Mechanosensitive Piezo1 Calcium Channel Activates Connexin 43 Hemichannels Through PI3K Signaling Pathway in Bone

Background: Mechanical loading promotes bone formation and osteocytes are a major mechanosensory cell in the bone. Both Piezo1 channels and connexin 43 hemichannels (Cx43 HCs) in osteocytes are important players in mechanotransduction and anabolic function by mechanical loading. However, the mechanism underlying mechanotransduction involving Piezo1 channels and Cx43 HCs in osteocytes and bone remains unknown.

Results: We showed that, like mechanical loading, Piezo1 specific agonist Yoda1 was able to increase intracellular Ca signaling and activate Cx43 HCs, while Yoda1 antagonist Dooku1 inhibited Ca and Cx43 HC activation induced by both mechanical loading and Yoda1. Moreover, the intracellular Ca signal activated by Yoda1 was reduced by the inhibition of Cx43 HCs and pannexin1 (Panx1) channels, as well as ATP-P2X receptor signaling. Piezo1 and Cx43 HCs were co-localized on the osteocyte cell surface, and Yoda1-activated PI3K-Akt signaling regulated the opening of Cx43 HCs. Furthermore, Cx43 HCs opening by mechanical loading on tibias was ablated by inhibition of Piezo1 activation in vivo.

Conclusion: We demonstrated that upon mechanical stress, increased intracellular Ca activated by Piezo1 regulates the opening of HCs through PI3K-Akt and opened Cx43 HCs, along with Panx1 channels, and ATP-P2X signaling sustain the intracellular Ca signal, leading to bone anabolic function.