Heparin inhibits proliferation of fetal vascular smooth muscle cells in the absence of platelet-derived growth factor

Platelet-derived growth factor receptor signaling is not involved in osteogenic differentiation of human mesenchymal stem cells

Platelet-derived growth factor (PDGF) receptor signaling plays an important role in the regulation of proliferation and migration of skeletal cells such as osteoblasts or mesenchymal stem cells (MSCs). However, involvement of these receptors in the process of osteoblastic differentiation of MSCs is still a matter of debate. The aim of our study was to examine the role of PDGF receptor signaling in osteogenic differentiation of human MSCs. For this purpose, we performed PDGF receptor stimulation as well as inhibition experiments. Inhibition experiments were carried out with Tyrphostin AG1296, a potent and specific inhibitor of PDGF receptor activity. As expected, Tyrphostin AG1296 treatment caused a concentration-dependent decrease in fetal calf serum and PDGF-BB-induced proliferation of MSCs and effectively inhibited PDGF-BB-induced phosphorylation of extracellular-regulated kinase 1/2. However, PDGF receptor inhibition had no significant effect on osteoblastic differentiation of MSCs, as evaluated histochemically by von Kossa, Alizarin-Red, and osteocalcin stainings. Moreover, mineralized matrix production, as assayed by quantitative Ca(2+)-measurements, was also not modulated by Tyrphostin AG1296 treatment. These results were noticeable irrespective of whether MSCs were grown under nonosteogenic or osteogenic differentiation conditions. Similarly, PDGF-BB treatment of MSCs in receptor stimulation experiments also failed to modulate mineralization. However, expression of alkaline phosphatase was suppressed by Tyrphostin AG1296 treatment at later stages of osteogenesis but not in the early stages, as assessed by enzyme activity and mRNA expression assays. Expression of other osteogenic marker genes such as osteocalcin, runt-related transcription factor 2, osteopontin, collagen type I, and bone sialoprotein was almost unaffected in our perturbation studies. From these experiments, we conclude that PDGF receptor signaling sustains proliferation without affecting osteogenic differentiation of MSCs.

Pathobiology of pulmonary hypertension

A variety of conditions can lead to the development of pulmonary arterial hypertension (PAH). Current treatments can improve symptoms and reduce the severity of the hemodynamic abnormality, but most patients remain quite limited, and deterioration in their condition necessitates a lung transplant. This review discusses current experimental and clinical studies that investigate the pathobiology of PAH. An emerging theme is the consideration of ways in which one might reverse the advanced occlusive structural changes in the pulmonary circulation causing PAH. The current debate concerning the role of regeneration through stem cells is presented. This review also highlights investigations in a number of laboratories relating the pathobiology of PAH to mutations causing loss of function of bone morphogenetic protein receptor II in patients with familial PAH, as well as sporadic cases.

Pulmonary arterial hypertension in children

Pulmonary arterial hypertension is a serious progressive condition with a poor prognosis if not identified and treated early. Because the symptoms are nonspecific and the physical findings can be subtle, the disease is often diagnosed in its later stages. Remarkable progress has been made in the field of pulmonary arterial hypertension over the past several decades. The pathology is now better defined, and significant advances have occurred in understanding the pathobiologic mechanisms. Risk factors have been identified, and the genetics have been characterized. Advances in technology allow earlier diagnosis as well as better assessment of disease severity. Therapeutic modalities such as new drugs, e.g., epoprostenol, treprostinil, and bosentan, and surgical/interventional options, e.g., transplantation and atrial septostomy, which were unavailable several decades ago, have had a significant impact on prognosis and outcome. Thus, despite our inability to cure pulmonary arterial hypertension, advances in medical treatments over the past two decades have resulted in significant improvement in outcomes for children with various forms of pulmonary arterial hypertension. This report is a review the current state of the art for pulmonary arterial hypertension in 2004, with an emphasis on childhood pulmonary arterial hypertension and specific recommendations for current practice and future directions.

Extracellular matrix controls myosin light chain phosphorylation and cell contractility through modulation of cell shape and cytoskeletal prestress

The mechanism by which vascular smooth muscle (VSM) cells modulate their contractility in response to structural cues from extracellular matrix remains poorly understood. When pulmonary VSM cells were cultured on increasing densities of immobilized fibronectin (FN), cell spreading, myosin light chain (MLC) phosphorylation, cytoskeletal prestress (isometric tension in the cell before vasoagonist stimulation), and the active contractile response to the vasoconstrictor endothelin-1 all increased in parallel. In contrast, MLC phosphorylation did not increase when suspended cells were allowed to bind FN-coated microbeads (4.5-microm diameter) or cultured on micrometer-sized (30 x 30 microm) FN islands surrounded by nonadhesive regions that support integrin binding but prevent cell spreading. Cell spreading and MLC phosphorylation also both decreased in parallel when the mechanical compliance of flexible FN substrates was raised. MLC phosphorylation was inhibited independently of cell shape when cytoskeletal prestress was dissipated using a myosin ATPase inhibitor in fully spread cells, whereas it increased to maximal levels when microtubules were disrupted using nocodazole in cells adherent to FN but not in suspended cells. These data demonstrate that changes in cell-extracellular matrix (ECM) interactions modulate smooth muscle cell contractility at the level of biochemical signal transduction and suggest that the mechanism underlying this regulation may involve physical interplay between ECM and the cytoskeleton, such that cell spreading and generation of cytoskeletal tension feed back to promote MLC phosphorylation and further increase tension generation.

Sodium spirulan as a potent inhibitor of arterial smooth muscle cell proliferation in vitro

Sodium spirulan (Na-SP) is a sulfated polysaccharide with M(r) approximately 220,000 isolated from the blue-green alga Spirulina platensis. The polysaccharide consists of two types of disaccharide repeating units, O-hexuronosyl-rhamnose (aldobiuronic acid) and O-rhamnosyl-3-O-methylrhamnose (acofriose) with sulfate groups, other minor saccharides and sodium ion. Since vascular smooth muscle cell proliferation is a crucial event in the progression of atherosclerosis, we investigated the effect of Na-SP on the proliferation of bovine arterial smooth muscle cells in culture. It was found that Na-SP markedly inhibits the proliferation without nonspecific cell damage. Either replacement of sodium ion with calcium ion or depolymerization of the Na-SP molecule to M(r) approximately 14,700 maintained the inhibitory activity, however, removal of sodium ion or desulfation markedly reduced the activity. Heparin and heparan sulfate also inhibited vascular smooth muscle cell growth but their effect was weaker than that of Na-SP; dextran sulfate, chondroitin sulfate, dermatan sulfate and hyaluronan failed to inhibit the cell growth. The present data suggest that Na-SP is a potent inhibitor of arterial smooth muscle cell proliferation, and the inhibitory effect requires a certain minimum sequence of polysaccharide structure whose molecular conformation is maintained by sodium ion bound to sulfate group.

