Abstract 532: Dioxin Modifies The Transcriptomic And Epigenetic Landscape Of Smooth Muscle Cells Leading To Adverse Remodeling Of Atherosclerosis

Background: Environmental exposure to dioxin, an active component of cigarette smoke and air pollution has been linked to increased myocardial infarction. Smooth muscle cells (SMC) in the coronary vasculature play a critical role in atherosclerotic plaque remodeling due to their phenotypic plasticity. We have previously found strong dioxin response element activity in modulated SMC of atherosclerotic lesion. In this study, we aimed to understand the effect of dioxin on vascular SMC and atherosclerosis phenotype.

Methods: Primary human coronary artery SMC (HCASMC) treated in culture with 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) or vehicle control were used to perform RNA-Seq and ATAC-Seq. ChIP-Seq was performed with antibodies against Aryl-hydrocarbon receptor (AHR) and TCF21. Tamoxifen inducible SMC-lineage tracing reporter mice were used to assess the in-vivo effect of TCDD on aortic SMC. After 8 weeks of high fat diet (HFD), followed by 8 weeks of TCDD injection and HFD, the aortic sinus was collected for histology and single-cell sequencing (10X Genomics).

Results: Analysis of the RNA-Seq from TCDD treated HCASMC showed differential enrichment of pathways related to cell migration and vascular development. Further, ATAC-Seq data showed a significant enrichment for pathways regulating vascular development, cell migration, and apoptosis. There was an overall increase in chromatin accessibility suggesting transcriptional activation with TCDD. We observed enrichment for AHR ChIP-Seq peaks in the open chromatin regions along with a significant reciprocal reduction in TCF21 occupancy. The scRNA-Seq of mice treated with TCDD exposure showed differential gene expression of SMC-lineage cells enriching for extracellular matrix (ECM) organization, inflammation, unfolded protein response, and apoptotic process, and histological analysis of the aortic sinus showed increased lesion area with increased presence of SMC-lineage cells and Cd68 + cells compared to control.

Conclusion: Dioxin adversely remodels atherosclerotic plaque affecting pathways of ECM organization, inflammation and unfolded protein response in SMC, partly by modifying chromatin accessibility and occupancy of key transcription factors of phenotypic modulation.

Abstract 222: The Molecular Mechanisms Of Coronary Artery Disease Risk At The Pdgfd Locus

Background: Atherosclerotic cardiovascular diseases, including coronary artery disease (CAD), are the worldwide leading cause of death. Recent genome wide association studies (GWAS) have now identified over 250 genetic loci that are associated with CAD, and efforts in this lab and others are investigating the mechanisms of association at these loci. The CAD GWAS locus at 11q22.3 is of potential interest because it encodes the PDGFD gene, a member of the platelet-derived growth factor family whose expression is up-regulated in atherosclerosis. But whether disease allelic variation regulates PDGFD expression and how this growth factor might influence the risk of CAD has not been studied.

Methods: The causal variant and gene were investigated with colocalization and in vitro transcription studies in cultured human coronary artery smooth muscle cells (SMC). Single-cell transcriptomic profiling (scRNAseq) and histological analyses were conducted in SMC-specific lineage tracing in an in vivo Pdgfd knockout mouse model of atherosclerosis.

Results: The causal variant rs2019090 was linked to PDGFD expression in SMC. In silico analysis of transcription factor binding site prediction and in vitro haplotype-specific chromatin immunoprecipitation combined with qPCR analysis revealed another causal CAD factor forkhead box c1 (FOXC1) preferentially binds to the A-allele of variant rs2019090 and controls the expression level of PDGFD . scRNAseq data identified that loss of Pdgfd resulted in a marked increase in differentiated SMC but a decrease in fibromyocyte (FMC) and chondromyocyte (CMC) transition populations, as well as a significant decrease in plaque macrophages. Differentially expressed gene analysis in SMC lineage cells was highly enriched for CMC genes such as Col2a1 and Ibsp. Lesion histology analysis identified an increase in medial SMC, but a decrease in fibrous cap SMC, with decreased Cd68 and Col2a1 stained area.

Conclusion: PDGFD is a causal CAD gene that increases disease risk by promoting SMC transition primarily to the CMC phenotype, and recruitment of monocyte-macrophage lineage cells to disease lesions. These findings support suppression of PDGFD as a possible therapy for human atherosclerotic disease.

Abstract 220: Smad3 Regulates Smooth Muscle Cell Fate And Governs Adverse Remodeling And Calcification Of Atherosclerotic Plaque

Atherosclerotic plaques consist mostly of smooth muscle cells (SMC), and genes that influence SMC phenotype can modulate coronary artery disease (CAD) risk. Allelic variation at 15q22.33 has been identified by genome-wide association studies to modify the risk of CAD, and is associated with expression of SMAD3 in SMC , however the mechanism by which this gene modifies CAD risk remains poorly understood. SMC-specific deletion of Smad3 in a murine atherosclerosis model resulted in greater plaque burden, more positive remodeling, and increased vascular calcification. Single-cell transcriptomic analyses revealed that loss of Smad3 altered SMC transition cell state toward two fates: a novel SMC phenotype that governs both vascular remodeling and recruitment of inflammatory cells, as well as a chondromyocyte fate. The remodeling population was marked by uniquely high Mmp3 and Cxcl12 expression, and its appearance correlated with higher risk plaque features such as increased positive remodeling and macrophage content. Further, investigation of transcriptional mechanisms by which Smad3 alters SMC cell fate revealed novel roles for Hox and Sox transcription factors whose direct interaction with Smad3 regulate an extensive transcriptional program balancing remodeling and vascular extracellular matrix. These findings have significant implications for atherosclerotic and Mendelian aortic aneurysmal diseases. Together, these data suggest that Smad3 expression in SMC inhibits the emergence of specific SMC phenotypic transition cells that mediate adverse plaque features, including positive remodeling, monocyte recruitment, and vascular calcification.

Abstract 107: A Human Arterial Cell Atlas

Background: Human vascular diseases are the worldwide leading causes of morbidity and mortality. Nearly all human vascular diseases have arterial segment-specific tropisms despite identical exposures to genetic and environmental risk factors. Understanding the cellular and transcriptomic determinants of arterial identities may hold the key to identifying novel pathophysiology and potential therapies.

Methods: To specifically determine arterial site-specific differences independent of inter-individual variation, we have generated a human arterial cellular atlas by simultaneously collecting and analyzing up to 8 arterial sites from multiple healthy transplant donors. We performed single cell transcriptomic analysis on arterial segments to determine the differences in cellular composition and transcriptomic programs. We subsequently integrated human genetic data with cell-type specific transcriptomic differences across vascular beds to identify probable causal cells and causal genes associated with human vascular phenotypes.

Results/Conclusions: Single cell transcriptomic analysis of > 150,000 cells sequenced at > 50,000 reads per cell revealed that the dominant cellular drivers of transcriptomic differences between distinct arterial segments, i.e. determinants of arterial identity, are fibroblasts and smooth muscle cells, not endothelial cells or macrophages. Adult vascular cells from different segments clustered not by anatomical proximity but by embryonic origin. Differentially regulated genes in fibroblast across different vascular beds were particularly enriched for vascular disease associated genetic signals, suggesting a prominent role for these cells in human disease. While the majority of endothelial cells were transcriptionally similar across vascular beds, a rare, previously undescribed, cluster of endothelial cells were identified who expressed segment-specific transcriptomic signatures. Differentially expressed genes in these cells were enriched for vascular disease signals, suggesting a possible role of these rare cells in human disease.

