The macrophage as an initiator of atherosclerosis

Evaluation of enzymes involved in proteoglycan degradation in the wall of abdominal aortic aneurysms

The abdominal aortic aneurysm (AAA) wall represents an extreme example of arterial remodeling with disturbed elastin, collagen and proteoglycan metabolism. The aim of this study was to evaluate enzymes involved in the degradation of glycosaminoglycan chains and core proteins of proteoglycans in the AAA wall. The study material consisted of wall samples from 10 AAA. Fragments of 5 normal abdominal aortas from organ donors were used as a control. The activity of endoglycosidases, exoglycosidases and sulfatases was measured using colorimetric methods. To assess matrix metalloproteinases (MMPs), Western blot and zymography were performed. The activity of endoglycosidase degrading chondroitin-4-sulfate was lower in the AAA wall. Endoglycosidase degrading heparan sulfate and dermatan sulfate, arylosulfatase B, as well as all the exoglycosidases assessed demonstrated higher activities in the AAA wall. Furthermore, increased expression of MMP1, MMP2 and MMP9 was also shown in the AAA wall. Zymography revealed decreased activity of pro-MMP2 and presence of pro-MMP9 in the AAA wall compared to the wall of normal aorta. Extensive changes in the activity of glycosaminoglycan-degrading enzymes and MMPs may influence the organization of the extracellular matrix network and lead to previously demonstrated changes in the proteoglycan and glycosaminoglycan content in the AAA wall.

Blockade of vascular smooth muscle cell proliferation and intimal thickening after balloon injury by the sulfated oligosaccharide PI-88: phosphomannopentaose sulfate directly binds FGF-2, blocks cellular signaling, and inhibits proliferation

Percutaneous transluminal coronary angioplasty is a frequently used interventional technique to reopen arteries that have narrowed because of atherosclerosis. Restenosis, or renarrowing of the artery shortly after angioplasty, is a major limitation to the success of the procedure and is due mainly to smooth muscle cell accumulation in the artery wall at the site of balloon injury. In the present study, we demonstrate that the antiangiogenic sulfated oligosaccharide, PI-88, inhibits primary vascular smooth muscle cell proliferation and reduces intimal thickening 14 days after balloon angioplasty of rat and rabbit arteries. PI-88 reduced heparan sulfate content in the injured artery wall and prevented change in smooth muscle phenotype. However, the mechanism of PI-88 inhibition was not merely confined to the antiheparanase activity of this compound. PI-88 blocked extracellular signal-regulated kinase-1/2 (ERK1/2) activity within minutes of smooth muscle cell injury. It facilitated FGF-2 release from uninjured smooth muscle cells in vitro, and super-released FGF-2 after injury while inhibiting ERK1/2 activation. PI-88 inhibited the decrease in levels of FGF-2 protein in the rat artery wall within 8 minutes of injury. PI-88 also blocked injury-inducible ERK phosphorylation, without altering the clotting time in these animals. Optical biosensor studies revealed that PI-88 potently inhibited (Ki 10.3 nmol/L) the interaction of FGF-2 with heparan sulfate. These findings show for the first time the capacity of this sulfated oligosaccharide to directly bind FGF-2, block cellular signaling and proliferation in vitro, and inhibit injury-induced smooth muscle cell hyperplasia in two animal models. As such, this study demonstrates a new role for PI-88 as an inhibitor of intimal thickening after balloon angioplasty. The full text of this article is available online at http://www.circresaha.org.

Human abdominal aortic aneurysm is closely associated with compositional and specific structural modifications at the glycosaminoglycan level

Human abdominal aortic aneurysm (AAA) is a commonly occuring disease of blood vessels and is related to alterations in extracellular matrix molecules. In this study we report on the type and fine structural characterization of glycosaminoglycans (GAGs) present in AAA as compared with those present in normal abdominal aorta. Hyaluronan (HA), the galactosaminoglycans-chondroitin sulfate (CS) and dermatan sulfate (DS) with average molecular size (Mr) of 35-kDa-as well as heparan sulfate (HS) with Mr of 40-kDa were identified in both tissues. No significant intrabatch differences in total GAG content were identified in normal and aneurysmal aortas. Comparing, however, tissue composition and structure of GAGs between AAAs and normal aortas, significant differences (P < or = 0.001) were found. The overall GAG content in AAAs was approx. 60% lower than the normal ones. A 90% decrease in HS content, and 65 and 73% in CS and HA, respectively, were also recorded. In contrast, only a slight decrease in the amount of DS was noted (8%). Structural alterations in disaccharide composition of GAGs correspond mainly to significant decreases (P < or = 0.001) of HS-derived N-sulfated disaccharides, CS-derived 6-sulfated disaccharide and DS-derived disulfated disaccharides. These results demonstrate that the development of AAA is related to dramatic quantitative and structural modifications at the GAG level and this may well be attributed to the destruction of arterial wall architecture and further significant functional inadequacies of the tissue.

