Pitx2 is functionally important in the early stages of vascular smooth muscle cell differentiation

Nuclear Control of Vascular Smooth Muscle Cell Plasticity during Vascular Remodeling

Control of vascular smooth muscle cell (SMC) gene expression is an essential process for establishing and maintaining lineage identity, contractility, and plasticity. Most mechanisms (epigenetic, transcriptional, and post-transcriptional) implicated in gene regulation occur in the nucleus. Still, intranuclear pathways are directly impacted by modifications in the extracellular environment in conditions of adaptive or maladaptive remodeling. Integration of extracellular, cellular, and genomic information into the nucleus through epigenetic and transcriptional control of genome organization plays a major role in regulating SMC functions and phenotypic transitions during vascular remodeling and diseases. This review aims to provide a comprehensive update on nuclear mechanisms, their interactions, and their integration in controlling SMC homeostasis and dysfunction. It summarizes and discusses the main nuclear mechanisms preponderant in SMCs in the context of vascular disease, such as atherosclerosis, with an emphasis on studies employing in vivo cell-specific loss-of-function and single-cell omics approaches.

SWI/SNF Complex in Vascular Smooth Muscle Cells and Its Implications in Cardiovascular Pathologies

Mature vascular smooth muscle cells (VSMC) exhibit a remarkable degree of plasticity, a characteristic that has intrigued cardiovascular researchers for decades. Recently, it has become increasingly evident that the chromatin remodeler SWItch/Sucrose Non-Fermentable (SWI/SNF) complex plays a pivotal role in orchestrating chromatin conformation, which is critical for gene regulation. In this review, we provide a summary of research related to the involvement of the SWI/SNF complexes in VSMC and cardiovascular diseases (CVD), integrating these discoveries into the current landscape of epigenetic and transcriptional regulation in VSMC. These novel discoveries shed light on our understanding of VSMC biology and pave the way for developing innovative therapeutic strategies in CVD treatment.

Human Induced Pluripotent Stem Cell-Derived Vascular Cells: Recent Progress and Future Directions

Human induced pluripotent stem cells (hiPSCs) hold great promise for cardiovascular regeneration following ischemic injury. Considerable effort has been made toward the development and optimization of methods to differentiate hiPSCs into vascular cells, such as endothelial and smooth muscle cells (ECs and SMCs). In particular, hiPSC-derived ECs have shown robust potential for promoting neovascularization in animal models of cardiovascular diseases, potentially achieving significant and sustained therapeutic benefits. However, the use of hiPSC-derived SMCs that possess high therapeutic relevance is a relatively new area of investigation, still in the earlier investigational stages. In this review, we first discuss different methodologies to derive vascular cells from hiPSCs with a particular emphasis on the role of key developmental signals. Furthermore, we propose a standardized framework for assessing and defining the EC and SMC identity that might be suitable for inducing tissue repair and regeneration. We then highlight the regenerative effects of hiPSC-derived vascular cells on animal models of myocardial infarction and hindlimb ischemia. Finally, we address several obstacles that need to be overcome to fully implement the use of hiPSC-derived vascular cells for clinical application.

PRRX1 deficiency induces mesenchymal-epithelial transition through PITX2/miR-200-dependent SLUG/CTNNB1 regulation in hepatocellular carcinoma

Metastasis is a major obstacle to better prognosis in patients with hepatocellular carcinoma (HCC). Mesenchymal-epithelial transition (MET) is the driving force for metastatic colonization in which E-cadherin re-expression is a critical procedure. It has been reported that the loss of paired-related homeobox transcription factor 1 (PRRX1) is required for cancer cell metastasis. However, the role of PRRX1 in MET and how its downregulation triggers E-cadherin re-expression are unknown. In this study, we performed a systematic, mechanistic study regarding the role of PRRX1 in MET of HCC. We observed PRRX1 downregulation in HCC tissues, which correlated with early metastasis and short overall survival. Overexpression of PRRX1 induced epithelial-mesenchymal transition (EMT), but did not promote metastasis formation, while knockdown of PRRX1 promoted metastasis and colonization of circulating HCC cells as shown in animal model. PRRX1 protein levels reversely correlated with E-cadherin levels in HCC cell lines. PRRX1 knockdown promoted E-cadherin re-expression and cell proliferation and inhibited cell invasion and migration. The microarray results showed that PRRX1 deficiency regulated extracellular matrix (ECM) interaction, focal adhesion, TGF-β signaling and cancer pathways. PRRX1 knockdown upregulated paired-like homeodomain 2 (PITX2) and inhibited catenin beta 1 (CTNNB1) and SNAIL family zinc finger 2 (SLUG). Silencing of PITX2 reversed CTNNB1 and SLUG inhibition and E-cadherin re-expression. PITX2 upregulation increased miR-200a and miR-200b/429, which further inhibited the transcription of CTNNB1 and SLUG, respectively, thus abrogating the inhibitory effect on E-cadherin. In conclusion, our data showed that the downregulation of PRRX1 induced E-cadherin re-expression through PITX2/miR-200a/CTNNB1 and PITX2/miR-200b/429/SLUG pathway.

Interleukin-12p35 knockout promotes macrophage differentiation, aggravates vascular dysfunction, and elevates blood pressure in angiotensin II-infused mice

AIMS

Numerous studies have demonstrated that inflammation is involved in the progression of hypertension. Inflammatory cytokines interleukin (IL)-12 and IL-35 belong to the IL-12 cytokine family and share the same IL-12p35 subunit. Accumulating evidence has demonstrated that IL-12p35 knockout (IL-12p35 KO) leads to cardiovascular disease by regulating the inflammatory response. This study aimed to investigate whether IL-12p35 KO elevates blood pressure in a hypertension mouse model.

METHODS AND RESULTS

Mice with angiotensin (Ang) II infusion showed marked aortic IL-12p35 expression; thus, aortic macrophages may be the main source of IL-12p35. Wild-type and IL-12p35 KO mice were infused with Ang II or saline. IL-12p35 KO promoted M1 macrophage differentiation, amplified the inflammatory response, aggravated vascular dysfunction, and elevated blood pressure in Ang II-treated mice. Then, some Ang II-infused mice were given phosphate buffer saline, mouse recombinant IL-12 (rIL-12), or rIL-35, and the results showed that rIL-12 but not rIL-35 treatment had an antihypertensive effect on Ang II-infused mice. In addition, detection of human plasma IL-12 levels in hypertensive patients and control subjects showed that IL-12 was significantly increased in hypertensive patients when compared with control subjects. In hypertensive patients, IL-12 levels were positively correlated with blood pressure.

CONCLUSION

IL-12p35 KO amplifies the inflammatory response and promotes blood pressure elevation in Ang II-treated mice. In addition, IL-12, but not IL-35, plays a protective role in the Ang II-induced hypertension model. Thus, IL-12 may be a novel therapeutic agent for the prevention and treatment of clinical hypertension.

