During bone development, FasL acts not only through the traditional apoptotic mechanism regulating the amount of bone-resorbing osteoclasts, but there is also growing evidence about its effect on cell differentiation. Expression of osteoblastic factors was followed in non differentiated and differentiating primary calvarial cells obtained from FasL-deficient (gld) mice. The gld cells showed decreased expression of the key osteoblastic molecules osteocalcin (Ocn), osteopontin (Opn), and alkaline phosphatase (Alpl) in both groups. Notably, receptor activator of nuclear factor kappa-B ligand (Rankl) was unchanged in non-differentiated gld vs. wild type (wt) cells but decreased in differentiating gld cells. Osteoprotegerin (Opg) in the gld samples was increased in both groups. Opg vs. Rankl expression levels favored Opg in the case of non-differentiated cells but Rankl in differentiating ones. These results expand information on the involvement of FasL in non-apoptotic cell pathways related to osteoblastogenesis and consequently also osteoclastogenesis and pathologies such as osteoporosis.

Department of Oral Biology University Clinic of Dentistry Medical University of Vienna Vienna Austria

Department of Physiology University of Veterinary Sciences Brno Czech Republic

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