following Akt inhibition with 1.0 or 10.0 nM MK-2206, which is an Akt-specific small molecule inhibitor, the senescence-cell value in the HG group was significantly decreased compared with the control group. These results indicated that HG induced MSCs senescence and this effect was primarily mediated via the Akt/mTOR signaling pathway.

Pericytes, an overlooked player in vascular pathobiology

Pericytes are a heterogeneous population of cells located in the blood vessel wall. They were first identified in the 19th century by Rouget, however their biological role and potential for drug targeting have taken time to be recognised. Isolation of pericytes from several different tissues has allowed a better phenotypic and functional characterization. These findings revealed a tissue-specific, multi-functional group of cells with multilineage potential. Given this emerging evidence, pericytes have acquired specific roles in pathobiological events in vascular diseases. In this review article, we will provide a compelling overview of the main diseases in which pericytes are involved, from well-established mechanisms to the latest findings. Pericyte involvement in diabetes and cancer will be discussed extensively. In the last part of the article we will review therapeutic approaches for these diseases in light of the recently acquired knowledge. To unravel pericyte-related vascular pathobiological events is pivotal not only for more tailored treatments of disease but also to establish pericytes as a therapeutic tool.

Astragaloside IV ameliorates renal injury in db/db mice

Diabetic nephropathy is a lethal complication of diabetes mellitus and a major type of chronic kidney disease. Dysregulation of the Akt pathway and its downstream cascades, including mTOR, NFκB, and Erk1/2, play a critical role in the development of diabetic nephropathy. Astragaloside IV is a major component of Huangqi and exerts renal protection in a mouse model of type 1 diabetes. The current study was undertaken to investigate the protective effects of diet supplementation of AS-IV on renal injury in db/db mice, a type 2 diabetic mouse model. Results showed that administration of AS-IV reduced albuminuria, ameliorated changes in the glomerular and tubular pathology, and decreased urinary NAG, NGAL, and TGF-β1 in db/db mice. AS-IV also attenuated the diabetes-related activation of Akt/mTOR, NFκB, and Erk1/2 signaling pathways without causing any detectable hepatotoxicity. Collectively, these findings showed AS-IV to be beneficial to type 2 diabetic nephropathy, which might be associated with the inhibition of Akt/mTOR, NFκB and Erk1/2 signaling pathways.

Effect of Novel Gasotransmitter hydrogen sulfide on renal fibrosis and connexins expression in diabetic rats

To explore the effects of hydrogen sulfide (H₂S) on renal fibrosis and the expressions of connexins and matrix metalloproteinase (MMP) in diabetic rats.

METHOD

SD rats were divided into 4 groups randomly: control group(n = 12), STZ group (n = 12), STZ+ H2S group (n = 12), and H₂S group (n = 12). Diabetic model was induced by intraperitoneal injections of STZ. After 72 h after injection, the rats whose blood glucose were higher than 16.7 mmol/L. STZ+H₂S group and H₂S group were injected NaHS by intraperitoneal. Control group and STZ group were injected with the same dose of normal saline (NS) in equal doses every day. 8 weeks later, urine were collected. The expression of connexin and matrix metalloproteinase was analyzed by Western blot. We measured the Kidney hydroxyproline content by hydrolysis method. Type II collagen content was detected by immunohistochemical method and Masson staining.

RESULTS

Compared with the control group, collagen accumulation was markedly enhanced, and the content of type II collagen, kidney hydroxyproline and timp-2 were boosted in STZ group mice (P < 0.01), while the expressions of CX40,CX43, CX45, MMP-1 and MMP-2 were obviously deceased (P < 0.01). Compared with STZ group, the expressions of CX40, CX43, CX45, MMP-1 and MMP-2 were significantly increased (P < 0.01), while the content of type II collagen, kidney hydroxyproline and timp-2 expression were markedly deceased in STZ+H₂S group.

CONCLUSION

H₂S may attenuate renal fibrosis by up-regulating the expressions of CX40, CX43, CX45 and regulating the MMPs/TIMPs parameters.

