Siglec-E retards atherosclerosis by inhibiting CD36-mediated foam cell formation

BACKGROUND

The accumulation of lipid-laden macrophages, foam cells, within sub-endothelial intima is a key feature of early atherosclerosis. Siglec-E, a mouse orthologue of human Siglec-9, is a sialic acid binding lectin predominantly expressed on the surface of myeloid cells to transduce inhibitory signal via recruitment of SH2-domain containing protein tyrosine phosphatase SHP-1/2 upon binding to its sialoglycan ligands. Whether Siglec-E expression on macrophages impacts foam cell formation and atherosclerosis remains to be established.

METHODS

ApoE-deficient (apoE^-/-) and apoE/Siglec-E-double deficient (apoE^-/-/Siglec-E^-/-) mice were placed on high fat diet for 3 months and their lipid profiles and severities of atherosclerosis were assessed. Modified low-density lipoprotein (LDL) uptake and foam cell formation in wild type (WT) and Siglec-E^-/-- peritoneal macrophages were examined in vitro. Potential Siglec-E-interacting proteins were identified by proximity labeling in conjunction with proteomic analysis and confirmed by coimmunoprecipitation experiment. Impacts of Siglec-E expression and cell surface sialic acid status on oxidized LDL uptake and signaling involved were examined by biochemical assays.

RESULTS

Here we show that genetic deletion of Siglec-E accelerated atherosclerosis without affecting lipid profile in apoE^-/- mice. Siglec-E deficiency promotes foam cell formation by enhancing acetylated and oxidized LDL uptake without affecting cholesterol efflux in macrophages in vitro. By performing proximity labeling and proteomic analysis, we identified scavenger receptor CD36 as a cell surface protein interacting with Siglec-E. Further experiments performed in HEK293T cells transiently overexpressing Siglec-E and CD36 and peritoneal macrophages demonstrated that depletion of cell surface sialic acids by treatment with sialyltransferase inhibitor or sialidase did not affect interaction between Siglec-E and CD36 but retarded Siglec-E-mediated inhibition on oxidized LDL uptake. Subsequent experiments revealed that oxidized LDL induced transient Siglec-E tyrosine phosphorylation and recruitment of SHP-1 phosphatase in macrophages. VAV, a downstream effector implicated in CD36-mediated oxidized LDL uptake, was shown to interact with SHP-1 following oxidized LDL treatment. Moreover, oxidized LDL-induced VAV phosphorylation was substantially lower in WT macrophages comparing to Siglec-E^-/- counterparts.

CONCLUSIONS

These data support the protective role of Siglec-E in atherosclerosis. Mechanistically, Siglec-E interacts with CD36 to suppress downstream VAV signaling involved in modified LDL uptake.

Gal-1 (Galectin-1) Upregulation Contributes to Abdominal Aortic Aneurysm Progression by Enhancing Vascular Inflammation

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a vascular degenerative disease causing sudden rupture of aorta and significant mortality in elders. Nevertheless, no prognostic and therapeutic target is available for disease management. Gal-1 (galectin-1) is a β-galactoside-binding lectin constitutively expressed in vasculature with roles in maintaining vascular homeostasis. This study aims to investigate the potential involvement of Gal-1 in AAA progression. Approach and Results: Gal-1 was significantly elevated in circulation and aortic tissues of Ang II (angiotensin II)-infused apoE-deficient mice developing AAA. Gal-1 deficiency reduced incidence and severity of AAA with lower expression of aortic MMPs (matrix metalloproteases) and proinflammatory cytokines. TNFα (tumor necrosis factor alpha) induced Gal-1 expression in cultured vascular smooth muscle cells and adventitial fibroblasts. Gal-1 deletion enhanced TNFα-induced MMP9 expression in fibroblasts but not vascular smooth muscle cells. Cysteinyl-labeling assay demonstrated that aortic Gal-1 exhibited susceptibility to oxidation in vivo. Recombinant oxidized Gal-1 induced expression of MMP9 and inflammatory cytokines to various extents in macrophages, vascular smooth muscle cells, and fibroblasts through activation of MAP (mitogen-activated protein) kinase signaling. Clinically, serum MMP9 level was significantly higher in both patients with AAA and coronary artery disease than in control subjects, whereas serum Gal-1 level was elevated in patients with AAA but not coronary artery disease when compared with controls.

CONCLUSIONS

Gal-1 is highly induced and contributes to AAA by enhancing matrix degradation activity and inflammatory responses in experimental model. The pathological link between Gal-1 and AAA is also observed in human patients. These findings support the potential of Gal-1 as a disease biomarker and therapeutic target of AAA.

Signal peptide peptidase promotes tumor progression via facilitating FKBP8 degradation

Signal peptide peptidase (SPP) is an endoplasmic reticulum (ER)-resident aspartyl protease mediating intramembrane cleavage of type II transmembrane proteins. Increasing evidence has supported the role of SPP in ER-associated protein degradation. In the present study, we show that SPP expression is highly induced in human lung and breast cancers and correlated with disease outcome. Stable depletion of SPP expression in lung and breast cancer cell lines significantly reduced cell growth and migration/invasion abilities. Quantitative analysis of the proteomic changes of microsomal proteins in lung cancer cells by the stable isotope labeling with amino acids in cell culture (SILAC) approach revealed that the level of FKBP8, an endogenous inhibitor of mTOR, was significantly increased following SPP depletion. Co-immunoprecipitation assay and confocal immunofluorescence demonstrated that SPP interacted and colocalized with FKBP8 in ER, supporting that FKBP8 is a protein substrate of SPP. Cycloheximide chase and proteasome inhibition experiments revealed that SPP-mediated proteolysis facilitated FKBP8 protein degradation in cytosol. Further experiment demonstrated that the levels of phosphorylation in mTOR and its downstream effectors, S6K and 4E-BP1, were significantly lower in SPP-depleted cells. The reduced mTOR signaling and decreases of growth and migration/invasion abilities induced by SPP depletion in cancer cells could be reversed by FKBP8 downregulation. The implication of FKBP8 in SPP-mediated tumorigenicity was also observed in the xenograft model. Together, these findings disclose that SPP promotes tumor progression, at least in part, via facilitating the degradation of FKBP8 to enhance mTOR signaling.

Galectin-1 Restricts Vascular Smooth Muscle Cell Motility Via Modulating Adhesion Force and Focal Adhesion Dynamics

Vascular smooth muscle cell (VSMC) migration play a key role in the development of intimal hyperplasia and atherosclerosis. Galectin-1 (Gal-1) is a redox-sensitive β-galactoside-binding lectin expressed in VSMCs with intracellular and extracellular localizations. Here we show that VSMCs deficient in Gal-1 (Gal-1-KO) exhibited greater motility than wild type (WT) cells. Likewise, Gal-1-KO-VSMC migration was inhibited by a redox-insensitive but activity-preserved Gal-1 (CSGal-1) in a glycan-dependent manner. Gal-1-KO-VSMCs adhered slower than WT cells on fibronectin. Cell spreading and focal adhesion (FA) formation examined by phalloidin and vinculin staining were less in Gal-1-KO-VSMCs. Concomitantly, FA kinase (FAK) phosphorylation was induced to a lower extent in Gal-1-KO cells. Analysis of FA dynamics by nocodazole washout assay demonstrated that FA disassembly, correlated with FAK de-phosphorylation, was faster in Gal-1-KO-VSMCs. Surface plasmon resonance assay demonstrated that CSGal-1 interacted with α5β1integrin and fibronectin in a glycan-dependent manner. Chemical crosslinking experiment and atomic force microscopy further revealed the involvement of extracellular Gal-1 in strengthening VSMC-fibronectin interaction. In vivo experiment showed that carotid ligation-induced neointimal hyperplasia was more severe in Gal-1-KO mice than WT counterparts. Collectively, these data disclose that Gal-1 restricts VSMC migration by modulating cell-matrix interaction and focal adhesion turnover, which limits neointimal formation post vascular injury.

Identification of danthron as an isoform-specific inhibitor of HEME OXYGENASE-1/cytochrome P450 reductase interaction with anti-tumor activity

Background

Heme oxygenase (HO) catalyzes NADPH-dependent degradation of heme to liberate iron, carbon monoxide and biliverdin. The interaction between HO and cytochrome P450 reductase (CPR), an electron donor, is essential for HO activity. HO-1 is a stress-inducible isoform whereas HO-2 is constitutively expressed. HO-1 induction is commonly seen in cancers and impacts disease progression, supporting the possibility of targeting HO-1 for cancer therapy.

Methods

We employed a cell-based bioluminescence resonance energy transfer assay to screen compounds with ability to inhibit HO-1/CPR interaction. The effect of the identified compound on HO-1/CPR interaction was confirmed by pull down assay. Moreover, the anti-tumorigenic activity of the identified compound on HO-1-enhanced tumor growth and migration was assessed by trypan blue exclusion method and wound healing assay.

