Activation of cannabinoid receptor CB2 regulates osteogenic and osteoclastogenic gene expression in human periodontal ligament cells.
OBJECTIVE
Cannabinoid receptor CB2, expressed in osteoblasts and osteoclasts, plays a crucial role in the regulation of bone metabolism. Since periodontal ligament (PDL) cells can differentiate into osteoblasts, this study was undertaken to investigate CB2 expression and the effect of CB2 activation on osteogenic differentiation of PDL cells.


METHODS
Human PDL (hPDL) cells were obtained from extracted teeth of periodontally healthy subjects. Expression of CB2 was observed in hPDL cells by RT-PCR, Western blotting and immunofluorescence assay. Then hPDL cells were treated with a CB2-specific agonist, HU-308 (10(-7) m), for 12, 24, 48 or 72 h. The mRNA expressions of osteogenic genes, such as runt-related transcription factor 2 (Runx2), bone sialoprotein (BSP), osteopontin (OPN), alkaline phosphatase (ALP), osteocalcin (OC) and collagen type I (COL I), and osteoclastogenic genes, including osteoprotegerin (OPG) and receptor activator of NF-kappaB ligand (RANKL), were examined using quantitative real-time PCR analysis. A mineralization assay was performed in hPDL cells in mineralization conditions with or without HU-308.


RESULTS
Expression of CB2 mRNA and protein was detected in hPDL cells. HU-308 enhanced the mRNA levels of the above osteogenic genes. Expression of the OPG gene was up-regulated, whereas RANKL gene expression was down-regulated, contributing to the elevated OPG/RANKL ratio. Accelerated mineralization was observed in hPDL cells in mineralization conditions with HU-308.


CONCLUSIONS
Our findings demonstrate that activation of CB2 is able to enhance osteogenic differentiation of hPDL cells and potentially create a favorable osteogenic microenvironment. This implies that CB2 might play an important role in alveolar bone metabolism.
Qian
H
H
Department of Orthodontics, School of Stomatology, Fourth Military Medical University, Xi'an, Shaanxi, China.
Zhao
Y
Y
Peng
Y
Y
Han
C
C
Li
S
S
Huo
N
N
Ding
Y
Y
Duan
Y
Y
Xiong
L
L
Sang
H
H
D000293:Adolescent; D000469:Alkaline Phosphatase / Q000032:analysis; D002113:Calcification, Physiologic / Q000502:physiology; D002186:Cannabinoids / Q000494:pharmacology; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D002648:Child; D024042:Collagen Type I / Q000032:analysis; D050659:Core Binding Factor Alpha 1 Subunit / Q000032:analysis; D003470:Culture Media; D015536:Down-Regulation; D006801:Humans; D058574:Integrin-Binding Sialoprotein; D008297:Male; D015675:Osteocalcin / Q000032:analysis; D010010:Osteoclasts / Q000502:physiology*; D010012:Osteogenesis / Q000235:genetics*; D053495:Osteopontin / Q000032:analysis; D053244:Osteoprotegerin / Q000032:analysis; D010513:Periodontal Ligament / Q000166:cytology*; D053245:RANK Ligand / Q000032:analysis; D043885:Receptor, Cannabinoid, CB2 / Q000819:agonists / Q000032:analysis / Q000502:physiology*; D012795:Sialoglycoproteins / Q000032:analysis; D013997:Time Factors; D015854:Up-Regulation
D002186:Cannabinoids; D024042:Collagen Type I; D050659:Core Binding Factor Alpha 1 Subunit; D003470:Culture Media; C546871:IBSP protein, human; D058574:Integrin-Binding Sialoprotein; D053244:Osteoprotegerin; D053245:RANK Ligand; C493709:RUNX2 protein, human; D043885:Receptor, Cannabinoid, CB2; D012795:Sialoglycoproteins; C506030:TNFRSF11B protein, human; D015675:Osteocalcin; D053495:Osteopontin; C402416:HU 308; D000469:Alkaline Phosphatase