Upregulatory Expression of Furin and Transforming Growth Factor-β by Fluid Shear Stress in Vascular Endothelial Cells

Mechanical regulation of the Notch signaling pathway

The mechanical regulation of Notch signaling is an emerging area of interest in cell biology. Notch is essential in many physiological processes in which mechanical stress plays an important role. This review provides an overview of the mechanoregulation of Notch signaling in multiple steps of the pathway. First, we discuss the current knowledge on the direct mechanoregulation of Notch receptor maturation and localization to the membrane and the effect of mechanical stress on the Notch components. Next, we explore how ligand-receptor interactions and membrane dynamics are possible subjects to mechano-regulation, emphasizing the role of cytoskeletal interactions, membrane stiffness, and endocytic complex formation. We further delve into the necessity of tension generation for negative regulatory region (NRR) domain unfolding, facilitated by ligand endocytosis and other microforces. Additionally, we examine the indirect mechano-regulation of S2 and S3 cleavages. Finally, we discuss the mechanoregulation of the Notch intracellular domain (NICD) trafficking and nuclear entry and the impact of mechanical stress on heterochromatin dynamics and nuclear NICD interactions. This review aims to draw attention to the intricate interplay between mechanical cues and Notch signaling regulation, offering novel insights into the multifaceted nature of cellular mechanobiology.

An Overview of the Role of Furin in Type 2 Diabetes

Post-translational modifications (PTMs) play important roles in regulating several human diseases, like cancer, neurodegenerative disorders, and metabolic disorders. Investigating PTMs' contribution to protein functions is critical for modern biology and medicine. Proprotein convertases (PCs) are irreversible post-translational modifiers that have been extensively studied and are considered as key targets for novel therapeutics. They cleave proteins at specific sites causing conformational changes affecting their functions. Furin is considered as a PC model in regulating growth factors and is involved in regulating many pro-proteins. The mammalian target of the rapamycin (mTOR) signaling pathway is another key player in regulating cellular processes and its dysregulation is linked to several diseases including type 2 diabetes (T2D). The role of furin in the context of diabetes has been rarely explored and is currently lacking. Moreover, furin variants have altered activity that could have implications on overall health. In this review, we aim to highlight the role of furin in T2D in relation to mTOR signaling. We will also address furin genetic variants and their potential effect on T2D and β-cell functions. Understanding the role of furin in prediabetes and dissecting it from other confounding factors like obesity is crucial for future therapeutic interventions in metabolic disorders.

Ectodomain shedding of proteins important for SARS-CoV-2 pathogenesis in plasma of tobacco cigarette smokers compared to electronic cigarette vapers: a cross-sectional study

The impact of tobacco cigarette (TCIG) smoking and electronic cigarette (ECIG) vaping on the risk of development of severe COVID-19 is controversial. The present study investigated levels of proteins important for SARS-CoV-2 pathogenesis present in plasma because of ectodomain shedding in smokers, ECIG vapers, and non-smokers (NSs). Protein levels of soluble angiotensin-converting enzyme 2 (ACE2), angiotensin (Ang) II (the ligand of ACE2), Ang 1-7 (the main peptide generated from Ang II by ACE2 activity), furin (a protease that increases the affinity of the SARS-CoV-2 spike protein for ACE2), and products of ADAM17 shedding activity that predict morbidity in COVID-19 (IL-6/IL-6R alpha (IL-6/IL-6Rα) complex, soluble CD163 (sCD163), L-selectin) were determined in plasma from 45 NSs, 30 ECIG vapers, and 29 TCIG smokers using ELISA. Baseline characteristics of study participants did not differ among groups. TCIG smokers had increased sCD163, L-selectin compared to NSs and ECIG vapers (p < 0.001 for all comparisons). ECIG vapers had higher plasma furin compared to both NSs (p < 0.001) and TCIG smokers (p < 0.05). ECIG vaping and TCIG smoking did not impact plasma ACE2, Ang 1-7, Ang II, and IL-6 levels compared to NSs (p > 0.1 for all comparisons). Further studies are needed to determine if increased furin activity and ADAM17 shedding activity that is associated with increased plasma levels of sCD163 and L-selectin in healthy young TCIG smokers may contribute to the future development of severe COVID-19 and cardiovascular complications of post-acute COVID-19 syndrome.

Effect of FURIN SNP rs17514846 on coronary atherosclerosis in human cardiac specimens: An autopsy study of 106 cases

BACKGROUND

Coronary artery disease (CAD), including coronary atherosclerosis (CAS), is one of the most common causes of death. The FURIN SNP rs17514846 is assumed to be a risk factor for CAD. We evaluated this relationship using autopsy specimens and autopsy data, such as the histopathological degree of CAS.

MATERIALS AND METHODS

A total of 106 samples were genotyped from obtained blood samples. Myocardial and coronary arterial FURIN levels were quantified by ELISA. The degree of CAS was classified histopathologically according to the Stary classification, and the localization of FURIN was examined by immunostaining. The obtained data were analyzed statistically.

RESULTS

FURIN expression was widely observed in the myocardium, vascular smooth muscle cells, endothelial cells, adipocytes, and macrophages. FURIN level in the myocardium of cases with the AA genotype at the FURIN SNP rs17514846 was higher than that in CC cases. Additionally, FURIN levels in both coronary arteries and myocardium were higher at the early stage of CAS than at the late stage microscopically.

CONCLUSION

Our study suggested that the A allele of rs17514846 is associated with higher FURIN level in the heart and that FURIN exhibits a higher level in the early stage of CAS. These findings deepen our understanding of the mechanism of CAS.

Mechano-regulated cell-cell signaling in the context of cardiovascular tissue engineering

Cardiovascular tissue engineering (CVTE) aims to create living tissues, with the ability to grow and remodel, as replacements for diseased blood vessels and heart valves. Despite promising results, the (long-term) functionality of these engineered tissues still needs improvement to reach broad clinical application. The functionality of native tissues is ensured by their specific mechanical properties directly arising from tissue organization. We therefore hypothesize that establishing a native-like tissue organization is vital to overcome the limitations of current CVTE approaches. To achieve this aim, a better understanding of the growth and remodeling (G&R) mechanisms of cardiovascular tissues is necessary. Cells are the main mediators of tissue G&R, and their behavior is strongly influenced by both mechanical stimuli and cell-cell signaling. An increasing number of signaling pathways has also been identified as mechanosensitive. As such, they may have a key underlying role in regulating the G&R of tissues in response to mechanical stimuli. A more detailed understanding of mechano-regulated cell-cell signaling may thus be crucial to advance CVTE, as it could inspire new methods to control tissue G&R and improve the organization and functionality of engineered tissues, thereby accelerating clinical translation. In this review, we discuss the organization and biomechanics of native cardiovascular tissues; recent CVTE studies emphasizing the obtained engineered tissue organization; and the interplay between mechanical stimuli, cell behavior, and cell-cell signaling. In addition, we review past contributions of computational models in understanding and predicting mechano-regulated tissue G&R and cell-cell signaling to highlight their potential role in future CVTE strategies.

