Tenascin-C is expressed in macrophage-rich human coronary atherosclerotic plaque

Extra cellular matrix remodelling after heterotopic rat heart transplantation: gene expression profiling and involvement of ED-A+ fibronectin, alpha-smooth muscle actin and B+ tenascin-C in chronic cardiac allograft rejection

Chronic cardiac rejection is represented by cardiac allograft vasculopathy (CAV) and cardiac interstitial fibrosis (CIF) known to cause severe complications. These processes are accompanied by remarkable changes in the cardiac extra cellular matrix (cECM). The aim of our study was to analyse the cECM remodelling in chronic rejection and to elucidate a potential role of ED-A domain containing fibronectin (ED-A(+) Fn), alpha smooth muscle actin (ASMA) and B domain containing tenascin-C (B(+) Tn-C). A model of chronic rejection after heterotopic rat heart transplantation was used. Allografts, recipient and control hearts were subjected to histological assessment of rejection grade, to real-time PCR based analysis of 84 genes of ECM and adhesion molecules and to immunofluorescence labelling procedures, including ED-A(+) Fn, ASMA and B(+) Tn-C antibodies. Histological analysis revealed different grades of chronic rejection. By gene expression analysis, a relevant up-regulation of the majority of ECM genes in association with chronic rejection could be shown. For 8 genes, there was a relevant up-regulation in allografts as well as in the corresponding recipient hearts. Association of ASMA positive cells with the grade of chronic rejection could be proven. In CAV and also in CIF there were extensive co-depositions of ED-A(+) Fn, ASMA and B(+) Tn-C. In conclusion, chronic cardiac allograft rejection is associated with a cECM remodelling. ASMA protein deposition in CAV, and CIF is a valuable marker to detect chronic rejection. Interactions of VSMCs and Fibro-/Myofibroblasts with ED-A(+) Fn and B(+) Tn-C might functionally contribute to the development of chronic cardiac rejection.

Bioengineered vascular graft grown in the mouse peritoneal cavity

BACKGROUND

We tested the hypothesis that the mouse peritoneum can function like a bioreactor to generate directed bio-engineered tissues such as those used for bypass grafting. Additionally, we reasoned that the mouse animal model would allow us to elucidate the underlying cellular and molecular mechanisms that are responsible for the generation of tissue in peritoneal cavity.

METHODS

Plastic tubes (two tubes/mouse) were implanted into the peritoneal cavity of three strains of mice (C57BL/6, BALB/c, and MRL). The tubes were harvested, tissue capsule surrounding the tubes was removed, and analyzed by immunostaining (five capsules/five mice/strain) and microarray (three capsules/three mice/strain). In addition, the tissue capsules that were harvested from MRL mice (n = 21) were grafted into abdominal aorta of the same mice as autografts. The patency of all grafts was monitored by micro-ultrasound, and their functionality was assessed by laser Doppler imaging of blood flow in femoral arteries. Venous (n = 13) and arterial isografts (n = 11) were used as positive controls. In a negative control group (five mice/strain), the abdominal aorta was occluded by double ligation with 9-0 silk.

RESULTS

The implanted plastic tubes required at least 8 weeks of incubation in the peritoneum of the three strains of mice in order to generate useful grafts. No vascular cells were found in the tissue capsules. Microarray analysis of tissue capsules revealed that the capsular cells express a gene expression program that is vastly shared among the three strains of mice, and the cells exhibit a high degree of plasticity. The micro-ultrasound analysis of the grafts showed that 62% of autografts remained patent compared with 77% of venous isografts and 91% of arterial isografts. The laser Doppler imaging analysis showed that blood flow dropped by 40% and 35% in the autografts and vein isografts, respectively, 1 day after surgery. The flow, however, rebounded to the level of arterial isografts 1 month post-surgery and remained unchanged among all grafts for the next 4 months. Immunostaining of the autografts showed a thick vessel wall with endothelial cells that lined the lumen and smooth muscle cells that constituted the graft wall.

CONCLUSION

The mouse peritoneal cavity of mice has the ability to function like a bioreactor to generate bio-engineered tissues. The tissue capsules harvested from peritoneal cavity of a mouse are composed of nonvascular cells that display phenotype of progenitor cells. After grafting, however, the capsule autografts become arterialized and remained patent for at least 4 months after surgery, similar to venous or arterial isografts.

DAMPening inflammation by modulating TLR signalling

Damage-associated molecular patterns (DAMPs) include endogenous intracellular molecules released by activated or necrotic cells and extracellular matrix (ECM) molecules that are upregulated upon injury or degraded following tissue damage. DAMPs are vital danger signals that alert our immune system to tissue damage upon both infectious and sterile insult. DAMP activation of Toll-like receptors (TLRs) induces inflammatory gene expression to mediate tissue repair. However, DAMPs have also been implicated in diseases where excessive inflammation plays a key role in pathogenesis, including rheumatoid arthritis (RA), cancer, and atherosclerosis. TLR activation by DAMPs may initiate positive feedback loops where increasing tissue damage perpetuates pro-inflammatory responses leading to chronic inflammation. Here we explore the current knowledge about distinct signalling cascades resulting from self TLR activation. We also discuss the involvement of endogenous TLR activators in disease and highlight how specifically targeting DAMPs may yield therapies that do not globally suppress the immune system.

Pleiotrophin (PTN) is expressed in vascularized human atherosclerotic plaques: IFN-{gamma}/JAK/STAT1 signaling is critical for the expression of PTN in macrophages

Neovascularization is critical to destabilization of atheroma. We previously reported that the angiogenic growth factor pleiotrophin (PTN) coaxes monocytes to assume the phenotype of functional endothelial cells in vitro and in vivo. In this study we show that PTN expression is colocalized with capillaries of human atherosclerotic plaques. Among the various reagents that are critical to the pathogenesis of atherosclerosis, interferon (IFN)-gamma was found to markedly induce PTN mRNA expression in a dose-dependent manner in macrophages. Mechanistic studies revealed that the Janus kinase inhibitors, WHI-P154 and ATA, efficiently blocked STAT1 phosphorylation in a concentration- and time-dependent manner. Notably, the level of phosphorylated STAT1 was found to correlate directly with the PTN mRNA levels. In addition, STAT1/STAT3/p44/42 signaling molecules were found to be phosphorylated by IFN-gamma in macrophages, and they were translocated into the nucleus. Further, PTN promoter analysis showed that a gamma-activated sequence (GAS) located at -2086 to -2078 bp is essential for IFN-gamma-regulated promoter activity. Moreover, electrophoretic mobility shift, supershift, and chromatin immunoprecipitation analyses revealed that both STAT1 and STAT3 bind to the GAS at the chromatin level in the IFN-gamma stimulated cells. Finally, to test whether the combined effect of STAT1/STAT3/p44/42 signaling is required for the expression of PTN in macrophages, gene knockdowns of these transcription factors were performed using siRNA. Cells lacking STAT1, but not STAT3 or p42, have markedly reduced PTN mRNA levels. These data suggest that PTN expression in the human plaques may be in part regulated by IFN-gamma and that PTN is involved in the adaptive immunity.-Li, F., Tian, F., Wang, L., Williamson, I. K., Sharifi, B. G., Shah, P. K. Pleiotrophin (PTN) is expressed in vascularized human atherosclerotic plaques: IFN-gamma/JAK/STAT1 signaling is critical for the expression of PTN in macrophages.

