Differential regulation of urokinase-type plasminogen activator expression by fluid shear stress in human coronary artery endothelial cells

HGF/c-Met: A Key Promoter in Liver Regeneration

Hepatocyte growth factor (HGF) is a peptide-containing multifunctional cytokine that acts on various epithelial cells to regulate cell growth, movement and morphogenesis, and tissue regeneration of injured organs. HGF is sequestered by heparin-like protein in its inactive form and is widespread in the extracellular matrix of most tissues. When the liver loses its average mass, volume, or physiological and biochemical functions due to various reasons, HGF binds to its specific receptor c-Met (cellular mesenchymal-epithelial transition) and transmits the signals into the cells, and triggers the intrinsic kinase activity of c-Met. The downstream cascades of HGF/c-Met include JAK/STAT3, PI3K/Akt/NF-κB, and Ras/Raf pathways, affecting cell proliferation, growth, and survival. HGF has important clinical significance for liver fibrosis, hepatocyte regeneration after inflammation, and liver regeneration after transplantation. And the development of HGF as a biological drug for regenerative therapy of diseases, that is, using recombinant human HGF protein to treat disorders in clinical trials, is underway. This review summarizes the recent findings of the HGF/c-Met signaling functions in liver regeneration.

Genetic and Cellular Contributions to Liver Regeneration

The regenerative capabilities of the liver represent a paradigm for understanding tissue repair in solid organs. Regeneration after partial hepatectomy in rodent models is well understood, while regeneration in the context of clinically relevant chronic injuries is less studied. Given the growing incidence of fatty liver disease, cirrhosis, and liver cancer, interest in liver regeneration is increasing. Here, we will review the principles, genetics, and cell biology underlying liver regeneration, as well as new approaches being used to study heterogeneity in liver tissue maintenance and repair.

G3BP2 regulates oscillatory shear stress-induced endothelial dysfunction

GTPase-activating SH3 domain-binding protein 2 (G3BP2) is a mediator that responds to environmental stresses through stress granule formation and is involved in the progression of chronic diseases. However, no studies have examined the contribution of G3BP2 in the oscillatory shear stress (OSS)-induced endothelial dysfunction. Here we assessed the effects of G3BP2 in endothelial cells (ECs) function and investigated the underlying mechanism. Using shear stress apparatus and partial ligation model, we identified that stress granule-related genes in ECs could be induced by OSS with RNA-seq, and then confirmed that G3BP2 was highly and specifically expressed in athero-susceptible endothelia in the OSS regions. G3bp2^–/–Apoe^–/– mice had significantly decreased atherosclerotic lesions associated with deficiency of G3BP2 in protecting endothelial barrier function, decreasing monocyte adhesion to ECs and inhibiting the proinflammatory cytokine levels. Furthermore, loss of G3BP2 diminished OSS-induced inflammation in ECs by increasing YAP nucleocytoplasmic shuttling and phosphorylation. These data demonstrate that G3BP2 is a critical OSS regulated gene in regulating ECs function and that G3BP2 inhibition in ECs is a promising atheroprotective therapeutic strategy.

A narrative review of liver regeneration-from models to molecular basis

Objective

To elucidate the characteristics of different liver regeneration animal models, understand the activation signals and mechanisms related to liver regeneration, and obtain a more comprehensive conception of the entire liver regeneration process.

Background

Liver regeneration is one of the most enigmatic and fascinating phenomena of the human organism. Despite suffering significant injuries, the liver still can continue to perform its complex functions through the regeneration system. Although advanced topics on liver regeneration have been proposed; unfortunately, complete regeneration of the liver has not been achieved until now. Therefore, increasing understanding of the liver regenerative process can help improve our treatment of liver failure. It will provide a new sight for the treatment of patients with liver injury in the clinic.

Methods

Literatures on liver regeneration animal models and involved basic research on molecular mechanisms were retrieved to analyze the characteristics of different models and those related to molecular basis.

Conclusions

The process of liver regeneration is complex and intricate, consisting of various and interactive pathways. There is sufficient evidence to demonstrate that liver regeneration is similar between humans and rodents. At the same time, many of the same cytokines, growth factors, and signaling pathways are relevant. There are many gaps in our current knowledge. Understanding of this knowledge will provide more supportive clinical treatment strategies, including small-scale liver transplantation and high-quality regenerative process after surgical resection, and offer possible targets to treat the dysregulation of regeneration that occurs in chronic hepatic diseases and tumors. Current research work, such as the use of animal models as in vivo vectors for high-quality human hepatocytes, represents a unique and significant cutting edge in the field of liver regeneration.

Critical Role of LSEC in Post-Hepatectomy Liver Regeneration and Failure

Liver sinusoids are lined by liver sinusoidal endothelial cells (LSEC), which represent approximately 15 to 20% of the liver cells, but only 3% of the total liver volume. LSEC have unique functions, such as fluid filtration, blood vessel tone modulation, blood clotting, inflammatory cell recruitment, and metabolite and hormone trafficking. Different subtypes of liver endothelial cells are also known to control liver zonation and hepatocyte function. Here, we have reviewed the origin of LSEC, the different subtypes identified in the liver, as well as their renewal during homeostasis. The liver has the exceptional ability to regenerate from small remnants. The past decades have seen increasing awareness in the role of non-parenchymal cells in liver regeneration despite not being the most represented population. While a lot of knowledge has emerged, clarification is needed regarding the role of LSEC in sensing shear stress and on their participation in the inductive phase of regeneration by priming the hepatocytes and delivering mitogenic factors. It is also unclear if bone marrow-derived LSEC participate in the proliferative phase of liver regeneration. Similarly, data are scarce as to LSEC having a role in the termination phase of the regeneration process. Here, we review what is known about the interaction between LSEC and other liver cells during the different phases of liver regeneration. We next explain extended hepatectomy and small liver transplantation, which lead to "small for size syndrome" (SFSS), a lethal liver failure. SFSS is linked to endothelial denudation, necrosis, and lobular disturbance. Using the knowledge learned from partial hepatectomy studies on LSEC, we expose several techniques that are, or could be, used to avoid the "small for size syndrome" after extended hepatectomy or small liver transplantation.