Effects of glycosaminoglycans on proliferation of epithelial and fibroblast human malignant mesothelioma cells: a structure-function relationship

Proteoglycans interact with other effective macromolecules regulating a variety of cellular events via their glycosaminoglycan (GAG) chains. The effects of all known glycosaminoglycans (GAGs) produced by normal cells and tissues on the proliferation of two human malignant mesothelioma cell lines, one with fibroblast-like morphology and the other with epithelial differentiation - both able to produce hyaluronan (HA), galactosaminoglycans (GalAGs) and heparan sulphate (HS) containing proteoglycans - have been studied. Cell proliferation was assessed by measuring [3H]thymidine incorporation and cell number. GalAGs, i.e. chondroitin sulphates (CSs) and dermatan sulphate (DS), strongly stimulate the proliferation of fibroblast-like cells in a dose-dependent manner (170-250% at 100 microg/ml), independently of their sulphation pattern. In epithelial cells, however, only DS stimulates cell proliferation. The effects of CSs on proliferation of epithelial cells are not depended on their sulphation pattern. Thus, CSs either with -[GlcA-GalNAc-(-6-O-SO(3)-)]- or -[GlcA-GalNAc-(-4-O-SO(3)-]- as the commonest unit, had no significant effect. L-Iduronic acid (IdoA)-rich heparin and fast-moving HS (fm-HS), a HS fraction with a heparin-like structure, had significant antiproliferative effects on mesothelioma cells of both types (30-70% at 1.0 microg/ml and 85-90% at 100 microg/ml, respectively). GlcA-rich HS, however, had no significant effects. HA inhibits only the proliferation of fibroblast-like cells by 25% at 50 and 100 microg/ml. Keratan sulphate suppresses cell proliferation (10-30%) in both cell lines. In the view of these findings, a structure-function relationship of GAGs on cell proliferation of the two human malignant mesothelioma cell lines is discussed. Other factors, such as chain conformation and geometry, as well as interactions of growth factors with GAGs, possibly involved in the regulation of cell proliferation, are also discussed.

Tissue concentration of heparin, not administered dose, correlates with the biological response of injured arteries in vivo

Drug activity is often studied in well controlled and characterized cellular environments in vitro. However, the biology of cells in culture is only a part of the tissue behavior in vivo. Quantitative studies of the dose response to drugs in vivo have been limited by the inability to reliably determine or predict the concentrations achieved in tissues. We developed a method to study the dose response of injured arteries to exogenous heparin in vivo by providing steady and predictable arterial levels of drug. Controlled-release devices were fabricated to direct heparin uniformly and at a steady rate to the adventitial surface of balloon-injured rat carotid arteries. We predicted the distribution of heparin throughout the arterial wall by using computational simulations of intravascular drug binding and transport, and we correlated these concentrations with the biologic response of the tissues. This allowed the estimation of the arterial concentration of heparin required to maximally inhibit intimal hyperplasia after injury in vivo, 0.3 mg/ml. This estimation of the required concentration of drug seen by a specific tissue is independent of the route of administration and holds for all forms of drug release. In this way we may now be able to evaluate the potential of widely disparate forms of drug release and to finally create some rigorous criteria by which to guide the development of particular delivery strategies for local diseases.

Heparin inhibits lung branching morphogenesis: potential role of smooth muscle cells in cleft formation

Lung branching morphogenesis is the process by which the embryonic lung undergoes repetitive branching to form the bronchial tree. This process occurs during the pseudoglandular stage of lung development and requires epithelial-mesenchymal interactions. Coinciding with lung branching morphogenesis is the appearance of parabronchial smooth muscle cells (PSMCs) and the accumulation of extracellular matrices (ECMs) around the developing airways. The authors previously reported in preliminary form that heparin prevents the branching of murine lung explants (Roman et al., Am Rev Respir Dis. 1991; 143:A401); this article corroborates those early observations and expands them by demonstrating that heparin results in disruption of PSMC distribution and abnormal organization of ECMs around the developing airways. These changes were associated with inhibition of lung branching morphogenesis in the absence of effects on cell proliferation. The data provide further support for the role of ECMs in lung branching morphogenesis, and points to PSMCs as potential players in this process.

Extracellular matrix and pulmonary hypertension: control of vascular smooth muscle cell contractility

Pulmonary hypertension is characterized by increased vascular resistance due to smooth muscle cell hyper-activity and excess deposition of extracellular matrix (ECM) in the vessel wall. We investigated the possibility that changes in cell-ECM interactions may play an active role in this process by modifying the contractile response of pulmonary vascular smooth muscle (PVSM) cells. Contractility was measured within individual cultured PVSM cells, when resting or stimulated with vasoactive agents, by quantitating changes in stiffness of the cytoskeleton (CSK) using magnetic twisting cytometry (N. Wang, J. P. Butler, and D. E. Ingber. Science 260: 1124-1127, 1993). Control studies confirmed that changes in CSK stiffness closely paralleled alterations in cell contraction and relaxation as measured in response to endothelin-1 (ET-1) and dibutyryl guanosine 3',5'-cyclic monophosphate (cGMP), respectively, in a collagen gel contraction assay. CSK stiffness and contractile tone in cultured PVSM cells increased in direct proportion as the density of fibronectin (FN) coating was raised from 10 to 500 ng/well in 96-well plates. Dibutyryl cGMP had no effect in cells on low FN, although it completely inhibited the FN-dependent increase in CSK stiffness on higher ECM densities. In contrast, ET-1 induced the greatest increase in CSK stiffness on the intermediate FN density (100 ng/well). The reduced sensitivity to ET-1 on high FN was not due to dysfunction of the contractile apparatus nor to changes in protein tyrosine phosphorylation. Taken together, these results show that ECM can modulate PVSM cell contractility and suggest that the changes in ECM observed in hypertensive vessels could play an important role in the etiology of this disease.

