Myocardin is required for maintenance of vascular and visceral smooth muscle homeostasis during postnatal development.

Myocardin is a muscle-restricted transcriptional coactivator that activates a serum response factor (SRF)-dependent gene program required for cardiogenesis and embryonic survival. To identify myocardin-dependent functions in smooth muscle cells (SMCs) during postnatal development, mice harboring a SMC-restricted conditional, inducible Myocd null mutation were generated and characterized. Tamoxifen-treated SMMHC-Cre(ERT2)/Myocd(F/F) conditional mutant mice die within 6 mo of Myocd gene deletion, exhibiting profound derangements in the structure of great arteries as well as the gastrointestinal and genitourinary tracts. Conditional mutant mice develop arterial aneurysms, dissection, and rupture, recapitulating pathology observed in heritable forms of thoracic aortic aneurysm and dissection (TAAD). SMCs populating arteries of Myocd conditional mutant mice modulate their phenotype by down-regulation of SMC contractile genes and up-regulation of extracellular matrix proteins. Surprisingly, this is accompanied by SMC autonomous activation of endoplasmic reticulum (ER) stress and autophagy, which over time progress to programmed cell death. Consistent with these observations, Myocd conditional mutant mice develop remarkable dilation of the stomach, small intestine, bladder, and ureters attributable to the loss of visceral SMCs disrupting the muscularis mucosa. Taken together, these data demonstrate that during postnatal development, myocardin plays a unique, and important, role required for maintenance and homeostasis of the vasculature, gastrointestinal, and genitourinary tracts. The loss of myocardin in SMCs triggers ER stress and autophagy, which transitions to apoptosis, revealing evolutionary conservation of myocardin function in SMCs and cardiomyocytes.

Foxp1 coordinates cardiomyocyte proliferation through both cell-autonomous and nonautonomous mechanisms.

Cardiomyocyte proliferation is high in early development and decreases progressively with gestation, resulting in the lack of a robust cardiomyocyte proliferative response in the adult heart after injury. Little is understood about how both cell-autonomous and nonautonomous signals are integrated to regulate the balance of cardiomyocyte proliferation during development. In this study, we show that a single transcription factor, Foxp1, can control the balance of cardiomyocyte proliferation during development by targeting different pathways in the endocardium and myocardium. Endocardial loss of Foxp1 results in decreased Fgf3/Fgf16/Fgf17/Fgf20 expression in the heart, leading to reduced cardiomyocyte proliferation. This loss of myocardial proliferation can be rescued by exogenous Fgf20, and is mediated, in part, by Foxp1 repression of Sox17. In contrast, myocardial-specific loss of Foxp1 results in increased cardiomyocyte proliferation and decreased differentiation, leading to increased myocardial mass and neonatal demise. We show that Nkx2.5 is a direct target of Foxp1 repression, and Nkx2.5 expression is increased in Foxp1-deficient myocardium. Moreover, transgenic overexpression of Nkx2.5 leads to increased cardiomyocyte proliferation and increased ventricular mass, similar to the myocardial-specific loss of Foxp1. These data show that Foxp1 coordinates the balance of cardiomyocyte proliferation and differentiation through cell lineage-specific regulation of Fgf ligand and Nkx2.5 expression.

Knockout of Adamts7, a novel coronary artery disease locus in humans, reduces atherosclerosis in mice.

BACKGROUND: Genome-wide association studies have established ADAMTS7 as a locus for coronary artery disease in humans. However, these studies fail to provide directionality for the association between ADAMTS7 and coronary artery disease. Previous reports have implicated ADAMTS7 in the regulation of vascular smooth muscle cell migration, but a role for and the direction of impact of this gene in atherogenesis have not been shown in relevant model systems. METHODS AND RESULTS: We bred an Adamts7 whole-body knockout mouse onto both the Ldlr and Apoe knockout hyperlipidemic mouse models. Adamts7(-/-)/Ldlr(-/-) and Adamts7(-/-)/Apoe(-/-) mice displayed significant reductions in lesion formation in aortas and aortic roots compared with controls. Adamts7 knockout mice also showed reduced neointimal formation after femoral wire injury. Adamts7 expression was induced in response to injury and hyperlipidemia but was absent at later time points, and primary Adamts7 knockout vascular smooth muscle cells showed reduced migration in the setting of tumor necrosis factor-α stimulation. ADAMTS7 localized to cells positive for smooth muscle cell markers in human coronary artery disease lesions, and subcellular localization studies in cultured vascular smooth muscle cells placed ADAMTS7 at the cytoplasm and cell membrane, where it colocalized with markers of podosomes. CONCLUSIONS: These data represent the first in vivo experimental validation of the association of Adamts7 with atherogenesis, likely through modulation of vascular cell migration and matrix in atherosclerotic lesions. These results demonstrate that Adamts7 is proatherogenic, lending directionality to the original genetic association and supporting the concept that pharmacological inhibition of ADAMTS7 should be atheroprotective in humans, making it an attractive target for novel therapeutic interventions.

