Mechanisms of inhibition by heparin of PDGF stimulated MAP kinase activation in vascular smooth muscle cells

Heparinized Acellular Hydrogels for Magnetically Induced Wound Healing Applications

The control of angiogenesis has the potential to be used for regulation of several pathological and physiological processes, which can be instrumental on the development of anticancer and wound healing therapeutical approaches. In this study, mesenchymal stem/stromal cells (MSCs) were seeded on magnetic-responsive gelatin, with or without heparin functionalization, and exposed to a static 0.08 T magnetic field (MF), for controlling their anti-inflammatory and angiogenic activity, with the aim of accelerating tissue healing. For the first time, it was examined how the amount of heparin and magnetic nanoparticles (MNPs) distributed on gelatin scaffolds affected the mechanical properties of the hydrogels and the morphology, proliferation, and secretome profiling of MSCs. The findings demonstrated that the addition of MNPs and heparin affects the hydrogel swelling capacity and renders distinct MSC proliferation rates. Additionally, MF acts as a topographical cue to guide MSCs alignment and increases the level of expression of specific genes and proteins that promote angiogenesis. The results also suggested that the presence of higher amounts of heparin (10 μg/cm3) interferes with the secretion and limits the capacity of angiogenic factors to diffuse through the hydrogel and into the culture medium. Ultimately, this study shows that acellular heparinized hydrogels efficiently retain the angiogenic growth factors released by magnetically stimulated MSCs thus rendering superior wound contraction (55.8% ± 0.4%) and cell migration rate (49.4% ± 0.4%), in comparison to nonheparinized hydrogels (35.2% ± 0.7% and 37.8% ± 0.7%, respectively). Therefore, these heparinized magnetic hydrogels can be used to facilitate angiogenesis in various forms of tissue damage including bone defects, skin wounds, and cardiovascular diseases, leading to enhanced tissue regeneration.

Remodeling of Structurally Reinforced (TPU+PCL/PCL)-Hep Electro-spun Small Diameter Bilayer Vascular Grafts Interposed in Rat Ab-dominal Aorta

As the thermoplastic polyurethane (TPU) elastomer possesses good biocompatibility and mechanical properties similar to native vascular tissues as well, it is intended to co-electrospin with poly(ε-caprolactone) (PCL) onto the outer...

Endothelial nitric oxide synthase activation is required for heparin receptor effects on vascular smooth muscle cells

Published studies indicate that TMEM184A is a heparin receptor that interacts with and transduces stimulation from heparin in vascular cells. Previous studies have indicated that heparin increases endothelial nitric oxide synthase (eNOS) activity in bovine endothelial cells. However, the precise mechanism remains unknown. In this study, we investigated the impact of heparin treatment and TMEM184A on eNOS's activation and the role of eNOS in heparin signaling in the cloned A7r5 rat vascular smooth muscle cell line and confirmed results in endothelial cells. We employed a combination of TMEM184A knockdown A7r5 cells along with transient eNOS knockdown and enzyme inhibitor strategies. The results indicate that heparin induces phosphorylation of eNOS. eNOS can be immunoprecipitated with TMEM184A and is internalized to the perinuclear region in a TMEM184A-dependent manner in response to heparin. We also examined how heparin treatment leads to phosphorylation of eNOS and confirmed that TMEM184A and Ca²⁺ were required to mediate heparin-elicited eNOS phosphorylation. Evidence supporting the involvement of transient receptor potential cation channel subfamily V member 4 with TMEM184A in this eNOS activation process is also presented.

Aqueous humour-induced lens epithelial cell proliferation requires FGF-signalling

The eye lens grows by systematic proliferation of its epithelial cells and their differentiation into fibre cells. The anterior aqueous humour regulates lens epithelial cell proliferation whereas posteriorly, the vitreous stimulates lens fibre differentiation. Vitreous-derived members of the fibroblast growth factor (FGF) family induce fibre differentiation, with added support for FGFs as putative regulators of aqueous-induced lens cell proliferation. To further characterize this, given FGFs' known affinity for proteoglycans, we compared the effect of proteoglycan sulphation in growth factor- and aqueous-induced lens cell proliferation. Disruption of proteoglycan sulphation in lens cells specifically impacted on aqueous- and FGF-induced MAPK/ERK1/2-signalling, but not on that induced by other mitogens such as PDGF; however, cell proliferation was reduced in all treatment groups, regardless of the mitogen. Overall, by disrupting proteoglycan activity, we further highlight the significant role of FGFs in aqueous-induced ERK1/2 phosphorylation leading to lens cell proliferation.

Heparin Decreases in Tumor Necrosis Factor α (TNFα)-induced Endothelial Stress Responses Require Transmembrane Protein 184A and Induction of Dual Specificity Phosphatase 1

Despite the large number of heparin and heparan sulfate binding proteins, the molecular mechanism(s) by which heparin alters vascular cell physiology is not well understood. Studies with vascular smooth muscle cells (VSMCs) indicate a role for induction of dual specificity phosphatase 1 (DUSP1) that decreases ERK activity and results in decreased cell proliferation, which depends on specific heparin binding. The hypothesis that unfractionated heparin functions to decrease inflammatory signal transduction in endothelial cells (ECs) through heparin-induced expression of DUSP1 was tested. In addition, the expectation that the heparin response includes a decrease in cytokine-induced cytoskeletal changes was examined. Heparin pretreatment of ECs resulted in decreased TNFα-induced JNK and p38 activity and downstream target phosphorylation, as identified through Western blotting and immunofluorescence microscopy. Through knockdown strategies, the importance of heparin-induced DUSP1 expression in these effects was confirmed. Quantitative fluorescence microscopy indicated that heparin treatment of ECs reduced TNFα-induced increases in stress fibers. Monoclonal antibodies that mimic heparin-induced changes in VSMCs were employed to support the hypothesis that heparin was functioning through interactions with a receptor. Knockdown of transmembrane protein 184A (TMEM184A) confirmed its involvement in heparin-induced signaling as seen in VSMCs. Therefore, TMEM184A functions as a heparin receptor and mediates anti-inflammatory responses of ECs involving decreased JNK and p38 activity.

Transmembrane Protein 184A Is a Receptor Required for Vascular Smooth Muscle Cell Responses to Heparin

Vascular cell responses to exogenous heparin have been documented to include decreased vascular smooth muscle cell proliferation following decreased ERK pathway signaling. However, the molecular mechanism(s) by which heparin interacts with cells to induce those responses has remained unclear. Previously characterized monoclonal antibodies that block heparin binding to vascular cells have been found to mimic heparin effects. In this study, those antibodies were employed to isolate a heparin binding protein. MALDI mass spectrometry data provide evidence that the protein isolated is transmembrane protein 184A (TMEM184A). Commercial antibodies against three separate regions of the TMEM184A human protein were used to identify the TMEM184A protein in vascular smooth muscle cells and endothelial cells. A GFP-TMEM184A construct was employed to determine colocalization with heparin after endocytosis. Knockdown of TMEM184A eliminated the physiological responses to heparin, including effects on ERK pathway activity and BrdU incorporation. Isolated GFP-TMEM184A binds heparin, and overexpression results in additional heparin uptake. Together, these data support the identification of TMEM184A as a heparin receptor in vascular cells.

Extracellular matrix-mimetic poly(ethylene glycol) hydrogels engineered to regulate smooth muscle cell proliferation in 3-D

The goal of this project is to engineer a defined, synthetic poly(ethylene glycol) (PEG) hydrogel as a model system to investigate smooth muscle cell (SMC) proliferation in three-dimensions (3-D). To mimic the properties of extracellular matrix, both cell-adhesive peptide (GRGDSP) and matrix metalloproteinase (MMP) sensitive peptide (VPMSMRGG or GPQGIAGQ) were incorporated into the PEG macromer chain. Copolymerization of the biomimetic macromers results in the formation of bioactive hydrogels with the dual properties of cell adhesion and proteolytic degradation. Using these biomimetic scaffolds, the authors studied the effect of scaffold properties, including RGD concentration, MMP sensitivity, and network crosslinking density, as well as heparin as an exogenous factor on 3-D SMC proliferation. The results indicated that the incorporation of cell-adhesive ligand significantly enhanced SMC spreading and proliferation, with cell-adhesive ligand concentration mediating 3-D SMC proliferation in a biphasic manner. The faster degrading hydrogels promoted SMC proliferation and spreading. In addition, 3-D SMC proliferation was inhibited by increasing network crosslinking density and exogenous heparin treatment. These constructs are a good model system for studying the effect of hydrogel properties on SMC functions and show promise as a tissue engineering platform for vascular in vivo applications.