The effects of growth factors on Tenon's capsule fibroblasts in serum-free culture

This study was performed to develop and improve a completely defined in vitro ocular wound-healing model of fibroblast proliferation for glaucoma filtration surgery. This model is essential for the investigation of protein-sensitive drugs and cytokines. Tenon's capsule fibroblasts in their third passage were incubated overnight, washed free of serum, and fed defined media, Aim V or Clonetics FBM serum-free medium containing platelet-derived growth factor, basic fibroblast growth factor, epidermal growth factor, or fibronectin at various dilutions and in combinations at optimum concentrations. Proliferation was measured by 3H-thymidine incorporation at 1, 3, and 7 days. Morphology was compared to controls fed Minimum Essential Medium + 10% serum. Single factors stimulated the greatest amount of thymidine uptake on day 3. Optimum concentrations were epidermal growth factor at 5 ng/ml, basic fibroblast growth factor at 10 ng/ml and platelet-derived growth factor at 20 ng/ml. Identical combinations of factors stimulated nearly twice the thymidine uptake in Clonetics medium as in Aim V. Epidermal growth factor activity was inhibited by either basic fibroblast growth factor or platelet-derived growth factor. Basic fibroblast growth factor and platelet-derived growth factor together produced a less than additive effect. The performance of either serum-free medium may be improved by the addition of basic fibroblast growth factor or platelet-derived growth factor. The optimum serum-free medium (Clonetics FBM) with growth factors was unable to stimulate proliferation as much as Minimum Essential Medium + 10% NBS, but was successful in maintaining viability during the 7 day test period.

Heparin inhibits the accumulation of re-esterified cholesterol in macrophages loaded with acetylated low-density lipoprotein

Heparin enhances the endocytosis of low density lipoprotein (LDL) in macrophages via a formation of complex with LDL. The direct effect of heparin on the metabolism of cholesterol in macrophages has not been elucidated. We therefore evaluated the effects of heparin on the accumulation and reesterification of cholesterol in cultured macrophages. We used acetylated LDL (acetyl-LDL), which lacks an affinity for heparin. Rat peritoneal macrophages induced with thioglycollate were incubated with 100 micrograms of acetyl-LDL for 14 h. Heparin significantly inhibited the accumulation of total and esterified cholesterol but did not affect the binding of 125I-labeled acetyl-LDL to macrophages or its cellular degradation. Heparin at concentration above 5 micrograms/ml inhibited the incorporation of [3H]oleate into cholesteryl oleate in macrophages. Heparin significantly inhibited the acyl CoA:cholesterol acyl transferase (ACAT) activity of macrophages by 68%. Data suggest that heparin inhibits the accumulation and reesterification of cholesterol in macrophages loaded with acetyl-LDL. Heparin-like proteoglycans may thus protect the macrophages against the excessive accumulation of esterified cholesterol.

Probing transmembrane mechanical coupling and cytomechanics using magnetic twisting cytometry

We recently developed a magnetic twisting cytometry technique that allows us to apply controlled mechanical stresses to specific cell surface receptors using ligand-coated ferromagnetic microbeads and to simultaneously measure the mechanical response in living cells. Using this technique, we have previously shown the following: (i) beta 1 integrin receptors mediate mechanical force transfer across the cell surface and to the cytoskeleton, whereas other transmembrane receptors (e.g., scavenger receptors) do not; (ii) cytoskeletal stiffness increases in direct proportion to the level of stress applied to integrins; and (iii) the slope of this linear stiffening response differs depending on the shape of the cell. We now show that different integrins (beta 1, alpha V beta 3, alpha V, alpha 5, alpha 2) and other transmembrane receptors (scavenger receptor, platelet endothelial cell adhesion molecule) differ in their ability to mediate force transfer across the cell surface. In addition, the linear stiffening behavior previously observed in endothelial cells was found to be shared by other cell types. Finally, we demonstrate that dynamic changes in cell shape that occur during both cell spreading and retraction are accompanied by coordinate changes in cytoskeletal stiffness. Taken together, these results suggest that the magnetic twisting cytometry technique may be a powerful and versatile tool for studies analyzing the molecular basis of transmembrane mechanical coupling to the cytoskeleton as well as dynamic relations between changes in cytoskeletal structure and alterations in cell form and function.

Inhibition of serum-induced proliferation of bovine tracheal smooth muscle cells in culture by heparin and related glycosaminoglycans

1. The effect of heparin and related glycosaminoglycans on bovine airway smooth muscle proliferation has been investigated. 2. Foetal bovine serum stimulated division of bovine trachealis smooth muscle cells in a concentration-dependent fashion at concentrations between 1 and 30%. 3. Heparin (0.1-100 micrograms ml-1), heparan sulphate (0.1-100 micrograms ml-1) and fragmin (0.1-100 micrograms ml-1) inhibited smooth muscle division in a concentration-dependent fashion between 0.1-100 micrograms ml-1. A heparin disaccharide did not exhibit inhibition of division at 100 micrograms ml-1. 4. Dextran sulphate at molecular weights of 5 x 10(3) and 5 x 10(5) concentration-dependently inhibited division between 0.1-100 micrograms ml-1. Dextran without sulphation did not exhibit inhibition of division at 100 micrograms ml-1. 5. The magnitude of inhibition of proliferation did not reach 100% for any compounds examined at concentrations up to 100 micrograms ml-1 during incubations for 5 and 14 days. IC50 values for inhibition of proliferation ranged between 1-5 micrograms ml-1. 6. These findings suggest that heparin and related glycosaminoglycans inhibit bovine airway smooth muscle cell division.

