Structure and characterization of the 5'-flanking region of the mouse smooth muscle myosin heavy chain (SM1/2) gene

Fabrication of engineered tubular tissue for small blood vessels via three-dimensional cellular assembly and organization ex vivo

Although there is a great need for suitable vascular replacements in clinical practice, much progress needs to be made toward the development of a fully functional tissue-engineered construct. We propose a fabrication method of engineered tubular tissue for small blood vessels via a layer-by-layer cellular assembly technique using mouse smooth muscle cells, the construction of a poly-(l-lactide-co-ε-caprolactone) (PLCL) scaffold, and integration in a microfluidic perfusion culture system. The cylindrical PLCL scaffold is incised, expanded, and its surface is laminated with the cell layers. The construct confirms into tubular structures due to residual stress imposed by the cylindrical PLCL scaffold. The perfusion culture system allows simulation of static, perfusion (laminar flow), and perfusion with pulsatile pressure (Pulsatile flow) conditions in which mimicking the in vivo environments. The aim of this evaluation was to determine whether fabricated tubular tissue models developed their mechanical properties. The cellular response to hemodynamic stimulus imposed by the dynamic culture system is monitored through expression analysis of fibrillin-1 and fibrillin-2, elastin and smooth muscle myosin heavy chains isoforms transcription factors, which play an important role in tissue elastogenesis. Among the available materials for small blood vessel construction, these cellular hybrid vascular scaffolds hold much potential due to controllability of the mechanical properties of synthetic polymers and biocompatibility of integrated cellular components.

Conversion from mouse embryonic to extra-embryonic endoderm stem cells reveals distinct differentiation capacities of pluripotent stem cell states

The inner cell mass of the mouse pre-implantation blastocyst comprises epiblast progenitor and primitive endoderm cells of which cognate embryonic (mESCs) or extra-embryonic (XEN) stem cell lines can be derived. Importantly, each stem cell type retains the defining properties and lineage restriction of their in vivo tissue of origin. Recently, we demonstrated that XEN-like cells arise within mESC cultures. This raises the possibility that mESCs can generate self-renewing XEN cells without the requirement for gene manipulation. We have developed a novel approach to convert mESCs to XEN cells (cXEN) using growth factors. We confirm that the downregulation of the pluripotency transcription factor Nanog and the expression of primitive endoderm-associated genes Gata6, Gata4, Sox17 and Pdgfra are necessary for cXEN cell derivation. This approach highlights an important function for Fgf4 in cXEN cell derivation. Paracrine FGF signalling compensates for the loss of endogenous Fgf4, which is necessary to exit mESC self-renewal, but not for XEN cell maintenance. Our cXEN protocol also reveals that distinct pluripotent stem cells respond uniquely to differentiation promoting signals. cXEN cells can be derived from mESCs cultured with Erk and Gsk3 inhibitors (2i), and LIF, similar to conventional mESCs. However, we find that epiblast stem cells (EpiSCs) derived from the post-implantation embryo are refractory to cXEN cell establishment, consistent with the hypothesis that EpiSCs represent a pluripotent state distinct from mESCs. In all, these findings suggest that the potential of mESCs includes the capacity to give rise to both extra-embryonic and embryonic lineages.

Selective modulation of the SM22alpha promoter by the binding of BTEB3 (basal transcription element-binding protein 3) to TGGG repeats

We have previously identified a C2H2 zinc-finger transcription factor [BTEB3 (basal transcription element-binding protein 3)/KLF13 (Krüppel-like factor 13)] that activates the minimal promoter for the smooth muscle-specific SM22alpha gene in other types of cell. We show that recombinant BTEB3 binds to three TGGG motifs in the minimal SM22alpha promoter. By mutation analysis, only one of these boxes is required for BTEB3-dependent promoter activation in P19 cells and BTEB3 activates or inhibits reporter gene expression depending on the TGGG box to which it binds. Transient transfection experiments show that BTEB3 also activates reporter gene expression from the SM22alpha promoter in VSMCs (vascular smooth muscle cells). Similar studies showed that BTEB3 did not activate expression from the promoter regions of the smooth muscle myosin heavy chain or smooth muscle alpha-actin promoters, which contain similar sequences, implying that promoter activation by BTEB3 is selective. The expression of BTEB3 is readily detectable in VSMCs in vitro and is modulated in response to injury in vivo.

