Andrew P. Kendle

The role of microRNAs in cardiac development and regenerative capacity

The mammalian heart has long been considered to be a postmitotic organ. It was thought that, in the postnatal period, the heart underwent a transition from hyperplasic growth (more cells) to hypertrophic growth (larger cells) due to the conversion of cardiomyocytes from a proliferative state to one of terminal differentiation. This hypothesis was gradually disproven, as data were published showing that the myocardium is a more dynamic tissue in which cardiomyocyte karyokinesis and cytokinesis produce new cells, leading to the hyperplasic regeneration of some of the muscle mass lost in various pathological processes. microRNAs have been shown to be critical regulators of cardiomyocyte differentiation and proliferation and may offer the novel opportunity of regenerative hyperplasic therapy. Here we summarize the relevant processes and recent progress regarding the functions of specific microRNAs in cardiac development and regeneration.

Mitigation of myocardial fibrosis by molecular cardiac surgery–mediated gene overexpression

OBJECTIVE Heart failure is accompanied by up-regulation of transforming growth factor beta signaling, accumulation of collagen and dysregulation of sarcoplasmic reticulum calcium adenosine triphosphatase cardiac isoform 2a (SERCA2a). We examined the fibrotic response in small and large myocardial infarct, and the effect of overexpression of the SERCA2a gene. METHODS Ischemic cardiomyopathy was induced via creation of large or small infarct in 26 sheep. Animals were divided into 4 groups: small infarct; large infarct with heart failure; gene-treated (large infarct with heart failure followed by adeno-associated viral vector, serotype 1.SERCA2a gene construct transfer by molecular cardiac surgery with recirculating delivery); and control. RESULTS Heart failure was significantly less pronounced in the gene-treated and small-infarct groups than in the large-infarct group. Expression of transforming growth factor beta signaling components was significantly higher in the large-infarct group, compared with the small-infarct and gene-treated groups. Both the angiotensin II type 1 receptor and angiotensin II were significantly elevated in the small- and large-infarct groups, whereas gene treatment diminished this effect. Active fibrosis with de novo collagen synthesis was evident in the large-infarct group; the small-infarct and gene-treated groups showed less fibrosis, with a lower ratio of de novo to mature collagen. CONCLUSIONS The data presented provide evidence that progression of fibrosis is mediated through increased transforming growth factor beta and angiotensin II signaling, which is mitigated by increased SERCA2a gene expression.

MiRNAs as potential molecular targets in heart failure.

Pathogenesis of heart diseases is associated with an altered expression profile of hundreds of genes. miRNAs are a newly identified layer of gene regulation operating at the post-transcriptional level by pairing to complementary base sequences in target mRNAs. Genetic data have identified the roles of miRNAs in basic pathological processes associated with heart failure: apoptosis, fibrosis, myocardial hypertrophy and cardiac remodeling. Many reports demonstrated that aberrantly expressed miRNAs and their modulation have effects on cardiac insufficiency. Here, we overview the advances in miRNAs as potential targets in the modulation of the heart failure phenotype. miRNA-based therapy holds great promise as a future strategy for treating heart diseases and identifying emerging signaling pathways responsible for the progression of heart failure.

Liquid jet delivery method featuring S100A1 gene therapy in the rodent model following acute myocardial infarction

The S100A1 gene is a promising target enhancing contractility and survival post myocardial infarction (MI). Achieving sufficient gene delivery within safety limits is a major translational problem. This proof of concept study evaluates viral mediated S100A1 overexpression featuring a novel liquid jet delivery (LJ) method. Twenty-four rats after successful MI were divided into three groups (n=8 ea.): saline control (SA); ssAAV9.S100A1 (SS) delivery; and scAAV9.S100A1 (SC) delivery (both 1.2 × 1011 viral particles). For each post MI rat, the LJ device fired three separate 100 μl injections into the myocardium. Following 10 weeks, all rats were evaluated with echocardiography, quantitative PCR (qPCR) and overall S100A1 and CD38 immune protein. At 10 weeks all groups demonstrated a functional decline from baseline, but the S100A1 therapy groups displayed preserved left ventricular function with significantly higher ejection fraction %; SS group (60±3) and SC group (57±4) versus saline (46±3), P<0.05. Heart qPCR testing showed robust S100A1 in the SS (10 147±3993) and SC (35 155±5808) copies per 100 ng DNA, while off-target liver detection was lower in both SS (40±40), SC (34 841±3164), respectively. Cardiac S100A1 protein expression was (4.3±0.2) and (6.1±0.3) fold higher than controls in the SS and SC groups, respectively, P<0.05.

