TNFα-dependent mTOR activity is required for tenotomy-induced ectopic ossification in mice

Ectopic ossifications often occur in skeletal muscles or tendons following local trauma or internal hemorrhage, and occasionally cause severe pain that limits activities of daily living. However, mechanisms underlying their development remain unknown. Here we show that dissection of the Achilles tendon promotes ectopic ossification at dissection sites in wild-type mice. We observed mTOR activation at dissection sites, and development of ectopic ossification was significantly inhibited by administration of rapamycin, an mTOR inhibitor, to wild-type mice. Moreover, administration of the histamine 2 blocker cimetidine, which reportedly inhibits ectopic ossification in tendons, was not effective in inhibiting ectopic ossification in our models. The inflammatory cytokine TNFα reportedly stimulates mTOR signaling, and we show that TNFα-expressing F4/80-positive macrophages accumulate at dissection sites and that ectopic ossification of the Achilles tendon dissection was significantly inhibited in TNFα-deficient mice in vivo . We also show that ectopic ossification is significantly inhibited by administration of either celecoxib or loxoprofen, both anti-inflammatory agents, in wild-type mice. Finally, we report that mTOR activation by Achilles tendon tenotomy is inhibited in TNFα-deficient mice. Thus, the TNFα-mTOR axis could be targeted therapeutically to prevent trauma-induced ectopic ossification in tendons.