Endothelial-targeted Gene Transfer of Hypoxia-inducible Factor-1α Augments Ischemic Neovascularization Following Systemic Administration

Vascular Endothelial Cells: Heterogeneity and Targeting Approaches

Forming the inner layer of the vascular system, endothelial cells (ECs) facilitate a multitude of crucial physiological processes throughout the body. Vascular ECs enable the vessel wall passage of nutrients and diffusion of oxygen from the blood into adjacent cellular structures. ECs regulate vascular tone and blood coagulation as well as adhesion and transmigration of circulating cells. The multitude of EC functions is reflected by tremendous cellular diversity. Vascular ECs can form extremely tight barriers, thereby restricting the passage of xenobiotics or immune cell invasion, whereas, in other organ systems, the endothelial layer is fenestrated (e.g., glomeruli in the kidney), or discontinuous (e.g., liver sinusoids) and less dense to allow for rapid molecular exchange. ECs not only differ between organs or vascular systems, they also change along the vascular tree and specialized subpopulations of ECs can be found within the capillaries of a single organ. Molecular tools that enable selective vascular targeting are helpful to experimentally dissect the role of distinct EC populations, to improve molecular imaging and pave the way for novel treatment options for vascular diseases. This review provides an overview of endothelial diversity and highlights the most successful methods for selective targeting of distinct EC subpopulations.

Specific overexpression of 15-lipoxygenase in endothelial cells promotes cancer cell death in an in vivo Lewis lung carcinoma mouse model

PURPOSE

Lipoxygenases (LOX) have been implicated in carcinogenesis, however both pro- and anti-carcinogenic effects have been reported in different cancer models. Using transgenic mice, which specifically overexpress human 15-lipoxygenase (ALOX15) in endothelial cells (EC), we previously demonstrated significant inhibition of tumor development. In the Lewis lung carcinoma (LLC) model, the primary tumor developed similarly in both wild type (WT) and ALOX15 overexpressing mice. However, metastases development was significantly inhibited in the transgenic mice. Here, we explored the molecular basis for the anti-metastatic effect of endothelial cell specific ALOX15 overexpression.

MATERIALS/METHODS

We used ALOX15 overexpressing mice, and in-vitro cell model to evaluate the molecular effect of ALOX15 on EC and LLC cells.

RESULTS

When LLC cells were injected in WT and ALOX15 overexpressing mice, we observed a higher degree of apoptosis and necrosis in primary and metastatic tumors of ALOX15 overexpressing animals. These anti-carcinogenic and anti-metastatic effects were paralleled by augmented expression of cyclin-dependent kinase inhibitor 1A (CDKN1A; p21) and of the peroxisome proliferators-activated receptor (PPAR)γ and by downregulation of the steady state concentrations of connexin26 mRNA. Consistent with these in vivo effects, ALOX15 overexpression in LLC and HeLa cancer cells in vitro significantly reduced cell viability in culture. In contrast, similar treatment of non-cancerous B2B epithelial cells did not impact cell viability.

CONCLUSIONS

Taken together, our data suggests that endothelial cell specific overexpression of ALOX15 promotes apoptosis and necrosis in primary and metastatic tumors in mice, by upregulation of P21 and PPARγ expression in adjacent cancer cells.

Targeting Hypoxia Inducible Factors-1α As a Novel Therapy in Fibrosis

Fibrosis, characterized by increased extracellular matrix (ECM) deposition, and widespread vasculopathy, has the prominent trait of chronic hypoxia. Hypoxia inducible factors-1α (HIF-1α), a key transcriptional factor in response to this chronic hypoxia, is involved in fibrotic disease, such as Systemic sclerosis (SSc). The implicated function of HIF-1α in fibrosis include stimulation of excessive ECM, vascular remodeling, and futile angiogenesis with further exacerbation of chronic hypoxia and deteriorate pathofibrogenesis. This review will focus on the molecular biological behavior of HIF-1α in regulating progressive fibrosis. Better understanding of the role for HIF-1α-regulated pathways in fibrotic disease will accelerate development of novel therapeutic strategies that target HIF-1α. Such new therapeutic strategies may be particularly effective for treatment of the prototypic, multisystem fibrotic, autoimmune disease SSc.