Inflammation and plaque vulnerability

Development of a thrombus at the site of an atherosclerotic plaque initiates abrupt arterial occlusion and is the proximate event responsible for the vast majority of acute ischemic syndromes. In nearly 75% of cases thrombus overlies a disrupted or ruptured plaque whereas the remainder of the thrombi overly an intact plaque with superficial endothelial erosion. Over the past several years, it has been recognized that plaque composition rather than plaque size or stenosis severity is important for plaque rupture and subsequent thrombosis. Ruptured plaques, and by inference, plaques prone to rupture, tend to be large in size with associated expansive arterial remodeling, thin fibrous cap with a thick or large necrotic lipid core with immuno-inflammatory cell infiltration in fibrous cap and adventitia and increased plaque neovascularity and intraplaque hemorrhage. The size of the necrotic lipid core and extent and location of plaque inflammation appear to be key factors in determining plaque instability. Inflammation and immune cell activation appears to play a key role in the loss of collagen in the fibrous cap, a prelude to fibrous cap rupture, through release of collagen degrading enzymes. Furthermore, inflammation may also play a key role in the death of collagen synthesizing smooth muscle cells which further contributes to loss of fibrous cap integrity. Inflammation also is likely a key player in the ensuing thrombosis that follows plaque disruption through the elaboration of the pro-coagulant protein, tissue factor. An improved understanding of the pathophysiology of plaque vulnerability and subsequent athero-thrombosis should provide novel insights into improved prevention of athero-thrombotic cardiovascular events.

Noninvasive detection of cardiac repair after acute myocardial infarction in rats by 111 In Fab fragment of monoclonal antibody specific for tenascin-C

Left ventricular (LV) remodeling after acute myocardial infarction (MI) causes heart failure, and thus it is important to evaluate cardiac repair as the early stage of LV remodeling. Tenascin-C (TNC), an extracellular matrix glycoprotein, is transiently and abundantly expressed in the heart during the early stage of tissue remodeling after MI. However, it is not expressed in healthy adult heart. This study was undertaken to develop a new noninvasive diagnostic technique to detect cardiac repair after acute MI using 111 In Fab fragment of a monoclonal antibody specific for TNC. 111 In-anti-TNC-Fab was injected intravenously in 13 rats at 1 (D1, n = 3), 3 (D3, n = 5), and 5 (D5, n = 5) days after producing MI and in 5 sham-operated rats (S). We performed autoradiography and dual-isotope single-photon emission computed tomography imaging (SPECT) of 111 In-anti-TNC-Fab and 99mTc methoxyisobutyl isonitrile (MIBI). The radioactivity in the heart was significantly higher in D (D1, 0.45 +/- 0.06% injected-dose/g; D3, 0.64 +/- 0.12; D5, 0.38 +/- 0.07) than S (0.27 +/- 0.06, P < 0.01 versus D1 and D3, P < 0.05 versus D5). By autoradiography, higher radioactivities were observed in the infarcted area than in the noninfarcted area of MI hearts. Dual-isotope SPECT demonstrated the regional myocardial uptake of 111 In-anti-TNC-Fab, which was complementary to the perfusion image. The results of the present study indicated that we can localize the infarcted region in the heart by ex vivo and in vivo imaging methods using 111 In-anti-TNC-Fab, and suggested the potential usefulness of noninvasive detection of cardiac repair.

Differential elastin and tenascin immunolabeling in the uterosacral ligaments in postmenopausal women with and without pelvic organ prolapse

Connective tissue, consisting mainly of collagen and structural glycoproteins, is an important part of the supportive structures of the genitourinary region. Relatively few data have been published with respect to the role of elastin and glycoproteins in pelvic organ prolapse (POP). Connective tissue of the uterosacral ligament in postmenopausal women with and without genital prolapse was compared. Fifty-nine consecutive women referred for hysterectomy were included in the study. The patients had POP or benign gynecological disease (e.g. myoma of the uterus). Tissue samples from the uterosacral ligament were investigated for localization and distribution of tenascin and elastin using immunofluorescence microscopy. Tissue samples of women with prolapse showed a significantly (p<0.001) weaker immunofluorescent labeling of tenascin compared to samples taken from women without prolapse. Tenascin was detectable in tissues of all women with POP, whereas its immunolabeling was decreased in the uterosacral ligament in women without POP. Intact elastin fibers were observed in tissues of all women without POP, whereas elastin was undetectable or sometimes fragmented in the uterosacral ligament in women with POP. Greater amounts of tenascin and lesser amounts of elastin were therefore found in patients with POP. These results suggest that an altered turnover of connective tissue in the uterosacral ligament might be responsible for the presence of pelvic floor relaxation in postmenopausal women. These data indicate a complex architecture of the extracellular matrix in the uterosacral ligaments, with marked differences in tenascin and elastin expression between postmenopausal women with or without POP.

Proteomic identification of endothelial proteins isolated in situ from atherosclerotic aorta via systemic perfusion

The functional and structural alterations of vascular endothelium contribute to the initiation, progression, and complications of atherosclerotic plaque formation, but limited information is known about the molecular composition and pathways underlying pathological changes during atherosclerosis. We have developed an affinity proteomic strategy for in situ isolation and differential mapping of vascular endothelial proteins in normal and atherosclerotic aorta tissues. The selective labeling was carried out by perfusion of the blood vessels with an active biotin reagent for covalent modification of accessible vascular endothelial proteins. The biotinylated proteins were then enriched by streptavidin affinity chromatography, separated by SDS-PAGE, and subsequently characterized by LC-MS/MS. The described procedure led to the identification of 454 distinct proteins in normal and atherosclerotic aorta tissues. A majority of the proteins are plasma membrane associated and extracellular matrix proteins, and 81 showed altered expressions in atherosclerotic aorta tissue. The differentially expressed proteins are involved in immune and inflammatory responses, cell adhesion, and lipid metabolism. The method provides a new avenue for investigating the endothelial dysfunction and development of atherosclerosis.

Molecular mechanisms of plaque instability

PURPOSE OF REVIEW

Coronary artery thrombosis superimposed on a disrupted atherosclerotic plaque initiates abrupt arterial occlusion and is the proximate event responsible for 60-80% cases of acute coronary syndromes. This article provides a concise update on the evolving concepts in the pathophysiology of plaque rupture and thrombosis.

RECENT FINDINGS

Over the past several years, the critical role of plaque composition rather than plaque size or stenosis severity, in plaque rupture and thrombosis have been recognized. The necrotic lipid core and plaque inflammation appear to be key factors. Extracellular matrix loss in the fibrous cap, a prelude to rupture, is attributed to matrix degrading enzymes as well as to death of matrix synthesizing smooth muscle cells; inflammation appears to play a critical role in both these processes. Inflammatory cell derived tissue factor is a key contributor to plaque thrombogenicity. Inflammation has also been implicated in plaque neovascularity, intraplaque hemorrhage and plaque expansion. Recent observations have also highlighted the important modulatory role of immune system in atherosclerosis and plaque composition.

SUMMARY

Improved understanding of mechanisms causing plaque instability should provide novel insights into prevention of athero-thrombotic cardiovascular events.

Macrophage depletion impairs wound healing and increases left ventricular remodeling after myocardial injury in mice

Macrophages have been suggested to be beneficial for myocardial wound healing. We investigated the role of macrophages in myocardial wound healing by inhibition of macrophage infiltration after myocardial injury. We used a murine cryoinjury model to induce left ventricular damage. Infiltrating macrophages were depleted during the 1st week after cryoinjury by serial intravenous injections of clodronate-containing liposomes. After injury, the presence of macrophages, which secreted high levels of transforming growth factor-beta and vascular endothelial growth factor-A, led to rapid removal of cell debris and replacement by granulation tissue containing inflammatory cells and blood vessels, followed by myofibroblast infiltration and collagen deposition. In macrophage-depleted hearts, nonresorbed cell debris was still observed 4 weeks after injury. Secretion of transforming growth factor-beta and vascular endothelial growth factor-A as well as neovascularization, myofibroblast infiltration, and collagen deposition decreased. Moreover, macrophage depletion resulted in a high mortality rate accompanied by increased left ventricular dilatation and wall thinning. In conclusion, infiltrating macrophage depletion markedly impairs wound healing and increases remodeling and mortality after myocardial injury, identifying the macrophage as a key player in myocardial wound healing. Based on these findings, we propose that increasing macrophage numbers early after myocardial infarction could be a clinically relevant option to promote myocardial wound healing and subsequently to reduce remodeling and heart failure.

