Splicing of HDAC7 modulates the SRF-myocardin complex during stem-cell differentiation towards smooth muscle cells

Functional impact of heterogeneous nuclear ribonucleoprotein A2/B1 in smooth muscle differentiation from stem cells and embryonic arteriogenesis

Heterogeneous nuclear ribonucleoproteins (hnRNPs) play various roles in transcriptional and post-transcriptional modulation of gene expression. However, it remains unclear if hnRNPs are associated with smooth muscle cell (SMC) differentiation from stem cells and embryonic arteriogenesis. In this study, mouse embryonic stem (ES) cells were cultivated on collagen IV-coated plates and smooth muscle differentiation medium. We found that hnRNPA2/B1 gene and protein expression was significantly up-regulated following 3-7 days of cell differentiation. hnRNPA2/B1 knockdown resulted in down-regulation of specific smooth muscle markers and transcription factors, whereas enforced expression of hnRNPA2/B1 enhanced the expression of these genes. Moreover, we demonstrated by using luciferase and chromatin immunoprecipitation assays that hnRNPA2/B1 could transcriptionally regulate SMC gene expression through direct binding to promoters of Smαa and Sm22α genes. We further demonstrated that chromobox protein homolog gene 3, a previously identified SMC differentiation regulatory nuclear protein, is required for hnRNPA2/B1-mediated SMC differentiation gene expression. Importantly, specifically designed Hnrnpa2/b1 morpholinos for in vivo knockdown could inhibit the migration and differentiation of neural crest cells into SMCs in chick embryos. This resulted in the maldevelopment of branchial arch arteries and increased embryo lethality at a later developmental stage. Our findings demonstrated that hnRNPA2/B1 plays a functional role in SMC differentiation from stem cells in vitro and embryonic branchial arch artery development. This indicates that hnRNPA2/B1 is a potential modulating target for deriving SMCs from stem cells and cardiovascular regenerative medicine.

Nrf3-Pla2g7 interaction plays an essential role in smooth muscle differentiation from stem cells

OBJECTIVE

Phospholipase A2, group 7 (Pla2g7) is an important mediator in cardiovascular development and diseases because of its divergent physiological and pathological functions in inflammation and oxidative stress. However, little is known about the functional role of Pla2g7 in smooth muscle cell (SMC) differentiation from stem cells.

METHODS AND RESULTS

In the present study, embryonic stem cells were cultivated on collagen IV-coated plates to allow SMC differentiation. Pla2g7 gene expression and activity were upregulated significantly following 4 to 14 days of cell differentiation and colocalized with SMC differentiation markers in the differentiated SMCs. Knockdown of Pla2g7 resulted in downregulation of smooth muscle-specific markers in vitro and impairment of SMC differentiation in vivo, whereas enforced expression of Pla2g7 enhanced SMC differentiation and increased reactive oxygen species generation. Importantly, enforced expression of Pla2g7 significantly increased the binding of serum response factor to SMC differentiation gene promoters, resulting in SMC differentiation, which was abolished by free radical scavenger and flavoprotein inhibitor of NADPH oxidase but not hydrogen peroxide inhibitor. Moreover, we demonstrated that nuclear factor erythroid 2-related factor 3 (Nrf3) regulates Pla2g7 gene expression through direct binding to the promoter regions of Pla2g7 gene.

CONCLUSION

Our findings demonstrated that Pla2g7 plays a crucial physiological role in SMC differentiation from stem cells, and the fine interactions between Nrf3 and Pla2g7 are essential for SMC differentiation.

Class IIa HDACs: from important roles in differentiation to possible implications in tumourigenesis

Histone deacetylases (HDACs) are important regulators of gene expression. Specific structural features and distinct regulative mechanisms rationalize the separation of the 18 different human HDACs into four classes. The class II comprises a heterogeneous group of nuclear and cytosolic HDACs involved in the regulation of several cellular functions, not just limited to transcriptional repression. In particular, HDAC4, 5, 7 and 9 belong to the subclass IIa and share many transcriptional partners, including members of the MEF2 family. Genetic studies in mice have disclosed the fundamental contribution of class IIa HDACs to specific developmental/differentiation pathways. In this review, we discuss about the recent literature, which hints a role of class IIa HDACs in the development, growth and aggressiveness of cancer cells.

