β3-Adrenoceptor activation relieves oxidative inhibition of the cardiac Na+-K+ pump in hyperglycemia induced by insulin receptor blockade

Abstract

Dysregulated nitric oxide (NO)- and superoxide (O2·−)-dependent signaling contributes to the pathobiology of diabetes-induced cardiovascular complications. We examined if stimulation of β3-adrenergic receptors (β3-ARs), coupled to endothelial NO synthase (eNOS) activation, relieves oxidative inhibition of eNOS and the Na+-K+ pump induced by hyperglycemia. Hyperglycemia was established in male New Zealand White rabbits by infusion of the insulin receptor antagonist S961 for 7 days. Hyperglycemia increased tissue and blood indexes of oxidative stress. It induced glutathionylation of the Na+-K+ pump β1-subunit in cardiac myocytes, an oxidative modification causing pump inhibition, and reduced the electrogenic pump current in voltage-clamped myocytes. Hyperglycemia also increased glutathionylation of eNOS, which causes its uncoupling, and increased coimmunoprecipitation of cytosolic p47 phox and membranous p22 phox NADPH oxidase subunits, consistent with NADPH oxidase activation. Blocking translocation of p47 phox to p22 phox with the gp91ds-tat peptide in cardiac myocytes ex vivo abolished the hyperglycemia-induced increase in glutathionylation of the Na+-K+ pump β1-subunit and decrease in pump current. In vivo treatment with the β3-AR agonist CL316243 for 3 days eliminated the increase in indexes of oxidative stress, decreased coimmunoprecipitation of p22 phox with p47 phox, abolished the hyperglycemia-induced increase in glutathionylation of eNOS and the Na+-K+ pump β1-subunit, and abolished the decrease in pump current. CL316243 also increased coimmunoprecipitation of glutaredoxin-1 with the Na+-K+ pump β1-subunit, which may reflect facilitation of deglutathionylation. In vivo β3-AR activation relieves oxidative inhibition of key cardiac myocyte proteins in hyperglycemia and may be effective in targeting the deleterious cardiac effects of diabetes.