Pancreatic Islet APJ Deletion Reduces Islet Density and Glucose Tolerance in Mice

Protection and replenishment of a functional pancreatic β-cell mass (BCM) are key goals of all diabetes therapies. Apelin, a small regulatory peptide, is the endogenous ligand for the apelin receptor (APJ) receptor. The apelin-APJ signaling system is expressed in rodent and human islet cells. Apelin exposure has been shown to inhibit and to stimulate insulin secretion. Our aim was to assess the influence of a selective APJ deletion in pancreatic islet cells on islet homeostasis and glucose tolerance in mice. Cre-LoxP strategy was utilized to mediate islet APJ deletion. APJ deletion in islet cells (APJ(Δislet)) resulted in a significantly reduced islet size, density and BCM. An ip glucose tolerance test showed significantly impaired glucose clearance in APJ(Δislet) mice. APJ(Δislet) mice were not insulin resistant and in vivo glucose-stimulated insulin secretion was reduced modestly. In vitro glucose-stimulated insulin secretion showed a significantly reduced insulin secretion by islets from APJ(Δislet) mice. Glucose clearance in response to ip glucose tolerance test in obese APJ(Δislet) mice fed a chronic high-fat (HF) diet, but not pregnant APJ(Δislet) mice, was impaired significantly. In addition, the obesity-induced adaptive elevations in mean islet size and fractional islet area were reduced significantly in obese APJ(Δislet) mice when compared with wild-type mice. Together, these findings demonstrate a stimulatory role for the islet cell apelin-APJ signaling axis in regulation of pancreatic islet homeostasis and in metabolic induced β-cell hyperplasia. The results indicate the apelin-APJ system can be exploited for replenishment of BCM.

Supratentorial glioblastoma multiforme metastasizing to the cervical spinal cord

Cases of glioblastoma multiforme (GBM) metastasizing to the leptomeninges or the intramedullary spine are rare and their prognosis are relatively poor. We present a case of supratentorial glioblastoma WHO grade IV which was later diagnosed to have cervical intramedullary metastasis 7 months after the primary surgery.

Abstract 664: The Coronary Heart Disease--Associated Transcription Factor TCF21 Regulates Disease-Related Genes and May Contribute to the Migration of SMC Progenitors to the Fibrous Cap

Introduction: Recent genome-wide association studies have identified a number of genes that contribute to the risk for coronary heart disease, including TCF21, a bHLH transcription factor believed to serve a critical role in the differentiation of epicardial progenitor cells that give rise to coronary smooth muscle.

Methods and Results: Results of immunolocalization and in situ hybridization studies showed that TCF21 is not expressed in medial smooth muscle cells (SMC) of adult human coronary arteries but primarily within the adventitia and within cells of unknown origin in atherosclerotic lesions. LacZ reporter animal studies with ApoE null background showed a shift in Tcf21 expression from adventitial and medial cells to the neointima, notably into the area below and within the forming fibrous cap, suggesting that Tcf21 expressing cells migrate into the forming atherosclerotic lesion. To investigate disease-related functions of TCF21 in SMCs, knockdown and overexpression studies were performed in human coronary artery smooth muscle cells, revealing an effect on migration, proliferation and SMC marker gene expression.

Genome-wide RNA-seq studies in these cells with siRNA treatment identified putative TCF21 downstream genes and pathways involved in vascular development as well as atherosclerosis. Supporting ChIP-seq data suggests that these - as over half of all differentially expressed genes - are direct transcriptional targets. To elucidate the behavior of Tcf21 expressing cells in the development of disease lesions, we are employing an in vivo Tcf21 lineage tracing model. Preliminary data from these studies suggests that Tcf21 expressing cells give rise to fibrous cap SMCs, and ongoing studies are aimed at the further characterization of molecular pathways that are active in these Tcf21 expressing cells.

Conclusions: The gene regulatory and expression profile of Tcf21 during disease progression strongly implies a key role in Coronary Heart Disease. Tcf21 is likely to play a role in the migration of SMC progenitors from the adventitia into the forming atherosclerotic plaque. As a source of differentiated SMCs of the fibrous cap Tcf21 may therefore promote plaque stability and protect from lesion rupture.

Abstract 141: Coronary Heart Disease-Associated Variation in TCF21 Disrupts a MicroRNA-224 Binding Site and miRNA-Mediated Regulation

Introduction: Genome-wide association studies (GWAS) have identified chromosomal loci that affect risk of coronary heart disease (CHD) independent of classical risk factors. One such association signal has been identified at 6q23.2 in both Caucasians and East Asians. The lead CHD-associated variant in this region, rs12190287, resides in the 3’ untranslated region of the basic-helix-loop-helix transcription factor, TCF21 , and is predicted to alter the seed binding site for miR-224. Allelic imbalance studies demonstrated significant imbalance of the TCF21 transcript that correlated with genotype at rs12190287.

Hypothesis: We hypothesize that genetic variation at rs12190287 contributes to allele-specific TCF21 expression imbalance via miR-224 regulation, thus altering CHD risk.

Methods and Results: Reporter assays in human coronary artery smooth muscle cells (HCASMC) showed that the disease-associated C allele is selectively targeted by miR-224, leading to reduced expression compared to the protective G allele. Kinetic analyses in vitro revealed faster RNA-RNA complex formation and greater binding of miR-224 with the TCF21 C allelic transcript. In addition, in vitro probing with Pb 2+ and RNase T1 revealed structural differences between the TCF21 variants in proximity of the rs12190287 variant, which are predicted to provide greater access to the C allele for miR-224 binding. miR-224 and TCF21 expression levels were anti-correlated in HCASMC, and miR-224 modulates the transcriptional response of TCF21 to transforming growth factor- and platelet derived growth factor signaling in an allele-specific manner. Lastly, miR-224 and TCF21 were localized in human coronary artery lesions and anti-correlated during atherosclerosis in vivo .

Conclusions: Together, these data suggest that miR-224 interaction with the TCF21 transcript contributes to allelic imbalance of this gene, thus partly explaining the genetic risk for CHD at 6q23.2. These studies implicating rs12190287 in the miRNA-dependent regulation of TCF21 , in conjunction with previous studies showing that this variant modulates transcriptional regulation through AP-1, suggests a unique bimodal level of complexity previously unreported for disease-associated variants.

Coronary heart disease-associated variation in TCF21 disrupts a miR-224 binding site and miRNA-mediated regulation

Genome-wide association studies (GWAS) have identified chromosomal loci that affect risk of coronary heart disease (CHD) independent of classical risk factors. One such association signal has been identified at 6q23.2 in both Caucasians and East Asians. The lead CHD-associated polymorphism in this region, rs12190287, resides in the 3′ untranslated region (3′-UTR) of TCF21, a basic-helix-loop-helix transcription factor, and is predicted to alter the seed binding sequence for miR-224. Allelic imbalance studies in circulating leukocytes and human coronary artery smooth muscle cells (HCASMC) showed significant imbalance of the TCF21 transcript that correlated with genotype at rs12190287, consistent with this variant contributing to allele-specific expression differences. 3′ UTR reporter gene transfection studies in HCASMC showed that the disease-associated C allele has reduced expression compared to the protective G allele. Kinetic analyses in vitro revealed faster RNA-RNA complex formation and greater binding of miR-224 with the TCF21 C allelic transcript. In addition, in vitro probing with Pb²⁺ and RNase T1 revealed structural differences between the TCF21 variants in proximity of the rs12190287 variant, which are predicted to provide greater access to the C allele for miR-224 binding. miR-224 and TCF21 expression levels were anti-correlated in HCASMC, and miR-224 modulates the transcriptional response of TCF21 to transforming growth factor-β (TGF-β) and platelet derived growth factor (PDGF) signaling in an allele-specific manner. Lastly, miR-224 and TCF21 were localized in human coronary artery lesions and anti-correlated during atherosclerosis. Together, these data suggest that miR-224 interaction with the TCF21 transcript contributes to allelic imbalance of this gene, thus partly explaining the genetic risk for coronary heart disease associated at 6q23.2. These studies implicating rs12190287 in the miRNA-dependent regulation of TCF21, in conjunction with previous studies showing that this variant modulates transcriptional regulation through activator protein 1 (AP-1), suggests a unique bimodal level of complexity previously unreported for disease-associated variants.

Both genetic and environmental factors cumulatively contribute to coronary heart disease risk in human populations. Large-scale meta-analyses of genome-wide association studies have now leveraged common genetic variation to identify multiple sites of disease susceptibility; however, the causal mechanisms for these associations largely remain elusive. One of these disease-associated variants, rs12190287, resides in the 3′untranslated region of the vascular developmental transcription factor, TCF21. Intriguingly, this variant is shown to disrupt the seed binding sequence for microRNA-224, and through altered RNA secondary structure and binding kinetics, leads to dysregulated TCF21 gene expression in response to disease-relevant stimuli. Importantly TCF21 and miR-224 expression levels were perturbed in human atherosclerotic lesions. Along with our previous reports on the transcriptional regulatory mechanisms altered by this variant, these studies shed new light on the complex heritable mechanisms of coronary heart disease risk that are amenable to therapeutic intervention.

