Cell division cycle 7 is a novel regulator of transforming growth factor-β-induced smooth muscle cell differentiation

Direct contact with endothelial cells drives dental pulp stem cells toward smooth muscle cells differentiation via TGF-β1 secretion

AIM

Prevascularization is vital to accelerate functional blood circulation establishment in transplanted engineered tissue constructs. Mesenchymal stem cells (MSCs) or mural cells could promote the survival of implanted endothelial cells (ECs) and enhance the stabilization of newly formed blood vessels. However, the dynamic cell-cell interactions between MSCs, mural cells and ECs in the angiogenic processes remain unclear. This study aimed to explore the interactions of human umbilical vein ECs (HUVECs) and dental pulp stem cells (DPSCs) in an in vitro cell coculture model.

METHODOLOGY

Human umbilical vascular ECs and DPSCs were directly cocultured or indirectly cocultured with transwell inserts in endothelial basal media-2 (EBM-2) supplemented with 5% FBS for 6 days. Expression of SMC-specific markers in DPSCs monoculture and HUVEC+DPSC cocultures was assessed by western blot and immunofluorescence. Activin A and transforming growth factor-beta 1 (TGF-β1) in conditioned media (CM) of HUVECs monoculture (E-CM), DPSCs monoculture (D-CM) and HUVEC+DPSC cocultures (E+D-CM) were analysed by enzyme-linked immunosorbent assay. TGF-β RI kinase inhibitor VI, SB431542, was used to block TGF-β1/ALK5 signalling in DPSCs.

RESULTS

The expression of SMC-specific markers, α-SMA, SM22α and Calponin, were markedly increased in HUVEC+DPSC direct cocultures compared to that in DPSCs monoculture, while no differences were demonstrated between HUVEC+DPSC indirect cocultures and DPSCs monoculture. E+D-CM significantly upregulated the expression of SMC-specific markers in DPSCs compared to E-CM and D-CM. Activin A and TGF-β1 were considerably higher in E+D-CM than that in D-CM, with upregulated Smad2 phosphorylation in HUVEC+DPSC cocultures. Treatment with activin A did not change the expression of SMC-specific markers in DPSCs, while treatment with TGF-β1 significantly enhanced these markers' expression in DPSCs. In addition, blocking TGF-β1/ALK5 signalling inhibited the expression of α-SMA, SM22α and Calponin in DPSCs.

CONCLUSIONS

TGF-β1 was responsible for DPSC differentiation into SMCs in HUVEC+DPSC cocultures, and TGF-β1/ALK5 signalling pathway played a vital role in this process.

DPSCs treated by TGF-β1 regulate angiogenic sprouting of three-dimensionally co-cultured HUVECs and DPSCs through VEGF-Ang-Tie2 signaling

Background

Maintaining the stability and maturation of blood vessels is of paramount importance for the vessels to carry out their physiological function. Smooth muscle cells (SMCs), pericytes, and mesenchymal stem cells (MSCs) are involved in the maturation process of the newly formed vessels. The aim of this study was to investigate whether transforming growth factor beta 1 (TGF-β1) treatment could enhance pericyte-like properties of dental pulp stem cells (DPSCs) and how TGF-β1-treated DPSCs for 7 days (T-DPSCs) stabilize the newly formed blood vessels.

Methods

We utilized TGF-β1 to treat DPSCs for 1, 3, 5, and 7 days. Western blotting and immunofluorescence were used to analyze the expression of SMC markers. Functional contraction assay was conducted to assess the contractility of T-DPSCs. The effects of T-DPSC-conditioned media (T-DPSC-CM) on human umbilical vein endothelial cell (HUVEC) proliferation and migration were examined by MTT, wound healing, and trans-well migration assay. Most importantly, in vitro 3D co-culture spheroidal sprouting assay was used to investigate the regulating role of vascular endothelial growth factor (VEGF)-angiopoietin (Ang)-Tie2 signaling on angiogenic sprouting in 3D co-cultured spheroids of HUVECs and T-DPSCs. Angiopoietin 2 (Ang2) and VEGF were used to treat the co-cultured spheroids to explore their roles in angiogenic sprouting. Inhibitors for Tie2 and VEGFR2 were used to block Ang1/Tie2 and VFGF/VEGFR2 signaling.