Fluid shear stress and endothelial cells synergistically promote osteogenesis of mesenchymal stem cells via integrin β1-FAK-ERK1/2 pathway

Prevascularization and mechanical stimulation have been reported as effective methods for the construction of functional bone tissue. However, their combined effects on osteogenic differentiation and its mechanism remain to be explored. Here, the effects of fluid shear stress (FSS) on osteogenic differentiation of rat bone-marrow-derived mesenchymal stem cells (BMSCs) when cocultured with human umbilical vein endothelial cells (HUVECs) were investigated, and underlying signaling mechanisms were further explored. FSS stimulation for 1-4 h/day increased alkaline phosphatase (ALP) activity and calcium deposition in coculture systems and promoted the proliferation of cocultured cells. FSS stimulation for 2 h/day was selected as the optimized protocol according to osteogenesis in the coculture. In this situation, the mRNA levels of ALP, runt-related transcriptional factor 2 (Runx2) and osteocalcin (OCN), and protein levels of OCN and osteopontin (OPN) in BMSCs were upregulated. Furthermore, FSS and coculture with HUVECs synergistically increased integrin β1 expression in BMSCs and further activated focal adhesion kinases (FAKs) and downstream extracellular signal-related kinase (ERK), leading to the enhancement of Runx2 expression. Blocking the phosphorylation of FAK abrogated FSS-induced ERK phosphorylation and inhibited osteogenesis of cocultured BMSCs. These results revealed that FSS and coculture with HUVECs synergistically promotes the osteogenesis of BMSCs, which was mediated by the integrin β1-FAK-ERK signaling pathway.

It Takes Two to Tango: Endothelial TGFβ/BMP Signaling Crosstalk with Mechanobiology

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-beta (TGFβ) superfamily of cytokines. While some ligand members are potent inducers of angiogenesis, others promote vascular homeostasis. However, the precise understanding of the molecular mechanisms underlying these functions is still a growing research field. In bone, the tissue in which BMPs were first discovered, crosstalk of TGFβ/BMP signaling with mechanobiology is well understood. Likewise, the endothelium represents a tissue that is constantly exposed to multiple mechanical triggers, such as wall shear stress, elicited by blood flow or strain, and tension from the surrounding cells and to the extracellular matrix. To integrate mechanical stimuli, the cytoskeleton plays a pivotal role in the transduction of these forces in endothelial cells. Importantly, mechanical forces integrate on several levels of the TGFβ/BMP pathway, such as receptors and SMADs, but also global cell-architecture and nuclear chromatin re-organization. Here, we summarize the current literature on crosstalk mechanisms between biochemical cues elicited by TGFβ/BMP growth factors and mechanical cues, as shear stress or matrix stiffness that collectively orchestrate endothelial function. We focus on the different subcellular compartments in which the forces are sensed and integrated into the TGFβ/BMP growth factor signaling.

Recruitment and maturation of the coronary collateral circulation: Current understanding and perspectives in arteriogenesis

The coronary collateral circulation is a rich anastomotic network of primitive vessels which have the ability to augment in size and function through the process of arteriogenesis. In this review, we evaluate the current understandings of the molecular and cellular mechanisms by which this process occurs, specifically focussing on elevated fluid shear stress (FSS), inflammation, the redox state and gene expression along with the integrative, parallel and simultaneous process by which this occurs. The initiating step of arteriogenesis occurs following occlusion of an epicardial coronary artery, with an increase in FSS detected by mechanoreceptors within the endothelium. This must occur within a 'redox window' where an equilibrium of oxidative and reductive factors are present. These factors initially result in an inflammatory milieu, mediated by neutrophils as well as lymphocytes, with resultant activation of a number of downstream molecular pathways resulting in increased expression of proteins involved in monocyte attraction and adherence; namely vascular cell adhesion molecule 1 (VCAM-1), monocyte chemoattractant protein 1 (MCP-1) and transforming growth factor beta (TGF-β). Once monocytes and other inflammatory cells adhere to the endothelium they enter the extracellular matrix and differentiate into macrophages in an effort to create a favourable environment for vessel growth and development. Activated macrophages secrete inflammatory cytokines such as tumour necrosis factor-α (TNF-α), growth factors such as fibroblast growth factor-2 (FGF-2) and matrix metalloproteinases. Finally, vascular smooth muscle cells proliferate and switch to a contractile phenotype, resulting in an increased diameter and functionality of the collateral vessel, thereby allowing improved perfusion of the distal myocardium subtended by the occluded vessel. This simultaneously reduces FSS within the collateral vessel, inhibiting further vessel growth.

TGFβ (Transforming Growth Factor-Beta)-Activated Kinase 1 Regulates Arteriovenous Fistula Maturation

OBJECTIVE

Arteriovenous fistulae (AVF) are the optimal conduit for hemodialysis access but have high rates of primary maturation failure. Successful AVF maturation requires wall thickening with deposition of ECM (extracellular matrix) including collagen and fibronectin, as well as lumen dilation. TAK1 (TGFβ [transforming growth factor-beta]-activated kinase 1) is a mediator of noncanonical TGFβ signaling and plays crucial roles in regulation of ECM production and deposition; therefore, we hypothesized that TAK1 regulates wall thickening and lumen dilation during AVF maturation. Approach and Results: In both human and mouse AVF, immunoreactivity of TAK1, JNK (c-Jun N-terminal kinase), p38, collagen 1, and fibronectin was significantly increased compared with control veins. Manipulation of TAK1 in vivo altered AVF wall thickening and luminal diameter; reduced TAK1 function was associated with reduced thickness and smaller diameter, whereas activation of TAK1 function was associated with increased thickness and larger diameter. Arterial magnitudes of laminar shear stress (20 dyne/cm²) activated noncanonical TGFβ signaling including TAK1 phosphorylation in mouse endothelial cells.

CONCLUSIONS

TAK1 is increased in AVF, and TAK1 manipulation in a mouse AVF model regulates AVF thickness and diameter. Targeting noncanonical TGFβ signaling such as TAK1 might be a novel therapeutic approach to improve AVF maturation.

Brain-derived neurotrophic factor is a full endothelium-derived factor in rats

Most of what is known on vascular brain-derived neurotrophic factor (BDNF) derived from experiments on cultured endothelial cells. Therefore, the present study compared BDNF levels/localization in artery (aorta) vs vein (vena cava) from a same territory in rats either sedentary (SED) or exposed to treadmill exercise (EX) as a mean to stimulate endogenous endothelial nitric oxide (NO) production. In SED rats, for both artery and vein, BDNF was strongly expressed by endothelial cells, while only a faint and scattered expression was observed throughout the media. Endothelial and muscular BDNF staining as vascular BDNF protein levels were however higher in artery than in vein, while BDNF mRNA levels did not differ between vessels. Irrespective of the vessels, EX resulted in an increase (+50%) in BDNF protein levels with no change in BDNF mRNA levels, a selective endothelial BDNF overexpression (x4) and an increase in vascular levels of tropomyosin related kinase B receptors (TrkB) phosphorylated at tyrosine 816 (p-TrkB^Tyr816). Endothelial expressions of BDNF and p-TrkB^Tyr816 were positively associated when SED and EX rats were simultaneously examined. The results incite to consider endothelial BDNF as a full and NO-dependent endothelium-derived factor that exerts autocrine effects.

