Mammalian target of rapamycin complex 1 (mTORC1) is a protein complex that controls protein synthesis, and activation of mTORC1 in subchondral preosteoblasts promotes arthritis by stimulating bone sclerosis (abnormal hardening) and secreting C-X-C motif chemokine 12 (CXCL12). The gene discussed is CXCL12; the disease is arthritic joint disease.