Endoplasmic Reticulum Stress-mediated Mitochondrial Dysfunction in Aged Hearts

Aging impairs the mitochondrial electron transport chain (ETC), especially in interfibrillar mitochondria (IFM). Mitochondria are in close contact with the endoplasmic reticulum (ER). Induction of ER stress leads to ETC injury in adult heart mitochondria. We asked if ER stress contributes to the mitochondrial dysfunction during aging. Subsarcolemmal mitochondria (SSM) and IFM were isolated from 3, 18, and 24 mo. C57Bl/6 mouse hearts. ER stress progressively increased with age, especially in 24 mo. mice that manifest mitochondrial dysfunction. OXPHOS was decreased in 24 mo. IFM oxidizing complex I and complex IV substrates. Proteomic analysis showed that the content of multiple complex I subunits was decreased in IFM from 24 mo. hearts, but remained unchanged in in 18 mo. IFM without a decrease in OXPHOS. Feeding 24 mo. old mice with 4-phenylbutyrate (4-PBA) for two weeks attenuated the ER stress and improved mitochondrial function. These results indicate that ER stress contributes to the mitochondrial dysfunction in aged hearts. Attenuation of ER stress is a potential approach to improve mitochondrial function in aged hearts.