Disease-related growth factor and embryonic signaling pathways modulate an enhancer of TCF21 expression at the 6q23.2 coronary heart disease locus

Coronary heart disease (CHD) is the leading cause of mortality in both developed and developing countries worldwide. Genome-wide association studies (GWAS) have now identified 46 independent susceptibility loci for CHD, however, the biological and disease-relevant mechanisms for these associations remain elusive. The large-scale meta-analysis of GWAS recently identified in Caucasians a CHD-associated locus at chromosome 6q23.2, a region containing the transcription factor TCF21 gene. TCF21 (Capsulin/Pod1/Epicardin) is a member of the basic-helix-loop-helix (bHLH) transcription factor family, and regulates cell fate decisions and differentiation in the developing coronary vasculature. Herein, we characterize a cis-regulatory mechanism by which the lead polymorphism rs12190287 disrupts an atypical activator protein 1 (AP-1) element, as demonstrated by allele-specific transcriptional regulation, transcription factor binding, and chromatin organization, leading to altered TCF21 expression. Further, this element is shown to mediate signaling through platelet-derived growth factor receptor beta (PDGFR-β) and Wilms tumor 1 (WT1) pathways. A second disease allele identified in East Asians also appears to disrupt an AP-1-like element. Thus, both disease-related growth factor and embryonic signaling pathways may regulate CHD risk through two independent alleles at TCF21.

Increased bone mass in mice lacking the adipokine apelin

Adipose tissue plays an important role in skeletal homeostasis, and there is interest in identifying adipokines that influence bone mass. One such adipokine may be apelin, a ligand for the Gi-G protein-coupled receptor APJ, which has been reported to enhance mitogenesis and suppress apoptosis in MC3T3-E1 cells and primary human osteoblasts (OBs). However, it is unclear whether apelin plays a physiological role in regulating skeletal homeostasis in vivo. In this study, we compared the skeletal phenotypes of apelin knockout (APKO) and wild-type mice and investigated the direct effects of apelin on bone cells in vitro. The increased fractional cancellous bone volume at the distal femur was observed in APKO mice of both genders at 12 weeks of age and persisted until the age of 20. Cortical bone perimeter at the femoral midshaft was significantly increased in males and females at both time points. Dynamic histomorphometry revealed that APKO mice had increased rates of bone formation and mineral apposition, with evidences of accelerated OB proliferation and differentiation, without significant alteration in osteoclast activity. An in vitro study showed that apelin increased proliferation of primary mouse OBs as well as suppressed apoptosis in a dose-dependent manner with the maximum effect at 5nM. However, it had no effect on the formation of mineralized nodules. We did not observed significantly altered in osteoclast parameters in vitro. Taken together, the increased bone mass in mice lacking apelin suggested complex direct and paracrine/endocrine effects of apelin on bone, possibly via modulating insulin sensitivity. These results indicate that apelin functions as a physiologically significant antianabolic factor in bone in vivo.

Apelin-APJ signaling is a critical regulator of endothelial MEF2 activation in cardiovascular development

RATIONALE

The peptide ligand apelin and its receptor APJ constitute a signaling pathway with numerous effects on the cardiovascular system, including cardiovascular development in model organisms such as xenopus and zebrafish.

OBJECTIVE

This study aimed to characterize the embryonic lethal phenotype of the Apj-/- mice and to define the involved downstream signaling targets.

METHODS AND RESULTS

We report the first characterization of the embryonic lethality of the Apj-/- mice. More than half of the expected Apj-/- embryos died in utero because of cardiovascular developmental defects. Those succumbing to early embryonic death had markedly deformed vasculature of the yolk sac and the embryo, as well as poorly looped hearts with aberrantly formed right ventricles and defective atrioventricular cushion formation. Apj-/- embryos surviving to later stages demonstrated incomplete vascular maturation because of a deficiency of vascular smooth muscle cells and impaired myocardial trabeculation and ventricular wall development. The molecular mechanism implicates a novel, noncanonical signaling pathway downstream of apelin-APJ involving Gα13, which induces histone deacetylase (HDAC) 4 and HDAC5 phosphorylation and cytoplasmic translocation, resulting in activation of myocyte enhancer factor 2. Apj-/- mice have greater endocardial Hdac4 and Hdac5 nuclear localization and reduced expression of the myocyte enhancer factor 2 (MEF2) transcriptional target Krüppel-like factor 2. We identify a number of commonly shared transcriptional targets among apelin-APJ, Gα13, and MEF2 in endothelial cells, which are significantly decreased in the Apj-/- embryos and endothelial cells.

CONCLUSIONS

Our results demonstrate a novel role for apelin-APJ signaling as a potent regulator of endothelial MEF2 function in the developing cardiovascular system.

Loss of CDKN2B promotes p53-dependent smooth muscle cell apoptosis and aneurysm formation

OBJECTIVE

Genomewide association studies have implicated allelic variation at 9p21.3 in multiple forms of vascular disease, including atherosclerotic coronary heart disease and abdominal aortic aneurysm. As for other genes at 9p21.3, human expression quantitative trait locus studies have associated expression of the tumor suppressor gene CDKN2B with the risk haplotype, but its potential role in vascular pathobiology remains unclear.

METHODS AND RESULTS

Here we used vascular injury models and found that Cdkn2b knockout mice displayed the expected increase in proliferation after injury, but developed reduced neointimal lesions and larger aortic aneurysms. In situ and in vitro studies suggested that these effects were attributable to increased smooth muscle cell apoptosis. Adoptive bone marrow transplant studies confirmed that the observed effects of Cdkn2b were mediated through intrinsic vascular cells and were not dependent on bone marrow-derived inflammatory cells. Mechanistic studies suggested that the observed increase in apoptosis was attributable to a reduction in MDM2 and an increase in p53 signaling, possibly due in part to compensation by other genes at the 9p21.3 locus. Dual inhibition of both Cdkn2b and p53 led to a reversal of the vascular phenotype in each model.

CONCLUSIONS

These results suggest that reduced CDKN2B expression and increased smooth muscle cell apoptosis may be one mechanism underlying the 9p21.3 association with aneurysmal disease.

FGD5 mediates proangiogenic action of vascular endothelial growth factor in human vascular endothelial cells

OBJECTIVE

Vascular endothelial growth factor (VEGF) exerts proangiogenic action and induces activation of a variety of proangiogenic signaling pathways, including the Rho family small G proteins. However, regulators of the Rho family small G proteins in vascular endothelial cells (ECs) are poorly understood. Here we attempted to clarify the expression, subcellular localization, downstream effectors, and proangiogenic role of FGD5, a member of the FGD family of guanine nucleotide exchange factors.

METHODS AND RESULTS

FGD5 was shown to be selectively expressed in cultured human vascular ECs. Immunofluorescence microscopy showed that the signal for FGD5 was observed at peripheral membrane ruffles and perinuclear regions in human umbilical vein ECs. Overexpression of FGD5 increased Cdc42 activity, whereas knockdown of FGD5 by small interfering RNAs inhibited the VEGF-induced activation of Cdc42 and extracellular signal-regulated kinase. VEGF-promoted capillary-like network formation, permeability, directional movement, and proliferation of human umbilical vein ECs and the reorientation of the Golgi complex during directional cell movement were attenuated by knockdown of FGD5.

CONCLUSIONS

This study provides the first demonstration of expression, subcellular localization, and function of FGD5 in vascular ECs. The results suggest that FGD5 regulates proangiogenic action of VEGF in vascular ECs, including network formation, permeability, directional movement, and proliferation.

The angiogenic factor Del1 prevents apoptosis of endothelial cells through integrin binding

BACKGROUND

Del1 is a secreted protein that is expressed in the endothelium during development and can stimulate angiogenesis through integrin binding and signaling. We were interested in the specific effects of del1 on endothelial cell biology to gain insight into its biologic role during angiogenesis.

METHODS

Primary endothelial cells were treated with a variety of inducers of apoptosis and anoikis followed by assays for numbers of apoptotic cells, and harvest of total protein for immunoblot analysis.

RESULTS

Del1 prevented endothelial cell apoptosis in response to TNFα/IFNγ, etoposide, and anoikis, but had no effect on proliferation. The anti-apoptotic effect was mediated specifically through binding of integrin αvβ3 by the RGD motif. FAK/ERK and Akt signaling were both necessary to mediate the anti-apoptotic effect of Del1 with the exception of anoikis, which required only Akt activation.