Circulating anti-geronic factors from heterochonic parabionts promote vascular rejuvenation in aged mice: transcriptional footprint of mitochondrial protection, attenuation of oxidative stress, and rescue of endothelial function by young blood

Aging-induced functional and phenotypic alterations of the vasculature (e.g., endothelial dysfunction, oxidative stress) have a central role in morbidity and mortality of older adults. It has become apparent in recent years that cell autonomous mechanisms alone are inadequate to explain all aspects of vascular aging. The present study was designed to test the hypothesis that age-related changes in circulating anti-geronic factors contribute to the regulation of vascular aging processes in a non-cell autonomous manner. To test this hypothesis, through heterochronic parabiosis we determined the extent, if any, to which endothelial function, vascular production of ROS, and shifts in the vascular transcriptome (RNA-seq) are modulated by the systemic environment. We found that in aortas isolated from isochronic parabiont aged (20-month-old) C57BL/6 mice [A-(A); parabiosis for 8 weeks] acetylcholine-induced endothelium-dependent relaxation was impaired and ROS production (dihydroethidium fluorescence) was increased as compared with those in aortas from young isochronic parabiont (6-month-old) mice [Y-(Y)]. The presence of young blood derived from young parabionts significantly improved endothelium-dependent vasorelaxation and attenuated ROS production in vessels of heterochronic parabiont aged [A-(Y)] mice. In aortas derived from heterochronic parabiont young [Y-(A)] mice, acetylcholine-induced relaxation and ROS production were comparable with those in aortas derived from Y-(Y) mice. Using RNA-seq we assessed transcriptomic changes in the aortic arch associated with aging and heterochronic parabiosis. We identified 347 differentially expressed genes in A-(A) animals compared with Y-(Y) controls. We have identified 212 discordant genes, whose expression levels differed in the aged phenotype, but have shifted back toward the young phenotype by the presence of young blood in aged A-(Y) animals. Pathway analysis shows that vascular protective effects mediated by young blood-regulated genes include mitochondrial rejuvenation. In conclusion, a relatively short-term exposure to young blood can rescue vascular aging phenotypes, including attenuation of oxidative stress, mitochondrial rejuvenation, and improved endothelial function. Our findings provide additional evidence supporting the significant plasticity of vascular aging and evidence for the existence of anti-geronic factors capable of exerting rejuvenating effects on the aging vasculature.

Transcription factor TEAD1 is essential for vascular development by promoting vascular smooth muscle differentiation

TEAD1 (TEA domain transcription factor 1), a transcription factor known for the functional output of Hippo signaling, is important for tumorigenesis. However, the role of TEAD1 in the development of vascular smooth muscle cell (VSMC) is unknown. To investigate cell-specific role of Tead1, we generated cardiomyocyte (CMC) and VSMC-specific Tead1 knockout mice. We found CMC/VSMC-specific deletion of Tead1 led to embryonic lethality by E14.5 in mice due to hypoplastic cardiac and vascular walls, as a result of impaired CMC and VSMC proliferation. Whole transcriptome analysis revealed that deletion of Tead1 in CMCs/VSMCs downregulated expression of muscle contractile genes and key transcription factors including Pitx2c and myocardin. In vitro studies demonstrated that PITX2c and myocardin rescued TEAD1-dependent defects in VSMC differentiation. We further identified Pitx2c as a novel transcriptional target of TEAD1, and PITX2c exhibited functional synergy with myocardin by directly interacting with myocardin, leading to augment the differentiation of VSMC. In summary, our study reveals a critical role of Tead1 in cardiovascular development in mice, but also identifies a novel regulatory mechanism, whereby Tead1 functions upstream of the genetic regulatory hierarchy for establishing smooth muscle contractile phenotype.

gga-mir-133a-3p Regulates Myoblasts Proliferation and Differentiation by Targeting PRRX1

Non-coding RNAs play a regulatory role in the growth and development of skeletal muscle. Our previous study suggested that gga-mir-133a-3p was a potential candidate for regulating myoblast proliferation and differentiation in skeletal muscle. The purpose of our study was to reveal the regulatory mechanism of gga-mir-133a-3p in the proliferation and differentiation of chicken myoblasts. Through the detection of cell proliferation activity, cell cycle progression and EdU, we found that gga-mir-133a-3p can significantly inhibit the proliferation of myoblasts. In the process of myogenic differentiation, gga-mir-133a-3p is up-regulated, while gga-mir-133a-3p can significantly promote the up-regulation of differentiation-related muscle-derived factors, indicating that gga-mir-133a-3p can promote the differentiation of myoblasts. Validation at the transcriptional level and protein level proved that gga-mir-133a-3p can inhibit the expression of PRRX1, and the dual-luciferase assay also showed their direct targeting relationship. Correspondingly, PRRX1 can significantly promote myoblast proliferation and inhibit myoblast differentiation. In our study, we confirmed that gga-mir-133a-3p participates in the regulation of proliferation and differentiation of myoblasts by targeting PRRX1.

Lineage dynamics of murine pancreatic development at single-cell resolution

Organogenesis requires the complex interactions of multiple cell lineages that coordinate their expansion, differentiation, and maturation over time. Here, we profile the cell types within the epithelial and mesenchymal compartments of the murine pancreas across developmental time using a combination of single-cell RNA sequencing, immunofluorescence, in situ hybridization, and genetic lineage tracing. We identify previously underappreciated cellular heterogeneity of the developing mesenchyme and reconstruct potential lineage relationships among the pancreatic mesothelium and mesenchymal cell types. Within the epithelium, we find a previously undescribed endocrine progenitor population, as well as an analogous population in both human fetal tissue and human embryonic stem cells differentiating toward a pancreatic beta cell fate. Further, we identify candidate transcriptional regulators along the differentiation trajectory of this population toward the alpha or beta cell lineages. This work establishes a roadmap of pancreatic development and demonstrates the broad utility of this approach for understanding lineage dynamics in developing organs.

Coordinated proliferation and differentiation of diverse cell populations drive pancreatic epithelial and mesenchymal development. Here, the authors profile cell type dynamics in the developing mouse pancreas using single-cell RNA sequencing, identifying mesenchymal subtypes and undescribed endocrine progenitors.

microRNA-21 and hypertension

Hypertension, a multifactorial disease, is a major risk factor for the development of stroke, coronary artery disease, heart failure, and chronic renal failure. However, its underlying cellular and molecular mechanisms remain largely elusive. Numerous studies have shown that microRNAs (miRNAs) are involved in a variety of cellular processes, including cellular proliferation, apoptosis, differentiation, and the development of diseases. microRNA-21 (miR-21), a conserved single-stranded non-coding RNA that is composed of approximately 22 nucleotides, is one of the most intensively studied miRNAs in recent years, and it can regulate gene expression at the post-transcriptional level. miR-21 is expressed in many kinds of tumors and in the cardiovascular system, and it plays an important role in the occurrence and development of cardiovascular diseases. In recent years, more and more evidence indicates that miR-21 plays an important role in hypertension. This article reviews the source, function, and altered levels of miR-21 in hypertension and the role of miR-21 in the pathogenesis of hypertension and target organ damage (TOD). The potential role of miR-21 as a new target for predicting and treating hypertension is also explored.

Arterial smooth muscle dynamics in development and repair

Arterial vasculature distributes blood from early embryonic development and provides a nutrient highway to maintain tissue viability. Atherosclerosis, peripheral artery diseases, stroke and aortic aneurysm represent the most frequent causes of death and are all directly related to abnormalities in the function of arteries. Vascular intervention techniques have been established for the treatment of all of these pathologies, yet arterial surgery can itself lead to biological changes in which uncontrolled arterial wall cell proliferation leads to restricted blood flow. In this review we describe the intricate cellular composition of arteries, demonstrating how a variety of distinct cell types in the vascular walls regulate the function of arteries. We provide an overview of the developmental origin of arteries and perivascular cells and focus on cellular dynamics in arterial repair. We summarize the current knowledge of the molecular signaling pathways that regulate vascular smooth muscle differentiation in the embryo and in arterial injury response. Our review aims to highlight the similarities as well as differences between cellular and molecular mechanisms that control arterial development and repair.

