Abstract 414: Adipose Angiotensin AT2 Receptors Modulate Thermogenesis Though Interactions with Epidermal Growth Factor Signaling

Abstract

The brain renin-angiotensin system (RAS) stimulates resting metabolic rate (RMR) in part through a mechanism involving suppression of the circulating RAS. This effect appears to be mediated through the loss of tonic adipose angiotensin AT2 receptor (AT2R) activation specifically within inguinal fat. Mice with hyperactivity of the brain RAS (“sRA” mice, expressing human renin via the synapsin promoter and human angiotensinogen via its own promoter) and littermate controls were chronically infused with vehicle or the AT2R agonist, CGP-42112a (CGP, 90 ng/hr, 8 wk, sc). To identify altered signaling pathways in sRA mice and their response to CGP treatment, total RNA was isolated from inguinal adipose tissue and transcript abundance was quantitated by RNA-Seq (50 bp paired reads sequenced with the Illumina HiSeq 2000). There was a significant (P<0.001) change in expression of 123 genes in sRA mice (n=3) compared to littermate controls (n=3), which were generally reversed by CGP treatment (n=4). By manual inspection, we observed that 51 of these genes are associated with epidermal growth factor (EGF) signaling. Consistent with this, Gene Set Enrichment Analysis of the RNA-Seq data demonstrated that genes in the EGF receptor signaling pathway were, as a group, statistically upregulated (P=0.02) in sRA and suppressed (P=0.02) by CGP treatment. Therefore, to further explore the impact of increased EGF signaling on RMR and to isolate a potential modulatory effect of AT2R activation on this response, wildtype C57Bl/6J male mice (9 wk) were infused with EGF (833 ng/hr, 2 wk, sc) with or without co-infusion of CGP. This brief EGF infusion caused a possible increase in RMR (vehicle n=20, 0.173 ± 0.009; EGF n=20, 0.192 ± 0.012 kcal/hr, P=0.13), which was significantly reduced with co-infusion of CGP (90 ng/hr, 2 wk, sc) (EGF+CGP n=17, 0.165 ± 0.005, P<0.05 vs EGF alone; CGP alone n=9, 0.156 ± 0.010). Together these data implicate elevated EGF signaling in the elevated RMR of mice with elevated brain RAS activity. Further, these data suggest a suppressive effect of AT2R activation upon RMR specifically in the context of elevated EGF signaling. Studies utilizing primary inguinal adipose cultures are underway to investigate the molecular basis of the EGF-AT2R interaction.