Novel regulatory sites of the human heme oxygenase-1 promoter region

Novel Acetamide-Based HO-1 Inhibitor Counteracts Glioblastoma Progression by Interfering with the Hypoxic-Angiogenic Pathway

Glioblastoma multiforme (GBM) represents the deadliest tumor among brain cancers. It is a solid tumor characterized by uncontrolled cell proliferation generating the hypoxic niches in the cancer core. By inducing the transcription of hypoxic inducible factor (HIF), hypoxia triggers many signaling cascades responsible for cancer progression and aggressiveness, including enhanced expression of vascular endothelial growth factor (VEGF) or antioxidant enzymes, such as heme oxygenase-1 (HO-1). The present work aimed to investigate the link between HO-1 expression and the hypoxic microenvironment of GBM by culturing two human glioblastoma cell lines (U87MG and A172) in the presence of a hypoxic mimetic agent, deferoxamine (DFX). By targeting hypoxia-induced HO-1, we have tested the effect of a novel acetamide-based HO-1 inhibitor (VP18/58) on GBM progression. Results have demonstrated that hypoxic conditions induced upregulation and nuclear expression of HO-1 in a cell-dependent manner related to malignant phenotype. Moreover, our data demonstrated that the HO-1 inhibitor counteracted GBM progression by modulating the HIFα/HO-1/VEGF signaling cascade in cancer cells bearing more malignant phenotypes.

Clinical Significance of Heme Oxygenase 1 in Tumor Progression

Heme oxygenase 1 (HO-1) plays a key role in cell adaptation to stressors through the antioxidant, antiapoptotic, and anti-inflammatory properties of its metabolic products. For these reasons, in cancer cells, HO-1 can favor aggressiveness and resistance to therapies, leading to poor prognosis/outcome. Genetic polymorphisms of HO-1 promoter have been associated with an increased risk of cancer progression and a high degree of therapy failure. Moreover, evidence from cancer biopsies highlights the possible correlation between HO-1 expression, pathological features, and clinical outcome. Indeed, high levels of HO-1 in tumor specimens often correlate with reduced survival rates. Furthermore, HO-1 modulation has been proposed in order to improve the efficacy of antitumor therapies. However, contrasting evidence on the role of HO-1 in tumor biology has been reported. This review focuses on the role of HO-1 as a promising biomarker of cancer progression; understanding the correlation between HO-1 and clinical data might guide the therapeutic choice and improve the outcome of patients in terms of prognosis and life quality.

The Role of Heme Oxygenase-1 Promoter Polymorphisms in Perinatal Disease

Heme oxygenase (HO) is the rate-limiting enzyme in the heme catabolic pathway, which degrades heme into equimolar amounts of carbon monoxide, free iron, and biliverdin. Its inducible isoform, HO-1, has multiple protective functions, including immune modulation and pregnancy maintenance, showing dynamic alteration during perinatal periods. As its contribution to the development of perinatal complications is speculated, two functional polymorphisms of the HMOX1 gene, (GT)_n repeat polymorphism (rs3074372) and A(-413)T single nucleotide polymorphism (SNP) (rs2071746), were studied for their association with perinatal diseases. We systematically reviewed published evidence on HMOX1 polymorphisms in perinatal diseases and clarified their possible significant contribution to neonatal jaundice development, presumably due to their direct effect of inducing HO enzymatic activity in the bilirubin-producing pathway. However, the role of these polymorphisms seems limited for other perinatal complications such as bronchopulmonary dysplasia. We speculate that this is because the antioxidant or anti-inflammatory effect is not directly mediated by HO but by its byproducts, resulting in a milder effect. For better understanding, subtyping each morbidity by the level of exposure to causative environmental factors, simultaneous analysis of both polymorphisms, and the unified definition of short and long alleles in (GT)_n repeats based on transcriptional capacity should be further investigated.

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.

The non-canonical functions of the heme oxygenases

Heme oxygenase (HO) isoforms catalyze the conversion of heme to carbon monoxide (CO) and biliverdin with a concurrent release of iron, which can drive the synthesis of ferritin for iron sequestration. Most of the studies so far were directed at evaluating the protective effect of these enzymes because of their ability to generate antioxidant and antiapoptotic molecules such as CO and bilirubin. Recent evidences are suggesting that HO may possess other important physiological functions, which are not related to its enzymatic activity and for which we would like to introduce for the first time the term “non canonical functions”. Recent evidence suggest that both HO isoforms may form protein-protein interactions (i.e. cytochrome P450, adiponectin, CD91) thus serving as chaperone-like protein. In addition, truncated HO-1 isoform was localized in the nuclear compartment under certain experimental conditions (i.e. excitotoxicity, hypoxia) regulating the activity of important nuclear transcription factors (i.e. Nrf2) and DNA repair. In the present review, we discuss three potential signaling mechanisms that we refer to as the non-canonical functions of the HO isoforms: protein-protein interaction, intracellular compartmentalization, and extracellular secretion. The aim of the present review is to describe each of this mechanism and all the aspects warranting additional studies in order to unravel all the functions of the HO system.

Withaferin A induces Nrf2-dependent protection against liver injury: Role of Keap1-independent mechanisms

Small molecules of plant origin offer presumptively safe opportunities to prevent carcinogenesis, mutagenesis and other forms of toxicity in humans. However, the mechanisms of action of such plant-based agents remain largely unknown. In recent years the stress responsive transcription factor Nrf2 has been validated as a target for disease chemoprevention. Withania somnifera (WS) is a herb used in Ayurveda (an ancient form of medicine in South Asia). In the recent past, withanolides isolated from WS, such as Withaferin A (WA) have been demonstrated to be preventive and therapeutic against multiple diseases in experimental models. The goals of this study are to evaluate withanolides such as WA as well as Withania somnifera root extract as inducers of Nrf2 signaling, to probe the underlying signaling mechanism of WA and to determine whether prevention of acetaminophen (APAP)-induced hepatic toxicity in mice by WA occurs in an Nrf2-dependent manner. We observed that WA profoundly protects wild-type mice but not Nrf2-disrupted mice against APAP hepatotoxicity. WA is a potent inducer of Nrf2-dependent cytoprotective enzyme expression both in vivo and in vitro. Unexpectedly, WA induces Nrf2 signaling at least in part, in a Keap1-independent, Pten/Pi3k/Akt-dependent manner in comparison to prototypical Nrf2 inducers, sulforaphane and CDDO-Im. The identification of WA as an Nrf2 inducer that can signal through a non-canonical, Keap1-independent pathway provides an opportunity to evaluate the role of other regulatory partners of Nrf2 in the dietary and pharmacological induction of Nrf2-mediated cytoprotection.