Hypoxia-Inducible Factor (HIF) as a Target for Novel Therapies in Rheumatoid Arthritis

Hypoxia is an important micro-environmental characteristic of rheumatoid arthritis (RA). Hypoxia-inducible factors (HIF) are key transcriptional factors that are highly expressed in RA synovium to regulate the adaptive responses to this hypoxic milieu. Accumulating evidence supports hypoxia and HIFs in regulating a number of important pathophysiological characteristics of RA, including synovial inflammation, angiogenesis, and cartilage destruction. Experimental and clinical data have confirmed the upregulation of both HIF-1α and HIF-2α in RA. This review will focus on the differential expression of HIFs within the synovial joint and its functional behavior in different cell types to regulate RA progression. Potential development of new therapeutic strategies targeting HIF-regulated pathways at sites of disease in RA will also be addressed.

The myeloid-binding peptide adenoviral vector enables multi-organ vascular endothelial gene targeting

Vascular endothelial cells (ECs) are ideal gene therapy targets as they provide widespread tissue access and are the first contact surfaces following intravenous vector administration. Human recombinant adenovirus serotype 5 (Ad5) is the most frequently used gene transfer system because of its appreciable transgene payload capacity and lack of somatic mutation risk. However, standard Ad5 vectors predominantly transduce liver but not the vasculature following intravenous administration. We recently developed an Ad5 vector with a myeloid cell-binding peptide (MBP) incorporated into the knob-deleted, T4 fibritin chimeric fiber (Ad.MBP). This vector was shown to transduce pulmonary ECs presumably via a vector handoff mechanism. Here we tested the body-wide tropism of the Ad.MBP vector, its myeloid cell necessity, and vector-EC expression dose response. Using comprehensive multi-organ co-immunofluorescence analysis, we discovered that Ad.MBP produced widespread EC transduction in the lung, heart, kidney, skeletal muscle, pancreas, small bowel, and brain. Surprisingly, Ad.MBP retained hepatocyte tropism albeit at a reduced frequency compared with the standard Ad5. While binding specifically to myeloid cells ex vivo, multi-organ Ad.MBP expression was not dependent on circulating monocytes or macrophages. Ad.MBP dose de-escalation maintained full lung-targeting capacity but drastically reduced transgene expression in other organs. Swapping the EC-specific ROBO4 for the CMV promoter/enhancer abrogated hepatocyte expression but also reduced gene expression in other organs. Collectively, our multilevel targeting strategy could enable therapeutic biological production in previously inaccessible organs that pertain to the most debilitating or lethal human diseases.

Pluronic L64-mediated stable HIF-1α expression in muscle for therapeutic angiogenesis in mouse hindlimb ischemia

Intramuscular injection of plasmid DNA (pDNA) to express a therapeutic protein is a promising method for the treatment of many diseases. However, the therapeutic applications are usually hindered by gene delivery efficiency and expression level. In this study, critical factors in a pDNA-based gene therapy system, such as gene delivery materials, a therapeutic gene, and its regulatory elements, were optimized to establish an integrated system for the treatment of mouse hindlimb ischemia. The results showed that Pluronic^® L64 (L64) was an efficient and safe material for gene delivery into mouse skeletal muscle. It also showed intrinsic ability to promote in vivo angiogenesis in a concentration-dependent manner, which might be through the activation of nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB)-regulated angiogenic factors. The combination of 0.1% L64 with a hybrid gene promoter (pSC) increased the gene expression level, elongated the gene expression duration, and enhanced the number of transfected muscle fibers. In mice ischemic limbs, a gene medicine (pSC-HIF1α^tri/L64) composed of L64 and pSC-based expression plasmid encoding hypoxia-inducible factor 1-alpha triple mutant (HIF-1α^tri), improved the expression of stable HIF-1α, and in turn, the expression of multiple angiogenic factors. As a result, the ischemic limbs showed accelerated function recovery, reduced foot necrosis, faster blood reperfusion, and higher capillary density. These results indicated that the pSC-HIF1α^tri/L64 combination presented a potential and convenient venue for the treatment of peripheral vascular diseases, especially critical limb ischemia.

