Network for activation of human endothelial cells by oxidized phospholipids: a critical role of heme oxygenase 1

RATIONALE

Oxidized palmitoyl arachidonyl phosphatidylcholine (Ox-PAPC) accumulates in atherosclerotic lesions, is proatherogenic, and influences the expression of more than 1000 genes in endothelial cells.

OBJECTIVE

To elucidate the major pathways involved in Ox-PAPC action, we conducted a systems analysis of endothelial cell gene expression after exposure to Ox-PAPC.

METHODS AND RESULTS

We used the variable responses of primary endothelial cells from 149 individuals exposed to Ox-PAPC to construct a network that consisted of 11 groups of genes, or modules. Modules were enriched for a broad range of Gene Ontology pathways, some of which have not been identified previously as major Ox-PAPC targets. Further validating our method of network construction, modules were consistent with relationships established by cell biology studies of Ox-PAPC effects on endothelial cells. This network provides novel hypotheses about molecular interactions, as well as candidate molecular regulators of inflammation and atherosclerosis. We validated several hypotheses based on network connections and genomic association. Our network analysis predicted that the hub gene CHAC1 (cation transport regulator homolog 1) was regulated by the ATF4 (activating transcription factor 4) arm of the unfolded protein response pathway, and here we showed that ATF4 directly activates an element in the CHAC1 promoter. We showed that variation in basal levels of heme oxygenase 1 (HMOX1) contribute to the response to Ox-PAPC, consistent with its position as a hub in our network. We also identified G-protein-coupled receptor 39 (GPR39) as a regulator of HMOX1 levels and showed that it modulates the promoter activity of HMOX1. We further showed that OKL38/OSGN1 (oxidative stress-induced growth inhibitor), the hub gene in the blue module, is a key regulator of both inflammatory and antiinflammatory molecules.

CONCLUSIONS

Our systems genetics approach has provided a broad view of the pathways involved in the response of endothelial cells to Ox-PAPC and also identified novel regulatory mechanisms.

Haem arginate infusion stimulates haem oxygenase-1 expression in healthy subjects

BACKGROUND AND PURPOSE

Haem oxygenase 1 (HO-1) is an inducible protein that plays a major protective role in conditions such as ischaemia-reperfusion injury and inflammation. In this study, we have investigated the role of haem arginate (HA) in human male subjects in the modulation of HO-1 expression and its correlation with the GT length polymorphism (GT(n)) in the promoter of the HO-1 gene.

EXPERIMENTAL APPROACH

In a dose-escalation, randomized, placebo-controlled trial, seven healthy male subjects with a homozygous short (S/S) and eight with a long (L/L) GT(n) genotype received intravenous HA. HO-1 protein expression and mRNA levels in peripheral blood monocytes, bilirubin, haptoglobin, haemopexin and haem levels were analysed over a 48 h observation period.

KEY RESULTS

We found that the baseline mRNA levels of HO-1 were higher in L/L subjects, while protein levels were higher in S/S subjects. HA induced a dose-dependent increase in the baseline corrected area under the curve values of HO-1 mRNA and protein over 48 h. The response of HO-1 mRNA was more pronounced in L/L subjects but the protein level was similar across the groups.

CONCLUSIONS AND IMPLICATION

HA is an effective inducer of HO-1 in humans irrespective of the GT(n) genotype. The potential therapeutic application of HA needs to be evaluated in clinical trials.

Association between the heme oxygenase-1 promoter polymorphism and renal transplantation outcome in Greece

BACKGROUND

Heme oxygenase-1 (HO-1) is the enzyme that catabolizes heme into carbon monoxide, biliverdin, and free iron. The induction of this enzyme is an important cytoprotective mechanism, which occurs as an adaptive and beneficial response to a wide variety of oxidant stimuli. HO-1 has recently been suggested to protect transplants from ischemia/reperfusion and immunologic injury. HO-1 inducibility is mainly modulated by a (GT)(n) repeat polymorphism in the promoter region, and has been shown that short repeats (S) are associated with greater upregulation of HO-1, compared with long repeats (L). In the present study we investigated the influence of this HO-1 gene polymorphism on clinical outcome after transplantation and on renal transplant function.

