Smad3-mediated myocardin silencing: a novel mechanism governing the initiation of smooth muscle differentiation

Nupr1 mediates renal fibrosis via activating fibroblast and promoting epithelial-mesenchymal transition

Renal interstitial fibrosis (RIF) is a pathological process that fibrotic components are excessively deposited in the renal interstitial space due to kidney injury, resulting in impaired renal function and chronic kidney disease. The molecular mechanisms controlling renal fibrosis are not fully understood. In this present study, we identified Nuclear protein 1 (Nupr1), a transcription factor also called p8, as a novel regulator promoting renal fibrosis. Unilateral ureteral obstruction (UUO) time-dependently induced Nupr1 mRNA and protein expression in mouse kidneys while causing renal damage and fibrosis. Nupr1 deficiency (Nupr1^-/- ) attenuated the renal tubule dilatation, tubular epithelial cell atrophy, and interstitial collagen accumulation caused by UUO. Consistently, Nupr1^-/- significantly decreased the expression of type I collagen, myofibroblast markers smooth muscle α-actin (α-SMA), fibroblast-specific protein 1 (FSP-1), and vimentin in mouse kidney that were upregulated by UUO. These results suggest that Nupr1 protein was essential for fibroblast activation and/or epithelial-mesenchymal transition (EMT) during renal fibrogenesis. Indeed, Nupr1 was indispensable for TGF-β-induced myofibroblast activation of kidney interstitial NRK-49F fibroblasts, multipotent mesenchymal C3H10T1/2 cells, and the EMT of kidney epithelial NRK-52E cells. It appears that Nupr1 mediated TGF-β-induced α-SMA expression and collagen synthesis by initiating Smad3 signaling pathway. Importantly, trifluoperazine (TFP), a Nupr1 inhibitor, alleviated UUO-induced renal fibrosis. Taken together, our results demonstrate that Nupr1 promotes renal fibrosis by activating myofibroblast transformation from both fibroblasts and tubular epithelial cells.

Surfactant Protein A, a Novel Regulator for Smooth Muscle Phenotypic Modulation and Vascular Remodeling-Brief Report

OBJECTIVE

The objective of this study is to determine the role of SPA (surfactant protein A) in vascular smooth muscle cell (SMC) phenotypic modulation and vascular remodeling. Approach and Results: PDGF-BB (Platelet-derived growth factor-BB) and serum induced SPA expression while downregulating SMC marker gene expression in SMCs. SPA deficiency increased the contractile protein expression. Mechanistically, SPA deficiency enhanced the expression of myocardin and TGF (transforming growth factor)-β, the key regulators for contractile SMC phenotype. In vivo, SPA was induced in medial and neointimal SMCs following mechanical injury in both rat and mouse carotid arteries. SPA knockout in mice dramatically attenuated the wire injury-induced intimal hyperplasia while restoring SMC contractile protein expression in medial SMCs. These data indicate that SPA plays an important role in SMC phenotype modulation and vascular remodeling in vivo.

CONCLUSIONS

SPA is a novel protein factor modulating SMC phenotype. Blocking the abnormal elevation of SPA may be a potential strategy to inhibit the development of proliferative vascular diseases.

The effects of progenitor and differentiated cells on ectopic calcification of engineered vascular tissues

Ectopic vascular calcification associated with aging, diabetes mellitus, atherosclerosis, and chronic kidney disease is a considerable risk factor for cardiovascular events and death. Although vascular smooth muscle cells are primarily implicated in calcification, the role of progenitor cells is less known. In this study, we engineered tubular vascular tissues from embryonic multipotent mesenchymal progenitor cells either without differentiating or after differentiating them into smooth muscle cells and studied ectopic calcification through targeted gene analysis. Tissues derived from both differentiated and undifferentiated cells calcified in response to hyperphosphatemic inorganic phosphate (Pi) treatment suggesting that a single cell-type (progenitor cells or differentiated cells) may not be the sole cause of the process. We also demonstrated that Vitamin K, which is the matrix gla protein activator, had a protective role against calcification in engineered vascular tissues. Addition of partially-soluble elastin upregulated osteogenic marker genes suggesting a calcification process. Furthermore, partially-soluble elastin downregulated smooth muscle myosin heavy chain (Myh11) gene which is a late-stage differentiation marker. This latter point, in turn, suggests that SMC may be switching into a synthetic phenotype which is one feature of vascular calcification. Taken together, our approach presents a valuable tool to study ectopic calcification and associated gene expressions relevant to clinical therapeutic targets.

LncRNA GAS5 attenuates fibroblast activation through inhibiting Smad3 signaling

Transforming growth factor-β (TGF-β)-induced fibroblast activation is a key pathological event during tissue fibrosis. Long noncoding RNA (lncRNA) is a class of versatile gene regulators participating in various cellular and molecular processes. However, the function of lncRNA in fibroblast activation is still poorly understood. In this study, we identified growth arrest-specific transcript 5 (GAS5) as a novel regulator for TGF-β-induced fibroblast activation. GAS5 expression was downregulated in cultured fibroblasts by TGF-β and in resident fibroblasts from bleomycin-treated skin tissues. Overexpression of GAS5 suppressed TGF-β-induced fibroblast to myofibroblast differentiation. Mechanistically, GAS5 directly bound mothers against decapentaplegic homolog 3 (Smad3) and promoted Smad3 binding to Protein phosphatase 1A (PPM1A), a Smad3 dephosphatase, and thus accelerated Smad3 dephosphorylation in TGF-β-treated fibroblasts. In addition, GAS5 inhibited fibroblast proliferation. Importantly, local delivery of GAS5 via adenoviral vector suppressed bleomycin-induced skin fibrosis in mice. Collectively, our data revealed that GAS5 suppresses fibroblast activation and fibrogenesis through inhibiting TGF-β/Smad3 signaling, which provides a rationale for an lncRNA-based therapy to treat fibrotic diseases.

MYOCD and SMAD3/SMAD4 form a positive feedback loop and drive TGF-β-induced epithelial-mesenchymal transition in non-small cell lung cancer

Myocardin (MYOCD) promotes Smad3-mediated transforming growth factor-β (TGF-β) signaling in mouse fibroblast cells. Our previous studies show that TGF-β/SMADs signaling activation enhances epithelial-mesenchymal transition (EMT) in human non-small cell lung cancer (NSCLC) cells. However, whether and how MYOCD contributes to TGF-β-induced EMT of NSCLC cells are poorly elucidated. Here, we found that TGF-β-induced EMT was accompanied by increased MYOCD expression. Interestingly, MYOCD overexpression augmented EMT and invasion of NSCLC cells induced by TGF-β, whereas knockdown of MYOCD expression attenuated these effects. Overexpression and knockdown of MYOCD resulted in the upregulation and downregulation of TGF-β-induced Snail mRNA, respectively. Moreover, MYOCD overexpression promoted TGF-β-stimulated NSCLC cell metastasis in vivo. MYOCD was highly expressed and positively correlated with Snail in metastatic NSCLC tissues. Mechanistically, MYOCD directly interacted with SMAD3 and sustained the formation of TGF-β-induced nuclear SMAD3/SMAD4 complex, facilitating TGF-β/SMAD3-induced transactivation of Snail. Importantly, MYOCD was transcriptionally activated by TGF-β-induced SMAD3/SMAD4 complex and CRISPR/Cas9-mediated silencing of SMAD3/SMAD4 led to a reduction in MYOCD mRNA expression. Taken together, our findings indicate that MYOCD promotes TGF-β-induced EMT and metastasis of NSCLC and identify a positive feedback loop between MYOCD and SMAD3/SMAD4 driving TGF-β-induced EMT.