Hemodynamic Forces, Endothelial Mechanotransduction, and Vascular Diseases

Cells in the tissues and organs of a living body are subjected to mechanical forces, such as pressure, friction, and tension from their surrounding environment. Cells are equipped with a mechanotransduction mechanism by which they perceive mechanical forces and transmit information into the cell interior, thereby causing physiological or pathogenetic mechano-responses. Endothelial cells (ECs) lining the inner surface of blood vessels are constantly exposed to shear stress caused by blood flow and a cyclic strain caused by intravascular pressure. A number of studies have shown that ECs are sensitive to changes in these hemodynamic forces and alter their morphology and function, sometimes by modifying gene expression. The mechanism of endothelial mechanotransduction has been elucidated, and the plasma membrane has recently been shown to act as a mechanosensor. The lipid order and cholesterol content of plasma membranes change immediately upon the exposure of ECs to hemodynamic forces, resulting in a change in membrane fluidity. These changes in a plasma membrane's physical properties affect the conformation and function of various ion channels, receptors, and microdomains (such as caveolae and primary cilia), thereby activating a wide variety of downstream signaling pathways. Such endothelial mechanotransduction works to maintain circulatory homeostasis; however, errors in endothelial mechanotransduction can cause abnormalities in vascular physiological function, leading to the initiation and progression of various vascular diseases, such as hypertension, thrombosis, aneurysms, and atherosclerosis. Recent advances in detailed imaging technology and computational fluid dynamics analysis have enabled us to evaluate the hemodynamic forces acting on vascular tissue accurately, contributing greatly to our understanding of vascular mechanotransduction and the pathogenesis of vascular diseases, as well as the development of new therapies for vascular diseases.

Cellular and molecular basis of liver regeneration

Recent advances in genetics and genomics have reinvigorated the field of liver regeneration. It is now possible to combine lineage-tracing with genome-wide studies to genetically mark individual liver cells and their progenies and detect precise changes in their genome, transcriptome, and proteome under normal versus regenerative settings. The recent use of single-cell RNA sequencing methodologies in model organisms has, in some ways, transformed our understanding of the cellular and molecular biology of liver regeneration. Here, we review the latest strides in our knowledge of general principles that coordinate regeneration of the liver and reflect on some conflicting evidence and controversies surrounding this topic. We consider the prominent mechanisms that stimulate homeostasis-related vis-à-vis injury-driven regenerative responses, highlight the likely cellular sources/depots that reconstitute the liver following various injuries and discuss the extrinsic and intrinsic signals that direct liver cells to proliferate, de-differentiate, or trans-differentiate while the tissue recovers from acute or chronic damage.

Genetic and Functional Variants Analysis of the GATA6 Gene Promoter in Acute Myocardial Infarction

Background: Acute myocardial infarction (AMI) which is a specific type of coronary artery disease (CAD), is caused by the combination of genetic factors and acquired environment. Although some common genetic variations have been recorded to contribute to the development of CAD and AMI, more genetic factors and potential molecular mechanisms remain largely unknown. The GATA6 gene is expressed in the heart during embryogenesis and is also detected in vascular smooth muscle cells (VSMCs), different human primary endothelial cells (ECs), and vascular ECs in mice. To date, no studies have directly linked GATA6 gene with regulation of the CAD.

Methods: In this study, we used a case-control study to investigate and analyze the genetic variations and functional variations of the GATA6 gene promoter region in AMI patients and controls. A variety of statistical analysis methods were utilized to analyze the association of single nucleotide polymorphisms (SNPs) with AMI. Functional analysis of DNA sequence variants (DSVs) was performed using a dual luciferase reporter assay. In vitro, electrophoretic mobility shift assay (EMSA) was selected to examine DNA-protein interactions.

Results: A total of 705 subjects were enrolled in the study. Ten DSVs were found in AMI patients (n = 352) and controls (n = 353), including seven SNPs. One novel heterozygous DSV, (g.22168409 A > G), and two SNPs, [g.22168362 C > A(rs1416421760) and g.22168521 G > T(rs1445501474)], were reported in three AMI patients, which were not found in controls. The relevant statistical analysis, including allele and genotype frequencies between AMI patients and controls, five genetic models, linkage disequilibrium (LD) and haplotype analysis, and SNP–SNP interactions, suggested no statistical significance (P > 0.05). The transcriptional activity of GATA6 gene promoter was significantly increased by the DSV (g.22168409 A > G) and SNP [g.22168362 C > A(rs1416421760)]. The EMSA revealed that the DSV (g.22168409 A > G) and SNP [g.22168362 C > A(rs1416421760)] evidently influenced the binding of transcription factors.

Conclusion: In conclusion, the DSV (g.22168409 A > G) and SNP [g.22168362 C > A(rs1416421760)] may increase GATA6 levels in both HEK-293 and H9c2 cell lines by affecting the binding of transcription factors. Whether the two variants identified in the GATA6 gene promoter can promote the development and progression of human AMI by altering GATA6 levels still requires further studies to verify.

Fluid shear stress stimulates breast cancer cells to display invasive and chemoresistant phenotypes while upregulating PLAU in a 3D bioreactor

Breast cancer cells experience a range of shear stresses in the tumor microenvironment (TME). However most current in vitro three-dimensional (3D) models fail to systematically probe the effects of this biophysical stimuli on cancer cell metastasis, proliferation, and chemoresistance. To investigate the roles of shear stress within the mammary and lung pleural effusion TME, a bioreactor capable of applying shear stress to cells within a 3D extracellular matrix was designed and characterized. Breast cancer cells were encapsulated within an interpenetrating network hydrogel and subjected to shear stress of 5.4 dynes cm^-2 for 72 hr. Finite element modeling assessed shear stress profiles within the bioreactor. Cells exposed to shear stress had significantly higher cellular area and significantly lower circularity, indicating a motile phenotype. Stimulated cells were more proliferative than static controls and showed higher rates of chemoresistance to the anti-neoplastic drug paclitaxel. Fluid shear stress-induced significant upregulation of the PLAU gene and elevated urokinase activity was confirmed through zymography and activity assay. Overall, these results indicate that pulsatile shear stress promotes breast cancer cell proliferation, invasive potential, chemoresistance, and PLAU signaling.

