Translational profiling of macrophages infected withLeishmania donovaniidentifies mTOR- and eIF4A-sensitive immune-related transcripts
Authors: Chaparro Visnu , Leroux Louis-Philippe , Masvidal Laia , Lorent Julie , Graber Tyson E. , Zimmermann Aude , Duque Guillermo Arango , Descoteaux Albert , Alain Tommy , Larsson Ola , Jaramillo Maritza 
Published: December 2019

The protozoan parasiteLeishmania donovani(L. donovani) causes visceral leishmaniasis, a chronic infection which is fatal when untreated. While previous studies showed thatL. donovanireprograms 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 withL. donovanipromastigotes 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 uponL. donovaniinfection (Papbpc1, Eif2ak2,andTgfb) confirmed, as indicated by polysome-profiling, increased protein levels despite largely unaltered mRNA levels. Mechanisticin silicoanalyses 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 reversedL. donovani-induced PABPC1 without affecting corresponding transcript levels. Similarly, the production of TGF-β decreased in presence of the eIF4A inhibitor silvestrol despite unalteredTgfbmRNA levels. Consistent with parasite modulation of host eIF4A-sensitive translation to promote infection, silvestrol suppressedL. donovanireplication 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 inL. donovani-infected macrophages. Although the net outcome of such translation programs favours parasite propagation, individual translation programs appear to have opposing roles duringL. donovaniinfection, thereby suggesting their selective targeting as key for therapeutic effects.

Author Summary

Fine-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 parasiteLeishmania donovanialters 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 duringL. donovaniinfection. Herein, we report that one third of protein-coding mRNAs expressed in macrophages are differentially translated upon infection withL. 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 duringL. donovaniinfection and suggests that novel regulatory nodes could be targeted for therapeutic intervention.