Immune regulation by histone deacetylases: a focus on the alteration of FOXP3 activity

Several histone deacetylases (HDACs) are involved in the regulation of forkhead box protein P3 (FOXP3) expression and function by affecting features of FOXP3 protein stability. FOXP3, a forkhead family transcription factor specially expressed in regulatory T (Treg) cells, controls the expression of many key immune-regulatory genes. Treg cells are a population of T lymphocytes that have critical roles in the immune system homeostasis and tolerance to self and foreign antigens, the body's response to cancer and infectious agents. FOXP3 forms oligomeric complexes with other proteins, the components of which are believed to be regulated dynamically. In addition, HDAC activities influence FOXP3 interactions with other partners to form transcriptional regulatory complexes. By understanding the details of the biochemical and structural basis of the regulation of FOXP3 acetylation, therapeutic strategies for diseases related to Treg cells may emerge.

Adventitial biology: differentiation and function

Recent evidence indicates that stem/progenitor cells are present in the adventitia and participate in vascular repair and the formation of neointimal lesions in severely damaged vessels. Data have also demonstrated that these resident stem/progenitor cells could differentiate into endothelial or smooth muscle cells in response to different stimuli. Under pathological conditions, adventitial inflammation results in releasing a panel of cytokines, such as stromal cell-derived factor-1 and tumor necrosis factor-α, that may lead to local stem/progenitor mobilization and differentiation. Overall, these data support the impact of the adventitial progenitors in pathophysiological processes of lesion development in the arterial wall. In the present review, we aim to summarize the data concerning the presence of the resident stem cells and discuss the pathological impact of the adventitia in vascular diseases. We will also discuss the possible signal pathways orchestrating stem cell differentiation toward vascular lineage and highlight controversial issues related to the role of adventitial progenitors.

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

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

NO points to epigenetics in vascular development

Our understanding of epigenetic mechanisms important for embryonic vascular development and cardiovascular differentiation is still in its infancy. Although molecular analyses, including massive genome sequencing and/or in vitro/in vivo targeting of specific gene sets, has led to the identification of multiple factors involved in stemness maintenance or in the early processes of embryonic layers specification, very little is known about the epigenetic commitment to cardiovascular lineages. The object of this review will be to outline the state of the art in this field and trace the perspective therapeutic consequences of studies aimed at elucidating fundamental epigenetic networks. Special attention will be paid to the emerging role of nitric oxide in this field.

Sp1-dependent activation of HDAC7 is required for platelet-derived growth factor-BB-induced smooth muscle cell differentiation from stem cells

We have previously demonstrated that histone deacetylase 7 (HDAC7) expression and splicing play an important role in smooth muscle cell (SMC) differentiation from embryonic stem (ES) cells, but the molecular mechanisms of increased HDAC7 expression during SMC differentiation are currently unknown. In this study, we found that platelet-derived growth factor-BB (PDGF-BB) induced a 3-fold increase in the transcripts of HDAC7 in differentiating ES cells. Importantly, our data also revealed that PDGF-BB regulated HDAC7 expression not through phosphorylation of HDAC7 but through transcriptional activation. By dissecting its promoters with progressive deletion analysis, we identified the sequence between -343 and -292 bp in the 5'-flanking region of the Hdac7 gene promoter as the minimal PDGF-BB-responsive element, which contains one binding site for the transcription factor, specificity protein 1 (Sp1). Mutation of the Sp1 site within this PDGF-BB-responsive element abolished PDGF-BB-induced HDAC7 activity. PDGF-BB treatment enhanced Sp1 binding to the Hdac7 promoter in differentiated SMCs in vivo as demonstrated by the chromatin immunoprecipitation assay. Moreover, we also demonstrated that knockdown of Sp1 abrogated PDGF-BB-induced HDAC7 up-regulation and SMC differentiation gene expression in differentiating ES cells, although enforced expression of Sp1 alone was sufficient to increase the activity of the Hdac7 promoter and expression levels of SMC differentiation genes. Importantly, we further demonstrated that HDAC7 was required for Sp1-induced SMC differentiation of gene expression. Our data suggest that Sp1 plays an important role in the regulation of Hdac7 gene expression in SMC differentiation from ES cells. These findings provide novel molecular insights into the regulation of HDAC7 and enhance our knowledge in SMC differentiation and vessel formation during embryonic development.

Histone deacetylase 7 controls endothelial cell growth through modulation of beta-catenin

RATIONALE

Histone deacetylase (HDAC)7 is expressed in the early stages of embryonic development and may play a role in endothelial function.

