ATF3 regulates hepatic ApoA4 upon metabolic stress
The liver plays essential roles in maintaining systemic glucolipid homeostasis under ever changing metabolic stressors.  Metabolic dysregulation can lead to both adaptive and maladaptive changes that impact systemic physiology.  Here we examined disparate genetic and environmental metabolic stressors and identified Apolipoprotein A4 (ApoA4) as a circulating protein upregulated in liver-specific knockouts for Carnitine Palmitoyltransferase 2 and Pyruvate Carboxylase. We found this upregulation to be exacerbated by fasting and high fat or ketogenic diets.  Unique among these models was a concomitant increase in Activating Transcription Factor 3 (Atf3).  Liver-specific overexpression of Atf3 resulted in increased ApoA4 expression in a sex-dependent manner.  To understand the requirement of Atf3 to metabolic stress, we generated liver-specific Atf3, Cpt2 double knockout mice.  These experiments demonstrated the requirement for Atf3 in the induction of ApoA4 mRNA, ApoA4 protein, and serum triglycerides that were also sex dependent.  These experiments reveal the roles of hepatic Atf3 and ApoA4 in response to metabolic stress in vivo. Overall design: RNA-seq on whole livers was performed to investigate differentially regulated genes between 24hr fasted livers of Atf3;Cpt2 liver-specific DKO mice, Cpt2 liver-specific knockout mice, and control mice. Liver-specific knockouts were generated by crossing floxed lines to and albumin-Cre transgenic mouse line.