Pro-inflammatory genetic profiles in subjects with peripheral arterial occlusive disease and critical limb ischemia.

OBJECTIVES: Single nucleotide polymorphisms in genes encoding inflammatory molecules may determine genetic profiles associated with increased risk of development and progression of cardiovascular diseases. In this study, we evaluated distribution and reciprocal interaction of a set of functionally important polymorphisms of genes encoding prototypical inflammatory molecules in subjects with peripheral arterial occlusive disease (PAOD) and critical limb ischemia (CLI). We also investigated whether synergistic interactions between these pro-inflammatory gene polymorphisms influence the risk of PAOD and CLI. DESIGN, SUBJECTS AND METHODS: In a genetic association study that included 157 PAOD patients and 206 controls, the following gene polymorphisms were analysed: C-reactive protein (CRP) 1059 G/C, interleukin-6 (IL-6)-174 G/C, macrophage migration inhibitory factor (MIF)-173 G/C, monocyte chemoattractant protein (MCP-1) - 2518 A/G, E-selectin (E-Sel) Ser128Arg, intercellular adhesion molecule-1 (ICAM-1) 469 E/K, matrix metalloproteinase (MMP)-1 -1607 1G/2G, MMP-3-1171 5A/6A and MMP-9-1563 C/T. RESULTS: We found that IL-6, E-sel, ICAM-1, MCP-1, MMP-1 and MMP-3 gene polymorphisms were significantly and independently associated with PAOD. We also found that these pro-inflammatory polymorphisms determine genetic profiles that are associated with different levels of risk for PAOD and CLI, depending on the number of high-risk genotypes concomitantly carried by a given individual. CONCLUSIONS: Pro-inflammatory genetic profiles are significantly more common in subjects with PAOD. Synergistic effects between pro-inflammatory genotypes might be potential markers for the presence and severity of atherosclerotic disorders.

COP-1, a member of the CCN family, is a heparin-induced growth arrest specific gene in vascular smooth muscle cells.

Vascular smooth muscle cell (VSMC) hyperplasia is responsible for the failure of 15-30% of vascular surgical procedures such as coronary artery bypass grafts and angioplasties. We and others have shown that heparin suppresses VSMC proliferation in vivo and in cell culture. We hypothesize that heparin inhibits VSMC proliferation by binding to cell surface receptors, resulting in selective modulation of mitogenic signal transduction pathways and altered transcription of a specific subset of growth regulatory genes. To test this idea, we used subtractive hybridization to identify differentially expressed mRNAs in heparin-treated and untreated VSMC. We identified a heparin induced mRNA identical to Cop-1, a member of the CCN family of proteins which are secreted, cysteine-rich modular proteins involved in growth regulation and migration. Cop-1 from smooth muscle cells appears to have a different expression pattern and possibly different functions than Cop-1 from other cells. Cop-1 mRNA is expressed at high levels in quiescent VSMC and at low levels in proliferating VSMC, an expression pattern highly characteristic of growth arrest specific genes. Cop-1 mRNA is expressed at high levels in heparin treated VSMC and COP-1 protein is secreted into culture medium. In tissues, Cop-1 expression is observed in the uninjured rat aorta suggesting a possible role for Cop-1 in vivo. We found PDGF, but not EGF, inhibits the expression of Cop-1 in VSMC. Neither TGF-beta nor interferon-beta, two inhibitors of VSMC proliferation, were able to induce Cop-1 expression. In addition, heparin does not induce Cop-1 mRNA in endothelial cells and VSMC resistant to the antiproliferative effect of heparin. Conditioned medium from cells over-expressing COP-1 protein inhibits VSMC proliferation in culture. Together, our data indicate that COP-1 may play a role in the antiproliferative mechanism of action of heparin.

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 suppresses sgk, an early response gene in proliferating vascular smooth muscle cells.

