Abstract
We showed previously that antioxidant enzyme heme oxygenase 1 (HO-1) is critical for Leishmania survival in visceral leishmaniasis. HO-1 inhibits host oxidative burst and inflammatory cytokine production, leading to parasite persistence. In the present study, screening of reported HO-1 transcription factors revealed that infection upregulated (4.1-fold compared to control [P < 0.001]) nuclear factor erythroid 2 (NFE2)-related factor 2 (NRF2). Silencing of NRF2 reduced both HO-1 expression and parasite survival. Investigation revealed that infection-induced transient reactive oxygen species (ROS) production dissociated NRF2 from its inhibitor KEAP1 and enabled phosphorylation-dependent nuclear translocation. Both NRF2 and HO-1 silencing in infection increased production of proinflammatory cytokines. But the level was greater in NRF2-silenced cells than in HO-1-silenced ones, suggesting the presence of other targets of NRF2. Another stress responsive transcription factor ATF3 is also induced (4.6-fold compared to control [P < 0.001]) by NRF2 during infection. Silencing of ATF3 reduced parasite survival (59.3% decrease compared to control [P < 0.001]) and increased proinflammatory cytokines. Infection-induced ATF3 recruited HDAC1 into the promoter sites of tumor necrosis factor alpha (TNF-α) and interleukin 12b (IL-12b) genes. Resulting deacetylated histones prevented NF-κB promoter binding, thereby reducing transcription of inflammatory cytokines. Administering the NRF2 inhibitor trigonelline hydrochloride to infected BALB/c mice resulted in reduced HO-1 and ATF3 expression, decreased spleen and liver parasite burdens, and increased proinflammatory cytokine levels. These results suggest that Leishmania upregulates NRF2 to activate both HO-1 and ATF3 for disease progression.