Results

Danthron was identified as an effective small molecule able to interfere with the interaction between HO-1 and CPR but not HO-2 and CPR. Additional experiments with structural analogues of danthron revealed that the positions of hydroxyl moieties significantly affected the potency of inhibition on HO-1/CPR interaction. Pull-down assay confirmed that danthron inhibited the interaction of CPR with HO-1 but not HO-2. Danthron suppressed growth and migration of HeLa cells with stable HO-1 overexpression but not mock cells. In contrast, anthrarufin, a structural analog with no ability to interfere HO-1/CPR interaction, exhibited no significant effect on HO-1-overexpressing HeLa cells.

Conclusions

These findings demonstrate that danthron is an isoform-specific inhibitor for HO-1/CPR interaction and may serve as a lead compound for novel anticancer drug.

Biomimicking Platelet-Monocyte Interactions as a Novel Targeting Strategy for Heart Healing

In patients who survive myocardial infarction, many go on to develop congestive heart failure (CHF). Despite ongoing efforts to develop new approaches for postinfarction therapy, there are still no effective therapeutic options available to CHF patients. Currently, the delivery of cardioprotective drugs relies entirely on passive uptake via the enhanced permeability and retention (EPR) effect which occurs in proximity to the infarction site. However, in ischemic disease, unlike in cancer, the EPR effect only exists for a short duration postinfarction and thus insufficient for meaningful cardioprotection. Splenic monocytes are recruited to the heart in large numbers postinfarction, and are known to interact with platelets during circulation. Therefore, the strategy is to exploit this interaction by developing platelet-like proteoliposomes (PLPs), biomimicking platelet interactions with circulating monocytes. PLPs show strong binding affinity for monocytes but not for endothelial cells in vitro, mimicking normal platelet activity. Furthermore, intravital multiphoton imaging shows that comparing to plain liposomes, PLPs do not aggregate on uninjured endothelium but do accumulate at the injury site 72 h postinfarction. Importantly, PLPs enhance the targeting of anti-inflammatory drug, cobalt protoporphyrin, to the heart in an EPR-independent manner, which result in better therapeutic outcome.

TRC8 downregulation contributes to the development of non-alcoholic steatohepatitis by exacerbating hepatic endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress is implicated in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). TRC8 is an ER-resident E3 ligase with roles in modulating lipid and protein biosynthesis. In this study we showed that TRC8 expression was downregulated in steatotic livers of patients and mice fed with a high fat diet (HFD) or a methionine and choline deficient (MCD) diet. To investigate the impact of TRC8 downregulation on steatosis and the progression to non-alcoholic steatohepatitis (NASH), we placed TRC8 knockout (KO) mice and wild type (WT) controls on a HFD or MCD diet and the severities of steatosis and NASH developed were compared. We found that TRC8 deficiency did not significantly affect diet-induced steatosis. Nevertheless, MCD diet-induced NASH as characterized by hepatocyte death, inflammation and fibrosis were exacerbated in TRC8-KO mice. The hepatic ER stress response, as evidenced by increased eIF2α phosphorylation and expression of ATF4 and CHOP, and the level of activated caspase 3, an apoptosis indicator, were augmented by TRC8 deficiency. The hepatic ER stress and NASH induced in mice could be ameliorated by adenovirus-mediated hepatic TRC8 overexpression. Mechanistically, we found that TRC8 deficiency augmented lipotoxic-stress-induced unfolded protein response in hepatocytes by attenuating the arrest of protein translation and the misfolded protein degradation. These findings disclose a crucial role of TRC8 in the maintenance of ER protein homeostasis and its downregulation in steatotic liver contributes to the progression of NAFLD.

Heme oxygenase-1: emerging target of cancer therapy

Heme oxygenase-1 (HO-1) is a rate-limiting enzyme catalyzing oxidative degradation of cellular heme to liberate free iron, carbon monoxide (CO) and biliverdin in mammalian cells. In addition to its primary role in heme catabolism, HO-1 exhibits anti-oxidative and anti-inflammatory functions via the actions of biliverdin and CO, respectively. HO-1 is highly induced in various disease states, including cancer. Several lines of evidence have supported the implication of HO-1 in carcinogenesis and tumor progression. HO-1 deficiency in normal cells enhances DNA damage and carcinogenesis. Nevertheless, HO-1 overexpression in cancer cells promotes proliferation and survival. Moreover, HO-1 induces angiogenesis through modulating expression of angiogenic factors. Although HO-1 is an endoplasmic reticulum resident protein, HO-1 nuclear localization is evident in tumor cells of cancer tissues. It has been shown that HO-1 is susceptible to proteolytic cleavage and translocates to nucleus to facilitate tumor growth and invasion independent of its enzymatic activity. HO-1 also impacts cancer progression through modulating tumor microenvironment. This review summarizes the current understanding of the protumorigenic role of HO-1 and its potential as a molecular target for cancer therapy.

Myeloid heme oxygenase-1 promotes metastatic tumor colonization in mice

Heme oxygenase-1 (HO-1) is a heme degradation enzyme with antioxidant and immune-modulatory functions. HO-1 promotes tumorigenesis by enhancing tumor cell proliferation and invasion. Whether HO-1 has an effect on cancer progression through stromal compartments is less clear. Here we show that the growth of tumor engrafted subcutaneously in syngeneic mice was not affected by host HO-1 expression. However, lung metastasis arisen from subcutaneous tumor or circulating tumor cells was significantly reduced in HO-1^+/− mice comparing to wild type (WT) mice. The reduced lung metastasis was also observed in B6 mice bearing HO-1^+/− bone marrow as comparing to WT chimeras, indicating that HO-1 expression in hematopoietic cells impacts tumor colonization at the metastatic site. Further experiments demonstrated that the numbers of myeloid cells recruited to pulmonary premetastatic niches and metastatic loci were significantly lower in HO-1^+/− mice than in WT mice. Likewise, the extents of tumor cell extravasation and colonization at the metastatic loci in the early phase of metastasis were significantly lower in HO-1^+/− mice. Mechanistic studies revealed that HO-1 impacted chemoattractant-induced myeloid cell migration by modulating p38 kinase signaling. Moreover, myeloid HO-1-induced expressions of vascular endothelial growth factor and interleukin-10 promoted tumor cell transendothelial migration and STAT3 activation in vitro. These data support a pathological role of myeloid HO-1 in metastasis and suggest a possibility of targeting myeloid HO-1 for cancer treatment.

Activator protein-2α mediates carbon monoxide-induced stromal cell-derived factor-1α expression and vascularization in ischemic heart

OBJECTIVE

Increased cardiac stromal cell-derived factor-1α (SDF-1α) expression promotes neovascularization and myocardial repair after ischemic injury through recruiting stem cells and reducing cardiomyocyte death. Previous studies have shown that heme oxygenase-1 and its reaction byproduct, carbon monoxide (CO), induce SDF-1α expression in ischemic heart. However, the mechanism underlying heme oxygenase-1/CO-induced cardiac SDF-1α expression remains elusive. This study aims to investigate the signaling pathway and the transcriptional factor that mediate CO-induced SDF-1α gene expression and cardioprotection.

APPROACH AND RESULTS

CO gas and a CO-releasing compound, tricarbonyldichlororuthenium (II) dimer, dose-dependently induced SDF-1α expression in primary neonatal cardiomyocytes and H9C2 cardiomyoblasts. Promoter luciferase-reporter assay, electrophoretic mobility shift assay, and chromatin immunoprecipitation demonstrated that the activator protein 2α (AP-2α) mediated tricarbonyldichlororuthenium (II) dimer-induced SDF-1α gene transcription. Tricarbonyldichlororuthenium (II) dimer induced AP-2α expression via protein kinase B (AKT)-dependent signaling. AKT inhibition or AP-2α knockdown reduced tricarbonyldichlororuthenium (II) dimer-induced SDF-1α expression. Coronary ligation induced transient increases of cardiac AP-2α and SDF-1α expression, which were declined at 1 week postinfarction in mice. Periodic exposure of coronary-ligated mice to CO (250 ppm for 1 hour/day, 6 days) resumed the induction of AP-2α and SDF-1α gene expression in infarcted hearts. Immunohistochemistry and echocardiography performed at 4 weeks after coronary ligation revealed that CO treatment enhanced neovascularization in the myocardium of peri-infarct region and improved cardiac function. CO-mediated SDF-1α expression and cardioprotection was ablated by intramyocardial injection of lentivirus bearing specific short hairpin RNA targeting AP-2α.

CONCLUSIONS

Our data demonstrate that AKT-dependent upregulation of AP-2α is essential for CO-induced SDF-1α expression and myocardial repair after ischemic injury.

