Heme Oxygenase-1 Deficient Mice Research Articles

Circadian dependency of microglial heme oxygenase-1 expression and inflammation determine neuronal injury in hemorrhagic stroke

BackgroundThe heme oxygenase-1 (HO-1) enzyme pathway is of crucial importance in the removal of toxic blood components and regulation of neuroinflammation following hemorrhagic stroke. Although a circadian pattern dependency in the incidence and severity of hemorrhagic stroke exists, it is unknown whether the activity of the HO-1 system in the context of hemorrhagic injury also exhibits circadian dependency. We hypothesized that the circadian regulation of microglial HO-1 would determine the extent of neuroinflammation and neuronal injury in a murine model of subarachnoid hemorrhage (SAH).MethodsIn vitro expression patterns of HO-1 and circadian rhythm genes were analyzed in the microglial BV-2 cell line and primary microglia (PMG) using Western blot and qPCR. PMG isolated from Hmox1fl/fl and LyzM-Cre-Hmox1fl/fl mice were used to evaluate the role of microglial HO-1. We further investigated the in vivo relevance in a murine subarachnoid hemorrhage (SAH) model using Hmox1fl/fl and LyzM-Cre-Hmox1fl/fl mice with myeloid cell HO-1 deficiency, inducing SAH at different zeitgeber (ZT) times and analyzing the expression of HO-1 and the circadian control gene Period-2 (Per-2), respectively. Furthermore, we measured the inflammatory cytokine Monocyte Chemoattractant Protein-1 (MCP-1) in the cerebrospinal fluid of SAH patients in correlation with clinical outcome.ResultsHO-1 baseline expression and response to CO with blood exposure depended on ZT. In vitro expression of circadian control genes was de-synchronized in LyzM-Cre-Hmox1fl/fl PMG and did not respond to exogenous CO exposure. We found that circadian rhythm plays a crucial role in brain damage after SAH. At ZT2, we observed less phagocytic function, more vasospasm and increased microglial activation. CO reduced mortality at ZT12 in HO-1 deficient mice and reduced the difference between ZT2 and ZT12 in the inflammatory response. Induction of MCP-1 in the CSF from SAH patients was time-dependent and correlated with the expression of circadian control genes, SAH severity, functional impairment and delirium.ConclusionsOur data point towards a crucial role for the HO-1 enzyme system and circadian control in neuronal injury after a hemorrhagic stroke.

Role of HO-1 in B Lymphocyte Proliferation and Development in Mice

Background: B lymphocytes are essential for an efficient immune response against a variety of pathogens. Not only a large fraction of hematologic malignancies is of B cell origin, but the immunity reconstruction is also depended on its normal growth. Then, it's very important to pay more attention on tightly regulating the development and activation of B cells. Heme oxygenase-1 (HO-1) is thought initially to be a key enzyme that provides potent cyto-protection, cell proliferation, malignancy development and drug resistance. In our primary studies, we have already reported its roles in various of hematological malignancies. However, As we noticed thatObjective: Herein, there is something different with before we observed. The count of B lymphocyte in HO-1 deficient mice decreased significantly. It never be reported yet. Therefore, we aimed to explore the regulation of HO-1 to B lymphocyte development in HO-1 knockout mice model.Method: Originally, HO-1 deficient C57BL6 mice model was constructed by CRISPR/Cas9 assay for examining the effect of HO-1 on bone marrow-derived cells. After immune-phenotyping by flow cytometry and colony formation assay, we accidently noticed that its quantity of CD19+ cells in peripheral blood was less than HO-1 wild type mice, while the other cells kept relative balance. Then, to further explore which stage was the direct target for HO-1, the absolute quantity of B lymphocyte in each stage from bone marrow cells and mature B lymphocyte from spleen were detected by flow cytometry. Our staining strategy to distinguish between pro-B (B220+IgM−CD43+) and pre-B (B220+IgM−CD43−) lymphocytes revealed the presence of cells expressing intermediate CD43 levels in bone marrow from HO-1-deficient mice. B220+ IgM+ immature B cells, and B220+ IgM+ IgD+ mature recirculating B cells. CD21brightCD23+ for marginal zone B cells, CD21+CD23brightCD93− for follicular B cells and CD21+CD23brightCD93+ for transitional B cells. In additional, to get an insight into the mechanisms underlying the early B lymphocyte development, we detected cell proliferation, cell cycle and cell death in pro-B subsets in the absence of HO-1. And PCR Array was used to explore the pathway involved in B cells development. Real-time PCR and Western blot were used to identify it.Results: It revealed that absence of HO-1 resulted in a block in B cell development at the pro-B to pre-B cell transition. The absolute count of pro-B cells in HO-1 deficient mice was 71.2% compare with control(p<0.05). Fewer B cells in spleen and peripheral blood were observed comparing with control group. In particular, the analysis of immature B cells, marginal zone B cells, follocular B cells and transtional B cells revealed that the absolute numbers of all B cell subtypes were significantly lower in HO-1-deficient mice. Proliferation rate of pro-B cells were decreased significantly, while cell cycle and death were not sensibly in the absence of HO-1. In addition, we also observed intracellular IgHμexpression to test whether HO-1 is required for V(D)J recombination. The results still revealed that the effect of HO-1 on B lymphocyte development depends on promoting cells proliferation. Then, PCR array was preliminary used and showed that MAPK signaling pathway was possibly involved in regulation of early B lymphocyte development induced by HO-1 deficiency. And BAFF expression was possible to relate with HO-1 knockout. Lenti-virus with HO-1 was injected into HO-1 deficient mice through tail vein. We found that absolute quantity of B cells increased significantly in vivo.Conclusion: In conclusion, all results indicate HO-1 is a crucial role in early B lymphocyte proliferation and development.Disclosures: No relevant conflicts of interest to declare. DisclosuresNo relevant conflicts of interest to declare.

