Pathologic profibrotic activation of distinct myeloid cell subsets in a model of impaired healing after anterior cruciate ligament reconstruction

Abstract

Anterior cruciate ligament reconstruction (ACLR) may fail due to poor bone-to-tendon integration, yet the cellular mechanisms underlying this process remain incompletely understood. Using a murine model of ACLR, we show that host-derived immune cells are the primary drivers of early healing, while tendon graft-derived stromal cells also contribute at the tendon-bone interface. We developed a model of impaired post-ACLR healing by a surgical approach, that led to increased infiltration of immune cells at the tendon-bone interface, particularly CX3CR1+ monocytes/macrophages (MonoMacs). Single-cell RNA sequencing revealed dynamic monocyte-to-macrophage transitions, with an enrichment of fibrotic, mechanosensitive CX3CR1+ MonoMacs in the impaired healing model. These findings suggest that excessive recruitment or functional shifts in host-derived MonoMacs may disrupt normal healing dynamics. Our study identifies CX3CR1+ MonoMacs as a key cell population related to inferior bone-to-tendon healing after ACLR and potential therapeutic targets to improve surgical outcomes.