Heme oxygenase-1/carbon monoxide induces vascular endothelial growth factor expression via p38 kinase-dependent activation of Sp1

Heme oxygenase-1 (HO-1) is a stress-inducible enzyme catalyzing the oxidative degradation of heme to free iron, CO, and biliverdin. Previous studies demonstrated that HO-1 overexpression promoted VEGF expression and angiogenesis in the ischemic heart. However, the underlying mechanism remained elusive. Here we show that adenovirus-mediated HO-1 transduction of rat primary cardiomyocytes and H9C2 myocytes resulted in significant induction of VEGF expression, and a similar effect was seen in cells directly exposed to CO gas or a CO-releasing compound, tricarbonyldichlororuthenium (II) dimer. HO-1/CO-induced VEGF expression was significantly suppressed by pharmacological inhibition of p38 kinase, but not of AKT, activation. VEGF promoter-luciferase reporter assays, electrophoretic mobility shift assays, supershift assay, and chromatin immunoprecipitation showed that CO-induced VEGF promoter activation requires the binding of the Sp1 transcriptional factor to a cis-regulatory sequence located at the VEGF promoter. Western blot analysis and immunostaining experiments demonstrated that HO-1/CO induced p38-dependent phosphorylation of Sp1 at Thr-453 and Thr-739 both in vitro and in vivo. Overexpression of Sp1 protein with an alanine mutation at Thr-453 or Thr-739 suppressed CO-induced Sp1 binding to the VEGF promoter and its transcriptional activation. Collectively, these data suggest that p38-dependent phosphorylation of Sp1 at Thr-453/Thr-739 is crucial for HO-1/CO-induced VEGF expression in myocytes.

Transgenic expression of haem oxygenase-1 in pancreatic beta cells protects non-obese mice used as a model of diabetes from autoimmune destruction and prolongs graft survival following islet transplantation

AIMS/HYPOTHESIS

Haem oxygenase 1 (HO-1) has strong anti-apoptotic, anti-inflammatory and antioxidative effects that help protect cells against various forms of immune attack. We investigated whether transgenic expression of Ho-1 (also known as Hmox1) in pancreatic beta cells would protect NOD mice from autoimmune damage and prolong graft survival following islet transplantation.

METHODS

To evaluate the protective effect of beta cell-specific HO-1 in autoimmune diabetes, we used an insulin promoter-driven murine Ho-1 construct (pIns-mHo-1) to generate a transgenic NOD mouse. Transgene expression, insulitis and the incidence of diabetes in mice were characterised. Lymphocyte composition, the development of T helper (Th)1, Th2 and T regulatory (Treg) cells, T cell proliferation and lymphocyte-mediated disease transfer were analysed. The potential effects of transgenic islets and islet transplantation on apoptosis, inflammation and the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) were evaluated.

RESULTS

Transgenic mice showed less severe insulitis and a lower incidence of diabetes than non-transgenic control littermates. Lymphocyte composition and functions were not affected. Islets from transgenic mice expressed lower levels of proinflammatory cytokines/chemokines, proapoptotic gene expression and amounts of ROS/RNS, and were more resistant to TNF-α- and IFN-γ-induced apoptosis. Islet grafts from transgenic mice also survived longer in diabetic recipients than control islets.

CONCLUSIONS/INTERPRETATION

Transgenic overexpression of Ho-1 in beta cells protected NOD mice from diabetes and delayed the autoimmune destruction of islet grafts, providing valuable insight into the development of better strategies for clinical islet transplantation in patients with type 1 diabetes.

Shorter GT repeat polymorphism in the heme oxygenase-1 gene promoter has protective effect on ischemic stroke in dyslipidemia patients

Background

The microsatellite polymorphism of heme oxygenase (HO)-1 gene promoter has been shown to be associated with the susceptibility to ischemic event, including coronary artery disease (CAD), myocardial infarction, and peripheral vascular disease. We aimed to examine whether the length of (GT)_n repeats in HO-1 gene promoter is associated with ischemic stroke in people with CAD risk factors, especially low level of HDL.

Methods

A total of 183 consecutive firstever ischemic stroke inpatients and 164 non-stroke patients were screened for the length of (GT)_n repeats in HO-1 promoter. The long (L) and short (S) genotype are defined as the averaged repeat number >26 and ≦26, respectively.

Results

Stroke patients tended to have more proportions of hypertension, diabetics and genotype L, than those of genotype S. Patients with genotype L of HO-1 gene promoter have higher stroke risk in comparison with genotype S especially in dyslipidemia individuals. The significant differences on stroke risk in multivariate odds ratios were found especially in people with low HDL-C levels.

Conclusions

Subjects carrying longer (GT)_n repeats in HO-1 gene promoter may have greater susceptibility to develop cerebral ischemic only in the presence of low HDL-C, suggesting the protective effects in HO-1 genotype S in the process of ischemic stroke, particularly in subjects with poor HDL-C status.

Shorter GT repeat polymorphism in the heme oxygenase-1 gene promoter has protective effect on ischemic stroke in dyslipidemia patients

BACKGROUND

The microsatellite polymorphism of heme oxygenase (HO)-1 gene promoter has been shown to be associated with the susceptibility to ischemic event, including coronary artery disease (CAD), myocardial infarction, and peripheral vascular disease. We aimed to examine whether the length of (GT)(n) repeats in HO-1 gene promoter is associated with ischemic stroke in people with CAD risk factors, especially low level of HDL.

METHODS

A total of 183 consecutive firstever ischemic stroke inpatients and 164 non-stroke patients were screened for the length of (GT)(n) repeats in HO-1 promoter. The long (L) and short (S) genotype are defined as the averaged repeat number >26 and <==26, respectively.

RESULTS

Stroke patients tended to have more proportions of hypertension, diabetics and genotype L, than those of genotype S. Patients with genotype L of HO-1 gene promoter have higher stroke risk in comparison with genotype S especially in dyslipidemia individuals. The significant differences on stroke risk in multivariate odds ratios were found especially in people with low HDL-C levels.

CONCLUSIONS

Subjects carrying longer (GT)(n) repeats in HO-1 gene promoter may have greater susceptibility to develop cerebral ischemic only in the presence of low HDL-C, suggesting the protective effects in HO-1 genotype S in the process of ischemic stroke, particularly in subjects with poor HDL-C status.

Heme oxygenase-1 in cardiovascular diseases: molecular mechanisms and clinical perspectives

Heme oxygenase (HO) catalyzes the rate-limiting step in the oxidative degradation of cellular heme that liberates iron, carbon monoxide (CO), and biliverdin. Two distinct HO isoforms have been identified in mammalian system. Compared to HO-2, which is constitutively expressed, HO-1 is a stressresponsive protein that is highly induced by many agents, including cytokines, endotoxin, heavy metals, nitric oxide and its own substrate heme. In addition to its well-defined role in heme catabolism and erythrocyte turnover, HO-1 also plays an important function in various physiological and pathophysiological states associated with cellular stress. Over the past decade, compelling evidence has revealed that the induction of HO-1 represents an important defensive mechanism against further oxidative injury in tissues and cells following various insults; this occurs by virtue of the anti-inflammatory and antioxidant capacities of CO, biliverdin, and the subsequent metabolite of biliverdin, bilirubin. In line with the findings from the basic research, numerous studies have supported the importance of HO-1 in various clinical diseases, including coronary artery disease, cardiac hypertrophy, diabetes mellitus, ischemic/reperfusion injury, atherosclerosis and cancer. This review provides an overview on the regulation and function of HO-1, ranging from the molecular mechanisms involved to various clinical perspectives. Specifically, there is a focus on the enzyme's role in various cardiovascular diseases.

Overexpression of HO-1 protects against TNF-alpha-mediated airway inflammation by down-regulation of TNFR1-dependent oxidative stress

Oxidative stresses are believed to play an important role in the induction of both cell adhesion molecules and pro-inflammatory cytokines, a key event in a variety of inflammatory processes. The enzyme heme oxygenase-1 (HO-1) functions as an antioxidant and serves to protect against tissue injury. In this study, we report that HO-1 was induced in cultured human tracheal smooth muscle cells after either treatment with a potent inducer of HO-1 activity, cobalt protoporphyrin IX, or infection with a recombinant adenovirus that carries the human HO-1 gene. Overexpression of HO-1 protected against tumor necrosis factor (TNF)-alpha-mediated airway inflammation via the down-regulation of oxidative stress, adhesion molecules, and interleukin-6 in both cultured human tracheal smooth muscle cells and the airways of mice. In addition, HO-1 overexpression inhibited TNF-alpha-induced intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression, adherence of THP-1 cells, generation of interleukin-6, p47(phox) translocation, and nuclear factor-kappaB activation. HO-1 overexpression also attenuated TNF-alpha-induced oxidative stress, which was abrogated in the presence of both the HO-1 inhibitor, zinc protoporphyrin IX, as well as a carbon monoxide scavenger. In addition, HO-1 overexpression reduced the formation of a TNFR1/c-Src/p47(phox) complex. These results suggest that HO-1 functions as a suppressor of TNF-alpha signaling, not only by inhibiting the expression of adhesion molecules and generation of interleukin-6, but also by diminishing intracellular reactive oxygen species production and nuclear factor-kappaB activation in both cultured human tracheal smooth muscle cells and the airways of mice.