A novel combination of promoter and enhancers increases transgene expression in vascular smooth muscle cells in vitro and coronary arteries in vivo after adenovirus-mediated gene transfer

Recombinant adenoviruses are employed widely for vascular gene transfer. Vascular smooth muscle cells (SMCs) are a relatively poor target for transgene expression after adenovirus-mediated gene delivery, however, even when expression is regulated by powerful, constitutive viral promoters. The major immediate-early murine cytomegalovirus enhancer/promoter (MIEmCMV) elicits substantially greater transgene expression than the human cytomegalovirus promoter (MIEhCMV) in all cell types in which they have been compared. The Woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) increases transgene expression in numerous cell lines, and fragments of the smooth muscle myosin heavy chain (SMMHC) promoter increase expression within SMC from heterologous promoters. We therefore, compared the expression of beta-galactosidase after adenovirus-mediated gene transfer of lacZ under the transcriptional regulation of a variety of combinations of the promoters and enhancers described, in vitro and in porcine coronary arteries. We demonstrate that inclusion of WPRE and a fragment of the rabbit SMMHC promoter along with MIEmCMV increases beta-galactosidase expression 90-fold in SMC in vitro and approximately 40-fold in coronary arteries, compared with vectors in which expression is regulated by MIEhCMV alone. Expression cassette modification represents a simple method of improving adenovirus-mediated vascular gene transfer efficiency and has important implications for the development of efficient cardiovascular gene therapy strategies.

The smooth muscle myosin heavy chain gene exhibits smooth muscle subtype-selective modular regulation in vivo

Previous studies in our laboratory demonstrated that the transgene consisting of the -4.2 to +11.6 kilobase (kb) region of the smooth muscle (SM) myosin heavy chain (MHC) gene was expressed in virtually all SM tissue types in vivo in transgenic mice and that the multiple CArG elements within this region were differentially required in SMC subtypes, implying that the SM-MHC gene was controlled by multiple transcriptional regulatory modules. To investigate this hypothesis, we analyzed specific regulatory regions within the SM-MHC -4.2 to +11.6 kb region by a combination of deletion analyses of various SM-MHC transgenes as well as by DNaseI hypersensitivity assays and in vivo footprinting in intact SMC tissues. The results showed that SM-MHC transgene expression depended on a large number of required regulatory modules that were widely spread over the -4.2 to +11.6 region. Moreover, the results revealed several unexpected novel features of regulation of the SM-MHC gene including: 1) unique combinations of regulatory modules were required for SM-MHC expression in different SMC-subtypes; 2) repressor modules as well as activator modules were both critical for SMC specificity of the gene; 3) certain modules were required in certain contexts but were dispensable in others within a given SMC-subtype (i.e. the net activity of the module was determined by interaction between modules not simply by the sum of module activities); and 4) we identified a highly conserved 200-base pair transcriptional regulatory module at +8 kb that was required in the large arteries but dispensable in the coronary arteries and airways in transgenic mice and contained multiple potential cis-elements that were occupied by nuclear proteins in the intact aorta based on in vivo footprinting. Taken together, the results suggest a model of complex modular control of expression of the SM-MHC gene that varies between SMC subtypes. Moreover, the studies establish the possibility of designing derivatives of the SM-MHC promoter that might be used for targeting gene expression to specific SMC subtypes in vivo.

