LPS/IFN-gamma cytotoxicity in oligodendroglial cells: role of nitric oxideand protection by the anti-inflammatory cytokine IL-10

Proinflammatory mediators have been implicated in demyelinating disorders, including multiple sclerosis, whereas it has been proposed that the anti-in flammatory cytokines interleukin- (IL-) 4 and IL-10 participate in disease recovery. The present study analysed the effect of interferon-gamma (IFN-ga mma) and bacterial endotoxin (lipopolysaccharide, LPS) on proliferation and survival of progenitors and differentiated oligodendrocytes. We also inves tigated the presence of receptors for IL-4 and IL-10 in oligodendroglial ce lls and explored a possible protective action of IL-4 and IL-10 in cultures following LPS/IFN-gamma. Finally, the role of endogenous nitric oxide (NO) on cell viability and the modulatory action of IL-4 and IL-10 on inducible nitric oxide synthase (iNOS) expression were also analysed. We report that LPS and/or IFN-gamma reduced proliferation and viability of oligodendrogli al cells. Cell death, presumably by apoptosis as evidence by TUNEL and Anne xin V binding, was observed following LPS/IFN-gamma, progenitors being more sensitive than differentiated cells. At both developmental stages, LPS/IFN -gamma -treated cultures expressed iNOS protein and released micromolar con centrations of NO. In progenitors, LPS/IFN-gamma -mediated cell damage was partially dependent on endogenous NO production, whereas NO was fundamental for cytotoxicity of differentiated oligodendrocytes. Both cell types expre ssed mRNA for IL-4 and IL-10 receptors and expression of IL-10 receptors at the protein level was also demonstrated. Treatment with either cytokine in hibited the expression of iNOS resulting from the proinflammatory stimulati on. IL-10 was more effective than IL-4 in suppressing iNOS expression and, interestingly, IL-10 conferred protection against oligodendroglial death ev oked by LPS/IFN-gamma. Our data raise the question of whether IL-10 may pla y a protective role in demyelinating diseases, not only downregulating the function of inflammatory cells but also promoting survival of progenitors a nd differentiated oligodendrocytes.