Abstract

Aims

Heme oxygenase-1 (HMOX1) is a cytoprotective enzyme degrading heme to biliverdin, iron ions, and carbon monoxide, whose expression is induced in response to oxidative stress. Its overexpression has been suggested as a strategy improving survival of transplanted muscle precursors. Results: Here we demonstrated that HMOX1 inhibits differentiation of myoblasts and modulates miRNA processing: downregulates Lin28 and DGCR8, lowers the total pool of cellular miRNAs, and specifically blocks induction of myomirs. Genetic or pharmacological activation of HMOX1 in C2C12 cells reduces the abundance of miR-1, miR-133a, miR-133b, and miR-206, which is accompanied by augmented production of SDF-1 and miR-146a, decreased expression of MyoD, myogenin, and myosin, and disturbed formation of myotubes. Similar relationships between HMOX1 and myomirs were demonstrated in murine primary satellite cells isolated from skeletal muscles of HMOX1+/+, HMOX1+/−, and HMOX1−/− mice or in human rhabdomyosarcoma cell lines. Inhibition of myogenic development is independent of antioxidative properties of HMOX1. Instead it is mediated by CO-dependent inhibition of c/EBPδ binding to myoD promoter, can be imitated by SDF-1, and partially reversed by enforced expression of miR-133b and miR-206. Control C2C12 myoblasts injected to gastrocnemius muscles of NOD-SCID mice contribute to formation of muscle fibers. In contrast, HMOX1 overexpressing C2C12 myoblasts form fast growing, hyperplastic tumors, infiltrating the surrounding tissues, and disseminating to the lungs. Innovation: We evidenced for the first time that HMOX1 inhibits differentiation of myoblasts, affects the miRNA processing enzymes, and modulates the miRNA transcriptome. Conclusion: HMOX1 improves the survival of myoblasts, but concurrently through regulation of myomirs, may act similarly to oncogenes, increasing the risk of hyperplastic growth of myogenic precursors. Antioxid. Redox Signal. 16, 113–127.

Background

Heme oxygenase-1 (HO-1) is induced in many cell types as a defense mechanism against stress. We have investigated the possible role of endogenous HO-1 in the effector phase of arthritis using the K/BxN serum transfer model of arthritis in HO-1 heterozygous and homozygous knock-out mice.

Methodology/Principal Findings

Arthritis was induced in C57/Black-6 xFVB (HO-1+/+, HO-1+/− and HO-1−/−) mice by intraperitoneal injection of 150 µl serum from arthritic K/BxN mice at days 0 and 2. Blood was collected and animals were sacrificed at day 10. Histological analysis was performed in ankle sections. The levels of inflammatory mediators were measured in serum and paw homogenates by enzyme-linked immunosorbent assay or Multiplex technology. The incidence of arthritis was higher in HO-1+/− and HO-1−/− groups compared with HO-1+/+. The inflammatory response was aggravated in HO-1+/− mice as shown by arthritic score and the migration of inflammatory cells that could be related to the enhancement of CXCL-1 production. In addition, the HO-1+/− group showed proteoglycan depletion significantly higher than HO-1+/+ mice. Serum levels of matrix metalloproteinase-3, monocyte chemotactic protein-1, plasminogen activator inhibitor-1, E-selectin and intercellular adhesion molecule-1 were increased in arthritic HO-1−/− mice, whereas vascular endothelial growth factor and some cytokines such as interferon-γ showed a reduction compared to HO-1+/+ or HO-1+/− mice. In addition, down-regulated gene expression of ferritin, glutathione S-reductase A1 and superoxide dismutase-2 was observed in the livers of arthritic HO-1+/− animals.

Conclusion/Significance

Endogenous HO-1 regulates the production of systemic and local inflammatory mediators and plays a protective role in K/BxN serum transfer arthritis.

