In the livestock industry, the quality of animal product is in close association with the regulation of lipid contents. Especially for the bovine and porcine meat and(or) milk production, reducing back fat, enhancing lean meat, controlling of proper extent of marbling, and energy balancing during lactation are among the critical goals for the benefit of both producers and consumers. Therefore, the understanding of the orchestrated mechanisms of lipid mobilization in the food animal species is of great interest by providing potential targets of genes and applicable approaches to achieve the improvement of related animal production. Sharing a high conservation, the knowledge of genes and proteins related to lipid metabolism in the livestock species could also bring insight for the development of human obesity treatment.
Comparative gene identification- 58 (CGI-58) has been recently identified as the co-activator of adipose triglyceride lipase (ATGL), which is the rate-limiting enzyme to breakdown trigacylglycerol as lipid storage within the lipid droplet of adipocytes.
This study reported the CGI-58 cDNA and deduced the amino acid sequences in 3 breeds of bovine (Angus, Holstein, and Hanwoo) and swine (Duroc, Berkshire and Landrace) respectively. The result revealed bovine CGI-58 to be 1,047 bp (348 AA) and swine CGI-58 to be 1,050 bp (349 AA) in full lengths. Homologies are found between the human, cattle, swine, mouse and chicken for CGI-58’s lipid droplet binding domain, the α/β hydrolase-fold domain and the lysophosphatidic acid acyltransferase (LPAAT) domain, which demonstrated conservation across species.
Two unique alternatively spliced variants of bovine CGI-58 and one in the swine species were identified with varied deletions of exons, resulting in different protein isoforms. These isoforms are deduced with unique characteristics in lipid droplet binding, ATGL stimulation and LPAAT activity. These findings suggest the possibility of the involvement of alternative splicing events in the regulation of lipolytic process via fine controlling the activity of related proteins.
Developmental investigation of porcine CGI-58 in adipose and stromal-vascular (SV) cell fractionation revealed that CGI-58 and ATGL are highly expressed (P<0.01) in mature adipocytes. The expressions of CGI-58 and ATGL mRNA are found to increase (P<0.05) at d 6 of SV cell culture. On the aspect of hormonal regulation, the result from in vitro cell culture showed that insulin decreased (P<0.05) the expressions of both CGI-58 and ATGL in dose dependent manner. Also, the expression of CGI-58 and ATGL mRNA significantly increased after 24 h of fasting in Berkshire pigs (p<0.05). However, restoring of mRNA expression at 6 h after re-feeding only occurred for CGI-58 but not ATGL. The uncorrelated pattern was also shown by the increase of ATGL mRNA expression after 14 days of feed-restriction in Landrace pigs with unaltered CGI-58 mRNA expression level.
The result of the study provided the complete cDNA and amino acid sequences of full-length and alternatively spliced variants of bovine and porcine CGI-58. It also revealed the developmental, hormonal, and nutritional regulations of porcine CGI-58 gene, which contributes to the understanding of CGI-58’s role in lipid metabolism.