Ureter tissue engineering with vessel extracellular matrix and differentiated urine-derived stem cells

OBJECTIVE

To assess the possibility of ureter tissue engineering using vessel extracellular matrix (VECM) and differentiated urine-derived stem cells (USCs) in a rabbit model.

METHODS

VECM was prepared by a modified technique. USCs were isolated from human urine samples and cultured with an induction medium for the differentiation of the cells into urothelium and smooth muscle phenotypes. For contractile phenotype conversion, the induced smooth muscle cells were transfected with the miR-199a-5p plasmid. The differentiated cells were seeded onto VECM and cultured under dynamic conditions in vitro for 2 weeks. The graft was tubularized and wrapped by two layers of the omentum of a rabbit for vascularization. Then, the maturated graft was used for ureter reconstruction in vivo.

RESULTS

VECM has microporous structures that allow cell infiltration and exhibit adequate biocompatibility with seeding cells. USCs were isolated and identified by flow cytometry. After induction, the urothelium phenotype gene was confirmed at mRNA and protein levels. With the combined induction by TGF-β1 and miR-199a-5p, the differentiated cells can express the smooth muscle phenotype gene and convert to the contractile phenotype. After seeding cells onto VECM, the induced urothelium cells formed a single epithelial layer, and the induced smooth muscle cells formed a few cell layers during dynamic culture. After 3 weeks of omental maturation, tubular graft was vascularized. At 2 months post ureter reconstruction, histological evaluation showed a clearly layered structure of ureter with multilayered urothelium over the organized smooth muscle tissue.

CONCLUSION

By seeding differentiated USCs onto VECM, a tissue-engineered graft could form multilayered urothelium and organized smooth muscle tissue after ureteral reconstruction in vivo.

STATEMENT OF SIGNIFICANCE

Cell-based tissue engineering offers an alternative technique for urinary tract reconstruction. In this work, we describe a novel strategy for ureter tissue engineering. We modified the techniques of vessel extracellular matrix (VECM) preparation and used a dynamic culture system for seeding cells onto VECM. We found that VECM had the trait of containing VEGF and exhibited blood vessel formation potential. Urine-derived stem cells (USCs) could be differentiated into urothelial cells and functional contractile phenotype smooth muscle cells in vitro. By seeding differentiated USCs onto VECM, a tissue-engineered graft could form multilayered urothelium and organized smooth muscle tissue after ureteral reconstruction in vivo. This strategy might be applied in clinical research for the treatment of long-segment ureteral defect.

Coronary artery disease genes SMAD3 and TCF21 promote opposing interactive genetic programs that regulate smooth muscle cell differentiation and disease risk

Although numerous genetic loci have been associated with coronary artery disease (CAD) with genome wide association studies, efforts are needed to identify the causal genes in these loci and link them into fundamental signaling pathways. Recent studies have investigated the disease mechanism of CAD associated gene SMAD3, a central transcription factor (TF) in the TGFβ pathway, investigating its role in smooth muscle biology. In vitro studies in human coronary artery smooth muscle cells (HCASMC) revealed that SMAD3 modulates cellular phenotype, promoting expression of differentiation marker genes while inhibiting proliferation. RNA sequencing and chromatin immunoprecipitation sequencing studies in HCASMC identified downstream genes that reside in pathways which mediate vascular development and atherosclerosis processes in this cell type. HCASMC phenotype, and gene expression patterns promoted by SMAD3 were noted to have opposing direction of effect compared to another CAD associated TF, TCF21. At sites of SMAD3 and TCF21 colocalization on DNA, SMAD3 binding was inversely correlated with TCF21 binding, due in part to TCF21 locally blocking chromatin accessibility at the SMAD3 binding site. Further, TCF21 was able to directly inhibit SMAD3 activation of gene expression in transfection reporter gene studies. In contrast to TCF21 which is protective toward CAD, SMAD3 expression in HCASMC was shown to be directly correlated with disease risk. We propose that the pro-differentiation action of SMAD3 inhibits dedifferentiation that is required for HCASMC to expand and stabilize disease plaque as they respond to vascular stresses, counteracting the protective dedifferentiating activity of TCF21 and promoting disease risk.

Mesenchyme homeobox 1 mediates transforming growth factor-β (TGF-β)-induced smooth muscle cell differentiation from mouse mesenchymal progenitors

Differentiation of smooth muscle cells (SMCs) is critical for proper vasculogenesis and angiogenesis. However, the molecular mechanisms controlling SMC differentiation are not completely understood. During embryogenesis, the transcription factor mesenchyme homeobox 1 (Meox1) is expressed in the early developing somite, which is one of the origins of SMCs. In the present study, we identified Meox1 as a positive regulator of SMC differentiation. We found that transforming growth factor-β (TGF-β) induces Meox1 expression in the initial phase of SMC differentiation of pluripotent murine C3H10T1/2 cells. shRNA-mediated Meox1 knockdown suppressed TGF-β-induced expression of SMC early markers, whereas Meox1 overexpression increased expression of these markers. Mechanistically, Meox1 promoted SMAD family member 3 (Smad3) nuclear retention during the early stage of TGF-β stimulation because Meox1 inhibited protein phosphatase Mg²⁺/Mn²⁺-dependent 1A (PPM1A) and thereby prevented PPM1A-mediated Smad3 dephosphorylation. Meox1 appears to promote PPM1A degradation, leading to sustained Smad3 phosphorylation, thus allowing Smad3 to stimulate SMC gene transcription. In vivo, Meox1 knockdown in mouse embryos impaired SMC marker expression in the descending aorta of neonatal mice, indicating that Meox1 is essential for SMC differentiation during embryonic development. In summary, the transcriptional regulator Meox1 controls TGF-β-induced SMC differentiation from mesenchymal progenitor cells by preventing PPM1A-mediated Smad3 dephosphorylation, thereby supporting SMC gene expression.

