Smoothelin-B deficiency results in reduced arterial contractility, hypertension, and cardiac hypertrophy in mice

Bioinformatic analysis of smoothelin family members supports tissue-specific functions of unique C-terminal calponin homology domains

Smoothelins are cytoskeletal proteins with a single C-terminal calponin homology domain type 2 (CHD2). Little is known about the significance of variation in SMTN CHD2 domains, addressed here through analysis of public databases. A conserved 152 nt penultimate constitutive exon present in all SMTNs encodes helices II-IV of CHD2 with high identity (nt/aa 63/65%). Variable CHD2s of SMTN (helices IV-VI) are generated by alternative splicing of 165 nt exon E20. E20 and the CHD2 it encodes have high homology with the terminal constitutive exon of SMTNL1 (E8; nt/aa 72/75% identity). Unique to these CHD2 variants are a conserved extended nine amino acid C-terminal tail containing KTKK ubiquitination motifs. When E20 of SMTN is skipped (SMTN E20-), constitutive terminal E21 codes for helices IV-VI of CHD2. SMTN E21 has high identity with the terminal exon of SMTNL2 (E8; nt/aa 75/81% identity of aligned sequences) except for coding for a unique extended C-terminus (24 nt; 8aa) conserved only in mammals. SMTN isoform expression is tissue-specific: SMTNE20- and SMTNE20+ are highly expressed in SMC and non-muscle cells, respectively, while SMTNL1 + 2 are highly expressed in skeletal muscle cells. Tissue-specific expression of SMTN CHD2s with unique helices IV-VI suggest tissue-specific functions that require further study.

Organ-specific endothelial cell heterogenicity and its impact on regenerative medicine and biomedical engineering applications

Endothelial cells (ECs) are a key cellular component of the vascular system as they form the inner lining of the blood vessels. Recent findings highlight that ECs express extensive phenotypic heterogenicity when following the vascular tree from the major vasculature down to the organ capillaries. However, in vitro models, used for drug development and testing, or to study the role of ECs in health and disease, rarely acknowledge this EC heterogenicity. In this review, we highlight the main differences between different EC types, briefly summarize their different characteristics and focus on the use of ECs in in vitro models. We introduce different approaches on how ECs can be utilized in co-culture test systems in the field of brain, pancreas, and liver research to study the role of the endothelium in health and disease. Finally, we discuss potential improvements to current state-of-the-art in vitro models and future directions.

Retene, pyrene and phenanthrene cause distinct molecular-level changes in the cardiac tissue of rainbow trout (Oncorhynchus mykiss) larvae, part 2 - Proteomics and metabolomics

Polycyclic aromatic hydrocarbons (PAHs) are global contaminants of concern. Despite several decades of research, their mechanisms of toxicity are not very well understood. Early life stages of fish are particularly sensitive with the developing cardiac tissue being a main target of PAHs toxicity. The mechanisms of cardiotoxicity of the three widespread model polycyclic aromatic hydrocarbons (PAHs) retene, pyrene and phenanthrene were explored in rainbow trout (Oncorhynchus mykiss) early life stages. Newly hatched larvae were exposed to sublethal doses of each individual PAH causing no detectable morphometric alterations. Changes in the cardiac proteome and metabolome were assessed after 7 or 14 days of exposure to each PAH. Phase I and II enzymes regulated by the aryl hydrocarbon receptor were significantly induced by all PAHs, with retene being the most potent compound. Retene significantly altered the level of several proteins involved in key cardiac functions such as muscle contraction, cellular tight junctions or calcium homeostasis. Those findings were quite consistent with previous reports regarding the effects of retene on the cardiac transcriptome. Significant changes in proteins linked to iron and heme metabolism were observed following exposure to pyrene. While phenanthrene also altered the levels of several proteins in the cardiac tissue, no clear mechanisms or pathways could be highlighted. Due to high variability between samples, very few significant changes were detected in the cardiac metabolome overall. Slight but significant changes were still observed for pyrene and phenanthrene, suggesting possible effects on several energetic or signaling pathways. This study shows that early exposure to different PAHs can alter the expression of key proteins involved in the cardiac function, which could potentially affect negatively the fitness of the larvae and later of the juvenile fish.

Regulation of Blood Pressure by Targeting CaV1.2-Galectin-1 Protein Interaction

BACKGROUND

L-type Ca_V1.2 channels play crucial roles in the regulation of blood pressure. Galectin-1 (Gal-1) has been reported to bind to the I-II loop of Ca_V1.2 channels to reduce their current density. However, the mechanistic understanding for the downregulation of Ca_V1.2 channels by Gal-1 and whether Gal-1 plays a direct role in blood pressure regulation remain unclear.

METHODS

In vitro experiments involving coimmunoprecipitation, Western blot, patch-clamp recordings, immunohistochemistry, and pressure myography were used to evaluate the molecular mechanisms by which Gal-1 downregulates Ca_V1.2 channel in transfected, human embryonic kidney 293 cells, smooth muscle cells, arteries from Lgasl1^-/- mice, rat, and human patients. In vivo experiments involving the delivery of Tat-e9c peptide and AAV5-Gal-1 into rats were performed to investigate the effect of targeting Ca_V1.2-Gal-1 interaction on blood pressure monitored by tail-cuff or telemetry methods.

