Cristi L. Galindo

Anti‐Remodeling and Anti‐Fibrotic Effects of the Neuregulin‐1β Glial Growth Factor 2 in a Large Animal Model of Heart Failure

Background Neuregulin‐1β (NRG‐1β) is a growth factor critical for cardiac development and repair with therapeutic potential for heart failure. We previously showed that the glial growth factor 2 (GGF2) isoform of NRG‐1β improves cardiac function in rodents after myocardial infarction (MI), but its efficacy in a large animal model of cardiac injury has not been examined. We therefore sought to examine the effects of GGF2 on ventricular remodeling, cardiac function, and global transcription in post‐MI swine, as well as potential mechanisms for anti‐remodeling effects. Methods and Results MI was induced in anesthetized swine (n=23) by intracoronary balloon occlusion. At 1 week post‐MI, survivors (n=13) received GGF2 treatment (intravenous, biweekly for 4 weeks; n=8) or were untreated (n=5). At 5 weeks post‐MI, fractional shortening was higher (32.8% versus 25.3%, P=0.019), and left ventricular (LV) end‐diastolic dimension lower (4.5 versus 5.3 cm, P=0.003) in GGF2‐treated animals. Treatment altered expression of 528 genes, as measured by microarrays, including collagens, basal lamina components, and matricellular proteins. GGF2‐treated pigs exhibited improvements in LV cardiomyocyte mitochondria and intercalated disk structures and showed less fibrosis, altered matrix structure, and fewer myofibroblasts (myoFbs), based on trichrome staining, electron microscopy, and immunostaining. In vitro experiments with isolated murine and rat cardiac fibroblasts demonstrate that NRG‐1β reduces myoFbs, and suppresses TGFβ‐induced phospho‐SMAD3 as well as αSMA expression. Conclusions These results suggest that GGF2/NRG‐1β prevents adverse remodeling after injury in part via anti‐fibrotic effects in the heart.

Intravenous Glial Growth Factor 2 (GGF2) Isoform of Neuregulin-1β Improves Left Ventricular Function, Gene and Protein Expression in Rats after Myocardial Infarction

Aims Recombinant Neuregulin (NRG)-1β has multiple beneficial effects on cardiac myocytes in culture, and has potential as a clinical therapy for heart failure (HF). A number of factors may influence the effect of NRG-1β on cardiac function via ErbB receptor coupling and expression. We examined the effect of the NRG-1β isoform, glial growth factor 2 (GGF2), in rats with myocardial infarction (MI) and determined the impact of high-fat diet as well as chronicity of disease on GGF2 induced improvement in left ventricular systolic function. Potential mechanisms for GGF2 effects on the remote myocardium were explored using microarray and proteomic analysis. Methods and Results Rats with MI were randomized to receive vehicle, 0.625 mg/kg, or 3.25 mg/kg GGF2 in the presence and absence of high-fat feeding beginning at day 7 post-MI and continuing for 4 weeks. Residual left ventricular (LV) function was improved in both of the GGF2 treatment groups compared with the vehicle treated MI group at 4 weeks of treatment as assessed by echocardiography. High-fat diet did not prevent the effects of high dose GGF2. In experiments where treatment was delayed until 8 weeks after MI, high but not low dose GGF2 treatment was associated with improved systolic function. mRNA and protein expression analysis of remote left ventricular tissue revealed a number of changes in myocardial gene and protein expression altered by MI that were normalized by GGF2 treatment, many of which are involved in energy production. Conclusions This study demonstrates that in rats with MI induced systolic dysfunction, GGF2 treatment improves cardiac function. There are differences in sensitivity of the myocardium to GGF2 effects when administered early vs. late post-MI that may be important to consider in the development of GGF2 in humans.

