Plasminogen Activator Expression Correlates with Genetic Differences in Vascular Remodeling

Fibronectin-Mediated Inflammatory Signaling Through Integrin α5 in Vascular Remodeling

Background

Adhesion of vascular endothelial cells to the underlying basement membrane potently modulates endothelial cells to cells' inflammatory activation. The normal basement membrane proteins laminin and collagen IV attenuate inflammatory signaling in part through integrin α2β1. In contrast, fibronectin, the provisional matrix protein found in injured, remodeling or inflamed vessels, sensitizes endothelial cells to inflammatory stimuli through integrins α5β1and and αvβ3. A chimeric integrin in which the cytoplasmic domain of α5 is replaced with that of α2 pairs with β1 and binds fibronectin but signals like α2β1.

Methods and Results

Here, we examined mice in which integrin α5 is replaced with the α5/2 chimera, using the transverse aortic constriction and partial carotid ligation models of vessel remodeling. Following transverse aortic constriction and partial carotid ligation surgery, wild‐type mice showed increased fibronectin deposition and expression of inflammatory markers, which were strongly attenuated in a5/2 mice. α5/2 mice also showed reduced artery wall hypertrophy in the transverse aortic constriction model and diminished inward remodeling in the partial carotid ligation model. Acute atherosclerosis after partial carotid ligation in hyperlipidemic ApoE^−/− mice on a high fat diet was dramatically decreased in α5/2 mice.

Conclusions

Fibronectin and integrin α5 signaling is a key element of pathological vascular remodeling in acute models of both hypertension and disturbed flow. These results underscore the key role for integrin α5 signaling in pathological vascular remodeling associated with hypertension and atherosclerosis and support its potential as a therapeutic target.

Effect of MMP-9 gene knockout on retinal vascular form and function

Retinal degeneration from inherited gene mutation(s) is a common cause of blindness because of structural and functional alterations in photoreceptors. Accordingly, various approaches are being tested to ameliorate or even cure neuroretinal blinding conditions in susceptible patients by employing neuroprotective agents, gene therapeutics, optogenetics, regenerative therapies, and retinal prostheses. The FVB/NJ mouse strain inherently has a common Pde6b rd1 homozygous allele that renders its progeny blind by the time pups reach weaning age. To study the role matrix metalloproteinase-9 (MMP-9) in retinal structure and function, we examined a global MMP-9 knockout (KO) mouse model that has been engineered on the same FVB/NJ background to test the hypothesis whether lack of MMP-9 activity diminishes neuroretinal degenerative changes and thus helps improve the vision. We compared side-by-side various aspects of the ocular physiology in the wild-type (WT) C57BL/6J, FVB/NJ, and MMP-9 KO strains of mice. The results suggest that MMP-9 KO mice display subdued changes in their retinae as reflected by both structural and functional enhancement in the overall ocular neurophysiological parameters. Altogether, the findings appear to have clinical relevance for targeting conditions wherein MMPs and their overactivities are suspected to play dominant pathophysiological roles in advancing neurodegenerative retinal diseases.

Model-based vascular elastography improves the detection of flow-induced carotid artery remodeling in mice

Increased arterial thickness measured with ultrasound correlates with future cardiovascular events, but conventional ultrasound imaging techniques cannot distinguish between intima, media, or atherosclerotic plaque in the carotid artery. In this work, we evaluated how well vascular elastography can detect intimal changes in a mouse model of carotid remodeling. We ligated the left external and internal branches of the carotid artery of male FVB mice and performed sham operations for 2 weeks. High-resolution ultrasound imaging accurately detected lower blood velocities and low blood volume flow in the carotid arteries after ligation in FVB mice. However, ultrasound could not detect differences in the carotid wall even at 2 weeks post-surgery. The Young’s modulus was measured based on displacements of the carotid artery wall, and Young’s modulus was 2-fold greater in shams at 1 week post ligation, and 3-fold greater 2 weeks after ligation. Finally, the higher Young’s modulus was most associated with higher intimal thickness but not medial or adventitial thickness as measured by histology. In conclusion, we developed a robust ultrasound-based elastography method for early detection of intimal changes in small animals.

Autonomic dysfunction determines stress-induced cardiovascular and immune complications in mice

BACKGROUND

Clinical studies suggest that acute inflammation in patients with elevated heart rate (HR) increases morbidity and mortality. The SJL/J (SJL) inbred mouse strain is a unique genetic model that has higher HR and systemic and vascular inflammation compared with C3HeB/FeJ (C3HeB) mice. The goal of this study was to investigate the role of stress on cardiac and vascular complications between 2 strains.