Galectin-1-Matured Human Monocyte-Derived Dendritic Cells Have Enhanced Migration through Extracellular Matrix

Dendritic cells (DCs) are potent mediators of the immune response, and can be activated by exogenous pathogen components. Galectin-1 is a member of the conserved beta-galactoside-binding lectin family that binds galactoside residues on cell surface glycoconjugates. Galectin-1 is known to play a role in immune regulation via action on multiple immune cells. However, its effects on human DCs are unknown. In this study, we show that galectin-1 induces a phenotypic and functional maturation in human monocyte-derived DCs (MDDCs) similar to but distinct from the activity of the exogenous pathogen stimuli, LPS. Immature human MDDCs exposed to galectin-1 up-regulated cell surface markers characteristic of DC maturation (CD40, CD83, CD86, and HLA-DR), secreted high levels of IL-6 and TNF-alpha, stimulated T cell proliferation, and showed reduced endocytic capacity, similar to LPS-matured MDDCs. However, unlike LPS-matured DCs, galectin-1-treated MDDCs did not produce the Th1-polarizing cytokine IL-12. Microarray analysis revealed that in addition to modulating many of the same DC maturation genes as LPS, galectin-1 also uniquely up-regulated a significant subset of genes related to cell migration through the extracellular matrix (ECM). Indeed, compared with LPS, galectin-1-treated human MDDCs exhibited significantly better chemotactic migration through Matrigel, an in vitro ECM model. Our findings show that galectin-1 is a novel endogenous activator of human MDDCs that up-regulates a significant subset of genes distinct from those regulated by a model exogenous stimulus (LPS). One unique effect of galectin-1 is to increase DC migration through the ECM, suggesting that galectin-1 may be an important component in initiating an immune response.

Pleiotrophin induces transdifferentiation of monocytes into functional endothelial cells

OBJECTIVE

Pleiotrophin (PTN) is a cytokine that is expressed by monocytes/macrophages in ischemic tissues and that promotes neovascularization, presumably by stimulating proliferation of local endothelial cells. However, the effect of PTN on monocytes/macrophages remains unknown. We investigated the role of PTN in regulating the phenotype of monocytes/macrophages.

METHODS AND RESULTS

RT-PCR, real-time PCR, and fluorescence-activated cell sorter analysis revealed that the expression of PTN by monocytic cells led to a downregulation of CD68, c-fms, and CD14 monocytic cell markers and an upregulation of FLK-1, Tie-2, vascular endothelial-cadherin, platelet endothelial cell adhesion molecule-1, endothelial NO synthase, von Willebrand factor, CD34, GATA-2, and GATA-3 endothelial cell markers. Fibrin gel assays showed that the treatment of mouse and human monocytic cells with PTN led to the formation of tube-like structures. In vivo studies showed that PTN-expressing monocytic cells incorporated into the blood vessels of the quail chorioallantoic membrane. The intracardial injection of PTN-expressing monocytic cells into chicken embryos showed that cells integrated only into the developing vasculature. Finally, the injection of PTN-expressing monocytes into a murine ischemic hindlimb model significantly improved perfusion of the ischemic tissue.

CONCLUSIONS

PTN expression by monocytes/macrophages led to a downregulation of their monocytic cell markers and an upregulation of endothelial cell characteristics, thus inducing the transdifferentiation of monocytes into functional endothelial cells.

Tenascin-C—coated platinum coils for acceleration of organization of cavities and reduction of lumen size in a rat aneurysm model

Object. Detachable platinum coils are widely used in the endovascular treatment of intracranial aneurysms. The use of coil placement produces a higher incidence of aneurysm recurrence compared with surgical clipping. To reduce the incidence of recurrence by promoting clot organization, the authors designed a platinum coil coated with tenascin-C (TNC), an extracellular matrix glycoprotein, and then histologically examined tissue responses.

Methods. Platinum coils were prepared by successive coatings with cationic polyethyleneimine and anionic heparin and then TNC or basic fibroblast growth factor (bFGF) was immobilized by affinity binding to the heparin. Six unmodified, six heparin-coated, six bFGF-coated, or eight TNC-coated platinum coils were inserted into ligated common carotid arteries (CCAs) of adult male rats, and CCA segments were harvested after 14 or 28 days.

The percentages of organized areas occupying the luminal cavity in unmodified, heparin-coated, bFGF-coated, and TNC-coated groups were 4.8 ± 4.6, 1.6 ± 1.1, 17.9 ± 10.7, and 93.4 ± 6.9%, respectively. In addition, the mean lumen size in the TNC-coated group (0.35 ± 0.23 mm2) was reduced to less than half that of the unmodified group (0.72 ± 0.21 mm2). Immunohistochemical analysis revealed that α—smooth muscle actin—positive cells were a major cellular component of the organized tissue within the TNC-coated coils but not in the bFGF group. Collagen fibrils in the organized areas were also much thicker and denser with TNC-coated coils than with bFGF-coated coils.

Conclusions. Placement of TNC-coated coils can remarkably accelerate organization of luminal cavities and reduce their volume, providing improved efficacy of these coils for endovascular embolization.

Interleukin-4 and dexamethasone counterregulate extracellular matrix remodelling and phagocytosis in type-2 macrophages

Alternatively activated macrophages (Mphi2) are induced by Th2 cytokines and by glucocorticoids (GC), and can be distinguished from classically activated effector macrophages (Mphi1) on the basis of their anti-inflammatory properties. In addition, Mphi2 are involved in Th2/Th1 skewing, enhance antigen uptake and processing and support tissue remodelling and healing. In order to elucidate the heterogeneity of Mphi2 population systematically, we analysed a number of genes involved in extracellular matrix (ECM) remodelling, inflammation and phagocytosis in Mphi2 populations generated with interleukin-4 (IL-4) or GC. Using real-time polymerase chain reaction, we demonstrated that the ECM component, tenascin-C, is stimulated by IL-4, whereas it is suppressed by dexamethasone. The ECM remodelling enzymes--MMP-1 and MMP-12--and tissue transglutaminase (TG) showed a similar regulation pattern. FXIIIa, another putative Mphi2-associated TG, was synergistically regulated by IL-4 and GC. Enzyme-linked immunosorbent assay analysis revealed that the production of Mphi2-associated chemokines, AMAC-1, MCP-4 or TARC, was induced by IL-4 and was modulated by GC. Phagocytosis of opsonized and non-opsonized particles was stimulated by GC, whereas IL-4 had only a modulatory effect, what may be partially explained by the expression pattern of hMARCO, a scavenger receptor for non-opsonized particles, that was strongly and selectively induced by GC. In conclusion, stimulation of Mphi with IL-4 and GC regulate antagonistically the expression of ECM remodelling-related molecules and phagocytosis of opsonized and non-opsonized particles.