Opposing Actions of AKT (Protein Kinase B) Isoforms in Vascular Smooth Muscle Injury and Therapeutic Response

OBJECTIVE

Drug-eluting stent delivery of mTORC1 (mechanistic target of rapamycin complex 1) inhibitors is highly effective in preventing intimal hyperplasia after coronary revascularization, but adverse effects limit their use for systemic vascular disease. Understanding the mechanism of action may lead to new treatment strategies. We have shown that rapamycin promotes vascular smooth muscle cell differentiation in an AKT2-dependent manner in vitro. Here, we investigate the roles of AKT (protein kinase B) isoforms in intimal hyperplasia.

APPROACH AND RESULTS

We found that germ-line-specific or smooth muscle-specific deletion of Akt2 resulted in more severe intimal hyperplasia compared with control mice after arterial denudation injury. Conversely, smooth muscle-specific Akt1 knockout prevented intimal hyperplasia, whereas germ-line Akt1 deletion caused severe thrombosis. Notably, rapamycin prevented intimal hyperplasia in wild-type mice but had no therapeutic benefit in Akt2 knockouts. We identified opposing roles for AKT1 and AKT2 isoforms in smooth muscle cell proliferation, migration, differentiation, and rapamycin response in vitro. Mechanistically, rapamycin induced MYOCD (myocardin) mRNA expression. This was mediated by AKT2 phosphorylation and nuclear exclusion of FOXO4 (forkhead box O4), inhibiting its binding to the MYOCD promoter.

CONCLUSIONS

Our data reveal opposing roles for AKT isoforms in smooth muscle cell remodeling. AKT2 is required for rapamycin's therapeutic inhibition of intimal hyperplasia, likely mediated in part through AKT2-specific regulation of MYOCD via FOXO4. Because AKT2 signaling is impaired in diabetes mellitus, this work has important implications for rapamycin therapy, particularly in diabetic patients.

Curcumin enhances vascular contractility via induction of myocardin in mouse smooth muscle cells

A variety of cardiovascular diseases is accompanied by the loss of vascular contractility. This study sought to investigate the effects of curcumin, a natural polyphenolic compound present in turmeric, on mouse vascular contractility and the underlying mechanisms. After mice were administered curcumin (100 mg·kg-1·d-1, ig) for 6 weeks, the contractile responses of the thoracic aorta to KCl and phenylephrine were significantly enhanced compared with the control group. Furthermore, the contractility of vascular smooth muscle (SM) was significantly enhanced after incubation in curcumin (25 μmol/L) for 4 days, which was accompanied by upregulated expression of SM marker contractile proteins SM22α and SM α-actin. In cultured vascular smooth muscle cells (VSMCs), curcumin (10, 25, 50 μmol/L) significantly increased the expression of myocardin, a "master regulator" of SM gene expression. Curcumin treatment also significantly increased the levels of caveolin-1 in VSMCs. We found that as a result of the upregulation of caveolin-1, curcumin blocked the activation of notch1 and thereby abolished Notch1-inhibited myocardin expression. Knockdown of caveolin-1 or activation of Notch1 signaling with Jagged1 (2 μg/mL) diminished these effects of curcumin in VSMCs. These findings suggest that curcumin induces the expression of myocardin in mouse smooth muscle cells via a variety of mechanisms, including caveolin-1-mediated inhibition of notch1 activation and Notch1-mediated repression of myocardin expression. This may represent a novel pathway, through which curcumin protects blood vessels via the beneficial regulation of SM contractility.

Olfactomedin 2 Regulates Smooth Muscle Phenotypic Modulation and Vascular Remodeling Through Mediating Runt-Related Transcription Factor 2 Binding to Serum Response Factor

OBJECTIVE

The objective of this study is to investigate the role and underlying mechanism of Olfactomedin 2 (Olfm2) in smooth muscle cell (SMC) phenotypic modulation and vascular remodeling.

APPROACH AND RESULTS

Platelet-derived growth factor-BB induces Olfm2 expression in primary SMCs while modulating SMC phenotype as shown by the downregulation of SMC marker proteins. Knockdown of Olfm2 blocks platelet-derived growth factor-BB-induced SMC phenotypic modulation, proliferation, and migration. Conversely, Olfm2 overexpression inhibits SMC marker expression. Mechanistically, Olfm2 promotes the interaction of serum response factor with the runt-related transcription factor 2 that is induced by platelet-derived growth factor-BB, leading to a decreased interaction between serum response factor and myocardin, causing a repression of SMC marker gene transcription and consequently SMC phenotypic modulation. Animal studies show that Olfm2 is upregulated in balloon-injured rat carotid arteries. Knockdown of Olfm2 effectively inhibits balloon injury-induced neointima formation. Importantly, knockout of Olfm2 in mice profoundly suppresses wire injury-induced neointimal hyperplasia while restoring SMC contractile protein expression, suggesting that Olfm2 plays a critical role in SMC phenotypic modulation in vivo.

CONCLUSIONS

Olfm2 is a novel factor mediating SMC phenotypic modulation. Thus, Olfm2 may be a potential target for treating injury-induced proliferative vascular diseases.

TGF-β/SMAD3 Pathway Stimulates Sphingosine-1 Phosphate Receptor 3 Expression: IMPLICATION OF SPHINGOSINE-1 PHOSPHATE RECEPTOR 3 IN LUNG ADENOCARCINOMA PROGRESSION

Previously, we showed that levels of sphingosine-1 phosphate receptor 3 (S1PR3) are increased in a panel of cultured human lung adenocarcinoma cell lines, and that S1PR3-mediated signaling pathways regulate proliferation, soft agar growth, and invasion of human lung adenocarcinoma cells in vitro In the present study, we examine S1PR3 levels in human lung adenocarcinoma specimens. cDNA array and tumor microarray analysis shows that mRNA and protein levels of S1PR3 are significantly increased in human lung adenocarcinomas when compared with normal lung epithelial cells. Promoter analysis shows 16 candidate SMAD3 binding sites in the promoter region of S1PR3. ChIP indicates that TGF-β treatment stimulates the binding of SMAD3 to the promoter region of S1PR3. Luciferase reporter assay demonstrates that SMAD3 transactivates S1PR3 promoter. TGF-β stimulation or ectopic expression of TGF-β up-regulates S1PR3 levels in vitro and ex vivo Pharmacologic inhibition of TGF-β receptor or SMAD3 abrogates the TGF-β-stimulated S1PR3 up-regulation. Moreover, S1PR3 knockdown dramatically inhibits tumor growth and lung metastasis, whereas ectopic expression of S1PR3 promotes the growth of human lung adenocarcinoma cells in animals. Pharmacological inhibition of S1PR3 profoundly inhibits the growth of lung carcinoma in mice. Our studies suggest that levels of S1PR3 are up-regulated in human lung adenocarcinomas, at least in part due to the TGF-β/SMAD3 signaling axis. Furthermore, S1PR3 activity promotes the progression of human lung adenocarcinomas. Therefore, S1PR3 may represent a novel therapeutic target for the treatment of deadly lung adenocarcinomas.