Impact of Staphylococcus epidermidis lysates on middle ear epithelial proinflammatory and mucogenic response

BACKGROUND

Chronic otitis media with effusion (COME) develops after sustained inflammation and is characterized by secretory middle ear epithelial metaplasia and effusion, most frequently mucoid. Staphylococcus epidermidis, typically considered a commensal organism, is very frequently recovered in chronic middle ear fluid and in middle ear biofilms. Although it has been shown to drive inflammation in sinonasal epithelium, the impact of S. epidermidis on COME is markedly understudied. The goal of this study was to examine the in vitro effects of S. epidermidis lysates on murine and human middle ear epithelial cells.

METHODS

Staphylococcus epidermidis lysates were generated and used to stimulate submerged and differentiated human and murine epithelial cells (MEECs) for 24 to 48 hours. Quantitative real time-polymerase chain reaction, Western blot, enzyme-linked immunosorbent assay, and immunocytochemistry techniques were performed to interrogate the mucin gene MUC5AC and MUC5B expression and protein production, chemokine response, as well as NF-κB activation. Luciferase reporter assays were performed to further evaluate nuclear factor κB (NF-κB) activation and query specific promoter responses after S. epidermidis exposure.

RESULTS

Staphylococcus epidermidis induced a time- and dose-dependent MUC5AC and MUC5B overexpression along with a parallel overexpression of Cxcl2 in mouse MEEC and IL-8 in human MEEC. Further investigations in mMEEC showed a 1.3 to 1.5 induction of the MUC5AC and MUC5B promoters. As potential mechanisms for these responses, induction of an oxidative stress marker, along with early nuclear translocation and activation of NF-κB, was found. Finally, chronic exposure induced marked epithelial thickening of cells differentiated at the air liquid interface.

CONCLUSIONS

Staphylococcus epidermidis lysates activate a proinflammatory response in MEEC, including mucin gene expression and protein production. Although typically considered a nonpathogenic commensal organism in the ear, these results suggest that they may play a role in the perpetuation of an inflammatory and mucogenic response in COME.

Heme oxygenase-1 dysregulation in the brain: implications for HIV-associated neurocognitive disorders

Heme oxygenase-1 (HO-1) is a highly inducible and ubiquitous cellular enzyme that subserves cytoprotective responses to toxic insults, including inflammation and oxidative stress. In neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and multiple sclerosis, HO-1 expression is increased, presumably reflecting an endogenous neuroprotective response against ongoing cellular injury. In contrast, we have found that in human immunodeficiency virus (HIV) infection of the brain, which is also associated with inflammation, oxidative stress and neurodegeneration, HO-1 expression is decreased, likely reflecting a unique role for HO-1 deficiency in neurodegeneration pathways activated by HIV infection. We have also shown that HO-1 expression is significantly suppressed by HIV replication in cultured macrophages which represent the primary cellular reservoir for HIV in the brain. HO-1 deficiency is associated with release of neurotoxic levels of glutamate from both HIV-infected and immune-activated macrophages; this glutamate-mediated neurotoxicity is suppressed by pharmacological induction of HO-1 expression in the macrophages. Thus, HO-1 induction could be a therapeutic strategy for neuroprotection against HIV infection and other neuroinflammatory brain diseases. Here, we review various stimuli and signaling pathways regulating HO-1 expression in macrophages, which could promote neuronal survival through HO-1-modulation of endogenous antioxidant and immune modulatory pathways, thus limiting the oxidative stress that can promote HIV disease progression in the CNS. The use of pharmacological inducers of endogenous HO-1 expression as potential adjunctive neuroprotective therapeutics in HIV infection is also discussed.

Cholinergic precursors modulate the expression of heme oxigenase-1, p21 during astroglial cell proliferation and differentiation in culture

Heme oxygenase-1 (HO-1) plays a crucial role in oxidative stress processes, apoptosis and cell differentiation. Further, some proteins related to cell cycle including cyclins and p21 are important markers of astrocyte cultures. Aim of investigation was to study the effects of cholinergic precursors (choline, CDP-choline, Acetylcholine and α-Glyceril-Phosphorylcholine) on HO-1 and p21 expression during astroglial cell proliferation and differentiation in primary cultures at 14 and 35 days in vitro (DIV) treated for 24 h with choline metabolites. Our results showed a slight reduction of HO-1 expression (data not statistical significant) in astroglial cell cultures treated with CDP-choline at 14 DIV and 35 DIV. On the contrary, ACh and choline induced a significant increase of HO-1 expression in 14 DIV astrocyte cultures. Surprisingly, choline and ACh dramatically reduced HO-1 expression at 35 DIV. A slight decrease not statistical significant was detectable for α-GPC at 14 DIV and particularly significant at 35 DIV. Data concerning p21 expression, a well known protein inhibiting cell cycle, evidenced a significant increase at 14 and 35 DIV after α-GPC treatment. CDP-choline treatment caused a high increase of p21 expression in 14 DIV astrocyte cultures, but no modification at 35 DIV. Instead, ACh treatment induced a marked increment of p21 expression at 35 DIV. Our data suggest that cholinergic precursors modulate HO-1 and p21 expression during astroglial cell proliferation and differentiation in culture and could be considered a tool to study the induced effects of ischemia and hypoxia diseases in some in vitro models to prevent and reduce its effects after treatment with cholinergic drugs.

Heme oxygenase 1 is induced by miR-155 via reduced BACH1 translation in endothelial cells

Heme oxygenase 1 (HO-1) is a stress-inducible enzyme that degrades redox-active heme-producing biliverdin, carbon monoxide, and Fe(2+). It protects cells under various stress conditions and mediates anti-inflammatory and vasodilatory effects in the endothelium. The expression of HMOX1, the HO-1 gene, is highly inducible and its transcriptional regulation is complex. HMOX1 is induced by various proinflammatory stimuli via NF-κB in human endothelial cells, but functional NF-κB-binding elements have not been identified from the human gene. However, the regulation of HMOX1 by the antioxidant-response element is firmly established, with the transcription factor BACH1 serving as a repressor and Nrf2 as an enhancer. miR-155 is one of the TNFα-inducible endothelial microRNAs predicted to bind to the BACH1 mRNA. Oligonucleotides mimicking miR-155 efficiently inhibited BACH1 protein translation, resulting in a concentration-dependent increase in HMOX1 mRNA and protein expression in human umbilical vein endothelial cells. Moreover, endogenous miR-155 was upregulated by TNFα via an NF-κB-dependent mechanism with a subsequent increase in HMOX1 expression. We propose that increased HMOX1 expression in endothelial cells by TNFα results from miR-155-induced repression of BACH1 rather than direct induction of HMOX1 via NF-κB, and that miR-155 is cytoprotective during inflammation by elevating HO-1 expression in endothelial cells.