Results

Western blotting and immunofluorescence showed that the expression of SMC-specific markers (α-SMA and SM22α) were significantly increased after treatment with TGF-β1. Contractility of T-DPSCs was greater compared with that of DPSCs. T-DPSC-CM inhibited HUVEC migration. In vitro sprouting assay demonstrated that T-DPSCs enclosed HUVECs, resembling pericyte-like cells. Compared to co-culture with DPSCs, a smaller number of HUVEC sprouting was observed when co-cultured with T-DPSCs. VEGF and Ang2 co-stimulation significantly enhanced sprouting in HUVEC and T-DPSC co-culture spheroids, whereas VEGF or Ang2 alone exerted insignificant effects on HUVEC sprouting. Blocking Tie2 signaling reversed the sprouting inhibition by T-DPSCs, while blocking VEGF receptor (VEGFR) signaling boosted the sprouting inhibition by T-DPSCs.

Conclusions

This study revealed that TGF-β1 can induce DPSC differentiation into functional pericyte-like cells. T-DPSCs maintain vessel stability through Ang1/Tie2 and VEGF/VEGFR2 signaling.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02349-y.

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.

Low expression of ANT1 confers oncogenic properties to rhabdomyosarcoma tumor cells by modulating metabolism and death pathways

Rhabdomyosarcoma (RMS) is the most frequent form of pediatric soft-tissue sarcoma. It is divided into two main subtypes: ERMS (embryonal) and ARMS (alveolar). Current treatments are based on chemotherapy, surgery, and radiotherapy. The 5-year survival rate has plateaued at 70% since 2000, despite several clinical trials. RMS cells are thought to derive from the muscle lineage. During development, myogenesis includes the expansion of muscle precursors, the elimination of those in excess by cell death and the differentiation of the remaining ones into myofibers. The notion that these processes may be hijacked by tumor cells to sustain their oncogenic transformation has emerged, with RMS being considered as the dark side of myogenesis. Thus, dissecting myogenic developmental programs could improve our understanding of RMS molecular etiology. We focused herein on ANT1, which is involved in myogenesis and is responsible for genetic disorders associated with muscle degeneration. ANT1 is a mitochondrial protein, which has a dual functionality, as it is involved both in metabolism via the regulation of ATP/ADP release from mitochondria and in regulated cell death as part of the mitochondrial permeability transition pore. Bioinformatics analyses of transcriptomic datasets revealed that ANT1 is expressed at low levels in RMS. Using the CRISPR-Cas9 technology, we showed that reduced ANT1 expression confers selective advantages to RMS cells in terms of proliferation and resistance to stress-induced death. These effects arise notably from an abnormal metabolic switch induced by ANT1 downregulation. Restoration of ANT1 expression using a Tet-On system is sufficient to prime tumor cells to death and to increase their sensitivity to chemotherapy. Based on our results, modulation of ANT1 expression and/or activity appears as an appealing therapeutic approach in RMS management.

TRPC6 regulates phenotypic switching of vascular smooth muscle cells through plasma membrane potential-dependent coupling with PTEN

Vascular smooth muscle cells (VSMCs) play critical roles in the stability and tonic regulation of vascular homeostasis. VSMCs can switch back and forth between highly proliferative synthetic and fully differentiated contractile phenotypes in response to changes in the vessel environment. Although abnormal phenotypic switching of VSMCs is a hallmark of vascular disorders such as atherosclerosis and restenosis after angioplasty, how control of VSMC phenotypic switching is dysregulated in pathologic conditions remains obscure. We found that inhibition of canonical transient receptor potential 6 (TRPC6) channels facilitated contractile differentiation of VSMCs through plasma membrane hyperpolarization. TRPC6-deficient VSMCs exhibited more polarized resting membrane potentials and higher protein kinase B (Akt) activity than wild-type VSMCs in response to TGF-β1 stimulation. Ischemic stress elicited by oxygen-glucose deprivation suppressed TGF-β1-induced hyperpolarization and VSMC differentiation, but this effect was abolished by TRPC6 deletion. TRPC6-mediated Ca²⁺ influx and depolarization coordinately promoted the interaction of TRPC6 with lipid phosphatase and tensin homolog deleted from chromosome 10 (PTEN), a negative regulator of Akt activation. Given the marked up-regulation of TRPC6 observed in vascular disorders, our findings suggest that attenuation of TRPC6 channel activity in pathologic VSMCs could be a rational strategy to maintain vascular quality control by fine-tuning of VSMC phenotypic switching.-Numaga-Tomita, T., Shimauchi, T., Oda, S., Tanaka, T., Nishiyama, K., Nishimura, A., Birnbaumer, L., Mori, Y., Nishida, M. TRPC6 regulates phenotypic switching of vascular smooth muscle cells through plasma membrane potential-dependent coupling with PTEN.

