P1458Telemonitoring of patients with chronic heart failure (CHF): evaluation of mortality, costs and utilization

Background

The telemonitoring program aims at optimizing the treatment for high risk CHF patients (NYHA II-IV) of a German sickness fund. All participants were equipped with remote monitoring devices such as body-scale, blood pressure monitor or 12-channel ECG system. With these devices information are collected in electronic medical records and analysed by a medical professional, who contacts the patient according to a predefined algorithm aiming for early interventions in order to prevent emergency hospitalization. The 24/7 intervention program is supported by coaching modules related to co-morbidities. All patient related data were provided by the sickness fund.

Methodology

For the evaluation the patient collective of a German sickness fund was screened for eligibility. Inclusion criteria are at least one inpatient stay due to heart failure or related conditions within the past 24 months before the start of the program as well as at least one outpatient diagnosis of heart failure or heart failure related diseases. Exclusion criteria are defined to eliminate patients with diagnoses such as cancer treatments, dialysis or mental illnesses.

After the first selection of all relevant patients for the study population patients are assigned to either intervention or control group. To ensure pre-treatment balance on important characteristics between treatment- and control group different methods such as propensity score matching and propensity weighting are used. For these methods patient characteristics e.g., on costs, medications and comorbidities are used for the period of 24 months before the start of the intervention. Intervention groups were enrolled in 11 waves. The observation period was 24 months (Q3/2015-Q2/2017). In a first analysis total health care costs consisting of inpatient and outpatient care, pharmaceutical as well as medical aids were analysed. Following this outpatient contacts, length of hospital stays and the number of prescribed drugs related to heart failure will be analysed. Further, mortality will be used as an outcome parameter.

Results

Preliminary results for the Gamma regression after propensity score matching on 714 patients in each group suggest a significant negative effect of the intervention of 0,1431 (p=0,005) for the total cost in the study, leading to an average decrease in cost of −2.187€ per patient. There were 998 hospitalizations accounted for in the intervention group vs. 1197 hospitalizations in the control group.

These effects appear to be driven by a decrease in inpatient costs, while costs in other areas such as outpatient care or drugs increased slightly.

Conclusion/Outlook

The preliminary results using propensity score matching suggest a sizable cost reduction for patients in the telemedical treatment group. Results on utilization and outcomes are still pending.

Acknowledgement/Funding

Funding by IKK Suedwest and SHL Telemedicine

Diagnostic and prognostic value of miR-1 and miR-29b on adverse ventricular remodeling after acute myocardial infarction - The SITAGRAMI-miR analysis

BACKGROUND

MicroRNAs (miRs) have shown to exert fibrotic and anti-fibrotic effects in preclinical models of acute myocardial infarction (AMI). The aim of this study was to evaluate miR-1, miR-21, miR-29b and miR-92a as circulating biomarkers for adverse ventricular remodeling (AVR) in post-AMI patients.

METHODS

Plasma levels of miR-1, miR-21, miR-29b and miR-92a were measured in 44 patients of the SITAGRAMI trial population at day 4, day 9 and 6month after AMI and in 18 matched controls (CTL). MiR expression patterns were correlated with magnetic resonance imaging (MRI) parameters for AVR (absolute change (Δ) in infarct volume (IV), left ventricular ejection fraction (LVEF) and left ventricular end-diastolic volume (LVEDV) between day 4 and 6months after AMI) and a combined cardiovascular endpoint.

RESULTS

Expression of miR-1, miR-21 and miR-29b but not miR-92a was increased in AMI vs. CTL cohort showing highest miR levels at d9. However, only miR-1 and miR-29b levels significantly correlated with ΔIV and showed a trend for correlation with ΔLVEF. Only miR-29b levels at day 9 correlated with ΔLVEDV at 6-month follow-up. There was no correlation of miR levels with an adverse outcome.

CONCLUSION

Mir-1 and miR-29b plasma levels post-AMI correlate with IV changes. In addition, miR-29b levels are associated with changes of LVEDV over time. These results provide insights into the role of miRs as diagnostic AVR surrogate markers. Further large scale clinical trials will be needed to evaluate the real prognostic relevance of these miRs with respect to a clinical implication in the future.

DPP-4 inhibition ameliorates atherosclerosis by priming monocytes into M2 macrophages

OBJECTIVE

Glipitins are widely used for the treatment of type 2 diabetic patients. In addition to their improvement of glycemic control, animal studies have suggested an independent anti-atherosclerotic effect of gliptins. Nevertheless, recent clinical trials regarding long-term effects of gliptin therapy on vascular events have been disappointing. This discrepancy led us to better dissect the functional role of SDF-1/CXCR4 signaling as a potential mechanism underlying gliptin action. The study should give improved understanding of the potential of gliptin therapy in the prevention and treatment of atherosclerosis.

METHODS AND RESULTS

In an ApoE-/- mouse model on high cholesterol diet, long-term treatment with the DPP-4 inhibitor Sitagliptin significantly reduced atherosclerosic plaque load in the aorta. Flow cytometry analyses showed an enrichment of M2 macrophages in the aortic wall under gliptin therapy. Importantly, the number of recruited CD206+ macrophages was inversely correlated with total plaque area while no correlation was found for the overall macrophage population or M1 macrophages. Blockade of CXCR4/SDF-1 signaling by AMD3100 inhibited aortic M2 accumulation and the therapeutic effect of Sitagliptin. Correspondingly, Sitagliptin shifted the polarization profile of macrophages towards a M2-like phenotype.

CONCLUSION

Sitagliptin-mediated inhibition of early atherosclerosis is based on M2-polarization during monocyte differentiation via the SDF-1/CXCR4 signaling. In contrast to earlier assumptions gliptin treatment might be especially effective in prevention of atherosclerosis.

Preconditioning with levosimendan before implantation of left ventricular assist devices

In this retrospective study, we investigated the impact of preconditioning of the right ventricle with the calcium sensitizer levosimendan immediately before left ventricular assist device (LVAD) implantation on outcome and survival. Nine consecutive LVAD patients (seven suffering from dilative cardiomyopathy and two from ischemic cardiomyopathy) with echocardiographic and invasive evidence of right heart insufficiency received levosimendan with 0.1 μg/kg body weight/min for 24 h before implantation of the assist device (seven HeartWare and two Jarvik 2000). Administration of levosimendan was safe and had not to be discontinued in any patient. We observed no relevant side effects. Twelve-month survival after implantation of the LVAD was 89% representing a superior outcome compared with the fifth INTERMACS registry data with 75% survival. Two temporary extracorporeal membrane-oxygenation implantations were necessary due to intraoperative right ventricular dysfunction. Only one patient died 5 weeks after LVAD implantation of multiorgan failure, five patients were successfully transplanted, and three patients underwent LVAD implantation for destination therapy. Levosimendan might improve clinical outcome and survival when used as pretreatment in patients with right heart insufficiency prior to LVAD implantation. However, we recommend a larger controlled trial in the future to confirm our preliminary results.

Antidiabetic gliptins in combination with G-CSF enhances myocardial function and survival after acute myocardial infarction

BACKGROUND

Medical stimulation of endogenous progenitor cell circulation may serve as a new therapeutic tool for treatment of acute myocardial infarction. We analyzed the effects of antidiabetic gliptins plus GCSF (granulocyte colony stimulating factor) on myocardial regeneration after myocardial infarction in a mouse model.

