ANALYSIS OF CELL-MEDIATED MINERALIZATION IN CULTURE OF BONE-DERIVED EMBRYONIC-CELLS WITH NEUROFIBROMATOSIS

von Recklinghausen neurofibromatosis (NF1) is an autosomal dominant ge netic disorder associated with congenital pseudoarthrosis and with sho rt stature. To examine whether the NF1 phenotype includes functional o steogenic defects, embryonic bone-derived cells affected with NF1 were tested in culture for specific alkaline phosphatase (ALP) activity an d cell-mediated mineralization and compared with other embryonic bone derived cells. NF1 showed a relatively higher specific ALP activity, w hich has further increased in response to dexamethasone + beta-glycero phosphate (PGP) (Dex medium) coordinately with a decrease in cell prol iferation. In the control group, two samples showed increased ALP acti vity, one showed decreased activity and the forth one did not show any change in ALP. NF1 cells were distinguished from other cells regardin g day 21 mineralization, they did not mineralize when cultured with as corbate alone in the abscence of Dex medium, whereas control cells did mineralize. Adding PCP resulted in mineralization by NF1 cells but le ss than in other cells. In addition, NF1 cells responded to dexamethas one by increasing the beta GP-induced mineralization, as opposed to ce lls from other embryonic bones, which either did not respond or have e ven decreased mineralization under dexamethasone. Upon cis-hydroxyprol ine exposure, Dex medium has also distinguished NF1 cell ALP activity from that of other cell origins. Inhibition of respiratory complex II by malonate showed that most embryonic bone-derived cells of 12 weeks gestation are malonate resistant; thus, malonate selection was ineffec tive. This is in contrast to rat marrow stromal cells previously shown to undergo mineralizing cell enrichment in response to malonate. Expo sure to levamisole, of Dex-treated cells, at days 0-11 has inhibited d ay 21 mineralization in all tested cultures in spite of the increase i n day 11-specific ALP activity. Both malonate and levamisole did not d istinguish NF1 cells from the osteogenic phenotype of other cells. Ess entially embryonic bone-derived cells from 12 weeks gestation, culture d in the absence of PGP, retained their mineralization capacity, which does not increase under dexamethasone, as distinguished from NF1 cell s which require PGP for mineralization and positively respond to dexam ethasone. Therefore, bone-derived NF1 cells may be useful for studying the regulation of the mineralization process. (C) 1995 Wiley-Liss, In c.