Aberrant Expression of microRNA-9 Contributes to Development of Intracranial Aneurysm by Suppressing Proliferation and Reducing Contractility of Smooth Muscle Cells

BACKGROUND MiR-9 is reportedly involved with many diseases, such as acute myeloid leukemia and liver oncogenesis. In the present study we investigated the molecular mechanism, including the potential regulator and signaling pathways, of MYOCD, which is the gene that in humans encodes the protein myocardin. MATERIAL AND METHODS We searched the online miRNA database (www.mirdb.org) with the "seed sequence" located within the 3'-UTR of the target gene, and then validated MYOCD to be the direct gene via luciferase reporter assay system, and further confirmed it in cultured cells by using Western blot analysis and realtime PCR. RESULTS We established the negative regulatory relationship between miR-9 and MYOCD via studying the relative luciferase activity. We also conducted realtime PCR and Western blot analysis to study the mRNA and protein expression level of MYOCD between different groups (intracranial aneurysm vs. normal control) or cells treated with scramble control, miR-9 mimics, MYOCD siRNA, and miR-9 inhibitors, indicating the negative regulatory relationship between miR-9 and MYOCD. We also investigated the relative viability of smooth muscle cells when transfected with scramble control, miR-9 mimics, MYOCD siRNA, and miR-9 inhibitors to validate that miR-9 t negatively interferes with the viability of smooth muscle cells. We then investigated the relative contractility of smooth muscle cells when transfected with scramble control, miR-9 mimics, MYOCD siRNA, and miR-9 inhibitors, and the results showed that miR-9 weakened contractility. CONCLUSIONS Our findings show that dysregulation of miR-9 is responsible for the development of IA via targeting MYOCD. miR-9 and its direct target, MYOCD, might novel therapeutic targets in the treatment of IA.

Smooth Muscle Cell Proangiogenic Phenotype Induced by Cyclopentenyl Cytosine Promotes Endothelial Cell Proliferation and Migration

Vascular smooth muscle cells (SMCs) and endothelial cells (ECs) are in close contact with blood vessels. SMC phenotypes can be altered during pathological vascular remodeling. However, how SMC phenotypes affect EC properties remains largely unknown. In this study, we found that PDGF-BB-induced synthetic SMCs suppressed EC proliferation and migration while exhibiting increased expression of anti-angiogenic factors, such as endostatin, and decreased pro-angiogenic factors, including CXC motif ligand 1 (CXCL1). Cyclopentenyl cytosine (CPEC), a CTP synthase inhibitor that has been reported previously to inhibit SMC proliferation and injury-induced neointima formation, induced SMC redifferentiation. Interestingly, CPEC-conditioned SMC culture medium promoted EC proliferation and migration because of an increase in CXCL1 along with decreased endostatin production in SMCs. Addition of recombinant endostatin protein or blockade of CXCL1 with a neutralizing antibody suppressed the EC proliferation and migration induced by CPEC-conditioned SMC medium. Mechanistically, CPEC functions as a cytosine derivate to stimulate adenosine receptors A1 and A2a, which further activate downstream cAMP and Akt signaling, leading to the phosphorylation of cAMP response element binding protein and, consequently, SMC redifferentiation. These data provided proof of a novel concept that synthetic SMC exhibits an anti-angiogenic SMC phenotype, whereas contractile SMC shows a pro-angiogenic phenotype. CPEC appears to be a potent stimulator for switching the anti-angiogenic SMC phenotype to the pro-angiogenic phenotype, which may be essential for CPEC to accelerate re-endothelialization for vascular repair during injury-induced vascular wall remodeling.

Yes-Associated Protein Inhibits Transcription of Myocardin and Attenuates Differentiation of Vascular Smooth Muscle Cell from Cardiovascular Progenitor Cell Lineage

Vascular smooth muscle cells (VSMCs) derived from cardiovascular progenitor cell (CVPC) lineage populate the tunica media of the aortic root. Understanding differentiation of VSMCs from CVPC will further our understanding of the molecular mechanisms contributing to aortic root aneurysms, and thus, facilitate the development of novel therapeutic agents to prevent this devastating complication. It is established that the yes-associated protein (YAP) and Hippo pathway is important for VSMC proliferation and phenotype switch. To determine the role of YAP in differentiation of VSMCs from CVPCs, we utilized the in vitro monolayer lineage specific differentiation method by differentiating human embryonic stem cells into CVPCs, and then, into VSMCs. We found that expression of YAP decreased during differentiation of VSMC from CVPCs. Overexpression of YAP attenuated expression of VSMC contractile markers and impaired VSMC function. Knockdown of YAP increased expression of contractile proteins during CVPC-VSMCs differentiation. Importantly, expression of YAP decreased transcription of myocardin during this process. Overexpression of YAP in PAC1 SMC cell line inhibited luciferase activity of myocardin proximal promoter in a dose dependent and NKX2.5 dependent manners. YAP protein interacted with NKX2.5 protein and inhibited binding of NKX2.5 to the 5'-proximal promoter region of myocardin in CVPC-derived VSMCs. In conclusion, YAP negatively regulates differentiation of VSMCs from CVPCs by decreasing transcription of myocardin in a NKX2.5-dependent manner. Stem Cells 2017;35:351-361.

Transforming growth factor β1 antagonizes the transcription, expression and vascular signaling of guanylyl cyclase/natriuretic peptide receptor A - role of δEF1

The objective of this study was to determine the role of transforming growth factor β1 (TGF-β1) in transcriptional regulation and function of the guanylyl cyclase A/natriuretic peptide receptor A gene (Npr1) and whether cross-talk exists between these two hormonal systems in target cells. After treatment of primary cultured rat thoracic aortic vascular smooth muscle cells and mouse mesangial cells with TGF-β1, the Npr1 promoter construct containing a δ-crystallin enhancer binding factor 1 (δEF1) site showed 85% reduction in luciferase activity in a time- and dose-dependent manner. TGF-β1 also significantly attenuated luciferase activity of the Npr1 promoter by 62%, and decreased atrial natriuretic peptide-mediated relaxation of mouse denuded aortic rings ex vivo. Treatment of cells with TGF-β1 increased the protein levels of δEF1 by 2.4-2.8-fold, and also significantly enhanced the phosphorylation of Smad 2/3, but markedly reduced Npr1 mRNA and receptor protein levels. Over-expression of δEF1 showed a reduction in Npr1 promoter activity by 75%, while deletion or site-directed mutagenesis of δEF1 sites in the Npr1 promoter eliminated the TGF-β1-mediated repression of Npr1 transcription. TGF-β1 significantly increased the expression of α-smooth muscle actin and collagen type I α2 in rat thoracic aortic vascular smooth muscle cells, which was markedly attenuated by atrial natriuretic peptide in cells over-expressing natriuretic peptide receptor A. Together, the present results suggest that an antagonistic cascade exists between the TGF-β1/Smad/δEF1 pathways and Npr1 expression and receptor signaling that is relevant to renal and vascular remodeling, and may be critical in the regulation of blood pressure and cardiovascular homeostasis.

