Postnatal development of extracellular matrix and vascular function in small arteries of the rat

Introduction: Vascular extracellular matrix (ECM) is dominated by elastic fibers (elastin with fibrillin-rich microfibrils) and collagens. Current understanding of ECM protein development largely comes from studies of conduit vessels (e.g., aorta) while resistance vessel data are sparse. With an emphasis on elastin, we examined whether changes in postnatal expression of arteriolar wall ECM would correlate with development of local vasoregulatory mechanisms such as the myogenic response and endothelium-dependent dilation. Methods: Rat cerebral and mesenteric arteries were isolated at ages 3, 7, 11, 14, 19 days, 2 months, and 2 years. Using qPCR mRNA expression patterns were examined for elastin, collagen types I, II, III, IV, fibrillin-1, and -2, lysyl oxidase (LOX), and transglutaminase 2. Results: Elastin, LOX and fibrillar collagens I and III mRNA peaked at day 11-14 in both vasculatures before declining at later time-points. 3D confocal imaging for elastin showed continuous remodeling in the adventitia and the internal elastic lamina for both cerebral and mesenteric vessels. Myogenic responsiveness in cannulated cerebral arteries was detectable at day 3 with constriction shifted to higher intraluminal pressures by day 19. Myogenic responsiveness of mesenteric vessels appeared fully developed by day 3. Functional studies were performed to investigate developmental changes in endothelial-dependent dilation. Endothelial-dependent dilation to acetylcholine was less at day 3 compared to day 19 and at day 3 lacked an endothelial-derived hyperpolarizing factor component that was evident at day 19. Conclusion: Collectively, in the rat small artery structural remodeling and aspects of functional control continue to develop in the immediate postnatal period.

Modification of Fibronectin by Non-Enzymatic Glycation Impairs K+ Channel Function in Rat Cerebral Artery Smooth Muscle Cells

Fibronectin (FN) enhances K+ channel activity by integrin-mediated mechanisms. As vascular smooth muscle (VSM) K+ channels mediate vasodilation, we hypothesized that modification of fibronectin, via advanced non-enzymatic glycation, would alter signaling of this extracellular matrix protein through these channels. Bovine FN (1 mg/ml) was glycated (gFN) for 5 days using methylglyoxal (50 mM), and albumin was similarly glycated as a non-matrix protein control. VSM cells were isolated from rat cerebral arteries for measurement of macroscopic K+ channel activity using whole cell patch clamp methodology. Pharmacological inhibitors, iberiotoxin (0.1 μM) and 4-aminopyridine (0.1 mM), were used to identify contributions of large-conductance, Ca2+-activated, K+ channels and voltage-gated K+ channels, respectively. Compared with baseline, native FN enhanced whole cell K+ current in a concentration-dependent manner, whereas gFN inhibited basal current. Furthermore, native albumin did not enhance basal K+ current, but the glycated form (gAlb) caused inhibition. gFN was shown to impair both the Kv and BKCa components of total macroscopic K+ current. Anti-integrin α5 and β1 antibodies attenuated the effects of both FN and gFN on macroscopic K+ current at +70 mV. Consistent with an action on BKCa activity, FN increased, whereas gFN decreased the frequency of spontaneous transient outward current (STOCs). In contrast, gAlb inhibited whole cell K+ current predominantly through Kv, showing little effect on STOCs. A function-blocking, anti-RAGE antibody partially reversed the inhibitory effects of gFN, suggesting involvement of this receptor. Further, gFN caused production of reactive oxygen species (ROS) by isolated VSMCs as revealed by the fluorescent indicator, DHE. Evoked ROS production was attenuated by the RAGE blocking antibody. Collectively, these studies identify ion channel-related mechanisms (integrin and ROS-mediated) by which protein glycation may modify VSMC function.

Changes in dynamics of tumor/endothelial cell adhesive interactions depending on endothelial cell growth state and elastic properties

Cancer cell adhesion to the endothelium is a crucial process in hematogenous metastasis, but how the integrity of the endothelial barrier and endothelial cell (EC) mechanical properties influence the adhesion between metastatic cancer cells and the endothelium remain unclear. In the present study, we have measured the adhesion between single cancer cells and two types of ECs at various growth states and their mechanical properties (elasticity) using atomic force microscopy single cell force spectroscopy. We demonstrated that the EC stiffness increased and adhesion with cancer cells decreased, as ECs grew from a single cell to a confluent state and developed cell-cell contacts, but this was reversed when confluent cells returned to a single state in a scratch assay. Our results suggest that the integrity of the endothelial barrier is an important factor in reducing the ability of the metastatic tumor cells to adhere to the vascular endothelium, extravasate and lodge in the vasculature of a distant organ where secondary metastatic tumors would develop.

Switching behaviour in vascular smooth muscle cell-matrix adhesion during oscillatory loading

Integrins regulate mechanotransduction between smooth muscle cells (SMCs) and the extracellular matrix (ECM). SMCs resident in the walls of airways or blood vessels are continuously exposed to dynamic mechanical forces due to breathing or pulsatile blood flow. However, the resulting effects of these forces on integrin dynamics and associated cell-matrix adhesion are not well understood. Here we present experimental results from atomic force microscopy (AFM) experiments, designed to study the integrin response to external oscillatory loading of varying amplitudes applied to live aortic SMCs, together with theoretical results from a mathematical model. In the AFM experiments, a fibronectin-coated probe was used cyclically to indent and retract from the surface of the cell. We observed a transition between states of firm adhesion and of complete detachment as the amplitude of oscillatory loading increased, revealed by qualitative changes in the force timecourses. Interestingly, for some of the SMCs in the experiments, switching behaviour between the two adhesion states is observed during single timecourses at intermediate amplitudes. We obtain two qualitatively similar adhesion states in the mathematical model, where we simulate the cell, integrins and ECM as an evolving system of springs, incorporating local integrin binding dynamics. In the mathematical model, we observe a region of bistability where both the firm adhesion and detachment states can occur depending on the initial adhesion state. The differences are seen to be a result of mechanical cooperativity of integrins and cell deformation. Switching behaviour is a phenomenon associated with bistability in a stochastic system, and bistability in our deterministic mathematical model provides a potential physical explanation for the experimental results. Physiologically, bistability provides a means for transient mechanical stimuli to induce long-term changes in adhesion dynamics-and thereby the cells' ability to transmit force-and we propose further experiments for testing this hypothesis.

Reduced stiffness and augmented traction force in type 2 diabetic coronary microvascular smooth muscle

Type 2 diabetic (T2DM) coronary resistance microvessels (CRMs) undergo inward hypertrophic remodeling associated with reduced stiffness and reduced coronary blood flow in both mice and pig models. Since reduced stiffness does not appear to be due to functional changes in the extracellular matrix, this study tested the hypothesis that decreased CRM stiffness in T2DM is due to reduced vascular smooth muscle cell (VSMC) stiffness, which impacts the traction force generated by VSMCs. Atomic force microscopy (AFM) and traction force microscopy (TFM) were conducted on primary low-passage CRM VSMCs from normal Db/db and T2DM db/db mice in addition to low-passage normal and T2DM deidentified human coronary VSMCs. Elastic modulus was reduced in T2DM mouse and human coronary VSMCs compared with normal (mouse: Db/db 6.84 ± 0.34 kPa vs. db/db 4.70 ± 0.19 kPa, P < 0.0001; human: normal 3.59 ± 0.38 kPa vs. T2DM 2.61 ± 0.35 kPa, P = 0.05). Both mouse and human T2DM coronary microvascular VSMCs were less adhesive to fibronectin compared with normal. T2DM db/db coronary VSMCs generated enhanced traction force by TFM (control 692 ± 67 Pa vs. db/db 1,507 ± 207 Pa; P < 0.01). Immunoblot analysis showed that T2DM human coronary VSMCs expressed reduced β₁-integrin and elevated β₃-integrin (control 1.00 ± 0.06 vs. T2DM 0.62 ± 0.14, P < 0.05 and control 1.00 ± 0.49 vs. T2DM 3.39 ± 1.05, P = 0.06, respectively). These data show that T2DM coronary VSMCs are less stiff and less adhesive to fibronectin but are able to generate enhanced force, corroborating previously published computational findings that decreasing cellular stiffness increases the cells' ability to generate higher traction force.NEW & NOTEWORTHY We show here that a potential causative factor for reduced diabetic coronary microvascular stiffness is the direct reduction in coronary vascular smooth muscle cell stiffness. These cells were also able to generate enhanced traction force, validating previously published computational models. Collectively, these data show that smooth muscle cell stiffness can be a contributor to overall tissue stiffness in the coronary microcirculation, and this may be a novel area of interest for therapeutic targets.