Aims

Haem oxygenase-1 (HO-1) is a haem-degrading enzyme that generates carbon monoxide, bilirubin, and iron ions. Through these compounds, HO-1 mitigates cellular injury by exerting antioxidant, anti-apoptotic, and anti-inflammatory effects. Here, we examined the influence of HO-1 deficiency and transient hypoxia/ischaemia-induced HO-1 overexpression on post-injury hindlimb recovery.

Methods and results

Mice lacking functional HO-1 (HO-1−/−) showed reduced reparative neovascularization in ischaemic skeletal muscles, impaired blood flow (BF) recovery, and increased muscle cell death compared with their wild-type littermates. Human microvascular endothelial cells (HMEC-1) transfected with plasmid vector (pHRE-HO-1) carrying human HO-1 driven by three hypoxia response elements (HREs) and cultured in 0.5% oxygen demonstrated markedly increased expression of HO-1. Such upregulated HO-1 levels were effective in conferring protection against H2O2-induced cell death and in promoting the proangiogenic phenotype of HMEC-1 cells. More importantly, when delivered in vivo, pHRE-HO-1 significantly improved the post-ischaemic foot BF in mice subjected to femoral artery ligation. These effects were associated with reduced levels of pro-inflammatory cytokines (IL-6 and CXCL1) and lower numbers of transferase-mediated dUTP nick-end labelling-positive cells. Moreover, HO-1 delivered into mouse skeletal muscles seems to influence the regenerative potential of myocytes as it significantly changed the expression of transcriptional (Pax7, MyoD, myogenin) and post-transcriptional (miR-146a, miR-206) regulators of skeletal muscle regeneration.

Conclusion

Our results suggest the therapeutic potential of HO-1 for prevention of adverse effects in critical limb ischaemia.

Recently we have shown that hypoxia as well as overexpression of the stable form of hypoxia-inducible factor-1α (HIF-1α) diminished the expression of interleukin-8 (IL-8) by inhibition of the Nrf2 transcription factor in HMEC-1 cells. Because HIF isoforms may exert different effects, we aimed to examine the influence of HIF-2α on IL-8 expression in endothelial cells. In contrast to HIF-1α, overexpression of HIF-2α obtained by adenoviral transduction resulted in increased expression of IL-8 in an Nrf2-independent way. Importantly, HIF-2α augmented the activity of SP-1, a transcription factor involved in IL-8 regulation and known coactivator of c-Myc. Additionally, HIF-1 decreased, whereas HIF-2 increased, c-Myc expression, and silencing of Mxi-1, a c-Myc antagonist, restored IL-8 expression downregulated by HIF-1α or hypoxia. Accordingly, binding of c-Myc to the IL-8 promoter was abolished in hypoxia. Importantly, both severe (0.5% O2) and mild (5% O2) hypoxia diminished IL-8 expression despite the stabilization of both HIF-1 and HIF-2. This study reveals the opposite roles of HIF-1α and HIF-2α in the regulation of IL-8 expression in endothelial cells. However, despite stabilization of both isoforms in hypoxia the effect of HIF-1 is predominant, and downregulation of IL-8 expression in hypoxia is caused by attenuation of Nrf2 and c-Myc.

Graphical abstract

Highlights

► HIF-1 decreases whereas HIF-2 increases the expression of IL-8 in endothelial cells. ► SP-1 and c-Myc are involved in the HIF-2α-dependent IL-8 upregulation. ► Mxi-1, a c-Myc antagonist, mediates IL-8 diminishment by hypoxia/HIF-1α. ► Inhibition of Nrf2 activity by hypoxia/HIF-1α adds to the downregulation of IL-8. ► Both HIF isoforms are stabilized in hypoxia but the effect of HIF-1α is predominant.