Carbon monoxide as an endogenous vascular modulator

Carbon monoxide (CO) is produced by heme oxygenase (HO)-catalyzed heme degradation to CO, iron, and biliverdin. HO has two active isoforms, HO-1 (inducible) and HO-2 (constitutive). HO-2, but not HO-1, is highly expressed in endothelial and smooth muscle cells and in adjacent astrocytes in the brain. HO-1 is expressed basally only in the spleen and liver but can be induced to a varying extent in most tissues. Elevating heme, protein phosphorylation, Ca(2+) influx, and Ca(2+)/calmodulin-dependent processes increase HO-2 activity. CO dilates cerebral arterioles and may constrict or dilate skeletal muscle and renal arterioles. Selected vasodilatory stimuli, including seizures, glutamatergic stimulation, hypoxia, hypotension, and ADP, increase CO, and the inhibition of HO attenuates the dilation to these stimuli. Astrocytic HO-2-derived CO causes glutamatergic dilation of pial arterioles. CO dilates by activating smooth muscle cell large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels. CO binds to BK(Ca) channel-bound heme, leading to an increase in Ca(2+) sparks-to-BK(Ca) channel coupling. Also, CO may bind directly to the BK(Ca) channel at several locations. Endothelial nitric oxide and prostacyclin interact with HO/CO in circulatory regulation. In cerebral arterioles in vivo, in contrast to dilation to acute CO, a prolonged exposure of cerebral arterioles to elevated CO produces progressive constriction by inhibiting nitric oxide synthase. The HO/CO system is highly protective to the vasculature. CO suppresses apoptosis and inhibits components of endogenous oxidant-generating pathways. Bilirubin is a potent reactive oxygen species scavenger. Still many questions remain about the physiology and biochemistry of HO/CO in the circulatory system and about the function and dysfunction of this gaseous mediator system.

Overexpression of the nuclear factor-κB subunit c-Rel protects against human islet cell death in vitro

The transcription factor nuclear factor (NF)-κB is known to modulate rates of apoptosis and may therefore play a role in the increased β-cell death that occurs in type 1 and type 2 diabetes. The aim of the present investigation was to study the expression of NF-κB subunits in human islet cells and whether overexpression of the NF-κB subunit c-Rel affects islet cell survival. We detected expression of p65, Rel-B, p50, p105, p52, and the ribosomal protein S3 (rpS3) in human islet cells. Among these, only p65 and rpS3 were translocated from the cytosolic to the nuclear fraction in response to cytokines. Interestingly, rpS3 participated in p65 binding to the κB-element in gel shift analysis experiments. We observed cytoplasmic c-Rel expression in vivo in 6J mice, and signs of nuclear translocation in β-cells of infiltrated nonobese diabetic islets. Human islet cells were also dispersed by trypsin treatment and transduced with a c-Rel adenoviral vector. This resulted in increased expression of c-Rel and inhibitory factor κB, increased κB-binding activity, and augmented protein levels of Bcl-X(L,) c-IAP2, and heat shock protein 72. c-Rel expression in human islet cells protected against cytokine-induced caspase 3 activation and cell death. c-Rel protected also against streptozotocin- and H(2)O(2)-induced cell death, in both intact rat islets and human islet cells. We conclude that rpS3 participates in NF-κB signaling and that a genetic increase in the activity of the NF-κB subunit c-Rel results in protection against cell death in human islets.

Heme oxygenase-1 and the vascular bed: from molecular mechanisms to therapeutic opportunities

Heme oxygenase-1, an enzyme degrading heme to carbon monoxide, iron, and biliverdin, has been recognized as playing a crucial role in cellular defense against stressful conditions, not only related to heme release. HO-1 protects endothelial cells from apoptosis, is involved in blood-vessel relaxation regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in blood-vessel formation by means of angiogenesis and vasculogenesis. The latter functions link HO-1 not only to cardiovascular ischemia but also to many other conditions that, like development, wound healing, or cancer, are dependent on neovascularization. The aim of this comprehensive review is to address the mechanisms of HO-1 regulation and function in cardiovascular physiology and pathology and to demonstrate some possible applications of the vast knowledge generated so far. Recent data provide powerful evidence for the involvement of HO-1 in the therapeutic effect of drugs used in cardiovascular diseases. Novel studies open the possibilities of application of HO-1 for gene and cell therapy. Therefore, research in forthcoming years should help to elucidate both the real role of HO-1 in the effect of drugs and the clinical feasibility of HO-1-based cell and gene therapy, creating the effective therapeutic avenues for this refined antioxidant system.

Regulation of haeme oxygenase-1 for treatment of neuroinflammation and brain disorders

Injury to the CNS elicits a host defense reaction that utilizes astrocytes, microglia, neurons and oligodendrocytes. Neuroinflammation is a major host defense mechanism designed to restore normal structure and function after CNS insult, but like other forms of inflammation, chronic neuroinflammation may contribute to pathogenesis. The inducible haeme oxygenase isoform, haeme oxygenase-1 (HO-1), is a phase 2 enzyme upregulated in response to electrophilic xenobiotics, oxidative stress, cellular injury and disease. There is emerging evidence that HO-1 expression helps mediate the resolution of inflammation, including neuroinflammation. Whether this is solely because of the catabolism of haeme or includes additional mechanisms is unclear. This review provides a brief background on the molecular biology and biochemistry of haeme oxygenases and the actions of haeme, bilirubin, iron and carbon monoxide in the CNS. It then presents our current state of knowledge regarding HO-1 expression in the CNS, regulation of HO-1 induction in neural cells and discusses the prospect of pharmacological manipulation of HO-1 as therapy for CNS disorders. Because of recognized species and cellular differences in HO-1 regulation, a major objective of this review is to draw attention to areas where gaps exist in the experimental record regarding regulation of HO-1 in neural cells. The results indicate the HO-1 system to be an important therapeutic target in CNS disorders, but our understanding of HO-1 expression in human neural cells is severely lacking.

(GT)N dinucleotide repeat polymorphism of haem oxygenase-1 promotor region is not associated with inflammatory bowel disease risk or disease course

Haem oxygenase-1 (HO-1) up-regulation was suggested to reduce mucosal tissue damage in inflammatory bowel disease (IBD) and an up-regulation of HO-1 expression in patients with Crohn's disease (CD) and ulcerative colitis (UC) was demonstrated. A HO-1 gene promoter microsatellite (GT)(n) dinucleotide repeat polymorphism was associated with regulation of HO-1 in response to inflammatory stimuli. We therefore hypothesized that IBD patients might segregate into phenotypes with high or low HO-1 inducibility. Ethylenediamine tetraacetic acid blood samples were obtained from 179 CD patients, 110 UC patients and 56 control patients without inflammation. Genomic DNA was purified and the 5'-flanking region of the HO-1 gene containing the (GT)(n) dinucleotide repeat was amplified. Polymerase chain reaction (PCR) products were purified and the length of the PCR fragments was analysed. The number of (GT)(n) repeats in the population studied ranged from 13 to 42. The distribution of the allele frequencies was comparable in patients and controls for both the short and the long alleles. The frequencies of short-, middle- and long-sized alleles were not changed among the groups studied. No correlation was found between IBD and microsatellite instability detected in five individals. Our data indicate that (GT)(n) dinucleotide repeats of the HO-1 promotor region have no significance for the pathophysiology and disease course of IBD.