RESULTS

Our study reveals that Gal-1 is a key regulator for proteasomal degradation of Ca_V1.2 channels. Gal-1 competed allosterically with the Ca_Vβ subunit for binding to the I-II loop of the Ca_V1.2 channel. This competitive disruption of Ca_Vβ binding led to Ca_V1.2 degradation by exposing the channels to polyubiquitination. It is notable that we demonstrated that the inverse relationship of reduced Gal-1 and increased Ca_V1.2 protein levels in arteries was associated with hypertension in hypertensive rats and patients, and Gal-1 deficiency induces higher blood pressure in mice because of the upregulated Ca_V1.2 protein level in arteries. To directly regulate blood pressure by targeting the Ca_V1.2-Gal-1 interaction, we administered Tat-e9c, a peptide that competed for binding of Gal-1 by a miniosmotic pump, and this specific disruption of Ca_V1.2-Gal-1 coupling increased smooth muscle Ca_V1.2 currents, induced larger arterial contraction, and caused hypertension in rats. In contrasting experiments, overexpression of Gal-1 in smooth muscle by a single bolus of AAV5-Gal-1 significantly reduced blood pressure in spontaneously hypertensive rats.

CONCLUSIONS

We have defined molecularly that Gal-1 promotes Ca_V1.2 degradation by replacing Ca_Vβ and thereby exposing specific lysines for polyubiquitination and by masking I-II loop endoplasmic reticulum export signals. This mechanistic understanding provided the basis for targeting Ca_V1.2-Gal-1 interaction to demonstrate clearly the modulatory role that Gal-1 plays in regulating blood pressure, and offering a potential approach for therapeutic management of hypertension.

Exposure to Blast Overpressure Impairs Cerebral Microvascular Responses and Alters Vascular and Astrocytic Structure

Exposure to blast overpressure may result in cerebrovascular impairment, including cerebral vasospasm. The mechanisms contributing to this vascular response are unclear. The aim of this study was to evaluate the relationship between blast and functional alterations of the cerebral microcirculation and to investigate potential underlying changes in vascular microstructure. Cerebrovascular responses were assessed in sham- and blast-exposed male rats at multiple time points from 2 h through 28 days after a single 130-kPa (18.9-psi) exposure. Pial microcirculation was assessed through a cranial window created in the parietal bone of anesthetized rats. Pial arteriolar reactivity was evaluated in vivo using hypercapnia, barium chloride, and serotonin. We found that exposure to blast leads to impairment of arteriolar reactivity >24 h after blast exposure, suggesting delayed injury mechanisms that are not simply attributed to direct mechanical deformation. Observed vascular impairment included a reduction in hypercapnia-induced vasodilation, increase in barium-induced constriction, and reversal of the serotonin effect from constriction to dilation. A reduction in vascular smooth muscle contractile proteins consistent with vascular wall proliferation was observed, as well as delayed reduction in nitric oxide synthase and increase in endothelin-1 B receptors, mainly in astrocytes. Collectively, the data show that exposure to blast results in delayed and prolonged alterations in cerebrovascular reactivity that are associated with changes in the microarchitecture of the vessel wall and astrocytes. These changes may contribute to long-term pathologies involving dysfunction of the neurovascular unit, including cerebral vasospasm.

Identification of Filamin A Mechanobinding Partner I: Smoothelin Specifically Interacts with the Filamin A Mechanosensitive Domain 21

Filamin A (FLNA) is a ubiquitously expressed actin cross-linking protein and a scaffold of numerous binding partners to regulate cell proliferation, migration, and survival. FLNA is a homodimer, and each subunit has an N-terminal actin-binding domain followed by 24 immunoglobulin-like repeats (R). FLNA mediates mechanotransduction by force-induced conformational changes of its cryptic integrin-binding site on R21. Here, we identified two novel FLNA-binding partners, smoothelins (SMTN A and B) and leucine zipper protein 1 (LUZP1), using stable isotope labeling by amino acids in cell culture (SILAC)-based proteomics followed by an in silico screening for proteins having a consensus FLNA-binding domain. We found that, although SMTN does not interact with full-length FLNA, it binds to FLNA variant 1 (FLNAvar-1) that exposes the cryptic CD cleft of R21. Point mutations on the C strand that disrupt the integrin binding also block the SMTN interaction. We identified FLNA-binding domains on SMTN using mutagenesis and used the mutant SMTN to investigate the role of the FLNA-SMTN interaction on the dynamics and localization of SMTN in living cells. Fluorescence recovery after photobleaching (FRAP) of GFP-labeled SMTN in living cells demonstrated that the non-FLNA-binding mutant SMTN diffuses faster than wild-type SMTN. Moreover, inhibition of Rho-kinase using Y27632 also increases the diffusion. These data demonstrated that SMTN specifically interacts with FLNAvar-1 and mechanically activated FLNA in cells. The companion report (Wang and Nakamura, 2019) describes the interactions of FLNA with the transcript of the LUZP1 gene.