CONCLUSION

Del1 has been previously shown to promote vascular smooth muscle cell adhesion, migration, and proliferation. We demonstrate here that Del1 prevented apoptosis of endothelial cells in cell culture through integrin binding without any effect on proliferation.

MicroRNA-26a is a novel regulator of vascular smooth muscle cell function

Aberrant smooth muscle cell (SMC) plasticity has been implicated in a variety of vascular disorders including atherosclerosis, restenosis, and abdominal aortic aneurysm (AAA) formation. While the pathways governing this process remain unclear, epigenetic regulation by specific microRNAs (miRNAs) has been demonstrated in SMCs. We hypothesized that additional miRNAs might play an important role in determining vascular SMC phenotype. Microarray analysis of miRNAs was performed on human aortic SMCs undergoing phenotypic switching in response to serum withdrawal, and identified 31 significantly regulated entities. We chose the highly conserved candidate miRNA-26a for additional studies. Inhibition of miRNA-26a accelerated SMC differentiation, and also promoted apoptosis, while inhibiting proliferation and migration. Overexpression of miRNA-26a blunted differentiation. As a potential mechanism, we investigated whether miRNA-26a influences TGF-β-pathway signaling. Dual-luciferase reporter assays demonstrated enhanced SMAD signaling with miRNA-26a inhibition, and the opposite effect with miRNA-26a overexpression in transfected human cells. Furthermore, inhibition of miRNA-26a increased gene expression of SMAD-1 and SMAD-4, while overexpression inhibited SMAD-1. MicroRNA-26a was also found to be downregulated in two mouse models of AAA formation (2.5- to 3.8-fold decrease, P < 0.02) in which enhanced switching from contractile to synthetic phenotype occurs. In summary, miRNA-26a promotes vascular SMC proliferation while inhibiting cellular differentiation and apoptosis, and alters TGF-β pathway signaling. MicroRNA-26a represents an important new regulator of SMC biology and a potential therapeutic target in AAA disease.

Disruption of the apelin-APJ system worsens hypoxia-induced pulmonary hypertension

OBJECTIVE

The G-protein-coupled receptor APJ and its ligand apelin are highly expressed in the pulmonary vasculature, but their function in this vascular bed is unclear. We hypothesized that disruption of apelin signaling would lead to worsening of the vascular remodeling associated with pulmonary hypertension (PH).

METHODS AND RESULTS

We found that apelin-null mice developed more severe PH compared with wild-type mice when exposed to chronic hypoxia. Micro-computed tomography of the pulmonary arteries demonstrated significant pruning of the microvasculature in the apelin-null mice. Apelin-null mice had a significant reduction of serum nitrate levels. This was secondary to downregulation of endothelial nitric oxide synthase (eNOS), which was associated with reduced expression of Kruppel-like factor 2 (KLF2), a known regulator of eNOS expression. In vitro knockdown studies targeting apelin in human pulmonary artery endothelial cells demonstrated decreased eNOS and KLF2 expression, as well as impaired phosphorylation of AMP-activated kinase and eNOS. Moreover, serum apelin levels of patients with PH were significantly lower than those of controls.

CONCLUSIONS

These data demonstrate that disruption of apelin signaling can exacerbate PH mediated by decreased activation of AMP-activated kinase and eNOS, and they identify this pathway as a potentially important therapeutic target for treatment of this refractory human disease.

Apelin decreases lipolysis via G(q), G(i), and AMPK-Dependent Mechanisms

The release of free fatty acids (FFAs) from adipocytes (i.e. lipolysis) is increased in obesity and is a contributory factor to the development of insulin resistance. A recently identified adipokine, apelin, is up-regulated in states of obesity. Although apelin is secreted by adipocytes, its functions in them remain largely unknown. To determine whether apelin affects lipolysis, FFA, glycerol, and leptin levels, as well as abdominal adiposity, were measured at baseline and after reintroduction of exogenous apelin in apelin-null mice. To examine apelin's effects in vitro, isoproterenol-induced FFA/glycerol release, and hormone-sensitive lipase (HSL) and acetyl CoA carboxylase phosphorylation were investigated in 3T3-L1 cells and isolated wild-type adipocytes. Serum FFA, glycerol, and leptin concentrations, as well as abdominal adiposity, were significantly increased in apelin-null vs. wild-type mice; these changes were ameliorated in response to exogenous apelin. Apelin also reduced isoproterenol-induced FFA release in adipocytes isolated from wild-type but not APJ-null mice. In 3T3-L1 cells and isolated adipocytes, apelin attenuated isoproterenol-induced FFA/glycerol release. Apelin's inhibition was reversed by pertussis toxin, the G(q) inhibitor glycoprotein antagonist 2A, and the AMP-activated protein kinase inhibitors compound C and dorsomorphin. Apelin increased HSL phosphorylation at Ser-565 and also abrogated isoproterenol-induced HSL phosphorylation at Ser-563. Notably, apelin increased acetyl CoA carboxylase phosphorylation, suggesting AMPK activation. In conclusion, apelin negatively regulates lipolysis. Its actions may be mediated by pathways involving G(q), G(i), and AMP-activated protein kinase.

Endothelial cell-selective adhesion molecule modulates atherosclerosis through plaque angiogenesis and monocyte-endothelial interaction

Endothelial cell-selective adhesion molecule (ESAM) is a new member of the immunoglobulin superfamily, which is expressed in vascular endothelial cells. Previous studies have demonstrated that ESAM regulates angiogenesis, endothelial permeability, and leukocyte transmigration. However, little is known concerning the role of ESAM in atherosclerosis. In this study, we assessed the effects of ESAM inactivation on atherosclerosis in mice. ESAM-/- mice were bred with apoE-/- mice to generate double knockout mice, and the aortic lesion size of apoE-/- and ESAM-/-apoE-/- mice was compared histologically. Although plasma cholesterol levels were higher in ESAM-/-apoE-/- mice, the lesion size was markedly smaller than in apoE-/- mice. ESAM-/-apoE-/- mice exhibited a decrease in the number of vasa vasorum and macrophages in the vessel wall. In vitro adhesion assays showed that THP-1 cells, which did not express ESAM, bound to the ESAM-coated culture plates, suggesting that ESAM may interact with heterophilic ligand(s) on monocytes. Moreover, downregulation of ESAM by siRNA in the endothelial monolayer diminished transendothelial migration of THP-1 cells. In conclusion, ESAM inactivation can reduce susceptibility to atherosclerosis by inhibiting plaque neovascularization and macrophage infiltration into the atheroma.

Upregulation of the apelin-APJ pathway promotes neointima formation in the carotid ligation model in mouse

AIMS

To investigate apelin-APJ (angiotensin receptor-like 1) signalling in vascular remodelling, we have examined the pathophysiological response to carotid ligation in apelin knockout mice.

METHODS AND RESULTS

Apelin null animals compared with wild-type mice had significantly decreased neointimal lesion area (1.17 +/- 0.17 vs. 3.33 +/- 1.04 x 10(4) microm(2), P < 0.05) and intima/media ratio (0.81 +/- 0.23 vs. 1.49 +/- 0.44, P < 0.05), averaged over four sites 0.5-2 mm from the ligation. Exogenous apelin infusion rescued the apelin-KO phenotype, promoting neointima formation in the null animals. Apelin null animals showed decreased smooth muscle positive area in the neointima (82.3 +/- 2.4 vs. 63.9 +/- 8.4, P < 0.05), and a smaller percentage BrdU positive cells in the neointima and media (11.06 +/- 1.00 vs. 6.53 +/- 0.86, P < 0.05). Apelin mRNA expression increased initially (5.2-fold, P < 0.01) followed by increased apelin receptor expression (10.1-fold, P < 0.05) in the ligated artery. Cytochemistry studies localized apelin expression to luminal endothelial cells and apelin receptor upregulation to smooth muscle cells (SMC) in the media and neointima. In vitro experiments with cultured rat aortic SMC revealed that apelin stimulation increased migration. In contrast to the increased expression of apelin and apelin receptor in carotid remodelling, expression was not upregulated in the apoE high fat model, and correlated with the known disease-inhibitory effect in this model.

CONCLUSION

These data suggest that increased apelin receptor expression by SMC provides a paracrine pathway in injured vessels that allows endothelial-derived apelin to stimulate their division and migration into the neointima.

