Localization of PDGF-B protein in macrophages in all phases of atherogenesis

Lymphocyte transendothelial migration toward smooth muscle cells in interleukin-1 beta-stimulated co-cultures is related to fibronectin interactions with alpha 4 beta 1 and alpha 5 beta 1 integrins

We previously reported infiltration of immune-inflammatory cells in coronary arteries from cardiac allografts, associated with increased endothelial and smooth muscle cell fibronectin synthesis regulated by interleukin (IL)-1 beta. We now investigate, using a porcine endothelial-smooth muscle cell co-culture system, whether IL-1 beta-stimulated fibronectin production is functionally important in lymphocyte transendothelial migration. Lymphocytes were harvested from porcine peripheral blood and, in the unactivated state or following activation with phorbol myristic acetate (PMA) and IL-2, were characterized by fluorescence-activated cell sorter (FACS) analysis and added to a confluent endothelial monolayer on the upper chamber of a transwell system. Endothelial cells, as well as smooth muscle cells (in the bottom of the chamber), were stimulated with IL-1 beta. Then transendothelial lymphocyte migration was determined in the presence of CS1 and RGD (fibronectin) peptides, blocking alpha 4 beta 1 and alpha 5 beta 1 integrin receptors on lymphocyte surfaces, respectively. A 55-70% inhibition of lymphocyte migration was observed when compared to control peptides. The combination of CS1 and RGD peptides did not significantly enhance the inhibitory effect of either peptide alone. A similar decrease in lymphocyte transendothelial migration toward smooth muscle cells was documented using a monoclonal antibody to cellular fibronectin. Furthermore, using smooth muscle cell conditioned medium, we reproduced the enhanced transendothelial lymphocyte migration as well as the inhibition with blocking peptides or fibronectin antibodies. Our data suggest that cytokine-mediated fibronectin synthesis in vascular cells recruits inflammatory cells through interactions of specific peptides with cell surface alpha 4 beta 1 and alpha 5 beta 1 integrins.

Detection of platelet-derived growth factor (PDGF)-AA in actively healing human wounds treated with recombinant PDGF-BB and absence of PDGF in chronic nonhealing wounds

Some human chronic dermal wounds treated with recombinant platelet-derived growth factor-BB (rPDGF-BB) show increased healing coupled with fibroblast activation and granulation tissue formation. To determine whether endogenous PDGF is associated with healing and nonhealing dermal ulcer phenotypes, we developed monoclonal antibodies capable of recognizing the three isoforms of PDGF, AA, AB, and BB dimers, and capable of discriminating between two alternatively spliced A chain transcripts. We detected little PDGF isoform expression in normal skin and in nonhealing dermal ulcers. In contrast, in surgically created acute wounds and chronic ulcers treated with rPDGF-BB, markedly upregulated levels of PDGF-AA (long form) were found. In both types of wounds, increased PDGF-AA was detected primarily in capillaries and fibroblasts, although in rPDGF-BB-treated chronic wounds, widespread expression of PDGF-AA was somewhat delayed. With continued treatment, the long form of PDGF-AA, which can preferentially bind extracellular matrix, was expressed only in capillaries, while fibroblasts began synthesizing the short form of PDGF-AA. Within capillaries, all endothelial cells and varying numbers of pericytes and smooth muscle cells contained PDGF-AA. In all wounds, macrophages and keratinocytes were not a major contributor. While PDGF-BB and PDGF-AB were present in a minority of healing wounds, they were usually present at lower levels than PDGF-AA. PDGF-beta receptors, which bind only PDGF-BB and not other isoforms, were found in normal skin and granulation tissue, providing a molecular basis for treating human chronic wounds with exogenous rPDGF-BB.

Platelet-derived growth factors-AA and -BB regulate collagen and collagenase gene expression differentially in human fibroblasts

Platelet-derived growth factor (PDGF) is a mitogen associated with tissue repair, a process involving collagen synthesis and remodelling by interstitial collagenase. This study examines and compares the regulation of interstitial collagenase and collagen gene expression by PDGF-AA and -BB in human fibroblasts. Time-course analysis showed that neither PDGF-AA or -BB had a consistent effect on the expression of pro-alpha 1(I) or pro-alpha 2(I) type-I collagen genes. In contrast, interstitial collagenase gene expression was found to be consistently up-regulated severalfold by PDGF-BB. Enhanced expression of the collagenase gene was not apparently due to up-regulation of its promoter activity in human dermal fibroblasts, as indicated by transient and stable transfection experiments. Unlike PDGF-BB, PDGF-AA did not alter collagenase mRNA levels under low-serum culture conditions. Thus, the biological activities of the PDGF homodimers are different, with PDGF-BB being clearly more potent than PDGF-AA in its regulation of collagenase gene expression.

Expression of platelet-derived growth factor B-chain in the mature rat brain and pituitary gland

For better understanding of the role of platelet-derived growth factor (PDGF) B-chain in the brain, the expression of PDGF B-chain was studied in the mature rat brain at both protein and mRNA levels, by assay of PDGF B-chain-related mitogenic activity, Northern blot, in situ hybridization and immunohistochemistry. It was shown that (1) mature rat brain contained substantial PDGF B-chain-related mitogenic activity, (2) significant amounts of two sizes of transcripts (3.5 kb, widely, and 2.6 kb, weakly and in narrower areas) were expressed in the brain, and (3) the transcripts were localized in ubiquitous neurons by in situ hybridization, with the strongest signal in hippocampal pyramidal cells, which distribution almost corresponded with that of the immunoreactive products. The abundant neuronal localization of the transcript and protein, as well as the neuronal expression of the receptor reported elsewhere, suggests the role of the growth factor in neuronal cells as a neuronal regulatory and/or trophic agent acting by autocrine loop or by neuron to neuron interaction. However, there was an apparent discrepancy in part, in the distribution between transcripts and immunoreactivity; that is, transcripts were expressed intensely in the intermediate pituitary lobe with only a scattered immunoreactivity, and the opposite situation was observed in the accessory olfactory nerve and posterior pituitary lobe. This might suggest that PDGF B-chain is transported or secreted in these foci.

T lymphocytes that infiltrate tumors and atherosclerotic plaques produce heparin-binding epidermal growth factor-like growth factor and basic fibroblast growth factor: a potential pathologic role

Despite significant infiltration into tumors and atherosclerotic plaques, the role of T lymphocytes in these pathological conditions is still unclear. We have demonstrated that tumor-infiltrating lymphocytes (TILs) and plaque-infiltrating lymphocytes (PILs) produce heparin-binding epidermal growth factor-like growth factor (HB-EGF) and basic fibroblast growth factor (bFGF) in vitro under nonspecific conditions and in vivo in tumors by immunohistochemical staining. HB-EGF and bFGF derived from TILs and PILs directly stimulated tumor cells and vascular smooth muscle cells (SMCs) in vitro, respectively, while bFGF displayed angiogenic properties. Therefore, T cells may play a critical role in the SMC hyperplasia of atherosclerosis and support tumor progression by direct stimulation and angiogenesis.

