Toll-Like Receptor- and Protein Kinase R-Induced Type I Interferon Sustains Infection of Leishmania donovani in Macrophages

Abstract

Leishmania donovani is a protozoan parasite that causes visceral leishmaniasis, provoking liver and spleen tissue destruction that is lethal unless treated. The parasite replicates in macrophages and modulates host microbicidal responses. We have previously reported that neutrophil elastase (NE) is required to sustain L. donovani intracellular growth in macrophages through the induction of interferon beta (IFN-β). Here, we show that the gene expression of IFN-β by infected macrophages was reduced by half when TLR4 was blocked by pre-treatment with neutralizing antibodies or in macrophages from tlr2-/- mice, while the levels in macrophages from myd88-/- mice were comparable to those from wild-type C57BL/6 mice. The neutralization of TLR4 in tlr2-/- macrophages completely abolished induction of IFN-β gene expression upon parasite infection, indicating an additive role for both TLRs. Induction of type I interferon (IFN-I), OASL2, SOD1, and IL10 gene expression by L. donovani was completely abolished in macrophages from NE knock-out mice (ela2-/-) or from protein kinase R (PKR) knock-out mice (pkr-/-), and in C57BL/6 macrophages infected with transgenic L. donovani expressing the inhibitor of serine peptidase 2 (ISP2). Parasite intracellular growth was impaired in pkr-/- macrophages but was fully restored by the addition of exogenous IFN-β, and parasite burdens were reduced in the spleen of pkr-/- mice at 7 days, as compared to the 129Sv/Ev background mice. Furthermore, parasites were unable to grow in macrophages lacking TLR3, which correlated with lack of IFN-I gene expression. Thus, L. donovani engages innate responses in infected macrophages via TLR2, TLR4, and TLR3, via downstream PKR, to induce the expression of pro-survival genes in the host cell, and guarantee parasite intracellular development.

Tissue specific dual RNA-seq defines host-parasite interplay in murine visceral leishmaniasis caused by Leishmania donovani and Leishmania infantum

“…Adding to this picture, enzymes for phenylalanine and tyrosine metabolism were likewise among the L. donovani-induced unique DEGs, revealing an enrichment of genes related to nutritional metabolism. Intriguingly, such changes in IDO-1 and nutritional metabolism are also found in leprosy (36) and we have recently described at the cellular level, a close parallel of gene expression in macrophages infected in vitro with L. donovani (46) with those described for macrophages infected with M. leprae (47), including the induction of Type-I IFNs and OASL2.…”

Tissue Specific Dual RNA-Seq Defines Host–Parasite Interplay in Murine Visceral Leishmaniasis Caused by Leishmania donovani and Leishmania infantum

“…Adding to this picture, enzymes for phenylalanine and tyrosine metabolism were likewise among the L. donovani -induced unique DEGs, revealing an enrichment of genes related to nutritional metabolism. Intriguingly, such changes in IDO -1 and nutritional metabolism are also found in leprosy ( 38 ), and we have recently described at the cellular level a close parallel of gene expression in macrophages infected in vitro with L. donovani ( 48 ) with that described for macrophages infected with M. leprae ( 49 ), including the induction of Type-I IFNs and OASL2.…”

Macrophage Mitochondrial Biogenesis and Metabolic Reprogramming Induced by Leishmania donovani Require Lipophosphoglycan and Type I Interferon Signaling

“…These results establish a role for TLR4 in mediating mitochondriogenesis in response to L. donovani metacyclic promastigotes. Endosomal TLRs also contribute to host cell responses triggered by Leishmania ( 48 – 53 ). To determine the potential role(s) of endosomal TLRs in mitochondriogenesis, we used BMM derived from Unc93b1 Letr/Letr mice ( 54 ).…”

“…Activation of TLRs leads to the production of type I IFNs in response to various pathogens, including Leishmania ( 47 , 52 , 53 , 55 – 57 ). Given that type I IFNs were reported to modulate mitochondrial metabolism in plasmacytoid dendritic cells ( 58 ), we investigated the possibility that autocrine signaling triggered by these cytokines regulates mitochondrial biogenesis in response to L. donovani .…”