Phosphorylation of GATA-6 is required for vascular smooth muscle cell differentiation after mTORC1 inhibition

Restoration of ARA metabolic disorders in vascular smooth muscle cells alleviates intimal hyperplasia

Intimal hyperplasia (IH) is an innegligible issue for patients undergoing interventional therapy. The proliferation and migration of vascular smooth muscle cells (VSMCs) induced by platelet-derived growth factor-BB (PDGF-BB) are critical events in the development of IH. While the exact mechanism and effective target for IH needs further investigation. Metabolic disorders of arachidonic acid (ARA) are involved in the occurrence and progression of various diseases. In this study, we found that the expressions of soluble epoxide hydrolase (sEH) and cyclooxygenase-2 (COX-2) were significantly increased in the VSMCs during balloon injury-induced IH. Then, we employed a COX-2/sEH dual inhibitor PTUPB to increase the concentration of epoxyeicosatrienoic acids (EETs) while prevent the release of pro-inflammatory prostaglandins. Results showed that PTUPB treatment significantly reduced neointimal thickening induced by balloon injury in rats in vivo and inhibited PDGF-BB-induced proliferation and migration of VSMCs in vitro. Our results showed that PTUPB may reverse the phenotypic transition of VSMCs by inhibiting Pttg1 expression. In conclusion, we found that the dysfunction of ARA metabolism in VSMCs contributes to IH, and the COX-2/sEH dual inhibitor PTUPB attenuates IH progression by reversing the phenotypic switch in VSMC through the Sirt1/Pttg1 pathway.

(Homo-)harringtonine prevents endothelial inflammation through IRF-1 dependent downregulation of VCAM1 mRNA expression and inhibition of cell adhesion molecule protein biosynthesis

The plant alkaloid homoharringtonine (HHT) is a Food and Drug Administration (FDA)-approved drug for the treatment of hematologic malignancies. In addition to its well-established antitumor activity, accumulating evidence attributes anti-inflammatory effects to HHT, which have mainly been studied in leukocytes to date. However, a potential influence of HHT on inflammatory activation processes in endothelial cells, which are a key feature of inflammation and a prerequisite for the leukocyte-endothelial cell interaction and leukocyte extravasation, remains poorly understood. In this study, the anti-inflammatory potential of HHT and its derivative harringtonine (HT) on the TNF-induced leukocyte-endothelial cell interaction was assessed, and the underlying mechanistic basis of these effects was elucidated. HHT affected inflammation in vivo in a murine peritonitis model by reducing leukocyte infiltration and proinflammatory cytokine expression as well as ameliorating abdominal pain behavior. In vitro, HT and HHT impaired the leukocyte-endothelial cell interaction by decreasing the expression of the endothelial cell adhesion molecules intracellular adhesion molecule -1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). This effect was mediated by a bipartite mechanism. While HHT did not affect the prominent TNF-induced pro-inflammatory NF-ĸB signaling cascade, the compound downregulated the VCAM1 mRNA expression in an IRF-1-dependent manner and diminished active ICAM1 mRNA translation as determined by polysome profiling. This study highlights HHT as an anti-inflammatory compound that efficiently hampers the leukocyte-endothelial cell interaction by targeting endothelial activation processes.

The transcription factor GATA6 accelerates vascular smooth muscle cell senescence-related arterial calcification by counteracting the role of anti-aging factor SIRT6 and impeding DNA damage repair

Arterial calcification is a hallmark of vascular pathology in the elderly and in individuals with chronic kidney disease (CKD). Vascular smooth muscle cells (VSMCs), after attaining a senescent phenotype, are implicated in the calcifying process. However, the underlying mechanism remains to be elucidated. Here, we reveal an aberrant upregulation of transcriptional factor GATA6 in the calcified aortas of humans, mice with CKD and mice subjected to vitamin D3 injection. Knockdown of GATA6, via recombinant adeno-associated virus carrying GATA6 shRNA, inhibited the development of arterial calcification in mice with CKD. Further gain- and loss-of function experiments in vitro verified the contribution of GATA6 in osteogenic differentiation of VSMCs. Samples of human aorta exhibited a positive relationship between age and GATA6 expression and GATA6 was also elevated in the aortas of old as compared to young mice. Calcified aortas displayed senescent features with VSMCs undergoing premature senescence, blunted by GATA6 downregulation. Notably, abnormal induction of GATA6 in senescent and calcified aortas was rescued in Sirtuin 6 (SIRT6)-transgenic mice, a well-established longevity mouse model. Suppression of GATA6 accounted for the favorable effect of SIRT6 on VSMCs senescence prevention. Mechanistically, SIRT6 inhibited the transcription of GATA6 by deacetylation and increased degradation of transcription factor Nkx2.5. Moreover, GATA6 was induced by DNA damage stress during arterial calcification and subsequently impeded the Ataxia-telangiectasia mutated (ATM)-mediated DNA damage repair process, leading to accelerated VSMCs senescence and osteogenic differentiation. Thus, GATA6 is a novel regulator in VSMCs senescence. Our findings provide novel insight in arterial calcification and a potential new target for intervention.

Single-cell transcriptomics identifies adipose tissue CD271+ progenitors for enhanced angiogenesis in limb ischemia

Therapeutic angiogenesis using mesenchymal stem/stromal cell grafts have shown modest and controversial effects in preventing amputation for patients with critical limb ischemia. Through single-cell transcriptomic analysis of human tissues, we identify CD271+ progenitors specifically from subcutaneous adipose tissue (AT) as having the most prominent pro-angiogenic gene profile distinct from other stem cell populations. AT-CD271+ progenitors demonstrate robust in vivo angiogenic capacity over conventional adipose stromal cell grafts, characterized by long-term engraftment, augmented tissue regeneration, and significant recovery of blood flow in a xenograft model of limb ischemia. Mechanistically, the angiogenic capacity of CD271+ progenitors is dependent on functional CD271 and mTOR signaling. Notably, the number and angiogenic capacity of CD271+ progenitors are strikingly reduced in insulin-resistant donors. Our study highlights the identification of AT-CD271+ progenitors with in vivo superior efficacy for limb ischemia. Furthermore, we showcase comprehensive single-cell transcriptomics strategies for identification of suitable grafts for cell therapy.

Role of ascorbic acid in cardiac allograft vasculopathy

PURPOSE OF THE REVIEW

Cardiac allograft vasculopathy (CAV) is a progressive fibroproliferative disease which occurs after heart transplantation and is associated with significant long-term morbidity and mortality. Currently available strategies including statins, mammalian target of rapamycin (mTOR) inhibitors, and revascularization, have limited overall effectiveness in treating this pathology once the disease process is established. mTOR inhibitors, while effective when used early in the disease process, are not well tolerated, and hence not routinely used in post-transplant care.