Regulation of smooth muscle contractility by competing endogenous mRNAs in intracranial aneurysms

Alterations in vascular smooth muscle cells (SMCs) contribute to the pathogenesis of intracranial aneurysms (IAs), but the genetic mechanisms underlying these alterations are unclear. We used microarray analysis to compare tissue small noncoding RNA and messenger RNA expression profiles in vessel wall samples from patients with late-stage IAs. We identified myocardin (MYOCD), a key contractility regulator of vascular SMCs, as a critical factor in IA progression. Using a multifaceted computational and experimental approach, we determined that depletion of competitive endogenous RNAs (ARHGEF12, FGF12, and ADCY5) enhanced factors that downregulate MYOCD, which induces the conversion of SMCs from differentiated contractile states into dedifferentiated phenotypes that exhibit enhanced proliferation, synthesis of new extracellular matrix, and organization of mural thrombi. These effects may lead to the repair and maintenance of IAs. This study presents guidelines for the prediction and validation of the IA regulator MYOCD in competitive endogenous RNA networks and facilitates the development of novel therapeutic and diagnostic tools for IAs.

Myocardin in biology and disease

Myocardin (MYOCD) is a potent transcriptional coactivator that functions primarily in cardiac muscle and smooth muscle through direct contacts with serum response factor (SRF) over cis elements known as CArG boxes found near a number of genes encoding for contractile, ion channel, cytoskeletal, and calcium handling proteins. Since its discovery more than 10 years ago, new insights have been obtained regarding the diverse isoforms of MYOCD expressed in cells as well as the regulation of MYOCD expression and activity through transcriptional, post-transcriptional, and post-translational processes. Curiously, there are a number of functions associated with MYOCD that appear to be independent of contractile gene expression and the CArG-SRF nucleoprotein complex. Further, perturbations in MYOCD gene expression are associated with an increasing number of diseases including heart failure, cancer, acute vessel disease, and diabetes. This review summarizes the various biological and pathological processes associated with MYOCD and offers perspectives to several challenges and future directions for further study of this formidable transcriptional coactivator.

Transcriptional profiling reveals crosstalk between mesenchymal stem cells and endothelial cells promoting prevascularization by reciprocal mechanisms

Mesenchymal stem cells (MSCs) show great promise in blood vessel restoration and vascularization enhancement in many therapeutic situations. Typically, the co-implantation of MSCs with vascular endothelial cells (ECs) is effective for the induction of functional vascularization in vivo, indicating its potential applications in regenerative medicine. The effects of MSCs-ECs-induced vascularization can be modeled in vitro, providing simplified models for understanding their underlying communication. In this article, a contact coculture model in vitro and an RNA-seq approach were employed to reveal the active crosstalk between MSCs and ECs within a short time period at both morphological and transcriptional levels. The RNA-seq results suggested that angiogenic genes were significantly induced upon coculture, and this prevascularization commitment might require the NF-κB signaling. NF-κB blocking and interleukin (IL) neutralization experiments demonstrated that MSCs potentially secreted IL factors including IL1β and IL6 to modulate NF-κB signaling and downstream chemokines during coculture. Conversely, RNA-seq results indicated that the MSCs were regulated by the coculture environment to a smooth muscle commitment within this short period, which largely induced myocardin, the myogenic co-transcriptional factor. These findings demonstrate the mutual molecular mechanism of MSCs-ECs-induced prevascularization commitment in a quick response.

Generation of a Cre knock-in into the Myocardin locus to mark early cardiac and smooth muscle cell lineages

The molecular events that control cell fate determination in cardiac and smooth muscle lineages remain elusive. Myocardin is an important transcription cofactor that regulates cell proliferation, differentiation, and development of the cardiovascular system. Here, we describe the construction and analysis of a dual Cre and enhanced green fluorescent protein (EGFP) knock-in mouse line in the Myocardin locus (Myocd(KI)). We report that the Myocd(KI) allele expresses the Cre enzyme and the EGFP in a manner that recapitulates endogenous Myocardin expression patterns. We show that Myocardin expression marks the earliest cardiac and smooth muscle lineages. Furthermore, this genetic model allows for the identification of a cardiac cell population, which maintains both Myocardin and Isl-1 expression, in E7.75-E8.0 embryos, highlighting the contribution and merging of the first and second heart fields during cardiogenesis. Therefore, the Myocd(KI) allele is a unique tool for studying cardiovascular development and lineage-specific gene manipulation.

Deletion of chromosome 9p21 noncoding cardiovascular risk interval in mice alters Smad2 signaling and promotes vascular aneurysm

BACKGROUND

Vascular aneurysm is an abnormal local dilatation of an artery that can lead to vessel rupture and sudden death. The only treatment involves surgical or endovascular repair or exclusion. There is currently no approved medical therapy for this condition. Recent data established a strong association between genetic variants in the 9p21 chromosomal region in humans and the presence of cardiovascular diseases, including aneurysms. However, the mechanisms linking this 9p21 DNA variant to cardiovascular risk are still unknown.

METHODS AND RESULTS

Here, we show that deletion of the orthologous 70-kb noncoding interval on mouse chromosome 4 (chr4(Δ70kb/Δ70kb) mice) is associated with reduced aortic expression of cyclin-dependent kinase inhibitor genes p19Arf and p15Inkb. Vascular smooth muscle cells from chr4(Δ70kb/Δ70kb) mice show reduced transforming growth factor-β-dependent canonical Smad2 signaling but increased cyclin-dependent kinase-dependent Smad2 phosphorylation at linker sites, a phenotype previously associated with tumor growth and consistent with the mechanistic link between reduced canonical transforming growth factor-β signaling and susceptibility to vascular diseases. We also show that targeted deletion of the 9p21 risk interval promotes susceptibility to aneurysm development and rupture when mice are subjected to a validated model of aneurysm formation. The vascular disease of chr4(Δ70kb/Δ70kb) mice is prevented by treatment with a cyclin-dependent kinase inhibitor.

CONCLUSIONS

The results establish a direct mechanistic link between 9p21 noncoding risk interval and susceptibility to aneurysm and may have important implications for the understanding and treatment of vascular diseases.

