Abstract 14800: Presenilin 1 and Presenilin 2 Contribute to Mitophagy Including Alternative Pathway

Introduction: Presenilin 1 (PS1) and presenilin 2 (PS2) are proteins that compose γ-secretase, which is a protease present in late endosome lysosomes. Recently, amyloid beta accumulation was found in the cardiomyocytes of Alzheimer's disease patients and cause cardiac dysfunction. Mutations in PSEN1 and PSEN2 , the causative genes of familial Alzheimer's disease, are involved in the development of dilated cardiomyopathy (DCM); however, their roles in cardiomyocytes have not been elucidated thoroughly. Hypothesis: We hypothesized that PS1 and PS2 might be playing a role in mitochondria-selective autophagy (mitophagy) of cardiomyocytes. Methods: Whole-exome sequencing of 32 DCM patients was focused on 29 autophagy-related genes and 16 genes encoding autophagy-related proteins. Based on the results, the expression of autophagy and mitophagy markers was examined using cultured rat cardiomyocytes silenced for PSEN1 or PSEN2 and exposed to starvation, 100 μM bafilomycin A1, inhibiting fusion between autophagosomes and lysosomes, or 10 μM carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP), a mitochondrial uncoupler used to induce mitophagy. Results: A variant of PSEN2 (c.1262C>T) may be the cause of DCM in a 50-year-old Japanese man. Electron microscopic observation of myocardium revealed a fibrillar substance in the expanded T-tube, suggesting failure to clear aggregates. FCCP treatment caused an increase in microtubule-associated protein 1 light chain 3 (LC3)-II and p62 which was further enhanced in cells with silenced PS1 or PS2. Rab9, which is associated with the alternative pathway of mitophagy, was also increased in cells silenced for PS1 or PS2. Parkin was decreased with FCCP treatment, suggesting its clearance via mitophagy, and this was further enhanced when PS1 was silenced. Voltage-dependent anion channel (VDAC) levels, a reflection of mitochondrial content, were slightly increased when PS1 and PS2 were silenced. LC3-II increased with starvation and further increased with bafilomycin A1 treatment: however, silencing PS2 did not result in further increase, suggesting that flux was impaired. Conclusions: PS2 and probably PS1 are required to support autophagic flux necessary for cardiomyocyte homeostasis.