Fluid shear stress induces a biphasic response of human monocyte chemotactic protein 1 gene expression in vascular endothelium

Effects of Calcium Fructoborate on Levels of C-Reactive Protein, Total Cholesterol, Low-Density Lipoprotein, Triglycerides, IL-1β, IL-6, and MCP-1: a Double-blind, Placebo-controlled Clinical Study

Calcium fructoborate (CFB) has been reported as supporting healthy inflammatory response. In this study, we assess the effects of CFB on blood parameters and proinflammatory cytokines in healthy subjects. This was a randomized, double-blinded, placebo-controlled trial. Participants received placebo or CFB at a dose of 112 mg/day (CFB-1) or 56 mg/day (CFB-2) for 30 days. Glucose, total cholesterol (TC), low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglycerides (TG), C-reactive protein (CRP), homocysteine, interleukin 1 beta (IL-1β), IL-6, and monocyte chemoattractant protein-1 (MCP-1) were determined before and after supplementation. CFB-1 showed a reduction in blood levels of CRP by 31.3 % compared to baseline. CFB-1 and CFB-2 reduced LDL levels by 9.8 and 9.4 %, respectively. CFB-1 decreased blood homocysteine by 5.5 % compared with baseline, whereas CFB-2 did not have a significant effect. Blood levels of TG were reduced by 9.1 and 8.8 % for CFB-1 and CFB-2, respectively. Use of both CFB-1 and CFB-2 resulted in significantly reduced IL-6 levels, when compared within and between groups. IL-1β was reduced by 29.2 % in the CFB-1 group. Finally, CFB-1 and CFB-2 reduced MCP-1 by 31 and 26 %, respectively. Our data indicate that 30-day supplementation with 112 mg/day CFB (CFB-1) resulted in a significant reduction of LDL, TG, TC, IL-1β, IL-6, MCP-1, and CRP. HDL levels were increased, when compared to baseline and placebo. These results suggest that CFB might provide beneficial support to healthy cardiovascular systems by positively affecting these blood markers (ClinicalTrials.gov, ISRCTN90543844; May 24, 2012 ( http://www.controlled-trials.com/ISRCTN90543844 )).

The factors affecting recurrence of symptoms after infrainguinal arterial endovascular angioplasty

Background

This study reports the result of endovascular treatment for arterial occlusive disease limited to femoropopliteal lesions, focusing on the recurrence of symptoms instead of patency.

Methods

This was a retrospective, single-center study. From April 2007 to November 2011, 48 limbs in 38 patients underwent endovascular stenting or balloon angioplasty to treat femoropopliteal arterial occlusive disease. The factors affecting the recurrence of symptoms were analyzed.

Results

The mean age of the patients was 69.60±7.62 years. Among the baseline characteristics of the patients, initial hyperlipidemia was the most important factor affecting the recurrence of symptoms (relative risk=5.810, p=0.031). The presence of a dorsal arch was also a significant factor (relative risk=0.675, p=0.047).

Conclusion

The major factors that affect the recurrence of symptoms after endovascular treatment for femoropopliteal arterial occlusive lesions are hyperlipidemia and the presence of a dorsal arch. Therefore, the usage of lipid-lowering agents after endovascular treatment and taking the presence of a dorsal arch into consideration are important elements of managing the recurrence of symptoms.

Melanocyte pigmentation inversely correlates with MCP-1 production and angiogenesis-inducing potential

The incidence of certain angiogenesis-dependent diseases is higher in Caucasians than in African Americans. Angiogenesis is amplified in wound healing and cornea models in albino C57 mice compared with black C57 mice. Moreover, mouse and human melanocytes with low pigmentation stimulate endothelial cell (EC) proliferation and migration in vitro more than melanocytes with high pigmentation. This effect is due, in part, to the secretion of an angiogenic protein called fibromodulin (FMOD) from lowly pigmented melanocytes. Herein, we expand upon the mechanism contributing to increased angiogenesis in lighter skin and report that monocyte chemotactic protein-1 (MCP-1) is secreted by nonpigmented mouse melanocytes by 5- to 10-fold more than pigmented melanocytes. MCP-1 protein stimulates EC proliferation and migration in vitro and angiogenesis in vivo. Mechanistic studies determine that FMOD is upstream of MCP-1 and promotes its secretion from both melanocytes and activated ECs via stimulation of NF-κB activity. Mice injected with FMOD-neutralizing antibodies show 2.3-fold decreased levels of circulating MCP-1. Human studies confirmed that, on average, Caucasians have 2-fold higher serum levels of MCP-1 than African Americans. Taken together, this study implicates the FMOD/MCP-1 pathway in the regulation of angiogenesis by local melanocytes and suggests that melanogenic activity may protect against aberrant angiogenic diseases.

Histamine receptors expressed in circulating progenitor cells have reciprocal actions in ligation-induced arteriosclerosis

Histamine is synthesized as a low-molecular-weight amine from L-histidine by histidine decarboxylase (HDC). Recently, we demonstrated that carotid artery-ligated HDC gene-deficient mice (HDC(-/-)) showed less neointimal formation than wild-type (WT) mice, indicating that histamine participates in the process of arteriosclerosis. However, little is known about the roles of histamine-specific receptors (HHRs) in arteriosclerosis. To define the roles of HHRs in arteriosclerosis, we investigated intimal remodeling in ligated carotid arteries of HHR-deficient mice (H1R(-/-) or H2R(-/-)). Quantitative analysis showed that H1R(-/-) mice had significantly less arteriosclerogenesis, whereas H2R(-/-) mice had more, as compared with WT mice. Bone marrow transplantation from H1R(-/-) or H2R(-/-) to WT mice confirmed the above observation. Furthermore, the increased expression of monocyte chemoattractant protein (MCP-1), platelet-derived growth factor (PDGF), adhesion molecules and liver X receptor (LXR)-related inflammatory signaling factors, including Toll-like receptor (TLR3), interleukin-1 receptor (IL-1R) and tumor necrosis factor receptor (TNF-R), was consistent with the arteriosclerotic phenotype of H2R(-/-) mice. Peripheral progenitor cells in H2R(-/-) mice accelerate ligation-induced arteriosclerosis through their regulation of MCP-1, PDGF, adhesion molecules and LXR-related inflammatory signaling factors. In contrast, peripheral progenitor cells act to suppress arteriosclerosis in H1R(-/-) mice, indicating that HHRs reciprocally regulate inflammation in the ligation-induced arteriosclerosis.

Postsurgical hemodynamics of the aortic valve bypass operation evaluated with phase contrast magnetic resonance

PURPOSE

To characterize the postsurgical hemodynamics in aortic valve bypass (AVB) patients, and to determine the relationship between presurgical native aortic valve pressure gradient and postsurgical hemodynamics.

MATERIALS AND METHODS

Twenty patients scheduled for AVB surgery underwent presurgical transthoracic Doppler echocardiography to assess the degree of aortic stenosis and postsurgical cardiac magnetic resonance imaging (MRI) to acquire phase contrast magnetic resonance (PCMR) flow values along the ascending and descending aorta, and in the conduit. Net flow values were calculated from the PCMR images and compared to presurgical aortic valve pressure gradient measurements.

