Shear flow attenuates serum-induced STAT3 activation in endothelial cells

IL-4-STAT6 axis amplifies histamine-induced vascular endothelial dysfunction and hypovolemic shock

BACKGROUND

Mast cell-derived mediators induce vasodilatation and fluid extravasation, leading to cardiovascular failure in severe anaphylaxis. We previously revealed a synergistic interaction between the cytokine IL-4 and the mast cell-derived mediator histamine in modulating vascular endothelial (VE) dysfunction and severe anaphylaxis. The mechanism by which IL-4 exacerbates histamine-induced VE dysfunction and severe anaphylaxis is unknown.

OBJECTIVE

We sought to identify the IL-4-induced molecular processes regulating the amplification of histamine-induced VE barrier dysfunction and the severity of IgE-mediated anaphylactic reactions.

METHODS

RNA sequencing, Western blot, Ca2+ imaging, and barrier functional analyses were performed on the VE cell line (EA.hy926). Pharmacologic degraders (selective proteolysis-targeting chimera) and genetic (lentiviral short hairpin RNA) inhibitors were used to determine the roles of signal transducer and activator of transcription 3 (STAT3) and STAT6 in conjunction with in vivo model systems of histamine-induced hypovolemic shock.

RESULTS

IL-4 enhancement of histamine-induced VE barrier dysfunction was associated with increased VE-cadherin degradation, intracellular calcium flux, and phosphorylated Src levels and required transcription and de novo protein synthesis. RNA sequencing analyses of IL-4-stimulated VE cells identified dysregulation of genes involved in cell proliferation, cell development, and cell growth, and transcription factor motif analyses revealed a significant enrichment of differential expressed genes with putative STAT3 and STAT6 motif. IL-4 stimulation in EA.hy926 cells induced both serine residue 727 and tyrosine residue 705 phosphorylation of STAT3. Genetic and pharmacologic ablation of VE STAT3 activity revealed a role for STAT3 in basal VE barrier function; however, IL-4 enhancement and histamine-induced VE barrier dysfunction was predominantly STAT3 independent. In contrast, IL-4 enhancement and histamine-induced VE barrier dysfunction was STAT6 dependent. Consistent with this finding, pharmacologic knockdown of STAT6 abrogated IL-4-mediated amplification of histamine-induced hypovolemia.

CONCLUSIONS

These studies unveil a novel role of the IL-4/STAT6 signaling axis in the priming of VE cells predisposing to exacerbation of histamine-induced anaphylaxis.

Reversal of atherosclerosis by restoration of vascular copper homeostasis

Atherosclerosis has traditionally been considered as a disorder characterized by the accumulation of cholesterol and thrombotic materials within the arterial wall. However, it is now understood to be a complex inflammatory disease involving multiple factors. Central to the pathogenesis of atherosclerosis are the interactions among monocytes, macrophages, and neutrophils, which play pivotal roles in the initiation, progression, and destabilization of atherosclerotic lesions. Recent advances in our understanding of atherosclerosis pathogenesis, coupled with results obtained from experimental interventions, lead us to propose the hypothesis that atherosclerosis may be reversible. This paper outlines the evolution of this hypothesis and presents corroborating evidence that supports the potential for atherosclerosis regression through the restoration of vascular copper homeostasis. We posit that these insights may pave the way for innovative therapeutic approaches aimed at the reversal of atherosclerosis.

Aqueous Humor Circulation in the Era of Minimally Invasive Surgery for Glaucoma

Glaucoma surgery with implantation of aqueous humor draining microstents may compromise long-term corneal health by disrupting aqueous humor circulation. The effect of stent numbers on this circulation was interrogated to determine the number of stents associated with minimal circulation disruption. An in vitro anterior eye model perfusion system was constructed with multiple exit ports. A 3-D model of the anterior eye was imported into ABAQUS CFD, analyzes were carried out for unsteady laminar flow and solved using Navier-Stokes equations. DT Vision Foundry was used to analyze velocity contour plot images. The field variable results output for the CFD model were fluid wall shear, fluid pressure and fluid velocity. In vitro, "aqueous" fluid flow is high through a single stent and "aqueous" stagnation is greatest in the quadrants 180° away. Increasing stent port numbers, results in an exponential decrease in the stagnant flow locations. High wall shear stress was seen in the single stent model and is markedly reduced after a second and subsequent stents are introduced. We identify two factors potentially contributing to corneal compromise post glaucoma drainage surgery: aqueous humor stagnation, remote to the stent site and higher exit flows imparting increased stent exit shear stress (particularly with a single stent). With 4 stents, there is minimal disruption of anterior chamber circulation (mimicking physiological conditions). Furthermore we propose that aqueous humor circulation disruption via the usual single-exit port approach disrupts aqueous humor circulation with long-term consequences for corneal health.