METHODS

DNA from 175 donor/recipient pairs who underwent transplantation between October 2002 and June 2007 was genotyped. We divided the HO-1 alleles into 2 subclasses, the S ≤ 27 repeats and L > 27 repeats.

RESULTS

There has been significant relevance between the genotype of the donor and the outcome of the graft, as far as recipients with normal graft function and recipients with deteriorated graft function are concerned (P = .021). In patients with normal graft function, grafts from L-homozygotes were found in 24%, whereas in patients with deteriorated function, grafts from L-homozygotes exhibited in higher rate (50%). Neither the donor's nor the recipient's polymorphism influenced the graft survival (log-rank test P = .228 for the donors and log-rank test P = 0.844 for the recipients). There was no evidence of a gene-dose effect on graft survival (P = .469). Recipients of allografts from S-carriers donors had significantly lower serum creatinine levels at 24 months compared with recipients of allografts from L-homozygotes donors (P = .016).

Effect of interactions of glutathione S-transferase T1, M1, and P1 and HMOX1 gene promoter polymorphisms with heavy smoking on the risk of rheumatoid arthritis

OBJECTIVE

Glutathione S-transferase (GST) genes as well as heme oxygenase 1 gene (HMOX1) encode enzymes that detoxify carcinogens and protect against oxidative stress. This study was undertaken to examine the impact of gene-smoking interactions on susceptibility to rheumatoid arthritis (RA).

METHODS

Caucasian patients with RA and matched control subjects (n = 549 each) were selected from the Nurses' Health Study. Genotyping of the patients' blood by TaqMan and BioTrove assays identified homozygous deletions at the M1 and T1 loci of GST (GSTM1-null and GSTT1-null, respectively) as well as alleles for GSTP1 (rs1695) and HMOX1 (rs2071746). In addition, the effect of gene-smoking interactions on the risk of all RA and RA serologic phenotypes was studied in separate logistic models that were adjusted for covariates. Multiplicative interactions were assessed by including a product term in a logistic model, and additive interactions were assessed using the attributable proportion (AP) due to interaction. For replication of the results, analyses revealing significant interactions were repeated in an independent case-control cohort from the Epidemiological Investigation of Rheumatoid Arthritis study.

RESULTS

For the risk of all RA, multiplicative (P = 0.05) and additive (AP = 0.53, P = 0.0005) interactions between the GSTT1-null polymorphism and smoking and multiplicative interactions (P = 0.05) between HMOX1 and smoking were observed. For the risk of seropositive RA, multiplicative (P = 0.01) and additive (AP = 0.62, P < 0.0001) interactions between GSTT1-null and smoking and additive interactions (AP = 0.41, P = 0.03) between HMOX1 and smoking were observed. After correction for multiple comparisons, the additive interactions between GSTT1-null and smoking remained significant. The M1-null and P1 variants of GST did not show significant interactions, and no associations with seronegative RA were observed. In replication analyses, significant multiplicative interactions (P = 0.04) and additive interactions (AP = 0.32, P = 0.02) were observed between GSTT1-null and smoking in the risk of anti-citrullinated protein antibody-positive RA.

CONCLUSION

Significant gene-environment interactions between the GSTT1-null polymorphism and heavy smoking were observed when assessing the risk of RA. Future studies are needed to assess the impact of these interactions on RA prediction.

Association of an intronic variant of the heme oxygenase-1 gene with hypertension in northern Chinese Han population

Heme oxygenase was regarded as a regulator of oxidative stress, which was believed to underlie the etiology of hypertension. To assess the effect of its encoded genes (HMOX1 and HMOX2) on hypertension, we designed a case-control study in 503 cases and 490 controls. The results indicated that the rs9607267 of the HMOX1 gene was significantly associated with essential hypertension (EH) and the Hap3(T-C-G) of the HMOX1 gene was also significantly associated with the risk of EH. No association was observed between the HMOX2 gene and EH. The multifactor-dimensionality reduction analyses results did not show any interaction between the HMOX1 and HMOX2 genes underlying the development of hypertension.