Regulation of insulin-like growth factor (IGF) binding protein-2 synthesis and degradation by platelet-derived growth factor and the IGFs is enhanced by serum deprivation in vascular smooth muscle cells

Growth factors such as platelet-derived growth factor (PDGF) and insulin-like growth factor (IGF-I) stimulated proliferation and migration of vascular smooth muscle cells (SMC). IGF-I bioactivity is modulated by high-affinity binding proteins (IGFBP) which are important regulators of these processes. Porcine vascular SMC synthesize IGFBP-2 and IGFBP-4 in vitro. In the present study, levels of IGFBP-2 in conditioned media (CM) were increased approximately 1.6 to 2.2-fold when cells were exposed to PDGF (20 ng/ml) or insulin (5 micrograms/ml) for 24 hr following a 24 hr incubation in serum-free media, or following a 72 hr exposure to either growth factor. Similar increases in IGFBP-2 mRNA levels were observed. Exposure of cells to PDGF for 24 hr without prior serum deprivation resulted in smaller (47 +/- 11%) increases in IGFBP-2 protein levels but failed to alter mRNA levels. IGF-I, FGF, TGF-beta and EGF failed to increase IGFBP-2 using either experimental paradigm. In contrast, IGFBP-2 protein levels were consistently decreased (75 +/- 14%) after 72 hr of exposure to IGF-II without corresponding decreases in IGFBP-2 mRNA levels. Immunoprecipitation of [35S]methionine-labeled IGFBP-2 indicated that this decrease was not due to a decrease in synthesis of IGFBP-2. Immunoblot analysis of CM from cells treated with IGF-II indicated that the decrease in intact protein corresponded with an increase in two non-IGF binding IGFBP-2 fragments of 22 and 14 kD. Increased abundance of these fragments was also observed following IGF-I exposure, although corresponding decreases in intact IGFBP-2 were not usually observed. The relative abundance of these fragments did not appear to be affected by treatment with PDGF or insulin. In contrast to IGFBP-2, regulation of the levels of IGFBP-4 in CM did not appear to be altered by serum deprivation. Insulin consistently increased IGFBP-4 mRNA and protein levels under all situations. PDGF tended to increase IGFBP-4 protein levels, although this effect was less consistent and not as great as the increase observed with insulin. Treatment with IGF-I or -II consistently decreased IGFBP-4 levels in CM but tended to increase their mRNA levels under all situations. These data indicate that insulin, PDGF, and the IGFs regulate both IGFBP-2 and IGFBP-4. While PDGF and insulin stimulate IGFBP-2 and 4 synthesis, the IGFs appear to activate protease(s) which regulate IGFBP-2 and -4 levels post-translationally.(ABSTRACT TRUNCATED AT 400 WORDS)

Sphingosine-1-phosphate inhibits PDGF-induced chemotaxis of human arterial smooth muscle cells: spatial and temporal modulation of PDGF chemotactic signal transduction

Activation of the PDGF receptor on human arterial smooth muscle cells (SMC) induces migration and proliferation via separable signal transduction pathways. Sphingosine-1-phosphate (Sph-1-P) can be formed following PDGF receptor activation and therefore may be implicated in PDGF-receptor signal transduction. Here we show that Sph-1-P does not significantly affect PDGF-induced DNA synthesis, proliferation, or activation of mitogenic signal transduction pathways, such as the mitogen-activated protein (MAP) kinase cascade and PI 3-kinase, in human arterial SMC. On the other hand, Sph-1-P strongly mimics PDGF receptor-induced chemotactic signal transduction favoring actin filament disassembly. Although Sph-1-P mimics PDGF, exogenously added Sph-1-P induces more prolonged and quantitatively greater PIP2 hydrolysis compared to PDGF-BB, a markedly stronger calcium mobilization and a subsequent increase in cyclic AMP levels and activation of cAMP-dependent protein kinase. This excessive and prolonged signaling favors actin filament disassembly by Sph-1-P, and results in inhibition of actin nucleation, actin filament assembly and formation of focal adhesion sites. Sph-1-P-induced interference with the dynamics of PDGF-stimulated actin filament disassembly and assembly results in a marked inhibition of cell spreading, of extension of the leading lamellae toward PDGF, and of chemotaxis toward PDGF. The results suggest that spatial and temporal changes in phosphatidylinositol turnover, calcium mobilization and actin filament disassembly may be critical to PDGF-induced chemotaxis and suggest a possible role for endogenous Sph-1-P in the regulation of PDGF receptor chemotactic signal transduction.

Growth-related signaling as a target of toxic insult in vascular smooth muscle cells: implications in atherogenesis

Aberrant smooth muscle cell proliferation is a focal point in the genesis and progression of atherosclerosis. To date, limited information is available on the molecular and cellular basis of the atherogenic response and the potential contribution of environmental chemicals to the overall process. This review highlights major findings in this laboratory on the mechanism(s) responsible for the acquisition of a proliferative phenotype in vascular smooth muscle cells following repeated cycles of treatment with allylamine and benzo(a)pyrene, known atherogenic chemicals. These agents share the ability to induce and promote aberrant proliferative behavior in smooth muscle cells, but appear to interfere with distinct molecular targets.

Isoforms of platelet-derived growth factor and its receptors in epiretinal membranes: immunolocalization to retinal pigmented epithelial cells

Epiretinal membranes (ERMs) form on the inner surface of the retina in conjunction with various ocular disease processes, but the factors controlling their development are not understood. The predominant cell types involved are retinal pigmented epithelial (RPE) cells and retinal glia. Cultured RPE cells secrete platelet-derived growth factor (PDGF), which is chemotactic and mitogenic for both RPE cells and retinal glia and, therefore, could be involved in the development of ERMs. In the present study, we performed immunohistochemical staining for PDGF A chain (PDGF-A), PDGF B chain (PDGF-B), and both types of PDGF receptors (PDGFr alpha and PDGFr beta) on ERMs associated with various disease processes. PDGF-A is detected in most ERMs, regardless of the associated disease process, and it appears to be localized predominantly in RPE cells, recognized by the presence of pigment and the immunohistochemical demonstration of some or all of the following RPE-associated epitopes: class III beta-tubulin, keratin, the 65-kDa microsomal protein recognized by the RPE9 antibody, and cellular retinaldehyde-binding protein. PDGF-B is found only in minor subpopulations of cells in about half of the ERMs evaluated and, with only occasional exceptions, appears to be localized almost entirely in blood-borne cells found in and around vessels in vascularized ERMs. Both PDGFr alpha and PDGFr beta are demonstrated in most ERMs with neither isotype consistently predominating: they are found predominantly on RPE cells with many cells expressing both receptor types. ERMs with little or no RPE cell component contain little or no PDGF and PDGF receptor, whereas those in which the RPE cell represents the major cell type, have widespread PDGF and PDGF receptor positivity. These findings show that RPE cells in ERMs produce PDGF-A and PDGF alpha and PDGF beta receptors and suggest that autocrine and paracrine stimulation with PDGF may be involved in ERM pathogenesis.

