Leishmania infantum Induces Mild Unfolded Protein Response in Infected Macrophages

Unraveling the Role of Proteinopathies in Parasitic Infections

Proteinopathies, characterized by the misfolding, aggregation, and deposition of proteins, are hallmarks of various neurodegenerative and systemic diseases. Increasingly, research has highlighted the role of protein misfolding in parasitic infections, unveiling intricate interactions between host and parasite that exacerbate disease pathology and contribute to chronic outcomes. The life cycles of parasitic protozoa, including Plasmodium, Toxoplasmosis, and Leishmania species, are complicated and involve frequent changes between host and vector environments. Their proteomes are severely stressed during these transitions, which calls for highly specialized protein quality control systems. In order to survive harsh intracellular conditions during infection, these parasites have been demonstrated to display unique adaptations in the unfolded protein response, a crucial pathway controlling endoplasmic reticulum stress. In addition to improving parasite survival, these adaptations affect host cell signaling and metabolism, which may jeopardize cellular homeostasis. By causing oxidative stress, persistent inflammation, and disturbance of cellular proteostasis, host-parasite interactions also contribute to proteinopathy. For instance, Plasmodium falciparum disrupts normal protein homeostasis and encourages the accumulation of misfolded proteins by influencing host redox systems involved in protein folding. In addition to interfering with host chaperone systems, the parasitic secretion of effector proteins exacerbates protein misfolding and aggregate formation. Autophagy, apoptosis regulation, organelle integrity, and other vital cellular processes are all disrupted by these pathological protein aggregates. Long-term misfolding and aggregation can cause irreversible tissue damage, which can worsen the clinical course of illnesses like visceral leishmaniasis, cerebral malaria, and toxoplasmosis. Treating parasite-induced proteinopathies is a potentially fruitful area of therapy. According to recent research, autophagy modulators, proteasome enhancers, and small-molecule chaperones may be repurposed to lessen these effects. Pharmacological agents that target the UPR, for example, have demonstrated the ability to decrease parasite survival while also reestablishing host protein homeostasis. Targeting the proteins secreted by parasites that disrupt host proteostasis may also offer a novel way to stop tissue damage caused by proteinopathies. In conclusion, the intersection of protein misfolding and parasitic infections represents a rapidly advancing field of research. Dissecting the molecular pathways underpinning these processes offers unprecedented opportunities for developing innovative therapies. These insights could not only transform the management of parasitic diseases but also contribute to a broader understanding of proteinopathies in infectious and non-infectious diseases alike.

Histone H3 K4 trimethylation occurs mainly at the origins of polycistronic transcription in the genome of Leishmania infantum promastigotes and intracellular amastigotes

BACKGROUND

Trypanosomatids include the genera Trypanosoma and Leishmania, which are the etiological agents of important human diseases. These pathogens present unique mechanisms of gene expression characterized by functionally unrelated genes positioned in tandem and organized into polycistronic transcription units transcribed in a large pre-mRNA by RNA Polymerase II. Since most of the genome is constitutively transcribed, gene expression is primarily controlled by post-transcriptional processes. As in other organisms, histones in trypanosomatids contain a considerable number of post-translational modifications, highly conserved across evolution, such as the acetylation and methylation of some lysines on histone H3 and H4. These modifications have been mainly studied in Trypanosoma spp. The aim of this work was to elucidate the distribution of histone H3 lysine 4 trimethylation (H3K4me3) over the chromatin landscape of Leishmania infantum, the causative agent of canine and human leishmaniasis in the Mediterranean region. To this end, we investigated by chromatin immunoprecipitation (ChIP)-sequencing either the promastigotes (the flagellated motile form) and the amastigotes (the intracellular form) in an in vitro infection model.

RESULTS

The chromatin was prepared from THP-1 cells non infected, THP-1 cells infected with L. infantum MHOM/FR/78/LEM75, and THP-1 cells non infected and mixed with L. infantum MHOM/FR/78/LEM75 promastigotes. ChIP was conducted using anti-H3K4me3 or anti-H3K27me3 antibodies and ChIP-seq was performed on an Ion S5 sequencer. We showed that histone H3K4me3 is mainly enriched at transcription start sites (67%) or internally within the polycistronic transcription units (30%), with no differences between L. infantum promastigotes and amastigotes. Moreover, the enriched regions co-localize with another hallmark of transcriptional activation (histone H3 acetylation) in L. major, a species characterized by a high degree of synteny with L. infantum.

CONCLUSIONS

These findings expand our knowledge of the epigenomics of Leishmania parasites, focusing on epigenetic markers associated with transcription in L. infantum, and will contribute to elucidate the transcriptional mechanisms in these pathogens.

Endoplasmic reticulum stress triggers unfolded protein response as an antiviral strategy of teleost erythrocytes

Introduction

Fish nucleated red blood cells (RBCs), also known as erythrocytes, play a crucial role in maintaining immune system balance by modulating protein expression in response to various stimuli, including viral attack. This study explores the intriguing behavior of rainbow trout RBCs when faced with the viral hemorrhagic septicemia virus (VHSV), focusing on the endoplasmic reticulum (ER) stress and the unfolded protein response (UPR).

Methods

Rainbow trout RBCs were Ficoll-purified and exposed to ultraviolet (UV)-inactivated VHSV or live VHSV at different multiplicities of infection (MOIs). Using cryo-soft X-ray tomography (cryo-SXT), we uncovered structural and cellular modifications in RBCs exposed to UV-inactivated VHSV. Moreover, RBCs were treated with 4-phenylbutyric acid (4-PBA), an ER stress inhibitor, to investigate its effect on viral replication. Quantitative real-time PCR was also used to analyze the expression of genes related to the UPR and other related cellular pathways.

Results and discussion

Beyond their antiviral response, RBCs undergo notable intracellular changes to combat the virus. Cryo-SXT highlighted a significant increase in the ER volume. This increase is associated with ER stress and the activation of the UPR pathway. Interestingly, VHSV replication levels augmented in RBCs under ER-stress inhibition by 4-PBA treatment, suggesting that rainbow trout RBCs tune up ER stress to control viral replication. Therefore, our findings suggested the induction of ER stress and subsequent activation UPR signaling in the antiviral response of RBCs to VHSV. The results open a new line of investigation to uncover additional mechanisms that may become novel cellular targets for the development of RBC-targeted antiviral strategies.