METHODS AND RESULTS

After surgical LAD-ligation (left anterior descending artery), Sitagliptin/Vildagliptin was applied yielding sufficient blood levels verified by mass spectrometry and significantly reducing activity of dipeptidyl peptidase (DPP) IV. GCSF or saline was administered intraperitoneally for 6 days. We assessed stem cell mobilization and homing (flow cytometry), infarct size (histology), neovascularization and cellular proliferation (immunohistology), heart function (Millar tip catheterization) and survival (Kaplan-Meier-curves). Gliptins±GCSF administration increased mobilization and cardiac homing of bone-marrow derived stem cells by stabilization of cardiac SDF1 (stromal cell-derived factor). For Sitagliptin, it could be shown that resident cardiac stem cells were stimulated, neovascularization was enhanced and cardiac remodeling was reduced. These effects finally improved myocardial function and increased survival for both gliptins. Although gliptins as a mono therapy lead to remarkable effects in a dose dependent manner and were superior to G-CSF mono-therapy, dual application of GCSF and gliptins revealed the best results. Since both gliptins yielded comparable effects concerning stem cell homing, cardiac function and survival, we suggest a class-effect of DPP-IV-inhibitors.

CONCLUSIONS

Thus, gliptins+GCSF and in high concentrations even as mono therapy have beneficial effects on cardiac regeneration after myocardial infarction beyond its anti-diabetic potential.

Cardiac differentiation in Xenopus is initiated by mespa

AIMS

Future cardiac repair strategies will require a profound understanding of the principles underlying cardiovascular differentiation. Owing to its extracorporal and rapid development, Xenopus laevis provides an ideal experimental system to address these issues in vivo. Whereas mammalian MesP1 is currently regarded as the earliest marker for the cardiovascular system, several MesP1-related factors from Xenopus-mespa, mespb, and mespo-have been assigned only to somitogenesis so far. We, therefore, analysed these genes comparatively for potential contributions to cardiogenesis.

METHODS AND RESULTS

RNA in situ hybridizations revealed a novel anterior expression domain exclusively occupied by mespa during gastrulation, which precedes the prospective heart field. Correspondingly, when overexpressed mespa most strongly induced cardiac markers in vivo as well as ex vivo. Transference to murine embryonic stem (ES) cells and subsequent FACS analyses for Flk-1 and Troponin I confirmed the high potential of mespa as a cardiac inducer. In vivo, Morpholino-based knockdown of mespa protein led to a dramatic loss of pro-cardiac and sarcomeric markers, which could be rescued either by mespa itself or human MesP1, but neither by mespb nor mespo. Epistatic analysis positioned mespa upstream of mespo and mespb, and revealed positive autoregulation for mespa at the time of its induction.

CONCLUSIONS

Our findings contribute to the understanding of conserved events initiating vertebrate cardiogenesis. We identify mespa as functional amphibian homologue of mammalian MesP1. These results will enable the dissection of cardiac specification from the very beginning in the highly versatile Xenopus system.

Combined anatomical and functional imaging using coronary CT angiography and myocardial perfusion SPECT in symptomatic adults with abnormal origin of a coronary artery

There has been a lack of standardized workup guidelines for patients with congenital abnormal origin of a coronary artery from the opposite sinus (ACAOS). We aimed to evaluate the use of cardiac hybrid imaging using multi-detector row CT (MDCT) for coronary CT angiography (Coronary CTA) and stress-rest myocardial perfusion SPECT (MPS) for comprehensive diagnosis of symptomatic adult patients with ACAOS. Seventeen symptomatic patients (12 men; 54 ± 13 years) presenting with ACAOS underwent coronary CTA and MPS. Imaging data were analyzed by conventional means, and with additional use of 3D image fusion to allocate stress induced perfusion defects (PD) to their supplying coronary arteries. An anomalous RCA arose from the left anterior sinus in eight patients, an abnormal origin from the right sinus was detected in nine patients (5 left coronary arteries, LCA and 4 LCx). Five of the 17 patients (29%) demonstrated a reversible PD in MPS. There was no correlation between the anatomical variants of ACAOS and the presence of myocardial ischemia. Image fusion enabled the allocation of reversible PD to the anomalous vessel in three patients (two cases in the RCA and the other in the LCA territory); PD in two patients were allocated to the territory of artery giving rise to the anomalies, rather than the anomalies themselves. In a small cohort of adult symptomatic patients with ACAOS anomaly there was no relation found between the specific anatomical variant and the appearance of stress induced myocardial ischemia using cardiac hybrid imaging.

The use of stem cells for the repair of cardiac tissue in ischemic heart disease

Ischemic heart diseases are the leading cause of death in the Western world. With increasing numbers of patients surviving their acute myocardial infarction owing to effective heart catheter techniques and intensive care treatment, congestive heart failure has become an increasing health concern. With therapeutic options for the prevention and treatment of ischemic heart disease being limited at present, huge efforts have been made in the field of stem cell research to try to establish new approaches for myocardial tissue regeneration. Owing to their pronounced differentiation potential, pluripotent stem cells seem to represent the most promising cell source for future engineering of myocardial replacement tissue. However, several crucial hurdles regarding cell yield and purity of the cultured cardiovascular progenitor cells have still not been overcome to facilitate a clinical application today. By contrast, plenty of adult stem and progenitor cells have already been well characterized and investigated in human disease. However, all of these heterogeneous cell lines primarily seem to work in a paracrine manner on ischemic myocardial tissue, rather than transdifferentiating into contractile cardiomyocytes. This article will focus on the production, application and present limitations of stem cells potentially applicable for myocardial repair.

Dual stem cell therapy after myocardial infarction acts specifically by enhanced homing via the SDF-1/CXCR4 axis

BACKGROUND

G-CSF based stem cell mobilization and stabilization of cardiac SDF-1 by DPP-IV-inhibition (dual stem cell therapy) improve heart function and survival after myocardial infarction. However, it is barely understood whether this new approach acts specifically through the SDF-1/CXCR4 axis, stimulation of resident cardiac stem cells and improved myocardial perfusion. Therefore, we aimed to clarify the role of the SDF1/CXCR4 axis with respect to the benefits of a dual stem cell based therapy.

METHODOLOGY/PRINCIPAL FINDINGS

After surgically induced ligation of the LAD, SDF-1/CXCR4 interactions were specifically blocked by the CXCR4 receptor antagonist AMD3100 in G-CSF and Diprotin A treated C57BL/6 mice. G-CSF+DipA treated and non-treated animals served as controls. Because AMD3100 is known to mobilize bone marrow derived stem cells (BMCs) in high concentrations, the optimal dosage (1.25mg per kg body weight) sufficient to block CXCR4 without stimulating mobilization was established. AMD3100 treatment of G-CSF and Diprotin A stimulated mice significantly decreased myocardial homing of circulating stem cells (FACS analysis) and inverted the beneficial effects of (i) cardiac remodeling (histological analyses), (ii) heart function (Millar tip catheterization) and (iii) survival (Kaplan-Meier curves). G-CSF treatment in combination with DPP-IV inhibition enhanced neovascularization at the infarct border zone which was related to an improved myocardial blood flow as measured by SPECT. Moreover, dual stem cell treatment effectively stimulated the pool of resident cardiac stem cells (FACS) which was reversed by AMD3100 treatment.

CONCLUSIONS/SIGNIFICANCE

Our data give final proof that homing through the SDF-1/CXCR-4 axis is essential for the success of dual stem cell therapy.

Safety and efficacy of SITAgliptin plus GRanulocyte-colony-stimulating factor in patients suffering from Acute Myocardial Infarction (SITAGRAMI-Trial)--rationale, design and first interim analysis

AIMS

Our pre-clinical studies demonstrated that G-CSF based stem cell mobilization in combination with genetic or pharmaceutical CD26/DPP-IV inhibition after acute myocardial infarction leads to improved cardiac homing of stem cells, enhanced heart function and increased survival. Thereupon, we initiated a phase III, multi-centre, randomised, placebo-controlled efficacy and safety study (n=100) analyzing the effect of combined application of G-CSF and Sitagliptin, which is a clinically admitted, anti-diabetic DPP-IV-inhibitor, after acute myocardial infarction ("SITAGRAMI-Trial"; EudraCT Number: 2007-003941-34).

