Protective role of heme oxygenase-1 in Listeria monocytogenes-induced abortion. PLoS One. 2011;6:e25046. [PMID: 21949846 PMCID: PMC3174987 DOI: 10.1371/journal.pone.0025046]

Inhibition of Heme Oxygenase-1 by Zinc Protoporphyrin IX Improves Adverse Pregnancy Outcomes in Malaria During Early Gestation

The enzyme heme oxygenase-1 (HO-1) has cytoprotective effects by catalyzing the degradation of heme to produce carbon monoxide, iron and biliverdin. Furthermore, HO-1 activity has been associated with successful pregnancy. On the other hand, in the context of certain inflammatory conditions, HO-1 can induce iron overload and cell death. To investigate the role of HO-1 in gestational malaria, pregnant BALB/c mice were infected with Plasmodium berghei ANKA in early, mid and late gestation. We found that malaria affected the pregnancy outcome in the three periods evaluated. However, only poor pregnancy outcomes in early pregnancy were related to HO-1 upregulation, iron overload, lipid peroxidation and necrosis of the decidua, which were prevented by HO-1 inhibition. In conclusion, HO-1 expression must be finely tuned in gestational malaria to avoid the deleterious effect of increased enzyme activity.

An Update Review on Listeria Infection in Pregnancy

Listeria monocytogenes (LM) is an intracellular, aerobic and facultative anaerobic, Gram-positive bacterium, which is primarily transmitted to humans orally via food. LM could occur in asymptomatic pregnant women; however, fetal infection is a serious condition, entailing premature birth, abortion, sepsis, central nervous system (CNS) involvement, or even death. If a pregnant woman exhibits symptoms, the performance is almost like influenza, such as fever, headache, diarrhea, myalgia, or other digestive-related symptoms. This review collected clinical and empirical results regarding the mechanism, clinical manifestations, obstetrical outcome, diagnosis, treatment, vertical transmission, neonatal infection, and prevention of listeriosi according to articles published in PubMed from January 1, 1980, to March 20, 2021. The early detection and diagnosis of pregnancy-associated listeriosis are significant since sensitive antibiotics are effective at enhancing the prognosis of newborns. Listeriosis can be diagnosed using positive cultures from maternal or neonatal blood, neonatal cerebrospinal fluid (CSF), amniotic fluid, intrauterine mucosa, or the placenta. Two weeks of high-dose intravenous amoxicillin (more than 6 g/day) is recommended for LM pregnant women without allergy. Terminating the pregnancy to save the mother’s life should be considered if maternal and fetal conditions aggravate. Neonatal Listeria infection is primarily transmitted through the placenta, which is a critical illness associated with a high mortality rate. The necessary dietary guidance for pregnant women can reduce the incidence rate of pregnancy-related listeriosis.

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.

Haem oxygenases play a pivotal role in placental physiology and pathology

BACKGROUND

Haem oxygenases (HO) catabolise haem, which is the prosthetic group of numerous haemoproteins. Thus, multiple primary cellular pathways and functions rely on haem availability. HO exists in two isoforms, both expressed in the placenta, namely HO-1 and HO-2, the first being inducible. Haem oxygenases, particularly HO-1, have garnered specific interest in the field of physiological and pathological placental function. These enzymes mediate haem degradation by cleaving the alpha methene bridge to produce biliverdin, which is subsequently converted to bilirubin, carbon monoxide and iron. HO-1 has anti-inflammatory and antioxidant activities.

SEARCH METHODS

An initial literature analysis was performed using PubMed on 3 October 2018 using key terms such as 'haem oxygenase and pregnancy', 'haem oxygenase and placenta', 'HO-1 and pregnancy', 'HO-1 and placenta', 'HO and placenta', 'HO and pregnancy', 'genetic variant and HO', 'CO and pregnancy', 'CO and placenta', 'Bilirubin and pregnancy', 'Iron and pregnancy' and 'PPAR and Haem', selecting consensus conferences, recommendations, meta-analyses, practical recommendations and reviews. A second literature analysis was performed, including notable miscarriages, foetal loss and diabetes mellitus, on 20 December 2019. The three authors studied the publications independently to decipher whether they should be included in the manuscript.

