Cytosolic dsRNA sensors as regulators of transgene expression from AAV vectors in human iPSC-derived cardiomyocytes

Background

Adeno-associated viral vectors (AAVs) are safe and efficient tools for delivery of therapeutic genes in numerous applications. Although they elicit only limited immune response in host cells, a recent study has demonstrated an association between decreasing transgene expression in the liver and induction of the immune response to cytoplasmic dsRNA. While AAVs are DNA vectors, it appears that their unique genome structure allows the generation of dsRNA in transduced cells. Since the expression cassette is flanked by inverted terminal repeats (ITRs), which can function as bidirectional promoters, assembly of sense and antisense transcripts can potentially result in formation of dsRNA structures, especially in cells exhibiting high transgene expression.

Purpose

In this study, we explored the mechanism of dsRNA recognition in cardiomyocytes, to unravel its role in the regulation of transgene expression from AAV vectors.

Methods

For this purpose, we utilised human iPSC-derived cardiomyocytes transduced with self-complementary AAV6 or AAV9 vectors encoding GFP. Since we focused on the long-term effects of transgene expression, all the analyses were performed 7–9 days after AAV transduction.

Results

We confirmed that ITR serves as a functional promoter in the cells, capable of maintaining approximately half of the fluorescence signal compared to the CMV promoter. Long-term transgene expression was associated with elevated expression of dsRNA sensors (MDA5, RIG-I, LGP2 and TLR3) and the appearance of small foci of dsRNA in the perinuclear region. Unlike an artificial ligand for dsRNA sensors, poly (I:C), dsRNA in AAV-transduced cells did not interact with the LGP2 protein. To induce dsRNA recognition, we stimulated the cells with IFNβ for 1 week, starting from day 1 after transduction. We found that transgene expression is significantly hampered in such conditions. Furthermore, IFNβ induced the direct interaction of dsRNA with the OAS1 protein in transduced cells. During viral infections, OAS1 and its effector nuclease RNAse L promote the degradation of mRNA to restrict the production of viral proteins. Since RNAse L is not specific for particular transcripts, we hypothesize that activation of the OAS1 pathway in transduced cells is responsible for downregulation of transgene expression. While IFNβ induced OAS1-dsRNA recognition, we did not observe such an event in cells transduced with AAV and maintained under standard conditions. In turn, AAV transduction resulted in a reduction in OAS1 expression at the mRNA and protein level, suggesting a possible reason for tolerance to dsRNA in transduced cardiomyocytes.

Conclusions

Our data present a novel mechanism of regulation of transgene expression in AAV-transduced cells involving OAS1–RNAse L pathway and provide deeper insight into the general signal transduction routes activated in response to cytosolic dsRNA in human iPSC-derived cardiomyocytes.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National Science Centre - PRELUDUM grant 2019/33/N/NZ1/03066Jagiellonian University, Faculty of Biochemistry, Biophysics and Biotechnology - grant for young scientists MNS 6/2020

HNF1A-MODY disease modeling in a dish - a possible role of IL-8 in the increased vascular permeability

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National Science Centre

Maturity Onset Diabetes of the Young (MODY) is an autosomal inherited disease and its most prevalent form is caused by mutations in the hepatocyte nuclear factor 1-alpha (HNF1A). HNF1A-MODY patients often develop vascular complications and have increased incidents of cardiovascular-related death. In our recent work (1), we have established a disease model based on human induced pluripotent stem cells (hiPSCs) derived from a healthy donor and isogenic lines with the mutations either in one of the HNF1A alleles (monoallelic, MAC) or in both of them (biallelic, BAC). After differentiation of these lines toward endothelial cells (hiPSC-ECs), we have shown that HNF1A-mutated hiPSC-ECs have increased permeability after TNFα stimulation. Interleukin 8 (IL-8) could be an important player in this process (2), but its possible role in HNF1A-related increased permeability has not been studied yet.

The aim of this study was to evaluate whether increased vascular permeability in HNF1A-mutated hiPSC-ECs could be related to IL-8 production of these cells.

Results were based on our previously described isogenic hiPSC-ECs. IL-8 production was assessed with ELISA, proliferation through BrdU incorporation test and apoptosis was evaluated with PO-PRO1/7-AAD kit.

There was an increased IL-8 production in BAC line under basic conditions, meaning that these cells present more activated proinflammatory status. After stimulation with TNFα, all hiPSC-ECs increased IL-8 levels, however HNF1A-mutated cells were less efficient. BAC hiPSC-ECs had the lowest IL-8 production after TNFα, meaning that increased vascular permeability in these cells could not be related to IL-8. As IL-8 has also an important role in the proliferation and survival of the ECs (3), we checked whether increased IL-8 production under basic conditions in BAC could have an impact on the proliferation and apoptosis of these cells. The BAC hiPSC-ECs had significantly decreased proliferation compared to both control and MAC lines. Additionally, both HNF1A-mutated lines had an increase in the percentage of the apoptotic cells. After stimulation with TNFα, BAC hiPSC-ECs failed to further increase the percentage of the apoptotic cells, as compared to MAC and control cells.

