Abstract 18426: Secreted Frizzled-Related Protein 1 Mediates Adipogenic Differentiation of Vascular Cell Adhesion Protein 1 Fibroadipogenic Progenitors in the Ischemic Limb

Introduction: Chronic limb threatening ischemia (CLTI) patients display a skeletal muscle myopathy that is hallmarked by fatty infiltration. The replacement of functional muscle fibers with adipocytes impairs ambulatory function and is associated with poor clinical outcomes. The cell type responsible for fatty infiltration is a mesenchymal stromal cellular population, term fibroadipogenic progenitors (FAPs). We previously demonstrated that Vcam1+ FAPs represent a sub-population with increased adipogenic potential. However, the molecular mechanisms which govern Vcam1+ FAP mediated adipogenesis remain unknown. Herein, we sought to identify the intracellular mechanisms that drive Vcam1+ FAPs into an adipogenic cellular fate.

Methods: We used single cell and bulk RNA-sequencing to identify Sfrp1 as an enriched gene in Vcam1+ FAPs. Next, to determine the sufficiency and necessity of Sfrp1, we overexpress Sfrp1 with a recombinant protein and inhibit Sfrp1 with a siRNA and assess adipogenesis. To assess the clinical significance of this FAP subpopulation, we apply single-cell RNA sequencing to CLTI patients.

Results: We show in a CLTI murine model that Vcam1+ FAPs are enriched in Sfrp1. Next, we demonstrate that Sfrp1 is both sufficient and necessary for the differentiation of Vcam1+ FAPs into adipocytes. Finally, we demonstrate that human CLTI patients also have a pathologic FAP population that is enriched in Vcam1 and Sfrp1Conclusions: Our results reveal a novel mechanism for fatty infiltration, a histologic hallmark of CLTI patients, in the ischemic limb. We also validate the clinical significance of Vcam1+ Sfrp1+ FAPs by demonstrating the presence of this population in human CLTI patients. This work lays the foundation for future studies aimed at inhibiting fatty infiltration and promoting skeletal muscle regeneration in CLTI patients.