Vascular Smooth Muscle Cells and Arterial Stiffening: Relevance in Development, Aging, and Disease

The cushioning function of large arteries encompasses distension during systole and recoil during diastole which transforms pulsatile flow into a steady flow in the microcirculation. Arterial stiffness, the inverse of distensibility, has been implicated in various etiologies of chronic common and monogenic cardiovascular diseases and is a major cause of morbidity and mortality globally. The first components that contribute to arterial stiffening are extracellular matrix (ECM) proteins that support the mechanical load, while the second important components are vascular smooth muscle cells (VSMCs), which not only regulate actomyosin interactions for contraction but mediate also mechanotransduction in cell-ECM homeostasis. Eventually, VSMC plasticity and signaling in both conductance and resistance arteries are highly relevant to the physiology of normal and early vascular aging. This review summarizes current concepts of central pressure and tensile pulsatile circumferential stress as key mechanical determinants of arterial wall remodeling, cell-ECM interactions depending mainly on the architecture of cytoskeletal proteins and focal adhesion, the large/small arteries cross-talk that gives rise to target organ damage, and inflammatory pathways leading to calcification or atherosclerosis. We further speculate on the contribution of cellular stiffness along the arterial tree to vascular wall stiffness. In addition, this review provides the latest advances in the identification of gene variants affecting arterial stiffening. Now that important hemodynamic and molecular mechanisms of arterial stiffness have been elucidated, and the complex interplay between ECM, cells, and sensors identified, further research should study their potential to halt or to reverse the development of arterial stiffness.

Myostatin mediates abdominal aortic atherosclerosis progression by inducing vascular smooth muscle cell dysfunction and monocyte recruitment

Myostatin (Mstn) is a skeletal muscle growth inhibitor involved in metabolic disorders and heart fibrosis. In this study we sought to verify whether Mstn is also operative in atherosclerosis of abdominal aorta. In human specimens, Mstn expression was almost absent in normal vessels, became detectable in the media of non-progressive lesions and increased with the severity of the damage. In progressive atherosclerotic lesions, Mstn was present in the media, neointima, plaque shoulder and in infiltrating macrophages. Mstn co-localized with α-smooth muscle actin (α-SMA) staining and with some CD45+ cells, indicating Mstn expression in VSMCs and bloodstream-derived leukocytes. In vitro, Mstn was tested in VSMCs and monocytes. In A7r5 VSMCs, Mstn downregulated proliferation and Smoothelin mRNA, induced cytoskeletal rearrangement, increased migratory rate and MCP-1/CCR2 expression. In monocytes (THP-1 cells and human monocytes), Mstn acted as a chemoattractant and increased the MCP-1-dependent chemotaxis, F-actin, α-SMA, MCP-1 and CCR2 expression; in turn, MCP-1 increased Mstn mRNA. Mstn induced JNK phosphorylation both in VSMCs and monocytes. Our results indicate that Mstn is overexpressed in abdominal aortic wall deterioration, affects VSMCs and monocyte biology and sustains a chronic inflammatory milieu. These findings propose to consider Mstn as a new playmaker in atherosclerosis progression.

Effect of oxidative stress on the expression of thin filament-associated proteins in gastric smooth muscle cells

Thin filament-associated proteins such as calponin, caldesmon, and smoothelin are believed to regulate acto-myosin interaction and thus, muscle contraction. Oxidative stress has been found to affect the normal contractile behavior of smooth muscle and is involved in the pathogenesis of a number of human diseases such as diabetes mellitus, hypertension, and atherosclerosis. However, very little is known about the effect of oxidative stress on the expression of smooth muscle contractile proteins. The aim of the current study is to investigate the effect of oxidative stress on the expression of thin filament-associated proteins in rat gastric smooth muscle. Single smooth muscle cells of the stomach obtained from Sprague-Dawley rats were used. Muscle cells were treated with hydrogen peroxide (H2O2) (500 μM) for 30 min or the peroxynitrite donor 3-morpholinosydnonimine (SIN-1) (1 mM) for 90 min to induce oxidative stress. Calponin, caldesmon, and smoothelin expressions were measured via specifically designed enzyme-linked immunosorbent assay. We found that exposure to exogenous H2O2 or incubation of dispersed gastric muscle cells with SIN-1 significantly increased the expression of calponin, caldesmon, and smoothelin proteins. In conclusion: oxidative stress increases the expression of thin filament-associated proteins in gastric smooth muscle, suggesting an important role in gastrointestinal motility disorders associated with oxidative stress.

