Elevated extracellular calcium increases fibroblast growth factor-2 gene and protein expression levels via a cAMP/PKA dependent pathway in cementoblasts.
Cementoblasts, tooth root lining cells, are responsible for laying down cementum on the root surface, a process that is indispensable for establishing a functional periodontal ligament. Cementoblasts share phenotypical features with osteoblasts. Elevated levels of extracellular Ca(2+) have been implicated in osteogenesis by stimulating the proliferation and differentiation of osteoblasts; however, the role of extracellular Ca(2+) signaling in cementogenesis has not been examined. Using RT-PCR, we found that elevated levels of extracellular Ca(2+) increase fibroblast growth factor (FGF)-2 gene expression with a peak at 6h. Pretreatment with a protein kinase A (PKA) inhibitor, H89, or an adenylate cyclase inhibitor, MDL-12,330A, inhibited Ca(2+)-stimulated Fgf-2 expression. In contrast, pretreatment with the protein kinase C (PKC) inhibitor GF-109203X or the phospholipase C (PLC) inhibitor U73122 did not affect the expression of Fgf-2 transcripts, suggesting that the increase in Fgf-2 expression was dependent on the PKA but not the PLC/PKC signaling pathway. Treatment with an activator of adenylate cyclase, forskolin, or a cell-permeable analog of cAMP, 8-Br-cAMP, enhanced Ca(2+)-stimulated Fgf-2 expression, but a single treatment with forskolin or 8-Br-cAMP did not, suggesting that cAMP generation is indispensable but not sufficient for Ca(2+)-stimulated FGF2 expression. Next, we examined the cation specificity of the putative receptor and showed that treatment with trivalent/divalent inorganic ions, Ca(2+), Gd(3+), Sr(2+), or Al(3+), caused a dose-dependent increase in Fgf-2 mRNA levels in a cAMP-dependent fashion, whereas Mg(2+) and the organic ions neomycin and spermine had no effect on Fgf-2 gene expression levels. These findings suggest that an extracellular Ca(2+)-sensing mechanism is present in cementoblasts and its activation leads to FGF-2 stimulation in a cAMP/PKA dependent fashion. Understanding the pathway regulating key genes involved in modulating the regeneration of oral tissues will assist in designing regenerative therapies based on reliable biological principles.
Kanaya
Sousuke
S
Department of Periodontology and Endodontology, Tohoku University Graduate School of Dentistry, Sendai 980-8575, Japan.
Nemoto
Eiji
E
Ebe
Yukari
Y
Somerman
Martha J
MJ
Shimauchi
Hidetoshi
H
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002122:Calcium Chloride / Q000494:pharmacology; D002460:Cell Line; D005576:Colforsin / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D003739:Dental Cementum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D016222:Fibroblast Growth Factor 2 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
D012333:RNA, Messenger; D016222:Fibroblast Growth Factor 2; D005576:Colforsin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D002122:Calcium Chloride; D002118:Calcium