Dysfunctional Vascular Endothelium as a Driver of Atherosclerosis: Emerging Insights Into Pathogenesis and Treatment

Atherosclerosis, the chronic accumulation of cholesterol-rich plaque within arteries, is associated with a broad spectrum of cardiovascular diseases including myocardial infarction, aortic aneurysm, peripheral vascular disease, and stroke. Atherosclerotic cardiovascular disease remains a leading cause of mortality in high-income countries and recent years have witnessed a notable increase in prevalence within low- and middle-income regions of the world. Considering this prominent and evolving global burden, there is a need to identify the cellular mechanisms that underlie the pathogenesis of atherosclerosis to discover novel therapeutic targets for preventing or mitigating its clinical sequelae. Despite decades of research, we still do not fully understand the complex cell-cell interactions that drive atherosclerosis, but new investigative approaches are rapidly shedding light on these essential mechanisms. The vascular endothelium resides at the interface of systemic circulation and the underlying vessel wall and plays an essential role in governing pathophysiological processes during atherogenesis. In this review, we present emerging evidence that implicates the activated endothelium as a driver of atherosclerosis by directing site-specificity of plaque formation and by promoting plaque development through intracellular processes, which regulate endothelial cell proliferation and turnover, metabolism, permeability, and plasticity. Moreover, we highlight novel mechanisms of intercellular communication by which endothelial cells modulate the activity of key vascular cell populations involved in atherogenesis, and discuss how endothelial cells contribute to resolution biology - a process that is dysregulated in advanced plaques. Finally, we describe important future directions for preclinical atherosclerosis research, including epigenetic and targeted therapies, to limit the progression of atherosclerosis in at-risk or affected patients.

The Prognostic Significance of Anisomycin-Activated Phospho-c-Jun NH2-Terminal Kinase (p-JNK) in Predicting Breast Cancer Patients' Survival Time

This study aims to investigate the prognostic significance of p-JNK in breast cancer patients receiving neoadjuvant chemotherapy (NACT) and analyze the relationship between anisomycin, p-JNK. A total of 104 breast cancer patients had NACT were enrolled in this study. The western blot and immunohistochemistry assays were used to determine the protein expressions of p-JNK in human breast cancer cell lines and patients’ cancer tissues. The chi-square test and Fisher’s exact test were adopted to gauge the associations between breast cancer and clinicopathological variables by p-JNK expression, whereas the univariate and multivariate Cox proportional hazards regression models were used to analyze the prognostic value of p-JNK expression. The Kaplan-Meier plots and the log-rank test were adopted to determine patients’ disease-free survival (DFS) and overall survival (OS). Findings indicated that the p-JNK expression had prognostic significance in univariate and multivariate Cox regression survival analyses. Results of log-rank methods showed that: (1) the mean DFS and OS times in patients with high p-JNK expression were significantly longer than those in patients with low p-JNK expression (χ² = 5.908, P = 0.015 and χ² = 6.593, P = 0.010, respectively). p-JNK expression is a significant prognostic factor that can effectively predict the survival in breast cancer patients receiving NACT. Treatment with the JNK agonist anisomycin can induce apoptosis, lead to increased p-JNK expression and decreased p-STAT3 expression. Moreover, the p-JNK expression was inversely correlated with p-STAT3 expression.

Glutaredoxin 1 mediates the protective effect of steady laminar flow on endothelial cells against oxidative stress-induced apoptosis via inhibiting Bim

Endothelial cell apoptosis induced by oxidative stress is an early event in the development of atherosclerosis. Several antioxidant enzymes which can cope with oxidative stress are up-regulated by the anti-atherogenic laminar blood flow often seen in straight or unbranched regions of blood vessels. However, the molecular mechanism responsible for flow-induced beneficial effects is incompletely understood. Here we report the role of glutaredoxin 1 (Grx1), an antioxidant enzyme, in flow-mediated protective effect in endothelial cells. Specifically, we found that Grx1 is markedly up-regulated by the steady laminar flow. Increasing Grx1 reduces the pro-apoptotic protein Bim expression through regulating Akt-FoxO1 signaling and also attenuates H2O2-induced Bim activation via inhibiting JNK phosphorylation, subsequently preventing the apoptosis of endothelial cells. Grx1 knockdown abolishes the inhibitory effect of steady laminar flow on Bim. The inhibitory effect of Grx1 on Bim is dependent on Grx1's thioltransferase activity. These findings indicate that Grx1 induction plays a key role in mediating the protective effect of laminar blood flow and suggest that Grx1 may be a potential therapeutic target for atherosclerosis.