Matrix metalloproteinase inhibitors prevent sepsis-induced refractoriness to vasoconstrictors in the cecal ligation and puncture model in rats

Previous studies have shown that the loss of contractility in aortas from lipopolysaccharide (LPS)-treated rats is related to intracellular activation of matrix metalloproteinase (MMPs). However, the role of MMPs in the vascular refractoriness to vasoconstrictors has not been investigated in a model of polymicrobial sepsis. We evaluated the effects of the oral administration of the MMP inhibitors doxycycline or ONO-4817 in the in vitro vascular reactivity of aortic rings from rats subjected to the cecal ligation and puncture (CLP) model of sepsis. Both doxycycline and ONO-4817 did not change vascular responses in sham-operated rats, but fully prevented hyporeactivity to KCl, phenylephrine and angiotensin II in vessels from CLP rats. This protective effect was not associated with changes in hematological parameters or blood nitrate and nitrite. The refractoriness to contractile agents was accompanied by enhanced activity of MMP-2 in aorta from CLP rats, which was abrogated by MMP inhibitors. CLP-induced sepsis did not impair the levels of MMP-2 in aorta, but significantly reduced calponin-1, a regulatory protein of vascular contraction. In addition, augmented levels of TIMP-1 were found in vessels from CLP rats. All these differences were prevented by either doxycycline or ONO-4817. Our study shows, for the first time in the CLP rat model of sepsis, that the vascular refractoriness to different contractile agents induced by polymicrobial sepsis is associated with increased activity of MMP-2 and reduced amounts of calponin-1 in the aorta. These findings reinforce the importance of the enhanced activity of MMPs for vascular failure in septic shock.

Small animal cardiovascular MR imaging and spectroscopy

The use of MR imaging and spectroscopy for studying cardiovascular disease processes in small animals has increased tremendously over the past decade. This is the result of the remarkable advances in MR technologies and the increased availability of genetically modified mice. MR techniques provide a window on the entire timeline of cardiovascular disease development, ranging from subtle early changes in myocardial metabolism that often mark disease onset to severe myocardial dysfunction associated with end-stage heart failure. MR imaging and spectroscopy techniques play an important role in basic cardiovascular research and in cardiovascular disease diagnosis and therapy follow-up. This is due to the broad range of functional, structural and metabolic parameters that can be quantified by MR under in vivo conditions non-invasively. This review describes the spectrum of MR techniques that are employed in small animal cardiovascular disease research and how the technological challenges resulting from the small dimensions of heart and blood vessels as well as high heart and respiratory rates, particularly in mice, are tackled.

Smooth muscle cell phenotypic switch: implications for foam cell formation

PURPOSE OF REVIEW

It is well accepted that LDLs and its modified form oxidized-LDL (ox-LDL) play a major role in the development of atherosclerosis and foam cell formation. Whereas the majority of these cells have been demonstrated to be derived from macrophages, smooth muscle cells (SMCs) give rise to a significant number of foam cells as well. During atherosclerotic plaque formation, SMCs switch from a contractile to a synthetic phenotype. The contribution of this process to foam cell formation is still not well understood.

RECENT FINDINGS

It has been confirmed that a large proportion of foam cells in human atherosclerotic plaques and in experimental intimal thickening arise from SMCs. SMC-derived foam cells express receptors involved in ox-LDL uptake and HDL reverse transport. In-vitro studies show that treatment of SMCs with ox-LDL induces typical foam-cell formation; this process is associated with a transition of SMCs toward a synthetic phenotype.

SUMMARY

This review summarizes data regarding the phenotypic switch of arterial SMCs within atherosclerotic lesion and their contribution to intimal foam cell formation.

Smoothelin-B is not a target of matrix metalloproteinase (MMP)-2 in the vasculature of endotoxemic rats

Smoothelin-B (SMTL-B) and calponin-1 are important regulators of vascular contraction. SMTL-B contains a calponin-homology domain and is structurally similar to cardiac troponin T. As calponin-1 and troponin T are proteolyzed by intracellular matrix metalloproteinase (MMP)-2 in oxidative stress injury, we hypothesized that SMTL-B is also cleaved by MMP-2 and contributes to lipopolysaccharide (LPS)-induced vascular hypocontractility. Rats received ONO-4817 (an MMP inhibitor) or its vehicle, 2 h prior to being administered lipopolysaccharide (LPS). LPS-induced aorta hypocontractility to potassium chloride or phenylephrine, and reduction of calponin-1 levels, were abolished by ONO-4817 at 6 but not 3 h after LPS. However, the level of SMTL-B was unaltered in LPS aortas and further unaffected by ONO-4817. Despite the importance of SMTL-B in vascular tone, it is not a target of MMP-2 in LPS-induced hypocontractility.

Altered vascular smooth muscle cell differentiation in the endometrial vasculature in menorrhagia

STUDY QUESTION

How does the smooth muscle content and differentiation stage of vascular smooth muscle cells (VSMCs) in endometrial blood vessels change according to the different phases of the menstrual cycle and is this altered in women with menorrhagia?

SUMMARY ANSWER

The smooth muscle content (as a proportion of the vascular cross-sectional area) of endometrial blood vessels remained unchanged during the normal menstrual cycle and in menorrhagia; however, expression of the VSMC differentiation markers, smoothelin and calponin, was dysregulated in endometrial blood vessels in samples from women with menorrhagia compared with controls.