Lack of Association of rs1192415 in TGFBR3-CDC7 With Visual Field Progression: A Cohort Study in Chinese Open Angle Glaucoma Patients

To investigate the association of known candidate genes with the visual field (VF) progression of primary open angle glaucoma (POAG) in a Han Chinese population. We included 440 POAG patients in this study. Fourteen previously reported single nucleotide polymorphisms (SNPs) at five different gene regions (TGFBR3-CDC7, TMCO1, CDKN2B-AS1, ATOH7, and SIX1/SIX6) were genotyped. Age at diagnosis, gender, intraocular pressure (IOP), mean defect (MD) of VF, vertical cup disk ratio (VCDR), best corrected visual acuity (BCVA), central corneal thickness (CCT), and axial length (AL) were recorded at baseline. Patients were followed up for 5 years to evaluate VF progression over time. Clinical information and allele frequencies of 14 SNPs were compared between patients who progressed and who did not within 5 years by multivariate logistic regression. Survival analysis was performed to evaluate the contribution of the associated SNP by cox regression. Greater MD (P < 0.0001), increased VCDR (P = 0.0001), higher IOP (P = 0.0003), worse BCVA (P = 0.002), and older age (P = 0.030) at the baseline were associated with VF progression. Both multivariate logistic regression and cox regression survival analysis showed none of the 14 SNPs statistically associated with VF progression adjusted with age at diagnosis, gender, baseline MD, follow-up IOP, CCT, and AL. There were lack of association of SNPs at TGFBR3-CDC7, TMCO1, ATOH7, CDKN2B-AS1, SIX1/SIX6 loci with VF progression in POAG patients in Han Chinese. Further studies are needed to evaluate the association of genetic variants with VF progression.

Immunohistochemical Expression of CDC7 in Dentigerous Cyst, Odontogenic Keratocyst and Radicular Cyst

CDC7 is a serine/threonine kinase which has an essential role in initiation of DNA proliferation and S phase. It increases the invasion and proliferation in many pathologic lesions. This study aimed to evaluate the expression of CDC7 in the most common odontogenic cysts. We evaluated 17 dentigerous cysts, 18 odontogenic keratocysts (OKC) and 13 radicular cysts immunohistochemically. The mean expression of CDC7 was analyzed using ANOVA and Post-HOC methods. All specimens revealed CDC7 expression. Higher expression of CDC7 in OKC and radicular cyst was shown in comparison to dentigerous cyst (P < 0.001), while radicular cyst and OKC groups showed no difference in CDC7 expression (P = 0.738). The high expression of CDC7 in OKC suggests that this protein could be related to the higher proliferation rate and invasiveness of OKC. On the other hand, the higher CDC7 expression in radicular cyst may simply be related to inflammation as this cyst is neither aggressive nor invasive.

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.

TGF-β1-induced differentiation of SHED into functional smooth muscle cells

BACKGROUND

Adequate vascularization is crucial for supplying nutrition and discharging metabolic waste in freshly transplanted tissue-engineered constructs. Obtaining the appropriate building blocks for vascular tissue engineering (i.e. endothelial and mural cells) is a challenging task for tissue neovascularization. Hence, we investigated whether stem cells from human exfoliated deciduous teeth (SHED) could be induced to differentiate into functional vascular smooth muscle cells (vSMCs).

