Abstract Body: Introduction: Peripheral artery disease (PAD) affects millions of Americans and can lead to limb loss in advanced states. Advanced age is a risk factor for PAD and is associated with structural changes in vessel walls as well as poor angiogenic capacity. Ischemic myopathy is a recognized effect of chronic tissue malperfusion in the setting of chronic limb-threatening ischemia. Differences in the severity and manifestation of ischemic myopathy with advanced age have not been fully investigated.

Hypothesis: We hypothesized that aged animals would differ in their response to limb ischemia and revascularization efficiency.

Methods: Hindlimb ischemia was created in young (9-12 week, n=9) and aged (72 week, n=11) C57Bl/6 mice under anesthesia. Animals were followed for 21-days by laser speckle contrast imaging (LSCI) to compare perfusion between ischemic and non-ischemic (contralateral) limbs. After humane sacrifice, ischemic and contralateral non-ischemic gastrocnemius muscles were collected for histologic and molecular analysis. CD31 immunohistochemistry was performed to evaluate angiogenesis. Transmission Electron Microscopy (TEM) evaluated cellular ultrastructural differences between ischemic and control muscle.

Results: Mean limb perfusion in young and aged animals did not differ after initial arterial ligation (aged 46% baseline, young 36% baseline, P=0.19). After the 21-day revascularization period, aged animal limb perfusion trended poorer (mean 77% baseline) compared to young (mean 91% baseline, P=0.12). Histologic indices of ischemic myopathy differed between young and aged animals with mean aged myofiber diameter 8.4 µm compared to 11.2 µm in young animals (P<0.001). Control (non-ischemic) myofiber diameter also differed by age with mean 15.2 µm in aged animals compared to 19.7 µm in young (P<0.001). TEM documented centralization of nuclei with condensation of chromatin as well as significant distortions in sarcomere and myofibril structure in ischemic muscle as compared to control. Ischemic muscle cells contained significantly more mitochondria, glycogen and collagen.

Conclusion: Hindlimb ischemia secondary to arterial occlusion in both young and aged mice lead to reproducible perfusion deficits with subsequent tissue recovery. Aged animals demonstrated evidence of myopathy in non-ischemic limbs as well as more severe ischemic myopathic injury at the tissue and cellular ultrastructural levels compared to young.