Abstract 15560: Mitophagy Dysfunction and Activation of the Inflammasome Cause Aortic Stiffness in Low Aerobic Capacity Aged Rats

Abstract

Aging and low aerobic capacity are associated with an increased risk of cardiovascular events and mortality. We reported that a polygenic rat model selectively bred for low aerobic capacity (LCR) showed aortic stiffness and dysfunction with age compared to rats bred for a high aerobic capacity (HCR). We observed increased aortic mitochondrial ROS and extracellular mtDNA DAMPs levels, activation of AIM2 inflammasome and its downstream effectors and increased collagen content in old LCR rat aortas. However, the molecular mechanisms linking low aerobic capacity to inflammation in aging have not been elucidated. In order to decipher the changes in genetic networks in low aerobic capacity and aging-associated aortic stiffness, a global transcriptome analysis was performed by RNA-Seq and gene ontology analysis of aortas from young (4 month) and old (27 month) LCR and HCR rats. Down-regulated pathways in old LCR aortas include mitochondrial biogenesis and mitophagy and up-regulated pathways include pro-inflammatory pathways, apoptosis/necroptosis/ferroptosis pathways, in contrast to HCR aortas which have higher levels of pathways regulating longevity, oxidative phosphorylation, and mitophagy and autophagy. In line with that, old LCR rats displayed a 54% reduction in mitophagy (colocalization of mitochondrial marker protein TOM20 with lysosomal marker protein LAMP1) in aortic media and a 76% reduction in cultured VSMCs in comparison to older HCR rats. Mitophagy levels did not differ significantly between young LCR and HCR rats. The autophagic vacuole formation rate was a 12-fold lower in old LCR than in old HCR aortic VSMCs, suggesting that impaired mitophagy may be responsible for accumulation of mtDNA-derived damage associated molecular patterns (mtDNA DAMPs). Treatment with various inducers of mitophagy (rapamycin, deferiprone, and MitoTEMPO) significantly increased mitophagy and decreased mtDNA DAMPs levels in old LCR VSMCs. This was also associated with a reduction in inflammasome activation, mitochondrial dysfunction, and ROS levels. We conclude that impaired mitophagy causes accumulation of DAMPs and inflammasome activation, inducing aortic stiffness and dysfunction in old age LCR rats.