Characterization of hepatic macrophages and evaluation of inflammatory response in heme oxygenase-1 deficient mice exposed to scAAV9 vectors

Adeno-associated viral (AAV) vectors are characterised by low immunogenicity, although humoral and cellular responses may be triggered upon infection. Following systemic administration high levels of vector particles accumulate within the liver. Kupffer cells (KCs) are liver resident macrophages and an important part of the liver innate immune system. Decreased functional activity of KCs can contribute to exaggerated inflammatory response upon antigen exposure. Heme oxygenase-1 (HO-1) deficiency is associated with considerably reduced numbers of KCs. In this study we aimed to investigate the inflammatory responses in liver and to characterise two populations of hepatic macrophages in adult wild type (WT) and HO-1 knockout (KO) mice following systemic administration of one or two doses (separated by 3 months) of self-complementary (sc)AAV9 vectors. At steady state, the livers of HO-1 KO mice contained significantly higher numbers of monocyte-derived macrophages (MDMs), but significantly less KCs than their WT littermates. Three days after re-administration of scAAV9 we observed increased mRNA level of monocyte chemoattractant protein-1 (Mcp-1) in the livers of both WT and HO-1 KO mice, but the protein level and the macrophage infiltration were not affected. Three days after the 1st and 3 days after the 2nd vector dose the numbers of AAV genomes in the liver were comparable between both genotypes indicating similar transduction efficiency, but the percentage of transgene-expressing MDMs and KCs was higher in WT than in HO-1 KO mice. In the primary culture, KCs were able to internalize AAV9 particles without induction of TLR9-mediated immune responses, but no transgene expression was observed. In conclusion, in vivo and in vitro cultured KCs have different susceptibility to scAAV9 vectors. Regardless of the presence or absence of HO-1 and initial numbers of KCs in the liver, scAAV9 exhibits a low potential to stimulate inflammatory response at the analysed time points.

Kidney injury by cyclosporine A is aggravated in heme oxygenase-1 deficient mice and involves regulation of microRNAs.

