Involvement of CREB / CRTC-2 in the activation of the genic program of hepatic gluconeogenesis induced by noradrenergic fibers, under cold stress, in mice

It is well established that the cAMP responsive element-binding protein (CREB) associated with its coactivator type 2 (CRTC-2) it is the key of activation of gluconeogenesis program in glucagon response. However, very little is known about the role of the Sympathetic Nervous System (SNS) in the modulation of this transcriptional complex and its resulting physiological effects. The work aimed to investigate the participation of CREB/CRTC-2 in the activation of the gene program of hepatic gluconeogenesis induced by sympathetic innervation, during cold stress, in mice. Initially, the architecture of noradrenergic innervation of the liver of male mice (C57Bl6J) was investigated by the 3DISCO (3D imaging of solvent-cleared organs) technique and it was found that the sympathetic nerves are restricted to the vasculature. In parallel, mice were sympathectomized (6-hydroxydopamine; 100 mg.kg-1.day-1; T0, T2 and T7 day of postnatal life; i.p) or treated with saline. After 8-10 weeks, the animals were exposed to cold (4ºC) or at room temperature, for 3 and 6 hours. The liver was extracted for protein quantification by Western blot and gene analysis by RT-PCR. The transcriptional activity of CREB in vivo was evaluated using mouse reporter CRE-luciferase. The results were expressed as mean ± SEM and submitted to appropriate statistical analysis (p<0.05). Cold exposure increased blood glucose, hepatic norepinephrine and PEPCK content, a key enzyme in gluconeogenesis, as well as phosphorylation and transcriptional activity in vivo of CREB and dephosphorylation of Ser275 CRTC-2. All of these effects have been abolished or attenuated by sympathectomy. It was also found that exposure to cold stimulated the signaling cascades of cAMP and Ca2+ and that sympathectomy was only able to modulate proteins related to the Ca2+ pathway. Although FoxO is also active in the liver of animals exposed to cold, this transcriptional factor is not modulated by the SNS. Together, the data indicate that CREB/CRTC-2 participates in the activation of the gene program of hepatic gluconeogenesis induced by sympathetic innervation, during acute cold stress. (AU)