Furin inhibition prevents hypoxic and TGFβ-mediated blood-brain barrier disruption

Hypoxic blood-brain barrier (BBB) dysfunction is a common feature of CNS diseases however mechanisms underlying barrier disturbance are still largely unknown. This study investigated the role of transforming growth factor β (TGFβ), a cytokine known to induce expression of the proprotein convertase Furin, in hypoxia-mediated barrier compromise. We show that exposure of brain endothelial cells (ECs) to hypoxia (1% O₂) rapidly stimulates their migration. Additional exogenous TGFβ (0.4 nM) exposure potentiated this effect and increased Furin expression in a TGFβ type I receptor activin-like kinase 5 (ALK5) - dependent manner (prevented by 10 μM SB431542). Furin inhibition prevented hypoxia-induced EC migration and blocked TGFβ-induced potentiation suggesting existence of a feedback loop. TGFβ and Furin were also critical for hypoxia-induced BBB dysfunction. TGFβ treatment aggravated hypoxia-induced BBB permeability but ALK5 or Furin blockade reversed injury-induced permeability changes. Thus during insult Furin compromises endothelial integrity by mediating the effects of TGFβ. Targeting the Furin or ALK5 pathway may offer novel therapeutic strategies for improving BBB stability and CNS function during disease.

TGF-β Signaling in Control of Cardiovascular Function

Genetic studies in animals and humans indicate that gene mutations that functionally perturb transforming growth factor β (TGF-β) signaling are linked to specific hereditary vascular syndromes, including Osler-Rendu-Weber disease or hereditary hemorrhagic telangiectasia and Marfan syndrome. Disturbed TGF-β signaling can also cause nonhereditary disorders like atherosclerosis and cardiac fibrosis. Accordingly, cell culture studies using endothelial cells or smooth muscle cells (SMCs), cultured alone or together in two- or three-dimensional cell culture assays, on plastic or embedded in matrix, have shown that TGF-β has a pivotal effect on endothelial and SMC proliferation, differentiation, migration, tube formation, and sprouting. Moreover, TGF-β can stimulate endothelial-to-mesenchymal transition, a process shown to be of key importance in heart valve cushion formation and in various pathological vascular processes. Here, we discuss the roles of TGF-β in vasculogenesis, angiogenesis, and lymphangiogenesis and the deregulation of TGF-β signaling in cardiovascular diseases.

Collateral Growth in the Peripheral Circulation: A Review

Arterial occlusive diseases are a major cause of morbidity and death in the United States. The enlargement of pre-existing vessels, which bypass the site of arterial occlusion, provide a natural way for the body to compensate for such obstructions. Individuals differ in their capacity to develop collateral vessels. In recent years much attention has been focused upon therapy to promote collateral development, primarily using individual growth factors. Such studies have had mixed results. Persistent controversies exist regarding the initiating stimuli, the processes involved in enlargement, the specific vessels that should be targeted, and the most appropriate terminology. Consequently, it is now recognized that more research is needed to extend our knowledge of the complex process of collateral growth. This basic science review addresses five questions essential in understanding current problems in collateral growth research and the development of therapeutic interventions.

Aerobic training and l-arginine supplementation promotes rat heart and hindleg muscles arteriogenesis after myocardial infarction

Arteriogenesis is a main defense mechanism to prevent heart and local tissues dysfunction in occlusive artery disease. TGF-β and angiostatin have a pivotal role in arteriogenesis. We tested the hypothesis that aerobic training and l-arginine supplementation promotes cardiac and skeletal muscles arteriogenesis after myocardial infarction (MI) parallel to upregulation of TGF-β and downregulation of angiostatin. For this purpose, 4 weeks after LAD occlusion, 50 male Wistar rats were randomly distributed into five groups: (1) sham surgery without MI (sham, n = 10), (2) control-MI (Con-MI, n = 10), (3) l-arginine-MI (La-MI, n = 10), (4) exercise training-MI (Ex-MI, n = 10), and (5) exercise and l-arginine-MI (Ex + La-MI). Exercise training groups running on a treadmill for 10 weeks with moderate intensity. Rats in the l-arginine-treated groups drank water containing 4 % l-arginine. Arteriolar density with different diameters (11-25, 26-50, 51-75, and 76-150 μm), TGF-β, and angiostatin gene expression were measured in cardiac (area at risk) and skeletal (soleus and gastrocnemius) muscles. Smaller arterioles decreased in cardiac after MI. Aerobic training and l-arginine increased the number of cardiac arterioles with 11-25 and 26-50 μm diameters parallel to TGF-β overexpression. In gastrocnemius muscle, the number of arterioles/mm(2) was only increased in the 11 to 25 μm in response to training with and without l-arginine parallel to angiostatin downregulation. Soleus arteriolar density with different size was not different between experimental groups. Results showed that 10 weeks aerobic exercise training and l-arginine supplementation promotes arteriogenesis of heart and gastrocnemius muscles parallel to overexpression of TGF-β and downregulation of angiostatin in MI rats.

Silencing p75(NTR) prevents proNGF-induced endothelial cell death and development of acellular capillaries in rat retina

Accumulation of the nerve growth factor precursor (proNGF) and its receptor p75(NTR) have been associated with several neurodegenerative diseases in both brain and retina. However, whether proNGF contributes to microvascular degeneration remain unexplored. This study seeks to investigate the mechanism by which proNGF/p75(NTR) induce endothelial cell (EC) death and development of acellular capillaries, a surrogate marker of retinal ischemia. Stable overexpression of the cleavage-resistant proNGF and molecular silencing of p75(NTR) were utilized in human retinal EC and rat retinas in vivo. Stable overexpression of proNGF decreased NGF levels and induced retinal vascular cell death evident by 1.9-fold increase in acellular capillaries and activation of JNK and cleaved-PARP that were mitigated by p75(NTR)shRNA. In vitro, overexpression of proNGF did not alter TNF-α level, reduced NGF, however induced EC apoptosis evident by activation of JNK and p38 MAPK, cleaved-PARP. Silencing p75(NTR) using siRNA restored expression of NGF and TrkA activation and prevented EC apoptosis. Treatment of EC with human-mutant proNGF induced apoptosis that coincided with marked protein interaction and nuclear translocation of p75(NTR) and the neurotrophin receptor interacting factor. These effects were abolished by a selective p75(NTR) antagonist. Therefore, targeting p75(NTR) represents a potential therapeutic strategy for diseases associated with aberrant expression of proNGF.

Fibrosis-related biomarkers and large and small vessel disease: the Cardiovascular Health Study

OBJECTIVE

Fibrosis has been implicated in a number of pathological, organ-based conditions of the liver, kidney, heart, and lungs. The objective of this study was to determine whether biomarkers of fibrosis are associated with vascular disease in the large and/or small vessels.

METHODS

We evaluated the associations of two circulating biomarkers of fibrosis, transforming growth factor-β (TGF-β) and procollagen type III N-terminal propeptide (PIIINP), with incident peripheral artery disease (PAD) and subclinical macrovascular (carotid intima-media thickness, flow-mediated vasodilation, ankle-brachial index, retinal vein diameter), and microvascular (retinal artery diameter and retinopathy) disease among older adults in the Cardiovascular Health Study. We measured TGF-β and PIIINP from samples collected in 1996 and ascertained clinical PAD through 2011. Measurements of large and small vessels were collected between 1996 and 1998.