The effects of oxidized low density lipoproteins on inducible mouse macrophage gene expression are gene and stimulus dependent

Oxidized LDL has been previously reported to suppress the expression of genes induced in mononuclear phagocytes by inflammatory stimuli. In this study we extend these findings to demonstrate that the suppressive effects of oxidized LDL vary depending upon the gene being monitored and the stimulus being used to induce or enhance its expression. The expression of a selection of LPS-inducible genes exhibited differential sensitivity to pretreatment with oxidized LDL. Furthermore, the ability of oxidized LDL to suppress gene expression varied markedly with the inducing stimulus used. TNF alpha and IP-10 mRNA expression induced by IFN gamma and IL-2 was markedly more sensitive to suppression by oxidized LDL than that induced by LPS. The cooperative effects of IFN gamma and LPS on the expression of the inducible nitric oxide synthase gene were suppressed by oxidized LDL while the antagonistic effect of IFN gamma on LPS-induced expression of the TNF receptor type II mRNA was not altered. The suppressive activity of LDL was acquired only after extensive oxidation and was localized in the extractable lipid component. These results suggest a potent and direct connection between the oxidative modification of LDL and the chronic inflammation seen in atherogenic lesions. Furthermore, the appreciable selectivity of oxidized LDL in mediating secondary control of cytokine gene expression demonstrates that the active material(s) is targeted to disrupt specific intracellular signaling pathways.

Pharmacologic enhancement of wound healing

The field of pharmacologic modulation of soft tissue repair is in its infancy. Although the soluble, cellular, and insoluble mediators that govern repair have not been elucidated, the application of pharmacologic concentrations of purified polypeptide growth factors, cytokines, and matrix molecules has nonetheless resulted in the acceleration of normal repair and the reversal of deficient repair in a wide variety of dermal wound models in animals. However, early clinical results using these factors have been less than encouraging, and their potential roles in the armamentarium of chronic wound therapies remain to be established.

Internephron heterogeneity of growth factors and sclerosis--modulation of platelet-derived growth factor by angiotensin II

We studied the early phase after 5/6 nephrectomy in Munich-Wistar rats to determine whether treatment with angiotensin II receptor antagonist (AIIRA) modulates the expression of platelet-derived growth factor (PDGF) mRNA and its protein among the glomeruli which are undergoing progressive hypertrophy and sclerosis. Average PDGF-B immunohistochemistry staining score (IHS, 0 to 3 scale) in glomeruli and PDGF-B chain mRNA from kidneys were both increased in 5/6 nephrectomy rats (N = 6) versus age-matched normal (N = 5) at week 4, when glomeruli were at early stages of sclerosis (IHS, 0.81 +/- 0.12 vs. 0.19 +/- 0.05; sclerosis index, S.I., 0 to 4 scale: 0.41 +/- 0.04 vs. 0.05 +/- 0.01, both P < 0.05). AIIRA (80 mg/liter drinking water, N = 6) started at time of 5/6 nephrectomy prevented the development of sclerosis (S.I. 0.08 +/- 0.03) and decreased PDGF-B protein (IHS 0.22 +/- 0.08, both P = NS vs. normal), and PDGF-B chain mRNA. In contrast, triple therapy (TRX; hydralazine, reserpine and hydrochlorothiazide, N = 5) in doses which controlled systemic blood pressure resulted in intermediate level of glomerulosclerosis at this early time point of progressive injury. Concurrently, TRX failed to affect the expression of PDGF-B protein (IHS 0.86 +/- 0.19) or its mRNA expression. The PDGF-B distribution was not uniform amongst the glomeruli with varying stages of sclerosis. There was a strong correlation in individual glomeruli of increased PDGF-B staining with early sclerotic changes (P < 0.01), with the disappearance of this correlation in glomeruli with advanced sclerosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Estrogen modulates the inducible expression of platelet-derived growth factor mRNA by monocyte/macrophages

We examined the effects of estrogen, 12-O-tetradecanoylphorbol 13 acetate (TPA), and lipopolysaccharide (LPS) on the gene expression of platelet-derived growth factor (PDGF) by the monocyte/macrophage cell line, THP-1. THP-1 cells were exposed to TPA for 48 or 96 hours to induce differentiation. Some were treated with LPS in the last 3 hours and/or ethinyl estradiol (estrogen) (10(-9) M) in the last 20 hours. Total cellular RNA was isolated and cDNA was synthesized and then coamplified (with an internal control, beta-actin, product size 1126 bp) using polymerase chain reaction (PCR) and a set of primers for PDGF-A (product size 225 bp), PDGF-B (217 bp), or PDGF beta-receptor (PDGF-R) (228 bp). The products were separated on an agarose gel and the ratios of radioactivity incorporated into PDGF PCR products to beta-actin products were used to assess the relative changes in the levels of PDGF mRNA abundance in response to various inducers. TPA induced the expression of PDGF-A mRNA, whereas LPS had no effect. Treatment of TPA-stimulated cells with estrogen caused a 61% and 190% increase in PDGF-A mRNA (p < 0.05) at 48 and 96 hours, respectively. Addition of estrogen to cells treated with both TPA and LPS did not cause any significant change in the amounts of the transcripts. In contrast to PDGF-A mRNA, attempts to visualize and estimate PDGF-B and PDGF-R mRNA were unsuccessful. This was probably due to low levels of these transcripts in THP-1 cells. The results indicate that estrogen modulates PDGF-A gene expression by monocyte/macrophages and suggest that estrogen may influence atherogenesis at the vascular level.

Growth factor and procollagen type I gene expression in human liver disease

BACKGROUND/AIMS

Growth factors have been implicated in the pathogenesis of liver fibrosis, a major determinant of the clinical course of chronic liver disease. The aim of this study was to study the relationship of growth factor expression to inflammation and fibrosis in a variety of human liver diseases.

METHODS

We studied by in situ hybridization the expression of transforming growth factor (TGF) beta 1, platelet-derived growth factor (PDGF) A and PDGF-B, and procollagen type I (pro-I) messenger RNAs (mRNAs) in liver diseases of various etiologies.