Role of endothelial cell-selective adhesion molecule in hematogeneous metastasis

The spread of malignant cells from a localized tumor is thought to be directly related to the number of microvessels in the tumor. The endothelial cell-selective adhesion molecule (ESAM) is a member of the immunoglobulin superfamily that mediates homophilic interactions between endothelial cells. Previous studies have indicated that ESAM regulates angiogenesis in the primary tumor growth and endothelial permeability. In this study, we aimed to further elucidate the role of ESAM in tumor metastasis through angiogenic processes. ESAM expression was higher in hypervascular metastatic tumor tissues than in normal tissues in human lungs. Cell culture studies found that conditioned medium from B16F10 melanoma cells increased ESAM expression in endothelial cells and promoted endothelial migration and tube formation. The B16F10 medium-induced endothelial migration and tube formation were significantly attenuated when ESAM was downregulated by siRNA transfection. Intravenous injection of B16F10 cells into ESAM+/+ and ESAM-/- mice for comparison of metastatic potential resulted in the number of metastatic lung nodules in ESAM-/- mice being 83% lower than of those in ESAM+/+ mice. The microvascular density in the tumor was also lower in ESAM-/- than in ESAM+/+ mice. These findings indicate that ESAM regulates tumor metastasis through endothelial cell migration and tube formation in metastatic nodules. Inhibition of ESAM may therefore inhibit tumor metastasis by inhibiting the angiogenic processes.

Apelin is necessary for the maintenance of insulin sensitivity

The recently discovered peptide apelin is known to be involved in the maintenance of insulin sensitivity. However, questions persist regarding its precise role in the chronic setting. Fasting glucose, insulin, and adiponectin levels were determined on mice with generalized deficiency of apelin (APKO). Additionally, insulin (ITT) and glucose tolerance tests (GTT) were performed. To assess the impact of exogenously delivered apelin on insulin sensitivity, osmotic pumps containing pyroglutamated apelin-13 or saline were implanted in APKO mice for 4 wk. Following the infusion, ITT/GTTs were repeated and the animals euthanized. Soleus muscles were harvested and homogenized in lysis buffer, and insulin-induced Akt phosphorylation was determined by Western blotting. Apelin-13 infusion and ITTs/GTTs were also performed in obese diabetic db/db mice. To probe the underlying mechanism for apelin's effects, apelin-13 was also delivered to cultured C2C12 myotubes. 2-[3H]deoxyglucose uptake and Akt phosphorylation were assessed in the presence of various inhibitors. APKO mice had diminished insulin sensitivity, were hyperinsulinemic, and had decreased adiponectin levels. Soleus lysates had decreased insulin-induced Akt phosphorylation. Administration of apelin to APKO and db/db mice resulted in improved insulin sensitivity. In C2C12 myotubes, apelin increased glucose uptake and Akt phosphorylation. These events were fully abrogated by pertussis toxin, compound C, and siRNA knockdown of AMPKalpha1 but only partially diminished by LY-294002 and not at all by L-NAME. We conclude that apelin is necessary for the maintenance of insulin sensitivity in vivo. Apelin's effects on glucose uptake and Akt phosphorylation are in part mediated by a G(i) and AMPK-dependent pathway.

Endogenous regulation of cardiovascular function by apelin-APJ

Studies have shown significant cardiovascular effects of exogenous apelin administration, including the potent activation of cardiac contraction. However, the role of the endogenous apelin-APJ pathway is less clear. To study the loss of endogenous apelin-APJ signaling, we generated mice lacking either the ligand (apelin) or the receptor (APJ). Apelin-deficient mice were viable, fertile, and showed normal development. In contrast, APJ-deficient mice were not born in the expected Mendelian ratio, and many showed cardiovascular developmental defects. Under basal conditions, both apelin and APJ null mice that survived to adulthood manifested modest decrements in contractile function. However, with exercise stress both mutant lines demonstrated consistent and striking decreases in exercise capacity. To explain these findings, we explored the role of autocrine signaling in vitro using field stimulation of isolated left ventricular cardiomyocytes lacking either apelin or APJ. Both groups manifested less sarcomeric shortening and impaired velocity of contraction and relaxation with no difference in calcium transient. Taken together, these results demonstrate that endogenous apelin-APJ signaling plays a modest role in maintaining basal cardiac function in adult mice with a more substantive role during conditions of stress. In addition, an autocrine pathway seems to exist in myocardial cells, the ablation of which reduces cellular contraction without change in calcium transient. Finally, differences in the developmental phenotype between apelin and APJ null mice suggest the possibility of undiscovered APJ ligands or ligand-independent effects of APJ.

Role of endothelial lipase in plasma HDL levels in a murine model of hypertriglyceridemia

AIM

Hypertriglyceridemia is the most common cause of low plasma high-density lipoprotein cholesterol (HDL-C) levels; however, the correlation between high triglyceride (TG) and low HDL-C remains unclear. Endothelial lipase (EL) is a determinant of plasma HDL levels. We investigated the role of EL in HDL metabolism in a murine model of acute hypertriglyceridemia.

METHODS AND RESULTS

To establish TG-dominant hyperlipidemia, EL-/- and wild-type (WT) mice were injected with Poloxamer-407 (P-407, 0.5 g/kg, i.p.). A single injection of P-407 resulted in a marked increase in plasma TG and cholesterol levels together with a decrease in HDL-C levels. Although plasma TG levels were similar in EL-/- and WT mice after P-407 injection, HDL-C levels were 80% higher and the HDL particle size was significantly larger in EL-/- mice than in WT mice. P-407 treatment inhibited plasma lipoprotein lipase activity and EL phospholipase activity, without decreasing their expressions. Adenovirus-mediated overexpression of EL in the liver reduced plasma HDL-C levels in both normo- and hyperlipidemic mice, while overexpression of catalytically inactive EL reduced HDL-C levels in hyperlipidemic mice. Cell culture experiments revealed that both catalytically active and inactive EL promoted cellular HDL uptake to the same extent.

CONCLUSION

EL regulates plasma HDL levels in mice in the normolipidemic as well as the acute hypertriglyceridemic state. EL can modulate plasma HDL-CHOL levels through both its lipolytic and ligand-binding functions in hypertriglyceridemic mice, while lipolytic activity appears to be the main determinant for its effects on HDL metabolism in normolipidemic mice.

Apelin prevents aortic aneurysm formation by inhibiting macrophage inflammation

Apelin is a potent inodilator with recently described antiatherogenic properties. We hypothesized that apelin might also attenuate abdominal aortic aneurysm (AAA) formation by limiting disease-related vascular wall inflammation. C57BL/6 mice implanted with osmotic pumps filled with apelin or saline were treated with pancreatic elastase to create infrarenal AAAs. Mice were euthanized for aortic PCR analysis or followed ultrasonographically and then euthanized for histological analysis. The cellular expression of inflammatory cytokines and chemokines in response to apelin was also assessed in cultured macrophages, smooth muscle cells, and fibroblasts. Apelin treatment resulted in diminished AAA formation, with a 47% reduction in maximal cross-sectional area (0.74 vs. 1.39 mm(2), P < 0.03) and a 57% reduction in macrophage infiltrate (113 vs. 261.3 cells/high-power field, P < 0.0001) relative to the saline-treated group. Apelin infusion was also associated with significantly reduced aortic macrophage colony-stimulating factor expression and decreased monocyte chemattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-1alpha, interleukin (IL)-6, and tumor necrosis factor (TNF)-alpha mean mRNA levels. Apelin stimulation of cultured macrophages significantly reduced MCP-1 and TNF-alpha mRNA levels relative to baseline (2.03- and 1.89-fold reduction, P < 0.03, respectively) but did not affect intimal adhesion molecule expression or medial or adventitial cell cytokine production. Apelin significantly reduces aneurysm formation in the elastase model of human AAA disease. The mechanism appears to be decreased macrophage burden, perhaps related to an apelin-mediated decrease in proinflammatory cytokine and chemokine activation.