Gene expression profiling of cathepsin D, metallothioneins-1 and -2, osteopontin, and tenascin-C in a mouse spinal cord injury model by cDNA microarray analysis

The purpose of this study was to use a cDNA microarray to identify new genes involved in healing of spinal cord injury. C57BL/6 mice (7-8 weeks, male) were subjected to spinal cord compression injury (SCI) at the T7/8 level (20 g, 5 min; SCI group). For the control group, mice underwent only laminectomy. Mice were killed at 1, 3 and 7 days. cDNA transcribed from mRNA was hybridized to NIA mice 15K microarrays at each time point. We found 84 genes showing significant expressional changes, including higher and lower expression levels in the SCI groups than in the control [more than 1.0 or less than -1.0 using log ratio (base 2)]. Five genes were selected for further quantitative gene expression analysis by real-time reverse transcription (RT)-PCR. For histological examination, we applied in situ hybridization and fluorescence immunohistochemistry. Cathepsin D, metallothionein-1 (MT-1), metallothionein-2 (MT-2), osteopontin (OPN), and tenascin-C were selected for quantitative and histological analysis. Microarray analysis revealed that SCI led to the up-regulation of OPN and cathepsin D expression at 7 days and also of MT-1, MT-2, and tenascin-C expression at 1 day. Tenascin-C was re-up-regulated at 7 days. These values agreed with those of real-time RT-PCR analysis. By double labeling with in situ hybridization and fluorescence immunohistochemistry, MT-1, MT-2 and tenascin-C expression was observed in neurons and glial cells at 1 day, whereas at 7 days the main MT-2 and tenascin-C expression was found in fibronectin-positive fibroblasts. The main cathepsin D and OPN expression was observed in activated macrophages/microglia at 3 and 7 days. The five genes picked up by microarray gene expression profiling were shown to exhibit temporal and spatial changes of expression after SCI. This system is potentially useful for identifying genes that are involved in the response to SCI.

Dual role of matrix metalloproteinases (matrixins) in intimal thickening and atherosclerotic plaque rupture

Intimal thickening, the accumulation of cells and extracellular matrix within the inner vessel wall, is a physiological response to mechanical injury, increased wall stress, or chemical insult (e.g., atherosclerosis). If excessive, it can lead to the obstruction of blood flow and tissue ischemia. Together with expansive or constrictive remodeling, the extent of intimal expansion determines final lumen size and vessel wall thickness. Plaque rupture represents a failure of intimal remodeling, where the fibrous cap overlying an atheromatous core of lipid undergoes catastrophic mechanical breakdown. Plaque rupture promotes coronary thrombosis and myocardial infarction, the most prevalent cause of premature death in advanced societies. The matrix metalloproteinases (MMPs) can act together to degrade the major components of the vascular extracellular matrix. All cells present in the normal and diseased blood vessel wall upregulate and activate MMPs in a multistep fashion driven in part by soluble cytokines and cell-cell interactions. Activation of MMP proforms requires other MMPs or other classes of protease. MMP activation contributes to intimal growth and vessel wall remodeling in response to injury, most notably by promoting migration of vascular smooth muscle cells. A broader spectrum and/or higher level of MMP activation, especially associated with inflammation, could contribute to pathological matrix destruction and plaque rupture. Inhibiting the activity of specific MMPs or preventing their upregulation could ameliorate intimal thickening and prevent myocardial infarction.

The Mechanism of In-Stent Restenosis in Radius Stent-An Experimental Porcine Study-

BACKGROUND

We investigated the mechanism of in-stent restenosis in radius stents in comparison to balloon-expandable stent (NIR stent) in pigs, with a focus on extracellular matrix (ECM).

METHODS AND RESULTS

Radius (n = 4) or NIR (n = 4) stents were implanted in the left coronary arteries of miniature pigs. Quantitative coronary ultrasound (QCU) was performed before, immediately after, and at 1 and 4 weeks after the implantation. The stented-coronary arteries were harvested at 4 weeks after the implantation followed by immunohistochemical, histological, reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR studies. In QCU, mean luminal areas at 4 weeks did not differ between both groups, whereas the mean stent area and neointimal area were significantly greater in the radius (p < 0.01). The immunohistochemical study revealed a significantly decreased number of neointimal macrophages and neovascularizations (p < 0.05, p < 0.01, respectively), and a stronger expression of tenascin-C in the radius. The histological study showed a larger ECM area and less neointimal cell density in the radius than in the NIR. The RT-PCR and real-time PCR analysis revealed an enhanced expression of tanascin-C mRNA in the radius than in the NIR.

CONCLUSIONS

Increased production of ECM, especially tenascin-C, played a greater role in the neointimal formation in the radius stent than inflammation.

Tenascin C expression is upregulated in pancreatic cancer and correlates with differentiation

BACKGROUND

Tenascin C is a large, hexameric, extracellular matrix protein that is present during embryonic development but essentially absent in adult tissues. It is involved in remodelling processes, such as wound healing and tumour development. Tissue expression of tenascin C correlates with prognosis in colorectal, cervical, and breast cancer and in carcinoma of the papilla of Vater.

AIM

To study the expression of tenascin C in pancreatic cancer and to compare the staining results with the patients' clinicopathological data.

MATERIAL AND METHODS

Formalin fixed, paraffin wax embedded specimens from 146 patients with pancreatic adenocarcinoma were stained with an anti-tenascin C monoclonal antibody.

RESULTS

Tenascin C immunoreactivity was seen in most samples of pancreatic carcinoma: staining was weak in 72 (49%), moderate in 52 (36%), strong in 10 (7%), and negative in 12 (8%) samples. Tenascin C expression correlated with age (< or = 66 v >66 years) and poor differentiation (grades 1-2 v 3). There was no correlation between tenascin C expression and survival, clinical stage, tumour size, nodal status, distant metastasis, tumour location, or sex.

CONCLUSION

Tenascin C expression was increased in most pancreatic carcinomas, but contrary to the results in other cancers, it is not a prognostic factor in pancreatic cancer.

Technology Insight: targeting of biological molecules for evaluation of high-risk atherosclerotic plaques with magnetic resonance imaging

Identification of high-risk atherosclerotic lesions prone to rupture and thrombosis may greatly decrease the morbidity and mortality associated with atherosclerosis. The development of magnetic resonance imaging contrast agents that specifically target components of the atherosclerotic plaque might enable non-invasive detection of high-risk lesions. This review discusses a variety of molecules present in atherosclerotic plaque that could serve as targets for specific contrast agents. Ultimately, such agents may allow the identification of high-risk atherosclerotic lesions in patients and enable treatment of these patients before lesion progression and complications.

Locally applied cilostazol suppresses neointimal hyperplasia by inhibiting tenascin-C synthesis and smooth muscle cell proliferation in free artery grafts

OBJECTIVE

Accumulation of smooth muscle cells and extracellular matrix in the intima of artery bypass grafts induces neointimal hyperplasia, resulting in graft failure. We investigated the inhibitory effect of locally applied cilostazol, an inhibitor of cyclic adenosine monophosphate phosphodiesterase III, on neointimal hyperplasia and the role of tenascin-C synthesis and smooth muscle cell proliferation in free artery grafts. Methods and results We established a distal anastomotic stricture model of free artery graft stenosis using rat abdominal aorta. In this model, neointimal hyperplasia was observed not only in the distal anastomotic site but also in the graft body at postoperative day 14 and was markedly progressed at day 28. Strong expression of tenascin-C was found in the media and neointima of the graft body. When cilostazol was locally administered around the graft using Pluronic gel, neointimal hyperplasia of the graft was significantly suppressed in comparison with gel-treated control graft. The mean neointima/media area ratio was reduced by 86.6% for the graft body and by 75.8% for the distal anastomotic site versus the control. Cilostazol treatment decreased cell proliferation and tenascin-C expression in the neointima. In an in vitro experiment using cultured smooth muscle cells isolated from rat aorta, cilostazol completely suppressed the tenascin-C mRNA expression induced by platelet-derived growth factor-BB.

CONCLUSION

A single topical administration of cilostazol may suppress neointimal hyperplasia by inhibiting cell proliferation and tenascin-C synthesis in free artery grafts, presenting the potential for clinical use in vascular surgery.

Tenascin-C is associated with coronary plaque instability in patients with acute coronary syndromes

BACKGROUND

Tenascin-C (TNC) is an extracellular matrix glycoprotein that increases after inflammation and injury. In cultured cells TNC has been reported to markedly induce the expression of matrix metalloproteinase-9, which stimulates collagen degradation in the fibrous cap of human atherosclerotic plaque.