HO-1 polymorphism as a genetic determinant behind the malaria resistance afforded by haemolytic disorders

Malaria affects thousands of people around the world representing a critical issue regarding health policies in tropical countries. Similarly, also haemolytic diseases such as sickle cell disease and thalassemias are a concern in different parts of the globe. It is well established that haemolytic diseases, such as sickle cell disease (SCD) and thalassemias, represent a resistance factor to malaria, which explains the high frequencies of such genetic variants in malaria endemic areas. In this context, it has been shown that the rate limiting enzyme heme oxygenase I (HO-1), responsible for the catabolism of the free heme in the body, is an important resistance factor in malaria and is also important in the physiopathology of haemolytic diseases. Here, we suggest that allelic variants of HO-1, which display significant differences in terms of protein expression, have been selected in endemic malaria areas since the HO-1 enzyme can enhance the protection against malaria conferred by haemolytic diseases This protection apply mainly in what concerns protection against severe malaria forms. Therefore, HO-1 genotyping would be fundamental to determine resistance of a given individual to lethal forms of malaria as well as to common clinical complications typical to haemolytic diseases and would be helpful in the establishment of public health politics.

The involvement of heat-shock proteins in the pathogenesis of autoimmune arthritis: a critical appraisal

OBJECTIVES

To review the literature on the role of heat-shock proteins (HSPs) in the pathogenesis of autoimmune arthritis in animal models and patients with rheumatoid arthritis (RA).

METHODS

The published literature in Medline (PubMed), including our published work on the cell-mediated as well as humoral immune response to various HSPs, was reviewed. Studies in the preclinical animal models of arthritis as well as RA were examined critically and the data are presented.

RESULTS

In experimental arthritis, disease induction by different arthritogenic stimuli, including an adjuvant, led to immune response to mycobacterial HSP65 (BHSP65). However, attempts to induce arthritis by a purified HSP have not met with success. There are several reports of a significant immune response to HSP65 in RA patients. However, the issue of cause and effect is difficult to address. Nevertheless, several studies in animal models and a couple of clinical trials in RA patients have shown the beneficial effect of HSPs against autoimmune arthritis.

CONCLUSIONS

There is a clear association between immune response to HSPs, particularly HSP65, and the initiation and propagation of autoimmune arthritis in experimental models. The correlation is relatively less convincing in RA patients. In both cases, the ability of HSPs to modulate arthritis offers support, albeit an indirect one, for the involvement of these antigens in the disease process.

Association between heme oxygenase-1 gene promoter polymorphisms and type 2 diabetes in a Chinese population

The authors aimed to determine whether 2 functional polymorphisms in the heme oxygenase-1 (HO-1) gene promoter are associated with type 2 diabetes mellitus (T2DM). A Chinese case-control study involving 1,103 newly diagnosed T2DM patients, 371 patients with impaired glucose regulation (IGR), and 1,615 controls was performed (December 2004-December 2007). A (GT)(n) microsatellite polymorphism and a single nucleotide polymorphism, T(-413)A, were genotyped, and their functional relevance was evaluated by examining the level of HO-1 protein expression. For the (GT)(n) microsatellite polymorphism, genotypes with the L (GT)(n) allele (>or=25 GT repeats) were associated with increased odds of IGR or T2DM compared with the S/S genotype (<25 GT repeats) (S/L genotype: odds ratio (OR) = 1.35, P = 0.048; L/L genotype: OR = 1.65, P = 0.006). Subsequent haplotype analysis showed that haplotype TL contributed to increased odds of IGR or T2DM compared with haplotype TS (OR = 1.56, P = 0.003). In functional analyses, HO-1 expression level was significantly reduced in persons with IGR and T2DM carrying the L/L (GT)(n) genotype compared with persons with the S/S genotype. Further haplotype combination assay confirmed the functional dominance of the (GT)(n) microsatellite polymorphism over the T(-413)A single nucleotide polymorphism. These results support an association between the HO-1 (GT)(n) microsatellite polymorphism, HO-1 expression levels, and the odds of T2DM.

