Mitochondrial DNA drives AD Phenotypes in Cell Models

AbstractBackgroundMitochondrial DNA (mtDNA) inheritance influences Alzheimer’s Disease (AD) risk. Adult children of mother’s afflicted with AD show decreased cognition and increased AD biomarkers (both peripheral and brain) at earlier ages than adult children with father’s afflicted with AD. These human derived data paired with prior in vitro work support a maternal inheritance association of AD risk. However, the exact mechanism linking mtDNA inheritance patterns and AD is not understood.MethodsCytoplasmic hybrid (cybrid) cells were derived by fusing platelet mitochondria with SH‐SY5Y cells devoid of mtDNA. Cybrid cells have the same nuclear DNA background with varying mtDNA sequences derived from human subjects. We examined mitochondrial function parameters in cybrids derived from 8 cognitively healthy (CH), 7 AD, and 5 mild cognitive impairment (MCI) subjects. Mitochondrial electron transport chain (ETC) function was measured using Seahorse XF technology. Mitochondrial membrane potential, mitochondrial superoxide, and mitochondrial calcium were measured using fluorescent assays (TMRE, MitoSox, and Rhod2AM). Mitophagy and mitochondrial biogenesis/mass were measured using adenoviral constructs (EGFP‐Cox8 and MitoTimer).ResultsCybrids derived from AD subjects had elevated mitochondrial superoxide production when compared to CH cybrid cells. MCI cybrids did not show changes to mitochondrial superoxide production. Mitochondrial membrane potential and mitochondrial calcium were not changed in MCI or AD cybrids compared to CH. AD cybrids, but not MCI cybrids, showed reduced flux through all ETC components, including complex I, II, III, and IV. Finally, AD cybrids showed increased mitophagy levels but no change in mitochondrial biogenesis. MCI cybrids did not reflect these changes. Data do indicate AD cybrids might have increased mitochondrial mass, but further assays are needed to verify these findings.ConclusionsTransfer of mtDNA from AD patients to cells harboring consistent nuclear DNA recapitulates mitochondrial phenotypes observed in AD. We are currently measuring AD biomarkers in these models and working to examine their correlation with clinical data from this cohort of research subjects.