Arango Duque, G. | bioRxiv Science

bioRxiv2021

Leishmania donovani metacyclic promastigotes impair phagosome properties in inflammatory monocytes

Leishmaniasis, a debilitating disease with clinical manifestations ranging from self-healing ulcers to life-threatening visceral pathologies, is caused by protozoan parasites of the Leishmania genus. These professional vacuolar pathogens are transmitted by infected sand flies to mammalian hosts as metacyclic promastigotes and are rapidly internalized by various phagocyte populations. Classical monocytes are among the first myeloid cells to migrate to infection sites. Recent evidence shows that recruitment of these cells contributes to parasite burden and to the establishment of chronic disease. However, the nature of Leishmania-inflammatory monocyte interactions during the early stages of host infection has not been well investigated. Here, we aimed to assess the impact of Leishmania donovani metacyclic promastigotes on antimicrobial responses within these cells. Our data showed that inflammatory monocytes were readily colonized by L. donovani metacyclic promastigotes, while infection with Escherichia coli was efficiently cleared. Upon internalization, metacyclic promastigotes inhibited superoxide production at the parasitophorous vacuole (PV) through a mechanism involving exclusion of NADPH oxidase subunits gp91phox and p47phox from the PV membrane. Moreover, we observed that unlike phagosomes enclosing zymosan particles, vacuoles containing parasites acidified poorly. Interestingly, whereas the parasite surface coat virulence glycolipid lipophosphoglycan was responsible for the inhibition of PV acidification, impairement of the NADPH oxidase assembly was independent of lipophosphoglycan and of the metalloprotease GP63. Collectively, these observations indicate that permissiveness of inflammatory monocytes to L. donovani may thus be related to the ability of this parasite to impair the microbicidal properties of phagosomes.

immunology↗

bioRxiv2020

Sec22b regulates inflammatory responses by controlling the nuclear translocation of NF-κB

Soluble NSF attachment receptor (SNARE) proteins regulate the vesicle transport machinery in phagocytic cells. Within the secretory pathway, Sec22b is an ER-Golgi intermediate compartment (ERGIC)-resident SNARE that controls phagosome maturation and function in macrophages and dendritic cells. The secretory pathway controls the release of cytokines and may also impact the secretion of nitric oxide (NO), which is synthesized by the Golgi-active inducible nitric oxide synthase (iNOS). Whether ERGIC SNARE Sec22b controls NO and cytokine secretion, is unknown. Using bone marrow-derived dendritic cells (BMDC), we demonstrated that iNOS colocalizes with ERGIC/Golgi markers, notably Sec22b and its partner syntaxin-5 (Stx5), in the cytoplasm and at the phagosome. Pharmacological blockade of the secretory pathway hindered NO and cytokine release, and inhibited NF-{kappa}B translocation to the nucleus. Importantly, RNAi-mediated silencing of Sec22b revealed that NO and cytokine production were abrogated at the protein and mRNA levels. This correlated with deregulated mitogen-activated protein kinase signalling and reduced nuclear translocation of NF-{kappa}B. We also found that Sec22b co-occurs with NF-{kappa}B in both the cytoplasm and nucleus, pointing to a role for this SNARE in the shuttling of NF-{kappa}B. Collectively, our data unveiled a novel function for the ER-Golgi, and its resident SNARE Sec22b, in the production and release of inflammatory mediators.

cell biology↗

bioRxiv2019

Translational profiling of macrophages infected with Leishmania donovani identifies mTOR- and eIF4A-sensitive immune-related transcripts

The protozoan parasite Leishmania donovani (L. donovani) causes visceral leishmaniasis, a chronic infection which is fatal when untreated. While previous studies showed that L. donovani reprograms transcription to subvert host cell functions, it remains unclear whether the parasite also alters host mRNA translation to establish a successful infection. To assess this, we compared transcriptome-wide translation in primary mouse macrophages infected with L. donovani promastigotes or amastigotes using polysome-profiling. This identified ample selective changes in translation (3,127 transcripts) which were predicted to target central cellular functions by inducing synthesis of proteins related to chromatin remodeling and RNA metabolism while inhibiting those related to intracellular trafficking and antigen presentation. Parallel quantification of protein and mRNA levels for a set of transcripts whose translation was activated upon L. donovani infection (Papbpc1, Eif2ak2, and Tgfb) confirmed, as indicated by polysome-profiling, increased protein levels despite largely unaltered mRNA levels. Mechanistic in silico analyses suggested activated translation depending on the kinase mTOR (e.g. Pabpc1) and the RNA helicase eIF4A (e.g. Tgfb) during infection. Accordingly, treatment with mTOR inhibitors torin-1 or rapamycin reversed L. donovani-induced PABPC1 without affecting corresponding transcript levels. Similarly, the production of TGF-{beta} decreased in presence of the eIF4A inhibitor silvestrol despite unaltered Tgfb mRNA levels. Consistent with parasite modulation of host eIF4A-sensitive translation to promote infection, silvestrol suppressed L. donovani replication within macrophages. In contrast, parasite survival was favored under mTOR inhibition. In summary, infection-associated changes in translation of mTOR- and eIF4A-sensitive mRNAs contribute to modulate mRNA metabolism and immune responses in L. donovani-infected macrophages. Although the net outcome of such translation programs favours parasite propagation, individual translation programs appear to have opposing roles during L. donovani infection, thereby suggesting their selective targeting as key for therapeutic effects. Author SummaryFine-tuning the efficiency of mRNA translation into proteins allows cells to tailor their responses to stress without the need for synthesizing new mRNA molecules. It is well established that the protozoan parasite Leishmania donovani alters transcription of specific genes to subvert host cell functions. However, discrepancies between transcriptomic and proteomic data suggest that post-transcriptional regulatory mechanisms also contribute to modulate host gene expression programs during L. donovani infection. Herein, we report that one third of protein-coding mRNAs expressed in macrophages are differentially translated upon infection with L. donovani. Our computational analyses reveal that subsets of mRNAs encoding functionally related proteins share the same directionality of translational regulation, which is likely to impact metabolic and microbicidal activity of infected cells. We also show that upregulated translation of transcripts that encode central regulators of mRNA metabolism and inflammation is sensitive to the activation of mTOR or eIF4A during infection. Finally, we observe that inhibition of eIF4A activity reduces parasite survival within macrophages while selective blockade of mTOR has the opposite effect. Thus, our study points to a dual role for translational control of host gene expression during L. donovani infection and suggests that novel regulatory nodes could be targeted for therapeutic intervention.

immunology↗