RESULTS

Pro-I mRNA was expressed by mesenchymal cells at sites of inflammation and scarring, where TGF-beta 1 immunoreactivity was often found, and by perisinusoidal cells. TGF-beta 1 and PDGF-A mRNAs were expressed mainly by mononuclear cells and proliferating ductular cells. TGF-beta 1 mRNA was also expressed by perisinusoidal cells. PDGF-A gene expression was more common than that of PDGF-B. Pro-I and TGF-beta 1 expression correlated with both ductular proliferation and tissue inflammation, whereas PDGF-A and PDGF-B only correlated with ductular proliferation.

CONCLUSIONS

Our data suggest that TGF-beta 1 and PDGF are involved in human liver inflammation and fibrosis. The expression of growth factor mRNAs in proliferating ductular cells may indicate a role for these cells in liver fibrogenesis and may help explain the pathophysiology of conditions such as biliary atresia progressing to fibrosis despite the absence of marked inflammation.

Expression of ICAM-1 and VCAM-1 and monocyte adherence in arteries exposed to altered shear stress

Local shear stresses generated by blood flow exert direct mechanical effects on adhesion of circulating leukocytes to vascular endothelium, but their effects on expression of endothelial-leukocyte adhesion molecules have not been determined. Shear stress in rabbit carotid arteries was increased by 170% or decreased by 73% in 5 days by surgical manipulations. En face immunofluorescence staining with the monoclonal antibody Rb1/9 revealed that vascular cell adhesion molecule-1 (VCAM-1) expression was greatly increased under low shear stress, but the distribution of staining was patchy. Thus, 71.4 +/- 7.8% of fields were VCAM-1 positive versus 2.4 +/- 0.47% of fields in control arteries. Frequently, large regions showed consistent but heterogeneous staining. Occasionally, small islands of cells were labeled intensely. Monocytes, detected by use of the monocyte-specific antibody HAM 56, adhered to endothelium under low shear stress; 64.5 +/- 8.2% of the monocytes colocalized with detectable VCAM-1, although many (83.2 +/- 2.8%) VCAM-1-positive regions were devoid of monocytes. VCAM-1 expression also increased significantly but to a lesser extent when shear stress was approximately doubled. Thus, 8.7 +/- 1.5% of fields were VCAM-1 positive under high shear versus 2.5 +/- 0.87% under normal shear stress. No monocytes were detected at high shear stress. At normal shear stresses, intercellular adhesion molecule-1 (ICAM-1), detected by use of the monoclonal antibody Rb2/3, was extensively distributed; thus, 53.5 +/- 5.5% of fields contained ICAM-1-positive cells. The junctional regions of the cells were heavily stained.(ABSTRACT TRUNCATED AT 250 WORDS)

Signal transduction in atherosclerosis: second messengers and regulation of cellular cholesterol trafficking

The data summarized in this review demonstrate that the regulation of intracellular cholesterol trafficking is mediated not only by extracellular lipoprotein concentrations and transcriptional responses to alterations in intracellular free cholesterol content. Rather, the modulation of cholesterol trafficking is also regulated by the products synthesized following activation of signal transduction pathways originating at the cell surface. Furthermore, we have identified those cell-derived factors which utilize these signal transduction pathways to elicit alterations in cholesterol trafficking, and demonstrated the importance of the generation of second messengers, most notably eicosanoids, and cyclic AMP in promoting a modulatory influence on specific pro-atherogenic effects of mitogens.

Localization of heparin-binding EGF-like growth factor in the smooth muscle cells and macrophages of human atherosclerotic plaques

Heparin-binding EGF-like growth factor (HB-EGF) is a potent chemoattractant and mitogen for smooth muscle cells (SMC) in culture. To elucidate whether HB-EGF is implicated in the pathogenesis of human atherosclerosis, we examined immunohistochemical localization of HB-EGF in human aortic walls and atherosclerotic plaques. The medial SMC of the aorta in babies and children synthesized HB-EGF protein, while the number of SMC producing HB-EGF was dramatically decreased in young and middle-aged adults. In atherosclerotic plaques, however, marked production of HB-EGF protein was detected in SMC and macrophages of the plaques. Furthermore, EGF receptors, to which HB-EGF is known to bind, were detected in plaque SMC. These data suggest that HB-EGF may be implicated in the migration and proliferation of SMC that occurs in the normal development of arterial walls, and in the formation of atherosclerotic plaques.

Cyclic AMP stimulates platelet-derived growth factor B chain mRNA expression in murine macrophage cell lines

Prostaglandin E(2) plays a role in cytokine production presumably by altering intracellular levels of cAMP. In this paper, we report on the differential expression of cytokine genes in murine macrophages in response to stimulation with activators of cAMP. Macrophages were cultured with or without cAMP activators in the presence or absence of LPS. Prior to treatment, macrophages do not express interleukin-1beta, but do express low levels of tumour necrosis factor alpha and platelet-derived growth factor B chain mRNAs. After culture with cAMP-inducers, including PGE(2), dibutyryl cAMP and forskolin, PDGF B chain mRNA is induced. Forskolin, for example, induced expression PDGF B chain mRNA to a level ranging from 25% to 200% of the level induced by LPS in 6 h. In contrast, cAMP-inducers enhance the expression of IL-1beta and TNF-alpha mRNAs, but only in the presence of LPS. The combination of forskolin and LPS does not appear to act synergistically on PDGF B chain mRNA levels, suggesting that LPS-stimulated effects are not mediated through a cAMP-dependent pathway. Furthermore, macrophages differentially express cytokine genes in response to treatment with inducers of intracellular cAMP.

Cell adhesion molecules in coronary artery disease

To date, six families of cell adhesion molecules are known. These are cell surface receptors that mediate adhesion of cells to each other or to components of the extracellular matrix and include integrins, selectins, the immunoglobulin superfamily, cadherins, proteoglycans and mucins. These cell adhesion molecules play a key role in cell-cell interaction (such as among endothelium, monocytes, smooth muscle cells and platelets) and cell-extracellular matrix interaction (such as between leukocytes, platelets or fibroblasts and the extracellular matrix). The importance of these interactions has recently been demonstrated in clinical trials with the use of an antibody fragment directed against the platelet alpha IIb beta IIIa integrin, with reduction of arterial thrombosis and restenosis after percutaneous coronary interventions. A fundamental role for cell adhesion molecules has been suggested for several other relevant disease processes, including atherosclerosis, acute coronary syndromes, reperfusion injury and allograft vasculopathy. This review focuses on providing the clinically relevant biology of these families of adhesion molecules, setting the foundation for delineation of their emerging role in cardiovascular therapeutics.