Vascular smooth muscle cell (VSMC) hyperplasia plays a central role in chronic and acute vascular pathology including arteriosclerosis and restenosis following vascular surgery. The glycosaminoglycans of the heparan sulfate class, including heparin, inhibit VSMC proliferation in animals and in culture. Heparin binds to high affinity sites on the cell surface, selectively modulates mitogenic signal transduction pathway(s), and rapidly alters transcription of several genes. To further explore the molecular mechanisms responsible for this growth inhibition, we have employed the differential display technique to identify heparin-regulated genes. Here we demonstrate that heparin inhibits the expression of the early response gene sgk (serum and glucocorticoid-regulated kinase). The expression of sgk is not inhibited by chondroitin sulfate, a nonantiproliferative glycosaminoglycan, suggesting that sgk suppression may play a functional role in the antiproliferative effect of heparin. This idea is strengthened by the finding that heparin does not inhibit sgk expression in VSMCs resistant to the antiproliferative effect of heparin or in vascular endothelial cells which are unresponsive to heparin. Expression of sgk mRNA diminishes with increasing concentrations of heparin. Finally, sgk expression is not suppressed by other growth inhibitors such as transforming growth factor-beta 1 (TGF-beta 1) and interferon-beta (IFN-beta), suggesting separate and distinct effects of these growth inhibitors on the mitogenic pathway.

Synthesis and characterization of highly sensitive heparin probes for detection of heparin-binding proteins.

Three labeled heparin species were synthesized as probes for heparin-binding protein detection. Heparin conjugated with 5([4,6-dichlorotriazin-2-yl]amino)fluorescein can be iodinated to a high specific activity. This probe specifically detected 40 pg histone on a dot blot without affinity purification. Heparin biotinylated on its naturally occurring primary amino groups also detected known heparin-binding proteins in a specific manner. This probe detected lower amounts of collagen I and basic fibroblast growth factor on nitrocellulose membranes than did the iodinated probe, with comparable detection times. To create more attachment sites for biotin, we covalently attached amino groups to the hydroxyl groups of heparin using 3-bromopropylamine hydrobromide. After biotinylation, the amino-rich probe detected heparin-binding proteins at the same or higher sensitivity as the biotinylated native heparin probe, using 100-fold less probe and much shorter detection times. This method of labeling is generally applicable to other polysaccharides, and would be useful when the amount of ligand is limited. We show that these three probes detect essentially the same spectrum of proteins in detergent extract of smooth muscle cell plasma membrane, and expect them to be useful probes for detection of cell-surface heparin receptors.

Sulfated malto-oligosaccharides bind to basic FGF, inhibit endothelial cell proliferation, and disrupt endothelial cell tube formation.

The interaction of basic FGF (bFGF) with heparin, heparan sulfate and related sugars can potentiate or antagonize bFGF activity, depending on the size of the saccharide used. Oligosaccharides based on heparin structures, as small as six sugar residues, have been demonstrated to bind to bFGF and block its activity, while larger structures (> 10 sugar residues) tend to potentiate bFGF. In this study we have synthesized a series of compounds designed to test the requirements of size and sulfation for binding of oligosaccharides to bFGF. These oligosaccharides are not derived from heparin, but rather, are linear chains of glucose linked alpha 1-4 (malto-oligosaccharides) that have been chemically sulfated. In addition to bFGF binding, these compounds were tested for their ability to block basic functions of endothelial cells that are known to be mediated, at least in part, by bFGF. We report that the ability of sulfated malto-oligosaccharides to block binding of bFGF to heparan sulfate was dependent on the size (at least a tetrasaccharide is required), and the degree of sulfation. The activity profile in the bFGF ELISA closely correlated with the ability of these compounds to block REEC or HMVEC tube formation on Matrigel. There was a similar relationship of size and sulfation to the ability of the sulfated malto-oligosaccharides to inhibit endothelial cell growth for most human and rat EC types tested. The single exception was REEC cell growth. One isolate of these cells was stimulated by sulfated malto-oligosaccharides rather than inhibited by them, while a second isolate was neither stimulated nor inhibited. This stimulation showed no correlation with inhibition of bFGF binding in the ELISA assay, suggesting that growth of this cell type was probably not dependent on bFGF. Compounds derived from this series of sulfated, malto-oligosaccharides have the potential to function as bFGF antagonists, are relatively easy to produce, and possess relatively low anticoagulant properties.

Isolation of vascular smooth muscle cell cultures with altered responsiveness to the antiproliferative effect of heparin.

