Host heme oxygenase-1: Friend or foe in tackling pathogens?

Dual role of HO-1 in mediating antiviral immune responses and mitigating excessive inflammatory damage during influenza virus infection

Influenza A virus (IAV) remains a global health threat, with severe cases causing high morbidity and mortality. Type I interferons (IFN-α/β) are crucial for early innate immunity to IAV but can drive immunopathology. This study investigates the role of heme oxygenase-1 (HO-1), a stress-responsive protein with anti-inflammatory properties, in modulating the immune response to IAV. Lung-tropic adeno-associated virus (AAV)-mediated HO-1 overexpression reduces lung damage by limiting immune cells infiltration, including plasmacytoid dendritic cells and classical monocytes, while promoting regulatory T cells (Tregs) and nonclassical monocytes. Additionally, HO-1 increases macrophage populations, enhancing antiviral responses via IFN pathways. Consistent with this, HO-1 knockout mice experience more severe infections, and HO-1 recruit inhibited IAV replication and alleviated pulmonary inflammation. In addition, compared with wide-type, the catalytically inactive mutation (H25A) impairs HO-1's anti-inflammatory function. These findings underscore HO-1's critical role in balancing antiviral immunity and inflammation, positioning it as a potential therapeutic target for severe influenza.

Heme catabolism and heme oxygenase-1-expressing myeloid cells in pathophysiology

Although the pathological significance of myeloid cell heterogeneity is still poorly understood, new evidence indicates that distinct macrophage subsets are characterized by specific metabolic programs that influence disease onset and progression. Within this scenario, distinct subsets of macrophages, endowed with high rates of heme catabolism by the stress-responsive enzyme heme oxygenase-1 (HO-1), play critical roles in physiologic and pathological conditions. Of relevance, the substrates of HO-1 activity are the heme groups that derive from cellular catabolism and are converted into carbon monoxide (CO), biliverdin and Fe2+, which together elicit anti-apoptotic, anti-inflammatory activities and control oxidative damage. While high levels of expression of HO-1 enzyme by specialized macrophage populations (erythrophagocytes) guarantee the physiological disposal of senescent red blood cells (i.e. erythrocateresis), the action of HO-1 takes on pathological significance in various diseases, and abnormal CO metabolism has been observed in cancer, hematological diseases, hypertension, heart failure, inflammation, sepsis, neurodegeneration. Modulation of heme catabolism and CO production is therefore a feasible therapeutic opportunity in various diseases. In this review we discuss the role of HO-1 in different pathological contexts (i.e. cancer, infections, cardiovascular, immune-mediated and neurodegenerative diseases) and highlight new therapeutic perspectives on the modulation of the enzymatic activity of HO-1.

Water-soluble intracellular extract of Desmodesmus sp. YT enhanced the antioxidant capacity of human skin fibroblast to protect the skin from UV damage

BACKGROUND

The oxidative stress induced by ultraviolet (UV) radiation is a pivotal factor in skin aging and can even contribute to the development of skin cancer.

AIM

This study explored the antioxidant effect and mechanism of water-soluble intracellular extract (WIE) of Desmodesmus sp.YT (YT), aiming to develop a natural antioxidant suitable for incorporation into cosmetics.

METHODS

The study evaluated the scavenging capacity of YT-WIE against free radicals and assessed its impact on human skin fibroblasts (HSF) cell viability and UV resistance using Cell Counting Kit-8 (CCK-8). Transcriptome sequencing was employed to elucidate the mechanism of action, while RT-qPCR and western blot were used to validate the expression of key genes.

RESULTS

YT-WIE displayed robust antioxidant activity, demonstrating potent scavenging abilities against 2,2-diphenyl-1-picrylhydrazyl (DPPH; IC50 = 0.55 mg mL-1), 2,2'-Azino-bis (3 ethylbenzothiazoline-6-sulfonic acid; ABTS; IC50 = 3.11 mg mL-1), Hydroxyl (·OH; IC50 = 2.21 mg mL-1), and Superoxide anion (O2 •-; IC50 = 0.98 mg mL-1). Furthermore, compared to the control group, the YT-WIE group exhibited an 89.30% enhancement in HSF viability and a 44.63% increase in survival rate post-UV irradiation. Significant upregulation of antioxidant genes (GCLC, GCLM, TXNRD1, HMOX1, NQO1) was observed with YT-WIE treatment at 400 μg mL-1, with fold increases ranging from 1.13 to 5.85 times.

CONCLUSION

YT-WIE demonstrated considerable potential as an antioxidant, shielding human cells from undue oxidative stress triggered by external stimuli such as UV radiation. This suggests its promising application in cosmetics antioxidants.

The Role of the NRF2 Pathway in the Pathogenesis of Viral Respiratory Infections

In humans, acute and chronic respiratory infections caused by viruses are associated with considerable morbidity and mortality. Respiratory viruses infect airway epithelial cells and induce oxidative stress, yet the exact pathogenesis remains unclear. Oxidative stress activates the transcription factor NRF2, which plays a key role in alleviating redox-induced cellular injury. The transcriptional activation of NRF2 has been reported to affect both viral replication and associated inflammation pathways. There is complex bidirectional crosstalk between virus replication and the NRF2 pathway because virus replication directly or indirectly regulates NRF2 expression, and NRF2 activation can reversely hamper viral replication and viral spread across cells and tissues. In this review, we discuss the complex role of the NRF2 pathway in the regulation of the pathogenesis of the main respiratory viruses, including coronaviruses, influenza viruses, respiratory syncytial virus (RSV), and rhinoviruses. We also summarize the scientific evidence regarding the effects of the known NRF2 agonists that can be utilized to alter the NRF2 pathway.

