| Popis: |
Obesity is a global trend and major risk factor for serious diseases including type 2 diabetes. The pathogenic effects related to common obesity are largely attributed to dysregulated secretion of adipokines followed by insulin resistance in peripheral tissues. White adipose tissue serves as a dynamic endocrine organ as well as a major energy reservoir. Adipokines influence various metabolic processes; however, precise physiological roles of adipokines need to be further investigated. Gene expression omnibus (GEO) profile, a public repository for microarray data, was used to identify a novel adipose-specific gene, chordin-like 1 (Chrdl1). Further analysis showed that Chrdl1 encodes a new adipokine. Chrdl1 expression increases during adipogenesis. This pattern, combined with an increased lipid accumulation and adipocyte differentiation in Chrdl1-overexpressing 3T3-L1 cells suggests that Chrdl1 is a pro-adipogenic adipokine. Adipose tissue is also of great significance in the production of food animals. Reduction of adipose tissue mass will lead to enhancing feed efficiency. The net decrease in adiposity is achieved by up-regulation of lipolysis. The initial step of lipolysis is catalyzed by adipose triglyceride lipase (ATGL) which is the rate-limiting step in this process. CGI-58 and G0S2 are known to be an activator and an inhibitor of ATGL-mediated lipolysis, respectively. In the current study, porcine G0S2 was abundantly expressed in adipose tissue, and its expression was increased during adipogenesis, suggesting that G0S2 expression is related to adipocyte development (pro-adipogenic) as well as inhibition of ATGL (anti-lipolytic). In another study, the expression of bovine G0S2 and CGI-58 in muscle of high-marbled steers of Hanwoo was investigated. The regulation of lipolysis in muscle has a potential to increase marbling. The expression of G0S2 and CGI-58 was significantly high in muscle of high-marbled steers, suggesting that both genes are novel biomarkers of marbling. In addition, G0S2 was highly expressed in intramuscular fat portion, whereas CGI-58 expression was significantly high in the remaining portion of muscle. It suggests that G0S2 inhibits ATGL-mediated lipolysis in intramuscular fat while CGI-58 activates ATGL in intramyocellular triglycerides. In another recent study, RBP7 was identified as a novel adipose-specific gene in avian species through microarray along with Western blot analysis. Because the RBP7 promoter contains several binding sites for adipogenic transcription factors, transgenic quail containing a GFP gene under the control of the RBP7 promoter were generated. GFP expression in transgenic quail was specific to adipose tissue. These findings provide evidence that the RBP7 promoter-gene construct can be used to overexpress target genes in adipose tissue.In conclusion, this study has found a visceral adipokine (Chrdl1), marbling biomarkers (G0S2 and CGI-58), and an adipose-specific gene (RBP7) and its promoter for overexpression of target genes. Chrdl1 increases lipid accumulation and adipocyte differentiation of 3T3L1 preadipocytes. Expressions of G0S2 and CGI-58, regulators of ATGL-mediated lipolysis, were significantly higher in muscle of high-marbled steers. Avian RBP7 is adipose-specific and its promoter was used to generate transgenic quail expressing a GFP gene in adipose tissue. Together, this study advances adipose tissue biology through identification of genes related to adipokine, marbling, and adipose-specific expression. |