Exploring the impact of epidemiological and clinical factors on the progression of canine leishmaniosis by statistical and whole genome analyses: from breed predisposition to comorbidities

Canine leishmaniosis (CanL), caused by Leishmania infantum, is a complex disease of growing importance in Europe. Clinical manifestations result from the down-modulation of the host immune response through multiple host-parasite interactions. Although several factors might influence CanL progression, this is the first known study evaluating risk factors for its different clinical stages in a large referral hospital population (n = 35.669) from an endemic area, over a 20 year period. Genome-wide scans for selection signatures were also conducted to explore the genomic component of clinical susceptibility to L. infantum infection. The prevalence of CanL was 3.2% (16.7% stage I; 43.6% stage II; 32.1% stage III; 7.6% stage IV). Dog breed (crossbreed), bodyweight (<10 kg), living conditions (indoors), regular deworming treatment, and being vaccinated against Leishmania significantly decreased the transmission risk and the risk for developing severe clinical forms. Conversely, the detection of comorbidities was associated with advanced clinical forms, particularly chronic kidney disease, neoplasia, cryptorchidism, infectious tracheobronchitis and urate urolithiasis, although those did not impact the clinical outcome. Significant associations between an increased risk of severe clinical stages and findings in the anamnesis (renal or skin-related manifestations) and physical examination (ocular findings) were also detected, highlighting their diagnostic value in referred cases of CanL. Sixteen breeds were found to be significantly more susceptible to developing severe stages of leishmaniosis (e.g. Great Dane, Rottweiler, English Springer Spaniel, Boxer, American Staffordshire Terrier, Golden Retriever), while 20 breeds displayed a clinical resistantance phenotype and, thus, are more likely to mount an efficient immune response against L. infantum (e.g. Pointer, Samoyed, Spanish Mastiff, Spanish Greyhound, English Setter, Siberian Husky). Genomic analyses of these breeds retrieved 12 regions under selection, 63 candidate genes and pinpointed multiple biological pathways such as the IRE1 branch of the unfolded protein response, which could play a critical role in clinical susceptibility to L. infantum infection.

Transcriptional signatures in human macrophage-like cells infected by Leishmania infantum, Leishmania major and Leishmania tropica

BACKGROUND

In the Mediterranean basin, three Leishmania species have been identified: L. infantum, L. major and L. tropica, causing zoonotic visceral leishmaniasis (VL), zoonotic cutaneous leishmaniasis (CL) and anthroponotic CL, respectively. Despite animal models and genomic/transcriptomic studies provided important insights, the pathogenic determinants modulating the development of VL and CL are still poorly understood. This work aimed to identify host transcriptional signatures shared by cells infected with L. infantum, L. major, and L. tropica, as well as specific transcriptional signatures elicited by parasites causing VL (i.e., L. infantum) and parasites involved in CL (i.e., L. major, L. tropica).

METHODOLOGY/PRINCIPAL FINDINGS

U937 cells differentiated into macrophage-like cells were infected with L. infantum, L. major and L. tropica for 24h and 48h, and total RNA was extracted. RNA sequencing, performed on an Illumina NovaSeq 6000 platform, was used to evaluate the transcriptional signatures of infected cells with respect to non-infected cells at both time points. The EdgeR package was used to identify differentially expressed genes (fold change > 2 and FDR-adjusted p-values < 0.05). Then, functional enrichment analysis was employed to identify the enriched ontology terms in which these genes are involved. At 24h post-infection, a common signature of 463 dysregulated genes shared among all infection conditions was recognized, while at 48h post-infection the common signature was reduced to 120 genes. Aside from a common transcriptional response, we evidenced different upregulated functional pathways characterizing L. infantum-infected cells, such as VEGFA-VEGFR2 and NFE2L2-related pathways, indicating vascular remodeling and reduction of oxidative stress as potentially important factors for visceralization.

CONCLUSIONS

The identification of pathways elicited by parasites causing VL or CL could lead to new therapeutic strategies for leishmaniasis, combining the canonical anti-leishmania compounds with host-directed therapy.

Global Remodeling of Host Proteome in Response to Leishmania Infection

The protozoan parasite Leishmania possesses an intrinsic ability to modulate a multitude of pathways in the host, toward aiding its own proliferation. In response, the host reprograms its cellular, immunological, and metabolic machinery to evade the parasite's lethal impact. Besides inducing various antioxidant signaling pathways to counter the elevated stress response proteins like heme oxygenase-1 (HO-1), Leishmania also attempts to delay host cell apoptosis by promoting anti-apoptotic proteins like Bcl-2. The downstream modulation of apoptotic proteins is regulated by effector pathways, including the PI3K/Akt survival pathway, the mitogen-activated protein kinases (MAPKs) signaling pathway, and STAT phosphorylation. In addition, Leishmania assists in its infection in a time-dependent manner by modulating the level of various proteins of autophagic machinery. Immune effector cells, such as mast cells and neutrophils, entrap and kill the pathogen by secreting various granular proteins. In contrast, the host macrophages exert their leishmanicidal effect by secreting various cytokines, such as IL-2, IL-12, etc. An interplay of various signaling pathways occurs in an organized network that is highly specific to both pathogen and host species. This Review analyzes the modulation of expression of proteins, including the cytokines, providing a realistic approach toward understanding the pathophysiology of disease and predicting some prominent markers for disease intervention and vaccine support strategies.

Leishmania infection upregulates and engages host macrophage Argonaute 1, and system-wide proteomics reveals Argonaute 1-dependent host response

Leishmania donovani, an intracellular protozoan parasite, is the causative agent of visceral leishmaniasis, the most severe form of leishmaniasis in humans. It is becoming increasingly clear that several intracellular pathogens target host cell RNA interference (RNAi) pathways to promote their survival. Complexes of Argonaute proteins with small RNAs are core components of the RNAi. In this study, we investigated the potential role of host macrophage Argonautes in Leishmania pathogenesis. Using Western blot analysis of Leishmania donovani-infected macrophages, we show here that Leishmania infection selectively increased the abundance of host Argonaute 1 (Ago1). This increased abundance of Ago1 in infected cells also resulted in higher levels of Ago1 in active Ago-complexes, suggesting the preferred use of Ago1 in RNAi in Leishmania-infected cells. This analysis used a short trinucleotide repeat containing 6 (TNRC6)/glycine-tryptophan repeat protein (GW182) protein-derived peptide fused to Glutathione S-transferase as an affinity matrix to capture mature Ago-small RNAs complexes from the cytosol of non-infected and Leishmania-infected cells. Furthermore, Ago1 silencing significantly reduced intracellular survival of Leishmania, demonstrating that Ago1 is essential for Leishmania pathogenesis. To investigate the role of host Ago1 in Leishmania pathogenesis, a quantitative whole proteome approach was employed, which showed that expression of several previously reported Leishmania pathogenesis-related proteins was dependent on the level of macrophage Ago1. Together, these findings identify Ago1 as the preferred Argonaute of RNAi machinery in infected cells and a novel and essential virulence factor by proxy that promotes Leishmania survival.