CArG elements control smooth muscle subtype-specific expression of smooth muscle myosin in vivo

Expression of smooth muscle myosin heavy chain (SM-MHC) is tightly controlled depending on the differentiated state of smooth muscle cells (SMCs). To better understand the mechanisms that regulate transcription of the SM-MHC gene in vivo, we tested the function of several conserved CArG elements contained within the -4200 to +11,600 region of this gene that we had previously shown to drive SMC-specific expression in transgenic mice. CArG1 in the 5'-flanking sequence was required for all SMCs, while CArG2 and a novel intronic CArG element were differentially required in SMC subtypes. Of particular note, mutation of the intronic CArG selectively abolished expression in large arteries. A promoter construct containing three repeats of a conserved 227-bp intronic CArG-containing region was sufficient to direct transcription in vascular SMCs in transgenic mice, although this construct was also expressed in skeletal and cardiac muscle. These results support a model in which transcriptional regulation of SM-MHC is controlled by multiple positive and negative modular control regions that differ between SMCs and non-SMCs and among SMC subtypes. We also demonstrated that the CArG elements of the endogenous SM-MHC gene were bound by SRF in chromatin.

Nitric oxide regulates smooth-muscle-specific myosin heavy chain gene expression at the transcriptional level-possible role of SRF and YY1 through CArG element

Nitric oxide (NO) plays an important role in vascular regulation through its vasodilatory, antiatherogenic, and antithrombotic properties. NO inhibits platelet adhesion and aggregation and modulates smooth muscle cell (SMC) proliferation and migration. In animals with experimentally induced vascular injury, ec-NOS gene transfection not only restored NO production to normal levels but also increased vascular reactivity of the injured vessels. However, it is unclear whether NO regulates smooth-muscle-specific gene expression. We report here that addition of PDGF-BB to vascular smooth muscle cells suppressed SM-MHC expression but treatment with the NO donors FK409 and SNAP restored SM-MHC mRNA/protein expression. In vitro transfection and subsequent CAT assays demonstrated that exogenous NO can restore PDGF-BB-induced suppression of SM-MHC promoter activity. Promoter deletion analysis revealed that a CArG-3 box located at -1276 bp in the SM-MHC promoter was important for NO-dependent promoter regulation and as well as high level promoter activity. Gel mobility shift assays showed that CArG-3 contained the SRF binding site and a binding site for YY1, a nuclear factor which acts as a negative regulator on muscle-specific promoters. Interestingly, NO donor FK409 reduced YY1 binding to the CArG-3 element but increased SRF binding, suggesting that these two factors bind competitively to the overlapping sites. We also found that mutation to the YY1 binding site in the CArG-3 element resulted in a loss of PDGF-BB-induced suppression of the SM-MHC promoter activity. These findings indicate that NO regulates SM-MHC gene expression at the transcriptional level at least partially through the regulation of transcription factor binding activities on the CArG element. Thus we propose that NO plays a positive role in maintaining the differentiated state of VSMCs.

Doxorubicin represses CARP gene transcription through the generation of oxidative stress in neonatal rat cardiac myocytes: possible role of serine/threonine kinase-dependent pathways

Doxorubicin (Dox), an anthracyclin antineoplastic agent, causes dilated cardiomyopathy. CARP has been identified as a nuclear protein whose mRNA levels are exquisitely sensitive to Dox. In this study we investigated the molecular mechanisms underlying the repression of CARP expression by Dox in cultured neonatal rat cardiac myocytes. Dox (1 micromol/l)-mediated decrease in CARP mRNA levels was strongly correlated with BNP but not with ANP mRNA levels. Hydrogen peroxide scavenger catalase (1 mg/ml) but not hydroxyl radical scavengers dimethylthiourea (10 mmol/l) or mannitol (10 mmol/l) blunted the Dox-mediated decrease in CARP and BNP expression. Superoxide dismutase inhibitor diethyldithiocarbamic acid (10 mmol/l), which inhibits the generation of hydrogen peroxide from superoxide metabolism, attenuated the repression. PD98059 (MEK1 inhibitor, 50 micromol/l), SB203580 (p38 MAP kinase inhibitor, 10 micromol/l), calphostin C (protein kinase C (PKC) inhibitor, 1 micromol/l), non-selective protein tyrosine kinase inhibitors genistein (50 micromol/l) or herbimycin A (1 micromol/l) failed to abrogate the downregulation of CARP and BNP expression by Dox. In contrast, H7 (30 micromol/l), a potent inhibitor of serine/threonine kinase, significantly blocked Dox-mediated downregulation of CARP and BNP expression. Transient transfection of a series of 5'-deletion and site-specific mutation constructs revealed that M-CAT element located at -37 of the human CARP promoter mediates Dox-induced repression of CARP promoter activity. These results suggest that a genetic response to Dox is mediated through the generation of hydrogen peroxide, which is selectively linked to the activation of H7-sensitive serine/threonine kinase distinct from PKC and well characterized mitogen-activated protein (MAP) kinases (ERK and p38MAP kinase). Furthermore, our data implicated M-CAT element as a Dox-response element within the CARP promoter in cardiac myocytes.