OBJECTIVE AND RATIONALE

This review aimed to summarise current pieces of knowledge of haem oxygenase location, function and regulation in the placenta, either in healthy pregnancies or those associated with miscarriages and foetal loss, pre-eclampsia, foetal growth restriction and diabetes mellitus.

OUTCOMES

HO-1 exerts some protective effects on the placentation, probably by a combination of factors, including its interrelation with the PGC-1α/PPAR pathway and the sFlt1/PlGF balance, and through its primary metabolites, notably carbon monoxide and bilirubin. Its protective role has been highlighted in numerous pregnancy conditions, including pre-eclampsia, foetal growth restriction, gestational diabetes mellitus and miscarriages.

WIDER IMPLICATIONS

HO-1 is a crucial enzyme in physiological and pathological placentation. This protective enzyme is currently considered a potential therapeutic target in various pregnancy diseases.

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.

Microbial detection and identification methods: Bench top assays to omics approaches

Rapid detection of foodborne pathogens, spoilage microbes, and other biological contaminants in complex food matrices is essential to maintain food quality and ensure consumer safety. Traditional methods involve culturing microbes using a range of nonselective and selective enrichment methods, followed by biochemical confirmation among others. The time-to-detection is a key limitation when testing foods, particularly those with short shelf lives, such as fresh meat, fish, dairy products, and vegetables. Some recent detection methods developed include the use of spectroscopic techniques, such as matrix-assisted laser desorption ionization-time of flight along with hyperspectral imaging protocols.This review presents a comprehensive overview comparing insights into the principles, characteristics, and applications of newer and emerging techniques methods applied to the detection and identification of microbes in food matrices, to more traditional benchtop approaches. The content has been developed to provide specialist scientists a broad view of bacterial identification methods available in terms of their benefits and limitations, which may be useful in the development of future experimental design. The case is also made for incorporating some of these emerging methods into the mainstream, for example, underutilized potential of spectroscopic techniques and hyperspectral imaging.

Bacteroides fragilis enterotoxin upregulates heme oxygenase-1 in dendritic cells via reactive oxygen species-, mitogen-activated protein kinase-, and Nrf2-dependent pathway

BACKGROUND

Enterotoxigenic Bacteroides fragilis (ETBF) causes colitis and diarrhea, and is considered a candidate pathogen in inflammatory bowel diseases as well as colorectal cancers. These diseases are dependent on ETBF-secreted toxin (BFT). Dendritic cells (DCs) play an important role in directing the nature of adaptive immune responses to bacterial infection and heme oxygenase-1 (HO-1) is involved in the regulation of DC function.

AIM

To investigate the role of BFT in HO-1 expression in DCs.

METHODS

Murine DCs were generated from specific pathogen-free C57BL/6 and Nrf2^−/− knockout mice. DCs were exposed to BFT, after which HO-1 expression and the related signaling factor activation were measured by quantitative RT-PCR, EMSA, fluorescent microscopy, immunoblot, and ELISA.

RESULTS

HO-1 expression was upregulated in DCs stimulated with BFT. Although BFT activated transcription factors such as NF-κB, AP-1, and Nrf2, activation of NF-κB and AP-1 was not involved in the induction of HO-1 expression in BFT-exposed DCs. Instead, upregulation of HO-1 expression was dependent on Nrf2 activation in DCs. Moreover, HO-1 expression via Nrf2 in DCs was regulated by mitogen-activated protein kinases such as ERK and p38. Furthermore, BFT enhanced the production of reactive oxygen species (ROS) and inhibition of ROS production resulted in a significant decrease of phospho-ERK, phospho-p38, Nrf2, and HO-1 expression.

CONCLUSION

These results suggest that signaling pathways involving ROS-mediated ERK and p38 mitogen-activated protein kinases-Nrf2 activation in DCs are required for HO-1 induction during exposure to ETBF-produced BFT.