Unfolded protein response pathway in leishmaniasis: A review

Alteration in the physiological state of the endoplasmic reticulum (ER) leads to the specific response known as unfolded protein response (UPR) or ER stress response. The UPR is driven by three sensor proteins, namely: Inositol-Requiring Enzyme 1, Protein Kinase RNA-like ER kinase and Activating Transcription Factor 6 to restore ER homeostasis. Pathogenic infection can initiate UPR activation; some pathogens can subvert the UPR to promote their survival and replication. Many intracellular pathogens, including Leishmania, can interact and hijack ER for their survival and replication, triggering ER stress and subsequently ER stress response. This review aims to provide a comprehensive overview of the ER stress response in infections with the Leishmania species.

Leishmania (L.) amazonensis LaLRR17 increases parasite entry in macrophage by a mechanism dependent on GRP78

Leishmaniases affect 12 million people worldwide. They are caused by Leishmania spp., protozoan parasites transmitted to mammals by female phlebotomine flies. During the life cycle, promastigote forms of the parasite live in the gut of infected sandflies and convert into amastigotes inside the vertebrate macrophages. The parasite evades macrophage's microbicidal responses due to virulence factors that affect parasite phagocytosis, survival and/or proliferation. The interaction between Leishmania and macrophage molecules is essential to phagocytosis and parasite survival. Proteins containing leucine-rich repeats (LRRs) are common in several organisms, and these motifs are usually involved in protein–protein interactions. We have identified the LRR17 gene, which encodes a protein with 6 LRR domains, in the genomes of several Leishmania species. We show here that promastigotes of Leishmania (L.) amazonensis overexpressing LaLRR17 are more infective in vitro. We produced recombinant LaLRR17 protein and identified macrophage 78 kDa glucose-regulated protein (GRP78) as a ligand for LaLRR17 employing affinity chromatography followed by mass spectrometry. We showed that GRP78 binds to LaLRR17 and that its blocking precludes the increase of infection conferred by LaLRR17. Our results are the first to report LRR17 gene and protein, and we hope they stimulate further studies on how this protein increases phagocytosis of Leishmania.

Unfolded protein response is involved in resistance to Neospora caninum infection via IRE1α-XBP1s-NOD2 Axis

Neospora caninum, an intracellular protozoan parasite, causes neosporosis resulting in major losses in the livestock industry worldwide. However, no effective drugs or vaccines have been developed to control neosporosis. An in-depth study on the immune response against N. caninum could help to search for effective approaches to prevent and treat neosporosis. The host unfolded protein response (UPR) functions as a double-edged sword in several protozoan parasite infections, either to initiate immune responses or to help parasite survival. In this study, the roles of the UPR in N. caninum infection in vitro and in vivo were explored, and the mechanism of the UPR in resistance to N. caninum infection was analyzed. The results revealed that N. caninum triggered the UPR in mouse macrophages, such as the activation of the IRE1 and PERK branches, but not the ATF6 branch. Inhibition of the IRE1α-XBP1s branch increased the N. caninum number both in vitro and in vivo, while inhibition of the PERK branch did not affect the parasite number. Furthermore, inhibition of the IRE1α-XBP1s branch reduced the production of cytokines by inhibiting NOD2 signalling and its downstream NF-κB and MAPK pathways. Taken together, the results of this study suggest that the UPR is involved in the resistance of N. caninum infection via the IRE1α-XBP1s branch by regulating NOD2 and its downstream NF-κB and MAPK pathways to induce the production of inflammatory cytokines, which provides a new perspective for the research and development of anti-N. caninum drugs.

Transcriptional changes associated with apoptosis and Type I IFN underlie the early interaction between Besnoitia besnoiti tachyzoites and monocyte-derived macrophages

Besnoitia besnoiti-infected bulls may develop severe systemic clinical signs and orchitis that may ultimately cause sterility during the acute infection. Macrophages might play a relevant role in pathogenesis of the disease and the immune response raised against B. besnoiti infection. This study aimed to dissect the early interaction between B. besnoiti tachyzoites and primary bovine monocyte-derived macrophages in vitro. First, the B. besnoiti tachyzoite lytic cycle was characterized. Next, dual transcriptomic profiling of B. besnoiti tachyzoites and macrophages was conducted at early infection (4 h and 8 h p.i. by high-throughput RNA sequencing. Macrophages inoculated with heat-killed tachyzoites (MO-hkBb) and non-infected macrophages (MO) were used as controls. Besnoitia besnoiti was able to invade and proliferate in macrophages. Upon infection, macrophage activation was demonstrated by morphological and transcriptomic changes. Infected macrophages were smaller, round and lacked filopodial structures, which might be associated with a migratory phenotype demonstrated in other apicomplexan parasites. The number of differentially expressed genes (DEGs) increased substantially during infection. In B. besnoiti-infected macrophages (MO-Bb), apoptosis and mitogen-activated protein kinase (MAPK) pathways were regulated at 4 h p.i., and apoptosis was confirmed by TUNEL assay. The Herpes simplex virus 1 infection pathway was the only significantly enriched pathway in MO-Bb at 8 h p.i. Relevant DEGs of the Herpes simplex virus 1 infection (IFNα) and the apoptosis pathways (CHOP-2) were also significantly regulated in the testicular parenchyma of naturally infected bulls. Furthermore, the parasite transcriptomic analysis revealed DEGs mainly related to host cell invasion and metabolism. These results provide a deep overview of the earliest macrophage modulation by B. besnoiti that may favour parasite survival and proliferation in a specialized phagocytic immune cell. Putative parasite effectors were also identified.

Endoplasmic Stress Affects the Coinfection of Leishmania Amazonensis and the Phlebovirus (Bunyaviridae) Icoaraci

Viral coinfections can modulate the severity of parasitic diseases, such as human cutaneous leishmaniasis. Leishmania parasites infect thousands of people worldwide and cause from single cutaneous self-healing lesions to massive mucosal destructive lesions. The transmission to vertebrates requires the bite of Phlebotomine sandflies, which can also transmit Phlebovirus. We have demonstrated that Leishmania infection requires and triggers the Endoplasmic stress (ER stress) response in infected macrophages. In the present paper, we tested the hypothesis that ER stress is increased and required for the aggravation of Leishmania infection due to coinfection with Phlebovirus. We demonstrated that Phlebovirus Icoaraci induces the ER stress program in macrophages mediated by the branches IRE/XBP1 and PERK/ATF4. The coinfection with L. amazonensis potentiates and sustains the ER stress, and the inhibition of IRE1α or PERK results in poor viral replication and decreased parasite load in macrophages. Importantly, we observed an increase in viral replication during the coinfection with Leishmania. Our results demonstrated the role of ER stress branches IRE1/XBP1 and PERK/ATF4 in the synergic effect on the Leishmania increased load during Phlebovirus coinfection and suggests that Leishmania infection can also increase the replication of Phlebovirus in macrophages.

