Expression and promoter analysis of a highly restricted integrin alpha gene in vascular smooth muscle

Emerging role of YAP/TAZ in vascular mechanotransduction and disease

Cells have an incredible ability to physically interact with neighboring cells and their environment. They can detect and respond to mechanical forces by converting mechanical stimuli into biochemical signals in a process known as mechanotransduction. This is a key process for the adaption of vascular smooth muscle and endothelial cells to altered flow and pressure conditions. Mechanical stimuli, referring to a physical force exerted on cells, are primarily sensed by transmembrane proteins and the actin cytoskeleton, which initiate a cascade of intracellular events, including the activation of signaling pathways, ion channels, and transcriptional regulators. Recent work has highlighted an important role of the transcriptional coactivators YAP/TAZ for mechanotransduction in vascular cells. Interestingly, the activity of YAP/TAZ decreases with age, providing a potential mechanism for the detrimental effects of aging in the vascular wall. In this review, we summarize the current knowledge on the functional role of YAP and TAZ in vascular endothelial and smooth muscle cells for mechanotransduction in homeostasis and disease. In particular, the review is focused on in vivo observations from conditional knockout (KO) models of YAP/TAZ and the potential implications these studies may have for our understanding of vascular disease development.

Digital spatial profiling of segmental outflow regions in trabecular meshwork reveals a role for ADAM15

In this study we used a spatial transcriptomics approach to identify genes specifically associated with either high or low outflow regions in the trabecular meshwork (TM) that could potentially affect aqueous humor outflow in vivo. High and low outflow regions were identified and isolated from organ cultured human anterior segments perfused with fluorescently-labeled 200 nm FluoSpheres. The NanoString GeoMx Digital Spatial Profiler (DSP) platform was then used to identified genes in the paraffin embedded tissue sections from within those regions. These transcriptome analyses revealed that 16 genes were statistically upregulated in high outflow regions and 57 genes were statistically downregulated in high outflow regions when compared to low outflow regions. Gene ontology enrichment analysis indicated that the top three biological categories of these differentially expressed genes were ECM/cell adhesion, signal transduction, and transcription. The ECM/cell adhesion genes that showed the largest differential expression (Log2FC ±1.5) were ADAM15, BGN, LDB3, and CRKL. ADAM15, which is a metalloproteinase that can bind integrins, was upregulated in high outflow regions, while the proteoglycan BGN and two genes associated with integrin signaling (LDB3, and CRKL) were downregulated. Immunolabeling studies supported the differential expression of ADAM15 and showed that it was specifically upregulated in high outflow regions along the inner wall of Schlemm's canal and in the juxtacanalicular (JCT) region of the TM. In addition to these genes, the studies showed that genes for decorin, a small leucine-rich proteoglycan, and the α8 integrin subunit were enriched in high outflow regions. These studies identify several novel genes that could be involved in segmental outflow, thus demonstrating that digital spatial profiling could be a useful approach for understanding segmental flow through the TM. Furthermore, this study suggests that changes in the expression of genes involved in regulating the activity and/or organization of the ECM and integrins in the TM are likely to be key players in segmental outflow.

Tissue-specific Cre driver mice to study vascular diseases

Vascular diseases, including atherosclerosis and abdominal aneurysms, are the primary cause of mortality and morbidity among the elderly worldwide. The life quality of patients is significantly compromised due to inadequate therapeutic approaches and limited drug targets. To expand our comprehension of vascular diseases, gene knockout (KO) mice, especially conditional knockout (cKO) mice, are widely used for investigating gene function and mechanisms of action. The Cre-loxP system is the most common method for generating cKO mice. Numerous Cre driver mice have been established to study the main cell types that compose blood vessels, including endothelial cells, smooth muscle cells, and fibroblasts. Here, we first discuss the characteristics of each layer of the arterial wall. Next, we provide an overview of the representative Cre driver mice utilized for each of the major cell types in the vessel wall and their most recent applications in vascular biology. We then go over Cre toxicity and discuss the practical methods for minimizing Cre interference in experimental outcomes. Finally, we look into the future of tissue-specific Cre drivers by introducing the revolutionary single-cell RNA sequencing and dual recombinase system.