Understanding the marvels behind liver regeneration

Tissue regeneration is a process by which the remaining cells of an injured organ regrow to offset the missed cells. This field is relatively a new discipline that has been a focus of intense research by clinicians, surgeons, and scientists for decades. It constitutes the cornerstone of tissue engineering, creation of artificial organs, and generation and utilization of therapeutic stem cells to undergo transformation to different types of mature cells. Many medical experts, scientists, biologists, and bioengineers have dedicated their efforts to deeply comprehend the process of liver regeneration, striving for harnessing it to invent new therapies for liver failure. Liver regeneration after partial hepatectomy in rodents has been extensively studied by researchers for many years. It is divided into three important distinctive phases including (a) Initiation or priming phase which includes an overexpression of specific genes to prepare the liver cells for replication, (b) Proliferation phase in which the liver cells undergo a series of cycles of cell division and expansion and finally, (c) termination phase which acts as brake to stop the regenerative process and prevent the liver tissue overgrowth. These events are well controlled by cytokines, growth factors, and signaling pathways. In this review, we describe the function, embryology, and anatomy of human liver, discuss the molecular basis of liver regeneration, elucidate the hepatocyte and cholangiocyte lineages mediating this process, explain the role of hepatic progenitor cells and elaborate the developmental signaling pathways and regulatory molecules required to procure a complete restoration of hepatic lobule. This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Signaling Pathways > Global Signaling Mechanisms Gene Expression and Transcriptional Hierarchies > Cellular Differentiation.

Hepatic hypertrophy and hemodynamics of portal venous flow after percutaneous transhepatic portal embolization

Background

Percutaneous transhepatic portal embolization (PTPE) is useful for safe major hepatectomy. This study investigated the correlation between hepatic hypertrophy and hemodynamics of portal venous flow by ultrasound sonography after PTPE.

Methods

We analyzed 58 patients with PTPE, excluding those who underwent recanalization (n = 10). Using CT volumetry results 2 weeks after PTPE, the patients were stratified into a considerable hypertrophy group (CH; n = 15) with an increase rate of remnant liver volume (IR-RLV) ≥ 40% and a minimal hypertrophy group (MH; n = 33) with an IR-RLV < 40%. We investigated the hemodynamics of portal venous flow after PTPE and the favorable factors for hepatic hypertrophy.

Results

Univariate and multivariate analysis identified the indocyanine green retention rate at 15 min (ICGR15) and increase rate of portal venous flow volume (IR-pFV) at the non-embolized lobe on day 3 after PTPE as independent favorable factors of IR-RLV. Patients with IR-pFV on day 3 after PTPE ≥100% and ICGR15 ≤ 15% (n = 13) exhibited significantly increased IR-RLV compared with others (n = 35).

Conclusions

Cases with high IR-pFV on day 3 after PTPE exhibited better hepatic hypertrophy. Preserved liver function and increased portal venous flow on day 3 were important.

Sustained expression of MCP-1 by low wall shear stress loading concomitant with turbulent flow on endothelial cells of intracranial aneurysm

INTRODUCTION

Enlargement of a pre-existing intracranial aneurysm is a well-established risk factor of rupture. Excessive low wall shear stress concomitant with turbulent flow in the dome of an aneurysm may contribute to progression and rupture. However, how stress conditions regulate enlargement of a pre-existing aneurysm remains to be elucidated.

RESULTS

Wall shear stress was calculated with 3D-computational fluid dynamics simulation using three cases of unruptured intracranial aneurysm. The resulting value, 0.017 Pa at the dome, was much lower than that in the parent artery. We loaded wall shear stress corresponding to the value and also turbulent flow to the primary culture of endothelial cells. We then obtained gene expression profiles by RNA sequence analysis. RNA sequence analysis detected hundreds of differentially expressed genes among groups. Gene ontology and pathway analysis identified signaling related with cell division/proliferation as overrepresented in the low wall shear stress-loaded group, which was further augmented by the addition of turbulent flow. Moreover, expression of some chemoattractants for inflammatory cells, including MCP-1, was upregulated under low wall shear stress with concomitant turbulent flow. We further examined the temporal sequence of expressions of factors identified in an in vitro study using a rat model. No proliferative cells were detected, but MCP-1 expression was induced and sustained in the endothelial cell layer.

CONCLUSIONS

Low wall shear stress concomitant with turbulent flow contributes to sustained expression of MCP-1 in endothelial cells and presumably plays a role in facilitating macrophage infiltration and exacerbating inflammation, which leads to enlargement or rupture.

Mechanosensitive properties in the endothelium and their roles in the regulation of endothelial function

: Vascular endothelial cells (ECs) line the luminal surface of blood vessels, which are exposed constantly to mechanical stimuli, such as fluid shear stress, cyclic strain, and blood pressure. In recent years, more and more evidence indicates that ECs sense these mechanical stimuli and subsequently convert mechanical stimuli into intracellular signals. The properties of ECs that sense the mechanical stimuli are defined as mechanosensors. There are a variety of mechanosensors that have been identified in ECs. These mechanosensors play an important role in regulating the function of the endothelium and vascular function, including blood pressure. This review focuses on the mechanosensors that have been identified in ECs and on the roles that mechanosensors play in the regulation of endothelium function, and in the regulation of vascular function.

