MSCs rescue impaired wound healing in a murine LAD1 model by adaptive responses to low TGF‐β1 levels

Mutations in the CD18 gene encoding the common β‐chain of β2 integrins result in impaired wound healing in humans and mice suffering from leukocyte adhesion deficiency syndrome type 1 (LAD1). Transplantation of adipose tissue‐derived mesenchymal stem cells (MSCs) restores normal healing of CD18(−/−) wounds by restoring the decreased TGF‐β1 concentrations. TGF‐β1 released from MSCs leads to enhanced myofibroblast differentiation, wound contraction, and vessel formation. We uncover that MSCs are equipped with a sensing mechanism for TGF‐β1 concentrations at wound sites. Low TGF‐β1 concentrations as occurring in CD18(−/−) wounds induce TGF‐β1 release from MSCs, whereas high TGF‐β1 concentrations suppress TGF‐β1 production. This regulation depends on TGF‐β receptor sensing and is relayed to microRNA‐21 (miR‐21), which subsequently suppresses the translation of Smad7, the negative regulator of TGF‐β1 signaling. Inactivation of TGF‐β receptor, or overexpression or silencing of miR‐21 or Smad7, abrogates TGF‐β1 sensing, and thus prevents the adaptive MSC responses required for tissue repair.