METHODS AND RESULTS

Immunohistochemical techniques were used to analyze the expression of TNC protein in 51 coronary atherectomy specimens obtained from patients with stable angina pectoris (SAP, n=23) or acute coronary syndromes (ACS) (n=28; unstable angina pectoris, n=20, acute myocardial infarction, n=8). Immunostaining for alpha-smooth muscle actin, CD68, CD45, and CD31 was also performed in serial sections to identify the cell types that express TNC protein. The %TNC + area (percentage of the area of immunostaining for TNC protein in the total surface area of the plaque) was larger in coronary samples with the plaque characteristics of thrombus, angiogenesis, intraplaque hemorrhage, and macrophage (CD68(+)), and lymphocyte (CD45 (+)) clusters than in coronary samples without them (52+/-3.4 vs 39+/-4.8, p<0.05; 57+/-3.7 vs 36+/-3.7, p<0.01; 51+/-3.6 vs 39+/-4.8, p<0.05; 53+/-3.4 vs 33+/-4.5, p<0.01; 56+/-4.1 vs 37+/-3.6, p<0.01, respectively). The presence of other components, such as dense fibrous tissue, neointimal hyperplasia, atheromatous gruel and calcification, was not significantly correlated with the %TNC + area. The %TNC + area was larger in coronary samples from patients with ACS than in samples from patients with SAP (56+/-3.2% vs 34+/-4.3%, p<0.01).

CONCLUSIONS

The results suggest that TNC may have specific functions in coronary plaque formation and may be involved in the pathogenesis of coronary lesions in ACS.

Functional dichotomy: glutathione and vitamin E in homeostasis relevant to primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is a complex chronic neurological disease that can result in blindness. The goal of understanding the aetiology of POAG is to be able to target effective treatment to individuals who will eventually go blind without it. Epidemiological studies of POAG have not specifically addressed the possibility that nutrition may play a role in the development of POAG. A handful of papers have considered that nutrition may have an impact on POAG patients. POAG is not believed to be a 'vitamin-deficiency disease'. The concept of 'vitamin-deficiency diseases' and the recommended daily allowances have not kept pace with the growing understanding of the cellular and molecular functions of vitamins and other micronutrients. The aetiology of POAG remains a mystery. Discoveries in cell physiology can be assimilated from the literature and applied to known homeostatic mechanisms of the eye. In this way the possible roles of nutritional components involved in the aetiology of POAG can be described. The mechanisms may be subject to many influences in ways that have yet to be defined. Two distinct changes in the trabecular meshwork can be identified: trabecular meshwork changes that cause intra-ocular pressure to increase and trabecular meshwork changes that are directly correlated to optic nerve atrophy. Compelling evidence suggests that collagen trabecular meshwork extracellular matrix (ECM) remodelling is correlated to increased intraocular pressure in POAG. Elastin trabecular meshwork ECM remodelling is correlated to POAG optic nerve atrophy. There appear to be two different pathways of ECM remodelling and apoptosis induction in POAG. The pathway for collagen remodelling and apoptosis induction seems to be exogenously influenced by water-soluble antioxidants, for example, glutathione. The pathway for elastin remodelling and apoptosis induction seems to be influenced by endogenous lipid-soluble antioxidants, for example, vitamin E. Roles can be defined for antioxidants in the two different pathways of ECM remodelling and apoptosis induction. This suggests that antioxidants are important in maintaining cellular homeostasis relevant to the aetiology of POAG.

Mesenchymal stem cell injection induces cardiac nerve sprouting and increased tenascin expression in a Swine model of myocardial infarction

Stem Cell Induces Cardiac Nerve Sprouting.

INTRODUCTION

Mesenchymal stem cell (MSC) transplantation is a promising technique to improve cardiac function. Whether MSC can increase cardiac nerve density and contribute to the improved cardiac function is unclear.

METHODS AND RESULTS

Anterior wall myocardial infarction was created in 16 swine. One month later, 6 swine were given MSC and fresh bone marrow (BM) into infarcted myocardium (MSC group). Four swine were given fresh BM only (BM group), and 6 swine were given culture media (MI-only group). The swine were sacrificed 95.8 +/- 3.5 days after MI. Six normal swine were used as control. Immunocytochemical staining was performed using antibodies against growth-associated protein 43 (GAP43), tyrosine hydroxylase (TH), and three subtypes of tenascin (R, C, and X). Five fields per slide were counted for nerve density. The results show the following. (1). There were more GAP43-positive nerves in the MSC group than in the BM, MI-only, or Control group (P < 0.0001). TH staining showed higher nerve densities in the MSC group than in the MI-only (P < 0.01) or Control group (P < 0.0001) in the atria. (2). There were more sympathetic (TH-positive) nerves in myocardium distant from infarct than in the peri-infarct area (P < 0.05). (3). Optical intensity and color analyses showed significantly higher tenascin R and tenascin C expression in the MSC and BM groups than in the MI-only or Control group (P < 0.01).

CONCLUSION

MSC injected with BM into swine infarct results in overexpression of cardiac tenascin, increased the magnitude of cardiac nerve sprouting in both atria and ventricles, and increased the magnitude of atrial sympathetic hyperinnervation 2 months after injection.

Pathophysiology of plaque rupture and the concept of plaque stabilization

Atherosclerotic coronary artery disease is the major cause of death, in men and women, in the United States and in much of the Western world. Atherosclerosis is responsible for coronary heart disease, limb ischemia, and most strokes. Although luminal narrowing by an atherosclerotic plaque and exaggerated or anomalous vasoconstriction contribute to some of the clinical manifestations of atherosclerotic arterial disease, it is the superim-position of a thrombus over an underlying ruptured or eroded plaque that results in the acute coronary syndromes (unstable angina, acute myocardial infarction, and sudden death) that are the most serious clinical manifestations of this disease.

Tenascins: regulation and putative functions during pathological stress

In this review, we discuss the structure and function of the extracellular matrix protein family of tenascins with emphasis on their involvement in human pathologies. The article is divided into the following sections:

INTRODUCTION

the tenascin family of extracellular matrix proteins; Structural roles: tenascin-X deficiency and Ehlers-Danlos syndrome; Tenascins as modulators of cell adhesion, migration, and growth; Role of tenascin-C in inflammation; Regulation of tenascins by mechanical stress: implications for wound healing and regeneration; Association of tenascin-C with cancer: antibodies as diagnostic and therapeutic tools; Conclusion and perspectives.

Suppression subtractive hybridization identifies distinctive expression markers for coronary and internal mammary arteries

OBJECTIVE

We sought to identify differentially expressed genes in the athero-prone coronary artery and athero-resistant internal mammary arteries.

METHODS AND RESULTS

Using suppressive subtraction hybridization, we generated reciprocal cDNA collections of representative mRNAs specific to porcine coronary arteries versus porcine mammary arteries. We screened 1000 suppressive subtraction hybridization cDNA clones by dot blot array and sequenced 600 of those showing the most marked expression differences. Northern blot, in situ hybridization, and immunostaining confirmed the differential gene expression patterns identified by the dot blot arrays. Genes associated with mammary arteries included claudin-10 and h-cadherin, which are genes associated with tight junctions and intermediate junctions. In contrast, genes associated with proatherosclerotic processes, such as lipid retention and metabolism, inflammation, and cell growth, were preferentially expressed in coronary arteries.

CONCLUSIONS

Normal coronary arteries have gene expression program that is significantly different than internal mammary arteries. These differences may partly explain the resistance of coronary arteries and internal mammary arteries to atherosclerosis.

