Abstract Tu0080: Suppression of Intramuscular Adipose Tissue Improves Limb Outcomes in Mice with Hindlimb Ischemia

Background: Chronic limb threatening ischemia (CLTI) is the most severe form of the atherosclerotic disease peripheral arterial disease (PAD). Surgical revascularization and endovascular therapies are the primary interventions for CLTI which improve macrovascular blood flow, however limb muscle function is often still impaired following these procedures suggesting CLTI involves pathological changes to non-vascular cell types. The replacement of skeletal muscle with intramuscular adipose tissue (IMAT) is prominent among patients with CLTI and is likely formed by differentiation of fibro-adipogenic progenitor cells (FAPs) that reside within muscle into adipocytes. How IMAT impacts limb function in CLTI is unknown. To define the role of IMAT in CLTI, we deleted Pparγ[TR1] , a key regulator of adipogenesis, specifically in FAPs to suppress IMAT formation in mice subjected to hindlimb ischemia. Methods: FAP-specific inducible Pparγ knockout mice (Pparγ FAP-KO ) were used to inhibit the differentiation of FAPs into IMAT. Cre-negative (Pparγ fl/fl ) littermates served as controls. Twelve-week-old male and female mice underwent femoral artery ligation (FAL) to induce hindlimb ischemia. Resting perfusion was measured using laser Doppler imaging. A nerve mediated 6-min limb function test involving repetitive submaximal isotonic contractions and laser Doppler flowmetry was used to measure muscular performance and perfusion in the gastrocnemius. Levels of IMAT and capillary densities were assessed histologically. Results: FAP-specific deletion of Pparγ repressed IMAT formation following FAL ( p<0.01 ). Ablation of IMAT improved muscle strength in male ( p=0.016 ) and female ( p=0.0037 ) mice. Also, Pparγ FAP-KO mice performed significantly more work across the 6-min limb function test compared to Pparγ fl/fl controls in both sexes (ADD p value). No differences were observed in resting paw perfusion, yet in the contracting gastrocnemius, female Pparγ FAP-KO mice greater hyperemia and perfused capillary densities (Pparγ FAP-KO 74% ± 11% vs Pparγ fl/fl 56% ± 19%; p=0.0379 ). Linear regression analysis revealed a significant inverse relationship between IMAT and muscle strength ( p<0.0001 ), suggesting that IMAT formation impedes optimal muscle function in CLTI. Conclusions: These findings demonstrate that pathological IMAT deposition derived from FAPs worsens limb function in preclinical CLTI models and provide a basis for future therapeutic development.