Neuregulin as a Heart Failure Therapy and Mediator of Reverse Remodeling

The beta isoform of Neuregulin-1 (NRG-1β), along with its receptors (ErbB2–4), is required for cardiac development. NRG-1β, as well as the ErbB2 and ErbB4 receptors, is also essential for maintenance of adult heart function. These observations have led to its evaluation as a therapeutic for heart failure. Animal studies and ongoing clinical trials have demonstrated beneficial effects of two forms of recombinant NRG-1β on cardiac function. In addition to the possible role for recombinant NRG-1βs as heart failure therapies, endogenous NRG-1β/ErbB signaling appears to play a role in restoring cardiac function after injury. The potential mechanisms by which NRG-1β may act as both a therapy and a mediator of reverse remodeling remain incompletely understood. In addition to direct effects on cardiac myocytes NRG-1β acts on the vasculature, interstitium, cardiac fibroblasts, and hematopoietic and immune cells, which, collectively, may contribute to NRG-1β’s role in maintaining cardiac structure and function, as well as mediating reverse remodeling.

Neuregulin-1β induces proliferation, survival and paracrine signaling in normal human cardiac ventricular fibroblasts.

Neuregulin-1β (NRG-1β) is critical for cardiac development and repair, and recombinant forms are currently being assessed as possible therapeutics for systolic heart failure. We previously demonstrated that recombinant NRG-1β reduces cardiac fibrosis in an animal model of cardiac remodeling and heart failure, suggesting that there may be direct effects on cardiac fibroblasts. Here we show that NRG-1β receptors (ErbB2, ErbB3, and ErbB4) are expressed in normal human cardiac ventricular (NHCV) fibroblast cell lines. Treatment of NHCV fibroblasts with recombinant NRG-1β induced activation of the AKT pathway, which was phosphoinositide 3-kinase (PI3K)-dependent. Moreover, the NRG-1β-induced PI3K/AKT signaling in these cells required phosphorylation of both ErbB2 and ErbB3 receptors at tyrosine (Tyr)1248 and Tyr1289 respectively. RNASeq analysis of NRG-1β-treated cardiac fibroblasts obtained from three different individuals revealed a global gene expression signature consistent with cell growth and survival. We confirmed enhanced cellular proliferation and viability in NHCV fibroblasts in response to NRG-1β, which was abrogated by PI3K, ErbB2, and ErbB3 inhibitors. NRG-1β also induced production and secretion of cytokines (interleukin-1α and interferon-γ) and pro-reparative factors (angiopoietin-2, brain-derived neurotrophic factor, and crypto-1), suggesting a role in cardiac repair through the activation of paracrine signaling.

GRMD cardiac and skeletal muscle metabolism gene profiles are distinct

BackgroundDuchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene, which codes for the dystrophin protein. While progress has been made in defining the molecular basis and pathogenesis of DMD, major gaps remain in understanding mechanisms that contribute to the marked delay in cardiac compared to skeletal muscle dysfunction.MethodsTo address this question, we analyzed cardiac and skeletal muscle tissue microarrays from golden retriever muscular dystrophy (GRMD) dogs, a genetically and clinically homologous model for DMD. A total of 15 dogs, 3 each GRMD and controls at 6 and 12xa0months plus 3 older (47–93 months) GRMD dogs, were assessed.ResultsGRMD dogs exhibited tissue- and age-specific transcriptional profiles and enriched functions in skeletal but not cardiac muscle, consistent with a “metabolic crisis” seen with DMD microarray studies. Most notably, dozens of energy production-associated molecules, including all of the TCA cycle enzymes and multiple electron transport components, were down regulated. Glycolytic and glycolysis shunt pathway-associated enzymes, such as those of the anabolic pentose phosphate pathway, were also altered, in keeping with gene expression in other forms of muscle atrophy. On the other hand, GRMD cardiac muscle genes were enriched in nucleotide metabolism and pathways that are critical for neuromuscular junction maintenance, synaptic function and conduction.ConclusionsThese findings suggest differential metabolic dysfunction may contribute to distinct pathological phenotypes in skeletal and cardiac muscle.

Human monocyte transcriptional profiling identifies IL‐18 receptor accessory protein and lactoferrin as novel immune targets in hypertension

Monocytes play a critical role in hypertension. The purpose of our study was to use an unbiased approach to determine whether hypertensive individuals on conventional therapy exhibit an altered monocyte gene expression profile and to perform validation studies of selected genes to identify novel therapeutic targets for hypertension.