The host micro-RNA cfa-miR-346 is induced in canine leishmaniasis

Background

Leishmaniases are a group of anthropo-zoonotic parasitic diseases caused by a protozoan of the Leishmania genus, affecting both humans and other vertebrates, including dogs. L. infantum is responsible for the visceral and occasionally cutaneous form of the disease in humans and canine leishmaniasis. Previously, we have shown that L. infantum induces a mild but significant increase in endoplasmic reticulum (ER) stress expression markers to promote parasites survival in human and murine infected macrophages. Moreover, we demonstrated that the miRNA hsa-miR-346, induced by the UPR-activated transcription factor sXBP1, was significantly upregulated in human macrophages infected with different L. infantum strains. However, the ER stress response in infected dogs, which represent an important reservoir for Leishmania parasite, was described once recently, whereas the miR-346 expression was not reported before. Therefore, this study aimed to investigate these pathways in the canine macrophage-like cell line DH82 infected by Leishmania spp. and to evaluate the presence of cfa-miR-346 in plasma of non-infected and infected dogs. 

The DH82 cells were infected with L. infantum and L. braziliensis parasites and the expression of cfa-mir-346 and several ER stress markers was evaluated by quantitative PCR (qPCR) at different time points. Furthermore, the cfa-miR-346 was monitored in plasma collected from non-infected dogs (n = 11) and dogs naturally infected by L. infantum (n = 18).

Results

The results in DH82 cells showed that cfa-mir-346 was induced at both 24 h and 48 h post-infection with all Leishmania strains but not with tunicamycin, accounting for a mechanism of induction independent from sXBP1, unlike what was previously observed in human cell lines. Moreover, the cfa-miR-346 expression analysis on plasma revealed a significant increase in infected dogs compared to non-infected dogs.

Conclusions

Here for the first time, we report the upregulation of cfa-miR-346 induced by Leishmania infection in canine macrophage-like cells and plasma samples of naturally infected dogs. According to our results, the cfa-miR-346 appears to be linked to infection, and understanding its role and identifying its target genes could contribute to elucidate the mechanisms underlying the host–pathogen interaction in leishmaniasis.

Defective IGF-1 prohormone N-glycosylation and reduced IGF-1 receptor signaling activation in congenital disorders of glycosylation

The insulin-like growth factor-1 (IGF-1) signaling pathway is crucial for the regulation of growth and development. The correct processing of the IGF-1Ea prohormone (proIGF-1Ea) and the IGF-1 receptor (IGF-1R) peptide precursor requires proper N-glycosylation. Deficiencies of N-linked glycosylation lead to a clinically heterogeneous group of inherited diseases called Congenital Disorders of Glycosylation (CDG). The impact of N-glycosylation defects on IGF-1/IGF-1R signaling components is largely unknown. In this study, using dermal fibroblasts from patients with different CDG [PMM2-CDG (n = 7); ALG3-CDG (n = 2); ALG8-CDG (n = 1); GMPPB-CDG (n = 1)], we analyzed the glycosylation pattern of the proIGF-1Ea, IGF-1 secretion efficiency and IGF-1R signaling activity. ALG3-CDG, ALG8-CDG, GMPPB-CDG and some PMM2-CDG fibroblasts showed hypoglycosylation of the proIGF-1Ea and lower IGF-1 secretion when compared with control (CTR). Lower IGF-1 serum concentration was observed in ALG3-CDG, ALG8-CDG and in some patients with PMM2-CDG, supporting our in vitro data. Furthermore, reduced IGF-1R expression level was observed in ALG3-CDG, ALG8-CDG and in some PMM2-CDG fibroblasts. IGF-1-induced IGF-1R activation was lower in most PMM2-CDG fibroblasts and was associated with decreased ERK1/2 phosphorylation as compared to CTR. In general, CDG fibroblasts showed a slight upregulation of Endoplasmic Reticulum (ER) stress genes compared with CTR, uncovering mild ER stress in CDG cells. ER-stress-related gene expression negatively correlated with fibroblasts IGF-1 secretion. This study provides new evidence of a direct link between N-glycosylation defects found in CDG and the impairment of IGF-1/IGF-1R signaling components. Further studies are warranted to determine the clinical consequences of reduced systemic IGF-1 availability and local activity in patients with CDG.

Modulation of Host Immune Response during Leishmania infantum Natural Infection: A Whole-Transcriptome Analysis of the Popliteal Lymph Nodes in Dogs

Leishmania infantum, the etiological agent of canine leishmaniosis (CanL) in Europe, was responsible of the largest outbreak of human leishmaniosis in Spain. The parasite infects and survives within myeloid lineage cells, causing a potentially fatal disease if left untreated. The only treatment option relies on chemotherapy, although immunotherapy strategies are being considered as novel approaches to prevent progression of the disease. To this aim, a deeper characterization of the molecular mechanisms behind the immunopathogenesis of leishmaniosis is necessary. Thus, we evaluated, for the first time, the host immune response during L. infantum infection through transcriptome sequencing of the popliteal lymph nodes aspirates of dogs with CanL. Differential expression and weighted gene co-expression network analyses were performed, resulting in the identification of 5,461 differentially expressed genes (DEGs) and four key modules in sick dogs, compared to controls. As expected, defense response was the highest enriched biological process in the DEGs, with six genes related to immune response against pathogens (CHI3L1, SLPI, ACOD1, CCL5, MPO, BPI) included among the ten most expressed genes; and two of the key co-expression modules were associated with regulation of immune response, which also positively correlated with clinical stage and blood monocyte concentration. In particular, sick dogs displayed significant changes in the expression of Th1, Th2, Th17 and Tr1 cytokines (e. g. TNF-α, IFN-γ, IL-21, IL-17, IL-15), markers of T cell and NK cell exhaustion (e. g. LAG3, CD244, Blimp-1, JUN), and B cell, monocyte and macrophage disrupted functionality (e. g. CD40LG, MAPK4, IL-1R, NLRP3, BCMA). In addition, we found an overexpression of XBP1 and some other genes involved in endoplasmic reticulum stress and the IRE1 branch of the unfolded protein response, as well as one co-expression module associated with these processes, which could be induced by L. infantum to prevent host cell apoptosis and modulate inflammation-induced lymphangiogenesis at lymph nodes. Moreover, 21 lncRNAs were differentially expressed in sick dogs, and one key co-expression module was associated with chromatin organization, suggesting that epigenetic mechanisms could also contribute to dampening host immune response during natural L. infantum infection in the lymph nodes of dogs suffering from clinical leishmaniosis.