Cerebroprotective functions of HO-2

The constitutive isoform of heme oxygenase, HO-2, is highly expressed in the brain and in cerebral vessels. HO-2 functions in the brain have been evaluated using pharmacological inhibitors of the enzyme and HO-2 gene deletion in in vivo animal models and in cultured cells (neurons, astrocytes, cerebral vascular endothelial cells). Rapid activation of HO-2 via post-translational modifications without upregulation of HO-2 expression or HO-1 induction coincides with the increase in cerebral blood flow aimed at maintaining brain homeostasis and neuronal survival during seizures, hypoxia, and hypotension. Pharmacological inhibition or gene deletion of brain HO-2 exacerbates oxidative stress induced by seizures, glutamate, and inflammatory cytokines, and causes cerebral vascular injury. Carbon monoxide (CO) and bilirubin, the end products of HO-catalyzed heme degradation, have distinct cytoprotective functions. CO, by binding to a heme prosthetic group, regulates the key components of cell signaling, including BK(Ca) channels, guanylyl cyclase, NADPH oxidase, and the mitochondria respiratory chain. Cerebral vasodilator effects of CO are mediated via activation of BK(Ca) channels and guanylyl cyclase. CO, by inhibiting the major components of endogenous oxidant-generating machinery, NADPH oxidase and the cytochrome C oxidase of the mitochondrial respiratory chain, blocks formation of reactive oxygen species. Bilirubin, via redox cycling with biliverdin, is a potent oxidant scavenger that removes preformed oxidants. Overall, HO-2 has dual housekeeping cerebroprotective functions by maintaining autoregulation of cerebral blood flow aimed at improving neuronal survival in a changing environment, and by providing an effective defense mechanism that blocks oxidant formation and prevents cell death caused by oxidative stress.

Heme oxygenase-1/carbon monoxide: from basic science to therapeutic applications

The heme oxygenases, which consist of constitutive and inducible isozymes (HO-1, HO-2), catalyze the rate-limiting step in the metabolic conversion of heme to the bile pigments (i.e., biliverdin and bilirubin) and thus constitute a major intracellular source of iron and carbon monoxide (CO). In recent years, endogenously produced CO has been shown to possess intriguing signaling properties affecting numerous critical cellular functions including but not limited to inflammation, cellular proliferation, and apoptotic cell death. The era of gaseous molecules in biomedical research and human diseases initiated with the discovery that the endothelial cell-derived relaxing factor was identical to the gaseous molecule nitric oxide (NO). The discovery that endogenously produced gaseous molecules such as NO and now CO can impart potent physiological and biological effector functions truly represented a paradigm shift and unraveled new avenues of intense investigations. This review covers the molecular and biochemical characterization of HOs, with a discussion on the mechanisms of signal transduction and gene regulation that mediate the induction of HO-1 by environmental stress. Furthermore, the current understanding of the functional significance of HO shall be discussed from the perspective of each of the metabolic by-products, with a special emphasis on CO. Finally, this presentation aspires to lay a foundation for potential future clinical applications of these systems.

Glutamate induces oxidative stress and apoptosis in cerebral vascular endothelial cells: contributions of HO-1 and HO-2 to cytoprotection

In cerebral circulation, epileptic seizures associated with excessive release of the excitatory neurotransmitter glutamate cause endothelial injury. Heme oxygenase (HO), which metabolizes heme to a vasodilator, carbon monoxide (CO), and antioxidants, biliverdin/bilirubin, is highly expressed in cerebral microvessels as a constitutive isoform, HO-2, whereas the inducible form, HO-1, is not detectable. Using cerebral vascular endothelial cells from newborn pigs and HO-2-knockout mice, we addressed the hypotheses that 1) glutamate induces oxidative stress-related endothelial death by apoptosis, and 2) HO-1 and HO-2 are protective against glutamate cytotoxicity. In cerebral endothelial cells, glutamate (0.1–2.0 mM) increased formation of reactive oxygen species, including superoxide radicals, and induced major keystone events of apoptosis, such as NF-κB nuclear translocation, caspase-3 activation, DNA fragmentation, and cell detachment. Glutamate-induced apoptosis was greatly exacerbated in HO-2 gene-deleted murine cerebrovascular endothelial cells and in porcine cells with pharmacologically inhibited HO-2 activity. Glutamate toxicity was prevented by superoxide dismutase, suggesting apoptotic changes are oxidative stress related. When HO-1 was pharmacologically upregulated by cobalt protoporphyrin, apoptotic effects of glutamate in cerebral endothelial cells were completely prevented. Glutamate-induced reactive oxygen species production and apoptosis were blocked by a CO-releasing compound, CORM-A1 (50 μM), and by bilirubin (1 μM), consistent with the antioxidant and cytoprotective roles of the end products of HO activity. We conclude that both HO-1 and HO-2 have anti-apoptotic effects against oxidative stress-related glutamate toxicity in cerebral vascular endothelium. Although HO-1, when induced, provides powerful protection, HO-2 is an essential endogenous anti-apoptotic factor against glutamate toxicity in the cerebral vascular endothelium.

Carbon monoxide and hydrogen sulfide: gaseous messengers in cerebrovascular circulation

This review focuses on two gaseous cellular messenger molecules, CO and H2S, that are involved in cerebrovascular flow regulation. CO is a dilatory mediator in active hyperemia, autoregulation, hypoxic dilation, and counteracting vasoconstriction. It is produced from heme by a constitutively expressed enzyme [heme oxygenase (HO)-2] expressed highly in the brain and by an inducible enzyme (HO-1). CO production is regulated by controlling substrate availability, HO-2 catalytic activity, and HO-1 expression. CO dilates arterioles by binding to heme that is bound to large-conductance Ca2+-activated K+ channels. This binding elevates channel Ca2+ sensitivity, that increases coupling of Ca2+ sparks to large-conductance Ca2+-activated K+ channel openings and, thereby, hyperpolarizes the vascular smooth muscle. In addition to dilating blood vessels, CO can either inhibit or accentuate vascular cell proliferation and apoptosis, depending on conditions. H2S may also function as a cerebrovascular dilator. It is produced in vascular smooth muscle cells by hydrolysis of l-cysteine catalyzed by cystathione gamma-lyase (CSE). H2S dilates arterioles at physiologically relevant concentrations via activation of ATP-sensitive K+ channels. In addition to dilating blood vessels, H2S promotes apoptosis of vascular smooth muscle cells and inhibits proliferation-associated vascular remodeling. Thus both CO and H2S modulate the function and the structure of circulatory system. Both the HO-CO and CSE-H2S systems have potential to interact with NO and prostanoids in the cerebral circulation. Much of the physiology and biochemistry of HO-CO and CSE-H2S in the cerebral circulation remains open for exploration.

