Growth-arrest homeobox gene Gax: a molecular strategy to prevent arterial restenosis

Tissue remodeling and alterations in cellular differentiation occur during atherosclerosis and restenosis following balloon angioplasty, but little is known about the nuclear proteins that regulates these processes. Homeobox genes encode transcription factors that regulate cell growth, differentiation, migration, and body plan formation. The Gax (growth arrest homeobox) gene is expressed in adult cardiovascular tissues. Gax is expressed in normal quiescent smooth muscle cells, but its expression is rapidly down-regulated when these cells are stimulated to proliferate with mitogens. Gax expression is also down-regulated in vascular tissue immediately following balloon injury. These characteristics of Gax suggest it may be required to maintain the non-proliferative or contractile phenotype in vascular smooth muscle. Indeed, the mitogen-induced proliferation of cultured vascular smooth muscle cells is inhibited when these cells are microinjected with recombinant Gax protein. Gax also inhibits the proliferation of vascular smooth muscle cells when overexpressed with a replication-defective adenovirus vector, and the local delivery of this recombinant virus to denuded rat carotid arteries significantly reduces neointima formation and luminal narrowing. Currently we are performing percutaneous Gax adenovirus-mediated gene transfer into normal and atherosclerotic rabbit iliac arteries. These data suggest that overexpression of Gax gene may prevent the neointimal formation that is characteristic of a number of vascular disorders.

Molecular strategies to inhibit restenosis: modulation of the vascular myocyte phenotype

The transduction of vascular myocytes with exogenous genetic material will be a common feature of many gene-based therapies for cardiovascular disorders. Therefore, the successful application of cardiovascular gene therapy will require a thorough understanding of the molecular biology of the smooth muscle cell. Of key importance are the transcriptional regulatory events that coordinate the de-differentiation and proliferation of myocytes in response to vascular injury. The goal of this review is to highlight what is known about the regulators of vascular myocyte transcription that may serve as candidate genes for the development of genetic strategies to manage postinterventional restenosis.

Clinical evidence of angiogenesis after arterial gene transfer of phVEGF165 in patient with ischaemic limb

BACKGROUND

Preclinical findings suggest that intra-arterial gene transfer of a plasmid which encodes for vascular endothelial growth factor (VEGF) can improve blood supply to the ischaemic limb. We have used the method in a patient.

METHODS

Our patient was the eighth in a dose-ranging series. She was aged 71 with an ischaemic right leg. We administered 2,000 micrograms human plasmid phVEGF165 that was applied to the hydrogel polymer coating of an angioplasty balloon. By inflating the balloon, plasmid DNA was transferred to the distal popliteal artery.

FINDINGS

Digital subtraction angiography 4 weeks after gene therapy showed an increase in collateral vessels at the knee, mid-tibial, and ankle levels, which persisted at a 12-week view. Intra-arterial doppler-flow studies showed increased resting and maximum flows (by 82% and 72%, respectively). Three spider angiomas developed on the right foot/ankle about a week after gene transfer; one lesion was excised and revealed proliferative endothelium, the other two regressed. The patient developed oedema in her right leg, which was treated successfully.

INTERPRETATION

Administration of endothelial cell mitogens promotes angiogenesis in patients with limb ischaemia.

Resistance to apoptosis conferred by Cdk inhibitors during myocyte differentiation

Proliferating murine C2C12 myoblasts can undergo either terminal differentiation or programmed cell death under conditions of mitogen deprivation. Unlike myoblasts, differentiated myotubes were resistant to apoptosis. During myogenesis the appearance of the apoptosis-resistant phenotype was correlated with the induction of the cyclin-dependent kinase (Cdk) inhibitor p21(CIP1) but not with the appearance of myogenin, a marker expressed earlier in differentiation. Forced expression of the Cdk inhibitors p21(CIP1) or p16(INK4A) blocked apoptosis during myocyte differentiation. These data indicate that induction of Cdk inhibitors may serve to protect differentiating myocytes from programmed cell death as well as play a role in establishing the postmitotic state.

Decision-making in the care of cavity wounds

Good cavity-wound management requires a team approach. Nurses seeking autonomy may not recognise the responsibility that goes with it. There is still confusion and ignorance about wound dressings and agents used for cavity wounds.