RECENT DATA

Recent work on rodent models have given us a novel mechanistic understanding of effects of ascorbic acid in preventing CAV. TET methyl cytosine dioxygenase2 (TET2) reduces vascular smooth muscle cell (VSMC) apoptosis and intimal thickening. TET2 is repressed by interferon γ (IFNγ) in the setting of CAV. Ascorbic acid has been shown to promote TET2 activity and attenuate allograft vasculopathy in animal models and CAV progression in a small clinical trial.

SUMMARY

CAV remains a challenging disease process and needs better preventative strategies. Ascorbic acid improves endothelial dysfunction, reduces reactive oxygen species, and prevents development of intimal hyperplasia by preventing smooth muscle cell apoptosis and hyperproliferation. Further large-scale randomized control studies of ascorbic acid are needed to establish the role in routine post-transplant management.

Acne Transcriptomics: Fundamentals of Acne Pathogenesis and Isotretinoin Treatment

This review on acne transcriptomics allows for deeper insights into the pathogenesis of acne and isotretinoin's mode of action. Puberty-induced insulin-like growth factor 1 (IGF-1), insulin and androgen signaling activate the kinase AKT and mechanistic target of rapamycin complex 1 (mTORC1). A Western diet (hyperglycemic carbohydrates and milk/dairy products) also co-stimulates AKT/mTORC1 signaling. The AKT-mediated phosphorylation of nuclear FoxO1 and FoxO3 results in their extrusion into the cytoplasm, a critical switch which enhances the transactivation of lipogenic and proinflammatory transcription factors, including androgen receptor (AR), sterol regulatory element-binding transcription factor 1 (SREBF1), peroxisome proliferator-activated receptor γ (PPARγ) and signal transducer and activator of transcription 3 (STAT3), but reduces the FoxO1-dependent expression of GATA binding protein 6 (GATA6), the key transcription factor for infundibular keratinocyte homeostasis. The AKT-mediated phosphorylation of the p53-binding protein MDM2 promotes the degradation of p53. In contrast, isotretinoin enhances the expression of p53, FoxO1 and FoxO3 in the sebaceous glands of acne patients. The overexpression of these proapoptotic transcription factors explains isotretinoin's desirable sebum-suppressive effect via the induction of sebocyte apoptosis and the depletion of BLIMP1(+) sebocyte progenitor cells; it also explains its adverse effects, including teratogenicity (neural crest cell apoptosis), a reduced ovarian reserve (granulosa cell apoptosis), the risk of depression (the apoptosis of hypothalamic neurons), VLDL hyperlipidemia, intracranial hypertension and dry skin.

Single cell transcriptomics identifies adipose tissue CD271+ progenitors for enhanced angiogenesis in limb ischemia

Therapeutic angiogenesis using mesenchymal stem/stromal cell grafts have shown modest and controversial effects in preventing amputation for patients with critical limb ischemia. Through single-cell transcriptomic analysis of human tissues, we identified CD271 + progenitors specifically from subcutaneous adipose tissue (AT) as having the most prominent pro-angiogenic gene profile distinct from other stem cell populations. AT-CD271 + progenitors demonstrated robust in vivo angiogenic capacity, over conventional adipose stromal cell grafts, characterized by long-term engraftment, augmented tissue regeneration, and significant recovery of blood flow in a xenograft model of limb ischemia. Mechanistically, the angiogenic capacity of CD271 + progenitors is dependent on functional CD271 and mTOR signaling. Notably, the number and angiogenic capacity of CD271 + progenitors was strikingly reduced in insulin resistant donors. Our study highlights the identification of AT-CD271 + progenitors with in vivo superior efficacy for limb ischemia. Furthermore, we showcase comprehensive single-cell transcriptomics strategies for identification of suitable grafts for cell therapy.

HIGHLIGHTS

Adipose tissue stromal cells have a distinct angiogenic gene profile among human cell sources. CD271 + progenitors in adipose tissue have a prominent angiogenic gene profile. CD271 + progenitors show superior therapeutic capacities for limb ischemia. CD271 + progenitors are reduced and functionally impaired in insulin resistant donors.

GRAPHICAL ABSTRACT

Transcription factor GATA6 promotes migration of human coronary artery smooth muscle cells in vitro

Vascular smooth muscle cell plasticity plays a pivotal role in the pathophysiology of vascular diseases. Despite compelling evidence demonstrating the importance of transcription factor GATA6 in vascular smooth muscle, the functional role of GATA6 remains poorly understood. The aim of this study was to elucidate the role of GATA6 on cell migration and to gain insight into GATA6-sensitive genes in smooth muscle. We found that overexpression of GATA6 promotes migration of human coronary artery smooth muscle cells in vitro, and that silencing of GATA6 in smooth muscle cells resulted in reduced cellular motility. Furthermore, a complete microarray screen of GATA6-sensitive gene transcription resulted in 739 upregulated and 248 downregulated genes. Pathways enrichment analysis showed involvement of transforming growth factor beta (TGF-β) signaling which was validated by measuring mRNA expression level of several members. Furthermore, master regulators prediction based on microarray data revealed several members of (mitogen activated protein kinase) MAPK pathway as a master regulators, reflecting involvement of MAPK pathway also. Our findings provide further insights into the functional role of GATA6 in vascular smooth muscle and suggest that targeting GATA6 may constitute as a new approach to inhibit vascular smooth muscle migration.

Towards Understanding the Gene-Specific Roles of GATA Factors in Heart Development: Does GATA4 Lead the Way?

Transcription factors play crucial roles in the regulation of heart induction, formation, growth and morphogenesis. Zinc finger GATA transcription factors are among the critical regulators of these processes. GATA4, 5 and 6 genes are expressed in a partially overlapping manner in developing hearts, and GATA4 and 6 continue their expression in adult cardiac myocytes. Using different experimental models, GATA4, 5 and 6 were shown to work together not only to ensure specification of cardiac cells but also during subsequent heart development. The complex involvement of these related gene family members in those processes is demonstrated through the redundancy among them and crossregulation of each other. Our recent identification at the genome-wide level of genes specifically regulated by each of the three family members and our earlier discovery that gata4 and gata6 function upstream, while gata5 functions downstream of noncanonical Wnt signalling during cardiac differentiation, clearly demonstrate the functional differences among the cardiogenic GATA factors. Such suspected functional differences are worth exploring more widely. It appears that in the past few years, significant advances have indeed been made in providing a deeper understanding of the mechanisms by which each of these molecules function during heart development. In this review, I will therefore discuss current evidence of the role of individual cardiogenic GATA factors in the process of heart development and emphasize the emerging central role of GATA4.

