Hypoplastic left heart syndrome occurs in up to 3% of all infants born with congenital heart disease and is a leading cause of death in this population. Although there is strong evidence for a genetic component, a specific genetic cause is only known in a small subset of patients, consistent with a multifactorial etiology for the syndrome. There is controversy surrounding the mechanisms underlying the syndrome, which is likely due, in part, to the phenotypic variability of the disease. The most commonly held view is that the “decreased” growth of the left ventricle is due to a decreased flow during a critical period of ventricular development. Research has also been hindered by what has been, up until now, a lack of genetically engineered animal models that faithfully reproduce the human disease. There is a growing body of evidence, nonetheless, indicating that the hypoplasia of the left ventricle is due to a primary defect in ventricular development. In this review, we discuss the evidence demonstrating that, at least for a subset of cases, the chamber hypoplasia is the consequence of hyperplasia of the contained cardiomyocytes. In this regard, hypoplastic left heart syndrome could be viewed as a neonatal form of cardiomyopathy. We also discuss the role of the endocardium in the development of the ventricular hypoplasia, which may provide a mechanistic basis for how impaired flow to the developing ventricle leads to the anatomical changes seen in the syndrome.

Endothelial cells (ECs) are directly exposed to shear stress and modulate the neighboring vascular smooth muscle cells (VSMCs), which plays important roles in vascular remodeling during atherosclerosis. Our previous research revealed that insulin-like growth factors (IGFs) might participate in low shear stress (LowSS) induced vascular remodeling, which remains to be elucidated. Using EC/VSMC co-cultured parallel-plate flow chamber, LowSS (5 dyn/cm(2)) was applied and normal shear stress (NSS, 15 dyn/cm(2)) was used as control. LowSS induced IGF-1 secretion from ECs, which subsequently phosphorylated IGF-1 receptor (IGF-1R) on co-cultured VSMCs, then increased Akt phosphorylation and Sirt2 expression. Decreasing IGF-1 in ECs by RNA interference (RNAi) reversed these effects on VSMCs. Exogenous IGF-1 increased IGF-1R and Akt phosphorylation, Sirt2 expression, and proliferation of VSMCs, and induced VSMCs towards synthetic phenotype. PI3 K/Akt specific inhibitor wortmannin decreased Sirt2 expression, proliferation, and synthetic phenotype transformation of VSMCs, but had no effect on IGF-1R. Sirt2 RNAi repressed VSMC proliferation and phenotypic transformation, but had no effect on IGF-1R and Akt. Taken together, LowSS induces the secretion of IGF-1 from ECs, which subsequently paracrine influences the co-cultured VSMCs via IGF-1R and Akt phosphorylation, and Sirt2 expression, then results in the proliferation and synthetic phenotype transformation.

Rationale: Jacobsen syndrome is a rare chromosomal disorder caused by deletions in the long arm of human chromosome 11, resulting in multiple developmental defects including congenital heart defects. Combined studies in humans and genetically engineered mice implicate that loss of ETS1 (E26 transformation specific 1) is the cause of congenital heart defects in Jacobsen syndrome, but the underlying molecular and cellular mechanisms are unknown. Objective: To determine the role of ETS1 in heart development, specifically its roles in coronary endothelium and endocardium and the mechanisms by which loss of ETS1 causes coronary vascular defects and ventricular noncompaction. Methods and Results: ETS1 global and endothelial-specific knockout mice were used. Phenotypic assessments, RNA sequencing, and chromatin immunoprecipitation analysis were performed together with expression analysis, immunofluorescence and RNAscope in situ hybridization to uncover phenotypic and transcriptomic changes in response to loss of ETS1. Loss of ETS1 in endothelial cells causes ventricular noncompaction, reproducing the phenotype arising from global deletion of ETS1. Endothelial-specific deletion of ETS1 decreased the levels of Alk1, Cldn5, Sox18, Robo4, Esm1, and Kdr, 6 important angiogenesis-relevant genes in endothelial cells, causing a coronary vasculature developmental defect in association with decreased compact zone cardiomyocyte proliferation. Downregulation of ALK1 expression in endocardium due to the loss of ETS1, along with the upregulation of TGF (transforming growth factor)-β1 and TGF-β3, occurred with increased TGFBR2/TGFBR1/SMAD2 signaling and increased extracellular matrix expression in the trabecular layer, in association with increased trabecular cardiomyocyte proliferation. Conclusions: These results demonstrate the importance of endothelial and endocardial ETS1 in cardiac development. Delineation of the gene regulatory network involving ETS1 in heart development will enhance our understanding of the molecular mechanisms underlying ventricular and coronary vascular developmental defects and will lead to improved approaches for the treatment of patients with congenital heart disease.

Ets1 deletion in some mouse strains causes septal defects and has been implicated in human congenital heart defects in Jacobsen syndrome, in which one copy of the Ets1 gene is missing. Here, we demonstrate that loss of Ets1 in mice results in a decrease in neural crest cells migrating into the proximal outflow tract cushions during early heart development, with subsequent malalignment of the cushions relative to the muscular ventricular septum, resembling double outlet right ventricle (DORV) defects in humans. Consistent with this, we find that cultured cardiac neural crest cells from Ets1 mutant mice or derived from iPS cells from Jacobsen patients exhibit decreased migration speed and impaired cell-to-cell interactions. Together, our studies demonstrate a critical role for ETS1 for cell migration in cardiac neural crest cells that are required for proper formation of the proximal outflow tracts. These data provide further insights into the molecular and cellular basis for development of the outflow tracts, and how perturbation of neural crest cells can lead to DORV.

Activating antigen-presenting cells is essential to generate adaptive immunity, while the efficacy of conventional activation strategies remains unsatisfactory due to suboptimal antigen-specific priming. Here, in situ polymerization-mediated antigen presentation (IPAP) is described, in which antigen-loaded nanovaccines are spontaneously formed and efficiently anchored onto the surface of dendritic cells in vivo through co-deposition with dopamine. The resulting chemically bound nanovaccines can promote antigen presentation by elevating macropinocytosis-based cell uptake and reducing lysosome-related antigen degradation. IPAP is able to prolong the duration of antigen reservation in the injection site and enhance subsequent accumulation in the draining lymph nodes, thereby eliciting robust antigen-specific cellular and humoral immune responses. IPAP is also applicable for different antigens and capable of circumventing the disadvantages of complicated preparation and purification. By implementation with ovalbumin, IPAP induces a significant protective immunity against ovalbumin-overexpressing tumor cell challenge in a prophylactic murine model. The use of the SARS-CoV-2 Spike protein S1 subunit also remarkably increases the production of S1-specific immunoglobulin G in mice. IPAP offers a unique strategy for stimulating antigen-presenting cells to boost antigen-specific adaptive responses and proposes a facile yet versatile method for immunization against various diseases.