Protein quality control mechanisms decline during the process of cardiac aging. This enables the accumulation of protein aggregates and damaged organelles that contribute to age‐associated cardiac dysfunction. Macroautophagy is the process by which post‐mitotic cells such as cardiomyocytes clear defective proteins and organelles. We hypothesized that late‐in‐life exercise training improves autophagy, protein aggregate clearance, and function that is otherwise dysregulated in hearts from old vs. adult mice. As expected, 24‐month‐old male C57BL/6J mice (old) exhibited repressed autophagosome formation and protein aggregate accumulation in the heart, systolic and diastolic dysfunction, and reduced exercise capacity vs. 8‐month‐old (adult) mice (all p < 0.05). To investigate the influence of late‐in‐life exercise training, additional cohorts of 21‐month‐old mice did (old‐ETR) or did not (old‐SED) complete a 3‐month progressive resistance treadmill running program. Body composition, exercise capacity, and soleus muscle citrate synthase activity improved in old‐ETR vs. old‐SED mice at 24 months (all p < 0.05). Importantly, protein expression of autophagy markers indicate trafficking of the autophagosome to the lysosome increased, protein aggregate clearance improved, and overall function was enhanced (all p < 0.05) in hearts from old‐ETR vs. old‐SED mice. These data provide the first evidence that a physiological intervention initiated late‐in‐life improves autophagic flux, protein aggregate clearance, and contractile performance in mouse hearts.

There is evidence for a progressive decline of protein quality control mechanisms during the process of cardiac aging. This enables the accumulation of protein aggregates and damaged organelles that contribute to age-associated cardiac dysfunction. Macroautophagy (referred to as autophagy) is the process by which post-mitotic cells such as cardiomyocytes clear defective proteins and organelles. We hypothesized that late-in-life exercise training improves autophagy, protein aggregate clearance, and function that is otherwise dysregulated in hearts from old vs adult mice. As expected, 24-month old male C57BL/6J mice (old) exhibited : (i) repressed autophagosome formation and protein aggregate accumulation in the heart; (ii) systolic and diastolic dysfunction; and (iii) reduced exercise capacity, vs. 8-month old (adult) mice (all p< .05). Separate cohorts of 21 month old mice completed a 3-month progressive resistance treadmill-running program (old-ETR) that improved (all < .05) : (i) body composition; (ii) exercise capacity; and (iii) soleus muscle citrate synthase activity, vs. age-matched mice that did not train (old-SED). Importantly, (iv) protein expression of autophagy markers indicated trafficking of the autophagosome to the lysosome increased, (v) protein aggregate clearance improved, and (vi) overall function was enhanced (all p<0.05), in hearts from old-ETR vs. old-SED mice. Dietary maneuvers and pharmacological interventions shown to elevate basal autophagy are reported to mitigate / reverse age-associated cardiac dysfunction. Here we show the first evidence that a physiological intervention initiated late-in-life improves autophagic flux, protein aggregate clearance, and overall function in mouse hearts.

