Oxidized collagen stimulates proliferation of vascular smooth muscle cells

Oxidative Stress in the Developing Rat Brain due to Production of Reactive Oxygen and Nitrogen Species

Oxidative stress after birth led us to localize reactive oxygen and nitrogen species (RONS) production in the developing rat brain. Brains were assessed a day prenatally and on postnatal days 1, 2, 4, 8, 14, 30, and 60. Oxidation of dihydroethidium detected superoxide; 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate revealed hydrogen peroxide; immunohistochemical proof of nitrotyrosine and carboxyethyllysine detected peroxynitrite formation and lipid peroxidation, respectively. Blue autofluorescence detected protein oxidation. The foetuses showed moderate RONS production, which changed cyclically during further development. The periods and sites of peak production of individual RONS differed, suggesting independent generation. On day 1, neuronal/glial RONS production decreased indicating that increased oxygen concentration after birth did not cause oxidative stress. Dramatic changes in the amount and the sites of RONS production occurred on day 4. Nitrotyrosine detection reached its maximum. Day 14 represented other vast alterations in RONS generation. Superoxide production in arachnoidal membrane reached its peak. From this day on, the internal elastic laminae of blood vessels revealed the blue autofluorescence. The adult animals produced moderate levels of superoxide; all other markers reached their minimum. There was a strong correlation between detection of nitrotyrosine and carboxyethyllysine probably caused by lipid peroxidation initiated with RONS.

Regulation of vascular smooth muscle cell phenotype in three-dimensional coculture system by Jagged1-selective Notch3 signaling

The modulation of vascular smooth muscle cell (VSMC) phenotype is an essential element to fabricate engineered conduits of clinical relevance. In vivo, owing to their close proximity, endothelial cells (ECs) play a role in VSMC phenotype switching. Although considerable progress has been made in vascular tissue engineering, significant knowledge gaps exist on how the contractile VSMC phenotype is induced at the conclusion of the tissue fabrication process. The objectives of this study were as follows: (1) to establish ligand presentation modes on transcriptional activation of VSMC-specific genes, (2) to develop a three-dimensional (3D) coculture model using human coronary artery smooth muscle cells (HCASMCs) and human coronary artery endothelial cells (HCAECs) on porous synthetic scaffolds and, (3) to investigate EC-mediated Notch signaling in 3D cultures and the induction of the HCASMC contractile phenotype. Whereas transcriptional activation of VSMC-specific genes was not induced by presenting soluble Jagged1 and Jagged1 bound to protein G beads, a direct link between HCAEC-bound Jagged1 and HCASMC differentiation genes was observed. Our 3D culture results showed that HCASMCs seeded to scaffolds and cultured for up to 16 days readily attached, infiltrated the scaffold, proliferated, and formed dense confluent layers. HCAECs, seeded on top of an HCASMC layer, formed a distinct, separate monolayer with cell-type partitioning, suggesting that HCAEC growth was contact inhibited. While we observed EC monolayer formation with 200,000 HCAECs/scaffold, seeding 400,000 HCAECs/scaffold revealed the formation of cord-like structures akin to angiogenesis. Western blot analyses showed that 3D coculture induced an upregulation of Notch3 receptor in HCASMCs and its ligand Jagged1 in HCAECs. This was accompanied by a corresponding induction of the contractile HCASMC phenotype as demonstrated by increased expression of smooth muscle-α-actin (SM-α-actin) and calponin. Knockdown of Jagged1 with siRNA showed a reduction in SM-α-actin and calponin in cocultures, identifying a link between Jagged1 and the expression of contractile proteins in 3D cocultures. We therefore conclude that the Notch3 signaling pathway is an important regulator of VSMC phenotype and could be targeted when fabricating engineered vascular tissues.

Generation of hydrogen peroxide in the developing rat heart: the role of elastin metabolism

Reports describing production of reactive oxygen species in neonatal heart are missing. As lysyl oxidase is potentially important source of H(2)O(2), we studied its role during ontogenic development of rat heart. H(2)O(2) was detected in thin sections of developing rat heart by fluorescence microscopy with the use of fluorescence probe 2'-7'-dichlorofluorescin. The experimental design comprised foetuses 21 days after conception, and then the animals sampled on the 1st, 4th, 7th, 10th, 15th, 30th and 60th day after birth. We also used 7-month-old animals as an example of ageing effects. Since the day 4 on, H(2)O(2) was produced only extracellularly up to the day 15, between days 30 and 60 intracellular production was detected as well, and in 7-month-old animals only extracellular production was observed. The specific inhibitors of lysyl oxidase almost completely quenched the H(2)O(2)-dependent fluorescence. Starting from day 7, blue autofluorescence specific to oxidized proteins developed in the vessel wall. Intracellular blue autofluorescence specific to autoxidation products developed after day 30. Chloroform extraction diminished the intracellular blue fluorescence, leaving the extracellular fluorescence intact. This confirmed the protein nature of the fluorophores. Lysyl oxidase is significant source of H(2)O(2) in the heart vessel wall during development and H(2)O(2) oxidatively modifies elastin producing protein blue autofluorescence.

