CD37 impairs revascularization and muscle recovery in peripheral artery disease

Abstract

Peripheral artery disease (PAD) affects more than 14 million Americans, and its most advanced form, critical limb-threatening ischemia (CLTI), is associated with chronic inflammation, poor tissue perfusion, and impaired skeletal muscle repair. Although tetraspanins are known to organize immune receptor signaling, their contribution to ischemic tissue injury and recovery in CLTI remains incompletely understood. We investigated the leukocyte tetraspanin CD37 after identifying increased CD37 expression in human PAD gastrocnemius muscle. We analyzed human gastrocnemius muscle transcriptomic data from patients with PAD using deconvolution-based immune profiling to define associations between CD37 expression and immune cell programs. To examine the functional role of CD37 in ischemic tissue repair, we used a murine hindlimb ischemia model in wild-type and Cd37 -/- mice. Outcomes included perfusion recovery, skeletal muscle histology, transcriptomic profiling of post-ischemic muscle, tissue immune phenotyping, and ex vivo macrophage stimulation studies. In human PAD muscle, CD37 expression was associated with greater immune infiltration ( R = 0.51, p = 0.0002) and showed its strongest relationship with inflammatory macrophage programs ( R = 0.48, p = 0.0003). Cd37 -/- mice exhibited accelerated revascularization (87.6±9.8% vs. 62.9 ± 6.1% reperfusion, p < 0.04) and improved muscle recovery (mature fibers 77.9 ± 5.6% vs. 46.7 ± 8.2%, p < 0.02) versus wild-type. RNA-seq identified 594 differentially expressed genes (padj < 0.05), with Cd37 -/- muscle showing upregulation of pathways related to muscle mass and collagen degradation and downregulation of mitochondrial oxidative metabolism and proinflammatory signaling programs. Integrating RNA module scoring with immunohistochemistry, CD37 deficiency was associated with macrophage reprogramming toward resolution, characterized by higher proresolving and lower inflammatory macrophage signatures and increased CD163 + macrophages in Cd37 -/- muscle. Consistent with a shift away from a proinflammatory macrophage state, Cd37 -/- bone marrow–derived macrophages secreted lower levels of the inflammatory cytokines/chemokines. CD37 is associated with inflammatory immune remodeling in human PAD and appears to restrain tissue recovery after ischemic injury. In experimental hindlimb ischemia, loss of CD37 promotes perfusion recovery, improves muscle repair, and is accompanied by a less inflammatory, more pro-resolving macrophage phenotype. These findings identify CD37 as a potential immunomodulatory target to improve tissue repair and recovery in CLTI.