The Possibility that Periodontal Ligament Cells can Differentiate into Osteoblasts

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Ideally, healing after periodontal therapy is the acquisition of the new connective tissue attachment with the formation of new cementum. It has been reported that periodontal ligament (PDL) cells can form new connective attachment with the production of new cementum on curretted root surface. So we examined the possibility that PDL cells can differentiate into osteoblasts and/or cementoblasts in freshly isolated PDL tissues and in cultured cells derived from PDL. PDL tissues were obtained from the incosor teeth of bovine lower jaws. Gingival connective tissues and gingival fibroblasts of the same animals were used as controls. Freshly isolated PDL tissues and cultured PDL cells showed an intense alkaline phosphatase (ALPase) activity both histochemically and biochemically. The ALPase in PDL tissues is of the bone type. The production of 3',5'-cyclic adenosine monophosphate (cAMP) was greatly increased in response to human parathyroid hormone [PTH(1-34)], in both freshly isolated PDL t … More issues and cultured PDL cells. In contrast, neither ALPase activity nor PTH-dependent cAMP production was detected in gingival connective tissues and cultured gingival fibroblasts. Furthermore, cultured PDL cells synthesized a protein immunologically cross-reactive with bovine bone gla protein (BGP), a highly reliable marker of osteoblastic cells. When 10^<-8> M la, 25-dihydroxyvitamin D_3 [la,25(OH)_2D_3] was added to the PDL cell cultures, the synthesis of the BGP-like protein was increased 2- to 3-fold. The maximal level of the synthesis was obtained 72h after the addition of la, 25(OH)_2D_3. Gingival fibroblasts cultured with or without la, 25(OH)_2D_3 did not produce any appreciable amounts of the BGP-like protein. 25-hydroxyvitamin D_3, 24R, 25-dihydroxyvitamin D_3, PTH and PGE_2 had no effect on this protein production in the cultures of PDL cells and gingival fibroblasts. These results indicate that the PDL cells have phenotypes typical of osteoblasts, indicating that they may differentiate into osteoblasts and/or cementoblasts. Less