Functional involvements of heterogeneous nuclear ribonucleoprotein A1 in smooth muscle differentiation from stem cells in vitro and in vivo

To investigate the functional involvements of heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) in smooth muscle cell (SMC) differentiation from stem cells, embryonic stem cells were cultivated on collagen IV-coated plates to allow for SMC differentiation. We found that hnRNPA1 gene and protein expression was upregulated significantly during differentiation and coexpressed with SMC differentiation markers in the stem cell-derived SMCs as well as embryonic SMCs of 12.5 days of mouse embryos. hnRNPA1 knockdown resulted in downregulation of smooth muscle markers and transcription factors, while enforced expression of hnRNPA1 enhanced the expression of these genes. Importantly, knockdown of hnRNPA1 also resulted in impairment of SMC differentiation in vivo. Moreover, we demonstrated that hnRNPA1 could transcriptionally regulate SMC gene expression through direct binding to promoters of Acta2 and Tagln genes using luciferase and chromatin immunoprecipitation assays. We further demonstrated that the binding sites for serum response factor (SRF), a well-investigated SMC transcription factor, within the promoter region of the Acta2 and Tagln genes were responsible for hnRNPA1-mediated Acta2 and Tagln gene expression using in vitro site-specific mutagenesis and luciferase activity analyses. Finally, we also demonstrated that hnRNPA1 upregulated the expression of SRF, myocyte-specific enhancer factor 2c (MEF2c), and myocardin through transcriptional activation and direct binding to promoters of the SRF, MEF2c, and Myocd genes. Our findings demonstrated that hnRNPA1 plays a functional role in SMC differentiation from stem cells in vitro and in vivo. This indicates that hnRNPA1 is a potential modulating target for deriving SMCs from stem cells and cardiovascular regenerative medicine.

Cell division cycle 7 mediates transforming growth factor-β-induced smooth muscle maturation through activation of myocardin gene transcription

Smooth muscle (SM) development consists of several processes, including cell fate determination, differentiation, and maturation. The molecular mechanisms controlling SM early differentiation have been studied extensively. However, little is known about the mechanism underlying SM maturation. Cell division cycle 7 (Cdc7) has been shown to regulate cell fate determination in the initial phase of transforming growth factor-β (TGF-β)-induced SM differentiation. Our present study indicates that Cdc7 also regulates SM maturation. Knockdown of Cdc7 suppresses TGF-β-induced expression of SM myosin heavy chain, a late marker of SM differentiation. Cdc7 overexpression, on the other hand, enhances SM myosin heavy chain expression. Interestingly, Cdc7 activates the mRNA expression and promoter activity of myocardin (Myocd), a master regulator of SM differentiation, whose transcription is blocked in the initial phase of the differentiation because TGF-β does not induce Myocd mRNA until after the early SM markers are induced. These data suggest that Cdc7 mediates TGF-β-induced SM maturation via activation of Myocd transcription. Mechanistically, Cdc7 physically and functionally interacts with Nkx2.5 to regulate Myocd promoter activity. Cdc7 appears to enhance Nkx2.5 binding to Myocd promoter, leading to Myocd activation. Taken together, our studies demonstrate that Cdc7 regulates the initial and late phase of SM differentiation through distinct mechanisms.

Smad2 and myocardin-related transcription factor B cooperatively regulate vascular smooth muscle differentiation from neural crest cells

RATIONALE

Vascular smooth muscle cell (VSMC) differentiation from neural crest cells (NCCs) is critical for cardiovascular development, but the mechanisms remain largely unknown.

OBJECTIVE

Transforming growth factor-β (TGF-β) function in VSMC differentiation from NCCs is controversial. Therefore, we determined the role and mechanism of a TGF-β downstream signaling intermediate Smad2 in NCC differentiation to VSMCs.

METHODS AND RESULTS

By using Cre/loxP system, we generated a NCC tissue-specific Smad2 knockout mouse model and found that Smad2 deletion resulted in defective NCC differentiation to VSMCs in aortic arch arteries during embryonic development and caused vessel wall abnormality in adult carotid arteries where the VSMCs are derived from NCCs. The abnormalities included 1 layer of VSMCs missing in the media of the arteries with distorted and thinner elastic lamina, leading to a thinner vessel wall compared with wild-type vessel. Mechanistically, Smad2 interacted with myocardin-related transcription factor B (MRTFB) to regulate VSMC marker gene expression. Smad2 was required for TGF-β-induced MRTFB nuclear translocation, whereas MRTFB enhanced Smad2 binding to VSMC marker promoter. Furthermore, we found that Smad2, but not Smad3, was a progenitor-specific transcription factor mediating TGF-β-induced VSMC differentiation from NCCs. Smad2 also seemed to be involved in determining the physiological differences between NCC-derived and mesoderm-derived VSMCs.

CONCLUSIONS

Smad2 is an important factor in regulating progenitor-specific VSMC development and physiological differences between NCC-derived and mesoderm-derived VSMCs.

Spry1 and Spry4 differentially regulate human aortic smooth muscle cell phenotype via Akt/FoxO/myocardin signaling

Background

Changes in the vascular smooth muscle cell (VSMC) contractile phenotype occur in pathological states such as restenosis and atherosclerosis. Multiple cytokines, signaling through receptor tyrosine kinases (RTK) and PI3K/Akt and MAPK/ERK pathways, regulate these phenotypic transitions. The Spry proteins are feedback modulators of RTK signaling, but their specific roles in VSMC have not been established.

Methodology/Principal Findings

Here, we report for the first time that Spry1, but not Spry4, is required for maintaining the differentiated state of human VSMC in vitro. While Spry1 is a known MAPK/ERK inhibitor in many cell types, we found that Spry1 has little effect on MAPK/ERK signaling but increases and maintains Akt activation in VSMC. Sustained Akt signaling is required for VSMC marker expression in vitro, while ERK signaling negatively modulates Akt activation and VSMC marker gene expression. Spry4, which antagonizes both MAPK/ERK and Akt signaling, suppresses VSMC differentiation marker gene expression. We show using siRNA knockdown and ChIP assays that FoxO3a, a downstream target of PI3K/Akt signaling, represses myocardin promoter activity, and that Spry1 increases, while Spry4 decreases myocardin mRNA levels.

Conclusions

Together, these data indicate that Spry1 and Spry4 have opposing roles in VSMC phenotypic modulation, and Spry1 maintains the VSMC differentiation phenotype in vitro in part through an Akt/FoxO/myocardin pathway.

A novel in vitro model system for smooth muscle differentiation from human embryonic stem cell-derived mesenchymal cells

The objective of this study was to develop a novel in vitro model for smooth muscle cell (SMC) differentiation from human embryonic stem cell-derived mesenchymal cells (hES-MCs). We found that hES-MCs were differentiated to SMCs by transforming growth factor-β (TGF-β) in a dose- and time-dependent manner as demonstrated by the expression of SMC-specific genes smooth muscle α-actin, calponin, and smooth muscle myosin heavy chain. Under normal growth conditions, however, the differentiation capacity of hES-MCs was very limited. hES-MC-derived SMCs had an elongated and spindle-shaped morphology and contracted in response to the induction of carbachol and KCl. KCl-induced calcium transient was also evident in these cells. Compared with the parental cells, TGF-β-treated hES-MCs sustained the endothelial tube formation for a longer time due to the sustained SMC phenotype. Mechanistically, TGF-β-induced differentiation was both Smad- and serum response factor/myocardin dependent. TGF-β regulated myocardin expression via multiple signaling pathways including Smad2/3, p38 MAPK, and PI3K. Importantly, we found that a low level of myocardin was present in mesoderm prior to SMC lineage determination, and a high level of myocardin was not induced until the differentiation process was initiated. Taken together, our study characterized a novel SMC differentiation model that can be used for studying human SMC differentiation from mesoderm during vascular development.