Summarizing, the increased vascular permeability of HNF1A-mutated hiPSC-ECs in response to TNFα could not be attributed to IL-8. The increased IL-8 of BAC hiPSC-ECs under basic conditions did not improve their proliferation or survival capacity. Contrary, these cells showed decreased proliferation and increased percentage of apoptotic cells. Moreover, in response to proinflammatory cytokine, BAC hiPSC-ECs failed to further increase the percentage of the apoptotic cells, which could be related to alterations in the cell cycle of these cells. All these results show that HNF1A-mutated iPSC-ECs have impaired response to TNFα, which may contribute to increased incidence of vascular complications related to HNF1A-MODY.

Terminal glycosylation pattern as a determinant of human iPSC-derived cardiomyocytes transduction with AAV vectors

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Young scientists grant MNS9/2021

Polish National Science Centre PRELUDIUM grant 2019/33/N/NZ1/03066

Introduction

Although gene therapy has become a feasible alternative to regular treatment in numerous disorders, efficient targeting of human heart still seems out of reach. So far, adeno-associated viral vectors (AAVs) have been the most promising transgene carriers in in vivo applications. Transduction with AAVs relies on serotype-specific binding to the glycan residues on the cell surface. While AAV serotype 9 (AAV9) - binding galactose - was successfully used for delivery of therapeutic genes to cardiac muscle in murine models, its effect was underwhelming in large animals. Switching the serotype to AAV1 or AAV6 – binding sialic acids – enabled transduction of porcine hearts, and cardiomyocytes derived from human induced pluripotent stem cells (hiPSC) in 2D in vitro culture. But, as evidenced in clinical trials where less than 1% of heart cells contained delivered transgene, such strategy was not suitable for in vivo application in humans.

Purpose

Taking into account differences in glycosylation patterns between humans and other mammals, we aimed to investigate the role of surface glycans in AAV6 and AAV9 transduction mechanism in 2D and 3D cultures of human cardiomyocytes.

Methods

We generated hiPSC- derived cardiomyocytes (hiPSC-CMs) and epicardial fibroblasts (hiPSC-CFs). Cells were cultured in regular 2D conditions or 3D co-cultures (as spheroids), since direct cells interaction may influence the availability of terminal sugar residues. Surface glycans were stained with lectins and imaged using confocal microscope.

Results

While in 2D conditions AAV6 transduces hiPSC-CMs very efficiently, it is significantly less potent in 3D culture. Conversely, AAV9 maintains most of its functionality in 3D model. Our data collected from spheroids, indicate that cells in such 3D cultures undergo significant changes in terminal glycosylation pattern. While the level of galactose (AAV9 receptor) increased from day 1 to day 7, the signal from sialic acids attached to galactose (AAV6 receptor) decreased. This effect was accompanied by the upregulation of sialidase-3 expression, that regulates availability of galactose residues on the cell surface. As a result, transduction efficiency was improved in spheroids exposed to AAV9 on day 7 of 3D culture, in comparison to those transduced on day 1. Inhibition of sialidases activity with NADNA reduced the level of terminal galactose in both, hiPSC-CMs and hiPSC-CFs, and was associated with more efficient transduction of cardiomyocytes with AAV6, and less efficient transduction with AAV9. Additionally, we observed that galactosylation of collagen can be another factor that influences cell-vector interaction in 2D and 3D culture.

Conclusions

Our results demonstrate that the availability of terminal sugar residues is a key factor regulating transduction of hiPSC-CMs with AAV vectors, and underline the need for development of appropriate models for testing of AAV functionality in preclinical studies.

P2572Human iPSC-derived cardiomyocytes preserve murine heart function after myocardial infarction unlike adipose tissue-derived stromal cells

Introduction

Despite progress in pharmacological treatment of myocardial infarction (MI), there is still an immense need for novel therapies for this life-threatening condition. Accordingly, cell-based therapies have been extensively investigated with most studies focusing on mesenchymal stromal cells. However due to their inability to differentiate into cardiomyocytes as well as limited survival upon in vivo administration, no effective treatment of MI has been developed. In contrast, application of hiPSC-derived cardiomyocytes (hiPSC-CM) represent biologically rational approach with pre-clinical studies confirming their therapeutic potential in various models of MI. However further optimization is required due to limited survival of hiPSC-CM upon in vivo administration. Therefore, we evaluated the therapeutic potential of genetically modified hiPSC-CM in murine model of acute MI and compared it to the effect of adipose tissue-derived stromal cells (ADSC).

Methods

In the first step hiPSC overexpressing GFP, luciferase (Luc) and pro-angiogenic and cardioprotective factors: heme oxygenase-1 (HO-1, heme degrading enzyme) or stromal cell-derived factor-1 (SDF-1, pro-angiogenic chemokine) were subjected to cardiac differentiation which yielded in each group 70–90% cardiac troponin T-positive contracting cells. hiPSC-CM (5x105 in 10 μl) were administered into NOD-SCID mice which underwent permanent ligation of left anterior descending (LAD) coronary artery. The cells were injected into the peri-infarct zone. Mice subjected to sham operation as well as injected with saline after MI were used as controls. The ultrasonography of hearts was performed on day 7, 14, 28 and 42 whereas the presence of hiPSC-CM was monitored using IVIS Spectrum system upon administration of luciferin and analysed in sections of collected hearts. The same experimental scheme was used to assess therapeutic potential of ADSC (CD105+CD73+CD90+CD44+CD146-CD34-) overexpressing luciferase and GFP.

