engleski

The Role of Fas/Fas Ligand System in Estrogen Deficiency-induced Osteoporosis

The aim of this study was to estimate the role of Fas/Fas ligand system in vivo in the pathogenesis of estrogen deficiency induced bone loss. We first analyzed the expression of Fas gene by quantitative PCR in bones and bone cell cultures from wild-type mice, four weeks after the ovariectomy (ovx). Then we performed ovx in mice deficient for Fas gene (Fas -/-) and their wild-type controls. After four weeks we analyzed: 1) standard histomorphometric parameters of their femora, 2) differentiation of osteoblast (Obl) and osteoclasts (Ocl) in vitro from their bone marrow progenitors. Obl and Ocl differentiation was estimated histochemically (number of alkaline phosphatase positive Obl colonies, and number of TRAP-positive Ocl-like cells), and according to the expression of Obl (Runx2, alkaline phosphatase, osteocalcin and osteprotegerin) and Ocl (RANK, calcitonine receptor) differentiation genes. Our results showed that after four weeks, gene expression of Fas was increased in bone and mature Obl cultures from ovx (0.36± ; ; ; 0.06 and 2.6± ; ; ; 0.05 respectively) compared to sham operated animals (0.31± ; ; ; 0.01 and 1.8± ; ; ; 0.76, p<0.05). A mild decrease in Fas expression was also observed in the Ocl cultures from ovx animals. Trabecular bone volume was generally significantly higher in Fas -/- mice (p=0.01, t-test) than in wild-type controls. Furthermore, trabecular volume significantly decreased in wild-type mice four weeks after ovx (p=0.01, t-test), and remained unaltered in Fas -/- mice (p=0.67, t-test). Mean number of TRAP-positive Ocl on bone surface of wild-type mice increased four weeks after ovx (p=0.03), whereas this number was unchanged in Fas -/- mice (p=0.27). Ovx also significantly increased osteoclastogenesis in vitro in wild-type animals but this effect was absent in Fas -/- mice. Osteoblastogenesis in vitro was stimulated by ovx in both animal strains, but this effect was more pronounced in Fas -/- mice. Obl differentiation genes were had similar expression patterns in sham operated and ovx mice, although Fas -/- mice Obls generally had higher expression levels of Obl differentiation genes compared to wild-type controls. Our findings point to the conclusion that Fas/Fas ligand system may have an important role in the pathogenesis of postmenopausal osteoporosis and modulation of its effects on bone cells may contribute to the development of new strategies for osteoporosis treatment.

osteoblasts; osteoporosis; apoptosis

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