Acyl-CoA synthase ACSL4: an essential target in ferroptosis and fatty acid metabolism

ABSTRACT

Long-chain acyl-coenzyme A (CoA) synthase 4 (ACSL4) is an enzyme that esterifies CoA into specific polyunsaturated fatty acids, such as arachidonic acid and adrenic acid. Based on accumulated evidence, the ACSL4-catalyzed biosynthesis of arachidonoyl-CoA contributes to the execution of ferroptosis by triggering phospholipid peroxidation. Ferroptosis is a type of programmed cell death caused by iron-dependent peroxidation of lipids; ACSL4 and glutathione peroxidase 4 positively and negatively regulate ferroptosis, respectively. In addition, ACSL4 is an essential regulator of fatty acid (FA) metabolism. ACSL4 remodels the phospholipid composition of cell membranes, regulates steroidogenesis, and balances eicosanoid biosynthesis. In addition, ACSL4-mediated metabolic reprogramming and antitumor immunity have attracted much attention in cancer biology. Because it facilitates the cross-talk between ferroptosis and FA metabolism, ACSL4 is also a research hotspot in metabolic diseases and ischemia/reperfusion injuries. In this review, we focus on the structure, biological function, and unique role of ASCL4 in various human diseases. Finally, we propose that ACSL4 might be a potential therapeutic target.

Dietary Iron Intake and HIV-Related Outcomes Among Adults Initiating Antiretroviral Therapy in Tanzania

OBJECTIVE

Anemia is highly prevalent among people living with HIV (PLWHIV) and is often due to iron deficiency. This study evaluated the relationship of dietary iron intake levels and sources with mortality and clinical outcomes among adults initiating HAART.

DESIGN

We conducted a secondary analysis of a multivitamin supplementation trial among 2293 PLWHIV initiating HAART in Dar es Salaam, Tanzania.

METHODS

Dietary iron intake was assessed with a food frequency questionnaire at HAART initiation, and participants followed until death or censoring. Total, animal-, and plant-sourced iron were categorized into quartiles. Intake of food groups was categorized into 0-1, 2-3, and ≥4 servings/wk. Cox proportional hazards models estimated hazard ratios for mortality and incident clinical outcomes.

RESULTS

There were 175 deaths (8%). Red meat intake was associated with a lower risk of all-cause mortality (HR: 0.54; 95% CI: 0.35 to 0.83), AIDS-related mortality (HR: 0.49; 95% CI: 0.28 to 0.85), and severe anemia (HR: 0.57; 95% CI: 0.35 to 0.91), when intake ≥4 servings/wk, compared with 0-1 servings/wk. Legume intake was a lower risk of associated with all-cause mortality (HR: 0.49; 95% CI: 0.31 to 0.77) and AIDS-related mortality (HR: 0.37; 95% CI: 0.23 to 0.61), when intake ≥4 servings/wk, compared with 0-1 servings/wk. Although total dietary iron and overall plant-sourced iron intake were not associated with the risk of mortality or HIV-related outcomes, the highest quartile of animal-sourced iron intake was associated with a lower risk of all-cause mortality (HR: 0.56; 95% CI: 0.35 to 0.90) and a lower risk of AIDS-related mortality (HR: 0.50; 95% CI: 0.30 to 0.90), compared with the lowest quartile.

CONCLUSION

Intake of iron-rich food groups may be associated with a lower risk of mortality and critical HIV-related outcomes among adults initiating HAART.

TRIAL REGISTRATION

The parent trial was registered at Clinicaltrials.gov . Identifier: NCT00383669.

Iron metabolism in the cell as a target in the development of potential antimicrobial and antiviral agents

The search and creation of innovative antimicrobial drugs, acting against resistant and multiresistant strains of bacteria and fungi, are one of the most important tasks of modern bioorganic chemistry and pharmaceuticals. Since iron is essential for the vital activity of almost all organisms, including mammals and bacteria, the proteins involved in its metabolism can serve as potential targets in the development of new promising antimicrobial agents. Such targets include endogenous mammalian biomolecules, heme oxygenases, siderophores, protein 24p3, as well as bacterial heme oxygenases and siderophores. Other proteins that are responsible for the delivery of iron to cells and its balance between bacteria and the host organism also attract certain particular interest. The review summarizes data on the development of inhibitors and inducers (activators) of heme oxygenases, selective for mammals and bacteria, and considers the characteristic features of their mechanisms of action and structure. Based on the reviewed literature data, it was concluded that the use of hemin, the most powerful hemooxygenase inducer, and its derivatives as potential antimicrobial and antiviral agents, in particular against COVID-19 and other dangerous infections, would be a promising approach. In this case, an important role is attributed to the products of hemin degradation formed by heme oxygenases in vitro and in vivo. Certain attention has been paid to the data on the antimicrobial action of iron-free protoporphyrinates, namely complexes with Co, Ga, Zn, Mn, their advantages and disadvantages compared to hemin. Modification of the well-known antibiotic ceftazidime with a siderophore molecule increased its effectiveness against resistant bacteria.

