Rat and human aortic smooth muscle cells display differing migration and matrix metalloproteinase activities in response to dexamethasone

Intermittent hypoxia-induced epiregulin expression by IL-6 production in human coronary artery smooth muscle cells

Patients with obstructive sleep apnea (OSA) experience repetitive episodes of desaturation and resaturation of blood oxygen (known as intermittent hypoxia or IH), during sleep. We showed previously that IH induced excessive proliferation of rat vascular smooth muscle cells through upregulation of members of the epidermal growth factor family, especially epiregulin (EREG), and the erbB2 receptor. In this study, we exposed human coronary artery smooth muscle cells to IH and found that IH significantly increased the expression of EREG. IH increased the production of interleukin‐6 (IL‐6) in smooth muscle cells, and the addition of IL‐6 induced EREG expression. Small interfering RNA for IL‐6 or IL‐6 receptor attenuated the IH‐induced increase in EREG. IL‐6 may play a pivotal role in EREG upregulation by IH and consequently OSA‐related atherosclerosis.

Integrated approaches to spatiotemporally directing angiogenesis in host and engineered tissues

The field of tissue engineering has turned towards biomimicry to solve the problem of tissue oxygenation and nutrient/waste exchange through the development of vasculature. Induction of angiogenesis and subsequent development of a vascular bed in engineered tissues is actively being pursued through combinations of physical and chemical cues, notably through the presentation of topographies and growth factors. Presenting angiogenic signals in a spatiotemporal fashion is beginning to generate improved vascular networks, which will allow for the creation of large and dense engineered tissues. This review provides a brief background on the cells, mechanisms, and molecules driving vascular development (including angiogenesis), followed by how biomaterials and growth factors can be used to direct vessel formation and maturation. Techniques to accomplish spatiotemporal control of vascularization include incorporation or encapsulation of growth factors, topographical engineering, and 3D bioprinting. The vascularization of engineered tissues and their application in angiogenic therapy in vivo is reviewed herein with an emphasis on the most densely vascularized tissue of the human body - the heart.

STATEMENT OF SIGNIFICANCE

Vascularization is vital to wound healing and tissue regeneration, and development of hierarchical networks enables efficient nutrient transfer. In tissue engineering, vascularization is necessary to support physiologically dense engineered tissues, and thus the field seeks to induce vascular formation using biomaterials and chemical signals to provide appropriate, pro-angiogenic signals for cells. This review critically examines the materials and techniques used to generate scaffolds with spatiotemporal cues to direct vascularization in engineered and host tissues in vitro and in vivo. Assessment of the field's progress is intended to inspire vascular applications across all forms of tissue engineering with a specific focus on highlighting the nuances of cardiac tissue engineering for the greater regenerative medicine community.

Species-specific regulation of angiogenesis by glucocorticoids reveals contrasting effects on inflammatory and angiogenic pathways

Glucocorticoids are potent inhibitors of angiogenesis in the rodent in vivo and in vitro but the mechanism by which this occurs has not been determined. Administration of glucocorticoids is used to treat a number of conditions in horses but the angiogenic response of equine vessels to glucocorticoids and, therefore, the potential role of glucocorticoids in pathogenesis and treatment of equine disease, is unknown. This study addressed the hypothesis that glucocorticoids would be angiostatic both in equine and murine blood vessels.The mouse aortic ring model of angiogenesis was adapted to assess the effects of cortisol in equine vessels. Vessel rings were cultured under basal conditions or exposed to: foetal bovine serum (FBS; 3%); cortisol (600 nM), cortisol (600nM) plus FBS (3%), cortisol (600nM) plus either the glucocorticoid receptor antagonist RU486 or the mineralocorticoid receptor antagonist spironolactone. In murine aortae cortisol inhibited and FBS stimulated new vessel growth. In contrast, in equine blood vessels FBS alone had no effect but cortisol alone, or in combination with FBS, dramatically increased new vessel growth compared with controls. This effect was blocked by glucocorticoid receptor antagonism but not by mineralocorticoid antagonism. The transcriptomes of murine and equine angiogenesis demonstrated cortisol-induced down-regulation of inflammatory pathways in both species but up-regulation of pro-angiogenic pathways selectively in the horse. Genes up-regulated in the horse and down-regulated in mice were associated with the extracellular matrix. These data call into question our understanding of glucocorticoids as angiostatic in every species and may be of clinical relevance in the horse.

