Inhibition of MEK-ERK1/2-MAP kinase signalling pathway reduces rabies virus induced pathologies in mouse model

The extracellular signal-regulated kinase (ERK) pathway has been shown to regulate pathogenesis of many viral infections, but its role during rabies virus (RV) infection in vivo is not clear. In the present study, we investigated the potential role of MEK-ERK1/2 signalling pathway in the pathogenesis of rabies in mouse model and its regulatory effects on pro-inflammatory cytokines and other mediators of immunity, and kinetics of immune cells. Mice were infected with 25 LD₅₀ of challenge virus standard (CVS) strain of RV by intracerebral (i.c.) inoculation and were treated i.c. with U0126 (specific inhibitor of MEK1/2) at 10 μM/mouse at 0, 2, 4 and 6 days post-infection. Treatment with U0126 resulted in delayed disease development and clinical signs, increased survival time with lesser mortality than untreated mice. The better survival of inhibitor-treated and RV infected mice was positively correlated with reduced viral load and reduced viral spread in the brain as quantified by real-time PCR, direct fluorescent antibody test and immunohistochemistry. CVS-infected/mock-treated mice developed severe histopathological lesions with increased Fluoro-Jade B positive degenerating neurons in brain, which were associated with higher levels of serum nitric oxide, iNOS, TNF-α, and CXCL10 mRNA. Also CVS-infected/U0126-treated mice revealed significant decrease in caspase 3 but increase in Bcl-2 mRNA levels and less TUNEL positive apoptotic cells. CVS-infected/U0126-treated group also showed significant increase in CD4⁺, CD8⁺ T lymphocytes and NK cells in blood and spleen possibly due to less apoptosis of these cells. In conclusion, these data suggest that MEK-ERK1/2 signalling pathway play critical role in the pathogenesis of RV infection in vivo and opens up new avenues of therapeutics.