Effects of shear stress and stretch on endothelial function

Vascular endothelial cells (ECs) play a central role in the control of blood vessel function and circulatory system homeostasis. It is well known that that EC functions are regulated by chemical mediators, including hormones, cytokines, and neurotransmitters, but it has recently become apparent that EC functions are also controlled by hemodynamic forces such as shear stress and stretch (cyclic strain). ECs recognize shear stress and cyclic strain as mechanical stimuli, and transmit the signal into the interior of the cells, thereby triggering a variety of cellular responses that involve alterations in cell morphology, cell function, and gene expression. Impaired EC responses to shear stress and cyclic strain lead to vascular diseases, including hypertension, thrombosis, and atherosclerosis. A great deal of research has already been conducted on the mechanotransduction of shear stress and cyclic strain, and its molecular mechanisms are gradually coming to be understood. However, much remains unclear, and further studies of mechanotransduction should increase our understanding of the molecular basis of the hemodynamic-force-mediated control of vascular functions.

New molecular mechanisms for cardiovascular disease:blood flow sensing mechanism in vascular endothelial cells

Endothelial cells (ECs) lining blood vessels have a variety of functions and play a critical role in the homeostasis of the circulatory system. It has become clear that biomechanical forces generated by blood flow regulate EC functions. ECs are in direct contact with blood flow and exposed to shear stress, a frictional force generated by flowing blood. A number of recent studies have revealed that ECs recognize changes in shear stress and transmit signals to the interior of the cell, which leads to cell responses that involve changes in cell morphology, cell function, and gene expression. These EC responses to shear stress are thought to play important roles in blood flow-dependent phenomena such as vascular tone control, angiogenesis, vascular remodeling, and atherogenesis. Much research has been done on shear stress sensing and signal transduction, and their molecular mechanisms are gradually becoming understood. However, much remains uncertain, and many candidates have been proposed for shear stress sensors. More extensive studies of vascular mechanobiology should increase our understanding of the molecular basis of the blood flow-mediated control of vascular functions.

GATA6 promotes colon cancer cell invasion by regulating urokinase plasminogen activator gene expression

GATA6 is a zinc finger transcription factor expressed in the colorectal epithelium. We have examined the expression of GATA6 in colon cancers and investigated the mechanisms by which GATA6 regulates colon cancer cell invasion. GATA6 was overexpressed in colorectal polyps and primary and metastatic tumors. GATA6 was strongly expressed in both the nuclear and cytoplasmic compartments of the colon cancer cells. GATA6 expression was upregulated in invasive HT29 and KM12L4 cells compared with the parental HT29 and KM12 cells and positively correlated with urokinase-type plasminogen activator (uPA) gene expression. Small interfering RNA (siRNA) knockdown of GATA6 resulted in reduced uPA gene expression and cell invasion. GATA6 bound to the uPA gene regulatory sequences in vivo and activated uPA promoter activity in vitro. uPA promoter deletion analysis indicated that the promoter proximal Sp1 sites were required for GATA6 activation of the uPA promoter. Accordingly, GATA6 physically associated with Sp1 and siRNA knockdown of Sp1 decreased GATA6 activation of the uPA promoter activity suggesting that Sp1 recruits GATA6 to the uPA promoter and mediates GATA6 induced activation of the uPA promoter activity. On the basis of our results, we conclude that GATA6 is an important regulator of uPA gene expression, and the dysregulated expression of GATA6 contributes to colorectal tumorigenesis and tumor invasion.

[Blood flow sensing mechanism via calcium signaling in vascular endothelium]

The structure and function of blood vessels adapt to environmental changes, for example, physical development and exercise. This phenomenon is based on the ability of endothelial cells (ECs) to sense and respond to blood flow. ECs are in direct contact with blood flow and exposed to shear stress. A number of recent studies have revealed that ECs recognize changes in shear stress and transmit signals to the interior of the cell, which leads to cellular responses that involve changes in cell morphology, cell function, and gene expression. Cultured human pulmonary artery ECs (HPAECs) showed Ca²(+) influx via an ATP-operated cation channel, P2X4, in response to shear stress. We have recently found that shear-induced activation of P2X4 requires endogenously released ATP and that shear stress induced HPAECs to release ATP, which was mediated by cell-surface ATP synthase located in caveolae. To gain insight into its significance, we generated a P2X4-deficient mouse. P2X4(-/-) mice do not exhibit normal EC responses to flow, such as Ca²(+) influx and subsequent production of NO, a potent vasodilator. Additionally, vessel dilation induced by acute increases in blood flow is markedly suppressed in P2X4(-/-) mice. Furthermore, P2X4(-/-) mice have higher blood pressure than wild-type mice. Moreover, no adaptive vascular remodeling is observed in the P2X4(-/-) mice. Thus, P2X4-mediated shear stress mechanotransduction plays an important role in the vascular homeostasis, including the control of blood pressure and vascular remodeling.

Effect of endothelial cell proliferation on atherogenesis: a role of p21(Sdi/Cip/Waf1) in monocyte adhesion to endothelial cells

OBJECTIVE

Uniform laminar shear stress (LS) and disturbed turbulent shear stress (DS) are thought to play opposite roles in preventing or inducing atherosclerosis. Endothelial cell (EC) growth and monocyte adhesion to ECs, an early event in atherosclerosis, are also oppositely regulated by LS and DS. However, how atherogenesis is affected by the regulation of growth by blood flow is unknown. Here we examined the role of p21(Sdi/Cip/Waf1) (p21), a growth inhibitor induced by LS, in monocyte adhesion to ECs.

METHODS

p21 was overexpressed by transfecting a p21-expressing adenoviral vector into ECs. Factors linking EC growth, monocyte adhesion, and p21 were examined by microarray analysis, PCR and Western blotting.

RESULTS

Compared with DS, in the presence or absence of TNFalpha, LS significantly inhibited EC growth and monocyte adhesion to ECs. Both EC proliferation and monocyte adhesion induced by DS were inhibited by p21-overexpression. LS suppressed the expression of thioredoxin-interacting protein (TXNIP). Thioredoxin (TRX) activity, which is suppressed by TXNIP, was therefore higher under LS than DS, as reported previously. p21-overexpression significantly suppressed the DS-induced TXNIP expression, and inhibited the expression of vascular cell adhesion molecule 1 and chemokine (C-C motif) ligand 5 (CCL5/RANTES), which stimulates leukocyte recruitment and is downregulated by ROS scavenging.

