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

Proteome profiling of cutaneous leishmaniasis lesions due to dermotropic Leishmania donovani in Sri Lanka

BACKGROUND

Characterization of the host response in cutaneous leishmaniasis (CL) through proteome profiling has gained limited insights into leishmaniasis research compared to that of the parasite. The primary objective of this study was to comprehensively analyze the proteomic profile of the skin lesions tissues in patients with CL, by mass spectrometry, and subsequent validation of these findings through immunohistochemical methods.

METHODS

Eight lesion specimens from leishmaniasis-confirmed patients and eight control skin biopsies were processed for proteomic profiling by mass spectrometry. Formalin-fixed paraffin-embedded lesion specimens from thirty patients and six control skin specimens were used for Immunohistochemistry (IHC) staining. Statistical analyses were carried out using SPSS software. The chi-square test was used to assess the association between the degree of staining for each marker and the clinical and pathological features.

RESULTS

Sixty-seven proteins exhibited significant differential expression between tissues of CL lesions and healthy controls (p < 0.01), representing numerous enriched biological processes within the lesion tissue, as evident by both the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Reactome databases. Among these, the integrated endoplasmic reticulum stress response (IERSR) emerges as a pathway characterized by the up-regulated proteins in CL tissues compared to healthy skin. Expression of endoplasmic reticulum (ER) stress sensors, inositol-requiring enzyme-1 (IRE1), protein kinase RNA-like ER kinase (PERK) and activating transcription factor 6 (ATF6) in lesion tissue was validated by immunohistochemistry.

CONCLUSIONS

In conclusion, proteomic profiling of skin lesions carried out as a discovery phase study revealed a multitude of probable immunological and pathological mechanisms operating in patients with CL in Sri Lanka, which needs to be further elaborated using more in-depth and targeted investigations. Further research exploring the intricate interplay between ER stress and CL pathophysiology may offer promising avenues for the development of novel diagnostic tools and therapeutic strategies in combating this disease.

The role of Nrf2 signaling in parasitic diseases and its therapeutic potential

In response to invading parasites, one of the principal arms of innate immunity is oxidative stress, caused by reactive oxygen species (ROS). However, oxidative stresses play dual functions in the disease, whereby free radicals promote pathogen removal, but they can also trigger inflammation, resulting in tissue injuries. A growing body of evidence has strongly supported the notion that nuclear factor erythroid 2-related factor 2 (NRF) signaling is one of the main antioxidant pathways to combat this oxidative burst against parasites. Given the important role of NRF2 in oxidative stress, in this review, we investigate the activation mechanism of the NRF2 antioxidant pathway in different parasitic diseases, such as malaria, leishmaniasis, trypanosomiasis, toxoplasmosis, schistosomiasis, entamoebiasis, and trichinosis.

Advances in skin gene therapy: utilizing innovative dressing scaffolds for wound healing, a comprehensive review

The skin, serving as the body's outermost layer, boasts a vast area and intricate structure, functioning as the primary barrier against external threats. Disruptions in the composition and functionality of the skin can lead to a diverse array of skin conditions, such as wounds, burns, and diabetic ulcers, along with inflammatory disorders, infections, and various types of skin cancer. These disorders not only exacerbate concerns regarding skin health and beauty but also have a significant impact on mental well-being. Due to the complexity of these disorders, conventional treatments often prove insufficient, necessitating the exploration of new therapeutic approaches. Researchers develop new therapies by deciphering these intricacies and gaining a thorough understanding of the protein networks and molecular processes in skin. A new window of opportunity has opened up for improving wound healing processes because of recent advancements in skin gene therapy. To enhance skin regeneration and healing, this extensive review investigates the use of novel dressing scaffolds in conjunction with gene therapy approaches. Scaffolds that do double duty as wound protectors and vectors for therapeutic gene delivery are being developed using innovative biomaterials. To improve cellular responses and speed healing, these state-of-the-art scaffolds allow for the targeted delivery and sustained release of genetic material. The most recent developments in gene therapy techniques include RNA interference, CRISPR-based gene editing, and the utilization of viral and non-viral vectors in conjunction with scaffolds, which were reviewed here to overcome skin disorders and wound complications. In the future, there will be rare chances to develop custom methods for skin health care thanks to the combination of modern technology and collaboration among disciplines.