Heparin responses in vascular smooth muscle cells involve cGMP-dependent protein kinase (PKG)

Published data provide strong evidence that heparin treatment of proliferating vascular smooth muscle cells results in decreased signaling through the ERK pathway and decreases in cell proliferation. In addition, these changes have been shown to be mimicked by antibodies that block heparin binding to the cell surface. Here, we provide evidence that the activity of protein kinase G is required for these heparin effects. Specifically, a chemical inhibitor of protein kinase G, Rp-8-pCPT-cGMS, eliminates heparin and anti-heparin receptor antibody effects on bromodeoxyuridine incorporation into growth factor-stimulated cells. In addition, protein kinase G inhibitors decrease heparin effects on ERK activity, phosphorylation of the transcription factor Elk-1, and heparin-induced MKP-1 synthesis. Although transient, the levels of cGMP increase in heparin treated cells. Finally, knock down of protein kinase G also significantly decreases heparin effects in growth factor-activated vascular smooth muscle cells. Together, these data indicate that heparin effects on vascular smooth muscle cell proliferation depend, at least in part, on signaling through protein kinase G.

Simulated microgravity exposure modulates the phenotype of cultured vascular smooth muscle cells

Evidence from ground-based animal studies using tail-suspended hindlimb unloaded rats model has clearly demonstrated that simulated microgravity-induced smooth muscle cell phenotype conversion, a characteristic vascular structural and functional remodeling, may be one of the key contributors to postspaceflight orthostatic intolerance. However, the rats model involves multiple collective effects of microgravity including cephalic fluid shift and postural muscle unloading on smooth muscle cells (SMCs). It cannot isolate a single factor from the collective ones and therefore is not ideal to study the effects of gravitational vector alteration alone on SMCs. To test the hypothesis that gravitational vector alteration per se might affect smooth muscle cell phenotype, a roller culture apparatus was employed to expose cultured rat aortic smooth muscle cells (RASMCs) to simulated microgravity. Cell proliferation, cell cycle distribution, apoptosis, migration, and nitric oxide production rates were measured and compared between the control and the simulated microgravity groups. Cell cytoskeleton reorganization induced by simulated microgravity was observed by confocal microscopy. Specific contractile and synthetic Gene expression at the mRNA level was quantified by reverse transcriptional polymerase chain reaction. It was observed that simulated microgravity suppressed RASMC proliferation and migration, enhanced cell apoptosis, stimulated NO release, and destroyed the original well-organized cytoskeleton. Moreover, at the mRNA level, long-time exposure (≥ 72 h) to simulated microgravity induced a contractile phenotype tendency by up-regulating smMHC expression. All these findings suggest that the phenotype modulation of vascular smooth muscle cells may be gravity dependent.

Hierarchical scaffolding of an ERK1/2 activation pathway

Background

Scaffold proteins modulate cellular signaling by facilitating assembly of specific signaling pathways. However, there is at present little information if and how scaffold proteins functionally interact with each other.

Results

Here, we show that two scaffold proteins, caveolin-1 and IQGAP1, are required for phosphorylation of the actin associated pool of extracellular signal regulated kinase 1 and 2 (ERK1/2) in response to protein kinase C activation. We show by immunofluorescence and proximity ligation assays, that IQGAP1 tethers ERK1/2 to actin filaments. Moreover, siRNA experiments demonstrate that IQGAP1 is required for activation of actin-bound ERK1/2. Caveolin-1 is also necessary for phosphorylation of actin-bound ERK1/2 in response to protein kinase C, but is dispensible for ERK1/2 association with actin. Simultaneous knock down of caveolin-1 and IQGAP1 decreases total phorbol ester-induced ERK1/2 phosphorylation to the same degree as single knock down of either caveolin-1 or IQGAP1, indicating that caveolin-1 and IQGAP1 operate in the same ERK activation pathway. We further show that caveolin-1 knock down, but not IQGAP1 knock down, reduces C-Raf phosphorylation in response to phorbol ester stimulation.

Conclusions

Based on our data, we suggest that caveolin-1 and IQGAP1 assemble distinct signaling modules, which are then linked in a hierarchical arrangement to generate a functional ERK1/2 activation pathway.

Unfractionated heparin: multitargeted therapy for delayed neurological deficits induced by subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is associated with numerous "delayed neurological deficits" (DNDs) that have been attributed to multiple pathophysiological mechanisms, including ischemia, microthrombosis, free radical damage, inflammation, and vascular remodeling. To date, effective prophylactic therapy for SAH-induced DNDs has been elusive, due perhaps to the multiplicity of mechanisms involved that render typical, single-agent therapy seemingly futile. We hypothesized that heparin, which has multiple underappreciated salutary effects, might be useful as a multitargeted prophylactic agent against SAH-induced DNDs. We performed a comprehensive review of the literature to evaluate the potential utility of heparin in targeting the multiple pathophysiological mechanisms that have been identified as contributing to SAH-induced DNDs. Our literature review revealed that unfractionated heparin can potentially antagonize essentially all of the pathophysiological mechanisms known to be activated following SAH. Heparin binds >100 proteins, including plasma proteins, proteins released from platelets, cytokines, and chemokines. Also, heparin complexes with oxyhemoglobin, blocks the activity of free radicals including reactive oxygen species, antagonizes endothelin-mediated vasoconstriction, smooth muscle depolarization, and inflammatory, growth and fibrogenic responses. Our review suggests that the use of prophylactic heparin following SAH may warrant formal study.

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

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

Heparin treatment of vascular smooth muscle cells results in the synthesis of the dual-specificity phosphatase MKP-1

The ability of heparin to block proliferation of vascular smooth muscle cells has been well documented. It is clear that heparin treatment can decrease the level of ERK activity in vascular smooth muscle cells that are sensitive to heparin. In this study, the mechanism by which heparin induces decreases in ERK activity was investigated by evaluating the dual specificity phosphatase, MKP-1, in heparin treated cells. Heparin induced MKP-1 synthesis in a time and concentration dependent manner. The time-course of MKP-1 expression correlated with the decrease in ERK activity. Over the same time frame, heparin treatment did not result in decreases in MEK-1 activity which could have, along with constitutive phosphatase activity, accounted for the decrease in ERK activity. Antibodies against a heparin receptor also induced the synthesis of MKP-1 along with decreasing ERK activity. Blocking either phosphatase activity or synthesis also blocked heparin-induced decreases in ERK activity. Consistent with a role for MKP-1, a nuclear phosphatase, heparin treated cells exhibited decreases in nuclear ERK activity more rapidly than cells not treated with heparin. The data support MKP-1 as a heparin-induced phosphatase that dephosphorylates ERK, decreasing ERK activity, in vascular smooth muscle cells.

Low-concentration heparin suppresses ionomycin-activated CAMK-II/EGF receptor- and ERK-mediated signaling in mesangial cells

Heparin and endogenous heparinoids inhibit the proliferation of smooth muscle cells, including renal mesangial cells; multiple effects on signaling pathways are well established, including effects on PKC, Erk, and CaMK-II. Many studies have used heparin at concentrations of 100 microg/ml or higher, whereas endogenous concentrations of heparinoids are much lower. Here we report the effects of low-concentration (1 microg/ml) heparin on activation of several kinases and subsequent induction of the c-fos gene in mesangial cells in response to the calcium ionophore, ionomycin, in the absence of serum factors. Ionomycin rapidly increases the phosphorylation of CaMK-II (by 30 s), and subsequently of the EGF receptor (EGFR), c-Src, and Erk 1/2. Low-dose heparin suppresses the ionomycin-dependent phosphorylation of EGFR, c-Src, and Erk 1/2, but not of CaMK-II, whereas inhibition of activated CaMK-II reduces phosphorylation of EGFR, c-Src, and Erk. Our data support a mechanism whereby heparin acts at the cell surface to suppress downstream targets of CaMK-II, including EGFR, leading in turn to a decrease in Erk- (but not c-Src-) dependent induction of c-fos.

The low-molecular-weight heparin, nadroparin, inhibits tumour angiogenesis in a rodent dorsal skinfold chamber model

BACKGROUND

Recently, low-molecular-weight heparins (LMWHs) were found to confer a survival advantage in cancer patients. The mechanism underlying this observation is unclear, but may involve inhibition of tumour angiogenesis. We aimed to examine the effects of nadroparin on tumour angiogenesis using a dorsal skinfold window chamber model in the Syrian hamster.