Oligomerization is crucial for the stability and function of heme oxygenase-1 in the endoplasmic reticulum

Heme oxygenase-1 (HO-1), a stress-inducible enzyme anchored in the endoplasmic reticulum (ER) by a single transmembrane segment (TMS) located at the C terminus, interacts with NADPH cytochrome P450 reductase and biliverdin reductase to catalyze heme degradation to biliverdin and its metabolite, bilirubin. Previous studies suggested that HO-1 functions as a monomer. Using chemical cross-linking, co-immunoprecipitation, and fluorescence resonance energy transfer (FRET) experiments, here we showed that HO-1 forms dimers/oligomers in the ER. However, oligomerization was not observed with a truncated HO-1 lacking the C-terminal TMS (amino acids 266-285), which exhibited cytosolic and nuclear localization, indicating that the TMS is essential for the self-assembly of HO-1 in the ER. To identify the interface involved in the TMS-TMS interaction, residue Trp-270, predicted by molecular modeling as a potential interfacial residue of TMS alpha-helices, was mutated, and the effects on protein subcellular localization and activity assessed. The results showed that the W270A mutant was present exclusively in the ER and formed oligomers with similar activity to those of the wild type HO-1. Interestingly, the W270N mutant was localized not only in the ER, but also in the cytosol and nucleus, suggesting it is susceptible to proteolytic cleavage. Moreover, the microsomal HO activity of the W270N mutant was significantly lower than that of the wild type. The W270N mutation appears to interfere with the oligomeric state, as revealed by a lower FRET efficiency. Collectively, these data suggest that oligomerization, driven by TMS-TMS interactions, is crucial for the stabilization and function of HO-1 in the ER.

Hemin promotes proliferation and differentiation of endothelial progenitor cells via activation of AKT and ERK

Increased neovascularization is commonly observed in hemorrhagic plaques and associated with rupture of atherosclerotic lesions. This study aims to investigate whether hemin accumulated at the site of hematoma promotes neovascularization through affecting the growth and function of endothelial progenitor cells (EPCs) and the possible mechanism involved. Here we demonstrated that hemin promoted a significant increase in neovessel formation in matrigel plugs embedded in vivo and enhanced the proliferation and endothelial gene expression in EPCs in vitro. VEGF-induced migration response and the capability to incorporate into the vascular networks were markedly enhanced in hemin-treated EPCs. Hemin induced the phosphorylation of ERK and AKT but not p38 or JNK. The inhibition of AKT or ERK activation significantly attenuated the effect of hemin on cell proliferation. However, the enhanced migration response induced by hemin was significantly suppressed by the inhibition of AKT but not ERK. Hemin induced significant increase in reactive oxygen species (ROS) production and hemin-induced angiogenic response of EPCs was substantially reduced by treatment with N-acetylcysteine. Collectively, these data support that hemin-induced ROS mediates the activation of AKT and ERK signaling pathways, which in turn promotes the cell proliferation and function of EPCs. J. Cell. Physiol. 219: 617-625, 2009. (c) 2009 Wiley-Liss, Inc.

Serum bilirubin and ferritin levels link heme oxygenase-1 gene promoter polymorphism and susceptibility to coronary artery disease in diabetic patients

OBJECTIVE

Heme oxygenase (HO) leads to the generation of free iron, carbon monoxide, and bilirubin. A length polymorphism of GT repeats in the promoter of human HO-1 gene has been shown to modulate gene transcription. The aim of this study was to assess the association of the length of (GT)(n) repeats in the HO-1 gene promoter with serum bilirubin, markers of iron status, and the development of coronary artery disease (CAD).

RESEARCH DESIGN AND METHODS

We screened the allelic frequencies of (GT)(n) repeats in the HO-1 gene promoter in 986 unrelated individuals who underwent coronary angiography. Serum bilirubin and markers of iron status were evaluated.

RESULTS

The distribution of numbers of (GT)(n) repeats was divided into two subclasses: class S included shorter (<27) repeats, and class L included longer (>or=27) repeats. Among those with diabetes, subjects with the L/L genotype had significantly lower bilirubin levels than those with S/S and S/L genotypes (0.70 +/- 0.22 vs. 0.81 +/- 0.24 mg/dl, P = 0.001) and higher serum ferritin values (4.76 +/- 0.72 vs. 4.28 +/- 1.05 mug/l for log ferritin, P = 0.001). Compared with those carrying the S allele, diabetic subjects with the L/L genotype had an almost threefold increase in CAD risk after controlling for conventional risk factors (odds ratio 2.81, [95% CI 1.22-6.47], P = 0.015). With adjustment for both serum bilirubin and ferritin, the effect of HO-1 promoter polymorphism on susceptibility to CAD disappeared.

CONCLUSIONS

Length polymorphism in the HO-1 gene promoter is correlated with susceptibility to CAD in diabetic patients, and this effect might be conveyed through its influence on serum bilirubin and ferritin.

Ubiquitin-proteasome system mediates heme oxygenase-1 degradation through endoplasmic reticulum-associated degradation pathway

The present study investigated the cellular mechanism underlying the degradation of heme oxygenase-1 (HO-1), an endoplasmic reticulum (ER)-anchored protein. The turnover of HO-1 induced in vascular smooth muscle cells (VSMCs) was significantly attenuated by proteasome inhibitors, suggesting the involvement of a proteasome-mediated pathway. High molecular weight ubiquitin conjugates were co-immunoprecipitated with HO-1 from VSMCs after proteasome inhibition, and HO-1 ubiquitination was confirmed in HEK293 cells overexpressing His-tagged HO-1 and HA-tagged ubiquitin. Endogenous p97, an ATPase, and Ufd1, both implicated as essential components in the ER-associated degradation pathway (ERAD), were co-eluted with His-tagged HO-1 from metal affinity resin. Knockdown of either p97 or Ufd1 in HEK293 cells using specific siRNA significantly prolonged the half-life of endogenously induced HO-1 and slowed the degradation of ubiquitinated HO-1. HO-1 ubiquitination in HEK293 cells was enhanced by zinc chloride, but suppressed with a zinc chelator (N,N,N',N'-tetrakis(2-pyridylmethyl)ethyl-enediamine), suggesting the involvement of a RING-E3 ligase in this process. Collectively, these data indicate that HO-1 protein turnover is regulated by the ubiquitin-proteasome system through the ERAD pathway.

Systemic expression of heme oxygenase-1 ameliorates type 1 diabetes in NOD mice

Heme oxygenase-1 (HO-1) is an enzyme with potent immunoregulatory capacity. To evaluate the effect of HO-1 on autoimmune diabetes, female NOD mice at 9 weeks of age received a single intravenous injection of a recombinant adeno-associated virus bearing HO-1 gene (AAV-HO-1; 0.5 x 10(10)-2.5 x 10(10) viruses/mouse). In a dose-dependent manner, HO-1 transduction reduced destructive insulitis and the incidence of overt diabetes examined over a 15-week period. HO-1-mediated protection was associated with a lower type 1 T-helper cell (Th1)-mediated response. Adaptive transfer experiments in NOD.scid mice demonstrated that splenocytes isolated from AAV-HO-1-treated mice were less diabetogenic. Flow cytometry analysis revealed no significant difference in the percentages of CD4(+)CD25(+) regulatory T-cells between saline-treated and AAV-HO-1-treated groups. However, the CD11c(+) major histocompatibility complex II(+) dendritic cell population was much lower in the AAV-HO-1-treated group. A similar protective effect against diabetes was observed in NOD mice subjected to carbon monoxide (CO) gas (250 ppm CO for 2 h, twice per week). These data suggest that HO-1 slows the progression to overt diabetes in pre-diabetic NOD mice by downregulating the phenotypic maturity of dendritic cells and Th1 effector function. CO appears to mediate at least partly the beneficial effect of HO-1 in this disease setting.

Effects of adenovirus-expressing IL-10 in alleviating airway inflammation in asthma

BACKGROUND

Allergic asthma strongly correlates with airway inflammation caused by cytokines secreted by allergen-specific type-2 T helper (Th2) cells, but the immunologic regulation of cell function is yet to be acquired. Further, IL-10 has been found to exert both antiinflammatory and immunoregulatory activities. This study aimed to elucidate the therapeutic effects of IL-10 administration via adenovirus-mediated gene delivery on airway inflammation in the ovalbumin (OVA)-induced murine model of asthma.

METHODS

BALB/c mice were sensitized by intraperitoneal injections with OVA and challenged by nebulized OVA. The sensitized mice were given an intratracheal delivery of adenoviral vector expressing the murine IL-10 gene (AdIL-10), or mock adenoviral vector 4 days before the inhalation challenge of the OVA. Inflammatory parameters, such as the development of airway hyper-responsiveness (AHR), bronchial lavage fluid eosinophils, and chemokines were assayed.