Activity of the Di-Substituted Urea-Derived Compound I-17 in Leishmania In Vitro Infections

Protein synthesis has been a very rich target for developing drugs to control prokaryotic and eukaryotic pathogens. Despite the development of new drug formulations, treating human cutaneous and visceral Leishmaniasis still needs significant improvements due to the considerable side effects and low adherence associated with the current treatment regimen. In this work, we show that the di-substituted urea-derived compounds I-17 and 3m are effective in inhibiting the promastigote growth of different Leishmania species and reducing the macrophage intracellular load of amastigotes of the Leishmania (L.) amazonensis and L. major species, in addition to exhibiting low macrophage cytotoxicity. We also show a potential immunomodulatory effect of I-17 and 3m in infected macrophages, which exhibited increased expression of inducible Nitric Oxide Synthase (NOS2) and production of Nitric Oxide (NO). Our data indicate that I-17, 3m, and their analogs may be helpful in developing new drugs for treating leishmaniasis.

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.

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.

Roles of Oxidative Stress and Nrf2 Signaling in Pathogenic and Non-Pathogenic Cells: A Possible General Mechanism of Resistance to Therapy

The coordinating role of nuclear factor erythroid-2-related factor 2 (Nrf2) in cellular function is undeniable. Evidence indicates that this transcription factor exerts massive regulatory functions in multiple signaling pathways concerning redox homeostasis and xenobiotics, macromolecules, and iron metabolism. Being the master regulator of antioxidant system, Nrf2 controls cellular fate, influencing cell proliferation, differentiation, apoptosis, resistance to therapy, and senescence processes, as well as infection disease success. Because Nrf2 is the key coordinator of cell defence mechanisms, dysregulation of its signaling has been associated with carcinogenic phenomena and infectious and age-related diseases. Deregulation of this cytoprotective system may also interfere with immune response. Oxidative burst, one of the main microbicidal mechanisms, could be impaired during the initial phagocytosis of pathogens, which could lead to the successful establishment of infection and promote susceptibility to infectious diseases. There is still a knowledge gap to fill regarding the molecular mechanisms by which Nrf2 orchestrates such complex networks involving multiple pathways. This review describes the role of Nrf2 in non-pathogenic and pathogenic cells.

Exploring the role of secretory proteins in the human infectious diseases diagnosis and therapeutics

Secretory proteins are playing important role during the host-pathogen interaction to develop the infection or protection into the cell. Pathogens developing infectious disease to human being are taken up by host macrophages or number of immune cells, play an important role in physiological, developmental and immunological function. At the same time, infectious agents are also secreting various proteins to neutralize the resistance caused by host cells and also helping the pathogens to develop the infection. Secretory proteins (secretome) are only developed at the time of host-pathogen interaction, therefore they become very important to develop the targeted and potential therapeutic strategies. Pathogen specific secretory proteins released during interaction with host cell provide opportunity to develop point of care and rapid diagnostic kits. Proteins secreted by pathogens at the time of interaction with host cell have also been found as immunogenic in nature and numbers of vaccines have been developed to control the spread of human infectious diseases. This chapter highlights the importance of secretory proteins in the development of diagnostic and therapeutic strategies to fight against human infectious diseases.

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.