Cross talk between miR-214 and PTEN attenuates glomerular hypertrophy under diabetic conditions

Glomerular mesangial cells (MCs) hypertrophy is one of the earliest pathological abnormalities in diabetic nephropathy (DN), which correlates with eventual glomerulosclerosis. This study aimed to investigate the therapeutic role of miRNA in diabetic glomerular MCs hypertrophy and synthesis of extracellular matrix (ECM). Microarray analysis revealed a significant up-regulation of miR-214 in the renal cortex of diabetic db/db mice, which was confirmed by real-time PCR of isolated glomeruli and primary cultured human MCs. In vitro studies showed that inhibition of miR-214 significantly reduced expression of α-SMA, SM22 and collagen IV, and partially restored phosphatase and tensin homolog (PTEN) protein level in high glucose-stimulated human MCs. Furthermore, we identified PTEN as the target of miR-214 by a luciferase assay in HEK293 cells. Moreover, overexpression of PTEN ameliorated miR-214-mediated diabetic MC hypertrophy while knockdown of PTEN mimicked the MC hypertrophy. In vivo study further confirmed that inhibition of miR-214 significantly decreased the expression of SM22, α-SMA and collagen IV, partially restored PTEN level, and attenuated albuminuria and mesangial expansion in db/db mice. In conclusion, cross talk between miR-214 and PTEN attenuated glomerular hypertrophy under diabetic conditions in vivo and in vitro. Therefore, miR-214 may represent a novel therapeutic target for DN.

Hydrophobic motif site-phosphorylated protein kinase CβII between mTORC2 and Akt regulates high glucose-induced mesangial cell hypertrophy

PKCβII controls the pathologic features of diabetic nephropathy, including glomerular mesangial cell hypertrophy. PKCβII contains the COOH-terminal hydrophobic motif site Ser-660. Whether this hydrophobic motif phosphorylation contributes to high glucose-induced mesangial cell hypertrophy has not been determined. Here we show that, in mesangial cells, high glucose increased phosphorylation of PKCβII at Ser-660 in a phosphatidylinositol 3-kinase (PI3-kinase)-dependent manner. Using siRNAs to downregulate PKCβII, dominant negative PKCβII, and PKCβII hydrophobic motif phosphorylation-deficient mutant, we found that PKCβII regulates activation of mechanistic target of rapamycin complex 1 (mTORC1) and mesangial cell hypertrophy by high glucose. PKCβII via its phosphorylation at Ser-660 regulated phosphorylation of Akt at both catalytic loop and hydrophobic motif sites, resulting in phosphorylation and inactivation of its substrate PRAS40. Specific inhibition of mTORC2 increased mTORC1 activity and induced mesangial cell hypertrophy. In contrast, inhibition of mTORC2 decreased the phosphorylation of PKCβII and Akt, leading to inhibition of PRAS40 phosphorylation and mTORC1 activity and prevented mesangial cell hypertrophy in response to high glucose; expression of constitutively active Akt or mTORC1 restored mesangial cell hypertrophy. Moreover, constitutively active PKCβII reversed the inhibition of high glucose-stimulated Akt phosphorylation and mesangial cell hypertrophy induced by suppression of mTORC2. Finally, using renal cortexes from type 1 diabetic mice, we found that increased phosphorylation of PKCβII at Ser-660 was associated with enhanced Akt phosphorylation and mTORC1 activation. Collectively, our findings identify a signaling route connecting PI3-kinase to mTORC2 to phosphorylate PKCβII at the hydrophobic motif site necessary for Akt phosphorylation and mTORC1 activation, leading to mesangial cell hypertrophy.

Kidney glycosphingolipids are elevated early in diabetic nephropathy and mediate hypertrophy of mesangial cells

Glycosphingolipids (GSLs) play a role in insulin resistance and diabetes, but their role in diabetic nephropathy (DN) has received limited attention. We used 9- and 17-wk-old nondiabetic db/m and diabetic db/db mice to examine the role of GSLs in DN. Cerebrosides or monoglycosylated GSLs [hexosylceramides (HexCers); glucosyl- and galactosylceramides] and lactosylceramide (LacCers) were elevated in db/db mouse kidney cortices, specifically in glomeruli, and also in urine. In our recent paper (25), we observed that the kidneys exhibited glomerular hypertrophy and proximal tubular vacuolization and increased fibrosis markers at these time points. Mesangial cells contribute to hyperglycemia-induced glomerular hypertrophy in DN. Hyperglycemic culture conditions, similar to that present in diabetes, were sufficient to elevate mesangial cell HexCers and increase markers of fibrosis, extracellular matrix proteins, and cellular hypertrophy. Inhibition of glucosylceramide synthase or lowering glucose levels decreased markers of fibrosis and extracellular matrix proteins and reversed mesangial cell hypertrophy. Hyperglycemia increased phosphorylated (p)SMAD3 and pAkt levels and reduced phosphatase and tensin homolog levels, which were reversed with glucosylceramide synthase inhibition. These data suggest that inhibition of glucosylceramide synthase reversed mesangial cell hypertrophy through decreased pAkt and pSmad3 and increased pathways responsible for protein degradation. Importantly, urinary GSL levels were higher in patients with DN compared with healthy control subjects, implicating a role for these lipids in human DN. Thus, hyperglycemia in type II diabetes leads to renal dysfunction at least in part by inducing accumulation of HexCers and LacCers in mesangial cells, resulting in fibrosis, extracellular matrix production, and hypertrophy.