The role of smooth muscle cells in vessel wall pathophysiology and reconstruction using bioactive synthetic polymers

This review summarizes recent trends in the construction of bioartificial vascular replacements, i.e. hybrid grafts containing synthetic polymeric scaffolds and cells. In these advanced replacements, vascular smooth muscle cells (VSMC) should be considered as a physiological component, although it is known that activation of the migration and proliferation of VSMC plays an important role in the onset and development of vascular diseases, and also in restenosis of currently used vascular grafts. Therefore, in novel bioartificial vascular grafts, VSMCs should be kept in quiescent mature contractile phenotype. This can be achieved by (1) appropriate physical and chemical properties of the material, such as its chemical composition, polarity, wettability, surface roughness and topography, electrical charge and conductivity, functionalization with biomolecules and mechanical properties, (2) appropriate cell culture conditions, such as composition of cell culture media and dynamic load, namely cyclic strain, and (3) the presence of a confluent, mature, semipermeable, non-thrombogenic and non-immunogenic endothelial cell (EC) barrier, covering the luminal surface of the graft and separating the VSMCs from the blood. Both VSMCs and ECs can also be differentiated from stem and progenitor cells of various sources. In the case of degradable scaffolds, the material will gradually be removed by the cells and will be replaced by their own new extracellular matrix. Thus, the material component in advanced blood vessel substitutes acts as a temporary scaffold that promotes regeneration of the damaged vascular tissue.

KLF6 Gene and early melanoma development in a collagen I-rich extracellular environment

BACKGROUND

A putative tumor suppressor gene at chromosome 10p15, which contains KLF6 and other genes, is predicted to be lost during melanoma development, and its identity is unknown. In this study, we investigated the biological roles and identity of this tumor suppressor gene.

METHODS

The human UACC 903 melanoma cell line containing introduced DNA fragments from the 10p15 region with (10E6/3, 10E6/11, and 10E6/18) and without (10ER4S.2/1) the tumor suppressor gene was used. Xenograft tumors were generated in a total of 40 mice with melanoma cell lines, and tumor size was measured. Cells were cultured on plastic or a gel of type I collagen. Viability, proliferation, and apoptosis were assessed. Expression of KLF6 protein was assessed by immunohistochemistry and immunoblot analysis. Expression of phosphorylated Erk1/2 and cyclin D1 was assessed by immunoblot analysis. Protein expression of KLF6 was inhibited with small interfering RNA (siRNA). KLF6 protein expression was assessed in 17 human nevi and human melanoma specimens from 29 patients. Statistical analyses were adjusted for multiple comparisons by use of Dunnett method. All statistical tests were two-sided.

RESULTS

Melanoma cells containing KLF6 generated smaller subcutaneous xenograft tumors with fewer proliferating cells than control cells. When grown on collagen 1, viability of cells with ectopic KLF6 expression (72%) was lower than that of control cells (100%) (group difference = -28%, 95% confidence interval = -31.3% to -25.2%, P < .001). Viability of melanoma cells with or without the KLF6 tumor suppressor gene on plastic dishes was similar. When KLF6 expression was inhibited with KLF6 siRNA, viability of cells with the tumor suppressor gene on collagen I gel increased compared with that of control cells carrying scrambled siRNA. KLF6 protein was detected in all nevi examined but not in human metastatic melanoma tissue examined. Ectopic expression of KLF6 protein in melanoma cells grown on collagen I decreased levels of phosphorylated Erk1/2 and cyclin D1 in the mitogen-activated protein kinase signaling pathway.

CONCLUSIONS

In melanoma cells, the tumor suppressor gene at 10p15 appears to be KLF6. Signaling from the collagen I-rich extracellular matrix appears to be involved in the tumor suppressive activity of KLF6 protein.