Glucocorticoid-mediated inhibition of angiogenic changes in human endothelial cells is not caused by reductions in cell proliferation or migration

Background

Glucocorticoid-mediated inhibition of angiogenesis is important in physiology, pathophysiology and therapy. However, the mechanisms through which glucocorticoids inhibit growth of new blood vessels have not been established. This study addresses the hypothesis that physiological levels of glucocorticoids inhibit angiogenesis by directly preventing tube formation by endothelial cells.

Methodology/Principal Findings

Cultured human umbilical vein (HUVEC) and aortic (HAoEC) endothelial cells were used to determine the influence of glucocorticoids on tube-like structure (TLS) formation, and on cellular proliferation (5-bromo-2′-deoxyuridine (BrdU) incorporation), viability (ATP production) and migration (Boyden chambers). Dexamethasone or cortisol (at physiological concentrations) inhibited both basal and prostaglandin F_2α (PGF_2α)-induced and vascular endothelial growth factor (VEGF) stimulated TLS formation in endothelial cells (ECs) cultured on Matrigel, effects which were blocked with the glucocorticoid receptor antagonist RU38486. Glucocorticoids had no effect on EC viability, migration or proliferation. Time-lapse imaging showed that cortisol blocked VEGF-stimulated cytoskeletal reorganisation and initialisation of tube formation. Real time PCR suggested that increased expression of thrombospodin-1 contributed to glucocorticoid-mediated inhibition of TLS formation.

Conclusions/Significance

We conclude that glucocorticoids interact directly with glucocorticoid receptors on vascular ECs to inhibit TLS formation. This action, which was conserved in ECs from two distinct vascular territories, was due to alterations in cell morphology rather than inhibition of EC viability, migration or proliferation and may be mediated in part by induction of thrombospodin-1. These findings provide important insights into the anti-angiogenic action of endogenous glucocorticoids in health and disease.

Leptin-induced vascular smooth muscle cell proliferation via regulating cell cycle, activating ERK1/2 and NF-kappaB

Leptin is a peptide hormone primarily involved in the regulation of food intake and energy expenditure. Recent studies have suggested that leptin is one of the risk factors for cardiovascular diseases including atherosclerosis and hypertension. Vascular smooth muscle cells (VSMCs) play a vital role in arterial intimal thickening and vascular remodeling. In this study, we investigated the effect of leptin on VSMC cell-cycle regulation and the possible pathway. We found that leptin stimulated VSMC proliferation and increased cell progression to S and G2/M phases. The expression of cyclinD1, phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2), and nuclear factor (NF)-kappaBp65 was increased. Treatment of the cells with leptin antagonist triple mutant attenuated the leptininduced ERK1/2 and NF-kappaB activation. These results suggested that leptin stimulated VSMC proliferation by promoting transition from G1 to S phase and ERK1/2 and NF-kappaB pathway might contribute to this procession.

Effect of maternal administration of betamethasone on peripheral arterial development in fetal rabbit lungs

OBJECTIVES

Glucocorticoids promote lung maturation and reduce the incidence of respiratory distress syndrome in premature newborns. We hypothesized that betamethasone (BM), which is known to induce thinning of the alveolar walls, would also thin the arterial media and adventitia of intra-parenchymatic vessels in developing rabbit lungs.

STUDY DESIGN

112 fetuses from 21 time-mated, pregnant, giant white rabbits received maternal injections of BM at either 0.05 or 0.1 mg/kg/day on days 25-26 of gestational age. Controls received either saline (10 does, 56 fetuses) or no injection (10 does, 59 fetuses). Fetuses were harvested from day 27 onwards until term (day 31). 44 additional fetuses (8 does) were harvested between days 23 and 26. Endpoints were wet lung-to-body weight ratio, vascular morphometric indices and immunohistochemistry staining for alpha-smooth muscle actin, Flk-1, vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS). ANOVA (Tukey's test) and independent t test (p < 0.05) were used for comparison between BM and saline groups.

RESULTS

Maternal BM injected on days 25-26 to pregnant rabbits induced a significant decrease in fetal body and lung weight and the lung-to-body weight ratio in the preterm pups shortly after injection. BM led to a dose-dependent thinning of the arterial media and adventitia (pulmonary arteries with an external diameter (ED) of <100 microm), to an increase in the percentage of non-muscularized peripheral vessels (ED <60 microm), in eNOS and VEGF immunoreactivity of the endothelial and smooth muscle cells in the pulmonary vessels and to an increase in Flk-1-positive pulmonary epithelial cell density.

CONCLUSIONS

Maternal administration of BM caused thinning of the arterial wall of pulmonary vessels (ED <100 microm) and a decrease in muscularization in peripheral vessels (ED <60 microm). This coincided with increased expression of Flk-1 in the endothelium and smooth muscle cells of the pulmonary arteries. All the effects studied were dose-dependent.