Myocardial transcription factors in diastolic dysfunction: clues for model systems and disease

There are multiple intrinsic mechanisms for diastolic dysfunction ranging from molecular to structural derangements in ventricular myocardium. The molecular mechanisms regulating the progression from normal diastolic function to severe dysfunction still remain poorly understood. Recent studies suggest a potentially important role of core cardio-enriched transcription factors (TFs) in the control of cardiac diastolic function in health and disease through their ability to regulate the expression of target genes involved in the process of adaptive and maladaptive cardiac remodeling. The current relevant findings on the role of a variety of such TFs (TBX5, GATA-4/6, SRF, MYOCD, NRF2, and PITX2) in cardiac diastolic dysfunction and failure are updated, emphasizing their potential as promising targets for novel treatment strategies. In turn, the new animal models described here will be key tools in determining the underlying molecular mechanisms of disease. Since diastolic dysfunction is regulated by various TFs, which are also involved in cross talk with each other, there is a need for more in-depth research from a biomedical perspective in order to establish efficient therapeutic strategies.

Smooth Muscle-Selective Nuclear Factor-κB Inhibition Reduces Phosphate-Induced Arterial Medial Calcification in Mice With Chronic Kidney Disease

Background

Hyperphosphatemia is a major factor promoting the formation of arterial medial calcification in chronic kidney disease (CKD). However, arterial medial calcification begins to occur during the early stages of CKD, when hyperphosphatemia is not yet apparent. It is predicted that other factors also play a role. The aim of the present study was to determine the role of pro‐inflammatory nuclear factor‐κB (NF‐κB) signaling in smooth muscle cells (SMCs) for phosphate‐induced arterial medial calcification in CKD mice.

Methods and Results

We first sought to establish a novel mouse model of CKD with arterial medial calcification. CKD was induced in DBA/2 mice by feeding them a low concentration of adenine, and these mice were fed a normal or high‐phosphorus diet. Severe calcification was seen in CKD mice fed the high‐phosphorus diet, while it was undetectable in CKD mice fed the normal phosphorus diet or control mice fed the high‐phosphorus diet. Arterial medial calcification was accompanied by phenotypic switching of SMCs into osteogenic cells. Interestingly, NF‐κB inhibitors, tempol and triptolide, both reduced arterial medial calcification in CKD mice fed the high‐phosphorus diet. Moreover, formation of arterial medial calcification, as well as SMC phenotypic switching, was also markedly attenuated in transgenic mice, in which the NF‐κB activity was inhibited selectively in SMCs. Mechanistic studies revealed that Krüppel‐like factor 4 was involved in NF‐κB‐induced SMC phenotypic switching and calcification.

Conclusions

Results of the present studies suggest that the NF‐κB signaling in SMCs plays an important role in high phosphate‐induced arterial medial calcification in CKD.

Gene expression profiles and signaling mechanisms in α2B-adrenoceptor-evoked proliferation of vascular smooth muscle cells

BACKGROUND

α2-adrenoceptors are important regulators of vascular tone and blood pressure. Regulation of cell proliferation is a less well investigated consequence of α2-adrenoceptor activation. We have previously shown that α2B-adrenoceptor activation stimulates proliferation of vascular smooth muscle cells (VSMCs). This may be important for blood vessel development and plasticity and for the pathology and therapeutics of cardiovascular disorders. The underlying cellular mechanisms have remained mostly unknown. This study explored pathways of regulation of gene expression and intracellular signaling related to α2B-adrenoceptor-evoked VSMC proliferation.

RESULTS

The cellular mechanisms and signaling pathways of α2B-adrenoceptor-evoked proliferation of VSMCs are complex and include redundancy. Functional enrichment analysis and pathway analysis identified differentially expressed genes associated with α2B-adrenoceptor-regulated VSMC proliferation. They included the upregulated genes Egr1, F3, Ptgs2 and Serpine1 and the downregulated genes Cx3cl1, Cav1, Rhoa, Nppb and Prrx1. The most highly upregulated gene, Lypd8, represents a novel finding in the VSMC context. Inhibitor library screening and kinase activity profiling were applied to identify kinases in the involved signaling pathways. Putative upstream kinases identified by two different screens included PKC, Raf-1, Src, the MAP kinases p38 and JNK and the receptor tyrosine kinases EGFR and HGF/HGFR. As a novel finding, the Src family kinase Lyn was also identified as a putative upstream kinase.

CONCLUSIONS

α2B-adrenoceptors may mediate their pro-proliferative effects in VSMCs by promoting the activity of bFGF and PDGF and the growth factor receptors EGFR, HGFR and VEGFR-1/2. The Src family kinase Lyn was also identified as a putative upstream kinase. Lyn is known to be expressed in VSMCs and has been identified as an important regulator of GPCR trafficking and GPCR effects on cell proliferation. Identified Ser/Thr kinases included several PKC isoforms and the β-adrenoceptor kinases 1 and 2. Cross-talk between the signaling mechanisms involved in α2B-adrenoceptor-evoked VSMC proliferation thus appears to involve PKC activation, subsequent changes in gene expression, transactivation of EGFR, and modulation of kinase activities and growth factor-mediated signaling. While many of the identified individual signals were relatively small in terms of effect size, many of them were validated by combining pathway analysis and our integrated screening approach.

Benzyl butyl phthalate decreases myogenic differentiation of endometrial mesenchymal stem/stromal cells through miR-137-mediated regulation of PITX2

Phthalate, an environmental toxin, has been considered as an endocrine-disrupting chemical. Growing evidence has demonstrated links between endocrine-disrupting chemicals, tissue development, and reproductive physiology, but the mechanisms of gene expression regulation by environmental factors that affect cell differentiation are unclear. Herein, we investigated the effects of butyl benzyl phthalate (BBP) on human endometrial mesenchymal stem/stromal cell (EN-MSC) differentiation and identified a novel signaling pathway. Differentiation of endometrial mesenchymal stem/stromal cells decreased after administration of BBP. We analyzed BBP regulation of gene expression in EN-MSC using cDNA microarrays and Ingenuity Pathway Analysis software to identify affected target genes and their biological functions. PITX2 emerged as a common gene hit from separate screens targeting skeletal and muscular disorders, cell morphology, and tissue development. BBP decreased transcription of PITX2 and elevated expression of the microRNA miR-137, the predicted upstream negative regulator of PITX2. These data indicated that BBP affects PITX2 expression through miR-137 targeting of the 3' untranslated region of PITX2 mRNA. PITX2 down-regulation also decreased MyoD transcript levels in EN-MSC. Our results demonstrate that BBP decreases EN-MSC myogenic differentiation through up-regulation of miR-137, contribute to our understanding of EN-MSC differentiation, and underline the hazardous potential of environmental hormones.

