RANKL (receptor activator of NF-κB ligand) expressed on osteoblasts/stromal cells activates RANK on osteoclast precursors, driving osteoclastogenesis. Osteoprotegerin (OPG) acts as a decoy receptor for RANKL. In postmenopausal osteoporosis, estrogen deficiency alters the RANKL:OPG ratio. Which statement correctly describes this alteration and its consequence?

• A Estrogen deficiency increases RANKL expression and reduces OPG production by osteoblasts, increasing the RANKL:OPG ratio and stimulating osteoclastogenesis → net bone resorption ✓
• B Estrogen deficiency decreases RANKL expression and increases OPG, tipping the balance toward osteoclast suppression
• C Estrogen deficiency increases OPG production, neutralizing RANKL, but bone loss occurs due to reduced osteoblast differentiation only
• D Estrogen deficiency directly activates mature osteoclasts without altering RANKL:OPG ratio

Explanation

Estrogen normally promotes OPG production and suppresses RANKL expression in osteoblasts/T-cells. In estrogen deficiency, RANKL is upregulated and OPG is reduced, raising the RANKL:OPG ratio. This promotes differentiation and activation of osteoclasts → increased bone resorption exceeding formation → net bone loss. Denosumab, a monoclonal antibody against RANKL, mimics OPG and is used in postmenopausal osteoporosis and cancer bone metastases. Estrogen therapy (HRT) increases OPG and reduces RANKL, normalizing the ratio and protecting bone.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.