Tamoxifen and estrogen lower circulating lipoprotein(a) concentrations in healthy postmenopausal women

Data in the literature suggest that circulating levels of lipoprotein(a) [Lp(a)] and insulinlike growth factor I (IGF-I) respond similarly to therapy with growth hormone, estrogen, or tamoxifen. To more clearly document these relations, we designed a randomized, double-blind, placebo-controlled study of the effects of tamoxifen and continuous estrogen on circulating levels of Lp(a), IGF-I, and IGF binding protein 3 (IGFBP-3) in healthy postmenopausal women. Both estrogen and tamoxifen decreased serum levels of IGF-I to 30% below baseline during the 3 months of treatment, while IGFBP-3 levels were unchanged. Plasma Lp(a) levels decreased to 24% below baseline after 1 month of treatment with either estrogen or tamoxifen (P < .05 for estrogen only); after 3 months Lp(a) decreased to 34% below baseline with tamoxifen therapy (P < .05) but returned to only 16% below baseline with estrogen. The correlation between Lp(a) and IGF-I was highly significant (P < .0001). We conclude that (1) tamoxifen lowers plasma Lp(a) levels in healthy postmenopausal women, (2) the suppressive effects of tamoxifen and estrogen on circulating Lp(a) concentration diverge after the first month of therapy, and (3) circulating levels of Lp(a) and IGF-I are strongly correlated with each other, an indication that they may share regulatory influences.

Regulation of platelet-derived growth factor secretion and gene expression in human liver fat-storing cells

BACKGROUND/AIMS

Liver fat-storing cells (FSCs) actively proliferate and secrete extracellular matrix during liver injury. Platelet-derived growth factor (PDGF) is a potent mitogen for cultured FSCs. In the present study, we investigated the regulation of PDGF gene expression and production in cultured human liver FSCs.

METHODS

PDGF A-chain and B-chain expression was analyzed by Northern blotting and ribonuclease protection assay, respectively. Secretion of PDGF was evaluated by immunoprecipitation and immunoblotting of conditioned medium and metabolic labeling of FSC followed by immunoprecipitation.

RESULTS

Three PDGF A-chain transcripts were detectable. Stimulation of FSC with phorbol myristate acetate (10(-7) mol/L) or PDGF BB (20 ng/mL) increased steady-state levels of PDGF A-chain and B-chain messenger RNA. PDGF AA had a small stimulatory effect on A-chain but not B-chain messenger RNA levels. FSCs secrete PDGF in the conditioned medium. The secreted protein is bioactive, because concentrated conditioned medium induced an increase in thymidine incorporation that was inhibited by anti-PDGF antibodies.

CONCLUSIONS

This study shows that cultured FSCs express PDGF A- and B-chain genes and release bioactive PDGF in the culture medium. These data raise the possibility of an autocrine or short-loop paracrine effect of PDGF in FSCs as a mechanism contributing to the maintenance of the proliferative state during liver injury.

Increased platelet-derived growth factor in the kidneys of cyclosporin-treated rats

We have examined the histological changes and the distribution of immunoreactive platelet-derived growth factor (PDGF) in the kidneys of Sprague-Dawley rats injected with cyclosporin A (CsA, 25 mg/kg/day). Control rats were injected with the olive oil vehicle alone. Groups of rats were killed after 1, 2, 3, 4 weeks of injection and 8 weeks after a 4 week period of injection. Additional controls included groups of rats injected with different doses of CsA and a group of rats subjected to chronic renal ischemia by partial of the aorta. CsA-treated rats gained weight more slowly than olive oil-treated controls (45%, P < 0.05). In rats injected with CsA, a significant increase in serum creatinine concentration (64 +/- 2 mumol/liter vs. 39 +/- 1 mumol/liter, P < 0.01) and a reduction in creatinine clearance rates (0.23 +/- 0.07 ml/min/100 g body wt vs. 0.43 +/- 0.07 ml/min/100 g body wt, P < 0.01) occurred after 3 weeks. After 1 week of CsA treatment, segments of the walls of some afferent and intralobular arterioles were thickened and stained strongly by the periodic acid Schiff (PAS) procedure. Immunostainable PDGF-BB and PDGF-AB were detected within short segments of the afferent and intralobular arterioles of the kidneys of CsA-treated rats and in the kidneys subjected to renal ischemia but not in tissue from other control animals. No PAS staining or immunostaining was evident in CsA treated kidneys eight weeks after the discontinuation of treatment. We conclude that CsA-induced ischemia results in increased accumulation of PDGF in the walls of renal arterioles.

Does platelet-derived growth factor-A chain stimulate proliferation of arterial mesenchymal cells in human atherosclerotic plaques?

Previous studies have indicated the focal presence of growth factors and focal low levels of cell proliferation in human atherosclerotic plaques. Using human carotid plaques and an antibody to platelet-derived growth factor (PDGF)-A chain, we have begun to assess growth factor significance by spatially correlating growth factor gene expression with actual cell proliferation. Since PDGF is a mitogen for smooth muscle and related cells and since inflammatory cells (eg, macrophages) can also proliferate in these lesions, it was important to exclude inflammatory cell proliferation from this consideration. Therefore, we have used a triple immunolabeling approach, combining the above anti-PDGF-A chain antibody with an inflammatory cell cocktail (CD68+CD45 for monocyte/macrophages and lymphocytes) and adding an anti-proliferating cell nuclear antigen (PCNA) antibody to mark proliferating cells. In the carotid atherosclerotic plaques, PDGF immunostaining was distributed focally, preferentially in the fibrous cap and vascularized regions, and was present in two distinct patterns: cytoplasmic and diffuse extracellular staining. When we considered colocalization within the same cells, cytoplasmic PDGF-A staining did not appear to colocalize with inflammatory markers. PCNA nuclear staining combined with PDGF cytoplasmic staining of the same cell was detected extremely rarely. Considering colocalization within the same microscopic fields, PDGF-A staining was detected more frequently than noninflammatory PCNA positivity. Quantitative logistic regression analysis demonstrated that localization in vascularized regions and (independently) the presence of PDGF-A are good predictors of noninflammatory cell proliferation, within the same microscopic fields. Therefore, PDGF-A and other factors especially associated with vascularized regions may be involved in the regulation of mesenchymal cell proliferation in human atherosclerotic plaques.