Eukaryotic Initiation Factor 2α Kinases Regulate Virulence Functions, Stage Conversion, and the Stress Response in Entamoeba invadens

Entamoeba histolytica is a protozoan parasite that causes amoebic dysentery and liver abscess. This pathogen possesses a two-stage life cycle consisting of an environmentally stable cyst and a pathogenic amoeboid trophozoite. Since infection is acquired by ingestion of cysts from contaminated food and water, this parasite is prevalent in underdeveloped countries. A reptilian pathogen, Entamoeba invadens, which can encyst in culture, has long served as a surrogate to study stage conversion. In the host, Entamoeba species must manage stress, including nutrient deprivation and host immune pressure. In many systems, the stress response is characterized by downregulation of translation, which is initiated by the phosphorylation of eukaryotic initiation factor-2 alpha (eIF2α). In mammalian cells, this phosphorylation is carried out by a family of eIF2α kinases. A canonical eIF2α translational control system exists in Entamoeba species; however, no eIF2α kinases have been characterized. In this study, we identified two eIF2α kinases in E. invadens, EiIF2K-A and EiIF2K-B. Their identity as eIF2α kinases was validated using a heterologous yeast system. We used an RNA interference (RNAi) trigger-mediated silencing system to reduce expression of EiIF2K-A, which also reduced expression of EiIF2K-B. Parasites with decreased kinase expression exhibited decreased phosphorylation of eIF2α and increased sensitivity to oxidative stress. Diminished kinase expression also correlated with an increased rate of encystation, a decreased rate of excystation, and an increase in several virulence functions, erythrophagocytosis and adhesion to host cells. Taken together, these data suggest that EiIF2K-A and EiIF2K-B are authentic eIF2α kinases that may regulate the Entamoeba stress response.

IMPORTANCEEntamoeba histolytica is a human pathogen that causes dysentery and affects millions of people worldwide. This parasite possesses a two-stage life cycle: an environmentally stable cyst and the pathogenic trophozoite. Cysts are ingested from contaminated food and water; thus, this parasite in prevalent in underdeveloped countries. Current therapies commonly cause adverse side effects; therefore, new treatments are needed. In the host, Entamoeba experiences stress brought on, in part, by the host immune system. Understanding stage conversion and the stress response of this pathogen may lead to new drug therapies. Using the model organism E. invadens, we identified two kinases similar to those involved in stress and stage conversion in other systems. We determined that these kinases may regulate the oxidative stress response, stage conversion, and virulence. This work is significant, as it will inform future studies on the life cycle and pathogenicity of Entamoeba species.

Albendazole reduces hepatic inflammation and endoplasmic reticulum-stress in a mouse model of chronic Echinococcus multilocularis infection

BACKGROUND

Echinococcus multilocularis causes alveolar echinococcosis (AE), a rising zoonotic disease in the northern hemisphere. Treatment of this fatal disease is limited to chemotherapy using benzimidazoles and surgical intervention, with frequent disease recurrence in cases without radical surgery. Elucidating the molecular mechanisms underlying E. multilocularis infections and host-parasite interactions ultimately aids developing novel therapeutic options. This study explored an involvement of unfolded protein response (UPR) and endoplasmic reticulum-stress (ERS) during E. multilocularis infection in mice.

METHODS

E. multilocularis- and mock-infected C57BL/6 mice were subdivided into vehicle, albendazole (ABZ) and anti-programmed death ligand 1 (αPD-L1) treated groups. To mimic a chronic infection, treatments of mice started six weeks post i.p. infection and continued for another eight weeks. Liver tissue was then collected to examine inflammatory cytokines and the expression of UPR- and ERS-related genes.

RESULTS

E. multilocularis infection led to an upregulation of UPR- and ERS-related proteins in the liver, including ATF6, CHOP, GRP78, ERp72, H6PD and calreticulin, whilst PERK and its target eIF2α were not affected, and IRE1α and ATF4 were downregulated. ABZ treatment in E. multilocularis infected mice reversed, or at least tended to reverse, these protein expression changes to levels seen in mock-infected mice. Furthermore, ABZ treatment reversed the elevated levels of interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α and interferon (IFN)-γ in the liver of infected mice. Similar to ABZ, αPD-L1 immune-treatment tended to reverse the increased CHOP and decreased ATF4 and IRE1α expression levels.