Results

Ultrasonography demonstrated that upon delivery of hiPSC-CM the left ventricle ejection fraction (LVEF) was very significantly higher in comparison to control group injected with saline after induction of MI. In contrast, no improvement of LVEF was observed after administration of ADSC. Interestingly, measurements of luciferase activity revealed the strongest bioluminescent signal in the hearts of mice transplanted with iPSC-CM-HO1 42 days after MI. Importantly, the survival of hiPSC-CM in murine myocardium six weeks upon administration was further confirmed with immunofluorescent analysis of heart sections using human specific anti-Ku80 antibody. Again, luciferase activity was not observed upon delivery of ADSC.

Conclusion

These results strongly indicate that administration of hiPSC-CM, unlike ADSC, preserve murine heart function in acute MI model. Additionally, overexpression of HO-1 may positively influence their survival upon in vivo delivery into infarcted tissue.

Acknowledgement/Funding

The National Centre for Research and Development (STRATEGMED 2/269415/11/NCBR/2015), National Science Centre of Poland (HARMONIA 2014/14/M/NZ1/00010)

Involvement of microRNAs in the inflammatory pathways of pulmonary sarcoidosis

Sarcoidosis is a multi-organ disease in which affected tissues are invaded with non-necrotizing granulomatous structures, mostly consisted of T helper 1 (Th1) cells and multinucleate giant cells. However, the etiology and pathogenesis of sarcoidosis is not known and the diagnosis is usually based on clinical examination involving radiography and histopathological analysis of biopsies of affected organs. Although the knowledge on the molecular background of sarcoidosis is limited, it seems that the important pathways involve transforming growth factor-β (TGF-β) and JAK/STAT, which may influence the interferon-γ (IFN-γ)-mediated signaling. Additionally, recently the role of microRNAs (miRNAs), the small non-coding RNA molecules, has been emphasized in different pathological conditions including autoimmune diseases. This review summarizes the current knowledge on the molecular pathways in the pathogenesis of sarcoidosis with a special emphasis on cytokines and miRNAs controlling immune cells proliferation and differentiation. Moreover, the possible role of T regulatory cells (CD4(+) CD25(+) FoxP3(+)) in this disease has been discussed.

Induced pluripotent stem cells as a model for diabetes investigation

Mouse and human induced pluripotent stem cells (iPSCs) may represent a novel approach for modeling diabetes. Taking this into consideration, the aim of this study was to generate and evaluate differentiation potential of iPSCs from lep^db/db (db/db) mice, the model of diabetes type 2 as well as from patients with Maturity Onset Diabetes of the Young 3 (HNF1A MODY). Murine iPSC colonies from both wild type and db/db mice were positive for markers of pluripotency: Oct3/4A, Nanog, SSEA1, CDy1 and alkaline phosphatase and differentiated in vitro and in vivo into cells originating from three germ layers. However, our results suggest impaired differentiation of db/db cells into endothelial progenitor-like cells expressing CD34 and Tie2 markers and their reduced angiogenic potential. Human control and HNF1A MODY reprogrammed cells also expressed pluripotency markers: OCT3/4A, SSEA4, TRA-1–60, TRA-1-81, formed embryoid bodies (EBs) and differentiated into cells of three germ layers. Additionally, insulin expressing cells were obtained from those partially reprogrammed cells with direct as well as EB-mediated differentiation method. Our findings indicate that disease-specific iPSCs may help to better understand the mechanisms responsible for defective insulin production or vascular dysfunction upon differentiation toward cell types affected by diabetes.

Elevated serum osteoprotegerin is associated with decreased osteoclastic differentiation in stenotic aortic valves

Calcific aortic valve stenosis (CAVS) is an actively regulated process that involves mechanisms of bone development, including the receptor activator of nuclear factor κB, its ligand, and osteoprotegerin (RANK/RANKL/OPG) regulatory system. The aim of this study was to investigate whether the levels of circulating OPG and RANKL can be correlated with some histopathological features of the stenotic valves. Serum levels of osteoprotegerin (OPG) and soluble RANKL (sRANKL) were assessed in 27 patients with CAVS prior to valve replacement surgery and in 12 control subjects. The removed valves were examined macroscopically and microscopically. Valve sections were stained with hematoxylin and eosin for general morphology, with Oil Red O for lipids and immunostained with antibodies against markers visualizing osteoclastic cells (tartrate-resistant acid phosphatase, TRAP), macrophages (CD68) and blood vessels (CD34). Patients with CAVS had elevated levels of OPG as compared to the control group (p=0.005). Within the CAVS group, patients with osteoclastic TRAP-positive cells in their valves had significantly lower serum levels of OPG (p=0.009) and lipid content (p=0.03) than those without such cells. Moreover, osteogenic metaplasia was observed exclusively in the valves containing TRAP-positive cells. Results of this study suggest that the circulating OPG can influence the processes occurring in the calcifying valves by inhibiting osteoclastic differentiation of cells involved in calcification and by preventing osteogenic metaplasia.

Modulation of inflammatory response by pentoxifylline is independent of heme oxygenase-1 pathway

OBJECTIVE

It was reported that some effects of pentoxifylline (PTX) are mediated by heme oxygenase-1 (HO-1) induction. We investigated the role of HO-1 in anti-inflammatory activity of PTX.

