Regulation of adipose triglyceride lipase by fasting and refeeding in avian species

Lipolysis in fat tissue is a process that is not fully understood. Increasing knowledge of the process could allow for increased feed efficiency and reduced fat content, which would lower feeding costs for poultry production. Adipose triglyceride lipase (ATGL) is an adipose-specific enzyme that cleaves at the Sn-1 position of triglycerides, releasing nonesterified fatty acids (NEFA) into the bloodstream. Adipose triglyceride lipase has recently been cloned in avian species. For further understanding of how ATGL responds to environmental stimuli, we fasted 21-d-old Ross 308 broiler chickens for 24 h. Adipose and liver tissues were collected before the fasting period and at its conclusion, as well as 4, 8, 12, and 24 h after being refed. Blood samples were also collected at these time points. Additionally, tissue samples were collected from 30 quails subjected to the same fasting period, with refeeding time points of 2, 4, and 8 h. Adipose triglyceride lipase in tissue samples was analyzed via Western blot and quantitative real-time PCR. Protein and RNA levels of ATGL were high in the birds after the fasting period. Ribonucleic acid levels quickly returned to control levels following refeeding. Protein levels, however, remained high in the chicken throughout the 4- and 8-h refeeding time points. For the quail samples, ATGL protein returned to normal levels at 8 h. To relate the release of NEFA into the blood with ATGL expression, plasma analysis was done. Nonesterified fatty acids were significantly higher after the fasting period than the control and returned to control levels by 4 h after refeeding. The quick return of the RNA to control levels suggests that ATGL production was stimulated during the fasting period but inhibited once food was reintroduced. The immediately lowered NEFA levels suggest that the residual high amounts of ATGL protein shown by Western blot were no longer functioning. This suggests the existence of a mechanism to inactivate the active form of ATGL, possibly through posttranslational modification of the protein.