Arterial gene transfer for therapeutic angiogenesis in patients with peripheral artery disease

The age-adjusted prevalence of peripheral arterial disease (PAD) in the U.S. population has been estimated to approach 12%. The clinical consequences of occlusive peripheral arterial disease (PAD) include pain on walking (claudication), pain at rest, and loss of tissue integrity in the distal limbs; the latter may ultimately lead to amputation of a portion of the lower extremity. Surgical bypass techniques and percutaneous catheter-based interventions may be used to successfully revascularize the limbs of certain patients with PAD. In many patients, however, the anatomic extent and distribution of arterial occlusion is too severe to permit relief of pain and/or healing of ischemic ulcers. No effective medical therapy is available for the treatment of such patients. The purpose of this clinical protocol is to document the safety of therapeutic angiogenesis achieved in this case by percutaneous catheter-based delivery of the gene encoding vascular endothelial growth factor (VEGF) in patients with PAD; and, as secondary objectives, investigate the bioactivity of this strategy to relieve rest pain and heal ischemic ulcers of the lower extremities. The rationale for this human protocol is based upon preclinical studies performed in a rabbit model of hindlimb ischemia. These studies are described in detail below and in the manuscripts enclosed in the Appendix to this proposal. In brief, a single intra-arterial bolus of VEGF recombinant human protein, delivered percutaneously to the ischemic limb via an intravascular catheter, resulted in angiographic, hemodynamic, physiologic, and histologic evidence of augmented collateral artery development. Subsequently, similar results were achieved using an angioplasty catheter with a hydrogel-coated balloon to deliver 400 micrograms of a plasmid containing the cDNA for VEGF to the internal iliac artery in the same animal model. Accordingly, we propose to administer arterial gene (VEGF) therapy to patients with rest pain and/or ischemic leg ulcers considered not to be candidates for conventional revascularization techniques. The dose of plasmid to be administered will be progressively escalated beginning with 500 micrograms for the first four patients, 1000 micrograms for the following six patients, 2000 micrograms for the third group of six patients, and 400 micrograms for the fourth group of six patients.

Prognosis of supravalve aortic stenosis in 81 patients in Liverpool (1960-1993)

OBJECTIVE

To determine the prognosis of supravalve aortic stenosis into early adult life and the factors affecting this prognosis.

DESIGN

81 patients with supravalve aortic stenosis were followed for a median duration of 8.3 (range 1 to 29) years.

PATIENTS

40 patients (49.4%) had Williams' syndrome, 18 (22.2%) familial supravalve aortic stenosis, 18 (22.2%) sporadic supravalve aortic stenosis, and five (6.2%) other syndromes. Nineteen patients had additional levels of left ventricular outflow tract obstruction.

RESULTS

47 patients (58%) underwent operation; 20% within a year of presentation. Multivariable analysis predicted that 88% of patients would undergo intervention within 30 years of follow up. The chance of intervention was increased by more severe aortic stenosis at presentation and the presence of multilevel obstruction in patients with sporadic supravalve aortic stenosis. Three deaths occurred before operation and 13 within a month of operation. Ten (62.5%) of the postoperative deaths were in patients with multilevel obstruction. Predicted survival 30 years after presentation was 66%. Risk factors for survival were age and severity of aortic stenosis at presentation. Multilevel obstruction did not emerge as a significant risk factor for death because of the high association with the severity of stenosis at presentation. 74% of survivors had mild or insignificant stenosis at follow up.

CONCLUSIONS

Long-term survival is related to age and the severity of aortic stenosis at presentation. Most patients will require intervention, and most survivors will have mild stenosis.

Tuberculous pericarditis in a child

A 14-year-old boy with tuberculous pericarditis and tamponade is described. Confirmation was by culture of pericardial aspirate. Though he did not have a cough, acid-fast bacilli were detected following induced sputum. Chest X-ray did not show evidence of pulmonary tuberculosis, but enlarged mediastinal nodes were detected by computerized tomography. He made an excellent response to anti-tuberculous chemotherapy and corticosteroids.