RESULTS

Intratracheal administration of AdIL-10 could efficiently inhibit antigen-induced AHR and significantly decrease the number of eosinophils and neutrophils in the bronchoalveolar lavage fluid of OVA-sensitized and challenged mice during the effector phase.

CONCLUSIONS

Our data showed that the intratracheal transfer of the IL-10 gene could affect the recruitment of inflammatory cells during the challenge phase in a way that would result in the inhibition of airway inflammation. These findings suggest that the development of an immunoregulatory strategy based on IL-10 might shed light on more effective treatment.

Carbon Monoxide-Induced Early Thrombolysis Contributes to Heme Oxygenase-1-Mediated Inhibition of Neointimal Growth after Vascular Injury in Hypercholesterolemic Mice

Arterial thrombosis is a critical event in the pathogenesis of lesion development. In this study, we evaluated the effect of heme oxygenase-1 (HO-1), a stress-inducible enzyme with vasoprotective functions, on arterial thrombosis following vascular mechanical injury. The carotid arteries of apoE-deficient mice were subjected to angioplasty with a modified beaded-needle. Arterial thrombosis occurred at 12 h after injury. Treatment of the injured vessels with an adenovirus bearing HO-1 gene (Adv-HO-1) (1 x 10(8) pfu), but not saline or empty adenovirus (Adv), immediately after angioplasty resulted in earlier thrombolysis and restoration of blood flow detected at 24 h. Immunohistochemistry revealed that the arterial plasminogen activator inhibitor-1 (PAI-1) expression was markedly reduced in Adv-HO-1-treated injured arteries as compared to control counterparts. The thrombolytic effect was also observed by exposing animals with existing arterial thrombosis to carbon monoxide (CO) (250 ppm, 2 h), a byproduct derived from heme degradation by HO-1. In parallel with less fibrin(ogen) deposition, the macrophage infiltration, monocyte chemoattractant protein-1 expression and neointimal formation assessed at 2 weeks after angioplasty were substantially reduced in injured arteries treated with Adv-HO-1. These results support a role of early thrombolysis induced by CO in HO-1-mediated protection against intimal hyperplasia after vascular injury.

Inhibition of Experimental Autoimmune Anterior Uveitis by Adenovirus-Mediated Transfer of the Interleukin-10 Gene

AIMS

The aim of this study was to investigate the efficiency of adenoviral-mediated transfer of the interleukin (IL)-10 gene for inhibition of experimental autoimmune anterior uveitis, a rat model of human acute anterior uveitis. Uveitis was induced in the Lewis rat by simultaneous injection of melanin-associated antigen intraperitoneally (i.p.) and into the left footpad. The animals were treated by systemic administration of adenoviral construct expressing IL-10 (Ad-IL-10) or Ad-Mock carrying no cytokine transgene.

RESULTS

A significant reduction in ocular inflammation was noted for rats that received one or two divided i.p. administrations of Ad-IL-10 (one 10 x 10(9) and two 5 x 10(9) particles of adenoviral construct, respectively), as judged by reduced clinical scores and decreased leukocyte infiltration in the anterior chamber and confirmed by histological examinations, relative to control animals. Systemic Ad-IL-10, treatment also revealed a higher serum level of IL-10, compared to the controls.

CONCLUSIONS

The results suggest that systemic adenovirus-mediated IL-10 gene therapy has an anti-inflammatory effect on immune-mediated ocular inflammation and that this approach may be promising for the treatment of acute anterior uveitis.

Heme oxygenase-1 attenuates interleukin-1beta-induced nitric oxide synthase expression in vascular smooth muscle cells

Heme oxygenase-1 (HO-1) has been implicated in antioxidant and anti-inflammatory actions. To characterize the role of HO-1 in the vascular inflammatory response, we examined the effect of HO-1 on the expression of inducible nitric oxide synthase (iNOS) induced by interleukin-1beta (IL-1beta) in rat vascular smooth muscle cells (VSMCs). Western blot analysis demonstrated that IL-1beta-induced iNOS expression was significantly reduced by hemin cotreatment or adenovirus-mediated HO-1 gene transfer. Scavenging carbon monoxide (CO), one of the by-products of heme degradation by HO-1, significantly attenuated HO-1-mediated suppression of iNOS gene induction as revealed by Northern blot analysis. Exposure of cells to CO or a CO donor, the tricarbonyldichlororuthenium(II) dimer, also markedly inhibited IL-1beta-induced iNOS expression. Transient transfection experiments with a reporter gene construct carrying the rat iNOS gene promoter demonstrated that IL-1beta-induced promoter activity was substantially reduced by cotreatment with CO or a CO donor. Furthermore, the effects of CO on iNOS gene promoter activity and protein expression were diminished by cotreatment with the specific guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo-(4,3-a)quinoxalin-1-one. These data support the finding that HO-1 attenuates IL-1beta-induced iNOS gene expression in VSMCs. CO appears to mediate the suppressive effect of HO-1, at least in part, through downregulating transcriptional activation of the iNOS gene via a cGMP-dependent pathway.

Adenoviral transfer of the heme oxygenase-1 gene protects striatal astrocytes from heme-mediated oxidative injury

Heme oxygenase-1 (HO-1) is induced in the CNS after hemorrhage, and may have an effect on injury to surrounding tissue. Hemin, the preferred substrate of HO, is a neurotoxin that is present in intracranial hematomas. In a prior study, we observed that HO inhibitors increased the vulnerability of cultured cortical astrocytes to heme-mediated oxidative injury. To investigate the effect of HO more specifically, we used an adenoviral vector encoding the human HO-1 gene to specifically increase HO-1 expression. Incubation with 100 MOI of the HO-1 adenovirus (Adv-HHO-1) for 24 h increased both HO-1 protein and HO activity; a control adenovirus lacking the HO-1 gene had no effect. Using a DNA probe that was specific for human HO-1, 80.5 +/- 7.2% of astrocytes were observed to be infected by in situ hybridization. The cell death produced by 30-60 microM hemin was significantly reduced by pretreatment with 100 MOI Adv-HHO-1, as assessed by LDH release, propidium iodide exclusion, and MTT reduction assay. The threefold increase in cell protein oxidation produced by hemin was also attenuated in cultures pretreated with Adv-HHO-1. These results support the hypothesis that HO-1 protects astrocytes from heme-mediated oxidative injury. Specifically increasing astrocytic HO-1 by gene transfer may have a beneficial effect on hemorrhagic CNS injury.

Heme oxygenase-1 inhibits angiotensin II-induced cardiac hypertrophy in vitro and in vivo

BACKGROUND

Heme oxygenase-1 (HO-1) is a stress-response enzyme implicated in cardioprotection. To explore whether HO-1 has a role in cardiac remodeling response, the effect of its overexpression on angiotensin II (Ang II)-induced cardiac hypertrophy was examined.

METHODS AND RESULTS

HO-1 was induced in cultured rat neonatal cardiomyocytes by treatment with cobalt protoporphyrin IX (CoPPIX) or a recombinant adenovirus carrying the human HO-1 gene. Ang II-induced myocyte hypertrophy assessed by increments in cell size, [3H]leucine uptake, and protein content was suppressed by HO-1 overexpression. Cotreatment of cells with tin protoporphyrin IX, a HO inhibitor, significantly reversed the suppressive effect of HO-1. Bilirubin, one of the byproducts of heme degradation by HO-1, mediated the suppressive effect through the inhibition of Ang II-induced production of reactive oxygen species, as detected by a 2',7'-dichlorofluorescein probe. The antihypertrophic effect of HO-1 was also demonstrated in rats receiving chronic Ang II infusions. Cotreatment of animals with CoPPIX significantly attenuated Ang II-induced left ventricular hypertrophy and hyperdynamic contractions, whereas concomitant treatment with tin protoporphyrin IX abolished CoPPIX-mediated cardioprotection in vivo.

CONCLUSIONS

HO-1 attenuates Ang II-induced cardiac hypertrophy both in vitro and in vivo, and bilirubin mediates, at least in part, the antihypertrophic effect of HO-1 via inhibition of reactive oxygen species production after Ang II stimulation.

Heme oxygenase-1 gene promotor microsatellite polymorphism is associated with angiographic restenosis after coronary stenting

AIMS

Heme oxygenase-1 (HO-1) is a rate-limiting enzyme in heme degradation, leading to the generation of free iron, biliverdin, and carbon monoxide (CO). CO exerts potent antiproliferative and anti-inflammatory effects in the vascular walls, thereby influencing neointimal formation after vascular injury. A dinucleotide GT repeat in the promotor region of human HO-1 gene shows a length polymorphism that modulates the level of gene transcription. This study aimed to assess the association of the length of (GT)(n)repeats in HO-1 gene promotor with restenosis and adverse cardiac events after coronary stenting.