Chemical-induced gene expression ranking and its application to pancreatic cancer drug repurposing

Chemical-induced gene expression profiles provide critical information of chemicals in a biological system, thus offering new opportunities for drug discovery. Despite their success, large-scale analysis leveraging gene expressions is limited by time and cost. Although several methods for predicting gene expressions were proposed, they only focused on imputation and classification settings, which have limited applications to real-world scenarios of drug discovery. Therefore, a chemical-induced gene expression ranking (CIGER) framework is proposed to target a more realistic but more challenging setting in which overall rankings in gene expression profiles induced by de novo chemicals are predicted. The experimental results show that CIGER significantly outperforms existing methods in both ranking and classification metrics. Furthermore, a drug screening pipeline based on CIGER is proposed to identify potential treatments of drug-resistant pancreatic cancer. Our predictions have been validated by experiments, thereby showing the effectiveness of CIGER for phenotypic compound screening of precision medicine.

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A new deep-learning method (CIGER) for chemical-induced gene expression ranking

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CIGER can predict gene expression for de novo chemicals from chemical structures

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We discovered drugs for the treatment of drug-resistant pancreatic cancer

In recent years, a phenotype-based drug discovery approach using chemical-induced gene expressions has shown to be effective in drug discovery and precision medicine. However, it is not feasible to experimentally determine chemical-induced gene expressions for all available chemicals of interest, thereby hindering the application of gene expression-based compound screening on a large scale. Thus, it is crucial to design a computational approach that can generate gene expression information for any chemicals. We proposed a new, deep-learning framework named chemical-induced gene expression ranking (CIGER) to predict a landmark gene expression profile (i.e., gene ranking) induced by de novo chemicals based on their chemical structures. Leveraging CIGER, we predicted and experimentally validated that several existing drugs can increase the therapeutic response on drug-resistant pancreatic cancer. Our results demonstrated the effectiveness of CIGER for precision drug discovery in practice.

Targeting smooth muscle cell phenotypic switching in vascular disease

Objective

The phenotypic plasticity of vascular smooth muscle cells (VSMCs) is central to vessel growth and remodeling, but also contributes to cardiovascular pathologies. New technologies including fate mapping, single cell transcriptomics, and genetic and pharmacologic inhibitors have provided fundamental new insights into the biology of VSMC. The goal of this review is to summarize the mechanisms underlying VSMC phenotypic modulation and how these might be targeted for therapeutic benefit.

Methods

We summarize findings from extensive literature searches to highlight recent discoveries in the mechanisms underlying VSMC phenotypic switching with particular relevance to intimal hyperplasia. PubMed was searched for publications between January 2001 and December 2020. Search terms included VSMCs, restenosis, intimal hyperplasia, phenotypic switching or modulation, and drug-eluting stents. We sought to highlight druggable pathways as well as recent landmark studies in phenotypic modulation.

Results

Lineage tracing methods have determined that a small number of mature VSMCs dedifferentiate to give rise to oligoclonal lesions in intimal hyperplasia and atherosclerosis. In atherosclerosis and aneurysm, single cell transcriptomics reveal a striking diversity of phenotypes that can arise from these VSMCs. Mechanistic studies continue to identify new pathways that influence VSMC phenotypic plasticity. We review the mechanisms by which the current drug-eluting stent agents prevent restenosis and note remaining challenges in peripheral and diabetic revascularization for which new approaches would be beneficial. We summarize findings on new epigenetic (DNA methylation/TET methylcytosine dioxygenase 2, histone deacetylation, bromodomain proteins), transcriptional (Hippo/Yes-associated protein, peroxisome proliferator-activity receptor-gamma, Notch), and β3-integrin-mediated mechanisms that influence VSMC phenotypic modulation. Pharmacologic and genetic targeting of these pathways with agents including ascorbic acid, histone deacetylase or bromodomain inhibitors, thiazolidinediones, and integrin inhibitors suggests potential therapeutic value in the setting of intimal hyperplasia.

Conclusions

Understanding the molecular mechanisms that underlie the remarkable plasticity of VSMCs may lead to novel approaches to treat and prevent cardiovascular disease and restenosis.

Platelet-Derived Microvesicles Promote VSMC Dedifferentiation After Intimal Injury via Src/Lamtor1/mTORC1 Signaling

Phenotypic switch of vascular smooth muscle cells (VSMCs) is important in vascular remodeling which causes hyperplasia and restenosis after intimal injury. Platelets are activated at injured intima and secrete platelet-derived microvesicles (PMVs). Herein, we demonstrated the role of PMVs in VSMC phenotypic switch and the potential underlying mechanisms. In vivo, platelets were locally adhered and activated at intimal injury site, while Lamtor1 was promoted and VSMCs were dedifferentiated. PMVs, collected from collagen-activated platelets in vitro which mimicked collagen exposure during intimal injury, promoted VSMC dedifferentiation, induced Lamtor1 expression, and activated mTORC1 signaling, reflected by the phosphorylation of two downstream targets, i.e., S6K and 4E-BP1. Knockdown of Lamtor1 with small interfering RNA attenuated these processes induced by PMVs. Based on the previously published proteomic data, Ingenuity Pathway Analysis revealed that Src may participate in regulating effects of PMVs. Src inhibitor significantly reversed the effects of PMVs on VSMC dedifferentiation, Lamtor1 expression and mTORC1 activation. Furthermore, in SMC-specific Lamtor1 knockout mice, intimal hyperplasia was markedly attenuated after intimal injury compared with the wild type. Our data suggested that PMVs secreted by activated platelets promoted VSMC dedifferentiation via Src/Lamtor1/mTORC1 signaling pathway. Lamtor1 may be a potential therapeutic target for intimal hyperplasia after injury.

Curcumin enhances the membrane trafficking of the sodium iodide symporter and augments radioiodine uptake in dedifferentiated thyroid cancer cells via suppression of the PI3K-AKT signaling pathway

Radioactive iodine (RAI) is commonly used to treat differentiated thyroid cancer (DTC). A major challenge is the dedifferentiation of DTC with the loss of radioiodine uptake. Patients with distant metastases have persistent or recurrent disease and develop resistance to RAI therapy due to tumor dedifferentiation. Hence, tumor redifferentiation to restore sensitivity to RAI therapy is considered a promising strategy to overcome RAI resistance. In the present study, curcumin, a natural polyphenolic compound, was found to re-induce cell differentiation and increase the expression of thyroid-specific transcription factors, TTF-1, TTF-2 and transcriptional factor paired box 8 (PAX8), and iodide-metabolizing proteins, including thyroid stimulating hormone receptor (TSHR), thyroid peroxidase (TPO) and sodium iodide symporter (NIS) in dedifferentiated thyroid cancer cell lines, BCPAP and KTC-1. Importantly, curcumin enhanced NIS glycosylation and its membrane trafficking, resulting in a significant improvement of radioiodine uptake in vitro. Additionally, AKT knockdown phenocopied the restoration of thyroid-specific gene expression; however, ectopic expressed AKT inhibited curcumin-induced up-regulation of NIS protein, demonstrating that curcumin might improve radioiodine sensitivity via the inhibition of the PI3K-AKT-mTOR signaling pathway. Our study demonstrates that curcumin could represent a promising adjunctive therapy for restoring iodide avidity and improve radioiodine therapeutic efficacy in patients with RAI-refractory thyroid carcinoma.