A Calcium Mediated Mechanism Coordinating Vascular Smooth Muscle Cell Adhesion During KCl Activation

Efficient mechanotransduction in vascular smooth muscle cells (VSMCs) is intimately coupled to physical coupling of the cell to extracellular matrix proteins (ECM) by integrins. Integrin adhesion receptors are essential for normal vascular function and defective integrin signaling is associated with cardiovascular disease. However, less is known about the mechanism of integrin activation in VSMCs in relation to vasoregulation. Our laboratory previously demonstrated that the vasoconstrictor Angiotensin II increases VSMC stiffness in concert with enhanced adhesion to fibronectin (FN), indicating an important role for adhesion in contraction. However, the mechanism of this coordination remains to be clarified. In this study, intracellular Ca²⁺ ([Ca²⁺]_i) was hypothesized to link integrin activation through inside-out signaling pathways leading to enhanced adhesion in response to AII. By using atomic force microscopy (AFM) with an anti-α₅ antibody coated AFM probe, we confirmed that cell stiffness was increased by AII, while we observed no change in adhesion to an α₅ integrin antibody. This indicated that increases in cell adhesion to FN induced by AII were occurring through an integrin activation process, as increased membrane integrin expression/receptor density would have been accompanied by increased adhesion to the anti-α₅ antibody. Further studies were performed using either KCl or BAPTA-AM to modulate the level of [Ca²⁺]_i. After KCl, VSMCs showed a rapid transient increase in cell stiffness as well as cell adhesion to FN, and these two events were synchronized with superimposed transient increases in the level of [Ca²⁺]_i, which was measured using the Ca²⁺ indicator, fluo-4. These relationships were unaffected in VSMCs pretreated with the myosin light chain kinase inhibitor, ML-7. In contrast, unstimulated VSMCs incubated with an intracellular calcium chelator, BAPTA-AM, showed reduced cell adhesion to FN as well the expected decrease in [Ca²⁺]_i. These data suggest that in VSMCs, integrin activation is linked to signaling events tied to levels of [Ca²⁺]_i while being less dependent on events at the level of contractile protein activation. These findings provide additional evidence to support a role for adhesion in VSMC contraction and suggest that following cell contractile activation, that adhesion may be regulated in tandem with the contractile event.

Temporal and molecular dynamics of human metastatic breast carcinoma cell adhesive interactions with human bone marrow endothelium analyzed by single-cell force spectroscopy

Bone is a common site of metastasis for breast cancer and the mechanisms of metastasis are not fully elucidated. The purpose of our study was to characterize temporal and molecular dynamics of adhesive interactions between human breast cancer cells (HBCC) and human bone marrow endothelium (HBME) with piconewton resolution using atomic force microscopy (AFM). In adhesion experiments, a single breast cancer cell, MDA-MB-231 (MB231) or MDA-MB-435 (MB435) was attached to the AFM cantilever and brought into contact with a confluent HBME monolayer for different time periods (0.5 to 300 sec). The forces required to rupture individual molecular interactions and completely separate interacting cells were analyzed as measures of cell-cell adhesion. Adhesive interactions between HBME and either MB231 or MB435 cells increased progressively as cell-cell contact time was prolonged from 0.5 to 300 sec due to the time-dependent increase in the number and frequency of individual adhesive events, as well as to the involvement of stronger ligand-receptor interactions over time. Studies of the individual molecule involvement revealed that Thomsen-Friedenreich antigen (TF-Ag), galectin-3, integrin-β1, and integrin-α3 are all contributing to HBCC/HBME adhesion to various degrees in a temporally defined fashion. In conclusion, cell-cell contact time enhances adhesion of HBCC to HBME and the adhesion is mediated, in part, by TF-Ag, galectin-3, integrin-α3, and integrin-β1.

Nonenzymatic glycation interferes with fibronectin-integrin interactions in vascular smooth muscle cells

OBJECTIVE

We aimed to investigate whether advanced nonenzymatic glycation of the ECM protein, fibronectin, impacts its normal integrin-mediated interaction with arteriolar VSMC.

METHODS

AFM was performed on cultured VSMC from rat cremaster arterioles to study native and glycated fibronectin (FN and gFN) interactions with cellular integrins. AFM probes were functionalized with FN or gFN or with native or glycated albumin (gAlb) as controls.

RESULTS

VSMC showed increased adhesion probability to gFN (72.9±3.5%) compared with native FN (63.0±1.6%). VSMC similarly showed increased probability of adhesion (63.8±1.7%) to gAlb compared with native Alb (40.1±4.7%). Adhesion of native FN to VSMC was α5 and β1 integrin dependent whereas adhesion of gFN to VSMC was integrin independent. The RAGE-selective inhibitor, FPS-ZM1, blocked gFN (and gAlb) adhesion, suggesting that adhesion of glycated proteins was RAGE dependent. Interaction of FN with VSMC was not altered by soluble gFN while soluble native FN did not inhibit adhesion of gFN to VSMC. In contrast, gAlb inhibited adhesion of gFN to VSMC in a concentration-dependent manner.

CONCLUSIONS

Glycation of FN shifts the nature of cellular adhesion from integrin- to RAGE-dependent mechanisms.

Spontaneous oscillation in cell adhesion and stiffness measured using atomic force microscopy

Atomic force microscopy (AFM) is an attractive technique for studying biomechanical and morphological changes in live cells. Using real-time AFM monitoring of cellular mechanical properties, spontaneous oscillations in cell stiffness and cell adhesion to the extracellular matrix (ECM) have been found. However, the lack of automated analytical approaches to systematically extract oscillatory signals, and noise filtering from a large set of AFM data, is a significant obstacle when quantifying and interpreting the dynamic characteristics of live cells. Here we demonstrate a method that extends the usage of AFM to quantitatively investigate live cell dynamics. Approaches such as singular spectrum analysis (SSA), and fast Fourier transform (FFT) were introduced to analyze a real-time recording of cell stiffness and the unbinding force between the ECM protein-decorated AFM probe and vascular smooth muscle cells (VSMCs). The time series cell adhesion and stiffness data were first filtered with SSA and the principal oscillatory components were isolated from the noise floor with the computed eigenvalue from the lagged-covariance matrix. Following the SSA, the oscillatory parameters were detected by FFT from the noise-reduced time series data sets and the sinusoidal oscillatory components were constructed with the parameters obtained by FFT.

Small Artery Elastin Distribution and Architecture-Focus on Three Dimensional Organization

The distribution of ECM proteins within the walls of resistance vessels is complex both in variety of proteins and structural arrangement. In particular, elastin exists as discrete fibers varying in orientation across the adventitia and media as well as often resembling a sheet-like structure in the case of the IEL. Adding to the complexity is the tissue heterogeneity that exists in these structural arrangements. For example, small intracranial cerebral arteries lack adventitial elastin while similar sized arteries from skeletal muscle and intestinal mesentery exhibit a complex adventitial network of elastin fibers. With regard to the IEL, several vascular beds exhibit an elastin sheet with punctate holes/fenestrae while in others the IEL is discontinuous and fibrous in appearance. Importantly, these structural patterns likely sub-serve specific functional properties, including mechanosensing, control of external forces, mechanical properties of the vascular wall, cellular positioning, and communication between cells. Of further significance, these processes are altered in vascular disorders such as hypertension and diabetes mellitus where there is modification of ECM. This brief report focuses on the three-dimensional wall structure of small arteries and considers possible implications with regard to mechanosensing under physiological and pathophysiological conditions.

Small artery mechanobiology: Roles of cellular and non-cellular elements

Small arteries and their component cellular and non-cellular elements are continually subjected to, and interact with, mechanical forces. Such interactions are key in both short- and long-term adaptation of the structure and function of the microcirculation to its local environment and metabolic requirements. Following this brief introduction is a series of papers presented as a symposium (Small Artery Mechanobiology: Roles of Cellular and Non-Cellular Elements) at the World Congress for Microcirculation, Kyoto 2015.

Applications of Atomic Force Microscopy for Adhesion Force Measurements in Mechanotransduction

Adhesive interactions between living cells or ligand-receptor interactions can be studied at the molecular level using atomic force microscopy (AFM). Adhesion force measurements are performed with functionalized AFM probes. In order to measure single ligand-receptor interactions, a cantilever with a pyramidal tip is functionalized with a bio-recognized ligand (e.g., extracellular matrix protein). The ligand-functionalized probe is then brought into contact with a cell in culture to investigate adhesion between the respective probe-bound ligand and endogenously expressed cell surface receptors (e.g., integrins or other adhesion receptor). For experiments designed to examine cell-cell adhesions, a single cell is attached to a tipless cantilever which is then brought into contact with other cultured cells. Force curves are recorded to determine the forces necessary to rupture discrete adhesions between the probe-bound ligand and receptor, or to determine total adhesion force at cell-cell contacts. Here, we describe the procedures for measuring adhesions between (a) fibronectin and α5β1 integrin, and (b) breast cancer cells and bone marrow endothelial cells.