Heme oxygenase-1 (HO-1) is an antioxidative and cytoprotective enzyme, which may protect neoplastic cells against anticancer therapies, thereby promoting the progression of growing tumors. Our aim was to investigate the role of HO-1 in cancer induction. Experiments were performed in HO-1+/+, HO-1+/−, and HO-1−/− mice subjected to chemical induction of squamous cell carcinoma with 7,12-dimethylbenz[a]anthracene and phorbol 12-myristate 13-acetate. Measurements of cytoprotective genes in the livers evidenced systemic oxidative stress in the mice of all the HO-1 genotypes. Carcinogen-induced lesions appeared earlier in HO-1−/− and HO-1+/− than in wild-type animals. They also contained much higher concentrations of vascular endothelial growth factor and keratinocyte chemoattractant, but lower levels of tumor necrosis factor-α and interleukin-12. Furthermore, tumors grew much larger in HO-1 knockouts than in the other groups, which was accompanied by an increased rate of animal mortality. However, pathomorphological analysis indicated that HO-1−/− lesions were mainly large but benign papillomas. In contrast, in mice expressing HO-1, most lesions displayed dysplastic features and developed to invasive carcinoma. Thus, HO-1 may protect healthy tissues against carcinogen-induced injury, but in already growing tumors it seems to favor their progression toward more malignant forms.

Highlights

► We investigate the role of HO-1 in development of squamous cell carcinoma in mice. ► HO-1 deficient mice are more vulnerable to the DMBA/PMA-induced skin injury. ► Lack of HO-1 results in the development of large, but benign papillomas. ► HO-1 expression facilitates transformation of growing tumors to malignant carcinoma. ► HO-1 expression promotes the c-myc mediated transformation of primary fibroblasts.

Highlights

► AAI increases whereas OTA decreases production of proangiogenic VEGF. ► The upregulation of VEGF expression by AAI is caused by induction of SP-1 and HIFs. ► Hypoxia prevents OTA-diminished VEGF production ► The effect of hypoxia on OTA-reduced VEGF is mediated by HIF-2α but not HIF-1α.

Aristolochic acid I (AAI) and ochratoxin A (OTA) cause chronic kidney diseases. Recently, the contribution of hypoxic injuries and angiogenic disturbances to nephropathies has been suggested, but underlying mechanisms have not been fully clarified yet.

In porcine kidney epithelial cell line, LLC-PK1 cells, treatment with non-toxic doses of AAI increased whereas with OTA decreased production of vascular endothelial growth factor (VEGF), the angiogenic factor with well-defined functions in kidney. Moreover, the activity of transcription factors regulating VEGF expression was differentially affected by examined compounds. Activity of hypoxia inducible factors (HIFs) and SP-1 was increased by AAI but diminished by OTA. Interestingly, AP-1 activity was inhibited while NFκB was not influenced by both toxins. Mithramycin A, a SP-1 inhibitor, as well as chetomin, an inhibitor of HIFs, reversed AAI-induced up-regulation of VEGF synthesis, indicating the importance of SP-1 and HIFs in this effect. Additionally, adenoviral overexpression of HIF-2α but not HIF-1α prevented OTA-diminished VEGF production suggesting the protective effect of this isoform towards the consequences exerted by OTA.

These observations provide new insight into complex impact of AAI and OTA on angiogenic gene regulation. Additionally, it adds to our understanding of hypoxia influence on nephropathies pathology.

Objective

Heme oxygenase-1 (HO-1) is an anti-oxidative, anti-inflammatory, and cytoprotective enzyme, which is induced in response to cellular stress. HO-1 promoter contains a (GT)n microsatellite DNA, and number of GT repeats can influence the occurrence of cardiovascular diseases. We elucidated the effect of this polymorphism on endothelial cells (HUVEC) isolated from newborns of different genotypes.