Phenotype Screening of an Azole-bisindole Chemical Library Identifies URB1483 as a New Antileishmanial Agent Devoid of Toxicity on Human Cells

We report the evaluation of a small library of azole-bisindoles for their antileishmanial potential, in terms of efficacy on Leishmania infantum promastigotes and intracellular amastigotes. Nine compounds showed good activity on L. infantum MHOM/TN/80/IPT1 promastigotes with IC₅₀ values ranging from 4 to 10 μM. These active compounds were also tested on human (THP-1, HEPG2, HaCaT, and human primary fibroblasts) and canine (DH82) cell lines. URB1483 was selected as the best compound, with no quantifiable cytotoxicity in mammalian cells, to test the efficacy on intracellular amastigotes. URB1483 significantly reduced the infection index of both human and canine macrophages with an effect comparable to the clinically used drug pentamidine. URB1483 emerges as a new anti-infective agent with remarkable antileishmanial activity and no cytotoxic effects on human and canine cells.

Trichomonas vaginalis induces apoptosis via ROS and ER stress response through ER-mitochondria crosstalk in SiHa cells

Background

Trichomonas vaginalis causes lesions on the cervicovaginal mucosa in women; however, its pathogenesis remains unclear. We have investigated the involvement of the endoplasmic reticulum (ER) in the induction of apoptosis by T. vaginalis and its molecular mechanisms in human cervical cancer SiHa cells.

Methods

Apoptosis, reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP), ER stress response and Bcl-2 family protein expression were evaluated using immunocytochemistry, flow cytometry, 5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethyl-imidacarbocyanine iodide dye staining and western blotting.

Results

Trichomonas vaginalis induced mitochondrial ROS production, apoptosis, the ER stress response and mitochondrial dysfunction, such as MMP depolarization and an imbalance in Bcl-2 family proteins, in SiHa cells in a parasite burden- and infection time-dependent manner. Pretreatment with N-acetyl cysteine (ROS scavenger) or 4-phenylbutyric acid (4-PBA; ER stress inhibitor) significantly alleviated apoptosis, mitochondrial ROS production, mitochondrial dysfunction and ER stress response in a dose-dependent manner. In addition, T. vaginalis induced the phosphorylation of apoptosis signal regulating kinase 1 (ASK1) and c-Jun N-terminal kinases (JNK) in SiHa cells, whereas 4-PBA or SP600125 (JNK inhibitor) pretreatment significantly attenuated ASK1/JNK phosphorylation, mitochondrial dysfunction, apoptosis and ER stress response in SiHa cells, in a dose-dependent manner. Furthermore, T. vaginalis excretory/secretory products also induced mitochondrial ROS production, apoptosis and the ER stress response in SiHa cells, in a time-dependent manner.

Conclusions

Trichomonas vaginalis induces apoptosis through mitochondrial ROS and ER stress responses, and also promotes ER stress-mediated mitochondrial apoptosis via the IRE1/ASK1/JNK/Bcl-2 family protein pathways in SiHa cells. These data suggest that T. vaginalis-induced apoptosis is affected by ROS and ER stress response via ER–mitochondria crosstalk.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-05098-2.

Highlighting the interplay of microRNAs from Leishmania parasites and infected-host cells

Leishmania parasites, the causative agents of leishmaniasis, are protozoan parasites with the ability to modify the signalling pathway and cell responses of their infected host cells. These parasite strategies alter the host cell environment and conditions favouring their replication, survival and pathogenesis. Since microRNAs (miRNAs) are able to post-transcriptionally regulate gene expression processes, these biomolecules can exert critical roles in controlling Leishmania-host cell interplay. Therefore, the identification of relevant miRNAs differentially expressed in Leishmania parasites as well as in infected cells, which affect the host fitness, could be critical to understand the infection biology, pathogenicity and immune response against these parasites. Accordingly, the current review aims to address the differentially expressed miRNAs in both, the parasite and infected host cells and how these biomolecules change cell signalling and host immune responses during infection. A deep understanding of these processes could provide novel guidelines and therapeutic strategies for managing and treating leishmaniasis.

The Effect of Naja naja oxiana Snake Venom Against Leishmania tropica Confirmed by Advanced Assays

PURPOSE

The aim of this study was to explore the activity of Naja naja oxiana venom on Leishmania tropica and its modes of action.

METHODS

Different fractions of Naja naja oxiana venom (NNOV) were prepared and characterized by high-performance liquid chromatography. The superior component, fraction k (FK) was selected. The activity of the fraction was assessed using advanced assays.

RESULTS

Interleukin (IL)-12, TNF-α and iNOS gene expression as the indicators of Th1 significantly increased. In contrast, the level of IL-10, as the marker of T helper 2 substantially decreased (p < 0.001). Reactive oxygen species (ROS) detection showed a significant increase (p < 0.001) after treatment with different concentrations of NNOV-FK, unlike arginase (L-ARG) activity which showed a significant reduction (p < 0.001). The NNOV-FK showed significant lethal activity on the L. tropica stages.

CONCLUSION

The findings demonstrated that NNOV-FK represented a strong leishmanicidal activity on L. tropica stages. The major modes of NNOV-FK action are multidimensional, which perceives the induction of a synergistic response and upregulation of the immune-modulatory role towards Th1 response against L. tropica stages as well as apoptotic and anti-metabolic action as a model drug to generate ROS, block the polyamine synthesis and lead to parasite death.

Endoplasmic Reticulum Stress, a Target for Drug Design and Drug Resistance in Parasitosis

Endoplasmic reticulum stress (ER stress) can be induced when cellular protein homeostasis is damaged, and cells can activate the unfolded protein response (UPR) to restore protein homeostasis or induce cell death to facilitate the survival of the whole system. Globally, parasites are a constant threat to human health and are therefore considered a serious public health problem. Parasitic infection can cause ER stress in host cells, and parasites also possess part or all of the UPR under ER stress conditions. In this review, we aim to clarify the role of ER stress pathways and related molecules in parasites for their survival and development, the pathogenesis of parasitosis in hosts, and the artemisinin resistance of Plasmodium, which provides some potential drug design targets to inhibit survival of parasites, relieves pathological damage of parasitosis, and solves the problem of artemisinin resistance.