Effect of stretch on growth and collagen synthesis in cultured rat and lamb pulmonary arterial smooth muscle cells

There are no studies of the effect of stretch in cultured pulmonary vascular smooth muscle, and some data suggest that a stretch-mediated increase in connective tissue synthesis in pulmonary arteries is mediated by the endothelium. To investigate whether stretch can serve as a growth stimulus in this smooth muscle, we studied two types of cultured pulmonary arterial smooth muscle cells (a multiply passaged clonal line of rat cells [PAC1], and early passage lamb cells [EPTC]). Cells were grown on a collagen-coated silicone surface and subjected to repetitive stretch (0.33-0.5 Hz; 10-20% strain). The relative rates of total RNA, DNA, protein, and soluble collagen synthesis were determined using 3H precursors, and c-fos and collagen mRNAs by Northern blot analysis. Stretch caused no significant change in the rate of RNA synthesis in either PAC1 cells (+9%) or EPTC (-3%). The relative rate of total protein synthesis was decreased by stretch (6% in PAC1 cells and 36% in EPTC [both NS]) as was the rate of collagen synthesis (-24% in EPTC [NS]). In EPTC, the percentage of 3H-thymidine labeled cells was modestly increased with 24 h stretch (17 +/- 5.7%; P < .001), but trichloroacetic acid (TCA) precipitated 3H-thymidine was unaltered by stretch, and the number of cells not significantly changed with stretch. c-fos mRNA expression was only inconsistently induced by stretch x 30 min in EPTC, and not at all in PAC1 cells. Expression of mRNA for alpha 1 (I) and alpha 1 (III) collagen was not changed significantly by 24 h or 48 h of stretch. We conclude that stretch does not serve as a significant growth stimulus in cultured pulmonary vascular smooth muscle cells in this system. These findings do not rule out the possibility that stretch is a growth stimulus for these cells under different conditions, but do suggest that other models will be needed to determine if and how mechanical stimuli affect growth of pulmonary vascular smooth muscle.

Effect of exogenous heparin on anchorage-independent growth of fibroblasts induced by transforming cytokines

Heparin at concentrations below 100 micrograms/ml stimulated anchorage-independent growth of NRK 49F (normal rat kidney fibroblasts, American type culture collection) rat fibroblasts at suboptimal cytokine concentrations but inhibited it at higher heparin concentrations regardless of the cytokine concentration. Heparin did not stimulate growth above that seen at optimal cytokine concentrations, suggesting that it alters the cellular response to the cytokines. These data suggest natural protein-glycosaminoglycan interactions play a role in modulating or mediating the actions of transforming cytokines and suggest they may play a role in acquisition of the transformed phenotype.

Alterations in nonhuman primate (M. nemestrina) lung proteoglycans during normal development and acute hyaline membrane disease

Proteoglycans (PGs) and lung hyaluronan (HA) are important components of the lung matrix both during normal development and in response to injury. We combined morphologic and biochemical techniques to study changes in PG and HA in a developmental series of Macaca nemestrina lungs ranging from 62% gestation to 3 mo post-term (n = 16), in adult lungs (n = 6), and from prematurely delivered, mechanically ventilated monkeys with hyaline membrane disease (HMD) (n = 7). Three groups of cuprolinic blue-positive (CuB) precipitates, identified by size, location, and susceptibility to enzyme digestion were found in lungs from all animals. Immature alveolar interstitium is characterized by loosely woven collagen bundles and an abundance of large (100 to 200 nm) stained filaments representing chondroitin sulfate proteoglycans (CSPGs). As maturation proceeds, the interstitial matrix appears increasingly organized, with large collagen bundles associated with 20 nm CuB-stained deposits (dermatan sulfate proteoglycans, DSPGs), and fewer large CSPGs. Fetal alveolar basement membrane contains CuB-stained heparin sulfate proteoglycans (HSPGs) (10 nm) scattered throughout. Lung matrix from animals with HMD appeared to have a disruption of the collagen-DSPG relationship, in addition to an enrichment in large CSPG. Complementary biochemical analysis of lung PGs and HA was done. Minced lung parenchyma was cultured with [3H]-glucosamine and [35S]-sulfate for 24 h; PGs and HA were extracted and analyzed. While PG synthesis during development tended to be highest at 80% gestation, animals with HMD showed greatly increased synthesis, approximately 2.5-fold higher than comparable fetal animals. In the developmental series, [3H]-glucosamine incorporation into HA was maximal at term, falling abruptly thereafter. HMD animals, however, showed a 2.3-fold increase over controls in net HA synthesis. Extracted PGs were separated according to buoyant density by dissociative cesium chloride density gradient ultracentrifugation. Two peaks of 35S-labeled PGs were separated from each density gradient fraction by chromatography on Sepharose CL-4B. A large CSPG was the principal PG eluting in the voiding volume, while the second broad peak (K(av) = 0.42) contained a mixed population of CSPG, DSPG, and HSPGs, the proportions of which varied with age. Both ultrastructural and biochemical analyses indicate that production of a large, high buoyant density CSPG predominates in fetal lung tissue, and diminishes with developmental age. Synthesis of large CSPG is greatly increased in lung explants from prematurely delivered animals with HMD.(ABSTRACT TRUNCATED AT 400 WORDS)

Development and characterization of a cloned rat pulmonary arterial smooth muscle cell line that maintains differentiated properties through multiple subcultures

BACKGROUND

Pulmonary hypertension is associated with abnormal pulmonary arterial contractility and growth. The mechanisms for these abnormalities are largely unknown. To study these processes, we sought to develop an in vitro system. Even though cultured aortic and pulmonary artery smooth muscle cells (SMCs) have been of considerable value in studying smooth muscle biology, one drawback of this system has been that these cells often lose differentiated properties in an unpredictable manner when they are passaged in culture. In addition, there appear to be significant differences in physiological and pathological responses between the systemic and pulmonary circulations, many of which could be directly related to the smooth muscle. We therefore established a cloned population of rat pulmonary arterial SMCs (PASMCs) that maintain differentiated properties through multiple subcultures.

METHODS AND RESULTS

PASMCs were obtained initially by enzymatic dissociation from pulmonary arteries of adult Sprague-Dawley rats. From these cells, clones were isolated. The cloned cells retained expression of functional surface receptors for angiotensin II, norepinephrine, and alpha-thrombin and high levels of the smooth muscle isoforms of alpha-actin, myosin heavy chain, myosin regulatory light chain, and alpha-tropomyosin mRNAs even after multiple passages. The cells could also be transfected and processed exogenous transcripts in a smooth muscle-specific fashion.

CONCLUSIONS

These cloned PASMCs retain many differentiated characteristics and should be valuable for future studies of pulmonary vascular smooth muscle cell biology.

