Mechanistic Investigation Of The Effects Of Irisin On The Proliferation And Apoptosis Of Islet β Cells

Objective: The reducing number and dysfunction of islet β cells play an important role in the disease process of type 2 diabetes. Glucose toxicity can induce β cells apoptosis and dysfunction. Irisin, a novel exercise-induced myokine, can reduce obesity, improve insulin resistance and lower blood glucose by promoting the browning of white adipose tissue, enhancing thermogenesis and increasing energy expenditure. Recent studies have demonstrated that irisin can promote cell proliferation and has cell protection function. However, the effects of irisin on islet β cells are still unknown. Therefore, the present study was performed to investigate the effect of irisin on islet β cells proliferation and apoptosis induced by high glucose and explore the potential underlying mechanisms in vitro.Methods: Islet β cell line INS-1 cells were cultured and intervened with different concentrations(40, 60, 80, 100, 150 ng/ml) of irisin for 12 h or with 100 ng/ml irisin for different times(6, 12, 18, 24, 48h). The proliferation rate of INS-1 cells was measured using the Cell Counting Kit-8(CCK-8). INS-1 cells were pretreated with or without ERK inhibitor U0126, or P38 inhibitor SB203580(10 μmmol/l) for 30 minutes, followed by irisin(100 ng/ml) treatment for 24 h. Phosphorylated and total P38 and ERK proteins were detected by western blotting. The cells were pretreated with 25 mmol/l glucose for 24 h and followed treated with or without 100 ng/ml irisin for 24 h. The apoptosis rate of INS-1 cells was determined with the annexin V-FITC/propidium iodide assay. Meanwhile, the glucose-stimulated insulin secretion(GSIS) was measured by ELISA.Caspase-3, Caspase-9, Bad, Bax Bcl-2 and Bcl-xl protein levels were determined by western blot.Results: Irisin significantly increased INS-1 cells proliferation rate with the most significant effect seen at 100 ng/ml irisin treated for 24 h(P <0.05). Compared with the no-treatment control group, phosphorylated ERK and P38 protein levels were significantly increased after irisin intervention. Inhibition of p ERK by U0126 or p38 MAPK by SB203580 abolished the proliferation and up-regulatory effects of irisin on phosphorylated ERK and P38 protein levels(P<0.05). The apoptosis rate of INS-1 cells was significantly decreased and GSIS level was significantly increased after irisin intervention of high glucose treated INS-1 cells(P<0.05). Compared with high glucose treatment alone, Bcl-2 and Bcl-xl anti-apoptotic protein levels were increased and Caspase-3, Caspase-9, Bad and Bax pro-apoptotic protein levels were decreased in irisin treated INS-1 cells(P<0.05).Conclusion: Irisin can promote INS-1 cells proliferation via the ERK and P38 MAPK signaling pathways, protect the cell from high glucose-induced apoptosis by regulating Bcl-2, Bcl-xl, Bad, Bax and Caspase expression and improve islet β-cell function.