Methods and Results

On the basis of HO-1 expression we classified the HO-1 promoter alleles into three groups: S (most active, GT≤23), M (moderately active, GT=24-28), and L (least active, GT≥29). The presence of S allele led to the higher basal HO-1 expression and stronger induction in response to cobalt protoporphyrin, prostaglandin-J2, hydrogen peroxide, and lipopolysaccharide. Cells carrying S allele survived better under oxidative stress, a fact associated with the lower concentration of oxidized glutathione and more favourable oxidative status, as determined by measurement of the GSH:GSSG ratio. Moreover, they proliferated more efficiently in response to VEGF-A, although the VEGF-induced migration and sprouting of capillaries were not influenced. Finally, the presence of S allele was associated with lower production of some proinflammatory mediators, such as IL-1β, IL-6 and sICAM-1.

Conclusion

The (GT)n promoter polymorphism significantly modulates a cytoprotective, proangiogenic and anti-inflammatory function of HO-1 in human endothelium.

Background

Impaired wound healing in diabetes is related to decreased production of growth factors. Hence, gene therapy is considered as promising treatment modality. So far, efforts concentrated on single gene therapy with particular emphasis on vascular endothelial growth factor-A (VEGF-A). However, as multiple proteins are involved in this process it is rational to test new approaches. Therefore, the aim of this study was to investigate whether single AAV vector-mediated simultaneous transfer of VEGF-A and fibroblast growth factor 4 (FGF4) coding sequences will improve the wound healing over the effect of VEGF-A in diabetic (db/db) mice.

Methods

Leptin receptor-deficient db/db mice were randomized to receive intradermal injections of PBS or AAVs carrying β-galactosidase gene (AAV-LacZ), VEGF-A (AAV-VEGF-A), FGF-4 (AAV-FGF4-IRES-GFP) or both therapeutic genes (AAV-FGF4-IRES-VEGF-A). Wound healing kinetics was analyzed until day 21 when all animals were sacrificed for biochemical and histological examination.

Results

Complete wound closure in animals treated with AAV-VEGF-A was achieved earlier (day 19) than in control mice or animals injected with AAV harboring FGF4 (both on day 21). However, the fastest healing was observed in mice injected with bicistronic AAV-FGF4-IRES-VEGF-A vector (day 17). This was paralleled by significantly increased granulation tissue formation, vascularity and dermal matrix deposition. Mechanistically, as shown in vitro, FGF4 stimulated matrix metalloproteinase-9 (MMP-9) and VEGF receptor-1 expression in mouse dermal fibroblasts and when delivered in combination with VEGF-A, enhanced their migration.

Conclusion

Combined gene transfer of VEGF-A and FGF4 can improve reparative processes in the wounded skin of diabetic mice better than single agent treatment.

Background

The transcription factor Nrf2 (NF-E2-related factor 2) and its target gene products, including heme oxygenase-1 (HO-1), elicit an antioxidant response that may have therapeutic value for Parkinson's disease (PD). However, HO-1 protein levels are increased in dopaminergic neurons of Parkinson's disease (PD) patients, suggesting its participation in free-iron deposition, oxidative stress and neurotoxicity. Before targeting Nrf2 for PD therapy it is imperative to determine if HO-1 is neurotoxic or neuroprotective in the basal ganglia.

Methodology

We addressed this question by comparing neuronal damage and gliosis in Nrf2- or HO-1-knockout mice submitted to intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) for five consecutive days. Nrf2-knockout mice showed exacerbated gliosis and dopaminergic nigrostriatal degeneration, as determined by immunohistochemical staining of tyrosine hydroxylase in striatum (STR) and substantia nigra (SN) and by HPLC determination of striatal dopamine and 3,4- dihydroxyphenylacetic acid (DOPAC). On the other hand, the severity of gliosis and dopaminergic degeneration in HO-1-null mice was neither increased nor reduced. Regarding free-iron deposition, both Nrf2- and HO-1-deficient mice exhibited similar number of deposits as determined by Perl's staining, therefore indicating that these proteins do not contribute significantly to iron accumulation or clearance in MPTP-induced Parkinsonism.

Conclusions

These results suggest that HO-1 does not protect or enhance the sensitivity to neuronal death in Parkinson's disease and that pharmacological or genetic intervention on Nrf2 may provide a neuroprotective benefit as add on therapy with current symptomatic protocols.