Smooth muscle cell (SMC) hyperplasia in the arterial wall is an important component of both atherogenesis and post-vascular surgical restenosis. One naturally-occurring group of molecules which can suppress SMC proliferation in animal models and in cell culture systems are the complex carbohydrates of the heparan sulfate class, including heparin. In this communication, we have used retrovirus vectors to introduce several oncogenes into SMC: SV40 Large T antigen (SVLT), polyoma virus Large T antigen (PyLT), v-myc, and adenovirus E1a. We analyzed a total of 11 cultures. A combination of Western blot analysis, immunoprecipitation, and indirect immunofluorescence confirmed the expression of the infected oncogenic protein in each culture we isolated. All four oncogenes permitted the maintenance of a normal SMC phenotype, as assessed by the general morphology of cells in the light microscope and the presence of SMC-specific alpha-actin in an immunofluorescence assay. Doubling times in infected cells ranged from 20 to 33 hr, and final cell densities in infected cultures ranged from 4 x 10(4) to 5 x 10(5) cells per cm2. By comparison, the parent line had a doubling time of 30 hr and reached a final cell density of 1 x 10(5) cells per cm2. Despite the differences sometimes observed in these proliferation parameters, neither one was strongly correlated with heparin responsiveness. PyLT, v-myc, and E1a all produced SMC cultures or lines which retained sensitivity to the antiproliferative activity of heparin (ED50 = 50 micrograms/ml). In contrast, SVLT expression yielded SMC lines which were highly resistant to heparin (ED50 > 300 micrograms/ml). These results suggest that altered responsiveness to heparin is dependent upon which oncogenic protein is being expressed in the cells. The availability of cloned, immortal SMC lines with a wide range of heparin responsiveness should aid in the understanding of the cellular and molecular mechanism of action of this potentially important growth regulator and therapeutic agent.

Heparin binding, internalization, and metabolism in vascular smooth muscle cells: I. Upregulation of heparin binding correlates with antiproliferative activity.

Vascular smooth muscle cell (SMC) hyperplasia is an important component in the pathogenesis of arteriosclerotic lesions and is responsible for the failure of many vascular surgical procedures. SMC proliferation is inhibited by the glycosaminoglycan heparin; however, the precise mechanisms of action are still not understood. One important question in this regard is whether binding, internalization, and metabolism of heparin are necessary for the antiproliferative activity. In this study, we have analyzed SMC rendered resistant to the antiproliferative effect of heparin by drug selection and retroviral infection of SMC. We first examined the ability of heparin to bind to SMC. Experiments using [3H]heparin indicate the presence of saturable, heparin-displaceable, protease-sensitive binding sites on both sensitive and resistant SMC. The affinity of heparin binding does not correlate with the antiproliferative response. Using fluorescent and radiolabeled heparin probes, we observed that early heparin internalization kinetics in both sensitive and resistant SMC is similar, indicating that resistance to heparin is not due to changes in the ability of cells to take up heparin. In contrast, we observed during the continuous incubation with heparin that binding to resistant SMC is rapidly downregulated, whereas sensitive cells continue to bind and internalize heparin. These results suggest that upregulation of heparin binding to the SMC surface is required for an antiproliferative response. In an accompanying paper (Letourneur et al. [1995] J. Cell Physiol., 165:687-695, this issue), we describe the degradation and secretion of internalized heparin in both sensitive and resistant SMC.

Heparin binding, internalization, and metabolism in vascular smooth muscle cells: II. Degradation and secretion in sensitive and resistant cells.