Super-assembly platform for diverse nanoparticles with tunable topological architectures and surface morphologies.

Self-assembly leveraged by nature enables the sophisticated generation of a wide range of nanoparticles (NPs) with rich architectures and morphologies. However, existing artificial self-assembly platforms largely only allow for the fabrication of single type of NPs with limited structures, due to their inability to define interfacial interaction between seeds and growth materials, which is critically important to gain controllable growth patterns of the grown materials on the seeds' surface. Here, we report a versatile super-assembly platform that shows the capabilities to fabricate diverse NPs with tunable topological architectures and surface morphologies, e.g., molecular-like NPs, hollow asymmetric NPs, patchy NPs, etc. We unprecedentedly discovered the powerful functions of polyvinylpyrrolidone (PVP), which enable us to well define interfacial interaction between growth materials and seeds to achieve the controllable and tunable generation of various complex topological growth patterns. Moreover, the nucleation pattern (island nucleation or layered nucleation) of the patches can be thermodynamically modulated via the polarity of the solvent, while the number and size of the patches can be kinetically tuned by the ratio of polystyrene (PS), precursor, and catalyst. Interestingly, the hollow NPs can be generated by single-one processing step in our platform, unlike the multiple steps laboriously and widely employed by previously reported fabrication platforms. In addition, we demonstrate that our annealed NPs can not only selectively reflect visible light, and show well-controlled colors from gray, blue, to green, but also exhibit excellent photothermal conversion performances with a high photothermal conversion efficiency of 68.7% that are superior to currently routinely reported of 40%. This super-assembly platform can serve as a powerful toolset to sophisticatedly create varied NPs with tunable hierarchical architectures and controllable surface morphologies, which would significantly benefit the development of drug delivery, nanomaterial assembly, nano pigments, nanoreactors, and beyond.

Wnt2 signaling is necessary and sufficient to activate the airway smooth muscle program in the lung by regulating myocardin/Mrtf-B and Fgf10 expression.

Smooth muscle in the lung is thought to derive from the developing lung mesenchyme. Smooth muscle formation relies upon coordination of both autocrine and paracrine signaling between the budding epithelium and adjacent mesenchyme to govern its proliferation and differentiation. However, the pathways initiating the earliest aspects of smooth muscle specification and differentiation in the lung are poorly understood. Here, we identify the Wnt2 ligand as a critical regulator of the earliest aspects of lung airway smooth muscle development. Using Wnt2 loss and gain of function models, we show that Wnt2 signaling is necessary and sufficient for activation of a transcriptional and signaling network critical for smooth muscle specification and differentiation including myocardin/Mrtf-B and the signaling factor Fgf10. These studies place Wnt2 high in a hierarchy of signaling molecules that promote the earliest aspects of lung airway smooth muscle development.

NF1 regulates a Ras-dependent vascular smooth muscle proliferative injury response.

BACKGROUND: Neurofibromatosis type I (NF1) is a common autosomal dominant disorder with a broad array of clinical manifestations, including benign and malignant tumors, osseous dysplasias, and characteristic cutaneous findings. In addition, NF1 patients have an increased incidence of cardiovascular diseases, including obstructive vascular disorders. In animal models, endothelial expression of the disease gene, NF1, is critical for normal heart development. However, the pathogeneses of the more common vascular disorders are not well characterized. METHODS AND RESULTS: To examine the role of NF1 in vascular smooth muscle, we generated mice with homozygous loss of the murine homolog Nf1 in smooth muscle (Nf1smKO). These mice develop and breed normally. However, in response to vascular injury, they display a marked intimal hyperproliferation and abnormal activation of mitogen-activated protein kinase, a downstream effector of Ras. Vascular smooth muscle cells cultured from these mice also display enhanced proliferation and mitogen-activated protein kinase activity. Smooth muscle expression of the NF1 Ras-regulatory domain (GTPase activating protein-related domain) rescues intimal hyperplasia in Nf1smKO mice and normalizes vascular smooth muscle cell Ras effector activity and proliferation in vitro, similar to blockade of downstream effectors of Ras. CONCLUSIONS: In this in vivo model of NF1 obstructive vascular disease, we have shown that Nf1 regulation of Ras plays a critical role in vascular smooth muscle proliferation after injury. These results suggest opportunities for targeted therapeutics in the prevention and treatment of NF1-related vascular disease and in the treatment of neointimal proliferation in other settings.

Ash2l interacts with Tbx1 and is required during early embryogenesis.