Oxidative damage to extracellular matrix and its role in human pathologies

The extracellular compartments of most biological tissues are significantly less well protected against oxidative damage than intracellular sites and there is considerable evidence for such compartments being subject to a greater oxidative stress and an altered redox balance. However, with some notable exceptions (e.g., plasma and lung lining fluid) oxidative damage within these compartments has been relatively neglected and is poorly understood. In particular information on the nature and consequences of damage to extracellular matrix is lacking despite the growing realization that changes in matrix structure can play a key role in the regulation of cellular adhesion, proliferation, migration, and cell signaling. Furthermore, the extracellular matrix is widely recognized as being a key site of cytokine and growth factor binding, and modification of matrix structure might be expected to alter such behavior. In this paper we review the potential sources of oxidative matrix damage, the changes that occur in matrix structure, and how this may affect cellular behavior. The role of such damage in the development and progression of inflammatory diseases is discussed.

The cyclin-dependent kinase inhibitors p15INK4B and p21CIP1 are critical regulators of fibrillar collagen-induced tumor cell cycle arrest

The extracellular matrix is a crucial component in determining cell fate. Fibrillar collagen in its native form inhibits cell proliferation, whereas in its monomeric form it stimulates proliferation. The observation of elevated levels of p27(KIP1) in cells plated in the presence of fibrillar collagen has led to the assumption that this kinase inhibitor was responsible for cell cycle arrest on fibrillar collagen. Here we provide evidence that p15(INK4b), rather than p27(KIP1), is the cyclin-dependent kinase inhibitor responsible for G0/G1 arrest of human melanoma cells grown on fibrillar collagen. Additionally, we demonstrate that fibrillar collagen can also arrest cells at the G2 phase, which is mediated in part by p21(CIP1). Our data, in addition to identifying cyclin-dependent kinase inhibitors important in cell cycle arrest mediated by fibrillar collagen, demonstrate the complexity of cell cycle regulation and indicate that modulating a single cyclin-dependent kinase inhibitor does not disrupt cell proliferation in the presence of fibrillar collagen.

Acute and chronic hypoxia as well as 7-day recovery from chronic hypoxia affects the distribution of pulmonary mast cells and their MMP-13 expression in rats

Chronic hypoxia results in pulmonary hypertension due to vasoconstriction and structural remodelling of peripheral lung blood vessels. We hypothesize that vascular remodelling is initiated in the walls of prealveolar pulmonary arteries by collagenolytic metalloproteinases (MMP) released from activated mast cells. Distribution of mast cells and their expression of interstitial collagenase, MMP-13, in lung conduit, small muscular, and prealveolar arteries was determined quantitatively in rats exposed for 4 and 20 days to hypoxia as well as after 7-day recovery from 20-day hypoxia (10% O2). Mast cells were identified using Toluidine Blue staining, and MMP-13 expression was detected using monoclonal antibody. After 4, but not after 20 days of hypoxia, a significant increase in the number of mast cells and their MMP-13 expression was found within walls of prealveolar arteries. In rats exposed for 20 days, MMP-13 positive mast cells accumulated within the walls of conduit arteries and subpleurally. In recovered rats, MMP-13 positive mast cells gathered at the prealveolar arterial level as well as in the walls of small muscular arteries; these mast cells stayed also in the conduit part of the pulmonary vasculature. These data support the hypothesis that perivascular pulmonary mast cells contribute to the vascular remodelling in hypoxic pulmonary hypertension in rats by releasing interstitial collagenase.

Discoidin domain receptor 2 mediates tumor cell cycle arrest induced by fibrillar collagen

During malignant invasion tumor cells establish contact with extracellular matrix proteins, including fibrillar collagen. In addition to providing a physical barrier against invasion, fibrillar collagen also restricts cell proliferation. It has been assumed that the growth regulatory activity of fibrillar collagen is the result of an indirect restrictive effect on cell spreading and cytoskeletal organization. Here we provide evidence for a direct inhibitory effect of fibrillar collagen on proliferation of human melanoma and fibrosarcoma cells that involves activation of the tyrosine kinase discoidin domain receptor 2 and is independent of effects on cell spreading. Cells plated in the presence of fibrillar collagen were growth arrested in the G0/G1 phase of the cell cycle. However treatment with the tyrosine kinase inhibitor genistein, down-regulation of discoidin domain receptor 2, or collagen deglycosylation that prevents discoidin domain receptor 2 activation allowed cells to enter the cell cycle in the presence of fibrillar collagen without a requirement for spreading and actin organization. Our data provide evidence for a novel direct mechanism by which cell contact with fibrillar collagen restricts proliferation.