WHAT IS KNOWN ALREADY

Menorrhagia affects 30% of women of reproductive age and is the leading indication for hysterectomy. Previous studies have suggested important structural and functional roles for endometrial blood vessels, including impaired vascular contractility. Differentiation of VSMC from a synthetic to contractile state is associated with altered cellular phenotype that contributes to normal blood flow and pressure. This vascular maturation process has been little studied in endometrium both across the normal menstrual cycle and in menorrhagia.

STUDY DESIGN, SIZE, DURATION

Endometrial biopsies were taken from hysterectomy specimens or by pipelle biopsy prior to hysterectomy in controls without endometrial pathology and in women with menorrhagia (n = 7 for each of proliferative, early-secretory, mid-secretory and late-secretory phases for both groups). Biopsies were formalin fixed and embedded in paraffin wax.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Paraffin-embedded sections were immunostained for α smooth muscle actin (αSMA), myosin heavy chain (MyHC), H-caldesmon, desmin, smoothelin and calponin (h1 or basic). VSMC content was measured in 25 αSMA(+) vascular cross sections per sample and expressed as a ratio of the muscular area:gross vascular cross-sectional area. VSMC differentiation was analysed by the presence/absence of differentiation markers compared with αSMA expression. Smoothelin and calponin expression was also analysed in relation to total number of blood vessels by double immunostaining for endothelial cell markers.

MAIN RESULTS AND THE ROLE OF CHANCE

Study of VSMC differentiation markers revealed decreased expression of calponin both in αSMA(+) vessels (P = 0.008) and in relation to total number of vessels (P = 0.001) in late secretory phase endometrium in menorrhagia compared with controls. Smoothelin expression in αSMA(+) vessels was increased (P = 0.03) in menorrhagia, although this was not significant in relation to the total number of vessels. In normal endometrium, the proportion of blood vessels expressing αSMA increased from 63% in proliferative endometrium to 81% in the late secretory phase (P = 0.002). The overall arterial muscle content did not differ between control and menorrhagia at any phase of the menstrual cycle, occupying 78-81% of gross vascular cross-sectional area during the different menstrual cycle phases.

LIMITATIONS, REASONS FOR CAUTION

This study included both straight and spiral arterioles and analysed only stratum functionalis. The VSMC differentiation with respect to αSMA expression is an observational study and the data are presented as presence or absence of the differentiation markers in each field of view, corresponding with the vascular cross sections included in the study of vascular muscle content.

WIDER IMPLICATIONS OF THE FINDINGS

Smoothelin and calponin have been widely implicated as important regulators of vascular tone, vascular contractility and rate of blood flow. Our results have uncovered a disparate pattern of calponin expression, potentially indicating a dysfunctional contraction mechanism in the endometrial blood vessels in menorrhagia, thus implicating calponin as a potential therapeutic target.

STUDY FUNDING/COMPETING INTERESTS

This study was funded by Wellbeing of Women (RG1342) and Newcastle University. There are no competing interests to declare.

TRIAL REGISTRATION NUMBER

Not applicable.

Biological responses in stented arteries

Vascular walls change their dimension and mechanical properties in response to injury such as balloon angioplasty and endovascular stent implantation. Placement of bare metal stents induces neointimal proliferation/restenosis which progresses through different phases of repair with time involving a cascade of cellular reactions. These phases just like wound healing comprise distinct steps consisting of thrombosis, inflammation, proliferation, and migration followed by remodelling. It is noteworthy that animals show a rapid progression of healing after stent deployment compared with man. During stenting, endothelial cells are partially to completely destroyed or crushed along with medial wall injury and stretching promoting activation of platelets, and thrombus formation accompanied by inflammatory reaction. Macrophages and platelets play a central role through the release of cytokines and growth factors that induce vascular smooth muscle cell accumulation within the intima. Smooth muscle cells undergo complex phenotypic changes including migration and proliferation from the media towards the intima, and transition from a contractile to a synthetic phenotype; the molecular mechanisms responsible for this change are highlighted in this review. Since studies in animals and man show that smooth muscle cells play a dominant role in restenosis, drugs like rapamycin and paclitaxel have been coated on stent with polymers to allow local slow release of drugs, which have resulted in dramatic reduction of restenosis that was once the Achilles' heel of interventional cardiologists.

Self-gated CINE MRI for combined contrast-enhanced imaging and wall-stiffness measurements of murine aortic atherosclerotic lesions

Background

High-resolution contrast-enhanced imaging of the murine atherosclerotic vessel wall is difficult due to unpredictable flow artifacts, motion of the thin artery wall and problems with flow suppression in the presence of a circulating contrast agent.

Methods and Results

We applied a 2D-FLASH retrospective-gated CINE MRI method at 9.4T to characterize atherosclerotic plaques and vessel wall distensibility in the aortic arch of aged ApoE^−/− mice after injection of a contrast agent. The method enabled detection of contrast enhancement in atherosclerotic plaques in the aortic arch after I.V. injection of micelles and iron oxides resulting in reproducible plaque enhancement. Both contrast agents were taken up in the plaque, which was confirmed by histology. Additionally, the retrospective-gated CINE method provided images of the aortic wall throughout the cardiac cycle, from which the vessel wall distensibility could be calculated. Reduction in plaque size by statin treatment resulted in lower contrast enhancement and reduced wall stiffness.

