Protein kinase C epsilon deletion in AgRP neurons modulates hypothalamic glucose sensing and improves glucose tolerance in mice

Objectives

Global but not liver-specific deletion of protein kinase C epsilon (PKCε) improves glucose tolerance in fat-fed mice, suggesting that extra-hepatic tissues are involved. AgRP neurons within the arcuate nucleus (ARC) of the hypothalamus can affect glucose homeostasis acutely, in addition to their role in energy homeostasis. We therefore deleted PKCε specifically in AgRP neurons to examine its effects at this site.

Methods

Fat-fed AgRP-PKCε^−/− mice were subjected to glucose tolerance tests and euglycaemic-hyperinsulinaemic clamps. c-Fos and tyrosine hydroxylase were used as markers to map neuronal activity in serial brain sections. Transcriptional changes in liver and adipose tissue were examined by qRT-PCR while alterations in protein levels and phosphorylation were determined by immunoblotting and mass spectrometry.

Results

Fat-fed AgRP-PKCε^−/− mice exhibited improved glucose tolerance but not insulin sensitivity determined by clamp. c-Fos mapping demonstrated that glucose challenge resulted in greater activation of neurons in the paraventricular nucleus (PVN) in AgRP-PKCε^−/− mice, but reduced expression of tyrosine hydroxylase in the PVN, suggestive of reduced sympathetic outflow. This was associated with a reduction in hormone sensitive lipase phosphorylation and plasma fatty acid levels. Proteomic analysis indicated overlapping alterations in proteins and protein phosphorylation in adipose tissue and liver, consistent with changes in a common, potentially neuronal, cell type.

Conclusions

Ablation of PKCε in AgRP neurons improves glucose homeostasis in fat-fed mice. This appears to be mediated through glucose sensing mechanisms, potentially reducing sympathetic outflow from the hypothalamus to tissues such as adipose, reducing lipolysis to indirectly lower hepatic glucose production.