Smooth muscle cell (SMC) proliferation plays a critical role in several pathological states, including atherosclerosis and hypertension. Heparin suppresses SMC proliferation in vivo and in culture, but the mechanism of action is still poorly understood. In an accompanying article in this issue (Letourneur et al. [1995] J. Cell Physiol., 165:676-686), we observed that heparin binding was up-regulated in heparin-sensitive SMC but was rapidly down-regulated in heparin-resistant SMC continuously exposed to heparin. In this communication, we examine the degradation and secretion of internalized heparin in sensitive and resistant SMC, using gel filtration chromatography to analyze heparin degradation products. Pulse-chase experiments using radiolabeled heparin indicate that sensitive and resistant SMC secrete heparin during the first few hours after exposure. Experiments in which cells are continuously exposed to heparin indicate that degradation and secretion occur in both sensitive and resistant SMC for approximately 5-8 hr. After that time, however, binding and internalization in resistant SMC rapidly decrease and degradation and secretion stop. In contrast, heparin binding and uptake continue in sensitive SMC; degradation and secretion also continue. Chloroquine prevents degradation in both sensitive and resistant SMC, suggesting that catabolism occurs in the lysosomal compartment. The results presented in this and the accompanying article (Letourneur et al. [1995] J. Cell. Physiol., 165:676-686) suggest that heparin acts to upregulate its receptors, and that increased binding of heparin is required for the antiproliferative response. Degradation and secretion kinetics parallel the internalization kinetics and appear to be strongly linked to the binding process.

1-Butyryl-glycerol: a novel angiogenesis factor secreted by differentiating adipocytes.

Differentiation of adipocytes is accompanied by secretion of molecules stimulating angiogenesis in vivo and endothelial cell growth and motility in vitro. We demonstrate that the angiogenic and motility-stimulating activities secreted by adipocytes are separable from the endothelial cell mitogenic activity by fractionation of adipocyte-conditioned medium. The major differentiation-dependent angiogenic molecule was purified and identified by GCMS as 1-butyryl-glycerol (monobutyrin). Monobutyrin levels increase at least 200-fold during adipocyte differentiation and represent a major fraction of the total angiogenic activity. Synthetic monobutyrin shows the same spectrum of biological activities as the adipocyte-derived factor: stimulation of angiogenesis in vivo and microvascular endothelial cell motility in vitro, with no effect on endothelial cell proliferation. Angiogenesis is stimulated at doses as low as 20 pg when tested in the chick chorioallantoic membrane assay. These results strongly suggest that monobutyrin is a key regulatory molecule in an angiogenic process linked to normal cellular and tissue development.

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.

Heparin selectively inhibits a protein kinase C-dependent mechanism of cell cycle progression in calf aortic smooth muscle cells.

The proliferation of arterial smooth muscle cells (SMCs) plays a critical role in the pathogenesis of arteriosclerosis. Previous studies have indicated that the glycosaminoglycan heparin specifically inhibited the growth of vascular SMCs in vivo and in culture, although the precise mechanism(s) of action have not been elucidated. In this study, we have examined the ability of specific mitogens (PDGF, EGF, heparin-binding growth factors, phorbol esters, and insulin) to stimulate SMC proliferation. Our results indicate that SMCs derived from different species and vascular sources respond differently to these growth factors. We next examined the ability of heparin to inhibit the proliferative responses to these mitogens. In calf aortic SMCs, heparin inhibits a protein kinase C-dependent pathway for mitogenesis. Detailed cell cycle analysis revealed several new features of the effects of heparin on SMCs. For example, heparin has two effects on the Go----S transition: it delays entry into S phase and also reduces the number of cells entering the cycle from Go. Using two separate experimental approaches, we found that heparin must be present during the last 4 h before S phase, suggesting a mid-to-late G1 heparin block. In addition, our data indicate that heparin-treated SMCs, while initially blocked in mid-to-late G1, slowly move back into a quiescent growth state in the continued presence of heparin. These results suggest that heparin may have multiple targets for its antiproliferative effect.

Heparin suppresses the induction of c-fos and c-myc mRNA in murine fibroblasts by selective inhibition of a protein kinase C-dependent pathway.

Heparin is a complex glycosaminoglycan that inhibits the proliferation of several cell types in culture and in vivo. To begin to define the mechanism(s) by which heparin exerts its antiproliferative effects, we asked whether heparin interferes with the expression of the growth factor-inducible protooncogenes c-fos and c-myc. We show that heparin suppressed the induction of c-fos and c-myc mRNA by serum in murine (BALB/c) 3T3 fibroblasts. Using purified mitogens, we further show that suppression was most marked when protooncogene expression was induced by phorbol 12-myristate 13-acetate, an activator of protein kinase C. By contrast, there was little or no suppression when the cells were stimulated by epidermal growth factor, which, in these cells, utilizes a protein kinase C-independent pathway for the induction of gene expression. Heparin also inhibited the change in cell morphology induced by the phorbol ester but had no effect on the morphological change induced by epidermal growth factor and agents that raise intracellular cAMP. Heparin did not inhibit intracellular protein kinase C activity, phorbol ester-induced down-regulation of protein kinase C, or phosphorylation of the 80-kDa intracellular protein kinase C substrate. These results suggest that heparin inhibits a protein kinase C-dependent pathway for cell proliferation and suppresses the induction of c-fos and c-myc mRNA at a site distal to activation of the kinase.

