Aging and CR effects on the Plasma Membrane Redox System

National Institute On Aging

Investigators

Linked publications & trials

Abstract

Data from our laboratory and others, have demonstrated that the plasma membrane redox system is, at least in part, responsible of the maintenance of the antioxidant capacity during oxidative stress challenges induced by the diet and aging. The upregulation of the plasma membrane redox system that occurs during CR decreases the levels of oxidative stress in aged membranes. CR extends life span of yeasts by decreasing NADH levels, which would connect this intervention to plasma membrane NADH-dependent dehydrogenases. CR modifies composition of fatty acid in the plasma membrane, resulting in decreased oxidative damage including lipid peroxidation. More importantly, plasma membrane redox activities and also the content of CoQ, which decline with age, are enhanced by CR providing protection to phospholipids and preventing the lipid peroxidation reaction progression. We are focusing our efforts on the generation of transgenic and knock out animals of the different dehydrogenases involved in this antioxidant system. We have successfully created NQO1 and Cyt-b5-reductase overexpressors and obtained NQO1 and NRF2 KO animals. We are setting longevity studies as well as short term interventions to fully characterize these new mouse lines. In collaboration with the laboratory of Dr. Placido Navas we have shown that the Saccharomyces cerevisiae homolog of Cyt-b5-reductase, NQR1, resides at the plasma membrane and when overexpressed extends both replicative and chronological lifespan. We demonstrated that NQR1 extends replicative lifespan in a SIR2-dependent manner by shifting cells towards respiratory metabolism and decreasing the pyridine nucleotide pool without altering the NAD+/NADH ratio. Chronological lifespan extension, in contrast, occurs via a SIR2-independent decrease in ethanol production. We conclude that NQR1 is a key mediator of lifespan extension by CR through its effects on yeast metabolism and discuss how these findings could suggest a function for this protein in lifespan extension in mammals. We now have extended our previous observations on NQO1 and we are now demonstrating an important novel physiological role for NQO1. We have determined that NQO1 is a target if the insulin receptor which shifts its cellular localization by phosphorylation. NQO1 overexpression shifted the physiology of mice on a high fat diet towards that of mice on a standard diet. These phenomena occur through the NQO1-mediated reduction in oxidative stress damage and prevention of the activation of the proinflammatory NFKB pathway. Another emerging role of NQO1 is its ability to bind mRNAs, using ribonucleoprotein immunoprecipitation (RIP) and microarray analysis to identify comprehensively the subset of NQO1 target mRNAs in human hepatoma HepG2 cells. We discovered that one of its main targets, SERPINA1 mRNA, encodes the serine protease inhibitor -1-antitrypsin, A1AT, which is associated with disorders including obesity-related metabolic inflammation, chronic obstructive pulmonary disease (COPD), liver cirrhosis and hepatocellular carcinoma. Further analysis indicated that NQO1 can bind the 3 untranslated region (UTR) and the coding region (CR) of SERPINA1 mRNA. NQO1 did not affect SERPINA1 mRNA levels; instead, it enhanced the translation of SERPINA1 mRNA, as NQO1 silencing decreased the size of polysomes forming on SERPINA1 mRNA and lowered the abundance of A1AT. NQO1 regulates SERPINA1 mRNA translation through the SERPINA1 3UTR. Thus, NQO1-KO mice had reduced hepatic and serum levels of A1AT and increased activity of neutrophil elastase, one of the main targets of A1AT. We propose that this novel mechanism of action of NQO1 as RNA-binding protein may help to explain the pleiotropic biological effects of this enzyme. We are now reporting that NQO1 is protective against diet-induced obesity (DIO) through the regulation of insulin sensitivity and lipid metabolism. Inducible activation of Nrf2 and NQO1 transgenesis protect mice from DIO, insulin resistance, liver steatosis, and macrophage infiltration into fat depots. In tissues, there were metabolic signatures of improved glucose handling, cellular redox, and NAD+ metabolism. Using label-free quantitative mass spectrometry in skeletal muscle revealed a distinct dietdependent acetylation pattern of SIRT3 targets including oxidative phosphorylation, tricarboxylic acid cycle, fatty acid oxidation and amino acid catabolism, in addition to sirtuin signaling. Together, these results indicate that increased expression of NQO1 is protective against DIO through preservation of glucose homeostasis, insulin sensitivity, and lipid handling leading to enhanced health outcomes.