Lithium suppresses astrogliogenesis by neural stem and progenitor cells by inhibiting STAT3 pathway independently of glycogen synthase kinase 3 beta

Transplanted neural stem and progenitor cells (NSCs) produce mostly astrocytes in injured spinal cords. Lithium stimulates neurogenesis by inhibiting GSK3b (glycogen synthetase kinase 3-beta) and increasing WNT/beta catenin. Lithium suppresses astrogliogenesis but the mechanisms were unclear. We cultured NSCs from subventricular zone of neonatal rats and showed that lithium reduced NSC production of astrocytes as well as proliferation of glia restricted progenitor (GRP) cells. Lithium strongly inhibited STAT3 (signal transducer and activator of transcription 3) activation, a messenger system known to promote astrogliogenesis and cancer. Lithium abolished STAT3 activation and astrogliogenesis induced by a STAT3 agonist AICAR (5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside), suggesting that lithium suppresses astrogliogenesis by inhibiting STAT3. GSK3β inhibition either by a specific GSK3β inhibitor SB216763 or overexpression of GID5-6 (GSK3β Interaction Domain aa380 to 404) did not suppress astrogliogenesis and GRP proliferation. GSK3β inhibition also did not suppress STAT3 activation. Together, these results indicate that lithium inhibits astrogliogenesis through non-GSK3β-mediated inhibition of STAT. Lithium may increase efficacy of NSC transplants by increasing neurogenesis and reducing astrogliogenesis. Our results also may explain the strong safety record of lithium treatment of manic depression. Millions of people take high-dose (>1 gram/day) lithium carbonate for a lifetime. GSK3b inhibition increases WNT/beta catenin, associated with colon and other cancers. STAT3 inhibition may reduce risk for cancer.

Flow-Dependent Regulation of Kruppel-Like Factor 2 Is Mediated by MicroRNA-92a

BACKGROUND

Upregulated by atheroprotective flow, the transcription factor Krüppel-like factor 2 (KLF2) is crucial for maintaining endothelial function. MicroRNAs (miRNAs) are noncoding small RNAs that regulate gene expression at the posttranscriptional level. We examined the role of miRNAs, particularly miR-92a, in the atheroprotective flow-regulated KLF2.

METHODS AND RESULTS

Dicer knockdown increased the level of KLF2 mRNA in human umbilical vein endothelial cells, suggesting that KLF2 is regulated by miRNA. In silico analysis predicted that miR-92a could bind to the 3' untranslated region of KLF2 mRNA. Overexpression of miR-92a decreased the expression of KLF2 and the KLF2-regulated endothelial nitric oxide synthase and thrombomodulin at mRNA and protein levels. A complementary finding is that miR-92a inhibitor increased the mRNA and protein expression of KLF2, endothelial nitric oxide synthase, and thrombomodulin. Subsequent studies revealed that atheroprotective laminar flow downregulated the level of miR-92a precursor to induce KLF2, and the level of this flow-induced KLF2 was reduced by miR-92a precursor. Furthermore, miR-92a level was lower in human umbilical vein endothelial cells exposed to the atheroprotective pulsatile shear flow than under atheroprone oscillatory shear flow. Anti-Ago1/2 immunoprecipitation coupled with real-time polymerase chain reaction revealed that pulsatile shear flow decreased the functional targeting of miR-92a precursor/KLF2 mRNA in human umbilical vein endothelial cells. Consistent with these findings, mouse carotid arteries receiving miR-92a precursor exhibited impaired vasodilatory response to flow.

CONCLUSIONS

Atheroprotective flow patterns decrease the level of miR-92a, which in turn increases KLF2 expression to maintain endothelial homeostasis.