Effect of Doxazosin on Oxidative Stress-Related Proteins in Benign Prostatic Hyperplasia

BACKGROUND AND OBJECTIVES

Oxidative stress can induce cell mutations or proliferation which then can progress to carcinogenesis or remodeling. The same oxidative stress-mediated mechanism could participate in prostate cell proliferation and remodeling present in benign prostatic hyperplasia (BPH). Doxazosin induces prostate epithelial and stromal cell apoptosis through production of transforming growth factor-beta (TGF-beta), but cellular mechanisms are not completely clarified. In 10 prostate samples from BPH untreated patients who underwent TUR, we have assessed the gene and protein expression of: p22(phox) (subunit of NAD(P)H oxidase essential for O(2)(-) production); heme oxygenase-1 (HO-1) (induced by oxidative stress and antiapoptotic); TGF-beta (inhibitor of prostatic epithelial and stromal cell growth); the in vitro effect of doxazosin on expression of these markers.

METHODS

RT-PCR and Western blot with specific primers and antibodies. p22(phox), HO-1 and TGF-beta were quantified by the ratio between their PCR and Western blot products and GAPDH.

RESULTS

Doxazosin significantly reduced p22(phox) gene and protein expression (0.61 +/- 0.04 vs. 0.36 +/- 0.04 d.u., p < 0.0002; 0.85 +/- 0.03 vs. 0.47 +/- 0.03, p < 0.0001, respectively). Doxazosin concentration dependently reduced HO-1 gene and protein expression (0.57 +/- 0.07 vs. 0.49 +/- 0.06 d.u. (1 microM) p < 0.04, vs. 0.22 +/- 0.08 (10 microM) p < 0.0001; 0.78 +/- 0.04 vs. 0.44 +/- 0.1 (10 microM) p < 0.003 respectively) and increased TGF-beta protein expression (0.58 +/- 0.05 vs. 0.74 +/- 0.16 (1 microM) n.s. vs. 0.81 +/- 0.07 (10 microM) p < 0.01).

CONCLUSIONS

Induction of oxidative stress-related proteins seems to be involved in the prostate cell proliferation and remodeling present in BPH. Doxazosin may reduce oxidative stress through reduction of p22(phox). Surprisingly, HO-1, which is induced and protected by oxidative stress, is also reduced by doxazosin. HO-1 is a potent antiapoptotic factor and downregulator of TGF-beta. From the results of this preliminary study it could be proposed that the proapoptotic effect of doxazosin could be mediated, at least in part, through the contemporary inhibition of HO-1.

Molecular basis of heme oxygenase-1 induction: implications for chemoprevention and chemoprotection

Heme oxygenase (HO)-1, involved in the heme degradation process, is an important antioxidant enzyme. The induction of HO-1 gene expression, in response to diverse oxidative stimuli, represents a critical event in adaptive cellular response. Experimental models of various diseases, including acute inflammation, atherosclerosis, degenerative diseases, and carcinogenesis, have demonstrated that the induction of HO-1 can prevent or mitigate the symptoms associated with these ailments. Recent progress in our understanding of cellular signaling networks as critical modulators of gene transcription sheds light on the molecular basis of HO-1 gene expression. A panel of redox-sensitive transcription factors such as activator protein-1, nuclear factor- kappaB, and nuclear factor E2-related factor-2, and some of the upstream kinases have been identified as regulators of HO-1 gene induction. The scope of this review is limited to focus on molecular mechanisms underlying HO-1 expression and the significance of targeted induction of HO-1 as a strategy to achieve chemoprevention and chemoprotection.

Immunocytochemical localization and expression of heme oxygenase-1 in primary astroglial cell cultures during differentiation: effect of glutamate

Heme oxygenase-1 (HO-1) catalyzes the rate-limiting step in heme degradation releasing iron, carbon monoxide (CO), and biliverdin. We investigated subcellular localization of HO-1 using confocal laser scanning microscopy (CLSM) and the expression by Western blot in primary astroglial cells during differentiation and after exposure to glutamate (100microM). CLSM analysis of immunostained HO-1 in cultured astroglial cells during differentiation showed an increase of fluorescence between 7 and 14 days and a decrease between 14 and 21, although HO-1 peaked at 14 days it remained at high levels. The distribution of HO-1 protein undergoes modification in the various cellular compartments. Furthermore, localization of the protein in untreated astrocytes at 7 days appeared prevalently localized in the cytosol and in the perinuclear region. In contrast, at 14 and 21 days, fluorescence detection suggests that HO-1 was present also in the nucleus, and in the nucleoli. Fluorescence intensity significantly increased in glutamate-treated astrocytes during all development stages and the protein appeared in the cytosol, in the nucleus and in the nucleoli. The involvement of AMPA/Ka receptors was studied in glutamate-treated astroglial cells at 14 days by the preincubation of the cells with GYKI 52466, a specific receptor inhibitor, of AMPA/Ka receptor demonstrating the involvement of these receptors. Western blot analysis of HO-1 confirmed the CLSM results. Our results demonstrate that changes in HO-1 protein expression and localization in primary cultured astroglial cells may be part of the underlying mechanisms involved in brain development as well as in neurodegenerative diseases.

Heme and iron metabolism: role in cerebral hemorrhage

Heme and iron metabolism are of considerable interest and importance in normal brain function as well as in neurodegeneration and neuropathologically following traumatic injury and hemorrhagic stroke. After a cerebral hemorrhage, large numbers of hemoglobin-containing red blood cells are released into the brain's parenchyma and/or subarachnoid space. After hemolysis and the subsequent release of heme from hemoglobin, several pathways are employed to transport and metabolize this heme and its iron moiety to protect the brain from potential oxidative stress. Required for these processes are various extracellular and intracellular transporters and storage proteins, the heme oxygenase isozymes and metabolic proteins with differing localizations in the various brain-cell types. In the past several years, additional new genes and proteins have been discovered that are involved in the transport and metabolism of heme and iron in brain and other tissues. These discoveries may provide new insights into neurodegenerative diseases like Alzheimer's, Parkinson's, and Friedrich's ataxia that are associated with accumulation of iron in specific brain regions or in specific organelles. The present review will examine the uptake and metabolism of heme and iron in the brain and will relate these processes to blood removal and to the potential mechanisms underlying brain injury following cerebral hemorrhage.

