Nitric oxide accelerates the ascorbic acid-induced osteoblastic differentiation of mouse stromal ST2 cells by stimulating the production of prostaglandin E-2

Nitric oxide (NO) promoted the differentiation of clonal stromal cells (ST2 cells) derived from mouse bone marrow to osteoblast-like cells. The level of expression of mRNA for osteocalcin, a marker of osteoblastic differentia tion, and the formation of mineralized nodules, increased in ST2 cells trea ted with a donor of NO. We used the reverse transcriptase-polymerase chain reaction (RT-PCR) to identify the subtypes of NO synthase that were express ed in the ST2 cells and we detected the expression of an inducible NO synth ase gene in response to tumor necrosis factor-alpha (TNF-alpha). In various types of cell, NO induces the synthesis of prostaglandin E-2 and cGMP, whi ch are known as regulators of osteoblastic differentiation, by activating c yclooxygenases and soluble guanylate cyclase, respectively. Prostaglandin E -2 was generated in response to NO in ST2 cells, however, no synthesis of c GMP in response to NO was detected. Two inhibitors of cyclooxygenase-2,N-[4 -nitro-2-phenoxyphenyl]-methanesulfonamide (nimesulide) and 1-(4-chlorobenz oyl)-5-methoxy-2-methylindole-3-acetic acid (indomethacin), inhibited the f ormation of mineralized nodules by ST2 cells. Our observations suggest that NO might promote osteoblastic differentiation of ST2 cells by stimulating the production of prostaglandin E-2. (C) 2000 Elsevier Science B.V. All rig hts reserved.