Protein aggregates accumulate and organelles become damaged and/or dysfunctional during the process of aging. A progressive loss of the cellular quality control mechanism autophagy contributes to this age‐associated decline in cellular function in many organs. Evidence for an age‐associated repression in cardiac autophagy is not consistent. We hypothesized that 24‐month old (old) male C57Bl6/J mice exhibit repressed autophagosome formation in the heart, myocardial dysfunction, and reduced exercise capacity vs. 6‐month old (adult) mice. First, cardiac lysates from old mice displayed reduced (p<0.05) accumulation of LC3II/GAPDH and degradation of p62 vs. adult animals (n=12 per group). Second, the lysosomal acidification inhibitor chloroquine (CQ) induced accrual (p<0.05) of LC3II/GAPDH and p62 in hearts from adult but not old mice (n=7 per group). Third, left ventricular mass was greater (p<0.05), and indices of systolic, diastolic, and global left ventricular function (transthoracic echocardiography) were impaired, in old vs. adult animals (n=12 per group). Finally, maximal workload performed during a treadmill‐test was less (p<0.05) in aged (n=11) vs. adult (n=12) mice. To determine whether late‐in‐life exercise training induces cardiac autophagy, separate cohorts of male mice completed a progressive‐resistance treadmill‐running program (old‐ETR) or remained sedentary (old‐SED) from 21–24 months. Body composition, exercise performance during a maximal workload test, soleus muscle citrate synthase (CS) activity, indices of cardiac antioxidant enzyme activity, markers of cardiac autophagy, and indices of myocardial function, all improved (p<0.05) in old‐ETR (n=11) vs. old‐SED (n=12) mice. These data are the first to demonstrate that markers of cardiac autophagy are elevated, and indices of myocardial function are improved, in old mice that complete a treadmill‐training regimen that is sufficient to increase skeletal muscle CS activity and maximal exercise capacity. These data provide strong proof of concept to evaluate cause and effect relationships among exercise‐training, myocardial.Support or Funding InformationUU Research Fellowship (JMC); APS UGRF (CR); AHA17POST33670663 (SKP); NIHRO1DK098646‐01A1, NIHRO1DK099110, AHA16GRANT30990018 (SB); AHA16GRNT31050004, NIH RO3AGO52848, NIH RO1HL141540 (JDS).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Macroautophagy is operational during basal conditions to maintain intracellular organelle and protein quality control, but is upregulated during cellular stress (e.g, dynamic exercise) to adapt to changing nutritional and energy demands. We tested the hypothesis that intact endothelial cell (EC) autophagy is required to observe training‐induced vascular adaptations. Rationale for this hypothesis was provided by an earlier report that obese mice with germline, whole body mutation of a protein requisite for autophagy i.e., Bcl2‐AAA mice were refractory to training‐induced improvements concerning glucose homeostasis (He et al., Nature, 2012). First, we demonstrated that : (i) workload achieved during a maximal treadmill test; (ii) soleus muscle citrate synthase activity; (iii) mRNA and protein expression of vascular autophagy; and (iv) intraluminal flow‐mediated vasodilatory responses (FMD) of femoral arteries examined ex vivo, were greater (all p<0.05) in ~ 4‐month old male C57Bl/6 mice that completed 10‐weeks of treadmill‐training vs. age‐matched sedentary animals (n=10 mice per group). These findings indicate that our efficacious training protocol improves vascular autophagy and arterial function in adult mice. Next, ~ 4‐month old male mice on a C75Bl/6 background with inducible Cre/LoxP‐based impairment of autophagy‐related gene 3 (Atg3) specifically in ECs (iecAtg3KO mice) and their Cre negative littermates (WT) were treated with tamoxifen. Two weeks later, one cohort of iecAtg3KO mice initiated a treadmill training program (ETR; 10–60 min per day × 0–20% grade × 6 days per week × 10 weeks) or maintained familiarity with the treadmill by running 10 min per day × 5% grade × 1 day per week (SED). Two cohorts of WT littermates were treated identically. After 10‐weeks efficacy of the training protocol was established as described earlier and verification of our mutant was assessed. With regard to the latter, primary ECs obtained from the carotid artery and aorta indicated Atg3 mRNA and Atg3 protein, respectively, was minimal (p<0.05) in iecAtg3KO vs. WT mice, whereas vascular smooth muscle cell Atg3 was similar between groups. As expected, intraluminal FMD responses were greater (p<0.05) in WT‐ETR vs. WT‐SED mice, while vascular smooth muscle responses to sodium nitroprusside were not different between groups. Further, as anticipated, intraluminal FMD was blunted (p<0.05) in iecAtg3KO‐SED vs. WT‐SED mice, indicating the importance of intact EC autophagy to FMD. Contrary to our hypothesis, however, training‐induced vascular adaptations indeed were observed (p<0.05) in iecAtg3KO‐ETR vs. iecAtg3KO‐SED mice, while vascular smooth muscle responses were not different between groups. These findings indicate that intact EC Atg3 is not necessary for training‐induced vascular adaptations to occur. Support or Funding Information CR [APS UGRF, University of Utah (UU) Undergraduate Research Opportunities Program (UROP)]; JMC (UU Graduate Research Fellowship); SKP (AHA 17POST33670663); KL (APS STRIDE, UU UROP), LT (UU UROP); SB ...