METHODS

We utilized two cytokines of the TGF-β family, transforming growth factor beta 1 (TGF-β1) and bone morphogenetic protein 4 (BMP4), to induce SHED differentiation into SMCs. Quantitative real-time polymerase chain reaction (RT-qPCR) was used to assess mRNA expression, and protein expression was analyzed using flow cytometry, western blot and immunostaining. Additionally, to examine whether these SHED-derived SMCs possess the same function as primary SMCs, in vitro Matrigel angiogenesis assay, fibrin gel bead assay, and functional contraction study were used here.

RESULTS

By analyzing the expression of specific markers of SMCs (α-SMA, SM22α, Calponin, and SM-MHC), we confirmed that TGF-β1, and not BMP4, could induce SHED differentiation into SMCs. The differentiation efficiency was relatively high (α-SMA+ 86.1%, SM22α+ 93.9%, Calponin+ 56.8%, and SM-MHC+ 88.2%) as assessed by flow cytometry. In vitro Matrigel angiogenesis assay showed that the vascular structures generated by SHED-derived SMCs and human umbilical vein endothelial cells (HUVECs) were comparable to primary SMCs and HUVECs in terms of vessel stability. Fibrin gel bead assay showed that SHED-derived SMCs had a stronger capacity for promoting vessel formation compared with primary SMCs. Further analyses of protein expression in fibrin gel showed that cultures containing SHED-derived SMCs exhibited higher expression levels of Fibronectin than the primary SMCs group. Additionally, it was also confirmed that SHED-derived SMCs exhibited functional contractility. When SB-431542, a specific inhibitor of ALK5 was administered, TGF-β1 stimulation could not induce SHED into SMCs, indicating that the differentiation of SHED into SMCs is somehow related to the TGF-β1-ALK5 signaling pathway.

CONCLUSIONS

SHED could be successfully induced into functional SMCs for vascular tissue engineering, and this course could be regulated through the ALK5 signaling pathway. Hence, SHED appear to be a promising candidate cell type for vascular tissue engineering.

Identification of RSK and TTK as Modulators of Blood Vessel Morphogenesis Using an Embryonic Stem Cell-Based Vascular Differentiation Assay

Blood vessels are formed through vasculogenesis, followed by remodeling of the endothelial network through angiogenesis. Many events that occur during embryonic vascular development are recapitulated during adult neoangiogenesis, which is critical to tumor growth and metastasis. Current antiangiogenic tumor therapies, based largely on targeting the vascular endothelial growth factor pathway, show limited clinical benefits, thus necessitating the discovery of alternative targets. Here we report the development of a robust embryonic stem cell-based vascular differentiation assay amenable to small-molecule screens to identify novel modulators of angiogenesis. In this context, RSK and TTK were identified as angiogenic modulators. Inhibition of these pathways inhibited angiogenesis in embryoid bodies and human umbilical vein endothelial cells. Furthermore, inhibition of RSK and TTK reduced tumor growth, vascular density, and improved survival in an in vivo Lewis lung carcinoma mouse model. Our study suggests that RSK and TTK are potential targets for antiangiogenic therapy, and provides an assay system for further pathway screens.

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Development of ESC-based vascular differentiation assay amenable to drug screening

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Screening a kinase library identified RSK and TTK as angiogenic modulators

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RSK and TTK inhibition disrupted angiogenesis in vitro

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RSK and TTK inhibition inhibited Lewis lung tumor growth and angiogenesis in vivo

CYLD-mediated signaling and diseases

The conserved cylindromatosis (CYLD) codes for a deubiquitinating enzyme and is a crucial regulator of diverse cellular processes such as immune responses, inflammation, death, and proliferation. It directly regulates multiple key signaling cascades, such as the Nuclear Factor kappa B [NFkB] and the Mitogen-Activated Protein Kinase (MAPK) pathways, by its catalytic activity on polyubiquitinated key intermediates. Several lines of emerging evidence have linked CYLD to the pathogenesis of various maladies, including cancer, poor infection control, lung fibrosis, neural development, and now cardiovascular dysfunction. While CYLD-mediated signaling is cell type and stimuli specific, the activity of CYLD is tightly controlled by phosphorylation and other regulators such as Snail. This review explores a broad selection of current and past literature regarding CYLD's expression, function and regulation with emerging reports on its role in cardiovascular disease.