Cultured aortic smooth muscle cells from newborn and adult rats show distinct cytoskeletal features

It is well known that arterial smooth muscle cells (SMC) of adult rats, cultured in a medium containing fetal calf serum (FCS), replicate actively and lose the expression of differentiation markers, such as desmin, smooth muscle (SM) myosin and alpha-SM actin. We report here that compared to freshly isolated cells, primary cultures of SMC from newborn animals show no change in the number of alpha-SM actin containing cells and a less important decrease in the number of desmin and SM myosin containing cells than that seen in primary cultures of SMC from adult animals; moreover, contrary to what is seen in SMC cultured from adult animals, they show an increase of alpha-SM actin mRNA level, alpha-SM actin synthesis and expression per cell. These features are partially maintained at the 5th passage, when the cytoskeletal equipment of adult SMC has further evolved toward dedifferentiation. Cloned newborn rat SMC continue to express alpha-SM actin, desmin and SM myosin at the 5th passage. Thus, newborn SMC maintain, at least in part, the potential to express differentiated features in culture. Heparin has been proposed to control proliferation and differentiation of arterial SMC. When cultured in the presence of heparin, newborn SMC show an increase of alpha-SM actin synthesis and content but no modification of the proportion of alpha-SM actin total (measured by Northern blots) and functional (measured by in vitro translation in a reticulocyte lysate) mRNAs compared to control cells cultured for the same time in FCS containing medium. This suggests that heparin action is exerted at a translational or post-translational level. Cultured newborn rat aortic SMC furnish an in vitro model for the study of several aspects of SMC differentiation and possibly of mechanisms leading to the establishment and prevention of atheromatous plaques.

Heparin-like glycosaminoglycans influence growth and phenotype of human arterial smooth muscle cells in vitro. I. Evidence for reversible binding and inactivation of the platelet-derived growth factor by heparin

We have investigated the effects of interactions between growth factors and heparin-like glycosaminoglycans on untransformed human arterial smooth muscle cells (hASMC) in vitro. The results indicate that heparin in the presence of serum mitogens prevents the cells from entering the S phase of the cell cycle by binding and inactivating reversibly some serum mitogen(s). Our results suggest that platelet-derived growth factor (PDGF) is one of them and that it is the most potent stimulator of hASMC growth in vitro. Thymidine incorporation as well as increase in DNA content was inhibited not only by the presence of heparin in serum-containing medium but also when serum was chromatographed on Heparin-Sepharose at physiologic salt concentrations before exposure to the cells. The mitogenic activity of the unretained serum fraction was restored by the addition of PDGF AA, AB, or BB dimers or of a fraction (RF I) that dissociated from Heparin-Sepharose at 0.2 to 0.6 M NaCl. Radiolabeled recombinant PDGF (c-sis) dissociated from Heparin-Sepharose within a concentration range of NaCl similar to that of RF I. Neither the unretained material nor the RF I or PDGF dimers were effective alone. The effect of RF I was significantly decreased by the addition of an anti-PDGF IgG that is known to neutralize the PDGF mitogenic activity partially. Addition of heparin abolished DNA-synthesis when the PDGF dimers or RF I were combined with the unretained fraction. A second fraction (RF II) bound strongly to Heparin-Sepharose and eluted between 1.1 and 1.6 M NaCl. The RF II also induced DNA synthesis but was neither as efficient as RF I nor depending on other serum fractions for growth promotion and it was not inhibited by anti-PDGF IgG. A similar strong affinity for Heparin-Sepharose was found for labeled basic fibroblast growth factor and we cannot exclude the possibility that RF II represent fibroblast growth factor. Under these culture conditions, inhibition of hASMC proliferation was directly correlated with the expression of smooth muscle specific alpha actin isoforms in stress fibers and the suppression of a proliferating cell-specific nuclear antigen. Conversely, stimulation of hASMC proliferation was associated with the opposite phenomenon. We conclude that heparin-like glycosaminoglycans influence growth and phenotype of hASMCs in vitro by binding and inactivating PDGF. Inasmuch as heparin-like substances constitute a significant proportion of the proteoglycan-associated glycosaminoglycans of the arterial wall, such mechanisms might be important for the development of atherosclerotic lesions.

Trans-repressor activity of nuclear glycosaminoglycans on Fos and Jun/AP-1 oncoprotein-mediated transcription

Heparin blocks the phorbol ester-induced progression of nontransformed cells through the G0/G1 phase (Wright, T.C., L.A. Pukac, J.J. Castellot, M.J. Karnovsky, R.A. Levine, H.-Y. Kim-Park, and J. Campisi. 1989. Proc. Natl. Acad. Sci. USA. 86: 3199-3203) or G1 to S phase (Reilly, C. F., M. S. Kindy, K. E. Brown, R. D. Rosenberg, and G. E Sonenshein. 1989. J. Biol. Chem. 264:6990-6995) of the cell cycle. Cell cycle arrest was associated with decreased levels of stage-specific mRNAs suggesting transcriptional regulation of cell growth. In the present report, we show that heparin selectively repressed TPA-inducible AP-1-mediated gene expression. Heparin-induced trans-repression was observed in primary vascular smooth muscle cells, as well as in the transformed HeLa cell line and in nondifferentiated F9 teratocarcinoma cells. Inhibition of AP-1-mediated trans-activation occurred with heparin and pentosan polysulfate but not with chondroitin sulfate A or C. Heparin-binding peptides or heparitinase I addition to nuclear lysates of heparin-treated cells allowed enhanced recovery of endogenous AP-1-specific DNA binding activity. We propose a model in which nuclear glycosaminoglycans play a trans-regulatory role in altering the patterns of inducible gene expression.

Heparin uncouples the muscarinic receptors from GK protein in the atrial cell membrane of the guinea-pig heart

The effects of heparin on activation of the G protein-gated muscarinic K+ channel were examined in atrial cells of guinea-pig heart. The inside-out patch clamp technique was used. The pipette solution contained 1.1 microM acetylcholine (ACh). In the inside-out patches, intracellular GTP activated the muscarinic, K+ channel. When heparin (0.05-5 units/ml) was further added to the intracellular side of the patch membrane, the channel openings were depressed in a concentration-dependent fashion. The effects of heparin were reversible after wash-out. Heparin did not affect GTP-gamma S-induced activation of the K+ channel. Therefore, it is suggested that heparin may uncouple the muscarinic receptors from GK protein in the cardiac atrial cell membrane.

