Differential immediate-early gene responses to shear stress and intraluminal pressure in intact human conduit vessels

Cellular crosstalk during liver regeneration: unity in diversity

The liver is unique in its ability to regenerate from a wide range of injuries and diseases. Liver regeneration centers around hepatocyte proliferation and requires the coordinated actions of nonparenchymal cells, including biliary epithelial cells, liver sinusoidal endothelial cells, hepatic stellate cells and kupffer cells. Interactions among various hepatocyte and nonparenchymal cells populations constitute a sophisticated regulatory network that restores liver mass and function. In addition, there are two different ways of liver regeneration, self-replication of liver epithelial cells and transdifferentiation between liver epithelial cells. The interactions among cell populations and regenerative microenvironment in the two modes are distinct. Herein, we first review recent advances in the interactions between hepatocytes and surrounding cells and among nonparenchymal cells in the context of liver epithelial cell self-replication. Next, we discuss the crosstalk of several cell types in the context of liver epithelial transdifferentiation, which is also crucial for 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.

Regulation of Epithelial Cell Functions by the Osmolality and Hydrostatic Pressure Gradients: A Possible Role of the Tight Junction as a Sensor

Epithelia act as a barrier to the external environment. The extracellular environment constantly changes, and the epithelia are required to regulate their function in accordance with the changes in the environment. It has been reported that a difference of the environment between the apical and basal sides of epithelia such as osmolality and hydrostatic pressure affects various epithelial functions including transepithelial transport, cytoskeleton, and cell proliferation. In this paper, we review the regulation of epithelial functions by the gradients of osmolality and hydrostatic pressure. We also examine the significance of this regulation in pathological conditions especially focusing on the role of the hydrostatic pressure gradient in the pathogenesis of carcinomas. Furthermore, we discuss the mechanism by which epithelia sense the osmotic and hydrostatic pressure gradients and the possible role of the tight junction as a sensor of the extracellular environment to regulate epithelial functions.

Stabilization of cellular RNA in blood during storage at room temperature: a comparison of cell-free RNA BCT(®) with K3EDTA tubes

Background

Messenger RNA (mRNA) expression levels in blood cells are important in disease diagnosis, prognosis and biomarker discovery research. Accurate measurements of intracellular mRNA levels in blood cells depend upon several pre-analytical factors, including delays in RNA extraction from blood after phlebotomy. Dramatic changes in mRNA expression levels caused by delays in blood sample processing may render such samples unsuitable for gene expression analysis.

Objectives

This study was conducted to evaluate a blood collection tube, cell-free RNA-BCT^® (RNA-BCT), for its ability to stabilize mRNA expression level in blood cells post-phlebotomy using indicator mRNAs in reverse transcription quantitative real-time PCR (RT-qPCR) assays.

Methods

Blood samples from presumed healthy donors were drawn into both RNA-BCT and K₃EDTA tubes and maintained at room temperature (18–22 °C). The samples were processed to obtain white blood cells (WBCs) at days 0, 1, 2 and 3. Total cellular RNA was extracted from WBCs and mRNA concentrations were quantified by RT-qPCR for glyceraldehyde-3-phosphate dehydrogenase (GAPDH), c-fos, and p53 transcripts.

Results

While blood cells isolated from K₃EDTA tubes showed significant changes in cellular mRNA concentrations for GAPDH, c-fos, and p53, these mRNAs concentrations were stable in blood drawn into RNA-BCT.

Conclusion

The reagent in the RNA-BCT device stabilizes cellular mRNA concentrations for GAPDH, c-fos and p53 for at least three days at room temperature.

Membrane-less microfiltration using inertial microfluidics

Microfiltration is a ubiquitous and often crucial part of many industrial processes, including biopharmaceutical manufacturing. Yet, all existing filtration systems suffer from the issue of membrane clogging, which fundamentally limits the efficiency and reliability of the filtration process. Herein, we report the development of a membrane-less microfiltration system by massively parallelizing inertial microfluidics to achieve a macroscopic volume processing rates (~ 500 mL/min). We demonstrated the systems engineered for CHO (10-20 μm) and yeast (3-5 μm) cells filtration, which are two main cell types used for large-scale bioreactors. Our proposed system can replace existing filtration membrane and provide passive (no external force fields), continuous filtration, thus eliminating the need for membrane replacement. This platform has the desirable combinations of high throughput, low-cost, and scalability, making it compatible for a myriad of microfiltration applications and industrial purposes.