CD44 isoform expression follows two alternative splicing pathways in breast tissue

The repertoire of distinct CD44 protein isoforms is generated by means of alternative pre-mRNA splicing of 10 variable exons located in the central region of the CD44 gene. We have used human breast ductal carcinoma as a model to identify two alternative splicing pathways of the CD44 pre-mRNA variable region that account for the generation of all of the CD44 isoforms described in breast tissue. An alternative splicing pathway that reflects inclusion of variable exons in a gradual 3'-to-5' fashion is evidenced in breast ductal carcinoma and its lymph node metastases. This pathway is compatible with a mechanism that generates the standard form of CD44 (devoid of variable exons) and is distinguishable from an alternative splicing pathway that involves exclusively variant exon 3 and is observable in both normal and carcinoma breast tissue. We show that both pathways are detectable in the same cell type in the breast and provide a speculative model by which these splicing routes could take place.

Macrophages influence gap junctional intercellular communication between smooth muscle cells in a co-culture model

The present study demonstrates for the first time that cells cultured on pore membrane inserts (macrophages) modulate gap junctional intercellular communication (GJIC) between a second cell type (smooth muscle cells (SMC)) co-cultured in Transwell-COL cell culture chambers. Unstimulated J774A.1 murine macrophages reduced GJIC between human SMC. Stimulation of J774A.1 cells by lipopolysaccharide (LPS) or interferon-γ abrogated this modulation of GJIC. Unstimulated human monocyte-macrophages did not affect GJIC between human SMC. Upon stimulation of these monocyte-macrophages with LPS, a substantial increase in GJIC between co-cultured SMC was observed. Thus, activation of macrophages alters their interaction with co-cultured SMC. Since these results were obtained in an indirect co-culture system in which direct cell-cell contact is prevented, it is hypothesized that soluble factors released by macrophages may be involved in this modulation of GJIC between SMC. The possible nature of the responsible soluble factors is discussed in the context of atherosclerosis.

Synergistic interaction of interleukin-1 beta and growth factors in primary cultures of rat aortic smooth muscle cells

Activated macrophages release cytokines and growth factors that may contribute to the growth of vascular smooth muscle cells in injured blood vessels. In the present study, we investigated the interactions between interleukin-1 beta (IL-1 beta) and basic fibroblast growth factor (FGF-2) in primary rat aortic smooth muscle cells, relative to their effects on DNA synthesis and cell proliferation. We report that femtomolar levels of IL-1 beta, which alone were non-mitogenic or weakly mitogenic, synergistically increased FGF-2-induced [3H]thymidine incorporation and cell proliferation. The potentiating effect of IL-1 beta extended to PDGF-AB and EGF, but not to IGF-1-induced thymidine incorporation. An antagonist of the IL-1 receptor, IL-1ra, blocked the co-mitogenic effect of IL-1 beta. Stimulation of cells with FGF-2 and IL-1 beta increased both DNA content and proliferation, an observation that was consistent with the thymidine incorporation experiments. An inhibitor of NO synthase, N5-iminoethyl L-ornithine (L-NIO), did not block the co-mitogenic effect of IL-1 beta, despite effective inhibition of NO synthase activity, suggesting that the synergistic interaction between IL-1 beta and FGF-2 was independent of the NO/cGMP pathway. The mechanism of co-mitogenesis appeared to be independent of the intermediacy of PDGF-AA, IL-6, and prostanoids, and was not associated with increased levels of c-fos mRNA, FGF receptor-1 protein, or FGF-2-induced early and delayed tyrosine phosphorylation events. We conclude that IL-1 beta interacts with FGF-2 to amplify the proliferation of primary rat aortic smooth muscle cells, an effect that may be important in vascular smooth muscle cell proliferation following vascular injury.

Mechanisms of nitrosothiol-induced antimitogenesis in aortic smooth muscle cells

The purpose of this work was to investigate the effect of a nitrosothiol vasodilator, S-nitroso-N-acetylpenicillamine (SNAP), on serum-induced cell proliferation, thymidine uptake, RNA synthesis, protein synthesis and thymidine kinase activity in a cultured rat aortic smooth muscle cell line. SNAP decreased the rate of serum-stimulated cell proliferation, thymidine uptake and incorporation, uridine and leucine incorporation and thymidine kinase activity in concentration-dependent fashion. The threshold concentration of SNAP for inhibition of cell proliferation and thymidine uptake was similar and in the range of 1-3 microM. Uridine incorporation, indicative of RNA synthesis, was inhibited beginning at 10 microM SNAP, whereas leucine incorporation, indicative of protein synthesis, and thymidine kinase activity, an enzyme of importance to DNA synthesis, were inhibited beginning at 100 microM SNAP. These results indicate that inhibition of cell proliferation induced by relatively low concentrations of SNAP (1-10 microM) is independent of inhibition of protein synthesis or thymidine kinase activity, whereas higher concentrations of SNAP may inhibit cell proliferation by decreasing protein synthesis.