Metallothionein-I/II Knockout Mice Aggravate Mitochondrial Superoxide Production and Peroxiredoxin 3 Expression in Thyroid after Excessive Iodide Exposure

Purpose. We aim to figure out the effect of metallothioneins on iodide excess induced oxidative stress in the thyroid. Methods. Eight-week-old MT-I/II knockout (MT-I/II KO) mice and background-matched wild-type (WT) mice were used. Mitochondrial superoxide production and peroxiredoxin (Prx) 3 expression were measured. Results. In in vitro study, more significant increases in mitochondrial superoxide production and Prx 3 expression were detected in the MT-I/II KO groups. In in vivo study, significantly higher concentrations of urinary iodine level were detected in MT-I/II KO mice in 100 HI group. Compared to the NI group, there was no significant difference existing in serum thyroid hormones level in either groups (P > 0.05), while the mitochondrial superoxide production was significantly increased in 100 HI groups with significantly increased LDH activity and decreased relative cell viability. Compared to WT mice, more significant changes were detected in MT-I/II KO mice in 100 HI groups. No significant differences were detected between the NI group and 10 HI group in both the MT-I/II KO and WT mice groups (P > 0.05). Conclusions. Iodide excess in a thyroid without MT I/II protection may result in strong mitochondrial oxidative stress, which further leads to the damage of thyrocytes.

Mind the gap: connexins and cell-cell communication in the diabetic kidney

Connexins, assembled as a hexameric connexon, form a transmembrane hemichannel that provides a conduit for paracrine signalling of small molecules and ions to regulate the activity and function of adjacent cells. When hemichannels align and associate with similar channels on opposing cells, they form a continuous aqueous pore or gap junction, allowing the direct transmission of metabolic and electrical signals between coupled cells. Regulation of gap junction synthesis and channel activity is critical for cell function, and a number of diseases can be attributed to changes in the expression/function of these important proteins. Diabetic nephropathy is associated with several complex metabolic and inflammatory responses characterised by defects at the molecular, cellular and tissue level. In both type 1 and type 2 diabetes, glycaemic injury of the kidney is the leading cause of end-stage renal failure, a consequence of multiple aetiologies, including increased deposition of extracellular matrix, glomerular hyperfiltration, albuminuria and tubulointerstitial fibrosis. In diabetic nephropathy, loss of connexin mediated cell-cell communication within the nephron may represent an early sign of disease; however, our current knowledge of the role of connexins in the diabetic kidney is sparse. This review highlights recent evidence demonstrating that maintenance of connexin-mediated cell-cell communication could benefit region-specific renal function in diabetic nephropathy and suggests that these proteins should be viewed as a tantalising novel target for therapeutic intervention.

RhoA/rho kinase signaling reduces connexin43 expression in high glucose-treated glomerular mesangial cells with zonula occludens-1 involvement

RhoA/Rho kinase (ROCK) signaling has been suggested to be involved in diabetic nephropathy (DN) pathogenesis. Altered expression of connexin43 (Cx43) has been found in kidneys of diabetic animals. Both of them have been found to regulate nuclear factor kappa-B (NF-κB) activation in high glucose-treated glomerular mesangial cells (GMCs). The aim of this study was to investigate the relationship between RhoA/ROCK signaling and Cx43 in the DN pathogenesis. We found that upregulation of Cx43 expression inhibited NF-κB p65 nuclear translocation induced by RhoA/ROCK signaling in GMCs. Inhibition of RhoA/ROCK signaling attenuated the high glucose-induced decrease in Cx43. F-actin accumulation and an enhanced interaction between zonula occludens-1 (ZO-1) and Cx43 were observed in high glucose-treated GMCs. ZO-1 depletion or disruption of F-actin formation also inhibited the reduction in Cx43 protein levels induced by high glucose. In conclusion, activated RhoA/ROCK signaling induces Cx43 degradation in GMCs cultured in high glucose, depending on F-actin regulation. Increased F-actin induced by RhoA/ROCK signaling promotes the association between ZO-1 and Cx43, which possibly triggered Cx43 endocytosis, a mechanism of NF-κB activation in high glucose-treated GMCs.

