Fibulin-1c regulates transforming growth factor-β activation in pulmonary tissue fibrosis

Tissue remodeling/fibrosis is a major feature of all fibrotic diseases, including idiopathic pulmonary fibrosis (IPF). It is underpinned by accumulating extracellular matrix (ECM) proteins. Fibulin-1c (Fbln1c) is a matricellular ECM protein associated with lung fibrosis in both humans and mice, and stabilizes collagen formation. Here we discovered that Fbln1c was increased in the lung tissues of IPF patients and experimental bleomycin-induced pulmonary fibrosis. Fbln1c-deficient (-/-) mice had reduced pulmonary remodeling/fibrosis and improved lung function after bleomycin challenge. Fbln1c interacted with fibronectin, periostin and tenascin-c in collagen deposits following bleomycin challenge. In a novel mechanism of fibrosis Fbln1c bound to latent transforming growth factor (TGF)-β binding protein-1 (LTBP1) to induce TGF-β activation, and mediated downstream Smad3 phosphorylation/signaling. This process increased myofibroblast numbers and collagen deposition. Fbln1 and LTBP1 co-localized in lung tissues from IPF patients. Thus, Fbln1c may be a novel driver of TGF-β-induced fibrosis involving LTBP1 and may be an upstream therapeutic target.

Airway remodelling and inflammation in asthma are dependent on the extracellular matrix protein fibulin-1c

Asthma is a chronic inflammatory disease of the airways. It is characterized by allergic airway inflammation, airway remodelling, and airway hyperresponsiveness (AHR). Asthma patients, in particular those with chronic or severe asthma, have airway remodelling that is associated with the accumulation of extracellular matrix (ECM) proteins, such as collagens. Fibulin-1 (Fbln1) is an important ECM protein that stabilizes collagen and other ECM proteins. The level of Fbln1c, one of the four Fbln1 variants, which predominates in both humans and mice, is increased in the serum and airways fluids in asthma but its function is unclear. We show that the level of Fbln1c was increased in the lungs of mice with house dust mite (HDM)-induced chronic allergic airway disease (AAD). Genetic deletion of Fbln1c and therapeutic inhibition of Fbln1c in mice with chronic AAD reduced airway collagen deposition, and protected against AHR. Fbln1c-deficient (Fbln1c^-/- ) mice had reduced mucin (MUC) 5 AC levels, but not MUC5B levels, in the airways as compared with wild-type (WT) mice. Fbln1c interacted with fibronectin and periostin that was linked to collagen deposition around the small airways. Fbln1c^-/- mice with AAD also had reduced numbers of α-smooth muscle actin-positive cells around the airways and reduced airway contractility as compared with WT mice. After HDM challenge, these mice also had fewer airway inflammatory cells, reduced interleukin (IL)-5, IL-13, IL-33, tumour necrosis factor (TNF) and CXCL1 levels in the lungs, and reduced IL-5, IL-33 and TNF levels in lung-draining lymph nodes. Therapeutic targeting of Fbln1c reduced the numbers of GATA3-positive Th2 cells in the lymph nodes and lungs after chronic HDM challenge. Treatment also reduced the secretion of IL-5 and IL-13 from co-cultured dendritic cells and T cells restimulated with HDM extract. Human epithelial cells cultured with Fbln1c peptide produced more CXCL1 mRNA than medium-treated controls. Our data show that Fbln1c may be a therapeutic target in chronic asthma. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Fibulin-1 regulates the pathogenesis of tissue remodeling in respiratory diseases

Airway and/or lung remodeling, involving exaggerated extracellular matrix (ECM) protein deposition, is a critical feature common to pulmonary diseases including chronic obstructive pulmonary disease (COPD), asthma, and idiopathic pulmonary fibrosis (IPF). Fibulin-1 (Fbln1), an important ECM protein involved in matrix organization, may be involved in the pathogenesis of these diseases. We found that Fbln1 was increased in COPD patients and in cigarette smoke-induced (CS-induced) experimental COPD in mice. Genetic or therapeutic inhibition of Fbln1c protected against CS-induced airway fibrosis and emphysema-like alveolar enlargement. In experimental COPD, this occurred through disrupted collagen organization and interactions with fibronectin, periostin, and tenascin-c. Genetic inhibition of Fbln1c also reduced levels of pulmonary inflammatory cells and proinflammatory cytokines/chemokines (TNF-α, IL-33, and CXCL1) in experimental COPD. Fbln1c^-/- mice also had reduced airway remodeling in experimental chronic asthma and pulmonary fibrosis. Our data show that Fbln1c may be a therapeutic target in chronic respiratory diseases.

Expression of V3 Versican by Rat Arterial Smooth Muscle Cells Promotes Differentiated and Anti-inflammatory Phenotypes

Arterial smooth muscle cells (ASMCs) undergo phenotypic changes during development and pathological processes in vivo and during cell culture in vitro. Our previous studies demonstrated that retrovirally mediated expression of the versican V3 splice variant (V3) by ASMCs retards cell proliferation and migration in vitro and reduces neointimal thickening and macrophage and lipid accumulation in animal models of vascular injury and atherosclerosis. However, the molecular pathways induced by V3 expression that are responsible for these changes are not yet clear. In this study, we employed a microarray approach to examine how expression of V3 induced changes in gene expression and the molecular pathways in rat ASMCs. We found that forced expression of V3 by ASMCs affected expression of 521 genes by more than 1.5-fold. Gene ontology analysis showed that components of the extracellular matrix were the most significantly affected by V3 expression. In addition, genes regulating the formation of the cytoskeleton, which also serve as markers of contractile smooth muscle cells (SMCs), were significantly up-regulated. In contrast, components of the complement system, chemokines, chemokine receptors, and transcription factors crucial for regulating inflammatory processes were among the genes most down-regulated. Consistently, we found that the level of myocardin, a key transcription factor promoting contractile SMC phenotype, was greatly increased, and the proinflammatory transcription factors NFκB1 and CCAAT/enhancer-binding protein β were significantly attenuated in V3-expressing SMCs. Overall, these findings demonstrate that V3 expression reprograms ASMCs promoting differentiated and anti-inflammatory phenotypes.

Fibulin-1 suppresses endothelial to mesenchymal transition in the proximal outflow tract

Endothelial to mesenchymal transition (EMT) that occurs during cardiac outflow tract (OFT) development is critical for formation of the semilunar valves. Fibulin-1 (Fbln1) is an extracellular matrix protein that is present at several sites of EMT, including the OFT (i.e., E9.5-10.5). The aim of this study was to determine the role of Fbln1 in EMT during the earliest events of OFT development. Examination of proximal OFT cushions in Fbln1 null embryos detected hypercellularity at both E9.5 (93% increase; p = 0.002) and E10.5 (43% increase; p = 0.01) as compared to wild type, suggesting that Fbln1 normally suppresses OFT endocardial cushion EMT. This was supported by studies of proximal OFT cushion explants, which showed that explants from Fbln1 null embryos displayed a 58% increase in cells migrating from the explants as compared to wild type (p = 0.005). We next evaluated the effects of Fbln1 deficiency on the expression of factors that regulate proximal OFT EMT. At E9.5, Fbln1 null proximal OFT endocardium and EMT-derived mesenchyme showed increased TGFβ2 (58% increase; p = 0.01) and increased Snail1-positive nuclei (27% increase; p = 0.0003). Histological examination of OFT cushions in Fbln1 null embryos (E9.5) also detected cells present in the cushion that were determined to be erythrocytes based on round morphology, autofluorescence, and positive staining for hemoglobin. Erythrocytes were also detected in Fbln1 null OFT cushions at E10.5. Together, the findings indicate that Fbln1 normally suppresses proximal OFT EMT preventing proximal cushion hypercellularity and blood cell accumulation.