METHODS AND RESULTS

Radiotelemetry was used for continuous recordings of HR and blood pressure in mice. Hemodynamic differences between mouse strains were very small without stress; however, tail-cuff training generated mild stress and significantly increased HR (≈2-fold) in SJL compared with C3HeB mice. Circulating proinflammatory monocytes (CD11b(+)Ly6C(H) (i)) significantly increased in SJL mice but not in C3HeB mice after stress. Presence of Ly6C(+) cells in injured carotids was elevated only in SJL mice after stress; however, a transfer of bone marrow cells from SJL/C3HeB to C3HeB/SJL chimeras had no effect on HR or vascular inflammation following stress. Arterial inflammation (VCAM-1(+)) was greater in SJL inbred mice or SJL recipient chimeras, even without stress or injury. HR variability was reduced in SJL mice compared with C3HeB mice.

CONCLUSIONS

We found that impaired parasympathetic activity is central for stress-induced elevation of HR and systemic and vascular inflammation; however, immune cells from stress-susceptible mice had no effect on HR or vascular inflammation in stress-protected mice.

Endarteritis obliterans in the pathogenesis of Buerger's disease from the pathological and immunohistochemical points of view

Buerger's disease (thromboangiitis obliterans) is considered to be a nonatherosclerotic, inflammatory, and vaso-occlusive disease, although the details of the mechanisms of pathogenesis remain unknown. The occurrence of the disease is strongly related to tobacco abuse and its progression is closely linked to continued smoking. The purpose of this review article is to demonstrate the pathological characteristics of arteries affected with Buerger's disease from a possible immunoreactive point of view. In addition, we present the mechanisms for preserving the architecture of the arterial wall in affected vasculatures. Thereafter, we discuss the possibility that the pathogenesis of Buerger's disease is a type of endarteritis obliterans, deeply connected to the Notch pathway, distinct from arteriosclerosis obliterans and other vasculitides.

The PLAU P141L single nucleotide polymorphism is associated with collateral circulation in patients with coronary artery disease

INTRODUCTION AND OBJECTIVES

Urokinase-type plasminogen activator, which is encoded by the PLAU gene, plays a prominent role during collateral arterial growth. We investigated whether the PLAU P141L (C > T) polymorphism, which causes a mutation in the kringle domain of the protein, is associated with coronary collateral circulation in a cohort of 676 patients with coronary artery disease.

METHODS

The polymorphism was genotyped in blood samples using a TaqMan-based genotyping assay, and collateral circulation was assessed by the Rentrop method. Multivariate logistic regression models adjusted by clinically relevant variables to estimate odds ratios were used to examine associations of PLAU P141L allelic variants and genotypes with collateral circulation.

RESULTS

Patients with poor collateral circulation (Rentrop 0-1; n = 547) showed a higher frequency of the TT genotype than those with good collateral circulation (Rentrop 2-3; n = 129; P = .020). The T allele variant was also more common in patients with poor collateral circulation (P = .006). The odds ratio of having poorly developed collaterals in patients bearing the T allele (adjusted for clinically relevant variables) was statistically significant under the dominant model (odds ratio = 1.83 [95% confidence interval, 1.16-2.90]; P = .010) and the additive model (odds ratio = 1.73 [95% confidence interval, 1.14-2.62]; P = .009).

CONCLUSIONS

An association was found between coronary collateral circulation and the PLAU P141L polymorphism. Patients with the 141L variant are at greater risk of developing poor coronary collateral circulation.

Identification of a genetic locus on chromosome 11 that regulates leukocyte infiltration in mouse carotid artery

OBJECTIVE

We demonstrated that inflammatory cells and intima-media thickening are increased in carotids exposed to low-blood flow in the SJL/J (SJL) strain compared with other mouse strains. We hypothesized that the extent of inflammation associated with intima-media thickening is a genetically regulated trait.