Cyclosporine A (CsA), a widely used immunosuppressive drug, exerts nephrotoxic activities, as demonstrated by increased tubulointerstitial fibrosis, inflammation and podocyte damage. Recently, a number of microRNAs expressed in the kidney have been reported to be elevated during renal damage. Our aim was to investigate the effect of CsA on selected microRNAs in the mouse kidney after CsA treatment. Moreover, as heme oxygenase-1 (HO-1, encoded by the Hmox1 gene) was shown to play a protective role during kidney disorders, we assessed whether HO-1 deficiency in vivo influences the CsA-regulated microRNAs' expression. We have observed that the pro-fibrotic miR-21 and pro-apoptotic miR-34a expression was upregulated in kidneys of HO-1 deficient mice and it was further enhanced by CsA. Concomitantly, the level of anti-fibrotic microRNAs, belonging to miR-29 and miR-200 families, was down-regulated after CsA treatment. Generally, Hmox1 knock-out (Hmox1-/-) animals were more susceptible to CsA treatment, as the mortality rate was 4 out of 9 Hmox1-/- mice, and increased fibrosis (Tgfb2, Pai1), inflammation (Il6) and apoptosis (Cdkn1a-p21) were noticed in the HO-1 deficient kidneys. In summary, our data demonstrate that CsA induces significant changes in the expression of renal microRNAs and emphasize HO-1 deficiency as an important factor contributing to the CsA-mediated renal toxicity.

Heme Oxygenase-1 in Macrophages Drives Septic Cardiac Dysfunction via Suppressing Lysosomal Degradation of Inducible Nitric Oxide Synthase

To date, our understanding of the role of HO-1 (heme oxygenase-1) in inflammatory diseases has mostly been limited to its catalytic function and the potential for its heme-related catabolic products to suppress inflammation and oxidative stress. Whether and how HO-1 in macrophages plays a role in the development of septic cardiac dysfunction has never been explored. Here, we investigated the role of macrophage-derived HO-1 in septic cardiac dysfunction. Intraperitoneal injection of lipopolysaccharide significantly activated HO-1 expression in cardiac infiltrated macrophages. Surprisingly, we found that myeloid conditional HO-1 deletion in mice evoked resistance to lipopolysaccharide-triggered septic cardiac dysfunction and lethality in vivo, which was accompanied by reduced cardiomyocyte apoptosis in the septic hearts and decreased peroxynitrite production and iNOS (inducible NO synthase) in the cardiac infiltrated macrophages, whereas proinflammatory cytokine production and macrophage infiltration were unaltered. We further demonstrated that HO-1 suppression abolished the lipopolysaccharide-induced iNOS protein rather than mRNA expression in macrophages. Moreover, we confirmed that the inhibition of HO-1 promoted iNOS degradation through a lysosomal rather than proteasomal pathway in macrophages. Suppression of the lysosomal degradation of iNOS by bafilomycin A1 drove septic cardiac dysfunction in myeloid HO-1-deficient mice. Mechanistically, we demonstrated that HO-1 interacted with iNOS at the flavin mononucleotide domain, which further prevented iNOS conjugation with LC3 (light chain 3) and subsequent lysosomal degradation in macrophages. These effects were independent of HO-1's catabolic products: ferrous ion, carbon monoxide, and bilirubin. Our results indicate that HO-1 in macrophages drives septic cardiac dysfunction. The mechanistic insights provide potential therapeutic targets to treat septic cardiac dysfunction.

323: Pravastatin improves pregnancy outcome and placental development in heme oxygenase-1 deficient mice

Pravastatin is currently being studied clinically for prevention of preeclampsia. Low expression of heme oxygenase-1 (HO-1) due to polymorphisms in the human HO-1 promoter region may cause impaired placental development resulting in intrauterine growth restriction (IUGR), preeclampsia, and recurrent miscarriages. We have shown that pregnant HO-1 heterozygous (HO-1+/-, Het) mice have abnormal placental development, with thinner spongiotrophoblast layers and increased Sflt-1 levels (Zhao H. et al., 2009). We have also found that statins can induce HO-1 expression. Therefore, our aim was to evaluate the effect of pravastatin on pregnancy outcome and placental development in HO-1-deficient mice. We compared untreated Het mice (control, n=5) with Het mice treated with pravastatin (10 mg/g/d; n=9) added to their drinking water 1 wk prior to timed-pregnancy breeding for a total of 3.5 wks. At E14.5, dams were sacrificed, litter sizes recorded, and livers and placentas (fetal side) harvested for total HO activity (expressed as percent of Het controls). A subset of whole placentas (control n=3, pravastatin n=4) was stained for H&E to assess placental development. At E14.5, litter sizes of the pravastatin-treated dams were significantly larger (8.0±2.5 vs 5.0±2.0 p<0.05), with increases in HO activity in livers (154%, p=0.012) and in placentas (119%, p=0.059). Histologically, placentas of pravastatin-treated mice had less apoptosis, more glycogen-laden cells, and larger vessel diameters in the spongiotrophoblast (SP) layer, reflecting improved placental development (Figs. 1 and 2). Pravastatin induces liver and placental HO activity and appears to improve pregnancy outcome and placental development in HO-1-deficient mice. We conclude that pravastatin has potential for use in the treatment of not only preeclampsia, but also of IUGR due to its effects on placental development. We speculate that among women at risk, those with low HO-1 expression may specifically benefit from pravastatin.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Heme oxygenase-1 suppresses a pro-inflammatory phenotype in monocytes and determines endothelial function and arterial hypertension in mice and humans.