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

Background

HO-1 participates in the degradation of heme. Its products can exert unique cytoprotective effects. Numerous tumors express high levels of HO-1 indicating that this enzyme might be a potential therapeutic target. In this study we decided to evaluate potential cytostatic/cytotoxic effects of zinc protoporphyrin IX (Zn(II)PPIX), a selective HO-1 inhibitor and to evaluate its antitumor activity in combination with chemotherapeutics.

Methods

Cytostatic/cytotoxic effects of Zn(II)PPIX were evaluated with crystal violet staining and clonogenic assay. Western blotting was used for the evaluation of protein expression. Flow cytometry was used to evaluate the influence of Zn(II)PPIX on the induction of apoptosis and generation of reactive oxygen species. Knock-down of HO-1 expression was achieved with siRNA. Antitumor effects of Zn(II)PPIX alone or in combination with chemotherapeutics were measured in transplantation tumor models.

Results

Zn(II)PPIX induced significant accumulation of reactive oxygen species in tumor cells. This effect was partly reversed by administration of exogenous bilirubin. Moreover, Zn(II)PPIX exerted potent cytostatic/cytotoxic effects against human and murine tumor cell lines. Despite a significant time and dose-dependent decrease in cyclin D expression in Zn(II)PPIX-treated cells no accumulation of tumor cells in G1 phase of the cell cycle was observed. However, incubation of C-26 cells with Zn(II)PPIX increased the percentage of cells in sub-G1 phase of the cells cycle. Flow cytometry studies with propidium iodide and annexin V staining as well as detection of cleaved caspase 3 by Western blotting revealed that Zn(II)PPIX can induce apoptosis of tumor cells. B16F10 melanoma cells overexpressing HO-1 and transplanted into syngeneic mice were resistant to either Zn(II)PPIX or antitumor effects of cisplatin. Zn(II)PPIX was unable to potentiate antitumor effects of 5-fluorouracil, cisplatin or doxorubicin in three different tumor models, but significantly potentiated toxicity of 5-FU and cisplatin.

Conclusion

Inhibition of HO-1 exerts antitumor effects but should not be used to potentiate antitumor effects of cancer chemotherapeutics unless procedures of selective tumor targeting of HO-1 inhibitors are developed.

Heme oxygenase-1 (HO-1) catalyzes the oxidation of heme to biologically active products: carbon monoxide (CO), biliverdin, and ferrous iron. It participates in maintaining cellular homeostasis and plays an important protective role in the tissues by reducing oxidative injury, attenuating the inflammatory response, inhibiting cell apoptosis, and regulating cell proliferation. HO-1 is also an important proangiogenic mediator. Most studies have focused on the role of HO-1 in cardiovascular diseases, in which its significant, beneficial activity is well recognized. A growing body of evidence indicates, however, that HO-1 activation may play a role in carcinogenesis and can potently influence the growth and metastasis of tumors. HO-1 is very often upregulated in tumor tissues, and its expression is further increased in response to therapies. Although the exact effect can be tissue specific, HO-1 can be regarded as an enzyme facilitating tumor progression. Accordingly, inhibition of HO-1 can be suggested as a potential therapeutic approach sensitizing tumors to radiation, chemotherapy, or photodynamic therapy.

In order to gain a more comprehensive understanding of the aetiology of apolipoprotein E4 genotype-cardiovascular disease (CVD) associations, the impact of the apoE genotype on the macrophage inflammatory response was examined. The murine monocyte–macrophage cell line (RAW 264.7) stably transfected to produce equal amounts of human apoE3 or apoE4 was used. Following LPS stimulation, apoE4-macrophages showed higher and lower concentrations of tumour necrosis factor alpha (pro-inflammatory) and interleukin 10 (anti-inflammatory), respectively, both at mRNA and protein levels. In addition, increased expression of heme oxygenase-1 (a stress-induced anti-inflammatory protein) was observed in the apoE4-cells. Furthermore, in apoE4-macrophages, an enhanced transactivation of the key redox sensitive transcription factor NF-κB was shown. Current data indicate that apoE4 macrophages have an altered inflammatory response, which may contribute to the higher CVD risk observed in apoE4 carriers.

