Rationale:

Transplantation of stem cells into damaged hearts has had modest success as a treatment for ischemic heart disease. One of the limitations is the poor stem cell survival in the diseased microenvironment. Prolyl hydroxylase domain protein 2 (PHD2) is a cellular oxygen sensor that regulates two key transcription factors involved in cell survival and inflammation, hypoxia-inducible factor (HIF) and nuclear factor-κB (NF-κB).

Objective:

We studied if and how PHD2 silencing in human adipose-derived stem cells (ADSCs) enhances their cardioprotective effects after transplantation into infarcted hearts.

Methods and Results:

ADSCs were transduced with lentiviral shPHD2 to silence PHD2. ADSCs with or without shPHD2 were transplanted after myocardial infarction (MI) in mice. ADSCs reduced cardiomyocyte apoptosis, fibrosis and infarct size and improved cardiac function. shPHD2-ADSCs exerted significantly more protection. PHD2 silencing induced greater ADSCs survival, which was abolished by shHIF-1α Conditioned medium (CM) from shPHD2-ADSCs decreased cardiomyocyte apoptosis. Insulin-like growth factor 1 (IGF-1) levels were significantly higher in the CM of shPHD2-ADSCs versus ADSCs, and depletion of IGF-1 attenuated the cardioprotective effects of shPHD2-ADSCs-CM. NF-κB activation was induced by shPHD2 to induce IGF-1 secretion via binding to IGF-1 gene promoter.

Conclusions:

PHD2 silencing promotes ADSCs survival in MI hearts and enhances their paracrine function to protect cardiomyocytes. The pro-survival effect of shPHD2 on ADSCs is HIF-1α dependent and the enhanced paracrine function of shPHD2-ADSCs is associated with NF-κB-mediated IGF-1 up-regulation. PHD2 silencing in stem cells may be a novel strategy for enhancing the effectiveness of stem cell therapy after MI.

Rationale:

High-density lipoprotein (HDL) cholesterol elevation via cholesteryl ester transfer protein (CETP) inhibition represents a novel therapy for atherosclerosis, which may also have relevance for type 2 diabetes.

Objective:

The current study assessed the effects of a CETP inhibitor (CETPi) on postprandial insulin, ex vivo insulin secretion and cholesterol efflux from pancreatic β-cells.

Methods and Results:

Healthy participants received a daily dose of CETPi (n=10) or placebo (n=15) for 14 days in a randomized, double-blind study. Insulin secretion and cholesterol efflux from MIN6N8 β-cells was determined following incubation with treated plasma. CETP inhibition increased plasma HDL cholesterol, apoAI and postprandial insulin. MIN6N8 β-cells incubated with plasma from CETPi-treated individuals (vs placebo) exhibited an increase in both glucose-stimulated insulin secretion (GSIS) and cholesterol efflux over the 14 day treatment period.

Conclusions:

CETP inhibition increased postprandial insulin and promoted ex vivo β-cell GSIS, potentially via enhanced β-cell cholesterol efflux.

Rationale:

The recessive form of catecholaminergic polymorphic ventricular tachycardia (CPVT) is caused by mutations in the cardiac calsequestrin gene (CASQ2): this variant of CPVT is less well characterized than the autosomal dominant form caused by mutations in the RyR2 gene.

Objective:

We characterized intracellular Ca(2+) homeostasis, electrophysiological properties and the ultrastructural features of the Ca(2+) release units (CRUs) in the homozygous R33Q knock-in mouse model.

Methods and Results:

We studied isolated R33Q and wild-type (WT) ventricular myocytes and observed properties not previously identified in a CPVT model. As compared to WT cells, R33Q myocytes: 1) show spontaneous Ca(2+) waves unable to propagate as cell-wide waves; 2) show smaller Ca(2+) sparks with shortened coupling intervals suggesting a reduced refractoriness of Ca(2+) release events; 3) have a reduction of the area of membrane contact and the of junctions between jSR and T-tubules (couplons) and of jSR volume; 4) have a propensity to develop phase 2-4 afterdepolarizations that can elicit triggered beats 5) Viral gene transfer with WT CASQ2 is able to normalize structural abnormalities and restore cell-wide calcium wave propagation.

Conclusions:

Our data show that homozygous CASQ2-R33Q myocytes develop spontaneous Ca(2+) release events with a broad range of intervals coupled to preceding beats leading to the formation of early and delayed afterdepolarizations. They also display a major disruption of the CRU architecture that leads to fragmentation of spontaneous Ca(2+) waves. We propose that these two substrates in R33Q myocytes synergize to provide a new arrhythmogenic mechanism for CPVT.

Rationale:

Arteriogenesis, the shear stress-driven remodeling of collateral arteries, is critical in restoring blood flow to ischemic tissue following a vascular occlusion. Our previous work has shown that the adaptor protein Shc mediates endothelial responses to shear stress in vitro.

Objective:

To examine the role of the adaptor protein Shc in arteriogenesis and endothelial-dependent responses to shear stress in vivo.