Heme oxygenase-1 (HO-1) confers protection to the vasculature and suppresses inflammatory properties of monocytes and macrophages. It is unclear how HO-1 determines the extent of vascular dysfunction in mice and humans. Decreased HO-1 activity and expression was paralleled by increased aortic expression and activity of the nicotinamide dinucleotide phosphate oxidase Nox2 in HO-1 deficient Hmox1⁻/⁻ and Hmox1(⁺/⁻) compared with Hmox1⁺/⁺ mice. When subjected to angiotensin II-infusion, streptozotocin-induced diabetes mellitus and aging, HO-1 deficient mice showed increased vascular dysfunction inversely correlated with HO activity. In a primary prevention population-based cohort, we assessed length polymorphisms of the HMOX1 promoter region and established a bipolar frequency pattern of allele length (long vs. short repeats) in 4937 individuals. Monocytic HMOX1 mRNA expression was positively correlated with flow-mediated dilation and inversely with CD14 mRNA expression indicating pro-inflammatory monocytes in 733 hypertensive individuals of this cohort. Hmox1⁻/⁻ mice showed drastically increased expression of the chemokine receptor CCR2 in monocytes and the aorta. Angiotensin II-infused Hmox1⁻/⁻ mice had amplified endothelial inflammation in vivo, significantly increased aortic infiltration of pro-inflammatory CD11b⁺ Ly6C(hi) monocytes and Ly6G⁺ neutrophils and were marked by Ly6C(hi) monocytosis in the circulation and an increased blood pressure response. Finally, individuals with unfavourable HMOX1 gene promoter length had increased prevalence of arterial hypertension and reduced cumulative survival after a median follow-up of 7.23 years. Heme oxygenase-1 is a regulator of vascular function in hypertension via determining the phenotype of inflammatory circulating and infiltrating monocytes with possible implications for all-cause mortality.

Heme oxygenase-1 deficiency alters erythroblastic island formation, steady-state erythropoiesis and red blood cell lifespan in mice

Heme oxygenase-1 is critical for iron recycling during red blood cell turnover, whereas its impact on steady-state erythropoiesis and red blood cell lifespan is not known. We show here that in 8- to 14-week old mice, heme oxygenase-1 deficiency adversely affects steady-state erythropoiesis in the bone marrow. This is manifested by a decrease in Ter-119(+)-erythroid cells, abnormal adhesion molecule expression on macrophages and erythroid cells, and a greatly diminished ability to form erythroblastic islands. Compared with wild-type animals, red blood cell size and hemoglobin content are decreased, while the number of circulating red blood cells is increased in heme oxygenase-1 deficient mice, overall leading to microcytic anemia. Heme oxygenase-1 deficiency increases oxidative stress in circulating red blood cells and greatly decreases the frequency of macrophages expressing the phosphatidylserine receptor Tim4 in bone marrow, spleen and liver. Heme oxygenase-1 deficiency increases spleen weight and Ter119(+)-erythroid cells in the spleen, although α4β1-integrin expression by these cells and splenic macrophages positive for vascular cell adhesion molecule 1 are both decreased. Red blood cell lifespan is prolonged in heme oxygenase-1 deficient mice compared with wild-type mice. Our findings suggest that while macrophages and relevant receptors required for red blood cell formation and removal are substantially depleted in heme oxygenase-1 deficient mice, the extent of anemia in these mice may be ameliorated by the prolonged lifespan of their oxidatively stressed erythrocytes.