Stromal cell–derived factor 1 (SDF-1) plays a major role in the migration, recruitment, and retention of endothelial progenitor cells to sites of ischemic injury and contributes to neovascularization. We provide direct evidence demonstrating an important role for heme oxygenase 1 (HO-1) in mediating the proangiogenic effects of SDF-1. Nanomolar concentrations of SDF-1 induced HO-1 in endothelial cells through a protein kinase C ζ–dependent and vascular endothelial growth factor–independent mechanism. SDF-1–induced endothelial tube formation and migration was impaired in HO-1–deficient cells. Aortic rings from HO-1−/− mice were unable to form capillary sprouts in response to SDF-1, a defect reversed by CO, a byproduct of the HO-1 reaction. Phosphorylation of vasodilator-stimulated phosphoprotein was impaired in HO-1−/− cells, an event that was restored by CO. The functional significance of HO-1 in the proangiogenic effects of SDF-1 was confirmed in Matrigel plug, wound healing, and retinal ischemia models in vivo. The absence of HO-1 was associated with impaired wound healing. Intravitreal adoptive transfer of HO-1–deficient endothelial precursors showed defective homing and reendothelialization of the retinal vasculature compared with HO-1 wild-type cells following ischemia. These findings demonstrate a mechanistic role for HO-1 in SDF-1–mediated angiogenesis and provide new avenues for therapeutic approaches in vascular repair.

In order to gain a more comprehensive understanding of the aetiology of apolipoprotein E4 genotype-cardiovascular disease (CVD) associations, the impact of the apoE genotype on the macrophage inflammatory response was examined. The murine monocyte–macrophage cell line (RAW 264.7) stably transfected to produce equal amounts of human apoE3 or apoE4 was used. Following LPS stimulation, apoE4-macrophages showed higher and lower concentrations of tumour necrosis factor alpha (pro-inflammatory) and interleukin 10 (anti-inflammatory), respectively, both at mRNA and protein levels. In addition, increased expression of heme oxygenase-1 (a stress-induced anti-inflammatory protein) was observed in the apoE4-cells. Furthermore, in apoE4-macrophages, an enhanced transactivation of the key redox sensitive transcription factor NF-κB was shown. Current data indicate that apoE4 macrophages have an altered inflammatory response, which may contribute to the higher CVD risk observed in apoE4 carriers.

Stromal cell–derived factor 1 (SDF-1) plays a major role in the migration, recruitment, and retention of endothelial progenitor cells to sites of ischemic injury and contributes to neovascularization. We provide direct evidence demonstrating an important role for heme oxygenase 1 (HO-1) in mediating the proangiogenic effects of SDF-1. Nanomolar concentrations of SDF-1 induced HO-1 in endothelial cells through a protein kinase C ζ–dependent and vascular endothelial growth factor–independent mechanism. SDF-1–induced endothelial tube formation and migration was impaired in HO-1–deficient cells. Aortic rings from HO-1−/− mice were unable to form capillary sprouts in response to SDF-1, a defect reversed by CO, a byproduct of the HO-1 reaction. Phosphorylation of vasodilator-stimulated phosphoprotein was impaired in HO-1−/− cells, an event that was restored by CO. The functional significance of HO-1 in the proangiogenic effects of SDF-1 was confirmed in Matrigel plug, wound healing, and retinal ischemia models in vivo. The absence of HO-1 was associated with impaired wound healing. Intravitreal adoptive transfer of HO-1–deficient endothelial precursors showed defective homing and reendothelialization of the retinal vasculature compared with HO-1 wild-type cells following ischemia. These findings demonstrate a mechanistic role for HO-1 in SDF-1–mediated angiogenesis and provide new avenues for therapeutic approaches in vascular repair.