RESULTS

After adjustment for sociodemographic, clinical, and biochemical risk factors, TGF-β was associated with incident PAD (hazard ratio [HR] = 1.36 per doubling of TGF-β, 95% confidence interval [CI] = 1.04, 1.78) and retinal venular diameter (1.63 μm per doubling of TGF-β, CI = 0.23, 3.02). PIIINP was not associated with incident PAD, but was associated with carotid intima-media thickness (0.102 mm per doubling of PIIINP, CI = 0.029, 0.174) and impaired brachial artery reactivity (-0.20% change per doubling of PIIINP, CI = -0.39, -0.02). Neither TGF-β nor PIIINP were associated with retinal arteriolar diameter or retinopathy.

CONCLUSIONS

Serum concentrations of fibrosis-related biomarkers were associated with several measures of large vessel disease, including incident PAD, but not with small vessel disease. Fibrosis may contribute to large vessel atherosclerosis in older adults.

Fluid shear stress promotes proprotein convertase-dependent activation of MT1-MMP

During angiogenesis, endothelial cells (ECs(1)) initiate new blood vessel growth and invade into the extracellular matrix (ECM). Membrane type-1 matrix metalloproteinase (MT1-MMP) facilitates this process and translocates to the plasma membrane following activation to promote ECM cleavage. The N-terminal pro-domain within MT1-MMP must be processed for complete activity of the proteinase. This study investigated whether MT1-MMP activation was altered by sphingosine 1-phosphate (S1P) and wall shear stress (WSS), which combine to stimulate EC invasion in three dimensional (3D) collagen matrices. MT1-MMP was activated rapidly and completely by WSS but not S1P. Proprotein convertases (PCs) promoted MT1-MMP processing, prompting us to test whether WSS or S1P treatments increased PC activity. Like MT1-MMP, PC activity increased with WSS, while S1P had no effect. A pharmacological PC inhibitor completely blocked S1P- and WSS-induced EC invasion and MT1-MMP translocation to the plasma membrane. Further, a recombinant PC inhibitor reduced MT1-MMP activation and decreased lumen formation in invading ECs, a process known to be controlled by MT1-MMP. Thus, we conclude that PC and MT1-MMP activation are mechanosensitive events that are required for EC invasion into 3D collagen matrices.

Complex hemodynamic insult in combination with wall degeneration at the apex of an arterial bifurcation contributes to generation of nascent aneurysms in a canine model

BACKGROUND AND PURPOSE

The detailed mechanisms of cerebral aneurysm generation remain unclear. Our aim was to investigate whether specific hemodynamic insult in combination with arterial wall degeneration leads to the development of aneurysms in a canine model.

MATERIALS AND METHODS

New branch points in the common carotid artery were created in 18 dogs. Nine animals subsequently received elastase insult at the arterial bifurcation apex (elastase-treated bifurcation group); the control bifurcation group (n=9) received saline, and 3 dogs received an elastase insult to both straight common carotid arteries (elastase-treated straight group). Angiographic and hemodynamic analysis was performed immediately and 12 and 24 weeks' postsurgery; histologic response was evaluated at 12 and 24 weeks.

RESULTS

Angiography revealed nascent aneurysms (mean, 3.2±0.4 mm) at the arterial bifurcation apices in 5/9 models of the elastase-treated bifurcation group (versus 0 in the control bifurcation group and elastase-treated straight group) without any observed aneurysm rupture. Histologic analysis revealed internal elastic lamina discontinuity, elastic fiber disruption, a thinner muscular layer, reduced smooth-muscle cell proliferation, increased inflammatory cell (macrophage) infiltration, and expression of matrix metalloproteinase-2 and matrix metalloproteinase-9 in the media of the elastase-treated bifurcation group compared with that in either the control bifurcation group or the elastase-treated straight group (P<.001). Hemodynamic analysis after surgery indicated that the apex experienced extremely low wall shear stress and flow velocity and the highest relative and total pressure in the elastase-treated bifurcation group, while the values returned to normal after arterial wall remodelling.

CONCLUSIONS

In our study, combined hemodynamic insult and arterial wall degeneration at arterial bifurcations are required for the generation of aneurysms in a canine model.

Endothelial cell TIMP-1 is upregulated by shear stress via Sp-1 and the TGFβ1 signaling pathways

Laminar shear stress promotes vascular integrity by inhibiting proteolysis of the extracellular matrix (ECM) surrounding the microvasculature. We hypothesized that the matrix metalloproteinase inhibitor TIMP-1 would be upregulated in endothelial cells exposed to shear stress. Microvascular endothelial cells isolated from rat or mouse skeletal muscles were exposed to laminar shear stress for 2, 4, or 24 h. A biphasic increase in TIMP-1 protein was observed at 2 and 24 h of shear stress exposure. Sp-1 siRNA prevented the increase in TIMP-1 after 2, but not 24, hours of shear exposure. TGFβ production and Smad2/3 phosphorylation are increased by shear stress. Inhibition of TGFβ signaling, either by use of the TGFβ receptor 1 inhibitor SB-431542 or with Smad 2/3 siRNA, abrogated the shear stress-induced increase in TIMP-1 mRNA after 24 h of shear stress exposure. These results suggest that both acute and chronic elevated laminar shear stress act to maintain vessel integrity through increasing TIMP-1 production, but that the TGFβ signaling pathway is essential to maintain TIMP-1 expression during chronic shear stress.

Differential morphology and homogeneity of tissue-engineered cartilage in hydrodynamic cultivation with transient exposure to insulin-like growth factor-1 and transforming growth factor-β1

Successful tissue-engineering strategies for cartilage repair must maximize the efficacy of chondrocytes within their limited life span. To that end, the combination of exogenous growth factors with mechanical stimuli holds promise for development of clinically relevant cartilage tissue substitutes. The current study aimed to determine whether incorporation of transient exposure to growth factors into a hydrodynamic bioreactor system can improve the functional maturation of tissue-engineered cartilage. Chondrocyte-seeded polyglycolic acid scaffolds were cultivated within a wavy-walled bioreactor that imparts fluid flow-induced shear stress for 4 weeks. Constructs were nourished with 100 ng/mL insulin-like growth factor-1 (IGF-1) or 10 ng/mL transforming growth factor-β1 (TGF-β1) either for the first 15 days of the culture (transient) or throughout the entire cultivation (continuous). Transiently treated constructs were found to exhibit better functional properties than continuously nourished constructs. The limited development of engineered tissues continuously stimulated by IGF-1 or TGF-β1 was related to massive growth factor leftovers in the environments that downregulated the expression of the associated receptors. Treatment with TGF-β1 eliminated the formation of a fibrous capsule at the construct periphery possibly through suppression of Smad3 phosphorylation, yielding constructs with greater homogeneity. Furthermore, TGF-β1 reversely regulated Smad2 and Smad3 pathways in articular chondrocytes under hydrodynamic stimuli partially via Smad7. Collectively, transient exposure to growth factors is likely to maintain chondrocyte homeostasis, and thus promotes their anabolic activities under hydrodynamic stimuli. The present work suggests that robust hydrodynamically engineered neocartilage with a reduced fibrotic response and enhanced tissue homogeneity can be achieved through optimization of growth factor supplementation protocols and potentially through manipulation of intracellular signals such as Smad.

