Polycystin-1 Mediates Rapid Maxillary Expansion-Induced Osteoblastic Mechanoresponses Via Potentiation Of Intracellular Calcium And Akt/β-catenin Pathway

Orthodontists and Orthopedic surgeons often impose various forms of mechanical force to bony edge of sutures to correct craniofacial deformities.Orthopedic rapid maxillary expansion,or midpalatal expansion,is a usual treatment to correct transverse skeletal deficiency of maxilla in orthodontics.However,even after a long-term retention,the expanded maxillary arch still has a tendency back to its previous form.To date,the bone bow to adapt midpaiatal expansion has not yet been elucidated.Polycystin-1(PC1)is postulated to function as a mechanosensory molecule mediating mechanical signal transduction in renal epithelial cells.To investigate the involvement of PC1 and mechanical strain-induced signaling cascades in bio-mechanical osteogenesis during rapid maxillary expansion.We evaluated the changes in PC1 over time using a mouse midpalatal suture expansion model in vivo.Our data showed that expansive force significantly induced new bone formation at the edge of palatal sutures.The sutures prominently widened peaking on day 7.The immunopositive areas of PC1 peaked on day 3,showed a similar spatio-temporal pattern with bgn,ALP and Col-1.PC1,bgn,β-catenin,and osteogenic markers such as Runx2,ALP and Col-1 increased at protein or mRNA levels together.To further investigate the involvement of PC1 in mechanical strain-induced signaling cascades controlling osteogenesis,we examined the effect of tensile strain(2%magnitude,0.5 Hz)which represents clinical expansion force on osteoblastic cell line MC3T3-E1 whose PKD1 gene was stably silenced by using lentivirus-mediated shRNA technology in vitro.Here,our tindings showed that mechanical tensile strain sufficiently enhanced osteogenic gene expressions and osteoblastic proliferation.However,PC1 deficiency resulted in the loss of the ability to sense external mechanical stimuli thereby promoting osteoblastic osteogenesis and proliferation.The signal pathways implicated in this process were intracellular calcium and Akt/β-catenin pathway.The basal levels of intracellular calcium,phospho-Akt,phospho-GSK-3β and nuclear accumulation of active p-catenin were significantly attenuated in PC1 deficient osteoblasts.In addition,PC1 deficiency impaired mechanical strain-induced potentiation of intracellular calcium,and activation of Akt-dependent and Wnt/β-catenin pathways,which was able to be partially reversed by calcium ionophore A23187 treatment.Furthermore,applications of LiCl or A23187 in PC1 deficient osteoblasts could promote osteoblastic differentiation and proliferation under mechanical strain conditions.Therefore,our results demonstrated that osteoblasts require mechanosensory molecule PC1 to adapt to external mechanical tensile strain thereby inducing osteoblastic mechanoresponse,partially through the potentiation of intracellular calcium and downstream Akt/β-catenin signaling pathway.