CONCLUSION

p21 may function to prevent atherogenesis by regulating the redox balance, which leads to the inhibition of adhesion molecule and chemokine expression in ECs under LS.

Simvastatin restores down-regulated GATA-6 expression in pulmonary hypertensive rats

Vascular smooth muscle cell proliferation has been known to be predominant in vascular remodeling of pulmonary hypertensive. The GATA family proteins, a group of zinc finger transcription factors, play an important role during cell proliferation. The aim of present study was to investigate the expression of GATA-6 gene in experimental pulmonary hypertensive rats and explore the effect of regulation of GATA-6 expression by simvastatin on pulmonary vascular remodeling. The male Sprague-Dawley rats model was established with receiving pneumonectomy and monocrotaline (MCT) administration. Right pulmonary artery remodeling in these animals was compared with untreated rats or rats receiving simvastatin. The level of GATA-6 mRNA and protein expression was detected by reverse transcriptase–polymerase chain reaction (RT-PCR) and Western blotting, respectively. Pneumonectomized, MCT-treated rats had significantly increased mean pulmonary arterial pressure (mPAP), RV/(LV + S) ratio (ratio of the right ventricular to left ventricular and septum weights), vascular occlusion scores (VOSs), and percent media wall thickness on day 35, all the indices were significantly decreased after simvastatin administration in these rats. The level of GATA-6 mRNA and protein were markedly decreased in these pneumonectomy and MCT-treated rats, and they were significantly up-regulated in these rats after receiving simvastatin. These results indicate that the development and progression of pulmonary hypertension is prevented by simvastatin by up-regulating GATA-6 expression in the lung tissue.

Vascular mechanobiology: endothelial cell responses to fluid shear stress

Endothelial cells (ECs) lining blood vessel walls respond to shear stress, a fluid mechanical force generated by flowing blood, and the EC responses play an important role in the homeostasis of the circulatory system. Abnormal EC responses to shear stress impair various vascular functions and lead to vascular diseases, including hypertension, thrombosis, and atherosclerosis. Bioengineering approaches in which cultured ECs are subjected to shear stress in fluid-dynamically designed flow-loading devices have been widely used to analyze EC responses at the cellular and molecular levels. Remarkable progress has been made, and the results have shown that ECs alter their morphology, function, and gene expression in response to shear stress. Shear stress affects immature cells, as well as mature ECs, and promotes differentiation of bone-marrow-derived endothelial progenitor cells and embryonic stem cells into ECs. Much research has been done on shear stress sensing and signal transduction, and their molecular mechanisms are gradually coming to be understood. However, much remains uncertain, and many candidates have been proposed for shear stress sensors. More extensive studies of vascular mechanobiology should increase our understanding of the molecular basis of the blood-flow-mediated control of vascular functions.

A model of liver regeneration

The network of interactions underlying liver regeneration is robust and precise with liver resections resulting in controlled hyperplasia (cell proliferation) that terminates when the liver regains its lost mass. The interplay of cytokines and growth factors responsible for the inception and termination of this hyperplasia is not well understood. A model is developed for this network of interactions based on the known data of liver resections. This model reproduces the relevant published data on liver regeneration and provides geometric insights into the experimental observations. The predictions of this model are used to suggest two novel strategies for speeding up liver mass recovery and a strategy for enabling liver mass recovery in cases where a resection leaves <20% of the liver that would otherwise result in complete loss of liver mass.

Angiotensin II-inducible smooth muscle cell apoptosis involves the angiotensin II type 2 receptor, GATA-6 activation, and FasL-Fas engagement

RATIONALE

Fas ligand (FasL)-mediated smooth muscle cell (SMC) apoptosis within the vulnerable plaque may lead to plaque instability and rupture, events that underlie myocardial infarction and stroke.

OBJECTIVE

The molecular mechanisms underlying FasL transcription and FasL-dependent SMC apoptosis were investigated in this study in vitro and in vivo.

METHODS AND RESULTS

We demonstrate that GATA-6, the predominant GATA family member expressed in SMCs, stimulates SMC apoptosis in an extracellular FasL-dependent manner. Both GATA-6 and FasL were inducibly and transiently expressed following balloon injury to rat carotid arteries. We identified two potential GATA binding in the FasL promoter and demonstrated using DNA binding and chromatin immunoprecipitation assays that GATA-6 regulates FasL through one ((-298)TTATCA(-303)) but not both these elements. Angiotensin II (Ang II) stimulated expression of both GATA-6 and FasL. Ang II increased SMC apoptosis in an Ang II type 2 receptor-, caspase 8-, and FasL-dependent fashion. GATA-6 activation was MEK-ERK1/2- and JNK-dependent, and GATA-6 small interfering RNA blocked Ang II-inducible FasL expression and SMC apoptosis. Administration of Ang II to rats increased FasL expression and apoptosis in carotid artery SMCs in an Ang II type 2 receptor- and GATA-6-dependent manner.

CONCLUSIONS

This study provides new insights into the transcriptional events underpinning FasL-dependent SMC apoptosis after exposure to Ang II.

