Crosstalk between nitric oxide synthase, heme oxygenase and NADPH oxidase in macrophages

Abstract

It was shown that HO-1 plays a role in chronic metabolic inflammation (Jais, 2014). HO-1 deletion in macrophages resulted in increased mitochondrial respiration rates (OxPhos) and increased generation of H2O2. We hypothesize that HO regulates macrophage function via mitochondrial ROS (mtROS) that involve critical enzymes, such as nitric oxide synthase (NOS) and NADPH-oxidase (NOX). In order to understand the underlying mechanism, we determined OxPhos in macrophages (J774.A1 cells) and the effect of HO and NOS substrates and inhibitors on the generation of ROS by mitochondria and NOX. In presence of heme OxPhos was reduced, due to decreased capacity of the respiratory chain and decreased ATP-synthase activity. The HO-inhibitor Zinc protoporphyrin reverted these effects and simultaneously activated mtROS production without influencing ROS generation by NOX (NOXROS). In contrast, the NOS-inhibitor L-NAME reduced both, mtROS and NOXROS levels, similarly to the mitochondrial targeted antioxidant mitoTEMPO. Additionally, activation of NOS using the substrate arginine leads to inhibition of HO activity. We assume that HO downmodulates NOXROS generation. Activation of NOS may overcome deceleration of NOS/NOX ROS generation via inhibition of HO, suggesting that full bactericidal activity of macrophages requires - at least transient - inhibition of HO.