METHODS AND RESULTS

Quantitative coronary angiography was evaluated before, immediately after and 6 months after stent implantation in 323 consecutive patients with successful coronary stenting. In each patient, the allele frequency of (GT)(n)repeats in HO-1 gene promotor was examined. Compared with those with shorter (S, <26) GT repeats, patients with longer (L, > or =26) GT repeats on either allele had more frequent angiographic restenosis with an adjusted odds ratio (OR) of 3.74 (95% confidence interval, 1.61 to 8.70, P=0.002). Such association was even more prominent in patients with small coronary arteries or complex lesions before stenting. Besides, carriers of L/L genotype had an increased risk (adjusted OR, 3.26; 95% confidence interval, 1.58 to 6.72, P=0.001) for adverse cardiac events during follow-up.

CONCLUSIONS

The length polymorphism of GT repeat in HO-1 gene promoter is an independent risk factor for angiographic restenosis as well as adverse cardiac events after coronary stenting. These findings suggest the genetic contribution to stent restenosis and support the notion that the long dinucleotide GT repeat in promotor region may interfere with HO-1 gene transcription, leading to decreased vascular protection upon injury.

Dietary iron restriction increases plaque stability in apolipoprotein-e-deficient mice

Accumulative evidence has supported the role of iron in the development of atherosclerosis. To test whether iron-mediated oxidative stress influences plaque stability, apoliporotein-E (ApoE)-deficient mice (3 months old) were placed on a chow diet or a low-iron diet for 3 months, and the abundance of interstitial collagen and the expression of the matrix degradation-associated enzyme, matrix metalloproteinase-9 (MMP-9), in vascular lesions were assessed. A low-iron diet appeared to reduce iron deposition while substantially increasing collagen content of lesions in mice. Immunostaining demonstrated lower expression of MMP-9 in lesions of iron-restricted animals. Likewise, SDS-PAGE zymography revealed lower gelatinolytic activities in aortic tissues and sera of the same group of animals. When older ApoE-deficient mice (5 months old) received a low-iron diet for 2 months, development of the lesion area was not significantly affected. However, the lesional collagen content was much higher in the iron-restricted group of animals, and MMP-9 expression in aortic tissues from the same group of mice was significantly lower. Treatment of murine J774 macrophages with increasing concentrations of ferric ammonium citrate significantly enhanced the amount of MMP-9 secreted. Together, these data indicate that decreased vascular iron content following dietary iron restriction in ApoE-deficient mice leads to lower matrix degradation capacity and increased plaque stability.

Induction of heme oxygenase-1 expression in murine macrophages is essential for the anti-inflammatory effect of low dose 15-deoxy-Delta 12,14-prostaglandin J2

15-Deoxy-Delta 12,14-prostaglandin J2 (15d-PGJ2), a cyclopentenone prostaglandin, displays a potent anti-inflammatory effect at micromolar concentrations (>2 microM) through direct inhibition of nuclear factor (NF)-kappa B activation. Here we show that at submicromolar concentrations (0.1-0.5 microM) 15d-PGJ2 retains the ability to suppress the production of tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) in lipopolysaccharide (LPS)-activated murine J774 macrophages under the conditions of a prolonged incubation (>12 h). Western blot analysis revealed that the expression of the cytoprotective enzyme, heme oxygenase-1 (HO-1), was induced and coincident with the anti-inflammatory action of 15d-PGJ2. Inhibition of HO-1 activity or scavenging carbon monoxide (CO), a byproduct derived from heme degradation, significantly attenuated the suppressive activity of 15d-PGJ2. Furthermore, LPS-induced NF-kappa B activation assessed by the inhibitory protein of NF-kappa B(I kappa B) degradation and p50 nuclear translocation was diminished in cells subjected to prolonged treatment with the low concentration of 15d-PGJ2. Treatment of cells with the protein synthesis inhibitor, cycloheximide, or the specific p38 MAP kinase inhibitor, SB203580, blocked the induction of HO-1 and suppression of LPS-induced I kappa B degradation mediated by 15d-PGJ2. Likewise, HO inhibitor and CO scavenger were effective in abolishing the inhibitory effects of 15d-PGJ2 on NF-kappa B activation induced by LPS. The functional role of CO was further demonstrated by the use of a CO releasing molecule, tricarbonyldichlororuthenium(II) dimer, which significantly suppressed LPS-induced nuclear translocation of p50 as assessed by confocal immunofluorescence. Collectively, these data suggest that even at submicromolar concentrations 15d-PGJ2 can exert an anti-inflammatory effect in macrophages through a mechanism that involves the action of HO/CO.

Microsatellite polymorphism in promoter of heme oxygenase-1 gene is associated with susceptibility to coronary artery disease in type 2 diabetic patients

Heme oxygenase is a rate-limiting enzyme in heme degradation, leading to the generation of free iron, biliverdin, and carbon monoxide. Induction of heme oxygenase-1 is implicated in the antioxidant defense mechanism and can modulate vascular function. To test the association of microsatellite polymorphism in the promoter region of human HO-1 gene with the risk of coronary artery disease (CAD) in type 2 diabetic patients, we examined the allele frequencies of (GT) (n) repeats in HO-1 gene in 474 patients with CAD and in 322 controls. A transient-transfection assay with HO-1 promoter/luciferase fusion constructs carrying various lengths of (GT) (n) repeats was performed to explore the regulatory effect of (GT) (n) repeats on HO-1 gene expression in cultured rat aortic smooth muscle cells. Serum thiobarbituric acid-reactive substances (TBARs), a measure of lipid peroxidation, was significantly higher in subjects carrying the L/L genotype (> or =32 repeats). Among type 2 diabetic subjects, the frequencies of the L alleles and proportion of genotypes with L alleles were significantly higher in those with CAD than in those without CAD. The adjusted odds ratio for CAD in type 2 diabetic patients with L alleles was 4.7 (95% confidence interval, 1.9-12.0, P=0.001). Transfection experiments in aortic smooth muscle cells revealed that HO-1 promoter/luciferase fusion constructs containing longer (GT) (n) repeats exhibited lower transcriptional activity. These results imply that the length polymorphism in the HO-1 gene promoter modulate the transcription of the gene in vascular cells. Type 2 diabetics carrying longer (GT) (n) repeats might have higher oxidative stress and increased susceptibility to the development of CAD.

Heme oxygenase-1 mediates the anti-inflammatory effect of interleukin-10 in mice

The mechanisms underlying the action of the potent anti-inflammatory interleukin-10 (IL-10) are poorly understood. Here we show that, in murine macrophages, IL-10 induces expression of heme oxygenase-1 (HO-1), a stress-inducible protein with potential anti-inflammatory effect, via a p38 mitogen-activated protein kinase-dependent pathway. Inhibition of HO-1 protein synthesis or activity significantly reversed the inhibitory effect of IL-10 on production of tumor necrosis factor-alpha induced by lipopolysaccharide (LPS). Additional experiments revealed the involvement of carbon monoxide, one of the products of HO-1-mediated heme degradation, in the anti-inflammatory effect of IL-10 in vitro. Induction of HO-1 by IL-10 was also evident in vivo. IL-10-mediated protection against LPS-induced septic shock in mice was significantly attenuated by cotreatment with the HO inhibitor, zinc protoporphyrin. The identification of HO-1 as a downstream effector of IL-10 provides new possibilities for improved therapeutic approaches for treating inflammatory diseases.

Adenovirus-mediated heme oxygenase-1 gene transfer inhibits the development of atherosclerosis in apolipoprotein E-deficient mice

BACKGROUND

Increasing evidence supports the role of heme oxygenase-1 (HO-1) in cytoprotective response and iron homeostasis. The object of this study was to investigate whether adenovirus-mediated gene transfer of HO-1 in arteries reduces iron overload and inhibits lesion formation in apolipoprotein E (apoE)-deficient mice.

METHODS AND RESULTS

Infection of rat aortic smooth muscle cells with adenovirus carrying the human HO-1 gene (Adv-HO-1) resulted in a high-level expression of HO-1 protein, which effectively reduced the hemin-induced iron overload in these cells. Adenovirus-mediated gene transfer in arteries in vivo was achieved by direct injection of Adv-HO-1 into the left ventricles of anesthetized animals. Transgene was expressed in the endothelium and aortic lesion of apoE-deficient mice after they had received recombinant adenovirus for 1 week and gradually decayed during the next 5 weeks. When young apoE-deficient mice (14 weeks old) received Adv-HO-1 (2.5 x 10(9) pfu) for 6 weeks, lesions that developed in the aortic root or aortic arch were significantly smaller than those in control littermates receiving empty viral vector. Furthermore, the iron deposition as well as tissue iron content was much less in aortic tissue of Adv-HO-1-treated mice. The inhibitory effect of HO-1 gene transfer on the progression of advanced lesions was also observed in older apoE-deficient mice (20 weeks old) receiving Adv-HO-1 intraventricularly.

