A COLLAGENOUS CEMENTUM-DERIVED ATTACHMENT PROTEIN IS A MARKER FOR PROGENITORS OF THE MINERALIZED TISSUE-FORMING CELL LINEAGE OF THE PERIODONTAL-LIGAMENT

The periodontal ligament (PDL) is a fibrous and cellular connective ti ssue that mediates tooth attachment to bone, and it comprises fibrobla stic and mineralized tissue-forming (MTF) progenitors, The MTF progeni tors are believed to give rise to the cementoblastic and osteoblastic lineages, Cementum attachment protein (CAP) is a collagenous cementum- derived protein which binds strongly to osteoblasts, moderately to PDL cells, and weakly to gingival fibroblasts, The aim of the present stu dy was to determine the relationship between the capacity of PDL proge nitors to bind CAP and their potential to express alkaline phosphatase (ALP) and form mineralized-like tissue in culture. Cloned human PDL p rogenitor populations obtained from nine human donors were assayed for their constitutive capacity to bind CAP and express ALP, and for the dexamethasone-induced potential to form mineralized-like tissue in cul ture in the presence of ascorbic acid and beta-glycerophosphate, Forty percent of the progenitor clones produced mineralized-like tissue, Tw o patterns of mineralization were observed: a spread and hat pattern s imilar to that produced by human bone cells in culture and a nodular r idge-like type resembling that formed by human cementoma-derived cells , A direct correlation was found between tbe percentage of ALP positiv e cells in each progenitor clone and the amount of mineralized-like ti ssue formed (r = 0.565). Similar correlations were found between the n umber of ALP positive cells and the binding capacity of each clone (r = 0.392) and between the CAP binding capacity and mineralized-like tis sue formation (r = 0.584), Multiple regression analysis indicated that the constitutive capacity of a clone to bind CAP and express ALP is d irectly correlated to its dexamethasone-induced potential to form mine ralized tissue (r = 0.675), These results indicate that CAP binding an d ALP expression can serve as markers for the identification of MIF pr ogenitors in the heterogeneous cultured population of the human period ontal ligament, These data show for the first time that binding capaci ty to extracellular components of mineralized tissues can be a marker for mineralized tissue-forming progenitors.