Hypoxia changes expression of angiogenic genes. Statins were also reported to affect blood vessel formation. However, data on the effects of statins on endothelial cells in hypoxia are limited. Here, effect of hypoxia and atorvastatin was assessed in human microvascular endothelial cells (HMEC-1). Hypoxia (1% O2) up-regulated vascular endothelial growth factor-A (VEGF-A) but, unexpectedly, it decreased interleukin-8 (IL-8) and placenta growth factor (PlGF) expression. Atorvastatin (0.1–1 μM) attenuated PlGF in HMEC-1 in normoxia while it decreased VEGF-A and IL-8 production both in normoxia and hypoxia. Notably, the expression of VEGF-D, macrophage scavenger receptor-1 (MSR1), transforming growth factor β receptor III (TGFβR3) and inhibitor of DNA binding 3 (ID3) was augmented by atorvastatin in cells cultured in normoxia, while in hypoxia the statin attenuated their expression. These data showed that hypoxia influenced in the opposite way the expression of major endothelial genes, augmenting VEGF-A and decreasing IL-8 and PlGF. The influence of atorvastatin on angiogenic gene expression is complex, and final pro- or anti-angiogenic outcome of statin therapy remains to be established for numerous angiogenesis-related diseases.

Beneficial cardiovascular effects of statins, the inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, are particularly assigned to the modulation of inflammation. Endothelial nitric oxide synthase (eNOS) and heme oxygenase-1 (HO-1) are listed among the crucial protective, anti-inflammatory genes in the vasculature. Here we show that atorvastatin at pharmacologically relevant concentration (0.1 μM) enhanced the expression of eNOS in human microvascular endothelial cells (HMEC-1). Moreover, atorvastatin prevented hypoxia-induced decrease in eNOS expression. However, in the same cells atorvastatin was ineffective in modulation of HO-1 protein level. Therefore, we suggest that the protective effect of statins at their pharmacological concentrations is not mediated by enhancement of HO-1 activity, but may involve eNOS.

15-deoxy-12,14Δ-prostaglandin-J2 (15d-PGJ2) upregulates expression of vascular endothelial growth factor (VEGF), but may inhibit angiogenesis. We found that 15d-PGJ2 (1-10 μM) attenuated all VEGF-induced angiogenic activities in human umbilical vein endothelial cells (HUVEC). It blocked almost completely cell proliferation, potently reduced migration, assembly into tube-like network on matrigel, and growth of capillaries into collagen gel. 15d-PGJ2 inhibited expression of VEGFR-1 and VEGFR-2 receptors both at mRNA and protein levels. This inhibition, however, was transient (observed after 6-12 h, but not after 24 h) and weak (20-30%), and could not fully explain inhibition of response to VEGF. Accordingly, proliferation was inhibited when 15d-PGJ2 was added 24 h after VEGF or in cells stimulated with basic fibroblast growth factor. Interestingly, 15d-PGJ2 decreased activities of c-jun and c-myc in HUVEC and overexpression of c-myc attenuated its antiproliferative effects. This suggests that inhibition of this transcription factor by 15d-PGJ2 contributes to decrease in angiogenic response.

Background: Skin injury leads to the release of heme, a potent prooxidant which is degraded by heme oxygenase-1 (HO-1) to carbon monoxide, iron, and biliverdin, subsequently reduced to bilirubin. Recently the involvement of HO-1 in angiogenesis has been shown; however, the role of heme and HO-1 in wound healing angiogenesis has not been yet investigated.