Structural determinants of heparin's growth inhibitory activity. Interdependence of oligosaccharide size and charge.

The glycosaminoglycan heparin inhibits the growth of several cell types in vitro including smooth muscle cells and rat cervical epithelial cells. The commercially available heparin which has antiproliferative activity is a structurally heterogeneous polymer that undergoes extensive modifications during maturation. In this report we have performed structure-function studies on heparin's antiproliferative activity using three different cell types: both rat and calf vascular aortic smooth muscle cells and rat cervical epithelial cells. The minimal oligosaccharide size requirements for antiproliferative activity were determined for the three cell types by using oligosaccharide fragments of defined length prepared by nitrous acid cleavage and gel filtration and a synthetic pentasaccharide. The size requirements are similar but not identical for the different cell types. Hexasaccharide fragments are antiproliferative for all three cell types but the synthetic pentasaccharide inhibits the growth of only the rat and calf vascular aortic smooth muscle cells. The interdependence between size and charge for antiproliferative activity was investigated using chemically modified oligosaccharides as well as oligosaccharides prepared from heparin and separated into fractions of differing charge by ion-exchange chromatography. There is a strong interdependence between size and charge for antiproliferative activity. For example, increasing the charge of inactive tetrasaccharide fragments by O-oversulfation makes them antiproliferative whereas reducing the charge of active larger fragments causes them to loose their antiproliferative activity. Finally the importance of 2-O-sulfate glucuronic acid moieties for antiproliferative activity was investigated using heparin preparations that lack 2-O-sulfate glucuronic acid. These compounds possess antiproliferative activity indicating that 2-O-sulfate glucuronic acid is not required for antiproliferative activity.

Heparin modulates the secretion of a major excreted protein-like molecule by vascular smooth muscle cells.

Previous work from our laboratory has shown that heparin specifically induces the release of a pair of proteins of approximately 35,000 and 37,000 Da into the culture medium of vascular smooth muscle cells (SMC). In this report, we demonstrate that the previously identified 37,000-Da smooth muscle protein is composed of two protein species with very similar molecular weights based on migration patterns in SDS-polyacrylamide gels. The larger molecular weight species in this doublet has a similar molecular weight and shares antigenic determinants with major excreted protein (MEP), a lysosomal proteinase previously shown to be secreted by normal and transformed fibroblasts and epidermal cells. Antisera to MEP precipitated the higher molecular weight band from the doublet; preimmune serum was not reactive with the smooth muscle protein. Exposure of smooth muscle cells to heparin resulted in decreased amounts of immunoprecipitable protein released into the medium. Thus, it now appears that three proteins in the 35,000-38,000 molecular weight range are modulated by heparin, and that the largest of the heparin-modulated vascular SMC proteins has a similar molecular weight and is immunologically related to MEP. The release of MEP-like protein from SMC is decreased by heparin, while the remaining two heparin-modulated proteins are increased in the presence of heparin.

Size-dependent hyaluronate degradation by cultured cells.

Hyaluronate degradation was examined in cultures of vascular wall cells (bovine aortic endothelial cells, rat aortic smooth muscle cells) and in nonvascular cells (chick embryo fibroblasts). The three cell types examined all produced hyaluronidase activity in culture which had a strict acidic pH requirement for activity. This suggested that the enzyme was active only within an acidic intracellular compartment and therefore that hyaluronate degradation occurred at an intracellular site. This was supported by the observation that the presence of hyaluronidase activity alone was not sufficient to ensure degradation of extracellular hyaluronate. Rather, the key limiting factor in this process appeared to be hyaluronate internalization, and this was found to be hyaluronate size-dependent and to a degree, cell-specific. The relationship of these results to morphogenesis and tissue remodeling is discussed.