Targeted inactivation of endothelial lipase attenuates lung allergic inflammation through raising plasma HDL level and inhibiting eosinophil infiltration

Endothelial lipase (EL) is a novel phospholipase that determines plasma high-density lipoprotein cholesterol (HDL-C) levels. We have investigated the role of HDL-C in lung allergic inflammation by using EL knockout (EL-KO) mice that are high in HDL-C. EL-KO and wild-type control mice were sensitized and challenged with ovalbumin to evoke eosinophilic inflammation in the lung. EL was expressed in epithelial cells, alveolar type II cells, and endothelial cells in the lung, and its expression was upregulated during inflammation. Concomitant with attenuated hyperresponsiveness of the airway smooth muscles, the number of eosinophils in bronchoalveolar lavage and the expression of VCAM-1 were lower in EL-KO mice than in control mice. HDL reduced cytokine-induced VCAM-1 expression in cultured endothelial cells. When plasma HDL levels were decreased to similar levels in both mouse groups by adenovirus-mediated overexpression of EL, however, eosinophil infiltration was still lower in EL-KO mice. In vitro adhesion assays revealed that EL expression on the cell surface promoted the interaction of eosinophils through the ligand-binding function of EL. In summary, targeted inactivation of EL attenuated allergic inflammation in the lung, and the protective effects in EL-KO mice were associated with high plasma HDL levels, downregulation of VCAM-1, and loss of the direct ligand-binding function of EL. Thus EL is a novel modulator of the progression of allergic asthma.

Apelin signaling antagonizes Ang II effects in mouse models of atherosclerosis

Apelin and its cognate G protein-coupled receptor APJ constitute a signaling pathway with a positive inotropic effect on cardiac function and a vasodepressor function in the systemic circulation. The apelin-APJ pathway appears to have opposing physiological roles to the renin-angiotensin system. Here we investigated whether the apelin-APJ pathway can directly antagonize vascular disease-related Ang II actions. In ApoE-KO mice, exogenous Ang II induced atherosclerosis and abdominal aortic aneurysm formation; we found that coinfusion of apelin abrogated these effects. Similarly, apelin treatment rescued Ang II-mediated increases in neointimal formation and vascular remodeling in a vein graft model. NO has previously been implicated in the vasodepressor function of apelin; we found that apelin treatment increased NO bioavailability in ApoE-KO mice. Furthermore, infusion of an NO synthase inhibitor blocked the apelin-mediated decrease in atherosclerosis and aneurysm formation. In rat primary aortic smooth muscle cells, apelin inhibited Ang II-mediated transcriptional regulation of multiple targets as measured by reporter assays. In addition, we demonstrated by coimmunoprecipitation and fluorescence resonance energy transfer analysis that the Ang II and apelin receptors interacted physically. Taken together, these findings indicate that apelin signaling can block Ang II actions in vascular disease by increasing NO production and inhibiting Ang II cellular signaling.

Del-1, an endogenous leukocyte-endothelial adhesion inhibitor, limits inflammatory cell recruitment

Leukocyte recruitment to sites of infection or inflammation requires multiple adhesive events. Although numerous players promoting leukocyte-endothelial interactions have been characterized, functionally important endogenous inhibitors of leukocyte adhesion have not been identified. Here we describe the endothelially derived secreted molecule Del-1 (developmental endothelial locus-1) as an anti-adhesive factor that interferes with the integrin LFA-1-dependent leukocyte-endothelial adhesion. Endothelial Del-1 deficiency increased LFA-1-dependent leukocyte adhesion in vitro and in vivo. Del-1-/- mice displayed significantly higher neutrophil accumulation in lipopolysaccharide-induced lung inflammation in vivo, which was reversed in Del-1/LFA-1 double-deficient mice. Thus, Del-1 is an endogenous inhibitor of inflammatory cell recruitment and could provide a basis for targeting leukocyte-endothelial interactions in disease.

Glia maturation factor-gamma is preferentially expressed in microvascular endothelial and inflammatory cells and modulates actin cytoskeleton reorganization

Actin cytoskeleton reorganization is a fundamental process for actin-based cellular functions such as cytokinesis, phagocytosis, and chemotaxis. Regulating actin cytoskeleton reorganization is therefore an attractive approach to control endothelial and inflammatory cells function and to treat cardiovascular diseases. Here, we identified glia maturation factor-gamma (GMFG) as a novel factor in actin cytoskeleton reorganization and is expressed preferentially in microvascular endothelial and inflammatory cells. During mouse embryogenesis, GMFG was expressed predominantly in blood islands of the yolk sac, where endothelial and hematopoietic cells develop simultaneously. In endothelial cells, GMFG was colocalized with F-actin in membrane ruffles and was associated with F-actin assessed by actin co-sedimentation assay. Interestingly, GMFG was phosphorylated at N-terminal serine, and its phosphorylation was enhanced by coexpression of dominant active Rac1 and Cdc42. Furthermore, a pseudophosphorylated form of GMFG (GMFG-S2E) demonstrated higher association with F-actin. Stable expression of GMFG-S2E remarkably enhanced stimulus-responsive lamellipodia and subsequent membrane ruffle formation in HeLa cells presumably through its interaction with Arp2/3 complex. Expression of GMFG enhanced actin-based cellular functions such as migration and tube-formation in endothelial cells. Moreover, we found that GMFG expression was significantly increased in a cardiac ischemia/reperfusion model where inflammation and angiogenesis take place actively. Taken together, our findings define a novel pathway in the regulation of actin-based cellular functions. Regulating GMFG function may provide a novel approach to modulate the pathophysiology of cardiovascular diseases.

Molecular cloning of nonsecreted endothelial cell-derived lipase isoforms

To expand our knowledge of factors involved in lipid metabolism in the blood vessel wall, we have cloned unique molecular isoforms of endothelial cell-derived lipase (EDL) (HGMW-approved symbol/LIPG). One isoform encoded a truncated protein (EDL2a) lacking the first 80 amino acid residues of the previously characterized EDL1a isoform, including the signal peptide. A similar second clone (EDL2b) was identified that lacked not only the first 80 amino acids, but also a 74-amino-acid region that encodes a portion of the lid domain. RT-PCR analysis confirmed expression of EDL2a/2b isoforms in several human tissues and cultured cells, including endothelial cells. Western blot and immunofluorescence studies using stable transfectants revealed that EDL2a and EDL2b were localized in the cytosol, while, EDL1a was secreted into the culture medium. Cell extracts of EDL2a/2b transfectants did not have triglyceride or phospholipase activity. Thus endothelial cells express three EDL isoforms, two of which remain intracellular and do not function as lipases.

Endothelial Lipase Modulates Susceptibility to Atherosclerosis in Apolipoprotein-E-deficient Mice

Endothelial lipase (EL) expression correlates inversely with circulating high density lipoprotein (HDL) cholesterol levels in genetic mouse models, and human genetic variation in this locus has been linked to differences in HDL cholesterol levels. These data suggest a role for EL in the development of atherosclerotic vascular disease. To investigate this possibility, LIPG-null alleles were bred onto the apoE knockout background, and the homozygous double knockout animals were characterized. Both apoE knockout and double knockout mice had low HDL cholesterol levels when compared with wild-type mice, but the HDL cholesterol levels of the double knockout mice were higher than those of apoE knockout mice. Atherogenic very low density lipoprotein and intermediate density lipoprotein/low density lipoprotein cholesterol levels of the double knockout mice were also greater than those of the apoE knockout animals. Despite this lipid profile, there was a significant approximately 70% decrease in atherosclerotic disease area in double knockout mice on a regular diet. Immunohistochemistry and protein blot studies revealed increased EL expression in the atherosclerotic aortas of the apoE knockout animals. An observed decrease in macrophage content in vessels lacking EL correlated with ex vivo vascular monocyte adhesion assays, suggesting that this protein can modulate monocyte adhesion and infiltration into diseased tissues. These data suggest that EL may have indirect atherogenic actions in vivo through its effect on circulating HDL cholesterol and direct atherogenic actions through vascular wall processes such as monocyte recruitment and cholesterol uptake.