Physiologically Relevant Levels of Biliverdin Do Not Significantly Oppose Oxidative Damage in Plasma In Vitro

AbstractAntioxidants have important physiological roles in limiting the amount of oxidative damage that an organism experiences. One putative antioxidant is biliverdin, a pigment that is most commonly associated with the blue or green colors of avian eggshells. However, despite claims that biliverdin functions as an antioxidant, neither the typical physiological concentrations of biliverdin in most species nor the ability of biliverdin to oppose oxidative damage at these concentrations has been examined. Therefore, we quantified biliverdin in the plasma of six bird species and found that they circulated levels of biliverdin between 0.02 and 0.5 μM. We then used a pool of plasma from northern bobwhite quail (Colinus virginianus) and spiked it with one of seven different concentrations of biliverdin, creating plasma-based solutions ranging from 0.09 to 231 μM biliverdin. We then compared each solution's ability to oppose oxidative damage in response to hydrogen peroxide relative to a control addition of water. We found that hydrogen peroxide consistently induced moderate amounts of oxidative damage (quantified as reactive oxygen metabolites) but that no concentration of biliverdin ameliorated this damage. However, biliverdin and hydrogen peroxide interacted, as the amount of biliverdin in hydrogen peroxide-treated samples was reduced to approximately zero, unless the initial concentration was over 100 μM biliverdin. These preliminary findings based on in vitro work indicate that while biliverdin may have important links to metabolism and immune function, at physiologically relevant concentrations it does not detectably oppose hydrogen peroxide-induced oxidative damage in plasma.

HMOX1 silencing prevents doxorubicin-induced cardiomyocyte injury, mitochondrial dysfunction, and ferroptosis by downregulating CTGF

OBJECTIVES

Doxorubicin is a type of effective antitumor drug but can contribute to cardiomyocyte injuries. We aimed to dissect the mechanism of the HMOX1/CTGF axis in DOX-induced cardiomyocyte injury, mitochondrial dysfunction, and ferroptosis.

METHODS

Bioinformatics analysis was conducted to retrieve differentially expressed genes in a DOX-induced mouse model. Mouse cardiomyocytes, HL-1 cells, were induced with l µM DOX, after which gain- or loss-of-function assays were applied. CCK-8, fluorescent probe assay, flow cytometry, and corresponding kits were employed to detect cell viability, ROS levels, mitochondrial membrane potential and cell apoptosis, and GSH and Fe²⁺ contents, respectively. qRT-PCR or Western blot assay was adopted to test HMOX1, CTGF, BCL-2, Caspase3, Cleaved-Caspase3, and GPX4 expression.

RESULTS

Bioinformatics analysis showed that HMOX1 and CTGF were highly expressed in DOX-induced mice and correlated with each other. Also, HMOX1 and CTGF expression was high in HL-1 cells after DOX treatment, along with an obvious decrease in cell viability and GSH and GPX4 expression, an increase in ROS levels, apoptosis, and Fe²⁺ contents, and mitochondrial membrane potential dysfunction or loss. HMOX1 or CTGF silencing diminished cell apoptosis, Cleaved-Caspase3 expression, Fe²⁺ contents, and ROS levels, enhanced cell viability and the expression of GSH, GPX4, and BCL-2, and recovered mitochondrial membrane potential in DOX-induced HL-1 cells. Nevertheless, the effects of HMOX1 silencing on the viability, apoptosis, ferroptosis, and mitochondrial dysfunction of DOX-induced HL-1 cells were counteracted by CTGF overexpression.

CONCLUSIONS

In conclusion, HMOX1 silencing decreased CTGF expression to alleviate DOX-induced injury, mitochondrial dysfunction, and ferroptosis of mouse cardiomyocytes.

HMOX1 genetic polymorphisms and outcomes in infectious disease: A systematic review

INTRODUCTION

Heme-oxygenase 1 (HMOX1) is a critical stress response gene that catalyzes the multistep oxidation of heme. A GT(n) repeat of variable length in the promoter in has been associated with a wide range of human diseases, including infections. This paper aims to summarise and systematically review associations between the length of the HMOX1 GT(n) promoter and infectious disease in humans.

METHODS

A search using relevant terms was performed in PubMED and EMBASE through to 15/01/21 identifying all research that studied an association between the HMOX1 GT(n) repeat polymorphism and the incidence and/or outcome of any human infectious disease. Citations were screened for additional studies. Potential studies were screened for inclusion by two authors. Data was extracted on allele frequency, genotype, strength of association, mechanism of genotyping, and potential biases. A narrative review was performed across each type of infection.

RESULTS

1,533 studies were identified in the search, and one via citation screening. Sixteen studies were ultimately included, seven in malaria, three in HIV, three in sepsis, and one each in pneumonia, hepatitis C, and acute respiratory distress syndrome (ARDS). Sample sizes for nearly all studies were small (biggest study, n = 1,646). Allelic definition was different across all included studies. All studies were at some risk of bias. In malaria, three studies suggested that longer alleles were associated with reduced risk of severe malaria, particularly malaria-induced renal dysfunction, with four studies identifying a null association. In sepsis, two studies suggested an association with longer alleles and better outcomes.