METHODS

AMel-3 and HAP-T1 tumours were grown in donor animals and fragments implanted in the window chambers. Animals (N=46) were treated with 200 IU of nadroparin or saline for 10 days. Repeated intravital fluorescence microscopy was performed to calculate functional microcirculatory parameters: number (N) and length (L) of microvessels, vascular area fraction (AF), and red blood cell velocity (V). Microvessel density (MVD), fractal dimension, and pericyte coverage were assessed histologically.

RESULTS

Active angiogenesis was observed in control animals, resulting in a significant increase in N, L, and AF. In nadroparin-treated animals, however, N and L did not increase whereas AF decreased significantly. Both groups showed an initial increase in V, but nadroparin treatment resulted in an earlier decrease in red blood cell velocity over time. Compared with control animals, nadroparin-treated animals showed a significantly lower MVD and fractal dimension but significantly higher pericyte coverage index (PCI).

CONCLUSIONS

Taken together, these results suggest that the LMWH nadroparin inhibits tumour angiogenesis and results in microvessel normalisation.

The influence of RGD-bearing hydrogels on the re-expression of contractile vascular smooth muscle cell phenotype

This study reports on the ability of poly(ethylene glycol) diacrylate (PEGDA) hydrogel scaffolds with pendant integrin-binding GRGDSP peptides (RGD-gels) to support the re-differentiation of cultured vascular smooth muscle cells (SMCs) toward a contractile phenotype. Human coronary artery SMCs were seeded on RGD-gels, hydrogels with other extracellular matrix derived peptides, fibronectin (FN) and laminin (LN). Differentiation was induced on RGD-gels with low serum medium containing soluble heparin, and the differentiation status was monitored by mRNA expression, protein expression, and intracellular protein organization of the contractile smooth muscle markers, smooth muscle alpha-actin, calponin, and SM-22alpha. RGD-gels supported a rapid induction (2.7- to 25-fold up-regulation) of SMC marker gene mRNA, with expression levels that were equivalent to FN and LN controls. Marker protein levels mirrored the changes in mRNA expression, with levels on RGD-gels indistinguishable from FN and LN controls. Furthermore, these markers co-localized in stress fibers within SMCs on RGD-gels suggesting the recapitulation of a contractile apparatus within the cells. These results indicate that SMCs cultured on RGD-bearing hydrogels can re-differentiate toward a contractile phenotype suggesting this material is an excellent candidate for further development as a bioactive scaffold that regulates SMC phenotype.

The effects of heparin releasing hydrogels on vascular smooth muscle cell phenotype

Poly(ethylene glycol) diacrylate (PEGDA) hydrogel scaffolds were engineered to promote contractile smooth muscle cell (SMC) phenotype via controlled release of heparin. The scaffold design was evaluated by quantifying the effects of free heparin on SMC phenotype, engineering hydrogels to provide controlled release of heparin, and synthesizing cell-adhesive, heparin releasing hydrogels to promote contractile SMC phenotype. Heparin inhibited SMC proliferation and up-regulated expression of contractile SMC phenotype markers, including smooth muscle alpha-actin, calponin, and SM-22alpha, in a dose-dependent fashion (6 microg/ml to 3.2mg/ml). Heparin release from PEGDA hydrogels was controlled by altering PEGDA molecular weight (MW 1000-6000) and concentration at polymerization (10-30% w/w), yielding release profiles ranging from hours to weeks in duration. Heparin released from PEGDA gels, formulated for optimized heparin loading and release kinetics (30% w/w PEGDA, MW 3000), stimulated SMCs to up-regulate contractile marker mRNA. A cell-instructive scaffold construct was prepared by polymerizing a thin hydrogel film, with pendant RGD peptides for cell attachment, over the optimized hydrogel depots. SMCs seeded on these constructs had elevated levels of contractile marker mRNA after 3 d of culture compared with SMCs on control constructs. These results indicate that RGD-modified, heparin releasing PEGDA gels can act as cell-instructive scaffolds that promote contractile SMC phenotype.

Production of heparin-containing hydrogels for modulating cell responses

Successful tissue regeneration requires that biomaterials have optimal bioactivity and mechanical properties. Heparin-containing hydrogels that can be crosslinked in situ were designed to contain tunable amounts of biological components (e.g. heparin, arginine-glycine-aspartate (RGD)) as well as to exhibit controlled mechanical properties (e.g. shear modulus). These gel parameters can also be tuned to provide controlled delivery of proteins, such as growth factors, for regulating cellular behavior. Maleimide-functionalized low-molecular-weight heparin (LWMH) was conjugated to a poly(ethylene glycol) (PEG) hydrogel. The elastic shear modulus, as assessed via oscillatory rheology experiments, could be tuned by the concentration of polymer in the hydrogel, and by the end group functionality of PEG. Hydrogels of two different moduli (2.8 and 0.4kPa) were used to study differences in the response of human aortic adventitial fibroblasts (AoAF) in two-dimensional cell culture experiments. These experiments indicated that the AoAFs show improved adhesion to materials with the higher modulus. Evaluation of cell responses to hydrogels with RGD linked to the hydrogels via conjugation to PEG or to LMWH indicated improved cellular responses to these materials when the bioactive ligands were chemically attached through linkage to the PEG rather than to the LMWH. These results highlight important design considerations in the tailoring of these materials for cardiovascular tissue engineering applications.

Heparin suppresses lipid raft-mediated signaling and ligand-independent EGF receptor activation

Heparin is well known to suppress vascular smooth muscle cell (VSMC) proliferation, and attempts to exploit this therapeutically have led to recognition of multiple pathways for heparin's anti-mitogenic actions. At low concentrations (ca. 1 microg.ml(-1)), these suppressive effects may reflect physiological activities of endogenous heparan sulfates, and appear to be rapid responses to extracellular or cell surface-associated heparin. Because heparin has been shown to influence expression of caveolin proteins, and caveolae/lipid rafts are critical structures modulating cell signaling, we examined the effect of heparin on signaling involving cholesterol-rich membrane microdomains. The VSMC line PAC-1 activates the MAP kinase Erk in response to the cholesterol-sequestering agents methyl-beta-cyclodextrin and nystatin. This follows a temporal sequence that involves Ras-GTP activation of MEK, and is independent of PKC, Src, and PI3 kinase. However, ligand-independent phosphorylation of the EGF receptor (EGFR) by removal of cholesterol precedes Ras activation, and the EGFR kinase inhibitor AG1478 blocks Erk phosphorylation, supporting occurrence of the signaling sequence EGFR-Ras-MEK-Erk. Phosphorylation of EGFR occurs predominantly in caveolin-rich microdomains as identified by Western blotting of fractions from density gradient centrifugation of membranes prepared under detergent-free conditions. In these situations, heparin inhibits phosphorylation of EGFR on the Src-dependent site Tyr(845), but not the autophosphorylation of Tyr(1173), and decreases Ras activation and Erk phosphorylation. We conclude that heparin can suppress Erk signaling in VSMC with effects on site-specific phosphorylation of EGFR localized in caveolin-enriched lipid rafts.

Platelet-Derived Growth Factor-BB–Induced Human Smooth Muscle Cell Proliferation Depends on Basic FGF Release and FGFR-1 Activation

We have shown that the G protein–coupled receptor (GPCR) agonists, thrombin and Factor Xa, stimulate smooth muscle cell (SMC) proliferation through transactivation of the EGF receptor (EGFR) or the FGF receptor (FGFR), both of which are tyrosine kinase receptors. In the present study, we investigated whether platelet-derived growth factor (PDGF), a tyrosine kinase receptor agonist, might transactivate another tyrosine kinase receptor to induce SMC proliferation. Because heparin inhibits PDGF-mediated proliferation in human SMCs, we investigated whether the heparin-binding growth factor basic fibroblast growth factor (bFGF) and one of its receptors, FGFR-1, play a role in the response of human arterial SMCs to PDGF-BB. PDGF-BB induced the release of bFGF and sustained phosphorylation of FGFR-1 (30 minutes to 6 hours). A bFGF-neutralizing antibody inhibited PDGF-BB–mediated phosphorylation of FGFR-1, DNA synthesis, and cell proliferation. In the presence of bFGF antibody, PDGF-BB–induced early activation of ERK (0 to 60 minutes) was not affected, whereas late ERK activation (2 to 4 hours) was reduced. When FGFR-1 expression was suppressed using small interfering RNA (siRNA), ERK activation was reduced at late, but not early, time points after PDGF-BB stimulation. Addition of bFGF antibody to cells treated with siRNA to FGFR-1 had no further effect on ERK activation. Our results provide support for a novel mechanism by which PDGF-BB induces the release of bFGF and activation of FGFR-1 followed by the sustained activation of ERK and proliferation of human SMCs.

