Macrophages are required to coordinate mouse digit tip regeneration

ABSTRACT In mammals, macrophages are known to play a major role in tissue regeneration. These cells contribute to inflammation, histolysis, re-epithelialization, re-vascularization and cell proliferation. While macrophages have been shown to be essential for epimorphic regeneration in salamanders and fish, their role has not been elucidated in mammalian epimorphic regeneration. Here, using the mouse digit tip model as a mammalian model of epimorphic regeneration, we demonstrate that macrophages are essential for the regeneration process. Using cell depletion strategies, we show that regeneration is completely inhibited; bone histolysis does not occur, wound re-epithelization is inhibited and the blastema does not form. Rescue of epidermal wound closure, in the absence of macrophages, promotes blastema accumulation but not differentiation indicating that macrophage play a role in re-differentiation. Additionally, inhibition of osteoclasts and the degradation process is not sufficient to inhibit regeneration. These findings show that macrophages play an essential role in coordinating the epimorphic regenerative response in mammals.