Down-regulation of miR-34a alleviates mesangial proliferation in vitro and glomerular hypertrophy in early diabetic nephropathy mice by targeting GAS1

AIMS

Diabetic nephropathy (DN) is a major diabetic complication characterized by mesangial proliferation and glomerular hypertrophy. MicroRNAs might play an important role in these pathological processes. The aim of this study is to examine the possible association of miR-34a as one of the microRNAs with DN and underlying mechanisms in vitro and in vivo.

METHODS

According to previous results of microarray which compared the different microRNAs between diabetic and normal control mice, miR-34a was chosen and its expression was detected by qRT-PCR. Cell viability was then assessed using Cell Counting Kit-8 (CCK8) and 5-ethynyl-20-deoxyuridine (EDU) incorporation. Antagomir was injected in db/db mice to down regulate miR-34a. Average diameter of glomeruli was analyzed by periodic acid-Schiff (PAS) stain of kidney. Luciferase gene report assay was then performed to identify the target gene of miR-34a. Additional immunoblotting and immunohistochemical analyses were implemented to verify the expression level of growth arrest-specific 1 (GAS1).

RESULTS

MiR-34a expression level was increased under high glucose condition in vitro and in vivo. Down-regulation of miR-34a inhibits mice mesangial cells (MMCs) proliferation in vitro and alleviates glomerular hypertrophy in vivo. GAS1 was proved to be the target of miR-34a through luciferase report. Moreover, up-regulation of GAS1 expression was observed in the presence of miR-34a antagomir as compared with miR-34a antagomir-NC in high-glucose-treated MMCs and db/db mice, respectively.

CONCLUSIONS

MiR-34a regulated mesangial proliferation and glomerular hypertrophy by directly inhibiting GAS1 in early DN.

Never in mitosis gene A related kinase-6 attenuates pressure overload-induced activation of the protein kinase B pathway and cardiac hypertrophy

Cardiac hypertrophy appears to be a specialized form of cellular growth that involves the proliferation control and cell cycle regulation. NIMA (never in mitosis, gene A)-related kinase-6 (Nek6) is a cell cycle regulatory gene that could induce centriole duplication, and control cell proliferation and survival. However, the exact effect of Nek6 on cardiac hypertrophy has not yet been reported. In the present study, the loss- and gain-of-function experiments were performed in Nek6 gene-deficient (Nek6^−/−) mice and Nek6 overexpressing H9c2 cells to clarify whether Nek6 which promotes the cell cycle also mediates cardiac hypertrophy. Cardiac hypertrophy was induced by transthoracic aorta constriction (TAC) and then evaluated by echocardiography, pathological and molecular analyses in vivo. We got novel findings that the absence of Nek6 promoted cardiac hypertrophy, fibrosis and cardiac dysfunction, which were accompanied by a significant activation of the protein kinase B (Akt) signaling in an experimental model of TAC. Consistent with this, the overexpression of Nek6 prevented hypertrophy in H9c2 cells induced by angiotonin II and inhibited Akt signaling in vitro. In conclusion, our results demonstrate that the cell cycle regulatory gene Nek6 is also a critical signaling molecule that helps prevent cardiac hypertrophy and inhibits the Akt signaling pathway.

p21(WAF1/CIP1) Expression is Differentially Regulated by Metformin and Rapamycin

The mammalian target of rapamycin (mTOR) pathway plays an important role in the development of diabetic nephropathy and other age-related diseases. One of the features of DN is the elevated expression of p21^WAF1/CIP1. However, the importance of the mTOR signalling pathway in p21 regulation is poorly understood. Here we investigated the effect of metformin and rapamycin on mTOR-related phenotypes in cell lines of epithelial origin. This study reports that metformin inhibits high glucose-induced p21 expression. High glucose opposed metformin in regulating cell size, proliferation, and protein synthesis. These effects were associated with reduced AMPK activation, affecting downstream mTOR signalling. However, the inhibition of the mTOR pathway by rapamycin did not have a negative effect on p21 expression, suggesting that metformin regulates p21 upstream of mTOR. These findings provide support for the hypothesis that AMPK activation may regulate p21 expression, which may have implications for diabetic nephropathy and other age-related pathologies.