Transcriptional regulation of smooth muscle phenotypic modulation

Phenotypic modulation of vascular smooth muscle cell plays a pivotal role in the development of vascular pathology, such as atherosclerosis and restenosis after angioplasty. We have identified the zinc finger protein BTEB2 as a DNA binding protein that regulates the nonmuscle myosin heavy chain (SMemb) promoter. BTEB2 is expressed in fetal aorta but not in adult aorta and is induced in the neointima in response to vascular injury. BTEB2 also activates a number of vascular disease-associated genes, such as tissue factor, PAI-1 (plasminogen activator inhibitor-1), and Egr-1 gene. We have further isolated and characterized the human BTEB2 gene. Functional studies using 5'-deletion and site-directed mutation constructs demonstrated that phorbol ester induces Egr-1, which can activate the BTEB2 promoter through binding to -32 from the transcription start site. These results suggest that phenotypic modulation of vascular smooth muscle cells occurring in response to mitogen stimulation may be mediated by BTEB2 through Egr-1 induction.

Age dependence of smooth muscle myosin expression by cultured rat aortic smooth muscle cells

Vascular smooth muscle cells (SMC) in vivo are highly heterogeneous phenotypically, particularly during development and in the adult during periods of remodeling. Much remains to be learned, however, regarding regulation of the SMC phenotype at the gene level. Here, we studied smooth muscle myosin heavy chain (SMMHC) expression at the transcriptional and mRNA levels in SMC cultured from newborn, adult, and old animals, which express different patterns of differentiation markers. We also examined regulation of SMMHC gene expression by TGF-beta, a cytokine known to be involved in the differentiation process. The activity of SMMHC promoter constructs, the expression of which is smooth-muscle-specific, was greatest in SMC from newborn animals and least in cells from old animals. Thus, differences in the degree of differentiation of SMC from these three sources may at least in part be due to transcriptional events. SMC from the three animal sources each contained mRNAs for the SM-1A and SM-2A tail but not those for the SM-1B and SM-2B head isoforms. Total SMMHC mRNA levels reflected similar differences as found at the transcriptional level. SM-2A mRNA as a proportion of total SMMHC mRNA was greatest in SMC from newborn animals, consistent with their higher degree of differentiation. TGF-beta up-regulated both transcription and mRNA levels but did not change the proportions of SMMHC mRNAs. Though the levels of transcriptional activity and mRNA were widely different in untreated cells, the degree of TGF-beta stimulation was approximately the same in all cases.

Cloning and characterization of the promoters of the maxiK channel alpha and beta subunits