Mechanisms of plaque vulnerability and rupture

Rupture of atherosclerotic plaque has been identified as the proximate event in the majority of cases of acute ischemic syndromes. Plaque rupture exposes thrombogenic components of the plaque, activating the clotting cascade and promoting thrombus formation. Future culprit lesions are difficult to identify, however, and angiographic assessment of stenosis severity is prone to underestimation. Compared with plaques that cause severe luminal stenosis, vulnerable plaques may cause relatively minor stenosis, although they account for more cases of rupture and thrombosis. Such unstable, vulnerable plaques may be associated with outward remodeling of the vessel. Because severely stenotic plaques are more likely to stimulate collateral circulation to the post-stenotic segment, plaque rupture and thrombosis at such sites may be clinically silent. Characteristic histomorphologic features of vulnerable plaques include a high lipid content, increased numbers of inflammatory cells, and extensive adventitial and intimal neovascularity. The fibrous cap of an atherosclerotic plaque may become thin and rupture as a result of the depletion of matrix components through the activation of enzymes, such as matrix-degrading proteinases and cystine and aspartate proteases, and through the reduction in the number of smooth muscle cells. Activated T cells may also inhibit matrix synthesis through the production of interferon-gamma. A number of triggers of plaque rupture have been identified. Also, some thrombi may occur without rupture of the fibrous cap. Reducing the lipid component and inflammation in atherosclerotic plaques may help reduce the risk of plaque rupture. This may account for the clinical benefit of risk-factor reduction gained from changes in lifestyle and from drug therapy.

Histopathological findings in a human carotid artery after stent implantation. Case report

Despite the high technical success rates and the acceptable morbidity and mortality rates that are associated with carotid artery (CA) stent implantation, morphological changes in the vessel wall after this procedure are still unknown. The authors describe histopathological findings of the CA after stent implantation in a human autopsy specimen. A 75-year-old man with asymptomatic CA stenosis underwent successful CA stent implantation, but died 8 months afterward of complications surrounding treatment of a thoracic aortic artery aneurysm. The stented CA was isolated from the autopsy specimen and was analyzed macroscopically and with the aid of scanning electron microscopy and histopathological methods. Although there was focal persistence of a chronic inflammatory reaction around the stent struts, a stabilized neointima overlying the stent, which was principally composed of cells that stained positively for alpha-smooth muscle actin and collagen deposition with complete reendothelialization of the luminal surface, was confirmed in the internal CA. In contrast, residual mural thrombus around the stent struts in the common CA led to a concern about the potential risk for distal embolism in the future. The present case provides supportive evidence of stabilized neointima overlying the stent and valuable information regarding morphological characteristics useful for selecting a stent of an appropriate size.

Transgenic study of the function of chymase in heart remodeling

OBJECTIVES

To study the function of chymase on heart remodeling by overexpression of human chymase in the heart of transgenic mice.

METHODS

Transgenic mice were produced by microinjection. The chymase mRNA levels in the heart and other tissues were assessed by competitive reverse transcriptase-polymerase chain reaction (RT-PCR). The expression of collagen I/III genes was analyzed by Northern blot hybridization. Chymase and angiotensin-converting enzyme (ACE) activities, and angiotensin II (Ang II) content in the heart were determined by radioimmunoassay (RIA). The matrix metalloprotease-9 (MMP-9) in protein and activity levels were measured by Western blot and zymogram, respectively.

RESULTS

A model of transgenic mice with selective overexpression of a rat myosin light chain 2 promoter-human heart chymase (MLC(2-)-hChymase) fusion gene was produced. In MLC(2)-hChymase transgenic mice (the F(6) line), the human heart chymase gene was expressed at a high level in heart and at lower levels in skeletal muscle and kidney, while no expression was detected in the liver or lung. The heart chymase activity increased markedly in the F(6) transgenic mice versus non-transgenic mice (0.274 +/- 0.071 U/mg versus 0.152 +/- 0.021 U/mg) ( P < 0.05), with no difference in ACE activity. Heart Ang II level in the F(6) transgenic mice increased nearly threefold (1984 +/- 184 versus 568 +/- 88 pg/g protein) ( P < 0.05) but was unchanged in plasma. MMP-9 activity increased significantly in the cardiac tissue of F(6) transgenic mice ( P < 0.05), while both collagen I and the ratio of collagen I : III mRNA levels decreased significantly (both P < 0.05). The F(6) transgenic mice showed no significant changes in cardiac parameters.

CONCLUSIONS

We have demonstrated selective overexpression of human chymase gene in the heart of transgenic mice, and the results support the hypothesis of a dual Ang II-forming pathway from chymase and ACE in the cardiac tissue in vivo. The results also suggest that chymase may play a role in heart remodeling by increasing Ang II formation and activating MMP-9, and the regulation of collagen I gene expression.

Degradation of extracellular matrix protein tenascin-C by cathepsin B: an interaction involved in the progression of gliomas

Degradation of extracellular matrix proteins by proteases such as the cysteine protease cathepsin B is critical to malignant progression. We have established that procathepsin B presents on the surface of tumor cells through its interaction with the annexin II tetramer [Mai et al., J. Biol. Chem. 275 (2000),12806-12812]. Cathepsin B activity can also be detected on the tumor cell surface and in their culture medium. Interestingly, the annexin II tetramer also interacts with extracellular matrix proteins, such as collagen I, fibrin and tenascin-C. Both cathepsin B and tenascin-C are expressed at high levels in malignant tumors, especially at the invasive edges of tumors, and are implicated in tumor angiogenesis. In this study, we report that tenascin-C can be degraded by cathepsin B in vitro. We demonstrate by immunohistochemistry that both cathepsin B and tenascin-C are expressed highly in malignant anaplastic astrocytomas and glioblastomas as compared to normal brain tissues. Interestingly, cathepsin B and tenascin-C were also detected in association with tumor neovessels. We suggest that interactions between cathepsin B and tenascin-C are involved in the progression of gliomas including the angiogenesis that is a hallmark of anaplastic astrocytomas.

Balloon catheterization induces arterial expression of new Tenascin-C isoform

Migration of smooth muscle cells (SMCs) across the internal elastic lamina is a key step in the development of atherosclerotic or restenotic plaques. Cell movement is a complex and highly dynamic phenomenon, involving the continuous formation and breakage of attachments with the underlying substratum. Tenascin-C (Tn-C), a counter-adhesive extracellular matrix protein, is comprised of several isoforms with distinct biological activities. Neither the structure nor function of these isoforms in SMCs has been defined. We have used primers and RT-PCR to fully identify Tn-C isoforms expressed by SMCs. Cloning and sequence analysis of the PCR product indicated that SMCs express a Tn-C isoform with only repeats A1 and A2 of fibronectin type III repeats. Using A1A2-specific antibodies, cDNA probes and RNase mapping, we observed that the A1A2 isoform is predominantly expressed by cultured SMCs derived from aorta of newborn rats, and its expression is up-regulated by PDGF-BB. In contrast, the expression of this isoform is markedly down-regulated in the SMCs derived from adult rat aorta. Western and Northern blots of injured rat carotid arteries revealed that the A1A2-isoform is expressed in response to injury. Using cultured SMCs, we found that the recombinant A1A2 protein that was found in the newly discovered Tn-C isoform promotes SMC chemotaxis. We conclude that Tn-C isoforms are expressed in a regulated fashion in vascular system. Our findings suggest a new role of Tn-C isoforms in the remodeling of vascular wall.

Pathophysiology of coronary thrombosis: role of plaque rupture and plaque erosion

Coronary artery disease is the leading cause of death in much of the western world. Atherosclerotic plaques in the coronary arteries contribute to luminal obstruction leading to myocardial ischemia; however, abrupt coronary artery occlusion most frequently results from superimposition of a thrombus on a disrupted plaque, leading to the most serious clinical manifestations of coronary artery disease, ie, unstable angina, acute myocardial infarction, and sudden death. Plaque that have undergone disruption and, by inference, plaques at risk for disruption (vulnerable plaques), tend to demonstrate outward vessel remodeling, contain a large lipid core, thinned out fibrous cap, reduced collagen content, and increased inflammatory cell infiltration. Plaque stabilization through change in plaque composition may be responsible for reduced frequency of acute vaso-occlusive events observed with lipid and other risk-factor modifying interventions.