CONCLUSIONS AND SIGNIFICANCE

AE caused chronic inflammation, UPR activation and ERS in mice. The E. multilocularis-induced inflammation and consecutive ERS was ameliorated by ABZ and αPD-L1 treatment, indicating their effectiveness to inhibit parasite proliferation and downregulate its activity status. Neither ABZ nor αPD-L1 themselves affected UPR in control mice. Further research is needed to elucidate the link between inflammation, UPR and ERS, and if these pathways offer potential for improved therapies of patients with AE.

GSK2606414 attenuates PERK/p-eIF2α/ATF4/CHOP axis and augments mitochondrial function to mitigate high glucose induced neurotoxicity in N2A cells

Neuronal dysfunction and subsequent apoptosis under high glucose conditions during diabetes contribute majorly to the manifestation of diabetic peripheral neuropathy (DPN). PERK (protein kinase RNA (PKR)-like ER kinase) one among the three canonical arms of unfolded protein response (UPR), is believed to play a crucial role in determining the cell fate during endoplasmic reticulum stress (ERS/ER stress) conditions. We evaluated the role of PERK inhibitor GSK2606414 in high glucose (30 ​mM) treated neuroblastoma (N2A) cells. High glucose resulted in disruption of ER proteostasis by activation of UPR which is evident through increased (p ​< ​0.001) expression of GRP78, p-PERK, p-eIF2α, ATF-4 and CHOP when compared to normal cells. It is accompanied with enhanced GRP78 localization in Endoplasmic Reticulum (ER) lumen evident from ER labeling Immunofluorescence (IF) staining. PERK activation resulted in altered mitochondrial function evident by increased mitochondrial superoxide production and compromised mitochondrial homeostasis with decrease in Mfn-2 levels. Additionally, ER stress induced neuronal apoptosis was attenuated by GSK2606414 treatment via inhibiting the PERK-eIF2α-ATF4-CHOP axis that not only curtailed the levels of apoptotic proteins like Bax and caspase 3 but also elevated the levels of anti-apoptotic Bcl-2. Collectively, our findings revealed the neuroprotective potential of GSK2606414 against high glucose induced neurotoxicity in N2A cells.

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Unregulated ER stress drives neuronal (N2A) apoptosis following high glucose (HG) exposure (30 ​mM).

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Mitochondrial dysfunction aggravated by ER stress under hyperglycemic conditions.

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PERK/p-eIF2α/ATF4/CHOP axis underlies the apoptosis of N2A cells upon HG exposure.

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GSK2606414 attenuates PERK/p-eIF2α/ATF4/CHOP axis to mitigate HG induced neurotoxicity in N2A cells.

Therapeutic effect and mechanism of 4‑phenyl butyric acid on renal ischemia‑reperfusion injury in mice

The aim of the present study was to explore the effects and possible mechanism of 4-phenylbutyric acid (4-PBA) on renal ischemia-reperfusion injury (RIRI) in mice. A RIRI model of HK-2 cells was constructed using hypoxia/reoxygenation (H/R) treatment. Dexmedetomidine and 4-PBA were used to treat the cells before and after modeling. Apoptosis and expression levels of cyclophilin D (CypD), cytochrome c, eukaryotic translation initiation factor 2α (eIF2α), glucose-regulated protein 78 (GRP78), intercellular adhesion molecule (ICAM)-1 and vascular adhesion molecule (VCAM)-1 were measured using flow cytometry, western blotting and immunohistochemistry. The renal volume, weight and renal arterial resistance index (RRI) were determined using the renal ischemia model. Compared with untreated model cells, 4-PBA treatment significantly decreased apoptosis and the expression levels of CypD, Cytochrome c, eIF2α and GRP78 in HK-2 cells. There was no significant change in renal volume and weight after modeling, but RRI was significantly decreased after 4-PBA treatments in the model. Western blotting and immunohistochemistry analysis demonstrated that 4-PBA treatment also significantly decreased the expression of ICAM-1 and VCAM-1. Overall, 4-PBA had a therapeutic effect on RIRI in mice. This protection may be mediated by decreasing the expression levels of CypD, Cytochrome c, eIF2α and GRP78, and subsequent reduction of cellular oxygen free radicals and apoptosis, leading to an alleviated endoplasmic reticulum stress response and RIRI.