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.

Derivation and maturation of synthetic and contractile vascular smooth muscle cells from human pluripotent stem cells

AIMS

Embryonic vascular smooth muscle cells (vSMCs) have a synthetic phenotype; in adults, they commit to the mature contractile phenotype. Research shows that human pluripotent stem cells (hPSCs) differentiate into vSMCs, but nobody has yet documented their maturation into the synthetic or contractile phenotypes. This study sought to control the fate decisions of hPSC derivatives to guide their maturation towards a desired phenotype.

METHODS AND RESULTS

The long-term differentiation of hPSCs, including the integration-free-induced PSC line, in high serum with platelet-derived growth factor-BB (PDGF-BB) and transforming growth factor-β1, allowed us to induce the synthetic vSMC (Syn-vSMC) phenotype with increased extracellular matrix (ECM) protein expression and reduced expression of contractile proteins. By monitoring the expression of two contractile proteins, smooth muscle myosin heavy chain (SMMHC) and elastin, we show that serum starvation and PDGF-BB deprivation caused maturation towards the contractile vSMC (Con-vSMC) phenotype. Con-vSMCs differ distinctively from Syn-vSMC derivatives in their condensed morphology, prominent filamentous arrangement of cytoskeleton proteins, production and assembly of elastin, low proliferation, numerous and active caveolae, enlarged endoplasmic reticulum, and ample stress fibres and bundles, as well as their high contractility. When transplanted subcutaneously into nude mice, the human Con-vSMCs aligned next to the host's growing functional vasculature, with occasional circumferential wrapping and vascular tube narrowing.

CONCLUSION

We control hPSC differentiation into synthetic or contractile phenotypes by using appropriate concentrations of relevant factors. Deriving Con-vSMCs from an integration-free hiPSC line may prove useful for regenerative therapy involving blood vessel differentiation and stabilization.

In search of novel targets for heart disease: myocardin and myocardin-related transcriptional cofactors

Growing evidence suggests that gene-regulatory networks, which are responsible for directing cardiovascular development, are altered under stress conditions in the adult heart. The cardiac gene regulatory network is controlled by cardioenriched transcription factors and multiple-cell-signaling inputs. Transcriptional coactivators also participate in gene-regulatory circuits as the primary targets of both physiological and pathological signals. Here, we focus on the recently discovered myocardin-(MYOCD) related family of transcriptional cofactors (MRTF-A and MRTF-B) which associate with the serum response transcription factor and activate the expression of a variety of target genes involved in cardiac growth and adaptation to stress via overlapping but distinct mechanisms. We discuss the involvement of MYOCD, MRTF-A, and MRTF-B in the development of cardiac dysfunction and to what extent modulation of the expression of these factors in vivo can correlate with cardiac disease outcomes. A close examination of the findings identifies the MYOCD-related transcriptional cofactors as putative therapeutic targets to improve cardiac function in heart failure conditions through distinct context-dependent mechanisms. Nevertheless, we are in support of further research to better understand the precise role of individual MYOCD-related factors in cardiac function and disease, before any therapeutic intervention is to be entertained in preclinical trials.

Transforming growth factor-β and smooth muscle differentiation

Transforming growth factor (TGF)-β family members are multifunctional cytokines regulating diverse cellular functions such as growth, adhesion, migration, apoptosis, and differentiation. TGF-βs elicit their effects via specific type I and type II serine/threonine kinase receptors and intracellular Smad transcription factors. Knockout mouse models for the different components of the TGF-β signaling pathway have revealed their critical roles in smooth muscle cell (SMC) differentiation. Genetic studies in humans have linked mutations in these signaling components to specific cardiovascular disorders such as aorta aneurysm and congenital heart diseases due to SMC defects. In this review, the current understanding of TGF-β function in SMC differentiation is highlighted, and the role of TGF-β signaling in SMC-related diseases is discussed.

Cooperation of myocardin and Smad2 in inducing differentiation of mesenchymal stem cells into smooth muscle cells

Several reports demonstrated that mesenchymal stem cells (MSCs) might differentiate into smooth muscle cells (SMCs) in vitro and in vivo. It has been shown that myocardin protein is a strong inducer of smooth muscle genes and MSCs can differentiate into SMCs in response to transforming growth factor-β (TGF-β). However, the relationship or link between myocardin and TGF-β3-induced MSC differentiation has not been fully elucidated. Here, we demonstrated that both myocardin and TGF-β3 were able to induce differentiation of rat bone marrow-derived MSCs toward smooth-muscle-like cell types, as evidenced by increasing expression of SMC-specific genes. Of note, myocardin cooperated with Smad2 to synergistically activate SM22α promoter and significantly enhance the expression of SM22α. Report assays with site-direct mutation analysis of SM22α promoter demonstrated that myocardin and Smad2 coactivated SM22α promoter mainly depending on CArG box and less on smad binding elements (SBE) sites as well. These findings reveal the cooperation of myocardin and Smad2 in process of MSC differentiation into SMCs.

Manganese superoxide dismutase inhibits neointima formation through attenuation of migration and proliferation of vascular smooth muscle cells

Superoxide anion is elevated during neointima development and is essential for neointimal vascular smooth muscle cell (VSMC) proliferation. However, little is known about the role of manganese superoxide dismutase (MnSOD, SOD2) in the neointima formation following vascular injury. SOD2 in the mitochondria plays an important role in cellular defense against oxidative damage. Because of its subcellular localization, SOD2 is considered the first line of defense against oxidative stress and plays a central role in metabolizing superoxide. Because mitochondria are the most important sources of superoxide anion, we speculated that SOD2 may have therapeutic benefits in preventing vascular remodeling. In this study, we used a rat carotid artery balloon-injury model and an adenoviral gene delivery approach to test the hypothesis that SOD2 suppresses vascular lesion formation. SOD2 was activated along with the progression of neointima formation in balloon-injured rat carotid arteries. Depletion of SOD2 by RNA interference markedly promoted the lesion formation, whereas SOD2 overexpression suppressed the injury-induced neointima formation via attenuation of migration and proliferation of VSMCs. SOD2 exerts its inhibitory effect on VSMC migration induced by angiotensin II by scavenging superoxide anion and suppressing the phosphorylation of Akt. Our data indicate that SOD2 is a negative modulator of vascular lesion formation after injury. Therefore, SOD2 augmentation may be a promising therapeutic strategy for the prevention of lesion formation in proliferative vascular diseases such as restenosis.