Alternate-day fasting reverses the age-associated hypertrophy phenotype in rat heart by influencing the ERK and PI3K signaling pathways

The age-related increased impedance in large arteries overloads the senescent heart, and the myocardial phenotype is hypertrophic. Together with qualitative changes observed in the senile heart, this can be responsible for impaired diastolic function. A restricted diet providing adequate nutrient intake, e.g. alternate-day fasting (ADF), has been shown to extend life-span and decrease incidence and progression of age-associated diseases in laboratory rodents, and to ameliorate some metabolic markers of aging in rhesus monkeys and humans. This study reports an age-related increase of some biological and morphological hypertrophy markers in the rat heart, together with increased plasma BNP, a well known marker of heart failure. The tissue modifications might likely be related to hyper-activation of two of the signaling pathways associated with myocardial pathological hypertrophy: ERK1/2 and PI3Kγ. Increased ERK1/2 activation might be in part related to the disturbance of STAT3, with a consequent decrease of SOCS3. In this context, the down-modulation of ERK1/2 and PI3Kγ signaling, together with the restoration of STAT3 activity and SOCS3 content, both observed with ADF, might help to reduce pathological hypertrophy stimuli and to rescue an important cardioprotective pathway, possibly opening new preventive and therapeutic perspectives in age-related heart failure.

A biohybrid artificial lung prototype with active mixing of endothelialized microporous hollow fibers

Acute respiratory distress syndrome (ARDS) affects nearly 150,000 patients per year in the US, and is associated with high mortality ( approximately 40%) and suboptimal options for patient care. Mechanical ventilation and extracorporeal membrane oxygenation are limited to short-term use due to ventilator-induced lung injury and poor biocompatibility, respectively. In this report, we describe the development of a biohybrid lung prototype, employing a rotating endothelialized microporous hollow fiber (MHF) bundle to improve blood biocompatibility while MHF mixing could contribute to gas transfer efficiency. MHFs were surface modified with radio frequency glow discharge (RFGD) and protein adsorption to promote endothelial cell (EC) attachment and growth. The MHF bundles were placed in the biohybrid lung prototype and rotated up to 1,500 revolutions per minute (rpm) using speed ramping protocols to condition ECs to remain adherent on the fibers. Oxygen transfer, thrombotic deposition, and EC p-selectin expression were evaluated as indicators of biohybrid lung functionality and biocompatibility. A fixed aliquot of blood in contact with MHF bundles rotated at either 250 or 750 rpm reached saturating pO(2) levels more quickly with increased rpm, supporting the concept that fiber rotation would positively contribute to oxygen transfer. The presence of ECs had no effect on the rate of oxygen transfer at lower fiber rpm, but did provide some resistance with increased rpm when the overall rate of mass transfer was higher due to active mixing. RFGD followed by fibronectin adsorption on MHFs facilitated near confluent EC coverage with minimal p-selectin expression under both normoxic and hyperoxic conditions. Indeed, even subconfluent EC coverage on MHFs significantly reduced thrombotic deposition adding further support that endothelialization enhances, blood biocompatibility. Overall these findings demonstrate a proof-of-concept that a rotating endothelialized MHF bundle enhances gas transfer and biocompatibility, potentially producing safer, more efficient artificial lungs.

MicroRNA-19a mediates the suppressive effect of laminar flow on cyclin D1 expression in human umbilical vein endothelial cells

Endothelial cells (ECs) respond to changes in mechanical forces, leading to the modulation of signaling networks and cell function; an example is the inhibition of EC proliferation by steady laminar flow. MicroRNAs (miRs) are short noncoding 20-22 nucleotide RNAs that negatively regulate the expression of target genes at the posttranscriptional level. This study demonstrates that miRs are involved in the flow regulation of gene expression in ECs. With the use of microRNA chip array, we found that laminar shear stress (12 dyn/cm(2), 12 h) regulated the EC expression of many miRs, including miR-19a. We further showed that stable transfection of miR-19a significantly decreased the expression of a reporter gene controlled by a conserved 3'-untranslated region of the cyclinD1 gene and also the protein level of cyclin D1, leading to an arrest of cell cycle at G1/S transition. Laminar flow suppressed cyclin D1 protein level, and this suppressive effect was diminished when the endogenous miR-19a was inhibited. In conclusion, we demonstrated that miR-19a plays an important role in the flow regulation of cyclin D1 expression. These results revealed a mechanism by which mechanical forces modulate endothelial gene expression.

