Acute Activation of Oxidative Pentose Phosphate Pathway as First-Line Response to Oxidative Stress in Human Skin Cells

Abstract

Integrity of human skin is endangered by exposure to UV irradiation and chemical stressors, which can provoke a toxic production of reactive oxygen species (ROS) and oxidative damage. Since oxidation of proteins and metabolites occurs virtually instantaneously, immediate cellular countermeasures are pivotal to mitigate the negative implications of acute oxidative stress. We investigated the short-term metabolic response in human skin fibroblasts and keratinocytes to H2O2 and UV exposure. In time-resolved metabolomics experiments, we observed that within seconds after stress induction, glucose catabolism is routed to the oxidative pentose phosphate pathway (PPP) and nucleotide synthesis independent of previously postulated blocks in glycolysis (i.e., of GAPDH or PKM2). Through ultra-short (13)C labeling experiments, we provide evidence for multiple cycling of carbon backbones in the oxidative PPP, potentially maximizing NADPH reduction. The identified metabolic rerouting in oxidative and non-oxidative PPP has important physiological roles in stabilization of the redox balance and ROS clearance.

Cancer, Oxidative Stress, and Metastasis

“…2). The pentose phosphate pathway is the first line of defense against oxidative stress in many human cells and can promote the survival of cells during neoplastic transformation and during detachment from extracellular matrix (Boada et al 2000;Debnath et al 2002;Debnath and Brugge 2005;Bensaad et al 2006;Sukhatme and Chan 2012;Hu et al 2013;Kuehne et al 2015).…”

Metabolic Remodeling in Times of Stress: Who Shoots Faster than His Shadow?

“…Using human skin cells, Kuehne et al (2015) have studied the fastest known oxidative stress response, which is the activation of the oxidative pentose phosphate pathway (PPP) that occurs when cells are exposed to increased levels of H 2 O 2 . As originally described in budding yeast, PPP activity increases within seconds upon encounter with the stressor, and delivers NADPH to the antioxidant machinery (Ralser et al, 2007(Ralser et al, , 2009).…”

“…For vertebrate cells, additional mechanisms have been proposed to trigger PPP activation, namely the enhancement of G6PDH activity through post-translational modifications or protein-protein interactions via SirT2, HSP27, or TIGAR (reviewed in Stincone et al, 2015). Interestingly, the time-resolved metabolomics experiments conducted by Kuehne et al (2015) imply that the previously proposed mechanisms are insufficient to explain rapid PPP activation. While Kuehne et al (2015) confirm rapid GAPDH inactivation, they do not observe the expected accumulation of upper glycolytic intermediates.…”

“…Interestingly, the time-resolved metabolomics experiments conducted by Kuehne et al (2015) imply that the previously proposed mechanisms are insufficient to explain rapid PPP activation. While Kuehne et al (2015) confirm rapid GAPDH inactivation, they do not observe the expected accumulation of upper glycolytic intermediates. If there is no tailback in glycolysis, something else must stimulate PPP flux, at least initially.…”

Glutaredoxin Desensitizes Lens to Oxidative Stress by Connecting and Integrating Specific Signaling and Transcriptional Regulation for Antioxidant Response

“…The overexpression of PKM2 has been detected in a various types of cancer, where it has been proven to contribute to the Warburg effect, a hallmark of cancer [59]. The direct oxidation of PKM2 at Cys358 inhibits its catalytic activity [45,60], which allows for the synthesis of NADPH and reduced glutathione for ROS detoxification. However, the way in which Grx1 modulates PKM2 expression remains to be investigated.…”