Heparin inhibits c-fos and c-myc mRNA expression in vascular smooth muscle cells

Heparin is a potent inhibitor of vascular smooth muscle cell (VSMC) growth. In this paper we show that heparin suppressed the induction of c-fos and c-myc mRNA in rat and calf VSMC. This effect of heparin is closely associated with its growth-inhibitory activity, as shown by isolating and characterizing a strain of rat VSMC that was resistant to heparin's antiproliferative effect; heparin did not suppress c-fos mRNA induction in these cells. Moreover, neither a nonantiproliferative heparin fragment or other glycosaminoglycans that lack growth-inhibitory activity repressed c-fos or c-myc mRNA levels. The effect of heparin on c-fos mRNA induction was selective for specific mitogens, as heparin inhibited c-fos mRNA induction in phorbol 12-myristate 13-acetate (TPA) stimulated but not epidermal growth factor (EGF) stimulated VSMC. The effect of heparin on gene expression is independent of ongoing protein synthesis, and inhibition of c-fos mRNA is at the transcriptional level. These results suggest that heparin may selectively inhibit a protein kinase C-dependent pathway for protooncogene induction and that this may be one mechanism used by heparin to inhibit cell proliferation.

Endothelial heparan sulfate proteoglycan. I. Inhibitory effects on smooth muscle cell proliferation

Proliferation of smooth muscle cells is an important component of pulmonary arterial morphogenesis, both during normal development and pathologic remodeling. However, little is known of the factors that regulate smooth muscle proliferation in these vessels. To investigate the hypothesis that factors produced by endothelial cells may regulate smooth muscle cell growth, we studied the effects of culture medium conditioned by fetal bovine pulmonary arterial endothelium on proliferation of smooth muscle cells in culture. This conditioned medium contains an inhibitor of smooth muscle proliferation that is degraded by nitrous acid, heparinase, and heparitinase, but resists degradation by protease, boiling, and chondroitin ABC lyase, indicating that the inhibitor is structurally similar to heparin. Inhibitor release occurs in both growing and confluent endothelial cell cultures and in the presence and absence of serum. A growth-inhibiting proteoglycan purified to homogeneity from endothelial cell-conditioned medium has physicochemical characteristics similar to those of the prototypic basement membrane heparan sulfate proteoglycan of the Englebreth-Holm-Swarm tumor: an overall size of approximately 10(6) D, heparan sulfate chains of 60,000 D, and a buoyant density of 1.33 g/ml. Antibody raised against the tumor basement proteoglycan recognizes this endothelial heparan sulfate proteoglycan, and Western blotting after SDS-PAGE demonstrates that the core proteins of both proteoglycans migrate as a doublet at apparent molecular weights of 450,000 and 360,000 D. Heparan sulfate glycosaminoglycan prepared from purified medium proteoglycan is a potent inhibitor of smooth muscle cell growth, exhibiting activity approximately 1,000 times greater than that of heparin. These results indicate that endothelial cells cultured from fetal bovine pulmonary arteries produce a basement membrane heparan sulfate proteoglycan that is a potent inhibitor of smooth muscle proliferation. This proteoglycan may mediate endothelial regulation of smooth muscle growth during development or pathologic pulmonary arterial remodeling.

Modulation of growth of human carcinoma SW-13 cells by heparin and growth factors

This study reports on the effects of heparin, basic and acidic fibroblast growth factors (bFGF and aFGF, respectively), and transforming growth factor type-e (TGFe) on the growth of a human adrenocortical carcinoma cell line, SW-13. Heparin has previously been shown to inhibit growth in several cell types, including smooth muscle cells, certain fibroblasts, and epithelial cells, and to modulate the effects of fibroblast growth factors. Whereas bFGF and aFGF bind tightly to heparin and elute from a heparin-Sepharose column with 2 M NaCl and 1.6 M NaCl, respectively, TGFe binds to heparin with lower affinity and can be eluted from heparin-Sepharose column with 0.5 M NaCl. TGFe is a polypeptide unrelated to FGF, is present in neoplastic and nonneoplastic tissues, and stimulates the growth of certain epithelial cells and fibroblasts in soft agar and monolayer. Since the growth of SW-13 cells is stimulated by TGFe and by bFGF, we hypothesized that heparin would inhibit the growth of SW-13 cells by binding to these growth factors and that the effects of heparin could be overcome with the addition of either growth factor. Our experiments confirmed that heparin inhibits the growth of SW-13 cells. A dose-dependent growth inhibition was observed in both monolayer and soft agar. The inhibition in monolayer was partially reversed upon heparin withdrawal. The effects of heparin in both monolayer and soft agar were at least partially overcome by TGFe and by basic or acidic FGF. Overall protein synthesis does not appear to be affected by heparin as measured by [35S]methionine uptake. In contrast, epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) were unable to overcome heparin-induced inhibition both in monolayer and in soft agar. Heparin also inhibited [3H]thymidine incorporation in AKR-2B and partially inhibited AKR-2B cell stimulation by TGFe; however, it further potentiated the already potent stimulation by bFGF. We propose that heparin, TGFe, bFGF, and aFGF modulate the growth of SW-13 cells and possibly of other epithelial cells in complex ways and that heparin-like substances present in the extracellular matrix play an important role in the control of epithelial growth.

Transforming growth factor-beta activity is potentiated by heparin via dissociation of the transforming growth factor-beta/alpha 2-macroglobulin inactive complex

The control of smooth muscle cell (SMC) proliferation is determined by the combined actions of mitogens, such as platelet-derived growth factor, and the opposing action of growth inhibitory agents, such as heparin and transforming growth factor-beta (TGF-beta). The present studies identify an interaction between heparin and TGF-beta in which heparin potentiates the biological action of TGF-beta. Using a neutralizing antibody to TGF-beta, we observed that the short term antiproliferative effect of heparin depended upon the presence of biologically active TGF-beta. This effect was observed in rat and bovine aortic SMC and in CCL64 cells, but not in human saphenous vein SMC. Binding studies demonstrated that the addition of heparin (100 micrograms/ml) to medium containing 10% plasma-derived serum resulted in a 45% increase in the specific binding of 125I-TGF-beta to cells. Likewise, heparin induced a twofold increase in the growth inhibitory action of TGF-beta at concentrations of TGF-beta near its apparent dissociation constant. Using 125I-labeled TGF-beta, we demonstrated that TGF-beta complexes with the plasma component alpha 2-macroglobulin, but not with fibronectin. Heparin increases the electrophoretic mobility of TGF-beta apparently by freeing TGF-beta from its complex with alpha 2-macroglobulin. Dextran sulfate, another highly charged antiproliferative molecule, but not chondroitin sulfate or dermatan sulfate, similarly modified TGF-beta's mobility. Relatively high, antiproliferative concentrations of heparin (1-100 micrograms/ml) were required to dissociate the TGF-beta/alpha 2-macroglobulin complex. Thus, it appears that the antiproliferative effect of heparin may be partially attributed to its ability to potentiate the biological activity of TGF-beta by dissociating it from alpha 2-macroglobulin, which normally renders it inactive. We suggest that heparin-like agents may be important regulators of TGF-beta's biological activity.