Abstract 18540: Heme Oxygenase 1 Activity and Expression Suppresses a Proinflammatory Phenotype in Monocytes and Correlates With Endothelial Function in Mice and Humans

Background: Heme oxygenase-1 (HO-1) confers protection to the vasculature and suppresses inflammatory properties of monocytes and macrophages. It is unclear how HO-1 activity and expression determine the extent of vascular dysfunction in mice and humans. Methods and results: Decreasing HO activity was parallelled by decreasing aortic HO-1, eNOS and phospho-eNOS (ser1177) protein expression in HO-1 deficient mice, whereas aortic expression of nox2 showed a stepwise increase in HO-1+/- and HO-1-/- mice as compared to HO-1+/+ controls. Aortic superoxide formation increased depending on the extent of HO-1 deficiency and was blunted by the PKC inhibitor chelerythrine, indicating activation of the NADPH oxidase. When subjected to disease models of vascular dysfunction - angiotensin II-infusion (ATII, 0.1mg/kg/d for 7d), streptozotocin-induced diabetes mellitus and aging - HO-1 deficient mice showed an increased vascular dysfunction (shown by isometric tension studies) that was inversely correlated with HO activity. In a primary prevention population based cohort (the Gutenberg Health Study, GHS), we assessed length polymorphisms of the HO-1 promoter region, established a bipolar frequency pattern of allele length (long vs short repeats) in 4937 individuals and found a moderately significant association with flow mediated dilation of the brachial artery (FMD) in individuals with arterial hypertension. Monocytic HO-1 mRNA expression was positively correlated with CD14 expression indicating proinflammatory monocytes (p&lt;0.001) and inversely with FMD in 733 hypertensive individuals of the GHS. ATII-infused HO-1+/+ mice had a significant infiltration of proinflammatory CD11b+Ly6Chi monocytes into the aortic wall, which was sharpely increased in HO-1+/- and HO-1-/- mice, providing a mechanistic link of the monocyte phenotype determined by HO-1 and vascular dysfunction in arterial hypertension. Conclusions: We here present evidence that HO activity and expression and inversely correlates with vascular dysfunction and NADPH oxidase mediated oxidative stress in mice and humans. We conclude, that HO-1 is a regulator of vascular function in hypertension via determining the phenotype of inflammatory circulating and infiltrating monocytes.

Heme Oxygenase-1 as a Novel Metabolic Player

Heme Oxygenase-1 as a Novel Metabolic Player

Heme oxygenase-1 regulates the immune response to influenza virus infection and vaccination in aged mice.

Underlying mechanisms of individual variation in severity of influenza infection and response to vaccination are poorly understood. We investigated the effect of reduced heme oxygenase-1 (HO-1) expression on vaccine response and outcome of influenza infection. HO-1-deficient and wild-type (WT) mice (kingdom, Animalia; phylum, Chordata; genus/species, Mus musculus) were infected with influenza virus A/PR/8/34 with or without prior vaccination with an adenoviral-based influenza vaccine. A genome-wide association study evaluated the expression of single-nucleotide polymorphisms (SNPs) in the HO-1 gene and the response to influenza vaccination in healthy humans. HO-1-deficient mice had decreased survival after influenza infection compared to WT mice (median survival 5.5 vs. 6.5 d, P=0.016). HO-1-deficient mice had impaired production of antibody following influenza vaccination compared to WT mice (mean antibody titer 869 vs. 1698, P=0.02). One SNP in HO-1 and one SNP in the constitutively expressed isoform HO-2 were independently associated with decreased antibody production after influenza vaccination in healthy human volunteers (P=0.017 and 0.014, respectively). HO-1 deficient mice were paired with sex- and age-matched WT controls. HO-1 affects the immune response to both influenza infection and vaccination, suggesting that therapeutic induction of HO-1 expression may represent a novel adjuvant to enhance influenza vaccine effectiveness.

