Abstract 12906: Exercise Training Protects Against Ischemic Muscle Damage in a Large-Animal Model of Peripheral Artery Disease

Abstract

Peripheral artery disease (PAD) causes an ischemic myopathy in the lower extremity muscles, which contributes to patient functional disability. Although structured exercise therapy is a leading therapeutic to improve ambulatory function, the impact of exercise on PAD myopathy is unclear. Using our porcine model of PAD, we sought to elucidate the effect of hindlimb ischemia on markers of 1) muscle damage (caspase 3, myogenic differentiation 1 (MyoD), and Forkhead box protein O1 (FOXO1)), 2) muscle protein turnover (autophagic flux and proteolytic activity), and 3) whether these indices were altered with exercise training. Methods: Seven Yorkshire swine were exposed to right hindlimb ischemia by endovascular external iliac artery occlusion. Following ischemia onset, the swine were divided into 2 training groups: supervised exercise trained (ET) (n=4) and sedentary controls (SED) (n=3). ET pigs followed an incremental treadmill protocol 3 times weekly for 4 weeks. SED pigs had standard ambulation. The tibialis anterior from ischemic and non-ischemic limbs was excised after animal termination. Markers of muscle damage and proteolytic activity were assessed via RT-PCR and enzymatic activity kits, respectively. The ratio of intramuscular microtubule-associated protein light chain 3 (LC3)-II:LC3-I, as well as sequestosome (p62), and mitofusion2 (MFN2) content from immunoblots were used to monitor autophagic flux. Results: Gene expression of intramuscular damage was significantly higher in SED ischemic muscle compared to ET muscle (caspase 3 (SED: 5.59±1.5; ET: 1.67±1.5), MyoD (SED: 4.55±1.2; ET: 1.24±1.5) and FOXO1 (SED: 1.74±0.5; ET: 1.07±1.1), p<0.0001). Moreover, ischemic muscle from ET pigs showed no alteration in markers of muscle damage when compared to the SED and ET non-ischemic conditions (p>0.05). Although proteolytic activity was unaltered (p>0.05), autophagic flux tended to be increased in ET ischemic muscle (LC3-II:LC3-I ratio (ET: 0.21±0.1; SED: 0.10±0.1 AU, p=0.099), p62 (ET: 15.80±5.1; SED: 7.75±2.8 AU, p=0.068) and MFN2 (ET: 42.72±15.9; SED: 16.82±11.3 AU, p=0.214). Conclusions: These data suggest exercise therapy is protective against ischemic muscle damage and may improve muscle quality via accelerating autophagic flux.