Targeting Fas in osteoresorptive disorders.

IMPORTANCE OF THE FIELD: Fas receptor is a mediator of the external apoptotic pathway in many cells and tissues. It is proposed that Fas receptor mediates osteoresorptive effects of estrogen deficiency and local/systemic inflammation. AREAS COVERED IN THIS REVIEW: This review covers the past two decades of research on the expression and function of the Fas-Fas ligand system on bone cells, involvement in the pathogenesis of osteoresorption and potential therapeutic modulation. WHAT THE READER WILL GAIN: We review the structure, biological function and intracellular signaling pathways of the Fas-Fas ligand system emphasizing the role of the non-apoptotic signaling pathways in bone cells, particularly osteoblast differentiation. We also present data on the in vitro expression and function of the Fas-Fas ligand system on osteoblast/osteoclast lineage cells, animal and human studies confirming its involvement in osteoresorptive disorders and potential therapeutic approaches to modulate its function. TAKE HOME MESSAGE: Tissue specific therapeutic approaches need to be established to modify the Fas-Fas ligand system in osteoresorptive disorders as systemic targeting has many side effects. The most promising approach would be to target Fas signaling molecules coupled with osteoblast/osteoclast differentiation pathways, but a precise definition of these targets is still needed.