Gleevec and Rapamycin Synergistically Reduce Cell Viability and Inhibit Proliferation and Angiogenic Function of Mouse Bone Marrow-Derived Endothelial Progenitor Cells

OBJECTIVE

This study investigates the synergistic effects of Gleevec (imatinib) and rapamycin on the proliferative and angiogenic properties of mouse bone marrow-derived endothelial progenitor cells (EPCs).

MATERIALS AND METHODS

EPCs were isolated from mouse bone marrow and treated with different concentrations of Gleevec or rapamycin individually or in combination. The cell viability and proliferation were examined using the MTT assay. An analysis of cell cycle and apoptosis was performed using flow cytometry. Formation of capillary-like tubes was examined in vitro, and the protein expression of cell differentiation markers was determined using Western blot analysis.

RESULTS

Gleevec significantly reduced cell viability, cell proliferation, and induced cell apoptosis in EPCs. Rapamycin had similar effects on EPCs, but it did not induce cell apoptosis. The combination of Gleevec and rapamycin reduced the cell proliferation but increased cell apoptosis. Although rapamycin had no demonstratable effect on tube formation, the combined therapy of Gleevec and rapamycin significantly reduced tube formation when compared with Gleevec alone. Mechanistically, Gleevec, but not rapamycin, induced a significant elevation in caspase-3 activity in EPCs, and it attenuated the expression of the endothelial protein marker platelet-derived growth factor receptor α. Functionally, rapamycin, but not Gleevec, significantly enhanced the expression of endothelial differentiation marker proteins, while attenuating the expression of mammalian target of rapamycin signaling-related proteins.

CONCLUSIONS

Gleevec and rapamycin synergistically suppress cell proliferation and tube formation of EPCs by inducing cell apoptosis and endothelial differentiation. Mechanistically, it is likely that rapamycin enhances the proapoptotic and antiangiogenic effects of Gleevec by promoting the endothelial differentiation of EPCs. Given that EPCs are involved in the pathogenesis of some cardiovascular diseases and critical to angiogenesis, pharmacological inhibition of EPC proliferation by combined Gleevec and rapamycin therapy may be a promising approach for suppressing cardiovascular disease pathologies associated with angiogenesis.

LncRNA LINC00680 promotes lung adenocarcinoma growth via binding to GATA6 and canceling GATA6-mediated suppression of SOX12 expression

Lung adenocarcinoma (LUAD) is a major subtype of non-small-cell lung cancers (NSCLC). LINC00680 has been characterized as a novel oncogenic lncRNA in LUAD, but its regulatory mechanisms remain largely unclear. This study aimed to explore the subcellular localization of LINC00680 in LUAD and its regulation on the transcriptional process. LUAD cell lines (A549, H1650, and H1299) were used for in vitro and in vivo studies. Results showed LINC00680 depletion resulted in G0/G1 phase arrest of LUAD cells and reduced CDK4 and cyclin D1 expression in H1650 and H1299 cells. LINC00680 overexpression promoted A549 cell proliferation and increased CDK4 and cyclin D1 expression. RNA-fluorescence in situ hybridization (FISH) assay showed that LINC00680 has both cytoplasmic and nuclear distribution in LUAD cells. RNA pulldown and western blotting assays confirmed a physical interaction between LINC00680 and GATA6. In LUAD cells, GATA6 overexpression only slightly suppressed SOX12 transcription. ChIP-qPCR and dual-luciferase assay showed that GATA6 only weakly bound to the SOX12 promoter and decreased its activity. However, when LINC00680 was depleted, these transcriptional suppressive effects were significantly enhanced. These findings suggested that LINC00680 forms a complex with GATA6 and weakens its transcriptional suppressive effect on SOX12 expression. In the nude mice model, LINC00680 overexpression partly abrogated the growth-suppressive effects of GATA6 on A549 derived tumors. In summary, this study revealed a novel LINC00680-GATA6-SOX12 axis in promoting LUAD cell cycle progression and proliferation. Future studies should be conducted for a better understanding of the complex networking of LINC00680 in LUAD.

The GATA Transcription Factor Gaf1 Represses tRNAs, Inhibits Growth, and Extends Chronological Lifespan Downstream of Fission Yeast TORC1

Target of Rapamycin Complex 1 (TORC1) signaling promotes growth and aging. Inhibition of TORC1 leads to reduced protein translation, which promotes longevity. TORC1-dependent post-transcriptional regulation of protein translation has been well studied, while analogous transcriptional regulation is less understood. Here we screen fission yeast mutants for resistance to Torin1, which inhibits TORC1 and cell growth. Cells lacking the GATA factor Gaf1 (gaf1Δ) grow normally even in high doses of Torin1. The gaf1Δ mutation shortens the chronological lifespan of non-dividing cells and diminishes Torin1-mediated longevity. Expression profiling and genome-wide binding experiments show that upon TORC1 inhibition, Gaf1 directly upregulates genes for small-molecule metabolic pathways and indirectly represses genes for protein translation. Surprisingly, Gaf1 binds to and downregulates the tRNA genes, so it also functions as a transcription factor for RNA polymerase III. Thus, Gaf1 controls the transcription of both protein-coding and tRNA genes to inhibit translation and growth downstream of TORC1.

Protective Role of RNA Helicase DEAD-Box Protein 5 in Smooth Muscle Cell Proliferation and Vascular Remodeling

RATIONALE

RNA helicases, highly conserved enzymes, are currently believed to be not only involved in RNA modulation, but also in other biological processes. We recently reported that RNA helicase DDX (DEAD-box protein)-5 is required for maintaining the homeostasis of vascular smooth muscle cells (SMCs). However, the expression and function of RNA helicase in vascular physiology and disease is unknown.

OBJECTIVE

To investigate the role of RNA helicase in vascular diseases.

METHODS AND RESULTS

We showed here that DDX-5 was the most abundant DEAD-box protein expressed in human and rodent artery, which mainly located in SMCs. It was demonstrated that DDX-5 levels were reduced in cytokine-stimulated SMCs and vascular lesions. DDX-5 knocking down or deficiency increased SMC proliferation and migration, whereas overexpression of DDX-5 prevented aberrant proliferation and migration of SMCs. Mechanistic studies revealed transcription factor GATA (GATA-binding protein)-6 as a novel downstream target of DDX-5, which directly interacted with GATA-6 and protected it from MDM (mouse double minute)-2-mediated degradation. Our ChIP assay identified a previously unreported binding of p27^Kip1 promoter to GATA-6. DDX-5 increased the recruitment of GATA-6 to p27^Kip1 promoter, which enhanced p27^Kip1 expression and maintained SMC quiescence. Finally, we showed exacerbated neointima formation in DDX-5 SMC-deficient mice after femoral artery injury, whereas overexpression of DDX-5 potently inhibited vascular remodeling in balloon-injured rat carotid artery.