Large conductance, calcium-activated potassium (maxiK) channels are expressed in nerve, muscle, and other cell types and are important determinants of smooth muscle tone. To determine the mechanisms involved in the transcriptional regulation of maxiK channels, we characterized the promoter regions of the pore forming (alpha) and regulatory (beta) subunits of the human channel complex. Maximum promoter activity (up to 12.3-fold over control) occurred between nucleotides -567 and -220 for the alpha subunit (hSlo) gene. The minimal promoter is GC-rich with 5 Sp-1 binding sites and several TCC repeats. Other transcription factor-binding motifs, including c/EBP, NF-kB, PU.1, PEA-3, Myo-D, and E2A, were observed in the 5'-flanking sequence. Additionally, a CCTCCC sequence, which increases the transcriptional activity of the SM1/2 gene in smooth muscle, is located 27 bp upstream of the TATA-like sequence, a location identical to that found in the SM1/2 5'-flanking region. However, the promoter directed equivalent expression when transfected into smooth muscle and other cell types. Analysis of the hSlo beta subunit 5'-flanking region revealed a TATA box at position -77 and maximum promoter activity (up to 11.0-fold) in a 200 bp region upstream from the cap site. Binding sites for GATA-1, Myo-D, c-myb, Ets-1/Elk-1, Ap-1, and Ik-2 were identified within this sequence. Two CCTCCC elements are present in the hSlo beta subunit promoter, but tissue-specific transcriptional activity was not observed. The lack of tissue-specific promoter activity, particularly the finding of promoter activity in cells from tissues in which the maxiK gene is not expressed, suggests a complex channel regulatory mechanism for hSlo genes. Moreover, the lack of similarity of the promoters of the two genes suggests that regulation of coordinate expression of the subunits does not occur through equivalent cis-acting sequences.

Molecular control of vascular smooth muscle cell differentiation

Changes in the differentiated state of the vascular smooth muscle cell (SMC) including enhanced growth responsiveness, altered lipid metabolism, and increased matrix production are known to play a key role in development of atherosclerotic disease. As such, there has been extensive interest in understanding the molecular mechanisms and factors that regulate differentiation of vascular SMC, and how this regulation might be disrupted in vascular disease. Key questions include determination of mechanisms that control the coordinate expression of genes required for the differentiated function of the smooth muscle cell, and determination as to how these regulatory processes are influenced by local environmental cues known to be important to control of smooth muscle differentiation. Of particular interest, a number of common cis regulatory elements including highly conserved CArG [CC(A/T)6GG] motifs or CArG-like motifs and a TGF beta control element have been identified in the promoters of virtually all smooth muscle differentiation marker genes characterized to date including smooth muscle alpha-actin, smooth muscle myosin heavy chain, telokin, and SM22 alpha and shown to be required for expression of these genes both in vivo and in vitro. In addition, studies have identified a number of trans factors that interact with these cis elements, and shown how the expression or activity of these factors is modified by local environmental cues such as contractile agonists that are known to influence differentiation of smooth muscle.

Transcriptional regulation of smooth muscle contractile apparatus expression

The transcriptional regulatory mechanisms that control gene expression during differentiation and contractile protein accumulation are becoming well understood in skeletal and cardiac muscle lineages. Current understanding of smooth muscle-specific gene transcription is much more limited, though recent studies have begun to shed light on this topic. In this review, we summarize some of the themes emerging from these studies and identify transcriptional regulatory elements common to several smooth muscle genes. These include potential binding sites for serum response factor, Sp1, AP2, Mhox, and YY1, as well as a potential transforming growth factor-beta control element. We speculate that it may be possible to manipulate smooth muscle-specific gene expression in asthma or pulmonary arterial hypertension as an eventual therapy.

Lung smooth muscle differentiation

The vascular and visceral smooth muscle tissues of the lung perform a number of tasks that are critical to pulmonary function. Smooth muscle function often is compromised as a result of lung disease. Though a great deal is known about regulation of smooth muscle cell replication and cell and tissue contractility, much less is understood regarding the phenotype of the contractile protein machinery of lung smooth muscle cells. This review focuses on the expression of cytoskeletal and contractile proteins of lung vascular and airway smooth muscle cells during development, in the adult and during vascular and airway remodeling. Emphasis is placed on the expression of the heavy chain of smooth muscle myosin, as well as the regulation of its gene. Important areas for future research are discussed.

