Article Test

Osteoporosis is related to estrogen deficiency and aging. Bone loss can also occur as a result of inflammation-associated diseases such as rheumatoid arthritis and periodontitis, which share several pathologic features with osteoporosis. Estrogen deficiency is associated with increased osteoclast activation, decreased osteoblast function, and increased inflammatory bone-resorbing cytokines (e.g., interleukin-1, -6, and tumor necrosis factor –α). The differentiation of osteoclasts is regulated by the cytokines macrophage colony-stimulating factor, RANK ligand, and osteoprotegerin secreted by osteoblasts. Bone resorption is the unique function of osteoclasts. Podosomes are essential features of osteoclast migration. Podosomes are F-actin rich structures joined radially by actin fibers called F-actin cloud. Upon attachment to the bone surface,  osteoclasts reorganize their cytoskeleton to form sealing zones. Sealing zone formation is required for efficient bone resorption to occur by osteoclasts. Integrin αvβ3 and TNF-alpha mediated signaling mechanisms regulate the assembly/disassembly of podosomes during migration and the organization of sealing zones during bone resorption. A brief description is provided on these aspects in this review.