Neonatal vascularization and oxygen tension regulate appropriate perinatal renal medulla/papilla maturation

Congenital medullary dysplasia with obstructive nephropathy is a common congenital disorder observed in paediatric patients and represents the foremost cause of renal failure. However, the molecular processes regulating normal papillary outgrowth during the postnatal period are unclear. In this study, transcriptional profiling of the renal medulla across postnatal development revealed enrichment of non-canonical Wnt signalling, vascular development, and planar cell polarity genes, all of which may contribute to perinatal medulla/papilla maturation. These pathways were investigated in a model of papillary hypoplasia with functional obstruction, the Crim1(KST264/KST264) transgenic mouse. Postnatal elongation of the renal papilla via convergent extension was unaffected in the Crim1(KST264/KST264) hypoplastic renal papilla. In contrast, these mice displayed a disorganized papillary vascular network, tissue hypoxia, and elevated Vegfa expression. In addition, we demonstrate the involvement of accompanying systemic hypoxia arising from placental insufficiency, in appropriate papillary maturation. In conclusion, this study highlights the requirement for normal vascular development in collecting duct patterning, development of appropriate nephron architecture, and perinatal papillary maturation, such that disturbances contribute to obstructive nephropathy.

Role played by Prx1-dependent extracellular matrix properties in vascular smooth muscle development in embryonic lungs

Although there are many studies focusing on the molecular pathways underlying lung vascular morphogenesis, the extracellular matrix (ECM)-dependent regulation of mesenchymal cell differentiation in vascular smooth muscle development needs better understanding. In this study, we demonstrate that the paired related homeobox gene transcription factor Prx1 maintains the elastic ECM properties, which are essential for vascular smooth muscle precursor cell differentiation. We have found that Prx1(null) mouse lungs exhibit defective vascular smooth muscle development, downregulated elastic ECM expression, and compromised transforming growth factor (TGF)-β localization and signaling. Further characterization of ECM properties using decellularized lung ECM scaffolds derived from Prx1 mice demonstrated that Prx1 is required to maintain lung ECM stiffness. The results of cell culture using stiffness-controlled 2-D and 3-D synthetic substrates confirmed that Prx1-dependent ECM stiffness is essential for promotion of smooth muscle precursor differentiation for effective TGF-β stimulation. Supporting these results, both decellularized Prx1(null) lung ECM and Prx1(WT) (wild type) ECM scaffolds with blocked TGF-β failed to support mesenchymal cell to 3-D smooth muscle cell differentiation. These results suggest a novel ECM-dependent regulatory pathway of lung vascular development wherein Prx1 regulates lung vascular smooth muscle precursor development by coordinating the ECM biophysical and biochemical properties.

Origin and differentiation of vascular smooth muscle cells

Vascular smooth muscle cells (SMCs), a major structural component of the vessel wall, not only play a key role in maintaining vascular structure but also perform various functions. During embryogenesis, SMC recruitment from their progenitors is an important step in the formation of the embryonic vascular system. SMCs in the arterial wall are mostly quiescent but can display a contractile phenotype in adults. Under pathophysiological conditions, i.e. vascular remodelling after endothelial dysfunction or damage, contractile SMCs found in the media switch to a secretory type, which will facilitate their ability to migrate to the intima and proliferate to contribute to neointimal lesions. However, recent evidence suggests that the mobilization and recruitment of abundant stem/progenitor cells present in the vessel wall are largely responsible for SMC accumulation in the intima during vascular remodelling such as neointimal hyperplasia and arteriosclerosis. Therefore, understanding the regulatory mechanisms that control SMC differentiation from vascular progenitors is essential for exploring therapeutic targets for potential clinical applications. In this article, we review the origin and differentiation of SMCs from stem/progenitor cells during cardiovascular development and in the adult, highlighting the environmental cues and signalling pathways that control phenotypic modulation within the vasculature.

Deletion of yes-associated protein (YAP) specifically in cardiac and vascular smooth muscle cells reveals a crucial role for YAP in mouse cardiovascular development

RATIONALE

Our previous study has shown that yes-associated protein (YAP) plays a crucial role in the phenotypic modulation of vascular smooth muscle cells (SMCs) in response to arterial injury. However, the role of YAP in vascular SMC development is unknown.

OBJECTIVE

The goal of this study was to investigate the functional role of YAP in cardiovascular development in mice and determine the mechanisms underlying YAP's actions.

METHODS AND RESULTS

YAP was deleted in cardiomyocytes and vascular SMCs by crossing YAP flox mice with SM22α-Cre transgenic mice. Cardiac/SMC-specific deletion of YAP directed by SM22α-Cre resulted in perinatal lethality in mice because of profound cardiac defects including hypoplastic myocardium, membranous ventricular septal defect, and double outlet right ventricle. The cardiac/SMC-specific YAP knockout mice also displayed severe vascular abnormalities including hypoplastic arterial wall, short/absent brachiocephalic artery, and retroesophageal right subclavian artery. Deletion of YAP in mouse vascular SMCs induced expression of a subset of cell cycle arrest genes including G-protein-coupled receptor 132 (Gpr132). Silencing Gpr132 promoted SMC proliferation, whereas overexpression of Gpr132 attenuated SMC growth by arresting cell cycle in G0/G1 phase, suggesting that ablation of YAP-induced impairment of SMC proliferation was mediated, at least in part, by induction of Gpr132 expression. Mechanistically, YAP recruited the epigenetic repressor histone deacetylase-4 to suppress Gpr132 gene expression via a muscle CAT element in the Gpr132 gene.

CONCLUSIONS

YAP plays a critical role in cardiac/SMC proliferation during cardiovascular development by epigenetically regulating expression of a set of cell cycle suppressors.

Deletion of Krüppel-like factor 4 in endothelial and hematopoietic cells enhances neointimal formation following vascular injury

Background

Krüppel‐like factor 4 (Klf4) is involved in a variety of cellular functions by activating or repressing the transcription of multiple genes. Results of previous studies showed that tamoxifen‐inducible global deletion of the Klf4 gene in mice accelerated neointimal formation following vascular injury, in part via enhanced proliferation of smooth muscle cells (SMCs). Because Klf4 is also expressed in non‐SMCs including endothelial cells (ECs), we determined if Tie2 promoter‐dependent deletion of Klf4 in ECs and hematopoietic cells affected injury‐induced neointimal formation.

Methods and Results

Klf4 conditional knockout (cKO) mice were generated by breeding Tie2‐Cre mice and Klf4 floxed mice, and their phenotype was analyzed after carotid ligation injury. Results showed that injury‐induced repression of SMC differentiation markers was unaffected by Tie2 promoter‐dependent Klf4 deletion. However, of interest, neointimal formation was significantly enhanced in Klf4‐cKO mice 21 days following carotid injury. Moreover, Klf4‐cKO mice exhibited an augmented proliferation rate, enhanced accumulation of macrophages and T lymphocytes, and elevated expression of cell adhesion molecules including vascular cell adhesion molecule–1 (Vcam1) and E‐selectin in injured arteries. Mechanistic analyses in cultured ECs revealed that Klf4 inhibited tumor necrosis factor‐α–induced expression of Vcam1 through blocking the binding of nuclear factor‐κB to the Vcam1 promoter.

Conclusions

These results provide evidence that Klf4 in non‐SMCs such as ECs regulates neointimal formation by repressing arterial inflammation following vascular injury.