RESULTS

PCMR showed that: 1) The blood flow split between the aorta and the conduit was 35%:65% of cardiac output and 2) 60% of patients had net retrograde blood flow in the superior thoracic aorta over the cardiac cycle. Patients with presurgical pressure gradient (ΔP) > 45 mmHg had significantly less blood flow out of the native aorta than patients with ΔP < 45 mmHg, and had significantly more retrograde flow in the superior thoracic aorta postsurgery.

CONCLUSION

In patients undergoing AVB, presurgical aortic valve pressure gradient is associated with the volume of blood flow out the aorta and the direction of blood flow in the superior thoracic aorta after conduit addition as measured by PCMR.

Brain arteriovenous malformation modeling, pathogenesis, and novel therapeutic targets

Patients harboring brain arteriovenous malformation (bAVM) are at life-threatening risk of rupture and intracranial hemorrhage (ICH). The pathogenesis of bAVM has not been completely understood. Current treatment options are invasive, and ≈ 20 % of patients are not offered interventional therapy because of excessive treatment risk. There are no specific medical therapies to treat bAVMs. The lack of validated animal models has been an obstacle for testing hypotheses of bAVM pathogenesis and testing new therapies. In this review, we summarize bAVM model development and bAVM pathogenesis and potential therapeutic targets that have been identified during model development.

Epigenetic Mechanism in Regulation of Endothelial Function by Disturbed Flow: Induction of DNA Hypermethylation by DNMT1

There is increasing evidence that epigenetic mechanisms such as changes in DNA methylation and histone modification play an important role in regulating cellular functions in physiological and pathophysiological states. We investigated the effects of hemodynamic force disturbance, one of the risk factors for atherogenesis, on DNA methylation in HUVECs and rat carotid arteries. Our results demonstrated that athero-prone oscillatory shear flow (OS) without a clear direction induces DNA hypermethylation in comparison to the athero-protective pulsatile shear flow (PS) with a definite direction. Furthermore, OS increases the expression and nuclear translocation of DNA methyltransferase 1 (DNMT1), which is a major maintenance DNA methyltransferase that adds methyl groups to hemi-methylated DNA to repress gene expression. Pharmacological inhibition of DNMT1 by 5-Aza-2'-deoxycytidine abolished the OS-induced DNA hypermethylation. In vivo experiments also showed increases of DNMT1 expression and DNA methylation in the partially-ligated rat carotid arteries where the shear flow is disturbed. These in vitro and in vivo findings have provided novel evidence of the differential regulation of DNA methylation by different hemodynamic forces acting on vascular endothelium and identified DNMT1 as a key protein that governs the epigenetic changes in response to the pathophysiological stimuli due to disturbed flow.

Fluid Mechanics, Arterial Disease, and Gene Expression

This review places modern research developments in vascular mechanobiology in the context of hemodynamic phenomena in the cardiovascular system and the discrete localization of vascular disease. The modern origins of this field are traced, beginning in the 1960s when associations between flow characteristics, particularly blood flow-induced wall shear stress, and the localization of atherosclerotic plaques were uncovered, and continuing to fluid shear stress effects on the vascular lining endothelial) cells (ECs), including their effects on EC morphology, biochemical production, and gene expression. The earliest single-gene studies and genome-wide analyses are considered. The final section moves from the ECs lining the vessel wall to the smooth muscle cells and fibroblasts within the wall that are fluid me chanically activated by interstitial flow that imposes shear stresses on their surfaces comparable with those of flowing blood on EC surfaces. Interstitial flow stimulates biochemical production and gene expression, much like blood flow on ECs.

Fluid Mechanics, Arterial Disease, and Gene Expression

This review places modern research developments in vascular mechanobiology in the context of hemodynamic phenomena in the cardiovascular system and the discrete localization of vascular disease. The modern origins of this field are traced, beginning in the 1960s when associations between flow characteristics, particularly blood flow-induced wall shear stress, and the localization of atherosclerotic plaques were uncovered, and continuing to fluid shear stress effects on the vascular lining endothelial) cells (ECs), including their effects on EC morphology, biochemical production, and gene expression. The earliest single-gene studies and genome-wide analyses are considered. The final section moves from the ECs lining the vessel wall to the smooth muscle cells and fibroblasts within the wall that are fluid me chanically activated by interstitial flow that imposes shear stresses on their surfaces comparable with those of flowing blood on EC surfaces. Interstitial flow stimulates biochemical production and gene expression, much like blood flow on ECs.

Vimentin is a target of PKCβ phosphorylation in MCP-1-activated primary human monocytes

OBJECTIVE AND DESIGN

We designed a study to detect downstream phosphorylation targets of PKCβ in MCP-1-induced human monocytes.

METHODS

Two-dimensional gel electrophoresis was performed for monocytes treated with MCP-1 in the presence or absence of PKCβ antisense oligodeoxyribonucleotides (AS-ODN) or a PKCβ inhibitor peptide, followed by phospho- and total protein staining. Proteins that stained less intensely with the phospho-stain, when normalized to the total protein stain, in the presence of PKCβ AS-ODN or the PKCβ inhibitor peptide, were sequenced.

RESULTS

Of the proteins identified, vimentin was consistently identified using both experimental approaches. Upon (32)P-labeling and vimentin immunoprecipitation, increased phosphorylation of vimentin was observed in MCP-1 treated monocytes as compared to the untreated monocytes. Both PKCβ AS-ODN and the PKCβ inhibitor reduced MCP-1-induced vimentin phosphorylation. The IP of monocytes with anti-vimentin antibody and immunoblotting with a PKCβ antibody revealed that increased PKCβ becomes associated with vimentin upon MCP-1 activation. Upon MCP-1 treatment, monocytes were shown to secrete vimentin and secretion depended on PKCβ expression and activity.

CONCLUSIONS

We conclude that vimentin, a major intermediate filament protein, is a phosphorylation target of PKCβ in MCP-1-treated monocytes and that PKCβ phosphorylation is essential for vimentin secretion. Our recently published studies have implicated vimentin as a potent stimulator of the innate immune receptor Dectin-1 as reported by Thiagarajan et al. (Cardiovasc Res 99:494-504, 2013). Taken together our findings suggest that inhibition of PKCβ regulates vimentin secretion and, thereby, its interaction with Dectin-1 and downstream stimulation of superoxide anion production. Thus, PKCβ phosphorylation of vimentin likely plays an important role in propagating inflammatory responses.

Extracorporeal shock wave stimulates expression of the angiogenic genes via mechanosensory complex in endothelial cells: mimetic effect of fluid shear stress in endothelial cells

BACKGROUND

Extracorporeal shock wave has been used in the noninvasive treatment of various diseases including musculoskeletal disorders. In particular, shock wave with low energy level showed anti-inflammatory effect and increased angiogenesis in ischemic tissues. However, the detailed cellular pathway in endothelial signaling is not fully understood. We investigate the role of shock wave with low energy level in angiogenic gene expression and underlying molecular mechanism by comparing the laminar and oscillatory fluid shear stresses in endothelial cells.