Isorhapontigenin ameliorates cerebral ischemia/reperfusion injury via modulating Kinase Cε/Nrf2/HO-1 signaling pathway

BACKGROUND

Isorhapontigenin (ISO) has been shown to have antioxidant activity. This study aimed to investigate the antioxidant effects of ISO on cerebral ischemia/reperfusion (I/R) injury and its possible molecular mechanisms.

METHODS

Focal cerebral ischemia-reperfusion injury (MCAO/R) model and primary cortical neurons were established an oxygen-glucose deprivation (OGD / R) injury model. After 24 hr of reperfusion, the neurological deficits of the rats were analyzed and HE staining was performed, and the infarct volume was calculated by TTC staining. In addition, the reactive oxygen species (ROS) in rat brain tissue, the content of 4-Hydroxynonenal (4-HNE), and 8-hydroxy2deoxyguanosine (8-OHdG) were detected. Neuronal cell viability was determined by MTT assay. Western blot analysis was determined for protein expression.

RESULTS

ISO treatment significantly improved neurological scores, reduced infarct volume, necrotic neurons, ROS production, 4-HNE, and 8-OHdG levels. At the same time, ISO significantly increased the expression of Nrf2 and HO-1. The neuroprotective effects of ISO can be eliminated by knocking down Nrf2 and HO-1. In addition, knockdown of the PKCε blocked ISO-induced nuclear Nfr2, HO-1 expression.

CONCLUSION

ISO protected against oxidative damage induced by brain I/R, and its neuroprotective mechanism may be related to the PKCε/Nrf2/HO-1 pathway.

Geranylgeranylacetone decreases the production of hepatitis B virus-related antigen by comprehensive downregulation of mRNA transcription activity

BACKGROUND AND AIM

Elimination of hepatitis B virus (HBV) is infrequently achieved with current therapies. Therefore, more effective anti-HBV therapy is needed. We previously reported that geranylgeranylacetone (GGA) showed anti-hepatitis C virus activity in human hepatoma cells. In this study, we examined the anti-HBV activity of GGA.

METHODS

We used HepG2.2.15.7 cells, PXB cells infected with HBV, Huh7 cells transfected with linear HBV, and PLC/PRF/5 cells as HBV-infected hepatocyte models. After GGA treatment, HBV-related antigen was measured by chemiluminescent immunoassay. HBV-related mRNA was examined by Northern blot. cccDNA and endoplasmic reticulum stress markers were measured by real-time polymerase chain reaction. The activities of HBV promoters and enhancer regions were examined using luciferase vectors.

RESULTS

After GGA treatment, hepatitis B surface antigen and hepatitis B e antigen secretion was decreased in all HBV-infected hepatocyte models. HBV-related mRNA was also decreased by GGA treatment, although cccDNA levels were not affected. Additionally, the activity of HBV S1 and S2 promoter region and Enhancer 1/Enhancer 2/core promoter region was reduced by GGA treatment. The mRNA expression of the main transcription factors, hepatocyte nuclear factor 3 and 4 and CCAAT/enhancer binding protein, was also decreased. Further, the expression levels of endoplasmic reticulum stress markers were increased by GGA treatment, which reflected the change in HBV-related antigen secretion.

CONCLUSIONS

Geranylgeranylacetone treatment reduces HBV-related protein levels by suppressing comprehensive downregulation of HBV promoter and enhancer activity, which might be caused by decreased hepatic transcription factor expression. GGA treatment may enhance anti-HBV effects in combination with other therapies.

ATF4-dependent heme-oxygenase-1 attenuates diabetic nephropathy by inducing autophagy and inhibiting apoptosis in podocyte

AIM

Podocyte injury plays an important role in diabetic nephropathy (DN), yet the underlying molecular mechanisms of podocyte injury in DN is not clear. Here, we investigated the role of activating transcription factor 4 (ATF4) and HO-1 in DN-induced podocyte injury.