METHODS

Experiments were performed in human and murine monocytes and endothelial cells and in HO-1 deficient mice.

RESULTS

PTX dose-dependently decreased expression of HO-1 in cell lines studied. As expected, PTX reduced also production of TNF. This effect was independent of HO-1 activity, as demonstrated in cells treated with HO-1 activators and inhibitors or in cells overexpressing HO-1. Moreover, inhibition of TNF was the same in human endothelial cells of different HO-1 genotypes, showing that PTX is similarly efficient in carriers of more and less active HO-1 promoter variants. In mice, PTX did not influence HO-1 expression, as measured in liver, kidney, spleen, heart, and skin. Accordingly, the response of PTX treated animals to LPS was the same in wild type and HO-1 deficient mice. PTX to a similar extent increased influx of leukocyte into peritoneal cavity, decreased production of TNF and reduced expression of VCAM-1 in vascular intima.

CONCLUSION

PTX inhibits production of TNF and may decrease inflammatory reaction both in vitro and in vivo, but these effects are independent of HO-1.

New vectors and strategies for cardiovascular gene therapy

Cardiovascular diseases are the major cause of morbidity and mortality in both men and women in industrially developed countries. These disorders may result from impaired angiogenesis, particularly in response to hypoxia. Despite many limitations, gene therapy is still emerging as a potential alternative for patients who are not candidates for traditional revascularization procedures, like angioplasty or vein grafts. This review focuses on recent approaches in the development of new gene delivery vectors, with great respect to newly discovered AAV serotypes and their modified forms. Moreover, some new cardiovascular gene therapy strategies have been highlighted, such as combination of different angiogenic growth factors or simultaneous application of genes and progenitor cells in order to obtain stable and functional blood vessels in ischemic tissue.

Heme oxygenase-1 protects tumor cells against photodynamic therapy-mediated cytotoxicity

Photodynamic therapy is a promising antitumor treatment modality approved for the management of both early and advanced tumors. The mechanisms of its antitumor action include generation of singlet oxygen and reactive oxygen species that directly damage tumor cells and tumor vasculature. A number of mechanisms seem to be involved in the protective responses to PDT that include activation of transcription factors, heat shock proteins, antioxidant enzymes and antiapoptotic pathways. Elucidation of these mechanisms might result in the design of more effective combination strategies to improve the antitumor efficacy of PDT. Using DNA microarray analysis to identify stress-related genes induced by Photofrin-mediated PDT in colon adenocarcinoma C-26 cells, we observed a marked induction of heme oxygenase-1 (HO-1). Induction of HO-1 with hemin or stable transfection of C-26 with a plasmid vector encoding HO-1 increased resistance of tumor cells to PDT-mediated cytotoxicity. On the other hand, zinc (II) protoporphyrin IX, an HO-1 inhibitor, markedly augmented PDT-mediated cytotoxicity towards C-26 and human ovarian carcinoma MDAH2774 cells. Neither bilirubin, biliverdin nor carbon monoxide, direct products of HO-1 catalysed heme degradation, was responsible for cytoprotection. Importantly, desferrioxamine, a potent iron chelator significantly potentiated cytotoxic effects of PDT. Altogether our results indicate that HO-1 is involved in an important protective mechanism against PDT-mediated phototoxicity and administration of HO-1 inhibitors might be an effective way to potentiate antitumor effectiveness of PDT.

Heme oxygenase-1-dependent and -independent regulation of angiogenic genes expression: effect of cobalt protoporphyrin and cobalt chloride on VEGF and IL-8 synthesis in human microvascular endothelial cells

Induction of heme oxygenase-1 (HO-1) expression can be achieved by stimulation with cobalt protoporphyrin (CoPPIX) or cobalt chloride (CoCl2). HO-1 has been recently implicated in regulation of angiogenesis and CoCl2 is known to potently activate hypoxia inducible factor-1 (HIF-1) transcription factor, a key regulator of angiogenic response in hypoxia. Here we determined the effect of CoPPIX and CoCl2 on the expression of vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8), the two major angiogenic mediators, in human microvascular endothelial cells (HMEC-1). CoPPIX induced HO-1 expression and strongly enhanced VEGF and IL-8 synthesis, through the activation of VEGF and IL-8 promoters. Inhibition of HO activity by SnPPIX decreased VEGF production, while, interestingly, it did not affect IL-8. CoCl2 activated hypoxia-responsive element (HRE) and consequently VEGF generation via the enhancement of production of reactive oxygen species (ROS). On the other hand, CoCl2 did not influence IL-8 expression, while CoPPIX did not induce ROS elevation neither it affected HRE activity in VEGF promoter. Our data show that although both CoCl2 and CoPPIX induce HO-1, the influence of CoCl2 on VEGF does not involve HO-1 and is HIF-1-dependent, while the effect of CoPPIX does not involve HIF-1 but relies on HO-1.

