Glycogen synthase kinase-3β (GSK3β) inhibition suppresses the inflammatory response to Francisella infection and protects against tularemia in mice

Francisella tularensis, the causative agent of tularemia, is currently considered a category A bioterrorism agent due to its high virulence. Infection with F. tularensis results in an inflammatory response that plays an important role in the pathogenesis of the disease; however, the cellular mechanisms regulating this response are poorly understood. Glycogen synthase kinase-3β (GSK3β) is a serine/threonine protein kinase that has recently emerged as a key regulatory switch in the modulation of the inflammatory response. In this study, we investigated the effect of GSK3β inhibition in regulating F. tularensis LVS-induced inflammatory responses. F. tularensis LVS infection of murine peritoneal macrophages induced a TLR2 dependent phosphorylation of GSK3β. Inhibition of GSK3β resulted in a significant decrease in the production of pro-inflammatory cytokine IL-6, IL-12p40 and TNF-α, as well as a significant increase in the production of the anti-inflammatory cytokine IL-10. GSK3β regulated the F. tularensis LVS-induced cytokine response by differentially affecting the activation of transcription factors NF-κB and CREB. Inhibition of GSK3β by lithium in vivo suppressed the inflammatory response in mice infected with F. tularensis LVS and conferred a survival advantage. In addition, we show that the production of IFN-γ contributed to the development of tularemia and to the fatal outcome of the infected animals, depending on the timing and the relative level of the IFN-γ produced. IFN-γ potentiated F. tularensis LVS-induced cytokine production by increasing GSK3β activity and the nuclear translocation of NF-κB. Taken together, these results demonstrate a regulatory function of GSK3β in modulating inflammatory responses that can be detrimental to the host during an F. tularensis LVS infection, and suggest that inhibition of GSK3β may represent a novel therapeutic approach in the treatment of tularemia.