Mechanisms Study On Secreted MicroRNA Affecting The Metabolism Of Adult Mice And The Development Of Fetal Mice

THESIS: Mechanisms study on secreted micro RNA affecting the metabolism of adult mice and the development of fetal mice SPECIALIZATION: Biology POSTGRADUATE: Dameng Li MENTOR: Professor Chenyu ZhangAbstractType 2 diabetes(T2DM)is a complex metabolic disease characterized by hyperglycemia due to insulin resistance or a relative lack of insulin secretion.Diabetes currently affects nearly 400 million people worldwide,and as populations age and lifestyles change,the number of people affected by the disease is expected to reach 600 million by 2040.At present,there is no effective treatment for T2 DM.As a chronic disease,even if it is properly treated,long-term chronic hyperglycemia will still lead to various complications,which will seriously affect human health and life.Diabetes has become one of the most common causes of death in humans.Therefore,the urgent task is to explore the pathogenesis of type 2 diabetes and better treatment.Obesity is the leading cause of insulin resistance,which is a hallmark of type 2diabetes.Obesity is a disease characterized by excessive body fat.The most important characteristic of obesity is the excessive accumulation of fat,which leads to chronically elevated plasma free fatty acids(FFA)levels.FFA plays an important role in the development of obesity-induced insulin resistance.FFA can induce insulin resistance in a variety of ways including lipid metabolism,inflammatory factors,and oxidative stress.However,the molecular mechanism of FFAs promoting insulin resistance still needs further exploration.Micro RNAs are small non-coding RNAs consisting of 19 to 24 nucleotides that can serve as negative regulators of post-transcriptional gene expression by pairing to the 3’-UTR of target m RNAs.With the help of the RNA-induced silencing complex(RISC),mi RNAs repress gene expression by translational inhibition and m RNA degradation.In 2008,our lab found micro RNA is stable in serum and various mi RNAs exist in the circulation system as well as in tissues.Meanwhile,in 2010,we found that mi RNAs in exosomes could be delivered from donor cells to recipient cells to trigger downstream signaling events.These secreted mi RNAs act as signaling molecules that are involved in various biological processes,including development,immune responses,and tumourigenesis.Recently,more and more studies demonstrated that secreted mi RNAs play an important role in the pathogenesis of type 2 diabetes.Our study suggests that secreted mi RNAs are involved in the development of insulin resistance induced by FFAs.The first part studied that pancreatic islet-secreted exosomal mi R-29 family members(mi R-29s)induced hepatic insulin resistance(IR).Previous studies found that the mi R-29 s level in plasma from obese individuals was significantly increased.The expression levels of mi R-29 s were significantly elevated in FFA-treated pancreatic islet cells and its exosomes.In addition,mice treated with FFA-induced mi R-29 s secreted by pancreatic islet cells showed insulin resistance.These results suggest that the mi R-29 s family secreted by pancreatic islets stimulated by FFA plays an important role in the development of insulin resistance.To test this hypothesis,we constructed three transgenic mice,including mi R-29 s TG mice,mi R-29 amut mice,and mi R-29 sdef mice.The expression levels of mi R-29 s in the islets and plasma of transgenic mice overexpressing mi R-29 s in their β-cells were significantly elevated.Meanwhile,mi R-29 s TG mice exhibited inhibited insulin-mediated suppression of hepatic gluconeogenesis.These results suggest that mi R-29 s secreted by pancreatic islets can indeed induce insulin resistance in mice,possibly by acting on the liver.Subsequently,we used the mi R-29 amut as a tracer,which was selectively overexpressed in β-cells in mi R-29 amut mice.The results showed that mi R-29 s secreted by pancreatic islets was mainly delivered to the liver and damaged the insulin sensitivity of the liver by inhibiting the PI3 K pathway.In addition,disruption of mi R-29 s expression in β-cells reversed insulin resistance induced by a high-fat diet.In conclusion,we found that mi R-29 s secreted by β-cells play an important role in the development of insulin resistance in the liver.The second part studied whether micro RNA in the maternal system can transfer through the placenta to the fetus’ s side.We found that exogenous plant mi RNA could transfer through the placenta and enter into a fetus.In addition,we gavage fed synthetic AFP-si RNA to pregnant mice and found that exogenous si RNA could pass through the placenta and regulate the gene expression in the fetus liver.Moreover,we found that mi R-29 a,which was significantly elevated in the serum of obese pregnant mice,can pass through the placenta and enter into fetuses with the help of exosomes.This result suggests that endogenous mi RNA in the maternal system can transfer through the placenta to the fetal side.In conclusion,mi RNA may be a new tool for fetal-maternal crosstalk.