The Adipokine Chemerin Induces Lipolysis And Differentiation In Bovine Intramuscular Adipocytes

The content of intramuscular fat(IMF)is positively correlated with the quality of meat,which directly affects the tenderness and juiciness of meat,and IMF content is an important parameter in meat quality index.Adipogenesis and lipid homeostasis reflects a balance of processes in adipocytes metabolism,fat synthesis and decomposition of the relative speed determined the amount of body fat content.It is quite clear that adipose tissue is not only an organ for energy storing,but also works as a multifunctional endocrine tissue.What's more,it is reported that the adipose factor Chemerin regulated adipose formation and glucose in 3T3-L1 cells,which is an important factor in regulating fat deposition.However,most studies have focused on the process of metabolism and differentiation of mouse adipocytes.The effects and mechanisms of Chemerin in the differentiation and lipolysis of mammalian intramuscular adipocytes remain unknown.In this study,intramuscular adipocytes were used as experimental materials,and the effect of Chemerin on the metabolism of adipocytes and intramuscular adipocytes in bovine intramuscular adipocytes was investigated.1.Primary culture of bovine intramuscular adipocytesIn this study,three methods were used to isolate and culture bovine intramuscular preadipocytes in order to establish a more pure model of bovine intramuscular preadipocytes.The results showed that the cultured time used in tissue block cultivation method and ceiling culture method were longer than the time used in the traditional digestion method,and the time used in traditional digestion method was shorter,but the number of hybrid cells shown in traditional digestion method was more.Moreover,obtained bovine intramuscular preadipocytes were stained with oil red O,the data show that the differentiation rate of intramuscular adipocytes obtained by tissue block cultivation method and the traditional digestion method is lower,while the differentiation rate of bovine intramuscular preadipocytes obtained by the ceiling culture method is higher and these preadipocytes are more purer.In general,the results indicate that the ceiling culture method is the better way to establish bovine intramuscular preadipocytes with high purity and high differentiation rate.2.Chemerin induces lipolysis of bovine intramuscular adipocytes through activation of the ERK 1/2 pathwayIn this study,bovine intramuscular adipocytes were cultured in DMEM medium with Chemerin from day 0 to day 8.The process of lipolysis of mature adipocytes and the adipogenesis of de-differentiated preadipocytes were investigated.The results showed that Chemerin induced significant lipolytic metabolism in intramuscular mature adipocytes on day 4,indicated by increased levels of glycerol,FFA and up-regulated expression of the lipolysis-critical factor HSL,LPL and leptin.Meanwhile,the expression of adipogenic key factors PPARy,C/EBP? and A-FABP were obviously decreased by Chemerin during lipolysis or dedifferentiation in mature adipocytes.To further confirm the role of Chemerin in the lipolysis or de-differentiation of bovine adipocytes,mature fat cells were exposed to culture medium with 0.1 ?g/mL Chemerin from day 0 to day 8,In this study,we selected 4 days for the mechanism of intramuscular lipolysis.The experiment were divided into 3 groups:control group,Chemerin group,Chemerin+ U0126 group.Chemerin significantly increased adipocyte glycerol and FFA release,which was inhibited by either ERK(U0126)inhibitors,suggesting that ERK were involved in mediating Chemerin enhanced lipolysis.Moerover,the content of TG in Chemerin-treated cells significantly decreased that the one in the control group,whereas this effect is reversed after the addition of the inhibitor.At the same time,mRNA and protein expression of HSL,LPL and PPARa were up-regulated by Chemerin during adipocytes lipolysis,which was reversed by the ERK inhibitor.Interestingly,the results indicated that Chemerin decreased the adipogenic key factors expression,including PPARy and C/EBPa,further demonstrated the lipolysis effect of Chemerin.In conclusion,these data supported that Chemerin promotes lipolysis in mature adipocytes involves activation of the ERK1/2 pathway,indicating that ERK 1/2 signaling pathway mediated the lipolysis of Chemerin on bovine intramuscular adipocytes.3.The adipokine Chemerin induces differentiation in bovine intramuscular adipocytesThis study was conducted to investigate the effects and molecular mechamisms of Chemerin in the lipolysis of bovine intramuscular mature adipocytes.Adipocytes were cultured with medium containing Chemerin for 4 days and 8 days.Oil Red O staining and absorbance confirmed that Chemerin promoted lipid synthesis in the differentiation of preadipocytes during the differentiation of intramuscular adipocytes.Others,the content of TG and TCH in the Chemerin-treated cells was significantly increased compared to the control cells.The expression of PPARy,C/EBPa,and A-FABP at the level of transcription and translation were all significantly increased compared with the control cells.These results suggest that Chemerin promotes differentiation of intramuscular adipocytes and induces adipogenesis,further demonstrating the important role of Chemerin in intramuscular fat deposition in ruminants.Taken together,the results of this study provide a theoretical basis to improve the understanding of Chemerin function in the specific deposition of animal intramuscular fat and meat quality.