METHODS AND RESULTS

We show that shock wave with low energy level (0.012-0.045 mJ/mm(2)) stimulated phosphorylation of Akt, eNOS and Erk 1/2 in a time-dependent manner which is similar to the effect of laminar fluid shear stress. The transfection of endothelial cells with siRNA encoding VEGFR2, VE-cadherin and PECAM-1 inhibited shock wave-induced phosphorylation of Akt, eNOS and Erk 1/2 and angiogenic gene expressions, including Akt, eNOS, KLF2/4, and Nur77. Moreover, mechanical stimulation through extracorporeal shock wave induced endothelial cell migration and tube formation.

CONCLUSIONS

Our results demonstrate that shock wave-induced Akt/eNOS phosphorylation and angiogenic gene expression were mediated through the mechanosensory complex formation involving VEGFR-2, VE-cadherin and PECAM-1 which was similar to the effect of laminar shear stress.

Local delivery of polarized macrophages improves reperfusion recovery in a mouse hind limb ischemia model

AIMS

Enhancement of collateral development in coronary or peripheral artery disease is a therapeutic target, but it has proven difficult to achieve. Macrophages are key players in collateral remodeling, yet the effect of different macrophage subsets on arteriogenesis has not been investigated.

METHODS AND RESULTS

Murine macrophages were cultured from bone marrow and polarized into M1 (IFNγ), M2a (IL-4) or M2c (IL-10) subsets. C57BL/6 mice underwent femoral artery ligation followed by intramuscular injection of macrophage subsets. Using eGFP expressing macrophages, cells could be detected at least 6 days after ligation and were located in the perivascular space of collateral vessels. After 14 days, perfusion ratio was increased in animals treated with M1 as well as M2a and M2c macrophages compared to control. Depletion of circulating monocytes by clodronate liposome injections did not hamper reperfusion recovery, however, treatment with exogenous polarized macrophages improved perfusion ratio after 14 days again. We used IL10R(fl/fl)/LysMCre(+) mice to study the effect of inhibition of endogenous polarization towards specifically M2c macrophages on arteriogenesis. Deletion of the IL10-receptor (IL10R) in the myeloid lineage did not affect reperfusion recovery, yet the pro-arteriogenic effect of exogenously injected M2c macrophages was still present.

CONCLUSIONS

Local injection of polarized macrophages promotes reperfusion recovery after femoral artery ligation and is not influenced by depletion of circulatory monocytes. Preventing endogenous M2c polarization did not affect reperfusion recovery suggesting that M2c's are not required for collateralization, but are sufficient to induce collateral formation upon exogenous administration. This is the first study using local injection of macrophage subsets showing the pro-arteriogenic effect of polarized macrophages.

Proximal superficial femoral artery occlusion, collateral vessels, and walking performance in peripheral artery disease

OBJECTIVES

We studied associations of magnetic resonance imaging (MRI)-measured superficial femoral artery (SFA) occlusions with functional performance, leg symptoms, and collateral vessel number in peripheral artery disease (PAD). We studied associations of collateral vessel number with functional performance in PAD.

BACKGROUND

Associations of MRI-detected SFA occlusion and collateral vessel number with functional performance among individuals with PAD have not been reported.

METHODS

A total of 457 participants with an ankle brachial index (ABI) <1.00 had MRI measurement of the proximal SFA with 12 consecutive 2.5-μm cross-sectional images. An occluded SFA was defined as an SFA in which at least 1 segment was occluded. A nonoccluded SFA was defined as absence of any occluded slices. Collateral vessels were visualized with magnetic resonance angiography. Lower extremity functional performance was measured with the 6-min walk, 4-m walking velocity at usual and fastest pace, and the Short Physical Performance Battery (SPPB) (0 to 12 scale, 12 = best).

RESULTS

Adjusting for age, sex, race, comorbidities, and other confounders, the presence of an SFA occlusion was associated with poorer 6-min walk performance (1,031 vs. 1,169 feet, p = 0.006), slower fast-paced walking velocity (1.15 vs. 1.22 m/s, p = 0.042), and lower SPPB score (9.07 vs. 9.75, p = 0.038) compared with the absence of an SFA occlusion. More numerous collateral vessels were associated with better 6-min walk performance (0 to 3 collaterals-1,064 feet, 4 to 7 collaterals-1,165 feet, ≥8 collaterals-1,246 feet, p trend = 0.007), faster usual-paced walking speed (0 to 3 collaterals-0.84 m/s, 4 to 7 collaterals-0.88 m/s, ≥8 collaterals-0.91 m/s, p trend = 0.029), and faster rapid-paced walking speed (0 to 3 collaterals-1.17 m/s, 4 to 7 collaterals-1.22 m/s, ≥8 collaterals-1.29 m/s, p trend = 0.002), adjusting for age, sex, race, comorbidities, ABI, and other confounders.

CONCLUSIONS

Among PAD participants, MRI-visualized occlusions in the proximal SFA are associated with poorer functional performance, whereas more numerous collaterals are associated with better functional performance. (Magnetic Resonance Imaging to Identify Characteristics of Plaque Build-Up in People With Peripheral Arterial Disease; NCT00520312).

Effect of shunting of collateral flow into the venous system on arteriogenesis and angiogenesis in rabbit hind limb

The aim of this study was to characterize the vascular remodeling in the external iliac artery (EIA) and the lower leg muscles in a rabbit shunt model created between the distal stump of the occluded femoral artery and the accompanying vein. Histology and immunoconfocal microscopy were used in this study. We found that: 1) both endothelial nitric oxide synthase (eNOS) and phosphorylated eNOS (P-eNOS) proteins were significantly increased in the shunt-side EIA; 2) matrix metalloproteinase-2 (MMP-2) expression was 5.5 times in shunt side EIA over that in normal EIA; 3) intercellular adhension molecule-1 (ICAM-1) expression was strongly induced in endothelial cells (EC) and vascular adhension molecule-1 (VCAM-1) expression was significantly increased in both EC and the adventitia of the shunt-side EIA; 4) augmentation of cell proliferation and extracellular proteolysis by macrophage infiltration was observed in shunt-side EIA; 5) cell proliferation was active in shunt side EIA, but quiet in shunt side lower leg’s arterial vessels; 6) capillary density in shunt side lower leg muscles was 2 times over that in normal side.

In conclusion, our data demonstrate the paradigm that the power of shear stress takes the reins in arteriogenesis, whereas ischemia in angiogenesis, but not in arteriogenesis.

Effects of shear stress on germ lineage specification of embryonic stem cells

Mechanobiology to date has focused on differentiated cells or progenitors, yet the effects of mechanical forces on early differentiation of pluripotent stem cells are still largely unknown. To study the effects of cellular deformation, we utilize a fluid flow bioreactor to apply steady laminar shear stress to mouse embryonic stem cells (ESCs) cultured on a two dimensional surface. Shear stress was found to affect pluripotency, as well as germ specification to the mesodermal, endodermal, and ectodermal lineages, as indicated by gene expression of OCT4, T-BRACHY, AFP, and NES, respectively. The ectodermal and mesodermal response to shear stress was dependent on stress magnitude (ranging from 1.5 to 15 dynes cm(-2)). Furthermore, increasing the duration from one to four days resulted in a sustained increase in T-BRACHY and a marked suppression of AFP. These changes in differentiation occurred concurrently with the activation of Wnt and estrogen pathways, as determined by PCR arrays for signalling molecules. Together these studies show that the mechanical microenvironment may be an important regulator during early differentiation events, including gastrulation. This insight furthers understanding of normal and pathological events during development, as well as facilitates strategies for scale up production of stem cells for clinical therapies.