Physical inactivity interacts with an endothelial lipase polymorphism to modulate high density lipoprotein cholesterol in the GOLDN study

BACKGROUND

Plasma high density lipoprotein (HDL) cholesterol (HDL-C) concentration is highly heritable but is also modifiable by environmental factors including physical activity. HDL-C response to exercise varies among individuals, and this variability may be associated with genetic polymorphisms in the key regulators of HDL metabolism including endothelial lipase (LIPG).

METHODS

We examined associations between variants LIPG T111I (rs2000813) and LIPG i24582 (rs6507931), HDL and television viewing/computer use ("screen time") as a marker for physical inactivity in a population with high prevalence of metabolic syndrome. Subjects consisted of 539 White men and 584 women (mean+/-S.D., 49+/-16 years) participating in the GOLDN study.

RESULTS

We did not observe an association with either LIPG SNP or HDL independently of screen time. In multi-adjusted linear regression models, HDL interacted significantly with screen time as a continuous variable in LIPG i24582 subjects with TT genotype (P<0.05). By dichotomizing screen time into high and low levels, we found significant genotype-associated differences in HDL in women but not men. When screen time was >or=2.6h/day, the concentrations of total HDL-C, large HDL, large low density lipoprotein (LDL) were lower, the concentration of small LDL was higher and HDL and LDL particle sizes were smaller in subjects with LIPG i24582 TT compared to CT and CC subjects (P<0.05).

CONCLUSIONS

We found a significant gene-physical inactivity interaction for HDL and some LDL measures for the LIPG i24582 polymorphism. Higher levels of physical activity may be protective for HDL-C concentrations and low activity detrimental in LIPG i24582 TT individuals, especially in women.

Functional and intracellular signaling differences associated with the Helicobacter pylori AlpAB adhesin from Western and East Asian strains

Following adhesion of Helicobacter pylori to gastric epithelial cells, intracellular signaling leads to cytokine production, which causes H. pylori-related gastric injury. Two adjacent homologous genes (alpA and alpB), which encode H. pylori outer membrane proteins, are thought to be associated with adhesion and cytokine induction. We co-cultured gastric epithelial cells with wild type H. pylori strains and their corresponding alpA/alpB-deleted mutants (DeltaalpAB). Results were confirmed by complementation. Flow cytometry confirmed that AlpAB was involved in cellular adhesion. Deletion of alpAB reduced interleukin (IL)-6 induction in gastric epithelial cells. Deletion of alpAB reduced IL-8 induction with East Asian but not with Western strains. All AlpAB-positive strains tested activated the extracellular signal-regulated kinase, c-Fos, and cAMP-responsive element-binding protein. Activation of the Jun-N-terminal kinase, c-Jun, and NF-kappaB was exclusive to AlpAB from East Asian strains. DeltaalpAB mutants poorly colonized the stomachs of C57BL/6 mice and were associated with lower mucosal levels of KC and IL-6. Our results suggest that AlpAB may induce gastric injury by mediating adherence to gastric epithelial cells and by modulating proinflammatory intracellular signaling cascades. Known geographical differences in H. pylori-related clinical outcomes may relate to differential effects of East Asian and Western types of AlpAB on NF-kappaB-related proinflammatory signaling pathways.

Balance between polyoma enhancing activator 3 and activator protein 1 regulates Helicobacter pylori-stimulated matrix metalloproteinase 1 expression

