Ibandronate concomitantly blocks immobilization-induced bone and muscle atrophy

Abstract

Both bone and muscle volume is concomitantly reduced under immobilization conditions; however, no single drug is currently available to block these outcomes simultaneously. Bisphosphonates are utilized clinically to inhibit osteoclast-dependent bone resorption, but their effects on muscle are largely unknown. Here we show that skeletal muscle is a direct target of the bisphosphonate ibandronate (IBN) and that reduced muscle volume and induction of Atrogin-1 and MuRF1, both atrogenes, are significantly inhibited by IBN administration in vivo using a mouse model of muscle atrophy. IBN treatment also significantly blocked immobilization-induced bone loss in vivo. We also report that expression of Atrogin-1 and MuRF1 and accumulation of Smad2/3 proteins, which are upstream of atrogines, occurred following serum starvation of myogenic C2C12 cells in vitro, effects significantly inhibited by IBN treatment. Interestingly, IBN effects on C2C12 cells were abrogated by MG132, an ubiquitin/proteasome inhibitor, suggesting that IBN functions via the ubiquitin-proteasome system. Our findings lend new insight into the role of IBN in preventing muscle atrophy.

Keywords: Bisphosphonate; Bone loss; Ibandronate; Immobilization; Muscle atrophy; Osteoclast.