Smooth muscle-selective inhibition of nuclear factor-κB attenuates smooth muscle phenotypic switching and neointima formation following vascular injury

BACKGROUND

Vascular proliferative diseases such as atherosclerosis are inflammatory disorders involving multiple cell types including macrophages, lymphocytes, endothelial cells, and smooth muscle cells (SMCs). Although activation of the nuclear factor-κB (NF-κB) pathway in vessels has been shown to be critical for the progression of vascular diseases, the cell-autonomous role of NF-κB within SMCs has not been fully understood.

METHODS AND RESULTS

We generated SMC-selective truncated IκB expressing (SM22α-Cre/IκBΔN) mice, in which NF-κB was inhibited selectively in SMCs, and analyzed their phenotype following carotid injury. Results showed that neointima formation was markedly reduced in SM22α-Cre/IκBΔN mice after injury. Although vascular injury induced downregulation of expression of SMC differentiation markers and myocardin, a potent activator of SMC differentiation markers, repression of these markers and myocardin was attenuated in SM22α-Cre/IκBΔN mice. Consistent with these findings, NF-κB activation by interleukin-1β (IL-1β) decreased expression of SMC differentiation markers as well as myocardin in cultured SMCs. Inhibition of NF-κB signaling by BAY 11-7082 attenuated repressive effects of IL-1β. Of interest, Krüppel-like factor 4 (Klf4), a transcription factor critical for regulating SMC differentiation and proliferation, was also involved in IL-1β-mediated myocardin repression. Promoter analyses and chromatin immunoprecipitation assays revealed that NF-κB repressed myocardin by binding to the myocardin promoter region in concert with Klf4.

CONCLUSIONS

These results provide novel evidence that activation of the NF-κB pathway cell-autonomously mediates SMC phenotypic switching and contributes to neointima formation following vascular injury.

Prevention of alveolar destruction and airspace enlargement in a mouse model of pulmonary lymphangioleiomyomatosis (LAM)

Pulmonary lymphangioleiomyomatosis (LAM) is a rare genetic disease characterized by neoplastic growth of atypical smooth muscle-like LAM cells, destruction of lung parenchyma, obstruction of lymphatics, and formation of lung cysts, leading to spontaneous pneumothoraces (lung rupture and collapse) and progressive loss of pulmonary function. The disease is caused by mutational inactivation of the tumor suppressor gene tuberous sclerosis complex 1 (TSC1) or TSC2. By injecting TSC2-null cells into nude mice, we have developed a mouse model of LAM that is characterized by multiple random TSC2-null lung lesions, vascular endothelial growth factor-D expression, lymphangiogenesis, destruction of lung parenchyma, and decreased survival, similar to human LAM. The mice show enlargement of alveolar airspaces that is associated with progressive growth of TSC2-null lesions in the lung, up-regulation of proinflammatory cytokines and matrix metalloproteinases (MMPs) that degrade extracellular matrix, and destruction of elastic fibers. TSC2-null lesions and alveolar destruction were differentially inhibited by the macrolide antibiotic rapamycin (which inhibits TSC2-null lesion growth by a cytostatic mechanism) and a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, simvastatin (which inhibits growth of TSC2-null lesions by a predominantly proapoptotic mechanism). Treatment with simvastatin markedly inhibited MMP-2, MMP-3, and MMP-9 levels in lung and prevented alveolar destruction. The combination of rapamycin and simvastatin prevented both growth of TSC2-null lesions and lung destruction by inhibiting MMP-2, MMP-3, and MMP-9. Our findings demonstrate a mechanistic link between loss of TSC2 and alveolar destruction and suggest that treatment with rapamycin and simvastatin together could benefit patients with LAM by targeting cells with TSC2 dysfunction and preventing airspace enlargement.

Mitogen-activated protein kinase 14 is a novel negative regulatory switch for the vascular smooth muscle cell contractile gene program

OBJECTIVE

Several studies have shown through chemical inhibitors that p38 mitogen-activated protein kinase (MAPK) promotes vascular smooth muscle cell (VSMC) differentiation. Here, we evaluate the effects of knocking down a dominant p38MAPK isoform on VSMC differentiation.

METHODS AND RESULTS

Knockdown of p38MAPKα (MAPK14) in human coronary artery SMCs unexpectedly increases VSMC differentiation genes, such as miR145, ACTA2, CNN1, LMOD1, and TAGLN, with little change in the expression of serum response factor (SRF) and 2 SRF cofactors, myocardin (MYOCD) and myocardin-related transcription factor A (MKL1). A variety of chemical and biological inhibitors demonstrate a critical role for a RhoA-MKL1-SRF-dependent pathway in mediating these effects. MAPK14 knockdown promotes MKL1 nuclear localization and VSMC marker expression, an effect partially reversed with Y27632; in contrast, MAP2K6 (MKK6) blocks MKL1 nuclear import and VSMC marker expression. Immunostaining and Western blotting of injured mouse carotid arteries reveal elevated MAPK14 (both total and phosphorylated) and reduced VSMC marker expression.

CONCLUSIONS

Reduced MAPK14 expression evokes unanticipated increases in VSMC contractile genes, suggesting an unrecognized negative regulatory role for MAPK14 signaling in VSMC differentiation.

TGFβ1-induced Baf60c regulates both smooth muscle cell commitment and quiescence

Smooth muscle cells (SMCs) play critical roles in a number of diseases; however, the molecular mechanism underlying their development is unclear. Although the role of TGFβ1 signaling in SMC development is well established, the downstream molecular signals are not fully understood. We used several rat multipotent adult progenitor cell ((r)MAPC) lines that express levels of Oct4 mRNA similar to hypoblast stem cells (HypoSC), and can differentiate robustly to mesodermal and endodermal cell types. TGFβ1 alone, or with PDGF-BB, induces differentiation of rMAPCs to SMCs, which expressed structural SMC proteins, including α-smooth muscle actin (αSMA), and contribute to the SMC coat of blood vessels in vivo. A genome-wide time-course transcriptome analysis revealed that transcripts of Baf60c, part of the SWI/SNF actin binding chromatin remodeling complex D-3 (SMARCD3/BAF60c), were significantly induced during MAPC-SMC differentiation. We demonstrated that BAF60c is a necessary co-regulator of TGFβ1 mediated induction of SMC genes. Knock-down of Baf60c decreased SMC gene expression in rMAPCs whereas ectopic expression of Baf60c was sufficient to commit rMAPCs to SMCs in the absence of exogenous cytokines. TGFβ1 activates Baf60c via the direct binding of SMAD2/3 complexes to the Baf60c promoter region. Chromatin- and co-immunoprecipitation studies demonstrated that regulation of SMC genes by BAF60c is mediated via interaction with SRF binding CArG box-containing promoter elements in SMC genes. We noted that compared with TGFβ1, Baf60c overexpression in rMAPC yielded SMC with a more immature phenotype. Similarly, Baf60c induced an immature phenotype in rat aortic SMCs marked by increased cell proliferation and decreased contractile marker expression. Thus, Baf60c is important for TGFβ-mediated commitment of primitive stem cells (rMAPCs) to SMCs and is associated with induction of a proliferative state of quiescent SMCs. The MAPC-SMC differentiation system may be useful for identification of additional critical (co-)regulators of SMC development.

