NOX2 activated by α1-adrenoceptors modulates hepatic metabolic routes stimulated by β-adrenoceptors

Abstract

The NADPH oxidase (NOX) family of enzymes oxidase catalyzes the transport of electrons from NADPH to molecular oxygen and generates O2•−, which is rapidly converted into H2O2. We aimed to identify in hepatocytes the protein NOX complex responsible for H2O2 synthesis after α1-adrenoceptor (α1-AR) stimulation, its activation mechanism, and to explore H2O2 as a potential modulator of hepatic metabolic routes, gluconeogenesis, and ureagenesis, stimulated by the ARs. The dormant NOX2 complex present in hepatocyte plasma membrane (HPM) contains gp91phox, p22phox, p40phox, p47phox, p67phox and Rac 1 proteins. In HPM incubated with NADPH and guanosine triphosphate (GTP), α1-AR-mediated H2O2 synthesis required all of these proteins except for p40phox. A functional link between α1-AR and NOX was identified as the Gα13 protein. Alpha1-AR stimulation in hepatocytes promotes Rac1-GTP generation, a necessary step for H2O2 synthesis. Negative cross talk between α1-/β-ARs for H2O2 synthesis was observed in HPM. In addition, negative cross talk of α1-AR via H2O2 to β-AR-mediated stimulation was recorded in hepatocyte gluconeogenesis and ureagenesis, probably involving aquaporine activity. Based on previous work we suggest that H2O2, generated after NOX2 activation by α1-AR lightening in hepatocytes, reacts with cAMP-dependent protein kinase A (PKA) subunits to form an oxidized PKA, insensitive to cAMP activation that prevented any rise in the rate of gluconeogenesis and ureagenesis.