Conclusions

The retrospective-gated CINE MRI provides a robust and simple way to detect and quantify contrast enhancement in atherosclerotic plaques in the aortic wall of ApoE^−/− mice. From the same scan, plaque-related changes in stiffness of the aortic wall can be determined. In this mouse model, a correlation between vessel wall stiffness and atherosclerotic lesions was found.

Functional vascular smooth muscle-like cells derived from adult mouse uterine mesothelial cells

In mammalian visceral organs, vascular smooth muscle cells (VSMCs) originate from an epithelial-to-mesenchymal transition (EMT) of embryonic mesothelial cells (MCs). The ability of adult MCs to recapitulate EMT and to acquire smooth muscle (SM) markers upon provasculogenic culture suggested they might retain embryonic vasculogenic differentiation potential. However, it remains unknown whether adult MCs-derived SM-like cells may acquire specific vascular SM lineage markers and the functionality of differentiated contractile VSMCs. Here, we describe how a gentle trypsinization of adult mouse uterine cords could selectively detach their outermost uterine mesothelial layer cells. As other MCs; uterine MCs (UtMCs) uniformly expressed the epithelial markers β-catenin, ZO-1, E-cadherin, CD54, CD29, and CK18. When cultured in a modified SM differentiation media (SMDM) UtMCs initiated a loss of epithelial characteristics and gained markers expression of EMT (Twist, Snail, and Slug), stem and progenitor (Nanog, Sox2, C-kit, Gata-4, Isl-1, and nestin), SM (α-SMA, calponin, caldesmon, SM22α, desmin, SM-MHC, and smoothelin-B) and cardiac (BMP2, BMP4, ACTC1, sACTN, cTnI, cTnT, ANF, Cx43, and MLC2a). UtMCs repeatedly subcultured in SMDM acquired differentiated VSM-like characteristics and expressed smoothelin-B in the typical stress-fiber pattern expression of contractile VSMCs. Relevantly, UtMCs-derived VSM-like cells could generate "mechanical force" to compact collagen lattices and displayed in diverse degree voltage (K(+)) and receptor (endothelin-1, oxytocin, norepinephrine, carbachol and vasopressin)-induced [Ca(2+)](i) rises and contraction. Thus, we show for the first time that UtMCs could recapitulate in vitro differentiative events of early cardiovascular differentiation and transdifferentiate in cells exhibiting molecular and functional characteristics of VSMCs.

Haplotype of smoothelin gene associated with essential hypertension

Smoothelin is a specific cytoskeletal protein that is associated with smooth muscle cells. The human SMTN gene encodes smoothelin-A and smoothelin-B, and studies using SMTN gene knockout mice have demonstrated that these animals develop hypertension. The aim of the present study was to investigate the association between the human SMTN gene and essential hypertension (EH) using a haplotype-based case-control study. This is the first study to assess the association between essential hypertension and this gene. A total of 255 EH patients and 225 controls were genotyped for the five single-nucleotide polymorphisms (rs2074738, rs5997872, rs56095120, rs9621187 and rs10304) used as genetic markers for the human SMTN gene. Data were analyzed for three separate groups: total subjects, men and women. Although there were no differences for genotype distributions, or the dominant and recessive model distributions noted for total subjects, men and women for all of the SNPs selected for the present study, for the total subjects group, the frequency of the G-C-A-C haplotype constructed with rs2074738-rs5997872-rs56095120-rs9621187 was significantly lower in the essential hypertension patients than in the controls (P = 0.002). The G-C-A-C haplotype appears to be a useful protective marker of essential hypertension in Japanese, and the SMTN gene might also be a genetic marker for essential hypertension.

Novel pathways in the pathobiology of human abdominal aortic aneurysms

OBJECTIVES

Abdominal aortic aneurysm (AAA), a dilatation of the infrarenal aorta, typically affects males >65 years. The pathobiological mechanisms of human AAA are poorly understood. The goal of this study was to identify novel pathways involved in the development of AAAs.

METHODS

A custom-designed 'AAA-chip' was used to assay 43 of the differentially expressed genes identified in a previously published microarray study between AAA (n = 15) and control (n = 15) infrarenal abdominal aorta. Protein analyses were performed on selected genes.

RESULTS

Altogether 38 of the 43 genes on the 'AAA-chip' showed significantly different expression. Novel validated genes in AAA pathobiology included ADCY7, ARL4C, BLNK, FOSB, GATM, LYZ, MFGE8, PRUNE2, PTPRC, SMTN, TMODI and TPM2. These genes represent a wide range of biological functions, such as calcium signaling, development and differentiation, as well as cell adhesion not previously implicated in AAA pathobiology. Protein analyses for GATM, CD4, CXCR4, BLNK, PLEK, LYZ, FOSB, DUSP6, ITGA5 and PTPRC confirmed the mRNA findings.

CONCLUSION

The results provide new directions for future research into AAA pathogenesis to study the role of novel genes confirmed here. New treatments and diagnostic tools for AAA could potentially be identified by studying these novel pathways.

