Correlation Analysis And Mechanism Research On Betatrophin And Insulin Resistance

Research Backgrounds and AimsAccording to the data from the International Diabetes Federation (IDF), the global prevalence of diabetes in2011was4.4%. The number is estimated to reach7.7%by2030.As we all know, type2diabetes (T2D) is characterized by a series of metabolic disorders that consist of insulin resistance (IR) and β-cell dysfunction. In normal physiological conditions, normoglycemia is maintained under a balance between insulin sensitivity and insulin secretion, and when insulin sensitivity decreases, insulin secretion increases to maintain normoglycemia. When the magnitude of the increased demand for insulin due to insulin resistance caused by excess caloric intake and physical inactivity exceeds the magnitude of P-cell mass expansion, P-cell workload will increase. In individuals who are susceptible to T2D, increased P-cell workload may lead to β-cell failure and the development of T2D.It has long been known that IR induces compensatory increases in P-cell mass and function to maintain normaglycemia, likely due to circulating growth factors. Based on this theory, numerous studies have been reported in the last few decades that have aimed to identify these circulating factors that involved in the regulation of β-cell mass and function and may provide novel potential therapeutic strategies. Gut-derived incretins such as glucagon-like peptide-1, muscle-derived myokines such as interleukin-6, macrophage-derived cytokines and adipocyte derived adipokines including leptin and adiponectin were expected to develop regenerative P-cell therapy. However, the clinical practice of these hormones has been restricted due to their lack of specificity and modest effect.Very recently, Yi et al. from Harvard stem cell institute reported the identification of a new hormone named betatrophin that could specifically increase β-cell mass in a novel pharmacological marine model of IR and therefore rases hope for regenerative β-cell therapy in humans.Although, betatrophin exerts strong antidiabetic properties in animal models, an exact knowledge of its bioactivity and its mode of action remains to be investigated. To explore the clinical relevance of betatrophin in humans, here, we examined circulating betatrophin levels in subjects with different glucose tolerance status and its correlation with IR.MethodsSerum betatrophin levels were measured using ELISA in age-, sex-, BMI-and blood lipids-matched subjects with normal glucose tolerance (NGT)(n=137), isolated impaired fasting glucose (IFG)(n=69), isolated impaired glucose tolerance (IGT)(n=120) and newly diagnosed T2D (n=112) from the Risk Evaluation of cAncers in Chinese diabeTic Individuals:a lONgitudinal (REACTION) study.ResultsSerum betatrophin levels were elevated in patients with T2D compared to subjects with NGT, isolated IFG or isolated IGT (798.6±42.5vs.692.7±29.0, P<0.05; vs.682.7±43.0, P<0.05; vs.646.8±34.3pg/ml, P<0.01). Betatrophin levels positively correlated with index of homeostasis model assessment of insulin resistance (HOMA-IR)(partial r=0.11); inversely correlated with quantitative insulin sensitivity check index (QUICKI)(partial r=-0.11), the Gutt insulin sensitivity index (ISIg)(partial r=-0.12) and the Matsuda insulin sensitivity index (ISIm)(partial r=-0.11) after controlling for age, sex, BMI and blood lipid in all participants (all P values<0.05).ConclusionsCirculating betatrophin levels are increased in patients with T2DM and associated with indexes of insulin resistance. Research Backgrounds and AimsBetatrophin, also known as ANGPTL8/TD26/RIFL/C19orf8/lipansin, is a liver-derived hormone for the pancreatic β cell proliferation. A number of recent observations showed that insulin resistance was related with betatrophin expression. In many murine models of insulin resistance, including db/db, ob/ob, pregnant and insulin receptor antagonist S961-infused mice, betatrophin levels were elevated. In humans, we found that circulating betatrophin levels were increased in patients with T2D, which was consistent with other studies. Meanwhile, betatrophin levels in obese individuals with insulin resistance (including adults, children and adolescents) were also elevated. The expression of betatrophin was correlated positively with insulin resistance and negatively with insulin sensitivity. Based on these observations, it is well known that a state of insulin resistance was specifically involved in the induction of betatrophin gene expression. However, the roles of insulin resistance in betatrophin expression remain to be fully clarified.Therefore, in this study, to explore the roles of insulin resistance in betatrophin expression and the mechanisms, we induced in vitro insulin-resistance models in human hepatocytes L02by a variety of treatments and determined betatrophin levels in different insulin-resistance models.Methods and Results(1) We induced in vitro insulin-resistance models in human hepatocytes L02using TNF-a (4ng/ml), IL-1β (20ng/ml), dexamethasone (1μM), palmitate (500μM), high glucose (33mM) and high insulin (10-6M) separately. All six models exhibited compromised insulin responses as determined by phosphorylation of Akt at serine473and2-NBDG uptake.(2) We examined betatrophin levels with ELISA in six models and found that betatrophin levels were only enhanced in insulin-resistance model induced by high insulin.(3) We stimulated L02cells with various concentrations of insulin (0-10-5M) and when insulin was up to10-6M (presence of insulin resistance), betatrophin expression started to increase.(4) To figure out the cause of betatrophin expression is insulin-induced insulin resistance or insulin itself, we used insulin signaling pathway PI3K/Akt inhibitor LY294002to block the action of insulin and strengthen insulin resistance. The results showed that high insulin induced betatrophin expression could be reduced by LY294002. Moreover, IGF-1(PI3K/Akt agonist) could also increase betatrophin expression and IGF-1induced betatrophin elevation could be reduced by LY294002.(5) In humans, we recruited7type2diabetic patients with exogenous insulin injection (±metformin) and7age-, sex-, BMI-and blood lipid-matched type2diabetic patients without insulin injection (±metformin). Betatrophin levels in the fasting serum were assessed using ELISA. The results showed that betatrophin levels were increased in patients who have received insulin injection compared with those without any anti-diabetic treatment or only with metformin (785.5±117.8vs.240.1±53.0pg/ml, P<0.01).ConclusionsTherefore, we believe that it is high insulin, but not insulin resistance, that stimulates betatrophin secretion by PI3K/Akt signaling pathway activation.