[Mechanisms of the mechanically activated ion channel Piezo1 protein in mediating osteogenic differentiation of periodontal ligament stem cells via the Notch signaling pathway].

OBJECTIVE: To explore the mechanism of Piezo1 protein in mediating the osteogenic differentiation of human periodontal ligament stem cells (hPDLSCs) via the Notch signaling pathway.
METHODS: In this study, young permanent teeth extracted from impacted teeth of 8-14-year-
old children from January 1, 2016 to January 1, 2018 in the Department of Orthodontic, Beijing Children's Hospital were selected as cell sources. hPDLSCs were extracted by enzymatic digestion. Immunohistochemical staining was used to detect the expression of keratin and vimentin, and flow cytometry was used to identify the markers (CD146 and STRO-1) of hPDLSCs. The construction and screening of Piezo1 siRNA gene interference vector and Piezo1 gene overexpression plasmid were completed. Flexcell 4000T mechanical distraction stress instrument was used to construct hPDLSC cell model in vitro. According to the preliminary results, the experiment was divided into five groups: siRNA interference group, overexpression group, blank control group, stretch stress group, and negative control group. Real time quantitative polymerase chain reaction (RT-qPCR) was used to detect the expression of Piezo1, Notch1, alkaline phosphatase (ALP), Runt-related transcription factor 2 (Runx2), osteocalcin (OCN), and bone sialoprotein (BSP). Western blot was used to detect the expression of ALP and Runx2. Fluo-3 AM probe was used to detect intracellular calcium content.
RESULTS: Vimentin staining of hPDLSCs was positive, and keratin staining was negative. Flow cytometry was used to detect the expression of STRO-1 and CD146, markers of hPDLSC. Empty viral vectors, siRNA-Piezo1 interference sequence, and Piezo1 overexpression vector sequence could be transfected into hPDLSC by lentivirus, and the transfection efficiency was high (approximately 90%). The reverse transcription-polymerase chain reaction (RT-PCR) results showed that there were significant differences in Piezo1 gene levels among the siRNA interference group, overexpression group, blank control group, stretch stress group, and negative control group (F=9.573, P<0.05). The level of Piezo1 in the overexpression group was significantly higher than that in the siRNA interference group (q=3.893, P<0.05). The level of Piezo1 in the stretch stress group was significantly higher than that in the blank control group (q=2.006, P<0.05). The expression of Notch1 and osteogenic genes ALP, Runx2, OCN, and BSP had the same trend. Western blot results showed that there were significant differences in the expression of ALP in the siRNA interference group, overexpression group, blank control group, stretch stress group, and negative control group (F=11.207, P<0.001). The expression level of ALP in the overexpression group was significantly higher than that in the siRNA interference group (q=2.991, P<0.05). The expression of ALP in the stretch stress group was significantly higher than that in the blank control group (q=3.007, P<0.05). The expression of Runx2 protein showed the same trend. The intracellular calcium fluorescence intensity of the overexpression group was significantly higher than that of the siRNA interference group, and the intracellular calcium fluorescence intensity of the stretch stress group was significantly higher than that of the siRNA interference group.
CONCLUSIONS: Mechanical stretch stress can promote the expression of Piezo1 protein. Ca2+ is the second messenger, activates the Notch1 signaling pathway and the expression of ALP, Runx2, OCN, and BSP; and promotes the osteogenic differentiation of hPDLSC. The siRNA-Piezo1 interfering plasmid can block this process. On the contrary, the overexpression plasmid of Piezo1 can promote the osteogenic differentiation of PDLSCs.