Hypoxia-based strategies for angiogenic induction: the dawn of a new era for ischemia therapy and tissue regeneration

Therapeutic angiogenesis promises to aid the healing and regeneration of tissues suffering from a compromised vascular supply. Ischaemia therapy has so far primarily focused on delivering isolated angiogenic growth factors. The limited success of these strategies in clinical trials, however, is increasingly forcing researchers to recognize the difficulties associated with trying to mimic the angiogenic process, due to its natural complexity. Instead, a new school of thought is gradually emerging, focusing on how to induce angiogenesis at its onset, by utilizing hypoxia, the primary angiogenic stimulus in physiological, as well pathological states. This shift in therapeutic approach is underlined by the realization of the importance of depressed HIF-1 α-mediated gene programming in non-healing ischemic tissues, which could explain their apparent habituation to chronic hypoxic stress and the limited capacity to generate adaptive angiogenesis. Hypoxia-based strategies, then effectively aim to override the habituated angiogenic cellular response, re-start the regenerative process and drive it to completion. Here we make a distinction between those strategies that utilize hypoxia in vitro as a preconditioning tool to optimize the angiogenic potential of tissue/cells before transplantation, vs. strategies that aim to induce hypoxia-induced signaling in vivo, directly, through pharmacological means or gene transfer. We then discuss possible future directions for the field, as it moves into the phase of clinical trials.

Effects of orally administered bacteria carrying HIF-1α gene in an experimental model of intestinal ischemia

BACKGROUND AND AIMS

Bactofection is delivery of therapeutic genes into target cells using bacteria penetrating the target cell membrane and releasing the gene into the cell. Hypoxia-inducible factor 1α (HIF-1α) represents a potential therapeutic gene to be used for gene delivery in ischemic diseases. The aim of this study was to prove the effects of bacteria-mediated transfer of hypoxia-inducible factor 1α (HIF-1α) in an experimental model of intestinal ischemia in rats.

METHODS

Male Wistar rats with a surgically induced ischemia of colon (cecum) or sham-operated rats were treated by per os application of E. coli carrying therapeutic genes. After 1 week, samples were taken for measurement of oxidative stress markers and expression analyses.

RESULTS

According to our observation, there were no signs or symptoms of ongoing ischemia in gastrointestinal tissue. Interestingly, all experimental groups treated by bacteria, regardless of their ability to invade cells or the presence of HIF-1α gene, showed decreased levels of vascular endothelial growth factor (VEGF) compared to control groups. Similarly, all treatment groups showed increased hematocrit.

CONCLUSIONS

We conclude ineffectiveness of the bacterial gene delivery system. However, the effect of bacteria themselves was obvious. HIF-1 can be activated hypoxia-independently by the action of pathogenic bacteria in the rat intestine. We hypothesize that therapeutic bacterial strain used may compete with siderophore-expressing bacteria present in the gut of rats to force them out and prevent their ability to activate HIF-1 in a hypoxia-independent manner. This phenomenon should be analyzed in detail in further studies.

Construction of a novel expression cassette for increasing transgene expression in vivo in endothelial cells of large blood vessels