Leptin inhibits cell growth of human vascular smooth muscle cells

Elevated leptin levels are thought to contribute to the individual cardiovascular risk, however, the role of leptin in the pathogenesis of atherosclerosis remains unclear. The aim of our study was to elucidate the effects of leptin on growth of human vascular smooth muscle cells (VSMC) and leptin receptor expression. By establishing a new quantitative real-time PCR for leptin receptor (ObR) isoforms we showed that the short isoforms of ObR were expressed in a 10- to 27-fold excess compared to the long isoform in cultured human VSMCs. Incubation of VSMCs with 100 ng/ml leptin downregulated the short isoforms significantly, whereas the long isoform was not influenced. Increasing leptin concentrations of 50 and 100 ng/ml significantly reduced the cell number of VSMCs compared to untreated controls. Our findings suggest a role for leptin in vascular smooth muscle cell growth, associated to a downregulation of leptin receptor isoforms.

Hypoxia attenuates insulin-induced proliferation and migration of human diabetic infrapopliteal vascular smooth muscle cells

The proliferative effects of insulin on infrapopliteal vascular smooth muscle cells (VSMCs) have been established. We examined the effect of hypoxia in the presence and absence of insulin on the proliferation and migration of human diabetic infrapopliteal VSMCs in vitro. VSMCs isolated from the infrapopliteal arteries of male diabetic patients of identical disease and clinical patterns undergoing below-knee amputation were harvested and grown to subconfluence. Cells were then exposed to control medium (M199/1% fetal bovine serum/2% antibiotic-antimycotic) or control medium with 100 ng/mL insulin in oxygen concentrations of 17% (normoxia), 5%, and 1%. Cellular proliferation was assayed using [methyl-3H]-thymidine incorporation. Migration assays were performed using the Corning Costar Transwell system. Lactate dehydrogenase was assayed and compared among groups as a marker for cytotoxicity. VSMCs in normoxic conditions (17%) had a significant increase in both proliferation (100 +/- 6.5% vs. 124 +/- 4.7%, p = 0.007) and migration [73.2 +/- 9.3 vs. 118.1 +/- 14.9 cells/4 high-power fields (HPF), p = 0.03] when exposed to insulin. Of cells exposed to insulin, those at both 5% (75.9 +/- 7.9%, p = 0.0001) and 1% (73.6 +/- 4%, p < 0.0001) hypoxia proliferated at a significantly decreased rate compared with cells at normoxia (124 +/- 4.7%). Migration of these insulin-exposed cells was significantly decreased at 1% hypoxia (63.1 +/- 9.0 cells/4HPF) compared to those at normoxia (118.1 +/- 14.9 cells/4HPF, p = 0.006) and 5% hypoxia (101.2 +/- 10.0 cells/4HPF, p = 0.01). There were no significant differences in migration between cells at normoxia and 5% hypoxia. Finally, hypoxia and insulin exerted no significant effect on cytotoxicity. The proliferative and promigratory effects of insulin on diabetic VSMCs are attenuated in hypoxic conditions in a manner unrelated to cytotoxicity.

Preventing local regeneration of glucocorticoids by 11beta-hydroxysteroid dehydrogenase type 1 enhances angiogenesis

Angiogenesis restores blood flow to healing tissues, a process that is inhibited by high doses of glucocorticoids. However, the role of endogenous glucocorticoids and the potential for antiglucocorticoid therapy to enhance angiogenesis is unknown. Using in vitro and in vivo models of angiogenesis in mice, we examined effects of (i) endogenous glucocorticoids, (ii) blocking endogenous glucocorticoid action with the glucocorticoid receptor antagonist RU38486, and (iii) abolishing local regeneration of glucocorticoids by the enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11betaHSD1). Glucocorticoids, administered at physiological concentrations, inhibited angiogenesis in an in vitro aortic ring model and in vivo in polyurethane sponges implanted s.c. RU38486-enhanced angiogenesis in s.c. sponges, in healing surgical wounds, and in the myocardium of mice 7 days after myocardial infarction induced by coronary artery ligation. 11betaHSD1 knockout mice showed enhanced angiogenesis in vitro and in vivo within sponges, wounds, and infarcted myocardium. Endogenous glucocorticoids, including those generated locally by 11betaHSD1, exert tonic inhibition of angiogenesis. Inhibition of 11betaHSD1 in liver and adipose has been advocated to reduce cardiovascular risk in the metabolic syndrome: these data suggest that 11betaHSD1 inhibition offers a previously uncharacterized therapeutic approach to improve healing of ischemic or injured tissue.