Heme induces programmed necrosis on macrophages through autocrine TNF and ROS production

AbstractDiseases that cause hemolysis or myonecrosis lead to the leakage of large amounts of heme proteins. Free heme has proinflammatory and cytotoxic effects. Heme induces TLR4-dependent production of tumor necrosis factor (TNF), whereas heme cytotoxicity has been attributed to its ability to intercalate into cell membranes and cause oxidative stress. We show that heme caused early macrophage death characterized by the loss of plasma membrane integrity and morphologic features resembling necrosis. Heme-induced cell death required TNFR1 and TLR4/MyD88-dependent TNF production. Addition of TNF to Tlr4−/− or to Myd88−/− macrophages restored heme-induced cell death. The use of necrostatin-1, a selective inhibitor of receptor-interacting protein 1 (RIP1, also known as RIPK1), or cells deficient in Rip1 or Rip3 revealed a critical role for RIP proteins in heme-induced cell death. Serum, antioxidants, iron chelation, or inhibition of c-Jun N-terminal kinase (JNK) ameliorated heme-induced oxidative burst and blocked macrophage cell death. Macrophages from heme oxygenase-1 deficient mice (Hmox1−/−) had increased oxidative stress and were more sensitive to heme. Taken together, these results revealed that heme induces macrophage necrosis through 2 synergistic mechanisms: TLR4/Myd88-dependent expression of TNF and TLR4-independent generation of ROS.

Disrupted postnatal lung development in heme oxygenase-1 deficient mice

BackgroundHeme oxygenase (HO) degrades cellular heme to carbon monoxide, iron and biliverdin. The HO-1 isoform is both inducible and cyto-protective during oxidative stress, inflammation and lung injury. However, little is known about its precise role and function in lung development. We hypothesized that HO-1 is required for mouse postnatal lung alveolar development and that vascular expression of HO-1 is essential and protective during postnatal alveolar development.MethodsNeonatal lung development in wildtype and HO-1 mutant mice was evaluated by histological and molecular methods. Furthermore, these newborn mice were treated with postnatal dexamethasone (Dex) till postnatal 14 days, and evaluated for lung development.ResultsCompared to wildtype littermates, HO-1 mutant mice exhibited disrupted lung alveolar structure including simplification, disorganization and reduced secondary crest formation. These defects in alveolar development were more pronounced when these mice were challenged with Dex treatment. Expression levels of both vascular endothelial and alveolar epithelial markers were also further decreased in HO-1 mutants after Dex treatment.ConclusionsThese experiments demonstrate that HO-1 is required in normal lung development and that HO-1 disruption and dexamethasone exposure are additive in the disruption of postnatal lung growth. We speculate that HO-1 is involved in postnatal lung development through modulation of pulmonary vascular development.

HO-1 in Control of a Self-Eating Kidney

HO-1 in Control of a Self-Eating Kidney

Heme Oxygenase-1 Accelerates Cutaneous Wound Healing in Mice

Heme oxygenase-1 (HO-1), a cytoprotective, pro-angiogenic and anti-inflammatory enzyme, is strongly induced in injured tissues. Our aim was to clarify its role in cutaneous wound healing. In wild type mice, maximal expression of HO-1 in the skin was observed on the 2nd and 3rd days after wounding. Inhibition of HO-1 by tin protoporphyrin-IX resulted in retardation of wound closure. Healing was also delayed in HO-1 deficient mice, where lack of HO-1 could lead to complete suppression of reepithelialization and to formation of extensive skin lesions, accompanied by impaired neovascularization. Experiments performed in transgenic mice bearing HO-1 under control of keratin 14 promoter showed that increased level of HO-1 in keratinocytes is enough to improve the neovascularization and hasten the closure of wounds. Importantly, induction of HO-1 in wounded skin was relatively weak and delayed in diabetic (db/db) mice, in which also angiogenesis and wound closure were impaired. In such animals local delivery of HO-1 transgene using adenoviral vectors accelerated the wound healing and increased the vascularization. In summary, induction of HO-1 is necessary for efficient wound closure and neovascularization. Impaired wound healing in diabetic mice may be associated with delayed HO-1 upregulation and can be improved by HO-1 gene transfer.