Angiotensin II Type 1 Receptor Mechanoactivation Involves RGS5 (Regulator of G Protein Signaling 5) in Skeletal Muscle Arteries: Impaired Trafficking of RGS5 in Hypertension

Studies suggest that arteriolar pressure-induced vasoconstriction can be initiated by GPCRs (G protein-coupled receptors), including the AT₁R (angiotensin II type 1 receptor). This raises the question, are such mechanisms regulated by negative feedback? The present studies examined whether RGS (regulators of G protein signaling) proteins in vascular smooth muscle cells are colocalized with the AT₁R when activated by mechanical stress or angiotensin II and whether this modulates AT₁R-mediated vasoconstriction. To determine whether activation of the AT₁R recruits RGS5, an in situ proximity ligation assay was performed in primary cultures of cremaster muscle arteriolar vascular smooth muscle cells treated with angiotensin II or hypotonic solution in the absence or presence of candesartan (an AT₁R blocker). Proximity ligation assay results revealed a concentration-dependent increase in trafficking/translocation of RGS5 toward the activated AT₁R, which was attenuated by candesartan. In intact arterioles, knockdown of RGS5 enhanced constriction to angiotensin II and augmented myogenic responses to increased intraluminal pressure. Myogenic constriction was attenuated to a higher degree by candesartan in RGS5 siRNA-transfected arterioles, consistent with RGS5 contributing to downregulation of AT₁R-mediated signaling. Further, translocation of RGS5 was impaired in vascular smooth muscle cells of spontaneously hypertensive rats. This is consistent with dysregulated (RGS5-mediated) AT₁R signaling that could contribute to excessive vasoconstriction in hypertension. In intact vessels, candesartan reduced myogenic vasoconstriction to a greater extent in spontaneously hypertensive rats compared with controls. Collectively, these findings suggest that AT₁R activation results in translocation of RGS5 toward the plasma membrane, limiting AT₁R-mediated vasoconstriction through its role in G_q/11 protein-dependent signaling.

Dipeptidyl Peptidase-4 Inhibition With Saxagliptin Ameliorates Angiotensin II-Induced Cardiac Diastolic Dysfunction in Male Mice

Activation of the renin-angiotensin-aldosterone system is common in hypertension and obesity and contributes to cardiac diastolic dysfunction, a condition for which no treatment currently exists. In light of recent reports that antihyperglycemia incretin enhancing dipeptidyl peptidase (DPP)-4 inhibitors exert cardioprotective effects, we examined the hypothesis that DPP-4 inhibition with saxagliptin (Saxa) attenuates angiotensin II (Ang II)-induced cardiac diastolic dysfunction. Male C57BL/6J mice were infused with either Ang II (500 ng/kg/min) or vehicle for 3 weeks receiving either Saxa (10 mg/kg/d) or placebo during the final 2 weeks. Echocardiography revealed Ang II-induced diastolic dysfunction, evidenced by impaired septal wall motion and prolonged isovolumic relaxation, coincident with aortic stiffening. Ang II induced cardiac hypertrophy, coronary periarterial fibrosis, TRAF3-interacting protein 2 (TRAF3IP2)-dependent proinflammatory signaling [p-p65, p-c-Jun, interleukin (IL)-17, IL-18] associated with increased cardiac macrophage, but not T cell, gene expression. Flow cytometry revealed Ang II-induced increases of cardiac CD45+F4/80+CD11b+ and CD45+F4/80+CD11c+ macrophages and CD45+CD4+ lymphocytes. Treatment with Saxa reduced plasma DPP-4 activity and abrogated Ang II-induced cardiac diastolic dysfunction independent of aortic stiffening or blood pressure. Furthermore, Saxa attenuated Ang II-induced periarterial fibrosis and cardiac inflammation, but not hypertrophy or cardiac macrophage infiltration. Analysis of Saxa-induced changes in cardiac leukocytes revealed Saxa-dependent reduction of the Ang II-mediated increase of cardiac CD11c messenger RNA and increased cardiac CD8 gene expression and memory CD45+CD8+CD44+ lymphocytes. In summary, these results demonstrate that DPP-4 inhibition with Saxa prevents Ang II-induced cardiac diastolic dysfunction, fibrosis, and inflammation associated with unique shifts in CD11c-expressing leukocytes and CD8+ lymphocytes.

Uric acid promotes vascular stiffness, maladaptive inflammatory responses and proteinuria in western diet fed mice

OBJECTIVE

Aortic vascular stiffness has been implicated in the development of cardiovascular disease (CVD) and chronic kidney disease (CKD) in obese individuals. However, the mechanism promoting these adverse effects are unclear. In this context, promotion of obesity through consumption of a western diet (WD) high in fat and fructose leads to excess circulating uric acid. There is accumulating data implicating elevated uric acid in the promotion of CVD and CKD. Accordingly, we hypothesized that xanthine oxidase(XO) inhibition with allopurinol would prevent a rise in vascular stiffness and proteinuria in a translationally relevant model of WD-induced obesity.

MATERIALS/METHODS

Four-week-old C57BL6/J male mice were fed a WD with excess fat (46%) and fructose (17.5%) with or without allopurinol (125mg/L in drinking water) for 16weeks. Aortic endothelial and extracellular matrix/vascular smooth muscle stiffness was evaluated by atomic force microscopy. Aortic XO activity, 3-nitrotyrosine (3-NT) and aortic endothelial sodium channel (EnNaC) expression were evaluated along with aortic expression of inflammatory markers. In the kidney, expression of toll like receptor 4 (TLR4) and fibronectin were assessed along with evaluation of proteinuria.

RESULTS

XO inhibition significantly attenuated WD-induced increases in plasma uric acid, vascular XO activity and oxidative stress, in concert with reductions in proteinuria. Further, XO inhibition prevented WD-induced increases in aortic EnNaC expression and associated endothelial and subendothelial stiffness. XO inhibition also reduced vascular pro-inflammatory and maladaptive immune responses induced by consumption of a WD. XO inhibition also decreased WD-induced increases in renal TLR4 and fibronectin that associated proteinuria.

CONCLUSIONS

Consumption of a WD leads to elevations in plasma uric acid, increased vascular XO activity, oxidative stress, vascular stiffness, and proteinuria all of which are attenuated with allopurinol administration.

Abstract 120: Endothelial Specific Sodium Channel Activation in Endothelium Dysfunction and Vascular Stiffness in Obese Female Mice

Excessive activation of endothelial cell (EC) mineralocorticoid receptor (ECMR) signaling induces EC epithelial sodium channel (EnNaC) activity to promote cardiovascular stiffness. Our previous study has demonstrated that activated ECMR signaling prompts expression and translocation of EnNaC to the EC surface inducing fibrosis, inflammation, and macrophage infiltration in the vasculature of female mice fed a western diet (WD). As ECMR KO also prevented these abnormalities, we posit that ECMR/EnNaC activation was critical. Accordingly, we hypothesized that EC-specific EnNaC activation would mediate endothelium dysfunction, vascular stiffness, and impair flow-mediated vasodilation through reduction of bioavailable NO. Four week old C57BL6/J mice were fed a WD containing high fat (46%), sucrose (17.5%), and high fructose corn syrup (17.5%) with or without a low dose of amiloride (1 mg/kg/day) for 16 weeks. Female EnNaC KO and wild-type littermate females were treated with aldosterone (250 μg/kg/day) via osmotic minipumps for 3 weeks. Amiloride, an antagonist for EnNaC, significantly inhibited inward Na+ currents and EnNaC activity in the cultured endothelial cells. Amiloride treatment significantly attenuated WD-induced increases in aortic stiffness in vivo as measured by pulse wave velocity and in vitro endothelial stiffness measured by atomic force microscopy. In addition, amiloride improved flow mediated dilation in mesenteric arteries and endothelium-dependent relaxation in response to acetylcholine (10 -9 -10 -4 mol/L). Furthermore, amiloride prevented WD-induced increases in coronary endothelium permeability that were associated with decreased expression of claudin-5 and occluding. This also resulted in reduction of total macrophage recruitment (CD11b) and M1 polarization (CD11c). Importantly, genetic knock-out EnNaC KO also prevented aldosterone-induced endothelium stiffening and impairment of endothelium-dependent relaxation. These data indicate that EC specific EnNaC activation decreases bioavailable NO, increases vascular endothelium dysfunction, and prompts vascular stiffening in obese female mice.

N-Cadherin, a novel and rapidly remodelling site involved in vasoregulation of small cerebral arteries

KEY POINTS

N-cadherin formed punctate adherens junctions (AJ) along the borders between vascular smooth muscle cells (VSMCs) in the pressurized rat superior cerebellar artery. The formation of N-cadherin AJs in the vessel wall depends on the intraluminal pressure and was responsive to treatment with phenylephrine (PE) (10^-5  m) and ACh (10^-5  m). N-cadherin-coated beads were able to induce clustering of N-cadherin-enhanced green fluorescent protein (EGFP) on the plasma membrane of isolated VSMCs, whereas treatment with PE (10^-5  m) or sodium nitroprusside (10^-5  m) induced a significant increase or decrease in the N-cadherin-EGFP clustering, respectively. Application of pulling force (∼1 nN) to the N-cadherin-coated beads via an atomic force microscope induced a localized mechanical response from the VSMCs that opposed the pulling.