Letter to the editor: Characterizing preclinical model of ischemic heart failure: difference between LAD and LCx infarctions

to the editor: We read with great interest the recently published article of Ishikawa and colleagues ([1][1]). The authors established heart failure (HF) models via left anterior descending coronary artery (LAD) and left circumflex artery (LCx) occlusion. We would like to address several issues that

Molecular Cardiac Surgery with Recirculating Delivery (MCARD): Procedure and Vector Transfer

Despite progress in clinical treatment, cardiovascular diseases are still the leading cause of morbidity and mortality worldwide. Therefore, novel therapeutic approaches are needed, targeting the underlying molecular mechanisms of disease with improved outcomes for patients. Gene therapy is one of the most promising fields for the development of new treatments for the advanced stages of cardiovascular diseases. The establishment of clinically relevant methods of gene transfer remains one of the principal limitations on the effectiveness of gene therapy. Recently, there have been significant advances in direct and transvascular gene delivery methods. The ideal gene transfer method should be explored in clinically relevant large animal models of heart disease to evaluate the roles of specific molecular pathways in disease pathogenesis. Characteristics of the optimal technique for gene delivery include low morbidity, an increased myocardial transcapillary gradient, esxtended vector residence time in the myocytes, and the exclusion of residual vector from the systemic circulation after delivery to minimize collateral expression and immune response. Here we describe myocardial gene transfer techniques with molecular cardiac surgery with recirculating delivery in a large animal model of post ischemic heart failure.

Bochdalek Congenital Diaphragmatic Hernia in an Adult Sheep

Congenital diaphragmatic hernia (CDH) is a rare condition. The aetiology of CDH is often unclear. In our case, a hollow mass was noted on MRI. Cardiac ejection fraction was diminished (47.0%) compared to 60.5% (average of 10 other normal animals, P < 0.05). The final diagnosis of congenital diaphragmatic hernia (Bochdalek type) was made when the sheep underwent surgery. The hernia was right‐sided and contained the abomasum. Lung biopsy demonstrated incomplete development with a low number of bronchopulmonary segments and vessels. The likely cause of this hernia was genetic malformation.

Gene Therapy in Cardiovascular Disease

Cardiovascular gene therapy applications began about 25 years ago. Since then, an in-depth understanding has accumulated on the underlying mechanisms of molecular structure as well as the development and function of the cardiovascular system in normal and disease states. In accordance with this, gene-based approaches have undergone substantial changes. Cardiovascular gene therapy should ideally deliver the genetic material to a specific target and reach a level of expression sufficient for therapeutic action. To achieve this, one needs to select a strategy with gene overexpression or gene silencing, suitable vectors and promoters, specific molecular targets known to be involved in a certain cardiovascular disease, and organ-targeted delivery techniques. Pharmacologic intervention has substantially increased survival and decreased morbidity in acquired and congenital cardiovascular diseases but still has multiple limitations including the targeting of symptoms rather than the pathological mechanism, difficulty in achieving efficacy, large variation between dose and concentration-dependent pharmacokinetics, and side effects. The progress in molecular biology and pharmacogenomics technology could allow for the development of gene containing drugs, which have the potential in the near future to momentously improve the management of a variety of clinical cardiovascular problems.

548. Self-Complementary Adeno-Associated Virus 9 Encoding S100A1 Decreases Serum Levels of Proinflammatory Cytokines Compared To Single-Stranded AAV9 after Myocardial Delivery Post MI

Despite the cardiospecificity of recombinant vectors based on adeno-associated virus (AAV) serotype 9, transgene expression is limited. One important factor is AAVs single-stranded (ss) DNA genome that is transcriptionally inactive until uncoated, converted into double-stranded DNA, and transported to the nucleus. Self-complementary (sc) AAV enters the cardiomyocyte as double stranded DNA, eliminating the efficiency-limiting step of second-strand synthesis. Previous studies have demonstrated that scAAV9 vector has superior transduction in vivo and in vitro.