Fibulin-1 is required for bone formation and Bmp-2-mediated induction of Osterix

The extracellular matrix protein Fibulin-1 (Fbln1) has been shown to be involved in numerous processes including cardiovascular and lung development. Here we have examined the role of Fbln1 in bone formation. Alizarin red staining of skulls from Fbln1-deficient mice showed reduced mineralization of both membranous and endochondral bones. MicroCT (μCT) analysis of the calvarial bones (i.e., frontal, parietal and interparietal bones collectively) indicated that bone volume in Fbln1 nulls at neonatal stage P0 were reduced by 22% (p=0.015). Similarly, Fbln1 null frontal bones showed a 16% (p=0.035) decrease in bone volume, with a reduction in the interfrontal bone, and a discontinuity in the leading edge of the frontal bone. To determine whether Fbln1 played a role in osteoblast differentiation during bone formation, qPCR was used to measure the effects of Fbln1 deficiency on the expression of Osterix (Osx), a transcription factor essential for osteoblast differentiation. This analysis demonstrated that Osx mRNA was significantly reduced in Fbln1-deficient calvarial bones at developmental stages E16.5 (p=0.049) and E17.5 (p=0.022). Furthermore, the ability of Bmp-2 to induce Osx expression was significantly diminished in Fbln1-deficient mouse embryo fibroblasts. Together, these findings indicate that Fbln1 is a new positive modulator of the formation of membranous bone and endochondral bone in the skull, acting as a positive regulator of Bmp signaling.

Low-dose spironolactone reduces plasma fibulin-1 levels in patients with type 2 diabetes and resistant hypertension

Diabetic patients with hypertension are at particularly high risk of vascular damage and consequently cardiovascular and renal disease. Fibulin-1, an extracellular matrix glycoprotein, is increased in arterial tissue and plasma from individuals with type 2 diabetes. This study aimed to evaluate whether antihypertensive treatment with spironolactone changes plasma fibulin-1 levels. In a multicenter, double-blind, randomized, placebo-controlled study, 119 patients with type 2 diabetes and resistant hypertension were included. A dose of spironolactone 25 mg or matching placebo was added to previous treatment at randomization. Blood pressure (BP) and plasma fibulin-1 were measured at baseline and at 16 weeks follow-up. Overall, 112 patients completed the study. All measures of BP were reduced in the spironolactone group at follow-up. Plasma fibulin-1 was significantly reduced after spironolactone treatment (P=0.009), but increased after placebo (P=0.017). Baseline plasma fibulin-1 correlated with BP and estimated glomerular filtration rate. Increased levels of plasma fibulin-1 (P=0.004) were observed in diabetic participants reporting erectile dysfunction as compared with participants who did not. Treatment with low-dose spironolactone reduced plasma fibulin-1 levels in patients with type 2 diabetes and resistant hypertension. This supports the hypothesis that the antihypertensive effect of the mineralocorticoid receptor blocker in part may be due to regression of vascular remodeling.

Helicobacter pylori-induced posttranscriptional regulation of H-K-ATPase α-subunit gene expression by miRNA

Acute Helicobacter pylori infection of gastric epithelial cells induces CagA oncoprotein- and peptidoglycan (SLT)-dependent mobilization of NF-κB p50 homodimers that bind to H-K-ATPase α-subunit (HKα) promoter and repress HKα gene transcription. This process may facilitate gastric H. pylori colonization by induction of transient hypochlorhydria. We hypothesized that H. pylori also regulates HKα expression posttranscriptionally by miRNA interaction with HKα mRNA. In silico analysis of the HKα 3' untranslated region (UTR) identified miR-1289 as a highly conserved putative HKα-regulatory miRNA. H. pylori infection of AGS cells transfected with HKα 3' UTR-Luc reporter construct repressed luciferase activity by 70%, whereas ΔcagA or Δslt H. pylori infections partially abrogated repression. Transfection of AGS cells expressing HKα 3' UTR-Luc construct with an oligoribonucleotide mimetic of miR-1289 induced maximal repression (54%) of UTR activity within 30 min; UTR activity was unchanged by nontargeting siRNA transfection. Gastric biopsies from patients infected with cagA(+) H. pylori showed a significant increase in miR-1289 expression compared with uninfected patients or those infected with cagA(-) H. pylori. Finally, miR-1289 expression was necessary and sufficient to attenuate biopsy HKα protein expression in the absence of infection. Taken together, these data indicate that miR-1289 is upregulated by H. pylori in a CagA- and SLT-dependent manner and targets HKα 3' UTR, affecting HKα mRNA translation. The sensitivity of HKα mRNA 3' UTR to binding of miR-1289 identifies a novel regulatory mechanism of gastric acid secretion and offers new insights into mechanisms underlying transient H. pylori-induced hypochlorhydria.

Metformin, but not rosiglitazone, attenuates the increasing plasma levels of a new cardiovascular marker, fibulin-1, in patients with type 2 diabetes

OBJECTIVE The extracellular matrix protein fibulin-1 is upregulated in the arterial wall in type 2 diabetes (T2D) and circulates in increased concentrations in diabetes. Metformin is an antidiabetic drug with beneficial cardiovascular disease effects in diabetes. We hypothesized that metformin would influence the increased level of plasma fibulin-1 in diabetes. RESEARCH DESIGN AND METHODS After a 4-week run-in period, 371 eligible patients with T2D were randomized to treatment groups in a factorial design including insulin alone (control), +metformin, +rosiglitazone, or +both metformin and rosiglitazone. Plasma fibulin-1 was analyzed at the beginning of the study and after 18 and 24 months. RESULTS Plasma fibulin-1 increased in all groups throughout the 2-year period; however, the increase was strongly attenuated among patients treated with metformin. A highly significant difference was observed when the mean change in plasma fibulin-1 was compared between metformin- and non-metformin-treated individuals both at 18 and 24 months of treatment, but rosiglitazone had no effect. Metformin and rosiglitazone alone reduced the HbA1c levels to comparable levels and in combination even further. CONCLUSIONS Metformin attenuates the increase in plasma fibulin-1 concentrations in T2D, independently of glycemic effects. Changes in fibulin-1 may reflect an important element in diabetic arteriopathy that can be influenced by metformin.

Cubilin maintains blood levels of HDL and albumin

Cubilin is an endocytic receptor highly expressed in renal proximal tubules, where it mediates uptake of albumin and filtered forms of apoA-I/HDL. Cubilin deficiency leads to urinary loss of albumin and apoA-I; however, the consequences of cubilin loss on the homeostasis of blood albumin and apoA-I/HDL have not been studied. Using mice heterozygous for cubilin gene deletion (cubilin HT mice), we show that cubilin haploinsufficiency leads to reduced renal proximal tubular uptake of albumin and apoA-I and significantly increased urinary loss of albumin and apoA-I. Moreover, cubilin HT mice displayed significantly decreased blood levels of albumin, apoA-I, and HDL. The levels of albumin and apoA-I protein or mRNA expressed in the liver, kidney, or intestine of cubilin HT mice did not change significantly. The clearance rate of small HDL3 particles (density>1.13 g/ml) from the blood increased significantly in cubilin HT mice. In contrast, the rate of clearance of larger HDL2 particles from the blood did not change significantly, indicating a decreased half-life for HDL particles capable of filtering through the glomerulus. On the basis of these findings, we conclude that cubilin deficiency reduces renal salvage and delivery back to the blood of albumin and apoA-I, which decreases blood levels of albumin and apoA-I/HDL. These findings raise the possibility that therapeutic increase of renal cubilin expression might reduce proteinuria and increase blood levels of albumin and HDL.