Intrinsically disordered N-terminus of calponin homology-associated smooth muscle protein (CHASM) interacts with the calponin homology domain to enable tropomyosin binding

The calponin homology-associated smooth muscle (CHASM) protein plays an important adaptive role in smooth and skeletal muscle contraction. CHASM is associated with increased muscle contractility and can be localized to the contractile thin filament via its binding interaction with tropomyosin. We sought to define the structural basis for the interaction of CHASM with smooth muscle tropomyosin as a first step to understanding the contribution of CHASM to the contractile capacity of smooth muscle. Herein, we provide a structure-based model for the tropomyosin-binding domain of CHASM using a combination of hydrogen/deuterium exchange mass spectrometry (HDX-MS) and NMR analyses. Our studies provide evidence that a portion of the N-terminal intrinsically disordered region forms intramolecular contacts with the globular C-terminal calponin homology (CH) domain. Ultimately, cooperativeness between these structurally dissimilar regions is required for CHASM binding to smooth muscle tropomyosin. Furthermore, it appears that the type-2 CH domain of CHASM is required for tropomyosin binding and presents a novel function for this protein domain.

The management of patients with atrial fibrillation and dronedarone's place in therapy

The pharmacologic management of atrial fibrillation (AF) includes rate and rhythm control strategies. Antiarrhythmic agents (eg, amiodarone, flecainide, and propafenone) are limited by serious toxicities (including proarrhythmic effects and pulmonary toxicity), which may lead to a reduced net clinical efficacy of rhythm control strategies. Dronedarone, a new antiarrhythmic agent, is effective in the maintenance of sinus rhythm. Dronedarone has also been shown to reduce ventricular rate and the incidence of hospitalization due to cardiovascular events. Dronedarone is recommended by the 2011 American College of Cardiology Foundation/American Heart Association/Heart Rhythm Society guidelines update for the management of AF patients with no or minimal heart disease, coronary artery disease, and hypertension with no left ventricular hypertrophy. Dronedarone is contraindicated in patients with New York Heart Association (NYHA) class IV heart failure or NYHA class II-III heart failure with a recent decompensation requiring hospitalization or referral to a specialized heart failure clinic.

Mapping and functional characterization of the murine smoothelin-like 1 promoter

Background

Smoothelin-like 1 (SMTNL1, also known as CHASM) plays a role in promoting relaxation as well as adaptive responses to exercise, pregnancy and sexual development in smooth and skeletal muscle. Investigations of Smtnl1 transcriptional regulation are still lacking. Thus, in this study, we identify and characterize key regulatory elements of the mouse Smtnl1 gene.

Results

We mapped the key regulatory elements of the Smtnl1 promoter region: the transcriptional start site (TSS) lays -44 bp from the translational start codon and a TATA-box motif at -75 bp was conserved amongst all mammalian Smtnl1 promoters investigated. The Smtnl1 proximal promoter enhances expression up to 8-fold in smooth muscle cells and a second activating region lays 500 bp further upstream. Two repressing motifs were present (-118 to -218 bp and -1637 to -1869 bp). The proximal promoter is highly conserved in mammals and contains a mirror repeat sequence. In silico analysis suggests many transcription factors (notably MyoD) could potentially bind within the Smtnl1 proximal promoter sequence.

Conclusion

Smtnl1 transcript was identified in all smooth muscle tissues examined to date, albeit at much lower levels than found in skeletal muscle. It is unlikely that multiple SMTNL1 isoforms exist since a single Smtnl1 transcription start site was identified in both skeletal and intestinal smooth muscle. Promoter studies suggest restrictive control of Smtnl1 expression in non-muscle cells.

Post-ATHENA and beyond

Dronedarone, an amiodarone analog, was developed to be a safer alternative to amiodarone. Dronedarone is useful in suppressing atrial fibrillation/flutter and controlling the ventricular response. Dronedarone reduced cardiovascular hospitalization in the ATHENA trial (A placebo-controlled, double-blind, parallel arm Trial to assess the efficacy of dronedarone 400 mg bid for the prevention of cardiovascular Hospitalization or death from any cause in patiENts with Atrial fibrillation/atrial flutter). This paper reviews the results of ATHENA, including subsequent sub-analyses of the trial. These results raise the hypothesis that many of the benefits noted from this trial may be secondary to more than the antiarrhythmic properties of dronedarone. Future studies will clarify the mechanisms of this beneficial effect.

Molecular regulation of contractile smooth muscle cell phenotype: implications for vascular tissue engineering

The molecular regulation of smooth muscle cell (SMC) behavior is reviewed, with particular emphasis on stimuli that promote the contractile phenotype. SMCs can shift reversibly along a continuum from a quiescent, contractile phenotype to a synthetic phenotype, which is characterized by proliferation and extracellular matrix (ECM) synthesis. This phenotypic plasticity can be harnessed for tissue engineering. Cultured synthetic SMCs have been used to engineer smooth muscle tissues with organized ECM and cell populations. However, returning SMCs to a contractile phenotype remains a key challenge. This review will integrate recent work on how soluble signaling factors, ECM, mechanical stimulation, and other cells contribute to the regulation of contractile SMC phenotype. The signal transduction pathways and mechanisms of gene expression induced by these stimuli are beginning to be elucidated and provide useful information for the quantitative analysis of SMC phenotype in engineered tissues. Progress in the development of tissue-engineered scaffold systems that implement biochemical, mechanical, or novel polymer fabrication approaches to promote contractile phenotype will also be reviewed. The application of an improved molecular understanding of SMC biology will facilitate the design of more potent cell-instructive scaffold systems to regulate SMC behavior.