Targeted disruption of endothelial cell-selective adhesion molecule inhibits angiogenic processes in vitro and in vivo

Endothelial cell-selective adhesion molecule (ESAM) is a member of the immunoglobulin receptor family that mediates homophilic interactions between endothelial cells. To address potential in vivo angiogenic functions of this molecule, mice lacking ESAM (ESAM-/-) were generated by gene-targeted deletion. ESAM-/- mice did not show overt morphological defects in the vasculature. To evaluate the role of ESAM in pathological angiogenesis, wild type (WT) and ESAM-/- mice were injected with melanoma and Lewis lung carcinoma cells. By 14 days after injection, tumor volumes of B16F10 and LL/2 in ESAM-/- mice were 48 and 37% smaller, respectively, compared with WT mice. Vascular density of the tumors, as determined by CD31 staining, was also decreased in the ESAM null animals. Matrigel plug assays showed less neovascularization in ESAM-/- mice than in WT mice. ESAM-/- endothelial cells exhibited less in vitro tube formation and decreased migration in response to basic fibroblast growth factor when compared with WT cells, and endothelial-like yolk sac cells engineered to overexpress ESAM showed accelerated tube formation in vitro. These in vitro and in vivo studies suggest that ESAM has a redundant functional role in physiological angiogenesis but serves a unique and essential role in pathological angiogenic processes such as tumor growth.

Endothelial lipase is a major determinant of HDL level

A new member of the lipase gene family, initially termed endothelial lipase (gene nomenclature, LIPG; protein, EL), is expressed in a variety of different tissues, suggesting a general role in lipid metabolism. To assess the hypothesis that EL plays a physiological role in lipoprotein metabolism in vivo, we have used gene targeting of the native murine locus and transgenic introduction of the human LIPG locus in mice to modulate the level of EL expression. Evaluation of these alleles in a C57Bl/6 background revealed an inverse relationship between HDL cholesterol level and EL expression. Fasting plasma HDL cholesterol was increased by 57% in LIPG(-/-) mice and 25% in LIPG(+/-) mice and was decreased by 19% in LIPG transgenic mice as compared with syngeneic controls. Detailed analysis of lipoprotein particle composition indicated that this increase was due primarily to an increased number of HDL particles. Phospholipase assays indicated that EL is a primary contributor to phospholipase activity in mouse. These data indicate that expression levels of this novel lipase have a significant effect on lipoprotein metabolism.

Phenotypic differentiation of TGF-beta1-responsive pluripotent premesenchymal prehematopoietic progenitor (P4 stem) cells from murine bone marrow

On the horizon of modern molecular medicine is the requisite technology to capture multipotent human stem cells that are capable of self-renewal and to direct these stem cells along defined lineages for therapeutic purposes. In this article, we describe the hematopoietic and mesenchymal differentiation potential of a unique population of transforming growth factor-beta1 (TGF-beta1)-responsive stem cells derived from murine bone marrow. Stringent selection of the stem cells was accomplished under low serum conditions by virtue of an inherent survival response to a TGF-beta1-vWF fusion protein that was bound to collagen matrices. The TGF-beta1-responsive stem cells initially exhibited a non-adherent and uniformly blastoid morphology, underwent expansion into colonies upon serum reconstitution, and were capable of overt cytodifferentiation along fibrogenic, osteogenic, chondrogenic, or adipogenic lineages upon growth factor stimulation. Remarkably, these stem cells also underwent rapid expansion in the presence of either hematopoietic stem cell factor (SCF) or interleukin3 (IL-3), and differentiated into myeloid and lymphoid phenotypes upon exposure to the latter. Taken together, these results support the hypothesis that pluripotent premesenchymal prehematopoietic progenitor cells, designated P4 stem cells, are present postnatally in murine bone marrow and, thus, may be summarily isolated for various cell-based experimental therapies.

Molecular mechanism of decreased glutathione content in human immunodeficiency virus type 1 Tat-transgenic mice

Human immunodeficiency virus (HIV) progressively depletes GSH content in humans. Although the accumulated evidence suggests a role of decreased GSH in the pathogenesis of HIV, significant controversy remains concerning the mechanism of GSH depletion, especially in regard to envisioning appropriate therapeutic strategies to help compensate for such decreased antioxidant capacity. Tat, a transactivator encoded by HIV, is sufficient to cause GSH depletion in vitro and is implicated in AIDS-associated Kaposi's sarcoma and B cell lymphoma. In this study, we report a decrease in GSH biosynthesis with Tat, using HIV-1 Tat transgenic (Tat+) mice. A significant decline in the total intracellular GSH content in liver and erythrocytes of Tat+ mice was accompanied by decreased gamma-glutamylcysteine synthetase regulatory subunit mRNA and protein content, which resulted in an increased sensitivity of gamma-glutamylcysteine synthetase to feedback inhibition by GSH. Further study revealed a significant reduction in the activity of GSH synthetase in liver of Tat+ mice, which was linearly associated with their GSH content. Therefore, Tat appears to decrease GSH in vivo, at least partially, through modulation of GSH biosynthetic enzymes.

Epidermal dysplasia and abnormal hair follicles in transgenic mice overexpressing homeobox gene MSX-2

The homeobox gene Msx-2 is expressed specifically in sites of skin appendage formation. To explore its part in skin morphogenesis, we produced transgenic mice expressing Msx-2 under the control of the cytomegalovirus promoter. The skin of these transgenic mice was flaky, exhibiting desquamation and shorter hairs. Histologic analysis showed thickened epidermis with hyperproliferation, which was restricted to the basal layer. Hyperkeratosis was also evident. A wide zone of suprabasal cells were misaligned and coexpressed keratins 14 and 10. There was reduced expression of integrin beta 1 and DCC in the basal layer. Hair follicles were misaligned with a shrunken matrix region. The dermis showed increased cellularity and empty vacuoles. We suggest that Msx-2 is involved in the growth control of skin and skin appendages.

Expression of the human immunodeficiency virus-Tat gene in lymphoid tissues of transgenic mice is associated with B-cell lymphoma

The human immunodeficiency virus type 1 (HIV-1) Tat gene, a potent transactivator of viral and cellular genes, has been proposed as a key agent in the pathogenesis of acquired immune deficiency syndrome related disorders, including non-Hodgkin's lymphoma. In cultured cells, the HIV-1 Tat protein can induce the expression of the cytokines interleukin-6 (IL-6) and IL-10, which are known to induce proliferation and differentiation of lymphoid cells. Such alterations in cytokine expression, together with a secondary genetic event, are thought to ultimately lead to oncogenic transformation. To address the influence of Tat on lymphoid development in the context of the whole organism, we produced several transgenic mouse lines that express the Tat gene under the control of an actin promoter. We show here that this promoter directs expression to a variety of sites, including spleen, bone marrow, and lymph nodes. Approximately 25% to 30% of the Tat-transgenic population developed enlarged spleens within 1 year after birth. On histological examination, a significant number of spleens from Tat-transgenic mice exhibited malignant lymphoma of B-cell origin. IgG heavy chain rearrangement confirmed the clonal B-cell nature of these lymphoproliferations. In contrast, T-cell receptor genes exhibited a germline (unrearranged) structure. Reverse transcription polymerase chain reaction analysis of transgenic spleens revealed that mRNA encoding cytokines IL-6 and IL-10 was upregulated, suggesting a possible mechanism for the B-cell expansion in vivo.

Evaluation of 9-[(3-18F-fluoro-1-hydroxy-2-propoxy)methyl]guanine ([18F]-FHPG) in vitro and in vivo as a probe for PET imaging of gene incorporation and expression in tumors

Preparation of 9-[(3-18F-fluoro-1-hydroxy-2-propoxy)methyl]-guanine ([18F]-FHPG) for clinical use, and its evaluation as a positron emission tomography (PET) imaging agent for gene incorporation and expression in tumors are reported. In vitro studies in human colon cancer cells, HT-29, transduced with the retroviral vector G1Tk1SvNa and nontransduced (wild type) showed 4, 8, 12, and 15 times higher uptake of the probe in 1, 3, 5, and 7 h, respectively, in transduced cells compared with the controls. In vivo studies in tumor-bearing nude mice demonstrated that the tumor uptake of the radiotracer is three and six-fold higher in 2 and 5 h, respectively, in transduced cells compared with the control cells. These results suggest that [18F]-FHPG is a potential in vivo PET imaging agent for monitoring gene incorporation and expression in gene therapy of cancer.