Signal transducer and activator of transcription 3 is required for abnormal proliferation and survival of TSC2-deficient cells: relevance to pulmonary lymphangioleiomyomatosis

Tumor suppressor complex TSC1/TSC2 represents a key negative regulator of mammalian target of rapamycin (mTOR)-S6 kinase 1 signaling. Mutational inactivation of TSC1 or TSC2, linked to a rare lung disease, lymphangioleiomyomatosis (LAM), manifests as neoplastic growth of smooth-muscle (SM)-like cells and cystic destruction of the lungs that induces loss of pulmonary function. However, the precise mechanisms of abnormal cell growth in LAM remain uncertain. Here, we demonstrate increased signal transducer and activator of transcription (STAT) 3 expression, phosphorylation, and nuclear localization in SM-like cells in LAM lungs and in TSC2-null xenographic tumors. Treatment of TSC2-null tumors with mTOR inhibitor rapamycin attenuated STAT3 expression and phosphorylation. Increased STAT3 level and activation were also observed in LAM-dissociated (LAMD) cell cultures compared with normal human bronchus fibroblasts (HBFs) from LAM patients. Although interferon (IFN)-gamma inhibited proliferation of HBFs, IFN-gamma treatment had little effect on proliferation of LAMD and TSC2-null cells. Re-expression of TSC2 or treatment with rapamycin inhibited IFN-gamma-induced STAT3 phosphorylation and synergized with IFN-gamma in inhibiting TSC2-null and LAMD cell proliferation. Reduction of STAT3 protein levels or activity using specific small interfering RNA or inhibitory peptide, respectively, decreased proliferation and induced apoptosis in TSC2-null and LAMD cells and sensitized cells to growth-inhibitory and proapoptotic effects of IFN-gamma. Collectively, our data demonstrate that STAT3 activation is required for proliferation and survival of cells with TSC2 dysfunction, that STAT3 impedes growth-inhibitory and proapoptotic effects of IFN-gamma, and that TSC2- and rapamycin-dependent inhibition of STAT3 restores antiproliferative effects of IFN-gamma. Thus, STAT3 may provide a novel therapeutic target for diseases associated with TSC1/TSC2 dysfunction.

Effect of low-dose mifepristone administration on day 2 after ovulation on transcript profiles in implantation-stage endometrium of rhesus monkeys

Progesterone is essential for endometrial receptivity in primates. In studies previously performed using global gene profiling based on microarray technology, attempts have been made to identify changes in gene expression between early luteal-phase and mid-luteal-phase endometria. However, the issue of the putative impact of preimplantation embryo-derived signal in the process of endometrial receptivity was missing in the previous studies. In the present study, an attempt has been made to delineate the transcripts profile in implantation-stage endometrium under combinatorial regulation of progesterone and embryo-derived signal in the rhesus monkey. To this effect, we have compared transcript profiles for 409 known genes between control receptive stage (n=13), and mifepristone-induced desynchronized and non-receptive stage (n=12) monkey endometrial samples collected on days 4 (n=12) and 6 (n=13) after ovulation from mated, potential conception cycles, using cDNA arrays containing sequence-verified clones. Statistical analysis of correlation of estimated transcript abundance between arrays and qRT-PCR for nine selected gene products yielded significant (P<0.05) concordance. Of 409 genes, a total of 40 gene transcripts were seen to be affected, nine gene transcripts in endometrial samples were found to progressively increase between days 4 and 6 following mifepristone treatment, while an additional five genes showed differential expression profile depending on the day after treatment. Additionally, different sets of 12 and 14 gene products showed changes in days 4 and 6 post-ovulation samples respectively. A new cohort of 28 gene products in implantation-stage endometrium was seen to be affected by luteal-phase mifepristone.

Regulation of shear-induced nuclear translocation of the Nrf2 transcription factor in endothelial cells

Background

Vascular endothelial cells (ECs) constantly experience fluid shear stresses generated by blood flow. Laminar flow is known to produce atheroprotective effects on ECs. Nrf2 is a transcription factor that is essential for the antioxidant response element (ARE)-mediated induction of genes such as heme-oxygenase 1 (HO-1). We previously showed that fluid shear stress increases intracellular reactive oxygen species (ROS) in ECs. Moreover, oxidants are known to stimulate Nrf2. We thus examined the regulation of Nrf2 in cultured human ECs by shear stress.

Results

Exposure of human umbilical vein endothelial cells (HUVECs) to laminar shear stress (12 dyne/cm²) induced Nrf2 nuclear translocation, which was inhibited by a phosphatidylinositol 3-kinase (PI3K) inhibitor, a protein kinase C (PKC) inhibitor, and an antioxidant agent N-acetyl cysteine (NAC), but not by other protein kinase inhibitors. Therefore, PI3K, PKC, and ROS are involved in the signaling pathway that leads to the shear-induced nuclear translocation of Nrf2. We also found that shear stress increased the ARE-binding activity of Nrf2 and the downstream expression of HO-1.