Changes in mechanical properties and cellularity during long-term culture of collagen fiber ACL reconstruction scaffolds

Resorbable scaffolds for anterior cruciate ligament (ACL) reconstruction should provide temporary mechanical function then gradually breakdown while promoting matrix synthesis by local cells. Crosslinking influences collagen's mechanical properties, degradation rate, and interactions with cells. Our objective was to compare the effects of different crosslinkers on cellularity and mechanical properties during long-term (8 week) culture of collagen fiber scaffolds. Fibers were fabricated from an acid-insoluble dispersion of bovine dermal collagen and crosslinked with either ultraviolet irradiation (UV; a physical crosslinker) or 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC; a chemical crosslinker). Scaffolds consisted of 50 fibers bundled in parallel. Initial attachment of fibroblasts was similar on both scaffolds; however, from 1 to 8 weeks in culture, UV-crosslinked scaffolds had significantly more cells attached than EDC-crosslinked scaffolds. The initial breaking load (3.50 N) and stiffness (2.23 N/mm) of EDC-crosslinked scaffolds were significantly greater than those of UV-crosslinked scaffolds (2.32 N; 1.21 N/mm) and were unaffected by long-term fibroblast culture. In contrast, the load-bearing capacity of fibroblast-seeded UV-crosslinked scaffolds decreased 60% to 0.91 N after 8 weeks in culture. EDC-crosslinked scaffolds maintained strength and moderate cellularity; UV-crosslinked scaffolds, in contrast, were highly cellular, but had poor mechanical properties that decreased during culture. These in vitro results suggest that collagen fiber scaffolds crosslinked with EDC may be more suitable for ACL reconstruction than those crosslinked with UV.

Metalloproteinase inhibition by Batimastat attenuates pulmonary hypertension in chronically hypoxic rats

Chronic hypoxia induces lung vascular remodeling, which results in pulmonary hypertension. We hypothesized that a previously found increase in collagenolytic activity of matrix metalloproteinases during hypoxia promotes pulmonary vascular remodeling and hypertension. To test this hypothesis, we exposed rats to hypoxia (fraction of inspired oxygen = 0.1, 3 wk) and treated them with a metalloproteinase inhibitor, Batimastat (30 mg/kg body wt, daily ip injection). Hypoxia-induced increases in concentration of collagen breakdown products and in collagenolytic activity in pulmonary vessels were inhibited by Batimastat, attesting to the effectiveness of Batimastat administration. Batimastat markedly reduced hypoxic pulmonary hypertension: pulmonary arterial blood pressure was 32 +/- 3 mmHg in hypoxic controls, 24 +/- 1 mmHg in Batimastat-treated hypoxic rats, and 16 +/- 1 mmHg in normoxic controls. Right ventricular hypertrophy and muscularization of peripheral lung vessels were also diminished. Batimastat had no influence on systemic arterial pressure or cardiac output and was without any effect in rats kept in normoxia. We conclude that stimulation of collagenolytic activity in chronic hypoxia is a substantial causative factor in the pathogenesis of pulmonary vascular remodeling and hypertension.

Fluorine ion-implanted polystyrene improves growth and viability of vascular smooth muscle cells in culture

Vascular smooth muscle cells derived from the rat aorta were cultured on unmodified or F(+) ion-implanted polystyrene (5 x 10(12) or 5 x 10(14) ions/cm(2), energy 150 keV). In 1-day-old cultures, the cells adhered to the modified polystyrene in higher numbers and over larger contact areas. Increased resistance of the cells to trypsin-mediated detachment from the growth support indicated an improved adhesion of cells to the modified polymer at later culture intervals. The cells cultured on ion-modified polymers also were larger and had a higher total protein content. By use of immunocytochemistry, several specific protein species were increased, including the cytoskeletal alpha-actin and vimentin and the plasma membrane-associated vinculin, talin, alpha-v integrins, ICAM-1, and VCAM-1, which account for stronger cell-cell and cell-extracellular matrix adhesion. The lower number of cells found floating in the medium suggests that the spontaneous detachment of cells from the modified polystyrene was lower and that the viability of the adhered cell population was higher. As was shown by the two-parameter flow-cytometric measurements of BrdU incorporation and DNA content, as well as by (3)H-thymidine autoradiography, the cell proliferation on samples modified by the dose of 5 x 10(12) ions/cm(2) was similar to that in controls; and at the dose of 5 x 10(14) ions/cm(2), it tended to be even lower. The cells grown on the polymer implanted with the dose of 5 x 10(12) ions/cm(2) responded to a new artificially created cell-free area in a confluent cell layer by more intense migration whereas at the dose of 5 x 10(14) ions/cm(2), the migration ability of cells was similar to that on the unmodified polymer. The data revealed a higher biocompatibility of ion-implanted polystyrene with vascular smooth muscle cells in culture. There was better adhesion, differentiation, and survival, and there was neither excessive migration nor proliferation.