Hemodynamic shear stress characteristic of atherosclerosis-resistant regions promotes glycocalyx formation in cultured endothelial cells

The endothelial glycocalyx, a glycosaminoglycan layer located on the apical surface of vascular endothelial cells, has been shown to be important for several endothelial functions. Previous studies have documented that the glycocalyx is highly abundant in the mouse common carotid region, where the endothelium is exposed to laminar shear stress, and it is resistant to atherosclerosis. In contrast, the glycocalyx is scarce or absent in the mouse internal carotid sinus region, an area exposed to nonlaminar shear stress and highly susceptible to atherosclerosis. On the basis of these observations, we hypothesized that the expression of components of the endothelial glycocalyx is differentially regulated by distinct hemodynamic environments. To test this hypothesis, human endothelial cells were exposed to shear stress waveforms characteristic of atherosclerosis-resistant or atherosclerosis-susceptible regions of the human carotid, and the expression of several components of the glycocalyx was assessed. These experiments revealed that expression of several components of the endothelial glycocalyx is differentially regulated by distinct shear stress waveforms. Interestingly, we found that heparan sulfate expression is increased and evenly distributed on the apical surface of endothelial cells exposed to the atheroprotective waveform and is irregularly present in cells exposed to the atheroprone waveform. Furthermore, expression of a heparan sulfate proteoglycan, syndecan-1, is also differentially regulated by the two waveforms, and its suppression mutes the atheroprotective flow-induced cell surface expression of heparan sulfate. Collectively, these data link distinct hemodynamic environments to the differential expression of critical components of the endothelial glycocalyx.

Exercise training and peripheral arterial disease

Peripheral arterial disease (PAD) is a common vascular disease that reduces blood flow capacity to the legs of patients. PAD leads to exercise intolerance that can progress in severity to greatly limit mobility, and in advanced cases leads to frank ischemia with pain at rest. It is estimated that 12 to 15 million people in the United States are diagnosed with PAD, with a much larger population that is undiagnosed. The presence of PAD predicts a 50% to 1500% increase in morbidity and mortality, depending on severity. Treatment of patients with PAD is limited to modification of cardiovascular disease risk factors, pharmacological intervention, surgery, and exercise therapy. Extended exercise programs that involve walking approximately five times per week, at a significant intensity that requires frequent rest periods, are most significant. Preclinical studies and virtually all clinical trials demonstrate the benefits of exercise therapy, including improved walking tolerance, modified inflammatory/hemostatic markers, enhanced vasoresponsiveness, adaptations within the limb (angiogenesis, arteriogenesis, and mitochondrial synthesis) that enhance oxygen delivery and metabolic responses, potentially delayed progression of the disease, enhanced quality of life indices, and extended longevity. A synthesis is provided as to how these adaptations can develop in the context of our current state of knowledge and events known to be orchestrated by exercise. The benefits are so compelling that exercise prescription should be an essential option presented to patients with PAD in the absence of contraindications. Obviously, selecting for a lifestyle pattern that includes enhanced physical activity prior to the advance of PAD limitations is the most desirable and beneficial.

Macrophages in collateral arteriogenesis

Arteriosclerotic vascular disease is the most common cause of death and a major cause of disability in the developed world. Adverse outcomes of arteriosclerotic vascular disease are related to consequences of tissue ischemia and necrosis affecting the heart, brain, limbs, and other organs. Collateral artery growth or arteriogenesis occurs naturally and can help restore perfusion to ischemic tissues. Understanding the mechanisms of collateral artery growth may provide therapeutic options for patients with ischemic vascular disease. In this review, we examine the evidence for a role of monocytes and macrophages in collateral arteriogenesis.

Mechanotransduction in embryonic vascular development

A plethora of biochemical signals provides spatial and temporal cues that carefully orchestrate the complex process of vertebrate embryonic development. The embryonic vasculature develops not only in the context of these biochemical cues, but also in the context of the biomechanical forces imparted by blood flow. In the mature vasculature, different blood flow regimes induce distinct genetic programs, and significant progress has been made toward understanding how these forces are perceived by endothelial cells and transduced into biochemical signals. However, it cannot be assumed that paradigms that govern the mature vasculature are pertinent to the developing embryonic vasculature. The embryonic vasculature can respond to the mechanical forces of blood flow, and these responses are critical in vascular remodeling, certain aspects of sprouting angiogenesis, and maintenance of arterial-venous identity. Here, we review data regarding mechanistic aspects of endothelial cell mechanotransduction, with a focus on the response to shear stress, and elaborate upon the multifarious effects of shear stress on the embryonic vasculature. In addition, we discuss emerging predictive vascular growth models and highlight the prospect of combining signaling pathway information with computational modeling. We assert that correlation of precise measurements of hemodynamic parameters with effects on endothelial cell gene expression and cell behavior is required for fully understanding how blood flow-induced loading governs normal vascular development and shapes congenital cardiovascular abnormalities.

PEG-albumin plasma expansion increases expression of MCP-1 evidencing increased circulatory wall shear stress: an experimental study

Treatment of blood loss with plasma expanders lowers blood viscosity, increasing cardiac output. However, increased flow velocity by conventional plasma expanders does not compensate for decreased viscosity in maintaining vessel wall shear stress (WSS), decreasing endothelial nitric oxide (NO) production. A new type of plasma expander using polyethylene glycol conjugate albumin (PEG-Alb) causes supra-perfusion when used in extreme hemodilution and is effective in treating hemorrhagic shock, although it is minimally viscogenic. An acute 40% hemodilution/exchange-transfusion protocol was used to compare 4% PEG-Alb to Ringer's lactate, Dextran 70 kDa and 6% Hetastarch (670 kDa) in unanesthetized CD-1 mice. Serum cytokine analysis showed that PEG-Alb elevates monocyte chemotactic protein-1 (MCP-1), a member of a small inducible gene family, as well as expression of MIP-1α, and MIP-2. MCP-1 is specific to increased WSS. Given the direct link between increased WSS and production of NO, the beneficial resuscitation effects due to PEG-Alb plasma expansion appear to be due to increased WSS through increased perfusion and blood flow rather than blood viscosity.

Mechanical regulation of cellular phenotype: implications for vascular tissue regeneration

Cells sense a myriad of cues from their surrounding microenvironment to regulate their function. In recent years, it has become clear that physical and mechanical cues are as critical as biochemical factors in regulating cellular function. The geometry of the extracellular matrix (ECM), degree of cell spreading, and ECM rigidity all influence the physical connection between cells and their microenvironment and play a major role in regulating proliferation, differentiation, and migration. Leveraging these findings to promote specific cell behaviours will be paramount to realize the full potential of cellular therapies. In this review, I examine our current understanding of how mechanical cues-specifically, geometric control of cell shape and matrix rigidity-are transduced by stem cells to control their stemness, proliferation, and differentiation. The implications of these findings for vascular smooth muscle cell differentiation and cardiovascular tissue engineering will be highlighted.

