Scarless regeneration requires post-translational proteolytic regulation via macrophage-derived Legumain

Macrophages express proteolytic factors in response to injury but how proteases are deployed and regulated during regeneration are incompletely defined. Beyond their transcriptomic expression, activity of individual proteases is defined both by their unique substrate specificity and post-translational modifications of their active forms. Here we show a key role for the lysosomal protease Legumain in controlling ECM dynamics and post-translational processing of the regenerative proteome. Injury interface-targeted Ctsla localization and post-translational processing requires Lgmn in macrophages. Extracellular cues from physical remodeling control differentiation state and injury response of ligament resident fibroblasts. Loss of ECM turnover, including localized Fibronectin 1a/b remodeling, impairs dedifferentiation in legumain mutants and leads to fibrotic scarring. Taken together, we demonstrate a role for macrophage-derived lysosomal proteases as specialized tools required to fine-tune proteome composition and function in regeneration.