Interaction of CArG elements and a GC-rich repressor element in transcriptional regulation of the smooth muscle myosin heavy chain gene in vascular smooth muscle cells

We have previously shown that maximal expression of the rat smooth muscle myosin heavy chain (SM-MHC) gene in cultured rat aortic smooth muscle cells (SMCs) required the presence of a highly conserved domain (nucleotides -1321 and -1095) that contained two positive-acting serum response factor (SRF) binding elements (CArG boxes 1 and 2) and a negative-acting GC-rich element that was recognized by Sp1 (Madsen, C. S., Hershey, J. C., Hautmann, M. B., White, S. L., and Owens, G. K. (1997) J. Biol. Chem. 272, 6332-6340). In this study, to better understand the functional role of these three cis elements, we created a series of SM-MHC reporter-gene constructs in which each element was mutated either alone or in combination with each other and tested them for activity in transient transfection assays using primary cultured rat aortic SMCs. Results demonstrated that the most proximal SRF binding element (CArG-box1) was active in the absence of CArG-box2, but only upon removal of the GC-rich repressor. In contrast, regardless of sequence context, CArG-box2 was active only when CArG-box1 was present. We further demonstrated using electrophoretic mobility shift assays that Sp1 binding to the GC-rich repressor element did not prevent SRF binding to the adjacent CArG-box2. Thus, unlike other proteins reported to inhibit SRF activity, the repressor activity associated with the GC-rich element does not appear to function through direct inhibition of SRF binding. As a first step toward understanding the importance of these elements in vivo, we performed in vivo footprinting on the intact rat aorta. We demonstrated that both CArG boxes and the GC-rich element were bound by protein within the animal. Additionally, using the rat carotid injury model we showed that Sp1 protein was significantly increased in SMCs located within the myointimal lesion, suggesting that increased expression of this putative repressor factor may contribute to the decreased SM MHC expression within SMCs found in myointimal lesions.

Isolation of the embryonic form of smooth muscle myosin heavy chain (SMemb/NMHC-B) gene and characterization of its 5'-flanking region

To examine the molecular mechanisms that regulate the expression of the SMemb/NMHC-B gene, a nonmuscle myosin heavy chain isoform predominantly expressed in fetal aorta, we have isolated and characterized the 5'-flanking region of the rabbit SMemb/NMHC-B gene. Transient transfection experiments demonstrated that 105 base pairs of 5'-flanking sequence was necessary to direct high level transcription in C2/2 cells, vascular smooth muscle cells derived from rabbit aorta. An essential cis-regulatory element was localized between -100 and -91 base pairs from the transcription start site based on the results that replacement mutagenesis within this region significantly reduced promoter activity. Sequence of this region is completely conserved between mouse and rabbit and fits no known DNA binding consensus. Gel mobility shift assays revealed that a specific DNA-protein complex was formed at this site with nuclear extracts from C2/2 cells, which can be competed by H-2Kb CCAAT box but not by Hsp70 CCAAT box or other CCAAT-containing sequences. We conclude that expression of the SMemb/NMHC-B gene is regulated through an interaction between a sequence element located at -100 and a distinct member of CCAAT-binding proteins.

Expression of the smooth muscle myosin heavy chain gene is regulated by a negative-acting GC-rich element located between two positive-acting serum response factor-binding elements

To identify cis- and trans-acting factors that regulate smooth muscle-specific gene expression, we studied the smooth muscle myosin heavy chain gene, a rigorous marker of differentiated smooth muscle. A comparison of smooth muscle myosin heavy chain promoter sequences from multiple species revealed the presence of a highly conserved 227-base pair domain (nucleotides -1321 to -1095 in rat). Results of a deletion analysis of a 4.3-kilobase pair segment of the rat promoter (nucleotides -4220 to +88) demonstrated that this domain was necessary for maximal transcriptional activity in smooth muscle cells. Gel-shift analysis and site-directed mutagenesis demonstrated that one true CArG and another CArG-like element contained within this domain were both recognized by the serum response factor and were both required for the positive activity attributable to this domain. Additional studies demonstrated that mutation of a GC-rich sequence within the 227-base pair conserved domain resulted in a nearly 100% increase in transcriptional activity. Gel-shift analysis showed that this GC-rich repressor element was recognized by both Sp1 and Sp3. These data demonstrate that transcriptional control of the smooth muscle myosin heavy chain gene is highly complex, involving both negative and positive regulatory elements, including CArG sequences found in the promoters of multiple smooth muscle differentiation marker genes.