Metabolic reprogramming of skeletal muscle by resident macrophages points to CSF1R inhibitors as muscular dystrophy therapeutics (RNA-Seq).

The role of tissue resident macrophages during tissue regeneration or fibrosis is not well-understood, mainly due to the lack of a specific marker for their identification. Here, we identified two populations of skeletal muscle resident macrophages: TIM4- macrophages which are replenished from the blood and LYVE1+TIM4+ macrophages that locally self-renew (self-renewing resident macrophages, SRRMs). Using a CSF1R inhibition/withdrawal approach to specifically deplete SRRMs, we found that they provide a non-redundant function in clearing damage-induced apoptotic cells early after extensive acute injury. In contrast, in chronic mild injury as seen in a mouse model of Duchenne muscular dystrophy, we showed that depletion of both resident populations through long term CSF1R inhibition changes muscle fiber composition from damage-sensitive glycolytic fibers towards damage-resistant glycolytic-oxidative fibers protecting muscle against contraction induced injury. This later finding reveals a new role for resident macrophages in modulating tissue metabolism and has therapeutic potential in light of the ongoing clinical testing of CSF1R inhibitors. Characterization of skeletal muscle resident macroophages; identification of their role in muscle regeneration and fibrosis;