PDK regulated Warburg effect protects differentiated adipocytes against ROS

Abstract

Literature has demonstrated the ability of human adipose tissue to generate large amounts of lactate. However, it is not understood why adipose tissue produces lactate, how the production of lactate is regulated, and what potential benefit this has to the adipocyte or the organism. We first characterized a human model of adipogenic differentiation with minimal donor to donor variability to assess metabolic changes associated with mature adipocytes compared to their precursors. Indeed, similar to what was observed in human clinical studies, the differentiated adipocytes demonstrated increased lactate production. However, the differentiated adipocytes compared to their precursors (preadipocytes or ASCs) demonstrate an aerobic glycolysis-like (also called Warburg effect-like) increase in glycolysis characterized by a 5.2 fold increase in lactate production in normoxic conditions (atmospheric oxygen tension). Remarkably, this increase in lactate occurred even though the differentiated adipocytes simultaneously demonstrate an increase in oxidative capacity. This low fraction of oxidative capacity coupled with increased lactate production indicated regulation of oxidative rates most likely at the point of pyruvate conversion to either acetyl-CoA (oxidative metabolism) or lactate (glycolytic metabolism). To investigate the potential regulation of this metabolic phenotype, PDK isoform expression was assessed and we found PDK 1 and 4 transcript and protein elevated in the differentiated cells. Non-selective pharmacologic inhibition of the PDKs resulted in decreased lactate production, supporting a regulatory role for PDK in modulation of the observed Warburg effect. PDK inhibition also resulted in increased ROS production in the adipocytes after several hours of treatment and a decrease in cell viability when PDK inhibition was carried out over 36 hours. The resulting loss in viability could be rescued by antioxidant (Tempol) treatment, indicating the decrease in viability was ROS mediated. Similar to what is seen in cancer cells, our data demonstrate that differentiation of human adipocytes is accompanied by a PDK-dependent increase in glycolytic metabolism (Warburg effect) that not only leads to lactate production, but also seems to protect the cells from increased and detrimental generation of ROS.