PPARG and arthritic joint disease: PPARγ agonists rosiglitazone and pioglitazone reduced bone erosions and inflammatory bone loss in a collagen-induced arthritis model,63 and PPARγ signaling pathway genes are upregulated during the osteoblast mineralization process.64 Although reduced expression of PPARγ is thought to play a role in the pathogenesis of OA,22,25,44 its role in bone metabolism during OA remains to be defined.