Helicobacter pylori infection and elevated expression of tissue matrix metalloproteinase 1 (MMP-1) are both associated with gastric cancer. We investigated the regulation of MMP-1 expression during H. pylori infection. Real-time reverse transcription-PCR was used to examine mucosal MMP-1 mRNA levels in 55 patients with gastric cancers and 61 control patients. Increased MMP-1 mRNA levels in the gastric mucosa and epithelial cells were observed in H. pylori infections in which both the cag pathogenicity island (PAI) and outer inflammatory protein A (OipA) were expressed. The combined induction of c-fos, c-jun, and polyoma enhancing activator-3 (pea-3) by H. pylori caused maximal increase in MMP-1 expression. Activation of the MMP-1 promoter by H. pylori involved occupation of the activator protein 1 (AP-1) sites at -72 and -181 and, surprisingly, vacancy of the -88 PEA-3 site. Electrophoretic mobility shift, supershift, and chromatin immunoprecipitation assays showed increased binding of c-Fos and c-Jun to the -72 and -181 AP-1 sites during H. pylori infection. Importantly, during wild-type H. pylori infection, we detected increased PEA-3 binding to the -72AP-1 site and decreased PEA-3 binding to the -88 PEA-3 site. However, during infection with the cag PAI and oipA mutants, PEA-3 binding to the -88 site was detected. MMP-1 and pea-3 activities are increased in gastric cancers. Maximal activation of MMP-1 transcription requires the cag PAI and OipA, which regulate AP-1 and PEA-3 binding. Thus, cag PAI and OipA provide a possible link between bacterial virulence factors and important host factors related to disease pathogenesis.

Endothelial dysfunction in growth hormone transgenic mice

Acromegaly [overproduction of GH (growth hormone)] is associated with cardiovascular disease. Transgenic mice overexpressing bGH (bovine GH) develop hypertension and hypercholesterolaemia and could be a model for cardiovascular disease in acromegaly. The aims of the present study were to investigate the effects of excess GH on vascular function and to test whether oxidative stress affects endothelial function in bGH transgenic mice. We studied the ACh (acetylcholine)-induced relaxation response in aortic and carotid rings of young (9–11 weeks) and aged (22–24 weeks) female bGH transgenic mice and littermate control mice, without and with the addition of a free radical scavenger {MnTBAP [Mn(III)tetrakis(4-benzoic acid)porphyrin chloride]}. We also measured mRNA levels of eNOS (endothelial nitric oxide synthase) and EC-SOD (extracellular superoxide dismutase). Intracellular superoxide anion production in the vascular wall was estimated using a dihydroethidium probe. Carotid arteries from bGH transgenic mice had an impaired ACh-induced relaxation response (young, 46±7% compared with 69±8%; aged, 52±5% compared with 80±3%; P<0.05), whereas endothelial function in aorta was intact in young but impaired in aged bGH transgenic mice. Endothelial dysfunction was corrected by addition of MnTBAP in carotid arteries from young mice and in aortas from aged mice; however, MnTBAP did not correct endothelial dysfunction in carotid arteries from aged bGH transgenic mice. There was no difference in intracellular superoxide anion production between bGH transgenic mice and control mice, whereas mRNA expression of EC-SOD and eNOS was increased in aortas from young bGH transgenic mice compared with control mice (P<0.05). We interpret these data to suggest that bGH overexpression is associated with a time- and vessel-specific deterioration in endothelial function, initially caused by increased oxidative stress and later by other alterations in vascular function.

PREVENTION OF ISCHEMIA REPERFUSION INJURY BY POSITIVE PULMONARY VENOUS PRESSURE IN ISOLATED RAT LUNG

Pulmonary ischemia-reperfusion (I/R) without tissue hypoxia induces inflammatory cytokine mRNA expression in the lung under the condition of 0 mm Hg pulmonary venous pressure (0PVP), which might be a cause of I/R injury. Our aim is to determine whether the pulmonary vascular endothelium expresses cytokine mRNAs and their corresponding proteins or develops I/R injury when positive PVP is maintained during ischemia to provide a positive stretch to the endothelium throughout the ischemic period. In isolated, perfused, and ventilated rat lungs, the right and left pulmonary arteries were isolated, and the left lung was selectively occluded for 60 min and then reperfused for 30 min. During ischemia, the left atrial pressure was maintained at 5 mm Hg (5PVP) or 0PVP. TNF-alpha, IL-1beta, IL-6, and IL-10 mRNA expression in the lungs was evaluated by RT-PCR and in situ hybridization, and the production and localization of corresponding proteins were determined by staining with fluorescence-labeled antibodies against the cytokines and an antibody against CD34. Pulmonary vascular/epithelial permeability was evaluated by measuring albumin content in bronchoalveolar lavage (BAL) fluid and wet/dry ratio. At 5PVP, there were no increases in the left lung perfusion pressure, albumin content in BAL fluid, wet/dry ratio, or expression of cytokine mRNAs and their corresponding proteins on the vascular endothelium by I/R. In contrast, at 0PVP, the increased expression of cytokine mRNAs and their corresponding proteins on the vascular endothelium by I/R was verified. The finding that the application of 5PVP during ischemia abolished the expression of cytokine mRNAs and their corresponding proteins as well as the I/R injury gives us new insights in the study of lung preservation for transplantation.