CONCLUSIONS

Despite the importance of HMOX1 in survival from infection, and the association between repeat length and gene expression, the clinical data supporting an association between repeat length and incidence and/or outcome of infection remain inconclusive.

The Role of Iron in Staphylococcus aureus Infection and Human Disease: A Metal Tug of War at the Host—Microbe Interface

Iron deficiency anemia can be treated with oral or intravenous Fe supplementation. Such supplementation has considerable effects on the human microbiome, and on opportunistic pathogenic micro-organisms. Molecular understanding of the control and regulation of Fe availability at the host-microbe interface is crucial to interpreting the side effects of Fe supplementation. Here, we provide a concise overview of the regulation of Fe by the opportunistic pathogen Staphylococcus aureus. Ferric uptake regulator (Fur) plays a central role in controlling Fe uptake, utilization and storage in order to maintain a required value. The micro-organism has a strong preference for heme iron as an Fe source, which is enabled by the Iron-regulated surface determinant (Isd) system. The strategies it employs to overcome Fe restriction imposed by the host include: hijacking host proteins, replacing metal cofactors, and replacing functions by non-metal dependent enzymes. We propose that integrated omics approaches, which include metalloproteomics, are necessary to provide a comprehensive understanding of the metal tug of war at the host-microbe interface down to the molecular level.

Resolvin D1 protects against Aspergillus fumigatus keratitis in diabetes by blocking the MAPK-NF-κB pathway

Fungal keratitis (FK) is one of the main causes of blindness in China. People with diabetes are susceptible to corneal epithelial disease, even fungal keratitis. At present, there are few studies on this disease. Resolvins (Rv) has been reported as a mediators that exert crucial anti-inflammatory and immune regulation roles in serval diseases. In order to investigate the roles and underlying mechanism of Resolvins D1 (RvD1) on the Aspergillus fumigatus (A. fumigatus) keratitis in diabetes, we established in vivo and in vitro models of A. fumigatus keratitis, which were then exposed to high glucose. The expression levels of RvD1, 5-lipoxygenase (5-LOX), and 15-lipoxygenase (15-LOX) in A. fumigatus keratitis patients with diabetes were determined through Enzyme Linked Immunosorbent Assay (ELISA), Western blot and immunohistochemistry. Reactive Oxygen Species (ROS) production, ELISA, flow cytometry, Hematoxylin-Eosin (HE) staining and fungal loading determination were conducted to evaluate the severity of A. fumigatus infection. Lymphangiogenesis and angiogenesis were examined by immunofluorescence assay. Western blot was applied to detect the proteins of the MAPK-NF-κB pathway. The results showed that RvD1 diminished the high glucose-induced oxidative stress and inflammatory response, as evidenced by the reduction of ROS production, Interleukin-6 (IL-6), Interleukin-8 (IL-8), Heme Oxygenase-1 (HMOX-1), and the elevation of Cyclooxygenase-2 (COX2), Superoxide Dismutase (SOD-1), and Glutathione Peroxidase-2 (GPX2) levels in A. fumigatus-infected Human Corneal Endothelial Cells (HCECs). Additionally, lymphangiogenesis and angiogenesis prominently decreased after intervention with RvD1. Furthermore, RvD1 significantly reduced the levels of p-MEK1/2 and p-ERK1/2, and restrained the NF-κB and GPR32 activation. The above results showed that RvD1 protects against A. fumigatus keratitis in diabetes by suppressing oxidative stress, inflammatory response, fungal growth, and immunoreaction via modulating MAPK-NF-κB pathway. RvD1 provides clues for the therapeutic targets of Fungal keratitis complicated with diabetes.

Host metabolic shift during systemic Salmonella infection revealed by comparative proteomics

Salmonella enterica serovar Typhimurium (S. Typhimurium) is a food-borne bacterium that causes acute gastroenteritis in humans and typhoid fever in mice. Salmonella pathogenicity island II (SPI-2) is an important virulence gene cluster responsible for Salmonella survival and replication within host cells, leading to systemic infection. Previous studies have suggested that SPI-2 function to modulate host vesicle trafficking and immune response to promote systemic infection. However, the molecular mechanism and the host responses triggered by SPI-2 remain largely unknown. To assess the roles of SPI-2, we used a differential proteomic approach to analyse host proteins levels during systemic infections in mice. Our results showed that infection by WT S. Typhimurium triggered the reprogramming of host cell metabolism and inflammatory response. Salmonella systemic infection induces an up-regulation of glycolytic process and a repression of the tricarboxylic acid (TCA) cycle. WT-infected tissues prefer to produce adenosine 5′-triphosphate (ATP) through aerobic glycolysis rather than relying on oxidative phosphorylation to generate energy. Moreover, our data also revealed that infected macrophages may undergo both M1 and M2 polarization. In addition, our results further suggest that SPI-2 is involved in altering actin cytoskeleton to facilitate the Salmonella-containing vacuole (SCV) biogenesis and perhaps even the release of bacteria later in the infection process. Results from our study provide valuable insights into the roles of SPI-2 during systemic Salmonella infection and will guide future studies to dissect the molecular mechanisms of how SPI-2 functions in vivo.

