Lipolytic enzymes involving lipolysis in Teleost: Synteny, structure, tissue distribution, and expression in grass carp (Ctenopharyngodon idella)

Lipolysis is the biochemical pathway responsible for the sequential hydrolysis of triacylglycerols (TAGs) stored in cellular lipid droplets. Three enzymes are known to participate in TAGs hydrolysis, including adipose triglyceride lipase (ATGL), hormone-sensitive lipase (HSL), and monoglyceride lipase (MGL), and each is present in mammals as only one isoform. Here we show that the genome of grass carp (Ctenopharyngodon idella) and other teleosts codes for one ATGL, two HSLs, and one MGL isoforms. Two isoforms of HSL gene, HSLa and HSLb, derived from paralogous genes that could be originated from teleost-specific genome duplication (TSGD) event. The genes encoding for fish ATGL and MGL were conserved and contained nine and seven coding exons, respectively. However, two isoforms of HSL gene had a remarkable variation in gene structure, such as HSLa gene contained ten and HSLb contained thirteen exons. All three enzymes, including two isoforms of HSL, were expressed in a wide range of tissues, but the abundance of each gene mRNA showed the tissue-dependent expression patterns. During fasting, only ATGL and HSLa showed a significant increase in adipose tissue and adipocyte, indicating that ATGL and HSLa may be the main rate-limiting enzymes controlling the hydrolysis of TAGs in fasting-induced lipolysis. Different expression of HSLa and HSLb suggests that they might serve different roles in fasting-induced lipolysis. These results provide evidence about the conservation and divergence of genes of fish lipolytic enzymes.