Effects of plant extracts on angiogenic activities of endothelial cells and keratinocytes

Numerous bioactive chemical compounds of plant origin may influence the angiogenic activity of various cell types and may thus affect the formation of blood vessels. Here we present the angiogenic effects of extracts of edible plants collected in Crete, Southern Italy and Southern Spain. Extracts have been applied to cultured human microvascular endothelial cells (HMEC-1), human umbilical vein endothelial cells (HUVEC) and human keratinocytes (HaCaT). About half out of 96 extracts exerted an inhibitory effect on HMEC-1 proliferation. Additionally, we have noted the inhibitory effects of extracts on HUVEC differentiation on a Matrigel layer. None of the extracts showed a stimulatory activity. The extract of Thymus piperella exerted moderate inhibitory effect on cobalt-chloride induced VEGF synthesis, however, CoCl(2)-induced activation of hypoxia responsive element of VEGF promoter was significantly attenuated only by extract of Origanum heracleoticum. Our study indicates that extracts of local food plants, of potential value as nutraceuticals, contain chemical compounds which may inhibit angiogenesis. Demonstration of their real influence on human health requires, however, extensive animal studies and controlled clinical investigations.

Nutraceuticals as anti-angiogenic agents: hopes and reality

Angiogenesis, the formation of new blood vessels from preexisting vascular network is a driving force of organ development in ontogeny, is necessary for ovulation and hair growth, and is prerequisite for proper wound healing. It is also a critical mechanism of numerous diseases, the most important of which are cancer and atherosclerosis. Therefore, modulation of angiogenesis is considered as therapeutic strategies of great importance for human health. Numerous bioactive plant compounds, often referred to as nutraceuticals are recently tested for the potential clinical applications. Among the most frequently studied are resveratrol, a polyphenol present in red-wine and grape-seed, epigallocatechin-3-gallate (EGCG) from green tea and curcumin from Curcuma longa. It is also possible that components of other plants, including the constituents of local food diet may find application for modulation of angiogenesis, provided that their effectiveness will be confirmed in controlled, scientifically validated trials.

Delivery of high dose VEGF plasmid using fibrin carrier does not influence its angiogenic potency

Delivery of DNA mixed with a degradable matrix carrier was supposed to improve transgene expression. Using a rabbit hind-limb ischemia model, we tested the angiogenic potency of plasmid encoding human vascular endothelial growth factor (pSG5-VEGF165) entrapped in fibrin sealant. Animals were injected intramuscularly with 500 microg of pSG5-VEGF165 or control plasmid, dissolved in saline (PBS) or fibrin glue. After 14 days, presence of delivered constructs and expression of transgene was confirmed in injected muscles of all animals. There were no significant differences in the levels of human VEGF mRNA and protein between VEGF-PBS and VEGF-fibrin groups (Mann-Whitney test). Accordingly, pSG5-VEGF165 regardless of the way of delivery, induced similar increases in capillary density within treated muscles (ANOVA). Control plasmid did not show any effects. In conclusion, injection of pSG5-VEGF165 into ischemic adductor muscle leads to synthesis of human VEGF and increases the number of capillaries. Fibrin carrier does not influence its angiogenic potential.

Vascular endothelial growth factor (VEGF) in ankylosing spondylitis--a pilot study

INTRODUCTION

Angiogenesis is important for the pathogenesis of chronic inflammatory diseases in joints. Inflammation itself may upregulate the expression of VEGF in rheumatic diseases. Angiogenesis may become a new target for therapeutic intervention in inflammatory joint disease.

AIM OF THE STUDY

To examine plasma levels of VEGF in AS patients and to test a possible correlation with serological and/or clinical parameters.

PATIENTS AND METHODS

Sixteen consecutive patients with definite AS were recruited from the Gasteiner Heilstollen Hospital and compared to eight healthy probands as controls. VEGF was determined in EDTA plasma samples by using an ELISA kit. Data are given as mean values (+/- SEM). The Spearman two-sided test was used to test possible correlations.

RESULTS

EDTA-plasma levels of VEGF were 75.3 +/- 19.0 pg/ml, compared to 13.8 +/- 4.7 pg/ml measured in the control group (P = 0.001). A significant correlation was found between plasma VEGF of AS patients and the BASMI score (r = 0.665, P = 0.013). Whereas VEGF was elevated in patients without treatment or NSAIDs (88.9 +/- 24.2 pg/ml), lower levels up to 43.8 pg/ml were found in patients treated with corticosteroids (34.7 +/- 4.0 pg/ml, P = 0.039).

CONCLUSIONS

Disease status of AS appears to be associated with elevated VEGF plasma levels. Whether this reflects inflammation or a truly angiogenic pathomechanism requires further investigation.

Ligands of peroxisome proliferator-activated receptor-gamma increase the generation of vascular endothelial growth factor in vascular smooth muscle cells and in macrophages

Peroxisome proliferator-activated receptors-gamma (PPARgamma) are ligand-inducible transcription factors of the nuclear hormone receptor superfamily. We examined the effect of PPARgamma activation on the generation of vascular endothelial growth factor (VEGF), one of the major angiogenic agents. Rat vascular smooth muscle cells (VSMC) and murine macrophages RAW264.7 were incubated for 24 h with PPARgamma activators: prostaglandin J2 and ciglitazone. PPARgamma were expressed in VSMC and RAW cells and their activity was upregulated in the presence of PGJ2 and ciglitazone. Incubation of the cells with PPARgamma activators significantly augmented the release of VEGF protein into the media, both in resting and in IL-1beta- or LPS-stimulated cultures. The higher protein generation was connected with the increased expression of mRNA and transcriptional activation of VEGF promoter. We conclude that the activation of PPARgamma upregulates the generation of VEGF and may be involved in the regulation of angiogenesis.

