| Co-Investigator(Kenkyū-buntansha) |
TOGARI Akifumi School of Dent.,Aichi-Gakuin Univ., Pharmacol., Professor, 歯学部, 教授 (80126325)
ARAI Michitsugu School of Dent.,Aichi-Gakuin Univ., Pharmacol., Assistant Professor, 歯学部, 講師 (20097538)
KONDO Ayami School of Dent.,Aichi-Gakuin Univ., Pharmacol., Research Associate, 歯学部, 助手 (70301629)
HIRUKAWA Koji School of Dent.,Aichi-Gakuin Univ., Pharmacol., Research Associate, 歯学部, 助手 (60340147)
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| Research Abstract |
Activation of caspases required for osteoblastic differentiation.
Bone morphogenetic protein (BMP)s are important regulators of osteoblast differentiation. Because regulation of osteoblastic differentiation is poorly understood, we sought to determine if BMP-4-induced differentiation of osteoblastic cells depends on the activity of the key apoptotic proteases, i.e.,the caspases. BMP-4 induced the growth arrest and differentiation of osteoblastic cell line MC3T3-E1,as evidenced by the appearance of osteoblastic phenotypes such as alkaline phosphatase (ALP) activation and parathyroid hormone (PTH)-dependent production of cAMP. Surprisingly, BMP-4 induced transient and potent activation of caspase-8,caspase-2,and caspase-3,in this order. However, no apoptosis or necrosis in BMP-4-treated cells could be detected by FACS using Annexin-V/propodium iodine double staining. Peptide inhibition of caspase activity led to a dramatic reduction in ALP activation and PTH-induced production of cAMP in
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BMP-4-treated cells. Although BMP-4 treatment resulted in cell-cycle G0/G1 arrest as detected by FACS cell-cycle analysis, caspase inhibitors (caspase-8,caspase-2,and caspase-3 inhibitors) could block the G0/G1 arrest in MC3T3-E1 cells. Taken together, these results confirm a unique and unanticipated role for the caspase-mediated signal cascade in the differentiation of osteoblasts.
Differential expression of RANKT, and osteoprotegerin in gingival crevicular fluid of patients with Periodontitis.
The receptor activator for NF-kB ligand (RANKL) plays an important role in osteoclast formation. However, no one has examined the level of RANKL in the body fluid of human subjects. This communication reports on the in vivo concentrations of RANKL and the RANKL decoy receptor osteoprotegerin (OPG) in thegingival crevicular fluid (GCF) of periodontal subjects with severe, moderate, and mild forms of the disease. An increased concentration o RANKL and a decreased concentration of OPG were detected in GCF from patients with periodontitis (^*p<0.05 vs.control subjects). The ratio of the concentration of RANKL to that of OPG in the GCF was significantly higher for periodontal disease patients than for healthy subjects (^*p<0.01). Taken together, these data suggest that RANKL and OPG contribute to osteoclastic bone destruction in periodontal disease.
Dual roles for NF-kB activation in osteoblastic cells by serum deprivation : Osteoblastic apoptosis and cell-cycle arrest.
To clarify the mechanisms of osteoblastic cell death, we examined whether serum deprivation would cause activation of the apoptotic signal cascade and arrest of the cell cycle in mouse osteoblastic MC3T3-E1 cells. Serum withdrawal from osteoblastic cell cultures resulted in growth arrest and cell-cycle arrest at G0/G1, which actions were accompanied by transient and potent activation of NF-kB,caspase-8,caspase-2,caspase-3,and caspase-9 in this order. Apoptosis, but not necrosis, in serum-deprived cells could be detected by FACS using Annexin-V/propidium iodine double staining. Serum deprivation also resulted in transient activation of the 20S proteasome, which is an important component for regulation of the cell cycle by the ubiquitin-proteasome system. The 20S proteasome inhibitor (PSI) but not NF-kB inhibitor SN50 suppressed the activation of proteasomes in serum-deprived cells. Although caspase inhibitors could not prevent the G0/G1 arrest in the serum-deprived cells, SN50 and the 20S proteasome inhibitor could block it. Since SN50,20S proteasome inhibitor, and caspase inhibitor could rescue cells from serum deprivation-induced apoptosis, the pathway for NF-kB/caspase activation is independent of the NF-kB/cell-cycle pathway, and the events down-stream of the NF-kB/caspase-9 cascade lead to apoptosis. Taken together, our present results identify a novel role for NF-kB in cell-cycle and apoptosis regulation, and underscore the significance of each independent signal cascade in serum-deprived osteoblastic cells. Less
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