Myogenin expression, cell cycle withdrawal, and phenotypic differentiation are temporally separable events that precede cell fusion upon myogenesis

During terminal differentiation of skeletal myoblasts, cells fuse to form postmitotic multinucleated myotubes that cannot reinitiate DNA synthesis. Here we investigated the temporal relationships among these events during in vitro differentiation of C2C12 myoblasts. Cells expressing myogenin, a marker for the entry of myoblasts into the differentiation pathway, were detected first during myogenesis, followed by the appearance of mononucleated cells expressing both myogenin and the cell cycle inhibitor p21. Although expression of both proteins was sustained in mitogen-restimulated myocytes, 5-bromodeoxyuridine incorporation experiments in serum-starved cultures revealed that myogenin-positive cells remained capable of replicating DNA. In contrast, subsequent expression of p21 in differentiating myoblasts correlated with the establishment of the postmitotic state. Later during myogenesis, postmitotic (p21-positive) mononucleated myoblasts activated the expression of the muscle structural protein myosin heavy chain, and then fused to form multinucleated myotubes. Thus, despite the asynchrony in the commitment to differentiation, skeletal myogenesis is a highly ordered process of temporally separable events that begins with myogenin expression, followed by p21 induction and cell cycle arrest, then phenotypic differentiation, and finally, cell fusion.

Characterization of cardiac gene cis-regulatory elements in the early stages of chicken heart morphogenesis

To study transcriptional regulation during early stages of cardiogenesis, stage 10-17 chicken embryo hearts were transfected efficiently within the intact embryo by application of plasmid DNA complexed to liposomes. Viral regulatory sequences and the skeletal alpha-actin, SERCA2 and ANF promoters activated expression of reporter genes in the primitive heart tube. Deletion and mutation analysis of the skeletal alpha-actin promoter revealed the importance of CArG cis-regulatory elements in enhancing transcription of the gene during early heart development. These results demonstrate the utility of this method for the identification of gene regulatory elements that specify the cardiac phenotype during early stages of heart morphogenesis.

Structures and chromosome locations of the human MEF2A gene and a pseudogene MEF2AP

The MEF2 family of transcription factors control the expression of muscle-specific and mitogen-induced genes. Here we describe the isolation and structure of the human MEF2A gene. The protein coding region of MEF2A is divided by 10 introns. The 3' untranslated region (UTR) is 3.7 kb in length, and it contains a region that is highly homologous with a portion of the 3' UTR of Xenopus MEF2A. A partially processed pseudogene (MEF2AP) corresponding to MEF2A was also isolated and characterized. Human MEF2A was mapped by fluorescence in situ hybridization to chromosome 15q26, and MEF2AP was mapped to chromosome 1q24 --> q25.

Randomised comparison of silicone versus Teflon cannulas for peripheral intravenous nutrition

The use of peripheral intravenous nutrition using standard Teflon cannulas is limited by a high incidence of thrombophlebitis, with resultant frequent line changes and compromised nutritional therapy. Fine-bore silicone catheters may reduce the incidence of thrombophlebitis; we prospectively compared the silicone catheter with a Teflon cannula in a randomised trial. Seventy-nine surgical patients were randomised to receive peripheral nutrition (10 g nitrogen; 1770 kcal; 650 mOsm/l) either via a Teflon cannula (18G, 4.4 cm long) or via a silicone catheter (23G, 15 cm long). Compared with the group randomised to a standard Teflon cannula, patients fed via a silicone catheter had a significant (P < 0.001) improvement in (a) median time to survival of the first catheter (125 h vs 48 h); (b) incidence of catheter reinsertions (13% vs 75%); and (c) incidence of thrombophlebitis (10% vs 48%). Delivery of a moderately hypertonic nutritional solution through a fine-bore silicone catheter is safe, durable and well tolerated, with a low incidence of complications relative to a Teflon cannula. An expanded role for this catheter in nutritional therapy is feasible, which may reduce the requirement for central venous parenteral nutrition.