Elevated transferrin saturation, health-related quality of life and telomere length

We sought to examine the relationship between elevated transferrin saturation (TS) and measures of health status (telomere length and patient-reported health-related quality of life) to assess whether elevated TS is associated with negative patient outcomes beyond increased risk for morbidity and mortality, using a cross-sectional analysis of the Hemochromatosis and Iron Overload Screening Study supplemented with assays for leukocyte telomere length in adults ≥25 years old (n = 669). Among individuals with elevated TS (≥45 % for women and ≥50 % for men), who also had a usual source of care, only 5.2 % reported ever being told by a doctor that they had an elevated iron condition. In a fully adjusted general linear regression model controlling for demographic characteristics as well as health conditions associated with iron overload, elevated TS versus non-elevated TS was associated with worse general health status (60.4 vs. 63.8, P < 0.05), mental health status (76.5 vs. 82.2, P < 0.0001) and shorter telomere length (241.4 vs. 261.3, P < 0.05). Increased surveillance of elevated TS may be in order as elevated TS is associated with decreased health status and very few patients with elevated TS are aware of their condition.

Aortic valve stenosis and atrial fibrillation influence plasma fibulin-1 levels in patients treated with coronary bypass surgery

OBJECTIVES

Aortic valve stenosis (AS) causes cardiac fibrosis and left ventricular hypertrophy, and over time heart failure can occur. To date, a reliable marker to predict progression of AS or the development of heart failure is still lacking. In this study, we addressed the hypothesis that fibulin-1 levels reflect myocardial fibrosis.

METHODS

Patients undergoing heart surgery at the Odense University were investigated. By 2012 data on outcome were obtained.

RESULTS

In 293 patients, plasma fibulin-1 levels were measured. Patients with AS or atrial fibrillation (AF) had significantly higher fibulin-1 levels compared to those with coronary artery disease only (p = 0.005). Patients with preoperatively diagnosed chronic AF had significantly higher levels of fibulin-1 compared to those without (p = 0.004). Plasma fibulin-1 levels showed no relationship to echocardiographic size and had no impact on outcome, death or other adverse events.

CONCLUSION

This study shows that plasma fibulin-1 levels are increased in patients with AS and AF compared to patients with coronary disease only. Our study results suggest fibulin-1, a vascular extracellular matrix (ECM) protein, as a marker of ECM turnover perhaps due to the increased myocardial stretch that is related to pressure overload.

Abstract 291: Fibulin-1 is Required to Prevent Hypoplastic Semilunar Valve Formation

Fibulin-1 (Fbln1), an extracellular matrix protein, is prominently expressed during outflow tract (OFT) morphogenesis as a component of both the endocardial cushions and OFT valves. Here we sought to investigate the role of Fbln1 in the process of OFT valvulogenesis. Since Fbln1 null mice die perinatally, we first evaluated the effects of Fbln1 deficiency on OFT valve morphology in hearts of embryos at E17.5. Morphometric analysis of 3D reconstructions revealed that in Fbln1 nulls the volume of the anterior leaflet of the pulmonary valve, and the left and non-coronary leaflets of the aortic valve were significantly reduced as compared to wild type (WT) (30-40% reduction; WT n=6, null n=8; p<0.05). The reduced leaflet size correlated with decreased leaflet cell numbers (45%, 30% and 30% respectively; p<0.05). TUNEL and BrdU analysis showed no difference between E17.5 WT and Fbln1 null OFT valves. To determine when abnormalities of OFT valve leaflet cell numbers first occurs, OFT endocardial cushions and prevalvular mesenchyme from E10.5-14.5 null and WT embryos were analyzed. At E10.5, the proximal OFT cushions of Fbln1 nulls were hypercellular (34% increase; p<0.05; n=5 for each genotype) whereas cellularity of distal cushions was not different from WT (p= 0.49). The fact that the ratio of proximal OFT cushion mesenchymal cells to endothelial cells was increased in E10.5 Fbln1 null cushions suggests that alteration in EMT might contribute to the hypercellularity. At E12.5, cellularity of the proximal OFT cushions was observed to decrease by 35% (p<0.05; WT n=4; null n=4). This was accompanied by a 172% increase in apoptosis, with no alteration in the level of proliferation (p<0.05; WT n=3; null n=4). Decreased cellularity and increased apoptosis persisted in the OFT prevalvular mesenchyme of Fbln1 nulls at E14.5 (p<0.05; WT n=2; null n=2). Taken together, Fbln1 specifically regulates cellularization of the proximal endocardial cushion and prevalvular mesenchyme. Mechanistically, Fbln1 may act as a suppressor of cushion EMT and indirectly or directly as an inhibitor of apoptosis.

Plasma levels of the arterial wall protein fibulin-1 are associated with carotid-femoral pulse wave velocity: a cross-sectional study

BACKGROUND

The arterial system in diabetic patients is characterized by generalized non-atherosclerotic alterations in the vascular extracellular matrix causing increased arterial stiffness compared with subjects without diabetes. The underlying pathophysiology remains elusive. The elastin-associated extracellular matrix protein, fibulin-1, was recently found in higher concentrations in the arterial wall and in plasma in patients with long duration type 2 diabetes. Furthermore, plasma fibulin-1 independently predicted total mortality and was associated with pulse pressure, an indirect measure of arterial stiffness. Whether plasma fibulin-1 is associated with arterial stiffness at earlier phases of type 2 diabetes has not been determined.

METHODS

In this cross-sectional study, we examined 90 patients with recently diagnosed type 2 diabetes (< 5 years) and 90 gender- and age-matched controls. Plasma fibulin-1 was measured immunochemically. Arterial stiffness was assessed by carotid-femoral Pulse Wave Velocity (PWV). Differences in means were assessed by t-tests. Associations were assessed by multivariate regression analyses.

RESULTS

Plasma fibulin-1 levels were lower in the diabetic group compared with the control group, 93 ± 28 vs 106 ± 30 μg/mL, p = 0.005. In unadjusted analysis of the total study sample, plasma fibulin-1 was not associated with PWV, p = 0.46. However, with adjustment for the confounders age, gender, mean blood pressure, heart rate, body mass index, diabetes and glomerular filtration rate, a 10 μg/mL increase in plasma fibulin was associated with 0.09 ± 0.04 m/s increase in PWV, p < 0.05. In subgroup analysis, plasma fibulin-1 was associated with PWV in the diabetes group, (0.16 ± 0.07 m/s increase in PWV per 10 μg/mL increase in plasma fibulin-1, p<0.05), but not controls, β = 0.021 ± 0.057 m/s per 10 μg/mL, p = 0.70. The association remained significant in the diabetes group after adjustment for covariates, p < 0.05.

CONCLUSIONS

Plasma fibulin-1 is independently associated with PWV. Yet, as the plasma level of fibulin-1 was lower in patients with recently diagnosed type 2 diabetes than in healthy controls, plasma fibulin-1 levels are not a simple marker of the degree of arterial stiffening. Further studies are needed to determine the exact role of fibulin-1 in arterial stiffness and cardiovascular risk in patients with type 2 diabetes.

Cubilin expression is monoallelic and epigenetically augmented via PPARs

Background

Cubilin is an endocytic receptor that is necessary for renal and intestinal absorption of a range of ligands. Endocytosis mediated by cubilin and its co-receptor megalin is the principal mechanism for proximal tubule reabsorption of proteins from the glomerular filtrate. Cubilin is also required for intestinal endocytosis of intrinsic factor-vitamin B₁₂ complex. Despite its importance, little is known about the regulation of cubilin expression.

Results

Here we show that cubilin expression is under epigenetic regulation by at least two processes. The first process involves inactivation of expression of one of the cubilin alleles. This monoallelic expression state could not be transformed to biallelic by inhibiting DNA methylation or histone deacetylation. The second process involves transcriptional regulation of cubilin by peroxisome proliferator-activated receptor (PPAR) transcription factors that are themselves regulated by DNA methylation and histone deacetylation. This is supported by findings that inhibitors of DNA methylation and histone deacetylation, 5Aza and TSA, increase cubilin mRNA and protein in renal and intestinal cell lines. Not only was the expression of PPARα and γ inducible by 5Aza and TSA, but the positive effects of TSA and 5Aza on cubilin expression were also dependent on both increased PPAR transcription and activation. Additionally, 5Aza and TSA had similar effects on the expression of the cubilin co-receptor, megalin.

