Enzymes involved in hepatic acylglycerol metabolism in the chicken

Abstract

In laying hens, massive hepatic mobilization of fatty acids is required for the synthesis of oocyte-targeted very-low density lipoproteins (VLDL). The current study aims at identification of enzymes that hydrolyze hepatic acylglycerol stores regulated in a fashion compatible with supporting enhanced VLDL synthesis. We show that unlike mammals, chickens express adipose triglyceride lipase (ATGL) also in liver, where it is upregulated by fasting, while the enzyme patatin-like phospholipase domain-containing lipase 3 (PNPLA3) is suppressed. For the first time in any system, we show that hepatic arylacetamide deacetylase (AADA) is upregulated by fasting, and that its affinity for an insoluble carboxylester substrate is compatible with an in-vivo function similar to that of ATGL. Unknown heretofore, hepatic expression of chicken AADA is estrogen-responsive, and is induced to the same degree as the stimulation of VLDL-production by estrogen. These observations support roles of chicken ATGL, PNPLA3, and AADA in acylglycerol metabolism related to the high rates of VLDL synthesis that are essential for reproduction.