Conclusion

Our data suggest that the atheroprotective effect of laminar flow is partially attributed to Nrf2 activation which results in ARE-mediated gene transcriptions, such as HO-1 expression, that are beneficial to the cardiovascular system.

Modulation of PKCdelta signaling alters the shear stress-mediated increases in endothelial nitric oxide synthase transcription: role of STAT3

We have previously shown that the regulation of endothelial nitric oxide synthase (eNOS) in endothelial cells isolated from fetal lamb under static conditions is positively regulated by PKCdelta. In this study, we explore the role of PKCdelta in regulating shear-induced upregulation of eNOS. We found that shear caused a decrease in PKCdelta activation. Modulation of PKCdelta before shear with a dominant negative mutant of PKCdelta (DN PKCdelta) or bryostatin (a known PKCdelta activator) demonstrated that PKCdelta inhibition potentiates the shear-mediated increases in eNOS expression and activity, while PKCdelta activation inhibited these events. To gain insight into the mechanism by which PKCdelta inhibits shear-induced eNOS expression, we examined activation of STAT3, a known target for PKCdelta phosphorylation. We found that shear decreased the phosphorylation of STAT3. Further the transfection of cells with DN PKCdelta reduced, while PKCdelta activation enhanced, STAT3 phosphorylation in the presence of shear. Transfection of cells with a dominant negative mutant of STAT3 enhanced eNOS promoter activity and nitric oxide production in response to shear. Finally, we found that mutating the STAT3 binding site sequence within the eNOS promoter increased promoter activity in response to shear and that this was no longer inhibited by bryostatin. In conclusion, shear decreases PKCdelta activity and, subsequently, reduces STAT3 binding to the eNOS promoter. This signaling pathway plays a previously unidentified role in the regulation of eNOS expression by shear stress.

Flow Antagonizes TNF-α Signaling in Endothelial Cells by Inhibiting Caspase-Dependent PKCζ Processing

Unidirectional laminar flow is atheroprotective, in part by inhibiting cytokine-mediated endothelial cell (EC) inflammation and apoptosis. Previously, we showed that flow inhibited TNF-α signaling by preventing activation of JNK. Recently, PKCζ was identified as the PKC isoform most strongly regulated by flow pattern, with increased PKCζ activity in regions of disturbed flow versus unidirectional flow. Interestingly, PKCζ is cleaved by caspases after TNF-α stimulation to generate a 50-kDa truncated form (CATζ, catalytic domain of PKCζ) with a higher kinase activity than the full-length protein. We hypothesized that flow would inhibit TNF-α–mediated PKCζ cleavage and thereby CATζ formation. We found that PKCζ activity was required for TNF-α–mediated JNK and caspase-3 activation in ECs. PKCζ was rapidly cleaved to generate CATζ in cultured bovine and human aortic ECs and in intact rabbit vessels stimulated with TNF-α. This truncated form of PKCζ enhanced JNK and caspase-3 activation. Interestingly, PKCζ cleavage was prevented by inhibitors of PKCζ, JNK, and caspase activities, suggesting that these enzymes, via regulating CATζ formation, modulate caspase-3 activity in ECs. Finally, we found that flow reduced caspase-dependent processing of PKCζ and caspase-3 activation. These results define a novel role for PKCζ as a shared signaling mediator for flow and TNF-α, and important for flow-mediated inhibition of proinflammatory and apoptotic events in ECs.

Embryonic stem cells remain highly pluripotent following long term expansion as aggregates in suspension bioreactors

Increasing attention has been drawn towards pluripotent embryonic stem cells (ESCs) and their potential use as the primary material in various tissue engineering applications. Successful clinical implementation of this technology would require a quality controlled reproducible culture system for the expansion of the cells to be used in the generation of functional tissues. Recently, we showed that suspension bioreactors could be used in the regulated large-scale expansion of highly pluripotent murine ESCs. The current study illustrates that these bioreactor protocols can be adapted for long term culture and that murine ESC cultures remain highly undifferentiated, when serially passaged in suspension bioreactors for extended periods. Flow cytometry analysis and gene expression profiles of several pluripotency markers, in addition to colony and embryoid body (EB) formation tests were conducted at the start and end of the experiment and all showed that the ESC cultures remained highly undifferentiated over extended culture time in suspension. In vivo teratoma formation and in vitro differentiation into neural, cardiomyocyte, osteoblast and chondrocyte lineages, performed at the end of the long term culture, further supported the presence of functional and undifferentiated ESCs in the expanded population. Overall, this system enables the controlled expansion of highly pluripotent murine ESC populations.