ABSTRACT

N-cadherin is the major cell-cell adhesion molecule in vascular smooth muscle cells (VSMCs). We tested the hypothesis that N-cadherin is part of a novel mechanosensory mechanism in VSMCs and plays an active role in both the arteriolar myogenic response and during changes in vascular tone induced by vasomotor agonists. Intact and pressurized rat superior cerebellar arteries were labelled for confocal immunofluorescence imaging. N-cadherin formed punctate adherens junctions (AJ) along the borders between VSMCs. When the lumen pressure was raised from 50 to 90 mmHg, both the density and the average size of N-cadherin AJs increased significantly. Similarly, arteriolar constriction with phenylephrine (PE) (10^-5  m) induced a significant increase of N-cadherin AJ density at 50 mmHg, whereas vasodilatation induced by ACh (10^-5  m) was accompanied by a significant decrease in density and size of N-cadherin AJs. An atomic force microscope (AFM) was employed to further examine the mechano-responsive properties of N-cadherin adhesion sites in isolated VSMCs. AFM probes with an attached N-cadherin-coated microbead (5 μm) induced a progressive clustering of N-cadherin-enhanced green fluorescent protein (EGFP) on the VSMC surface. Application of pulling force (∼1 nN) to the N-cadherin-coated-beads with the AFM induced a localized mechanical response from the VSMCs that opposed the pulling. Treatment with PE (10^-5  m) or sodium nitroprusside (10^-5  m) induced a significant increase or decrease of the N-cadherin-EGFP clustering, respectively. These observations provide compelling evidence that N-cadherin AJs are sensitive to pressure and vasomotor agonists in VSMCs and support a functional role of N-cadherin AJs in vasomotor regulation.

Fascin2 regulates cisplatin-induced apoptosis in NRK-52E cells

Previous studies have shown that the aging kidney has a marked loss of α(E)-catenin in proximal tubular epithelium. α-Catenin, a key regulator of the actin cytoskeleton, interacts with a variety of actin-binding proteins. Cisplatin-induced loss of fascin2, an actin bundling protein, was observed in cells with a stable knockdown of α(E)-catenin (C2 cells), as well as in aging (24 mon), but not young (4 mon), kidney. Fascin2 co-localized with α-catenin and the actin cytoskeleton in NRK-52E cells. Knockdown of fascin2 increased the susceptibility of tubular epithelial cells to cisplatin-induced injury. Overexpression of fascin2 in C2 cells restored actin stress fibers and attenuated the increased sensitivity of C2 cells to cisplatin-induced apoptosis. Interestingly, fascin2 overexpression attenuated cisplatin-induced mitochondrial dysfunction and oxidative stress in C2 cells. These data demonstrate that fascin2, a putative target of α(E)-catenin, may play important role in preventing cisplatin-induced acute kidney injury.

Mechanical activation of angiotensin II type 1 receptors causes actin remodelling and myogenic responsiveness in skeletal muscle arterioles

KEY POINTS

Candesartan, an inverse agonist of the type 1 angiotensin II receptor (AT₁ R), causes a concentration-dependent inhibition of pressure-dependent myogenic tone consistent with previous reports of mechanosensitivity of this G protein-coupled receptor. Mechanoactivation of the AT₁ R occurs independently of local angiotensin II production and the type 2 angiotensin receptor. Mechanoactivation of the AT₁ R stimulates actin polymerization by a protein kinase C-dependent mechanism, but independently of a change in intracellular Ca²⁺ . Using atomic force microscopy, changes in single vascular smooth muscle cell cortical actin are observed to remodel following mechanoactivation of the AT₁ R.

ABSTRACT

The G_q/11 protein-coupled angiotensin II type 1 receptor (AT₁ R) has been shown to be activated by mechanical stimuli. In the vascular system, evidence supports the AT₁ R being a mechanosensor that contributes to arteriolar myogenic constriction. The aim of this study was to determine if AT₁ R mechanoactivation affects myogenic constriction in skeletal muscle arterioles and to determine underlying cellular mechanisms. Using pressure myography to study rat isolated first-order cremaster muscle arterioles the AT₁ R inhibitor candesartan (10^-7 -10^-5  m) showed partial but concentration-dependent inhibition of myogenic reactivity. Inhibition was demonstrated by a rightward shift in the pressure-diameter relationship over the intraluminal pressure range, 30-110 mmHg. Pressure-induced changes in global vascular smooth muscle intracellular Ca²⁺ (using Fura-2) were similar in the absence or presence of candesartan, indicating that AT₁ R-mediated myogenic constriction relies on Ca²⁺ -independent downstream signalling. The diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG) reversed the inhibitory effect of candesartan, while this rescue effect was prevented by the protein kinase C (PKC) inhibitor GF 109203X. Both candesartan and PKC inhibition caused increased G-actin levels, as determined by Western blotting of vessel lysates, supporting involvement of cytoskeletal remodelling. At the single vascular smooth muscle cell level, atomic force microscopy showed that cell swelling (stretch) with hypotonic buffer also caused thickening of cortical actin fibres and this was blocked by candesartan. Collectively, the present studies support growing evidence for novel modes of activation of the AT₁ R in arterioles and suggest that mechanically activated AT₁ R generates diacylglycerol, which in turn activates PKC which induces the actin cytoskeleton reorganization that is required for pressure-induced vasoconstriction.

Abstract 127: Enhanced Endothelial Mineralocorticoid Receptor Signaling Prompts Vascular Inflammation and Stiffness Through MiRNA-103-mediated Suppression of KLF4

Enhanced activation of mineralocorticoid receptors (MRs) impairs insulin metabolic signaling, increases oxidative stress, and induces inflammation with associated cardiovascular abnormalities. Our previous data in female mice suggests that activation of endothelial cell MRs (ECMR) contributes to development of vascular stiffness partly by impairing insulin metabolic signaling and reducing endothelial derived nitic oxide (NO) production. Emerging information suggests that microRNA 103 (miR103) is upregulated and thus promotes endothelial inflammation and atherosclerosis in both ob/ob mice and western diet-induced obese C57BL/6J mice. However, the interaction of ECMR and miR103 in the promotion of vascular inflammation and stiffness has not been explored. We hypothesized that ECMR signaling prompts vascular inflammation and stiffness through miRNA-103-mediated suppression of Kruppel-like factor-4 (KLF4). Female ECMR knockout (ECMR -/- ) and wild-type littermate females were treated with aldosterone (Aldo) (250 μg/kg/day) via osmotic minipumps for 4 weeks. Aldo infusion induced endothelium stiffness and impaired aortic relaxation in wild-type mice as determined by ex vivo atomic force microscopy and wire myograph techniques, respectively. The elevated aortic stiffness and impaired relaxation was accompanied by increases in expression of miR103 and intercellular adhesion molecule 1 (ICAM-1) and a reduction in phosphorylation of serine (Ser) 1177/activation of endothelial NO synthase (eNOS). These Aldo-induced endothelial abnormalities were prevented in ECMR -/- mice. Furthermore, application of a miR103 inhibitor to ECs in vitro attenuated Aldo (10 8 M)-induced a decrease in KLF4 expression, which has anti-inflammatory functions mediated by upregulation of phosphorylation of eNOS and downregulation of ICAM-1. These findings suggest that increased ECMR signaling and associated miR103 activation plays a key role in Aldo-induced KLF4 suppression and associated vascular inflammation and aortic stiffness in females.

Abstract P293: Endothelial Sodium Channel Activation Promotes Vascular Stiffness in Obese Female Mice

Obesity-associated arterial stiffening is an independent predictor of cardiovascular disease (CVD) events. Although premenopausal non-obese women are protected against CVD, aortic stiffening in obese women is more common than in men. This disproportionate increase in vascular stiffness in obese females may partly explain their loss of sex-related CVD protection. Recent studies have suggested a role for endothelial sodium channel (ENaC) activation in promotion of endothelial stiffness and suppression of flow-(nitric oxide) mediated vasodilation. Increased mineralocorticoid receptor (MR) activation mediated endothelial stiffness is promoted, in part, by ENaC activation. In this regard, we have recently reported increased aortic stiffness, MR and ENaC expression and endothelial dysfunction in female mice fed a high fat and high fructose diet (western diet [WD]). This increase in aortic stiffness was prevented by very low dose MR antagonism. Accordingly, we hypothesized that inhibition of MR-mediated ENaC activation by using a very low dose of the ENaC inhibitor, amiloride, would prevent arterial stiffening and vascular dysfunction in WD-fed female mice. Four week old C57BL6/J mice were fed a WD containing high fat (46%), sucrose (17.5%), and high fructose corn syrup (17.5%) with or without a very low dose of amiloride (1mg/kg/day) for 16 weeks. Amiloride significantly attenuated WD-induced increases in aortic stiffness in vivo as measured by pulse wave velocity as well as in vitro endothelial stiffness as measured by atomic force microscopy. Moreover, incubation of aortic explants with very low dose of amiloride (1 μM) inhibited WD-induced aortic stiffness in aorta explants from WD-fed female mice. Amiloride also prevented WD-induced impairment in acetylcholine-induced aortic vasodilatation and flow-mediated dilation in mesenteric arteries. Taken together, these observations support a role for ENaC activation in diet-induced vascular stiffening in obese females.

