Appu, A. | bioRxiv Science

bioRxiv2026

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

BackgroundPeripheral 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. MethodsWe 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 Ppar{gamma}, 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. ResultsPatients 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. ConclusionsIMAT 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 PERSPECTIVEO_ST_ABSWhat is new?C_ST_ABSO_LIIntramuscular 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. C_LIO_LIGenetic 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. C_LIO_LIAdipogenic 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. C_LI What are the clinical implications?O_LIIMAT accumulation represents an underappreciated, non-vascular mechanism contributing to leg dysfunction in PAD/CLTI. C_LIO_LITherapies 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. C_LIO_LIIdentifying and targeting cellular pathways regulating IMAT formation from fibro-adipogenic progenitors may complement vascular interventions to enhance functional recovery after revascularization. C_LI

physiology↗

bioRxiv2022

Hedgehog signaling acts as cell fate determinant during adult tissue repair

Successful muscle regeneration relies on the interplay of multiple cell populations. However, the signals required for this coordinated intercellular crosstalk remain largely unknown. Here, we describe how the Hedgehog (Hh) signaling pathway controls the fate of fibro/adipogenic progenitors (FAPs), the cellular origin of intramuscular fat (IMAT) and fibrotic scar tissue. Using conditional mutagenesis and pharmacological Hh modulators in vivo and in vitro, we identify DHH as the key ligand that acts as a potent adipogenic brake by preventing the adipogenic differentiation of FAPs. Hh signaling also impacts muscle regeneration, albeit indirectly through induction of myogenic factors in FAPs. Our results also indicate that ectopic and sustained Hh activation forces FAPs to adopt a fibrogenic fate resulting in widespread fibrosis. In this work, we reveal novel post-developmental functions of Hh signaling in balancing tissue regeneration and fatty fibrosis. Moreover, they provide the exciting possibility that mis-regulation of the Hh pathway with age and disease could be a major driver of pathological IMAT formation.

developmental biology↗