CB1 Promotes Osteogenic Differentiation Potential of Periodontal Ligament Stem Cells by Enhancing Mitochondrial Transfer of Bone Marrow Mesenchymal Stem Cells

Objective: To reveal the role and mechanism of cannabinoid receptor 1 (CB1) and mitochondria in promoting osteogenic differentiation of periodontal ligament stem cells (PDLSCs) in the inflammatory microenvironment.
Methods: Bidirectional mitochondrial transfer was performed in bone mesenchymal stem cells (BMSCs) and PDLSCs. Laser confocal microscopy and quantitative flow cytometry were used to observe the mitochondrial transfer and quantitative mitochondrial transfer efficiency. Realtime reverse transcription polymerase chain reaction (RT-PCR) was employed to detect gene expression. Alkaline phosphatase (ALP) activity, alizarin red staining (ARS) and quantitative calcium ion analysis were used to evaluate the degree of osteogenic differentiation of PDLSCs.
Results: Bidirectional mitochondrial transfer was observed between BMSCs and PDLSCs. The indirect co-culture system could simulate intercellular mitochondrial transfer. Compared with the conditioned medium (CM) for BMSCs, that for HA-CB1 BMSCs could significantly enhance the mineralisation ability of PDLSCs. The mineralisation ability of PDLSCs could not be enhanced after removing the mitochondria in CM for HA-CB1 BMSCs. The expression level of HO-1, PGC-1α, NRF-1, ND1 and HK2 was significantly increased in HA-CB1 BMSCs.
Conclusion: CM for HA-CB1 BMSCs could significantly enhance the damaged osteogenic differentiation ability of PDLSCs in the inflammatory microenvironment, and the mitochondria of CM played an important role. CB1 was related to the activation of the HO-1/PGC-1α/NRF-1 mitochondrial biogenesis pathway, and significantly increased the mitochondrial content in BMSCs.