Ca(2+)/calmodulin-dependent protein kinase II inhibition by heparin in mesangial cells

Heparin exerts an antiproliferative effect in smooth muscle cells, and the Ca(2+)/calmodulin-dependent protein kinase (CaMK) signaling pathway is heparin sensitive. Here, we report that transfection with a truncated 326-amino acid fragment of CaMK-IIalpha increases basal activity of CaMK-II in mesangial cells. Ionomycin increased CaMK-II activity in both transfected and untransfected cells, with a concomitant increase in activated Ca(2+)/calmodulin. Heparin (1 microg/ml), but not chondroitin or dermatan sulfate, significantly attenuated both serum- or ionomycin-induced CaMK-II activity, and attendant c-fos mRNA expression, but did not affect upstream Ca(2+)/calmodulin. Autophosphorylation of Thr286 generates an autonomously active CaMK-II. Both serum and ionomycin increased phosphorylation at this site and increased CaMK-II activity in antiphosphothreonine immunoprecipitates. Heparin (1 microg/ml) did not inhibit phosphorylation of Thr286 (although much higher concentrations did). Replacement of Thr286 with Asp produces a constitutively active mutant that was insensitive to ionomycin but was inhibited by heparin maximally at 1 microg/ml. These results suggest that heparin at physiological concentrations acts at or downstream of CaMK-II to suppress its activity independent of an effect on autophosphorylation.

Enoxaparin--a low molecular weight heparin, restores the altered vascular reactivity of resistance arteries in aged and aged-diabetic hamsters

We questioned whether the low molecular weight heparin enoxaparin acts upon the altered vascular reactivity of the resistance arteries in normal biological aging and in aging associated with diabetes. Experiments were performed on isolated resistance arteries of young (4 months old), aged (16 months old), and aged-diabetic hamsters (16 months old and 5 months since streptozotocin injection), and the reactivity was assessed by the myograph technique. The results showed that enoxaparin (60 microg/ml) had favorable effects on the vascular reactivity in aged and aged-diabetic conditions, i.e., diminished the contractility of the arterial wall to 10(-8)-10(-6) M noradrenaline (NA) and to K(+), and potentiated the impeded endothelium-dependent relaxation to 10(-8)-10(-4) M acetylcholine (ACh). The effect was more pronounced compared to that produced by unfractionated heparin (UFH). These pharmacological effects supplement the anticoagulant properties of enoxaparin and may be of relevance for improving perfusion/circulation in the microvasculature of aged and of aged-diabetic persons.

Increased expression of the MBP mRNA binding protein HnRNP A2 during oligodendrocyte differentiation

Heterogeneous nuclear ribonucleoprotein (hnRNP) A2, a trans-acting factor that mediates intracellular trafficking of myelin basic protein (MBP) mRNA to the myelin compartment in oligodendrocytes, is most abundant in the nucleus, but shuttles between the nucleus and cytoplasm. In the cytoplasm, it is associated with granules that transport mRNA from the cell body to the processes of oligodendrocytes. We found that the overall level of hnRNP A2 increased in oligodendrocytes as they differentiated into MBP-positive cells, and that this augmentation was reflected primarily in the cytoplasmic pool of hnRNP A2 present in the form of granules. The extranuclear distribution of hnRNP A2 was also observed in brain during the period of myelination in vivo. Methylation and phosphorylation have been implicated previously in the nuclear to cytoplasmic distribution of hnRNPs, so we used drugs that block methylation and phosphorylation of hnRNPs to assess their effect on hnRNP A2 distribution and mRNA trafficking. Cultures treated with adenosine dialdehyde (AdOx), an inhibitor of S-adenosyl-L-homocysteine hydrolase, or with 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), a drug that inhibits casein kinase 2 (CK2), maintained the preferential nuclear distribution of hnRNP A2. Treatment with either drug affected the transport of RNA trafficking granules that remained confined to the cell body.

Cardiovascular hypertrophy in one-kidney, one-clip renal hypertension is resistant to heparin

OBJECTIVE

Heparin inhibits vascular hypertrophy in angiotensin-induced hypertension, in addition to its well-known role in inhibiting injury-induced vascular smooth muscle proliferation. We tested whether hypertension and vascular hypertrophy could be reduced by heparin independently from the renin-angiotensin system.

METHODS

Rats were made hypertensive with a one-kidney, one-clip (1K1C) procedure and received heparin from osmotic minipumps (0.3 mg/h per kg i.v.) or saline vehicle for 2 weeks. Blood pressure was measured by the tail-cuff method and vessel cross-sectional area was measured by morphometry in the aorta and mesenteric arteries. Proliferation was assessed with bromodeoxyuridine labelling.

RESULTS

Blood pressure elevation and cardiovascular hypertrophy were evident in 1K1C rats. The media of mesenteric arteries was increased by 25%, and the media : lumen ratio by 35%, in hypertensive rats. DNA synthesis by smooth muscle cells in the mesenteric arteries was increased sevenfold in renal hypertension. Heparin treatment did not influence either the increase in blood pressure, the cardiovascular hypertrophy response or hypertension-mediated proliferation of arterial smooth muscle cells.

CONCLUSIONS

These data suggest that the vascular hypertrophy mechanisms operating in 1K1C renal hypertension are not inhibited by heparin and thus are different from those in angiotensin-mediated hypertension. Identifying such mechanisms in the future will be important for devising appropriate intervention strategies in angiotensin-independent forms of vascular hypertrophy.

Contribution of PKC-dependent and -independent processes in temporal ERK regulation by ET-1, PDGF, and EGF in rat myometrial cells

Endothelin-1 (ET-1), platelet-derived growth factor (PDGF), and epidermal growth factor (EGF) stimulated thymidine incorporation with different efficiency (PDGF ≫ EGF = ET-1) in rat myometrial cells. They also stimulated ERK activation, which culminated at 5 min and then declined to reach a plateau (at 45 min: EGF > 90%, PDGF = 50%, and ET-1 < 10% of maximum). Inhibition and downregulation of PKC demonstrated that ERK activation at 5 min involved PKCδ and -ζ for ET-1 and PKCα plus another PKC isoform for PDGF. By contrast, the EGF response did not involve PKC. Stimulation of Ras was more important with EGF than with PDGF, with ET-1 being the weakest activator. The simultaneous incubation of the cells with EGF and ET-1 potentiated the ERK activation at 5 min and mimicked the plateau phase obtained with PDGF. Under these conditions thymidine incorporation was comparable to that induced by PDGF. Taken together, our results indicated that the kinetic profile of ERK activation and its impact on cell proliferation can be modulated by the differential involvement of PKC isoforms and the amplitude of Ras activation.

Long-term in vitro analysis of limb cartilage development: Involvement of Wnt signaling

Endochondral skeletal development involves the condensation of mesenchymal cells, their differentiation into chondrocytes, followed by chondrocyte maturation, hypertrophy, and matrix mineralization, and replacement by osteoblasts. The Wnt family of secreted proteins have been shown to play important roles in vertebrate limb formation. To examine the role(s) of Wnt members and their transmembrane-spanning receptor(s), Frizzled (fz), we retrovirally misexpressed Wnt-5a, Wnt-7a, chicken frizzled-1 (Chfz-1), and frizzled-7 (Chfz-7) in long-term (21 day) high density, micromass cultures of stage 23/24 chick embryonic limb mesenchyme. This culture system recapitulates in vitro the entire differentiation (days 1-10), growth (days 5-12), and maturation and hypertrophy (from day 12 on) program of cartilage development. Wnt-7a misexpression severely inhibited chondrogenesis from day 7 onward. Wnt-5a misexpression resulted in a poor hypertrophic phenotype by day 14. Chfz-7 misexpression caused a slight delay of chondrocyte maturation based on histology, whereas Chfz-1 misexpression did not affect the chondrogenic phenotype. Misexpression of all Wnt members decreased collagen type X expression and alkaline phosphatase activity at day 21. Our findings implicate functional role(s) for Wnt signaling throughout embryonic cartilage development, and show the utility of the long-term in vitro limb mesenchyme culture system for such studies.

