Activation of Glucose-6-phosphate Dehydrogenase Promotes Acute Hypoxic Pulmonary Artery Contraction

Abstract

Hypoxic pulmonary vasoconstriction (HPV) is a physiological response to a decrease in airway O 2 tension, but the underlying mechanism is incompletely understood. We studied the contribution of glucose-6-phosphate dehydrogenase (Glc-6-PD), an important regulator of NADPH redox and production of reactive oxygen species, to the development of HPV. We found that hypoxia (95% N 2 , 5% CO 2 ) increased contraction of bovine pulmonary artery (PA) precontracted with KCl or serotonin. Depletion of extracellular glucose reduced NADPH, NADH, and HPV, substantiating the idea that glucose metabolism and Glc-6-PD play roles in the response of PA to hypoxia. Our data also show that inhibition of glycolysis and mitochondrial respiration (indicated by an increase in NAD ؉ and decrease in the ATP-to-ADP ratio) by hypoxia, or by inhibitors of pyruvate dehydrogenase or electron transport chain complexes I or III, increased generation of reactive oxygen species, which in turn activated Glc-6-PD. Inhibition of Glc-6-PD decreased Ca 2؉ sensitivity to the myofilaments and diminished Ca 2؉ -independent and -dependent myosin light chain phosphorylation otherwise increased by hypoxia. Silencing Glc-6-PD expression in PA using a targeted small interfering RNA abolished HPV and decreased extracellular Ca 2؉ -dependent PA contraction increased by hypoxia. Similarly, Glc-6-PD expression and activity were significantly reduced in lungs from Glc-6-PD mut(؊/؊) mice, and there was a corresponding reduction in HPV. Finally, regression analysis relating Glc-6-PD activity and the NADPH-to-NADP ؉ ratio to the HPV response clearly indicated a positive linear relationship between Glc-6-PD activity and HPV. Based on these findings, we propose that Glc-6-PD and NADPH redox are crucially involved in the mechanism of HPV and, in turn, may play a key role in increasing pulmonary arterial pressure, which is involved in the development of pulmonary hypertension.Pulmonary hypertension (PH) 2 is a major cause of morbidity and mortality, the incidence of which is increasing around the world. The mechanisms underlying the development of PH remain unclear, however, and current medical treatment is inadequate. That said, it has been noted that in people living at high altitude and in patients suffering from chronic obstructive pulmonary disease, the chronic reduction in inhaled O 2 induces sustained hypoxic pulmonary vasoconstriction (HPV), which eventually leads to development of PH (1, 2). HPV is a phenomenon that balances the ventilation-to-respiration quotient by constricting the pulmonary artery (PA) and redirecting blood flow in the lungs in response to local reductions in inspired pO 2 (3). Since its discovery nearly a century ago, numerous studies have been conducted to identify the mechanisms responsible for HPV. To date, however, no unifying mechanism has been identified. In 1982, McMurtry et al. (4) proposed that inhibition of glycolysis and oxidative phosphorylation mimics HPV and suggested that inhibition of the mitochondrial electron transport chain...

Glucose-6-phosphate dehydrogenase plays a critical role in hypoxia-induced CD133+progenitor cells self-renewal and stimulates their accumulation in the lungs of pulmonary hypertensive rats

“…The pentose phosphate pathway is also oxygen sensitive. In coronary arterial smooth muscle, the pentose phosphate pathway activity is decreased by reductions in PO 2 (21), but in the pulmonary arterial smooth muscle (10,18) and in solid tumors (15) the activity is increased by hypoxia. Similarly, we found that G6PD activity is enhanced in hypoxic CD133…”

“…In addition, TGF-␤ upregulates glucose-6-phosphate dehydrogenase (G6PD) expression in fetal brown adipocytes and increases levels of NOX4-derived ROS (45). Because production of superoxide anion from NOX is dependent on G6PD-derived NADPH (18,20), we hypothesized that increases in G6PD-dependent NA-DPH redox and NOX-derived ROS act in concert to mediate hypoxia-induced CD133 ϩ cell expansion and differentiation. …”

20-HETE-induced mitochondrial superoxide production and inflammatory phenotype in vascular smooth muscle is prevented by glucose-6-phosphate dehydrogenase inhibition

“…G6PD inhibition relaxes pulmonary arteries by decreasing intracellular calcium (20), prevents switching of vascular smooth muscle cells to a synthetic phenotype (9,10), and reduces pulmonary hypertension (9,47). However, whether prolonged hypoxia-induced 20-HETE-synthesis is G6PD dependent or independent and whether G6PD modulates 20-HETE signaling in the vascular smooth muscle remain unknown.…”

“…Endothelium denuded artery rings were mounted on Radnoti Instruments' force displacement transducers for recording isometric force development through Powerlab data acquisition system from AD Instruments, as previously described (20). Arterial rings were incubated in Krebs-bicarbonate buffer containing 118 mM NaCl, 4.7 mM KCl, 1.5 mM CaCl 2, 25 mM NaHCO3, 1.1 mM MgSO4, 1.2 mM KH2PO4, and 5.6 mM glucose for 1 h under resting tension of 5 g. In all studies, arterial rings were depolarized with KCl (120 mM) containing Krebs bicarbonate buffer and then the rings were equilibrated with Krebs-bicarbonate buffer for 30 min.…”

“…Previous work done in our laboratory has demonstrated that G6PD activation contributes to the development of hypoxic pulmonary vasoconstriction (20) and inhibition of G6PD with 6-AN (1 mM) blocked it in a PKGindependent and -dependent manner (10,21). To determine whether G6PD inhibition activated PKG, we treated the arterial rings with DHEA and 6-AN for 12 h. G6PD inhibition by DHEA (100 M) and 6-AN (1 mM) did not increase cGMP ( Fig.…”