Moderate overexpression of glucose-6-phosphate dehydrogenase improves healthspan in mice. Implications in skeletal muscle regeneration

An enormous increment in the average lifespan of diverse populations occurred worldwide in the 20th century. In the last 10–15 years, the importance has changed from extending average and even maximal longevity to favoring healthy aging, and many researchers have focused their studies on the aim at extending healthspan. Prolonging lifespan without taking care of improving healthspan can derive in a long time of living with disabilities and constitutes a risk factor for the old population to suffer a higher prevalence of aging-related diseases. Indeed, modern disease treatments frequently diminish mortality without any effect on the deterioration of overall health. Understanding the mechanisms underlying the biology of aging allows the design of interventions and treatments oriented to diminish chronic diseases. Many theories agree in considering that the underlying cause of aging is the accumulation of molecular damage, which is originated principally by reactive oxygen species (ROS). In this regard, the free radical theory of aging postulated by Denham Harman in 1956, states that aging and the degenerative diseases associated with it are due to the progressive and irreversible accumulation of oxidative damage caused by ROS. The interventions aim at potentiating the antioxidant systems have acquired much relevance in the field, and it has been demonstrated that the overexpression of antioxidant enzymes in mice improves healthspan and, in some few cases, increases lifespan. Protection against oxidative damage largely relies on the reductive power of the molecule nicotinamide adenine dinucleotide phosphate in its reduced form (NAPDH), whose levels are mostly determined by the enzyme glucose-6-phosphate dehydrogenase (G6PD). Genetic manipulation is one of the mechanisms by which we can act on the levels of ROS in the organism. The general aim of this PhD thesis is to study in vivo the effect of G6PD moderate overexpression on oxidative stress parameters and on several indicators of organismal functionality declining with age, as well as to determine the effect of this genetic manipulation on the skeletal muscle regeneration capacity. This general objective is to be achieved using a transgenic mouse model with moderate ubiquitous overexpression of human G6PD under the control of its natural promoter (named as G6PD-Tg mice). The results show that G6PD-Tg mice present ~ 2-fold overexpression of G6PD mRNA, a similar increase in G6PD protein levels, and higher G6PD activity in the tissues examined. This overexpression is accompanied by an increase in NADPH levels, as well as higher plasma uric acid and lactate levels, indicating an activation of the PPP pathway. In addition, G6PD-Tg mice have lower levels of ROS-derived damage compared to their control littermates. In particular, females and males accumulate less oxidized DNA in the liver and brain, and females also display in the liver lower levels of lipid peroxidation as well as an increase in the GSH:GSSG ratio, due to higher GSH levels. All of this is accompanied by partial protection from aging-associated functional decline, including extended median lifespan in females, improved glucose tolerance and insulin sensitivity in males, and better neuromuscular fitness in females. However, skeletal muscle regeneration after cardiotoxin injury is not modified in young G6PD-Tg female mice. This genetic manipulation does not overstimulate protein synthesis. On the contrary, it induces a prooxidant environment, which might be attributed to the NADPH oxidase enzyme. The main conclusion of this PhD thesis is that moderate systemic overexpression of G6PD constitutes a beneficial intervention in mice for improving healthspan. This improvement is achieved through higher cellular NADPH levels and, as a consequence, better protection from the age-related ROS damage. This genetic manipulation neither improves or worsens skeletal muscle regeneration