CONCLUSIONS

These findings provide the first evidence for a role of RNA helicase DDX-5 in the protection against SMC proliferation, migration, and neointimal hyperplasia. Our data extend the fundamental role of RNA helicase beyond RNA modulation, which provides the basic information for new therapeutic strategies for vascular diseases.

Cell-Specific Effects of GATA (GATA Zinc Finger Transcription Factor Family)-6 in Vascular Smooth Muscle and Endothelial Cells on Vascular Injury Neointimal Formation

Objective- Transcription factor GATA (GATA zinc finger transcription factor family)-6 is highly expressed in vessels and rapidly downregulated in balloon-injured carotid arteries and viral delivery of GATA-6 to the vessels limited the neointimal formation, however, little is known about its cell-specific regulation of in vivo vascular smooth muscle cell (VSMC) phenotypic state contributing to neointimal formation. This study aims to determine the role of vascular cell-specific GATA-6 in ligation- or injury-induced neointimal hyperplasia in vivo. Approach and Results- Endothelial cell and VSMC-specific GATA-6 deletion mice are generated, and the results indicate that endothelial cell-specific GATA-6 deletion mice exhibit significant decrease of VSMC proliferation and attenuation of neointimal formation after artery ligation and injury compared with the wild-type littermate control mice. PDGF (platelet-derived growth factor)-B is identified as a direct target gene, and endothelial cell-GATA-6-PDGF-B pathway regulates VSMC proliferation and migration in a paracrine manner which controls the neointimal formation. In contrast, VSMC-specific GATA-6 deletion promotes injury-induced VSMC transformation from contractile to proliferative synthetic phenotype leading to increased neointimal formation. CCN (cysteine-rich 61/connective tissue growth factor/nephroblastoma overexpressed family)-5 is identified as a novel target gene, and VSMC-specific CCN-5 overexpression in mice reverses the VSMC-GATA-6 deletion-mediated increased cell proliferation and migration and finally attenuates the neointimal formation. Conclusions- This study gives us a direct in vivo evidence of GATA-6 cell lineage-specific regulation of PDGF-B and CCN-5 on VSMC phenotypic state, proliferation and migration contributing to neointimal formation, which advances our understanding of in vivo neointimal hyperplasia, meanwhile also provides opportunities for future therapeutic interventions.

Persistent myopathy despite release of partial obstruction: in vivo reversal of dysfunction and transcriptional responses using rapamycin

Current and potential medical therapy for obstruction-induced myopathic bladder dysfunction (from benign prostatic hyperplasia or posterior urethral valves) focuses on symptoms. The persistent tissue pathology and dysfunction after release of obstruction is often deemed irreversible without any systematic therapeutic approaches. As rapamycin can attenuate bladder smooth muscle hypertrophy and dysfunction during the genesis of partial obstruction in vivo, we tested whether rapamycin could improve persistent function after release of obstruction (de-obstruction or REL). Female Sprague-Dawley rat bladders were partially obstructed (PBO) by suturing around both the urethra and a para-urethral steel rod, then removing the rod. One day prior to release of obstruction (preREL), voiding parameters and residual urine volume of preREL+future rapa, preREL+future veh groups were recorded. Release of obstruction (REL) was performed by suture removal following 6 weeks of PBO. For 4 more weeks after the de-obstruction, REL animals were randomized to rapamycin (REL+rapa) or vehicle (REL+veh). PBO for 6 weeks were used as positive controls. In shams, the urethra was exposed, but no suture tied. Voiding parameters and residual urine volume were measured prior to sacrifice of sham and REL+veh or REL+rapa, and PBO. Rapamycin efficacy was tested by pair-wise comparison of changes in individual voiding data from preREL+future veh or preREL+future rapa versus REL+veh or REL+rapa, respectively, as well as by comparisons of REL+veh to REL+rapa groups. Bladders were weighed and processed for a high-throughput QPCR array, and histopathology. Bladder/body mass ratios with PBO increased significantly and remained higher in the release phase in REL+veh animals. REL+rapa versus REL+veh improved residual volumes and micturition fractions toward sham levels. Three genes encoding extracellular proteins, BMP2, SOD3, and IGFBP7, correlated with functional improvement by Pearson's correlations. The promoters of these genes showed enrichment for several motifs including circadian E-boxes. While obstruction and REL augmented CLOCK and NPAS2 expression above sham levels, rapamycin treatment during release significantly blocked their expression. This experimental design of pharmaco-intervention during the de-obstruction phase revealed a novel pathway dysregulated during the clinically relevant treatment phase of obstructive bladder myopathy.

Targeting GATA4 for cardiac repair

Various strategies have been applied to replace the loss of cardiomyocytes in order to restore reduced cardiac function and prevent the progression of heart disease. Intensive research efforts in the field of cellular reprogramming and cell transplantation may eventually lead to efficient in vivo applications for the treatment of cardiac injuries, representing a novel treatment strategy for regenerative medicine. Modulation of cardiac transcription factor (TF) networks by chemical entities represents another viable option for therapeutic interventions. Comprehensive screening projects have revealed a number of molecular entities acting on molecular pathways highly critical for cellular lineage commitment and differentiation, including compounds targeting Wnt- and transforming growth factor beta (TGFβ)-signaling. Furthermore, previous studies have demonstrated that GATA4 and NKX2-5 are essential TFs in gene regulation of cardiac development and hypertrophy. For example, both of these TFs are required to fully activate mechanical stretch-responsive genes such as atrial natriuretic peptide and brain natriuretic peptide (BNP). We have previously reported that the compound 3i-1000 efficiently inhibited the synergy of the GATA4-NKX2-5 interaction. Cellular effects of 3i-1000 have been further characterized in a number of confirmatory in vitro bioassays, including rat cardiac myocytes and animal models of ischemic injury and angiotensin II-induced pressure overload, suggesting the potential for small molecule-induced cardioprotection.

LMO7 Is a Negative Feedback Regulator of Transforming Growth Factor β Signaling and Fibrosis

BACKGROUND

Vascular smooth muscle cells (SMCs) synthesize extracellular matrix (ECM) that contributes to tissue remodeling after revascularization interventions. The cytokine transforming growth factor β (TGF-β) is induced on tissue injury and regulates tissue remodeling and wound healing, but dysregulated signaling results in excess ECM deposition and fibrosis. The LIM (Lin11, Isl-1 & Mec-3) domain protein LIM domain only 7 (LMO7) is a TGF-β1 target gene in hepatoma cells, but its role in vascular physiology and fibrosis is unknown.

