ApoE4 mediates a distinct polyunsaturated fatty acid response from stimulated microglia

ApoE4 is the strongest genetic risk factor for Alzheimer’s disease (AD), yet its functional role in disease progression remains unclear. Much of the research on apoE4 has focused on its genetic identity, rather than its activity as a lipid transporter in the brain. Polyunsaturated fatty acids (PUFAs) are abundantly transported by apolipoproteins. Here, we compare extracellular PUFA concentrations in cultured microglia upon exposure to different apoE isoforms. We hypothesized that, in stimulated microglia, apoE4 would have different effects on PUFA exchange between cell compartments and media compared to apoE3 or apoA-I. Immortalized mouse microglia (IMG) were exposed to either apoE4 or apoE3 at 25 µg/mL, apoA-I at 40 µg/mL, or PBS in a factorial design. Cells were stimulated with 5 ng/mL TNFα or saline. Prior to treatment, cells were pre-conditioned with 10 µM LXR-623 and 50 µM cAMP to induce ABCA1, and 5 µM exogenous PUFAs to ensure adequate substrate for oxylipin production. Total and non-esterified fractions of media were analyzed by targeted LC-MS/MS lipidomics. Addition of TNFα increased PUFA concentrations 4.3-fold in the non-esterified media in apoE4-treated microglia (p < 0.0001). Conversely, the addition of TNFα decreased PUFA concentrations in the non-esterified media in apoE3-treated microglia by 2.1-fold (p = 0.05). Acute inflammation with TNFα increased PUFA concentrations in apoE4-treated microglia in the non-esterified media compared to apoA-1-treated microglia 2.7-fold (p = 0.01). PUFAs in apoE4-treated microglia were more concentrated compared to apoE3-treated microglia upon treatment with 0 ng/ml TNFα in the non-esterified media by 2.2-fold (p = 0.04), and upon treatment with 5 ng/ml TNFα in both the non-esterified (p = 0.0002) and total media (p < 0.0001) by 4.3 and 4.2-fold, respectively. Taken together, treatments with apolipoprotein isoforms in microglia, with both inflammatory stimuli and saline, elicit changes in PUFA concentrations in media, with apoE4-treated microglia exhibiting increased concentrations compared to other isoforms. These differences could provide further understanding into the mechanism as to which apoE4 increases the genetic risk of AD development. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.