Phenotypic Switching of Vascular Smooth Muscle Cells in Atherosclerosis

The medial layer of the arterial wall is composed mainly of vascular smooth muscle cells (VSMCs). Under physiological conditions, VSMCs assume a contractile phenotype, and their primary function is to regulate vascular tone. In contrast with terminally differentiated cells, VSMCs possess phenotypic plasticity, capable of transitioning into other cellular phenotypes in response to changes in the vascular environment. Recent research has shown that VSMC phenotypic switching participates in the pathogenesis of atherosclerosis, where the various types of dedifferentiated VSMCs accumulate in the atherosclerotic lesion and participate in the associated vascular remodeling by secreting extracellular matrix proteins and proteases. This review article discusses the 9 VSMC phenotypes that have been reported in atherosclerotic lesions and classifies them into differentiated VSMCs, intermediately dedifferentiated VSMCs, and dedifferentiated VSMCs. It also provides an overview of several methodologies that have been developed for studying VSMC phenotypic switching and discusses their respective advantages and limitations.

Vascular smooth muscle-specific YAP/TAZ deletion triggers aneurysm development in mouse aorta

Inadequate adaption to mechanical forces, including blood pressure, contributes to development of arterial aneurysms. Recent studies have pointed to a mechanoprotective role of YAP and TAZ in vascular smooth muscle cells (SMCs). Here, we identified reduced expression of YAP1 in human aortic aneurysms. Vascular SMC-specific knockouts (KOs) of YAP/TAZ were thus generated using the integrin α8-Cre (Itga8-Cre) mouse model (i8-YT-KO). i8-YT-KO mice spontaneously developed aneurysms in the abdominal aorta within 2 weeks of KO induction and in smaller arteries at later times. The vascular specificity of Itga8-Cre circumvented gastrointestinal effects. Aortic aneurysms were characterized by elastin disarray, SMC apoptosis, and accumulation of proteoglycans and immune cell populations. RNA sequencing, proteomics, and myography demonstrated decreased contractile differentiation of SMCs and impaired vascular contractility. This associated with partial loss of myocardin expression, reduced blood pressure, and edema. Mediators in the inflammatory cGAS/STING pathway were increased. A sizeable increase in SOX9, along with several direct target genes, including aggrecan (Acan), contributed to proteoglycan accumulation. This was the earliest detectable change, occurring 3 days after KO induction and before the proinflammatory transition. In conclusion, Itga8-Cre deletion of YAP and TAZ represents a rapid and spontaneous aneurysm model that recapitulates features of human abdominal aortic aneurysms.

Generation and Comparative Analysis of an Itga8-CreER T2 Mouse with Preferential Activity in Vascular Smooth Muscle Cells

All current smooth muscle cell (SMC) Cre mice similarly recombine floxed alleles in vascular and visceral SMCs. Here, we present an Itga8-CreER T2 knock-in mouse and compare its activity with a Myh11-CreER T2 mouse. Both Cre drivers demonstrate equivalent recombination in vascular SMCs. However, Myh11-CreER T2 mice, but not Itga8-CreER T2 mice, display high activity in visceral SMC-containing tissues such as intestine, show early tamoxifen-independent activity, and produce high levels of CreERT2 protein. Whereas Myh11-CreER T2 -mediated knockout of serum response factor (Srf) causes a lethal intestinal phenotype precluding analysis of the vasculature, loss of Srf with Itga8-CreER T2 (Srf Itga8 ) yields viable mice with no evidence of intestinal pathology. Male and female Srf Itga8 mice exhibit vascular contractile incompetence, and angiotensin II causes elevated blood pressure in wild type, but not Srf Itga8 , male mice. These findings establish the Itga8-CreER T2 mouse as an alternative to existing SMC Cre mice for unfettered phenotyping of vascular SMCs following selective gene loss.

The Transcriptional Landscapes and Key Genes in Brain Arteriovenous Malformation Progression in a Venous Hypertension Rat Model Revealed by RNA Sequencing

Background

Brain arteriovenous malformations (bAVM) are abnormal vascular lesions characterized by direct connections between arteries and veins without an intervening capillary bed. The primary goal for brain AVM treatment is to prevent rupture and hemorrhage; however, the underlying molecular mechanisms are still unknown.