Platelet-derived growth factor is an autocrine growth stimulator in retinal pigmented epithelial cells

The retinal pigmented epithelium (RPE) plays a major role in normal and exaggerated retinal wound repair; the latter can result in epiretinal membrane formation and loss of vision. The RPE forms a stable monolayer of highly differentiated cells that proliferates only during wound repair. The mechanism underlying the change to the proliferating phenotype is unknown. When grown on a plastic substratum, cultured RPE cells mimic the proliferating phenotype in situ; they escape density arrest and proliferate in serum-free medium. In this study, we have demonstrated that a platelet-derived growth factor (PDGF) autocrine loop is involved in RPE growth in serum-free medium, because: (1) RPE cells secrete PDGF into their media and express PDGF receptors; (2) the PDGF receptors on RPE cells are autophosphorylated in serum-free medium and suramin, an agent that displaces PDGF and other growth factors from their receptors, blocks the autophosphorylation; and (3) a neutralizing antibody to PDGF significantly decreases RPE growth in serum-free medium. When a linear scrape is made in an RPE monolayer, the cells migrate and proliferate to fill in the gap mimicking wound repair in situ. Cells along the edge of the scrape show increased expression of PDGF and PDGF-beta receptors, and increased staining for proliferating cell nuclear antigen. Immunohistochemistry and in situ hybridization demonstrate expression of PDGF in ganglion cells and cells of retinal blood vessels. PDGF is not detected in the outer retina or RPE in untreated eyes, but is detected in RPE participating in wound repair, either adjacent to laser burns or underlying retinal detachment. PDGF and PDGF receptors are also expressed in RPE in epiretinal membranes removed during vitreous surgery. These data suggest that PDGF is an autocrine stimulator of growth in RPE that plays a role in retinal wound repair and epiretinal membrane formation.

Ischemia induces the expression of the platelet-derived growth factor-B chain in neurons and brain macrophages in vivo

To elucidate the role of the platelet-derived growth factor (PDGF)-B chain in the brain, we examined its expression in rat brains with focal ischemia. Focal ischemia was induced by permanent tandem occlusion of the middle cerebral and common carotid arteries in spontaneously hypertensive rats (SHRs). Northern analysis demonstrated that ischemia transiently increased mRNA expression of the PDGF-B chain, but not the PDGF-A chain, in the injured neocortex. The larger transcript (3.5 kb) of the B chain gradually increased to threefold by 16 h, whereas the smaller transcript (2.6 kb) of the B chain markedly increased sixfold by 4 h. Immunohistochemistry revealed enhanced immunoreactivity in the neurons in the infarct and in the periinfarct area from 16 h to days 4-7, with a peak at 24 h. Furthermore, the brain macrophages that accumulated in the infarct showed intense immunostaining in their perinuclear region from days 2 to 14, with a peak at days 5-6. The present study demonstrates that ischemia induces the expression of the PDGF-B chain, first in neurons and later in brain macrophages, and suggests an important role of the PDGF-B chain in the healing process of the injured brain.

Platelet-derived growth factor B-chain-like immunoreactivity in injured rat brain

Platelet-derived growth factor (PDGF) is a potent mitogen for mesenchymal cells and glial cells. For a better understanding of the role of PDGF B-chain in the brain, the expression of PDGF B-chain was examined immunohistochemically in penetrating injury to the rat brain. Shrunken neurons were distributed with enhanced PDGF B-chain-related immunoreactivity (PBRI) in the vicinity of the lesion during a period from day 1 to day 4 post injury. Platelet-derived growth factor B-chain-related immunoreactivity was transiently observed also in the cytoplasm of the numerous brain macrophages in the lesion on day 3 and day 4. These distributions of PBRI in the lesion were closely related to the neovascularization and astrogliosis there. The close time and spatial correlation between the expression of PBRI and cellular responses to injury seen in this study suggests PDGF B-chain has an important role in the healing process of cerebral wound.

Expression of platelet-derived growth factor and c-myc in atherosclerotic lesions in cholesterol-fed chickens: immunohistochemical and in situ hybridization study

Immunohistochemical examination showed no significant expression of platelet-derived growth factor-A (PDGF-A), PDGF-B, PDGF receptors, or of c-myc in the thoracic and abdominal aortas of normal roosters. In cholesterol-fed roosters, intense immunohistochemical reaction for PDGF-B, PDGF receptor, and c-myc was seen in the lipid-rich thickened intimal lesions of the thoracic and abdominal aortas while no significant immunoreaction for PDGF-A was demonstrated in the same lesions. In accordance with immunohistochemical findings, in situ hybridization demonstrated a significant level of expression of PDGF-B, PDGF-A receptor, PDGF-B receptor, and c-myc genes in proliferating intimal cells of the thoracic and abdominal aortas. These results suggest that coordinate actions of PDGF-B and c-myc play an important role in proliferation of intimal cells in the developing atherosclerotic lesions in chickens.

Cytokine gene expression in aortic adventitial inflammation associated with advanced atherosclerosis (chronic periaortitis)

AIMS

To determine whether aortic adventitial chronic inflammation associated with advanced atherosclerosis ("chronic periaortitis") is associated with any detectable cytokine gene expression.

METHODS

RNA was extracted from six fresh surgical specimens of atherosclertic aortic aneurysm wall showing a spectrum of chronic periaortitis. Controls included four normal aortas and an HUT 78 T cell line. Reverse transcriptase and the polymerase chain reaction (PCR) were used to amplify mRNA for interleukins-1 alpha (IL-1 alpha), -2 (IL-2), -4 (IL-4), IL-2 receptor-alpha (IL-2R-alpha), tumour necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma) with beta-actin as an internal control.

RESULTS

No TNF-alpha mRNA was detected in any of the inflamed aortic tissue samples, in contrast to the aortic T lymphocytes propagated in culture in IL-2 conditioned medium (aortic cultured T cells) and peripheral blood mononuclear cells from these patients. In contrast, IFN-gamma, IL-1 alpha, IL-2, IL-2 receptor and IL-4 PCR products were detected for each inflamed aortic tissue RNA sample with IFN-gamma mRNA expression increasing with increasing degrees of adventitial inflammation. Only beta-actin mRNA was present in the normal aorta.

CONCLUSIONS

These findings indicate the active nature of aortic adventitial chronic inflammation associated with human advanced atherosclerosis ("chronic periaortitis") and show its possible progressive potential to the clinically important diseases termed "idiopathic retroperitoneal fibrosis" and "inflammatory aneurysm".

Involvement of adhesion molecules in human monocyte adhesion to and transmigration through endothelial cells in vitro

Although the accumulation of monocyte-derived foam cells in the subendothelium is a key step in early atherogenesis, the mechanism responsible for monocyte adhesion to and subsequent transmigration through endothelial cells (ECs) has not been defined fully. We investigated the kinetics and the role played by adhesion molecules in the adhesion and transmigration of human monocytes using an in vitro three-dimensional model system comprising ECs cultured on collagen gels. Monocyte adhesion to untreated EC layers increased with time, reached a maximum after 3 h, and then declined. Monocyte transmigration through untreated EC layers also increased with time and reached a plateau after 3-4 h. Prestimulation of ECs with interleukin-1 beta (IL-1 beta; 25 U/ml) for 4 h enhanced monocyte adhesion (40.7 +/- 1.4%) and transmigration (37.9 +/- 1.6%) significantly compared with the value for untreated EC layers. In unstimulated EC layers, anti-leukocyte function-associated antigen-1 (LFA-1) plus anti-intercellular adhesion molecule-1 (ICAM-1) monoclonal antibodies (mAbs) inhibited monocyte adhesion and transmigration significantly by 19% and 20%, respectively, whereas anti-very late antigen-4 (VLA-4) plus anti-vascular cell adhesion molecule-1 (VCAM-1) mAbs did not. In IL-1 beta-stimulated EC layers, anti-LFA 1 plus anti-ICAM-1 mAbs inhibited the adhesion and transmigration by 32% and 30%, respectively and anti-VLA-4 plus anti-VCAM-1 mAbs did so by 18% and 27%, respectively. These results suggest that the monocyte-EC interaction in unstimulated ECs is mediated, in part, by the LFA-1-ICAM-1 pathway and in IL-1 beta-stimulated ECs, in part, by both LFA-1-ICAM-1 and VLA-4-VCAM-1 pathways.