CONCLUSIONS

Overexpression of HO-1 in vascular cells facilitates iron metabolism and attenuates development of atherosclerosis in apoE-deficient mice.

Differential regulation of H- and L-ferritin messenger RNA subunits, ferritin protein and iron following focal cerebral ischemia-reperfusion

Iron may catalyse the production of reactive oxygen species during post-ischemic reoxygenation and subsequently lead to brain damage. Ferritin, an iron sequestering and storage protein, can also be a source of iron after ischemic insult. However, its role in ischemia-reperfusion has not been carefully investigated. In the present study, we examined the temporal and spatial induction profiles of both H- and L-ferritin messenger RNA and protein in a well-defined focal cerebral ischemia model. Results of northern blot analysis showed a delayed and prolonged induction of both H- and L-ferritin messenger RNA in the ischemic cortex of rats subjected to 60min ischemic insult. A significant induction of both H- and L-ferritin messenger RNA was observed at 12h and remained elevated for up to 336h after the onset of reperfusion. At the peak level, quantitative analysis of the blot indicated a 2.5-fold and a six-fold increase in H- and L-ferritin messenger RNA, respectively, compared with the sham-operated controls. No apparent change in the levels of either messenger RNA was observed in the contralateral side. Results of in situ hybridization studies revealed constitutive expression of both H- and L-ferritin messenger RNA throughout the brain in sham-operated animals, in particular the hippocampus and the piriform cortex. Nevertheless, the signal intensity of H-ferritin messenger RNA was much higher than that of L-ferritin messenger RNA. Seventy-two hours after 60min ischemia, marked expression of H-ferritin messenger RNA was observed in the area surrounding the middle cerebral artery irrigated cortex, the medial part of the caudoputamen and in the subfield of the CA1 hippocampal region of the ipsilateral hemisphere. Similarly, a large induction of L-ferritin messenger RNA was also noted in several areas, including the middle cerebral artery irrigated cortex, the lateral part of the caudoputamen and the stratum pyramidale of the CA1 hippocampal region, which were totally different from areas where H-ferritin messenger RNA was found. At 336h after ischemia, increased expression of H-ferritin messenger RNA was observed in the peri-necrosis and ipsilateral thalamus regions, while L-ferritin messenger RNA was noted exclusively at the edge within the necrosis. Results of immunohistochemical study further revealed that ferritin immunoreactivity was present in the same areas where increased ferritin messenger RNA was found. Sixty-minute ischemia also led to iron deposition in discrete areas. Iron deposition was highly associated with the induction of ferritin, particularly in the macrophage- and microglia-positive areas where cell death or tissue necrosis was noted.In summary, our initial findings indicate that ischemic insult leads to induction of both H- and L-ferritin messenger RNA. In the present study, although the temporal induction profiles were similar, the major expression areas for these two genes were totally different. Ferritin immunoreactivity was observed in the same areas where increased ferritin messenger RNA was found. Ischemia also resulted in iron deposition, which highly associated with the ferritin immunoreactivity. The exact regulatory mechanism and pathological significance for the differential expression of H- and L-ferritin genes following ischemia/reperfusion remain to be clarified.

Iron and atherosclerosis

Iron is a vital element in life. However, it may participate in diverse pathological processes by catalyzing the formation of reactive oxygen free radicals. During the past decade, considerable evidence has supported the role of oxidative stress in the development of atherosclerosis and related cardiovascular diseases. The oxidation of low-density lipoprotein (LDL) and lipid is believed to be one of the crucial events leading to plaque formation in vasculature. It has been hypothesized that iron-mediated oxidation is involved in this process. In favor of this idea, several epidemiological studies have shown that the level of body iron stores is positively correlated with the incidence of coronary heart disease in human populations. However, some studies have yielded conflicting results. Recently, studies conducted in our laboratory and others have demonstrated that iron deposition is prominent in human atherosclerotic lesions. The iron deposits appear to colocalize with ceroid, which is an end product of extensively oxidized lipid and protein complex, in lesions, providing histological evidence to support the iron hypothesis. Additional experiments in animals have further revealed that the severity of atherosclerosis can be markedly influenced by iron overload or deficiency. Collectively, these data provide a strong pathological basis to support the detrimental role of iron in vascular damage and progression of the disease.

Post-transcriptional regulation of H-ferritin mRNA. Identification of a pyrimidine-rich sequence in the 3'-untranslated region associated with message stability in human monocytic THP-1 cells

We have previously demonstrated that phorbol myristate acetate (PMA) up-regulates H-ferritin gene expression in myeloid cells by stabilization of its message. In the present report, we showed that insertion of the 3'-untranslated region (3'-UTR) of H-ferritin mRNA at the 3'-end of luciferase coding sequence significantly reduced the stability of luciferase mRNA in human monocytic THP-1 cells. However, the half-life of the chimeric transcript was markedly prolonged after PMA treatment. A cytosolic protein factor from THP-1 cells was found to specifically bind to H-ferritin 3'-UTR. PMA treatment of THP-1 cells resulted in the reduction of the RNA binding activity in a time-dependent manner. Deletion analysis and RNase T1 mapping revealed a pyrimidine-rich sequence within the 3'-UTR which interacts with the protein factor. Competition experiments with homoribopolymers further demonstrated the importance of uridines for the binding activity. Point mutations in uridines of the pyrimidine-rich sequence reduced the protein binding to 3'-UTR, while increasing the stability of the chimeric luciferase transcript. Together, these results demonstrate that the pyrimidine-rich sequence in the 3'-UTR is involved in post-transcriptional regulation of H-ferritin gene expression in myeloid cells.

Copper-induced apoptosis and immediate early gene expression in macrophages

The death of macrophage-derived foam cells contributes to the formation of the lipid core in atherosclerotic lesions. Although the underlying mechanism is not yet clear, apoptosis has been shown to be responsible, at least in part, for the cell death of lipid-laden macrophages in atherosclerotic plaques. In the present study, we demonstrated that copper, in the presence of 8-hydroxyquinoline, was able to induce apoptosis of murine J774.A1 cells in culture. Ceruloplasmin exerts similar a effect, but not iron or hemin. Further experiments demonstrated that the expression of immediate early genes, including c-jun, c-fos and egr-1, was also induced by copper treatment in these cells, although only egr-1 mRNA was induced in a time- and dose-dependent manner. The antioxidant, N-acetylcysteine, exhibited remarkable inhibitory effect on the copper-induced apoptosis dose-dependently. Time course experiment revealed that prior treatment of cells with N-acetylcysteine is essential for the anti-apoptotic effect of this compound. Results also demonstrated that under the condition; in which N-acetylcysteine inhibited the copper-induced apoptosis, this antioxidant also abolished the gene expression of egr-1. Collectively, these results suggest that egr-1 gene expression is closely associated with the apoptosis induced by copper in macrophages.

Erythrophagocytosis and iron deposition in atherosclerotic lesions

Iron deposition has been shown to be prominent in atherosclerotic lesions. However, the source of iron accumulated in arterial walls is unclear. In present report, we provide the histological evidence to demonstrate the localization of erythrocytes in atherosclerotic lesions from experimental animals. As revealed by scanning and transmission electron microscopy, the circulating erythrocytes were found to be present in intima of atherosclerotic aortas from apoE-deficient mice. These erythrocytes appeared to be readily phagocytosed by macrophages in lesions. The erythrophagocytosis was also evident in lesions from cholesterol-fed rabbits. Furthermore, the iron deposition was detectable in the region with erythrocytes. When the aortic sections of humans and apoE-deficient mice were immunostained with specific antibody to hemoglobin, it was clearly shown that the positive stain was detectable in macrophage-derived foam cells. Immunostaining of serial sections with specific antibodies to heme oxygenase-1 (HO-1) and ferritin further demonstrated the colocalization of HO-1 and ferritin in area with positive immunoreactivity for hemoglobin. Likewise, Perls' reaction revealed the positive iron stain in the same region. Collectively, these results suggest that hemoglobin/heme released from the phagocytosed erythrocytes may contribute to at least part of iron deposited in atherosclerotic lesions.

Iron-deficient diet reduces atherosclerotic lesions in apoE-deficient mice

BACKGROUND

Iron deposition is evident in human atherosclerotic lesions, suggesting that iron may play a role in the development of atherosclerosis. To test this idea, the correlation between the extent of iron deposition and the severity of atherosclerosis in apolipoprotein E (apoE)-deficient mice was investigated. Furthermore, the effect of a low-iron diet on the progression of atherosclerotic lesions in these animals was evaluated.