Methods

We constructed venous hypertension (VH) rat model with end-to-end anastomosis of the proximal left common carotid artery and the left distal external jugular vein. Thirty-eight adult rats were randomly assigned to four groups: the 0-week (n=5), the 1-week VH group (n=12), the 3-week VH group (n=9), and the 6-week VH group (n=12). We measured the hemodynamics and diameter of the arterialized veins. An RNA sequencing of arterialized veins was conducted, followed by comprehensive bioinformatics analysis to identify key genes and biological pathways involved in VH progression. The candidate genes from RNA-Seq were validated by RT-qPCR and immunostaining in human tissues.

Results

We observed high-flow and low resistance characteristics in VH models. A total of 317 upregulated and 258 downregulated common genes were consistently differentially expressed during VH progression. Thirteen co-expression modules were obtained by WGCNA analysis, and 4 key modules were identified. Thirteen genes: Adamts8, Adamtsl3, Spon2, Adamtsl2, Chad, Itga7, Comp, Itga8, Bmp6, Fst, Smad6, Smad7, Grem1, and Nog with differential expressions were identified using the density of maximum neighborhood component (DMNC) algorithm in Cytohubba. The expression of five potential genes (Adamts8, Adamtsl3, Spon2, Adamtsl2, Itga8) were increased in RT-qPCR, while in human bAVM tissue, the protein levels of Adamtsl2 and Itga8 were significant elevated and Spon2 and Adamtsl3 were decreased.

Conclusion

The identified gene networks of Adamtsl3, Spon2, Adamtsl2, and Itga8 provided key genes for further intervention.

Identification of crucial genes involved in pathogenesis of regional weakening of the aortic wall

Background

The diameter of the abdominal aortic aneurysm (AAA) is the most commonly used parameter for the prediction of occurrence of AAA rupture. However, the most vulnerable region of the aortic wall may be different from the most dilated region of AAA under pressure. The present study is the first to use weighted gene coexpression network analysis (WGCNA) to detect the coexpressed genes that result in regional weakening of the aortic wall.

Methods

The GSE165470 raw microarray dataset was used in the present study. Differentially expressed genes (DEGs) were filtered using the “limma” R package. DEGs were assessed by Gene Ontology biological process (GO-BP) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. WGCNA was used to construct the coexpression networks in the samples with regional weakening of the AAA wall and in the control group to detect the gene modules. The hub genes were defined in the significant functional modules, and a hub differentially expressed gene (hDEG) coexpression network was constructed with the highest confidence based on protein–protein interactions (PPIs). Molecular compound detection (MCODE) was used to identify crucial genes in the hDEG coexpression network. Crucial genes in the hDEG coexpression network were validated using the GSE7084 and GSE57691 microarray gene expression datasets.

Result

A total of 350 DEGs were identified, including 62 upregulated and 288 downregulated DEGs. The pathways were involved in immune responses, vascular smooth muscle contraction and cell–matrix adhesion of DEGs in the samples with regional weakening in AAA. Antiquewhite3 was the most significant module and was used to identify downregulated hDEGs based on the result of the most significant modules negatively related to the trait of weakened aneurysm walls. Seven crucial genes were identified and validated: ACTG2, CALD1, LMOD1, MYH11, MYL9, MYLK, and TPM2. These crucial genes were associated with the mechanisms of AAA progression.

Conclusion

We identified crucial genes that may play a significant role in weakening of the AAA wall and may be potential targets for medical therapies and diagnostic biomarkers. Further studies are required to more comprehensively elucidate the functions of crucial genes in the pathogenesis of regional weakening in AAA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41065-021-00200-1.

miR-145 transgenic mice develop cardiopulmonary complications leading to postnatal death

BACKGROUND

Both downregulation and elevation of microRNA miR-145 has been linked to an array of cardiopulmonary phenotypes, and a host of studies suggest that it is an important contributor in governing the differentiation of cardiac and vascular smooth muscle cell types.

METHODS AND RESULTS

To better understand the role of elevated miR-145 in utero within the cardiopulmonary system, we utilized a transgene to overexpress miR-145 embryonically in mice and examined the consequences of this lineage-restricted enhanced expression. Overexpression of miR-145 has detrimental effects that manifest after birth as overexpressor mice are unable to survive beyond postnatal day 18. The miR-145 expressing mice exhibit respiratory distress and fail to thrive. Gross analysis revealed an enlarged right ventricle, and pulmonary dysplasia with vascular hypertrophy. Single cell sequencing of RNA derived from lungs of control and miR-145 transgenic mice demonstrated that miR-145 overexpression had global effects on the lung with an increase in immune cells and evidence of leukocyte extravasation associated with vascular inflammation.