In Vitro Reduced Susceptibility to Pentavalent Antimonials of a Leishmania infantum Isolate from a Human Cutaneous Leishmaniasis Case in Central Italy

Cutaneous leishmaniasis (CL) caused by Leishmania (Leishmania) infantum is endemic in the Mediterranean basin. Here we report an autochthonous case of CL in a patient living in central Italy with an unsatisfactory response to treatment with intralesional Meglumine Antimoniate and in vitro demonstration of reduced susceptibility to SbIII. Parasitological diagnosis was first achieved by histopathology on tissue biopsy and the patient was treated with a local infiltration of Meglumine Antimoniate. Since the clinical response at 12 weeks from the treatment's onset was deemed unsatisfactory, two further skin biopsies were taken for histopathological examination, DNA extraction and parasite isolation. L. (L.) infantum was identified by molecular typing. The low susceptibility to Meglumine Antimoniate was confirmed in vitro: the promastigotes from the patient strain showed significantly lower susceptibility to SbIII (the active trivalent form of antimonial) compared to the reference strain MHOM/TN/80/IPT1. The patient underwent a new treatment course with intravenous liposomal Amphotericin B, reaching complete healing of the lesion. Additional studies are needed to confirm the epidemiological and clinical relevance of reduced susceptibility to SbIII of human L. (L.) infantum isolate in Italy.

Activation of NRF2 and ATF4 Signaling by the Pro-Glutathione Molecule I-152, a Co-Drug of N-Acetyl-Cysteine and Cysteamine

I-152 combines two pro-glutathione (GSH) molecules, namely N-acetyl-cysteine (NAC) and cysteamine (MEA), to improve their potency. The co-drug efficiently increases/replenishes GSH levels in vitro and in vivo; little is known about its mechanism of action. Here we demonstrate that I-152 not only supplies GSH precursors, but also activates the antioxidant kelch-like ECH-associated protein 1/nuclear factor E2-related factor 2 (KEAP1/NRF2) pathway. The mechanism involves disulfide bond formation between KEAP1 cysteine residues, NRF2 stabilization and enhanced expression of the γ-glutamil cysteine ligase regulatory subunit. Accordingly, a significant increase in GSH levels, not reproduced by treatment with NAC or MEA alone, was found. Compared to its parent compounds, I-152 delivered NAC more efficiently within cells and displayed increased reactivity to KEAP1 compared to MEA. While at all the concentrations tested, I-152 activated the NRF2 pathway; high doses caused co-activation of activating transcription factor 4 (ATF4) and ATF4-dependent gene expression through a mechanism involving Atf4 transcriptional activation rather than preferential mRNA translation. In this case, GSH levels tended to decrease over time, and a reduction in cell proliferation/survival was observed, highlighting that there is a concentration threshold which determines the transition from advantageous to adverse effects. This body of evidence provides a molecular framework for the pro-GSH activity and dose-dependent effects of I-152 and shows how synergism and cross reactivity between different thiol species could be exploited to develop more potent drugs.

Pseudomonas Aeruginosa and Streptococcus Pyogenes Exposed to Malaysian Trigona Honey In Vitro Demonstrated Downregulation of Virulence Factor

Background

Honey has been known as a traditional medicine for centuries with its antibacterial properties. It is considered one of the most enduring substances used in wound management.

Objectives

This study aimed to: (i) evaluate the effects of Malaysian Trigona honey on bacterial structure and (ii) assess the anti-virulence potential of this honey by examining their impacts on the expression of selected genes (involved in stress survival and biofilm formation) in a test organism.

Materials and Methods

Trigona honey's impacts on the bacterial structure (cell morphology) and the expression profiles of select Pseudomonas Aeruginosa and Streptococcus Pyogenes genes were examined using scanning electron microscopy (SEM) and real-time PCR (RT-qPCR) analysis, respectively.

Results

SEM showed that the decreased cell density deformed, disrupted, and damaged cells for both bacteria. RT-qPCR showed that the expression of fleN, fleQ, and fleR genes of P.aeruginosa were decreased, 4.26-fold, 3.80-fold and 2.66- fold respectively. In addition, scpA, ftsY, and emm13 of S.pyogenes were decreased, 2.87-fold, 3.24-fold, and 4.65-fold respectively.

Conclusion

Our results indicate that Trigona honey may be an effective inhibitor and virulence modulator of P. aeruginosa and S. pyogenes via multiple molecular targets. This deduction needs to be investigated in vivo.

I-152, a supplier of N-acetyl-cysteine and cysteamine, inhibits immunoglobulin secretion and plasma cell maturation in LP-BM5 murine leukemia retrovirus-infected mice by affecting the unfolded protein response

Excessive production of immunoglobulins (Ig) causes endoplasmic reticulum (ER) stress and triggers the unfolded protein response (UPR). Hypergammaglobulinemia and lymphadenopathy are hallmarks of murine AIDS that develops in mice infected with the LP-BM5 murine leukemia retrovirus complex. In these mice, Th2 polarization and aberrant humoral response have been previously correlated to altered intracellular redox homeostasis. Our goal was to understand the role of the cell's redox state in Ig secretion and plasma cell (PC) maturation. To this aim, LP-BM5-infected mice were treated with I-152, an N-acetyl-cysteine and cysteamine supplier. Intraperitoneal I-152 administration (30 μmol/mouse three times a week for 9 weeks) decreased plasma IgG and increased IgG/Syndecan 1 ratio in the lymph nodes where IgG were in part accumulated within the ER. PC containing cytoplasmic inclusions filled with IgG were present in all animals, with fewer mature PC in those treated with I-152. Infection induced up-regulation of signaling molecules involved in the UPR, i.e. CHAC1, BiP, sXBP-1 and PDI, that were generally unaffected by I-152 treatment except for PDI and sXBP-1, which have a key role in protein folding and PC maturation, respectively. Our data suggest that one of the mechanisms through which I-152 can limit hypergammaglobulinemia in LP-BM5-infected mice is by influencing IgG folding/assembly as well as secretion and affecting PC maturation.

Generation and characterization of U937-TR: a platform cell line for inducible gene expression in human macrophages

Monocytes and macrophages are involved in a wide range of biological processes and parasitic diseases. The characterization of the molecular mechanisms governing such processes usually requires precise control of the expression of genes of interest. We implemented a tetracycline-controlled gene expression system in the U937 cell line, one of the most used in vitro models for the research of human monocytes and macrophages. Here we characterized U937-derived cell lines in terms of phenotypic (morphology and marker expression) and functional (capacity for phagocytosis and for Leishmania parasite hosting) changes induced by phorbol-12-myristate-13-acetate (PMA). Finally, we provide evidence of tetracycline-inducible and reversible Lamin-A gene silencing of the PMA-differentiated U937-derived cells.