Inherent rhythm of smooth muscle cells in rat mesenteric arterioles: An eigensystem formulation

On the basis of experimental data and mathematical equations in the literature, we remodel the ionic dynamics of smooth muscle cells (SMCs) as an eigensystem formulation, which is valid for investigating finite variations of variables from the equilibrium such as in common experimental operations. This algorithm provides an alternate viewpoint from frequency-domain analysis and enables one to probe functionalities of SMCs' rhythm by means of a resonance-related mechanism. Numerical results show three types of calcium oscillations of SMCs in mesenteric arterioles: spontaneous calcium oscillation, agonist-dependent calcium oscillation, and agonist-dependent calcium spike. For simple single and double SMCs, we demonstrate properties of synchronization among complex signals related to calcium oscillations, and show different correlation relations between calcium and voltage signals for various synchronization and resonance conditions. For practical cell clusters, our analyses indicate that the rhythm of SMCs could (1) benefit enhancements of signal communications among remote cells, (2) respond to a significant calcium peaking against transient stimulations for triggering globally oscillating modes, and (3) characterize the globally oscillating modes via frog-leap (non-molecular-diffusion) calcium waves across inhomogeneous SMCs.

Extracellular Matrix Disarray as a Mechanism for Greater Abdominal Versus Thoracic Aortic Stiffness With Aging in Primates

OBJECTIVE

Increased vascular stiffness is central to the pathophysiology of aging, hypertension, diabetes mellitus, and atherosclerosis. However, relatively few studies have examined vascular stiffness in both the thoracic and the abdominal aorta with aging, despite major differences in anatomy, embryological origin, and relation to aortic aneurysm.

APPROACH AND RESULTS

The 2 other unique features of this study were (1) to study young (9±1 years) and old (26±1 years) male monkeys and (2) to study direct and continuous measurements of aortic pressure and thoracic and abdominal aortic diameters in conscious monkeys. As expected, aortic stiffness, β, was increased P<0.05, 2- to 3-fold, in old versus young thoracic aorta and augmented further with superimposition of acute hypertension with phenylephrine. Surprisingly, stiffness was not greater in old thoracic aorta than in young abdominal aorta. These results can be explained, in part, by the collagen/elastin ratio, but more importantly, by disarray of collagen and elastin, which correlated best with vascular stiffness. However, vascular smooth muscle cell stiffness was not different in thoracic versus abdominal aorta in either young or old monkeys.

CONCLUSIONS

Thus, aortic stiffness increases with aging as expected, but the most severe increases in aortic stiffness observed in the abdominal aorta is novel, where values in young monkeys equaled, or even exceeded, values of thoracic aortic stiffness in old monkeys. These results can be explained by alterations in collagen/elastin ratio, but even more importantly by collagen and elastin disarray.

Endothelial Mineralocorticoid Receptor Mediates Diet-Induced Aortic Stiffness in Females

RATIONALE

Enhanced activation of the mineralocorticoid receptors (MRs) in cardiovascular tissues increases oxidative stress, maladaptive immune responses, and inflammation with associated functional vascular abnormalities. We previously demonstrated that consumption of a Western diet (WD) for 16 weeks results in aortic stiffening, and that these abnormalities were prevented by systemic MR blockade in female mice. However, the cell-specific role of endothelial cell MR (ECMR) in these maladaptive vascular effects has not been explored.

OBJECTIVE

We hypothesized that specific deletion of the ECMR would prevent WD-induced increases in endothelial sodium channel activation, reductions in bioavailable nitric oxide, increased vascular remodeling, and associated increases in vascular stiffness in females.

METHODS AND RESULTS

Four-week-old female ECMR knockout and wild-type mice were fed either mouse chow or WD for 16 weeks. WD feeding resulted in aortic stiffness and endothelial dysfunction as determined in vivo by pulse wave velocity and ex vivo by atomic force microscopy, and wire and pressure myography. The WD-induced aortic stiffness was associated with enhanced endothelial sodium channel activation, attenuated endothelial nitric oxide synthase activation, increased oxidative stress, a proinflammatory immune response and fibrosis. Conversely, cell-specific ECMR deficiency prevented WD-induced aortic fibrosis and stiffness in conjunction with reductions in endothelial sodium channel activation, oxidative stress and macrophage proinflammatory polarization, restoration of endothelial nitric oxide synthase activation.

CONCLUSIONS

Increased ECMR signaling associated with consumption of a WD plays a key role in endothelial sodium channel activation, reduced nitric oxide production, oxidative stress, and inflammation that lead to aortic remodeling and stiffness in female mice.

"Smooth Muscle Cell Stiffness Syndrome"-Revisiting the Structural Basis of Arterial Stiffness

In recent decades, the pervasiveness of increased arterial stiffness in patients with cardiovascular disease has become increasingly apparent. Though, this phenomenon has been well documented in humans and animal models of disease for well over a century, there has been surprisingly limited development in a deeper mechanistic understanding of arterial stiffness. Much of the historical literature has focused on changes in extracellular matrix proteins—collagen and elastin. However, extracellular matrix changes alone appear insufficient to consistently account for observed changes in vascular stiffness, which we observed in our studies of aortic stiffness in aging monkeys. This led us to examine novel mechanisms operating at the level of the vascular smooth muscle cell (VSMC)—that include increased cell stiffness and adhesion to extracellular matrix—which that may be interrelated with other mechanisms contributing to arterial stiffness. We introduce these observations as a new concept—the Smooth Muscle Cell Stiffness Syndrome (SMCSS)—within the field of arterial stiffness and posit that stiffening of vascular cells impairs vascular function and may contribute stiffening to the vasculature with aging and cardiovascular disease. Importantly, this review article revisits the structural basis of arterial stiffness in light of these novel findings. Such classification of SMCSS and its contextualization into our current understanding of vascular mechanics may be useful in the development of strategic therapeutics to directly target arterial stiffness.

Brief serotonin exposure initiates arteriolar inward remodeling processes in vivo that involve transglutaminase activation and actin cytoskeleton reorganization

Inward remodeling of the resistance vasculature is strongly associated with life-threatening cardiovascular events. Previous studies have demonstrated that both actin polymerization and the activation of transglutaminases mediate early stages of the transition from a structurally normal vessel to an inwardly remodeled one. Ex vivo studies further suggest that a few hours of exposure to vasoconstrictor agonists induces inward remodeling in the absence of changes in intraluminal pressure. Here we report that a short, 10-min, topical exposure to serotonin (5-HT) + N(ω)-nitro-l-arginine methyl ester hydrochloride (l-NAME) was sufficient to initiate inward remodeling processes in rat cremasteric feed arterioles (100-200 μm lumen diameter), in vivo. Addition of the transglutaminase inhibitor, cystamine, blocked the in vivo remodeling. We further demonstrate that, in isolated arterioles, 5-HT + l-NAME activates transglutaminases and modulates the phosphorylation state of cofilin, a regulator of actin depolymerization. The 5-HT + l-NAME-induced remodeling process in isolated arterioles was also inhibited by an inhibitor of Lim Kinase, the kinase that phosphorylates and inactivates cofilin. Therefore, our results indicate that a brief vasoconstriction induced by 5-HT + l-NAME is able to reduce the passive structural diameter of arterioles through processes that are dependent on the activation of transglutaminases and Lim kinase, and the subsequent phosphorylation of cofilin.

