Regulation of vulnerable plaque development by the heme oxygenase/carbon monoxide system

Heme oxygenase-1 in protozoan infections: A tale of resistance and disease tolerance

Heme oxygenase (HO-1) mediates the enzymatic cleavage of heme, a molecule with proinflammatory and prooxidant properties. HO-1 activity deeply impacts host capacity to tolerate infection through reduction of tissue damage or affecting resistance, the ability of the host to control pathogen loads. In this Review, we will discuss the contribution of HO-1 in different and complex protozoan infections, such as malaria, leishmaniasis, Chagas disease, and toxoplasmosis. The complexity of these infections and the pleiotropic effects of HO-1 constitute an interesting area of study and an opportunity for drug development.

Sulforaphane inhibits platelet-derived growth factor-induced vascular smooth muscle cell proliferation by targeting mTOR/p70S6kinase signaling independent of Nrf2 activation

Activation of nuclear factor erythroid 2-related factor 2 (Nrf2, a transcription factor) and/or inhibition of mammalian target of rapamycin (mTOR) are implicated in the suppression of vascular smooth muscle cell (VSMC) proliferation. The present study has examined the likely regulatory effects of sulforaphane (SFN, an antioxidant) on Nrf2 activation and platelet-derived growth factor (PDGF)-induced mTOR signaling in VSMCs. Using human aortic VSMCs, nuclear extraction and siRNA-mediated downregulation studies were performed to determine the role of Nrf2 on SFN regulation of PDGF-induced proliferative signaling. Immunoprecipitation and/or immunoblot studies were carried out to determine how SFN regulates PDGF-induced mTOR/p70S6K/S6 versus ERK and Akt signaling. Immunohistochemical analysis was performed to determine SFN regulation of S6 phosphorylation in the injured mouse femoral artery. SFN (5μM) inhibits PDGF-induced activation of mTOR without affecting mTOR association with raptor in VSMCs. While SFN inhibits PDGF-induced phosphorylation of p70S6K and 4E-BP1 (downstream targets of mTOR), it does not affect ERK or Akt phosphorylation. In addition, SFN diminishes exaggerated phosphorylation of S6 ribosomal protein (a downstream target of p70S6K) in VSMCs in vitro and in the neointimal layer of injured artery in vivo. Although SFN promotes Nrf2 accumulation to upregulate cytoprotective genes (e.g., heme oxygenase-1 and thioredoxin-1), downregulation of endogenous Nrf2 by target-specific siRNA reveals an Nrf2-independent effect for SFN-mediated inhibition of mTOR/p70S6K/S6 signaling and suppression of VSMC proliferation. Strategies that utilize local delivery of SFN at the lesion site may limit restenosis after angioplasty by targeting mTOR/p70S6K/S6 axis in VSMCs independent of Nrf2 activation.

Association of HO-1 (GT)n Promoter Polymorphism and Cardiovascular Disease: A Reanalysis of the Literature

BACKGROUND

Heme-oxygenase 1 (HO-1), an inducible heme-degrading enzyme, has antiatherogenic effects through its enzymatic end products. HO-1 gene expression is modulated by a guanidine thymidine dinucleotide ([GT]n) repeat polymorphism in the promoter region. Shorter repeats with (GT)n < 25 are associated with higher inducibility and activity of HO-1.

METHODS

We performed a systematic review of all literature from 1997 to 2013 on the association of the HO-1 (GT)n and cardiovascular disease (CVD). On the basis of predefined criteria (patient characteristics, genotype data format, allelic distribution, repeat length cutoff) 41 articles were selected. Patients were redistributed into 4 homogeneous subpopulations: patients with CVD (CVD group), patients without CVD (nonCVD), 'controls' with unknown cardiovascular status (unspecified) and children younger than 20 years of age (unselected). Genotype distributions (homozygous short [SS] or long [LL], and heterozygous) of the 4 patient categories were compared and odds ratios (ORs) for CVD were calculated using logistic regression analysis.

RESULTS

Overall, the proportion of the SS genotype was lower in CVD compared with nonCVD and unspecified. The ORs for CVD was highest in patients carrying the LL genotype (OR LL vs SS, 1.769 [95% confidence interval, 1.594-1.963]). Furthermore, genotype distribution differed between Caucasian and Asian individuals, the latter having a much higher proportion of the SS genotype (22% vs 11%).

CONCLUSIONS

This review of the available literature on the epidemiological association between the HO-1 (GT)n repeat polymorphism and CVD supports the presumed protective effects of HO-1. The second but probably even more relevant finding of our review is that racial disparities in HO-1 (GT)n repeat length distribution exist and might influence the associations of the genotype with CVD status.

Association between heme oxygenase 1 gene promoter polymorphisms and susceptibility to coronary artery disease: a HuGE review and meta-analysis

We performed a systematic review and meta-analysis of heme oxygenase 1 gene (HO-1) promoter polymorphisms and susceptibility to coronary artery disease (CAD) based on eligible studies retrieved from electronic databases from 2002 to 2013. Eleven studies, involving 10,170 patients with CAD and 6,868 controls, were included. Overall, no significantly decreased risk of CAD was found in persons with the SS genotype of the HO-1 (GT)n repeat length polymorphism compared with those with the LL + SL genotype. However, decreased risks of CAD were observed in the Asian subgroup, the coronary-artery-narrowing ≥50% subgroup, the myocardial infarction subgroup, the age- and sex-matched subgroup, and the good-quality-reports subgroup. The primary heterogeneity in the studies came from age and sex matching and the extent of coronary stenosis. CAD risk was significantly decreased for persons with the AA genotype of the T(-413)A single-nucleotide polymorphism versus those with the TT genotype, but most of the studies showed that the allele distribution was inconsistent with Hardy-Weinberg equilibrium. In this meta-analysis, we found that the (GT)n SS genotype was associated with decreased risk of CAD after controlling for biases due to age and sex matching, extent of coronary stenosis, ethnicity, and study quality. The relationship between the T(-413)A single-nucleotide polymorphism and CAD should be interpreted more cautiously.