Results: Treatment of HaCaT keratinocytes with hemin (heme chloride) induced HO-1 expression and activity. The effect of heme on vascular endothelial growth factor (VEGF) synthesis is variable: induction is significant after a short, 6-h treatment with heme, while longer stimulation may attenuate its production. The involvement of HO-1 in VEGF synthesis was confirmed by inhibition of VEGF expression by SnPPIX, a blocker of HO activity and by attenuation of HO-1 mRNA expression with specific siRNA. Importantly, induction of HO-1 by hemin was able to overcome the inhibitory effect of high glucose on VEGF synthesis. Moreover, HO-1 expression was also induced in keratinocytes cultured in hypoxia, with concomitant augmentation of VEGF production, which was further potentiated by hemin stimulation. Accordingly, conditioned media from keratinocytes overexpressing HO-1 enhanced endothelial cell proliferation and augmented formation of capillaries in angiogenic assay in vitro.

Conclusions: HO-1 is involved in hemin-induced VEGF expression in HaCaT and may play a role in hypoxic regulation of this protein. HO-1 overexpression may be beneficial in restoring the proper synthesis of VEGF disturbed in diabetic conditions.

The pleiotropic effects of statins, inhibitors of 3-hydroxy-3-methylglutaryl–coenzyme A (HMG-CoA) reductase, have been recently extended to the modulation of angiogenesis. Here, to get more insight into the statins action, the authors have investigated the effect of atorvastatin on the expression of several angiogenic and inflammatory genes in human umbilical endothelial cells (HUVECs). Atorvastatin was proangiogenic at the dose of 10 nM, and antiangiogenic at the concentrations of 1 to 10 μM. Moreover, these higher concentrations inhibited also the proliferation of HUVECs induced by vascular endothelial growth factor (VEGF). Lower doses of atorvastatin did not influence endothelial cell proliferation. Importantly, atorvastatin at the micromolar concentrations diminished the production of interleukin (IL)-8, a proinflammatory and proangiogenic chemokine, and inhibited the synthesis of urokinase plasminogen activator (uPA), a potent proinflammatory mediator. However, it decreased also the expression of plasminogen activator inhibitor-1 (PAI-1) and thrombospondin-1 (TSP-1), the inhibitors of angiogenesis. Atorvastatin stimulated the expression of angiopoietin (Ang)-2 and moderately enhanced the expression of endothelial nitric oxide synthase (eNOS), whereas heme oxygenase-1 (HO-1) was not significantly affected. In conclusion, the present findings points to other angiogenesis-related effects of atorvastatin, which may be of relevance to the beneficial influence of statins in cardiovascular system.

Enhancement of the generation of nitric oxide (NO) and vascular endothelial growth factor (VEGF) are suggested to prevent restenosis after angioplasty. Accordingly, we tested whether the local delivery of l-arginine (l-Arg), a substrate for NO generation and the VEGF gene, alone or in combination, can influence neointima formation in hypercholesterolemic rabbits. Balloon injury of the iliac arteries was performed in 24 New Zealand White rabbits fed a 1% cholesterol diet for 3 weeks followed by a local infusion of: (1) pSG5VEGF165 plasmid alone (1000 μg); (2) pSG5VEGF165 (1000 μg) with l-Arg (800 mg); (3) l-Arg (800 mg) alone; and (4) l-Arg (800 mg) with naked pSVβ-gal plasmid (1000 μg). The animals were kept on the hypercholesterolemic diets for a further 28 days, when vessels were taken for morphometric analysis and immunocytochemistry. Endogenous rabbit VEGF concentration in the plasma increased significantly at 7 days after injury (17.06 ± 1.57 vs 23.01 ± 1.9 pg/ml; p < 0.02) and remained elevated for up to 28 days (28.46 ± 5.24; p < 0.01). Injured arteries exhibited strong immunocytochemical staining for rabbit VEGF. Rabbits that received a VEGF gene transfer revealed more prominent neointima formation, whereas treatment with l-Arg was associated with significantly less intimal thickness (p < 0.05). Local transfer of the VEGF gene does not inhibit neointima formation in hypercholesterolemic rabbits. Our results suggest that VEGF gene therapy applied locally in atherosclerotic arteries may not be beneficial.