Conclusions

Together, these findings reveal that cubilin and megalin mRNA expression is under epigenetic control and thus point to new avenues for overcoming pathological suppression of these genes through targeting of epigenetic regulatory processes.

Telomere length and elevated iron: the influence of phenotype and HFE genotype

Elevated body iron stores are associated with morbidity and mortality due to oxidative stress. Hereditary hemochromatosis, a common condition caused by HFE gene mutations, can lead to excess iron storage and disease but clinical penetrance of HFE gene mutations is low and many people with elevated iron stores lack HFE mutations. We analyzed data from the Hemochromatosis and Iron Overload Screening Study to assess the relationship among HFE genotype (individuals with either homozygous or compound heterozygous status for C282Y and/or H63D HFE mutations were defined as genotype positive, or G+), elevated iron phenotype (individuals exceeding gender-specific transferrin saturation and serum ferritin threshold levels were considered phenotype positive, or P+), and leukocyte telomere length, a marker of biological aging and cumulative oxidative stress. In unadjusted analyses in comparison to individuals who were G-P-, G+P- were not significantly different (OR 0.74; 95% CI 0.26-2.04), while the G+P+ (OR 2.03; 95% CI 1.15-3.56), and G-P+ (OR 2.24; 95% CI 1.5-3.29) had increased risk of short telomeres (<=25th percentile) rather than long telomeres (>=75th percentile). In analyses adjusting for age, gender, and race/ethnicity, the effect of individuals with elevated iron phenotypes having short telomeres persisted with G+P+ individuals (OR 1.94; 95% CI 1.02-3.72), and G-P+ individuals (OR 2.17; 95% CI 1.39-3.39) being significantly different from the G-P- group. In conclusion, elevated iron phenotype, but not HFE genotype, was associated with shortened telomeres. Further studies will be needed to determine whether telomere length provides a marker for morbidities specifically associated with iron overload.

A cytokine axis regulates elastin formation and degradation

Underlying the dynamic regulation of tropoelastin expression and elastin formation in development and disease are transcriptional and post-transcriptional mechanisms that have been the focus of much research. Of particular importance is the cytokine-governed elastin regulatory axis in which the pro-elastogenic activities of transforming growth factor β-1 (TGFβ1) and insulin-like growth factor-I (IGF-I) are opposed by anti-elastogenic activities of basic fibroblast growth factor (bFGF/FGF-2), heparin-binding epidermal growth factor-like growth factor (HB-EGF), EGF, PDGF-BB, TGFα, tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β and noncanonical TGFβ1 signaling. A key mechanistic feature of the regulatory axis is that cytokines influence elastin formation through effects on the cell cycle involving control of cyclin-cyclin dependent kinase complexes and activation of the Ras/MEK/ERK signaling pathway. In this article we provide an overview of the major cytokines/growth factors that modulate elastogenesis and describe the underlying molecular mechanisms for their action on elastin production.

Plasma concentrations of extracellular matrix protein fibulin-1 are related to cardiovascular risk markers in chronic kidney disease and diabetes

BACKGROUND

Fibulin-1 is one of a few extracellular matrix proteins present in blood in high concentrations. We aimed to define the relationship between plasma fibulin-1 levels and risk markers of cardiovascular disease.

METHODS

Plasma fibulin-1 was determined in subjects with chronic kidney disease (n = 32; median age 62.5, inter-quartile range 51 - 73 years) and 60 age-matched control subjects. Among kidney disease patients serological biomarkers related to cardiovascular disease (fibrinogen, interleukin 6, C-reactive protein) were measured. Arterial applanation tonometry was used to determine central hemodynamic and arterial stiffness indices.

RESULTS

We observed a positive correlation of fibulin-1 levels with age (r = 0.38; p = 0.033), glycated hemoglobin (r = 0.80; p = 0.003), creatinine (r = 0.35; p = 0.045), and fibrinogen (r = 0.39; p = 0.027). Glomerular filtration rate and fibulin-1 were inversely correlated (r = -0.57; p = 0.022). There was a positive correlation between fibulin-1 and central pulse pressure (r = 0.44; p = 0.011) and central augmentation pressure (r = 0.55; p = 0.001). In a multivariable regression model, diabetes, creatinine, fibrinogen and central augmentation pressure were independent predictors of plasma fibulin-1.

CONCLUSION

Increased plasma fibulin-1 levels were associated with diabetes and impaired kidney function. Furthermore, fibulin-1 levels were associated with hemodynamic cardiovascular risk markers. Fibulin-1 is a candidate in the pathogenesis of cardiovascular disease observed in chronic kidney disease and diabetes.

Sphingosine 1-phosphate (S1P) carrier-dependent regulation of endothelial barrier: high density lipoprotein (HDL)-S1P prolongs endothelial barrier enhancement as compared with albumin-S1P via effects on levels, trafficking, and signaling of S1P1

Sphingosine 1-phosphate (S1P) is a blood-borne lysosphingolipid that acts to promote endothelial cell (EC) barrier function. In plasma, S1P is associated with both high density lipoproteins (HDL) and albumin, but it is not known whether the carriers impart different effects on S1P signaling. Here we establish that HDL-S1P sustains EC barrier longer than albumin-S1P. We showed that the sustained barrier effects of HDL-S1P are dependent on signaling by the S1P receptor, S1P1, and involve persistent activation of Akt and endothelial NOS (eNOS), as well as activity of the downstream NO target, soluble guanylate cyclase (sGC). Total S1P1 protein levels were found to be higher in response to HDL-S1P treatment as compared with albumin-S1P, and this effect was not associated with increased S1P1 mRNA or dependent on de novo protein synthesis. Several pieces of evidence indicate that long term EC barrier enhancement activity of HDL-S1P is due to specific effects on S1P1 trafficking. First, the rate of S1P1 degradation, which is proteasome-mediated, was slower in HDL-S1P-treated cells as compared with cells treated with albumin-S1P. Second, the long term barrier-promoting effects of HDL-S1P were abrogated by treatment with the recycling blocker, monensin. Finally, cell surface levels of S1P1 and levels of S1P1 in caveolin-enriched microdomains were higher after treatment with HDL-S1P as compared with albumin-S1P. Together, the findings reveal S1P carrier-specific effects on S1P1 and point to HDL as the physiological mediator of sustained S1P1-PI3K-Akt-eNOS-sGC-dependent EC barrier function.

Plasma fibulin-1 is linked to restrictive filling of the left ventricle and to mortality in patients with aortic valve stenosis

BACKGROUND

Plasma fibulin-1 levels have been associated with N-terminal pro-B-type natriuretic peptide levels and left atrial size and shown to be predictive of mortality in patients with diabetes. The mechanisms behind these connections are not fully understood but are probably related to its roles as an extracellular matrix protein in cardiovascular tissues.

METHODS AND RESULTS

One hundred twenty-five patients with severe aortic stenosis who were scheduled for aortic valve replacement (AVR) were evaluated with preoperative echocardiography and their plasma fibulin-1 levels were determined with ELISA. The cohort was followed for a median of 4 years after AVR. Increased restrictive left ventricular (LV) filling pattern was observed with increased plasma fibulin-1 levels (2% versus 29% versus 24% in low, middle, and high plasma fibulin-1 tertile groups, P=0.004). Likewise, reduced longitudinal systolic LV function (6.6 ± 1.1 versus 6.1 ± 1.3 versus 5.7 ± 1.5 cm/s, P=0.05) and increased LV filling pressures was systolic velocity of the mitral annulus observed with increasing plasma fibulin-1 concentrations (ratio of early transmitral flow velocity to early diastolic flow velocity of the mitral annulus 13 ± 4 versus 15 ± 5 versus 16 ± 6 in the fibulin-1 tertile groups, P=0.04).

CONCLUSIONS

In patients with symptomatic severe aortic stenosis undergoing AVR, plasma fibulin-1 is associated with restrictive filling of the LV, decreased longitudinal systolic function of the LV, and increased LV filling pressures.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrial.gov with Identifier: NCT00294775.

