Effect of HIV Infection and Highly Active Antiretroviral Treatment (HAART) on Bone Homeostasis

Advances in HAART have been a huge success story in the management of HIV infection. However, serious metabolic complications including osteoporosis and bone fractures are increasingly been seen with HAART, and the responsible mechanisms remain poorly elucidated. The skeleton continually regenerates through homeostatic bone remodeling. Osteoclasts the cells responsible for bone resorption form under the influence of the key osteoclastogenic cytokine Receptor- Activator of NF-KB (RANKL). The osteoclastogenic and pro-resorptive activities of RANKL are moderated by its physiological decoy receptor osteoprotegerin (OPG). Increase in the ratio of RANKL to OPG accelerates the rate of osteoclastic bone resorption leading to osteoporosis. The investigators' preliminary studies have now demonstrated that in an animal model of HIV/AIDS, the HIV-1 Transgenic rat, the development of osteoporosis is recapitulated as observed in human patients. Furthermore, the investigators found that B cell expression of OPG is significantly downregulated, concurrent with a significant upregulation in production of RANKL.