Control of cell division in hepatoma cells by exogenous heparan sulfate proteoglycan

The effects of cell surface heparan sulfate proteoglycan (HSPG) prepared from log and confluent monolayers of a rat hepatoma cell line on hepatoma cell growth were studied. When HSPG isolated from confluent cells was added exogenously to log phase cells, it was internalized and free heparan sulfate (HS) chains appeared transiently in the nucleus. Concurrently, the growth of the treated cells was inhibited, but the cells resumed logarithmic growth as the level of nuclear HS fell, and the cells grew to confluence and became contact inhibited. When HSPG prepared from log-phase hepatoma cells was added exogenously to log phase cells, it was internalized but very little of the internalized HS appeared in the nucleus, and there was no change in the rate of cell growth. However, when the rate of cell growth was reduced by culture of the cells in serum- and insulin-deficient medium, HSPG prepared from log-phase cells stimulated the growth rate of these slow-growing cells. The cell cycle dependency of HSPG uptake and growth inhibition was studied in cultures synchronized by a thymidine/aphidicolin double block. When [35SO4]HSPG from confluent cells was added to synchronized cells just as they were released from the second block, a portion of the [35SO4]HSPG was internalized and [35SO4]HS appeared in the nucleus. However, at mitosis the [35SO4]HS disappeared almost completely from all of the cellular pools, and after mitosis, more of the [35SO4]HSPG was taken up and [35SO4]HS reappeared in the nucleus and remained in the nucleus until the cells divided again. When cultures were released from the aphidicolin block, both control and HSPG-treated cells progressed through the S, the G2, and the M phases of the cell cycle. However, the length of the G1 phase of the cycle was increased in the HSPG-treated cells. The treated cultures then progressed through the second S, G2, and M phases. Thus, the inhibition of cell division occurred in the G1 phase of the cell cycle, prior to the G1/S boundary. Addition of the HSPG to the synchronized cultures just after the first mitosis resulted in an immediate arrest of the cell cycle in G1.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell biology of arterial proteoglycans

Although proteoglycans constitute a minor component of vascular tissue, these molecules have been shown to influence a number of arterial properties such as viscoelasticity, permeability, lipid metabolism, hemostasis, and thrombosis. A hallmark of early and late atherosclerosis is the accumulation of proteoglycans in the intimal lesions. Yet, it is not clear why this accumulation occurs. This article reviews the classes of proteoglycans synthesized by the two major cell types of the arterial wall--the endothelial and smooth muscle cell. Detailed consideration is then given to the modulation of proteoglycan metabolism and the role that proteoglycans play in a number of cellular events such as adhesion, migration, and proliferation--important processes in both the development and the pathogenesis of blood vessels. Last, the involvement of proteoglycans in two critical vascular wall processes--hemostasis and lipid metabolism--is reviewed, because these events pertain to atherogenesis. This review emphasizes the importance of proteoglycans in regulating several key events in normal and pathophysiological processes in the vascular tissue.

Presence of insulinlike growth factor receptors and lack of insulin receptors on fetal bovine smooth muscle cells

Previous investigations have demonstrated specific receptors and associated mitogenic actions for insulin and insulinlike growth factors I and II (IGF-I and II) in postnatal bovine aortic smooth muscle. Using fetal tissue we have observed different patterns of binding and action for these peptides. Smooth muscle cells isolated from near-term fetal bovine aortae were studied in early passage. Specific receptors for both IGF-I and IGF-II were identified. Specific binding averaged 5.7%/2.5 X 10(5) cells for IGF-I, and 16.2% for IGF-II, and 0.3% for insulin. High affinity Kd for both IGF receptors were nanomolar. IGF-II was fivefold less potent than IGF-I in displacing IGF-I binding. IGF-I showed no affinity for the IGF-II receptor. Insulin, at physiologic concentrations, was incapable of displacing either IGF-I or IGF-II binding. Cellular incorporation of [methyl-3H]thymidine was stimulated at the lowest dose of IGF-I tested, 0.5 ng/ml. IGF-II showed no effect up to 100 ng/ml, after which a sharp increase in incorporation was noted. Insulin had a similar effect only at concentrations greater than 0.5 micrograms/ml, with a maximal response noted at 5 to 10 micrograms/ml. Our results indicate that fetal bovine aortic smooth muscle cells have an abundance of IGF receptors but lack specific insulin receptors. In addition, IGF-II binding levels are three times higher than for IGF-I. These results are consistent with observations in other species, in which a predominance of IGF over insulin receptors has been demonstrated in fetal tissue, and provide further evidence for a role for the IGFs in embryonic cellular metabolism.

Heparin and heparinoids impair adrenaline and platelet-activating factor but not thrombin-induced inhibition of adenylate cyclase and stimulation of GTP hydrolysis in human platelet membranes

The effects of heparins and heparinoids were studied on adenylate cyclase and GTPase activities in human platelet membranes. Inhibition of adenylate cyclase by adrenaline and platelet activating factor was completely abolished by heparin at 1 microgram/ml. At similar concentration heparin blocked the stimulation of high affinity GTPase(s) by these hormonal factors. In contrast, heparin (up to 30 micrograms/ml) did not abolish adenylate cyclase inhibition and stimulation of GTP hydrolysis by thrombin in the absence of antithrombin III. In the presence of antithrombin III, thrombin action on adenylate cyclase was blocked by unfractionated and high molecular weight heparin at 0.1 microgram/ml. Low molecular weight heparins and pentosanpolysulfate were less or not effective. In contrast, all high and low molecular weight heparins tested were almost equally potent in inhibiting adrenaline-induced inhibition of adenylate cyclase in the absence of antithrombin III. The data indicate that heparins discriminate platelet activating factor and adrenaline-induced inhibition of adenylate cyclase from the inhibitory action of thrombin and delineate different structural requirements for the interaction of heparins with the adenylate cyclase system and antithrombin III.