Fluid shear stress induces arterial differentiation of endothelial progenitor cells

Endothelial progenitor cells (EPCs) are mobilized from bone marrow to peripheral blood and contribute to angiogenesis in tissues. In the process, EPCs are exposed to the shear stress generated by blood flow and tissue fluid flow. Our previous study showed that shear stress promotes differentiation of EPCs into mature endothelial cells. In this study, we investigated whether EPCs differentiate into arterial or venous endothelial cells in response to shear stress. When cultured EPCs derived from human peripheral blood were exposed to controlled levels of shear stress in a flow-loading device, the mRNA levels of the arterial endothelial cell markers ephrinB2, Notch1/3, Hey1/2, and activin receptor-like kinase 1 increased, but the mRNA levels of the venous endothelial cell markers EphB4 and neuropilin-2 decreased. Both the ephrinB2 increase and the EphB4 decrease were shear stress dependent rather than shear rate dependent. EphrinB2 protein was increased in shear-stressed EPCs, and the increase in ephrinB2 expression was due to activated transcription and not mRNA stabilization. Deletion analysis of the ephrinB2 promoter indicated that the cis-element (shear stress response element) is present within 106 bp 5' upstream from the transcription initiation site. This region contains the Sp1 consensus sequence, and a mutation in its sequence decreased the basal level of transcription and abolished shear stress-induced ephrinB2 transcription. Electrophoretic mobility shift assays and chromatin immunoprecipitation assays showed that shear stress markedly increased binding of Sp1 to its consensus sequence. These results indicate that shear stress induces differentiation of EPCs into arterial endothelial cells by increasing ephrinB2 expression in EPCs through Sp1 activation.

Shear stress-induced Ets-1 modulates protease inhibitor expression in microvascular endothelial cells

Elevated shear stress within the skeletal muscle microvasculature is implicated in the induction of a longitudinal splitting form of angiogenesis, which is characterized by the lack of basement membrane breakage. We investigated whether the transcriptional regulator, Ets-1, is responsive to changes in hemodynamic forces and if so, whether Ets-1 controls microvascular endothelial cell integrity by inducing the expression of inhibitors of matrix degrading proteases. Rats were treated with prazosin for 2, 4, and 7 days to increase in microvascular shear stress in hindlimb skeletal muscles. In complimentary in vitro experiments, rat microvascular skeletal muscle endothelial cells were exposed to laminar shear stress (15 dyne/cm(2)) for 0.5, 2, and 24 h. TaqMan PCR analysis of laser microdissected capillaries isolated from EDL muscles demonstrated transient (after 2 days) induction of Ets-1 gene expression. In cultured cells, a transient up-regulation of Ets-1 mRNA was observed after 2 h shear stimulation, accompanied by increased phosphorylation of Ets-1 and enhanced Ets-1 DNA binding activity. This response was modulated by ERK1/2 and p38 MAP kinases, but was not dependent on NOS or COX-2 activity. PAI-1, TIMP-1 and TIMP-3 mRNA were elevated significantly in prazosin treated EDL, and in response to shear stimulation in vitro. In cultured endothelial cells, Ets-1 RNA interference abolished the shear-induced increases in Ets-1, PAI-1, TIMP-1, and TIMP-3 mRNA expression. These results suggest that enhanced laminar shear stress may act to preserve the integrity of microvascular walls in part through Ets-1-dependent induction of protease inhibitors.

Vascular actions of estrogens: functional implications

The impact of estrogen exposure in preventing or treating cardiovascular disease is controversial. But it is clear that estrogen has important effects on vascular physiology and pathophysiology, with potential therapeutic implications. Therefore, the goal of this review is to summarize, using an integrated approach, current knowledge of the vascular effects of estrogen, both in humans and in experimental animals. Aspects of estrogen synthesis and receptors, as well as general mechanisms of estrogenic action are reviewed with an emphasis on issues particularly relevant to the vascular system. Recent understanding of the impact of estrogen on mitochondrial function suggests that the longer lifespan of women compared with men may depend in part on the ability of estrogen to decrease production of reactive oxygen species in mitochondria. Mechanisms by which estrogen increases endothelial vasodilator function, promotes angiogenesis, and modulates autonomic function are summarized. Key aspects of the relevant pathophysiology of inflammation, atherosclerosis, stroke, migraine, and thrombosis are reviewed concerning current knowledge of estrogenic effects. A number of emerging concepts are addressed throughout. These include the importance of estrogenic formulation and route of administration and the impact of genetic polymorphisms, either in estrogen receptors or in enzymes responsible for estrogen metabolism, on responsiveness to hormone treatment. The importance of local metabolism of estrogenic precursors and the impact of timing for initiation of treatment and its duration are also considered. Although consensus opinions are emphasized, controversial views are presented to stimulate future research.

Liver regeneration

Liver regeneration after partial hepatectomy is a very complex and well-orchestrated phenomenon. It is carried out by the participation of all mature liver cell types. The process is associated with signaling cascades involving growth factors, cytokines, matrix remodeling, and several feedbacks of stimulation and inhibition of growth related signals. Liver manages to restore any lost mass and adjust its size to that of the organism, while at the same time providing full support for body homeostasis during the entire regenerative process. In situations when hepatocytes or biliary cells are blocked from regeneration, these cell types can function as facultative stem cells for each other.

Liver regeneration

Liver regeneration after partial hepatectomy is a very complex and well-orchestrated phenomenon. It is carried out by the participation of all mature liver cell types. The process is associated with signaling cascades involving growth factors, cytokines, matrix remodeling, and several feedbacks of stimulation and inhibition of growth related signals. Liver manages to restore any lost mass and adjust its size to that of the organism, while at the same time providing full support for body homeostasis during the entire regenerative process. In situations when hepatocytes or biliary cells are blocked from regeneration, these cell types can function as facultative stem cells for each other.

Aryl hydrocarbon receptor mediates laminar fluid shear stress-induced CYP1A1 activation and cell cycle arrest in vascular endothelial cells

AIMS

We investigated the mechanisms of shear stress (SS)-induced activation of cytochrome P450 (CYP) 1A1 and cell cycle arrest with regard to the role of the aryl hydrocarbon receptor (AhR), since AhR mediates the expression of CYP1A1 induced by polycyclic aromatic hydrocarbons (PAHs) and is thought to be involved in the regulation of cell growth and differentiation.