A new flow co-culture system for studying mechanobiology effects of pulse flow waves

Artery stiffening is known as an important pathological change that precedes small vessel dysfunction, but underlying cellular mechanisms are still elusive. This paper reports the development of a flow co-culture system that imposes a range of arterial-like pulse flow waves, with similar mean flow rate but varied pulsatility controlled by upstream stiffness, onto a 3-D endothelial-smooth muscle cell co-culture. Computational fluid dynamics results identified a uniform flow area critical for cell mechanobiology studies. For validation, experimentally measured flow profiles were compared to computationally simulated flow profiles, which revealed percentage difference in the maximum flow to be <10, <5, or <1% for a high, medium, or low pulse flow wave, respectively. This comparison indicated that the computational model accurately demonstrated experimental conditions. The results from endothelial expression of proinflammatory genes and from determination of proliferating smooth muscle cell percentage both showed that cell activities did not vary within the identified uniform flow region, but were upregulated by high pulse flow compared to steady flow. The flow system developed and characterized here provides an important tool to enhance the understanding of vascular cell remodeling under flow environments regulated by stiffening.

Establishment of a microcarrier culture system with serial sub-cultivation for functionally active human endothelial cells

A microcarrier culture system was established for a large-scale production of functional human endothelial cells. It has been difficult to cultivate human endothelial cells in large quantities for the reasons that specific growth factor and extracellular matrix are required for the survival and proliferation of the cells and the life span of the primary cells are limited. A lot of studies have reported that the shear stress gives significant influences on the structure, growth rate and biological functions of endothelial cells. We aimed to develop a convenient microcarrier culture system for human endothelial cells which can reproduce the flow effects experienced in vivo or in vitro. In 200 mL volume culture, human umbilical vein endothelial cells (HUVEC) could be serially sub-cultivated by optimizing the culture conditions such as shear strength, growth factor, beads and seeding cell concentration, serum concentration, and passage timing. The growth rate was enhanced depending on the shear strength and the life span of the cells was elongated until over 43PDL which is much longer than those of monolayer cultures. The cells maintained the diploidy of over 80% without obvious abnormal changes in the chromosomes. The serially sub-cultured microcarrier cells maintained various endothelial cell functions such as the syntheses of von Willebrand factor (vWf), prostacyclin and other biological substances, the expression of CD31, and the VEGF(165) dependent growth characteristic. The synthesis of biological products was affected by shear strength. In the case of prostacyclin, a different synthesis response was observed between steady flow and transiently reduced shear strength. The synthesis of endothelin-1 (ET-1) was down-regulated by increase of shear strength different from those of other products. The culture system was scaled up until 2 L volume under the optimum DO control. The cells synthesized IL-6 in response to shear strength. These results indicate that the established microcarrier system might be able to contribute to the supply of functional human endothelial cells for various medical applications such as the reconstruction of injured blood vessels caused by atherosclerosis or restenosis of coronary arteries after angioplasty, and the construction of an anti-coagulable artificial blood vessel or an artificial skin with good transplant-ability.

Effects of different leukocyte subpopulations and flow conditions on leukocyte accumulation during reperfusion

BACKGROUND/AIMS

The study examined the interdependent effects of shear stress and different leukocyte subpopulations on endothelial cell activation and cell interactions during low flow and reperfusion.

METHODS

Human umbilical venous endothelial cells were perfused with either neutrophils or monocytes at different shear stress (2-0.25 dyn/cm(2)) and adhesion was quantified by microscopy. Effects of adherent neutrophils and monocytes on endothelial cell adhesion molecule expression were analyzed by flow cytometry after 4-hour static coincubation. After coincubation, the cocultures were reperfused with labeled neutrophils at 2 dyn/cm(2) and their adhesion was quantified selectively. For the control, endothelium monocultures with and without lipopolysaccharide activation were used.

RESULTS

At 2 dyn/cm(2), adhesion did not exceed baseline levels on nonactivated endothelium. Decreasing shear stress to 0.25 dyn/cm(2) largely increased the adhesion of both leukocyte subpopulations, similar to the effect of lipopolysaccharide at 2 dyn/cm(2). However, only adherent monocytes increased adhesion molecule expression, whereas neutrophils had no effect. As a functional consequence, adherent monocytes largely increased neutrophil adhesion during reperfusion, whereas adherent neutrophils did not.

CONCLUSION

Compromised shear stress is an autonomous trigger of leukocyte adhesion even in the absence of additional activators. Exceeding this immediate effect, adherent monocytes induce further endothelial activation and enhance further neutrophil adhesion during reperfusion.

Mechanotransduction of shear in the endothelium: basic studies and clinical implications

The endothelium plays an integral role in the development and progression of atherosclerosis. Hemodynamic forces, particularly shear stress, have a powerful influence on endothelial phenotype and function; however, there is no clear consensus on how endothelial cells sense shear. Nevertheless, multiple endothelial cell signal transduction pathways are activated when exposed to shear stress in vitro. The type of shear, laminar or oscillatory, impacts which signal transduction pathways are initiated as well as which subsequent genes are up- or down-regulated, thereby influencing endothelial phenotype and function. Recently, human studies have examined the impact of shear stress and different shear patterns at rest and during exercise on endothelial function. Current evidence supports the theory that augmented exercise-induced shear stress contributes to improved endothelial function following acute exercise and exercise training, whereas retrograde shear initiates vascular dysfunction. The purpose of this review is to examine the current theories on how endothelial cells sense shear stress, to provide an overview on shear stress-induced signal transduction pathways and subsequent gene expression, and to review the current literature pertaining to shear stress and shear patterns at rest as well as during exercise in humans and the related effects on endothelial function.

A hitchhiker's guide to mechanobiology

More than a century ago, it was proposed that mechanical forces could drive tissue formation. However, only recently with the advent of enabling biophysical and molecular technologies are we beginning to understand how individual cells transduce mechanical force into biochemical signals. In turn, this knowledge of mechanotransduction at the cellular level is beginning to clarify the role of mechanics in patterning processes during embryonic development. In this perspective, we will discuss current mechanotransduction paradigms, along with the technologies that have shaped the field of mechanobiology.

Fluid Shear Stress Effects on Endothelial Cell Cytosolic pH

Fluid flow can modulate endothelial cell intracellular pH (pH(i)). Venous and arterial shear stresses of 1.4 and 14 dyn/cm2, respectively, induced intracellular acidification. The kinetics of the process and magnitude of acidification were dependent on the level of shear stress. Endothelial cells exposed to a venous shear stress were able to recover from the acidification, whereas cells exposed to an arterial shear stress remained acidic. Addition of SITS (1 mM), a HCO(3) (-)/CI(-) exchange inhibitor, greatly reduced the shear stress induced acidification, suggesting that the HCO(3) (-)/C1(-) exchanger is activated by shear stress. Shear stress may activate the exchanger by lowering the [HCO(3) (-)] at the cell surface via convective mass transfer. Altering the HCO(3) (-) gradient across the cell membrane activates the exchanger and, as a consequence, results in intracellular acidification. Perfusion with media containing ATP (10 microM) altered the kinetics of flow-induced acidification observed at both shear stress levels. ATP modulation of pH(i) may be coupled to the rise in [Ca(2+)](j) known to occur with ATP stimulation. To summarize, media perfusion induces intracellular acidification in endothelial cells, and there is evidence to suggest that pH(i) may serve as a second messenger to modulate flow associated changes in endothelial cell metabolism.