The neointimal response to endovascular injury is increased in obese Zucker rats

BACKGROUND

Restenosis after revascularization procedures is accelerated in persons with type 2 diabetes.

AIM

The current study tested the hypothesis that the neointimal response to endovascular injury is enhanced in female obese Zucker (OZ) rats, a model of type 2 diabetes.

METHODS

Animals were randomized to receive either a standard diet (SD) or a diabetogenic diet (DD) for 6 weeks. Four weeks later, balloon injury of the right common carotid artery was induced. All rats were euthanized 2 weeks after injury. Lean Zucker (LZ) rats served as controls.

RESULTS

At the time of death, plasma glucose was elevated in OZ rats fed a SD (208 +/- 13 mg/dl) and a DD (288 +/- 21 mg/dl) compared to corresponding LZ rats (SD: 153 +/- 8; DD: 132 +/- 7 mg/dl). The ratio of high-density lipoprotein cholesterol (HDLc) to total cholesterol (Totc), an index of atherogenicity, was reduced in OZ rats on both diets (SD: 0.77 +/- 0.06; DD: 0.80 +/- 0.09) compared to LZ controls (SD: 1.11 +/- 0.02; DD: 1.20 +/- 0.05). Histomorphometric analysis of injured arteries showed that the intima to media (I : M) ratio was significantly increased in OZ (1.37 +/- 0.07) compared to LZ (0.79 +/- 0.08) rats. Elevations in plasma glucose and triglycerides (Tg) correlated positively and decreases in HDLc negatively with an increased I : M ratio. Administration of the DD did not further enhance the I : M ratio in LZ (0.87 +/- 0.06) or OZ (1.29 +/- 0.09) rats.

CONCLUSIONS

These results suggest that neointima formation following endoluminal injury of the carotid artery is enhanced at an early stage in the development of diabetes mellitus.

Suppression of mitogen-activated protein kinase phosphatase-1 (MKP-1) by heparin in vascular smooth muscle cells

Heparin inhibits vascular smooth muscle cell (VSMC) proliferation, but mechanisms remain elusive. Because heparin inhibits signaling through multiple kinase cascades, we investigated the possibility that phosphatases could be involved. Mitogen-activated protein kinase phosphatase-1 (MKP-1) was the predominant MKP detected in VSMC lines. MKP-1 protein was increased by serum stimulation of quiescent cells, and this increase was diminished by heparin (1 microg/mL). Increased MKP-1 expression was dependent on the mitogen-activated protein kinase, Erk. Decreased Erk activity in the presence of heparin preceded, and may account for, decreased MKP-1. The antimitogenic effects of heparin are therefore unlikely to act through a shift in the kinase/phosphatase balance, but rather through direct kinase suppression. However, because MKP-1 is known to cause an increase in activity of kinases upstream of Erk, that may signal through additional pathways, the decrease in MKP-1 activity may paradoxically enhance heparin's antiproliferative effects. VSMC selected to grow in the presence of heparin express decreased levels of MKP-1 that are unresponsive to heparin, and Erk activity becomes unresponsive to heparin in one cell line. We conclude that phosphatase activation is not a direct mechanism of suppression of multiple kinase cascades by heparin.

Phosphorylation of the platelet-derived growth factor receptor-beta and epidermal growth factor receptor by G protein-coupled receptor kinase-2. Mechanisms for selectivity of desensitization

Accumulating evidence suggests that receptor protein-tyrosine kinases, like the platelet-derived growth factor receptor-beta (PDGFRbeta) and epidermal growth factor receptor (EGFR), may be desensitized by serine/threonine kinases. One such kinase, G protein-coupled receptor kinase-2 (GRK2), is known to mediate agonist-dependent phosphorylation and desensitization of multiple heptahelical receptors. In testing whether GRK2 could phosphorylate and desensitize the PDGFRbeta, we first found by phosphoamino acid analysis that cells expressing GRK2 could serine-phosphorylate the PDGFRbeta in an agonist-dependent manner. Augmentation or inhibition of GRK2 activity in cells, respectively, reduced or enhanced tyrosine phosphorylation of the PDGFRbeta but not the EGFR. Either overexpressed in cells or as a purified protein, GRK2 demonstrated agonist-promoted serine phosphorylation of the PDGFRbeta and, unexpectedly, the EGFR as well. Because GRK2 did not phosphorylate a kinase-dead (K634R) PDGFRbeta mutant, GRK2-mediated PDGFRbeta phosphorylation required receptor tyrosine kinase activity, as does PDGFRbeta ubiquitination. Agonist-induced ubiquitination of the PDGFRbeta, but not the EGFR, was enhanced in cells overexpressing GRK2. Nevertheless, GRK2 overexpression did not augment PDGFRbeta down-regulation. Like the vast majority of GRK2 substrates, the PDGFRbeta, but not the EGFR, activated heterotrimeric G proteins allosterically in membranes from cells expressing physiologic protein levels. We conclude that GRK2 can phosphorylate and desensitize the PDGFRbeta, perhaps through mechanisms related to receptor ubiquitination. Specificity of GRK2 for receptor protein-tyrosine kinases, expressed at physiologic levels, may be determined by the ability of these receptors to activate heterotrimeric G proteins, among other factors.

Inhibition of rat smooth muscle cell adhesion and proliferation by non-anticoagulant heparins

Heparin is a well established growth inhibitor of arterial smooth muscle cells (SMCs) both in animal models and in vitro. Even though the cellular mechanisms involved in the anti-proliferative properties of heparin are being resolved, the structural requirements for the biological effects of heparin are not known in detail. Here, we have studied the effect of chemically modified heparins of different molecular weights and anticoagulant activities on proliferation and adhesion of rat aortic SMCs in vitro. The effects of native heparin (NH) and chemically modified heparins were examined after stimulation with fetal calf serum (FCS), platelet-derived growth factor BB (PDGF BB), basic fibroblast growth factor (bFGF), and heparin-binding epidermal growth factor (hbEGF) with respect to DNA synthesis and expression of phosphorylated and activated mitogen-activated protein kinase (pERK1 and 2). In a similar manner as NH, the modified heparins were capable of inhibiting activation of ERK1 and 2 and DNA synthesis induced by FCS and hbEGF whereas the modified heparins potentiated the mitogenic effect of bFGF and no compound affected PDGF BB-induced ERK activity and SMC growth. In contrast, cell adhesion to fibronectin was inhibited by NH and modified heparins in a size-dependent manner with the lowest effect by the smallest compound. The results show that heparins with varying anticoagulant activities and molecular weights but with similar sulfate content can retain anti-proliferative properties while the effect on some other biological processes such as cell adhesion is lost. Possibly, such chemical alterations may yield useful substances for the prevention of SMC proliferation after arterial injury.

The S18 ribosomal protein is a putative substrate for Ca2+/calmodulin-activated protein kinase II

The delta-isoform of Ca(2+)/calmodulin-activated protein kinase II (CaMK II) is abundantly expressed in vascular smooth muscle, but relatively little is known about its regulation or its potential cellular substrates. There are few, if any, known substrates of CaMK II that are physiologically relevant in vascular smooth muscle cells. Studies presented earlier (Mishra-Gorur, K., Singer, H. A., and Castellot, J. J., Jr. (2002) Am. J. Pathol., in press) by our laboratory show an inhibitory effect of heparin on CaMK II phosphorylation and activity. During these studies we observed the specific co-immunoprecipitation of a 20-kDa protein with CaMK II. Purification and sequence analysis indicate that this protein is the S18 protein of the 40 S ribosome. S18 was found to be abundantly phosphorylated in response to serum treatment, and this effect was strongly inhibited by heparin. In addition, KN-93, a specific CaMK II inhibitor, blocks S18 phosphorylation in vascular smooth muscle cells; a concomitant 24% reduction in protein synthesis was observed. Taken together these data support the idea that S18 could be a novel substrate for CaMK II, thus providing a potential link between Ca(2+)-mobilizing agents and protein translation.