METHODS AND RESULTS

Human umbilical vein endothelial cells (ECs) were exposed to laminar SS and thereafter collected to evaluate the expression, activity, and transcription of CYP1A1 and the expression of AhR and cell cycle-related proteins. A physiological level of laminar SS (15 dynes/cm(2)) markedly increased the expression level and enzymatic activity of CYP1A1. SS stimulated CYP1A1 promoter activity without influencing mRNA stability. Loss of two functional xenobiotic response elements (XREs) in the 5'-flanking region of the CYP1A1 gene suppressed the SS-induced transcription of CYP1A1. Laminar SS stimulated the expression and nuclear translocation of AhR. alpha-Naphthoflavone, an AhR antagonist, and a small interfering RNA (siRNA) for AhR significantly suppressed SS-induced CYP1A1 expression. The siRNA also abolished SS-induced cell cycle arrest, the expression of the cyclin-dependent kinase inhibitor p21(Cip1), and dephosphorylation of retinoblastoma protein.

CONCLUSION

Laminar SS stimulated the transcription of CYP1A1 through the activation of AhR in a way that is similar to the effects of PAHs. AhR was also involved in cell cycle arrest induced by SS. Our results suggest that sustained activation of AhR exposed to blood flow plays an important role in the regulation of EC functions.

Modulation of pulmonary endothelial endothelin B receptor expression and signaling: implications for experimental hepatopulmonary syndrome

The hepatopulmonary syndrome (HPS) results from intrapulmonary vasodilation in the setting of cirrhosis and portal hypertension. In experimental HPS, pulmonary endothelial endothelin B (ET(B)) receptor overexpression and increased circulating endothelin-1 (ET-1) contribute to vasodilation through enhanced endothelial nitric oxide synthase (eNOS)-derived nitric oxide (NO) production. In both experimental cirrhosis and prehepatic portal hypertension, ET(B) receptor overexpression correlates with increased vascular shear stress, a known modulator of ET(B) receptor expression. We investigated the mechanisms of pulmonary endothelial ET(B) receptor-mediated eNOS activation by ET-1 in vitro and in vivo. The effect of shear stress on ET(B) receptor expression was assessed in rat pulmonary microvascular endothelial cells (RPMVECs). The consequences of ET(B) receptor overexpression on ET-1-dependent ET(B) receptor-mediated eNOS activation were evaluated in RPMVECs and in prehepatic portal hypertensive animals exposed to exogenous ET-1. Laminar shear stress increased ET(B) receptor expression in RPMVECs without altering mRNA stability. Both shear-mediated and targeted overexpression of the ET(B) receptor enhanced ET-1-mediated ET(B) receptor-dependent eNOS activation in RPMVECs through Ca(2+)-mediated signaling pathways and independent of Akt activation. In prehepatic portal hypertensive animals relative to control, ET-1 administration also activated eNOS independent of Akt activation and triggered HPS. These findings support that increased pulmonary microvascular endothelial ET(B) receptor expression modulates ET-1-mediated eNOS activation, independent of Akt, and contributes to the development of HPS.

Meningococcal adhesion suppresses proapoptotic gene expression and promotes expression of genes supporting early embryonic and cytoprotective signaling of human endothelial cells

Neisseria meningitidis colonizes the human nasopharynx and occasionally causes lethal or damaging septicemia and meningitis. Here, we examined the adherence-mediated signaling of meningococci to human cells by comparing gene expression profiles of human umbilical vein endothelial cells (HUVEC) infected by adherent wild-type, frpC-deficient mutant, or the nonadherent (DeltapilD) N. meningitidis. Pili-mediated adhesion of meningococci resulted in alterations of expression levels of human genes known to regulate apoptosis, cell proliferation, inflammatory response, adhesion and genes for signaling pathway proteins such as TGF-beta/Smad, Wnt/beta-catenin and Notch/Jagged. This reveals that adhering piliated meningocci manipulate host signaling pathways controlling cell proliferation while establishing a commensal relationship.

Cyclic strain-mediated matrix metalloproteinase regulation within the vascular endothelium: a force to be reckoned with

The vascular endothelium is a dynamic cellular interface between the vessel wall and the bloodstream, where it regulates the physiological effects of humoral and biomechanical stimuli on vessel tone and remodeling. With respect to the latter hemodynamic stimulus, the endothelium is chronically exposed to mechanical forces in the form of cyclic circumferential strain, resulting from the pulsatile nature of blood flow, and shear stress. Both forces can profoundly modulate endothelial cell (EC) metabolism and function and, under normal physiological conditions, impart an atheroprotective effect that disfavors pathological remodeling of the vessel wall. Moreover, disruption of normal hemodynamic loading can be either causative of or contributory to vascular diseases such as atherosclerosis. EC-matrix interactions are a critical determinant of how the vascular endothelium responds to these forces and unquestionably utilizes matrix metalloproteinases (MMPs), enzymes capable of degrading basement membrane and interstitial matrix molecules, to facilitate force-mediated changes in vascular cell fate. In view of the growing importance of blood flow patterns and mechanotransduction to vascular health and pathophysiology, and considering the potential value of MMPs as therapeutic targets, a timely review of our collective understanding of MMP mechanoregulation and its impact on the vascular endothelium is warranted. More specifically, this review primarily summarizes our current knowledge of how cyclic strain regulates MMP expression and activation within the vascular endothelium and subsequently endeavors to address the direct and indirect consequences of this on vascular EC fate. Possible relevance of these phenomena to vascular endothelial dysfunction and pathological remodeling are also addressed.