METHODS AND RESULTS

Iron deposition in tissues of apoE-deficient mice was examined by Perls' staining method. The results clearly demonstrated that iron deposits are present in atherosclerotic lesions and tissue sections of heart and liver in an age-dependent manner. When the young mice received a low-iron diet for 3 months, the hematocrit, serum iron, hemoglobin, and cholesterol concentrations were not significantly altered compared with those of littermates placed on a chow diet. However, the serum ferritin level of animals in the iron-restricted group was 27% to 30% lower than that of the control group in either sex. Furthermore, the lipoproteins isolated from the iron-restricted group exhibited greater resistance to copper-induced oxidation. Histological examination revealed that atherosclerotic lesions developed in mice fed a low-iron diet were significantly smaller than those found in control littermates. Likewise, the iron deposition as well as tissue iron content was much less in aortic tissues of the iron-restricted animals. Circulating autoantibodies to oxidized LDL and immunostains for epitopes of malondialdehyde-modified LDL detected on lesions were also significantly lower in mice fed a low-iron diet.

CONCLUSIONS

Iron deposition is closely associated with the progression of atherosclerosis in apoE-deficient mice. Restriction in dietary iron intake leads to significant inhibition of lesion formation in these animals. These results suggest that the beneficial effect of a low-iron diet may be mediated, at least in part, by the reduction of iron deposition as well as LDL oxidation in vascular lesions.

The role of interleukin 12 in the development of atherosclerosis in ApoE-deficient mice

The cytokine profile of atherosclerotic aortas from apoE-deficient mice was assessed by reverse transcriptase-polymerase chain reaction. The results clearly showed that the expression of mRNA for IL-12p40 was evident in aortas from 3-month-old apoE-deficient mice. The mRNA for IL-10 was detected in aorta from these mice at the age of 6 months, indicating that expression of IL-12 is earlier than that of IL-10 in these animals. Concurrent with IL-12p40, the mRNA for the T-cell cytokine IFN-gamma, but not IL-4, was detected in aortas of mice at young and old ages. Both in situ hybridization and immunostaining further demonstrated the localization of IL-12 in macrophages of atherosclerotic lesions. Immunohistochemistry also demonstrated the expression of costimulatory molecules B7-1 and B7-2 in macrophages, suggesting that activation of T lymphocytes by macrophages may occur via surface antigens in lesions. When the immunoglobulin isotype of the antioxidized LDL antibodies in sera of apoE-deficient mice was determined, it revealed that both IgM and IgG were present. Furthermore, IgG2a is predominant and comprises approximately 50% of the antioxidized LDL IgG in sera from young mice (3 months), but decreased to lower levels (35%) in older mice (6 months). Daily administration of IL-12 led to an increase in serum levels of antioxidized LDL antibodies and accelerated atherosclerosis in young apoE-deficient mice compared with control mice injected with PBS alone. Taken together, these data suggest that IL-12 plays an active role in regulating the immune response during the early phase of atherosclerosis in apoE-deficient mice.

Colocalization of iron and ceroid in human atherosclerotic lesions

The presence of ceroid, a complex of protein associated with oxidized lipids, is commonly observed in human atherosclerotic lesions. When the human aortic walls were examined by Perls' staining, it was found that the iron deposits were evident in aortas with atherosclerosis. The extent of iron deposition was associated with the severity of the lesion. Furthermore, the iron deposits appeared to be colocalized with ceroids either extracellularly or intracellularly in foam cell-like macrophages or smooth muscle cells. Electron microscopy and X-ray microanalysis revealed that some of the extracellular iron aggregates were present within the ceroids. Likewise, some of the subcellular iron aggregates were found to be located near the lipid droplets or within the ceroids of foam cells. Collectively, these observations support the theory that the lipid oxidation occurring in lipid-laden cells of aortic lesions is facilitated by iron-overload in these cells.

Expression of heme oxygenase-1 in atherosclerotic lesions

Heme oxygenase-1 (HO-1) is a heme-degradation enzyme induced under various oxidative stress conditions. To elucidate the potential involvement of HO-1 in atherogenesis, the expression of this enzyme in atherosclerotic lesions of apolipoprotein E-deficient mice and humans were examined. Both immunostaining and in situ hybridization clearly demonstrated that the expression of HO-1 was prominent in endothelium and foam cells/macrophages of thickened intima in lesions from both humans and experimental animals. The expression of this enzyme was also detected in medial smooth muscle cells of advanced lesions. The induction of HO-1 mRNA was observed in murine peritoneal macrophages after treatment with oxidized low density lipoprotein (LDL) but not with native LDL in a dose-dependent manner. Time course study demonstrated that the induction was prominent at 3 hours, reached a maximal induction at 6 hours, and remained evident up to 24 hours after oxidized LDL treatment. The degree of induction was in concordant with the extent of oxidation in the LDL preparation. Lysophosphatidylcholine, one of the major components present in oxidized LDL, was ineffective to induce the gene expression, suggesting that other lipophilic substances derived from LDL oxidation are responsible for the induction of HO-1. These results clearly demonstrate that HO-1 is one of the stress proteins expressed in atherosclerotic lesions.

Analysis of the T cell receptor V beta repertoire in human aortic aneurysms

Human aortic aneurysm is commonly characterized by the presence of advanced atherosclerosis associated with variable chronic adventitial inflammation. Histological examination of human aortic aneurysmal specimens revealed the presence of plasma cells and lymphoid aggregates in media and adventitia of the vessels. Immunostaining further demonstrated that CD3-positive T lymphocytes are present in follicles. Using a highly sensitive reverse transcription-polymerase chain reaction amplification method, the T cell receptor (TCR) V beta gene expression in aortic aneurysms was shown to be polyclonal. Furthermore. there was no preferential expression of any TCR V beta gene in the aortic tissue as compared with that in peripheral blood in aneurysmal patients. These results indicate that the TCR repertoire in aortic aneurysm is not restricted.

Transcriptional regulation of platelet-activating factor receptor gene in B lymphoblastoid Ramos cells by TGF-beta

The expression of platelet-activating factor (PAF) receptor gene was up-regulated in a time- and dose-dependent manner in a B cell line (Ramos) following exposure to TGF-beta 2. The TGF-beta 2-induced increment of PAF receptor mRNA was at least partly due to an increase in transcriptional rate as demonstrated by nuclear run-off experiments. Transient transfection of cells with PAF receptor transcript I gene promoter fused to a luciferase reporter gene revealed that the TGF-beta-responsive element (T beta RE) lies between the sequence from -44 to -17 relative to the transcriptional start site. Insertion of the T beta RE upstream of the unresponsive minimal thymidine kinase promoter conferred the TGF-beta-inducibility. Gel mobility shift assay demonstrated the specific binding of nuclear factors to the T beta RE. The T beta RE binding activity was gradually increased and reached a maximum at 3 h and subsequently returned to basal level at 5 h in cells following TGF-beta 2-treatment. Concomitant treatment of cells with cycloheximide abolished the increases in both T beta RE-binding activity and expression of PAF receptor mRNA, indicating that de novo protein synthesis is required to exert TGF-beta 2 effect. Methylation interference analysis revealed that the T beta RE-binding protein recognized a purine-rich sequence, 5'-GGGGTG-3'. Point mutations of the consecutive guanine nucleotides significantly reduced the DNA-binding activity and the TGF-beta-induced promoter activity. Collectively, these results clearly demonstrate that a T beta RE proximal to the transcriptional initiation site of the human PAF receptor transcript I gene mediates the up-regulation of PAF receptor gene expression in Ramos cells by TGF-beta 2.

Transcriptional regulation of platelet-activating factor receptor gene in B lymphoblastoid Ramos cells by TGF-beta

The expression of platelet-activating factor (PAF) receptor gene was up-regulated in a time- and dose-dependent manner in a B cell line (Ramos) following exposure to TGF-beta 2. The TGF-beta 2-induced increment of PAF receptor mRNA was at least partly due to an increase in transcriptional rate as demonstrated by nuclear run-off experiments. Transient transfection of cells with PAF receptor transcript I gene promoter fused to a luciferase reporter gene revealed that the TGF-beta-responsive element (T beta RE) lies between the sequence from -44 to -17 relative to the transcriptional start site. Insertion of the T beta RE upstream of the unresponsive minimal thymidine kinase promoter conferred the TGF-beta-inducibility. Gel mobility shift assay demonstrated the specific binding of nuclear factors to the T beta RE. The T beta RE binding activity was gradually increased and reached a maximum at 3 h and subsequently returned to basal level at 5 h in cells following TGF-beta 2-treatment. Concomitant treatment of cells with cycloheximide abolished the increases in both T beta RE-binding activity and expression of PAF receptor mRNA, indicating that de novo protein synthesis is required to exert TGF-beta 2 effect. Methylation interference analysis revealed that the T beta RE-binding protein recognized a purine-rich sequence, 5'-GGGGTG-3'. Point mutations of the consecutive guanine nucleotides significantly reduced the DNA-binding activity and the TGF-beta-induced promoter activity. Collectively, these results clearly demonstrate that a T beta RE proximal to the transcriptional initiation site of the human PAF receptor transcript I gene mediates the up-regulation of PAF receptor gene expression in Ramos cells by TGF-beta 2.