Vascular endothelial growth factor synthesis in vascular smooth muscle cells is enhanced by 7-ketocholesterol and lysophosphatidylcholine independently of their effect on nitric oxide generation

Nitric oxide (NO) generated by inducible NO synthase (iNOS) enhances vascular endothelial growth factor (VEGF) synthesis in vascular smooth muscle cells (VSMC) and both NO and modified low density lipoprotein (LDL) augment VEGF production in macrophages. Oxidized LDL (oxLDL) are known inhibitors of NO generation in the cells of vascular wall. As the relationship between VEGF, iNOS and oxLDL has not been well elucidated, we studied the effect of two main components of oxLDL, 7-ketocholesterol (7-Kchol) and lysophosphatidylcholine (LPC), on VEGF and NO synthesis in rat VSMC and on VEGF synthesis in human VSMC. Both LPC and 7-Kchol significantly augmented VEGF production in rat and human VSMC. Increase in VEGF generation was related to the activation of VEGF promoter by both 7-Kchol and LPC and enhancement of VEGF mRNA transcription. In rat, VSMC IL-1beta-induced NO generation and enhanced VEGF synthesis. 7-Kchol decreased rat iNOS promoter activity, iNOS expression and NO generation, but it did not impair IL-1beta-induced VEGF synthesis. LPC did not significantly influence IL-1beta-induced NO production in rat VSMC and VEGF synthesis was significantly enhanced by combined treatment with IL-1beta and LPC in comparison to the effect of either compound alone. The results indicate that VEGF and NO synthesis in VSMC can be modulated by oxLDL. Those interactions might have an effect on the plaque growth and might be of relevance for the physiology of vascular wall cells.

Prostaglandin-J2 induces synthesis of interleukin-8 by endothelial cells in a PPAR-gamma-independent manner

PPARgamma is a transcription factor of nuclear receptor superfamily, involved in the regulation of inflammation. We investigated the influence of PPARgamma-ligands, 15-deoxy-delta12,14 prostaglandin-J2 (15d-PGJ2), and ciglitazone, on the generation of interleukin-8 (IL-8) by the human microvascular endothelial cell line (HMEC- 1). Expression of PPARgamma in HMEC-1 was confirmed by RT-PCR. Both PPARgamma-ligands tested induced the activation of PPAR, but the potency of ciglitazone was higher, as evidenced by luciferase assay. Resting HMEC-1 released about 150 pg/ml of IL-8 protein. Treatment with LPS increased the IL-8 secretion up to 1 ng/ml. 15d-PGJ2 potently and dose-dependently increased both the steady-state and LPS-induced generation of IL-8 mRNA and IL-8 protein. In contrast, neither basal nor LPS-elicited expression of IL-8 was influenced by ciglitazone. We conclude, that 15d-PGJ2 is a potent inducer of IL-8 production and can be a mediator of inflammatory response, but this effect is independent of PPARgamma activation.

Genetic augmentation of nitric oxide synthase increases the vascular generation of VEGF

OBJECTIVE

Vascular endothelial growth factor (VEGF) induces the release of nitric oxide (NO) from endothelial cells. There is also limited data suggesting that NO may enhance VEGF generation.

METHODS

To further investigate this interaction, we examined the effect of exogenous and endogenous NO on the synthesis of VEGF by rat and human vascular smooth muscle cells (VSMC) by exposing cells to exogenous NO donors, or to genetic augmentation of eNOS or iNOS.

RESULTS

NO-donors potentiated by 2-fold the generation of VEGF protein by rat or human VSMC. Similarly, rat or human VSMC transiently transfected with plasmid DNA encoding eNOS or iNOS, synthesized up to 3-fold more VEGF than those transfected with control plasmid DNA, an effect which was reversed after treatment with the NOS antagonist L-NAME. Rat VSMC stably transfected with pKeNOS plasmid, constitutively produced NO and released high concentrations of VEGF. In these cells, L-NAME significantly reduced NO synthesis and decreased VEGF generation. The VEGF protein produced by NOS-transfected VSMC was biologically active, as conditioned media harvested from these cells increased endothelial cell proliferation.

CONCLUSION

These studies reveal that NO derived from NO-donors or generated by NOS within the cells, upregulates the synthesis of VEGF in vascular smooth muscle cells. Administration of NO donors, or augmentation of endogenous NO synthesis, may be an alternative approach in therapeutic angiogenesis.

Ligands of peroxisome proliferator-activated receptor-gamma increase the generation of vascular endothelial growth factor in vascular smooth muscle cells and in macrophages

Peroxisome proliferator-activated receptors-gamma (PPARgamma) are ligand-inducible transcription factors of the nuclear hormone receptor superfamily. We examined the effect of PPARgamma activation on the generation of vascular endothelial growth factor (VEGF), one of the major angiogenic agents. Rat vascular smooth muscle cells (VSMC) and murine macrophages RAW264.7 were incubated for 24 h with PPARgamma activators: prostaglandin J2 and ciglitazone. PPARgamma were expressed in VSMC and RAW cells and their activity was upregulated in the presence of PGJ2 and ciglitazone. Incubation of the cells with PPARgamma activators significantly augmented the release of VEGF protein into the media, both in resting and in IL-1beta- or LPS-stimulated cultures. The higher protein generation was connected with the increased expression of mRNA and transcriptional activation of VEGF promoter. We conclude that the activation of PPARgamma upregulates the generation of VEGF and may be involved in the regulation of angiogenesis.

