Docosahexaenoic Acid Remodels the Cardiac Mitochondrial Phospholipidome and Impairs Respiratory Enzymatic Activity by Disrupting Lipid Domain Formation and Lipid-Protein Binding

Abstract

Phospholipids of the inner mitochondrial membrane regulate various mitochondrial processes including apoptosis and oxidative phosphorylation. In a range of cardiovascular diseases, mitochondrial inner membrane phospholipids undergo significant acyl chain remodeling during the course of the disease. One unique remodeling event that occurs in the cardiac mitochondrial phospholipidome is an increase in the levels of docosahexaenoic acid (DHA), an n-3 polyunsaturated fatty acid. Here, we used diet as a tool to investigate how DHA impacted cardiac mitochondrial phospholipid composition and thereby mitochondrial respiratory enzyme activities. Mice were administered DHA in the context of a western diet. Phospholipidomics with mass spectrometry analysis revealed that mice on a western diet enriched with DHA dramatically remodeled the acyl chain composition of cardiac mitochondrial cardiolipin, phosphatidylcholine, and phosphatidylethanolamine. These changes were associated with decreased complex I, IV, V, and I+III enzymatic activities. Mechanistically, lowered enzymatic activity was not driven by modifications to mitochondrial respiratory protein abundance or supercomplex formation. Instead, the replacement of tetralinoleoyl-CL [(18:2)4CL] with tetradocosahexaenoyl-CL [(22:6)4CL] in biomimetic membranes prohibited the formation of lipid microdomains, which was driven by DHA's influence on thermodynamics of phospholipid mixing. Furthermore, (22:6)4CL modified CL-protein binding kinetics relative to (18:2)4CL. The reintroduction of linoleic acid, via fusion of (18:2)4CL, to mitochondria isolated from mice consuming DHA, prevented the major losses in the mitochondrial phospholipidome and rescued complexes, I, IV, and V activities. Altogether, these results suggest that an increase in mitochondrial membrane DHA disrupts membrane organization and enzyme activities, which has major implications for the ongoing debate concerning polyunsaturated fatty acids and cardiac health.