METHODS

We use carotid ligation and femoral artery denudation models in mice with global or inducible smooth muscle-specific deletion of LMO7, and knockout, knockdown, overexpression, and mutagenesis approaches in mouse and human SMC, and human arteriovenous fistula and cardiac allograft vasculopathy samples to assess the role of LMO7 in neointima and fibrosis.

RESULTS

We demonstrate that LMO7 is induced postinjury and by TGF-β in SMC in vitro. Global or SMC-specific LMO7 deletion enhanced neointimal formation, TGF-β signaling, ECM deposition, and proliferation in vascular injury models. LMO7 loss of function in human and mouse SMC enhanced ECM protein expression at baseline and after TGF-β treatment. TGF-β neutralization or receptor antagonism prevented the exacerbated neointimal formation and ECM synthesis conferred by loss of LMO7. Notably, loss of LMO7 coordinately amplified TGF-β signaling by inducing expression of Tgfb1 mRNA, TGF-β protein, αv and β3 integrins that promote activation of latent TGF-β, and downstream effectors SMAD3 phosphorylation and connective tissue growth factor. Mechanistically, the LMO7 LIM domain interacts with activator protein 1 transcription factor subunits c-FOS and c-JUN and promotes their ubiquitination and degradation, disrupting activator protein 1-dependent TGF-β autoinduction. Importantly, preliminary studies suggest that LMO7 is upregulated in human intimal hyperplastic arteriovenous fistula and cardiac allograft vasculopathy samples, and inversely correlates with SMAD3 phosphorylation in cardiac allograft vasculopathy.

CONCLUSIONS

LMO7 is induced by TGF-β and serves to limit vascular fibrotic responses through negative feedback regulation of the TGF-β pathway. This mechanism has important implications for intimal hyperplasia, wound healing, and fibrotic diseases.

From embryogenesis to adulthood: Critical role for GATA factors in heart development and function

Cardiac development is governed by a complex network of transcription factors (TFs) that regulate cell fates in a spatiotemporal manner. Among these, the GATA family of zinc finger TFs plays prominent roles in regulating the development of the myocardium, endocardium, and outflow tract. This family comprises six members three of which, GATA4, 5, and 6, are predominantly expressed in cardiac cells where they activate specific downstream gene targets via interactions with one another and with other TFs and signaling molecules. Their critical function in heart formation is evidenced by the phenotypes of animal models lacking these factors and by the broad spectrum of human congenital heart diseases associated with mutations in their genes. Similarly, in the postnatal heart, these proteins play significant and nonredundant roles in cardiac function, regulating adaptive stress responses including cardiomyocyte hypertrophy and survival, as well as endothelial homeostasis and angiogenesis. As such, decreased expression of either GATA4, 5, or 6 results in impaired cardiovascular homeostasis and increased risk of premature and serious cardiovascular events such as hypertension, arrhythmia, aortopathy, and heart failure. Although a great deal of progress has been made in understanding GATA-dependent regulatory processes in the heart, the molecular mechanisms underlying the specificity of GATA factors and their upstream regulation remain incompletely understood. The knowledge and tools developed since their discovery 25 years ago should accelerate progress toward further elucidation of their mechanisms of action in health and disease. This in turn will greatly improve diagnosis and care for the millions of individuals affected by congenital and acquired cardiac disease worldwide.

Nuclear Focal Adhesion Kinase Controls Vascular Smooth Muscle Cell Proliferation and Neointimal Hyperplasia Through GATA4-Mediated Cyclin D1 Transcription

RATIONALE

Neointimal hyperplasia is characterized by excessive accumulation of vascular smooth muscle cells (SMCs) leading to occlusive disorders, such as atherosclerosis and stenosis. Blood vessel injury increases growth factor secretion and matrix synthesis, which promotes SMC proliferation and neointimal hyperplasia via FAK (focal adhesion kinase).

OBJECTIVE

To understand the mechanism of FAK action in SMC proliferation and neointimal hyperplasia.

METHODS AND RESULTS

Using combined pharmacological FAK catalytic inhibition (VS-4718) and SMC-specific FAK kinase-dead (Myh11-Cre-ER^T2) mouse models, we report that FAK regulates SMC proliferation and neointimal hyperplasia in part by governing GATA4- (GATA-binding protein 4) cyclin D1 signaling. Inhibition of FAK catalytic activity facilitates FAK nuclear localization, which is required for proteasome-mediated GATA4 degradation in the cytoplasm. Chromatin immunoprecipitation identified GATA4 binding to the mouse cyclin D1 promoter, and loss of GATA4-mediated cyclin D1 transcription diminished SMC proliferation. Stimulation with platelet-derived growth factor or serum activated FAK and redistributed FAK from the nucleus to cytoplasm, leading to concomitant increase in GATA4 protein and cyclin D1 expression. In a femoral artery wire injury model, increased neointimal hyperplasia was observed in parallel with elevated FAK activity, GATA4 and cyclin D1 expression following injury in control mice, but not in VS-4718-treated and SMC-specific FAK kinase-dead mice. Finally, lentiviral shGATA4 knockdown in the wire injury significantly reduced cyclin D1 expression, SMC proliferation, and neointimal hyperplasia compared with control mice.

CONCLUSIONS

Nuclear enrichment of FAK by inhibition of FAK catalytic activity during vessel injury blocks SMC proliferation and neointimal hyperplasia through regulation of GATA4-mediated cyclin D1 transcription.

Rapamycin prevents thoracic aortic aneurysm and dissection in mice

OBJECTIVE

The purpose of this study was to investigate whether rapamycin inhibits the development of thoracic aortic aneurysm and dissection (TAAD) in mice.

METHODS

Three-week-old C57BL/6J male mice were fed a normal diet and randomized into a control group (n = 6), β-aminopropionitrile fumarate (BAPN) group (Gp A; n = 15), BAPN plus rapamycin (5 mg) group (Gp B; n = 8), and BAPN plus rapamycin (10 mg) group (Gp C; n = 8). Gp A, Gp B, and Gp C were administered BAPN (1 g/kg/d) for 4 weeks. One week after BAPN administration, Gp B and Gp C were treated with rapamycin (5 mg/kg/d or 10 mg/kg/d) through gavage for 21 days. Thoracic aortas were harvested for Western blot and immunofluorescence staining at day 14 and for morphologic and histologic analyses at day 28.