Vascular endothelial growth factor is efficiently synthesized in spite of low transfection efficiency of pSG5VEGF plasmids in vascular smooth muscle cells

The limitation of lipotransfection with plasmid vectors is its low efficiency and the short-term expression of introduced genes. This is particularly important when the synthesis of high amounts of therapeutic products is required. However, growth factors with paracrine action overcome this problem. The aim of our study was to check whether the amounts of vascular endothelial growth factor (VEGF) generated after plasmid lipotransfection into vascular smooth muscle cells (VSMC) can be sufficient to stimulate endothelial cell proliferation. Two plasmids, pSG5-VEGF121 and pSG5-VEGF165, harboring human VEGF121 and VEGF165 isoforms were constructed and lipotransfected into COS-7 cells or to rat VSMC. The transfection efficiency, estimated by the expression of control, beta-galactosidase gene, was about 50% in COS-7 but rarely exceeded 5% in VSMC. However, despite this, the smooth muscle cells generated high amounts of VEGF protein, up to 3 ng/ml medium. The biological activity of this VEGF was confirmed by enhanced proliferation of human umbilical vein and coronary artery endothelial cells, stimulated with conditioned media of pSG5-VEGF transfected cells. Thus, the low transfection efficiency does not preclude the generation of high amounts of VEGF by VSMC. After reaching the maximum at about 48 h after transfection, the generation of VEGF decreased in the following days. Such a situation may be sufficient for the gene therapy of restenosis when the long-term expression of therapeutic gene(s) is not necessary. Thus, we suggest that the pSG5-VEGF121, and pSG5-VEGF165 plasmids can be used for therapeutic application.

Nitric oxide mediates the mitogenic effects of insulin and vascular endothelial growth factor but not of leptin in endothelial cells

The regulation of vascular wall homeostasis by nitric oxide (NO) generated by endothelium is being intensively studied. In the present paper, the involvement of NO in the vascular endothelial growth factor (VEGF), insulin or leptin-stimulated proliferation of human endothelial cells (HUVEC) was measured by [3H]thymidine or bromodeoxyuridine incorporation. VEGF and insulin, but not leptin, increased NO generation in HUVEC, as detected with ISO-NO electrode. Proliferation of HUVEC induced by leptin was not changed or was higher in the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME) a nitric oxide synthase (NOS) inhibitor. In contrast, L-NAME blunted the proproliferative effect of VEGF and insulin. Furthermore, we demonstrated that, in human arterial smooth muscle cells (hASMC) transfected with endothelial NOS (eNOS) gene, the generation of biologically active VEGF protein was NO-dependent. Inhibition of NO generation by L-NAME decreased the synthesis of VEGF protein and attenuated HUVEC proliferation induced by conditioned media from transfected hASMC. Endothelium-derived NO seems to participate in VEGF and insulin, but not leptin, mitogenic activity. Additionally, the small amounts of NO released from endothelial cells, as mimicked by eNOS transfection into hASMC, may activate generation of VEGF in sub-endothelial smooth muscle cells, leading to increased synthesis of VEGF protein necessary for turnover and restitution of endothelial cells.

Nitric oxide induces the synthesis of vascular endothelial growth factor by rat vascular smooth muscle cells

Vascular endothelial growth factor (VEGF) is known to induce the release of nitric oxide (NO) from endothelial cells. However, the effect of NO on VEGF synthesis is not clear. Accordingly, the effect of endogenous and exogenous NO on VEGF synthesis by rat vascular smooth muscle cells (VSMCs) was investigated. Two in vitro models were used: (1) VSMCs stimulated to produce NO by treatment with interleukin (IL)-1beta (10 ng/mL) and (2) VSMCs lipotransfected with pKecNOS plasmid, containing the endothelial constitutive NO synthase (ecNOS) cDNA. The synthesis of NO was inhibited by N(omega)-nitro-L-arginine methyl ester (L-NAME, 2 to 5 mmol/L) or diaminohydroxypyrimidine (DAHP, 2.5 to 5 mmol/L), inhibitors of NOS and GTP cyclohydrolase I, respectively. Some cells treated with L-NAME or DAHP were supplemented with L-arginine (10 mmol/L) or tetrahydrobiopterin (BH(4); 100 micromol/L), respectively. In addition, we studied the effect of sodium nitroprusside (SNP; 10 and 100 micromol/L) and chemically related compounds, potassium ferrocyanide and ferricyanide, on VEGF generation. IL-1beta induced iNOS expression and NO generation and significantly upregulated VEGF mRNA expression and protein synthesis. L-NAME and DAHP totally inhibited NO generation and decreased the IL-1beta-upregulated VEGF synthesis by 30% to 40%. Supplementation with L-arginine or BH(4) increased NO generation by L-NAME- or DAHP-treated cells, and VEGF synthesis was augmented by addition of BH(4). The cells generating NO after pKecNOS transfection released significantly higher amounts of VEGF than cells transfected with control plasmids. Inhibition of NO generation by L-NAME decreased VEGF synthesis. In contrast to the effect of endogenous NO, we observed the inhibition of VEGF synthesis in the presence of high (10 or 100 micromol/L) concentrations of SNP. This effect was mimicked by chemically related ferricyanide and ferrocyanide compounds, suggesting that the inhibitory effect of sodium nitroprusside may be mediated by an NO-independent mechanism. The results indicate that endogenous NO enhances VEGF synthesis. The positive interaction between endogenous NO and VEGF may have implications for endothelial regeneration after balloon angioplasty and for angiogenesis.