Activation of the JAK-STAT signaling pathway in the rat basilar artery after subarachnoid hemorrhage

The Janus kinase-signal transducer and activator of transcription (JAK-STAT) is one of the most important signaling pathways transducing signals from the cell surface in response to cytokines. Subarachnoid hemorrhage (SAH) produces cytokines in the CSF. We investigated whether this signaling pathway is activated in the rat basilar artery after SAH by cytokines. In a rat single-hemorrhage model of SAH, basilar arteries and CSF were obtained until 7 days after SAH. The concentration of interleukin-6 (IL-6) in CSF was measured by ELISA. Western blot analysis with JAK1, phosphospecific-JAK1, STAT3, phosphospecific STAT3 at Tyr705 and Ser727, cyclooxygenase-2 (COX-2), and actin antibodies was performed in basilar artery. The expressions of STAT3, phosphospecific STAT3 at Tyr705 and Ser727, and COX-2 in basilar artery were examined by immunohistochemical studies. The concentration of IL-6 immediately increased after SAH and Western blot analysis revealed that JAK1 was phosphorylated within 2 h, accompanied by phosphorylation of STAT3 at Tyr705, extending to Ser727 at days 1-2. Immunohistochemistry revealed phosphorylation of STAT3 to occur in endothelial and smooth muscle cells of the basilar artery. In addition, intracisternal injection of IL-6 by itself significantly increased phosphorylation of STAT3 at Tyr705 and Ser727. Expression of COX-2 was also upregulated in endothelial cells of the basilar artery. These results indicate that SAH produces the proinflammatory cytokine IL-6 in the CSF, which activates the JAK-STAT signaling pathway in the basilar artery and induces transcription of immediate early genes.

Role of mechanical and redox stress in activation of mitogen-activated protein kinases in primary cultured rat hepatocytes

Mechanical stress is known to activate signaling cascades, including mitogen-activated protein kinase (MAPK) pathways. Although mechanical stress has been implicated in hepatic cirrhosis and liver regeneration following hepatectomy, the signaling pathway(s) that may be activated in hepatocytes in response to mechanical stress have not been determined. Using primary cultured rat hepatocytes to examine cellular signaling in response to mechanical stress associated with medium change, we observed that the phosphorylation status of extracellular signal-regulated kinase 1/2 (ERK1/2), Jun N-terminal kinase and p38 MAPK, but not Akt, was altered. MAPK activation, especially ERK1/2, was rapidly increased within 5 min, followed by a subsequent decrease to below basal levels between 30 min and 1 h following medium change. MAPK/ERK kinase (MEK1/2) phosphorylation followed the same pattern. The phosphorylation of Raf-1 in response to medium change was also consistent with Raf-1 serving as an upstream regulator of MEK1/2-ERK1/2 signaling. Phosphorylation of ERK1/2 was increased by mechanical stress alone, suggesting that mechanical stress may be primarily responsible for ERK1/2 activation in response to medium change. Medium change produced a marked decline in oxidized glutathione and malondialdehyde levels, and the antioxidant N-acetyl-L-cysteine decreased basal ERK1/2 phosphorylation, suggesting a role for oxidative stress in maintaining basal ERK1/2 phosphorylation in cultured hepatocytes. These data suggest that medium change results in immediate activation of the MAPK signaling pathway due to mechanical stress, followed by a subsequent inactivation of MAPK signaling due to a reduction in oxidative stress levels. These processes may be associated with alteration of hepatic hemodynamic circulation observed in hepatic diseases and in liver transplantation.

The role of STAT-3 in the mediation of smooth muscle cell response to cyclic strain