Heparin inhibits skeletal muscle growth in vitro

Heparin or heparan sulfate proteoglycan (HeSPG), but not chondroitin sulfate or hyaluronic acid, exerts a pronounced inhibitory effect on muscle growth in vitro, as determined by total protein, myosin accumulation or synthesis, and [3H]thymidine incorporation studies. Primary muscle fibroblast culture growth is also inhibited by heparin but to a substantially lesser degree compared to muscle (30% and over 90% inhibition of growth, respectively). Heparin-induced inhibition of skeletal muscle growth is a consequence of its interaction with a growth factor(s) present in the media used to support myogenesis; heparin-Sepharose column absorbed horse serum can support muscle growth only in the presence of added heparin-binding growth factors like fibroblast growth factor (FGF) or chicken muscle growth factor (CMGF). Furthermore, heparin prevents the binding of iodinated FGF to the myoblast surface. We also show that the extent of muscle growth is a function of the relative amounts of heparin and FGF in culture. Finally, we provide evidence indicating that FGF can combine with endogenously occurring heparin-like components: immobilized FGF binds sodium-[35S]sulfate labeled components secreted in muscle culture conditioned medium, an interaction inhibited by anti-HeSPG antibodies or heparin, but not by other sulfated glycosaminoglycans. Since heparin binding growth factors not only stimulate myoblast proliferation but also actively inhibit the onset of muscle differentiation (G. Spitzz, D. Roman, and A. Strauss (1986). J. Biol. Chem. 261, 9483-9488), their interaction with naturally occurring heparin-like components may be an important physiological mechanism for modulating muscle growth and differentiation in development and regeneration.

Serum and growth factors regulate expression of a 43 kDa protein in smooth muscle cell cultures

Smooth muscle cells respond to injury and the presence of serum factors by modulating from a quiescent contractile cell to a motile synthetic phenotype. To evaluate the biochemical response to serum exposure, we examined the proteins synthesized and secreted in response to serum. The most prominent effect of serum was the rapid production of a protein with an apparent molecular weight of 43 kDa. Removal of serum from the culture environment led to a cessation of 43 kDa protein production. The effect of exogenous heparin on 43 kDa protein production was also evaluated. Neither the 43 kDa protein nor a previously described 38 kDa protein was induced by heparin. Further, heparin treatment did not counteract the effects of serum. These studies demonstrate that an early response of vascular smooth muscle cells to serum is the production of this previously undescribed protein and that other modifications of the culture conditions did not affect its synthesis.

Heparin uncouples alpha 2-adrenoceptors from the Gi-protein in membranes of human platelets

The influence of heparin was studied on the inhibitory regulation of adenylate cyclase in human platelet membranes. Heparin blocked the adrenaline-induced inhibition of adenylate cyclase and the stimulation of GTP hydrolysis with half-maximal and maximal efficiency at 0.3 and 1-3 micrograms/ml, respectively. The effect of heparin was reversed by washing the membranes. Heparin did not change the number of alpha-adrenoceptors. In contrast, the affinity of the alpha-adrenoceptor for adrenaline was decreased in the presence of heparin. The pertussis toxin-catalysed ADP-ribosylation of the inhibitory guanine nucleotide-binding Gi-protein was not altered by heparin. Heparin also abolished the inhibition of adenylate cyclase caused by GTP itself. The data indicate that heparin can impair the hormone-induced inhibition of adenylate cyclase and the stimulation of GTP hydrolysis and suggest that the effects of heparin are caused by an action at the Gi-protein of the adenylate cyclase system.

Effects of acidic and basic fibroblast growth factors (aFGF and bFGF) on the proliferation and the glutamine synthetase expression of rat astroblasts in culture

The two fibroblast growth factors called acidic and basic FGF (aFGF and bFGF) show a strong homology (55%) of their amino acid sequence (Esch et al.: Proc. Nat. Acad. Sci. USA 85:6507-6511, 1985). The effects of these factors on the rate of proliferation of rat astroblasts and on the expression of glutamine synthetase activity in cells grown in primary culture were investigated and compared under various culture conditions. In all the experimental conditions used, both growth factors triggered the proliferation of the cells to the same extent and with similar dose dependence. The mitogenic activities of aFGF and bFGF were potentiated similarly by heparan sulfate and by heparin, with a maximum stimulation of about 100% at 100 micrograms/ml heparin. Treatment of the cells with either of the two factors resulted in identical enhancement of the activity of glutamine synthetase relative to total proteins. These results suggest that both factors act either through the same membrane receptors or through different receptors that mediate nearly identical effects.

Metabolic effects of heparin on rat cervical epithelial cells

The glycosaminoglycan heparin inhibits the growth of a number of different cell types in vitro including smooth muscle cells, mesangial cells, fibroblasts, and rat cervical epithelial cells (RCEC). Studies investigating the antiproliferative effects of heparin on smooth muscle cells have demonstrated the site of the cell cycle block and revealed several metabolic alterations that could be causally associated with growth inhibition. We have investigated these metabolic parameters in RCEC to determine whether they are also associated with the antiproliferative effects of heparin in epithelial cells. Heparin acts rapidly to inhibit RCEC growth with inhibition detectable by autoradiography 7 h after the addition of heparin. Heparin treated RCEC begin to enter S-phase 12 h after the removal of heparin. These findings suggest that heparin blocks RCEC in the early-to-mid G1 phase of the cell cycle rather than late in G1 or early in S-phase as has previously been demonstrated for smooth muscle cells. Unlike smooth muscle cells, the uptake of thymidine and uridine is not inhibited by heparin in RCEC. Treatment of medium with heparin-Sepharose does not reduce the subsequent growth of RCEC; heparin inhibits the growth of RCEC in heparin-Sepharose treated medium in a manner identical to that in nontreated medium. Therefore the growth inhibitory effects of heparin cannot be explained by the inactivation of mitogens present in serum. In contrast to its effects on smooth muscle cells, heparin treatment of RCEC does not result in a reduction in the binding of epidermal growth factor (EGF) to the cells. These results indicate that although heparin inhibits the growth of a variety of cell types, significant differences exist in the responses of the different cells to heparin.