Endothelial Mineralocorticoid Receptor Deletion Prevents Diet-Induced Cardiac Diastolic Dysfunction in Females

Overnutrition and insulin resistance are especially prominent risk factors for the development of cardiac diastolic dysfunction in females. We recently reported that consumption of a Western diet (WD) containing excess fat (46%), sucrose (17.5%), and high fructose corn syrup (17.5%) for 16 weeks resulted in cardiac diastolic dysfunction and aortic stiffening in young female mice and that these abnormalities were prevented by mineralocorticoid receptor blockade. Herein, we extend those studies by testing whether WD-induced diastolic dysfunction and factors contributing to diastolic impairment, such as cardiac fibrosis, hypertrophy, inflammation, and impaired insulin signaling, are modulated by excess endothelial cell mineralocorticoid receptor signaling. Four-week-old female endothelial cell mineralocorticoid receptor knockout and wild-type mice were fed mouse chow or WD for 4 months. WD feeding resulted in prolonged relaxation time, impaired diastolic septal wall motion, and increased left ventricular filling pressure indicative of diastolic dysfunction. This occurred in concert with myocardial interstitial fibrosis and cardiomyocyte hypertrophy that were associated with enhanced profibrotic (transforming growth factor β1/Smad) and progrowth (S6 kinase-1) signaling, as well as myocardial oxidative stress and a proinflammatory immune response. WD also induced cardiomyocyte stiffening, assessed ex vivo using atomic force microscopy. Conversely, endothelial cell mineralocorticoid receptor deficiency prevented WD-induced diastolic dysfunction, profibrotic, and progrowth signaling, in conjunction with reductions in macrophage proinflammatory polarization and improvements in insulin metabolic signaling. Therefore, our findings indicate that increased endothelial cell mineralocorticoid receptor signaling associated with consumption of a WD plays a key role in the activation of cardiac profibrotic, inflammatory, and growth pathways that lead to diastolic dysfunction in female mice.

Abstract 131: Endothelial Cell Mineralocorticoid Receptor: A Critical Player in Aortic Stiffness and Cardiac Diastolic Dysfunction in Female Mice

Enhanced activation of mineralocorticoid receptors (MRs) impairs insulin metabolic signaling, increases oxidative stress, and induces maladaptive immune responses with associated CV abnormalities. Emerging information suggests that obesity and insulin resistance predict CV stiffness in females. However, the specific role of endothelial cell MR (ECMR) has not been explored. Accordingly, we hypothesized that ECMR signaling modulated by a western diet (WD) impairs insulin signaling and increases inflammation, fibrosis and CV stiffness in females. Four week-old ECMR knockout (ECMR -/- ) and wild-type female mice were fed a mouse chow or WD containing fat (46%), sucrose (17.5%), and high fructose (17.5%) for 16 weeks. WD prompted MR to bind the hormone response element (nGnACAnnnTGTnCn) on the site of ENaC promoter and induced an increase in ENaC expression that was associated with increased aortic and EC stiffness as determined by in vivo pulse wave velocity and ex vivo atomic force microscopy techniques, respectively The elevated aortic stiffness was accompanied by increased expression of cytokines IL-17, MCP-1 and M1 markers CD 86, and CD11c. ENaC expression was reduced in the ECMR -/- vasculature with a decrease in WD-increase in aortic and EC stiffness.. ECMR -/- also improved aortic vasorelaxation to Ach, SNP (10 -9 -10 -4 mol/L), and insulin (0.1- 300 ng/ml), which were impaired by WD. Additionally, ECMR -/- restored WD-induced cardiac diastolic dysfunction assessed by cardiac MRI and echocardiography. Diastolic dysfunction was related to cardiomyocyte hypertrophy, oxidative stress, and fibrosis and occurred with enhanced activation of S6 kinase-1, Erk 1/2, serine phosphorylation of IRS-1, inactivation of PI3K-AKT-eNOS signaling pathways and the pro-fibrotic TGF-β1/ Smad signaling pathway and increased macrophage pro-inflammatory polarization. ECMR -/- markedly attenuated the cardiac functional and changes signaling induced by WD. These findings suggest that increased ECMR signaling and associated ENaC activation plays a key role in WD induced insulin metabolic sinaling impairment, adaptive pro-inflammatory responses, macrophage polarization and associated aortic stiffness and cardiac diastolic dysfunction in females.

Vascular stiffness in insulin resistance and obesity

Obesity, insulin resistance, and type 2 diabetes are associated with a substantially increased prevalence of vascular fibrosis and stiffness, with attendant increased risk of cardiovascular and chronic kidney disease. Although the underlying mechanisms and mediators of vascular stiffness are not well understood, accumulating evidence supports the role of metabolic and immune dysregulation related to increased adiposity, activation of the renin angiotensin aldosterone system, reduced bioavailable nitric oxide, increased vascular extracellular matrix (ECM) and ECM remodeling in the pathogenesis of vascular stiffness. This review will give a brief overview of the relationship between obesity, insulin resistance and increased vascular stiffness to provide a contemporary understanding of the proposed underlying mechanisms and potential therapeutic strategies.

Attenuated sarcomere lengthening of the aged murine left ventricle observed using two-photon fluorescence microscopy

The Frank-Starling mechanism, whereby increased diastolic filling leads to increased cardiac output, depends on increasing the sarcomere length (Ls) of cardiomyocytes. Ventricular stiffness increases with advancing age, yet it remains unclear how such changes in compliance impact sarcomere dynamics in the intact heart. We developed an isolated murine heart preparation to monitor Ls as a function of left ventricular pressure and tested the hypothesis that sarcomere lengthening in response to ventricular filling is impaired with advanced age. Mouse hearts isolated from young (3-6 mo) and aged (24-28 mo) C57BL/6 mice were perfused via the aorta under Ca(2+)-free conditions with the left ventricle cannulated to control filling pressure. Two-photon imaging of 4-{2-[6-(dioctylamino)-2-naphthalenyl]ethenyl}1-(3-sulfopropyl)-pyridinium fluorescence was used to monitor t-tubule striations and obtain passive Ls between pressures of 0 and 40 mmHg. Ls values (in μm, aged vs. young, respectively) were 2.02 ± 0.04 versus 2.01 ± 0.02 at 0 mmHg, 2.13 ± 0.04 versus 2.23 ± 0.02 at 5 mmHg, 2.21 ± 0.03 versus 2.27 ± 0.03 at 10 mmHg, and 2.28 ± 0.02 versus 2.36 ± 0.01 at 40 mmHg, indicative of impaired sarcomere lengthening in aged hearts. Atomic force microscopy nanoindentation revealed that intact cardiomyocytes enzymatically isolated from aged hearts had increased stiffness compared with those of young hearts (elastic modulus: aged, 41.9 ± 5.8 kPa vs. young, 18.6 ± 3.3 kPa; P = 0.006). Impaired sarcomere lengthening during left ventricular filling may contribute to cardiac dysfunction with advancing age by attenuating the Frank-Starling mechanism and reducing stroke volume.

Low-Dose Mineralocorticoid Receptor Blockade Prevents Western Diet-Induced Arterial Stiffening in Female Mice

Women are especially predisposed to development of arterial stiffening secondary to obesity because of consumption of excessive calories. Enhanced activation of vascular mineralocorticoid receptors impairs insulin signaling, induces oxidative stress, inflammation, and maladaptive immune responses. We tested whether a subpressor dose of mineralocorticoid receptor antagonist, spironolactone (1 mg/kg per day) prevents aortic and femoral artery stiffening in female C57BL/6J mice fed a high-fat/high-sugar western diet (WD) for 4 months (ie, from 4-20 weeks of age). Aortic and femoral artery stiffness were assessed using ultrasound, pressurized vessel preparations, and atomic force microscopy. WD induced weight gain and insulin resistance compared with control diet-fed mice and these abnormalities were unaffected by spironolactone. Blood pressures and heart rates were normal and unaffected by diet or spironolactone. Spironolactone prevented WD-induced stiffening of aorta and femoral artery, as well as endothelial and vascular smooth muscle cells, within aortic explants. Spironolactone prevented WD-induced impaired aortic protein kinase B/endothelial nitric oxide synthase signaling, as well as impaired endothelium-dependent and endothelium-independent vasodilation. Spironolactone ameliorated WD-induced aortic medial thickening and fibrosis and the associated activation of the progrowth extracellular receptor kinase 1/2 pathway. Finally, preservation of normal arterial stiffness with spironolactone in WD-fed mice was associated with attenuated systemic and vascular inflammation and an anti-inflammatory shift in vascular immune cell marker genes. Low-dose spironolactone may represent a novel prevention strategy to attenuate vascular inflammation, oxidative stress, and growth pathway signaling and remodeling to prevent development of arterial stiffening secondary to consumption of a WD.