Donor-defined mesenchymal stem cell antimicrobial potency against nontuberculous mycobacterium

Chronic nontuberculous mycobacterial infections with Mycobacterium avium and Mycobacterium intracellulare complicate bronchiectasis, chronic obstructive airway disease, and the health of aging individuals. These insidious intracellular pathogens cause considerable morbidity and eventual mortality in individuals colonized with these bacteria. Current treatment regimens with antibiotic macrolides are both toxic and often inefficient at providing infection resolution. In this article, we demonstrate that human marrow‐derived mesenchymal stem cells are antimicrobial and anti‐inflammatory in vitro and in the context of an in vivo sustained infection of either M. avium and/or M. intracellulare.

Heme Oxygenase-1 Induction in Human BeWo Trophoblast Cells Decreases Toxoplasma gondii Proliferation in Association With the Upregulation of p38 MAPK Phosphorylation and IL-6 Production

Heme oxygenase-1 (HO-1) enzyme exerts beneficial effects at the maternal-fetal interface, especially in trophoblasts, being involved in survival and maturation of these cell phenotypes. Trophoblast cells play essential roles throughout pregnancy, being the gateway for pathogens vertically transmitted, such as Toxoplasma gondii. It was previously shown that HO-1 activity was involved in the control of T. gondii infection in vivo; however, its contribution in trophoblast cells during T. gondii infection, remain undefined. Thus, this study aimed to investigate the influence of HO-1 in T. gondii-infected BeWo and HTR-8/SVneo human trophoblast cells. For this purpose, trophoblast cells were infected and the HO-1 expression was evaluated. T. gondii-infected BeWo cells were treated with hemin or CoPPIX, as inducers of HO-1, or with bilirubin, an end-product of HO-1, and the parasitism was quantified. The involvement of p38 MAPK, a regulator of HO-1, and the cytokine production, were also evaluated. It was found that T. gondii decreased the HO-1 expression in BeWo but not in HTR-8/SVneo cells. When treated with the HO-1 inducers or bilirubin, BeWo cells reduced the parasite proliferation. T. gondii also decreased the p38 MAPK phosphorylation in BeWo cells; on the other hand, HO-1 induction sustained its activation. Finally, the IL-6 production was upregulated by HO-1 induction in T. gondii-infected cells, which was associated with the control of infection.

Carbon monoxide-triggered health effects: the important role of the inflammasome and its possible crosstalk with autophagy and exosomes

Carbon monoxide (CO) has long been known as a "silent killer" because of its ability to bind hemoglobin (Hb), leading to reduced oxygen carrying capacity of Hb, which is the main cause of CO poisoning (COP) in humans. Emerging studies suggest that mitochondria is a key target of CO action that can impact key biological processes, including apoptosis, cellular proliferation, inflammation, and autophagy. Despite its toxicity at high concentrations, CO also exhibits cyto- and tissue-protective effects at low concentrations in animal models of organ injury and disease. Specifically, CO modulates the production of pro- or anti-inflammatory cytokines and mediators by regulating the NLRP3 inflammasome. Given that human diseases are strongly associated with inflammation, a deep understanding of the exact mechanism is helpful for treatment. Autophagic factors and inflammasomes interact in various situations, including inflammatory disease, and exosomes might function as the bridge between the inflammasome and autophagy activation. Thus, the interplay among autophagy, mitochondrial dysfunction, exosomes, and the inflammasome may play pivotal roles in the health effects of CO. In this review, we summarize the latest research on the beneficial and toxic effects of CO and their underlying mechanisms, focusing on the important role of the inflammasome and its possible crosstalk with autophagy and exosomes. This knowledge may lead to the development of new therapies for inflammation-related diseases and is essential for the development of new therapeutic strategies and biomarkers of COP.

Hydrogen sulfide-induced GAPDH sulfhydration disrupts the CCAR2-SIRT1 interaction to initiate autophagy