Kruppel-like factor 4 contributes to high phosphate-induced phenotypic switching of vascular smooth muscle cells into osteogenic cells

Hyperphosphatemia in chronic kidney disease is highly associated with vascular calcification. Previous studies have shown that high phosphate-induced phenotypic switching of vascular smooth muscle cells (SMCs) into osteogenic cells plays an important role in the calcification process. In the present study, we determined whether Krüppel-like factor 4 (Klf4) and phosphorylated Elk-1, transcriptional repressors of SMC differentiation marker genes activated by intimal atherogenic stimuli, contributed to this process. Rat aortic SMCs were cultured in the medium with normal (0.9 mmol/liter) or high (4.5 mmol/liter) phosphate concentration. Results showed that high phosphate concentration induced SMC calcification. Moreover, high phosphate decreased expression of SMC differentiation marker genes including smooth muscle α-actin and SM22α, whereas it increased expression of osteogenic genes, such as Runx2 and osteopontin. High phosphate also induced Klf4 expression, although it did not phosphorylate Elk-1. In response to high phosphate, Klf4 selectively bound to the promoter regions of SMC differentiation marker genes. Of importance, siRNA-mediated knockdown of Klf4 blunted high phosphate-induced suppression of SMC differentiation marker genes, as well as increases in expression of osteogenic genes and calcium deposition. Klf4 was also induced markedly in the calcified aorta of adenine-induced uremic rats. Results provide novel evidence that Klf4 mediates high phosphate-induced conversion of SMCs into osteogenic cells.

Statins promote the regression of atherosclerosis via activation of the CCR7-dependent emigration pathway in macrophages

HMG-CoA reductase inhibitors (statins) decrease atherosclerosis by lowering low-density-lipoprotein cholesterol. Statins are also thought to have additional anti-atherogenic properties, yet defining these non-conventional modes of statin action remains incomplete. We have previously developed a novel mouse transplant model of atherosclerosis regression in which aortic segments from diseased donors are placed into normolipidemic recipients. With this model, we demonstrated the rapid loss of CD68+ cells (mainly macrophages) in plaques through the induction of a chemokine receptor CCR7-dependent emigration process. Because the human and mouse CCR7 promoter contain Sterol Response Elements (SREs), we hypothesized that Sterol Regulatory Element Binding Proteins (SREBPs) are involved in increasing CCR7 expression and through this mechanism, statins would promote CD68+ cell emigration from plaques. We examined whether statin activation of the SREBP pathway in vivo would induce CCR7 expression and promote macrophage emigration from plaques. We found that western diet-fed apoE^-/- mice treated with either atorvastatin or rosuvastatin led to a substantial reduction in the CD68+ cell content in the plaques despite continued hyperlipidemia. We also observed a significant increase in CCR7 mRNA in CD68+ cells from both the atorvastatin and rosuvastatin treated mice associated with emigration of CD68+ cells from plaques. Importantly, CCR7^-/-/apoE^-/- double knockout mice failed to display a reduction in CD68+ cell content upon statin treatment. Statins also affected the recruitment of transcriptional regulatory proteins and the organization of the chromatin at the CCR7 promoter to increase the transcriptional activity. Statins promote the beneficial remodeling of plaques in diseased mouse arteries through the stimulation of the CCR7 emigration pathway in macrophages. Therefore, statins may exhibit some of their clinical benefits by not only retarding the progression of atherosclerosis, but also accelerating its regression.

Smooth muscle cell differentiation in vitro: models and underlying molecular mechanisms

Development of in vitro models by which to study smooth muscle cell (SMC) differentiation has been hindered by some peculiarities intrinsic to these cells, namely their different embryological origins and their ability to undergo phenotypic modulation in cell culture. Although many in vitro models are available for studying SMC differentiation, careful consideration should be taken so that the model chosen fits the questions being posed. In this review, we summarize several well-established in vitro models available to study SMC differentiation from stem cells and outline novel mechanisms recently identified as underlying SMC differentiation programs.

WD repeat-containing protein 5, a ubiquitously expressed histone methyltransferase adaptor protein, regulates smooth muscle cell-selective gene activation through interaction with pituitary homeobox 2

WD repeat-containing protein 5 (WDR5) is a common component of mammalian mixed lineage leukemia methyltransferase family members and is important for histone H3 lysine 4 methylation (H3K4me), which has been implicated in control of activation of cell lineage genes during embryogenesis. However, WDR5 has not been considered to play a specific regulatory role in epigenetic programming of cell lineage because it is ubiquitously expressed. Previous work from our laboratory showed the appearance of histone H3K4me within smooth muscle cell (SMC)-marker gene promoters during the early stages of development of SMC from multipotential embryonic cells but did not elucidate the underlying mechanisms that mediate SMC-specific and locus-selective H3K4me. Results presented herein show that knockdown of WDR5 significantly decreased SMC-marker gene expression in cultured SMC differentiation systems and in Xenopus laevis embryos in vivo. In addition, we showed that WDR5 complexes within SMC progenitor cells contained H3K4 methyltransferase enzymatic activity and that knockdown of WDR5 selectively decreased H3K4me1 and H3K4me3 enrichment within SMC-marker gene promoter loci. Moreover, we present evidence that it is recruited to these gene promoter loci through interaction with a SMC-selective pituitary homeobox 2 (Pitx2). Taken together, studies provide evidence for a novel mechanism for epigenetic control of SMC-marker gene expression during development through interaction of WDR5, homeodomain proteins, and chromatin remodeling enzymes.

Vascular smooth muscle progenitor cells: building and repairing blood vessels

Molecular pathways that control the specification, migration, and number of available smooth muscle progenitor cells play key roles in determining blood vessel size and structure, capacity for tissue repair, and progression of age-related disorders. Defects in these pathways produce malformations of developing blood vessels, depletion of smooth muscle progenitor cell pools for vessel wall maintenance and repair, and aberrant activation of alternative differentiation pathways in vascular disease. A better understanding of the molecular mechanisms that uniquely specify and maintain vascular smooth muscle cell precursors is essential if we are to use advances in stem and progenitor cell biology and somatic cell reprogramming for applications directed to the vessel wall.

Myocardin is differentially required for the development of smooth muscle cells and cardiomyocytes

Myocardin is a serum response factor (SRF) coactivator exclusively expressed in cardiomyocytes and smooth muscle cells (SMCs). However, there is highly controversial evidence as to whether myocardin is essential for normal differentiation of these cell types, and there are no data showing whether cardiac or SMC subtypes exhibit differential myocardin requirements during development. Results of the present studies showed the virtual absence of myocardin(-/-) visceral SMCs or ventricular myocytes in chimeric myocardin knockout (KO) mice generated by injection of myocardin(-/-) embryonic stem cells (ESCs) into wild-type (WT; i.e., myocardin(+/+) ESC) blastocysts. In contrast, myocardin(-/-) ESCs readily formed vascular SMC, albeit at a reduced frequency compared with WT ESCs. In addition, myocardin(-/-) ESCs competed equally with WT ESCs in forming atrial myocytes. The ultrastructural features of myocardin(-/-) vascular SMCs and cardiomyocytes were unchanged from their WT counterparts as determined using a unique X-ray microprobe transmission electron microscopic method developed by our laboratory. Myocardin(-/-) ESC-derived SMCs also showed normal contractile properties in an in vitro embryoid body SMC differentiation model, other than impaired thromboxane A2 responsiveness. Together, these results provide novel evidence that myocardin is essential for development of visceral SMCs and ventricular myocytes but is dispensable for development of atrial myocytes and vascular SMCs in the setting of chimeric KO mice. In addition, results suggest that as yet undefined defects in development and/or maturation of ventricular cardiomyocytes may have contributed to early embryonic lethality observed in conventional myocardin KO mice and that observed deficiencies in development of vascular SMC may have been secondary to these defects.