APPROACH AND RESULTS

We performed a whole genome approach to measure leukocyte infiltration in the carotid intima as a quantitative trait in a genetic cross between C3HeB/FeJ (C3H/F) and SJL mice. Immunostaining for CD45(+) (a pan-specific leukocyte marker) was performed on carotids from C3H/F, SJL, F1, and N2 progeny to measure leukocyte infiltration. We identified a nearly significant quantitative trait locus for CD45(+) on chromosome (chr) 11 (17 cM, LOD=2.3; significance was considered at threshold P=0.05). Interval mapping showed that the CD45(+) locus on chr 11 accounted for 8% of the variation in the logarithm of odds backcross. Importantly, the CD45(+) locus colocalized with the intima-modifier 2 (Im2) locus, which controls 17% of intima variation. We created 2 Im2 congenic lines of mice (C3H/F.SJL.11.1 and C3H/F.SJL.11.2) to better understand the regulation of intima-media thickening by the chr 11 locus. The C3H/F.SJL.11.1 congenic mouse showed ≈30% of the SJL trait, confirming that CD45(+) cell infiltration contributed to the intima trait.

CONCLUSIONS

We discovered a novel locus on chr 11 that controls leukocyte infiltration in the carotid. Importantly, this locus overlaps with our previously published Im2 locus on chr 11. Our study reveals a potential mechanistic relationship between leukocyte infiltration and intima-media thickening in response to decreased blood flow.

Fibronectin is an important regulator of flow-induced vascular remodeling

OBJECTIVE

Fibronectin is an important regulator of cell migration, differentiation, growth, and survival. Our data show that fibronectin also plays an important role in regulating extracellular matrix (ECM) remodeling. Fibronectin circulates in the plasma and is also deposited into the ECM by a cell dependent process. To determine whether fibronectin affects vascular remodeling in vivo, we asked whether the fibronectin polymerization inhibitor, pUR4, inhibits intima-media thickening, and prevents excess ECM deposition in arteries using a mouse model of vascular remodeling.

METHODS AND RESULTS

To induce vascular remodeling, partial ligation of the left external and internal carotid arteries was performed in mice. pUR4 and the control peptide were applied periadventitially in pluronic gel immediately after surgery. Animals were euthanized 7 or 14 days after surgery. Morphometric analysis demonstrated that the pUR4 fibronectin inhibitor reduced carotid intima (63%), media (27%), and adventitial thickening (40%) compared to the control peptide (III-11C). Treatment with pUR4 also resulted in a dramatic decrease in leukocyte infiltration into the vessel wall (80%), decreased ICAM-1 and VCAM-1 levels, inhibited cell proliferation (60% to 70%), and reduced fibronectin and collagen I accumulation in the vessel wall. In addition, the fibronectin inhibitor prevented SMC phenotypic modulation, as evidenced by the maintenance of smooth muscle (SM) alpha-actin and SM myosin heavy chain levels in medial cells.

CONCLUSIONS

These data are the first to demonstrate that fibronectin plays an important role in regulating the vascular remodeling response. Collectively, these data suggest a therapeutic benefit of periadventitial pUR4 in reducing pathological vascular remodeling.

Regulation of arterial remodeling and angiogenesis by urokinase-type plasminogen activatorThis article is one of a selection of papers from the NATO Advanced Research Workshop on Translational Knowledge for Heart Health (published in part 2 of a 2-part Special Issue)

A wide variety of disorders are associated with an imbalance in the plasminogen activator system, including inflammatory diseases, atherosclerosis, intimal hyperplasia, the response mechanism to vascular injury, and restenosis. Urokinase-type plasminogen activator (uPA) is a multifunctional protein that in addition to its fibrinolytic and matrix degradation capabilities also affects growth factor bioavailability, cytokine modulation, receptor shedding, cell migration and proliferation, phenotypic modulation, protein expression, and cascade activation of proteases, inhibitors, receptors, and modulators. uPA is the crucial protein for neointimal growth and vascular remodeling. Moreover, it was recently shown to be implicated in the stimulation of angiogenesis, which makes it a promising multipurpose therapeutic target. This review is focused on the mechanisms by which uPA can regulate arterial remodeling, angiogenesis, and cell migration and proliferation after arterial injury and the means by which it modulates gene expression in vascular cells. The role of domain specificity of urokinase in these processes is also discussed.