The deacetylase SIRT1 (sirtuin 1) has emerged as a major regulator of nucleocytoplasmic distribution of macroautophagy/autophagy marker MAP1LC3/LC3 (microtubule-associated protein 1 light chain 3). Activation of SIRT1 leads to the deacetylation of LC3 and its translocation from the nucleus into the cytoplasm leading to an increase in the autophagy flux. Notably, hydrogen sulfide (H₂S) is a cytoprotective gasotransmitter known to activate SIRT1 and autophagy; however, the underlying mechanism for both remains unknown. Herein, we demonstrate that H₂S sulfhydrates the active site cysteine of the glycolytic enzyme GAPDH (glyceraldehyde-3-phosphate dehydrogenase). Sulfhydration of GAPDH leads to its redistribution into the nucleus. Importantly, nuclear localization of GAPDH is critical for H₂S-mediated activation of autophagy as H₂S does not induce autophagy in cells with GAPDH ablation or cells overexpressing a GAPDH mutant lacking the active site cysteine. Importantly, we observed that nuclear GAPDH interacts with CCAR2/DBC1 (cell cycle activator a nd apoptosis regulator 2) inside the nucleus. CCAR2 interacts with the deacetylase SIRT1 to inhibit its activity. Interaction of GAPDH with CCAR2 disrupts the inhibitory effect of CCAR2 on SIRT1. Activated SIRT1 then deacetylates MAP1LC3B/LC3B (microtubule-associated protein 1 light chain 3 beta) to induce its translocation into the cytoplasm and activate autophagy. Additionally, we demonstrate this pathway's physiological role in autophagy-mediated trafficking of Mycobacterium tuberculosis into lysosomes to restrict intracellular mycobacteria growth. We think that the pathway described here could be involved in H₂S-mediated clearance of intracellular pathogens and other health benefits.Abbreviations: ATG5: autophagy related 5; ATG7: autophagy related 7; BECN1: beclin 1, autophagy related; CCAR2/DBC1: cell cycle activator and apoptosis regulator 2; CFU: colony-forming units; DLG4/PSD95: discs large MAGUK scaffold protein 4; EX-527: 6-chloro-2,3,4,9-tetrahydro-1H-carbazole-1-carboxamide; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; H₂S: hydrogen sulfide; HEK: human embryonic kidney cells; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; MEF: mouse embryonic fibroblast; Mtb: Mycobacterium tuberculosis; MTOR: mechanistic target of rapamycin kinase; MOI: multiplicity of infection; NO: nitric oxide; PI3K: phosphatidylinositol-4,5-bisphosphate 3-kinase; PLA: proximity ligation assay; PRKAA: protein kinase, AMP-activated, alpha catalytic subunit; SIAH1: siah E3 ubiquitin protein ligase 1A; SIRT1: sirtuin 1; TB: tuberculosis; TP53INP2/DOR: transformation related protein 53 inducible nuclear protein 2; TRP53/TP53: transformation related protein 53.

Heme oxygenase-1 inhibition promotes IFNγ- and NOS2-mediated control of Mycobacterium tuberculosis infection

Mycobacterium tuberculosis (Mtb) infection induces pulmonary expression of the heme-degrading enzyme heme oxygenase-1 (HO-1). We have previously shown that pharmacological inhibition of HO-1 activity in experimental tuberculosis results in decreased bacterial loads and unexpectedly that this outcome depends on the presence of T lymphocytes. Here, we extend these findings by demonstrating that IFNγ production by T lymphocytes and NOS2 expression underlie this T-cell requirement and that HO-1 inhibition potentiates IFNγ-induced NOS2-dependent control of Mtb by macrophages in vitro. Among the products of heme degradation by HO-1 (biliverdin, carbon monoxide, and iron), only iron supplementation reverted the HO-1 inhibition-induced enhancement of bacterial control and this reversal was associated with decreased NOS2 expression and NO production. In addition, we found that HO-1 inhibition results in decreased labile iron levels in Mtb-infected macrophages in vitro and diminished iron accumulation in Mtb-infected lungs in vivo. Together these results suggest that the T-lymphocyte dependence of the therapeutic outcome of HO-1 inhibition on Mtb infection reflects the role of the enzyme in generating iron that suppresses T-cell-mediated IFNγ/NOS2-dependent bacterial control. In broader terms, our findings highlight the importance of the crosstalk between iron metabolism and adaptive immunity in determining the outcome of infection.

Immune Modulation by Inhibitors of the HO System

The heme oxygenase (HO) system involves three isoforms of this enzyme, HO-1, HO-2, and HO-3. The three of them display the same catalytic activity, oxidating the heme group to produce biliverdin, ferrous iron, and carbon monoxide (CO). HO-1 is the isoform most widely studied in proinflammatory diseases because treatments that overexpress this enzyme promote the generation of anti-inflammatory products. However, neonatal jaundice (hyperbilirubinemia) derived from HO overexpression led to the development of inhibitors, such as those based on metaloproto- and meso-porphyrins inhibitors with competitive activity. Further, non-competitive inhibitors have also been identified, such as synthetic and natural imidazole-dioxolane-based, small synthetic molecules, inhibitors of the enzyme regulation pathway, and genetic engineering using iRNA or CRISPR cas9. Despite most of the applications of the HO inhibitors being related to metabolic diseases, the beneficial effects of these molecules in immune-mediated diseases have also emerged. Different medical implications, including cancer, Alzheimer´s disease, and infections, are discussed in this article and as to how the selective inhibition of HO isoforms may contribute to the treatment of these ailments.

Modulation of Inflammation and Immune Responses by Heme Oxygenase-1: Implications for Infection with Intracellular Pathogens

Heme oxygenase-1 (HO-1) catalyzes the degradation of heme molecules releasing equimolar amounts of biliverdin, iron and carbon monoxide. Its expression is induced in response to stress signals such as reactive oxygen species and inflammatory mediators with antioxidant, anti-inflammatory and immunosuppressive consequences for the host. Interestingly, several intracellular pathogens responsible for major human diseases have been shown to be powerful inducers of HO-1 expression in both host cells and in vivo. Studies have shown that this HO-1 response can be either host detrimental by impairing pathogen control or host beneficial by limiting infection induced inflammation and tissue pathology. These properties make HO-1 an attractive target for host-directed therapy (HDT) of the diseases in question, many of which have been difficult to control using conventional antibiotic approaches. Here we review the mechanisms by which HO-1 expression is induced and how the enzyme regulates inflammatory and immune responses during infection with a number of different intracellular bacterial and protozoan pathogens highlighting mechanistic commonalities and differences with the goal of identifying targets for disease intervention.

