The Role And Mechanism Of Irisin In The Outcomes Of Newly Diagnosed Prediabetes

Objective:Diabetes mellitus is one of the fastest growing diseases around the world in this century,which has become a severe challenge for public health around the world.Prediabetes is a state between normal blood glucose and diabetes.It indicates that the risk of type 2 diabetes mellitus is much higher than that in the general people in the future.Most people go through prediabetes before they develop diabetes.However,drug treatment or lifestyle intervention has been confirmed to reverse abnormal glucose metabolism,prevent or delay the occurrence of diabetes in a large number of studies.Therefore,it is significant for the prevention and control of diabetes to identify those individuals who tend to develop diabetes and take effective interventions.Irisin is a newly discovered myokine in 2012.Studies have shown that irisin can increase the expression of uncoupling protein 1,induce the browning of white adipocytes,promote energy consumption,and also act on a variety of organs and tissues to regulate glucose homeostasis through a variety of pathophysiological mechanisms.Thus,irisin is highly expected in the treatment of metabolic diseases such as obesity and diabetes.However,findings on whether irisin is related to the development of diabetes are not consistent.To date,there is no specific study to reveal the possible role of irisin in different outcomes of prediabetes.The first part of our study aims to explore the relationship between irisin and the different outcomes of newly diagnosed prediabetes.On this basis,because insulin resistance is the key in the pathogenesis of type 2 diabetes mellitus,and the decrease of glucose uptake,transport and metabolic capacity of skeletal muscle under the stimulation of insulin is an important reason for the disorder of glucose metabolism,the second part of this study was to investigate the effect of irisin on glucose uptake and PI3K/AKT signaling pathway in insulin resistant skeletal muscle cells.Methods:1.The first part of our study was embedded in the Risk Evaluation of c Ancers in Chinese diabe Tic Individuals: a l ONgitudinal(REACTION)study.A total of 10015 participants completed physical examination,laboratory measurements and questionnaires including medical history,physical activities,and smoking and alcohol drinking status,and 7570 of these participants were followed up in July 2014.A total of 2530 participants were newly diagnosed with prediabetes at baseline and completed follow up.We excluded participants with a history of hypertension,cardiovascular disease,stroke,liver or kidney dysfunction,cancer,acute or chronic infection,and any medication use at baseline.Of the remaining 1238 participants,161 subjects who developed diabetes at follow up were selected as the case group,and161 individuals matched by sex and age who did not develop diabetes at follow up were included as the control group.We analyzed the relationship between baseline serum irisin levels and the risk of diabetes in newly diagnosed prediabetes.Of the 161 matched case-control pairs,75 pairs were excluded because either of them had the above accompanying diseases,or any medication use at follow up,or lacked samples.Finally,the serum irisin levels at follow up were measured in 86 matched case-control pairs.Fasting serum irisin levels were measured using enzyme-linked immunosorbent assay.2.We established the insulin resistance model in C2C12 myotubes using palmitic acid in the second part of this study.The insulin resistant C2C12 myotubes were treated with different concentrations(0 n M,2.5 n M,5 n M and 10 n M)of recombinant irisin for 24 hours,and insulin resistant C2C12 myotubes were treated with 5 n M recombinant irisin for 0,1,4 and 24 hours,respectively.The uptake of2-NBDG was detected by flow cytometry.The protein expression levels of p-PI3 K,AKT and p-AKT were detected using western blot analysis.Results:1.In the first part of our study,baseline serum irisin levels were higher in the cases than in the controls(P=0.002).Baseline serum irisin levels were positively correlated with age(r=0.191,P=0.001),systolic blood pressure(r=0.134,P=0.016)and 2-h post-load plasma glucose(r=0.161,P=0.004).High baseline serum irisin levels were an independent risk factor for the development of diabetes(OR=1.235,95%CI 1.025–1.488,P=0.027).After adjustment for confounding factors,subjects in the highest quartile of irisin levels had a much higher risk of diabetes than those in the lowest quartile(OR=3.065,95%CI 1.511–6.218).However,the extent of decrease in irisin levels during follow-up was greater in the cases than in the controls(P<0.001).The serum irisin levels in the cases were significantly lower than that in the controls at follow up(P<0.001).At follow up,serum irisin levels were negatively correlated with fasting blood glucose(r=-0.256,P=0.001),2-h post-load plasma glucose(r=-0.616,P<0.001),and Hb A1c(r=-0.347,P<0.001).At follow up,the serum irisin levels of 134 subjects were lower than that of baseline,and the extent of decrease were positively correlated with the baseline serum irisin levels(r=0.773,P<0.001).Among them,those with the extent of decrease in irisin above the median had a much higher risk of diabetes than that below the median(OR=5.077,95% CI2.112–12.206).2.In the second part of this study,compared with the control group,the glucose uptake of C2C12 cells in palmitic acid treatment group was significantly decreased(t=29.114,P<0.001).Compared with the palmitic acid treatment group,glucose uptake of C2C12 cells in 5 n M and 10 n M recombinant irisin co-incubation groups were significantly improved(P<0.01).Compared with the palmitic acid treatment group,5 n M recombinant irisin treatment for 1 h,4 h and 24 h significantly improved the glucose uptake of C2C12 cells(P<0.01).Compared with the control group,the protein expression levels of p-PI3 K and p-AKT in the palmitic acid treatment group were significantly decreased under the stimulation of insulin(P<0.05).There was no significant difference in the expression of p-PI3 K protein between palmitic acid treatment group and palmitic acid + irisin treatment group(P>0.05),but the expression of p-AKT protein was lower in palmitic acid + irisin treatment group(P<0.05).Conclusions:1.Irisin is closely related to the outcomes of newly diagnosed prediabetes.High baseline serum irisin levels may be a compensatory increase,and the occurrence of diabetes might be related to the impaired compensatory ability.Serum irisin levels and the extent of decrease may be a good predictor for developing diabetes.2.Irisin can reduce the inhibition of palmitic acid on glucose uptake of C2C12 cells and improve insulin resistance,but this effect may not be mediated by PI3K/AKT signaling pathway,and PI3K/AKT signaling pathway may not play a dominant role in irisin improving insulin resistance of C2C12 cells.