AMPK-mediated downregulation of connexin43 and premature senescence of mesangial cells under high-glucose conditions

Diabetic nephropathy is associated with premature senescence. Our previous study showed that glomerular mesangial cells (GMCs) appeared to take on senescent phenotypes under high-glucose conditions in conjunction with the downregulation of connexin43 (Cx43). In this study, we investigated whether AMPK-mediated Cx43 expression and premature senescence in diabetic nephropathy are associated with mTOR activation. From in vivo and in vitro studies, we found decreased expression of Cx43 and p-AMPK but increased expression of p21 both in the glomeruli of diabetic nephropathy and in primary GMCs cultured in high glucose. Activating AMPK or inhibiting mTOR prevented the downregulation of Cx43 and reversed GMC senescence. Dominant-negative AMPK expression both reduced Cx43 expression and induced GMC senescence. Furthermore, AMPK regulated Cx43 expression and GMC senescence mainly through the inhibition of mTOR, although other pathways cannot be ruled out. This study demonstrated that AMPK signaling pathways play an important role in the regulation of the Cx43 expression that accompanies GMC senescence under high-glucose conditions.

Alpha Lipoic Acid Modulated High Glucose-Induced Rat Mesangial Cell Dysfunction via mTOR/p70S6K/4E-BP1 Pathway

The aim of this study was to investigate whether alpha lipoic acid (LA) regulates high glucose-induced mesangial cell proliferation and extracellular matrix production via mTOR/p70S6K/4E-BP1 signaling. The effect of LA on high glucose-induced cell proliferation, fibronectin (FN), and collagen type I (collagen-I) expression and its mechanisms were examined in cultured rat mesangial cells by methylthiazol tetrazolium (MTT) assay, flow cytometry, ELISA assay, and western blot, respectively. LA at a relatively low concentration (0.25 mmol/L) acted as a growth factor in rat mesangial cells, promoted entry of cell cycle into S phase, extracellular matrix formation, and phosphorylated AKT, mTOR, p70S6K, and 4E-BP1. These effects disappeared when AKT expression was downregulated with PI3K/AKT inhibitor LY294002. Conversely, LA at a higher concentration (1.0 mmol/L) inhibited high glucose-induced rat mesangial cell proliferation, entry of cell cycle into S phase, and extracellular matrix exertion, as well as phosphorylation of mTOR, p70S6K, and 4E-BP1 but enhanced the activity of AMPK. However, these effects disappeared when AMPK activity was inhibited with CaMKK inhibitor STO-609. These results suggest that LA dose-dependently regulates mesangial cell proliferation and matrix protein secretion by mTOR/p70S6K/4E-BP1 signaling pathway under high glucose conditions.

Connexin43 mediates NF-κB signalling activation induced by high glucose in GMCs: involvement of c-Src

Background

Nuclear factor kappa-B (NF-κB) signalling plays an important role in diabetic nephropathy. Altered expression of connexin43 (Cx43) has been found in kidneys of diabetic animals. The aim of the current study was to investigate the role of Cx43 in the activation of NF-κB induced by high glucose in glomerular mesangial cells (GMCs) and to determine whether c-Src is involved in this process.

Results

We found that downregulation of Cx43 expression induced by high glucose activated NF-κB in GMCs. Orverexpression of Cx43 attenuated NF-κB p65 nuclear translocation induced by high glucose. High glucose inhibited the interaction between Cx43 and c-Src, and enhanced the interaction between c-Src and IκB-α. PP2, a c-Src inhibitor, also inhibited the tyrosine phosphorylation of IκB-α and NF-κB p65 nuclear translocation induced by high glucose. Furthermore, overexpression of Cx43 or inhibition of c-Src attenuated the upregulation of intercellular adhesion molecule-1 (ICAM-1), transforming growth factor-beta 1 (TGF-β1) and fibronectin (FN) expression induced by high glucose.

Conclusions

In conclusion, downregulation of Cx43 in GMCs induced by high glucose activates c-Src, which in turn promotes interaction between c-Src and IκB-α and contributes to NF-κB activation in GMCs, leading to renal inflammation.

