Chronic UCN2 Treatment Desensitizes CRHR2 and Improves Insulin Sensitivity

Abstract

Abstract The neuropeptide Urocortin 2 (UCN2) acts as a ligand for the G protein-coupled receptor (GPCR) corticotropin-releasing hormone receptor 2 (CRHR2) expressed in the brain and peripheral metabolic tissues. UCN2 has been reported to improve or worsen insulin sensitivity and glucose uptake in skeletal muscle and have opposing effects on glucose tolerance in vivo. In this report, we examined the acute and chronic effect of UCN2 on glucose metabolism and signaling pathways downstream of CRHR2. Consistent with previous reports, we found that acute dosing of UCN2 induced systemic insulin resistance and hyperglycemia in mice and skeletal muscle. Inversely, chronic elevation of UCN2 by injection with adenovirus encoding UCN2 (UCN2.AAV) resolved metabolic complications, improving glucose tolerance. Phosphoproteomic analysis of acutely treated skeletal muscle revealed dephosphorylation of IRS1 and AKT1S1, which was entirely reversed in UCN2.AAV skeletal muscle. Interestingly, pharmacological studies showed that all human isoforms of CRHR2 recruit Gs, as well as Gi and β-Arrestin, in response to stimulation with UCN2. However, Gi and β-Arrestin recruitment occurs at UCN2 concentrations 10-fold higher than Gs recruitment. Furthermore, pre-treating cells with UCN2 led to internalization of CRHR2 and dampened ligand-dependent increases in cAMP. Consistent with the in vivo results, treatment of mouse soleus muscle with UCN2 ex vivo showed AKT1S1 and IRS1 dephosphorylation and decreased glucose uptake in response to insulin; these responses were blunted when the muscle was pre-incubated with UCN2. These studies demonstrate that exposure to high, chronic concentrations of UCN2 desensitizes CRHR2, thus blocking the effects of acute UCN2, and improving insulin sensitivity, in skeletal muscle and systemically. On the other hand, acute treatment with UCN2 activates CRHR2 through recruitment of Gs which leads to blunted insulin signaling and glucose uptake. These results provide mechanistic insights into how UCN2 regulates insulin sensitivity and glucose metabolism in skeletal muscle and in vivo. Importantly, a working model was derived from these results that unifies the contradictory metabolic effects of UCN2.