Intramuscular Adipose Tissue Accumulation is a Key Determinant of Limb Function in Peripheral Artery Disease

ABSTRACT Background Peripheral artery disease (PAD) and its severe form, chronic limb-threatening ischemia (CLTI), significantly impair blood flow to the lower extremities, affecting millions of adults globally. Intramuscular adipose tissue (IMAT) and fibrosis accumulation distinguish patients with CLTI from those with mild PAD, suggesting a role in CLTI pathobiology. However, the functional consequences of IMAT in CLTI remain unclear. Methods We compared gastrocnemius muscle samples from patients with PAD/CLTI, intermittent claudication, and non-PAD individuals. We analyzed bulk RNA sequencing, proteomic, lipidomic, and single-cell/nucleus RNA sequencing datasets. Additionally, we used murine models of hindlimb ischemia (HLI) with genetic manipulation of Pparγ, a key adipogenic transcription factor, specifically in fibro-adipogenic progenitor cells (FAPs), the cellular source of IMAT, to modulate IMAT formation and assessed the impact on limb function and pathology. Results Patients with CLTI exhibited significantly elevated expression of adipogenic genes and proteins in muscle specimens when compared to non-PAD controls. Murine models showed that increasing IMAT formation significantly worsened ischemic limb muscle strength and work output. In contrast, preventing IMAT formation significantly improved ischemic limb muscle strength and work output. These findings were consistent across both male and female mice, although females had greater tendency to form IMAT compared with male mice. Conclusions IMAT accumulation is a key determinant of limb function in PAD/CLTI. Our studies demonstrate that targeting IMAT formation could improve limb function in mice with experimental PAD. Together, these findings suggest that developing strategies to limit or reduce IMAT may improve limb function and walking performance in patients with PAD/CLTI, providing a novel therapeutic avenue to address a critical unmet need. CLINICAL PERSPECTIVE What is new? Intramuscular adipose tissue accumulation (IMAT) distinguishes patients with chronic limb-threatening ischemia from those with milder peripheral artery disease or those without PAD and directly impairs ischemic limb muscle function. Genetic gain- and loss-of-function mouse models demonstrate that increasing IMAT worsens, while preventing IMAT formation improves, ischemic limb strength and performance independent of perfusion. Adipogenic signatures in human calf muscle negatively correlates with muscle strength and disease severity, identifying IMAT as a functional biomarker and modifiable target in PAD/CLTI. What are the clinical implications? IMAT accumulation represents an underappreciated, non-vascular mechanism contributing to leg dysfunction in PAD/CLTI. Therapies aimed at limiting or reversing IMAT formation may improve leg strength and walking performance in patients with PAD/CLTI, addressing a critical unmet clinical need. Identifying and targeting cellular pathways regulating IMAT formation from fibro-adipogenic progenitors may complement vascular interventions to enhance functional recovery after revascularization.