Diabetes as a risk factor for West Nile virus-associated encephalitis

Abstract

Background: Diabetes mellitus is a significant risk factor for West Nile virus (WNV) encephalitis (WNVE), the leading cause of arboviral encephalitis in the U.S. However, no experimental studies have elucidated the role of diabetes in WNV neuropathogenesis. Therefore, the objective of this study was to employ a diabetic mouse model, db/db, and evaluate the progression of WNV disease as well as the resultant host antiviral immune response to better understand WNV immunopathogenesis in diabetics. Methods: db/db mice and wild-type (WT) mice were inoculated with 10 PFU of WNV and clinical symptoms and mortality were observed for 21 days. Virus burden in the serum, peripheral organs and brain was analyzed by plaque assay. Host immune responses such as interferon, antibodies production, leukocyte infiltration, expression of cell adhesion molecules (CAM) and levels of cytokines and chemokines in the serum and brain were determined by qRT-PCR, WB, ELISA, Luminex assay, PCR arrays and flow cytometry. Further, activation of astrocytes and neuronal death were evaluated by immunohistochemistry and TUNEL assay. Results: Our results demonstrate that db/db mice were highly susceptible to WNV disease, exhibited increased tissue tropism and mortality than the WT mice, and were unable to clear the infection. Increased and sustained WNV replication was observed in the serum, peripheral tissues and brain of db/db mice. Antiviral immune response was impaired in db/db mice as characterized by delayed induction of IFN-α, significantly reduced levels of WNV-specific antibodies and reduced infiltration of immune cells in the brain. db/db mice exhibited attenuated expression of CAM such as Eselectin, and ICAM-1, which correlated with reduced immune cells recruitment in the brain. WNV infection in db/db mice was also associated with enhanced inflammatory response in the serum and brain. Elevated levels of cytokines correlated with increase in astrocytes activation and neuronal damage in the brain of db/db mice. Conclusion: These data suggest that compromised immune response coupled with failure to clear virus leads to increased mortality in db/db mice. Our findings provide direct experimental evidence of diabetes as a risk factor for WNVE and provide unique mechanistic insight into the immunopathogenesis of WNVE in diabetics.