METHODS

The primary objective of the study is to assess myocardial regeneration by improved myocardial homing of mobilized stem cells, as measured by cardiac function using MRI analysis. In this paper, we report on the study design and a planned first interim-analysis on safety issues without unblinding.

RESULTS

During the first 6 weeks of follow-up, only two major adverse cardiac events occurred (one de novo stenosis and one instent-restenosis) in the first 36 patients. Presumably, they were not related to any study medication. No other side effects like headache, bone pain, hypoglycaemias etc. were observed. Furthermore, no myocardial infarction or death occurred in any patient. Thus, the rate of serious adverse events lay within the expected range.

CONCLUSIONS

Our data demonstrate that the combined application of Sitagliptin and G-CSF seems to be safe on the short term and feasible after acute myocardial infarction and may represent a new therapeutic option in future.

G-CSF in patients suffering from late revascularised ST elevation myocardial infarction: final 1-year-results of the G-CSF-STEMI Trial

AIMS

The aims of this trial were to investigate the effect of granulocyte colony-stimulating factor (G-CSF) on left-ventricular ejection fraction and event-free survival in patients suffering from sub-acute myocardial infarction (STEMI).

METHODS

We enrolled 44 patients suffering from sub-acute STEMI with late revascularization achieved by percutaneous coronary intervention (PCI). Patients were randomized to receive either G-CSF (Filgrastim) at a dose of 10 μg/kg body weight/day subcutaneously or placebo. Changes of global and regional cardiac function from baseline (1 week after PCI) over 1 and 3 months to 12 months of follow-up were analyzed by magnetic resonance imaging.

RESULTS

Ejection fraction improved in G-CSF treated patients from 41.1±11.9% to 47.1±11.9% (3 months) and decreased slightly to 45.7±15.1% after 1 year. Ejection fraction also improved in the placebo group from 43.8±9.0% to 49.5±11.8% (3 months) and decreased slightly to 42.9±15.4% after 1 year (1 year MRI follow-up was performed in 23 out initial 44 patients). There was no significant difference between the two groups at any time point. Other parameters such as infarct size, myocardial perfusion, left ventricular end-diastolic and end-systolic volumes were not different between the two groups. Event-free survival of such as death, (re) myocardial infarction or acute coronary syndromes, coronary artery bypass grafting and target lesion revascularization was not significantly different between both groups.

CONCLUSIONS

G-CSF administration after sub-acute STEMI is feasible and safe but does not improve myocardial function or survival when used as a single substance.

G-CSF in patients suffering from late revascularized ST elevation myocardial infarction: analysis on the timing of G-CSF administration

OBJECTIVE

Granulocyte colony-stimulating factor (G-CSF) improves myocardial function after infarction in vivo. Placebo-controlled clinical studies failed to show beneficial effects on myocardial function. Recent data demonstrate that the time point of treatment initiation may be crucial for the efficacy of G-CSF. We investigated the influence of the timing of G-CSF treatment on myocardial function and perfusion in a subgroup study of the G-CSF-ST Elevation Myocardial Infarction trial.

MATERIALS AND METHODS

Patients with late revascularized myocardial infarction (n = 44) were treated with either G-CSF or placebo over 5 days after successful percutaneous coronary intervention (PCI). Of the G-CSF group, 13 patients had received G-CSF early treatment started within 24 hours after PCI (mean: 16 +/- 6 hours). In 10 patients, G-CSF was initiated late (>24 hours after PCI, mean: 49 +/- 26 hours). Global and regional myocardial function and perfusion were assessed from baseline to 3 months after PCI using magnetic resonance imaging in 37 patients who completed magnetic resonance follow-up.

RESULTS

G-CSF was safe when used early or late after PCI. Early G-CSF administration resulted in significantly improved perfusion at rest 1 month after PCI when compared to placebo (Up-slope, signal intensity 1.2 [0.4-1.8] vs 0.6 [0.1-1.3], p = 0.03). Timing of G-CSF had no influence on global and regional function.

CONCLUSION

This post-hoc analysis indicates that timing of G-CSF after myocardial infarction does not improve myocardial function but myocardial perfusion if the cytokine is given early. This urges the need to investigate alternative dosage regimens or combination with novel therapeutics promoting mobilization and homing.

Circulation of CD34+ progenitor cell populations in patients with idiopathic dilated and ischaemic cardiomyopathy (DCM and ICM)

AIMS

This study aimed at analysing the endogenous stem cell circulation in patients suffering from idiopathic dilated cardiomyopathy (DCM) and ischaemic cardiomyopathy (ICM).

METHODS AND RESULTS

Cytokines in peripheral blood were analysed using enzyme-linked immunosorbent assay and circulating CD34(+) stem cell populations (CD34(+)CD133(+), CD34(+)CD31(+), CD34(+)CXCR-4(+)) were measured by flow cytometry in DCM patients (n = 25), ICM patients (n = 15), and controls (n = 10). Explanted DCM (n = 5), ICM (n = 4) and normal hearts (n = 5) were analysed for the expression of several homing factors [stromal cell-derived factor-1 (SDF-1), Stem cell factor (SCF), HIF-1a, vascular cell adhesion molecule (VCAM), and Hepatocyte growth factor] by quantitative real-time polymerase chain reaction (PCR). SDF-1 was significantly elevated and positively correlated with brain natriuretic peptide (BNP) in peripheral blood of DCM and ICM patients showing the same New York heart association- (NYHA) class. In DCM patients circulating CD34(+) cell populations were significantly increased in comparison to ICM patients and controls. mRNA of SDF-1, SCF, HIF-1a, and VCAM related to glyceraldehyde-3-phosphate dehydrogenase was significantly upregulated in ICM hearts when compared with DCM hearts and controls.

CONCLUSION

Myocardial homing factors are upregulated in ICM when compared with DCM hearts. Reduced homing of stem cells might therefore explain the increased number of CD34(+) cells in DCM patients. These findings may open a new insight into the pathology and the treatment of idiopathic DCM.

Autologous bone marrow stem cell mobilization induced by granulocyte colony-stimulating factor after subacute ST-segment elevation myocardial infarction undergoing late revascularization: final results from the G-CSF-STEMI (Granulocyte Colony-Stimulating Factor ST-Segment Elevation Myocardial Infarction) trial

OBJECTIVES

The purpose of this investigator-driven, prospective, randomized, double-blinded, placebo-controlled phase II study was to compare the effects of granulocyte colony-stimulating factor (G-CSF) on the improvement of myocardial function in patients undergoing delayed percutaneous coronary intervention (PCI) for ST-segment elevation myocardial infarction (STEMI).

BACKGROUND

Experimental and early clinical studies suggest that transplantation of stem cells improves cardiac regeneration and neovascularization after acute myocardial infarction. Most investigators have utilized either a direct injection or intracoronary infusion of bone marrow-derived cells, but early cytokine-mediated mobilization of stem cells has been reported to show similar improvement in cardiac function.

METHODS

Forty-four patients with late revascularized subacute STEMI were treated either with G-CSF or placebo over 5 days after successful PCI. Primary end points were change of global and regional myocardial function from baseline (1 week after PCI) to 3 months after PCI assessed by magnetic resonance imaging (MRI). Secondary end points consisted of characterization of mobilized stem cell populations, assessment of safety parameters up to 12 months including 6-month angiography, as well as myocardial perfusion assessed by MRI.