Sustained induction of heme oxygenase-1 in the traumatized spinal cord

Oxidative stress contributes to secondary injury after spinal cord trauma. Among the consequences of oxidative stress is the induction of heme oxygenase-1 (HO-1), an inducible isozyme that metabolizes heme to iron, biliverdin, and carbon monoxide. Here we examine the induction of HO-1 in the hemisected spinal cord, a model that results in reproducible degeneration in the ipsilateral white matter. HO-1 was induced in microglia and macrophages from 24 h to at least 42 days after injury. Within the first week after injury, HO-1 was induced in both the gray and the white matter. Thereafter, HO-1 expression was limited to degenerating fiber tracts. HSP70, a heat shock protein induced mainly by the presence of denatured proteins, was consistently colocalized with HO-1 in the microglia and macrophages. This study to demonstrates long-term induction of HO-1 and HSP70 in microglia and macrophages after traumatic injury and an association between induction of HO-1 and Wallerian degeneration. White matter degeneration is characterized by phagocytosis of cellular debris and remodeling of surviving tissue. This results in the metabolism, synthesis, and turnover of heme and heme proteins. Thus, sustained induction of HO-1 and HSP70 in microglia and macrophages suggests that tissue degeneration is an ongoing process, lasting 6 weeks and perhaps even longer.

Vascular Events After Spinal Cord Injury: Contribution to Secondary Pathogenesis

Traumatic spinal cord injury results in the disruption of neural and vascular structures (primary injury) and is characterized by an evolution of secondary pathogenic events that collectively define the extent of functional recovery. This article reviews the vascular responses to spinal cord injury, focusing on both early and delayed events, including intraparenchymal hemorrhage, inflammation, disruption of the blood-spinal cord barrier, and angiogenesis. These vascular-related events not only influence the evolution of secondary tissue damage but also define an environment that fosters neural plasticity in the chronically injured spinal cord.

Expression of heme oxygenase-1 mediated by non-NMDA and metabotropic receptors in glial cells: possible involvement of reactive oxygen species production and protein kinase C activation

Heme oxygenase (HO) produces biliverdin and bilirubin which are physiological antioxidants and potent scavengers of oxygen radicals. Recently, we found that intracerebroventricular injection of kainic acid (KA) induced inducible HO (HO-1) predominantly in glial cells in the rat hippocampus in vivo. In this study, we examined the mechanism of HO-1 expression induced by agonists for glutamate receptors in cultured glial cells in vitro. The HO-1 protein level was significantly enhanced by several agonists for non-N-methyl-D-aspartate (non-NMDA) receptors and metabotropic glutamate receptors (mGluR) such as KA, quisqualic acid (QA), (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propanoic acid (AMPA), and trans-(+/-)-1-amino-(1S,3R)-cyclopentanedicarboxylic acid (ACPD). Among these agonists, QA had the greatest potency. KA-induced HO-1 expression was inhibited by the non-NMDA antagonist NBQX. In addition, KA induced the marked production of reactive oxygen species (ROS), and KA-induced HO-1 expression was also inhibited by the antioxidants allopurinol and ascorbic acid. ACPD-induced HO-1 expression was inhibited by the mGluR antagonist MCPG and the protein kinase C (PKC) inhibitor calphostin C. These results suggest that induction of HO-1 expression by the activation of non-NMDA receptors is mediated by ROS production, and that expression induced by mGluR activation is mediated by PKC activation in rat glial cells.

Induction of heme oxygenase-1 and major histocompatibility complex antigens in transient forebrain ischemia

Recent studies strongly suggest that oxidative stresses participate in ischemia/reperfusion-induced neurodegeneration. In addition, heme oxygenase (HO) and major histocompatibility complex (MHC) antigens serve as functional molecules against oxidative stress and as self-recognition markers in the immune system, respectively. In this study, we examined the induction of HO and MHC antigens in the rat hippocampus after transient forebrain ischemia. The protein level of HO-1 was significantly enhanced after an episode of ischemia. After ischemia, HO-1 expression was observed early but transiently in the CA1 pyramidal neurons and later but continuously in glial cells. Glial cells expressing HO-1 were predominantly ameboid microglia, but not astrocytes. Ameboid microglia expressing HO-1 were predominantly localized with MHC class II antigens. These results indicate that (1) HO-1 expression in CA1 pyramidal neurons may be harmful, and (2) ischemia induces HO-1 in ameboid microglia that express MHC class II antigens, indicating a very specific microglial stress protein response.

Effect of tumor necrosis factor-alpha and interleukin-1 alpha on heme oxygenase-1 expression in human endothelial cells

Heme iron exacerbates oxidant damage by catalyzing the production of free radicals. Heme oxygenase is the rate-limiting enzyme involved in heme catabolism. An inducible form of heme oxygenase, heme oxygenase-1 (HO-1), is upregulated in oxidant and inflammatory settings, and recent work suggests that HO-1 induction may serve a protective function against oxidant injury. The ability of the endogenous inflammatory mediators, interleukin (IL)-1 alpha, tumor necrosis factor-alpha (TNF-alpha), and IL-6, to enhance HO-1 expression in cultured human endothelial cells was examined in this study. HO-1 mRNA and protein expression were upregulated by IL-1 alpha and TNF-alpha exposure but not by IL-6. Induction of HO-1 mRNA by IL-1 alpha and TNF-alpha occurred in a concentration- and time-dependent fashion, with maximal expression occurring by 4 h for both cytokines. Induction depended on protein synthesis and occurred at the transcriptional level. Inhibition of the AP-1 transcription factor with curcumin decreased the cytokine induction of HO-1 mRNA, suggesting the involvement of this transcription factor in cytokine signaling of HO-1. The results of this study indicate that the endogenous inflammatory cytokines IL-1 alpha and TNF-alpha induce HO-1 in endothelial cells, providing further evidence that HO-1 may be an important cellular response to inflammatory stress.

Induction of heme oxygenase-1 after hyperosmotic opening of the blood-brain barrier

The induction of the stress protein heme oxygenase-1 (HO-1) was studied in the rat brain after intracarotid administration of hyperosmolar mannitol. HO-1 was immunolocalized in fixed sections of brain 24 h to 7 days after injection. Immunoglobulin G (IgG) was immunolocalized in adjacent sections to demonstrate areas of breakdown of the blood-brain barrier. Induction of HO-1 was also evaluated by Western immunoblots, performed at 24 h after the insult. Immunofluorescent double labelling with monoclonal antibodies to HO-1 and either glial fibrillary acidic protein or the complement C3bi receptor was used to determine if glia/macrophages expressed HO-1. There was pronounced, widespread induction of HO-1 in the ipsilateral hemisphere and cerebellum by 24 h both by immunocytochemistry and by Western blots. This induction was markedly attenuated at later times. HO-1 was induced in astrocytes and microglia/macrophages in the ipsilateral hemisphere. In addition, the protein was induced in Bergmann glia and scattered microglia/macrophages in the cerebellum. The mechanism of induction of HO-1 in glia after opening of the blood-brain barrier could include exposure to heme proteins, denatured proteins and other plasma constituents known to induce HO-1. This glial induction may reflect a protective response of these cells.