CONCLUSIONS

These data provide novel findings that demonstrate a pathological role for miR-145 in the cardiopulmonary system that extends beyond its normal function in governing smooth muscle differentiation.

The Aging Vasculature: Glucose Tolerance, Hypoglycemia and the Role of the Serum Response Factor

The fastest growing demographic in the U.S. at the present time is those aged 65 years and older. Accompanying advancing age are a myriad of physiological changes in which reserve capacity is diminished and homeostatic control attenuates. One facet of homeostatic control lost with advancing age is glucose tolerance. Nowhere is this more accentuated than in the high proportion of older Americans who are diabetic. Coupled with advancing age, diabetes predisposes affected subjects to the onset and progression of cardiovascular disease (CVD). In the treatment of type 2 diabetes, hypoglycemic episodes are a frequent clinical manifestation, which often result in more severe pathological outcomes compared to those observed in cases of insulin resistance, including premature appearance of biomarkers of senescence. Unfortunately, molecular mechanisms of hypoglycemia remain unclear and the subject of much debate. In this review, the molecular basis of the aging vasculature (endothelium) and how glycemic flux drives the appearance of cardiovascular lesions and injury are discussed. Further, we review the potential role of the serum response factor (SRF) in driving glycemic flux-related cellular signaling through its association with various proteins.

Single-cell analysis uncovers fibroblast heterogeneity and criteria for fibroblast and mural cell identification and discrimination

Many important cell types in adult vertebrates have a mesenchymal origin, including fibroblasts and vascular mural cells. Although their biological importance is undisputed, the level of mesenchymal cell heterogeneity within and between organs, while appreciated, has not been analyzed in detail. Here, we compare single-cell transcriptional profiles of fibroblasts and vascular mural cells across four murine muscular organs: heart, skeletal muscle, intestine and bladder. We reveal gene expression signatures that demarcate fibroblasts from mural cells and provide molecular signatures for cell subtype identification. We observe striking inter- and intra-organ heterogeneity amongst the fibroblasts, primarily reflecting differences in the expression of extracellular matrix components. Fibroblast subtypes localize to discrete anatomical positions offering novel predictions about physiological function(s) and regulatory signaling circuits. Our data shed new light on the diversity of poorly defined classes of cells and provide a foundation for improved understanding of their roles in physiological and pathological processes.

To define and distinguish fibroblasts from vascular mural cells have remained challenging. Here, using single-cell RNA sequencing and tissue imaging, the authors provide a molecular basis for cell type classification and reveal inter- and intra-organ diversity of these cell types.

Identification of the intermediate filament protein synemin/SYNM as a target of myocardin family coactivators

Myocardin (MYOCD) is a critical regulator of smooth muscle cell (SMC) differentiation, but its transcriptional targets remain to be exhaustively characterized, especially at the protein level. Here we leveraged human RNA and protein expression data to identify novel potential MYOCD targets. Using correlation analyses we found several targets that we could confirm at the protein level, including SORBS1, SLMAP, SYNM, and MCAM. We focused on SYNM, which encodes the intermediate filament protein synemin. SYNM rivalled smooth muscle myosin (MYH11) for SMC specificity and was controlled at the mRNA and protein levels by all myocardin-related transcription factors (MRTFs: MYOCD, MRTF-A/MKL1, and MRTF-B/MKL2). MRTF activity is regulated by the ratio of filamentous to globular actin, and SYNM was accordingly reduced by interventions that depolymerize actin, such as latrunculin treatment and overexpression of constitutively active cofilin. Many MRTF target genes depend on serum response factor (SRF), but SYNM lacked SRF-binding motifs in its proximal promoter, which was not directly regulated by MYOCD. Furthermore, SYNM resisted SRF silencing, yet the time course of induction closely paralleled that of the SRF-dependent target gene ACTA2. SYNM was repressed by the ternary complex factor (TCF) FLI1 and was increased in mouse embryonic fibroblasts lacking three classical TCFs (ELK1, ELK3, and ELK4). Imaging showed colocalization of SYNM with the intermediate filament proteins desmin and vimentin, and MRTF-A/MKL1 increased SYNM-containing intermediate filaments in SMCs. These studies identify SYNM as a novel SRF-independent target of myocardin that is abundantly expressed in all SMCs.