Abstract 246: Thoracic versus Abdominal Aortic Stiffness in Young and Old Non-Human Primates

We demonstrated that thoracic aortic stiffness is increased in aging monkeys, with the mechanism involving increased vascular smooth muscle cell (VSMC) stiffness. In view of the importance of increased abdominal aortic stiffness to greater incidence of abdominal aortic aneurysms, the goal of this investigation was to determine differences in thoracic vs. abdominal aortic stiffness in young and old monkeys (fascicularis and rhesus). Most prior studies on aortic stiffness have been conducted in vitro or in anesthetized animals with indirect measurements of stiffness. A novel feature of the current investigation was to measure aortic diameter and pressure instantaneously and continuously in chronically instrumented, conscious young (n=25, 5-12yrs) and old male (n=21, >24yrs) monkeys, instrumented with aortic pressure gauges and ultrasonic aortic diameter crystals on the thoracic and abdominal aorta. The aortic stiffness index, β[[Unable to Display Character: &#61484;]][[Unable to Display Character: &#61472;]]calculated as a ratio of systolic and diastolic aortic pressures and diameters, was markedly greater, p<0.05, in abdominal, compared with thoracic, aorta in both young (33±5.0 in abdominal vs. 14±2.2 in thoracic) and old monkeys (57±6.3 in abdominal vs. 34±0.4 in thoracic). Although both thoracic and abdominal aortic stiffness were greater in old monkeys, p<0.05, surprisingly, abdominal aortic stiffness in young monkeys (33±5.0) was equal to thoracic aortic stiffness in old monkeys (34±0.4). Using atomic force microscopy, aortic VSMC stiffness was 2 fold greater, p<0.05, in old monkeys vs. young monkeys, but there were no differences in abdominal vs. thoracic aortic VSMC stiffness in either young or old monkeys. In summary, as expected, aging increased aortic stiffness, with the mechanism, in part, due to increased VSMC stiffness. However, aortic stiffness was increased more in the abdominal than thoracic aorta both in young and old monkeys, with the magnitude of the increase in the abdominal aorta of the young monkeys, similar to that which occurs with aging in the thoracic aorta. These findings point out the major differences in stiffness along the aorta and have relevance to the greater frequency of abdominal aortic aneurysms.

Vascular smooth muscle cell stiffness and adhesion to collagen I modified by vasoactive agonists

In vascular smooth muscle cells (VSMCs) integrin-mediated adhesion to extracellular matrix (ECM) proteins play important roles in sustaining vascular tone and resistance. The main goal of this study was to determine whether VSMCs adhesion to type I collagen (COL-I) was altered in parallel with the changes in the VSMCs contractile state induced by vasoconstrictors and vasodilators. VSMCs were isolated from rat cremaster skeletal muscle arterioles and maintained in primary culture without passage. Cell adhesion and cell E-modulus were assessed using atomic force microscopy (AFM) by repetitive nano-indentation of the AFM probe on the cell surface at 0.1 Hz sampling frequency and 3200 nm Z-piezo travelling distance (approach and retraction). AFM probes were tipped with a 5 μm diameter microbead functionalized with COL-I (1mg\ml). Results showed that the vasoconstrictor angiotensin II (ANG-II; 10⁻⁶) significantly increased (p<0.05) VSMC E-modulus and adhesion probability to COL-I by approximately 35% and 33%, respectively. In contrast, the vasodilator adenosine (ADO; 10⁻⁴) significantly decreased (p<0.05) VSMC E-modulus and adhesion probability by approximately −33% and −17%, respectively. Similarly, the NO donor (PANOate, 10⁻⁶ M), a potent vasodilator, also significantly decreased (p<0.05) the VSMC E-modulus and COL-I adhesion probability by −38% and −35%, respectively. These observations support the hypothesis that integrin-mediated VSMC adhesion to the ECM protein COL-I is dynamically regulated in parallel with VSMC contractile activation. These data suggest that the signal transduction pathways modulating VSMC contractile activation and relaxation, in addition to ECM adhesion, interact during regulation of contractile state.

The role of reactive oxygen species in microvascular remodeling

The microcirculation is a portion of the vascular circulatory system that consists of resistance arteries, arterioles, capillaries and venules. It is the place where gases and nutrients are exchanged between blood and tissues. In addition the microcirculation is the major contributor to blood flow resistance and consequently to regulation of blood pressure. Therefore, structural remodeling of this section of the vascular tree has profound implications on cardiovascular pathophysiology. This review is focused on the role that reactive oxygen species (ROS) play on changing the structural characteristics of vessels within the microcirculation. Particular attention is given to the resistance arteries and the functional pathways that are affected by ROS in these vessels and subsequently induce vascular remodeling. The primary sources of ROS in the microcirculation are identified and the effects of ROS on other microcirculatory remodeling phenomena such as rarefaction and collateralization are briefly reviewed.

Oligomeric Amyloid-β Peptide on Sialylic Lewisx-Selectin Bonding at Cerebral Endothelial Surface

Introduction

Alzheimer’s disease (AD) is a chronic neurodegenerative disorder, which affects approximately 10% of the population aged 65 and 40% of people over the age 80. Currently, AD is on the list of diseases with no effective treatment. Thus, the study of molecular and cellular mechanisms of AD progression is of high scientific and practical importance. In fact, dysfunction of the blood-brain barrier (BBB) plays an important role in the onset and progression of the disease. Increased deposition of amyloid b peptide (Aβ) in cerebral vasculature and enhanced transmigration of monocytes across the BBB are frequently observed in AD brains and are some of the pathological hallmarks of the diseases. Since the transmigration of monocytes across the BBB is both a mechanical and a biochemical process, the expression of adhesion molecules and mechanical properties of endothelial cells are the critical factors that require investigation.

Methods

Because of recent advances in the biological applications of atomic force microscopy (AFM), we applied AFM with cantilever tips bio-functionalized by sLe^x in combination with the advanced immunofluorescent microscopy (QIM) to study the direct effects of Aβ₄₂ oligomers on the selectins expression, actin polymerization, and cellular mechanical and adhesion properties in cerebral endothelial cells (mouse bEnd3 line and primary human CECs) and find a possible way to attenuate these effects.

Results

QIM results showed that Aβ₄₂ increased the expressions of P-selectin on the cell surface and enhanced actin polymerization. Consistent with our QIM results, AFM data showed that Aβ₄₂ increased the probability of cell adhesion with sLe^x-coated cantilever and cell stiffness. These effects were counteracted by lovstatin, a cholesterol-lowering drug. Surprisingly, the apparent rupture force of sLe^x-selectin bonding was significantly lower after treatment with Aβ₄₂, as compared with the control (i.e. no treatment). Similar results were also obtained when cells were treated with latruculin A (F-actin-disrupting drug). These results suggest that the decrease in the apparent rupture force of sLe^x-selectin bonding is the consequence of the dissociation of adhesion between the cytoskeleton and the bilayer membrane induced by Aβ₄₂. The major causes of excess mortality in the first group were neoplams (30.6%), hypertension (23.8%), and myocardial infarction (22.6%). The effects of radiation influenced mortality in the second group were 2–2.5 times lower than the first group.

Conclusion

The studies of the effects of Aβ₄₂ on the adhesion properties of cerebral endothelial cells and how pharmacological agents (e.g. statin) counteract these effects should prove to provide insights into the mechanism of inflammation in Alzheimer’s brains and the design of therapeutic treatments of the disease.

Augmented vascular smooth muscle cell stiffness and adhesion when hypertension is superimposed on aging

Hypertension and aging are both recognized to increase aortic stiffness, but their interactions are not completely understood. Most previous studies have attributed increased aortic stiffness to changes in extracellular matrix proteins that alter the mechanical properties of the vascular wall. Alternatively, we hypothesized that a significant component of increased vascular stiffness in hypertension is due to changes in the mechanical and adhesive properties of vascular smooth muscle cells, and that aging would augment the contribution from vascular smooth muscle cells when compared with the extracellular matrix. Accordingly, we studied aortic stiffness in young (16-week-old) and old (64-week-old) spontaneously hypertensive rats and Wistar-Kyoto wild-type controls. Systolic and pulse pressures were significantly increased in young spontaneously hypertensive rats when compared with young Wistar-Kyoto rats, and these continued to rise in old spontaneously hypertensive rats when compared with age-matched controls. Excised aortic ring segments exhibited significantly greater elastic moduli in both young and old spontaneously hypertensive rats versus Wistar-Kyoto rats. were isolated from the thoracic aorta, and stiffness and adhesion to fibronectin were measured by atomic force microscopy. Hypertension increased both vascular smooth muscle cell stiffness and vascular smooth muscle cell adhesion, and these increases were both augmented with aging. By contrast, hypertension did not affect histological measures of aortic collagen and elastin, which were predominantly changed by aging. These findings support the concept that stiffness and adhesive properties of vascular smooth muscle cells are novel mechanisms contributing to the increased aortic stiffness occurring with hypertension superimposed on aging.

