In vitro and in vivo analysis of expression cassettes designed for vascular gene transfer

Short regulatory DNA sequences to target brain endothelial cells for gene therapy

Gene vectors targeting CNS endothelial cells allow to manipulate the blood-brain barrier and to correct genetic defects in the CNS. Because vectors based on the adeno-associated virus (AAV) have a limited capacity, it is essential that the DNA sequence controlling gene expression is short. In addition, it must be specific for endothelial cells to avoid off-target effects. To develop improved regulatory sequences with selectivity for brain endothelial cells, we tested the transcriptional activity of truncated promoters of eleven (brain) endothelial-specific genes in combination with short regulatory elements, i.e., the woodchuck post-transcriptional regulatory element (W), the CMV enhancer element (C), and a fragment of the first intron of the Tie2 gene (S), by transfecting brain endothelial cells of three species. Four combinations of regulatory elements and short promoters (Cdh5, Ocln, Slc2a1, and Slco1c1) progressed through this in-vitro pipeline displaying suitable activity. When tested in mice, the regulatory sequences C-Ocln-W and C-Slc2a1-S-W enabled a stronger and more specific gene expression in brain endothelial cells than the frequently used CAG promoter. In summary, the new regulatory elements efficiently control gene expression in brain endothelial cells and may help to specifically target the blood-brain barrier with gene therapy vectors.

Stable In Vivo Transgene Expression in Endothelial Cells with Helper-Dependent Adenovirus: Roles of Promoter and Interleukin-10

Our long-term goal is to prevent or reverse atherosclerosis by delivering gene therapy from stably transduced endothelial cells (EC). We previously reported that EC-directed gene therapy with a helper-dependent adenovirus (HDAd) expressing apolipoprotein A-I (apo A-I) retarded development of atherosclerosis in rabbit carotid arteries over a 1-month interval. However, a 70% decline in apo A-I expression during this time raised concerns about long-term efficacy of this approach. Here we report use of several approaches aimed either at preventing this decline or at increasing apo A-I expression from HDAd at all time points: codon optimization, deletion of 3' untranslated sequences, substitution of a synthetic mammalian-based promoter (4XETE) for the cytomegalovirus (CMV) promoter, and co-transduction with an HDAd expressing interleukin-10. We tested these approaches using plasmid transfection of cultured EC and in vivo transduction of rabbit carotid artery EC. Codon optimization did not increase apo A-I expression. Deletion of 3' untranslated sequences extinguished apo A-I expression. Both substitution of 4XETE for the CMV promoter and expression of interleukin-10 stabilized apo A-I expression in vivo, although at the cost of lower early (3-day) expression levels. Surprisingly, both interventions stabilized apo A-I expression without altering the rate at which HDAd genomes were lost. These data establish that transgene expression from HDAd in EC is inherently stable in vivo and suggest that the early decline of CMV promoter-driven expression from HDAd-transduced EC is due neither to active downregulation of transcription nor to loss of HDAd genomes. Instead, apparent loss of expression from the CMV promoter appears to be a consequence of early (3-day) upregulation of CMV promoter activity via inflammatory pathways. Our results yield new paradigms to explain the early loss of genomes and transgene expression after in vivo gene transfer. These new paradigms will redirect strategies for achieving high-level, stable expression of transgenes in EC.

The TIE Receptor Family

The endothelial TIE1 and TIE2 receptor tyrosine kinases form a distinct subfamily characterized by their unique extracellular domains. Together with the angiopoietin growth factors (ANGPT1, ANGPT2, ANGPT4, also abbreviated as ANG), the TIE receptors form an endothelial specific signaling pathway with important functions in the regulation of lymphatic and cardiovascular development and vascular homeostasis. Angiopoietins exist in multimeric forms that activate the TIE receptors via unique mechanism. In endothelial cell–cell contacts, angiopoietins induce the formation of homomeric in trans TIE receptor complexes extending across the cell junctions, whereas matrix-bound angiopoietin-1 (ANG1) activates the TIE receptors in a cis configuration. In comparison to the vascular endothelial growth factor receptors, the TIE receptors undergo little ubiquitin-mediated degradation after activation, whereas TIE2 signaling is negatively regulated by the vascular endothelial protein tyrosine phosphatase, VE-PTP. ANG1 activation of TIE2 supports vascular stabilization, whereas angiopoietin-2 (ANG2), a context-dependent weak TIE2 agonist/antagonist, promotes pathological tumor angiogenesis, vascular permeability, and inflammation. Recently, ANG2 has been found to mediate some of its vascular destabilizing and angiogenic functions via integrin signalling. The circulating levels of ANG2 are increased in cancer, and in several human diseases associated with inflammation and vascular leak, for example, in sepsis. Blocking of ANG2 has emerged as a potential novel therapeutic strategy for these diseases. In addition, preclinical results demonstrate that genetic TIE1 deletion in mice inhibits the vascularization and growth of tumor isografts and protects from atherosclerosis, with little effect on normal vascular homeostasis in adult mice. The ability of the ANG-TIE pathway to control vessel stability and angiogenesis makes it an interesting vascular target for the treatment of the various diseases.

Plasmid-mediated gene therapy for cardiovascular disease

Gene transfer within the cardiovascular system was first demonstrated in 1989 yet, despite extensive basic-science and clinical research, unequivocal benefit in the clinical setting remains to be demonstrated. Potential reasons for this include the fact that recombinant viral vectors, used in the majority of clinical studies, have inherent problems with immunogenicity that are difficult to circumvent. Attention has turned therefore to plasmid vectors, which possess many advantages over viruses in terms of safety and ease of use, and many clinical studies have now been performed using non-viral technology. This review will provide an overview of clinical trials for cardiovascular disease using plasmid vectors, recent developments in plasmid delivery and design, and potential directions for this modality of gene therapy.

From molecule to man: integrating molecular biology with whole organ physiology in studying respiratory disease

Chronic lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), and idiopathic pulmonary fibrosis (IPF) are all characterized by structural changes of the airways and/or lungs that limit airflow and/or gas exchange. Currently, there is no therapy available that adequately targets the structural remodeling of the airways and lungs in these diseases. This underscores the great need for insight into the mechanisms that underpin the development of airway remodeling, fibrosis and emphysema in these diseases, in order to identify suitable drug targets. It is increasingly evident that structural cell-cell communication within the lung is central to the development of remodeling, indicating that a more integrative approach should be considered when studying molecular and cellular mechanisms of remodeling. Therefore, there is a great need to study molecular and cellular physiological and pathophysiological mechanisms in as much detail as possible, but with as little as possible loss of the physiological context. Here, we will review the use of models such as cellular co-culture, tissue culture, and lung slice culture, in which cell-cell communication and tissue architecture are better preserved or mimicked than in cell culture, and zoom in on the usefulness of molecular and cellular biological tools in these complex model systems to read out or control signaling and gene/protein regulation.

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.

Development of viral vectors for use in cardiovascular gene therapy

Cardiovascular disease represents the most common cause of mortality in the developed world but, despite two decades of promising pre-clinical research and numerous clinical trials, cardiovascular gene transfer has so far failed to demonstrate convincing benefits in the clinical setting. In this review we discuss the various targets which may be suitable for cardiovascular gene therapy and the viral vectors which have to date shown the most potential for clinical use. We conclude with a summary of the current state of clinical cardiovascular gene therapy and the key trials which are ongoing.