Trypanosoma cruzi-mediated IFN-γ-inducible nitric oxide output in macrophages is regulated by iNOS mRNA stability

Although the effects of activated macrophages (M phi) on the intracellular parasite Trypanosoma cruzi are well documented, little is known about how host-M phi functions are affected by this pathogen before activation. This study is aimed at assessing the capacity of T. cruzi infection to modulate J77.4 murine M phi NO generation following IFN-gamma stimulation, and identifying mechanisms regulating this modulation. Results show that parasite infection potentiates M phi to produce inducible NO synthase (iNOS) mRNA and protein as well as NO following IFN-gamma stimulation above IFN-gamma alone controls. This potentiation occurs through the concomitant activation of NF-kappa B, ERK1/ERK2 MAPK, and stress-activated protein kinase signaling pathways. Activation of the JAK/STAT pathway by IFN-gamma then leads to STAT1 alpha translocation and the transcription of a stable iNOS mRNA species. A decreased rate of iNOS mRNA degradation results in elevated levels of iNOS protein, and NO production. Maximal iNOS expression is likely achieved through NF-kappa B activation by T. cruzi, whereas iNOS mRNA stability results from ERK1/ERK2 MAPK and stress-activated protein kinase activation by the infection. Taken together, our data show that T. cruzi-infected M phi NO generation is controlled at both pre- and posttranscriptional levels and relies on signaling pathway cross-talk. This is the first report of a parasite pathogen capable of heightening host mRNA stability.