Piezo1‐mediated M2 macrophage mechanotransduction enhances bone formation through secretion and activation of transforming growth factor‐β1

Macrophages are multifunctional immune system cells that are essential for the mechanical stimulation‐induced control of metabolism. Piezo1 is a non‐selective calcium channel expressed in multifarious tissues to convey mechanical signals. Here, a cellular model of tension was used to study the effect of mechanical stretch on the phenotypic transformation of macrophages and its mechanism. An indirect co‐culture system was used to explore the effect of macrophage activation on bone marrow mesenchymal stem cells (BMSCs), and a treadmill running model was used to validate the mechanism in vivo for in vitro studies. p53 was acetylated and deacetylated by macrophages as a result of mechanical strain being detected by Piezo1. This process is able to polarize macrophages towards M2 and secretes transforming growth factor‐beta (TGF‐β1), which subsequently stimulates BMSCs migration, proliferation and osteogenic differentiation. Knockdown of Piezo1 inhibits the conversion of macrophages to the reparative phenotype, thereby affecting bone remodelling. Blockade of TGF‐β I, II receptors and Piezo1 significantly reduced exercise‐increased bone mass in mice. In conclusion, we showed that mechanical tension causes calcium influx, p53 deacetylation, macrophage polarization towards M2 and TGF‐β1 release through Piezo1. These events support BMSC osteogenesis.