The Impact Of IL-15 And STAT3 On The Differentiation Of Porcine Intramuscular Preadipocytes

Intramuscular fat(IMF)refers to the fat distributed between muscle fibers and muscle bundles,and mainly includes phospholipids present in the cell membrane,and are important factors affecting pork quality.The early pursuit of high lean meat ratios led to a continuous decrease in the intramuscular fat content of pork,and decreased the taste and sensory quality.Increasing intramuscular fat content is a critical task in improvin g pork quality.Since intramuscular fat is distributed between muscle fibers and has special tissue physiological characteristics,so paracrine of muscle tissue and its microenvironment have potential effects on intramuscular fat.Interleukin-15(IL-15)is a major cytokine secreted by muscle that binds to its receptor and activates the JAK/STAT3 pathway.This study was intended to further explore the mechanism of IL-15 regulating porcine intramuscular fat maturation and differentiation through JAK/STAT3.The specific research process and results was as follows:First,the effect of IL-15 on adipocyte differentiation was detected.In this study,porcine intramuscular preadipocytes were obtained by "ceiling" method,and then treated with 200 ng/ml IL-15 to detect the differentiation ability and lipid droplet deposition of porcine intramuscular precursor adipocytes.The results of oil red O staining and triglyceride content determination showed that the differentiation and lipid deposition ability of intramuscular adipocytes were significantly enhanced by IL-15 treatment,qPCR results showed that the expression levels of PPARy and C/EBPa were significantly increased,and the FABP4 expression of adipose synthase increased significantly(FASN expression was unchanged),accompanied by increased levels of ATGL and HSL,enzymes involved in lipolysis.The above results show that 200 ng/ml IL-15 can promote the differentiation of intramuscular precursor adipocytes and the deposition of lipid droplets.Second,to explore the role of IL-15 signaling molecule STAT3 in the differentiation of porcine intramuscular adipocytes.This study to detected the expression trend of STAT3 during the differentiation of porcine intramuscular adipocytes,and to explore the effect of STAT3 on the differentiation of intramuscular fat cells by interfering endogenous STAT3 and overexpressing STAT3.The results showed that the expression level of STAT3 increased significantly in the early stage of differentiation and remained unchanged afterwards,and its phosphorylation level gradually decreased as differentiation progressed.Knockdown of endogenous STAT3 inhibited the differentiation and lipid deposition of intramuscular adipocytes,differentiation marker gene PPARy,C/EBPa and synthesis related enzyme FABP4,FASN expression significantly decreased,and the expressions of ATGL and HSL also decreased,involved in lipolysis related enzyme.Overexpression of STAT3 could promoted the differentiation and lipid droplet deposition of intramuscular adipocytes,differentiation marker gene PPARy,C/EBPa and synthesis related enzyme FABP4,FASN expression increased significantly,and the expressions of ATGL and HSL also increased.The above results indicated that IL-15 signaling transduction molecule STAT3 can promote the differentiation of porcine intramuscular adipocytes.Third,to study the role of STAT3 in promoted the differentiation of intramuscular adipocytes by IL-15.Treated of intramuscular adipocytes with IL-15 increased the expression of STAT3,the phosphorylation of STAT3 increased significantly,and the JAK/STAT3 signaling pathway was activated.IL-15 was used to treat differentiated adipocytes,while si-STAT3 interfered with the endogenous expression of STAT3,adipocyte differentiation and lipid droplet deposition ability was decreased,and decreased of the related genes expression was similar to that of si-STAT3 alone,indicated that STAT3 played a decisive role in the action of IL-15.Consistently,the ability and expression of genes involved in differentiation and adipogenesis were unregulated in intramuscular adipocytes co-treated with pc-STAT3 and IL-15 compared with that in pc-STAT3 alone infection group,indicating that IL-15 can enhance the fat-producing effect by activating the STAT3 signaling pathway.In summary,the results of this study indicated that the muscle secretory factor IL-15 could promoted differentiation and adipocytosis of porcine intramuscular adipocytes by activated the JAK/STAT3 signaling pathway.