Angiotensin II, type 2 receptor is not involved in the angiotensin II-mediated pro-atherogenic process in ApoE-/- mice

OBJECTIVE

Angiotensin II (Ang II) accelerates atherogenesis in ApoE mice via the angiotensin II, type 1 receptor (AT1) while the type 2 receptor (AT2) is suggested to counteract atherogenesis. To confirm and further explore this possibility, we studied the effect of AT2 receptor antagonism on Ang II-accelerated atherosclerosis.

METHODS

ApoE mice were fed a standard or high cholesterol diet (1.25%) for 4 weeks. Mice on each diet were treated with either Ang II (0.5 microg/kg per min) or Ang II in combination with PD123319 (3 mg/kg per day). Plaque distribution was assessed by en face quantification of the thoracic aorta and in cross-sections of the aortic root. Mean arterial pressure (MAP) was measured. AT1 and AT2 receptor expression were analysed using real-time polymerase chain reaction (PCR) and the localization of the AT2 receptor protein confirmed with immunohistochemistry.

RESULTS

Ang II infusion increased MAP only in mice on a standard diet (P < 0.001). Regardless of diet, Ang II-infused mice had 22-30 times increased plaque area in the thoracic aorta (P < 0.001 for both). Ang II had no effect on plaque in the aortic root. Plaque area was not affected by PD123319. AT2 receptor was heavily expressed in the plaques and increased six- to ninefold by a high cholesterol diet and Ang II infusion (P < 0.01).

CONCLUSION

Ang II increases the extent of atherosclerosis in ApoE mice. Despite up-regulation of the AT2 receptor, we found no support for an effect of the AT2 receptor on atherogenesis in this model.

Long-term activation of c-Fos and c-Jun in optic nerve head astrocytes in experimental ocular hypertension in monkeys and after exposure to elevated pressure in vitro

This study investigates whether the immediate early gene (IEG) products c-Fos and c-Jun are activated in vivo in monkeys with experimental glaucoma, and in vitro in cultured human ONH astrocytes exposed to hydrostatic pressure (HP). Three Rhesus monkeys with mild glaucomatous damage (mean intraocular pressure (IOP) 27 +/- 1.3 mm Hg approximately 42 weeks) and three with moderate glaucomatous damage (mean IOP 44 +/- 6.7% mm Hg approximately 11 weeks) were used for this study; the contralateral eye served as normal control (mean IOP 18.6 +/- 1.7 mm Hg). ONH tissues were stained with GFAP, DAPI, and c-Jun or c-Fos, and transcription factor positive and negative nuclei were counted to determine nuclear localization. Cultured human normal and glaucomatous ONH astrocytes exposed to elevated HP served as the in vitro model of elevated pressure. Activation and nuclear localization of c-Fos and c-Jun increased significantly in the monkeys with elevated IOP. These data correlated with axonal loss, reactive astrocytes, and remodeling of the optic disc. Cultured human ONH astrocytes showed increased nuclear localization of c-Fos and c-Jun under exposure to HP. Immunohistochemistry demonstrated that the upstream regulators of c-Fos and c-Jun, ERK-MAPK and MAPKp38 localized to the nuclei of ONH astrocytes in monkeys with experimental glaucoma. Taken together, these results demonstrate c-Fos and c-Jun activation in ONH astrocytes in vivo and in vitro, and that activation of both transcription factors is associated with ERK and MAPKp38 activation in experimental glaucoma, suggesting that activation of transcription factors may participate in the induction and maintenance of the reactive astrocyte phenotype in glaucomatous optic neuropathy.

