ApoCIII-induced hyperlipidemia alters lipid packing in erythrocyte membranes without affecting fluidity.

High levels of apolipoprotein CIII (apoCIII) promotes hypertriglyceridemia and increased risk of cardiovascular disease. However, the impact of apoCIII-induced hyperlipidemia on membrane composition and fluidity of red blood cells (RBC) is still unclear. Here, we report the fluidity, ordering, and lipid composition of the plasma membrane of RBC from transgenic mice that overexpress the human apoCIII. ApoCIII mice displayed marked hypertriglyceridemia (∼8-fold increase), moderate hypercholesterolemia (1.6-fold increase), followed by a shift toward increased plasma fatty acid unsaturation. RBC membranes from apoCIII mice demonstrated a significant increase in cholesterol content and cholesterol-to-phospholipid ratio, without alterations in sphingomyelin levels and the four major fatty acid analyzed. Fluorescence measurements using the probe Laurdan revealed unchanged membrane fluidity (anisotropy), but a significant reduction in generalized polarization (GP), indicative of increased lipid disorder and hydration at the phospholipid headgroup region. These findings suggest that moderate plasma cholesterol elevation alters RBC membrane lipid packing without affecting global fluidity or fatty acid profile. Overall, this study provides novel biophysical insights into the effects of dyslipidemia on erythrocyte membranes and support the potential of RBC membrane properties as sensitive biomarkers of systemic lipid perturbations.