Mecanismos moleculares determinantes da sensibilidade diferencial de macrófagos de camundongos C57BL/6 e BALB/c a LPS para produção de NO

Abstract

Macrophages from C57BL/6 mice innately produce higher levels of NO than macrophages from BALB/c mice when stimulated with LPS. The aim of this work was to investigate the molecular events that account for the intrinsic differential production of NO in C57BL/6 and BALB/c macrophages. By initially analyzing the influence of arginase, we observed that although the enzyme isoforms are differentially expressed in C57BL/6 and BALB/c macrophages, the total activity of arginase is equivalent in these cells, and therefore may not be responsible for the difference in the production of NO by these two strains of mice. The lower production of NO in BALB/c macrophages correlates with a lower iNOS mRNA and protein accumulation. Our group has previously shown that the lower expression of iNOS mRNA is not due to a higher degradation of this molecule and in the present work, we show that the lower expression of iNOS protein is also independent of its degradation rate. These data suggested that iNOS transcription is less efficient in BALB/c than in C57BL/6. Analysis of two transcription factors involved in iNOS transcription showed that activation of NF-B does not correlate with iNOS expression. Conversely, activation of STAT-1 was more prominent in C57BL/6 than BALB/c macrophages. Furthermore, we showed that C57BL/6 macrophages express more TLR4, IFN-, and IL-10 and less TNF- than BALB/c cells. However, there is no correlation between the expression of IL-10 and TNF-, since these cytokines respectively inhibit and stimulate the production of NO. The differential production of IL-10 and TNF- can also be due to the differential production of IFN-, since this cytokine induces the production of IL-10, which, in turn, inhibits production of TNF-. Anti-IFN- neutralizing antibodies abolished STAT-1 activation and reduced NO production in C57BL/6 macrophages to surplus of NO production in C57BL/6 macrophages in relation to BALB/c cells. Therefore, our results suggest that macrophages from BALB/c mice are innately lower NO producers than macrophages from C57BL/6 mice because they are defective in the TLR4-mediated signaling that induces the production of IFN- and consequently the activation of STAT-1.