RESULTS

Global myocardial function from baseline (1 week after PCI) to 3 months improved in both groups, but G-CSF was not superior to placebo (Delta(ejection fraction) 6.2 +/- 9.0 vs. 5.3 +/- 9.8%, p = 0.77). A slight but non-significant improvement of regional function occurred in both groups. Granulocyte colony-stimulating factor resulted in mobilization of endothelial progenitor cell populations and was well tolerated with a similar rate of target lesion revascularization from in-stent restenosis. In both groups major adverse cardiovascular events occurred in a comparable frequency. Granulocyte colony-stimulating factor resulted in significant improvement of myocardial perfusion 1 week and 1 month after PCI.

CONCLUSIONS

Granulocyte colony-stimulating factor treatment after PCI in subacute STEMI is feasible and relatively safe. However, patients do not benefit from G-CSF when PCI is performed late. Granulocyte colony-stimulating factor results in improved myocardial perfusion of the infarcted area, which may reflect enhanced neovascularization.

[Embryonic stem cells. Future perspectives]

Embryonic stem cells (ES cells) are able to differentiate into any cell type, and therefore represent an excellent source for cellular replacement therapies in the case of widespread diseases, for example heart failure, diabetes, Parkinson's disease and spinal cord injury. A major prerequisite for their efficient and safe clinical application is the availability of pure populations for direct cell transplantation or tissue engineering as well as the immunological compatibility of the transplanted cells. The expression of human surface markers under the control of cell type specific promoters represents a promising approach for the selection of cardiomyocytes and other cell types for therapeutic applications. The first human clinical trial using ES cells will start in the United States this year.

Improved cardiac gene transfer by transcriptional and transductional targeting of adeno-associated viral vectors

OBJECTIVE

Vectors based on recombinant adeno-associated virus 2 (AAV-2) are a promising tool for cardiac gene transfer. However, potential therapeutic applications need to consider the predominant transduction of the liver once AAV-2 vectors enter the systemic circulation. We therefore aimed to increase efficiency and specificity of cardiac vector delivery by combining transcriptional and cell surface targeting.

METHODS

For analysis of transcriptional targeting, recombinant AAV vectors were generated harboring a luciferase reporter gene under control of the cytomegalovirus (CMV) promoter or the 1.5-kb cardiac myosin light chain promoter fused to the CMV immediate-early enhancer (CMV(enh)/MLC1.5). Luciferase activities were determined in representative organs three weeks after intravenous injection of the vector into adult mice. Transductional targeting was studied using luciferase-reporter constructs crosspackaged into capsids of AAV serotypes 1 to 6 and modified AAV-2 capsids devoid of binding their primary receptor heparan sulfate proteoglycan.

RESULTS

Intravenous injections of AAV-2 vectors harboring the CMV(enh)/MLC1.5 promoter enabled a specific and 50-fold higher reporter gene expression in left ventricular myocardium of adult mice compared to vectors containing the CMV promoter. Comparison of AAV-2 vector genomes crosspackaged into capsids of AAV-1 to -6 showed that AAV-1, -4, -5, and -6 capsids increased cardiac transduction efficiency by about 10-fold. However, transduction of other organs such as the liver was also increased after systemic administration. In contrast, AAV-2-based vectors with ablated binding to their primary receptor heparan sulfate proteoglycan enabled a significantly increased efficiency of cardiac gene transfer and reduced transduction of the liver.

CONCLUSIONS

Combining transcriptional targeting by the CMV(enh)/MLC1.5 promoter and AAV vectors devoid of binding the AAV-2 primary receptor results in an efficient cardiac gene transfer with a significantly reduced hepatic transduction.

Increased SR Ca2+ cycling contributes to improved contractile performance in SERCA2a-overexpressing transgenic rats

OBJECTIVE

Heart failure is associated with reduced function of sarcoplasmic reticulum (SR) Ca2+-ATPase (SERCA2a) but increased function of sarcolemmal Na+/Ca2+ exchanger (NCX), leading to decreased SR Ca2+ content and loss of frequency-potentiation of contractile force. We reported that SERCA2a-overexpression in transgenic rat hearts (TG) results in improved contractility. However, it was not clear whether TG have improved contractility due to frequency-dependent improved SR Ca2+ handling.

METHODS

Therefore, we characterized TG (n=35) vs. wild-type (WT) control rats (n=39) under physiological conditions (37 degrees C, stimulation rate <8 Hz). Twitch force, intracellular Ca2+ transients ([Ca2+]i), and SR Ca2+ content were measured in isolated muscles. The contribution of transsarcolemmal Ca2+ influx (I(Ca)) through L-type Ca2+ channels (LTCC) and reverse mode NCX (I(Na/Ca)) to Ca2+ cycling were studied in isolated myocytes.

RESULTS

With increasing frequency, force increased in TG muscles by 168+/-35% (8 Hz; P<0.05) and SR Ca2+ content increased by maximally 118+/-31% (4 Hz; P<0.05). In WT, there was a flat force-frequency response without changes in SR Ca2+ content. Relaxation parameters of force and [Ca2+]i decay were accelerated at each frequency in TG vs. WT by approximately 10%. At prolonged rest intervals (<240 s), force and SR Ca2+ content increased significantly more in TG. Consequently, absolute SR Ca2+ content measured in myocytes was increased approximately 2-fold in TG. Transsarcolemmal Ca2+ fluxes estimated by I(Ca) (at 0 mV -10.2+/-1.1 vs. -16.9+/-1.3 pA/pF) and I(Na/Ca) (0.17+/-0.02 vs. 0.46+/-0.05 pA/pF) were decreased in TG vs. WT (P<0.05), whereas NCX and LTCC protein expression was only slightly reduced (P=n.s.).

CONCLUSION

In summary, SERCA2a-overexpression improved contractility in a frequency-dependent way due to increased SR Ca2+ loading whereas transsarcolemmal Ca2+ fluxes were decreased.

[Stem cell therapy in chronic heart failure]

BACKGROUND

An increasing number of patients survives acute myocardial infarction and reaches the stage of chronic heart failure-but today therapeutic possibilities in end stage of heart failure are limited because of a lack of donor organs.

RESULTS

Stem cell therapy is a promising new therapeutic strategy. In first clinical studies feasibility and efficacy of catheter-based application or cytokine-induced mobilisation of autologous stem cells have been examined in acute myocardial infarction and in chronic heart failure. While efficacy of autologous stem cells is uncertain and potential of regeneration might be to low, embryonic stem cells could represent another important option in future: because of pluripotency and a high potential of proliferation embryonic stem cells are the optimal resource for tissue engineering. Heart tissue which was generated in vitro could be transplanted in patients with chronic heart failure to increase cardiac function.

CONCLUSION

Whereas adult stem cells are applied in first clinical studies in myocardial infarction, embryonic stem cells are not clinically used yet. Nevertheless, embryonic stem cells might play an important role in therapy of chronic heart failure in future.

[Stem cell therapy for chronic cardiac insufficiency--therapy of the future?]

The incidence of chronic cardiac insufficiency is constantly increasing. However, the current therapeutic possibilities during the terminal stage are limited by a lack of donor organs. For this reason, stem cell therapy is seen as a potent therapeutic option for the future. Catheter application or cytokine-mediated mobilization of autologous adult stem cells is for acute myocardial infarction safe and potentially effective; however, for chronic cardiac insufficiency, the successes have not yet been verifiable. Hence, embryonic stem cells offer a therapeutic option that cannot be ignored: These cells are pluripotent and are, theoretically, able to continue dividing in cell culture indefinitely. Through "tissue engineering" they could generate new myocardium that could be transplanted into patients suffering from chronic cardiac insufficiency to support the pump function.