Tropomyosin-binding properties of the CHASM protein are dependent upon its calponin homology domain

The calponin homology-associated smooth muscle protein (CHASM) can modulate muscle contractility, and its biological action may involve an interaction with the contractile filament. In this study, we demonstrate an interaction between CHASM and tropomyosin. Deletion constructs of CHASM were generated, and pull-down assays revealed a minimal deletion construct that could bind tropomyosin. Removal of the calponin homology (CH) domain or expression of the CH domain alone did not enable binding. The interaction was characterized by microcalorimetry with a dissociation constant of 2.0x10(-6) M. Confocal fluorescence microscopy also showed green fluorescent protein (GFP)-CHASM localization to filamentous structures within smooth muscle cells, and this targeting was dependent upon the CH domain.

Development of the endothelium: an emphasis on heterogeneity

The endothelium is composed of specialized epithelial cells that line the vasculature, the lymph vessels, and the heart. These endothelial cells are characterized by their stratification and are connected via intercellular junctions that confer specific permeability. Although all endothelium acts as a barrier, considerable heterogeneity exists among different organs and even within vessels. During development, the endothelial cells are specified before they migrate to their final destination, and then they commit to an arterial or venous fate. From the venous endothelial cell population, a subset of cells is further specified as lymphatic endothelium. The endothelium can be highly permeable, as in the lymph vessels, or impenetrable, as in the blood-brain barrier. These differences arise during development and are orchestrated through a series of signaling pathways. This review details how endothelial cells arise and are directed to their specific fate, specifically targeting what differentiates endothelial populations.

MRI-determined carotid artery flow velocities and wall shear stress in a mouse model of vulnerable and stable atherosclerotic plaque

OBJECTIVES

We report here on the pre-clinical MRI characterization of an apoE-/- mouse model of stable and vulnerable carotid artery atherosclerotic plaques, which were induced by a tapered restriction (cast) around the artery. Specific focus was on the quantification of the wall shear stress, which is considered a key player in the development of the plaque phenotype.

MATERIALS AND METHODS

In vivo MRI was performed at 9.4 T. The protocol consisted of time-of-flight angiography, high-resolution T1- and T2-weighted black-blood imaging and phase-contrast flow velocity imaging as function of time in the cardiac cycle. Wall shear stress was determined by fitting the flow profile to a quadratic polynomial.

RESULTS

Time-of-flight angiography confirmed preservation of blood flow through the carotid arteries in all cases. T1- and T2-weighted MRI resulted in high-resolution images in which the position of the cast, luminal narrowing introduced by cast and plaque, as well as the arterial wall could be well identified. Laminar flow with low wall shear stress (11.2+/- 5.2 Pa) was measured upstream to the cast at the position of the vulnerable plaque. Downstream to the cast at the position of the stable plaque, the apparent velocities were low, which is consistent with vortices and an oscillatory nature of the flow.

CONCLUSIONS

Flow velocities and wall shear stress were successfully measured in this mouse model of stable and unstable plaque. The presented tools can be used to provide valuable insights in the pathogenesis of atherosclerosis.

In vivo high-resolution structural imaging of large arteries in small rodents using two-photon laser scanning microscopy

In vivo (molecular) imaging of the vessel wall of large arteries at subcellular resolution is crucial for unraveling vascular pathophysiology. We previously showed the applicability of two-photon laser scanning microscopy (TPLSM) in mounted arteries ex vivo. However, in vivo TPLSM has thus far suffered from in-frame and between-frame motion artifacts due to arterial movement with cardiac and respiratory activity. Now, motion artifacts are suppressed by accelerated image acquisition triggered on cardiac and respiratory activity. In vivo TPLSM is performed on rat renal and mouse carotid arteries, both surgically exposed and labeled fluorescently (cell nuclei, elastin, and collagen). The use of short acquisition times consistently limit in-frame motion artifacts. Additionally, triggered imaging reduces between-frame artifacts. Indeed, structures in the vessel wall (cell nuclei, elastic laminae) can be imaged at subcellular resolution. In mechanically damaged carotid arteries, even the subendothelial collagen sheet (approximately 1 microm) is visualized using collagen-targeted quantum dots. We demonstrate stable in vivo imaging of large arteries at subcellular resolution using TPLSM triggered on cardiac and respiratory cycles. This creates great opportunities for studying (diseased) arteries in vivo or immediate validation of in vivo molecular imaging techniques such as magnetic resonance imaging (MRI), ultrasound, and positron emission tomography (PET).