OBJECTIVE

This study aimed to investigate the role of HDAC7 in endothelial cell (EC) proliferation and growth and the underlying mechanism.

METHODS AND RESULTS

Overexpression of HDAC7 by adenoviral gene transfer suppressed human umbilical vein endothelial cell (HUVEC) proliferation by preventing nuclear translocation of beta-catenin and downregulation of T-cell factor-1/Id2 (inhibitor of DNA binding 2) and cyclin D1, leading to G(1) phase elongation. Further assays with the TOPFLASH reporter and quantitative RT-PCR for other beta-catenin target genes such as Axin2 confirmed that overexpression of HDAC7 decreased beta-catenin activity. Knockdown of HDAC7 by lentiviral short hairpin RNA transfer induced beta-catenin nuclear translocation but downregulated cyclin D1, cyclin E1 and E2F2, causing HUVEC hypertrophy. Immunoprecipitation assay and mass spectrometry analysis revealed that HDAC7 directly binds to beta-catenin and forms a complex with 14-3-3 epsilon, zeta, and eta proteins. Vascular endothelial growth factor treatment induced HDAC7 degradation via PLCgamma-IP3K (phospholipase Cgamma-inositol-1,4,5-trisphosphate kinase) signal pathway and partially rescued HDAC7-mediated suppression of proliferation. Moreover, vascular endothelial growth factor stimulation suppressed the binding of HDAC7 with beta-catenin, disrupting the complex and releasing beta-catenin to translocate into the nucleus.

CONCLUSIONS

These findings demonstrate that HDAC7 interacts with beta-catenin keeping ECs in a low proliferation stage and provides a novel insight into the mechanism of HDAC7-mediated signal pathways leading to endothelial growth.

Crucial role of nrf3 in smooth muscle cell differentiation from stem cells

RATIONALE

Nuclear factor erythroid 2-related factor (Nrf)3, a member of the cap 'N' collar family of transcription factors that bind to the DNA-antioxidant responsive elements, is involved in reactive oxygen species balancing and in muscle precursor migration during early embryo development.

OBJECTIVE

To investigate the functional role of Nrf3 in smooth muscle cell (SMC) differentiation in vitro and in vivo.

METHODS AND RESULTS

Nrf3 was upregulated significantly following 1 to 8 days of SMC differentiation. Knockdown of Nrf3 resulted in downregulation of smooth muscle specific markers expression, whereas enforced expression of Nrf3 enhanced SMC differentiation in a dose-dependent manner. SMC-specific transcription factor myocardin, but not serum response factor, was significantly upregulated by Nrf3 overexpression. Strikingly, the binding of SRF and myocardin to the promoter of smooth muscle differentiation genes was dramatically increased by Nrf3 overexpression, and Nrf3 can directly bind to the promoters of SMC differentiation genes as demonstrated by chromatin immunoprecipitation assay. Moreover, NADPH-derived reactive oxygen species production during SMC differentiation was further enhanced by Nrf3 overexpression through upregulation of NADPH oxidase and inhibition of antioxidant signaling pathway. In addition, Nrf3 was involved in the endoplasmic reticulum stressor induced SMC differentiation.

CONCLUSION

Our findings demonstrate for the first time that Nrf3 has a crucial role in SMC differentiation from stem cells indicating that Nrf3 could be a potential target for manipulation of stem cell differentiation toward vascular lineage.

Alternative Splicing Modulates Stem Cell Differentiation

Stem cells have the surprising potential to develop into many different cell types. Therefore, major research efforts have focused on transplantation of stem cells and/or derived progenitors for restoring depleted diseased cells in degenerative disorders. Understanding the molecular controls, including alternative splicing, that arise during lineage differentiation of stem cells is crucial for developing stem cell therapeutic approaches in regeneration medicine. Alternative splicing to allow a single gene to encode multiple transcripts with different protein coding sequences and RNA regulatory elements increases genomic complexities. Utilizing differences in alternative splicing as a molecular marker may be more sensitive than simply gene expression in various degrees of stem cell differentiation. Moreover, alternative splicing maybe provide a new concept to acquire induced pluripotent stem cells or promote cell–cell transdifferentiation for restorative therapies and basic medicine researches. In this review, we highlight the recent advances of alternative splicing regulation in stem cells and their progenitors. It will hopefully provide much needed knowledge into realizing stem cell biology and related applications.