Induction of cystine transport and other stress proteins by disulfiram: effects on glutathione levels in cultured cells

Disulfiram (Antabuse) (DSF) has been reported to protect rats and other animals from the effects of hyperbaric hyperoxia at 4 to 6 ATA (atmospheres). In contrast, DSF and diethyldithiocarbamate (DDC), its metabolite, accelerate the toxic effects in rats of 100% oxygen at 1 to 2 ATA. We have examined the effects of DSF and DDC on glutathione (GSH) levels in bovine pulmonary artery endothelial cells and Chinese hamster ovary cells. Increases in intracellular GSH occurred 8 to 24 h after addition of DSF to the culture media. These increases in intracellular GSH were associated with increases in the rate of uptake of cystine into the cells. DDC was a less effective inducer of cystine uptake and increased intracellular GSH levels than was DSF. At the concentrations used, neither DDC nor DSF caused significant decreases in intracellular superoxide dismutase levels. Exogenous sulfhydryl compounds including GSH and cysteine partially blocked the induction of cystine transport by DSF or DDC, suggesting that the induction might be mediated through a sulfhydryl reaction between DSF and some cellular components. The increases in GSH in the cultured cells were not significant by 4 h of exposure. In contrast, other stress proteins including heme oxygenase are induced by 2 to 4 h after DSF addition. In previously reported in vivo studies, DSF treatment protected against hyperbaric oxygen damage after as little as 1 to 4 h pre-exposure. This suggests that effects of DSF exposure other than GSH augmentation may be responsible for the protective effects seen in vivo.

Heme oxygenase-1 and heat shock protein 70 induction in glia and neurons throughout rat brain after experimental intracerebral hemorrhage

OBJECTIVE

Current experimental evidence demonstrates the development of ischemic regions adjacent to and spatially remote from an intracerebral hematoma. The cause of this ischemia is uncertain. Because ischemia is a known inducer of stress genes, we investigated the induction of two stress proteins, heme oxygenase (HO)-1 and heat shock protein (Hsp) 70, after intracerebral hemorrhage in the rat.

METHODS

Immunocytochemistry for HO-1, Hsp70, and HO-2, the constitutive isoform of the HO enzyme, was performed 1, 2, and 4 days after striatal injection of saline, whole blood, or lysed blood. Immunocytochemistry for HO-1, HO-2, and Hsp70 was also performed 1 day after cortical injection of saline, whole blood, or lysed blood.

RESULTS

After striatal injection of lysed and whole blood, the HO-1 protein was induced in glia throughout the hemisphere ipsilateral to the hematoma, and HO-1 immunoreactivity persisted for at least 4 days. After cortical injection of lysed and whole blood, HO-1 was induced in glia throughout the neocortex. Neuronal induction of HO-1 was also observed after cortical injection of lysed blood but not whole blood or saline. After striatal injection of lysed blood, Hsp70 was induced in glia surrounding the hematoma and in neurons from the neocortex overlying the hematoma and the striatum adjacent to the hematoma. After cortical injection of lysed blood, Hsp70 was induced in neurons throughout the neocortex and hippocampus bilaterally. In contrast, after whole blood and saline injection into cortex, Hsp70 induction was observed only in scattered neurons surrounding the hematoma cavity.

CONCLUSION

Our results demonstrate that blood in the brain parenchyma induces the HO-1 stress protein but does not significantly alter HO-2 immunostaining. Our results also demonstrate that lysed blood induces Hsp70 in multiple regions of the brain and that the stress response of the brain differs depending on whether lysed blood is injected into the cortex or striatum. These results suggest that blood lysis may play an unforeseen role in the stress response of the brain to intracerebral hemorrhage.

Focal hyperexpression of hemeoxygenase-1 protein and messenger RNA in rat brain caused by cellular stress following subarachnoid injections of lysed blood

Induction of the hemeoxygenase-1 (ho-1) stress gene is of importance for rapid heme metabolism and protection against oxidative injury in vitro and in vivo. Although ho-1 expression is observed in glia following exposure to whole blood and oxyhemoglobin, expression is mild, and other stress genes are not induced simultaneously in this setting. Hemeoxygenase-1 can be induced by several other physiological stresses in addition to heme. In the brain, ho-1 induction has been observed in the penumbra following focal cerebral ischemia. Because lysed blood is a spasmogen, the authors studied focal hyperexpression of the ho-1 gene after injection of lysed blood, whole blood, or saline into the cisterna magna of adult rats. Immunocytochemical analysis of HO-1 was performed at 1, 2, 3, and 4 days after the injections. Because the 70-kD inducible heat shock protein (HSP70) is induced by cellular stress, alternate sections were immunostained for HSP70 to assess whether focal hyperexpression was a stress phenomenon. An oligonucleotide probe was also used for in situ hybridization to demonstrate that ho-1 messenger (m)RNA was present. Focal HO-1 immunostained areas were observed after lysed blood injection only and were located mainly in the basal cortex and cerebellar hemisphere, although focal hyperexpression was also found in many other regions. The intensity of staining and the number of regions were maximum at 1 day. Double-labeled immunofluorescence revealed that many HO-1-immunoreactive cells were microglia. The HSP70 immunostaining of adjacent sections from the same animals demonstrated focal regions of immunoreactivity whose topography corresponded exactly with the topography of the HO-1-immunostained areas. Conventional histology in regions of HO-1 hyperexpression was often normal. In situ hybridization using the same oligonucleotide demonstrated that ho-1 mRNA was induced in focal areas of forebrain and in large regions of cerebellum within 6 hours of injection. These results demonstrate that focal hyperexpression of the ho-1 stress gene occurs after lysed blood injection and appears to be an indicator of cellular stress and injury in regions in which infarction does not occur. These results also suggest that cellular injury that occurs after injection of lysed blood may go undetected using conventional histology. Although direct heme metabolism was not investigated, our results indicate that rapid metabolism of heme, both intracellular and extracellular, may prove to be beneficial after subarachnoid hemorrhage.

Heme-oxygenase-1 induction in glia throughout rat brain following experimental subarachnoid hemorrhage

The heme released following subarachnoid hemorrhage is metabolized by heme-oxygenase (HO) to biliverdin and carbon monoxide (CO) with the release of iron. The HO reaction is important since heme may contribute to vasospasm and increase oxidative stress in cells. HO is comprised of at least two isozymes, HO-2 and HO-1. HO-1, also known as heat shock protein HSP32, is inducible by many factors including heme and heat shock. HO-2 does not respond to these stresses. To begin to examine HO activity following subarachnoid hemorrhage (SAH), the expression of HO-1 and HO-2 was investigated after experimental SAH in adult rats. Immunocytochemistry for HO-1, HO-2 and HSP70 proteins was performed at 1, 2, 3 and 4 days after injections of lysed blood, whole blood, oxyhemoglobin and saline into the cisterna magna. A large increase in HO-1 immunoreactivity was seen in cells throughout brain following injections of lysed blood, whole blood, and oxyhemoglobin but not saline. Lysed blood, whole blood and oxyhemoglobin induced HO-1 in all of the cortex, hippocampus, striatum, thalamus, forebrain white matter and in cerebellar cortex. HO-1 immunoreactivity was greatest in those regions adjacent to the basal subarachnoid cisterns where blood and oxyhemoglobin concentrations were likely highest. Double immunofluorescence studies showed the HO-1 positive cells to be predominately microglia, though HO-1 was induced in some astrocytes. HO-1 expression resolved by 48 h. HO-2 immunoreactivity was abundant but did not change following injections of blood. A generalized induction of HSP70 heat shock protein was not observed following injections of lysed blood, whole blood, oxyhemoglobin, or saline. These results suggest that HO-1 is induced in microglia throughout rat brain as a general, parenchymal response to the presence of oxyhemoglobin in the subarachnoid space and not as a stress response. This microglial HO-1 response could be protective against the lipid peroxidation and vasospasm induced by hemoglobin, by increasing heme clearance and iron sequestration, and enhancing the production of the antioxidant bilirubin.