Role of Carbon Monoxide in Host-Gut Microbiome Communication

Nature is full of examples of symbiotic relationships. The critical symbiotic relation between host and mutualistic bacteria is attracting increasing attention to the degree that the gut microbiome is proposed by some as a new organ system. The microbiome exerts its systemic effect through a diverse range of metabolites, which include gaseous molecules such as H₂, CO₂, NH₃, CH₄, NO, H₂S, and CO. In turn, the human host can influence the microbiome through these gaseous molecules as well in a reciprocal manner. Among these gaseous molecules, NO, H₂S, and CO occupy a special place because of their widely known physiological functions in the host and their overlap and similarity in both targets and functions. The roles that NO and H₂S play have been extensively examined by others. Herein, the roles of CO in host-gut microbiome communication are examined through a discussion of (1) host production and function of CO, (2) available CO donors as research tools, (3) CO production from diet and bacterial sources, (4) effect of CO on bacteria including CO sensing, and (5) gut microbiome production of CO. There is a large amount of literature suggesting the "messenger" role of CO in host-gut microbiome communication. However, much more work is needed to begin achieving a systematic understanding of this issue.

Heme Oxygenase-1 Induction by Blood-Feeding Arthropods Controls Skin Inflammation and Promotes Disease Tolerance

Hematophagous vectors lacerate host skin and capillaries to acquire a blood meal, resulting in leakage of red blood cells (RBCs) and inflammation. Here, we show that heme oxygenase-1 (HO-1), a pleiotropic cytoprotective isoenzyme that mitigates heme-mediated tissue damage, is induced after bites of sand flies, mosquitoes, and ticks. Further, we demonstrate that erythrophagocytosis by macrophages, including a skin-residing CD163⁺CD91⁺ professional iron-recycling subpopulation, produces HO-1 after bites. Importantly, we establish that global deletion or transient inhibition of HO-1 in mice increases inflammation and pathology following Leishmania-infected sand fly bites without affecting parasite number, whereas CO, an end product of the HO-1 enzymatic reaction, suppresses skin inflammation. This indicates that HO-1 induction by blood-feeding sand flies promotes tolerance to Leishmania infection. Collectively, our data demonstrate that HO-1 induction through erythrophagocytosis is a universal mechanism that regulates skin inflammation following blood feeding by arthropods, thus promoting early-stage disease tolerance to vector-borne pathogens.

Heme Oxygenase Protects against Placental Vascular Inflammation and Abortion by the Alarmin Heme in Mice

Both infectious as non-infectious inflammation can cause placental dysfunction and pregnancy complications. During the first trimester of human gestation, when palatogenesis takes place, intrauterine hematoma and hemorrhage are common phenomena, causing the release of large amounts of heme, a well-known alarmin. We postulated that exposure of pregnant mice to heme during palatogenesis would initiate oxidative and inflammatory stress, leading to pathological pregnancy, increasing the incidence of palatal clefting and abortion. Both heme oxygenase isoforms (HO-1 and HO-2) break down heme, thereby generating anti-oxidative and -inflammatory products. HO may thus counteract these heme-induced injurious stresses. To test this hypothesis, we administered heme to pregnant CD1 outbred mice at Day E12 by intraperitoneal injection in increasing doses: 30, 75 or 150 μmol/kg body weight (30H, 75H or 150H) in the presence or absence of HO-activity inhibitor SnMP from Day E11. Exposure to heme resulted in a dose-dependent increase in abortion. At 75H half of the fetuses where resorbed, while at 150H all fetuses were aborted. HO-activity protected against heme-induced abortion since inhibition of HO-activity aggravated heme-induced detrimental effects. The fetuses surviving heme administration demonstrated normal palatal fusion. Immunostainings at Day E16 demonstrated higher numbers of ICAM-1 positive blood vessels, macrophages and HO-1 positive cells in placenta after administration of 75H or SnMP + 30H. Summarizing, heme acts as an endogenous “alarmin” during pregnancy in a dose-dependent fashion, while HO-activity protects against heme-induced placental vascular inflammation and abortion.

Heme oxygenase-1 in protozoan infections: A tale of resistance and disease tolerance

Heme oxygenase (HO-1) mediates the enzymatic cleavage of heme, a molecule with proinflammatory and prooxidant properties. HO-1 activity deeply impacts host capacity to tolerate infection through reduction of tissue damage or affecting resistance, the ability of the host to control pathogen loads. In this Review, we will discuss the contribution of HO-1 in different and complex protozoan infections, such as malaria, leishmaniasis, Chagas disease, and toxoplasmosis. The complexity of these infections and the pleiotropic effects of HO-1 constitute an interesting area of study and an opportunity for drug development.