Voluntary physical exercise-induced vascular effects in spontaneously hypertensive rats

Forced training has been shown to have beneficial vascular effects in various animal exercise models. In the present study, we explored possible physiological and molecular effects of voluntary physical exercise on various vascular beds. SHR (spontaneously hypertensive rats) performed voluntary exercise for 5 weeks in a computerized wheel cage facility. Ex vivo myograph studies revealed an increased sensitivity of the ACh (acetylcholine)-mediated vasodilation in resistance arteries of the exercised animals (ED50=15.0+/-3.5 nmol/l) compared with the controls (ED50=37.0+/-8.8 nmol/l; P=0.05). The exercise/control difference was abolished after scavenging reactive oxygen radicals. In conduit arteries, ACh induced a similar vasodilatory response in both groups. The in vivo aortic wall stiffness, assessed by means of Doppler tissue echography, was significantly lower in the exercising animals than in controls. This was demonstrated by significantly increased peak systolic aortic wall velocity (P=0.03) and the velocity time integral (P=0.01) in exercising animals compared with controls. The relative gene expression of eNOS (endothelial nitric oxide synthase) was similar in both groups of animals, whereas Cu/ZnSOD (copper/zinc superoxide dismutase) gene expression was significantly increased (+111%; P=0.0007) in the exercising animal compared with controls. In conclusion, voluntary physical exercise differentially improves vascular function in various vascular beds. Increased vascular compliance and antioxidative capacity may contribute to the atheroprotective effects associated with physical exercise in conduit vessels.

Bases cellulaires de la mécanotransduction dans la cellule endothéliale

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

Cellular mechanics and gene expression in blood vessels

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

Shear stress-induced c-fos activation is mediated by Rho in a calcium-dependent manner

We aimed at elucidating the molecular basis of c-fos promoter activation in vascular endothelial cells (ECs) in response to shear stress, with emphases on Rho family GTPases (Rho, Cdc42, and Rac) and intracellular calcium. Dominant-negative and constitutively activated mutants of these GTPases were used to block the action of upstream signals and to activate the downstream pathways, respectively. The role of intracellular calcium was assessed with intracellular calcium chelators. Only Rho, but not Cdc42 or Rac, is involved in the shear stress induction of c-fos. This Rho-mediated shear-induction of c-fos is dependent on intracellular calcium, but not on the Rho effector p160ROCK or actin filaments. While the inhibition of p160ROCK and its ensuing disruption of actin filaments decreased the basal c-fos activity in static ECs (no flow), it did not affect the shear-inductive effect. The calcium chelator BAPTA-AM inhibits the shear-induction, as well as the static level, of c-fos activity.

Cardiovascular and renal phenotyping of genetically modified mice: a challenge for traditional physiology

1. The advent of techniques to genetically modify experimental animals and produce directed mutations in both a conditional and tissue-specific manner has dramatically opened up new fields for physiologists in cardiovascular and renal research. 2. A consequence of altering the genetic background of mice is the difficulty in predicting the phenotypic outcome of the genetic mutation. We therefore suggest that physiologists may need to change their current experimental paradigms to face this new era. Hence, our aim is to propose a complementary research philosophy for physiologists working in the post-genomic era. That is, instead of using strictly hypothesis-driven research philosophies, one will have to perform screening studies of mutant mice, within a field of interest, to find valuable phenotypes. Once a relevant phenotype is found, in-depth studies of the underlying mechanisms should be performed. These follow-up studies should be performed using a traditional hypothesis-driven research philosophy. 3. The rapidly increasing availability of mutated mouse models of human disease also necessitates the development of techniques to characterize these various mouse phenotypes. In particular, the miniaturization and refinement of techniques currently used to study the renal and cardiovascular system in larger animals will be discussed in the present review. Hence, we aim to outline what techniques are currently available and should be present in a laboratory to screen and study renal and cardiovascular phenotypes in genetically modified mice, with particular emphasis on methodologies used in the intact, conscious animal.