Response gene to complement 32 is essential for fibroblast activation in renal fibrosis

Response gene to complement 32 (RGC-32) is a downstream target of transforming growth factor-β (TGF-β). TGF-β is known to play a pathogenic role in renal fibrosis. In this study, we investigated RGC-32 function in renal fibrosis following unilateral ureteral obstruction (UUO) in mice, a model of progressive tubulointerstitial fibrosis. RGC-32 is normally expressed only in blood vessels of mouse kidney. However, UUO induces RGC-32 expression in renal interstitial cells at the early stage of kidney injury, suggesting that RGC-32 is involved in interstitial fibroblast activation. Indeed, expression of smooth muscle α-actin (α-SMA), an indicator of fibroblast activation, is limited to the interstitial cells at the early stage, and became apparent later in both interstitial and tubular cells. RGC-32 knockdown by shRNA significantly inhibits UUO-induced renal structural damage, α-SMA expression and collagen deposition, suggesting that RGC-32 is essential for the onset of renal interstitial fibrosis. In vitro studies indicate that RGC-32 mediates TGF-β-induced fibroblast activation. Mechanistically, RGC-32 interacts with Smad3 and enhances Smad3 binding to the Smad binding element in α-SMA promoter as demonstrated by DNA affinity assay. In the chromatin setting, Smad3, but not Smad2, binds to α-SMA promoter in fibroblasts. RGC-32 appears to be essential for Smad3 interaction with the promoters of fibroblast activation-related genes in vivo. Functionally, RGC-32 is crucial for Smad3-mediated α-SMA promoter activity. Taken together, we identify RGC-32 as a novel fibrogenic factor contributing to the pathogenesis of renal fibrosis through fibroblast activation.

β-catenin and Smad3 regulate the activity and stability of myocardin-related transcription factor during epithelial-myofibroblast transition

Two novel mechanisms are shown by which injury of intercellular junctions via β-catenin promotes epithelial–myofibroblast transition. β-Catenin interacts with Smad3, thereby preventing the inhibitory effect of the latter on myocardin-related transcription factor (MRTF), and maintains MRTF stability by inhibiting Smad3-mediated, GSK-3β–dependent degradation of MRTF.

Injury to the adherens junctions (AJs) synergizes with transforming growth factor-β1 (TGFβ) to activate a myogenic program (α-smooth muscle actin [SMA] expression) in the epithelium during epithelial–myofibroblast transition (EMyT). Although this synergy plays a key role in organ fibrosis, the underlying mechanisms have not been fully defined. Because we recently showed that Smad3 inhibits myocardin-related transcription factor (MRTF), the driver of the SMA promoter and many other CC(A/T)-rich GG element (CArG) box–dependent cytoskeletal genes, we asked whether AJ components might affect SMA expression through interfering with Smad3. We demonstrate that E-cadherin down-regulation potentiates, whereas β-catenin knockdown inhibits, SMA expression. Contact injury and TGFβ enhance the binding of β-catenin to Smad3, and this interaction facilitates MRTF signaling by two novel mechanisms. First, it inhibits the Smad3/MRTF association and thereby allows the binding of MRTF to its myogenic partner, serum response factor (SRF). Accordingly, β-catenin down-regulation disrupts the SRF/MRTF complex. Second, β-catenin maintains the stability of MRTF by suppressing the Smad3-mediated recruitment of glycogen synthase kinase-3β to MRTF, an event that otherwise leads to MRTF ubiquitination and degradation and the consequent loss of SRF/MRTF–dependent proteins. Thus β-catenin controls MRTF-dependent transcription and emerges as a critical regulator of an array of cytoskeletal genes, the “CArGome.”

down-regulation of Kruppel-like factor-4 (KLF4) by microRNA-143/145 is critical for modulation of vascular smooth muscle cell phenotype by transforming growth factor-beta and bone morphogenetic protein 4

In the postnatal vasculature, fully differentiated and quiescent vascular smooth muscle cells (VSMCs) in a "contractile" phenotype are required for the normal regulation of vascular tone. The transforming growth factor-β (TGF-β) superfamily of growth factors (TGF-βs and bone morphogenetic proteins (BMPs)) are potent inducers of contractile phenotype and mediate (i) induction of contractile genes, and (ii) inhibition of VSMC growth and migration. Transcription of contractile genes is positively regulated by a regulatory DNA element called a CArG box. The CArG box is activated by the binding of serum response factor and its coactivators, myocardin (Myocd) or Myocd-related transcription factors (MRTFs). Krüppel-like factor-4 (KLF4) is known to inhibit activation of the CArG box. However, the potential role of KLF4 in the contractile activities of TGF-β or BMP has not been explored. Here, we demonstrate that TGF-β and BMP4 rapidly down-regulate KLF4 through induction of microRNA-143 (miR-143) and miR-145, which leads to a reduction of KLF4 transcripts and decreased KLF4 protein expression. Inhibition of miR-145 prevents down-regulation of KLF4 and activation of contractile genes by TGF-β or BMP4, suggesting that modulation of KLF4 is a prerequisite for induction of contractile genes by TGF-β and BMP4. Interestingly, both TGF-β and BMP4 activate transcription of the miR-143/145 gene cluster through the CArG box, however, TGF-β mediates this effect through induction of Myocd expression, whereas BMP4 utilizes nuclear translocation of MRTF-A. Thus, this study sheds light on both the similarities and the differences of TGF-β and BMP4 signaling in the regulation of KLF4 and contractile genes.

Smad2 and PEA3 cooperatively regulate transcription of response gene to complement 32 in TGF-β-induced smooth muscle cell differentiation of neural crest cells

Response gene to complement 32 (RGC-32) is activated by transforming growth factor- β (TGF-β) and plays an important role in smooth muscle cell (SMC) differentiation from neural crest Monc-1 cells. The molecular mechanism governing TGF-β activation of RGC-32, however, remains to be determined. The present studies indicate that TGF-β regulates RGC-32 gene transcription. Sequence analysis revealed a Smad binding element (SBE) located in the region from -1344 to -1337 bp upstream of the transcription start site of RGC-32 gene. A polyomavirus enhancer activator (PEA3) binding site is adjacent to the SBE. Mutation at either SBE or PEA3 site significantly inhibited RGC-32 promoter activity. Mutations at both sites completely abolished TGF-β-induced promoter activity. Biochemically, TGF-β stimulated recruitment of Smad2, Smad4, and PEA3 to the RGC-32 promoter, as revealed by gel shift and chromatin immunoprecipitation analyses. Functionally, Smad2, but not Smad3, activated RGC-32 promoter. PEA3 appeared to enhance Smad2 activity. In agreement with their function, Smad2, but not Smad3, physically interacted with PEA3. In TGF-β-induced SMC differentiation of Monc-1 cells, knockdown of Smad2 by short hairpin RNA resulted in downregulation of RGC-32 and SMC marker genes. The downregulation of SMC markers, however, was rescued by exogenously introduced RGC-32. These results demonstrate that Smad2 regulation of RGC-32 transcription is essential for SMC differentiation from neural crest cells.