Atheroprotective roles of smooth muscle cell phenotypic modulation and the TCF21 disease gene as revealed by single-cell analysis

In response to various stimuli, vascular smooth muscle cells (SMCs) can de-differentiate, proliferate and migrate in a process known as phenotypic modulation. However, the phenotype of modulated SMCs in vivo during atherosclerosis and the influence of this process on coronary artery disease (CAD) risk have not been clearly established. Using single cell RNA sequencing, we comprehensively characterized the transcriptomic phenotype of modulated SMCs in vivo in atherosclerotic lesions of both mouse and human arteries and found that these cells transform into unique fibroblast-like cells, termed “fibromyocytes”, rather than into a classical macrophage phenotype. SMC-specific knockout of TCF21, a causal CAD gene, markedly inhibited SMC phenotypic modulation in mice, leading to the presence of fewer fibromyocytes within lesions as well as within the protective fibrous cap of the lesions. Moreover, TCF21 expression was strongly associated with SMC phenotypic modulation in diseased human coronary arteries, and higher levels of TCF21 expression were associated with decreased CAD risk human CAD-relevant tissues. These results establish a protective role for both TCF21 and SMC phenotypic modulation in this disease.

The mechanism of myocardial hypertrophy regulated by the interaction between mhrt and myocardin

As a strong transactivator of promoters containing CarG boxes, myocardin was critical for the cardiac muscle program and necessary for normal cardiogenesis. So it probably represents a viable therapeutic biomarker in the setting of cardiac hypertrophy and failure. In recent years, the studies of regulation of cardiac hypertrophy via myocardin are so common, and the molecular mechanism is becoming more and more clear. Here, we have revealed a kind of interaction between mhrt and myocardin shown as a feedback regulatory mechanism in the regulation of cardiac hypertrophy. That is, the lncRNA mhrt can affect the acetylation of myocardin by HDAC5 to inhibit cardiac hypertrophy induced by myocardin. Moreover, myocardin also can directly activate the mhrt transcription through binding to the CarG box. Thus, mhrt and myocardin form a regulation loop in the process of cardiac hypertrophy. This finding may play a positive role in revealing the complete mechanisms of cardiac hypertrophy.

Selective expression of TSPAN2 in vascular smooth muscle is independently regulated by TGF-β1/SMAD and myocardin/serum response factor

Tetraspanins (TSPANs) comprise a large family of 4-transmembrane domain proteins. The importance of TSPANs in vascular smooth muscle cells (VSMCs) is unexplored. Given that TGF-β1 and myocardin (MYOCD) are potent activators for VSMC differentiation, we screened for TGF-β1 and MYOCD/serum response factor (SRF)-regulated TSPANs in VSMC by using RNA-seq analyses and RNA-arrays. TSPAN2 was found to be the only TSPAN family gene induced by TGF-β1 and MYOCD, and reduced by SRF deficiency in VSMCs. We also found that TSPAN2 is highly expressed in smooth muscle-enriched tissues and down-regulated in in vitro models of VSMC phenotypic modulation. TSPAN2 expression is attenuated in mouse carotid arteries after ligation injury and in failed human arteriovenous fistula samples after occlusion by dedifferentiated neointimal VSMC. In vitro functional studies showed that TSPAN2 suppresses VSMC proliferation and migration. Luciferase reporter and chromatin immunoprecipitation assays demonstrated that TSPAN2 is regulated by 2 parallel pathways, MYOCD/SRF and TGF-β1/SMAD, via distinct binding elements within the proximal promoter. Thus, we identified the first VSMC-enriched and MYOCD/SRF and TGF-β1/SMAD-dependent TSPAN family member, whose expression is intimately associated with VSMC differentiation and negatively correlated with vascular disease. Our results suggest that TSPAN2 may play important roles in vascular disease.-Zhao, J., Wu, W., Zhang, W., Lu, Y. W., Tou, E., Ye, J., Gao, P., Jourd'heuil, D., Singer, H. A., Wu, M., Long, X. Selective expression of TSPAN2 in vascular smooth muscle is independently regulated by TGF-β1/SMAD and myocardin/serum response factor.

