Abstract 302: Autophagy in the Aging Heart
Autophagy maintains cellular homeostasis by lysosomal degradation and recycling of damaged/dysfunctional organelles, removal of aggregated proteins, and the provision of energy to cells in times of stress. Recently, autophagy has been shown to decline with age in the liver and thymus, prompting us to ask if there was a corresponding age-related decrease in autophagy in the heart. The comparison of membrane-associated LC3-II to cytosolic LC3-I is indicative of autophagosome formation, and is one of several parameters used to assess autophagic activity. Basal autophagy in C57BL/6 mice across five age groups from 2.5 to 24 months, assessed by Western Blot, demonstrated little variance in LC3-I but a significant decrease in LC3-II (ANOVA; n=3/age group; p>0.05 and p<0.0002, respectively). Also, a Triton-X insoluble fraction containing p62/SQSTM-1 and ubiquitinated proteins were shown to correlate with changes in aggrephagy. We found a significant increase in p62 and ubiquitinated proteins with increasing age (p<0.01). Both findings suggest a decline in basal autophagy with age. When subjected to an acute stress, such as fasting, the levels of LC3-II but not LC3-I increased in young and old mice (n=4/age group; p<0.05 and p>0.05, respectively). To determine if flux was impaired in the aged, we treated fasted mice with chloroquine, which prevents autophagosome/lysosome fusion resulting in LC3-II accumulation. We found LC3-II accumulated only in the young (n=4; p<0.01). Thus, the aged can mount an acute response but flux declines. Moreover, RT-qPCR analysis of cardiac tissue showed a significant decrease in atg5 and atg7 and a significant increase in atg8A, atg8B, lamp2A, atg4A, and atg4B expression with advancing age (> 2.5 fold change). The dysregulated mRNA levels are suggestive of overcompensation of clearance, and the data support an overall decline in function with age. Although not manifest in the same manner, autophagy dysregulation also occurs with age in BALB/c mice, a shorter-lived strain. Our findings may be relevant to cardiac injury, such as in ischemia/reperfusion, given the emerging importance of autophagy in cardioprotection.
- © 2012 by American Heart Association, Inc.