Reduction in postoperative high-density lipoprotein cholesterol levels in children undergoing the Fontan operation

Despite the emerging relevance of high-density lipoprotein (HDL) in the inflammatory cascade and vascular barrier integrity, HDL levels in children undergoing cardiac surgery are unexplored. As a measure of HDL levels, the HDL-cholesterol (HDL-C) in single-ventricle patients was quantified before and after the Fontan operation, and it was determined whether relationships existed between the duration and the type of postoperative pleural effusions. The study prospectively enrolled 12 children undergoing the Fontan operation. Plasma HDL-C levels were measured before and after cardiopulmonary bypass. The outcome variables of interest were the duration and type of chest tube drainage (chylous vs. nonchylous). The Kendall rank correlation coefficient and the Wilcoxon rank sum test were used. There were 11 complete observations. The median preoperative HDL-C level for all the subjects was 30 mg/dl (range, 24-53 mg/dl), and the median postcardiopulmonary bypass level was 21 mg/dl (range, 14-46 mg/dl) (p = 0.004). There was a tendency toward a moderate inverse correlation (-0.42) between the postcardiopulmonary bypass HDL-C level and the duration of chest tube drainage, but the result was not statistically significant (p = 0.07). In the chylous effusion group, the median postcardiopulmonary bypass HDL-C tended to be lower (16 vs. 23 mg/dl; p = 0.09). After the Fontan operation, the plasma HDL-C levels in children are significantly reduced. It is reasonable to conclude that the reduction in HDL-C reflects reduced plasma levels of HDL particles, which may have pertinent implications in postoperative pleural effusions given the antiinflammatory and endothelial barrier functions of HDL.

NT-proBNP is associated with fibulin-1 in Africans: the SAfrEIC study

OBJECTIVES

The N-terminal prohormone B-type natriuretic peptide (NT-proBNP) is involved in the regulation of volume load and secreted when systemic cardiac overload occurs. Fibulin-1 on the other hand is a component of many extracellular matrix proteins including those present in atherosclerotic lesions, expressed in elastin-containing fibres of blood vessels, and also in the heart. Due to an alarming prevalence of hypertensive heart disease in black South Africans, we investigated the associations of NT-proBNP with fibulin-1 and markers of arterial stiffness in Africans and Caucasians.

METHODS

We included 231 Africans and 238 Caucasians from South Africa aged 22-77 years. Serum NT-proBNP and fibulin-1 levels were determined, and arterial compliance and pulse wave velocity were measured.

RESULTS

Africans had significantly higher blood pressure and NT-proBNP levels than Caucasians and African men had higher fibulin-1 levels than Caucasian men. In single regression analysis, NT-proBNP was significantly associated with fibulin-1 in African men and Caucasian women. NT-proBNP correlated negatively with arterial compliance in all groups except Caucasian women. After partial adjustments, the association between NT-proBNP and fibulin-1 strengthened in African men only. After full adjustment in multiple regression analysis, the association of NT-proBNP with fibulin-1 was confirmed in African men (R(2)=0.41; β=0.26; p<0.01) and also in younger women (R(2)=0.34; β=0.251; p=0.012).

CONCLUSIONS

Only Africans indicated a significant independent association between NT-proBNP and fibulin-1, suggesting that cardiovascular alterations are already present in this relatively young African population as opposed to Caucasians.

Fibulin-1 is required during cardiac ventricular morphogenesis for versican cleavage, suppression of ErbB2 and Erk1/2 activation, and to attenuate trabecular cardiomyocyte proliferation

BACKGROUND

Trabeculation is an integral component of cardiac ventricular morphogenesis and is dependent on the matrix metalloproteinase, ADAMTS1. A substrate of ADAMTS1 is the proteoglycan versican which is expressed in the developing ventricle and which has been implicated in trabeculation. Fibulin-1 is a versican and ADAMTS1-binding extracellular matrix protein required for ventricular morphogenesis. Here we investigated the involvement of fibulin-1 in ADAMTS1-mediated cleavage of versican in vitro, and the involvement of fibulin-1 in versican cleavage in ventricular morphogenesis.

RESULTS

We show that fibulin-1 is a cofactor for ADAMTS1-dependent in vitro cleavage of versican V1, yielding a 70-kDa amino-terminal fragment. Furthermore, fibulin-1-deficiency in mice was found to cause a significant reduction (>90%) in ventricular levels of the 70-kDa versican V1 cleavage product and a 2-fold increase in trabecular cardiomyocyte proliferation. Decreased versican V1 cleavage and augmented trabecular cardiomyocyte proliferation in fibulin-1 null hearts is accompanied by increased ventricular activation of ErbB2 and Erk1/2. By contrast, versican deficiency was found to lead to decreased cardiomyocyte proliferation and reduced ventricular trabeculation.

CONCLUSION

We conclude that fibulin-1 regulates versican-dependent events in ventricular morphogenesis by promoting ADAMTS1 cleavage of versican leading to suppression of trabecular cardiomyocyte proliferation mediated by the ErbB2-Map kinase pathway.

S1P, dihydro-S1P and C24:1-ceramide levels in the HDL-containing fraction of serum inversely correlate with occurrence of ischemic heart disease

Background

The lysosphingolipid sphingosine 1-phosphate (S1P) is carried in the blood in association with lipoproteins, predominantly high density lipoproteins (HDL). Emerging evidence suggests that many of the effects of HDL on cardiovascular function may be attributable to its S1P cargo.

Methods

Here we have evaluated how levels of S1P and related sphingolipids in an HDL-containing fraction of human serum correlate with occurrence of ischemic heart disease (IHD). To accomplish this we used liquid chromatography-mass spectrometry to measure S1P levels in the HDL-containing fraction of serum (depleted of LDL and VLDL) from 204 subjects in the Copenhagen City Heart Study (CCHS). The study group consisted of individuals having high serum HDL cholesterol (HDL-C) (females:≥73.5 mg/dL; males:≥61.9 mg/dL) and verified IHD; subjects with high HDL-C and no IHD; individuals with low HDL-C (females:≤38.7 mg/dL; males:≤34.1 mg/dL) and IHD, and subjects with low HDL-C and no IHD.

Results

The results show a highly significant inverse relationship between the level of S1P in the HDL-containing fraction of serum and the occurrence of IHD. Furthermore, an inverse relationship with IHD was also observed for two other sphingolipids, dihydro-S1P and C24:1-ceramide, in the HDL-containing fraction of serum. Additionally, we demonstrated that the amount of S1P on HDL correlates with the magnitude of HDL-induced endothelial cell barrier signaling.

Conclusions

These findings indicate that compositional differences of sphingolipids in the HDL-containing fraction of human serum are related to the occurrence of IHD, and may contribute to the putative protective role of HDL in IHD.

Collective cell motion in endothelial monolayers

Collective cell motility is an important aspect of several developmental and pathophysiological processes. Despite its importance, the mechanisms that allow cells to be both motile and adhere to one another are poorly understood. In this study we establish statistical properties of the random streaming behavior of endothelial monolayer cultures. To understand the reported empirical findings, we expand the widely used cellular Potts model to include active cell motility. For spontaneous directed motility we assume a positive feedback between cell displacements and cell polarity. The resulting model is studied with computer simulations and is shown to exhibit behavior compatible with experimental findings. In particular, in monolayer cultures both the speed and persistence of cell motion decreases, transient cell chains move together as groups and velocity correlations extend over several cell diameters. As active cell motility is ubiquitous both in vitro and in vivo, our model is expected to be a generally applicable representation of cellular behavior.

Sphingosine-1-phosphate signaling in vasculogenesis and angiogenesis

Blood vessels either form de novo through the process of vasculogenesis or through angiogenesis that involves the sprouting and proliferation of endothelial cells in pre-existing blood vessels. A complex interactive network of signaling cascades downstream from at least three of the nine known G-protein-coupled sphingosine-1-phosphate (S1P) receptors act as a prime effector of neovascularization that occurs in embryonic development and in association with various pathologies. This review focuses on the current knowledge of the roles of S1P signaling in vasculogenesis and angiogenesis, with particular emphasis on vascular cell adhesion and motility responses.