Tenascin-C aptamers are generated using tumor cells and purified protein

Tenascin-C (TN-C) is an extracellular matrix protein that is overexpressed during tissue remodeling processes, including tumor growth. To identify an aptamer for testing as a tumor-selective ligand, SELEX (systematic evolution of ligands by exponential enrichment) procedures were performed using both TN-C and TN-C-expressing U251 glioblastoma cells. The different selection techniques yielded TN-C aptamers that are related in sequence. In addition, a crossover procedure that switched from tumor cell to purified protein selections was effective in isolating two high-affinity TN-C aptamers. When targeting tumor cells in vitro, the observed propensity of naive oligonucleotide pools to evolve TN-C aptamers may be due to the abundance of this protein. In vivo, TN-C abundance may also be well suited for aptamer accumulation in the tumor milieu. A size-minimized and nuclease-stabilized aptamer, TTA1, binds to the fibrinogen-like domain of TN-C with an equilibrium dissociation constant (K(d)) of 5 x 10(-9) m. At 13 kDa, this aptamer is intermediate in size between peptides and single chain antibody fragments, both of which are superior to antibodies for tumor targeting because of their smaller size. TTA1 defines a new class of ligands that are intended for targeted delivery of radioisotopes or chemical agents to diseased tissues.

Arterial wall chondroitin sulfate proteoglycans: diverse molecules with distinct roles in lipoprotein retention and atherogenesis

Chondroitin sulfate proteoglycans (CSPGs) of the arterial wall are generally considered to be atherogenic because of their ability to trap cholesterol-rich lipoproteins in vitro. Nevertheless, CSPGs are a diverse group of molecules with a long evolutionary history and distinct biologic functions. The three principal CSPGs in the arterial wall are versican, which is part of the hyalectan gene family; and decorin and biglycan, which are members of a separate gene family, the small leucine-rich proteoglycans. Importantly, there is now substantial evidence that the different molecular species of CSPGs participate unequally in lipoprotein retention, and that they exert unequal regulatory effects that are related to atherogenesis. Recently available murine models with genetic manipulations that affect CSPGs now allow causal studies of the roles of these molecules to be conducted in vivo, with occasionally surprising results. Moreover, tools are being developed to examine human genetic variations that are relevant to CSPGs, which may provide additional important insights into the human disease. The era in which proteoglycans are regarded as a nondescript backdrop, playing purely nonspecific structural roles, is over. Studies in manipulated animals and in human populations will continue to reveal precise, dynamic roles for these fascinating and ancient molecules.

Matrix metalloproteinase-2 is associated with tenascin-C in calcific aortic stenosis

We previously showed that the expression of tenascin (TN-C), an extracellular matrix glycoprotein found in developing bone and atherosclerotic plaque, and matrix metalloproteinase-2 (MMP-2) are coordinated and interdependent in cultured vascular smooth muscle cells. In this study, we hypothesized that TN-C and MMP-2 are mechanistically involved in the pathobiology of calcific aortic stenosis. Human calcific aortic stenosis cusps demonstrated immunohistochemically prominent deposition of TN-C, MMP-2, and alkaline phosphatase activity, as well as MMP-2 gelatinolytic activity. Although far lesser amounts of TN-C were noted in several of the grossly non-calcified valve cusps, MMP-2 and AP were never detected. Further, when aortic valve interstitial cells (both sheep and human) were cultivated on collagen supplemented with TN-C, both MMP-2 mRNA expression and MMP-2 gelatinolytic activity (both pro and active forms), were up-regulated compared to control. These observations support the view that accumulation of first TN-C and then MMP-2 are associated with progression of calcification. The residual presence of these proteins in severe calcifications is indicative of their involvement in the pathogenesis.

Blockade of alpha 5 beta 1 integrins reverses the inhibitory effect of tenascin on chemotaxis of human monocytes and polymorphonuclear leukocytes through three-dimensional gels of extracellular matrix proteins

Tenascin is an extracellular matrix protein found in adults in T cell-dependent areas of lymphoid tissues, sites of inflammation, and tumors. We report here that it inhibited chemotaxis of chemoattractant-stimulated human monocytes and chemoattractant-stimulated polymorphonuclear leukocytes (PMN) through three-dimensional gels composed of collagen I or Matrigel, and chemotaxis of leukotriene B4-stimulated PMN through fibrin gels. The inhibitory effect of tenascin on monocyte or PMN chemotaxis through these matrices was reversed by Abs directed against alpha5beta1 integrins or by a peptide (GRGDSP) that binds to beta1 integrins. Tenascin did not affect leukotriene B4- or fMLP-stimulated expression of beta1 or beta2 integrins, but did exert a small inhibitory effect on PMN adhesion and closeness of apposition to fibrin(ogen)-containing surfaces. Thus, alpha5beta1 integrins mediate the inhibitory effect of tenascin on monocyte and PMN chemotaxis, without promoting close apposition between these leukocytes and surfaces coated with tenascin alone or with tenascin bound to other matrix proteins. This contrasts with the role played by alpha5beta1 integrins in promoting close apposition between fMLP-stimulated PMN and fibrin containing surfaces, thereby inhibiting chemotaxis of fMLP-stimulated PMN through fibrin gels. Thus, chemoattractants and matrix proteins regulate chemotaxis of phagocytic leukocytes by at least two different mechanisms: one in which specific chemoattractants promote very tight adhesion of leukocytes to specific matrix proteins and another in which specific matrix proteins signal cessation of migration without markedly affecting strength of leukocyte adhesion.

Adventitial remodeling after angioplasty is associated with expression of tenascin mRNA by adventitial myofibroblasts

OBJECTIVES

The purpose of this study was to determine the temporospatial expression of tenascin-C (TnC) in balloon-injured rat and porcine arteries.

BACKGROUND

Recent studies suggest that cell migration, in addition to cell proliferation, is a critical component of neointima formation after vascular injury. We have previously shown that adventitial myofibroblasts synthesize growth factors that contribute to the formation of neointima after arterial injury. We have also shown that the extracellular matrix protein, TnC, regulates cell migration. Consequently, we investigated the temporospatial expression of TnC by myofibroblasts after vascular injury.

METHODS

In situ hybridization and immunohistochemistry were used to investigate the temporospatial expression of TnC in injured arteries. Northern and Western blots were used to determine the in vitro expression of TnC.

RESULTS

In situ hybridization revealed that the major site of TnC expression early after vascular injury was the adventitial myofibroblasts. Immunohistochemical staining demonstrated that TnC expression began in adventitial myofibroblasts three days after injury. Tenascin-C expression, however, did not persist in this region. Rather, it moved progressively across the vascular wall toward the luminal surface. By one week, TnC expression reached the developing neointima. In vitro, myofibroblasts did not express TnC mRNA under basal conditions. In contrast, angiotensin II and PDGF-BB, factors that have been implicated in remodeling of balloon-injured arteries, markedly upregulated TnC mRNA.

CONCLUSIONS

Tenascin-C is expressed in response to balloon injury. Tenascin-C expression begins with adventitial myofibroblasts. Over a period of 7 to 14 days, expression moves progressively across the vessel wall to the neointima. We hypothesize that adventitial myofibroblasts are actively involved in the formation of neointima and that TnC facilitates migration of these cells during adventitial remodeling.