METHODS

Protein expression was measured by western blotting (WB) and immunofluorescence. Cellular apoptosis was quantified by flow cytometry. ATF4 siRNA knockdown and HO-1 overexpression in podocyte were employed to evaluate the role of ER stress in DN-induced apoptosis and autophagy response. Urinary protein levels, nephrin expression, serum creatinine and BUN were evaluated and glomerulosclerosis was quantified by Periodic Acid-Schiff staining.

RESULTS

Expression of ATF4 was increased in podocytes exposed to serum from DN mice. ATF4 knockdown enhanced DN-induced podocyte apoptosis. HO-1 overexpression reduced the decline of DN-induced podocyte autophagy and inhibited apoptosis and the beneficial effects of HO-1 overexpression in DN were blocked by ATF4 knockdown. The diabetic mice were significantly ameliorated by HO-1 agonist hemin treatment.

CONCLUSIONS

ATF4 induces autophagy by enhancing the expression of HO-1, and inhibits podocyte apoptosis in DN. Treatment with the HO-1 agonist reduced proteinuria, apoptosis, and enhanced autophagy response, and thus improved renal function in DN mice.

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.

Hiding in Plain Sight: Formation and Function of Stress Granules During Microbial Infection of Mammalian Cells

Stress granule (SG) formation is a host cell response to stress-induced translational repression. SGs assemble with RNA-binding proteins and translationally silent mRNA. SGs have been demonstrated to be both inhibitory to viruses, as well as being subverted for viral roles. In contrast, the function of SGs during non-viral microbial infections remains largely unexplored. A handful of microbial infections have been shown to result in host SG assembly. Nevertheless, a large body of evidence suggests SG formation in hosts is a widespread response to microbial infection. Diverse stresses caused by microbes and their products can activate the integrated stress response in order to inhibit translation initiation through phosphorylation of the eukaryotic translation initiation factor 2α (eIF2α). This translational response in other contexts results in SG assembly, suggesting that SG assembly can be a general phenomenon during microbial infection. This review explores evidence for host SG formation in response to bacterial, fungal, and protozoan infection and potential functions of SGs in the host and for adaptations of the pathogen.

The antioxidant response favors Leishmania parasites survival, limits inflammation and reprograms the host cell metabolism

The oxidative burst generated by the host immune system can restrict intracellular parasite entry and growth. While this burst leads to the induction of antioxidative enzymes, the molecular mechanisms and the consequences of this counter-response on the life of intracellular human parasites are largely unknown. The transcription factor NF-E2-related factor (NRF2) could be a key mediator of antioxidant signaling during infection due to the entry of parasites. Here, we showed that NRF2 was strongly upregulated in infection with the human Leishmania protozoan parasites, its activation was dependent on a NADPH oxidase 2 (NOX2) and SRC family of protein tyrosine kinases (SFKs) signaling pathway and it reprogrammed host cell metabolism. In inflammatory leishmaniasis caused by a viral endosymbiont inducing TNF-α in chronic leishmaniasis, NRF2 activation promoted parasite persistence but limited TNF-α production and tissue destruction. These data provided evidence of the dual role of NRF2 in protecting both the invading pathogen from reactive oxygen species and the host from an excess of the TNF-α destructive pro-inflammatory cytokine.

Lipid Metabolism and Immune Checkpoints

Immune checkpoints are essential for the regulation of immune cell functions. Although the abrogation of immunosurveillance of tumor cells is known, the regulators of immune checkpoints are not clear. Lipid metabolism is one of the important metabolic activities in organisms. In lipid metabolism, a large number of metabolites produced can regulate the gene expression and activation of immune checkpoints through various pathways. In addition, increasing evidence has shown that lipid metabolism leads to transient generation or accumulation of toxic lipids that result in endoplasmic reticulum (ER) stress and then regulate the transcriptional and posttranscriptional modifications of immune checkpoints, including transcription, protein folding, phosphorylation, palmitoylation, etc. More importantly, the lipid metabolism can also affect exosome transportation of checkpoints and the degradation of checkpoints by affecting ubiquitination and lysosomal trafficking. In this chapter, we mainly empathize on the roles of lipid metabolism in the regulation of immune checkpoints, such as gene expression, activation, and degradation.