Inflammation and vascular smooth muscle cell dedifferentiation following carotid artery ligation

Following vascular injury medial smooth muscle cells dedifferentiate and migrate through the internal elastic lamina where they form a neointima. The goal of the current study was to identify changes in gene expression that occur before the development of neointima and are associated with the early response to injury. Vascular injury was induced in C57BL/6 mice and in Myh11-creER(T2) mTmG reporter mice by complete ligation of the left carotid artery. Reporter mice were used to visualize cellular changes in the injured vessels. Total RNA was isolated from control carotid arteries or from carotid arteries 3 days following ligation of C57BL/6 mice and analyzed by Affymetrix microarray and quantitative RT-PCR. This analysis revealed decreased expression of mRNAs encoding smooth muscle-specific contractile proteins that was accompanied by a marked increase in a host of mRNAs encoding inflammatory cytokines following injury. There was also marked decrease in molecules associated with BMP, Wnt, and Hedgehog signaling and an increase in those associated with B cell, T cell, and macrophage signaling. Expression of a number of noncoding RNAs were also altered following injury with microRNAs 143/145 being dramatically downregulated and microRNAs 1949 and 142 upregulated. Several long noncoding RNAs showed altered expression that mirrored the expression of their nearest coding genes. These data demonstrate that following carotid artery ligation an inflammatory cascade is initiated that is associated with the downregulation of coding and noncoding RNAs that are normally required to maintain smooth muscle cells in a differentiated state.

Cadherin-11 is a novel regulator of extracellular matrix synthesis and tissue mechanics

We discovered that Cadherin-11 (CDH11) regulates collagen and elastin synthesis, both affecting the mechanical properties and contractile function of animal tissues. Using a Cdh11-null mouse model, we observed a significant reduction in the mechanical properties [Youngs' modulus and ultimate tensile strength (UTS)] of Cdh11(-/-) as compared to wild-type (WT) mouse tissues, such as the aorta, bladder and skin. The deterioration of mechanical properties (Youngs' modulus and UTS) was accompanied by reduced collagen and elastin content in Cdh11(-/-) mouse tissues as well as in cells in culture. Similarly, knocking down CDH11 abolished collagen and elastin synthesis in human cells, and consequently reduced their ability to generate force. Conversely, engagement of CDH11 through homophilic interactions, led to swift activation of the TGF-β and ROCK pathways as evidenced by phosphorylation of downstream effectors. Subsequently, activation of the key transcription factors, MRTF-A (also known as MKL1) and MYOCD led to significant upregulation of collagen and elastin genes. Taken together, our results demonstrate a novel role of adherens junctions in regulating extracellular matrix (ECM) synthesis with implications for many important biological processes, including maintenance of tissue integrity, wound healing and tissue regeneration.

α8β1 integrin regulates nutrient absorption through an Mfge8-PTEN dependent mechanism

Coordinated gastrointestinal smooth muscle contraction is critical for proper nutrient absorption and is altered in a number of medical disorders. In this work, we demonstrate a critical role for the RGD-binding integrin α8β1 in promoting nutrient absorption through regulation of gastrointestinal motility. Smooth muscle-specific deletion and antibody blockade of α8 in mice result in enhanced gastric antral smooth muscle contraction, more rapid gastric emptying, and more rapid transit of food through the small intestine leading to malabsorption of dietary fats and carbohydrates as well as protection from weight gain in a diet-induced model of obesity. Mechanistically, ligation of α8β1 by the milk protein Mfge8 reduces antral smooth muscle contractile force by preventing RhoA activation through a PTEN-dependent mechanism. Collectively, our results identify a role for α8β1 in regulating gastrointestinal motility and identify α8 as a potential target for disorders characterized by hypo- or hyper-motility.

DOI:http://dx.doi.org/10.7554/eLife.13063.001

Animals absorb nutrients from the food they eat in a complicated process that involves multiple steps. In the mouth, teeth break down the food into smaller chunks. Then the food passes through the stomach and small intestine, where enzymes break it down into individual molecules that are small enough to be absorbed by cells that line the small intestine. These cells then package the molecules and release them into the bloodstream so that they can be distributed to the rest of the body.