Cardiomyopathies: from genetics to the prospect of treatment

Cardiomyopathies are defined as diseases of the myocardium associated with cardiac dysfunction ranging from lifelong symptomless forms to major health problems such as progressive heart failure, arrhythmia, thromboembolism, and sudden cardiac death. They are classified by morphological characteristics as hypertrophic (HCM), dilated (DCM), arrhythmogenic right ventricular (ARVC), and restrictive cardiomyopathy (RCM). A familial cause has been shown in 50% of patients with HCM, 35% with DCM, and 30% with ARVC. In HCM, nine genetic loci and more than 130 mutations in ten different sarcomeric genes and in the gamma 2 subunit of AMP-activated protein kinase (AMPK) have been identified, suggesting impaired force production associated with inefficient use of ATP as the crucial disease mechanism. In DCM, 16 chromosomal loci with defects of several proteins also involved in the development of skeletal myopathies have been detected. These mutated cytoskeletal and nuclear transporter proteins may alter force transmission or disrupt nuclear function, resulting in cell death. Further DCM mutations have also been identified in sarcomeric genes, which indicates that different defects of the same protein can result in either HCM or DCM. In ARVC, six genetic loci and mutations in the cardiac ryanodine receptor, which controls electromechanical coupling, and in plakoglobin and desmoglobin (molecules involved in desmosomal cell-junction integrity), have been identified. Yet, no genetic linkage has been shown in RCM. Apart from disease-causing mutations, other factors, such as environment, genetic background, and the recently identified modifier genes of the renin-angiotensin, adrenergic, and endothelin systems are likely to result in the wide variety of RCM clinical presentations. Treatment options are symptomatic and are mainly focused on treatment of heart failure and prevention of thromboembolism and sudden death. Identification of patients with high risk for major arrhythmic events is important because implantable cardioverter defibrillators can prevent sudden death. Clinical and genetic risk stratification may lead to prospective trials of primary implantation of cardioverter defibrillators in people with hereditary cardiomyopathy.

Selection of ventricular-like cardiomyocytes from ES cells in vitro

Ischemic disorders of the heart can cause an irreversible loss of cardiomyocytes resulting in a substantial decrease of cardiac output. The therapy of choice is heart transplantation, a technique that is hampered by the low number of donor organs. In the present study, we describe the specific labeling, rapid but gentle purification and characterization of cardiomyocytes derived from mouse pluripotent embryonic stem (ES) cells. To isolate the subpopulation of ventricular-like cardiomyocytes, ES cells were stable transfected with the enhanced green fluorescent protein (EGFP) under transcriptional control of the ventricular-specific 2.1 kb myosin light chain-2v (MLC-2v) promoter and the 0.5 kb enhancer element of the cytomegalovirus (CMV(enh).). First fluorescent cells were detected at day 6 + 8 of differentiation within EBs. Four weeks after initiation of differentiation 25% of the cardiomyocyte population displayed fluorescence. Immunohistochemistry revealed the exclusive cardiomyogenic nature of EGFP-positive cells. This was further corroborated by electrophysiological studies where preferentially ventricular phenotypes, but no pacemaker-like cardiomyocytes, were detected among the EGFP-positive population. The enzymatic digestion of EBs, followed by Percoll gradient centrifugation and fluorescence-activated cell sorting, resulted in a 97% pure population of cardiomyocytes. Based on this study, ventricular-like cardiomyocytes can be generated in vitro from EBs and labeled using CMV(enh)./MLC-2v-driven marker genes facilitating an efficient purification. This method may become an important tool for future cell replacement therapy of ischemic cardiomyopathy especially after the proof of somatic differentiation of human ES cells in vitro.

Preservation of myocardial function after adenoviral gene transfer in isolated myocardium

Adenoviral gene transfer to the heart represents a promising model for structure-function analyses. Rabbit hearts were subjected to an ex vivo perfusion protocol that achieves gene transfer in >90% of cardiac myocytes. Contractile function of isolated myocardial preparations of these hearts was then observed for 2 days in a recently developed trabecula culture system. In sham-infected hearts, the initial developed force (F(init)) (15.6 +/- 3.7 mN/mm(2); n = 12) did not change significantly after 48 h (17.0 +/- 1.9 mN/mm(2); P = 0.46). In adenovirus-infected preparations, F(init) (14.3 +/- 1. 8 mN/mm(2); n = 21) did not significantly differ from the control (P = 0.75) and was unchanged after 48 h (15.3 +/- 2.5 mN/mm(2); P = 0. 93). After 2 days of continuous contractions, we observed homogenous and high-level expression of the reporter genes LacZ coding for beta-galactosidase and Luc coding for firefly luciferase. Luciferase activity increased more than 2,500-fold from background levels of 8. 7 x 10(3 )+/- 5.0 x 10(3) relative light units (RLU)/mg protein (from hearts transfected with promotorless adenovirus with luciferase transgene construct AdNULLLuc, n = 5) to 23.4 x 10(6)+/- 11.1 x 10(6)RLU/mg protein (from hearts tranfected with adenovirus with Rous sarcoma virus promotor and luciferase transgene construct AdRSVLuc, n = 5) in infected myocardial preparations (P < 0.005). Our results demonstrate a new ex vivo approach to achieve homogenous and high-level expression of recombinant adenoviral genes in contracting myocardium without adverse functional effects.

Transgenic myocardial overexpression of fibroblast growth factor-1 increases coronary artery density and branching

Fibroblast growth factor (FGF)-1 plays important roles during myocardial and coronary morphogenesis. FGF-1 is also involved in the physiological response of the adult heart against ischemia, which includes cardiomyocyte protection and vascular growth. In the present study, we have generated transgenic mice with specific myocardial overexpression of the gene. Transgene expression was verified by Northern blot, and increased FGF-1 protein content was assessed by Western blot and immunoconfocal microscopy. Anatomic, histomorphological, and ultrastructural analyses revealed no major morphological or developmental abnormalities of transgenic hearts. Capillary density was unaltered, whereas the density of coronary arteries, especially arterioles, was significantly increased, as was the number of branches of the main coronary arteries. In addition, the coronary flow was significantly enhanced in transgenic mice ex vivo. These differences in the anatomic pattern of the coronary vasculature are established during the second month of postnatal life. The present findings demonstrate an important role of FGF-1 in the differentiation and growth of the coronary system and suggest that it is a key regulatory molecule of the differentiation of the arterial system.

Transgenic rat hearts expressing a human cardiac troponin T deletion reveal diastolic dysfunction and ventricular arrhythmias

OBJECTIVE

Familial hypertrophic cardiomyopathy (FHC) due to mutations of cardiac troponin T (cTnT) is associated with a high frequency of sudden death even in the absence of cardiac hypertrophy. To investigate the causal relationship of cTnT mutations and this particular phenotype, we sought to establish a transgenic rat model for the disease.

METHODS

Transgenic rats were generated expressing human wild-type cTnT or two truncated cTnT molecules (del ex16, del ex15/16), resulting from an intron 15 splice donor site mutation previously observed in FHC patients. Transgenic rat hearts were characterized by histology, immunohistochemistry and in the 'working heart'.

RESULTS

Human wild-type and del ex16 cTnT were stably expressed and incorporated into the sarcomere of transgenic cardiomyocytes. Del ex16 transgenic rats revealed a lower level of expression (4-5%) than human wt cTnT animals (25-40%). In the 'working heart' model del ex16 hearts exhibited significant systolic and diastolic dysfunction without cardiac hypertrophy. In contrast, human wt cTnT hearts showed improved contractile performance and moderate myocardial hypertrophy. After 6 months of daily physical exercise one del ex16 rat died suddenly and three out of five del ex16 hearts revealed ventricular tachycardia/fibrillation. No arrhythmia was observed in human wt cTnT expressors. Myofibrillar disarray was present in del ex16 hearts after training but not in human wild-type cTnT rats or non-transgenic controls.