Heme-Oxygenase-1 Expression Contributes to the Immunoregulation Induced by Fasciola hepatica and Promotes Infection

Fasciola hepatica, also known as the liver fluke, is a trematode that infects livestock and humans causing fasciolosis, a zoonotic disease of increasing importance due to its worldwide distribution and high economic losses. This parasite immunoregulates the host immune system by inducing a strong Th2 and regulatory T immune response by immunomodulating dendritic cell (DC) maturation and alternative activation of macrophages. In this paper, we show that F. hepatica infection in mice induces the upregulation of heme-oxygenase-1 (HO-1), the rate-limiting enzyme in the catabolism of free heme that regulates the host inflammatory response. We show and characterize two different populations of antigen presenting cells that express HO-1 during infection in the peritoneum of infected animals. Cells that expressed high levels of HO-1 expressed intermediate levels of F4/80 but high expression of CD11c, CD38, TGFβ, and IL-10 suggesting that they correspond to regulatory DCs. On the other hand, cells expressing intermediate levels of HO-1 expressed high levels of F4/80, CD68, Ly6C, and FIZZ-1, indicating that they might correspond to alternatively activated macrophages. Furthermore, the pharmacological induction of HO-1 with the synthetic metalloporphyrin CoPP promoted F. hepatica infection increasing the clinical signs associated with the disease. In contrast, treatment with the HO-1 inhibitor SnPP protected mice from parasite infection, indicating that HO-1 plays an essential role during F. hepatica infection. Finally, HO-1 expression during F. hepatica infection was associated with TGFβ and IL-10 levels in liver and peritoneum, suggesting that HO-1 controls the expression of these immunoregulatory cytokines during infection favoring parasite survival in the host. These results contribute to the elucidation of the immunoregulatory mechanisms induced by F. hepatica in the host and provide alternative checkpoints to control fasciolosis.

Tim-3 inhibits macrophage control of Listeria monocytogenes by inhibiting Nrf2

T cell immunoglobulin mucin-3 (Tim-3) is an immune checkpoint inhibitor and its dysregulation has been related to T cell tolerance and many immune disorders, such as tumors and infection tolerance. However, the physiopathology roles of Tim-3 in innate immunity remain elusive. Here, we demonstrate that Tim-3 inhibits macrophage phagocytosis of L. monocytogenes by inhibiting the nuclear erythroid 2-related factor 2 (Nrf2) signaling pathway and increases bacterial burden. Tim-3 signaling promotes Nrf2 degradation by increasing its ubiquitination and, as a result, decreasing its nuclear translocation. CD36 and heme oxygenase-1 (HO-1), two downstream molecules in the Tim-3-Nrf2 signaling axis, are involved in the Tim-3- mediated immune evasion of L. monocytogenes both in vitro and in vivo. We here identified new mechanisms by which Tim-3 induces infection tolerance. By modulating the Tim-3 pathway, we demonstrate the feasibility of manipulating macrophage function as a potent tool for treating infectious diseases, such as Listeria infection.

Heme oxygenase/carbon monoxide in the female reproductive system: an overlooked signalling pathway

For a long time, carbon monoxide (CO) was known for its toxic effect on organisms. But there are still many things left to discover on that molecule. CO is formed directly in the body by the enzymatic activity of heme oxygenase (HO). CO plays an important role in many physiological processes, such as cell protections (against various stress factors), and the regulation of metabolic processes. Recent research proves that CO also operates in the female reproductive system. At the centre of interest is the importance of CO for gestation. During the gestation period, CO is an important element affecting the proper function of the feto-placental unit and generally affects fetal survivability rates. Gestation is one of the most important processes of successful reproduction, although there are more relevant processes that need to be researched. While already proven that CO influences steroidogenesis and the corpus luteum survivability rate, our knowledge concerning the function and importance of CO in the reproductive system is still relatively limited. As an example, our knowledge of CO function in an oocyte, the most important cell for reproduction, is almost non-existent. The aim of this review is to summarize our current knowledge concerning the function of CO in the female reproductive system.

Heme Oxygenase-1 Deficiency Diminishes Methicillin-Resistant Staphylococcus aureus Clearance Due to Reduced TLR9 Expression in Pleural Mesothelial Cells