Msx2 gene dosage influences the number of proliferative osteogenic cells in growth centers of the developing murine skull: a possible mechanism for MSX2-mediated craniosynostosis in humans

Throughout its complex morphogenesis, the vertebrate skull must at once protect the brain and expand to accommodate its growth. A key structural adaptation that allows this dual role is the separation of the bony plates of the skull with sutures, fibrous joints that serve as growth centers and allow the calvarial bones to expand as the brain enlarges. Craniosynostosis, the premature fusion of one or more calvarial bones with consequent abnormalities in skull shape, is a common developmental anomaly that disrupts this process. We found previously that a single amino acid substitution in the homeodomain of the human MSX2 gene is associated with the autosomal dominant disorder craniosynostosis, Boston type. This mutation enhances the affinity of Msx2 for its target sequence, suggesting that the mutation acts by a dominant positive mechanism. Consistent with this prediction, we showed that general overexpression of Msx2 under the control of the broadly expressed CMV promoter causes the calvarial bones to invade the sagittal suture. Here we use tissue-specific overexpression of Msx2 within the calvarial sutures to address the developmental mechanisms of craniosynostosis and skull morphogenesis. We demonstrate that a segment of the Msx2 promoter directs reporter gene expression to subsets of cells within the sutures. In late embryonic and neonatal stages, this promoter is expressed in undifferentiated mesenchymal cells medial to the growing bone. By P4, promoter activity is reduced in the suture, exhibiting a punctate pattern in undifferentiated osteoblastic cells in the outer margin of the osteogenic front. Overexpression of Msx2 under the control of this promoter is sufficient to enhance parietal bone growth into the sagittal suture by P6. This phenotype is preceded by an increase in both the number and the BrdU labeling of osteoblastic cells in the osteogenic fronts of the calvarial bones. These findings suggest that an important early event in MSX2-mediated craniosynostosis in humans is a transient retardation of osteogenic cell differentiation in the suture and a consequent increase in the pool of osteogenic cells.

Targeted inactivation of the coagulation factor IX gene causes hemophilia B in mice

Hemophilia B is a leading target for gene therapy because current therapy is not optimal. Hence, a murine model of factor IX (F. IX) deficiency was generated to develop gene therapy strategies for hemophilia B. A targeting vector was created by replacing a 3.2-kb segment of the gene encompassing the catalytic domain with a phosphoglycerokinase promoter-driven neomycin resistant (neor) gene cassette. The transfected embryonic stem cell clones generated chimeric male mice, and germ line transmission of the inactivated F. IX gene was observed in their offsprings. Southern analysis confirmed the mutant genotype in hemizygous male and carrier female mice. F. IX transcripts were not detected in liver RNA isolated from hemizygous mice, and lower levels of F. IX mRNA were noted in carrier female mice when compared with those of normal litter mates. As expected, the mean F. IX coagulant titer of affected male mice was 2.8 U/dL (n = 10), while the mean F. IX titer of carrier female mice was 35 U/dL (n = 14), compared with 69 U/dL (n = 9) for the normal female mice and 92 U/dL (n = 22) for normal male and female litter mates. Further, the tail bleeding time of hemizygous mice was markedly prolonged (>3 hours) compared with those of normal and carrier female litter mates (15 to 20 minutes). Seven of 19 affected male mice died of exsanguination after tail snipping, and two affected mice died of umbilical cord bleeding. Currently, there are 10 affected mice surviving at 4 months of age. Aside from the factor IX defect, the carrier female and hemizygous male mice had no liver pathology by histologic examination, were fertile, and transmitted the F. IX gene mutation in the expected Mendelian frequency. Taken together, we have generated a F. IX knockout mouse for evaluation of novel gene therapy strategies for hemophilia B.

Capture and expansion of bone marrow-derived mesenchymal progenitor cells with a transforming growth factor-beta1-von Willebrand's factor fusion protein for retrovirus-mediated delivery of coagulation factor IX

Mesenchymal stem cells give rise to the progenitors of many differentiated phenotypes, including osteocytes, chrondocytes, myocytes, adipocytes, fibroblasts, and marrow stromal cells, which are capable of self-renewal and undergo expansion in the presence of transforming growth factor-beta1 (TGF-beta1). The present study was designed to test the concept that mesenchymal progenitor cells could be selected and expanded by virtue of their intrinsic physiologic responses to TGF-beta1. Human bone marrow aspirates were initially cultured, under low serum conditions, in collagen pads or gels impregnated with a genetically engineered TGF-beta1 fusion protein bearing an auxiliary von Willebrand's factor-derived collagen-binding domain (TGF-beta1-vWF). Histologic examination of TGF-beta1-vWF-supplemented collagen pads from 8-day cultures revealed the selective survival of a population of mononuclear blastoid cells. The TGF-beta-responsive cells were expanded to form stromal/fibroblastic colonies by serum reconstitution, and further to form osteogenic colonies upon supplementation with osteoinductive factors. In comparative studies, both marrow-derived progenitor cells and mature stromal cells were transduced with a retroviral vector bearing a human factor IX construct. Both the transduced progenitor cells and mature stromal cells expressed the factor IX transgene at levels comparable to those reported for human fibroblasts. Transplantation of murine progenitor cells bearing the human factor IX vector into syngeneic B6CBA mice resulted in detectable circulating levels of the human factor IX antigen. Taken together, these data demonstrate a novel physiologic approach for the selection of mesenchymal precursor cells followed by mitotic expansion, transduction, and transplantation of these progenitor cells with retroviral vectors bearing therapeutic genes.

Induction of (omega-1)-oxidation of monocarboxylic acids by acetylsalicylic acid

Monocarboxylic acids may be oxidized at the omega- and (omega-1)- positions to form dicarboxylic acids (DCAs) and (omega-1)-hydroxy- or (omega-1)-oxoacids. The significance of this pathway under normal conditions is unknown, but DCAs and (omega-1)-hydroxyacids are prominent features of disease states. The stimulation of this pathway has been linked to induction of fatty acid-binding protein and peroxisomal proliferation. In this study, we examined the effect of acetylsalicylic acid (ASA) on (omega-1)-oxidation. (Omega-1)-oxidation was assessed in subcellular fractions of rat liver. Rats were fed a normal diet or an ASA-supplemented diet. Products were identified by gas chromatography-mass spectrometry (GC-MS) and by comparison with the properties of authentic synthetic standards. Doses of ASA that produced relatively low serum concentrations (12-24 mg/dl) resulted in as much as a 20-fold increase in the capacity for (omega-1)-oxidation of medium (C12-C15) and long chain (C16-C20) monocarboxylic acids. Normal rat liver oxidizes monocarboxylic acids to (omega-1)-oxoacids, while liver from ASA-treated rats converts these substrates to (omega-1)-oxodicarboxylic acids and (omega-1)-oxoacids. The formation of oxoacids and oxodicarboxylic acids may be due to different enzymes. The formation of oxodicarboxylic acids appears to be more labile than the formation of oxoacids. These two processes also are differentially induced by ASA and have different substrate specificities. These results demonstrate that ASA is a potent stimulant of (omega-1)-oxidation and induces the formation of products that can be shortened in peroxisomes to key metabolic intermediates.

Induction of omega-oxidation of monocarboxylic acids in rats by acetylsalicylic acid

The accumulation of dicarboxylic acids, particularly long chain, is a prominent feature of Reye's syndrome and diseases of peroxisomal metabolism. We assessed the omega-oxidation of a spectrum of fatty acids in rats and asked whether pretreatment of rats with aspirin, which is known to predispose children to Reye's syndrome, would affect omega-oxidation of long chain fatty acids. We found that aspirin increased liver free fatty acids and increased the capacity for omega-oxidation three- to sevenfold. Omega-oxidation of long chain substrate was stimulated to a greater degree than medium chain substrate and was apparent within one day of treatment, at serum aspirin concentrations below the therapeutic range in humans. The apparent Km for lauric acid was 0.9 microM and 12 microM for palmitate. We also found a difference in the storage stability of activity toward medium and long chain substrate. Saturating concentrations of palmitate had no effect on the formation of dodecanedioic acid, whereas laurate decreased but never eliminated the omega-oxidation of palmitate. 97% of the total laurate omega-oxidative activity recovered was found in the microsomes, but 32% of palmitate omega-oxidative activity was present in the cytosol. These results demonstrate that aspirin is a potent stimulator of omega-oxidation and suggest that there may be multiple enzymes for omega-oxidation with overlapping substrate specificity.

Induction of carboxymethylcellulase in Macrophomina phaseolina

Macrophomina phaseolina, the well-known jute pathogenic fungus produces very low levels of both extra- and intracellular carboxymethylcellulase even in the absence of any cellulose as carbon source in the medium. However, the production of these enzymes is greatly induced by soluble carboxymethylcellulose. The carboxymethylcellulase in M. phaseolina is repressed by glucose.