The role of shear-induced transforming growth factor-β signaling in the endothelium

OBJECTIVE

Vascular endothelial cells (ECs) are continuously exposed to blood flow that contributes to the maintenance of vessel structure and function; however, the effect of hemodynamic forces on transforming growth factor-β (TGF-β) signaling in the endothelium is poorly described. We examined the potential role of TGF-β signaling in mediating the protective effects of shear stress on ECs.

APPROACH AND RESULTS

Human umbilical vein ECs (HUVECs) exposed to shear stress were compared with cells grown under static conditions. Signaling through the TGF-β receptor ALK5 was inhibited with SB525334. Cells were examined for morphological changes and harvested for analysis by real-time polymerase chain reaction, Western blot analysis, apoptosis, proliferation, and immunocytochemistry. Shear stress resulted in ALK5-dependent alignment of HUVECs as well as attenuation of apoptosis and proliferation compared with static controls. Shear stress led to an ALK5-dependent increase in TGF-β3 and Krüppel-like factor 2, phosphorylation of endothelial NO synthase, and NO release. Addition of the NO donor S-nitroso-N-acetylpenicillamine rescued the cells from apoptosis attributable to ALK5 inhibition under shear stress. Knockdown of TGF-β3, but not TGF-β1, disrupted the HUVEC monolayer and prevented the induction of Krüppel-like factor 2 by shear.

CONCLUSIONS

Shear stress of HUVECs induces TGF-β3 signaling and subsequent activation of Krüppel-like factor 2 and NO, and represents a novel role for TGF-β3 in the maintenance of HUVEC homeostasis in a hemodynamic environment.

Furin mRNA expression in peripheral blood correlates with chronic hepatitis B virus infection

AIM

  The mechanisms underlying development of chronic hepatitis B virus (HBV) infection are related to immune tolerance, but are as yet incompletely understood. Furin has been found to be essential for maintenance of peripheral immune tolerance mediated by regulatory T cells (Treg). Such effect of furin on chronic HBV infection was investigated in this study.

METHODS

  Peripheral blood from 40 individuals with self-limited HBV infection, 40 patients with asymptomatic persistent HBV infection and 40 patients with chronic hepatitis B (CHB) was collected and mRNA expression levels of furin, transforming growth factor (TGF)-β1 and the Treg-function-related forkhead transcription factor FoxP3 were detected using quantitative real-time polymerase chain reaction. CD4(+) CD25(+) FoxP3(+) Treg were detected using flow cytometry.

RESULTS

  Furin mRNA expression in peripheral blood was significantly higher in patients with persistent HBV infection than in individuals with self-limited infection (P < 0.01), and was much higher in CHB patients than in those with asymptomatic persistent infection (P < 0.01). Furthermore, furin mRNA was relatively higher in patients with positive hepatitis B e antigen and higher levels of serum HBV DNA (>10 000 copies/mL). In patients with CHB, furin mRNA expression was found to correlate with TGF-β1 mRNA and FoxP3 mRNA expression using Spearman's rank correlation coefficient test. It was 5.7-times higher in CD4(+) CD25(+) T cells than in CD4(+) CD25(-) T cells and correlated with the frequency of Treg (P < 0.05).

CONCLUSION

  Furin mRNA expression in peripheral blood correlates with chronic HBV infection and liver damage, and seems to participate in immune inhibitory and anti-inflammatory mechanisms in HBV infection, mediated by TGF-β1 and/or Treg.

Anti-neurotrophic effects from autoantibodies in adult diabetes having primary open angle glaucoma or dementia

AIM

To test for anti-endothelial and anti-neurotrophic effects from autoantibodies in subsets of diabetes having open-angle glaucoma, dementia, or control subjects.

METHODS

Protein-A eluates from plasma of 20 diabetic subjects having glaucoma or suspects and 34 age-matched controls were tested for effects on neurite outgrowth in rat pheochromocytoma PC12 cells or endothelial cell survival. The mechanism of the diabetic glaucoma autoantibodies' neurite-inhibitory effect was investigated in co-incubations with the selective Rho kinase inhibitor Y27632 or the sulfated proteoglycan synthesis inhibitor sodium chlorate. Stored protein-A eluates from certain diabetic glaucoma or dementia subjects which contained long-lasting, highly stable cell inhibitory substances were characterized using mass spectrometry and amino acid sequencing.

RESULTS

Diabetic primary open angle glaucoma (POAG) or suspects (n = 20) or diabetic dementia (n = 3) autoantibodies caused significantly greater mean inhibition of neurite outgrowth in PC12 cells (p < 0.0001) compared to autoantibodies in control diabetic (n = 24) or non-diabetic (n = 10) subjects without glaucoma (p < 0.01). Neurite inhibition by the diabetic glaucoma autoantibodies was completely abolished by 10 μM concentrations of Y27632 (n = 4). It was substantially reduced by 30 mM concentrations of sodium chlorate (n = 4). Peak, long-lasting activity survived storage ×5 years at 0-4°C and was associated with a restricted subtype of Ig kappa light chain. Diabetic glaucoma or dementia autoantibodies (n = 5) caused contraction and process retraction in quiescent cerebral cortical astrocytes effects which were blocked by 5 μM concentrations of Y27632.

CONCLUSION

These data suggest that autoantibodies in subsets of adult diabetes having POAG (glaucoma suspects) and/or dementia inhibit neurite outgrowth and promote a reactive astrocyte morphology by a mechanism which may involve activation of the RhoA/p160 ROCK signaling pathway.

TGFβ signaling and cardiovascular diseases

Transforming growth factor β (TGFβ) family members are involved in a wide range of diverse functions and play key roles in embryogenesis, development and tissue homeostasis. Perturbation of TGFβ signaling may lead to vascular and other diseases. In vitro studies have provided evidence that TGFβ family members have a wide range of diverse effects on vascular cells, which are highly dependent on cellular context. Consistent with these observations genetic studies in mice and humans showed that TGFβ family members have ambiguous effects on the function of the cardiovascular system. In this review we discuss the recent advances on TGFβ signaling in (cardio)vascular diseases, and describe the value of TGFβ signaling as both a disease marker and therapeutic target for (cardio)vascular diseases.

TGF-β1/ALK5-induced monocyte migration involves PI3K and p38 pathways and is not negatively affected by diabetes mellitus

AIMS

Monocytes contribute to arteriogenesis by infiltration to sites of collateral growth and subsequent production and release of growth factors. Transforming growth factor β1 (TGF-β1) mediates monocyte motility and stimulates arteriogenesis. TGF-β1 signalling mechanisms mediating monocyte motility are unknown so far. Moreover, the influence of cardiovascular risk factor diabetes on TGF-β1-induced monocyte migration remains to be elucidated.