CONCLUSION

A human cTnT deletion overexpressed in transgenic rats exerts a dominant-negative effect and mimics the phenotype of FHC with diastolic dysfunction and arrhythmias. By contrast, human cTnT wild-type animals reveal a gain of function and cardiac hypertrophy without arrhythmias.

Association of nonsense mutation of dystrophin gene with disruption of sarcoglycan complex in X-linked dilated cardiomyopathy

BACKGROUND

In a systematic analysis of inherited forms of cardiomyopathy, we previously identified a family with X-linked dilated cardiomyopathy characterised by a mutation in the rod region of dystrophin. We have now attempted to eludicate the genetic mechanism involved in this disease, as well as the role of dystrophin-associated glycoproteins.

METHODS

The affected dystrophin epitope, which lacks binding to the dys-1 antibody, was analysed by single-strand conformation polymorphism analysis, reverse-transcription PCR, and DNA sequencing. Effects on dystrophin-associated glycoproteins were studied by immunohistochemistry and western blotting.

FINDINGS

A translation-termination mutation (C4148T) in exon 29 of the dystrophin gene was found in all affected family members. Alternative splicing rescued the reading frame and led to the expression of a dystrophin molecule lacking 50 aminoacids both in cardiac and skeletal muscle. Immunohistochemical analysis of the dystrophin-associated proteins revealed a reduction of beta-sarcoglycan and delta-sarcoglycan in the sarcolemma of cardiac muscle but not skeletal muscle tissue. However, western blotting revealed similar amounts of sarcoglycan subunits in both tissues.

INTERPRETATION

The molecular mechanism of this subtype of X-linked cardiomyopathy may be explained by a conformational change in exon-29-deleted dystrophin, resulting in disruption of the sarcoglycan assembly in heart muscle but not skeletal muscle.

Contrasting obesity phenotypes uncovered by partial leptin receptor gene deletion in transgenic mice

Non-insulin-dependent diabetes mellitus (type 2 diabetes) is known to be a polygenic and polyfactorial disorder. Here we describe the long-term examination of a transgenic mouse line showing the disruption of the leptin receptor (Lepr, Ob-R) gene caused by transgene insertion. The absence of the expression of the long isoform Ob-Rb uncovered a strong variation of the obesity and diabetes phenotype in the homozygous mutant mice of the outbred strain used. One part of the homozygous mice developed severe persistent early-onset obesity, whereas the other part developed cachexia after having shown initial obesity in the examination period up to 26 weeks p.p. The leptin-receptor-defective mice of this line might serve as a model for the investigation of genes modulating the development and mode of expression of diabetes.

Myocardial gene transfer by selective pressure-regulated retroinfusion of coronary veins

Catheter-based percutaneous transluminal gene delivery (PTGD) into the coronary artery still falls behind the expectations of an efficient myocardial gene delivery system. In this study gene delivery was applied by selective pressure-regulated retroinfusion through the coronary veins to prolong adhesion of replication defective adenovirus within the targeted myocardium. Adenoviral vectors consisted either of luciferase (Ad.rsv-Luc) or beta-galactosidase (Ad.rsv-betaGal) reporter gene under control of an unspecific promotor derived from the Rous sarcoma virus (RSV). In this pig model, selective retrograde gene delivery into the anterior cardiac vein during a brief period of ischemia substantially increased reporter gene expression in the targeted myocardium (LAD region) compared with antegrade delivery as a control. Repeated retrograde delivery during two periods of brief ischemia resulted in a more homogeneous transmural expression predominantly observed in cardiomyocytes (X-gal-staining). In the nontargeted myocardium (CX region) there was no evidence for adenoviral transfection. From our data we infer that selective pressure-regulated retroinfusion is a promising approach for efficient percutaneous transluminal gene delivery to the myocardium. Gene Therapy (2000) 7, 232-240.

The 2.3 kb smooth muscle myosin heavy chain promoter directs gene expression into the vascular system of transgenic mice and rabbits

BACKGROUND

Smooth muscle cells (SMC) are a preferential target for gene therapeutic approaches in atherosclerosis and restenosis. However, the undesirable expression of putative therapeutic genes in tissues other than the vascular wall is a considerable safety limitation for clinical trials, thus requiring the identification of a smooth-muscle-specific promoter sequence. Since the 2.3 kb rabbit Smooth Muscle Myosin Heavy Chain (SMHC) promoter was shown to be transcriptionally active in primary vascular but not visceral or other non-SMC in vitro, this fragment was chosen for in vivo analysis.

METHODS AND RESULTS

Transgenic mice and rabbits were established expressing a luciferase reporter gene under control of the 2.3 kb rabbit SMHC promoter. In contrast to the endogenous expression pattern of the SMHC gene both species revealed light emission predominantly in the arterial system including coronary arteries. Low activities were measured in large veins and the gastrointestinal system. In situ hybridization of murine embryos using a luciferase riboprobe confirmed reporter gene expression in large arteries with no detectable mRNA in the viscera. Unlike adult animals, ectopic luciferase activities were found in ventricular myocardium during murine development ceasing 1 week post partum.

CONCLUSIONS

In two animal species, the 2.3 kb SMHC promoter appeared to be effective in discriminating between the pathways regulating vascular and visceral smooth muscle gene expression. The vascular-specific expression profile of the 2.3 kb SMHC promoter suggests that the 2.3 kb SMHC promoter contains the regulatory elements necessary for selective gene targeting into vascular SMC of large arteries including coronary arteries in vivo.

Heart-specific targeting of beta-galactosidase by the ventricle-specific cardiac myosin light chain 2 promoter using adenovirus vectors

Adenoviruses are attractive vectors for gene transfer into cardiac muscle. However, their promiscuous tissue tropism, which leads to an ectopic expression of the transgene, is a considerable limitation. To restrict expression to cardiomyocytes, we have constructed two recombinant adenoviruses (Ad-MLC2-250betagal and Ad-MLC2-2100betagal) containing the beta-galactosidase reporter gene under the control of the 250- or 2100-bp rat ventricle-specific cardiac myosin light chain-2v promoter (MLC-2v). Our in vitro and in vivo data have evidenced that the 2100-bp promoter allows stronger beta-galactosidase activity than the 250-bp promoter and that the deleted promoter allows a weak beta-galactosidase expression in skeletal muscle-derived cells in vitro. In contrast to the in vitro results, the highly deleted MLC-2v promoter of 250 pb conserved its heart specificity in in ovo and in vivo when introduced into the adenovirus genome, indicating that the specificity of this promoter is neither altered by the inverted terminal repeat nor by the enhancer of the Ela promoter, both of which located in the 5' flanking region of the promoter. Systemic injections of both recombinant adenoviruses into chicken embryos showed beta-galactosidase expression mainly in the right ventricle of the heart. We have confirmed the cardiac specificity of both promoters in mammalian species after injection of both recombinant adenoviruses into the heart of adult rats in vivo. The comparison of both promoters in vitro and in vivo has shown that the 250-bp MLC-2v promoter is 80% less active than the 2100-bp MLC-2v promoter and has enabled us to conclude that the MLC-2v promoter of 2100 bp is the most appropriate for efficient expression of a reporter gene or a therapeutic cardiac gene (e.g., SERCA2a or minidystrophin gene).

Analysis of tissue-specific gene delivery by recombinant adenoviruses containing cardiac-specific promoters

OBJECTIVE

To approach heart muscle diseases by gene transfer, an adenoviral vector system was intended to be established suitable for gene expression in ventricular and/or atrial myocardium.