Jarid2 is among a set of genes differentially regulated by Nkx2.5 during outflow tract morphogenesis

Nkx2.5, a transcription factor implicated in human congenital heart disease, is required for regulation of second heart field (SHF) progenitors contributing to outflow tract (OFT). Here, we define a set of genes (Lrrn1, Elovl2, Safb, Slc39a6, Khdrbs1, Hoxb4, Fez1, Ccdc117, Jarid2, Nrcam, and Enpp3) expressed in SHF containing pharyngeal arch tissue whose regulation is dependent on Nkx2.5. Further investigation shows that Jarid2, which has been implicated in OFT morphogenesis, is a direct target of Nkx2.5 regulation. Jarid2 expression was up-regulated in SHF mesoderm of Nkx2.5-deficient embryos. Chromatin immunoprecipitation analysis showed Nkx2.5 interaction with consensus binding sites in the Jarid2 promoter in pharyngeal arch cells. Finally, Jarid2 promoter activity and mRNA expression levels were down-regulated by Nkx2.5 overexpression. Given the role of Jarid2 as a regulator of early cardiac proliferation, these findings highlight Jarid2 as one of several potential mediators of the critical role played by Nkx2.5 during OFT morphogenesis.

Fusion of uniluminal vascular spheroids: a model for assembly of blood vessels

We evaluated the self-assembly properties of uniluminal vascular spheroids having outer layers of vascular smooth muscle cells and a contiguous inner layer of endothelial cells lining a central lumen. We showed that while pairs of uniluminal vascular spheroids suspended in culture medium fused to form a larger diameter spheroidal structure, spheroids in collagen hydrogels formed elongated structures. These findings highlight the potential use of uniluminal vascular spheroids as modules to engineer blood vessels. We also demonstrate that uniluminal vascular spheroid fusion conforms to models describing the coalescence of liquid drops. Furthermore, the fusion of uniluminal vascular spheroids in vitro closely resembled the in vivo process by which the descending aorta forms from the fusion of the paired dorsal aortae during embryonic development. Together, the findings indicate that tissue liquidity underlies uniluminal vascular spheroid fusion and that in vivo anastomosis of blood vessels may involve a similar mechanism.

GeneMesh: a web-based microarray analysis tool for relating differentially expressed genes to MeSH terms

BACKGROUND

An important objective of DNA microarray-based gene expression experimentation is determining inter-relationships that exist between differentially expressed genes and biological processes, molecular functions, cellular components, signaling pathways, physiologic processes and diseases.

RESULTS

Here we describe GeneMesh, a web-based program that facilitates analysis of DNA microarray gene expression data. GeneMesh relates genes in a query set to categories available in the Medical Subject Headings (MeSH) hierarchical index. The interface enables hypothesis driven relational analysis to a specific MeSH subcategory (e.g., Cardiovascular System, Genetic Processes, Immune System Diseases etc.) or unbiased relational analysis to broader MeSH categories (e.g., Anatomy, Biological Sciences, Disease etc.). Genes found associated with a given MeSH category are dynamically linked to facilitate tabular and graphical depiction of Entrez Gene information, Gene Ontology information, KEGG metabolic pathway diagrams and intermolecular interaction information. Expression intensity values of groups of genes that cluster in relation to a given MeSH category, gene ontology or pathway can be displayed as heat maps of Z score-normalized values. GeneMesh operates on gene expression data derived from a number of commercial microarray platforms including Affymetrix, Agilent and Illumina.

CONCLUSIONS

GeneMesh is a versatile web-based tool for testing and developing new hypotheses through relating genes in a query set (e.g., differentially expressed genes from a DNA microarray experiment) to descriptors making up the hierarchical structure of the National Library of Medicine controlled vocabulary thesaurus, MeSH. The system further enhances the discovery process by providing links between sets of genes associated with a given MeSH category to a rich set of html linked tabular and graphic information including Entrez Gene summaries, gene ontologies, intermolecular interactions, overlays of genes onto KEGG pathway diagrams and heatmaps of expression intensity values. GeneMesh is freely available online at http://proteogenomics.musc.edu/genemesh/.

Expression of Patched-1 and Smoothened in testicular meiotic and post-meiotic cells

Desert hedgehog (Dhh) signaling plays an essential role in the normal development of the testis and in the process of spermatogenesis. Little is known about the involvement in spermatogenesis of the prototypic member of the family, Ptc1, which acts to suppress hedgehog signaling through Smoothened (Smo). Here, we have examined the expression of Ptc1, Smo, and Dhh in mouse and rat seminiferous epithelium. Our findings demonstrate that Ptc1 and Smo are expressed by primary spermatocytes and by round and condensing spermatids whereas Dhh is expressed by Sertoli cells. The findings suggest that Sertoli cells coordinate Dhh-dependent spermatogenesis events via Ptc1 and Smo prior to the first meiotic division and in postmeiotic (haploid) cells, particularly during the first half of spermiogenesis.

ADAMTS metalloproteases generate active versican fragments that regulate interdigital web regression

We show that combinatorial mouse alleles for the secreted metalloproteases Adamts5, Adamts20 (bt), and Adamts9 result in fully penetrant soft-tissue syndactyly. Interdigital webs in Adamts5(-/-);bt/bt mice had reduced apoptosis and decreased cleavage of the proteoglycan versican; however, the BMP-FGF axis, which regulates interdigital apoptosis was unaffected. BMP4 induced apoptosis, but without concomitant versican proteolysis. Haploinsufficiency of either Vcan or Fbln1, a cofactor for versican processing by ADAMTS5, led to highly penetrant syndactyly in bt mice, suggesting that cleaved versican was essential for web regression. The local application of an aminoterminal versican fragment corresponding to ADAMTS-processed versican, induced cell death in Adamts5(-/-);bt/bt webs. Thus, ADAMTS proteases cooperatively maintain versican proteolysis above a required threshold to create a permissive environment for apoptosis. The data highlight the developmental significance of proteolytic action on the ECM, not only as a clearance mechanism, but also as a means to generate bioactive versican fragments.

Fibulin-1 and fibrinogen in human atherosclerotic lesions

Fibulin-1 is a fibrinogen-binding blood protein and a component of many extracellular matrices (ECM) including those of blood vessels. In this study, the deposition patterns of fibulin-1 and fibrinogen were examined in human coronary artery atherosclerotic lesions excised by atherectomy from 20 patients. Fibulin-1 deposition was found to be closely overlapping with fibrinogen located within the atherosclerotic lesions and in regions containing fresh thrombi. Pronounced intracellular fibulin-1 immunostaining was apparent in lesion areas rich in macrophages and foam cells, although THP-1 macrophages and foam cells were found not to express fibulin-1. Strong ECM deposition of fibulin-1 was observed in acellular atheromatous and myxomatous regions. By contrast, fibulin-1 was present at relatively low levels in the ECM associated with smooth muscle cells within and outside of lesions and was not detected in sclerotic regions. These results reveal the pattern of fibulin-1 within human atherosclerotic lesions and highlight the potential for fibulin-1, perhaps derived from the blood and acting in conjunction with fibrinogen, to play a role in the etiology and cardiovascular disease progression, particularly with respect to thrombotic aspects of atherosclerosis.