METHODS AND RESULTS

Stimulation of primary human monocytes with TGF-β1 endorsed phosphorylation of v-Akt murine thymoma viral oncogene analogues protein (AKT), p38, and extracellular signal-related kinase 1/2 (ERK1/2), besides the activation of the SMA/MAD homologues protein (SMAD) pathway. Inhibition of the TGF-βtype 1 receptor, alias activin receptor-like kinase 5 (ALK5), hindered monocyte chemotaxis towards TGF-β1 and TGF-β1-activated downstream signalling cascades. Individual genetic knock-downs for receptor-regulated SMAD2 and SMAD3 did not affect monocyte migration to TGF-β1. Inhibition of phosphoinositide 3 kinase (PI3K) activity, but not AKT, diminished both basal and TGF-β1-mediated monocyte motility. TGF-β1-induced monocyte chemotaxis did not rely on ERK1/2, but rather on p38. Remarkably, TGF-β1 was able to stimulate chemotaxis of diabetic monocytes.

CONCLUSION

The current study provides novel insights into the molecular mechanisms of TGF-β1-induced monocyte migration, requiring ALK5 kinase activity and signalling via PI3K and p38. TGF-β1-driven monocyte motogenicity is fully functional in diabetic conditions, which is in sharp contrast to the impaired chemotactic responses to certain other arteriogenic cytokines. Therefore, TGF-β1 may be a promising candidate for endogenously and exogenously stimulating collateral growth in diabetic patients.

Effects of disturbed flow on vascular endothelium: pathophysiological basis and clinical perspectives

Vascular endothelial cells (ECs) are exposed to hemodynamic forces, which modulate EC functions and vascular biology/pathobiology in health and disease. The flow patterns and hemodynamic forces are not uniform in the vascular system. In straight parts of the arterial tree, blood flow is generally laminar and wall shear stress is high and directed; in branches and curvatures, blood flow is disturbed with nonuniform and irregular distribution of low wall shear stress. Sustained laminar flow with high shear stress upregulates expressions of EC genes and proteins that are protective against atherosclerosis, whereas disturbed flow with associated reciprocating, low shear stress generally upregulates the EC genes and proteins that promote atherogenesis. These findings have led to the concept that the disturbed flow pattern in branch points and curvatures causes the preferential localization of atherosclerotic lesions. Disturbed flow also results in postsurgical neointimal hyperplasia and contributes to pathophysiology of clinical conditions such as in-stent restenosis, vein bypass graft failure, and transplant vasculopathy, as well as aortic valve calcification. In the venous system, disturbed flow resulting from reflux, outflow obstruction, and/or stasis leads to venous inflammation and thrombosis, and hence the development of chronic venous diseases. Understanding of the effects of disturbed flow on ECs can provide mechanistic insights into the role of complex flow patterns in pathogenesis of vascular diseases and can help to elucidate the phenotypic and functional differences between quiescent (nonatherogenic/nonthrombogenic) and activated (atherogenic/thrombogenic) ECs. This review summarizes the current knowledge on the role of disturbed flow in EC physiology and pathophysiology, as well as its clinical implications. Such information can contribute to our understanding of the etiology of lesion development in vascular niches with disturbed flow and help to generate new approaches for therapeutic interventions.

Development and characterisation of an assay for furin activity

Furin is a serine endoprotease that is responsible for the proteolytic processing of proteins within the secretory pathway, including cytokines, hormones, integrins, other proteases, and also pathogen-derived proteins. It is likely that the level of furin activity determines the extent of processing of these substrates. Furin is ubiquitously expressed across all tissues, at low levels, but can be induced in response to environmental cues such as hypoxia and cytokine stimulation. However, all studies to date that have investigated furin expression have been limited to analysis of furin mRNA; there has been no assay sensitive enough to quantify endogenous furin. Though activity-based assays have been described for furin-like enzyme activity, we demonstrate that these assays are dominated by the activity of other enzymes and cannot be used to approximate furin activity. A sensitive and specific assay for furin activity was therefore developed and characterised, using an antibody capture step to immobilise furin from whole cell lysates. Furin activity is quantified relative to that of recombinant active furin protein, to allow estimation of active furin protein concentration. The assay has a minimum detection limit of 0.006 nM; sensitive enough to determine the furin activity of many of the cell lines tested. The specificity of the assay was demonstrated by genetic modulation of furin expression. Furthermore, the assay was used to demonstrate that the cytokine transforming growth factor beta (TGF-β) stimulates increased furin activity in HepG2 cells, confirming and extending previous reports that TGF-β increases furin expression, and adding to the mounting body of evidence that cellular furin activity can be modulated.

TGF-β1: a novel target for cardiovascular pharmacology

Transforming growth factor beta-1 (TGF-beta1) plays a key role in cardiovascular disease by a process which allows the loss of its protective properties. The first therapeutic attempt to restore its function by selectively designed novel drugs are being made. In addition, it has been recognized that the TGF-beta1 pathway is involved in the vascular mechanism of action of some current clinical drugs, such as acetylsalicylic acid, thiazolidinediones and statins. The aim of this paper is to review the possible value of TGF-beta1 as both a disease marker and a therapeutical target for cardiovascular disease.

Proprotein convertases furin and PC5: targeting atherosclerosis and restenosis at multiple levels

Several growth factors, chemokines, adhesion molecules, and proteolytic enzymes important for cell-cell/cell-matrix interactions in atherosclerosis and restenosis are initially synthesized as inactive precursor proteins. Activation of proproteins to biologically active molecules is regulated by limited endoproteolytic cleavage at dibasic amino acid residues. This type of activation typically requires the presence of suitable proprotein convertases (PCs). The PC-isozymes furin and PC5 are expressed in human atherosclerotic lesions and have been found to be up-regulated, following vascular injury in animal models in vivo. In vitro, these PCs can regulate vascular smooth muscle cell and macrophage functions and signaling events, through activation of pro-alpha-integrins and/or pro-membrane-type matrix metalloproteinases. Integrins link the cytoskeleton with the extracellular matrix and mediate bidirectional signaling and mechanotransduction, whereas matrix metalloproteinases are the major matrix-degrading enzymes. Both activities are required for cell recruitment to the intima. Furthermore, cleavage of extracellular matrix molecules by matrix metalloproteinases potentially contributes to weakening of the fibrous cap, promoting plaque rupture. Based on these recent in vitro and in vivo data, furin and PC5 are potential contributors to the initiation, progression, and complications of atherosclerosis and restenosis. Targeting these PCs may provide future anti-atherosclerotic therapies.

Endothelial lipase is inactivated upon cleavage by the members of the proprotein convertase family

Mature endothelial lipase (EL) is a 68 kDa glycoprotein. In HepG2 cells infected with adenovirus encoding human EL, the mature EL was detectable in the cell lysates and heparin-releasable fractions. In contrast, cell media of these cells contained two EL fragments: an N-terminal 40 kDa fragment and a C-terminal 28 kDa fragment. N-terminal protein sequencing of the His-tagged 28 kDa fragment revealed that EL is cleaved on the C terminus of the sequence RNKR330, the consensus cleavage sequence for mammalian proprotein convertases (pPCs). Replacement of Arg-330 with Ser by site-directed mutagenesis totally abolished EL processing. EL processing could efficiently be attenuated by specific inhibitors of pPCs, alpha1-antitrypsin Portland (alpha1-PDX) and alpha1-antitrypsin variant AVRR. Coexpression of the pPCs furin, PC6A, and PACE4 with EL resulted in a complete conversion of the full-length EL to a truncated 40 kDa fragment. Exogenously added EL was also processed by cells, and the processing could be attenuated by alpha1-PDX. The expressed N-terminal 40 kDa fragment of EL (EL-40) harboring the catalytic site failed to hydrolyze [14C]NEFA from [14C]dipalmitoyl-PC-labeled HDL. EL-40 was incapable of bridging 125I-labeled HDL to the cells and had no impact on plasma lipid concentration when overexpressed in mice. Thus, our results demonstrate that pPCs are involved in the inactivation process of EL.

