Modulation of PGE2 production by 1,25(OH)2D3 and TGF-β in osteoarthritis osteoblasts. Confluent cells were incubated for their last 48 hours in Ham's F12/DMEM medium containing 0.5% BSA in the presence or absence of 50 nM 1,25-dihydroxyvitamin D3 1,25(OH)2D3; D3), 10 ng/ml transforming growth factor-β (TGF-β), or both. Top: prostaglandin E2 (PGE2) was measured in conditioned medium with the use of a very selective ELISA. Values are means ± SEM for n = 7 preparations for both low and high osteoarthritis (OA) osteoblast groups. *p < 0.01; **p < 0.05 compared with the respective basal value for the low or high OA group. Bottom: representative Western blot analysis of cyclooxygenase-2 (COX-2) production in five OA osteoblast preparations in response to 1,25(OH)2D3, TGF-β, or both. Loading between samples was measured by western blot analysis of actin. Low OA and high OA, n = 7 for each group for PGE2 determinations.