Methicillin Resistant Staphylococcus aureus (MRSA) cause pneumonia and empyema thoraces. TLR9 activation provides protection against bacterial infections and Heme oxygenase-1 (HO-1) is known to enhance host innate immunity against bacterial infections. However, it is still unclear whether HO-1 regulates TLR-9 expression in the pleura and modulates the host innate defenses during MRSA empyema. In order to determine if HO-1 regulates host innate immune functions via modulating TLR expression, in MRSA empyema, HO-1+/+ and HO-1-/- mouse pleural mesothelial cells (PMCs) were infected with MRSA (1:10, MOI) in the presence or absence of Cobalt Protoporphyrin (CoPP) and Zinc Protoporphyrin (ZnPP) or CORM-2 (a Carbon monoxide donor) and the expression of mTLR9 and mBD14 was assessed by RT-PCR. In vivo, HO-1+/+ and HO-1-/- mice were inoculated with MRSA (5x106 CFU) intra-pleurally and host bacterial load was measured by CFU, and TLR9 expression in the pleura was determined by histochemical-immunostaining. We noticed MRSA inducing differential expression of TLR9 in HO-1+/+ and HO-1 -/- PMCs. In MRSA infected HO-1+/+ PMCs, TLR1, TLR4, and TLR9 expression was several fold higher than MRSA infected HO-1-/- PMCs. Particularly TLR9 expression was very low in MRSA infected HO-1-/- PMCs both in vivo and in vitro. Bacterial clearance was significantly higher in HO-1+/+ PMCs than compared to HO-1-/- PMCs in vitro, and blocking TLR9 activation diminished MRSA clearance significantly. In addition, HO-1-/- mice were unable to clear the MRSA bacterial load in vivo. MRSA induced TLR9 and mBD14 expression was significantly high in HO-1+/+ PMCs and it was dependent on HO-1 activity. Our findings suggest that HO-1 by modulating TLR9 expression in PMCs promotes pleural innate immunity in MRSA empyema.

Modulation of antigen processing by haem-oxygenase 1. Implications on inflammation and tolerance

Haem-oxygenase-1 (HO-1) is an enzyme responsible for the degradation of haem that can suppress inflammation, through the production of carbon monoxide (CO). It has been shown in several experimental models that genetic and pharmacological induction of HO-1, as well as non-toxic administration of CO, can reduce inflammatory diseases, such as endotoxic shock, type 1 diabetes and graft rejection. Recently, it was shown that the HO-1/CO system can alter the function of antigen-presenting cells (APCs) and reduce T-cell priming, which can be beneficial during immune-driven inflammatory diseases. The molecular mechanisms by which the HO-1 and CO reduce both APC- and T-cell-driven immunity are just beginning to be elucidated. In this article we discuss recent findings related to the immune regulatory capacity of HO-1 and CO at the level of recognition of pathogen-associated molecular patterns and T-cell priming by APCs. Finally, we propose a possible regulatory role for HO-1 and CO over the recently described mitochondria-dependent immunity. These concepts could contribute to the design of new therapeutic tools for inflammation-based diseases.

Heme Oxygenase-1 Regulates Inflammation and Mycobacterial Survival in Human Macrophages during Mycobacterium tuberculosis Infection

Mycobacterium tuberculosis, the causative agent of tuberculosis, is responsible for 1.5 million deaths annually. We previously showed that M. tuberculosis infection in mice induces expression of the CO-producing enzyme heme oxygenase (HO1) and that CO is sensed by M. tuberculosis to initiate a dormancy program. Further, mice deficient in HO1 succumb to M. tuberculosis infection more readily than do wild-type mice. Although mouse macrophages control intracellular M. tuberculosis infection through several mechanisms, such as NO synthase, the respiratory burst, acidification, and autophagy, how human macrophages control M. tuberculosis infection remains less well understood. In this article, we show that M. tuberculosis induces and colocalizes with HO1 in both mouse and human tuberculosis lesions in vivo, and that M. tuberculosis induces and colocalizes with HO1 during primary human macrophage infection in vitro. Surprisingly, we find that chemical inhibition of HO1 both reduces inflammatory cytokine production by human macrophages and restricts intracellular growth of mycobacteria. Thus, induction of HO1 by M. tuberculosis infection may be a mycobacterial virulence mechanism to enhance inflammation and bacterial growth.