Expression of beta-galactosidase gene and endothelial nitric oxide synthase gene in rat vascular smooth muscle cells after in vitro lipotransfection

The aim of this study was to optimize the conditions for in vitro lipotransfection of rat vascular smooth muscle cells (VSMC) with bacterial beta-galactosidase gene and bovine endothelial nitric oxide synthase (ecNOS) gene. Transfection efficiency of four liposomes: Transfectam, Lipofectin, Unifectin-10, and Maxifectin was compared. The best results (efficiency 1-5%) were obtained with Maxifectin, when transfections were performed in VSMC cultures being at 50% confluency, with 1 microg DNA and 10 microl liposome per well, and when the liposome/DNA complexes were coincubated with the cells for 24 h. This method allowed detection of the transgene activity 12 h after the beginning of the transfection, with maximum values between the second and fourth days. The expression of the potentially therapeutic ecNOS gene was evidenced by confirmation of ecNOS mRNA generation, indirect detection of active ecNOS protein and by measurement of nitrite ion accumulation in the medium from the transfected cell cultures.

Gene transfer of nitric oxide synthase: effects on endothelial biology

OBJECTIVES

The purpose of the study was to investigate the role of nitric oxide (NO) in monocyte-endothelial interaction by augmenting NO release via transfection of human endothelial cells (ECs) with EC NO synthase (eNOS) DNA.

BACKGROUND

Enhancement of NO synthesis by L-arginine or shear stress reduces endothelial adhesiveness for monocytes and inhibits atherogenesis. To elucidate further the underlying mechanism, we augmented NO synthase expression by transfection of human EC.

METHODS

Liposome-mediated transfection of EC was performed with a plasmid construct containing the gene encoding eNOS. Expression of eNOS was confirmed by reverse transcription-polymerase chain reaction (RT-PCR). Endothelial cells were exposed to human monocytoid cells, and adherent cells were quantitated using a computer-assisted program. Nitric oxide was measured by chemiluminescence.

RESULTS

The NO levels were not different in EC that were either not transfected, transfected with beta-gal or liposomes only. The nitric oxide synthase (NOS) transfection increased NO release by +60% (n = 6), which increased further when EC were stimulated by shear stress (24 h) by +137% (n = 5) as compared with untransfected, unstimulated EC (both p < 0.05). The RT-PCR revealed diminished monocyte chemotactic protein-1 (MCP-1) expression in eNOS transfected EC. There was an inverse relation between NO levels and monocyte binding (r = -0.5669, p < 0.002). Stimulation of EC with tumor necrosis factor-alpha (TNF-alpha; 250 U/ml) led to a decrease in NO synthesis, and an increase in monocyte binding. Cells transfected with NOS were resistant to both effects of TNF-alpha.

CONCLUSIONS

Endothelial cells transfected with eNOS synthesize an increased amount of NO; this is associated with diminished MCP-1 expression and monocyte-endothelial binding. The reduction in monocyte-endothelial binding persists even after cytokine stimulation.

Nitric oxide mediates the mitogenic effects of insulin and vascular endothelial growth factor but not of leptin in endothelial cells

The regulation of vascular wall homeostasis by nitric oxide (NO) generated by endothelium is being intensively studied. In the present paper, the involvement of NO in the vascular endothelial growth factor (VEGF), insulin or leptin-stimulated proliferation of human endothelial cells (HUVEC) was measured by [3H]thymidine or bromodeoxyuridine incorporation. VEGF and insulin, but not leptin, increased NO generation in HUVEC, as detected with ISO-NO electrode. Proliferation of HUVEC induced by leptin was not changed or was higher in the presence of N(omega)-nitro-L-arginine methyl ester (L-NAME) a nitric oxide synthase (NOS) inhibitor. In contrast, L-NAME blunted the proproliferative effect of VEGF and insulin. Furthermore, we demonstrated that, in human arterial smooth muscle cells (hASMC) transfected with endothelial NOS (eNOS) gene, the generation of biologically active VEGF protein was NO-dependent. Inhibition of NO generation by L-NAME decreased the synthesis of VEGF protein and attenuated HUVEC proliferation induced by conditioned media from transfected hASMC. Endothelium-derived NO seems to participate in VEGF and insulin, but not leptin, mitogenic activity. Additionally, the small amounts of NO released from endothelial cells, as mimicked by eNOS transfection into hASMC, may activate generation of VEGF in sub-endothelial smooth muscle cells, leading to increased synthesis of VEGF protein necessary for turnover and restitution of endothelial cells.