MicroRNA-21 targets peroxisome proliferators-activated receptor-alpha in an autoregulatory loop to modulate flow-induced endothelial inflammation

Adhesion of circulating monocytes to vascular endothelial cells (ECs) is a critical event leading to vascular inflammation and, hence, development of atherosclerosis. MicroRNAs (miRs) are a class of endogenous, highly conserved, noncoding small RNAs that play important roles in regulating gene expression and cellular function, as well as pathogenesis of atherosclerosis. Here, we showed that oscillatory shear stress (OSS) induces the expression of miR-21 at the transcriptional level in cultured human umbilical vein ECs via an increased binding of c-Jun, which is a component of transcription factor activator protein-1 (AP-1), to the promoter region of miR-21. OSS induction of miR-21 inhibited the translation, but not transcription, of peroxisome proliferators-activated receptor-α (PPARα) by 3'-UTR targeting. Overexpression of miR-21 up-regulated AP-1 activation, which was attenuated by exogenous expression of PPARα. OSS and overexpression of miR-21 enhanced the expression of adhesion molecules vascular cell adhesion molecule-1 and monocyte chemotactic protein-1 and the consequential adhesion of monocytes to ECs. Overexpression of PPARα significantly attenuated the AP-1-mediated miR-21 expression. These results demonstrate a unique mechanism by which OSS induces AP-1-dependent miR-21 expression, which directly targets PPARα to inhibit its expression, thereby allowing activation of AP-1 and the promotion of monocyte adhesion. Our findings suggest the presence of a positive feedback loop that enables the sustained induction of miR-21, thus contributing to the proinflammatory responses of vascular endothelium under OSS.

Characterization of human late outgrowth endothelial progenitor-derived cells under various flow conditions

BACKGROUND

Endothelial progenitor-derived cells (EPC) are a cell therapy tool in peripheral arterial disease and for re-endothelialization of bypasses and stents.

OBJECTIVE

To assess EPC behavior under flow conditions normally found in vivo.

RESULTS

EPC were isolated from human cord blood, cultured on compliant tubes and exposed in an in vitro flow system mimicking hemodynamic environments normally found in medium and large arteries. EPC exposed for 24 h to unidirectional (0.3 ± 0.1 or 6 ± 3 dynes/cm(2)) shear stress oriented along flow direction, while those exposed to bidirectional shear stress (0.3 ± 3 dynes/cm(2)) or static conditions had random orientation. Under bidirectional flow, tissue factor (TF) activity and mRNA expression were significantly increased (2.5- and 7.0-fold) compared to static conditions. Under low shear unidirectional flow TF mRNA increased 4.9 ± 0.5-fold. Similar flow-induced increases were observed for TF in mature umbilical vein-derived endothelial cells. Expression of tissue-type plasminogen activator (t-PA), urokinase (u-PA) and monocyte chemotactic protein 1 (MCP1) were reduced by 40-60% in late outgrowth endothelial progenitor-derived cells (LO-EPC) exposed to any flow environment, while MCP1, but not t-PA or u-PA, was decreased in HUVEC.

CONCLUSIONS

Flow, in particular bidirectional, modifies the hemostatic balance in LO-EPC with increased TF and decreased plasminogen activator expression.

Growing tumor vessels: more than one way to skin a cat - implications for angiogenesis targeted cancer therapies

The establishment of a functional, integrated vascular system is instrumental for tissue growth and homeostasis. Without blood vessels no adequate nutrition and oxygen would be provided to cells, nor could the undesired waste products be efficiently removed. Blood vessels constitute therefore one of the largest and most complex body network whose assembly depends on the precise balance of growth factors acting in a complementary and coordinated manner with cells of several identities. However, the vessels that are crucial for life can also foster death, given their involvement in cancer progression towards malignancy and metastasis. Targeting tumor vasculature has thus arisen as an appealing anti-cancer therapeutic approach. Since the milestone achievements that vascular endothelial growth factor (VEGF) blockade suppressed angiogenesis and tumor growth in mice and prolonged the survival of cancer patients when administered in combination with chemotherapy, the clinical development of anti-VEGF(R) drugs has accelerated remarkably. FDA has approved the use of bevacizumab - a humanized monoclonal antibody against VEGF - in colorectal, lung and metastatic breast cancers in combination with standard chemotherapy. Additional broad-spectrum VEGF receptor tyrosine kinase inhibitors, such as sunitinib and sorafenib, are used in monotherapy for metastatic renal carcinoma, while sunitinib is also approved for imatinib resistant gastrointestinal stromal tumors and sorafenib for advanced stage hepatocellular carcinoma. Nevertheless, the survival benefit offered by VEGF(R) blockers, either as single agents or in combination with chemotherapy, is calculated merely in the order of months. Posterior studies in preclinical models have reported that despite reducing primary tumor growth, the inhibition of VEGF increased tumor invasiveness and metastasis. The clinical implications of these findings urge the need to reconcile these conflicting results. Anti-angiogenic therapy represents a significant step forth in cancer therapy and in our understanding of cancer biology, but it is also clear that we need to learn how to use it. What is the biological consequence of VEGF-blockade? Does VEGF inhibition starve the tumor to death - as initially postulated - or does it rather foster malignancy? Can anti-VEGF(R) therapy favor tumor vessel formation by VEGF-independent means? Tumors are very diverse and plastic entities, able to adapt to the harshest conditions; this is also reflected by the tumor vasculature. Lessons from the bench to the bedside and vice versa have taught us that the diversity of signals underlying tumor vessel growth will likely be responsive (or resistant) to distinct therapeutic approaches. In this review, we propose a reflection of the different strategies tumors use to grow blood vessels and how these can have impact on the (un)success of current anti-angiogenic therapies.

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

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

Fluid shear stress induces renal epithelial gene expression through polycystin-2-dependent trafficking of extracellular regulated kinase

BACKGROUND

The cilium and cilial proteins have emerged as principal mechanosensors of renal epithelial cells responsible for translating mechanical forces into intracellular signals. Polycystin-2 (PC-2), a cilial protein, regulates flow/shear-induced changes in intracellular Ca(2+) ([Ca(2+)](i)) and recently has been implicated in the regulation of mitogen-activated protein (MAP) kinases. We hypothesize that fluid shear stress (FSS) activates PC-2 which regulates MAP kinase and, in turn, induces MAP kinase-dependent gene expression, specifically, monocyte chemoattractant protein-1 (MCP-1).

METHODS

To test this, PC-2 expression was constitutively reduced in a murine inner medullary collecting duct (IMCD3) cell line, and the expression of FSS-induced MCP-1 expression and MAP kinase signaling compared between the parental (PC-2-expressing) and PC-2-deficient IMCD3 cells.