Left ventricular filling abnormalities and obesity-associated hypertension: relationship with overproduction of circulating transforming growth factor β1

This study has been designed to evaluate the relationship among transforming growth factor beta1 (TGFbeta1) and some measurements of diastolic function in a population of hypertensive subjects with normal left ventricular ejection fraction. We studied 67 hypertensive outpatients who according to their BMI levels were subdivided into three groups: lean (L), overweight (OW) and obese (OB) hypertensives (HT). Circulating TGFbeta1 and M- and B-mode echocardiography was determined. All hypertensives were further subgrouped, according to European Society of Cardiology Guidelines, into two subsets of patients with normal diastolic function or with diastolic dysfunction. Prevalence of left ventricular hypertrophy (LVH) was determined in all the groups. TGFbeta1, left ventricular mass (LVM), LVM/h(2.7), E-wave deceleration time and isovolumic relaxation time (IVRT) were significantly (P < 0.005) higher and E/A velocity ratio was significantly (P < 0.05) lower in OW-HT and OB-HT than in L-HT. Prevalence of LVH was significantly higher (P < 0.03) in group OB-HT than in L-HT. TGFbeta1 (P < 0.004), LVM/h(2.7) (P < 0.001) and prevalence of LVH were (P < 0.01) significantly higher in hypertensives with diastolic dysfunction than hypertensives with normal diastolic function. TGFbeta1 levels were positively correlated with BMI (r = 0.60; P < 0.0001), LVM/h(2.7) (r = 0.28; P < 0.03), IVRT (r = 0.30; P < 0.02) and negatively with E/A ratio (r = -0.38; P < 0.002) in all HT. Multiple regression analysis indicated that TGFbeta1, BMI and IVRT were independently related to E/A ratio explaining 71% of its variability (r = 0.84; P < 0.0001). This relationship was independent of LVH, age and HR suggesting that TGFbeta1 overproduction may be considered a pathophysiological mechanism in the development of left ventricular filling abnormalities in obesity-associated hypertension.

A novel polymorphism of the gene encoding furin, a TGF-β1 activator, and the influence on cardiac allograft vasculopathy formation

BACKGROUND

Coronary vasculopathy (CV) is an important determinant of survival following cardiac transplantation. We have previously shown that G915C polymorphism of the Transforming Growth Factor-beta1 (TGF-beta1) gene strongly influences CV development. Furin is a proprotein convertase enzyme important in TGF-beta1 activation. We investigated for polymorphism within the promoter region of the gene for furin (fur). Allelic variation of the fur gene, in conjunction with TGF-beta1 polymorphism, was subsequently related to the development of CV.

METHODS AND RESULTS

The fur gene promoter region (position -1199 to +39) was analysed by SSCP and sequencing. A C/T single nucleotide substitution polymorphism at position -231* was identified. Using PCR the fur and TGFB1 genotypes were identified in 115 cardiac transplant recipients. CV was diagnosed at routine surveillance post-transplant coronary angiography. Fur polymorphism had no influence on vasculopathy development; median time to diagnosis, *C/C homozygotes, 2.27 years (2.10-4.32), *C/T heterozygotes 2.97 years (2.09-4.24), *T/T homozygotes 2.65 years (2.33-4.08), (P=0.95). Allelic variation did not influence Kaplan Meier actuarial analysis of disease onset (P=0.54). Ninety-three percent of recipients were high TGF-beta1 producers. We used fur polymorphism to substratify patients with the +915*G/G TGFB1 (high producing) allele. Fur polymorphism did not influence CV development within this TGF-beta1 high producer cohort, when analysed by time to first diagnosis and Kaplan Meier testing.

CONCLUSIONS

We have described a novel polymorphism at position -231* in the gene encoding furin. The fur -231* single nucleotide polymorphism in isolation, or in conjunction with TGFB1 polymorphism, is not useful as a genetic risk marker for cardiac transplant associated coronary vasculopathy.

Adaptation of the endothelium to fluid flow: in vitro analyses of gene expression and in vivo implications

Biomechanical forces generated by blood flow play an important role in the pathogenesis of vascular disease. For example, regions exposed to non-uniform shear stresses develop early atherosclerotic lesions while areas exposed to uniform shear stresses are protected. A variety of in vitro flow apparatuses have been created to apply well-characterized flow patterns to endothelial cells in an effort to dissect the cellular and molecular pathways involved in these distinct processes. Recent advances in biotechnology have permitted large-scale transcriptional profiling techniques to replace candidate gene screens and have allowed the genome-wide examination of biomechanical force-induced endothelial gene expression profiles. This review provides an overview of biomechanical force-induced modulation of endothelial phenotype. It examines the effect of sustained laminar shear stress (LSS), a type of uniform shear stress, on in vitro endothelial gene expression by synthesizing data from the early candidate gene and differential display polymerase chain reaction (PCR) approaches to the numerous, recent, high throughput functional genomic analyses. These studies demonstrate that prolonged LSS regulates the expression of only a small percentage (approximately 1-5%) of endothelial genes, and this transcriptional profile produces an endothelial phenotype that is quiescent, being protected from apoptosis, inflammation and oxidative stress. These observations provide a possible molecular mechanism for the strong correlation between patterns of blood flow and the occurrence of vascular pathologies, such as atherosclerosis, in vivo.

Bases cellulaires de la mécanotransduction dans la cellule endothéliale

Blood vessels are permanently subjected to mechanical forces in the form of stretch and shear stress. Any alterations in the hemodynamic environment invariably produce transformations in the vessel wall that will aim to accommodate the new conditions and to ultimately restore basal levels of mechanical forces. Many receptors, present on the surface of endothelial cells, allow vessels to detect subtle changes in shear stress. Inside the cells, cytoskeletal proteins transmit and modulate the tension between integrins, focal adhesion sites, and the extracellular matrix. Besides inducing structural modifications, mechanical forces lead to changes in the ionic composition of cells, mediated by ion channels, stimulate various membrane receptors, and induce complex biochemical cascades. Many intracellular pathways such as the MAP kinase cascade are activated by shear stress and initiate via sequential phosphorylations the activation of transcription factors and subsequent gene expression. Thus, by purely local mechanisms, blood vessels are capable of true autonomic regulation which enables them to adapt to their mechanical environment.

