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

Nitric oxide (NO) is an important mediator of diverse physiological and pathological responses, NO-induced oxidative stress has been proposed in the pathogenesis of muscle tissue damage in inclusion-body myositis (IBM), which is characterized by deposition of beta-amyloid protein (A beta) in vacuolated muscle fibres, To determine whether A beta can induce NO production in skeletal muscle, we stimulated C2C12 mouse skeletal muscle cells in vitro with A beta[1-42] or A beta[25-35] peptides in the presence or absence of interferon gamma (IFN-gamma). Neither A beta peptides nor IFN-gamma were able to stimulate nitrite (NO2-) production by C2C12 cells when given alone, However, combination of IFN-gamma with either A beta[1-42] or A beta[25-35] resulted in significant NO2- release into cell-free supernatants. Northern blot analysis of RNA obtained from A beta/IFN-gamma-stimulated C2C12 cells revealed increased mRNA accumulation of inducible nitric oxide synthase (iNOS), Moreover, similar to 4% of muscle cells incubated with A beta peptides and IFN-gamma showed ultrastructural features of DNA fragmentation, These findings, taken together, indicate that the association of A beta with IFN-gamma stimulates NO2- production via induction of iNOS gene expression in skeletal muscle cells, with occasional evidence for nuclear changes suggesting apoptotic morphology, These data further support a role for A beta deposition in the pathogenesis of postulated oxidative damage in IBM.