Muscles in the wall of the small intestine control how quickly food travels through this part of the gut. If food moves too quickly, the cells that line the intestine have less time to absorb the food molecules and may fail to absorb enough nutrients. If the food moves too slowly, an individual may experience nausea or vomiting, or the contents of their stomach may spill into their lungs.

In 2014, researchers reported that a protein in breast milk called Mfge8 helps to boost the number of fat molecules absorbed from food. Now, Khalifeh-Soltani et al. – including some of the same researchers involved in the earlier work – show that Mfge8 also slows the rate at which food travels through the small intestine in mice. Mfge8 binds to another protein called integrin α8β1 to control how often the intestine muscles contract. Genetically engineered mice that lacked integrin α8β1 developed diarrhea and food passed through their intestines more quickly than in normal mice. Furthermore, these mice did not gain as much weight as normal mice when they were fed a high-fat diet.

Khalifeh-Soltani et al.’s findings show that Mfge8 has a dual role in controlling the absorption of food molecules in the small intestine. The next challenge is to find out whether drugs that alter the activity of integrin α8β1 could be used to help treat patients with diseases in which food moves too quickly, or too slowly, through the gut.

DOI:http://dx.doi.org/10.7554/eLife.13063.002

Ca2+/calmodulin-dependent protein kinase II-γ (CaMKIIγ) negatively regulates vascular smooth muscle cell proliferation and vascular remodeling

Vascular smooth muscle (VSM) expresses calcium/calmodulin-dependent protein kinase II (CaMKII)-δ and -γ isoforms. CaMKIIδ promotes VSM proliferation and vascular remodeling. We tested CaMKIIγ function in vascular remodeling after injury. CaMKIIγ protein decreased 90% 14 d after balloon injury in rat carotid artery. Intraluminal transduction of adenovirus encoding CaMKIIγC rescued expression to 35% of uninjured controls, inhibited neointima formation (>70%), inhibited VSM proliferation (>60%), and increased expression of the cell-cycle inhibitor p21 (>2-fold). Comparable doses of CaMKIIδ2 adenovirus had no effect. Similar dynamics in CaMKIIγ mRNA and protein expression were observed in ligated mouse carotid arteries, correlating closely with expression of VSM differentiation markers. Targeted deletion of CaMKIIγ in smooth muscle resulted in a 20-fold increase in neointimal area, with a 3-fold increase in the cell proliferation index, no change in apoptosis, and a 60% decrease in p21 expression. In cultured VSM, CaMKIIγ overexpression induced p53 mRNA (1.7 fold) and protein (1.8-fold) expression; induced the p53 target gene p21 (3-fold); decreased VSM cell proliferation (>50%); and had no effect on expression of apoptosis markers. We conclude that regulated CaMKII isoform composition is an important determinant of the injury-induced vasculoproliferative response and that CaMKIIγ and -δ isoforms have nonequivalent, opposing functions.

Myocardin Family Members Drive Formation of Caveolae

Caveolae are membrane organelles that play roles in glucose and lipid metabolism and in vascular function. Formation of caveolae requires caveolins and cavins. The make-up of caveolae and their density is considered to reflect cell-specific transcriptional control mechanisms for caveolins and cavins, but knowledge regarding regulation of caveolae genes is incomplete. Myocardin (MYOCD) and its relative MRTF-A (MKL1) are transcriptional coactivators that control genes which promote smooth muscle differentiation. MRTF-A communicates changes in actin polymerization to nuclear gene transcription. Here we tested if myocardin family proteins control biogenesis of caveolae via activation of caveolin and cavin transcription. Using human coronary artery smooth muscle cells we found that jasplakinolide and latrunculin B (LatB), substances that promote and inhibit actin polymerization, increased and decreased protein levels of caveolins and cavins, respectively. The effect of LatB was associated with reduced mRNA levels for these genes and this was replicated by the MRTF inhibitor CCG-1423 which was non-additive with LatB. Overexpression of myocardin and MRTF-A caused 5-10-fold induction of caveolins whereas cavin-1 and cavin-2 were induced 2-3-fold. PACSIN2 also increased, establishing positive regulation of caveolae genes from three families. Full regulation of CAV1 was retained in its proximal promoter. Knock down of the serum response factor (SRF), which mediates many of the effects of myocardin, decreased cavin-1 but increased caveolin-1 and -2 mRNAs. Viral transduction of myocardin increased the density of caveolae 5-fold in vitro. A decrease of CAV1 was observed concomitant with a decrease of the smooth muscle marker calponin in aortic aneurysms from mice (C57Bl/6) infused with angiotensin II. Human expression data disclosed correlations of MYOCD with CAV1 in a majority of human tissues and in the heart, correlation with MKL2 (MRTF-B) was observed. The myocardin family of transcriptional coactivators therefore drives formation of caveolae and this effect is largely independent of SRF.