Heparin amplifies platelet-derived growth factor (PDGF)- BB-induced PDGF alpha -receptor but not PDGF beta -receptor tyrosine phosphorylation in heparan sulfate-deficient cells. Effects on signal transduction and biological responses

Platelet-derived growth factor (PDGF) induces mitogenic and migratory responses in a wide variety of cells, by activating specific receptor tyrosine kinases denoted the PDGF alpha- and beta-receptors. Different PDGF isoforms bind in a distinct manner to glycosaminoglycans, particularly heparan sulfate. In the present study, we show potentiation by exogenous heparin of PDGF-BB-induced PDGF alpha-receptor tyrosine phosphorylation in heparan sulfate-deficient Chinese hamster ovary (CHO) 677 cells. This effect was not seen for PDGF-AA treatment, and heparin lacked a potentiating effect on PDGF-BB stimulation of the PDGF beta-receptor. Heparin did not affect the affinity of PDGF-BB binding for the PDGF receptors on CHO 677 cells. The PDGF-BB-stimulated PDGF alpha-receptor phosphorylation was enhanced in a dose-dependent fashion by heparin at low concentration. The effect was modulated by 2-O- and 6-O-desulfation of the polysaccharide. Maximal induction of PDGF alpha-receptor tyrosine phosphorylation (6-fold) in CHO 677 cells was achieved by treatment with a heparin decasaccharide, but shorter oligosaccharides consisting of four or more monosaccharide units were also able to augment PDGF alpha-receptor phosphorylation, albeit at higher concentrations. Heparin potentiated PDGF-BB-induced activation of mitogen-activated protein kinase and protein kinase B (Akt) and allowed increased chemotaxis of the CHO 677 cells toward PDGF-BB. In conclusion, heparin modulates PDGF-BB-induced PDGF alpha-receptor phosphorylation and downstream signaling, with consequences for cellular responsiveness to the growth factor.

Heparin inhibits hyperventilation-induced late-phase hyperreactivity in dogs

Inhalation of heparin attenuates hyperventilation-induced bronchoconstriction in humans and dogs. The purpose of this study was to determine whether heparin inhibits the late-phase response to hyperventilation, which is characterized by increased peripheral airway resistance (RP), eicosanoid mediator production, neutrophilic/ eosinophilic inflammation, and airway hyperreactivity (AHR) at 5 h after dry air challenge (DAC). Fiberoptic bronchoscopy was used to record RP and airway reactivity (DeltaRP) to aerosol and intravenous histamine before and 5 h after DAC. Bronchoalveolar lavage fluid (BALF) cells and eicosanoid mediators were also measured approximately 5 h after DAC. DAC of vehicle-treated bronchi resulted in late-phase airway obstruction (approximately 120% increase over baseline RP), inflammation, increased BALF concentrations of leukotriene (LT) C(4), LTD(4), and LTE(4) and prostaglandin (PG)D(2), and AHR. Pretreatment with aerosolized heparin attenuated late-phase airway obstruction by approximately 50%, inhibited eosinophil infiltration, reduced BALF concentrations of LTC(4), LTD(4), and LTE(4) and PGD(2), and abolished AHR. We conclude that heparin inhibits hyperventilation-induced late-phase changes in peripheral airway function, and does so in part via the inhibition of eosinophil migration and eicosanoid mediator production and release.

Vasoactive factors and growth factors alter vascular smooth muscle cell EC-SOD expression

Oxygen free radicals have been suggested to play important roles in atherogenesis and other pathological processes in the blood vessel wall. The vascular wall contains large amounts of extracellular superoxide dismutase (EC-SOD), which is produced and secreted to the extracellular space by smooth muscle cells. In this study, we investigated the influence of factors regulating tension and proliferation of vascular smooth muscle cells and of some interstitial matrix components on EC-SOD expression. The expression and secretion of EC-SOD were upregulated by histamine, vasopressin, oxytocin, endothelin-1, angiotensin II, serotonin, heparin, and heparan sulfate and were downregulated by platelet-derived growth factors-AA and -BB, acidic and basic fibroblast growth factors, and epidermal growth factor. The responses were slow and developed over several days. The findings suggest that various physiological and pathological conditions might markedly influence EC-SOD expression, significantly altering the susceptibility of the vascular wall to effects of the superoxide radical.

Regulation of renal proximal tubular epithelial cell fibroblast growth factor-2 generation by heparin

Progression of renal disease is closely correlated to the degree of renal interstitial fibrosis, and evidence is increasing that epithelial cells of the renal proximal tubule (PTCs) may contribute to its pathogenesis. Such cytokines as basic fibroblast growth factor (FGF-2) have been implicated in progressive renal injury, and we previously showed that PTCs are a source of this cytokine. FGF-2 is characterized by its high affinity for heparin, and numerous studies have suggested that heparin may modify the progression of renal disease. The current study examined how heparin influenced FGF-2 generation and bioactivity in the human renal epithelial PTC line, HK-2. Incubation of HK-2 cells with heparin led to a dose- and time-dependent increase in FGF-2 concentration in the culture supernatant that was not accompanied by alterations in FGF-2 messenger RNA expression, assessed by reverse-transcriptase polymerase chain reaction and Northern analysis. The heparin-induced increase in FGF-2 concentration was accompanied by a decrease in the amount of FGF-2 bound to the extracellular matrix, although this accounted for only a small proportion of the total FGF-2 generated. Induction of FGF-2 by 2-O-desulfated heparin, together with a reduction in total cell-associated FGF-2 and anti-FGF-2 antibody binding to fixed permeabilized cells after the addition of heparin, suggested that the FGF-2 released was mainly derived from a preformed intracellular source. That FGF-2 was predominantly derived from an intracellular pool was also confirmed by pulse chase experiments. The addition of heparin resulted in the generation of bioinactive FGF-2, judged by in vitro fibroblast proliferation. Conversely, heparitinase treatment of supernatant samples from heparin-treated cells and the addition of 2-O-desulfated heparin resulted in the generation of active FGF-2, suggesting that the generation of bioinactive FGF-2 was related to binding of FGF-2 by extracellular heparin after its release from cells. These data show that heparin depletes both the cell and surrounding matrix of FGF-2 and suggest that FGF-2 released from cells was mainly derived from a preformed intracellular source. Furthermore, FGF-2 released from epithelial PTCs after the application of heparin was bioinactive. This likely resulted from released FGF-2 binding to an excess of extracellular heparin. Results presented here therefore suggest a mechanism by which heparin, through its effect on depletion of matrix and cells of FGF-2 and its generation in an inactive form, may influence progressive renal interstitial fibrosis.

Low doses of EPO activate MAP kinases but not JAK2-STAT5 in rat vascular smooth muscle cells

Previous reports have shown a direct effect of erythropoietin (Epo) on vascular smooth muscle cells (VSMCs). Our aim was to assess expression of the Epo receptor (EpoR) on VSMCs and to study the activation of two major signaling cascades activated by Epo, namely JAK2/STAT5 and MAPK pathways. All experiments were performed in parallel using the Epo-responsive UT7 cell line. From semiquantitative RT-PCR experiments, VSMCs were estimated to express approximately 30-fold less EpoR mRNA than UT7 cells. Epo-induced phosphorylation of proteins involved in the EpoR/JAK2/STAT5 cascade could not be detected in VSMCs, even using pharmacological doses of Epo (250 IU/ml). In contrast, a strong activation of MAP kinase pathway was detected with as low as 10 IU/ml Epo. We suggest that MAPK activation reflects a physiologically relevant effect of Epo on VSMCs that may be correlated to cell proliferation.

Antibodies against a putative heparin receptor slow cell proliferation and decrease MAPK activation in vascular smooth muscle cells

Heparin has long been known to slow the growth of vascular smooth muscle cells. However, the mechanism(s) by which heparin acts has yet to be resolved. The identification of a putative heparin receptor in endothelial cells with antibodies that blocked heparin binding to the cells provided the means to further examine the possible involvement of a heparin receptor in smooth muscle cell responses to heparin. Immunoprecipitation of a smooth muscle cell protein with the anti-heparin receptor antibodies provided evidence that the protein was present in smooth muscle cells. Experiments with the anti-heparin receptor antibodies indicate that the antibodies can mimic heparin in decreasing PDGF induced thymidine and BrdU incorporation. The anti-heparin receptor antibodies were also found to decrease MAPK activity levels after activation similarly to heparin. These results support the identification of a heparin receptor and its role in heparin effects on vascular smooth muscle cell growth.

Fucoidan inhibits smooth muscle cell proliferation and reduces mitogen-activated protein kinase activity

OBJECTIVES AND DESIGN

fucoidan has previously been shown to inhibit the proliferation of arterial smooth muscle cells both in animal models and in vitro. However, the mechanisms behind the anti-proliferative effects of this polysulfated polysaccharide are not known in detail. Here, the inhibitory effect of fucoidan on rat aortic smooth muscle cell proliferation was examined and compared with the effects of heparin after stimulation with fetal calf serum, platelet-derived growth factor BB, basic fibroblast growth factor, heparin-binding epidermal growth factor, and angiotensin II.