XL413, a cell division cycle 7 kinase inhibitor enhanced the anti-fibrotic effect of pirfenidone on TGF-β1-stimulated C3H10T1/2 cells via Smad2/4

Pirfenidone is an orally bioavailable synthetic compound with therapeutic potential for idiopathic pulmonary fibrosis. It is thought to act through antioxidant and anti-fibrotic pathways. Pirfenidone inhibits proliferation and/or myofibroblast differentiation of a wide range of cell types, however, little studies have analyzed the effect of pirfenidone on the mesenchymal stem cells, which play an important role on the origin of myofibroblasts. We recently found that pirfenidone had anti-proliferative activity via G1 phase arrest and cell division cycle 7 (Cdc7) kinase expression decrease in transforming growth factor-β1 (TGF-β1)-stimulated murine mesenchymal stem C3H10T1/2 cells. Pirfenidone also had inhibiting effect on the migration and α-SMA expression. Moreover, in this study we showed for the first time that Cdc7 inhibitor XL413 enhanced the anti-fibrotic activity of pirfenidone via depressed the expression of Smad2/4 proteins, and also prevented the nuclear accumulation and translocation of Smad2 protein. In conclusion, we demonstrated that pirfenidone inhibited proliferation, migration and differentiation of TGF-β1-stimulated C3H10T1/2 cells, which could be enhanced by Cdc7 inhibitor XL413, via Smad2/4. Combination with pirfenidone and XL413 might provide a potential candidate for the treatment of TGF-β1 associated fibrosis. It needs in vivo studies to further validate its therapeutic function and safety in the future.

Characterization of a Drosophila ortholog of the Cdc7 kinase: a role for Cdc7 in endoreplication independent of Chiffon

Cdc7 is a serine-threonine kinase that phosphorylates components of the pre-replication complex during DNA replication initiation. Cdc7 is highly conserved, and Cdc7 orthologs have been characterized in organisms ranging from yeast to humans. Cdc7 is activated specifically during late G1/S phase by binding to its regulatory subunit, Dbf4. Drosophila melanogaster contains a Dbf4 ortholog, Chiffon, which is essential for chorion amplification in Drosophila egg chambers. However, no Drosophila ortholog of Cdc7 has yet been characterized. Here, we report the functional and biochemical characterization of a Drosophila ortholog of Cdc7. Co-expression of Drosophila Cdc7 and Chiffon is able to complement a growth defect in yeast containing a temperature-sensitive Cdc7 mutant. Cdc7 and Chiffon physically interact and can be co-purified from insect cells. Cdc7 phosphorylates the known Cdc7 substrates Mcm2 and histone H3 in vitro, and Cdc7 kinase activity is stimulated by Chiffon and inhibited by the Cdc7-specific inhibitor XL413. Drosophila egg chamber follicle cells deficient for Cdc7 have a defect in two types of DNA replication, endoreplication and chorion gene amplification. However, follicle cells deficient for Chiffon have a defect in chorion gene amplification but still undergo endocycling. Our results show that Cdc7 interacts with Chiffon to form a functional Dbf4-dependent kinase complex and that Cdc7 is necessary for DNA replication in Drosophila egg chamber follicle cells. Additionally, we show that Chiffon is a member of an expanding subset of DNA replication initiation factors that are not strictly required for endoreplication in Drosophila.