Sustained Cytoplasmic Delivery of Drugs with Intracellular Receptors Using Biodegradable Nanoparticles

Efficient cytoplasmic delivery of therapeutic agents is especially important for drugs with an intracellular site of action for elicitation of a maximal therapeutic effect. In this study, we demonstrate the efficacy of biodegradable nanoparticles for cytoplasmic delivery of dexamethasone, a glucocorticoid, whose site of action is intracellular. Equal doses of two formulations of drug-loaded nanoparticles releasing different doses of the encapsulated drug were tested for antiproliferative activity in vascular smooth muscle cells. The antiproliferative activity of the drug was significantly greater and sustained with nanoparticles that released a higher dose of the drug than with nanoparticles which released a lower dose of the drug. The greater antiproliferative activity of the nanoparticles that released a higher dose of the drug correlated with sustained and higher intracellular drug levels. The antiproliferative activity of the drug in solution was lower and relatively transient compared to that with drug-loaded nanoparticles. The mechanism of inhibition of cell proliferation was mediated through inhibition of cell-cycle progression with a relatively higher percentage of cells in the G0/G1 arrest phase in the group that was treated with drug-loaded nanoparticles compared to that treated with the drug in solution. Results of the study thus suggest that the dose and duration of a drug's availability at the intracellular site of action determine its therapeutic efficacy. In conclusion, biodegradable nanoparticles could be used as an effective delivery mechanism for sustained intracellular delivery of different therapeutic agents.

Cyclic AMP-mobilizing agents and glucocorticoids modulate human smooth muscle cell migration

Hyperplasia and cell migration of smooth muscle are features of both airway and pulmonary vascular diseases. The precise cellular and molecular mechanisms that regulate smooth muscle migration in the lungs remain unknown. In this study, we examined the effect of cAMP-mobilizing agents and steroids on smooth muscle cell migration. Platelet-derived growth factor (PDGF), transforming growth factor-alpha, vascular endothelial growth factor, and basic fibroblast growth factor significantly stimulated cell migration in pulmonary vascular smooth muscle (PVSM) cells. Airway smooth muscle (ASM) migration was also stimulated by PDGF, transforming growth factor-alpha, and basic fibroblast growth factor, but vascular endothelial growth factor was without effect. Interestingly, the smooth muscle mitogen thrombin did not stimulate migration of either cell type. Agents capable of elevating intracellular cAMP inhibited basal (unstimulated) cell migration in both cell types, whereas their effects on PDGF-stimulated migration were more variable. Prostaglandin E2, salmeterol, and the phosphodiesterase type 4 inhibitor cilomolast inhibited basal ASM and PVSM migration by 30-60%. Prostaglandin E2 and cilomolast also inhibited PDGF-stimulated migration of ASM and PVSM cells, but salmeterol was without effect. Preincubation of ASM cells with dexamethasone or fluticasone inhibited basal and PDGF-stimulated migration, and enabled an inhibitory effect of salmeterol on PDGF-induced cell migration. Steroids alone did not stimulate cAMP production or cAMP/PKA-dependent gene transcription (CRE-Luc activity), but slightly augmented salmeterol-stimulated CRE-Luc activity. Collectively, these findings demonstrate that cAMP-mobilizing agents and steroids modulate human smooth muscle cell migration, likely by distinct mechanisms.

Methylprednisolone causes matrix metalloproteinase-dependent emphysema in adult rats

Previous investigations have shown that corticosteroids affect the development and maturation of the developing lung in utero and in neonatal animals. Systemic corticosteroids are routinely used for the treatment of acute exacerbations of chronic obstructive pulmonary disease, and inhaled corticosteroids are more frequently being prescribed for the long-term treatment of patients with chronic obstructive pulmonary disease. Because corticosteroids can affect matrix metalloproteinases and because the concept of protease/antiprotease imbalance is an important concept regarding the pathogenesis of emphysema, we examined the effects of chronic steroid treatment on lung structure in adult rats. Rats treated with 2 mg/kg of methylprednisolone daily for 1, 2, or 4 weeks had an increased mean linear intercept and a decrease of the surface-volume ratio when compared with age-matched control animals, and the animals showed increased matrix metalloproteinase-9 activity in their lungs on zymography. Rats treated concomitantly with methylprednisolone and a broad-spectrum matrix metalloproteinase inhibitor (GM6001) did not develop emphysema. We conclude that systemic treatment of adult rats with the antiinflammatory steroid methylprednisolone increases the activity of matrix metalloproteinases in the lung and causes emphysema.