Genetic determinants of vascular remodelling

Vascular remodelling is an important physiological mechanism that occurs as a result of changes in hemodynamics, and is a pathological process that plays a major role in the clinical manifestations of cardiovascular diseases. Using a mouse model, it was recently established that vascular remodelling is partially based on ligation of the carotid. In this model, low flow was associated with intima media thickening (IMT). IMT is a major manifestation of atherosclerosis of the carotid artery, and it is an important predictor of cardiovascular events. Carotid IMT has a strong genetic component. It was hypothesized that there would be genetically determined differences in outward remodelling and IMT induced by carotid flow alterations. Vascular remodelling among five inbred strains of mice were compared. Despite similar changes in flow in the left carotid among the strains, dramatic differences in remodelling of the partially ligated left carotid relative to control were observed. IMT correlated significantly with heart rate, outward remodelling and changes in plasminogen activator expression, cell proliferation and apoptosis. There were significant strain-dependent differences in the remodelling index (measured as the ratio of vessel area to IMT), which suggest fundamental alterations in sensing or transducing hemodynamic signals among strains. This model should be useful to identify and characterize the role of genes that mediate vascular remodelling.

Mechanisms of kringle fragment of urokinase-induced vascular smooth muscle cell migration

BACKGROUND

Urokinase plasminogen activator (uPA) is involved in vessel remodeling and mediates smooth muscle cell migration. Migration in response to uPA is dependent on both the growth factor binding domain at the aminoterminal end and the kringle (K) domain of the molecule. uPA is readily degraded in vivo into these constitutive domains. The aim of this study was to examine cell signaling during the migration of smooth muscle cell in response to the kringle domain of urokinase.

MATERIALS AND METHODS

Murine arterial smooth muscle cells were cultured in vitro. Migration assays were performed in the presence of K with and without the plasmin inhibitors (aprotinin and -aminocaproic acid), the Galphai inhibitor Pertussis toxin, the MMP inhibitor (GM6001), the PI3-K inhibitors, Wortmannin and LY294002, and the MAPK inhibitors PD98089 (MEK1 inhibitor) and SB203580 (p38(MAPK) inhibitor). Western blotting was performed for ERK 1/2 and p38(MAPK) phosphorylation after stimulation with K in the presence and absence of the inhibitors. Statistics were analyzed by one-way ANOVA (n = 6).

RESULTS

The kringle domain (K) induced a plasmin-independent, MMP-dependent increase in cell migration (2-fold, P < 0.05) compared to control. This migratory response to K was Galphai mediated and dependent on both ERK 1/2 and p38(MAPK) activation. K induced time-dependent increases in the phosphorylation of ERK 1/2 (3-fold, P < 0.05) and p38(MAPK) (3-fold, P < 0.05). Activation of p38(MAPK) and ERK 1/2 was completely inhibited by the PI3-K inhibitors. We explored a potential role for the epidermal growth factor receptor (EGFR). K induced EGFR phosphorylation and the presence of AG1478, the EGFR inhibitor, inhibited both cell migration and akt activation in response to K.

CONCLUSION

Kringle domain of uPA induces smooth muscle cell migration through a G-protein-coupled PI3-K-dependent process involving both ERK 1/2 and p38(MAPK) and is mediated in part through EGFR. Defining the differences in response to key molecular domains of uPA is vital to understand its role in vessel remodeling.

Vascular remodeling: hemodynamic and biochemical mechanisms underlying Glagov's phenomenon

An important concept for vascular remodeling, termed Glagov's phenomenon, is that arteries remodel to maintain constant flow despite increases in atherosclerotic lesion mass. Although Glagov's phenomenon was originally described only for the case of arterial remodeling in response to growth of atherosclerotic plaques, experimental and clinical observations indicate that blood flow properties influence remodeling after angioplasty, hypertension, and flow diversion as well as atherosclerotic plaque progression. This review attempts to define Glagov's observation in terms of the physical parameters of blood in conduit arteries that must determine the remodeling response. Next we review experiments that have begun to identify specific molecules that influence vascular remodeling and therefore may serve as mediators for the phenomena. More comprehensive analyses of the specific molecular pathways in the vessels that determine constant flow may provide new therapeutic approaches to regulate vascular remodeling.

