Bacterial DNA induced iNOS expression through MyD88-p38 MAP kinase in mouse primary cultured glial cells

To study the role of bacterial DNA in the immune function of the brain, we examined the effect of CpG–DNA on the inducible nitric oxide synthase (iNOS) expression in mouse primary cultured glial cells. The expression of Toll-like receptor 9 (TLR9), the receptor of bacterial DNA, was detected by RT-PCR. We observed an increase in iNOS mRNA 6 h after CpG–DNA application. The expression of iNOS protein peaked at 12 h and declined thereafter. CpG–DNA increased p38 mitogen-activated protein kinase (MAPK) activation in primary cultured glial cells. SB203580, a specific inhibitor of p38 MAP kinase, inhibited the CpG–DNA-induced iNOS expression. Moreover, CpG–DNA failed to activate p38 MAP kinase and iNOS induction in the primary cultured glial cells prepared from myeloid differentiation factor 88 (MyD88) deficient mice. Therefore, it is suggested that functional receptor for bacterial DNA exists in primary cultured glial cells and CpG–DNA induces iNOS expression via the MyD88-p38 MAP kinase-dependent mechanisms. Thus, the present results point to the important role of bacterial DNA by acting on glial cells to operate brain immune function.