Mechanisms simultaneously regulate smooth muscle proliferation and differentiation

Vascular smooth muscle cell (VSMC) differentiation and proliferation are two important physiological processes during vascular development. The phenotypic alteration from differentiated to proliferative VSMC contributes to the development of several major cardiovascular diseases including atherosclerosis, hypertension, restenosis after angioplasty or bypass, diabetic vascular complications, and transplantation arteriopathy. Since the VSMC phenotype in these pathological conditions resembles that of developing VSMC during embryonic development, understanding of the molecular mechanisms that control VSMC differentiation will provide fundamental insights into the pathological processes of these cardiovascular diseases. Although VSMC differentiation is usually accompanied by an irreversible cell cycle exit, VSMC proliferation and differentiation occur concurrently during embryonic development. The molecular mechanisms simultaneously regulating these two processes, however, remain largely unknown. Our recent study demonstrates that cell division cycle 7, a key regulator of cell cycle, promotes both VSMC differentiation and proliferation through different mechanisms during the initial phase of VSMC differentiation. Conversely, Krüppel-like factor 4 appears to be a repressor for both VSMC differentiation and proliferation. This review attempts to highlight the novel role of cell division cycle 7 in TGF-β-induced VSMC differentiation and proliferation. The role of Krüppel-like factor 4 in suppressing these two processes will also be discussed.

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.

CTP synthase 1, a smooth muscle-sensitive therapeutic target for effective vascular repair

OBJECTIVE

Vascular remodeling as a result of smooth muscle cell (SMC) proliferation and neointima formation is a major medical challenge in cardiovascular intervention. However, antineointima drugs often indistinguishably block re-endothelialization, an essential step toward successful vascular repair, because of their nonspecific effect on endothelial cells (ECs). The objective of this study is to identify a therapeutic target that differentially regulates SMC and EC proliferation.

APPROACH AND RESULTS

Using both rat balloon injury and mouse wire injury models, we identified CTP synthase 1 (CTPS1) as one of the potential targets that may be used for developing therapeutics for treating neointima-related disorders. CTPS1 was induced in proliferative SMCs in vitro and neointima SMCs in vivo. Blockade of CTPS1 expression by small hairpin RNA or activity by cyclopentenyl cytosine suppressed SMC proliferation and neointima formation. Surprisingly, cyclopentenyl cytosine had much less effect on EC proliferation. Of importance, blockade of CTPS1 in vivo sustained the re-endothelialization as a result of induction of CTP synthesis salvage pathway enzymes nucleoside-diphosphate kinase A and B in ECs. Diphosphate kinase B seemed to preserve EC proliferation via use of extracellular cytidine to synthesize CTP. Indeed, blockade of both CTPS1 and diphosphate kinase B suppressed EC proliferation in vitro and the re-endothelialization in vivo.

CONCLUSIONS

Our study uncovered a fundamental difference in CTP biosynthesis between SMCs and ECs during vascular remodeling, which provided a novel strategy by using cyclopentenyl cytosine or other CTPS1 inhibitors to selectively block SMC proliferation without disturbing or even promoting re-endothelialization for effective vascular repair after injury.

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.

Response gene to complement 32 deficiency causes impaired placental angiogenesis in mice

AIMS

The objectives of this study are to determine the role of response gene to complement 32 (RGC-32) in the placental angiogenesis during pregnancy and explore the underlying mechanisms.

METHODS AND RESULTS

RGC-32-deficient (RGC32(-/-)) mice were generated from C57BL/6 embryonic stem cells with deletion of exon 2 and 3 of the RGC-32 gene. Most of the RGC32(-/-) mice can survive. However, their body sizes were much smaller compared with their wild-type littermates when they were born. By examining the embryo development and placentas at 16.5 days post-coitum, we found that RGC32(-/-) embryos and foetal placentas were significantly smaller than the wild-type. Further analysis showed that the labyrinth zone of RGC32(-/-) placenta was smaller with defective angiogenesis. Mechanistically, vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2) and placental growth factor (PlGF) were significantly down-regulated in RGC32(-/-) placentas, suggesting that VEGFR2 and PlGF may mediate RGC-32 function in placental angiogenesis. Indeed, knockdown of RGC-32 by shRNA inhibited VEGF-induced endothelial cell proliferation, migration, and tube formation while blocking VEGFR2 expression. RGC-32 appeared to regulate VEGFR2 expression via activation of NF-kB. Moreover, RGC-32 regulated trophoblasts proliferation via control of PlGF expression.

CONCLUSION

Absence of RGC-32 caused foetal growth restriction through interrupting the placental angiogenesis, which was due to the decrease in VEGFR2 expression through the NF-kB-dependent pathway in endothelial cells and PlGF expression in trophoblasts.