Rapamycin Re-Directs Lysosome Network, Stimulates ER-Remodeling, Involving Membrane CD317 and Affecting Exocytosis, in Campylobacter Jejuni-Lysate-Infected U937 Cells

The Gram-negative Campylobacter jejuni is a major cause of foodborne gastroenteritis in humans worldwide. The cytotoxic effects of Campylobacter have been mainly ascribed to the actions of the cytolethal distending toxin (CDT): it is mandatory to put in evidence risk factors for sequela development, such as reactive arthritis (ReA) and Guillain–Barré syndrome (GBS). Several researches are directed to managing symptom severity and the possible onset of sequelae. We found for the first time that rapamycin (RM) is able to largely inhibit the action of C. jejuni lysate CDT in U937 cells, and to partially avoid the activation of specific sub-lethal effects. In fact, we observed that the ability of this drug to redirect lysosomal compartment, stimulate ER-remodeling (highlighted by ER–lysosome and ER–mitochondria contacts), protect mitochondria network, and downregulate CD317/tetherin, is an important component of membrane microdomains. In particular, lysosomes are involved in the process of the reduction of intoxication, until the final step of lysosome exocytosis. Our results indicate that rapamycin confers protection against C. jejuni bacterial lysate insults to myeloid cells.

Overexpression of CiIKKβ enhances CIK cell viability against ER stress

Recently, studies have shown that IκB kinase β (IKKβ), a critical kinase in the nucleus factor kappa-B (NF-κB) pathway, participates in inflammatory responses associated with unfolded protein response (UPR) and plays an important role in ER stress-induced cell death. The unfolded protein response (UPR), which is a regulatory system to restore cellular homeostasis in the endoplasmic reticulum (ER), such as oxidative stress, bacterial infection, and virus invasion. The UPR pathways have been reported to be involved in immune responses in mammals, including the classical NF-κB pathway. However, the molecular mechanism of their crosstalk remains to be elucidated. Previously, we demonstrated that IKKβ also has some conserved functions between fish and human, as grass carp (Ctenopharyngodon idella) IKKβ (CiIKKβ) can activate NF-κB pathway. In this study, we found that CiIKKβ level in nucleus was elevated under ER stress and CiIKKβ can interact with grass carp X-box-binding protein 1 (CiXBP1S), a key transcription factor in UPR. Consistently, fluorescent histochemical analysis of grass carp kidney (CIK) cells indicated that CiIKKβ and CiXBP1S colocalized under ER stress. Furthermore, overexpression of CiIKKβ in CIK cells enhanced ER stress tolerance by regulating UPR signaling and resulted in the significant increase of cell viability.

Metformin prevents cell tumorigenesis through autophagy-related cell death

Autophagy is a cellular mechanism by which cells degrade intracellular components in lysosomes, maintaining cellular homeostasis. It has been hypothesized that autophagy could have a role in cancer prevention through the elimination of damaged proteins and organelles; this could explain epidemiological evidence showing the chemopreventive properties of the autophagy-inducer metformin. In this study, we analyzed the autophagy-related effect of metformin in both cancer initiation and progression in non-tumorigenic cells. We also analyzed the induction of tumorigenesis in autophagy-deficient cells, and its correlation with the ER stress. Our results showed that metformin induced massive cell death in preneoplastic JB6 Cl 41-5a cells treated with tumor promoter (phorbol) and in NIH/3T3 treated with H₂O₂. Inhibiting autophagy with wortmannin or ATG7 silencing, the effect of metformin decreased, indicating an autophagy-related cytotoxic activity under stress conditions. We also found an induction of tumorigenesis in ATG7-silenced NIH/3T3 cell clone (3T3-619C3 cells), but not in wild-type and in scrambled transfected cells, and an upregulation of unfolded protein response (UPR) markers in 3T3-619C3 cells treated with H₂O₂. These findings suggest that autophagic cell death could be considered as a new mechanism by which eliminate damaged cells, representing an attractive strategy to eliminate potential tumorigenic cells.

Exploiting genetic polymorphisms in metabolic enzymes for rapid screening of Leishmania infantum genotypes

Background

Leishmania infantum is the aetiological agent of visceral leishmaniasis (VL) and cutaneous leishmaniasis (CL). Numerous strains and/or zymodemes have been identified and characterized by multilocus enzyme electrophoresis (MLEE). MLEE is considered the reference method for L. infantum parasite typing and it is based upon enzyme electrophoretic mobility analysis from promastigote cultures. However, the MLEE technique is cumbersome, time-consuming and does not detect silent genetic mutations or nucleotide changes that give rise to amino acid changes that do not alter electrophoretic mobility. As a result of these difficulties, many DNA-based typing methods have been developed over the past few years. However, relative to the enzymes utilized in MLEE analysis, we observed a shortage of DNA sequences available in the GenBank database or an absolute lack of sequences belonging to specific zymodemes. The aims of the present study were to (i) implement the number of sequences coding for metabolic enzymes used in MLEE; (ii) identify polymorphisms that characterize L. infantum zymodemes most prevalent in the Mediterranean basin; and (iii) exploit these polymorphisms to develop a rapid screening test that would give results comparable with existing MLEE typing.

Results

Partial sequences of seven metabolic enzyme genes (malic enzyme, 6-phosphogluconate dehydrogenase, mitochondrial isocitrate dehydrogenase, glucose-6-phosphate isomerase, glucose-6-phosphate dehydrogenase, phosphoglucomutase and mannose phosphate isomerase) were obtained from 11 L. infantum strains. The comparison of these sequences with those obtained from GenBank allowed for the identification of a few polymorphisms that could distinguish several zymodemes. In particular, the polymorphism 390T>G in the malic enzyme gene has been exploited to develop a high-resolution melt (HRM)-based assay to rapidly differentiate the genotype 390T, associated with zymodemes MON-1, MON-72 and MON-201, evidencing a partial agreement between genotyping results and MLEE. The assay has been successfully applied to L. infantum clinical isolates and clinical samples.

Conclusions

A HRM-based assay for rapid identification of genotypes associated with the most common L. infantum zymodemes in the Mediterranean basin has been developed and its potential application in epidemiological research for L. infantum population screening, without parasite isolation and culturing, has been demonstrated.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3143-7) contains supplementary material, which is available to authorized users.