Differential expression of tenascin-C, tenascin-R, tenascin/J1, and tenascin-X in spinal cord scar tissue and in the olfactory system

The members of the tenascin family are involved in a number of developmental processes, mainly by their ability to regulate cell adhesion. We have here studied the distribution of mRNAs for tenascin-X, -C, and -R and the closely related molecule tenascin/J1 in the olfactory system and spinal cord. The olfactory bulb and nasal mucosa were studied during late embryonic and early postnatal development as well as in the adult. The spinal cord was studied during late embryonic development and after mechanical lesions. In the normal rat, the spinal cord and olfactory bulb displayed similar patterns of tenascin expression. Tenascin-C, tenascin-R, and tenascin/J1 were all expressed in the olfactory bulb and spinal cord during development, while tenascin/J1 was the only extensively expressed tenascin molecule in the adult. In both regions tenascin/J1 was expressed in both nonneuronal and neuronal cells. After a spinal cord lesion, mRNAs for tenascin-C, -X, -R, and/J1 were all upregulated and had their own specific spatial and temporal expression patterns. Thus, even if axonal outgrowth occurs to some extent both in the adult rat primary olfactory system and in spinal cord scar tissue after lesion, the tenascin expression patterns in these two situations are totally different.

Role of plaque rupture in acute coronary syndromes

Acute coronary syndromes are caused by plaque rupture. The conventional strategy of prevention of plaque rupture has been driven by the "lipid hypothesis"--if lipid levels are optimized to target levels, the risk of coronary events is decreased. Indeed, the hypothesis has been validated by the dramatic success of statin therapy. However, further major reductions in cardiac events is a realistic goal; various mechanistic and small clinical studies show that statins have beneficial effects in addition to their lipid-lowering properties. One of these beneficial effects is stabilization of plaque. Despite billions of dollars spent on randomized clinical trials, optimal therapy for coronary artery disease is yet to be tested. This therapy might include various combinations of the Mediterranean or low-fat diet, endothelial passivation, lipid-lowering drugs, antioxidants, antiplatelet agents and anti-inflammatory agents.

Identification of amino acid sequences in fibrinogen gamma -chain and tenascin C C-terminal domains critical for binding to integrin alpha vbeta 3

Integrin alpha(v)beta(3) recognizes fibrinogen gamma and alpha(E) chain C-terminal domains (gammaC and alpha(E)C) but does not require the gammaC dodecapeptide sequence HHLGGAKQAGDV(400-411) for binding to gammaC. We have localized the alpha(v)beta(3) binding sites in gammaC using gammaC-derived synthetic peptides. We found that two peptides GWTVFQKRLDGSV(190-202) and GVYYQGGTYSKAS(346-358) block the alpha(v)beta(3) binding to gammaC or alpha(E)C, block the alpha(v)beta(3)-mediated clot retraction, and induce the ligand-induced binding site 2 (LIBS2) epitope in alpha(v)beta(3). Neither peptide affects fibrinogen binding to alpha(IIb)beta(3). Scrambled or inverted peptides were not effective. These results suggest that the two gammaC-derived peptides directly interact with alpha(v)beta(3) and specifically block alpha(v)beta(3)-gammaC or alpha(E)C interaction. The two sequences are located next to each other in the gammaC crystal structure, although they are separate in the primary structure. Asp-199, Ser-201, Gln-350, Thr-353, Lys-356, Ala-357, and Ser-358 residues are exposed to the surface. This suggests that the two sequences are part of alpha(v)beta(3) binding sites in fibrinogen gammaC domain. We also found that tenascin C C-terminal fibrinogen-like domain specifically binds to alpha(v)beta(3). Notably, a peptide WYRNCHRVNLMGRYGDNNHSQGVNWFHWKG from this domain that includes the sequence corresponding to gammaC GVYYQGGTYSKAS(346-358) specifically binds to alpha(v)beta(3), suggesting that fibrinogen and tenascin C C-terminal domains interact with alpha(v)beta(3) in a similar manner.

The extracellular matrix can regulate vascular cell migration, proliferation, and survival: relationships to vascular disease

The extracellular matrix (ECM) of the normal artery wall is a collection of fibrous proteins and associated glycoproteins embedded in a hydrated ground substance of glycosaminoglycans and proteoglycans. These distinct molecules are organized into a highly ordered network that are closely associated with the vascular cells that produce them. In addition to providing the architectural framework for the artery wall that imparts mechanical support and viscoelasticity, the ECM can regulate the behaviour of vascular cells, including their ability to migrate, proliferate and survive injury. The composition of the ECM is different within intimal lesions of atherosclerosis, which are composed of monocytes and lymphocytes from the circulation and smooth muscle cells (SMC) that migrate from the media to the intima (Ross 1993, 1999), and these differences may contribute to the altered phenotype of vascular cells within lesions. This review will briefly outline the ECM changes observed in atherosclerosis and restenosis and the potential relationship of these changes to altered vascular cell functions.

The extracellular matrix dynamically regulates smooth muscle cell responsiveness to PDGF

Focal accumulation of smooth muscle (SMC) within the arterial intima contributes to the formation of lesions of atherosclerosis. Platelet-derived growth factor (PDGF) is a potent stimulant of SMC migration and proliferation in culture that may play a role in the accumulation of SMC in atherogenesis. SMCs normally reside in the media of the artery wall surrounded by extracellular matrix (ECM), including type I collagen. In atherogenesis, the ECM is degraded, new ECM components, such as fibronectin, are synthesized and assembled, and these alterations in ECM components are associated with changes in SMC phenotype. To model the changes in ECM in normal and diseased arteries, we have analyzed SMCs cultured on different forms of type I collagen. Our studies demonstrate that integrin-mediated signals from various forms of type I collagen lead to specific and rapid modulation of the integrin signaling complex, including cytoskeletal connections, and of the responsiveness of SMC to PDGF stimulation.

Spatiotemporal changes of fibronectin, tenascin-C, fibulin-1, and fibulin-2 in the skin during the development of chronic contact dermatitis

In order to elucidate how chronic inflammation affects the organization of the extracellular matrix in the skin, a prolonged allergic contact dermatitis was induced in a mouse by repeated application to the ear of 2,4-dinitrofluorobenzene every 3 d for 66 d. Subsequently, the spatiotemporal changes of fibronectin, tenascin-C, fibulin-1, and fibulin-2 in the skin were examined. In the acute phase of inflammation (day 3-day 12), the amount of fibronectin and tenascin-C increased markedly and were degraded, whereas the amount of fibulin-2 changed slightly. Abundant deposition of tenascin-C was observed in the connective tissue. Fibulin-1 and fibulin-2 distributed as fine fibrils. In contrast, the amounts of fibronectin and tenascin-C decreased and their degradation was suppressed in the chronic phase (day 15-day 66), but the amount of fibulin-2 increased. Tenascin-C was observed mainly at and underneath the epidermal basement membrane. In the subepidermal region, many fibulin-2-positive microfibrils were distributed. The amount and distribution of fibulin-1 did not change markedly in either phase. MMP-like enzymes of 62 kDa, probably activated MMP-2, were upregulated in the chronic phase, whereas components of 92, 85, or 67 kDa were highly induced in the acute phase. These results suggest that chronic inflammation in allergic contact dermatitis is associated with temporal changes in the expression, deposition, and degradation of inducible extracellular matrix components.

Plaque disruption and thrombosis. Potential role of inflammation and infection

Considerable data from in vitro and in vivo studies of vascular biology, together with indirect evidence from clinical trials of lipid-lowering or modifying and lifestyle or risk factor modifying interventions, provide strong support for the concept that disruption of atherosclerotic plaque and subsequent thrombosis is a key precipitant of potentially lethal, acute coronary syndromes. Certain characteristics of plaques, including the size and composition of the lipid core, the structure and composition of the fibrous cap, and the presence of a local inflammatory process, predispose the plaque to disruption. Stresses resulting from biomechanical and hemodynamic forces acting on plaques may then trigger disruption, releasing the thrombogenic contents of the lipid core. Alterations in endothelial function may also contribute to vulnerability of plaque rupture and thrombosis. Therefore, interventions aimed at decreasing plaque vulnerability to disruption--all based on the concept of plaque stabilization--may reduce the risk of acute coronary syndromes. Although not yet rigorously validated in humans, plaque stabilization may prove to be an important clinical strategy for preventing the lethal consequences of coronary atherosclerosis.