Serum opacity factor is a streptococcal receptor for the extracellular matrix protein fibulin-1

The adhesion of bacteria to host tissues is often mediated by interactions with extracellular matrices. Herein, we report on the interactions of the group A streptococcus, Streptococcus pyogenes, with the extracellular matrix protein fibulin-1. S. pyogenes bound purified fibulin-1 in a dose-dependent manner. Genetic ablation of serum opacity factor (SOF), a virulence determinant of S. pyogenes, reduced binding by approximately 50%, and a recombinant peptide of SOF inhibited binding of fibulin-1 to streptococci by approximately 45%. Fibulin-1 bound to purified SOF2 in a dose-dependent manner with high affinity (K(d) = 1.6 nm). The fibulin-1-binding domain was localized to amino acid residues 457-806 of SOF2, whereas the fibronectin-binding domain is contained within residues 807-931 of SOF2, indicating that these two domains are separate and distinct. Fibulin-1 bound to recombinant SOF from M types 2, 4, 28, and 75 of S. pyogenes, indicating that the fibulin-1-binding domain is likely conserved among SOF from different serotypes. Mixed binding experiments suggested that gelatin, fibronectin, fibulin-1, and SOF form a quaternary molecular complex that enhanced the binding of fibulin-1. These data indicate that S. pyogenes can interact with fibulin-1 and that SOF is a major streptococcal receptor for fibulin-1 but not the only receptor. Such interactions with fibulin-1 may be involved in the adhesion of S. pyogenes to extracellular matrices of the host.

Effects of spaceflight on murine skeletal muscle gene expression

Spaceflight results in a number of adaptations to skeletal muscle, including atrophy and shifts toward faster muscle fiber types. To identify changes in gene expression that may underlie these adaptations, we used both microarray expression analysis and real-time polymerase chain reaction to quantify shifts in mRNA levels in the gastrocnemius from mice flown on the 11-day, 19-h STS-108 shuttle flight and from normal gravity controls. Spaceflight data also were compared with the ground-based unloading model of hindlimb suspension, with one group of pure suspension and one of suspension followed by 3.5 h of reloading to mimic the time between landing and euthanization of the spaceflight mice. Analysis of microarray data revealed that 272 mRNAs were significantly altered by spaceflight, the majority of which displayed similar responses to hindlimb suspension, whereas reloading tended to counteract these responses. Several mRNAs altered by spaceflight were associated with muscle growth, including the phosphatidylinositol 3-kinase regulatory subunit p85alpha, insulin response substrate-1, the forkhead box O1 transcription factor, and MAFbx/atrogin1. Moreover, myostatin mRNA expression tended to increase, whereas mRNA levels of the myostatin inhibitor FSTL3 tended to decrease, in response to spaceflight. In addition, mRNA levels of the slow oxidative fiber-associated transcriptional coactivator peroxisome proliferator-associated receptor (PPAR)-gamma coactivator-1alpha and the transcription factor PPAR-alpha were significantly decreased in spaceflight gastrocnemius. Finally, spaceflight resulted in a significant decrease in levels of the microRNA miR-206. Together these data demonstrate that spaceflight induces significant changes in mRNA expression of genes associated with muscle growth and fiber type.

VEGF-mediated fusion in the generation of uniluminal vascular spheroids

Embryonic mouse allantoic tissue (E8.5) was cultured in hanging drops to generate a three-dimensional vascular micro-tissue. The resulting tissue spheroids had an inner network of small diameter vessels expressing platelet endothelial cell adhesion molecule-1 (PECAM-1) and an outer layer of cells expressing SMalphaA, SM22-alpha, and SM-MHC. In a subsequent phase of culture, the fusion-promoting activity of vascular endothelial growth factor (VEGF) was used to transform the inner network of small diameter endothelial tubes into a contiguous layer of cells expressing PECAM-1, CD34, and VE-cadherin that circumscribed a central lumen-like cavity. The blood vessel-like character of the VEGF-treated spheroids was further demonstrated by their physiologically relevant vasodilatory and contractile responses, including contraction induced by KCl and relaxation stimulated by high-density lipoproteins and acetylcholine-induced nitric oxide production.

High density lipoprotein-associated sphingosine 1-phosphate promotes endothelial barrier function

High density lipoproteins (HDL) are major plasma carriers of sphingosine 1-phosphate (S1P). Here we show that HDL increases endothelial barrier integrity as measured by electric cell substrate impedance sensing. S1P was implicated as the mediator in this process through findings showing that pertussis toxin, an inhibitor of Gi-coupled S1P receptors, as well as antagonists of the S1P receptor, S1P1, inhibited barrier enhancement by HDL. Additional findings show that HDL stimulates endothelial cell activation of Erk1/2 and Akt, signaling pathway intermediates that have been implicated in S1P-dependent endothelial barrier activity. HDL was also found to promote endothelial cell motility, a process that may also relate to endothelial barrier function in the context of a vascular injury response. The effects of HDL on endothelial cell Erk1/2 and Akt activation and motility were suppressed by pertussis toxin and S1P1 antagonists. However, both HDL-induced barrier enhancement and HDL-induced motility showed a greater dependence on Akt activation as compared with Erk1/2 activation. Together, the findings indicate that HDL has endothelial barrier promoting activities, which are attributable to its S1P component and signaling through the S1P1/Akt pathway.

Oxidized LDL immune complexes and oxidized LDL differentially affect the expression of genes involved with inflammation and survival in human U937 monocytic cells

OBJECTIVE

To compare the global effects of oxidized LDL (oxLDL) and oxLDL-containing immune complexes (oxLDL-IC) on gene expression in human monocytic cells and to identify differentially expressed genes involved with inflammation and survival.

METHODS AND RESULTS

U937 cells were treated with oxLDL-IC, oxLDL, Keyhole limpet hemocyanin immune complexes (KLH-IC), or vehicle for 4h. Transcriptome profiling was performed using DNA microarrays. oxLDL-IC uniquely affected the expression of genes involved with pro-survival (RAD54B, RUFY3, SNRPB2, and ZBTB24). oxLDL-IC also regulated many genes in a manner similar to KLH-IC. Functional categorization of these genes revealed that 39% are involved with stress responses, including the unfolded protein response which impacts cell survival, 19% with regulation of transcription, 10% with endocytosis and intracellular transport of protein and lipid, and 16% with inflammatory responses including regulation of I-kappaB /NF-kappaB cascade and cytokine activity. One gene in particular, HSPA6, greatly up-regulated by oxLDL-IC, was found to be required for the process by which oxLDL-IC augments IL1-beta secretion. The study also revealed genes uniquely up-regulated by oxLDL, including genes involved with growth inhibition (OKL38, NEK3, and FTH1), oxidoreductase activity (SPXN1 and HMOX1), and transport of amino acids and fatty acids (SLC7A11 and ADFP).

CONCLUSIONS

These findings highlight early transcriptional responses elicited by oxLDL-IC that may underlie its cytoprotective and pro-inflammatory effects. Cross-linking of Fc gamma receptors appears to be the trigger for most of the transcriptional responses to oxLDL-IC. The findings further strengthen the hypothesis that oxLDL and oxLDL-IC elicit disparate inflammatory responses and play distinct roles in the process of atherosclerosis.

Fibulin-1 is required for morphogenesis of neural crest-derived structures

Here we report that mouse embryos homozygous for a gene trap insertion in the fibulin-1 (Fbln1) gene are deficient in Fbln1 and exhibit cardiac ventricular wall thinning and ventricular septal defects with double outlet right ventricle or overriding aorta. Fbln1 nulls also display anomalies of aortic arch arteries, hypoplasia of the thymus and thyroid, underdeveloped skull bones, malformations of cranial nerves and hemorrhagic blood vessels in the head and neck. The spectrum of malformations is consistent with Fbln1 influencing neural crest cell (NCC)-dependent development of these tissues. This is supported by evidence that Fbln1 expression is associated with streams of cranial NCCs migrating adjacent to rhombomeres 2-7 and that Fbln1-deficient embryos display patterning anomalies of NCCs forming cranial nerves IX and X, which derive from rhombomeres 6 and 7. Additionally, Fbln1-deficient embryos show increased apoptosis in areas populated by NCCs derived from rhombomeres 4, 6 and 7. Based on these findings, it is concluded that Fbln1 is required for the directed migration and survival of cranial NCCs contributing to the development of pharyngeal glands, craniofacial skeleton, cranial nerves, aortic arch arteries, cardiac outflow tract and cephalic blood vessels.