Leishmania donovani induced Unfolded Protein Response delays host cell apoptosis in PERK dependent manner

Background

Endoplasmic reticulum (ER) stress generated unfolded stress response (UPR) is a basic survival mechanism which protects cell under unfavourable conditions. Leishmania parasite modulates host macrophages in various ways to ensure its survival. Modulation of PI3K-Akt pathway in delayed apoptotic induction of host; enables parasite to stabilize the infection for further propagation.

Methodology

Infected RAW macrophages were exposed to campothecin or thagsigargin and phosphorylation status of PERK, Akt, BAD and Cyt-C was determined through western blotting using phospho specific antibody. Expression at transcriptional level for cIAP1 &2, ATF4, CHOP, ATF3, HO-1 and sXBP1 was determined using real time PCR. For inhibition studies, RAW macrophages were pre-treated with PERK inhibitor GSK2606414 before infection.

Findings

Our studies in RAW macrophages showed that induction of host UPR against L.donovani infection activates Akt mediated pathway which delays apoptotic induction of the host. Moreover, Leishmania infection results in phosphorylation and activation of host PERK enzyme and increased transcription of genes of inhibitor of apoptosis gene family (cIAP) mRNA. In our inhibition studies, we found that inhibition of infection induced PERK phosphorylation under apoptotic inducers reduces the Akt phosphorylation and fails to activate further downstream molecules involved in protection against apoptosis. Also, inhibition of PERK phosphorylation under oxidative exposure leads to increased Nitric Oxide production. Simultaneously, decreased transcription of cIAP mRNA upon PERK phosphorylation fates the host cell towards apoptosis hence decreased infection rate.

Conclusion

Overall the findings from the study suggests that Leishmania modulated host UPR and PERK phosphorylation delays apoptotic induction in host macrophage, hence supports parasite invasion at early stages of infection.

Visceral Leishmaniasis or Kala-azar is one of the severe tropical neglected parasitic diseases caused by Leishmania donovani in Indian subcontinent. Modulation of host in terms of delayed apoptotic induction is one of the aspects which favours disease establishment; however the mechanism is not clearly understood yet. In the present study, we tried to explore the connection between L.donovani infection induced UPR in host with delayed onset of apoptosis. We found that L.donovani infection phosphorylates the PERK and Akt molecule in host along with delayed apoptosis. Simultaneously, the levels of cellular IAP (cIAP1 & 2) genes were also up-regulated in infected macrophages. To assess the involvement of PERK in delayed apoptosis of host, we inhibited the phosphorylation of PERK under the exposure to apoptotic inducers. We found that PERK inhibition decreased the Akt phosphorylation and fails to activate other associated downstream molecules involved in delayed apoptosis of host. Also, a significant reduction in cIAP levels was observed. Under oxidative exposure, inhibition of PERK phosphorylation debilitates infected RAW cell’s ability to maintain redox homeostasis leading to higher nitric oxide production. Altogether, L.donovani infection modulates host apoptosis in a PERK dependent manner and favours infection.

Leishmania Infection Induces MicroRNA hsa-miR-346 in Human Cell Line-Derived Macrophages

Leishmaniasis is an anthropo-zoonotic disease caused by various Leishmania species. The clinical manifestations of the disease vary according to the species and host characteristics. Leishmania infection leads to subversion/modulation of the host’s innate immune response and cellular metabolic pathways. In the last years, it has been shown that many host cell gene expression and signaling pathways are targeted by Leishmania to subvert host defenses (e.g., oxidative damage, immune activation, antigen presentation, apoptosis) and allow parasite survival and replication. However, the molecular mechanisms triggered by the parasite are not fully elucidated. The role of miRNA has recently been evaluated in human or murine macrophages infected with Leishmania (Leishmania) major, L. (L.) donovani or L. (L.) amazonensis. However, no literature exists regarding miRNA dysregulation in host cells infected with L. (L.) infantum or L. (Viannia) species. Since we previously showed that L. (L.) infantum infection induced unfolded protein response (UPR) in macrophages, we focused on miR-346, which has been shown to be induced by the UPR-activated transcription factor sXBP1 and has a potential role in the modulation of the immune response. Macrophages differentiated from U937 and/or THP-1 human monocytic cells were infected with four L. (L.) infantum strain/clinical isolates and one L. (V.) sp. clinical isolate. A significant upregulation of miR-346 (p < 0.05) was observed in infections with all the Leishmania species tested. Moreover, RFX1 (a miR-346 predicted target gene) was found to be significantly downregulated (p < 0.05) after 48h infection, and miR-346 was found to have a role in this downregulation. The induction of miR-346 in macrophages infected with L. (L.) infantum and L. (V.) sp., reported here for the first time, could play a role in regulating macrophage functions since several MHC- or interferon-associated genes are among the targets of this miRNA. Hence, miR-346 could be considered an attractive anti-Leishmania drug target.

Emerging Role for the PERK/eIF2α/ATF4 in Human Cutaneous Leishmaniasis

Leishmania parasites utilize adaptive evasion mechanisms in infected macrophages to overcome host defenses and proliferate. We report here that the PERK/eIF2α/ATF4 signaling branch of the integrated endoplasmic reticulum stress response (IERSR) is activated by Leishmania and this pathway is important for Leishmania amazonensis infection. Knocking down PERK or ATF4 expression or inhibiting PERK kinase activity diminished L. amazonensis infection. Knocking down ATF4 decreased NRF2 expression and its nuclear translocation, reduced HO-1 expression and increased nitric oxide production. Meanwhile, the increased expression of ATF4 and HO-1 mRNAs were observed in lesions derived from patients infected with the prevalent related species L.(V.) braziliensis. Our data demonstrates that Leishmania parasites activate the PERK/eIF2α/ATF-4 pathway in cultured macrophages and infected human tissue and that this pathway is important for parasite survival and progression of the infection.

Endoplasmic reticulum stress and unfolded protein response in infection by intracellular parasites

Perturbations of the physiological status of the endoplasmic reticulum (ER) trigger a specific response known as the ER stress response or unfolded protein response (UPR). In mammalian cells, the UPR is mediated by three ER transmembrane proteins (IRE1, PERK and ATF6) which activate three signaling cascades to restore ER homeostasis. In recent years, a cross-talk between UPR, inflammatory and microbial sensing pathways has been elucidated. Pathogen infection can lead to UPR activation; moreover, several pathogens subvert the UPR to promote their survival and replication. While the UPR in viral and bacterial infection has been characterized, little is known about the role of UPR in intracellular parasite infection. Here, we review recent findings on UPR induction/modulation by intracellular parasites in host cells.