Heme oxygenase-1–derived carbon monoxide enhances the host defense response to microbial sepsis in mice

Sepsis is characterized by a systemic response to severe infection. Although the inflammatory phase of sepsis helps eradicate the infection, it can have detrimental consequences if left unchecked. Therapy directed against inflammatory mediators of sepsis has shown little success and has the potential to impair innate antimicrobial defenses. Heme oxygenase-1 (HO-1) and the product of its enzymatic reaction, CO, have beneficial antiinflammatory properties, but little is known about their effects on microbial sepsis. Here, we have demonstrated that during microbial sepsis, HO-1-derived CO plays an important role in the antimicrobial process without inhibiting the inflammatory response. HO-1-deficient mice suffered exaggerated lethality from polymicrobial sepsis. Targeting HO-1 to SMCs and myofibroblasts of blood vessels and bowel ameliorated sepsis-induced death associated with Enterococcus faecalis, but not Escherichia coli, infection. The increase in HO-1 expression did not suppress circulating inflammatory cells or their accumulation at the site of injury but did enhance bacterial clearance by increasing phagocytosis and the endogenous antimicrobial response. Furthermore, injection of a CO-releasing molecule into WT mice increased phagocytosis and rescued HO-1-deficient mice from sepsis-induced lethality. These data advocate HO-1-derived CO as an important mediator of the host defense response to sepsis and suggest CO administration as a possible treatment for the disease.

Carbon monoxide and bilirubin from heme oxygenase-1 suppresses reactive oxygen species generation and plasminogen activator inhibitor-1 induction

Heme oxygenase-1 (HO-1) responds to a variety of oxidative stresses. We examined whether HO-1 expression influences pro-thrombotic processes, in which the involvement of oxidative stress has been reported. Since HO-1 knockout mice with a C57/BL6J background were not viable, embryonic cells from HO-1 deficient mice (E11.5) were used. Cell viability, the level of plasminogen activator inhibitor-1 (PAI-1) expression and reactive oxygen species (ROS) generation of HO-1 deficient cells in response to the exposures to hydrogen peroxide and oxidized LDL were compared to those with wild-type cells. We also examined the effects of glutathione (GSH), desferrioxamine (DFO) and diphenyleneiodonium (DPI: an NADPH oxidase inhibitor) as well as of the HO reaction products, bilirubin (BR) and carbon monoxide (CO) on PAI-1 expression and ROS generation. PAI-1 expression and ROS generation were markedly elevated in HO-1 deficient cells compared to wild-type cells. Exposure to oxidized LDL significantly elevated PAI-1 expression and ROS production in HO-1 deficient cells. Interestingly, these increases in HO-1 deficient cells were significantly lowered by BR, CO, GSH and DPI while DFO had little effect. Furthermore, BR and CO were effective to improve viabilities of HO-1 deficient cells. These results suggest that HO-1 may be required to suppress ROS generation and the production of pro-thrombotic molecules such as PAI-1.

Endotoxin-induced mortality is related to increased oxidative stress and end-organ dysfunction, not refractory hypotension, in heme oxygenase-1-deficient mice.

Heme oxygenase (HO)-1 is an enzyme that degrades heme to generate CO (a vasodilatory gas), iron, and the potent antioxidant bilirubin. A disease process characterized by decreases in vascular tone and increases in oxidative stress is endotoxic shock. Moreover, HO-1 is markedly induced in multiple organs after the administration of endotoxin (lipopolysaccharide [LPS]) to mice. To determine the role of HO-1 in endotoxemia, we administered LPS to mice that were wild-type (+/+), heterozygous (+/-), or homozygous null (-/-) for targeted disruption of HO-1. LPS produced a similar induction of HO-1 mRNA and protein in HO-1(+/+) and HO-1(+/-) mice, whereas HO-1(-/-) mice showed no HO-1 expression. Four hours after LPS, systolic blood pressure (SBP) decreased in all the groups. However, SBP was significantly higher in HO-1(-/-) mice (121+/-5 mm Hg) after 24 hours, compared with HO-1(+/+) (96+/-7 mm Hg) and HO-1(+/-) (89+/-13 mm Hg) mice. A sustained increase in endothelin-1 contributed to this SBP response. Even though SBP was higher, mortality was increased in HO-1(-/-) mice, and they exhibited hepatic and renal dysfunction that was not present in HO-1(+/+) and HO-1(+/-) mice. The end-organ damage and death in HO-1(-/-) mice was related to increased oxidative stress. These data suggest that the increased mortality during endotoxemia in HO-1(-/-) mice is related to increased oxidative stress and end-organ (renal and hepatic) damage, not to refractory hypotension.