NLRP3 inflammasome activation contributes to Listeria monocytogenes-induced animal pregnancy failure

Background

Listeria monocytogenes (LM), a foodborne pathogen, can cause pregnancy failure in animals, especially in ruminants. Recent studies have shown that LM activates inflammasomes to induce IL-1β release in macrophages, however, whether the inflammasome activation regulates LM-induced pregnancy failure remains largely unknown. Here we used mouse model to investigate the molecular mechanism by which LM-induced inflammsome activation contributes to LM-associated pregnancy failure

Results

We showed that wild-type, but not Listeriolysin O-deficient (Δhly) LM, significantly reduced mouse embryo survival, accompanied by the increase of IL-1β release and caspase-1 activation. IL-1β neutralization significantly reduced the LM-induced embryo losses, suggesting that LM-induced pregnancy failure was associated with LLO-induced inflammasome activation. To dissect the inflammasome sensor and components responsible for LM-induced caspase-1 activation and IL-1β production, we used wild-type and NLRP3^−/−, AIM2^−/−, NLRC4^−/−, ASC^−/−, caspase-1^−/− and cathepsin B^−/− mouse macrophages to test the roles of these molecules in LM-induce IL-1β production. We found that NLRP3 inflammasome was the main pathway in LM-induced caspase-1 activation and IL-1β production. To explore the mechanism of LM-induced pregnancy failure, we investigated the effects of LM-infected macrophages on SM9-1 mouse trophoblasts. We found that the conditioned medium from LM-infected-macrophage or the recombinant IL-1β significantly up-regulated TNFα, IL-6 and IL-8 productions in trophoblasts, suggesting that the LM-induced macrophage inflammasome activation increased trophoblast pro-inflammatory cytokine production, which was adverse to the animal pregnancy maintenance.

Conclusions

Our data demonstrated that the LLO-induced NLRP3 inflammasome activation plays a key role in LM-induced pregnancy failure, and inflammasome-mediated macrophage dysregulation on trophoblasts might be involved in the pregnancy failure.

Inactivation of the MAPK signaling pathway by Listeria monocytogenes infection promotes trophoblast giant cell death

Listeria monocytogenes has a well-characterized ability to cross the placental barrier, resulting in spontaneous abortion and fetal infections. However, the mechanisms resulting in infection-associated abortion are not fully understood. In this study, we demonstrate that the dephosphorylation of MAPK family proteins caused by L. monocytogenes infection of trophoblast giant (TG) cells, which are placental immune cells, contributes to infectious abortion. Dephosphorylation of c-Jun, p38, and ERK1/2 was observed in infected TG cells, causing the downregulation of cytoprotective heme oxygenase (HO)-1. Blocking the dephosphorylation of proteins, including MAPK family proteins, inhibited the decrease in HO-1 expression. Treatment with MAPK inhibitors inhibited bacterial internalization into TG cells. Moreover, Toll-like receptor 2 involved in the expression of MAPK family proteins. Infection with a listeriolysin O-deleted mutant impaired dephosphorylation of MAPK family proteins in TG cells and did not induce infectious abortion in a mouse model. These results suggest that inactivation of the MAPK pathway by L. monocytogenes induces TG cell death and causes infectious abortion.

Heme oxygenase and the immune system in normal and pathological pregnancies

Normal pregnancy is an immunotolerant state. Many factors, including environmental, socioeconomic, genetic, and immunologic changes by infection and/or other causes of inflammation, may contribute to inter-individual differences resulting in a normal or pathologic pregnancy. In particular, imbalances in the immune system can cause many pregnancy-related diseases, such as infertility, abortions, pre-eclampsia, and preterm labor, which result in maternal/fetal death, prematurity, or small-for-gestational age newborns. New findings imply that myeloid regulatory cells and regulatory T cells (Tregs) may mediate immunotolerance during normal pregnancy. Effector T cells (Teffs) have, in contrast, been implicated to cause adverse pregnancy outcomes. Furthermore, feto-maternal tolerance affects the developing fetus. It has been shown that the Treg/Teff balance affects litter size and adoptive transfer of pregnancy-induced Tregs can prevent fetal rejection in the mouse. Heme oxygenase-1 (HO-1) has a protective role in many conditions through its anti-inflammatory, anti-apoptotic, antioxidative, and anti-proliferative actions. HO-1 is highly expressed in the placenta and plays a role in angiogenesis and placental vascular development and in regulating vascular tone in pregnancy. In addition, HO-1 is a major regulator of immune homeostasis by mediating crosstalk between innate and adaptive immune systems. Moreover, HO-1 can inhibit inflammation-induced phenotypic maturation of immune effector cells and pro-inflammatory cytokine secretion and promote anti-inflammatory cytokine production. HO-1 may also be associated with T-cell activation and can limit immune-based tissue injury by promoting Treg suppression of effector responses. Thus, HO-1 and its byproducts may protect against pregnancy complications by its immunomodulatory effects, and the regulation of HO-1 or its downstream effects has the potential to prevent or treat pregnancy complications and prematurity.