HDL serves as a S1P signaling platform mediating a multitude of cardiovascular effects

The lysosphingolipid sphingosine 1-phosphate (S1P) is a component of HDL. Findings from a growing number of studies indicate that S1P is a mediator of many of the cardiovascular effects of HDL, including the ability to promote vasodilation, vasoconstriction, and angiogenesis, protect against ischemia/reperfusion injury, and inhibit/reverse atherosclerosis. These latter cardioprotective effects are being shown to involve the S1P-mediated suppression of inflammatory processes, including reduction of the endothelial expression of monocyte and lymphocyte adhesion molecules, decreased recruitment of polymorphonuclear cells to sites of infarction, and blocking of cardiomyocyte apoptosis after myocardial infarction. This review article summarizes the evidence that S1P as a component of HDL serves to regulate vascular cell and lymphocyte behaviors associated with cardiovascular (patho)physiology.

Oxidised, glycated LDL selectively influences tissue inhibitor of metalloproteinase-3 gene expression and protein production in human retinal capillary pericytes

AIMS/HYPOTHESIS

Matrix metalloproteinases (MMPs) and their natural inhibitors, tissue inhibitor of metalloproteinases (TIMPs), regulate important biological processes including the homeostasis of the extracellular matrix, proteolysis of cell surface proteins, proteinase zymogen activation, angiogenesis and inflammation. Studies have shown that their balance is altered in retinal microvascular tissues in diabetes. Since LDLs modified by oxidation/glycation are implicated in the pathogenesis of diabetic vascular complications, we examined the effects of modified LDL on the gene expression and protein production of MMPs and TIMPs in retinal pericytes.

METHODS

Quiescent human retinal pericytes were exposed to native LDL (N-LDL), glycated LDL (G-LDL) and heavily oxidised and glycated LDL (HOG-LDL) for 24 h. We studied the expression of the genes encoding MMPs and TIMPs mRNAs by analysis of microarray data and quantitative PCR, and protein levels by immunoblotting and ELISA.

RESULTS

Microarray analysis showed that MMP1, MMP2, MMP11, MMP14 and MMP25 and TIMP1, TIMP2, TIMP3 and TIMP4 were expressed in pericytes. Of these, only TIMP3 mRNA showed altered regulation, being expressed at significantly lower levels in response to HOG- vs N-LDL. Quantitative PCR and immunoblotting of cell/matrix proteins confirmed the reduction in TIMP3 mRNA and protein in response to HOG-LDL. In contrast to cellular TIMP3 protein, analysis of secreted TIMP1, TIMP2, MMP1 and collagenase activity indicated no changes in their production in response to modified LDL. Combined treatment with N- and HOG-LDL restored TIMP3 mRNA expression to a level comparable with that after N-LDL alone.

CONCLUSIONS/INTERPRETATION

Among the genes encoding for MMPs and TIMPs expressed in retinal pericytes, TIMP3 is uniquely regulated by HOG-LDL. Reduced TIMP3 expression might contribute to microvascular abnormalities in diabetic retinopathy.

Cartilage link protein 1 (Crtl1), an extracellular matrix component playing an important role in heart development

To expand our insight into cardiac development, a comparative DNA microarray analysis was performed using tissues from the atrioventricular junction (AVJ) and ventricular chambers of mouse hearts at embryonic day (ED) 10.5-11.0. This comparison revealed differential expression of approximately 200 genes, including cartilage link protein 1 (Crtl1). Crtl1 stabilizes the interaction between hyaluronan (HA) and versican, two extracellular matrix components essential for cardiac development. Immunohistochemical studies showed that, initially, Crtl1, versican, and HA are co-expressed in the endocardial lining of the heart, and in the endocardially derived mesenchyme of the AVJ and outflow tract (OFT). At later stages, this co-expression becomes restricted to discrete populations of endocardially derived mesenchyme. Histological analysis of the Crtl1-deficient mouse revealed a spectrum of cardiac malformations, including AV septal and myocardial defects, while expression studies showed a significant reduction in versican levels. Subsequent analysis of the hdf mouse, which carries an insertional mutation in the versican gene (CSPG2), demonstrated that haploinsufficient versican mice display septal defects resembling those seen in Crtl1(-/-) embryos, suggesting that reduced versican expression may contribute to a subset of the cardiac abnormalities observed in the Crtl1(-/-) mouse. Combined, these findings establish an important role for Crtl1 in heart development.

Versican proteolysis mediates myocardial regression during outflow tract development

An important phase of cardiac outflow tract (OFT) formation is the remodeling of the distal region of the common outlet in which the myocardial sleeve is replaced by with smooth muscle. Here we demonstrate that expression of the proteoglycan versican is reduced before the loss of myocardium from the distal cardiac outlet concomitant with an increase in production of the N-terminal cleavage fragment of versican. To test whether versican proteolysis plays a role in OFT remodeling, we determined the effects of adenoviral-mediated expression of a versican isoform devoid of known matrix metalloproteinase cleavage sites (V3) and an N-terminal fragment of versican (G1). V3 expression promoted an increase in thickness of the proximal OFT myocardial layer independent of proliferation. In contrast, the G1 domain caused thinning and interruptions of the OFT myocardium. These in vivo findings were consistent with findings using cultured primary cardiomyocytes showing that the V3 promoted myocardial cell-cell association while the G1 domain caused a loss of myocardial cell-cell association. Taken together, we conclude that intact versican and G1-containing versican cleavage products have opposing effects on myocardial cells and that versican proteolysis may facilitate the loss of distal myocardium during OFT remodeling.

Regulation of breast cancer response to chemotherapy by fibulin-1

Doxorubicin treatment was found to augment the expression of the extracellular matrix (ECM) protein fibulin-1 in cultured human breast cancer cell lines and in MDA-MB-361 tumors grown in athymic mice. Doxorubicin was also found to augment tumor expression of the fibulin-1-binding proteins fibronectin and laminin-1. Growth of breast cancer cell lines on Matrigel, an ECM extract containing fibulin-1 and laminin-1, resulted in lower levels of doxorubicin-induced apoptosis as compared with controls. Moreover, tumors formed by injection of athymic mice with MDA-MB-361 cells mixed with Matrigel were significantly more doxorubicin resistant and displayed lower levels of apoptosis compared with those that formed in the absence of Matrigel. Monoclonal antibodies against fibulin-1 reversed Matrigel-dependent doxorubicin resistance. Furthermore, small interfering RNA-mediated suppression of fibulin-1 expression in breast cancer cells resulted in a 10-fold increase in doxorubicin sensitivity as compared with control cells. Together, these findings point to a role for fibulin-1 in breast cancer chemoresistance.

Proteolytic cleavage of versican during cardiac cushion morphogenesis

The proteoglycan versican is essential to the formation of endocardial cushion mesenchyme by epithelial-mesenchymal transformation (EMT). A potentially important factor in the regulation of versican activity during cushion EMT is proteolysis by ADAMTS metalloproteinases. Using antibodies to the DPEAAE neoepitope created by ADAMTS proteolysis of versican, we detected the amino terminal 70-kDa versican cleavage fragment in cardiac cushions. Initially (i.e., 9.5 days post coitum [dpc]), the fragment is associated with endocardial cells undergoing EMT and with newly derived mesenchymal cells. ADAMTS-1 and its cofactor fibulin-1 were also associated with these cells. As cushions become increasingly populated with mesenchymal cells (10.5-12.5 dpc), the fragment remains asymmetrically distributed compared with the pattern of total versican. Highest levels of the fragment are present in regions immediately subjacent to the endocardium characterized as having densely packed, rounded cells, lacking cellular protrusions. With further development (i.e., 12.5-14.5 dpc), the pattern of fragment distribution within cushions broadens to include the ECM surrounding loosely packed mesenchymal cells in the cushion core. Together, the findings reveal that versican proteolysis leading to the production of the 70-kDa fragment is integral to the formation and differentiation of endocardial cushion mesenchyme.