Circulating healing (CH) cells expressing BST2 are functionally activated by the injury-regulated systemic factor HGFA

Background: Restoration of damaged tissues through the activation of endogenous progenitors is an attractive therapeutic option. A deep evaluation of the intrinsic stem/progenitor cell properties as well as the reciprocal interactions with injured environments is of critical importance. Methods: Here, we show that bone marrow stromal cell antigen 2 (BST2) allows the isolation of a population of circulating progenitors, the circulating healing (CH) cells, characterized by a distinctive core signature. The bone marrow (BM) origin of BST2pos CH cells has been strengthened by the co-expression of leptin receptor, the hallmark of a subpopulation of BM-skeletal stem cells. Results: BST2pos CH cells retained the capacity to (i) respond to injury signals generated by a bone fracture, (ii) modify the expression of cell motility genes following damage, and (iii) react to hepatocyte growth factor-activator (HGFA), an injury-related stimulus sufficient to induce their transition into GALERT, a state in which cells are functionally activated and participate in tissue repair. Conclusions: Taken together, these results could pave the way for the identification of new strategies to enhance and potentiate endogenous regenerative mechanisms for future therapies.