Shear stress induces hepatocyte PAI-1 gene expression through cooperative Sp1/Ets-1 activation of transcription

Partial hepatectomy causes hemodynamic changes that increase portal blood flow in the remaining lobe, where the expression of immediate-early genes, including plasminogen activator inhibitor-1 (PAI-1), is induced. We hypothesized that a hyperdynamic circulatory state occurring in the remaining lobe induces immediate-early gene expression. In this study, we investigated whether the mechanical force generated by flowing blood, shear stress, induces PAI-1 expression in hepatocytes. When cultured rat hepatocytes were exposed to flow, PAI-1 mRNA levels began to increase within 3 h, peaked at levels significantly higher than the static control levels, and then gradually decreased. The flow-induced PAI-1 expression was shear stress dependent rather than shear rate dependent and accompanied by increased hepatocyte production of PAI-1 protein. Shear stress increased PAI-1 transcription but did not affect PAI-1 mRNA stability. Functional analysis of the 2.1-kb PAI-1 5'-promoter indicated that a 278-bp segment containing transcription factor Sp1 and Ets-1 consensus sequences was critical to the shear stress-dependent increase of PAI-1 transcription. Mutations of both the Sp1 and Ets-1 consensus sequences, but not of either one alone, markedly prevented basal PAI-1 transcription and abolished the response of the PAI-1 promoter to shear stress. EMSA and chromatin immunoprecipitation assays showed binding of Sp1 and Ets-1 to each consensus sequence under static conditions, which increased in response to shear stress. In conclusion, hepatocyte PAI-1 expression is flow sensitive and transcriptionally regulated by shear stress via cooperative interactions between Sp1 and Ets-1.

Synthesis, regulation and production of urokinase using mammalian cell culture: a comprehensive review

Urokinase, a serine protease, catalyzes the conversion of plasminogen to plasmin, which is responsible for dissolution of clots in blood vessels. It is an important drug for treatment of thromboembolic disease. Production of urokinase by mammalian cell culture has the following important steps: synthesis, regulation and secretion. Production and accumulation of this product in a bioreactor is a real challenge for biochemical engineers. Considerable information at molecular level needs to be understood for production of urokinase in order to correlate different parameters, which in turn can maximize the productivity. This information will be highlighted in this review. Moreover, urokinase production is a product-inhibited process. Therefore, in situ urokinase separation strategy is required to operate a bioreactor at its maximum urokinase formation rate. Integrated urokinase production and isolation processes developed recently will also be discussed briefly in this review.

Shear stress contributes to t-PA mRNA expression in human endothelial progenitor cells and nonthrombogenic potential of small diameter artificial vessels

Seeding endothelial progenitor cells (EPCs) onto the surface of vascular grafts has been proved to be a promising strategy to improve nonthrombogenic potentials of small diameter artificial vessels. Here, we investigated whether in vitro shear stress modulates the tissue-type plasminogen activator (t-PA) secretion and mRNA expression in human EPCs and improves patency of the EPC-seeded polyurethane small diameter vascular grafts implanted in the canine carotid artery in vivo. In vitro shear stress, in a dose-dependent manner, increased t-PA secretion and mRNA expression of human EPCs. The in vivo implantation of EPC-seeded vascular grafts remained highly patent in shear stress pretreatment compared with stationary condition. The present findings demonstrate for the first time that in vitro shear stress can enhance t-PA secretion and gene expression in human EPCs, which contributes to improvement in nonthrombogenic potentials of EPC-seeded small diameter artificial vessels with maintenance of in vivo highly patency rate.

Expression of GATA6 in the human and mouse central nervous system

The mammalian GATA family of transcription factors comprises of 6 members that are involved in diverse roles. The expression profile of GATA6 has been poorly defined in the central nervous system (CNS). In this report, we identify GATA6 expression in the normal mouse and human CNS, using Northern blot analyses, immunohistochemistry (IHC), and immunofluorescence (IF). GATA6 is expressed as a 2.2 kb transcript in the adult mouse brain and several regions of the adult human brain. Furthermore, cellular characterization demonstrates GATA6 nuclear expression in neurons, astrocytes, choroids plexus epithelium, and endothelial cells.

Lack of insulin-like growth factor binding protein-3 protease activation by venous cannulation

Disruption of the endothelium activates thrombogenic and fibrinolytic enzymes that cleave insulin-like growth factor binding protein-3 (IGFBP-3) in vitro. The aim of the present human study was to determine whether blood sampling, i.e., venous stasis and cannulation increase IGFBP-3 proteolysis before and/or after surgery by activating these enzymes. Serum samples obtained immediately after cannulation were compared with samples obtained from a previously inserted venous catheter. Cannulation did not increase serum IGFBP-3 proteolytic activity pre- and post-operatively, as determined by in vitro degradation of 125I-IGFBP-3. Furthermore, there was no effect on in vivo IGFBP-3 fragmentation assessed by western immunoblot. In addition, a standardized venous stasis did not affect IGFBP-3 proteolytic activity or fragmentation. Comparison of IGFBP-3 proteolytic activity before and after surgery demonstrated a significant post-operative increase. However, this could not be demonstrated immediately after the initial cannulation, due to a large individual variation at this time-point before surgery.

In vivo gene delivery of urokinase-type plasminogen activator with regulatable lentivirus induces behavioural changes in chronic cocaine administration

Serine proteases play a key function in extracellular processes affecting central nervous system plasticity. Recently, the role of extracellular proteolytic processes in regulating synaptic structure and function has been described. However, to date direct evidence linking extracellular serine protease activity with drug-related behavioural changes has not been documented. Importantly, in a screening for genes induced after drug treatment we found that urokinase plasminogen-type activator (uPA) was strongly regulated by cocaine in several protocols of drug administration. Cocaine-induced up-regulation could be verified on microarray analysis under several protocols of drug administration, then further fully confirmed by means of qRT-PCR. As a result, we chose to investigate further uPA function in the mesolimbic dopaminergic pathway, a major target area of cocaine and drugs of misuse. Our approach was based on the characterization of cocaine-induced behavioural changes following lentiviral vector delivery of a doxycycline-regulated uPA expression cassette (or of its mutated form), into specific rat brain areas (the hippocampus, the nucleus accumbens and the ventral tegmental area). We show that doxycycline-dependent over-expression of uPA in these regions yields a 10- to 12.3-fold increase in locomotor activity after cocaine administration. These behavioural effects were completely abolished when the active site of the protease was point-mutated and used as a dominant negative. The physiological relevance of these drastic behavioural changes is discussed.