Past studies indicate that APOE4 promotes a metabolic shift toward greater fatty acid usage. We have shown that APOE4 is associated with lower increase in cerebrospinal fluid (CSF) polyunsaturated fatty acids (PUFAs) following supplementation with triglyceride (TG) based DHA. The purpose of this study is to define the effect of APOE4 on plasma and CSF lipids using a comprehensive lipidomic analysis. Plasma and CSF samples were obtained from the DHA Brain Delivery Pilot, a randomized clinical trial of DHA treatment (n=13) vs placebo (n=13) in non-demented older participants (CDR ≤ 0.5, age> 55 years old) and stratified by APOE4. Participants were provided 2,040 mg DHA daily in the form of TG-DHA for six months. Following supplementation, levels of phosphatidylcholine DHA (PC 38:6) and cholesterol ester DHA (CE 22:6) had the largest increase in CSF (p<0.0001). Using principal component analysis, changes in plasma TG (56:8), TG (58:10), ePE (40:8), TG (56:9), PC (40:6) and PC (38:6) had the strongest correlations with changes in CSF PC (38:6, p<0.001). Figure 1 shows Pearson correlation coefficients of all plasma and CSF lipids. Among all lipid species, changes in PUFA enriched TGs were significantly correlated between CSF and plasma. APOE4 had a significant effect on CSF TG (52:6) changes, with the mean increase in E4 carriers significantly (0.039 units) less than in E4 non-carriers (p=0.0072) after adjusting for baseline levels and treatment group. Our findings demonstrate the first time the existence of PUFAs within a TG pool in CSF that correlates with the corresponding plasma TG pool, suggesting an exchange of TG particles at the CSF-blood barrier. The effect of APOE4 on the metabolism of PUFAs is strongest on TG enriched PUFAs and supports their greater oxidation in APOE4. These findings help explain why APOE4 carriers are vulnerable to dietary omega-3 deficiency, and less responsive to short term omega-3 supplementation.

The contribution of apolipoprotein E (APOE) e4 to Alzheimer's disease (AD) pathology is characterized by the presence of severe cerebral amyloid angiopathy (CAA), increased blood-brain-barrier (BBB) breakdown and reduced cerebral vascularization in e4 carriers. It has been proposed that the diminished capacity of the apoE4 protein to transport docosahexaenoic acid (DHA), an essential fatty acid that is required for the structural and functional maintenance and vascular integrity of the brain also contributes to AD pathogenesis. However, it remains to be determined if there are changes in brain DHA content of phospholipids (PL) and in DHA transporters in relation to the e4 allele and AD diagnosis and brain cerebrovascular amyloid pathology. We performed liquid chromatography/mass spectrometry based PL analysis of the cerebrovascular and parenchymal fractions from autopsied human brain tissue of pathologically confirmed AD cases and controls. We performed antibody-based examination of the major facilitator superfamily domain containing 2A (mfsd2a) protein in the cerebrovasculature from these subjects. In the cerebrovascular and parenchymal fractions, DHA containing PL species were lower in e4 carriers with AD cases compared to control ε4 carriers. We observed an APOE e4 dependent decreases in mfsd2a expression in the brain cerebrovasculature. The mfsd2a expression was lower in e4 carriers compared to non-carriers. Stratification of DHA containing PL by CAA showed that these PL levels were reduced in e4 positive AD patients with severe CAA. These findings demonstrate that brain DHA deficiencies in e4 carriers may be due to reduced mfsd2a expression and partly associated with CAA. Thus, targeting this transport mechanism may improve the bioavailability of DHA to the brain of e4 carriers who are at risk of developing AD.

Traumatic brain injury (TBI) is a major epigenetic risk factor for AD. Several neurological conditions have demonstrated an important role for dysfunction in phospholipids as a driving factor for disease pathogenesis. However, their precise role in TBI and AD remain elusive. To address this, we employ a LC/MS lipidomic approach to examine longitudinal changes in brain phospholipid profiles in mouse models of TBI and AD (PSAPP mice). Samples from the cortex/hippocampus were collected at ‘pre’, ‘peri’ and ‘post’ onset of amyloid pathology (i.e. 3, 9, 15 months of age) and at timepoints post-injury (i.e. 24hrs, 3, 6, 9 and 12 months). Total levels of phosphatidylcholine (PC), phosphatidylethanolamine (PE), LysoPE, and phosphatidylinositol (PI), including their mono/poly-unsaturated and saturated fatty acid containing species were significantly increased at acute and/or chronic time points post-injury. These lipid species in AD mice were unchanged in the hippocampus, while in the cortex the levels were significantly decreased at time points post onset of amyloidopathy. LysoPC and sphingomyelin levels showed coincidental trends in both TBI and AD models in the hippocampus, an increase at early and/or later time points examined. Arachidonic acid to decosahexaenoic acid ratio for PE containing species was increased at acute time points in the hippocampus post-TBI, and in PSAPP mice there was an increase at all time points examined. Exploration of the secondary mechanisms triggered by the aberrant changes in phospholipids and their regulation at the appropriate time-windows of opportunity could help to identify new and potent therapeutic strategies to effectively ameliorate the consequences of TBI/AD pathogenesis.