Characterization of fibroblast clones from periodontal granulation tissue in vitro

Connective tissues are known to be composed of heterogeneous fibroblast subpopulations. The significance of this heterogeneity in different physiological and pathological conditions is poorly understood. Granulation tissue is formed in connective tissue during wound healing, chronic inflammation, and certain pathological conditions. In this study, heterogeneity of fibroblasts from granulation tissue was investigated by cell-cloning techniques. Granulation-tissue fibroblasts (GTFs) from both chronically inflamed periodontal lesions and healing wound granulation tissue behaved similarly. GTFs showed a more pronounced decrease in proliferative capacity with increasing cumulative population doubling levels (CPDLs) and 30-40% lower cloning efficiency compared with normal gingival fibroblasts (HGFs). Morphologically, cells in GTF cultures were mainly large, whereas HGFs were mainly small in size. Both cell-line types showed heterogeneity in cell morphology. Clones composed of large stellate-like cells predominated in GTF cultures, whereas clones composed of small spindle-shaped or epithelioid cells predominated in HGF cultures. In both cell-line type the proportion of clones composed of large cells increased without increasing CPDL. These findings show that the properties of the fibroblasts changed during their in vitro life spans. The finding that normal connective tissue and granulation tissues contain morphologically distinct fibroblast clones in different proportions suggests that local factors could stimulate local fibroblasts to differentiate into GTFs. Alternatively, local factors could select some fibroblast subpopulations to overgrow the others to form granulation tissue.