RESULTS

BAPN treatment induced TAAD formation in mice. The incidence of TAAD in control, Gp A, Gp B, and Gp C mice was 0%, 80%, 25%, and 37.5%, respectively. Smaller thoracic aortic diameters (ascending aorta and arch) were observed in Gp B and Gp C mice than in Gp A mice (Gp B vs Gp A: ascending aorta, ex vivo, 1.07 ± 0.21 mm vs 1.80 ± 0.67 mm [P < .05]; aortic arch, ex vivo, 1.51 ± 0.40 mm vs 2.70 ± 1.06 mm [P < .05]; Gp C vs Gp A: ascending aortas, ex vivo, 1.10 ± 0.33 mm vs 1.80 ± 0.67 mm [P < .05]; aortic arch, ex vivo, 1.55 ± 0.56 mm vs 2.70 ± 1.06 mm [P < .05]). TAAD mice exhibited elastin fragmentation, abundant inflammatory cell infiltration, and significantly increased matrix metalloproteinase production in the aorta, and rapamycin treatment alleviated these changes. The protein levels of p-S6K and p-S6 in TAAD aortic tissues increased significantly, whereas they were suppressed by rapamycin.

CONCLUSIONS

Rapamycin suppressed TAAD formation, probably by inhibition of mechanistic target of rapamycin signaling and reduction of inflammatory cell infiltration and matrix metalloproteinase 9 production. Targeting of the mechanistic target of rapamycin signaling pathway using rapamycin may be a favorable modulation for the clinical treatment of TAAD.

Smooth muscle cell-driven vascular diseases and molecular mechanisms of VSMC plasticity

Vascular smooth muscle cells (VSMCs) are the major cell type in blood vessels. Unlike many other mature cell types in the adult body, VSMC do not terminally differentiate but retain a remarkable plasticity. Fully differentiated medial VSMCs of mature vessels maintain quiescence and express a range of genes and proteins important for contraction/dilation, which allows them to control systemic and local pressure through the regulation of vascular tone. In response to vascular injury or alterations in local environmental cues, differentiated/contractile VSMCs are capable of switching to a dedifferentiated phenotype characterized by increased proliferation, migration and extracellular matrix synthesis in concert with decreased expression of contractile markers. Imbalanced VSMC plasticity results in maladaptive phenotype alterations that ultimately lead to progression of a variety of VSMC-driven vascular diseases. The nature, extent and consequences of dysregulated VSMC phenotype alterations are diverse, reflecting the numerous environmental cues (e.g. biochemical factors, extracellular matrix components, physical) that prompt VSMC phenotype switching. In spite of decades of efforts to understand cues and processes that normally control VSMC differentiation and their disruption in VSMC-driven disease states, the crucial molecular mechanisms and signalling pathways that shape the VSMC phenotype programme have still not yet been precisely elucidated. In this article we introduce the physiological functions of vascular smooth muscle/VSMCs, outline VSMC-driven cardiovascular diseases and the concept of VSMC phenotype switching, and review molecular mechanisms that play crucial roles in the regulation of VSMC phenotypic plasticity.

Genome Architecture Mediates Transcriptional Control of Human Myogenic Reprogramming

Genome architecture has emerged as a critical element of transcriptional regulation, although its role in the control of cell identity is not well understood. Here we use transcription factor (TF)-mediated reprogramming to examine the interplay between genome architecture and transcriptional programs that transition cells into the myogenic identity. We recently developed new methods for evaluating the topological features of genome architecture based on network centrality. Through integrated analysis of these features of genome architecture and transcriptome dynamics during myogenic reprogramming of human fibroblasts we find that significant architectural reorganization precedes activation of a myogenic transcriptional program. This interplay sets the stage for a critical transition observed at several genomic scales reflecting definitive adoption of the myogenic phenotype. Subsequently, TFs within the myogenic transcriptional program participate in entrainment of biological rhythms. These findings reveal a role for topological features of genome architecture in the initiation of transcriptional programs during TF-mediated human cellular reprogramming.

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4D Nucleome analysis of direct human fibroblast to muscle reprogramming

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A space-time bifurcation marks transit to a new cell identity

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Chromatin reorganization precedes significant transcriptional changes

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Myogenic master regulators have a role in entraining biological rhythms

Tollip Negatively Regulates Vascular Smooth Muscle Cell-Mediated Neointima Formation by Suppressing Akt-Dependent Signaling

BACKGROUND

Tollip, a well-established endogenous modulator of Toll-like receptor signaling, is involved in cardiovascular diseases. The aim of this study was to investigate the role of Tollip in neointima formation and its associated mechanisms.

METHODS AND RESULTS

In this study, transient increases in Tollip expression were observed in platelet-derived growth factor-BB-treated vascular smooth muscle cells and following vascular injury in mice. We then applied loss-of-function and gain-of-function approaches to elucidate the effects of Tollip on neointima formation. While exaggerated neointima formation was observed in Tollip-deficient murine neointima formation models, Tollip overexpression alleviated vascular injury-induced neointima formation by preventing vascular smooth muscle cell proliferation, dedifferentiation, and migration. Mechanistically, we demonstrated that Tollip overexpression may exert a protective role in the vasculature by suppressing Akt-dependent signaling, which was further confirmed in rescue experiments using the Akt-specific inhibitor (AKTI).

CONCLUSIONS

Our findings indicate that Tollip protects against neointima formation by negatively regulating vascular smooth muscle cell proliferation, dedifferentiation, and migration in an Akt-dependent manner. Upregulation of Tollip may be a promising strategy for treating vascular remodeling-related diseases.

Endothelial Cell Autonomous Role of Akt1: Regulation of Vascular Tone and Ischemia-Induced Arteriogenesis

OBJECTIVE

The importance of PI3K/Akt signaling in the vasculature has been demonstrated in several models, as global loss of Akt1 results in impaired postnatal ischemia- and VEGF-induced angiogenesis. The ubiquitous expression of Akt1, however, raises the possibility of cell-type-dependent Akt1-driven actions, thereby necessitating tissue-specific characterization.

APPROACH AND RESULTS

Herein, we used an inducible, endothelial-specific Akt1-deleted adult mouse model (Akt1iECKO) to characterize the endothelial cell autonomous functions of Akt1 in the vascular system. Endothelial-targeted ablation of Akt1 reduces eNOS (endothelial nitric oxide synthase) phosphorylation and promotes both increased vascular contractility in isolated vessels and elevated diastolic blood pressures throughout the diurnal cycle in vivo. Furthermore, Akt1iECKO mice subject to the hindlimb ischemia model display impaired blood flow and decreased arteriogenesis.

CONCLUSIONS

Endothelial Akt1 signaling is necessary for ischemic resolution post-injury and likely reflects the consequence of NO insufficiency critical for vascular repair.

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.

A tissue-specific, Gata6-driven transcriptional program instructs remodeling of the mature arterial tree

Connection of the heart to the systemic circulation is a critical developmental event that requires selective preservation of embryonic vessels (aortic arches). However, why some aortic arches regress while others are incorporated into the mature aortic tree remains unclear. By microdissection and deep sequencing in mouse, we find that neural crest (NC) only differentiates into vascular smooth muscle cells (SMCs) around those aortic arches destined for survival and reorganization, and identify the transcription factor Gata6 as a crucial regulator of this process. Gata6 is expressed in SMCs and its target genes activation control SMC differentiation. Furthermore, Gata6 is sufficient to promote SMCs differentiation in vivo, and drive preservation of aortic arches that ought to regress. These findings identify Gata6-directed differentiation of NC to SMCs as an essential mechanism that specifies the aortic tree, and provide a new framework for how mutations in GATA6 lead to congenital heart disorders in humans.

