Melatonin Suppresses Osteoclastogenesis via Inhibiting Iron/ROS-CREB/PGC-1β-Mediated Mitochondrial Biogenesis

Postmenopausal osteoporosis (PMOP) is linked to iron accumulation. Melatonin has iron-chelating and antioxidant properties, but its mechanism against osteoclastogenesis remains unclear. This study investigated whether melatonin suppresses osteoclast formation by targeting the iron/ROS-CREB-PGC-1β-mediated mitochondrial biogenesis pathway. In vitro, bone marrow-derived macrophages (BMMs) were treated with RANKL and melatonin (10-1000 nM). Melatonin concentration-dependently inhibited osteoclast differentiation, reduced intracellular ferrous and total iron levels, decreased ROS and oxidative stress markers, and suppressed mitochondrial biogenesis. Mechanistically, melatonin indirectly suppressed PGC‑1β expression via inhibition of CREB phosphorylation, without affecting PGC‑1α expression. The CREB activator forskolin reversed melatonin's effects, whereas the CREB inhibitor 666-15 mimicked them. In vivo, ovariectomized (OVX) mice received weekly injections of iron dextran to model moderate iron overload, with or without oral melatonin. Melatonin ameliorated iron‑induced bone loss, improved bone microarchitecture and biomechanical properties, reduced tissue iron stores and bone ROS levels, and suppressed osteoclast mitochondrial biogenesis and the CREB/PGC-1β pathway; these effects were counteracted by forskolin. In conclusion, melatonin prevents osteoclastogenesis and counters bone loss due to iron accumulation in estrogen‑deficient conditions by chelating iron, scavenging ROS, and blocking the iron/ROS‑activated CREB/PGC‑1β axis, thereby suppressing mitochondrial biogenesis. This study offers a mechanistic explanation for using melatonin as a possible treatment for PMOP, particularly when accompanied by iron overload.