RESULTS

FSS induces MAP kinase signaling and downstream MCP-1 mRNA expression in wild-type IMCD3 cells, while inhibitors of MAP kinase prevented the FSS-induced MCP-1 mRNA response. In contradistinction, FSS did not induce MCP-1 mRNA expression in PC-2-deficient cells, but did increase activation of the upstream MAP kinases. Wild-type cells exposed to FSS augmented the nuclear abundance of activated MAP kinase while PC-2-deficient cells did not.

CONCLUSIONS

PC-2 regulates FSS-induced MAP kinase trafficking into the nucleus of CD cells.

Role of PECAM-1 in arteriogenesis and specification of preexisting collaterals

RATIONALE

Hemodynamic forces caused by the altered blood flow in response to an occlusion lead to the induction of collateral remodeling and arteriogenesis. Previous work showed that platelet endothelial cell adhesion molecule (PECAM)-1 is a component of a mechanosensory complex that mediates endothelial cell responses to shear stress.

OBJECTIVE

We hypothesized that PECAM-1 plays an important role in arteriogenesis and collateral remodeling.

METHODS AND RESULTS

PECAM-1 knockout (KO) and wild-type littermates underwent femoral artery ligation. Surprisingly, tissue perfusion and collateral-dependent blood flow were significantly increased in the KO mice immediately after surgery. Histology confirmed larger caliber of preexisting collaterals in the KO mice. Additionally, KO mice showed blunted recovery of perfusion from hindlimb ischemia and reduced collateral remodeling, because of deficits in shear stress-induced signaling, including activation of the nuclear factor κB pathway and inflammatory cell accumulation. Partial recovery was associated with normal responses to circumferential wall tension in the absence of PECAM-1, as evidenced by the upregulation of ephrin B2 and monocyte chemoattractant protein-1, which are 2 stretch-induced regulators of arteriogenesis, both in vitro and in vivo.

CONCLUSIONS

Our findings suggest a novel role for PECAM-1 in arteriogenesis and collateral remodeling. Furthermore, we identify PECAM-1 as the first molecule that determines preexisting collateral diameter.

Analysis of haemodynamic factors involved in carotid atherosclerosis using computational fluid dynamics

Atherosclerosis presents a massive healthcare burden in both the developing and developed world. There is mounting evidence relating to the involvement of haemodynamic factors in the pathogenesis of this process. This article aims to review the current understandings that have developed in this area, and to present a demonstrative case study obtained using state of the art computational fluid dynamics (CFD) methodology to model and analyse haemodynamic factors within the atheromatous carotid artery bifurcation.

MCP-1: chemoattractant with a role beyond immunity: a review

BACKGROUND

Monocyte Chemoattractant Protein (MCP)-1, a potent monocyte attractant, is a member of the CC chemokine subfamily. MCP-1 exerts its effects through binding to G-protein-coupled receptors on the surface of leukocytes targeted for activation and migration. Role of MCP-1 and its receptor CCR2 in monocyte recruitment during infection or under other inflammatory conditions is well known.

METHOD

A comprehensive literature search was conducted from the websites of the National Library of Medicine (http://www.ncbl.nlm.nih.gov) and Pubmed Central, the US National Library of Medicine's digital archive of life sciences literature (http://www.pubmedcentral.nih.gov/). The data was assessed from books and journals that published relevant articles in this field.

RESULT

Recent and ongoing research indicates the role of MCP-1 in various allergic conditions, immunodeficiency diseases, bone remodelling, and permeability of blood - brain barrier, atherosclerosis, nephropathies and tumors.

CONCLUSION

MCP-1 plays an important role in pathogenesis of various disease states and hence MCP-1 inhibition may have beneficial effects in such conditions.

Intermittent pneumatic leg compressions acutely upregulate VEGF and MCP-1 expression in skeletal muscle

Application of intermittent pneumatic compressions (IPC) is an extensively used therapeutic strategy in vascular medicine, but the mechanisms by which this method works are unclear. We tested the hypothesis that acute application (150 min) of cyclic leg compressions in a rat model signals upregulation of angiogenic factors in skeletal muscle. To explore the impact of different pressures and frequency of compressions, we divided rats into four groups as follows: 120 mmHg (2 s inflation/2 s deflation), 200 mmHg (2 s/2 s), 120 mmHg (4 s/16 s), and control (no intervention). Blood flow and leg oxygenation (study 1) and the mRNA expression of angiogenic mediators in the rat tibialis anterior muscle (study 2) were assessed after a single session of IPC. In all three groups exposed to the intervention, a modest hyperemia (approximately 37% above baseline) between compressions and a slight, nonsignificant increase in leg oxygen consumption (approximately 30%) were observed during IPC. Compared with values in the control group, vascular endothelial growth factor (VEGF) and monocyte chemotactic protein-1 (MCP-1) mRNA increased significantly (P < 0.05) only in rats exposed to the higher frequency of compressions (2 s on/2 s off). Endothelial nitric oxide synthase, matrix metalloproteinase-2, and hypoxia-inducible factor-1alpha mRNA did not change significantly following the intervention. These findings show that IPC application augments the mRNA content of key angiogenic factors in skeletal muscle. Importantly, the magnitude of changes in mRNA expression appeared to be modulated by the frequency of compressions such that a higher frequency (15 cycles/min) evoked more robust changes in VEGF and MCP-1 compared with a lower frequency (3 cycles/min).

Intratubular hydrodynamic forces influence tubulointerstitial fibrosis in the kidney

PURPOSE OF REVIEW

Renal epithelial cells respond to mechanical stimuli with immediate transduction events (e.g. activation of ion channels), intermediate biological responses (e.g. changes in gene expression), and long-term cellular adaptation (e.g. protein expression). Progressive renal disease is characterized by disturbed glomerular hydrodynamics that contributes to glomerulosclerosis, but how intratubular biomechanical forces contribute to tubulointerstital inflammation and fibrosis is poorly understood.

RECENT FINDINGS

In-vivo and in-vitro models of obstructive uropathy demonstrate that tubular stretch induces robust expression of transforming growth factor beta-1, activation of tubular apoptosis, and induction of nuclear factor-kappaB signaling, which contribute to the inflammatory and fibrotic milieu. Nonobstructive structural kidney diseases associated with nephron loss follow a course characterized by compensatory increases of single nephron glomerular filtration rate and tubular flow rate. Resulting increases in tubular fluid shear stress reduce tissue-plasminogen activator and urokinase enzymatic activity, which diminishes breakdown of extracellular matrix. In models of high dietary Na intake, which increases tubular flow, urinary transforming growth factor beta-1 concentrations and renal mitogen-activated protein kinase activity are increased.

SUMMARY

In conclusion, intratubular biomechanical forces, stretch, and fluid shear stress generate changes in intracellular signaling and gene expression that contribute to the pathobiology of obstructive and nonobstructive kidney disease.