Identification of a cis-regulatory element for delta 12-prostaglandin J2-induced expression of the rat heme oxygenase gene

We recently reported that delta 12-prostaglandin (PG) J2 caused various cells to synthesize heme oxygenase, HO-1 (Koizumi, T., Negishi, M., and Ichikawa, A. (1992) Prostaglandins 43, 121-131). Here we examined the molecular mechanism underlying the delta 12-PGJ2-induced HO-1 synthesis. delta 12-PGJ2 markedly stimulated the promoter activity of the 5'-flanking region of the rat HO-1 gene from -810 to +101 in rat basophilic leukemia cells. From functional analysis of various deletion mutant genes we found that the delta 12-PGJ2-responsive element was localized in a region from -690 to -660, containing an E-box motif, which was essential for the delta 12-PGJ2-stimulated promoter activity. When the region containing the delta 12-PGJ2-responsive element was combined with a heterologous promoter, SV40 promoter, in the sense and antisense direction, the element showed an enhancer activity in response to delta 12-PGJ2. Gel mobility shift assays demonstrated that delta 12-PGJ2 specifically stimulated the binding of two nuclear proteins to the E-box motif of this region. These results indicate that delta 12-PGJ2 induces the expression of the rat HO-1 gene through nuclear protein binding to a specific element having an E-box motif.

Differential activation of heat-shock and oxidation-specific stress genes in chemically induced oxidative stress

Post-ischaemic reperfusion increases the level of the major heat-shock (stress) protein hsp 70 and of its mRNA by transcriptional mechanisms, and activates the binding of the heat-shock factor HSF to the consensus sequence HSE. In common with CoCl2 treatment, post-ischaemic reperfusion increases the level of haem oxygenase mRNA, an indicator of oxidative stress, but CoCl2 does not seem to induce the expression of the hsp 70 gene [Tacchini, Schiaffonati, Pappalardo, Gatti and Bernelli-Zazzera (1993) Lab. Invest. 68, 465-471]. Starting from these observations, we have now studied the expression of two genes of the hsp 70 family and of other possibly related genes under conditions of oxidative stress. Three different chemicals, which cause oxidative stress by various mechanisms and induce haem oxygenase, enhance the expression of the cognate hsc 73 gene, but do not activate the inducible hsp 70 gene. Expression of the other genes that have been studied seems to vary in intensity and/or time course, in relation to the particular mechanism of action of any single agent. The pattern of induction of the early-immediate response genes c-fos and c-jun observed during oxidative stress differs from that found in post-ischaemic reperfused livers. Oxidative-stress-inducing agents do not promote the binding of HSF to its consensus sequence HSE, such as occurs in heat-shock and post-ischaemic reperfusion, and fail to activate AP-1 (activator protein 1). With the possible exception of Phorone, the oxidative stress chemically induced in rat liver activates NFkB (nuclear factor kB) and AP-2 (activator protein 2) transcription factors.

Mechanisms of endotoxin-induced haem oxygenase mRNA accumulation in mouse liver: synergism by glutathione depletion and protection by N-acetylcysteine

In in vitro systems haem oxygenase-1 (HO-1) mRNA increases after exposure to agents causing oxidative stress. We lowered cellular antioxidant defence systems in vivo by giving mice increasing doses (0.15 g/kg-1.6 g/kg) of DL-buthionine-(S,R)-sulphoximine (BSO), a specific inhibitor of glutathione synthesis. Maximum glutathione depletion (80%) coincided with maximum hepatic HO-1 mRNA accumulation (about 20 times), whereas with 50% depletion, accumulation was only doubled. It has been suggested that reactive oxygen and nitrogen intermediates are involved in hepatic toxicity of endotoxin (lipopolysaccharide, LPS); LPS even at low doses [0.1 mg/kg, intraperitoneally (i.p.)] induces HO-1 mRNA about 25-fold after 1 h. Hepatic glutathione depletion (respectively 40% and 80%) after a low (0.3 g/kg) or a high (1.6 g/kg) BSO dose, resulted in potentiation of the HO-1 mRNA accumulation induced by LPS (0.1 mg/kg, i.p.). In the absence of BSO, N-acetylcysteine (NAC) (1 g/kg orally) reduced LPS-induced HO-1 mRNA accumulation to one fourth. Under the same experimental conditions S-adenosylmethionine (SAM) was not effective. NAC also reduced HO-1 mRNA accumulation when administered to mice in which glutathione was depleted and its synthesis blocked by BSO (1.6 g/kg). Thus reactive oxygen intermediates are likely mediators of LPS-induced HO-1 mRNA accumulation, and glutathione content appears to be one of the factors regulating this accumulation in the liver. Our findings are compatible with the theory that HO-1 induction might have a protective function in vivo when defence mechanisms against oxidants are challenged.

Characterization of a 142-bp fragment of the murine c-fos oncogene promoter upstream of the SIF-binding element

We previously reported that in transformed mouse sarcoma cells of spontaneous origin and in revertants transfected with a fos-cat fusion, the 600-bp c-fos promoter region provides chloramphenicol acetyltransferase activity. In the present study, we investigated the binding of transcriptional factor protein(s) to a region (-503 to -361) upstream of the sis (platelet-derived growth factor)-inducible factor (SIF)-binding element. Gel electrophoresis retardation (GER) assay clearly demonstrated the appearance of strong binding activity to a newly described fragment in the 142-bp region studied. Further analysis using synthetic oligodeoxyribonucleotides and GER defined a binding region of 30 bp (AvaI-AvaII) from -503 to -472 that partially overlaps with a region known to bind fos promoter binding site 2 (FBS2). DNase I footprint analysis discovered a novel sequence in the upstream region of the c-fos promoter to which protein(s) in nuclear extracts from various mouse and human cells bind. This factor(s) is not identical to most known transcriptional factors present in the promoter region of nuclear oncogenes. A proximal part of this fragment is very conservative and contains several AP-2-like-binding sites.