Axl, a receptor tyrosine kinase, mediates flow-induced vascular remodeling

Intima-media thickening (IMT) in response to hemodynamic stress is a physiological process that requires coordinated signaling among endothelial, inflammatory, and vascular smooth muscle cells (VSMC). Axl, a receptor tyrosine kinase, whose ligand is Gas6, is highly induced in VSMC after carotid injury. Because Axl regulates cell migration, phagocytosis and apoptosis, we hypothesized that Axl would play a role in IMT. Vascular remodeling in mice deficient in Axl (Axl(-/-)) and wild-type littermates (Axl(+/+)) was induced by ligation of the left carotid artery (LCA) branches maintaining flow via the left occipital artery. Both genotypes had similar baseline hemodynamic parameters and carotid artery structure. Partial ligation altered blood flow equally in both genotypes: increased by 60% in the right carotid artery (RCA) and decreased by 80% in the LCA. There were no significant differences in RCA remodeling between genotypes. However, in the LCA Axl(-/-) developed significantly smaller intima+media compared with Axl(+/+) (31+/-4 versus 42+/-6x10(-6) microm3, respectively). Quantitative immunohistochemistry of Axl(-/-) LCA showed increased apoptosis compared with Axl(+/+) (5-fold). As expected, p-Akt was decreased in Axl(-/-), whereas there was no difference in Gas6 expression. Cell composition also changed significantly, with increases in CD45+ cells and decreases in VSMC, macrophages, and neutrophils in Axl(-/-) compared with Axl(+/+). These data demonstrate an important role for Axl in flow-dependent remodeling by regulating vascular apoptosis and vascular inflammation.

Age-related increase in wall stress of the human abdominal aorta: an in vivo study

BACKGROUND

The regulation of wall stress in the abdominal aorta (AA) of humans might be of specific interest, because the AA is the most common site for aneurysm formation in which wall stress seems to be an important pathophysiological factor. We studied the age-related changes in wall stress of the AA in healthy subjects, with the common carotid artery (CCA) as a comparison.

METHODS

A total of 111 healthy subjects were examined with B-mode ultrasonography to determine the lumen diameter and intima-media thickness (IMT) in the AA and the CCA.

RESULTS

Aortic IMT was affected by age in men and by both age and lumen diameter in women. Carotid IMT was affected by age and pulse pressure in both men and women. Wall stress was higher in the AA than in the CCA (P < .001), and men had higher wall stress than women in both the AA (P < .001) and the CCA (P < .05). Furthermore, wall stress was constant during life in the CCA of men and women and in the AA of women. In the male aorta, however, wall stress increased with age (P < 0.01).

CONCLUSIONS

Arterial diameters increase with age, and a compensatory thickening of the arterial wall prevents the circumferential wall stress from increasing. However, this compensatory response is insufficient in the male AA and results in an increase in stress with age. These findings might explain the propensity for aneurysms to develop in the AA of men.

Urokinase-induced smooth muscle cell migration requires PI3-K and Akt activation

OBJECTIVE

To examine the role of the phospho-inositol-3'-kinase (PI3-K)-akt signaling axis during smooth muscle cell (SMC) migration in response to the aminoterminal fragment of urokinase (ATF).

BACKGROUND

Urokinase (uPA) is involved in vessel remodeling and mediates smooth muscle cell migration. Migration in response to urokinase is dependent on ATF. The role of PI3-K/akt signaling during migration in response to the uPA fragments is not understood.

METHODS

Murine arterial SMCs were cultured in vitro. Linear wound and Boyden microchemotaxis assays of migration were performed in the presence of ATF with and without the PI3-K inhibitors (Wortmannin, Wn [10 nm] and LY294002, LY [10 microm]) and an akt inhibitor (aktI, [10 microm]). Western blotting was performed for akt, ERK1/2, and GSK3beta phosphorylation after cells were stimulated with ATF in the presence and absence of the inhibitors. Statistics were analyzed by one-way ANOVA.

RESULTS

Both PI3-K and akt inhibitors blocked the migratory response to ATF in both assays. ATF induced time-dependent increases in akt phosphorylation at both S472 and T308 sites and ERK1/2 phosphorylation. Activation of akt and ERK1/2 was inhibited by Wn and LY. Manumycin A, a ras inhibitor, did not inhibit activation of akt but did inhibit ERK1/2 activation. Activation of akt and the dephosphorylation of its downstream kinase GSK3beta were inhibited by the akt inhibitor. Direct inhibition of akt did not influence ERK1/2 activation and inhibition of ERK1/2 did not influence akt activation.

CONCLUSION

ATF mediated migration is PI3-K dependent and activates two separate pathways: ERK1/2 and akt. ATF induces akt phosphorylation through a PI3K-mediated but ras-independent mechanism while both ras and PI3K are required for ERK1/2 activation. Defining key signaling pathways is vital to regulate vessel remodeling.