Cloning, chromosomal localization and expression analysis of the mouse Akt2 oncogene

We isolated mouse cDNA clones containing the entire coding region of the putative oncogene Akt2. Sequence analysis revealed that, like its human homolog, Akt2 encodes a protein-serine/threonine kinase containing a pleckstrin homology domain at its amino terminus. Fluorescence in situ hybridization of the mouse cDNA to rodent metaphase spreads demonstrated that the Akt2 gene maps to mouse chromosome band 7B1 and rat chromosome 1q22. Expression levels of mouse Akt2 mRNA and Akt2 protein varied among tissues, with the highest levels in skeletal muscle. Akt2 expression was low in a multipotent fibroblast cell line, but it was upregulated when these cells were transformed with Myod and induced to differentiate into myocytes. These data demonstrate that Akt2 expression is activated during cellular differentiation and suggest that it functions in the signaling pathways of some adult tissues.

Regulation of Gax homeobox gene transcription by a combination of positive factors including myocyte-specific enhancer factor 2

Homeobox-containing genes play an essential role in basic processes during embryogenesis and development, but little is known about the regulation of their expression. To elucidate regulatory networks that govern homeobox gene expression, we defined the core promoter of the mouse Gax homeobox gene and characterized its interactions with cellular proteins. Transient transfection experiments revealed Gax promoter activity in several cell types. Deletion analysis defined a 138-bp minimal promoter fragment between positions -125 and +13 relative to the transcription initiation site. Mutagenesis and protein-DNA binding assays suggested that at least three positive factors interact with this fragment and are required for transcriptional activity. One of these factors, HRF-1, recognizes a cis element consisting of an inverted palindromic motif. A second factor is Sp1, that binds to a G/C-rich element. The third is the MADS box factor referred to as MEF2 or RSRF. Mutations in the MEF2/RSRF site had the greatest effect on transcription in cell types that expressed the highest levels of endogenous MEF2 activity. Conversely, overexpression of MEF2A transactivated the Gax promoter more efficiently in cells lacking endogenous MEF2. These data provide evidence for a direct transcriptional link between members of the MADS and homeobox families of transcription factors.

MyoD-induced expression of p21 inhibits cyclin-dependent kinase activity upon myocyte terminal differentiation

The terminal differentiation of C2C12 skeletal muscle cells involves the activation of unique sets of genes and an irreversible withdrawal from the cell cycle. This process is associated with a decrease in cdk2 activity in cell extracts. The decrease in cdk2 activity correlates with diminished levels of cdk2 and cyclin A and with a marked induction of the p21 cyclin-dependent kinase (cdk) inhibitor. The upregulation of p21 occurred at the levels of mRNA and protein, and p21 formed a complex with the cyclin kinases in myotubes. Further, the immunodepletion of p21 from myotube extracts neutralized the heat-stable cdk2 inhibitory activity that was induced upon myogenic differentiation. The levels of p21 mRNA, protein, and activity remained constant in myotubes when they were reexposed to mitogen-rich growth medium, indicating that permanent changes in the cell's genetic program contribute to its sustained expression following terminal differentiation. Indeed, 10T1/2 fibroblasts transformed with the myogenic factor MyoD, but not the parental multipotent cells, upregulated p21 transcript levels when induced to differentiate by serum withdrawal, demonstrating that the upregulation is an integral feature of myogenic commitment and differentiation. The functional consequences of this upregulation were indicated by ectopically expressing p21 in myoblasts; this was sufficient for cell cycle arrest in mitogen-rich growth medium. The induction and sustained expression of p21 appears to be a contributory mechanism by which myocytes irreversibly exit the cell cycle upon terminal differentiation.

Serum induction of MEF2/RSRF expression in vascular myocytes is mediated at the level of translation

Vascular smooth muscle cells (VSMCs) reversibly coordinate the expression of VSMC-specific genes and the genes required for cell cycle progression. Here we demonstrate that isoforms of the MEF2/RSRF transcription factor are expressed in VSMCs and in vascular tissue. The MEF2A DNA-binding activity was upregulated when quiescent VSMCs were stimulated to proliferate with serum mitogens. The serum-induction of MEF2A DNA-binding activity occurred approximately 4 h following serum activation, and this correlated with an increase in the level of MEF2A protein without changes in the level of MEF2A mRNA or protein stability. These results indicate that MEF2A induction by serum is regulated at the level of translation.