Immune mechanisms in atherogenesis

Research in recent years has resulted in an increased understanding of the molecular mechanisms in the development of inflammatory processes. In atherosclerosis, focal expression of key adhesion molecules has been detected which may mediate the recruitment of mononuclear cells to the plaque. Local cytokine production could account for further cell migration and proliferation. The presence of substantial numbers of T lymphocytes in the plaque and local and circulating autoantibodies to modified lipoproteins suggest that T and B lymphocyte responses may play important roles in these processes.

TGF-beta 1 and 25-hydroxycholesterol stimulate osteoblast-like vascular cells to calcify

Previous studies in our laboratory demonstrated messenger RNA for bone morphogenetic protein-2a in human calcified plaque, suggesting that arterial calcification is a regulated process, similar to osteogenesis. To further test this hypothesis, we have isolated and cloned a subpopulation of cells from bovine aortic media that show osteoblastic potential. These novel cells are primarily distinguished from smooth muscle cells by expression of a surface marker preliminarily identified as a modified form of the ganglioside sialyl-lactosylceramide (GM3). Osteoblastic potential was indicated by high levels of alkaline phosphatase and collagen I, expression of osteopontin and osteonectin (SPARC), and production of bone-specific osteocalcin and hydroxyapatite. Cultures of these cells were stimulated to form increased numbers of calcium-mineral-producing nodules by the oxysterol 25-hydroxycholesterol as well as by transforming growth factor-beta 1, both known to be present in atherosclerotic lesions. The stimulation of calcifying vascular cells in the artery wall by these two factors suggests a possible mechanism for the colocalization of calcification with atherosclerosis in vivo.

The basis of molecular strategies for treating coronary restenosis after angioplasty

Excessive smooth muscle cell proliferation significantly contributes to restenosis, which occurs in 25% to 50% of patients within 6 months of coronary angioplasty. Because successful treatment will probably depend on our acquiring a comprehensive knowledge of the molecular and cellular mechanisms involved, this report reviews 1) information relevant to the molecular and cellular mechanisms responsible for the smooth muscle cell(s) response to vascular injury, and 2) several molecular-based therapeutic strategies currently being explored as possible approaches to the control of restenosis, including recombinant DNA technology to target delivery of cytotoxic molecules to proliferating smooth muscle cell(s), antisense strategies to inhibit expression of gene products necessary for cell proliferation and gene therapy.

A definition of initial, fatty streak, and intermediate lesions of atherosclerosis. A report from the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association

The compositions of lesion types that precede and that may initiate the development of advanced atherosclerotic lesions are described and the possible mechanisms of their development are reviewed. While advanced lesions involve disorganization of the intima and deformity of the artery, such changes are absent or minimal in their precursors. Advanced lesions are either overtly clinical or they predispose to the complications that cause ischemic episodes; precursors are silent and do not lead directly to complications. The precursors are arranged in a temporal sequence of three characteristic lesion types. Types I and II are generally the only lesion types found in children, although they may also occur in adults. Type I lesions represent the very initial changes and are recognized as an increase in the number of intimal macrophages and the appearance of macrophages filled with lipid droplets (foam cells). Type II lesions include the fatty streak lesion, the first grossly visible lesion, and are characterized by layers of macrophage foam cells and lipid droplets within intimal smooth muscle cells and minimal coarse-grained particles and heterogeneous droplets of extracellular lipid. Type III (intermediate) lesions are the morphological and chemical bridge between type II and advanced lesions. Type III lesions appear in some adaptive intimal thickenings (progression-prone locations) in young adults and are characterized by pools of extracellular lipid in addition to all the components of type II lesions.

A definition of initial, fatty streak, and intermediate lesions of atherosclerosis. A report from the Committee on Vascular Lesions of the Council on Arteriosclerosis, American Heart Association

The compositions of lesion types that precede and that may initiate the development of advanced atherosclerotic lesions are described and the possible mechanisms of their development are reviewed. While advanced lesions involve disorganization of the intima and deformity of the artery, such changes are absent or minimal in their precursors. Advanced lesions are either overtly clinical or they predispose to the complications that cause ischemic episodes; precursors are silent and do not lead directly to complications. The precursors are arranged in a temporal sequence of three characteristic lesion types. Types I and II are generally the only lesion types found in children, although they may also occur in adults. Type I lesions represent the very initial changes and are recognized as an increase in the number of intimal macrophages and the appearance of macrophages filled with lipid droplets (foam cells). Type II lesions include the fatty streak lesion, the first grossly visible lesion, and are characterized by layers of macrophage foam cells and lipid droplets within intimal smooth muscle cells and minimal coarse-grained particles and heterogeneous droplets of extracellular lipid. Type III (intermediate) lesions are the morphological and chemical bridge between type II and advanced lesions. Type III lesions appear in some adaptive intimal thickenings (progression-prone locations) in young adults and are characterized by pools of extracellular lipid in addition to all the components of type II lesions.

Expression of platelet-derived growth factor in a model of acute liver injury

Platelet-derived growth factor has been shown to play an important role in the repair process after acute tissue injury and in the pathogenesis of several fibrogenic disorders. The aim of this study was to evaluate whether increased expression of platelet-derived growth factor and its beta-receptor subunit occurs in a model of acute liver injury. Male Sprague-Dawley rats were given a single intragastric dose of carbon tetrachloride and killed at intervals of 24, 48 and 72 hr and 1 wk. Control animals were included in each group. Platelet-derived growth factor-B chain mRNA expression, analyzed by RNase protection assay, was not detectable in control samples or in samples obtained 24 hr or 1 wk after carbon tetrachloride. However, the presence of protected fragments of 130 kb was clearly detected after 48 hr and was still present, although less abundant, after 72 hr. The distribution of platelet-derived growth factor protein in liver tissue sections, evaluated by immunohistochemistry, was restricted to centrilobular veins and portal tracts in normal liver. In carbon tetrachloride-treated rats, prominent staining was observed in areas corresponding to hepatocellular necrosis and inflammatory infiltration. This feature, already present at 24 hr after carbon tetrachloride, became more marked at 48 hr with a gradual resolution after 72 hr. The expression of platelet-derived growth factor-receptor beta-subunit mRNA, evaluated by in situ hybridization, was markedly increased after carbon tetrachloride with a peak at 24 hr and was mainly localized over mesenchymal cells in the hepatic sinusoids.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin-like growth factor-I and platelet-derived growth factor-BB induce directed migration of human arterial smooth muscle cells via signaling pathways that are distinct from those of proliferation

