Cardiolipin Content has a Stronger Influence than Acyl Chain Composition on Select Membrane Properties of Biomimetic Mitochondrial Membranes

Abstract

Cardiolipin (CL), the hallmark phospholipid of the mitochondria, plays a fundamental role in maintaining mitochondrial inner membrane structure and function. In several ailments including cardiovascular diseases and Barth Syndrome, in which mitochondrial dysfunction contributes towards disease pathology, there is loss of CL content and remodeling of CL's acyl chains. However, it remains unclear how CL content and acyl chain composition impact the biophysical lipid organization of the inner mitochondrial membrane and thereby protein activity. Therefore, we discriminated how CL content and acyl chain composition influence distinct membrane properties of biomimetic mitochondrial membranes. In monolayer studies, the loss of tetralinoleoyl [(18:2)4] CL promoted lipid‐lipid miscibility, while replacement of (18:2)4CL acyl chains with tetraoleoyl [(18:1)4] CL or tetradocosahexaenoyl [(22:6)4] CL had no influence on lipid‐lipid miscibility. Replacement of (18:2)4CL acyl chains with tetramyristoyl [(14:0)4] CL, which has limited biological relevance for humans, promoted lipid‐lipid immiscibility. Supporting studies in bilayers revealed that substitution of (18:2)4CL with (18:1)4CL or (22:6)4CL lowered the phase transition temperature of phosphatidylcholine vesicles, whereas (14:0)4CL had no effect. Finally, quantitative confocal imaging of giant unilamellar vesicles (GUVs) showed that loss of CL content had a stronger influence than remodeling of CL acyl chains. Taken together, we propose that loss of (18:2)4CL content may have a stronger influence on select biophysical properties of membranes than CL acyl chain composition, which has implications for mitochondrial inner membrane structure/function and the design of CL‐specific therapeutics.Support or Funding InformationResearch was supported by NIH R01HL123647 (D.B. and S.R.S), an East‐West Collaboration Award (S.R.S. and A.K.), NIH R15HL122922 (D.B. and S.R.S.), Brody Brothers Foundation Award 213147 (S.R.S.), NIH K25GM100480 (S.R.S. and P. Wang), and NIH R01AT008375 (S.R.S.).