Short-Chain Fatty Acids and Palmitate Induce Distinct Metabolic and Phenotypic Signatures in Normal and Ischemic Skeletal Muscle Microvascular Endothelial Cells.

Background: Palmitate, a long-chain fatty acid, is well known to be a significant risk factor for cardiovascular diseases. In our current study, we wanted to determine whether palmitate treatment further aggravates ischemic endothelial cell (EC) injury and can serve as an in vitro model that emulates diabetic peripheral artery disease (diabetic-PAD). Short-chain fatty acid (SCFA) treatment was used as an additional comparator for palmitate-induced vascular dysfunction in normal or ischemic ECs in vitro. Methods: Hypoxia serum starvation (HSS) was used as an in vitro model for PAD. Cell survival or proliferation was determined by the CCK8 kit. EC angiogenic capacity was determined by in vitro tube formation assays on growth factor-reduced Matrigel. EC barrier integrity was determined by trans-endothelial electrical resistance measurements by EVOM3. EC metabolic phenotyping was performed by Seahorse glycolysis, mitochondrial respiration, and fatty acid oxidation metabolic assays. Results: Palmitate dramatically decreased the survival of normal and ischemic ECs, whereas SCFAs did not have a significant effect on ischemic EC survival. In vitro angiogenic assays showed that palmitate significantly decreased the angiogenic capacity of ischemic ECs, whereas SCFAs significantly induced their angiogenic capacity. While palmitate significantly decreased normal and ischemic EC barrier integrity, SCFAs improved normal and ischemic EC barrier integrity. Metabolic assays showed that palmitate significantly decreased normal EC mitochondrial respiration but not glycolysis. However, palmitate significantly decreased overall metabolic health, including mitochondrial respiration and glycolysis in ischemic ECs. On the contrary, SCFAs increased both mitochondrial respiration and glycolysis in normal ECs. In ischemic ECs, SCFAs induced mitochondrial respiration with a concomitant decrease in glycolysis. Fatty acid oxidation analysis showed that, unlike palmitate, which depends on carnitine palmitoyl transferases (CPTs) for β-oxidation in both normal and HSS ECs, SCFAs depend partly on CPTs to undergo β-oxidation in HSS ECs but not in normal ECs. Conclusions: While palmitate inhibits ischemic EC angiogenic capacity by decreasing overall metabolic health, SCFAs induce glycolysis-mitochondria OxPhos coupling to induce ischemic EC angiogenic capacity.