ABSTRACT
Recombinant human erythropoietin (rHuEPO) reduces serum insulin levels, increases insulin sensitivity, and reduces insulin resistance (IR). However, the mechanisms behind these effects are unclear. This study aimed to investigate the mechanism by which rHuEPO effects IR in 3T3L1 adipocytes. After treatment with different concentrations of rHuEPO, glucose consumption, and tumor necrosis factor (TNF-α), adiponectin, and leptin levels were assayed with a commercial enzyme-linked immunosorbent assays. Endogenous erythropoietin receptor (EPOR) expression was inhibited using small interfering RNA (siRNA). EPOR protein and mRNA expression was detected via immunofluorescence and real-time PCR analyses, respectively. The expression of pAKT/AKT and p-STAT5/STAT5 was determined via Western blot analysis. rHuEPO treatment improved glucose uptake, increased adiponectin levels, and reduced TNF-α and leptin levels in 3T3L1 adipocytes with dexamethasone-induced IR. Whereas EPOR protein and gene expression was absent in preadipocytes, it was observed in mature 3T3L1 adipocytes. However, the expression of EPOR in insulin resistant 3T3L1 adipocytes was significantly decreased (p<0.05). rHuEPO increased the expression of EPOR, and upregulated the expression of pAKT/AKT and pSTAT5/STAT5 in 3T3L1 adipocytes (p<0.05), which was blocked by siEPOR, the phosphatidylinositol-3-kinase (PI3K) inhibitor, LY294002, and a STAT5 inhibitor, respectively. In summary, rHuEPO reduced IR in adipocytes by increasing glucose uptake and improving the adipokine profile. rHuEPO-induced EPOR protein expression and subsequent induction of pAKT and pSTAT5 suggest that the EPO-EPOR system may play a role in glucose metabolism within adipocytes.
Subject(s)
Adipocytes/drug effects , Adipocytes/metabolism , Erythropoietin/pharmacology , Insulin Resistance , Receptors, Erythropoietin/metabolism , Signal Transduction/drug effects , 3T3-L1 Cells , Adipocytes/cytology , Adiponectin/metabolism , Animals , Cell Differentiation/drug effects , Cell Differentiation/genetics , Cell Proliferation/drug effects , Gene Expression Regulation/drug effects , Glucose/metabolism , Humans , Insulin Resistance/genetics , K562 Cells , Leptin/metabolism , Mice , Models, Biological , RNA, Messenger/genetics , RNA, Messenger/metabolism , Receptors, Erythropoietin/genetics , Recombinant Proteins/pharmacology , Signal Transduction/genetics , Staining and Labeling , Tumor Necrosis Factor-alpha/metabolismABSTRACT
The efficacy of homocysteine (Hcy)-lowering therapy in reducing the risk of CVD among patients with chronic kidney disease (CKD) remains controversial. We performed a meta-analysis to determine whether pooling the data from the few small randomised, controlled trials that address this topic would improve the statistical power of the analysis and resolve some of the inconsistencies in the results. Randomised, controlled clinical trials (RCT) were identified from MEDLINE, EMBASE, www.clinicaltrials.gov, the Cochrane Controlled Clinical Trials Register Database and Nephrology Filters. Independent extraction of articles was performed using predefined data fields. The primary outcome was relative risk (RR) of CVD, CHD, stroke and all-cause mortality for the pooled trials. A stratified analysis was planned, assessing the RR for cardiovascular events between the patients on and not on dialysis. Overall, ten studies met the inclusion criteria. The estimated RR were not significantly different for any outcomes, including CHD (RR 1·00, 95 % CI 0·75, 1·31, P = 0·97), CVD (RR 0·94, 95 % CI 0·84, 1·05, P = 0·30), stroke (RR 0·83, 95 % CI 0·57, 1·19, P = 0·31) and all-cause mortality (RR 1·00, 95 % CI 0·92, 1·09, P = 0·98). In the stratified analysis, the estimated RR were not significantly different for cardiovascular events regardless of dialysis or in combination with vitamin B therapy or the degree of reduction in Hcy levels. Our meta-analysis of RCT supports the conclusion that Hcy-lowering therapy was not associated with a significant decrease in the risk for CVD events, stroke and all-cause mortality among patients with CKD.
