MK2 and Fas Receptor Contribute to the Severity of CNS Demyelination

Models of inflammatory or degenerative diseases demonstrated that the protein-kinase MK2 is a key player in inflammation. In this study we examined the role of MK2 in MOG(35-55)-induced experimental autoimmune encephalomyelitis (EAE), the animal model for multiple sclerosis. In MK2-deficient (MK2(-/-)) mice we found a delayed onset of the disease and MK2(-/-) mice did not recover until day 24 after EAE induction. At this day a higher number of leukocytes in the CNS of MK2(-/-) mice was found. TNF alpha was not detectable in serum of MK2(-/-) mice in any stage of EAE, while high TNF alpha levels were found at day 16 in wild-type mice. Further investigation revealed an increased expression of FasR mRNA in leukocytes isolated from CNS of wild-type mice but not in MK2(-/-) mice, however in vitro stimulation of MK2(-/-) splenocytes with rmTNF alpha induced the expression of FasR. In addition, immunocomplexes between the apoptosis inhibitor cFlip and the FasR adapter molecule FADD were only detected in splenocytes of MK2(-/-) mice at day 24 after EAE induction. Moreover, the investigation of blood samples from relapsing-remitting multiple sclerosis patients revealed reduced FasR mRNA expression compared to healthy controls. Taken together, our data suggest that MK2 is a key regulatory inflammatory cytokines in EAE and multiple sclerosis. MK2(-/-) mice showed a lack of TNFa and thus might not undergo TNF alpha-induced up-regulation of FasR. This may prevent autoreactive leukocytes from apoptosis and may led to prolonged disease activity. The findings indicate a key role of MK2 and FasR in the regulation and limitation of the immune response in the CNS.