Altered ADAMTS5 Expression and Versican Proteolysis: A Possible Molecular Mechanism in Barlow's Disease

BACKGROUNDnWe hypothesized that gene expression profiles of mitral valve (MV) leaflets from patients with Barlows disease (BD) are distinct from those with fibroelastic deficiency (FED).nnnMETHODSnMVs were obtained from patients with BD (7 men, 3 women; 61.4 ± 12.7 years old) or FED (6 men, 5 women; 54.5 ± 6.0 years old) undergoing operations for severe mitral regurgitation (MR). Normal MVs were obtained from 6 donor hearts unmatched for transplant (3 men, 3 women; 58.3 ± 7.5 years old), and gene expression was assessed using cDNA microarrays. Select transcripts were validated by quantitative reverse-transcription polymerase chain reaction, followed by an assessment of protein levels by immunostaining.nnnRESULTSnThe global gene expression profile for BD was clearly distinct from normal and FED groups. A total of 4,684 genes were significantly differential (fold-difference >1.5, p < 0.05) among the three groups, 1,363 of which were commonly altered in BD and FED compared with healthy individuals (eg TGFβ2 [transforming growth factor β2] and TGFβ3 were equally upregulated in BD and FED). Most interesting were 329 BD-specific genes, including ADAMTS5 (a disintegrin-like and metalloprotease domain with thrombospondin-type 5), which was uniquely downregulated in BD based on microarrays and quantitative reverse-transcription polymerase chain reaction. Consistent with this finding, the ADAMTS5 substrate versican was increased in BD and conversely lower in FED.nnnCONCLUSIONSnMV leaflets in BD and FED exhibit distinct gene expression patterns, suggesting different pathophysiologic mechanisms are involved in leaflet remodeling. Moreover, downregulation of ADAMTS5 in BD, along with the accumulation of its substrate versican in the valvular extracellular matrix, might contribute to leaflet thickening and enlargement.

Increased Number of Circulating CD8/CD26 T Cells in the Blood of Duchenne Muscular Dystrophy Patients Is Associated with Augmented Binding of Adenosine Deaminase and Higher Muscular Strength Scores

Duchenne muscular dystrophy (DMD) is an X-linked disorder that leads to cardiac and skeletal myopathy. The complex immune activation in boys with DMD is incompletely understood. To better understand the contribution of the immune system into the progression of DMD, we performed a systematic characterization of immune cell subpopulations obtained from peripheral blood of DMD subjects and control donors. We found that the number of CD8 cells expressing CD26 (also known as adenosine deaminase complexing protein 2) was increased in DMD subjects compared to control. No differences, however, were found in the levels of circulating factors associated with pro-inflammatory activation of CD8/CD26 cells, such as tumor necrosis factor-α (TNFα), granzyme B, and interferon-γ (IFNγ). The number of CD8/CD26 cells correlated directly with quantitative muscle testing (QMT) in DMD subjects. Since CD26 mediates binding of adenosine deaminase (ADA) to the T cell surface, we tested ADA-binding capacity of CD8/CD26 cells and the activity of bound ADA. We found that mononuclear cells (MNC) obtained from DMD subjects with an increased number of CD8/CD26 T cells had a greater capacity to bind ADA. In addition, these MNC demonstrated increased hydrolytic deamination of adenosine to inosine. Altogether, our data demonstrated that (1) an increased number of circulating CD8/CD26 T cells is associated with preservation of muscle strength in DMD subjects, and (2) CD8/CD26 T cells from DMD subjects mediated degradation of adenosine by adenosine deaminase. These results support a role for T cells in slowing the decline in skeletal muscle function, and a need for further investigation into contribution of CD8/CD26 T cells in the regulation of chronic inflammation associated with DMD.

OSTEOPONTIN AND BRAIN DERIVED NEUROTROPHIC FACTOR: BIOMARKERS OF CARDIOVASCULAR DISEASE IN DUCHENNE MUSCULAR DYSTROPHY

Cardiomyopathy is the leading cause of death in Duchenne muscular dystrophy (DMD). Biomarkers such as troponin and brain natriuretic peptide are unable to reliably assess disease severity. We previously demonstrated abnormalities of osteopontin (OPN) and brain derived neurotrophic factor (BDNF) in