On the regulation of survival and death of synoviocytes and chondrocytes by nitric oxide

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It is known that nitric oxide production is up-regulated both in synovial tissues and articular cartilages in the joints of rheumatoid arthritis (RA) and osteoarthritis (OA) patients. NO is regarded as one of the important molecules to regulate cell death and survival, whereas the regulatory mechanism has not been fully elucidated. On the other hand, interleukin-1 (IL-1) acts as a key mediator of the degeneration of articular cartilage in RA and OA, where chondrocyte death is observed. In this study, the viability of mouse chondrocyte-like ATDC5 cells was reduced by the treatment with IL-1β for 48 h or longer. IL-1β augmented the expression of the catalytic subunit of NADPH-oxidase gp91^<phox> as well as inducible NO synthase in ATDC5 cells. Generation of nitrated guanosine and tyrosine suggested the formation of reactive nitrogen species including peroxynitrite (ONOO^-), a reaction product of NO and superoxide in ATDC5 cells and rat primary chondrocytes treated with IL-1β. Death of AT … More DC5 cells after IL-1β treatment was prevented by an NADPH-oxidase inhibitor 4-(2-aminoethyl) benzenesulfonyl fluoride (AEBSF), a NO synthase inhibitor N^G-nitro-L-arginine methyl ester (L-NAME), and a ONOO^- scavenger uric acid. The viability of ATDC5 cells was reduced by a ONOO^- generator 3-(4-morpholinyl)sydnonimine hydrochloride but not by either a NO donor 1-hydroxy-2-oxo-3-(N-methyl-2-aminopropyl)-3-methyl-1-triazene or S-nitrosoglutathione. Disruption of mitochondrial membrane potential and ATP deprivation were observed in IL-1β-treated ATDC5 cells, both of which were restored by L-NAME, AEBSF, or uric acid. On the other hand, any morphological or biochemical sign indicating apoptosis was not observed in these cells. These results suggest that the death of chondrocyte-like ATDC5 cells was mediated at least in part by mitochondrial dysfunction and energy depletion through ONOO^- formation after IL-1β treatment. We have also succeeded in the establishment of a fibroblastic cell line from the synoviocytes obtained from an RA patient. Less