Methods and Results:

Conditional knockout mice in which Shc is deleted from endothelial cells were subjected to femoral artery ligation. Hindlimb perfusion recovery was attenuated in Shc conditional knockout mice compared to littermate controls. Reduced perfusion was associated with blunted collateral remodeling and reduced capillary density. Bone marrow transplantation experiments revealed that endothelial Shc is required for perfusion recovery as loss of Shc in bone marrow-derived hematopoietic cells had no effect on recovery. Mechanistically, Shc deficiency resulted in impaired activation of the NF-κB-dependent inflammatory pathway and reduced CD45(+) cell infiltration. Unexpectedly, Shc was required for arterial specification of the remodeling arteriole by mediating upregulation of the arterial endothelial cell marker ephrinB2 and activation of the Notch pathway. In vitro experiments confirmed that Shc was required for shear stress-induced activation of the Notch pathway and downstream arterial specification through a mechanism that involves upregulation of Notch ligands Delta-like 1 and Delta-like 4.

Conclusions:

Shc mediates activation of two key signaling pathways that are critical for inflammation and arterial specification; collectively, these pathways contribute to arteriogenesis and recovery of blood perfusion.

Rationale:

In patients with Brugada syndrome, arrhythmias typically originate in the right ventricular outflow tract (RVOT). The RVOT develops from the slowly conducting embryonic outflow tract.

Objective:

We hypothesize that this embryonic phenotype is maintained in the fetal and adult RVOT and leads to conduction slowing, especially after sodium current reduction.

Methods and Results:

We determined expression patterns in the embryonic myocardium, and performed activation mapping in fetal and adult hearts, including hearts from adult mice heterozygous for a mutation associated with Brugada syndrome (Scn5a(1798insD/+)). The embryonic RVOT was characterized by expression of Tbx2, a repressor of differentiation, and absence of expression of both Hey2, a ventricular transcription factor, and Gja1, encoding the principal gap-junction subunit for ventricular fast conduction. Also, conduction velocity was lower in the RVOT than in the right ventricular free wall. Later in development, Gja1 and Scn5a expression remained lower in the subepicardial myocardium of the RVOT than in RV myocardium. Nevertheless, conduction velocity in the adult RVOT was similar to that of the right ventricular free wall. However, in hearts of Scn5a(1798insD/+) mice and in normal hearts treated with ajmaline, conduction was slower in the RVOT than in the right ventricular wall.

Conclusions:

The slowly conducting embryonic phenotype is maintained in the fetal and adult RVOT, and is unmasked when cardiac sodium channel function is reduced.

Rationale:

Four monocentric studies reported that circadian rhythms can affect left ventricular infarct size after ST-segment-elevation acute myocardial infarction (STEMI).

Objective:

To further validate the circadian dependence of infarct size after STEMI in a multicentric and multiethnic population.

Methods and Results:

We analyzed a prospective cohort of subjects with first STEMI from the First Acute Myocardial Infarction study that enrolled 1099 patients (ischemic time <6 hours) in Italy, Scotland, and China. We confirmed a circadian variation of STEMI incidence with an increased morning incidence (from 6:00 am till noon). We investigated the presence of circadian dependence of infarct size plotting the peak creatine kinase against time onset of ischemia. In addition, we studied the patients from the 3 countries separately, including 624 Italians; all patients were treated with percutaneous coronary intervention. We adopted several levels of analysis with different inclusion criteria consistent with previous studies. In all the analyses, we did not find a clear-cut circadian dependence of infarct size after STEMI.

Conclusions:

Although the circadian dependence of infarct size supported by previous studies poses an intriguing hypothesis, we were unable to converge toward their conclusions in a multicentric and multiethnic setting. Parameters that vary as a function of latitude could potentially obscure the circadian variations observed in monocentric studies. We believe that, to assess whether circadian rhythms can affect the infarct size, future study design should not only include larger samples but also aim to untangle the molecular time-dynamic mechanisms underlying such a relation.

The establishment and maintenance of the vascular system is critical for embryonic development and postnatal life. Defects in endothelial cell development and vessel formation and function lead to embryonic lethality and are important in the pathogenesis of vascular diseases. Here, we review the underlying molecular mechanisms of endothelial cell differentiation, plasticity, and the development of the vasculature. This review focuses on the interplay among transcription factors and signaling molecules that specify the differentiation of vascular endothelial cells. We also discuss recent progress on reprogramming of somatic cells toward distinct endothelial cell lineages and its promise in regenerative vascular medicine.

The elucidation of genes implicated in Mendelian forms of hypertension demonstrates rare variants with substantial effects are responsible, and often these genes lie within pathways managing sodium homeostasis. More recently with advances in affordable high-throughput genotyping strategies, multiple common genetic variants with modest effects on blood pressure (<1 mmHg systolic) have been discovered in the population. In aggregate, these common variants explain <3% of the variance of blood pressure. Although these findings may offer new mechanistic insights into the biology of blood pressure, a key question is can these findings translate into patient benefit? It is timely to reflect on recent advances in genomics, and the use of new resources, such as the 1000 Genomes Project and the Encyclopedia of DNA Elements, to annotate likely causal variants, and their relevance to cardiovascular disease. In this review, we discuss the advances in relation to our knowledge of the genetic architecture of blood pressure, and whether gene discoveries might influence cardiovascular risk assessment, help to stratify patient response to medicine, or identify new biological pathways for novel therapeutic targets.