Abstract
Background & Aim: Autophagy is a cytoprotective recycling mechanism,
capable of digesting dysfunctional cellular components, and this process
is associated with pro-survival outcomes. Autophagy may decline in the
aging myocardium, thereby contributing to cardiac dysfunction. However,
it remains to be established how autophagy responds to
ischemia-reperfusion stress with age. Methods: Samples from the right
atrium were collected from young (≤50 years; n=5) and aged (≥70 years;
n=11) patients prior to and immediately following cardioplegic arrest
during coronary artery bypass grafting (CABG) surgery, a model of human
ischemia-reperfusion injury. Results: Mitochondrial content did not
differ between the age groups, however a 32% reduction in UQCRC2 (0.74
vs 0.53, effect of age, p=0.03) was seen with age, indicating possible
compositional disruptions. In response to IR, VDAC (0.75 vs 1.05,
p=0.03) and COX-I protein (0.63 vs 1.10, p=0.03) was over expressed in
young, but not in aged patients. Reductions in Parkin (0.95 vs 0.49,
interaction effect, p=0.04) and NIX (0.60 vs 0.21, p=0.004) protein
expression with age suggest an impairment in mitochondrial recycling,
which may lead to an accumulation of dysfunctional mitochondria.
Following IR, our data suggest that in the young cohort, autophagy is
reduced as a Beclin-1 decreased by 63% (0.95 vs 0.36, p=0.001) and no
changes were observed in either p62 or LC3-II:I ratio. Conclusion: Our
data demonstrate a blunted cardiac mitochondrial response to ischemia
with age, accompanied by a possible impairment in mitophagy. These
findings support an age-associated inability of the atrial myocardium to
mount appropriate adaptive responses to stress.