Hemophagocytosis induced by Leishmania donovani infection is beneficial to parasite survival within macrophages

Visceral leishmaniasis (VL) is caused by parasitic protozoa of the genus Leishmania and is characterized by clinical manifestations such as fever, hepatosplenomegaly and anemia. Hemophagocytosis, the phenomenon of phagocytosis of blood cells by macrophages, is found in VL patients. In a previous study we established an experimental model of VL, reproducing anemia in mice for the first time, and identified hemophagocytosis by heavily infected macrophages in the spleen as a possible cause of anemia. However, the mechanism for parasite-induced hemophagocytosis or its role in parasite survival remained unclear. Here, we established an in vitro model of Leishmania-induced hemophagocytosis to explore the molecules involved in this process. In contrast to naïve RAW264.7 cells (mouse macrophage cell line) which did not uptake freshly isolated erythrocytes, RAW264.7 cells infected with L. donovani showed enhanced phagocytosis of erythrocytes. Additionally, for hemophagocytes found both in vitro and in vivo, the expression of signal regulatory protein α (SIRPα), one of the receptors responsible for the ‘don’t-eat-me’ signal was suppressed by post-transcriptional control. Furthermore, the overlapped phagocytosis of erythrocytes and Leishmania parasites within a given macrophage appeared to be beneficial to the parasites; the in vitro experiments showed a higher number of parasites within macrophages that had been induced to engulf erythrocytes. Together, these results suggest that Leishmania parasites may actively induce hemophagocytosis by manipulating the expression of SIRPα in macrophages/hemophagocytes, in order to secure their parasitism.

Parasites can manipulate host immune responses to build favorable environment to them. Because this parasite-driven immune modulation is often linked to symptoms in infected individuals, not only parasiticidal compounds but also immunological interventions limiting such the parasites’ abilities will serve as treatment options. In this study, we studied the mechanism and its role of hemophagocytosis (the phenomenon whereby macrophages engulf erythrocytes) caused by Leishmania donovani, a causative agent of VL. In vitro experiments revealed parasites have ability to directly disrupt macrophage’s recognition of self-cells, and that the induced engulfment of erythrocytes by L. donovani infection is beneficial to the parasites for their intracellular survival. These results suggest that Leishmania parasites actively induce hemophagocytosis by manipulating the ‘don’t-eat-me’ signal in macrophages for their survival. Although it is still to be determined how Leishmania parasites change the ‘don’t-eat-me’ signal in macrophages, our study may facilitate development of an immunotherapy which limits the change and lead to improvement of anemia due to hemophagocytosis as well as control of parasite survival.

Proteomic Analysis Reveals a Predominant NFE2L2 (NRF2) Signature in Canonical Pathway and Upstream Regulator Analysis of Leishmania-Infected Macrophages

CBA mice macrophages (MØ) control infection by Leishmania major and are susceptive to Leishmania amazonensis, suggesting that both parasite species induce distinct responses that play important roles in infection outcome. To evaluate the MØ responses to infection arising from these two Leishmania species, a proteomic study using a Multidimensional Protein Identification Technology (MudPIT) approach with liquid chromatography tandem mass spectrometry (LC-MS/MS) was carried out on CBA mice bone-marrow MØ (BMMØ). Following SEQUEST analysis, which revealed 2,838 proteins detected in BMMØ, data mining approach found six proteins significantly associated with the tested conditions. To investigate their biological significance, enrichment analysis was performed using Ingenuity Pathway Analysis (IPA). A three steps IPA approach revealed 4 Canonical Pathways (CP) and 7 Upstream Transcriptional Factors (UTFs) strongly associated with the infection process. NRF2 signatures were present in both CPs and UTFs pathways. Proteins involved in iron metabolism, such as heme oxigenase 1 (HO-1) and ferritin besides sequestosome (SQSMT1 or p62) were found in the NRF2 CPs and the NRF2 UTFs. Differences in the involvement of iron metabolism pathway in Leishmania infection was revealed by the presence of HO-1 and ferritin. Noteworty, HO-1 was strongly associated with L. amazonensis infection, while ferritin was regulated by both species. As expected, higher HO-1 and p62 expressions were validated in L. amazonensis-infected BMMØ, in addition to decreased expression of ferritin and nitric oxide production. Moreover, BMMØ incubated with L. amazonensis LPG also expressed higher levels of HO-1 in comparison to those stimulated with L. major LPG. In addition, L. amazonensis-induced uptake of holoTf was higher than that induced by L. major in BMMØ, and holoTf was also detected at higher levels in vacuoles induced by L. amazonensis. Taken together, these findings indicate that NRF2 pathway activation and increased HO-1 production, together with higher levels of holoTf uptake, may promote permissiveness to L. amazonensis infection. In this context, differences in protein signatures triggered in the host by L. amazonensis and L. major infection could drive the outcomes in distinct clinical forms of leishmaniasis.

Modulation of Iron Metabolism in Response to Infection: Twists for All Tastes

Iron is an essential nutrient for almost all living organisms, but is not easily made available. Hosts and pathogens engage in a fight for the metal during an infection, leading to major alterations in the host’s iron metabolism. Important pathological consequences can emerge from the mentioned interaction, including anemia. Several recent reports have highlighted the alterations in iron metabolism caused by different types of infection, and several possible therapeutic strategies emerge, based on the targeting of the host’s iron metabolism. Here, we review the most recent literature on iron metabolism alterations that are induced by infection, the consequent development of anemia, and the potential therapeutic approaches to modulate iron metabolism in order to correct iron-related pathologies and control the ongoing infection.