(180s) Endothelial Membrane Biomechanics Under Dyslipidemic Conditions

An elevation in circulating blood levels of lipoproteins, causing dyslipidemia, is a major risk factor for heart disease, diabetes, and stroke. One effect of elevated lipoprotein levels is the modification of the lipid composition of endothelial cell membranes, resulting in changes to membrane biomechanics. In the endothelium, the membrane/cytoskeleton biomechanics are believed to play an important role in multiple endothelial functions including permeability and angiogenic potential. In this study, we quantify changes to the mechanical properties of the aortic endothelial layer of dyslipidemic mice, as well as the membranes of cultured human aortic endothelial cells (HAECs), using microindentation by atomic force microscopy (AFM). With this technique, we obtain estimates of two essential parameters: (i) the elastic modulus, representing the stiffness of the membrane/cytoskeleton complex, and (ii) the force required for the formation of membrane tethers, which reflects membrane tension and membrane/cytoskeletal adhesion. We observe significant stiffening of the aortic endothelial layer in diet-induced dyslipidemic mice as compared to wild-type control mice. This result parallels our finding that significant membrane stiffening occurs in HAECs exposed to combined low density lipoprotein (LDL) and oxidized LDL at pathological levels. The stiffening that we observe in both freshly isolated tissues as well as live cultured cells is accompanied by a corresponding increase in the force required for membrane tether formation, signifying that dyslipidemic conditions result in a change in endothelial membrane tension and cytoskeleton adhesion. Our results suggest that dyslipidemia not only alters the membrane lipid composition, but fundamentally disrupts the biomechanical integrity of the aortic endothelial layer, including altering the cell membrane/cytoskeleton adhesion and the membrane tension.