The success of gene therapy hinges on achievement of adequate transgene expression. To ensure high transgene expression, many gene-therapy vectors include highly active virus-derived transcriptional elements. Other vectors include tissue-specific eukaryotic transcriptional elements, intended to limit transgene expression to specific cell types, avoid toxicity and prevent immune responses. Unfortunately, tissue specificity is often accompanied by lower transgene expression. Here, we use eukaryotic (murine) transcriptional elements and a virus-derived posttranscriptional element to build cassettes designed to express a potentially therapeutic gene (interleukin (IL)-10) in large-vessel endothelial cells (ECs) at levels as high as obtained with the cytomegalovirus (CMV) immediate early promoter, while retaining EC specificity. The cassettes were tested by incorporation into helper-dependent adenoviral vectors, and transduction into bovine aortic EC in vitro and rabbit carotid EC in vivo. The murine endothelin-1 promoter showed EC specificity, but expressed only 3% as much IL-10 mRNA as CMV. Inclusion of precisely four copies of an EC-specific enhancer and a posttranscriptional regulatory element increased IL-10 expression to a level at or above the CMV promoter in vivo, while retaining--and possibly enhancing--EC specificity, as measured in vitro. The cassette reported here will likely be useful for maximizing transgene expression in large-vessel EC, while minimizing systemic effects.

Combined gene therapy with hypoxia-inducible factor-1α and heme oxygenase-1 for therapeutic angiogenesis

Transfection with either hypoxia-inducible factor-1α (HIF-1α) or heme oxygenase-1 (HO-1) gene can induce neovascularization in ischemic tissues. Although expression of transfected HIF-1α gene occurs rapidly, the expressed HIF-1α protein degrades quickly, limiting its therapeutic efficacy. Meanwhile, expressed HO-1 protein does not rapidly undergo degradation, but gene expression occurs a couple of days after transfection, resulting in apoptosis and a delay in angiogenesis in ischemic tissues at the incipient period of HO-1 gene transfection. We hypothesize that combined delivery of HIF-1α and HO-1 gene will enhance antiapoptosis and neovascularization in ischemic tissue compared with HIF-1α or HO-1 single-gene therapy. To test this hypothesis, ischemic mouse hindlimbs were treated with HIF-1α and/or HO-1 gene therapy. The combined gene therapy proved superior to both single-gene therapies, resulting in rapid expression of HIF-1α gene and long-term maintenance of expressed HO-1 protein. The apoptosis in the ischemic region was significantly less, and angiogenic growth factor secretion and angiogenesis were greater in the combined gene therapy than in either of the single-gene therapies. Our results suggest that a combined gene therapy of HIF-1α and HO-1 enhances the transfection of both genes and improves angiogenesis compared with either single-gene therapy.

Effects of hypoxia-inducible factor-1alpha overexpression in pregnant mice: possible implications for preeclampsia and intrauterine growth restriction

Preeclampsia and intrauterine growth restriction (IUGR) are pregnancy-specific disorders that share a common pathophysiology. Hypoxia-inducible factor-1α (HIF-1α) is a transcription factor that plays an important role in placental development. HIF-1α is elevated in preeclamptic placentas and induces soluble vascular endothelial growth factor receptor-1 (sFLT-1), a central factor in preeclampsia and IUGR pathogenesis. Our objective was to investigate the effects of HIF-1α overexpression on pregnancy in mice. C57BL/6J pregnant mice were systemically administered either adenovirus expressing stabilized HIF-1α (cytomegalovirus [CMV]-HIF), luciferase control (CMV-Luc), or saline on gestational day 8. Pregnant mice overexpressing HIF-1α had significantly elevated blood pressure and proteinuria compared with pregnant controls. HIF-1α mice showed fetal IUGR, decreased placental weights, and histopathological placental abnormalities compared with control mice. Glomerular endotheliosis, the hallmark lesion of preeclampsia, was demonstrated in the kidneys of these mice relative to the normal histology in control mice. Moreover, liver enzyme levels were significantly elevated, whereas complete blood counts revealed significant anemia and thrombocytopenia in CMV-HIF mice compared with controls. Blood smears confirmed microangiopathic hemolytic anemia in CMV-HIF mice, consistent with HELLP (hemolysis, elevated liver enzymes, and low platelets)-like syndrome. CMV-HIF mice showed elevation in serum sFLT-1 and soluble endoglin, providing a mechanistic explanation for the observations. Collectively, our results suggest a possible role for HIF-1α in the pathogenesis of both preeclampsia and IUGR.