Interferon γ-induced GTPase promotes invasion of Listeria monocytogenes into trophoblast giant cells

Listeria monocytogenes is well known for having the ability to cross the placental barrier, leading to fetal infections and abortion. However, the mechanisms leading to infectious abortion are poorly understood. In this study, we demonstrate that interferon γ-induced GTPase (IGTP) contributes to the invasion of L. monocytogenes into trophoblast giant (TG) cells, which are placental immune cells. Knockdown of IGTP in TG cells decreased the relative efficiencies of L. monocytogenes invasion. Moreover, IGTP accumulated around infected L. monocytogenes in TG cells. Treatment of TG cells with phosphatidylinositol 3-kinase (PI3K)/Akt inhibitors also reduced bacterial invasion. PI3K/Akt inhibitor or IGTP knockdown reduced the amount of phosphorylated Akt. Monosialotetrahexosylganglioside (GM1) gangliosides, lipid raft markers, accumulated in the membrane of L. monocytogenes-containing vacuoles in TG cells. Furthermore, treatment with a lipid raft inhibitor reduced bacterial invasion. These results suggest that IGTP-induced activation of the PI3K/Akt signaling pathway promotes bacterial invasion into TG cells.

Heme oxygenase-1 is critically involved in placentation, spiral artery remodeling, and blood pressure regulation during murine pregnancy

The onset of pregnancy implies the appearance of a new organ, the placenta. One main function of the placenta is to supply oxygen to the fetus via hemoproteins. In this review, we highlight the importance of the enzyme heme oxygenase-1 (HO-1) for pregnancy to be established and maintained. HO-1 expression is pivotal to promote placental function and fetal development, thus determining the success of pregnancy. The deletion of the gene Hmox1 in mice leads to inadequate remodeling of spiral arteries and suboptimal placentation followed by intrauterine growth restriction (IUGR) and fetal lethality. A partial Hmox1 deletion leads to IUGR as well, with heterozygote and wild-type fetuses being born, but Hmox1 (-/-) significantly below the expected Mendelian rate. This strong phenotype is associated with diminished number of pregnancy-protective uterine natural killer (uNK) cells. Pregnant heterozygote females develop gestational hypertension. The protective HO-1 effects on placentation and fetal growth can be mimicked by the exogenous administration of carbon monoxide (CO), a product of heme catalyzed by HO-1. CO application promotes the in situ proliferation of uNK cells, restores placentation and fetal growth, while normalizing blood pressure. Similarly, HO-1 inhibition provokes hypertension in pregnant rats. The HO-1/CO axis plays a pivotal role in sustaining pregnancy and aids in the understanding of the biology of pregnancy and reveals a promising therapeutic application in the treatment of pregnancy complications.

Effects of heme oxygenase-1 on innate and adaptive immune responses promoting pregnancy success and allograft tolerance

The heme-degrading enzyme heme oxygenase-1 (HO-1) has cytoprotective, antioxidant, and anti-inflammatory properties. Moreover, HO-1 is reportedly involved in suppressing destructive immune responses associated with inflammation, autoimmune diseases, and allograft rejection. During pregnancy, maternal tolerance to foreign fetal antigens is a prerequisite for successful embryo implantation and fetal development. Here, HO-1 has been implicated in counteracting the overwhelming inflammatory immune responses towards fetal allo-antigens, thereby contributing to fetal acceptance. Accordingly, HO-1 ablation negatively impacts the critical steps of pregnancy such as fertilization, implantation, placentation, and fetal growth. In the present review, we summarize recent data on the immune modulatory capacity of HO-1 towards allo-antigens expressed by the semi-allogeneic fetus and organ allografts. In this regard, HO-1 has been shown to promote alloantigen tolerance by blocking dendritic cell maturation resulting in reduced T cell responses and increased numbers of regulatory T cells. Moreover, HO-1 is suggested to shift the uterine cytokine milieu towards a protective Th2 profile and protects fetal tissue from apoptosis by upregulating anti-apoptotic molecules. Thus, HO-1 is not only a pivotal regulator of the initial steps of pregnancy; but also, an important player in supporting the maternal immune system in tolerating the fetus.