Regulation of cellular immunity by activating transcription factor 4

Activating transcription factor 4 (ATF4) is a DNA binding transcription factor belonging to the family of basic Leucine zipper proteins. ATF4 can be activated in response to multiple cellular stress signals including endoplasmic reticulum stress in the event of improper protein folding or oxidative stress because of mitochondrial dysfunction as well as hypoxia. There are multiple downstream targets of ATF4 that can coordinate the regulation between survival and apoptosis of a cell based on time and exposure to stress. ATF4, therefore, has a broad range of control that results in the modulation of immune cells of the innate and adaptive responses leading to regulation of the cellular immunity. Studies provide evidence that ATF4 can regulate immune cells such as macrophages, T cells, B cells, NK cells and dendritic cells contributing to progression of disease. Immune cells can be exposed to stressed environment in the event of a pathogen attack, infection, inflammation, or in the tumor microenvironment leading to increased ATF4 activity to regulate these responses. ATF4 can further control differentiation and maturation of different immune cell types becoming a determinant of effective immune regulation. Additionally, ATF4 has been heavily implicated in rendering effector immune cells dysfunctional that are used to target tumorigenesis. Therefore, there is a need to evaluate where the literature stands in understanding the overall role of ATF4 in regulating cellular immunity to identify therapeutic targets and generalized mechanisms for different disease progressions.

The Potential Role of Nrf2 Signaling in Leishmania Infection Outcomes

Nrf2 [nuclear factor erythroid 2-related factor 2 (Nrf2)] regulates the expression of a plethora of genes involved in the response to oxidative stress due to inflammation, aging, and tissue damage, among other pathological conditions. Deregulation of this cytoprotective system may also interfere with innate and adaptive immune responses. Oxidative burst, one of the main microbicidal mechanisms, could be impaired during initial phagocytosis of parasites, which could lead to the successful establishment of infection and promote susceptibility to diseases. A wide diversity of infections, mainly those caused by intracellular pathogens such as viruses, bacteria, and protozoan parasites, modulate the activation of Nrf2 by interfering with post-translational modifications, interactions between different protein complexes and the immune response. Nrf2 may be induced by pathogens via distinct pathways such as those involving the engagement of Toll-like receptors, the activation of PI3K/Akt, and endoplasmic reticulum stress. Recent studies have revealed the importance of Nrf2 on leishmaniasis. This mini-review discusses relevant findings that reveal the connection between Leishmania-induced modifications of the host pathways and their relevance to the modulation of the Nrf2-dependent antioxidative response to the infection.

Leishmania Spp-Host Interaction: There Is Always an Onset, but Is There an End?

For a long time Leishmaniasis had been considered as a neglected tropical disease. Recently, it has become a priority in public health all over the world for different aspects such as geographic spread, number of population living at risk of infection as well as the potential lethality and/or the development of disfiguring lesions in the, respectively, visceral and tegumentary forms of the disease. As a result, several groups have been bending over this issue and many valuable data have been published. Nevertheless, parasite-host interactions are still not fully known and, consequently, we do not entirely understand the infection dynamics and parasite persistence. This knowledge may point targets for modulation or blockage, being very useful in the development of measures to interfere in the course of infection/ disease and to minimize the risks and morbidity. In the present review we will discuss some aspects of the Leishmania spp-mammalian host interaction in the onset of infection and after the clinical cure of the lesions. We will also examine the information already available concerning the parasite strategy to evade immune response mainly at the beginning of the infection, as well as during the parasite persistence. This knowledge can improve the conditions of treatment, follow-up and cure control of patients, minimizing the potential damages this protozoosis can cause to infected individuals.

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.