Regulation of Smooth Muscle Dystrophin and Synaptopodin 2 Expression by Actin Polymerization and Vascular Injury

Objective—

Actin dynamics in vascular smooth muscle is known to regulate contractile differentiation and may play a role in the pathogenesis of vascular disease. However, the list of genes regulated by actin polymerization in smooth muscle remains incomprehensive. Thus, the objective of this study was to identify actin-regulated genes in smooth muscle and to demonstrate the role of these genes in the regulation of vascular smooth muscle phenotype.

Approach and Results—

Mouse aortic smooth muscle cells were treated with an actin-stabilizing agent, jasplakinolide, and analyzed by microarrays. Several transcripts were upregulated including both known and previously unknown actin-regulated genes. Dystrophin and synaptopodin 2 were selected for further analysis in models of phenotypic modulation and vascular disease. These genes were highly expressed in differentiated versus synthetic smooth muscle and their expression was promoted by the transcription factors myocardin and myocardin-related transcription factor A. Furthermore, the expression of both synaptopodin 2 and dystrophin was significantly reduced in balloon-injured human arteries. Finally, using a dystrophin mutant mdx mouse and synaptopodin 2 knockdown, we demonstrate that these genes are involved in the regulation of smooth muscle differentiation and function.

Conclusions—

This study demonstrates novel genes that are promoted by actin polymerization, that regulate smooth muscle function, and that are deregulated in models of vascular disease. Thus, targeting actin polymerization or the genes controlled in this manner can lead to novel therapeutic options against vascular pathologies that involve phenotypic modulation of smooth muscle cells.

The short and long of noncoding sequences in the control of vascular cell phenotypes

The two principal cell types of importance for normal vessel wall physiology are smooth muscle cells and endothelial cells. Much progress has been made over the past 20 years in the discovery and function of transcription factors that coordinate proper differentiation of these cells and the maintenance of vascular homeostasis. More recently, the converging fields of bioinformatics, genomics, and next generation sequencing have accelerated discoveries in a number of classes of noncoding sequences, including transcription factor binding sites (TFBS), microRNA genes, and long noncoding RNA genes, each of which mediates vascular cell differentiation through a variety of mechanisms. Alterations in the nucleotide sequence of key TFBS or deviations in transcription of noncoding RNA genes likely have adverse effects on normal vascular cell phenotype and function. Here, the subject of noncoding sequences that influence smooth muscle cell or endothelial cell phenotype will be summarized as will future directions to further advance our understanding of the increasingly complex molecular circuitry governing normal vascular cell differentiation and how such information might be harnessed to combat vascular diseases.

Myocardin in biology and disease

Myocardin (MYOCD) is a potent transcriptional coactivator that functions primarily in cardiac muscle and smooth muscle through direct contacts with serum response factor (SRF) over cis elements known as CArG boxes found near a number of genes encoding for contractile, ion channel, cytoskeletal, and calcium handling proteins. Since its discovery more than 10 years ago, new insights have been obtained regarding the diverse isoforms of MYOCD expressed in cells as well as the regulation of MYOCD expression and activity through transcriptional, post-transcriptional, and post-translational processes. Curiously, there are a number of functions associated with MYOCD that appear to be independent of contractile gene expression and the CArG-SRF nucleoprotein complex. Further, perturbations in MYOCD gene expression are associated with an increasing number of diseases including heart failure, cancer, acute vessel disease, and diabetes. This review summarizes the various biological and pathological processes associated with MYOCD and offers perspectives to several challenges and future directions for further study of this formidable transcriptional coactivator.