METHODS

Two adenoviral vectors (Ad-mhcLuc, Ad-mlcLuc) were constructed, in which the luciferase reporter gene is under control of either the ventricle-specific myosin light chain-2 (mlc-2v) or the atrial- and ventricular-specific alpha-myosin heavy chain (alpha-mhc) promoter. For controls, a recombinant adenovirus without promoter (Ad-Luc) and one with the Rous sarcoma virus (rsv) promoter (Ad-rsvLuc) were generated. A volume of 20 microliters containing 2 x 10(9) plaque forming units (pfu) of the recombinant adenoviruses Ad-mhcLuc, Ad-mlcLuc, Ad-rsvLuc or Ad-Luc was injected into the cardiac cavity or the quadriceps femoris muscle of neonatal rats. After five days animals were sacrificed and nine different tissues were analyzed for reporter gene expression by detection of light activity relative to mg of tissue.

RESULTS

Injections of recombinant adenoviruses into the cardiac cavity of neonatal rats resulted in heart-specific gene expression of Ad-mlcLuc (20 fold of Ad-Luc; 11% of Ad-rsvLuc), whereas Ad-mhcLuc gave mainly luciferase activity in the heart (6.5-fold of Ad-Luc; 3% of Ad-rsvLuc) with additional activity in lung and liver (2-4 fold of Ad-Luc). In the ventricular tissue Ad-mlcLuc revealed a 35-fold higher luciferase activity, whereas Ad-mhcLuc, Ad-rsvLuc and Ad-Luc showed only 2-fold higher luciferase activities compared to the atrium. Viral DNA in atrial and ventricular tissue was detected by PCR at approximately the same abundance independent of the injected type of adenovirus. Direct injection of Ad-mhcLuc and Ad-mlcLuc into the thigh muscle revealed only background luciferase activities.

CONCLUSIONS

In the adenoviral system only the mlc-2v promoter may fulfil the safety requirements for a myocardial specific gene expression with a high selectivity for the ventricular myocardium, thus providing a promising tool for future gene therapy of cardiomyopathies.

Novel splice donor site mutation in the cardiac myosin-binding protein-C gene in familial hypertrophic cardiomyopathy. Characterization Of cardiac transcript and protein

Familial hypertrophic cardiomyopathy is a disease generally believed to be caused by mutations in sarcomeric proteins. In a family with hypertrophic cardiomyopathy linked to polymorphic markers on chromosome 11, we found a new mutation of a splice donor site of the cardiac myosin-binding protein-C gene. This mutation causes the skipping of the associated exon in mRNA from lymphocytes and myocardium. Skipping of the exon with a consecutive reading frame shift leads to premature termination of translation and is thus expected to produce a truncated cardiac myosin-binding protein-C with loss of the myosin- and titin-binding COOH terminus. However, Western blot analysis of endomyocardial biopsies from histologically affected left ventricular myocardium failed to show the expected truncated protein. These data show for the first time that a splice donor site mutation in the myosin-binding protein-C gene is transcribed to cardiac mRNA. Truncated cardiac myosin-binding protein-C does not act as a "poison polypeptide," since it seems not to be incorporated into the sarcomere in significant amounts. The absence of mutant protein and of significantly reduced amounts of wild-type protein in the presence of the mutated mRNA argues against the "poison protein" and the "null allele" hypotheses and suggests yet unknown mechanisms relevant to the genesis of chromosome-11- associated familial hypertrophic cardiomyopathy.

Retinoic acid accelerates embryonic stem cell-derived cardiac differentiation and enhances development of ventricular cardiomyocytes

Pluripotent embryonic stem (ES) cells spontaneously differentiate via embryo-like aggregates into cardiomyocytes of pacemaker-, atrium- and ventricle-like type, which can be distinguished by their specific patterns of action potentials. It has been shown that retinoic acid (RA) treatment during ES cell differentiation increases the number of cardiomyocytes in a time- and concentration-dependent manner. In order to test the effect of RA on cardiomyocyte differentiation and specialization into ventricle-like cardiomyocytes, we studied gene expression of beta-galactosidase driven by the ventricular myosin light chain-2 (MLC-2v) promoter as an indicator for ventricular differentiation. Clones containing the stably integrated expression vector pGNA/MLC-2.1 were selected, which revealed an increase of beta-galactosidase activity in cardiomyocytes of embryoid bodies at day 7 + 16. RA, both, in the all-trans and in the 9-cis configuration resulted in a significant acceleration of cardiomyocyte differentiation and a transient increase of beta-galactosidase activity. To test whether this acceleration of cardiac differentiation and RA-induced increase of the MLC-2v promotor/beta-galactosidase activity reflects an increase of cardiac- and ventricle-specific gene expression, a semi-quantitative RT-PCR analysis was performed for alpha-cardiac myosin heavy chain (alpha-MHC) and MLC-2v genes. It was shown that both 10(-8) M and 10(-9) M RA resulted in an increased level of alpha-cardiac MHC and MLC-2v mRNA in embryoid bodies in early, but not in terminal developmental stages. This led us to the conclusion that the RA-induced accelerated expression of cardiac-specific genes results in an enhanced development of ventricular cardiomyocytes. An increased number of ventricle-like cells after RA treatment was also found by patch-clamp analysis. The number of cardiomyocytes with Purkinje- and ventricle-like properties was shown to be increased by RA, whereas the number of pacemaker- and atrium-like cells was reduced and early pacemaker cells were not quantitatively affected.

Expression from cardiomyocyte-specific promoter after adenovirus-mediated gene transfer in vitro and in vivo

Adenoviruses are very attractive vectors for gene transfer into the cardiac muscle; however, their promiscuous tissue tropism, leading to an ectopic expression of the transgene, is a considerable practical limitation. To restrict expression of a reporter gene in cultured cardiomyocytes and in the heart of the rat, we have constructed a recombinant adenovirus (Ad-MLC2 beta gal) containing the beta-galactosidase gene under the control of the rat ventricle-specific cardiac myosin light chain 2 (MLC-2v) promoter. We show in this work that the MLC-2v promoter inside the adenoviral genome retains its cardiac specificity in vitro in cultured cardiomyocytes as well as in vivo in the animal heart. Northern blot studies after Ad-MLC2 beta gal infection show significant transcription only in cells derived from the cardiac muscle and not from the skeletal muscle. Quantitative analysis of the beta-galactosidase activity in a number of cell lines also confirms this result. The level of beta-galactosidase expression in rat neonatal cardiomyocytes infected with Ad-MLC2 beta gal is 8% of that found when primary cells are infected with Ad-RSV beta gal (containing a beta-galactosidase gene under the control of the Rous sarcoma virus promoter). The cardiomyocytes-specific expression is also found after injection of Ad-MLC2 beta gal directly into the rat myocardium, although the viral genome can be detected by polymerase chain reaction (PCR) in other tissues. Lack of expression after direct injection into liver and skeletal muscle confirms these results. The use of a tissue-specific promoter is a first step to restrict transgene expression to a particular cell type of the targeted tissue.