Influence of inflammatory cytokines on arteriogenesis

Blood vessel growth after birth is limited to two major processes. Angiogenesis is the growth of new capillaries by sprouting or intussusception. The major stimulus for angiogenesis is ischemia. In contrast, arteriogenesis describes the remodeling and growth of collateral arteries from a preexisting arteriolar network. Arteriogenesis is induced after the occlusion of a major artery which induces hemodynamic and mechanical effects on the collateral vessel wall which occur with increasing blood flow velocity due to the low pressure at the reentrant site of the collateral vessel. A variety of different cytokines that act by stimulating endothelial and smooth muscle cell proliferation and migration or recruitment and activation of monocytes have been identified to stimulate angiogenesis and/or arteriogenesis (i.e., MCP-1, FGF-2, TGF-beta, VEGF, and GM-CSF). Several clinical trials have been published in that field to suggest the feasibility and safety of treatment with such cytokines or their genes. However, the results indicate that further studies are needed before proangiogenic and proarteriogenic therapies are ready for clinical application.

Increased venous proinflammatory gene expression and intimal hyperplasia in an aorto-caval fistula model in the rat

We hypothesized that the venous limb of an arteriovenous (AV) fistula would evince up-regulation of genes relevant to vascular remodeling along with neointimal hyperplasia and relevant histological changes. Using the aorto-caval model of an AV fistula model in the rat, we demonstrate marked up-regulation in such proinflammatory genes as monocyte chemoattractant protein-1, plasminogen activator inhibitor-1, and endothelin-1, 2 weeks after the creation of the fistula. Neointimal hyperplasia occurred in variable degrees by 5 weeks after establishing the fistula, and by 16 weeks, such neointimal hyperplasia was progressive and pronounced; at this time point, abundant extracellular matrix was also observed. Smooth muscle cells were present in the hyperplastic neointima as evidenced by staining for alpha-smooth muscle actin; ultrastructurally, smooth muscle cells with a synthetic as well as a contractile phenotype were readily observed. Accumulation of extracellular matrix in the model at 16 weeks was accompanied by increased expression of transforming growth factor-beta1 mRNA, the latter finding contrasting with the suppression of transforming growth factor-beta1 mRNA observed in this model at 2 weeks. In summary, we describe marked up-regulation in proinflammatory genes and progressive neointimal formation in the venous vasculature in an AV fistula model in the rat. We suggest that such alteration in gene expression and histological injury, in conjunction with the relative simplicity of this model, offer a new approach in the study of such timely biological and clinically relevant phenomena as differential gene expression in response to hemodynamic forces, processes involved in vascular remodeling, mechanisms of injury in venous bypass grafts, and mechanisms of dysfunction of AV fistulae used in hemodialysis.

Cellular mechanics and gene expression in blood vessels

Blood vessels are permanently subjected to mechanical forces in the form of stretch, encompassing cyclic mechanical strain due to the pulsatile nature of blood flow, and shear stress. Alterations in stretch or shear stress invariably produce transformations in the vessel wall that will aim to accommodate the new conditions and to ultimately restore basal levels of tensile stress and shear stress. Vascular cells are equipped with numerous receptors that allow them to detect and respond to the mechanical forces generated by pressure and shear stress. The cytoskeleton and other structural components have an established role in mechanotransduction, being able to transmit and modulate tension within the cell via focal adhesion sites, integrins, cellular junctions and the extracellular matrix. Beyond the structural modifications incurred, mechanical forces can also initiate complex signal transduction cascades leading to functional changes within the cell. Many intracellular pathways, including the MAP kinase cascade, are activated by flow or stretch and initiate, via sequential phosphorylations, the activation of transcription factors and subsequent gene expression.

Gene expression profile of human endothelial cells exposed to sustained fluid shear stress

Biomechanical forces can modulate endothelial phenotype through changes in gene expression. We hypothesized that physiological laminar shear stresses (LSS) act as differentiative stimuli on endothelial cells (EC) to alter gene expression, creating an antioxidant, anti-apoptotic and anti-proliferative environment. The transcriptional profile of cultured human umbilical vein endothelial cells (HUVEC) exposed to LSS was evaluated by GeneCalling; 107 genes demonstrated at least a twofold change in expression at 24 h (LSS vs. static). These flow-responsive genes represent a limited number of functional clusters that include transcription factors, antioxidants, signaling molecules, cell cycle regulators, and genes involved in cellular differentiation. Immunohistochemistry and in situ hybridization confirmed that many of these flow-responsive genes, including the novel basic helix-loop-helix transcription factor Hath6, are expressed in EC in vivo. Thus these data identify a limited set of flow-responsive genes expressed in the endothelium that may be responsible for the establishment and maintenance of the flow-adapted endothelial phenotype in vivo.

Expression of TGF-beta1 and beta3 but not apoptosis factors relates to flow-induced aortic enlargement

BACKGROUND

Cell proliferation and apoptosis are both involved in arterial wall remodeling. Increase in blood flow induces arterial enlargement. The molecular basis of flow-induced remodeling in large elastic arteries is largely unknown.

METHODS

An aortocaval fistula (ACF) model in rats was used to induce enlargement in the abdominal aorta. Aortic gene expression of transforming growth factors beta (TGF-beta) and apoptosis-related factors was assessed at 1 and 3 days and 1, 2, 4, and 8 weeks. Expression levels were determined using a ribonuclease protection assay and western blotting. Cell proliferation and apoptosis were analyzed using BrdU incorporation and TUNEL techniques.

RESULTS

Blood flow increased 5-fold immediately after ACF (P<0.05). Lumen diameter of the aorta was 30% and 75% larger at 2 and 8 weeks respectively than those of controls (P<0.05). mRNA levels of TGF-beta1 and TGF-beta3 increased after ACF, peaked at 3 days (P<0.05) and returned to normal level at 1 week and thereafter. Western blotting showed enhanced expression of TGF-beta1 at 3 days and TGF-beta3 at 1 and 3 days and 1 week (P<0.05). mRNA levels of Bcl-xS initially decreased at 1 day, 3 days and 1 week, followed a return to baseline level at 2 weeks. Cell proliferation was observed at all time points after ACF (P<0.001 vs. controls) with proliferation in endothelial cells more significant than smooth muscle cells. Apoptosis was not significant.

CONCLUSIONS

Gene expression of TGF-beta1 and beta3 precedes arterial enlargement. Expression of apoptosis related factors is little regulated in the early stage of the flow-induced arterial remodeling.

Nestin as a marker for proliferative endothelium in gliomas

Nestin is one of the intermediate filaments abundantly produced in the developing central nervous system and somites in the embryonic stage. Nestin is also reportedly detected in gliomas/glioblastomas. We retested nestin expression in brain tumors having a range of malignancy grades using immunostaining. The intensity of nestin immunostaining roughly paralleled the malignancy grade of the gliomas. However, many tumors were negative for nestin immunostaining, while nestin immunostaining was invariably detected in tumor endothelium regardless of glioma malignancy grades or brain tumor types. We suspected that angiogenic epithelial cells may express nestin, and we found that nestin was highly positive in bovine aortic endothelial cells in static culture. However, nestin expression decreased when the endothelial cells underwent laminar shear stress flow, under which endothelial cells exhibit differentiated features and a decreased rate of growth. Because nestin is highly expressed in growing endothelial cells, we examined its expression in hemangioblastomas because hemangioblasts are thought to be a precursor for angiogenic epithelial cells. As expected, nestin immunostained strongly in all four samples of hemangioblastomas. We suggest that nestin is not only a marker for neuroepithelial stem cells and glioma cells but also for tumor endothelial cells during rapid growth.