Preoperative HO-1 levels as prognostic factor for adverse cardiac events in elder patients undergoing non-cardiac surgery

Background

Hypoxia-inducible factor-1α (HIF-1α) and heme oxygenase-1(HO-1) are involved in the tissue hypoxic response.

Hypothesis

HIF-1α and HO-1 levels may predict cardiac ischemia and adverse cardiac events during non-cardiac surgery.

Methods

HIF-1α and HO-1 levels were determined in elderly patients undergoing non-cardiac surgery preoperatively and at 30 minutes, 48 and 72 hours postoperatively. Results were analyzed with respect to the occurrence of adverse cardiac events.

Results

A total of 380 patients with a mean age of 65.3 years were included, and 54 (14.2%) who had adverse cardiac events during or after the surgery. HIF-1α and HO-1 levels in the adverse cardiac event group were significantly higher than in the group without adverse cardiac events at each time point (all, P<0.05). In multivariates regression analysis, the odds of an adverse cardiac event was increased by every 1-year increase in age (odd ratio [OR] 1.39, P<0.001), abnormal ECG at baseline (OR 2.27, P = 0.048), myocardial infarction history (OR 3.18, P = 0.015), and positive baseline cTnI level were associated with an increased likelihood of an adverse cardiac event (OR 8.78, P = 0.019), and for every 1 unit increase of HO-1, the odds of an adverse cardiac event increased by 1.30 (P = 0.002).

Conclusion

Determination of preoperative HO-1 levels may aid in identifying patients at risk of developing ischemic cardiac events.

PDGF-induced migration of vascular smooth muscle cells is inhibited by heme oxygenase-1 via VEGFR2 upregulation and subsequent assembly of inactive VEGFR2/PDGFRβ heterodimers

OBJECTIVE

In cardiovascular regulation, heme oxygenase-1 (HO-1) activity has been shown to inhibit vascular smooth muscle cell (VSMC) proliferation by promoting cell cycle arrest at the G1/S phase. However, the effect of HO-1 on VSMC migration remains unclear. We aim to elucidate the mechanism by which HO-1 regulates PDGFBB-induced VSMC migration.

METHODS AND RESULTS

Transduction of HO-1 cDNA adenoviral vector severely impeded human VSMC migration in a scratch, transmembrane, and directional migration assay in response to PDGFBB stimulation. Similarly, HO-1 overexpression in the remodeling process during murine retinal vasculature development attenuated VSMC coverage over the major arterial branches as compared with sham vector-transduced eyes. HO-1 expression in VSMCs significantly upregulated VEGFA and VEGFR2 expression, which subsequently promoted the formation of inactive PDGFRβ/VEGFR2 complexes. This compromised PDGFRβ phosphorylation and impeded the downstream cascade of FAK-p38 signaling. siRNA-mediated silencing of VEGFA or VEGFR2 could reverse the inhibitory effect of HO-1 on VSMC migration.

CONCLUSIONS

These findings identify a potent antimigratory function of HO-1 in VSMCs, a mechanism that involves VEGFA and VEGFR2 upregulation, followed by assembly of inactive VEGFR2/PDGFRβ complexes that attenuates effective PDGFRβ signaling.

Ets2 Determines the Inflammatory State of Endothelial Cells in Advanced Atherosclerotic Lesions

Rationale:

Neovascularization is required for embryonic development and plays a central role in diseases in adults. In atherosclerosis, the role of neovascularization remains to be elucidated. In a genome-wide microarray-screen of Flk1+ angioblasts during murine embryogenesis, the v-ets erythroblastosis virus E26 oncogene homolog 2 (Ets2) transcription factor was identified as a potential angiogenic factor.

Objectives:

We assessed the role of Ets2 in endothelial cells during atherosclerotic lesion progression toward plaque instability.

Methods and Results:

In 91 patients treated for carotid artery disease, Ets2 levels showed modest correlations with capillary growth, thrombogenicity, and rising levels of tumor necrosis factor-α (TNFα), monocyte chemoattractant protein 1, and interleukin-6 in the atherosclerotic lesions. Experiments in ApoE −/− mice, using a vulnerable plaque model, showed that Ets2 expression was increased under atherogenic conditions and was augmented specifically in the vulnerable versus stable lesions. In endothelial cell cultures, Ets2 expression and activation was responsive to the atherogenic cytokine TNFα. In the murine vulnerable plaque model, overexpression of Ets2 promoted lesion growth with neovessel formation, hemorrhaging, and plaque destabilization. In contrast, Ets2 silencing, using a lentiviral shRNA construct, promoted lesion stabilization. In vitro studies showed that Ets2 was crucial for TNFα-induced expression of monocyte chemoattractant protein 1, interleukin-6, and vascular cell adhesion molecule 1 in endothelial cells. In addition, Ets2 promoted tube formation and amplified TNFα-induced loss of vascular endothelial integrity. Evaluation in a murine retina model further validated the role of Ets2 in regulating vessel inflammation and endothelial leakage.

Conclusions:

We provide the first evidence for the plaque-destabilizing role of Ets2 in atherosclerosis development by induction of an intraplaque proinflammatory phenotype in endothelial cells.