Transgenic animal models: new avenues in cardiovascular physiology

Application of molecular genetic tools to inherited cardiovascular disorders has provided important insights into the molecular mechanisms underlying cardiomyopathies, arrhythmias, blood pressure regulation, and atherosclerosis. In addition, alteration of gene expression has been observed under common cardiovascular conditions such as cardiac hypertrophy and heart failure. Recent advances in transgenic and gene-targeting approaches allow a sophisticated manipulation of the mouse genome by gene addition, gene deletion, or gene modifications. These transgenic models enable the dissection of in vivo pathways responsible for these complex disease phenotypes. This review describes tissue-specific promoters suitable for targeting candidate genes to the cardiovascular system as well as a number of valuable transgenic animal models of blood pressure regulation, atherogenesis, defects in the coagulation system, cardiac hypertrophy, myocarditis, cardiomyopathies, and heart failure. Limitations and difficulties associated with these transgenic approaches are discussed. Animal models which may provide a basis for future gene therapy of cardiovascular diseases are introduced. Finally, methods are described to regulate the spatial and temporal expression level of a transgene, to inactivate a target gene in a tissue-specific manner, and to introduce specific mutations into the genome. These recent advances in transgenic technology are expected to have a considerable impact on cardiovascular research in the near future.

Heart muscle-specific gene expression using replication defective recombinant adenovirus

Adenoviruses are a promising vector system for future gene therapy of heart muscle diseases. The promiscuous tissue tropism of adenoviruses, however, may lead to the undesirable expression of putative therapeutic genes in nontarget cells and hence to considerable safety limitations for this vector system. To restrict gene expression to cardiomyocytes we constructed an adenoviral vector (Ad-mlcLuc) in which the luciferase gene is under the control of the ventricle-specific myosin light chain-2 (mlc-2v) promoter. For controls, we constructed a recombinant adenovirus without promoter (Ad-Luc) and one with the Rous sarcoma virus (RSV) promoter (Ad-rsvLuc). Our data demonstrate that the newly established viral vector Ad-mlcLuc was specifically active in rat neonatal cardiomyocytes in vitro but not in three established cell lines. Injections of the recombinant adenoviruses into the cardiac cavity of neonatal rats resulted in myocardial specific gene expression of Ad-mlcLuc in vivo, despite the fact that viral DNA was detected by PCR at different levels in all tissues investigated. In vitro and in vivo, Ad-mlcLuc was exclusively active in cardiac muscle cells, reaching 8-9% of the RSV-induced luciferase activity. Direct injection of Ad-mlcLuc into thigh muscle gave only background luciferase activity (0.05% of Ad-rsvLuc). Therefore, in the adenoviral system, the mlc-2v promoter allows heart-specific expression of a foreign gene thus providing a promising tool for gene transfer targeted to the myocardium.

X-linked dilated cardiomyopathy. Novel mutation of the dystrophin gene

We report on a family with a severe form of X-linked dilated cardiomyopathy (DCM). Two brothers, the elder requiring heart transplantation, and a maternal cousin presented elevated creatine kinase levels, increased right ventricular diameters and electrocardiographic abnormalities. All complained of exertional cramping myalgia, but none had muscle weakness or a pathological electromyogram. Muscle biopsies of these individuals revealed a mild myopathic picture with atrophic type I and hypertrophic type II fibers. Immunofluorescence using N- and C-terminal antibodies (dys-2, dys-3) against the dystrophin protein showed preserved, but reduced intensity of staining of the sarcolemmal membranes. Using the same two antibodies, Western blot analyses revealed a dystrophin molecule of the expected molecular weight, which was quantitatively reduced by 80%. However, the dys-1 antibody, directed against the mid rod region of the dystrophin protein, did not react with dystrophin both on Western blot and immunofluorescence. Linkage analysis with polymorphic markers of the dystrophin gene revealed an identical haplotype at the 5' region in all affected individuals (two point lod score of 1.93, phi = 0). A deletion of exons 48, 45-53, 2-7 and 1 including the promoter region of the dystrophin gene, as described in rare cases with similar clinical signs could be excluded by multiplex PCR and Southern blot analyses of this DCM family. In addition, a major splice-mutation of dystrophin mRNA was excluded by RT-PCR of skeletal and heart muscle tissue. Therefore, we conclude that a novel mutation in the 5' region of the dystrophin gene phenotypically leads to this severe form of DCM. Extensive analyses of the dystrophin gene, in particular of the sequences coding for the antigenic determinants of the dys-1 antibody in the mid rod region, may identify the molecular cause of this monogenetic form of DCM.

Characterization of a cardiac-selective and developmentally upregulated promoter in transgenic mice

Transcriptional regulatory mechanisms which mediate cardiac-specific gene expression have not yet been completely understood. Potential cardiac-specific promoter sequences, sharing similar protein binding motives, show either coexpression in skeletal muscle, local restriction to the atrium or late onset of expression during fetogenesis. Based on in situ hybridization studies that indicated the expression of the cardiac myosin-light-chain-2 (MLC-2) gene in ventricular myocardium and in the lower outflow tract, a model system for selective targeting of foreign genes to the heart of transgenic mice has been developed. The regulatory promoter element was derived from the rat cardiac MLC-2 gene. 2100 bp of the 5' regulatory MLC-2 sequences were found to drive constitutive cardiac expression of a firefly luciferase reporter gene from early tubular heart formation. During ventricular loop and septum formation luciferase activity was 10-fold upregulated in comparison to steady-state levels observed 10 days after birth. No luciferase activity was detectable in any other muscle or non-muscle tissue of transgenic mice. These data suggest that the 2.1 kb DNA sequences of the 5' flanking region of the cardiac MLC-2 gene contain sufficient regulatory elements for a selective gene expression in cardiac myocytes from embryogenesis. The transgenic model should aid in determining the influences of pathogenic gene products on developing and mature heart muscle to elucidate the etiology of myocardial diseases such as cardiomyopathies.

Heart-specific targeting of firefly luciferase by the myosin light chain-2 promoter and developmental regulation in transgenic mice

Based on hybridization studies indicating constitutive expression levels of the endogenous myosin light chain-2 (MLC-2) gene in embryonic, fetal, and adult myocardium, a model system for selective targeting of genes to the heart of transgenic mice has been developed. A 2.1-kb DNA fragment of the 5' flanking region of the rat cardiac MLC-2 gene was fused to the firefly luciferase reporter gene and introduced into fertilized mouse oocytes. In four independent transgenic mouse lines, the expression of the MLC-2-luciferase fusion gene was found exclusively in heart muscle. In contrast to the endogenous MLC-2 gene, no luciferase activity was detectable in slow-twitch skeletal muscle or any other tissue of transgenic mice. This result suggests that the 2.1-kb DNA fragment of the 5' flanking region of the cardiac MLC-2 gene contains the regulatory elements required for selective gene expression in cardiac myocytes in vivo. In contrast to the endogenous steady-state MLC-2 expression during development, transgenic luciferase activity was 10-fold higher during embryogenesis, when formation of the ventricular loop and septum takes place. The enhanced luciferase activity in early heart development may suggest a growth-dependent control mechanism, involving either transcriptional or posttranscriptional regulation. In conclusion, this model system with the 2.1-kb ventricle-specific MLC-2 promoter sequence should facilitate the overexpression of gene products in the developing and mature heart muscle and further elucidate molecular mechanisms of myocardial diseases such as cardiomyopathies.

Deletion of an N-terminal regulatory domain of the c-abl tyrosine kinase activates its oncogenic potential

The requirements for the oncogenic conversion of the c-abl proto-oncogene have been determined by the expression of N-terminal deleted forms and viral gag-fused forms of the c-abl proteins from a selectable retroviral vector. To activate the transforming potential of c-abl, it is necessary that (i) specific N-terminal amino acids are deleted to release the kinase from negative regulation in vivo; (ii) an N-terminal myristylation site is part of the activated kinase; (iii) the fatty-acylated, activated kinase is overproduced. The N-terminal amino acids found to be necessary for the cellular inhibition of c-abl tyrosine phosphorylation are part of a homologous region present in many non-receptor tyrosine kinases, the v-crk oncogene and phospholipase C-II. Overproduction of a deregulated and myristylated c-abl tyrosine kinase induces the transformation of NIH 3T3 cells.