Advanced Glycation End Product (AGE)-AGE Receptor (RAGE) System Upregulated Connexin43 Expression in Rat Cardiomyocytes via PKC and Erk MAPK Pathways

The remodeling of cardiac gap junction contributes to the arrhythmias in a diabetic heart. We previously reported that high glucose reduced Cx43 protein level in neonatal rat cardiomyocytes. But, the effect and mechanisms of advanced glycation end product (AGE) on Cx43 expression still remain unclear. In this study, we measured the AGE receptor (RAGE) and Cx43 expression by immunohistochemisty in AGE-infused Sprague-Dawley (SD) rats. In vitro, the Cx43 and RAGE levels were detected in AGE-treated cardiomyocytes by Western blot and real-time RT-PCR. The function of cells coupling was measured by Scrap loading dye transfer assay. Our results showed that the AGE-infused rat hearts exhibited increased cardiac RAGE and Cx43, as well as Cx43 redistribution. In cultured cardiomyocytes, AGE elevated RAGE expression in a time- and dose-dependent manner. Cx43 protein and mRNA levels were upregulated by AGE (200 mg/L, 24 h), but the gap junction function was not enhanced. RAGE-targeted knock-down or the addition of PKC, and Erk inhibitors abolished the effect of AGE on Cx43. Therefore, AGE-RAGE system might elevate Cx43 expression in rat cardiomyocytes by activating PKC and Erk MAPK pathways, and it also enhanced Cx43 redistribution in vivo, which might contribute to the arrhythmias in diabetes.

Mesangial cell biology

Mesangial cells originate from the metanephric mesenchyme and maintain structural integrity of the glomerular microvascular bed and mesangial matrix homeostasis. In response to metabolic, immunologic or hemodynamic injury, these cells undergo apoptosis or acquire an activated phenotype and undergo hypertrophy, proliferation with excessive production of matrix proteins, growth factors, chemokines and cytokines. These soluble factors exert autocrine and paracrine effects on the cells or on other glomerular cells, respectively. MCs are primary targets of immune-mediated glomerular diseases such as IGA nephropathy or metabolic diseases such as diabetes. MCs may also respond to injury that primarily involves podocytes and endothelial cells or to structural and genetic abnormalities of the glomerular basement membrane. Signal transduction and oxidant stress pathways are activated in MCs and likely represent integrated input from multiple mediators. Such responses are convenient targets for therapeutic intervention. Studies in cultured MCs should be supplemented with in vivo studies as well as examination of freshly isolated cells from normal and diseases glomeruli. In addition to ex vivo morphologic studies in kidney cortex, cells should be studied in their natural environment, isolated glomeruli or even tissue slices. Identification of a specific marker of MCs should help genetic manipulation as well as selective therapeutic targeting of these cells. Identification of biological responses of MCs that are not mediated by the renin-angiotensin system should help development of novel and effective therapeutic strategies to treat diseases characterized by MC pathology.

TGFβ modulates cell-to-cell communication in early epithelial-to-mesenchymal transition

AIMS/HYPOTHESIS

A key pathology in diabetic nephropathy is tubulointerstitial fibrosis. The condition is characterised by increased deposition of the extracellular matrix, fibrotic scar formation and declining renal function, with the prosclerotic cytokine TGF-β1 mediating many of these catastrophic changes. Here we investigated whether TGF-β1-induced epithelial-to-mesenchymal transition (EMT) plays a role in alterations in cell adhesion, cell coupling and cell communication in the human renal proximal tubule.

METHODS

Whole-cell and cell compartment abundance of E-cadherin, N-cadherin, snail, vimentin, β-catenin and connexin-43 was determined in human kidney cell line (HK)2 and human proximal tubule cells with or without TGF-β1, using western blotting and immunocytochemistry, followed by quantification by densitometry. The contribution of connexin-43 in proximal tubule cell communication was quantified using small interfering RNA knockdown, while dye-transfer was used to assess gap junctional intercellular communication (GJIC). Functional tethering was assessed by single-cell force spectroscopy with or without TGF-β1, or by immunoneutralisation of cadherin ligation.

RESULTS

High glucose (25 mmol/l) increased the secretion of TGF-β1 from HK2 cells. Analysis confirmed early TGF-β1-induced morphological and phenotypical changes of EMT, with altered levels of adhesion and adherens junction proteins. These changes correlated with impaired cell adhesion and decreased tethering between coupled cells. Impaired E-cadherin-mediated adhesion reduced connexin-43 production and GJIC, these effects being mimicked by neutralisation of E-cadherin ligation. Upregulation of N-cadherin failed to restore adhesion or connexin-43-mediated GJIC.

CONCLUSIONS/INTERPRETATION

We provide compelling evidence that TGF-β1-induced EMT instigates a loss of E-cadherin, cell adhesion and ultimately of connexin-mediated cell communication in the proximal tubule under diabetic conditions; these changes occur ahead of overt signs of renal damage.