Expression of lipogenic enzymes in chickens

Hubbard x Hubbard chickens (Gallus gallus) growing from 7 to 28 days of age were fed 12 or 30% protein diets and then switched to the diets containing the opposite level of protein. Birds were killed on days 28, 29, 30 and 31. Measurements taken included in vitro lipogenesis (IVL), malic enzyme (ME), isocitrate dehydrogenase (ICD) and aspartate aminotransferase (AAT) activities and the expression of the genes for ME, fatty acid synthase (FAS) and acetyl coenzyme carboxylase (ACC). Gene expression was determined with a combined RT-PCR using SYBR green as a fluorescent probe monitored in a real time mode. IVL and ME activity were inversely related to dietary protein levels (12 to 30%) and to acute changes in either level. In contrast, both ICD and AAT activities were increased by any increase in dietary protein. Lipogenic gene expression was inversely related to protein level, whether fed on an acute or chronic basis. It appears that real time RT-PCR is an acceptable method of estimating gene expression in birds. In addition, further work will focus on primer sizes that might further optimize RT-PCR as an instrument for studying the regulation of avian lipid metabolism. Results of the present study demonstrate a continued role for protein in the regulation of broiler metabolism. However, it should be pointed out that metabolic regulation at the gene level only occurs when feeding very high levels of dietary protein.