Heme oxygenase-1/carbon monoxide: from metabolism to molecular therapy

Heme oxygenase-1 (HO-1), a ubiquitous inducible stress-response protein, serves a major metabolic function in heme turnover. HO activity cleaves heme to form biliverdin-IXalpha, carbon monoxide (CO), and iron. Genetic experiments have revealed a central role for HO-1 in tissue homeostasis, protection against oxidative stress, and in the pathogenesis of disease. Four decades of research have witnessed not only progress in elucidating the molecular mechanisms underlying the regulation and function of this illustrious enzyme, but also have opened remarkable translational applications for HO-1 and its reaction products. CO, once regarded as a metabolic waste, can act as an endogenous mediator of cellular signaling and vascular function. Exogenous application of CO by inhalation or pharmacologic delivery can confer cytoprotection in preclinical models of lung/vascular injury and disease, based on anti-apoptotic, anti-inflammatory, and anti-proliferative properties. The bile pigments, biliverdin and bilirubin, end products of heme degradation, have also shown potential as therapeutics in vascular disease based on anti-inflammatory and anti-proliferative activities. Further translational and clinical trials research will unveil whether the HO-1 system or any of its reaction products can be successfully applied as molecular medicine in human disease.

Heme oxygenase-1 microsatellite polymorphism and haplotypes are associated with the development of acute respiratory distress syndrome

OBJECTIVE

Heme oxygenase-1 (HO-1) acts in cytoprotection against acute lung injury. The polymorphic (GT)n repeat in the HO-1 gene (HMOX1) promoter regulates HMOX1 expression. We investigated the associations of HMOX1 polymorphisms with acute respiratory distress syndrome (ARDS) risk and plasma HO-1 levels.

DESIGN

Unmatched, nested case-control study.

SETTING

Academic medical center.

PATIENTS

Consecutive patients with ARDS risk factors upon ICU admission were prospectively enrolled. Cases were 437 Caucasians who developed ARDS and controls were 1,014 Caucasians who did not.

MEASUREMENTS AND RESULTS

We genotyped the (GT)n polymorphism and three tagging single nucleotide polymorphisms (tSNPs) in 1,451 patients, and measured the plasma HO-1 levels in 106 ARDS patients. We clustered the (GT)n repeats into: S-allele (<24 repeats), M-allele (24-30 repeats) and L-allele (> or = 31 repeats). We found that longer (GT)n repeats were associated with reduced ARDS risk (Ptrend = 0.004 for both alleles and genotypes), but no individual tSNP was associated with ARDS risk. HMOX1 haplotypes were significantly associated with ARDS risk (global test, P = 0.016), and the haplotype S-TAG was associated with increased ARDS risk (OR, 1.75; 95% CI, 1.15-2.68; P = 0.010). Intermediate-phenotype analysis showed longer (GT)n repeats were associated with higher plasma HO-1 levels (Ptrend = 0.019 for alleles and 0.027 for genotypes).

CONCLUSIONS

Longer (GT)n repeats in the HMOX1 promoter are associated with higher plasma HO-1 levels and reduced ARDS risk. The common haplotype S-TAG is associated with increased ARDS risk. Our results suggest that HMOX1 variation may modulate ARDS risk through the promoter microsatellite polymorphism.

Co-stimulatory modulation in rheumatoid arthritis: the role of (CTLA4-Ig) abatacept

Associations between rheumatoid arthritis (RA) susceptibility and polymorphism in multiple immunoregulatory genes suggest a role of altered T cell function in the disease. The growing relevance of the oxidative stress in RA synovitis, which results in a number of T cell signalling abnormalities, is reinforced by the demonstration of a direct NO inducing activity through the shared epitope of the HLA class II molecules HLA-DRbeta1, with secondary lymphocytes oxidative damage. Direct T cell/macrophage contact-dependent activation, one of the driving mechanisms of synovitis, is mediated by co-stimulatory molecules as well as cell membrane cytokines and may also result in an impaired suppressive function of T regulatory cells (Treg) in RA joints. The fusion of CTLA4 extracellular binding domain to the Fcgamma1 allows to obtain a soluble CTLA4 receptor, the dimeric recombinant human fusion protein abatacept (CTLA4-Ig). The improved knowledge of the CTLA4-B7 co-stimulation regulatory mechanisms by signals delivered into DCs and Tregs provides multiple potential targets for the abatacept treatment. CTLA4-Ig shows the capacity, either ex vivo or in vivo, to interrupt at multiple steps the ongoing inflammatory and destructive process, and to concur in restoring the immunoregulatory balance in RA.