Advances in Understanding Leishmania Pathobiology: What Does RNA-Seq Tell Us?

Abstract

Leishmaniasis is a vector-borne disease caused by a protozoa parasite from over 20 Leishmania species. The clinical manifestations and the outcome of the disease vary greatly. Global RNA sequencing (RNA-Seq) analyses emerged as a powerful technique to profile the changes in the transcriptome that occur in the Leishmania parasites and their infected host cells as the parasites progresses through their life cycle. Following the bite of a sandfly vector, Leishmania are transmitted to a mammalian host where neutrophils and macrophages are key cells mediating the interactions with the parasites and result in either the elimination the infection or contributing to its proliferation. This review focuses on RNA-Seq based transcriptomics analyses and summarizes the main findings derived from this technology. In doing so, we will highlight caveats in our understanding of the parasite’s pathobiology and suggest novel directions for research, including integrating more recent data highlighting the role of the bacterial members of the sandfly gut microbiota and the mammalian host skin microbiota in their potential role in influencing the quantitative and qualitative aspects of leishmaniasis pathology.

Transcriptomic Profile of Canine DH82 Macrophages Infected by Leishmania infantum Promastigotes with Different Virulence Behavior

“…Although kinetoplastid parasites rely almost exclusively on posttranscriptional gene regulation, RNA-seq techniques have been used before to reveal interesting features of Leishmania spp. transcriptome under different conditions [61]. The success of this protozoa in establishing infection in mammalian hosts depends on its ability to differentiate into amastigotes and survive in the phagosomes of infected cells [62].…”

Dissection of the macrophage response towards infection by the Leishmania-viral endosymbiont duo and dynamics of the type I interferon response

“…Many studies have addressed, using RNA-Seq, the transcriptional changes in the macrophage response upon Leishmania infection ( Salloum et al., 2021 ). Traditionally, these studies have investigated differentially expressed genes with significantly altered expression across the groups of samples.…”

“…While an WGCNA approach has already been conducted in the blood of patients ( Gardinassi et al., 2016 ) and the popliteal lymph nodes of dogs ( Sanz et al., 2021 ) infected with L. infantum as well as in the cutaneous lesions of L. braziliensis– infected patients ( Christensen et al., 2016 ) and L. major– infected human dendritic cells ( Zhao et al., 2019 ), no WGCNA investigation has been piloted on Leishmania -infected macrophages. Aside from being, to our knowledge, the first study where WGCNA was conducted in Leishmania -infected macrophages in vitro , this study also represents the first comprehensive transcriptional study addressing the response mounted by macrophages upon infection by Lgy LRV1+, thus addressing the impact the presence of LRV1 has on the macrophage response ( Cantacessi et al., 2015 ; Salloum et al., 2021 ). The present WGCNA identified biologically relevant groups of transcripts, classified into modules, that were modified upon macrophage infection by Lgy LRV1- and Lgy LRV1+ after 8 or 24 h of infection.…”

“…The advent of transcriptomics has contributed to the global comprehension of how macrophages respond toward infection, including infection by Leishmania . A large number of genes modulated by Leishmania were related to the immune response (pro- and anti-inflammatory), glycolysis, lipid metabolism, biogenesis, and phagocytosis ( Fernandes et al., 2016 ; Aoki et al., 2017 ; Aoki et al., 2019 ; Shadab et al., 2019 ; Restrepo et al., 2021 ; Reverte et al., 2021 ; Salloum et al., 2021 ; Chaparro et al., 2022 ). While these studies have shed light on a plethora of mechanisms potentially perturbed by Leishmania , they have not explored the impact that coexposure to additional agents may have on the immune response mounted toward Leishmania .…”

Challenges and Tools for In Vitro Leishmania Exploratory Screening in the Drug Development Process: An Updated Review

“…Of those, 13 are interventional drug trials involving a curative treatment, and four of which involve a product being developed alone or in combination with others [97]. This difficulty in accurately identifying the molecular target(s) of hit compounds is even more surprising as the Leishmania genome sequence information [98,99] was described and made available, along with significant research into the parasites' biology [100,101]. However, classical genome manipulation methods encounter some limitations in Leishmania, including difficulties in achieving gene knockouts because of the parasites' high genomic plasticity [102].…”