Nitric oxide inhibits chondrocyte response to IGF-I: inhibition of IGF-IRbeta tyrosine phosphorylation

Chondrocytes in arthriticcartilage respond poorly to insulin-like growth factor I (IGF-I).Studies with inducible nitric oxide synthase (iNOS) knockout micesuggest that NO is responsible for part of the cartilage insensitivityto IGF-I. These studies characterize the relationship between NO andchondrocyte responses to IGF-I in vitro, and define a mechanism bywhich NO decreases IGF-I stimulation of chondrocyte proteoglycansynthesis. Lapine cartilage slices, chondrocytes, and cartilage fromosteoarthritic (OA) human knees were exposed to NO from the donorsS-nitroso-N-acetylpenicillamine (SNAP) or(Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate] (DETA NONOate), by transduction with adenoviral transfer of iNOS (Ad-iNOS), or by activation with interleukin-1 (IL-1). NOsynthesis was estimated from medium nitrite, and proteoglycan synthesis was measured as incorporation of ³⁵SO₄. IGF-Ireceptor phosphorylation was evaluated with Western analysis. SNAP,DETA NONOate, endogenously synthesized NO in Ad-iNOS-transduced cells,or IL-1 activation decreased IGF-I-stimulated proteoglycan synthesis incartilage and monolayer cultures of chondrocytes. OA cartilageresponded poorly to IGF-I; however, the response to IGF-I was restoredby culture withN^G-monomethyl-L-arginine(L-NMA). IGF-I receptor phosphotyrosine was diminished inchondrocytes exposed to NO. These studies show that NO is responsiblefor part of arthritic cartilage/chondrocyte insensitivity to anabolicactions of IGF-I; inhibition of receptor autophosphorylation ispotentially responsible for this effect.