Hemodynamic forces, including shear stress and cyclic strain, have been recognised as important modulators of vascular cell morphology and function. However, the mechanism by which vascular cells sense and transduce the extracellular mechanical signals into the cell nucleus has not yet been clarified. The purpose of our study was to assess the involvement of the signal transducer and activator of transcription-3 (STAT-3) in the signaling pathway mediating the response of vascular smooth muscle cells (SMC) to cyclic strain. Embryonic A7r5 SMC derived from thoracic aortas of DB1X rats were seeded on flexible collagen I-coated plates. Cells were subjected to 10% average strain at 60 cycles/min for various time periods. Activation of STAT-3, p38, extracellular signal-regulated kinase (ERK) 1/2 and Src was assessed by immunoblotting using phosphospecific antibodies. The interactions between STAT-3 phosphorylation and p38, ERK1/2, phosphatidylinositol-3 (PI3K), mammalian target of rapamycin (mTOR), Janus kinase (JAK) 2 and Src were evaluated by pretreating the cells with specific inhibitors including SB202190, PD98059, LY294002, wortmannin, rapamycin, AG490 and PP1. Serine phosphorylation of STAT-3 was increased by 2-fold after 15 min of cyclic strain, while tyrosine phosphorylation was increased by 2.3-fold after 60 min. Inhibition of ERK1/2 by PD98059 prevented serine phosphorylation of STAT-3, whereas inhibition of Src by PP1 prevented STAT-3 tyrosine phosphorylation. Pretreating the cells with SB202190, a specific inhibitor of p38, resulted in an increase in basal phosphorylation of ERK1/2 and a subsequent increase in basal serine phosphorylation of STAT-3. In conclusion, both serine and tyrosine phosphorylation of STAT-3 are involved in the signaling pathway mediating the effects of cyclic strain on vascular SMC. Serine phosphorylation of STAT-3 is mediated by ERK1/2, while tyrosine phosphorylation is mediated by Src. A negative feedback loop was also found between p38 and ERK1/2.

The role of shear stress in the pathogenesis of atherosclerosis

Although the pathobiology of atherosclerosis is a complex multifactorial process, blood flow-induced shear stress has emerged as an essential feature of atherogenesis. This fluid drag force acting on the vessel wall is mechanotransduced into a biochemical signal that results in changes in vascular behavior. Maintenance of a physiologic, laminar shear stress is known to be crucial for normal vascular functioning, which includes the regulation of vascular caliber as well as inhibition of proliferation, thrombosis and inflammation of the vessel wall. Thus, shear stress is atheroprotective. It is also recognized that disturbed or oscillatory flows near arterial bifurcations, branch ostia and curvatures are associated with atheroma formation. Additionally, vascular endothelium has been shown to have different behavioral responses to altered flow patterns both at the molecular and cellular levels and these reactions are proposed to promote atherosclerosis in synergy with other well-defined systemic risk factors. Nonlaminar flow promotes changes to endothelial gene expression, cytoskeletal arrangement, wound repair, leukocyte adhesion as well as to the vasoreactive, oxidative and inflammatory states of the artery wall. Disturbed shear stress also influences the site selectivity of atherosclerotic plaque formation as well as its associated vessel wall remodeling, which can affect plaque vulnerability, stent restenosis and smooth muscle cell intimal hyperplasia in venous bypass grafts. Thus, shear stress is critically important in regulating the atheroprotective, normal physiology as well as the pathobiology and dysfunction of the vessel wall through complex molecular mechanisms that promote atherogenesis.

Interleukin-6-induced JAK2/STAT3 signaling pathway in endothelial cells is suppressed by hemodynamic flow

Endothelial cells (ECs) are constantly exposed to shear stress, the action of which triggers signaling pathways and cellular responses. During inflammation, cytokines such as IL-6 increase in plasma. In this study, we examined the effects of steady flow on IL-6-induced endothelial responses. ECs exposed to IL-6 exhibited STAT3 activation via phosphorylation of Tyr705. However, when ECs were subjected to shear stress, shear force-dependent suppression of IL-6-induced STAT3 phosphorylation was observed. IL-6 treatment increased the phosphorylation of JAK2, an upstream activator of STAT3. Consistently, shear stress significantly reduced IL-6-induced JAK2 activation. Pretreatment of ECs with an inhibitor of MEK1 did not alter this suppression by shear stress, indicating that extracellular signal-regulated kinase (ERK1/2) was not involved. However, pretreatment of ECs with an endothelial nitric oxide synthase inhibitor (nitro-l-arginine methyl ester) attenuated this inhibitory effect of shear stress on STAT3 phosphorylation. Shear stress-treated ECs displayed decreased nuclear transmigration of STAT3 and reduced STAT3 binding to DNA. Intriguingly, ECs exposed to IL-6 entered the cell cycle, as evidenced by increasing G2/M phase, and shear stress to these ECs significantly reduced IL-6-induced cell cycle progression. STAT3-mediated IL-6-induced cell cycle was confirmed by the inhibition of the cell cycle in ECs infected with adenovirus carrying the inactive mutant of STAT3. Our study clearly shows that shear stress exerts its inhibitory regulation by suppressing the IL-6-induced JAK2/STAT3 signaling pathway and thus inhibits IL-6-induced EC proliferation. This shear force-dependent inhibition of IL-6-induced JAK2/STAT3 activation provides new insights into the vasoprotective effects of steady flow on ECs against cytokine-induced responses.