Neurons of the arcuate nucleus in mice express angiotensinogen

Abstract

Recent studies from our laboratory have demonstrated that angiotensin II (ANG) type 1A receptors (AT1A) specifically localize to the subset of neurons which express both the leptin receptor (LepR) and agouti‐related peptide (AgRP). These are critically involved in the control of thermogenic adipose sympathetic nerve activity (SNA) and thereby resting metabolic rate (RMR).This mechanism appears to involve AT1A‐mediated suppression of gamma‐aminobutyric acid (GABA) synthesis and packaging in AgRP neurons of the arcuate nucleus (ARC). It remains unclear, however, how LepR signaling results in AT1A activation within AgRP neurons. We hypothesize that activation of LepR in POMC and/or AgRP neurons results in de novo synthesis and local release of angiotensinogen (AGT) within the ARC, and consequently increased autocrine or paracrine ANG signaling within the ARC. To test this hypothesis, we examined the localization of AGT mRNA expression within the ARC of wildtype C57BL/6J mice by fluorescent in situ hybridization methods (RNAscope) and confocal fluorescent microscopy. Consistent with our working hypothesis, cells within the ARC expressing AGT mRNA colocalize with both AgRP and POMC. Cells within the ARC expressing insulin II (INS2) also expressed AGT. Finally, as expected, AGT was also expressed in astrocytes, colocalizing with glial fibrillary acidic protein (GFAP). We and others have previously demonstrated that LepR activation increases phosphorylation of the signal transduction and activator of transcription‐3 (STAT3) transcription factor, and that p‐STAT3 appears to stimulate AGT expression in other cell types including cardiac myocytes and hepatocytes. We therefore hypothesize that the phosphorylation of STAT3 by LepR activation is mechanistically involved in the regulation of AGT expression by leptin in POMC and AgRP neurons. Ongoing studies are aimed at (i) examining AGT expression control by pSTAT3 in POMC and AgRP neurons of the ARC, and (ii) using Cre‐lox recombination methods to selectively disrupt the AGT gene in LepR, POMC and AgRP neurons to study the functional significance of AGT in these cells in the control of SNA and RMR, and thereby energy homeostasis.