MATERIALS AND METHODS

the cultures were analysed with respect to cell proliferation and DNA synthesis by cell counting and measurement of(3)H-thymidine incorporation. Phosphorylation of mitogen-activated protein kinase and nuclear translocation of phosphorylated mitogen-activated protein kinase were studied by immunoblotting and immunocytochemistry.

RESULTS

fucoidan was shown to be a more potent inhibitor of smooth muscle cell proliferation than heparin. Fucoidan also reduced growth factor-induced activation of mitogen-activated protein kinase and prevented nuclear translocation of phosphorylated mitogen-activated protein kinase.

CONCLUSION

fucoidan is a more potent anti-proliferative polysulphated polysaccharide than heparin and may mediate its effects through inhibition of the mitogen-activated protein kinase pathway in a similar manner as heparin.

Heparin-like molecules inhibit pulmonary vascular pericyte proliferation in vitro

Proliferation of vascular pericytes (PCs), smooth muscle-like cells found in the distal microvasculature, contributes to vascular remodeling in pulmonary hypertension. The factors controlling lung PC quiescence in normal states are poorly understood. We demonstrate that exogenous heparin and heparan sulfate proteoglycans inhibit rat lung PC proliferation in vitro as does pulmonary vascular subendothelial matrix, particularly its heparan sulfate component. Heparin inhibits the intracellular alkalinization essential to proliferation, and we show that inhibition of alkalinization by 5-(N, N-dimethyl)amiloride also reduces PC proliferation. As shown by DNA staining and fluorescence-activated cell sorting analysis, heparin does not induce apoptosis in PCs. However, heparin maintains lung PCs in the G(0)/G(1) growth phase. Heparin induces production of p21, a potent inhibitor of cyclin-dependent kinases, thereby potentially identifying a fundamental mechanism by which heparin inhibits proliferation in smooth muscle-like cells. These studies establish additional similarities between lung PCs and smooth muscle cells and provide further understanding of growth control in the lung microvasculature. They also further support the rationale that heparin-like molecules might be therapeutically beneficial in pulmonary hypertension.

The regulation of caveolin expression and localization by serum and heparin in vascular smooth muscle cells

Caveolae have been implicated in growth factor receptor and G-protein coupled receptor signaling in vascular cells. It has been postulated that caveolin, the structural protein of caveolae, may act as a general tyrosine kinase inhibitor by binding and inhibiting signaling molecules involved in the activation of the MAP kinase proliferation cascade. Using an in vitro model of VSMC proliferation, we found that serum stimulation caused a dose dependent decrease in both caveolin-1 and caveolin-2 protein levels in human coronary artery smooth muscle cells. Heparin, an inhibitor of VSMC proliferation, inhibited the serum-induced loss of caveolin-1 and caveolin-2. In addition, heparin caused an increase in both caveolin-1 and caveolin-2 localization to caveolae-enriched sucrose gradient membrane fractions when compared to serum alone. Taken together, caveolin may play an important role in the regulation of VSMC proliferation and heparin and serum have opposing effects on caveolin expression and localization in VSMC.

Effects of dehydroepiandrosterone on mitogen-activated protein kinase in human aortic smooth muscle cells

The objective of the present study was to determine whether dehydroepiandrosterone (DHEA) modifies growth factor-induced mitogen-activated protein kinase (MAPK) activation, based on our previous study demonstrating that DHEA attenuates fetal calf serum-induced proliferation in human male aortic smooth muscle cells (human male aortic SMCs). Human male aortic SMCs were used for this study. Platelet-derived growth factor-BB (PDGF-BB), epidermal growth factor (EGF), and basic fibroblast growth factor (bFGF), but not insulin-like growth factor-1 (IGF-1), stimulated MAPK activity. Only MAPK activation induced by PDGF-BB was reduced by pretreatment with DHEA, although DHEA did not affect the MAPK activation induced by EGF or bFGF. The basal and PDGF-stimulated MAPK activity were decreased by two types of cyclic AMP (cAMP) elevating agents and increased by cAMP-dependent protein kinase (PKA) inhibitor in human male aortic SMCs, suggesting that cAMP regulates MAPK negatively. The intracellular cAMP was increased by PDGF-BB. The increase of cAMP by PDGF-BB was augmented by pretreatment with DHEA, although DHEA alone did not affect cAMP. Neither EGF nor bFGF affected cAMP with and without DHEA pretreatment. Secretion of PGE2 induced by PDGF was augmented by pretreatment with DHEA. Stimulatory effects of DHEA on the production of PGE2 and cAMP were partially canceled by aromatase inhibitor and completely canceled by indomethacin or selective inhibitor of cyclooxygenase-2. These results suggest that DHEA inhibited MAPK activation induced by PDGF-BB via PGE2 overproduction and subsequent cAMP-dependent pathway in human male aortic SMCs.

Heparin and enoxaparin enhance endotoxin-induced tumor necrosis factor-alpha production in human monocytes

OBJECTIVE

To determine whether heparin or the low-molecular-weight heparin enoxaparin alter lipopolysaccharide (LPS)-induced monocyte activation.

SUMMARY BACKGROUND DATA

Heparin is widely used in clinical practice to inhibit the coagulation cascade. However, heparin also is a naturally occurring glucosaminoglycan and a pleiotropic immunomodulator that binds to a variety of proteins. LPS is a component of gram-negative bacteria and is thought to be responsible for many of the deleterious effects seen in sepsis. The binding of LPS to CD14 induces a signaling cascade that results in the release of many inflammatory mediators, including tumor necrosis factor-alpha (TNF-alpha).

METHODS

Monocytes from healthy volunteers were isolated and cultured in the presence of saline, LPS (10 ng/ml), heparin (0.1 to 1000 microg/ml), or enoxaparin (0.1 to 1000 microg/ml). In blocking experiments, cells were pretreated for 60 minutes with the monoclonal anti-CD14 antibody MY4 (10 microg/ml) or with isotype-matched control IgG2 (10 microg/ml). TNF-alpha values were measured with enzyme-linked immunosorbent assay. Significance was assessed with analysis of variance.

RESULTS

Heparin (10 to 1000 microg/ml) and enoxaparin (1000 microg/ml) significantly enhanced LPS-induced TNF-alpha release. Heparin (1000 microg/ml) or enoxaparin (1000 microg/ml) did not produce TNF-alpha in the absence of LPS. Blockade of CD14 abrogated both LPS-induced TNF-alpha release and the effect of heparin or enoxaparin to enhance LPS-induced TNF-alpha release.

CONCLUSIONS

The effect of heparin to enhance LPS-induced TNF-alpha release is a biologic phenomenon that reveals a novel and potentially important host defense mechanism during endotoxemia and sepsis. Binding of LPS to CD14 is necessary to induce this phenomenon, suggesting that both heparin and enoxaparin induce signaling mechanisms that are downstream from the initial binding of LPS on CD14.

Heparin rapidly and selectively regulates protein tyrosine phosphorylation in vascular smooth muscle cells

Aberrant vascular smooth muscle cell (VSMC) hyperplasia is the hallmark of atherosclerosis and restenosis seen after vascular surgery. Heparin inhibits VSMC proliferation in animal models and in cell culture. To test our hypothesis that heparin mediates its antiproliferative effect by altering phosphorylation of key mitogenic signaling proteins in VSMC, we examined tyrosine phosphorylation of cellular proteins in quiescent VSMC stimulated with serum in the presence or absence of heparin. Western blot analysis with anti-phosphotyrosine antibodies shows that heparin specifically alters the tyrosine phosphorylation of only two proteins (42 kDa and 200 kDa). The 200 kDa protein (p200) is dephosphorylated within 2.5 min after heparin treatment with an IC50 that closely parallels the IC50 for growth inhibition. Studies using the tyrosine phosphatase inhibitor, sodium orthovanadate, indicate that heparin blocks p200 phosphorylation by inhibiting a kinase. Phosphorylation of p200 is not altered in heparin-resistant cells, supporting a role for p200 in mediating the antiproliferative effect of heparin. Purification and sequence analysis indicate that p200 exhibits very high homology to the heavy chain of nonmuscle myosin IIA. The 42 kDa protein, identified as mitogen activated protein kinase (MAPK), undergoes dephosphorylation within 15 min after heparin treatment, and this effect is also not seen in heparin-resistant cells. The identification of only two heparin-regulated tyrosine phosphoproteins suggests that they may be key mediators of the antiproliferative effect of heparin.