Serum Amyloid A Induces a Vascular Smooth Muscle Cell Phenotype Switch through the p38 MAPK Signaling Pathway

Atherosclerosis is an important pathological condition which is accompanied by a vascular smooth muscle cell (VSMC) phenotype switch toward a synthetic phenotype. As an acute-phase protein, Serum Amyloid A (SAA) is thought to have a close relationship to atherosclerosis development. However, no study has investigated the direct effect of SAA on the VSMC phenotype switch, as well as the underlying mechanisms. The purpose of our study was to explore the effect of SAA on the VSMC phenotype switch and the potential mechanisms involved. In our study, we found that SAA induced the VSMC phenotype switch which reduced expression of the smooth muscle cell (SMC) marker and enhanced expression of the matrix synthesis related marker. The proliferative ability of VSMCs was also increased by SAA treatment. Furthermore, our research found that SAA activated the ERK1/2 and p38 MAPK signaling pathways. Finally, by applying the ERK1/2 and p38 inhibitors, U0126 and SB203580, we demonstrated that the SAA-induced VSMC phenotype switch was p38-dependent. Taken together, these results indicated that SAA may play an important role in promoting the VSMC phenotype switch through the p38 MAPK signaling pathway.

Sulforaphane inhibits platelet-derived growth factor-induced vascular smooth muscle cell proliferation by targeting mTOR/p70S6kinase signaling independent of Nrf2 activation

Activation of nuclear factor erythroid 2-related factor 2 (Nrf2, a transcription factor) and/or inhibition of mammalian target of rapamycin (mTOR) are implicated in the suppression of vascular smooth muscle cell (VSMC) proliferation. The present study has examined the likely regulatory effects of sulforaphane (SFN, an antioxidant) on Nrf2 activation and platelet-derived growth factor (PDGF)-induced mTOR signaling in VSMCs. Using human aortic VSMCs, nuclear extraction and siRNA-mediated downregulation studies were performed to determine the role of Nrf2 on SFN regulation of PDGF-induced proliferative signaling. Immunoprecipitation and/or immunoblot studies were carried out to determine how SFN regulates PDGF-induced mTOR/p70S6K/S6 versus ERK and Akt signaling. Immunohistochemical analysis was performed to determine SFN regulation of S6 phosphorylation in the injured mouse femoral artery. SFN (5μM) inhibits PDGF-induced activation of mTOR without affecting mTOR association with raptor in VSMCs. While SFN inhibits PDGF-induced phosphorylation of p70S6K and 4E-BP1 (downstream targets of mTOR), it does not affect ERK or Akt phosphorylation. In addition, SFN diminishes exaggerated phosphorylation of S6 ribosomal protein (a downstream target of p70S6K) in VSMCs in vitro and in the neointimal layer of injured artery in vivo. Although SFN promotes Nrf2 accumulation to upregulate cytoprotective genes (e.g., heme oxygenase-1 and thioredoxin-1), downregulation of endogenous Nrf2 by target-specific siRNA reveals an Nrf2-independent effect for SFN-mediated inhibition of mTOR/p70S6K/S6 signaling and suppression of VSMC proliferation. Strategies that utilize local delivery of SFN at the lesion site may limit restenosis after angioplasty by targeting mTOR/p70S6K/S6 axis in VSMCs independent of Nrf2 activation.

Regulator of G protein signaling 4 is a novel target of GATA-6 transcription factor

GATA transcription factors regulate an array of genes important in cell proliferation and differentiation. Here we report the identification of regulator of G protein signaling 4 (RGS4) as a novel target for GATA-6 transcription factor. Although three sites (a, b, c) within the proximal region of rabbit RGS4 promoter for GATA transcription factors were predicted by bioinformatics analysis, only GATA-a site (16 bp from the core TATA box) is essential for RGS4 transcriptional regulation. RT-PCR analysis demonstrated that only GATA-6 was highly expressed in rabbit colonic smooth muscle cells but GATA-4/6 were expressed in cardiac myocytes and GATA-1/2/3 expressed in blood cells. Adenovirus-mediated expression of GATA-6 but not GATA-1 significantly increased the constitutive and IL-1β-induced mRNA expression of the endogenous RGS4 in colonic smooth muscle cells. IL-1β stimulation induced GATA-6 nuclear translocation and increased GATA-6 binding to RGS4 promoter. These data suggest that GATA factor could affect G protein signaling through regulating RGS4 expression, and GATA signaling may develop as a future therapeutic target for RGS4-related diseases.

TNF-insulin crosstalk at the transcription factor GATA6 is revealed by a model that links signaling and transcriptomic data tensors

Signal transduction networks coordinate transcriptional programs activated by diverse extracellular stimuli, such as growth factors and cytokines. Cells receive multiple stimuli simultaneously, and mapping how activation of the integrated signaling network affects gene expression is a challenge. We stimulated colon adenocarcinoma cells with various combinations of the cytokine tumor necrosis factor (TNF) and the growth factors insulin and epidermal growth factor (EGF) to investigate signal integration and transcriptional crosstalk. We quantitatively linked the proteomic and transcriptomic data sets by implementing a structured computational approach called tensor partial least squares regression. This statistical model accurately predicted transcriptional signatures from signaling arising from single and combined stimuli and also predicted time-dependent contributions of signaling events. Specifically, the model predicted that an early-phase, AKT-associated signal downstream of insulin repressed a set of transcripts induced by TNF. Through bioinformatics and cell-based experiments, we identified the AKT-repressed signal as glycogen synthase kinase 3 (GSK3)-catalyzed phosphorylation of Ser(37) on the long form of the transcription factor GATA6. Phosphorylation of GATA6 on Ser(37) promoted its degradation, thereby preventing GATA6 from repressing transcripts that are induced by TNF and attenuated by insulin. Our analysis showed that predictive tensor modeling of proteomic and transcriptomic data sets can uncover pathway crosstalk that produces specific patterns of gene expression in cells receiving multiple stimuli.

Vascular mTOR-dependent mechanisms linking the control of aging to Alzheimer's disease

Aging is the strongest known risk factor for Alzheimer's disease (AD). With the discovery of the mechanistic target of rapamycin (mTOR) as a critical pathway controlling the rate of aging in mice, molecules at the interface between the regulation of aging and the mechanisms of specific age-associated diseases can be identified. We will review emerging evidence that mTOR-dependent brain vascular dysfunction, a universal feature of aging, may be one of the mechanisms linking the regulation of the rate of aging to the pathogenesis of Alzheimer's disease. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.