FIGURE 7.

APOE genotype modulates lipid metabolism in brain endothelial cells. (A) Lipidomic analysis reveals 43 significant differences (dark blue = lower; dark red = higher) and 21 trending differences (light blue = lower; pink = higher) in APOE4 brain endothelial cells. Each circle represents a unique metabolite. Most of the metabolites are lower with APOE4 and include phosphatidylcholines (1-myristoyl-2-arachidonyl-GPC (14:0/20:4), phosphatidylethanolamines (1-palmitoyl-2-arachidonyl-GPE (16:0/20:4))), phosphatidylinositols, lysophospholipids (1-oleoyl-GPC (18:1)), and plasmalogens (1-(1-enyl-palmitoyl)-2-arachidonyl-GPC (P16:0/20:4)), with the exception of two ceramides (N-behenoyl-sphingadienine (d18:2/22:0) & actosyl-N-nervonoyl-sphingosine (d18:1/24:1)) that are higher. (B) Consistent with lipidomic analysis, phosphatidylcholine levels are lower with APOE4 when assessed by ELISA. (C) Although there are no differences in cellular cholesterol levels, (D) cellular triglyceride levels are lower in APOE4 brain endothelial cells. (E) Changes in membrane composition can alter mechanical properties of a cell. In the plasma membrane, this can manifest as changes in stiffness, which can contribute to cell stiffness when measured by atomic force microscopy (Askarova et al., 2013). In this technique, a cantilever tip approaches the plasma membrane, makes contact, and then indents the cell surface; the force required to make the indentation corresponds to cell stiffness. We found that cells stiffness is higher in APOE4 brain endothelial cells when measured by atomic force microscopy (analyzed by paired t-test). (F) Lactate dehydrogenase (LDH) is a cytosolic enzyme found in cell culture media when the plasma membrane is damaged, as found with cytotoxicity. Despite the lack of toxicity, levels of lactate dehydrogenase in the media are higher with APOE4. Data is expressed as mean ± S.E.M. *p < 0.05 by Student’s t-test with n = 6 (unless otherwise specified above).