Heparin proteoglycans released from rat serosal mast cells inhibit proliferation of rat aortic smooth muscle cells in culture

-Mast cells are present in the human arterial intima. To study whether mast-cell degranulation influences the rate of proliferation of smooth muscle cells, we cocultured sensitized (IgE-bearing) rat serosal mast cells and rat aortic smooth muscle cells (SMCs). When sensitized mast cells were stimulated to degranulate with antigen, the rate of proliferation of the cocultured SMCs decreased sharply. This inhibitory effect was found to be due mainly to the very high molecular weight (Mr) heparin proteoglycans (average Mr 750 000) released from the stimulated mast cells. When the heparin proteoglycans were purified from mast-cell granule remnants and added to the SMC culture, they were found to block the cell cycle at the G0-->S transition and the exit from the G2/M phase, their inhibitory effect resembling that of commercial heparin. However, in contrast to the reported dependence of the inhibitory effect of commercial heparin on the release of transforming growth factor-beta from serum, the inhibitory effect of the mast cell-derived heparin proteoglycans in the presence of serum was not transforming growth factor-beta dependent. Moreover, the effect of the mast cell-derived heparin proteoglycans was more efficient than that of commercial heparins of high (average Mr 15 000) and low (average Mr 5000) molecular weight. We also purified heparin glycosaminoglycans (average Mr 75 000) from the mast cell-derived heparin proteoglycans and found that they also inhibited SMC growth efficiently, although less strongly than their parent heparin proteoglycans. These results reveal, for the first time, that mast cells are able to regulate SMC growth. Thus, activated mast cells, by releasing heparin proteoglycans, possibly participate in the regulation of SMC growth in the human arterial intima, the site of atherogenesis.

Heparan sulfate upregulates platelet-derived growth factor receptors on human lung fibroblasts

Heparan sulfate is a molecule that possesses a large structural variability and which has been shown to inhibit the proliferation of fibroblasts in vitro. The aim of this study was to determine whether the anti-proliferative effects of heparan sulfate were exerted by regulation of the activity of the platelet-derived growth factor and/or of the platelet-derived growth factor receptors. Both l-iduronate-rich, anti-proliferative and the l-iduronate-poor, non-anti-proliferative heparan sulfate species, were incubated with confluent human embryonic lung fibroblasts for 24 h. The mRNA levels for PDGF-AA, PDGF-BB, and their receptors were measured. Binding studies were performed with [125I]-PDGF-BB and [125I]-EGF for 2 h at 4 degreesC in cultures preincubated with both types of heparan sulfate for 24 h. In separate experiments, cultures were incubated together with heparan sulfate and [125I]-PDGF-BB for 2 h at 4 degreesC. Increases of two- to threefold in the mRNA levels for both the alpha- and the beta-receptors of PDGF was obtained after treatment with both types of heparan sulfate, whereas the mRNA levels of both the PDGF-AA and the PDGF-BB were essentially unaffected. A sixfold increase in binding was only noted for [125I]-PDGF-BB in cultures pre-treated with the anti-proliferative heparan sulfate for 24 h, whereas no effect was noted with use of the non-anti-proliferative heparan sulfate. Incubating the [125I]-PDGF-BB and the anti-proliferative heparan sulfate together for 2 h resulted in a smaller, threefold increase in binding. This indicates that the anti-proliferative heparan sulfate both stabilizes and increases expression of the PDGF receptors. To investigate whether the increased number of PDGF receptors could affect cell activity, cells were preincubated with anti-proliferative heparan sulfate and then treated with PDGF-BB. This resulted in an increase in mitogenicity compared to cells treated only with PDGF-BB. Neither an increase in binding for [125I-EGF] nor an increase in the mitogenic response of EGF could be observed in cultures pre-treated with the anti-proliferative heparan sulfate. The results indicate that the extracellular matrix itself may regulate important biological phenomena such as cell proliferation and matrix production through affecting the expression of receptors of PDGF, which initiate both stimulatory and inhibitory signals.

Heparin fails to inhibit the proliferation of human vascular smooth muscle cells in the presence of human serum

The proliferation of vascular smooth muscle cells (VSMC) plays a significant part in both the developing atherosclerotic lesion and in restenosis. Heparin has been widely reported to inhibit the growth of VSMC in culture and intimal VSMC in some animal models of vascular hyperplasia. Clinical trials with heparin, however, have failed to inhibit restenosis following angioplasty. Bovine serum is normally used as a growth supplement in in vitro VSMC growth assays. We have compared the effects of human serum with those of bovine serum on the cellular response to heparin in human VSMC culture. While heparin inhibited the proliferation of human VSMC in the presence of bovine serum, it was totally ineffective in the presence of human serum. These observations were consistent over a wide range of serum and VSMC samples. Experiments utilizing neutralizing antibodies to a number of growth factors showed that cells in either serum were similarly dependent on platelet-derived growth factor for proliferation. In contrast, proliferation in the presence of bovine serum was shown to be dependent on extracellular basic fibroblast growth factor, whereas that in human serum was not. Direct binding of [3H]-heparin to VSMC was significantly reduced in the presence of human serum compared with bovine serum, and the former contained twice the concentration of heparin-binding factors of the latter. Removal of heparin-binding factors from either serum type significantly reduced the proliferation potential. Fractionation of heparin-binding factors from human serum showed that the major growth-promoting activity, together with heparin resistance, was contained within a fraction excluded by a 100,000 molecular weight membrane. We conclude that the mechanism of resistance to heparin in human serum is likely to be due to a combination of differential growth factor binding and interference with heparin interaction with cellular receptors by a high molecular weight heparin-binding factor. This phenomenon may significantly contribute to the lack of success of heparin as an antirestenotic agent in clinical trials.

Platelet-derived growth factor-BB, insulin-like growth factor-I, and phorbol ester activate different signaling pathways for stimulation of vascular smooth muscle cell migration

Vascular smooth muscle cell (VSMC) migration is an important process in the development of vascular occlusive disease. To investigate mitogen regulation of VSMC migration, a cell-layer-scrape assay was used to measure migration 20 h after stimulation of VSMC with platelet-derived growth factor-BB (PDGF-BB), insulin-like growth factor I (IGF-I), or phorbol 12-myristate 13-acetate (PMA). The contributions of cell proliferation were eliminated by treatment of VSMC with hydroxyurea, which suppressed DNA synthesis.PDGF-BB stimulated VSMC migration 2.5-fold, while PMA and IGF-I stimulated migration 1.7- and 1.5-fold, respectively. The importance of protein kinase C (PKC), ERK, and phosphoinositide-3' kinase (PI3 kinase) in mitogen-stimulated migration was investigated, using specific inhibitors of these signaling molecules. PDGF-BB-stimulated migration was inhibited by the general PKC inhibitor RO 31-8220 (40%), the MEK inhibitor PD98059 (31%), and the PI3 kinase inhibitor wortmannin (22%) but not by PMA-induced downregulation of conventional and novel PKC isoforms. IGF-I-stimulated migration was inhibited by RO 31-8220 (34%) and wortmannin (37%) but was much less affected by PD98059 (19%) or PKC downregulation (10%). PMA-stimulated migration was inhibited by RO 31-8220 (53%), PD98059 (50%), wortmannin (45%), and PKC downregulation (47%). Western analysis confirmed that ERK was strongly activated by PDGF-BB and PMA but not by IGF-I. To examine potential in vivo negative regulators of VSMC migration, we analyzed the ability of heparin, an analogue of heparan sulfate, and TGFbeta to attenuate mitogen-stimulated migration. Heparin but not TGFbeta inhibited VSMC migration stimulated by all three mitogens. Delayed-addition experiments showed that RO 31-8220 retained substantial inhibitory activity even if added 3 h after PMA or IGF-I stimulation and 5 h after PDGF-BB addition, suggesting that sustained PKC activation is important for migration. The MEK inhibitor retained some effectiveness for 5 h after PDGF-BB stimulation but only 1 h after PMA addition. Western analysis showed ERK activation was transient after PMA treatment but sustained for 6 h after PDGF-BB treatment. Heparin strongly inhibited migration even if added 5-7 h after mitogen stimulation, suggesting that heparin may inhibit both short- and long-term signals necessary for migration. The present studies indicate that PMA and IGF-I activate a limited number of second messengers resulting in moderate stimulation of migration; in contrast PDGF-BB stimulates multiple signaling pathways resulting in strong stimulation of migration and lessened sensitivity to inhibitory signals.