Leishmania donovani inhibits inflammasome‐dependent macrophage activation by exploiting the negative regulatory proteins A20 and UCP2

Abstract

In visceral leishmaniasis, we found that the antileishmanial drug Amp B produces a higher level of IL-1β over the infected control. Moreover, administering anti-IL-1β antibody to infected Amp B-treated mice showed significantly less parasite clearance. Investigation revealed that inhibits stimuli-induced expression of a multiprotein signaling platform, NLRP3 inflammasome, which in turn inhibits caspase-1 activation mediated maturation of IL-1β from its pro form. Attenuation of NLRP3 and pro-IL-1β in infection was found to result from decreased NF-κB activity. Transfecting infected cells with constitutively active NF-κB plasmid increased NLRP3 and pro-IL-1β expression but did not increase mature IL-1β, suggesting that IL-1β maturation requires a second signal, which was found to be reactive oxygen species (ROS). Decreased NF-κB was attributed to increased expression of A20, a negative regulator of NF-κB signaling. Silencing A20 in infected cells restored NLRP3 and pro-IL-1β expression, but also increased matured IL-1β, implying an NF-κB-independent A20-modulated IL-1β maturation. Macrophage ROS is primarily regulated by mitochondrial uncoupling protein 2 (UCP2), and UCP2-silenced infected cells showed an increased IL-1β level. Short hairpin RNA-mediated knockdown of A20 and UCP2 in infected mice independently documented decreased liver and spleen parasite burden and increased IL-1β production. These results suggest that exploits A20 and UCP2 to impair inflammasome activation for disease propagation.-Gupta, A. K., Ghosh, K., Palit, S., Barua, J., Das, P. K., Ukil, A. inhibits inflammasome-dependent macrophage activation by exploiting the negative regulatory proteins A20 and UCP2.

Recent advances in understanding Leishmania donovani infection: The importance of diverse host regulatory pathways

“…Similarly, infection by L. donovani results in shutting down the production of IL‐1β at the transcription and translational level . Furthermore, small hairpin RNA‐mediated knockdown of either A20 or UCP2 in infected mice induced inflammasome‐mediated IL‐1β production and significantly decreased liver and spleen parasite burden, creating a host favourable anti‐leishmanial milieu . Consistent with this observation, the study by Shio et al also reported that expression of the metalloprotease GP63 is indispensable for Leishmania ‐mediated inhibition of NLRP3 inflammosome activation and dampening of IL‐1β secretion.…”

“…Recently, a study on L. amazonensis demonstrated that ROS induced via NAD(P)H oxidase in macrophages during the early stages of L. amazonensis infection is critical for NLRP3 inflammasome activation . However, our work has documented that upon L. donovani infection, transcription of NLRP3 gets inhibited due to the upregulation of NF‐κB inhibitor A20 . Moreover, L. donovani simultaneously upregulates mitochondrial uncoupling protein‐2 (UCP2) , thereby inhibiting ROS production and ROS‐mediated pro‐IL‐1β processing .…”

“…On the contrary, L. major and L. mexicana significantly inhibit NLRP3 inflammasome activation and IL‐1β production . Our laboratory has shown that L. donovani inhibits IL‐1β production in macrophages , whereas inhibition of NLRP3 inflammasome activation, leading to impairment of IL‐1β synthesis has been documented in increasing resistance to L. major infection in BALB/c mice . These contradictory results may be due to use of different Leishmania species and versatile genetic background of the host.…”

“…However, our work has documented that upon L. donovani infection, transcription of NLRP3 gets inhibited due to the upregulation of NF‐κB inhibitor A20 . Moreover, L. donovani simultaneously upregulates mitochondrial uncoupling protein‐2 (UCP2) , thereby inhibiting ROS production and ROS‐mediated pro‐IL‐1β processing . Similarly, infection by L. donovani results in shutting down the production of IL‐1β at the transcription and translational level .…”

“…Moreover, L. donovani simultaneously upregulates mitochondrial uncoupling protein‐2 (UCP2) , thereby inhibiting ROS production and ROS‐mediated pro‐IL‐1β processing . Similarly, infection by L. donovani results in shutting down the production of IL‐1β at the transcription and translational level . Furthermore, small hairpin RNA‐mediated knockdown of either A20 or UCP2 in infected mice induced inflammasome‐mediated IL‐1β production and significantly decreased liver and spleen parasite burden, creating a host favourable anti‐leishmanial milieu .…”