Expression of paired-like homeodomain transcription factor 2c (PITX2c) in epidermal keratinocytes

Paired-like homeodomain transcription factor 2 (PITX2) has been implicated as one of the genes responsible for Rieger syndrome. It has been also shown to play a central role during development. In this study, we investigated the functional role of PITX2 in keratinocyte differentiation. RT-PCR analysis showed that PITX2c isoform was predominantly expressed in a differentiation-dependent manner. Consistent with, immunohistochemical staining showed that PITX2 expression was increased in the upper layer of epidermis. When PITX2c was overexpressed in cultured keratinocytes by a recombinant adenovirus, the differentiation markers such as involucrin and loricrin were significantly increased at both mRNA and protein levels. In addition, PITX2c overexpression led to the decrease of cell growth, concomitantly with the upregulation of cell cycle-related genes p21. To investigate the effect of PITX2c in vivo, we microinjected PITX2c expression vector into zebrafish embryo. Interestingly, overexpression of PITX2c in zebrafish embryo led to the formation of horn-like structure and thickening of epidermis, together with the increase of keratin 8 (K8) expression. These results suggest that PITX2c has a role in proliferation and differentiation of epidermal keratinocytes.

Pitx2 defines alternate pathways acting through MyoD during limb and somitic myogenesis

The MyoD gene is part of the core regulatory network that governs skeletal myogenesis and acts as an essential determinant of the myogenic cell fate. Although generic regulatory networks converging on this gene have been described, the specific mechanisms leading to MyoD expression in muscles of different ontology remain misunderstood. We now show that the homeobox gene Pitx2 is required for initial activation of the MyoD gene in limb muscle precursors through direct binding of Pitx2 to the MyoD core enhancer. Whereas Myf5 and Mrf4 are dispensable for limb muscle progenitor fate, inactivation of Myf5 and Mrf4 in Pitx2 mutants results in a drastic decrease of limb MyoD expression. Thus, Pitx2 and Myf5 define parallel genetic pathways for limb myogenesis. We show a similar dependence on Pitx2 and Myf5(Mrf4) in myotome, where MyoD expression is initially activated by Myf5 and Mrf4. In their absence, MyoD expression is eventually rescued by a Pax3-dependent mechanism. We now provide evidence that Pitx2 contributes to the rescue of MyoD expression and that it acts downstream of Pax3. We thus propose that myogenic differentiation of somite-derived muscle cells relies on two parallel genetic pathways, with the Pitx2 pathway being of primary importance for limb myogenesis but the Myf5 and Mrf4 pathway predominating in myotome. Muscle-specific wiring of regulatory networks composed of similar transcription factors thus underlies development of distinct skeletal muscles.

The actin associated protein palladin is important for the early smooth muscle cell differentiation

Palladin, an actin associated protein, plays a significant role in regulating cell adhesion and cell motility. Palladin is important for development, as knockdown in mice is embryonic lethal, yet its role in the development of the vasculature is unknown. We have shown that palladin is essential for the expression of smooth muscle cells (SMC) marker genes and force development in response to agonist stimulation in palladin deficient SMCs. The goal of the study was to determine the molecular mechanisms underlying palladin's ability to regulate the expression of SMC marker genes. Results showed that palladin expression was rapidly induced in an A404 cell line upon retinoic acid (RA) induced differentiation. Suppression of palladin expression with siRNAs inhibited the expression of RA induced SMC differentiation genes, SM α-actin (SMA) and SM22, whereas over-expression of palladin induced SMC gene expression. Chromatin immunoprecipitation assays provided evidence that palladin bound to SMC genes, whereas co-immunoprecipitation assays also showed binding of palladin to myocardin related transcription factors (MRTFs). Endogenous palladin was imaged in the nucleus, increased with leptomycin treatment and the carboxyl-termini of palladin co-localized with MRTFs in the nucleus. Results support a model wherein palladin contributes to SMC differentiation through regulation of CArG-SRF-MRTF dependent transcription of SMC marker genes and as previously published, also through actin dynamics. Finally, in E11.5 palladin null mouse embryos, the expression of SMA and SM22 mRNA and protein is decreased in the vessel wall. Taken together, our findings suggest that palladin plays a key role in the differentiation of SMCs in the developing vasculature.

Role of histone acetylation in cell physiology and diseases: An update

Although the role of histone acetylation in gene regulation has been the subject of many reviews, their impact on cell physiology and pathological states of proliferation, differentiation and genome stability in eukaryotic cells remain to be elucidated. Therefore, this review will discuss the molecular, physiological and biochemical aspects of histone acetylation and focus on the interplay of histone acetyltransferases (HATs) and histone deacetylases (HDACs) in different disease states. Current treatment strategies are mostly limited to enzyme inhibitors, though potential lies in targeting other imperative chromatin remodeling factors involved in gene regulation.

Smooth and cardiac muscle-selective knock-out of Kruppel-like factor 4 causes postnatal death and growth retardation

Krüppel-like factor 4 (Klf4) is a transcription factor involved in differentiation and proliferation in multiple tissues. We demonstrated previously that tamoxifen-induced deletion of the Klf4 gene in mice accelerated neointimal formation but delayed down-regulation of smooth muscle cell differentiation markers in carotid arteries following injury. To further determine the role of Klf4 in the cardiovascular system, we herein derived mice deficient for the Klf4 gene in smooth and cardiac muscle using the SM22alpha promoter (SM22alpha-CreKI(+)/Klf4(loxP/loxP) mice). SM22alpha-CreKI(+)/Klf4(loxP/loxP) mice were born at the expected Mendelian ratio, but they gradually died after birth. Although approximately 40% of SM22alpha-CreKI(+)/Klf4(loxP/loxP) mice survived beyond postnatal day 28, they exhibited marked growth retardation. In wild-type mice, Klf4 was expressed in the heart from late embryonic development through adulthood, whereas it was not expressed in smooth muscle. No changes were observed in morphology or expression of smooth muscle cell differentiation markers in vessels of SM22alpha-CreKI(+)/Klf4(loxP/loxP) mice. Of interest, cardiac output was significantly decreased in SM22alpha-CreKI(+)/Klf4(loxP/loxP) mice, as determined by magnetic resonance imaging. Moreover, a lack of Klf4 in the heart resulted in the reduction in expression of multiple cardiac genes, including Gata4. In vivo chromatin immunoprecipitation assays on the heart revealed that Klf4 bound to the promoter region of the Gata4 gene. Results provide novel evidence that Klf4 plays a key role in late fetal and/or postnatal cardiac development.

