Synergistic effect of beta-amyloid protein and interferon gamma on nitric oxide production by C2C12 muscle cells

Nitric oxide (NO) is an important mediator of diverse physiological and pat hological responses, NO-induced oxidative stress has been proposed in the p athogenesis of muscle tissue damage in inclusion-body myositis (IBM), which is characterized by deposition of beta-amyloid protein (A beta) in vacuola ted muscle fibres, To determine whether A beta can induce NO production in skeletal muscle, we stimulated C2C12 mouse skeletal muscle cells in vitro w ith A beta[1-42] or A beta[25-35] peptides in the presence or absence of in terferon gamma (IFN-gamma). Neither A beta peptides nor IFN-gamma were able to stimulate nitrite (NO2-) production by C2C12 cells when given alone, Ho wever, combination of IFN-gamma with either A beta[1-42] or A beta[25-35] r esulted in significant NO2- release into cell-free supernatants. Northern b lot analysis of RNA obtained from A beta/IFN-gamma-stimulated C2C12 cells r evealed increased mRNA accumulation of inducible nitric oxide synthase (iNO S), Moreover, similar to 4% of muscle cells incubated with A beta peptides and IFN-gamma showed ultrastructural features of DNA fragmentation, These f indings, taken together, indicate that the association of A beta with IFN-g amma stimulates NO2- production via induction of iNOS gene expression in sk eletal muscle cells, with occasional evidence for nuclear changes suggestin g apoptotic morphology, These data further support a role for A beta deposi tion in the pathogenesis of postulated oxidative damage in IBM.