TBX1 encodes a DNA binding transcription factor that is commonly deleted in human DiGeorge syndrome and plays an important role in heart development. Mechanisms of Tbx1 function, such as Tbx1 interacting regulatory proteins and transcriptional target specificity, are largely unknown. Ash2l is the mammalian homolog of Drosophila Ash2 (absent small homeotic 2) and is a core component of a multimeric histone methyltransferase complex that epigenetically regulates transcription via methylation of histone lysine residues. We undertook an unbiased yeast two-hybrid screen to look for functionally relevant Tbx1-interacting proteins and report a physical and functional interaction between Tbx1 and Ash2l. Tbx1 interacts with Ash2l in both yeast and mammalian cells and Ash2l acts as a transcriptional co-activator in luciferase reporter assays. Expression analysis shows that Tbx1 and Ash2l have overlapping mRNA and protein expression patterns during development. By generating an Ash2l knockout mouse utilizing gene-trap technology, we show that although Ash2l heterozygous mice are normal, Ash2l-null embryos die early during gestation. Thus, Ash2l is required for the earliest stages of embryogenesis. Furthermore, our finding of a physical interaction between Tbx1 and Ash2l suggest that at least some functions of Tbx1 may be mediated by direct interactions with a histone methyltransferase complex.

Characterization and in vivo pharmacological rescue of a Wnt2-Gata6 pathway required for cardiac inflow tract development.

Little is understood about the molecular mechanisms underlying the morphogenesis of the posterior pole of the heart. Here we show that Wnt2 is expressed specifically in the developing inflow tract mesoderm, which generates portions of the atria and atrio-ventricular canal. Loss of Wnt2 results in defective development of the posterior pole of the heart, resulting in a phenotype resembling the human congenital heart syndrome complete common atrio-ventricular canal. The number and proliferation of posterior second heart field progenitors is reduced in Wnt2(-/-) mutants. Moreover, these defects can be rescued in a temporally restricted manner through pharmacological inhibition of Gsk-3beta. We also show that Wnt2 works in a feedforward transcriptional loop with Gata6 to regulate posterior cardiac development. These data reveal a molecular pathway regulating the posterior cardiac mesoderm and demonstrate that cardiovascular defects caused by loss of Wnt signaling can be rescued pharmacologically in vivo.

A Gata6-Wnt pathway required for epithelial stem cell development and airway regeneration.

Epithelial organs, including the lung, are known to possess regenerative abilities through activation of endogenous stem cell populations, but the molecular pathways regulating stem cell expansion and regeneration are not well understood. Here we show that Gata6 regulates the temporal appearance and number of bronchioalveolar stem cells (BASCs) in the lung, its absence in Gata6-null lung epithelium leading to the precocious appearance of BASCs and concurrent loss in epithelial differentiation. This expansion of BASCs was the result of a pronounced increase in canonical Wnt signaling in lung epithelium upon loss of Gata6. Expression of the noncanonical Wnt receptor Fzd2 was downregulated in Gata6 mutants and increased Fzd2 or decreased beta-catenin expression rescued, in part, the lung epithelial defects in Gata6 mutants. During lung epithelial regeneration, canonical Wnt signaling was activated in the niche containing BASCs and forced activation of Wnt signaling led to a large increase in BASC numbers. Moreover, Gata6 was required for proper lung epithelial regeneration, and postnatal loss of Gata6 led to increased BASC expansion and decreased differentiation. Together, these data demonstrate that Gata6-regulated Wnt signaling controls the balance between progenitor expansion and epithelial differentiation required for both lung development and regeneration.

Endothelial lineage-mediated loss of the GATA cofactor Friend of GATA 1 impairs cardiac development.

GATA transcription factors, together with Friend of GATA (FOG) cofactors, are required for the differentiation of diverse cell types. Multiple aspects of hematopoiesis are controlled by the interaction of FOG-1 with the GATA-1/2/3 subfamily. Likewise, FOG-2 is coexpressed with the GATA-4/5/6 subfamily at other sites, including the heart and gonads. FOG-2 and GATA-4 are required for cardiac development. Through transgenic rescue of hematopoietic defects of FOG-1-/- embryos we define an unsuspected role for FOG-1 in heart development. In particular, rescued FOG-1-/- mice die at embryonic day (E) 14.5 with cardiac defects that include double outlet right ventricle and a common atrioventricular valve. Using conditional inactivation of Fog-1 we assign the cell of origin in which FOG-1 function is required. Neural crest cells migrate properly into FOG-1-/- hearts and mice with FOG-1 conditionally excised from neural crest derivatives fail to develop cardiac abnormalities. In contrast, conditional inactivation of FOG-1 in endothelial-derived tissues by means of Tie-2-expressed Cre recapitulates the rescue-knockout defects. These findings establish a nonredundant requirement for FOG-1 in the outlet tract and atrioventricular valves of the heart that depend on expression in endothelial-derived tissue and presumably reflect cooperation with the GATA-4/5/6 subfamily.