The heme oxygenases: important regulators of pregnancy and preeclampsia

The heme oxygenase system has long been believed to act largely as a housekeeping unit, converting prooxidant free heme from heme protein degradation into the benign bilirubin for conjugation and safe excretion. In recent decades, however, heme oxygenases have emerged as important regulators of cardiovascular function, largely through the production of their biologically active metabolites: carbon monoxide, bilirubin, and elemental iron. Even more recently, a number of separate lines of evidence have demonstrated an important role for the heme oxygenases in the establishment and maintenance of pregnancy. Early preclinical and clinical studies have associated defects in the heme oxygenase with the obstetrical complication preeclampsia, as well as failure to establish adequate placental blood flow, an underlying mechanism of the disorder. Several recent preclinical studies have suggested, however, that the heme oxygenase system could serve as a valuable therapeutic tool for the management of preeclampsia, which currently has few pharmacological options. This review will summarize the role of heme oxygenases in pregnancy and highlight their potential in advancing the management of patients with preeclampsia.

Heme oxygenase in pregnancy and preeclampsia

PURPOSE OF REVIEW

Emerging evidence supports an important role for the heme oxygenase system in the maintenance of a healthy pregnancy. This review attempts to collect these wide-ranging data and summarize the recent progress in the field.

RECENT FINDINGS

New studies looking at heme oxygenase depletion in a variety of animal models have demonstrated that the heme oxygenase system is an important regulator of placental development, particularly in vascular structure. Furthermore, emerging studies demonstrate a role for heme oxygenase in the maintenance of pregnancy, especially during pathological challenge. Intriguingly, it now appears that the heme oxygenase system can be dramatically altered by pathological disorders of pregnancy, in particular preeclampsia, perhaps functionally in the symptomatic phase of the disorder. Promisingly, however, recent data suggest that induction of the heme oxygenase system, or administration of its bioactive metabolites, could provide a promising novel therapeutic approach to the management of this currently untreatable disease.

SUMMARY

Long considered a molecular housekeeping system, the heme oxygenase system is now known to be an important stress response pathway. New evidence suggests that it is also an important player in pregnancy and preeclampsia. However, the evidence now also suggests that it may provide a therapeutic approach for this common disease with few management options.

Regulation of inducible heme oxygenase and cyclooxygenase isozymes in a mouse model of spotted fever group rickettsiosis

Vascular endothelial cells (ECs) lining the blood vessels are the preferred primary targets of pathogenic Rickettsia species in the host. In response to oxidative stress triggered by infection, ECs launch defense mechanisms such as expression of heme oxygenase-1 (HO-1). Previous evidence from an established animal model of Rocky Mountain spotted fever also suggests selective modulation of anti-oxidant enzyme activities in the target host tissues. In this study, we have examined the expression profiles of HO-1 and COX-2 in different tissues during Rickettsia conorii infection of susceptible C3H/HeN mice. RNA hybridization with murine HO-1 and COX-2-specific complementary DNA probes revealed increased HO-1 expression in the liver and brain of mice infected with three different doses of R. conorii ranging from 2.25×10(3) to 2.25×10(5) pfu, relatively non-remarkable changes in the lungs, and a trend for down-regulation in the spleen. The most prominent HO-1 response was evident in the liver with ∼4-fold increase on day 4 post-infection, followed by a decline on day 7. HO-1 expression in the brain, however, peaked with significantly higher levels on day 7. Following infection with both sub-lethal as well as lethal doses of infection, the transcript encoding COX-2 also displayed a pattern of increased expression in the liver and brain. Although immunohistochemical staining revealed increased abundance of HO-1 protein in the liver of infected mice, adjoining serial sections did not exhibit positive staining for COX-2 in infected tissues. The levels of monocyte chemoattractant protein-1 (MCP-1) and keratinocyte-derived cytokine (KC) were significantly higher in the sera of infected mice and corresponded with the onset and severity of the disease. Treatment of infected animals with anti-oxidants α-lipoic acid and N-acetylcysteine and HO inhibitor stannous protoporphyrin (SnPPIX) showed only selective beneficial effects on HO-1 and COX-2 expression in the liver and spleen and serum levels of KC and MCP-1. R. conorii infection of susceptible mice, therefore, results in selective regulation of the expression of HO-1 and COX-2 in a manner dependent on the target host tissue's cellular environment and the propensity of infection with rickettsiae.