Single-cell transcriptomics highlights macrophage-driven regulation of EndMT and repair in injured muscle

Following muscle injury, a series of well-coordinated events ensures proper healing. Among these, inflammatory cells, particularly macrophages (MPs), play a fundamental role by phagocytosing damaged tissue and coordinating the actions of other cells involved in regeneration. Partial depletion of infiltrating MPs has been associated with endothelial cells (ECs) undergoing endothelial-to-mesenchymal transition (EndMT), contributing to extracellular matrix accumulation. However, the specific mechanisms linking MPs to this process, as well as their role in influencing EC fate, remain unclear. Here, we adopt a single-cell transcriptomics approach in mice to define a specific signature of the regenerating muscle niche. We show that perturbing MP recruitment upon injury results in impaired MP polarization, creating an aberrant inflammatory, non-regenerative, and less angiogenic microenvironment, which in turn drives ECs toward EndMT. Furthermore, we highlight complex signalling interactions between MPs and ECs, with SPP1 emerging as one of the critical modulators of these processes. Using single-cell transcriptomics, the authors show that partial depletion of infiltrating macrophages impairs polarization, creating a non-regenerative, less angiogenic niche that drives endothelial-to-mesenchymal transition and compromises muscle repair, with SPP1 as a key mediator.