Directed migration or chemotaxis of arterial smooth muscle cells (SMC) contributes to intimal SMC accumulation, a key event in the development of atherosclerotic lesions and in restenosis after angioplasty. The present study compares and contrasts insulin-like growth factor I (IGF-I) and platelet-derived growth factor (PDGF-BB) as chemoattractants and mitogens for human arterial SMC. Compared with PDGF-BB, IGF-I is a weaker SMC mitogen. Thus, PDGF-BB, but not IGF-I, evokes a strong and rapid activation of mitogen-activated protein (MAP) kinase kinase and MAP kinase. However, IGF-I is a potent stimulator of directed migration of human arterial SMC, as measured in a Boyden chamber assay. The half-maximal concentration for migration is similar to the Kd for IGF-I receptor interaction. An IGF-I receptor-blocking antibody blocks the effects of IGF-I, IGF-II, and insulin, indicating that the effects are indeed mediated through the IGF-I receptor. The maximal effect of IGF-I on directed migration ranges between 50% and 100% of the effect of PDGF-BB, the strongest known chemoattractant for SMC. The ability of IGF-I and PDGF-BB to induce chemotaxis coincides with their ability to stimulate phosphatidylinositol turnover, diacylglycerol formation, and intracellular Ca2+ flux and suggests that these signaling pathways, but not activation of the MAP kinase cascade, are required for chemotaxis of human arterial SMC.

Endothelin-1-selective receptor in the arterial intima of patients with hypertension

Endothelin-1 is a potent vasoconstrictor produced by vascular endothelial cells. A recently cloned endothelin-1-selective receptor, the endothelin-A receptor, mediates the vasoconstrictive action of endothelin-1. Because endothelin-1 also possesses mitogenic properties, it may play a role in regulating the proliferation of intimal smooth muscle cells. In this study, we analyzed the expression of endothelin-A receptor gene in the thickened arterial intima of patients with hypertension. Internal mammary artery specimens obtained from 12 patients undergoing cardiovascular surgery were subjected to in situ hybridization using a digoxigenin-labeled cRNA probe. High, homogeneous signals of endothelin-A receptor mRNA were observed in the medial smooth muscle cells of all vessels examined but not in the endothelial cells. Patients with hypertension displayed more severe intimal thickening than those without hypertension. Immunohistochemical analysis suggested that almost all of the intimal proliferative cells originated from smooth muscle cells. In contrast to media, endothelin-A receptor mRNA signals in intimal smooth muscle cells were low and heterogeneous. In the thickened arterial intima of hypertensive patients, the signals were detected just beneath the luminal endothelium but not deep in the intimal smooth muscle cell layer. By contrast, staining with anti-alpha-smooth muscle actin antibody was more intense in the deep layer than in the subendothelium. These findings suggest that the modulation of endothelin-A receptor gene expression in smooth muscle cells differs between the intima and media. Its regulated expression in intimal smooth muscle cells might affect the proliferative activity of these cells in patients with hypertension.

Local expression of inflammatory cytokines in human atherosclerotic plaques

Human atherosclerotic plaques are heterogeneous tissues containing a number of different cell types, including macrophages, smooth muscle, endothelial and other undefined mesenchymal-appearing cells. Significant numbers of macrophages are found in human atherosclerotic plaques and have been postulated to be a major source of growth factor production during atherogenesis. In vitro evidence suggested that macrophages synthesize PDGF and might therefore contribute to the growth of the vessel wall in atherosclerosis. However, examination of PDGF synthesis in human atheroma by in situ hybridization revealed that while smooth muscle, mesenchymal, and endothelial cells synthesize this growth factor macrophages did not. Our inability to detect PDGF mRNA in macrophages was not due to any problems with hybridization to this cell type. In situ hybridization studies on human atherosclerotic plaques have demonstrated that plaque macrophages contain many different mRNAs other than PDGF including tissue factor, factor XIII, apoprotein E, transforming growth factor beta, and tumor necrosis factor. Recent studies have indicated that macrophages may be a major source as well of another group of inflammatory cytokines which are members of the RANTES/SIS cytokine family. In situ hybridization studies on human carotid endarterectomy specimens using probes specific for the inflammatory cytokines RANTES, LD78, HIMAP, and MCP-1 revealed numerous cells containing the mRNAs encoding for these proteins (5%, 13%, 8%, and 16% of plaque cells respectively). This is in contrast to generally low level expression found in normal human arteries (< 1% of normal medial cells contain these mRNAs). Cells expressing these cytokines were often found associated with inflammatory zones in human atherosclerotic plaques. Serial section immunohistochemistry suggests that macrophages and/or T cells may synthesize these proteins. In addition to localization to macrophages MCP-1 expression was also detected in smooth muscle cells and mesenchymal-appearing cells with many of the morphological characteristics of cells previously seen to express PDGF. In vitro evidence suggests that these proteins may be chemotactic to monocytes and lymphocytes. The finding of increased expression of these mRNAs in human atheroma suggests they may play a role in monocyte trafficking into the atherosclerotic plaque.

Glycosaminoglycan fractions from human arteries presenting diverse susceptibilities to atherosclerosis have different binding affinities to plasma LDL

The topographic distribution of atherosclerotic lesions is influenced by biochemical factors intrinsic to the arterial wall. In the present work we have investigated whether the composition/chemical structure of glycosaminoglycans constitutes one of these factors. Normal human arteries were obtained at necropsy, and in order of decreasing susceptibility to atherosclerosis, consisted of the abdominal and thoracic aortas and the iliac and pulmonary arteries. The results showed similar concentrations of total glycosaminoglycan and collagen. Of the glycosaminoglycans known to interact with low-density lipoprotein (LDL), dermatan sulfate was present in all arteries in comparable concentrations, but the aortas had a 30% higher content of chondroitin 4/6-sulfate, which in turn was slightly enriched in 6-sulfated disaccharide units. LDL-affinity chromatography with dermatan sulfate+chondroitin 4/6-sulfate fractions demonstrated that increasing affinity to LDL matched an increasing susceptibility to atherosclerosis. Analysis of glycosaminoglycans in the eluates indicated a positive correlation between affinity to LDL and increasing molecular weight and the existence of a fraction of glycosaminoglycans of high affinity to LDL in the aortas only. These results suggest that arterial glycosaminoglycans participate in the multifactorial mechanisms that modulate the differential localization of atherosclerotic lesions.