Early and sustained medial cell activation after aortocaval fistula creation in mice

BACKGROUND

The response of endothelial cells to altered flow conditions has been studied extensively. However, the indirect effects of shear stress on medial smooth muscle cells (SMCs) have been less well characterized and a murine model of high shear stress has not been available.

MATERIALS AND METHODS

The hemodynamic changes that occur in a mouse aorta proximal to an aortocaval fistula (ACF) were characterized by measuring blood flow, aortic diameter, and calculating wall shear stress. This model was next used to evaluate cellular activation by assessing beta-galactosidase expression in fos-lacZ transgenic mice. Aortic specimens were examined by a chemiluminescent beta-galactosidase assay, cross-sectional histology, and Hautchen prep en face histology.

RESULTS

Immediately after ACF construction, aortic diameter remained unchanged and wall shear stress increased 2.6-fold (49.57 +/- 5.89 to 134.93 +/- 15.69 dyn/cm(2), P < 0.05). Flow-induced aortic enlargement occurred gradually (0.61 +/- 0.03 to 1.18 +/- 0.05 mm at 21 days, P < 0.5) such that by 21 days after ACF, wall shear stress had returned to baseline (56.97 +/- 8.62 dyn/cm(2), P = ns compared to control). Aortas from fos-lacZ mice demonstrated increased beta-gal activity at 6 h and up to 7 days after ACF (1.81 +/- 0.22 rlu/microg in controls vs 41.41 +/- 16.28 rlu/microg at 6 h and 15.17 +/- 1.1 rlu/microg at 7 days, P < 0.5) On histologic evaluation, there was a significant increase in medial SMC staining that was most prominent in cells near the intima (2 +/- 0.3% positive cells in controls vs 67 +/- 10% at 6 h and 11 +/- 7.6 at 7 days, P < 0.5). Endothelial cells, evaluated by en face methods, did not demonstrate significant amounts of beta-gal positivity at the times studied.

CONCLUSIONS

These in vivo findings using a new high shear stress model suggest that early and sustained activation of medial SMCs is a critical component of flow-induced enlargement. Further evaluation of these events may provide important insights into the mechanisms of pathologic arterial remodeling.

Ventilation-induced lung injury and mechanotransduction: stretching it too far?

The Acute Respiratory Distress Syndrome Network clinical trial on ventilation of critically ill patients has drawn attention to the potential side effects of mechanical ventilation. Both clinical and basic research have demonstrated that injurious ventilation strategies can initiate or perpetuate local and systemic inflammatory responses. There are four principal mechanisms that can produce such a response. 1) Ventilation, especially with high ventilation pressures and zero positive end-expiratory pressure, can cause stress failure of the plasma membrane and of epithelial and endothelial barriers. Stress failure of the plasma membrane causes necrosis, which leads to liberation of both preformed inflammatory mediators and agents that stimulate other cells that are still intact to produce such mediators. 2) Stress failure of the barriers causes loss of compartmentalization with spread of mediators and bacteria throughout the body as a consequence. 3) Less injurious ventilation strategies that do not cause tissue destruction can elicit release of mediators by more specific mechanisms, presumably through activation of stretch-activated signaling cascades (mechanotransduction). 4) Ventilation with increasing positive pressures raises the pressure in the pulmonary circulation and thus vascular shear stress, both of which are known stimuli for endothelial cells. These different mechanisms should be taken into account in the design and the interpretation of studies on molecular mechanisms of ventilation-induced lung injury.

Mechanical signaling through connective tissue: a mechanism for the therapeutic effect of acupuncture

The mechanism of action of acupuncture remains largely unknown. The reaction to acupuncture needling known as 'de qi', widely viewed as essential to the therapeutic effect of acupuncture, may be a key to understanding its mechanism of action. De qi includes a characteristic needling sensation, perceived by the patient, and 'needle grasp' perceived by the acupuncturist. During needle grasp, the acupuncturist feels pulling and increased resistance to further movement of the inserted needle. We hypothesize that 1) needle grasp is due to mechanical coupling between the needle and connective tissue with winding of tissue around the needle during needle rotation and 2) needle manipulation transmits a mechanical signal to connective tissue cells via mechanotransduction. Such a mechanism may explain local and remote, as well as long-term effects of acupuncture.