Pitx2-dependent occupancy by histone deacetylases is associated with T-box gene regulation in mammalian abdominal tissue

The homeodomain transcription factor Pitx2 and the T-box transcription factors are essential for organogenesis. Pitx2 and T-box genes are induced by growth factors and function as transcriptional activators or repressors. Gene expression analyses on abdominal tissue were used to identify seven of the T-box genes of the genome as Pitx2 target genes in the abdomen at embryonic day.10.5. Pitx2 activated Tbx4, Tbx15, and Mga and repressed Tbx1, Tbx2, Tbx5, and Tbx6 expression. As expected, activated genes showed reduced expression patterns, and repressed T-box genes showed increased expression patterns in the abdomen of Pitx2 mutants. Pitx2 occupied chromatin sites near all of these T-box genes. Co-occupancy by coactivators, corepressors, and histone acetylation at these sites was frequently Pitx2-dependent. Genes repressed by Pitx2 generally showed increased histone acetylation and decreased histone deacetylase (HDAC)/corepressor occupancy in Pitx2 mutants. The lower N-CoR, HDAC1, and HDAC3 occupancy observed at multiple sites along Tbx1 chromatin in mutants is consistent with the model that increased histone acetylation and gene expression of Tbx1 may result from a loss of recruitment of corepressors by Pitx2. Genes activated by Pitx2 showed less consistent patterns in chromatin analyses. Reduced H4 acetylation and increased HDAC1/nuclear receptor corepressor (N-CoR) occupancy at some Tbx4 sites were accompanied by increased H3 acetylation and reduced HDAC3 occupancy at the same or other more distal chromatin sites in mutants. Pitx2-dependent occupancy by corepressors resulted in alteration of the acetylation levels of several T-box genes, whereas Pitx2-dependent occupancy by coactivators was more site-localized. These studies will provide the basic scientific underpinning to understand abdominal wall syndromes.

Defective pulmonary vascular remodeling in Smad8 mutant mice

Pulmonary artery hypertension (PAH), a progressive, lethal condition that results in pathologic changes in the pulmonary arterial tree, eventually leads to right heart failure. Work identifying mutations in the Type II Bone morphogenetic protein (Bmp) receptor, BmpRII, in families with PAH has implicated Bmp-signaling in the pathogenesis of PAH. However, the effectors downstream of BmpRII in PAH remain unclear since BmpRII signals via Smad-dependent and independent mechanisms. We investigated Smad8 function, a divergent receptor regulated Smad downstream of Bmp-signaling, using gene targeting in mice. We show that Smad8 loss of function in adults resulted in characteristic changes in distal pulmonary arteries including medial thickening and smooth muscle hyperplasia that is observed in patients with PAH. Smad8 mutant pulmonary vasculature had upregulated Activin/Tgfbeta signaling and pathologic remodeling with aberrant Prx1 and Tenascin-C expression. A subset of Smad8 mutants had pulmonary adenomas uncovering a function for Smad8 in normal growth control. These findings implicate Smad8 in both pulmonary hypertension and lung tumorigenesis and support Smad8 as a candidate gene for PAH in humans.

Induction and modulation of smooth muscle differentiation in Xenopus embryonic cells

By comparison with skeletal or cardiac developmental programs, little is known regarding the specific factors that promote specification and differentiation of smooth muscle cells from pluripotent cells. We have analyzed the developmental expression of a subset of smooth muscle genes during Xenopus early development and showed that similar to mammals and avians, Xenopus smooth muscle myosin heavy chain (SM-MHC) is a highly specific marker of smooth muscle differentiation. Embryonic cells from animal pole explants of Xenopus blastula can be induced by basic fibroblast growth factor, Wnt, and bone morphogenetic protein signals to adopt the smooth muscle pathway. Explants from early embryos that contain neural crest cells can also differentiate into cells expressing smooth muscle genes. We examined the interplay of several transcription factors, that is SRF, myocardin, and GATA6, that induce the expression of SM-MHC in animal cap cells and found that myocardin-dependent expression of smooth muscle genes in animal cap cells is synergized by SRF but is strongly antagonized by GATA6.

The actin-associated protein Palladin is required for development of normal contractile properties of smooth muscle cells derived from embryoid bodies

Palladin is a widely expressed actin-associated protein localized at stress fibers, focal adhesions, and other actin-based structures, playing a significant role in cell adhesion and cell motility. Knockout of Palladin in mice is embryonic lethal, demonstrating the importance of Palladin in development yet its role in the vasculature is not known. In the present study, smooth muscle cell (SMC) markers, such as myosin, actin, caldesmon, calponin, and LPP, were down-regulated in embryoid bodies (EBs) derived from embryonic stem cells lacking Palladin. Transgenic embryonic stem cell lines were generated that stably expressed a puromycin-resistance gene under the control of a SM alpha-actin (SMA) promoter. Negative selection was then used to purify SMCs from EBs. Purified SMCs expressing multiple SMC markers were designated APSCs (SMA-puromycin-selected cells). Palladin null APSCs express significantly less myosin, actin, calponin, and h-caldesmon. The filamentous (F) to globular (G) actin ratio, known to regulate myocardin family transcription factors, was also decreased. Palladin null APSCs showed increased cell adhesion and decreased cell motility. Importantly, Palladin null APSCs within collagen gels generated less maximum contractile force when stimulated with endothelin-1, sphingosine 1-phosphate (S1P), and thrombin. Myosin light chains (MLC20) were phosphorylated by lysophosphatidic acid to the same extent in Palladin null and wild type APSCs but myosin content/total protein was reduced by >50%, consistent with the observed decreases in contractility. All together, these results suggest that Palladin is essential for expression of the full complement of contractile proteins necessary for optimal force development of SMCs derived from EBs.

Kruppel-like factor 4, Elk-1, and histone deacetylases cooperatively suppress smooth muscle cell differentiation markers in response to oxidized phospholipids

Phenotypic switching of vascular smooth muscle cells (SMCs), such as increased proliferation, enhanced migration, and downregulation of SMC differentiation marker genes, is known to play a key role in the development of atherosclerosis. However, the factors and mechanisms controlling this process are not fully understood. We recently showed that oxidized phospholipids, including 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC), which accumulate in atherosclerotic lesions, are potent repressors of expression of SMC differentiation marker genes in cultured SMCs as well as in rat carotid arteries in vivo. Here, we examined the molecular mechanisms whereby POVPC induces suppression of SMC differentiation marker genes in cultured SMCs. Results showed that POVPC induced phosphorylation of ERK1/2 and Elk-1. The MEK inhibitors U-0126 and PD-98059 attenuated POVPC-induced suppression of smooth muscle (SM) alpha-actin and SM-myosin heavy chain. POVPC also induced expression of Krüppel-like factor 4 (Klf4). Chromatin immunoprecipitation assays revealed that POVPC caused simultaneous binding of Elk-1 and Klf4 to the promoter region of the SM alpha-actin gene. Moreover, coimmunoprecipitation assays showed a physical interaction between Elk-1 and Klf4. Results in Klf4-null SMCs showed that blockade of both Klf4 induction and Elk-1 phosphorylation completely abolished POVPC-induced suppression of SMC differentiation marker genes. POVPC-induced suppression of SMC differentiation marker genes was also accompanied by hypoacetylation of histone H4 at the SM alpha-actin promoter, which was mediated by the recruitment of histone deacetylases (HDACs), HDAC2 and HDAC5. Coimmunoprecipitation assays showed that Klf4 interacted with HDAC5. Results provide evidence that Klf4, Elk-1, and HDACs coordinately mediate POVPC-induced suppression of SMC differentiation marker genes.