Acidosis-triggered fatty acid overload induces endothelial cell dysfunction.

Vascular ischemia is characterized not only by hypoxia but also by acidosis, which affects endothelial cells (ECs) due to increased H+ production from glycolysis and a deficit in H+ washout. We recently documented that an acidic environment facilitates the flip-flop transport of the non-ionized form of fatty acids (FAs) across the plasma membrane of cancer cells. In this study, we investigated how acidosis influences the capacity of highly glycolytic ECs to manage FAs and participates to endothelial dysfunction. We first tracked lipid droplet (LD) formation using Oil Red O staining and holotomographic microscopy. Purified monounsaturated oleate but also a mixture of FAs that reflect in vivo serum composition, resulted in dose- and time-dependent LD accumulation through FA transporter-independent mechanisms. Acid-exposed ECs exhibited enhanced mitochondrial respiration fueled by FAs, and endoplasmic reticulum (ER) stress, as indicated by the expression of ATF4 and CHOP. This phenotype was further associated with elevated reactive oxygen species production, which correlated with reduced nitric oxide (NO) availability. FA removal from EC culture media promoted lipolysis from LDs, supported by ATGL lipase induction which however slowed under acidic conditions. While ER stress persisted upon FA washout, NO availability was restored to levels comparable to those in FA-unexposed ECs. This observation coincided with dynamic mobilization of antioxidant defenses in acid-exposed ECs, as evidenced by low levels of reduced glutathione and enhanced cystine uptake, alongside a decrease in carnitine and FA-fueled mitochondrial respiration. Collectively, these data underscore the vulnerability of ECs to passive FA capture promoted by local acidosis, thereby contributing to a silent source of endothelial dysfunction in the postprandial state or during chronic exposure to elevated lipid levels.