Lysophosphatidic acid induces integrin activation in vascular smooth muscle and alters arteriolar myogenic vasoconstriction

In vascular smooth muscle cells (VSMC) increased integrin adhesion to extracellular matrix (ECM) proteins, as well as the production of reactive oxygen species (ROS) are strongly stimulated by lysophosphatidic acid (LPA). We hypothesized that LPA-induced generation of ROS increases integrin adhesion to the ECM. Using atomic force microscopy (AFM) we determined the effects of LPA on integrin adhesion to fibronectin (FN) in VSMC isolated from rat (Sprague-Dawley) skeletal muscle arterioles. In VSMC, exposure to LPA (2 μM) doubled integrin-FN adhesion compared to control cells (P < 0.05). LPA-induced integrin-FN adhesion was reduced by pre-incubation with antibodies against β1 and β3 integrins (50 μg/ml) by 66% (P < 0.05). Inhibition of LPA signaling via blockade of the LPA G-protein coupled receptors LPAR1 and LPAR3 with 10 μM Ki16425 reduced the LPA-enhanced adhesion of VSCM to FN by 40% (P < 0.05). Suppression of ROS with tempol (250 μM) or apocynin (300 μM) also reduced the LPA-induced FN adhesion by 47% (P < 0.05) and 59% (P < 0.05), respectively. Using confocal microscopy, we observed that blockade of LPA signaling, with Ki16425, reduced ROS by 45% (P < 0.05), to levels similar to control VSMC unexposed to LPA. In intact isolated arterioles, LPA (2 μM) exposure augmented the myogenic constriction response to step increases in intraluminal pressure (between 40 and 100 mm Hg) by 71% (P < 0.05). The blockade of LPA signaling, with Ki16425, decreased the LPA-enhanced myogenic constriction by 58% (P < 0.05). Similarly, blockade of LPA-induced ROS release with tempol or gp91 ds-tat decreased the LPA-enhanced myogenic constriction by 56% (P < 0.05) and 55% (P < 0.05), respectively. These results indicate that, in VSMC, LPA-induced integrin activation involves the G-protein coupled receptors LPAR1 and LPAR3, and the production of ROS, and that LPA may play an important role in the control of myogenic behavior in resistance vessels through ROS modulation of integrin activity.

Abstract 012: Mineralocorticoid Receptors Mediate Western Diet-Induced Macrophage Polarization and Aortic Stiffness

Mineralocorticoid receptors (MRs) are expressed in vascular smooth muscle cells (VSMCs), macrophages, and endothelial cells (ECs) and signaling through these receptors may play a key role in development of aortic stiffness. Accordingly, we hypothesized that these vascular MRs are involved in the western diet (WD) - induced macrophage polarization and aortic stiffness. The stiffness of primary cultured VSMC and tissue ECs or VSMCs from mice was measured using cell nano-indentation with atomic force microscopy (AFM). Both Ang II (100 nM) and aldosterone (10 nM) increased VSMC stiffness in vitro. Also, B57 mice fed a WD for 16 weeks increased EC and VSMC stiffness as determined by in vivo pulse wave velocity and ex vivo AFM techniques. The elevated aortic stiffness was accompanied by increased mRNA expression of M1 markers MCP-1, CD 86, and CD11b. However, treatment with low dose spironolactone (Sp) (1.0 mg/kg/day), a dose not affecting blood pressure, significantly attenuated WD-induced increases in stiffness in murine ECs and VSMCs. Sp increased M2 marker IL10 and the expression ratio of M2/M1 marker genes in aorta by real time PCR. Interestingly, mice with EC MR knockout did not develop WD- induced aortic vasodilation dysfunction under both Ach and SNP (10-9-10-4 mol/L) stimulation. Furthermore, low dose Sp inhibited WD- caused up-regulation of ERK 1/2 and down-regulation Akt/eNOS signaling pathways in the aorta. These findings support the notion that increased vascular and macrophage MR signaling play a key role in macrophage polarization and associated aortic stiffness that result from consuming a WD high in fructose and fat.

Abstract 655: Dipeptidyl Peptidase-4 (dpp-4) Inhibition Decreases Cardiac And Vascular Stiffness And Improves Cardiac And Vascular Relaxation In Western Diet Fed Mice

A western diet (WD), high in sucrose and fat, is often accompanied by insulin resistance and cardiovascular disease characterized early by endothelial dysfunction and increased vascular and cardiac stiffness. Recently, Dipeptidyl peptidase-4 (DPP-4) inhibition has been shown to improve diastolic dysfunction in WD fed mice, but its effects on endothelial cell and cardiac stiffness have not been reported. We fed 4-week old C57BL/6 male mice with a WD with or without a DPP-4 inhibitor (MK0626) for 16 weeks and measured blood pressure by telemetry, insulin resistance via (HOMA), in vivo cardiac diastolic function (echocardiography), pulse wave velocity (PWV), and ex vivo aortic endothelial stiffness by atomic force microscopy. Systolic blood pressure and insulin resistance were increased by the WD. DPP-4 inhibition improved systemic insulin sensitivity and substantially reduced DPP-4 activity, but had no effect on 24-hour blood pressures. Heart weight was increased by WD in conjunction with S6 kinase translational signaling and DPP-4 inhibition reduced S6 kinase phosphorylation/activation in conjunction with a reduction in cardiac mass. Aortic stiffness, as assessed by PWV, was significantly increased in WD fed mice (16% increase) and was markedly decreased by DPP-4 inhibition. Endothelial cell stiffness was increased 5-fold in WD fed mice and DPP-4 inhibition significantly decreased endothelial stiffness (80% decrease). Acetylcholine but not sodium nitroprusside mediated vascular relaxation was impaired in WD fed mice and DPP-4 inhibition significantly improved this nitric oxide mediated relaxation. Increased vascular smooth muscle and endothelial stiffness was associated with impaired cardiac diastolic relaxation, which was also significantly improved by DPP-4 inhibition. Taken together, these results show that DPP-4 inhibition improves cardiac and vascular endothelial stiffness and cardiac diastolic dysfunction in a clinically translational mouse model (WD) of over nutrition and insulin resistance.

Vasoactive agonists exert dynamic and coordinated effects on vascular smooth muscle cell elasticity, cytoskeletal remodelling and adhesion

In this study, we examined the ability of vasoactive agonists to induce dynamic changes in vascular smooth muscle cell (VSMC) elasticity and adhesion, and tested the hypothesis that these events are coordinated with rapid remodelling of the cortical cytoskeleton. Real-time measurement of cell elasticity was performed with atomic force microscopy (AFM) and adhesion was assessed with AFM probes coated with fibronectin (FN). Temporal data were analysed using an Eigen-decomposition method. Elasticity in VSMCs displayed temporal oscillations with three components at approximately 0.001, 0.004 and 0.07 Hz, respectively. Similarly, adhesion displayed a similar oscillatory pattern. Angiotensin II (ANG II, 10(-6) M) increased (+100%) the amplitude of the oscillations, whereas the vasodilator adenosine (ADO, 10(-4) M) reduced oscillation amplitude (-30%). To test whether the oscillatory changes were related to the architectural alterations in cortical cytoskeleton, the topography of the submembranous actin cytoskeleton (100-300 nm depth) was acquired with AFM. These data were analysed to compare cortical actin fibre distribution and orientation before and after treatment with vasoactive agonists. The results showed that ANG II increased the density of stress fibres by 23%, while ADO decreased the density of the stress fibres by 45%. AFM data were supported by Western blot and confocal microscopy. Collectively, these observations indicate that VSMC cytoskeletal structure and adhesion to the extracellular matrix are dynamically altered in response to agonist stimulation. Thus, vasoactive agonists probably invoke unique mechanisms that dynamically alter the behaviour and structure of both the VSMC cytoskeleton and focal adhesions to efficiently support the normal contractile behaviour of VSMCs.

The role of tissue Renin-Angiotensin-aldosterone system in the development of endothelial dysfunction and arterial stiffness

Epidemiological studies support the notion that arterial stiffness is an independent predictor of adverse cardiovascular events contributing significantly to systolic hypertension, impaired ventricular-arterial coupling and diastolic dysfunction, impairment in myocardial oxygen supply and demand, and progression of kidney disease. Although arterial stiffness is associated with aging, it is accelerated in the presence of obesity and diabetes. The prevalence of arterial stiffness parallels the increase of obesity that is occurring in epidemic proportions and is partly driven by a sedentary life style and consumption of a high fructose, high salt, and high fat western diet. Although the underlying mechanisms and mediators of arterial stiffness are not well understood, accumulating evidence supports the role of insulin resistance and endothelial dysfunction. The local tissue renin-angiotensin-aldosterone system (RAAS) in the vascular tissue and immune cells and perivascular adipose tissue is recognized as an important element involved in endothelial dysfunction which contributes significantly to arterial stiffness. Activation of vascular RAAS is seen in humans and animal models of obesity and diabetes, and associated with enhanced oxidative stress and inflammation in the vascular tissue. The cross talk between angiotensin and aldosterone underscores the importance of mineralocorticoid receptors in modulation of insulin resistance, decreased bioavailability of nitric oxide, endothelial dysfunction, and arterial stiffness. In addition, both innate and adaptive immunity are involved in this local tissue activation of RAAS. In this review we will attempt to present a unifying mechanism of how environmental and immunological factors are involved in this local tissue RAAS activation, and the role of this process in the development of endothelial dysfunction and arterial stiffness and targeting tissue RAAS activation.