Non-invasive microfluidic gap junction assay

Gap junctions are protein channels between cells that allow direct electrical and metabolic coupling via the exchange of biomolecules and ions. Their expression, though ubiquitous in most mammalian cell types, is especially important for the proper functioning of cardiac and neuronal systems. Many existing methods for studying gap junction communication suffer from either unquantifiable data or difficulty of use. Here, we measure the extent of dye spread and effective diffusivities through gap junction connected cells using a quantitative microfluidic cell biology platform. After loading dye by hydrodynamic focusing of calcein/AM, dye transfer dynamics into neighboring, unexposed cells can be monitored via timelapse fluorescent microscopy. By using a selective microfluidic dye loading over a confluent layer of cells, we found that high expression of gap junctions in C6 cells transmits calcein across the monolayer with an effective diffusivity of 3.4 x 10(-13) m(2)/s, which are highly coupled by Cx43. We also found that the gap junction blocker 18alpha-GA works poorly in the presence of serum even at high concentrations (50 microM); however, it is highly effective down to 2.5 microM in the absence of serum. Furthermore, when the drug is washed out, dye spread resumes rapidly within 1 min for all doses, indicating the drug does not affect transcriptional regulation of connexins in these Cx43+ cells, in contrast to previous studies. This integrated microfluidic platform enables the in situ monitoring of gap junction communication, yielding dynamic information about intercellular molecular transfer and pharmacological inhibition and recovery.

Capillary arterialization requires the bone-marrow-derived cell (BMC)-specific expression of chemokine (C-C motif) receptor-2, but BMCs do not transdifferentiate into microvascular smooth muscle

Chemokine (C-C motif) receptor-2 (CCR2) regulates arteriogenesis and angiogenesis, facilitating the MCP-1-dependent recruitment of growth factor-secreting bone marrow-derived cells (BMCs). Here, we tested the hypothesis that the BMC-specific expression of CCR2 is also required for new arteriole formation via capillary arterialization. Following non-ischemic saphenous artery occlusion, we measured the following in gracilis muscles: monocyte chemotactic protein-1 (MCP-1) in wild-type (WT) C57Bl/6J mice by ELISA, and capillary arterialization in WT-WT and CCR2(-/-)-WT (donor-host) bone marrow chimeric mice, as well as BMC transdifferentiation in EGFP(+)-WT mice, by smooth muscle (SM) alpha-actin immunochemistry. MCP-1 levels were significantly elevated 1 day after occlusion in WT mice. In WT-WT mice at day 7, compared to sham controls, arterial occlusion induced a 34% increase in arteriole length density, a 46% increase in SM alpha-actin(+) vessels, and a 45% increase in the fraction of vessels coated with SM alpha-actin, indicating significant capillary arterialization. However, in CCR2(-/-)-WT mice, no differences were observed between arterial occlusion and sham surgery. In EGFP(+)-WT mice, EGFP and SM alpha-actin never colocalized. We conclude that BMC-specific CCR2 expression is required for skeletal muscle capillary arterialization following arterial occlusion; however, BMCs do not transdifferentiate into smooth muscle.

Laminar shear stress regulates endothelial kinin B1 receptor expression and function: potential implication in atherogenesis

OBJECTIVE

The proinflammatory phenotype induced by low laminar shear stress (LSS) is implicated in atherogenesis. The kinin B1 receptor (B1R), known to be induced by inflammatory stimuli, exerts many proinflammatory effects including vasodilatation and leukocyte recruitment. We investigated whether low LSS is a stimulus for endothelial B1R expression and function.

METHODS AND RESULTS

Human and mouse atherosclerotic plaques expressed high level of B1R mRNA and protein. In addition, B1R expression was upregulated in the aortic arch (low LSS region) of ApoE(-/-) mice fed a high-fat diet compared to vascular regions of high LSS and animals fed normal chow. Of interest, a greater expression of B1R was noticed in endothelial cells from regions of low LSS in aortic arch of ApoE(-/-) mice. B1R was also upregulated in human umbilical vein endothelial cells (HUVECs) exposed to low LSS (0 to 2 dyn/cm(2)) compared to physiological LSS (6 to 10 dyn/cm(2)): an effect similarly evident in murine vascular tissue perfused ex vivo. Functionally, B1R activation increased prostaglandin and CXCL5 expression in cells exposed to low, but not physiological, LSS. IL-1beta and ox-LDL induced B1R expression and function in HUVECs, a response substantially enhanced under low LSS conditions and inhibited by blockade of NFkappaB activation.

CONCLUSIONS

Herein, we show that LSS is a major determinant of functional B1R expression in endothelium. Furthermore, whereas physiological high LSS is a powerful repressor of this inflammatory receptor, low LSS occurring [corrected] at sites of atheroma is associated with substantial upregulation, identifying this receptor as a potential therapeutic target.

Molecular mechanisms responsible for the atheroprotective effects of laminar shear stress

The endothelium lining the inner surface of blood vessels of the cardiovascular system is constantly exposed to hemodynamic shear stress. The interaction between endothelial cells and hemodynamic shear stress has critical implications for atherosclerosis. Regions of arterial narrowing, curvatures, and bifurcations are especially susceptible to atherosclerotic lesion formation. In such areas, endothelial cells experience low, or oscillatory, shear stress. Corresponding changes in endothelial cell structure and function make them susceptible to the initiation and development of atherosclerosis. In contrast, blood flow with high laminar shear stress activates signal transductions as well as gene and protein expressions that play important roles in vascular homeostasis. In response to laminar shear stress, the release of vasoactive substances such as nitric oxide and prostacyclin decreases permeability to plasma lipoproteins as well as the adhesion of leukocytes, and inhibits smooth muscle cell proliferation and migration. In summary, different flow patterns directly determine endothelial cell morphology, metabolism, and inflammatory phenotype through signal transduction and gene and protein expression. Thus, high laminar shear stress plays a key role in the prevention of atherosclerosis through its regulation of vascular tone and long-term maintenance of the integrity and function of endothelial cells.

Hemodynamic shear stress and the endothelium in cardiovascular pathophysiology

Endothelium lining the cardiovascular system is highly sensitive to hemodynamic shear stresses that act at the vessel luminal surface in the direction of blood flow. Physiological variations of shear stress regulate acute changes in vascular diameter and when sustained induce slow, adaptive, structural-wall remodeling. Both processes are endothelium-dependent and are systemically and regionally compromised by hyperlipidemia, hypertension, diabetes and inflammatory disorders. Shear stress spans a range of spatiotemporal scales and contributes to regional and focal heterogeneity of endothelial gene expression, which is important in vascular pathology. Regions of flow disturbances near arterial branches, bifurcations and curvatures result in complex spatiotemporal shear stresses and their characteristics can predict atherosclerosis susceptibility. Changes in local artery geometry during atherogenesis further modify shear stress characteristics at the endothelium. Intravascular devices can also influence flow-mediated endothelial responses. Endothelial flow-induced responses include a cell-signaling repertoire, collectively known as mechanotransduction, that ranges from instantaneous ion fluxes and biochemical pathways to gene and protein expression. A spatially decentralized mechanism of endothelial mechanotransduction is dominant, in which deformation at the cell surface induced by shear stress is transmitted as cytoskeletal tension changes to sites that are mechanically coupled to the cytoskeleton. A single shear stress mechanotransducer is unlikely to exist; rather, mechanotransduction occurs at multiple subcellular locations.