Stretch-induced Changes Research Articles

Bioinspired Low-Angle-Dependent Photonic Crystal Elastomer for Highly Sensitive Visual Strain Sensor.

Photonic crystals (PCs) possess unique photonic band gap properties that can be used in the field of sensors and smart displays if modulated on the micronano structure. Both nonclose-packed (NCP) structure and high refractive index (RI) contrast of PC play important roles in response sensitivity during stretching. Herein, we constructed an NCP-structured PC strain sensor with high RI by a novel coating-etching strategy. Stretch-induced changes in structural color correspond to the strength of the force, enabling the detection of the strength of the acting force by the naked eye. The flexible 3D cross-linked network constructed by poly(ethylene glycol) phenyl ether acrylate and pentaerythritol tetrakis(3-mercaptopropionate) endows the sensor with excellent elasticity and robustness. The designed PC strain sensor achieves high mechanochromic sensitivity (∼8.3 nm/%, 0.02 to 4.21 MPa) and a substantial reflection peak shift (Δλ = 249 nm). More importantly, the high RI contrast (Δn = 0.43) between CdS and polymers imparts isotropic optical properties, ensuring a broad viewing angle while avoiding misleading signals. The research provides a novel fabrication strategy to construct sensitive PC strain sensors, expanding the prospective applicability to human movement monitoring and secure message encryption.

The effects of static and dynamic stretching on deep fascia stiffness: a randomized, controlled cross-over study

AimPrevious stretching studies mostly investigated effects on the skeletal muscle but comprehensive explorations regarding the role of the connective tissue are scarce. Since the deep fascia has been demonstrated to be sensitive to mechanical tension, it was hypothesized that the fascia would also respond to stretching, contributing to enhanced range of motion (ROM).MethodsForty (40) recreationally active participants (male: n = 25, female: n = 15) were included in the randomized controlled cross-over trial and allocated to different groups performing 5 min static (STAT) or dynamic (DYN) plantar flexor stretching or control condition (CC) in a random order. Pre- and immediately post-intervention, muscle and fascia stiffness, as well as muscle and fascia thickness were measured using high-resolution ultrasound and strain elastography. ROM was assessed in the ankle joint via the knee to wall test (KtW) and goniometer.ResultsSTAT reduced both, muscle and fascia stiffness (d = 0.78 and 0.42, p < 0.001, respectively), while DYN did not reduce stiffness compared to the control condition (p = 0.11–0.41). While both conditions showed significant increases in the KtW (d = 0.43–0.46, p = 0.02–0.04), no significant differences to the CC were observed for the isolated ROM testing (p = 0.09 and 0.77). There was a small correlation between fascia stiffness decreases and ROM increases (r = − 0.25, p = 0.006) but no association was found between muscle stiffness decreases and ROM increases (p = 0.13–0.40).ConclusionOur study is the first to reveal stretch-induced changes in fascia stiffness. Changes of fascia`s but not muscle`s mechanical properties may contribute to increased ROM following stretching.

Engineered cardiac tissue as a novel in vitro human myocardium model for studying cardiac stretch.

Heart disease is the largest contributor to death worldwide and research is limited by a lack of adequate human tissue in vitro models. To address this, we developed a protocol for generating 3D, atrial-like engineered cardiac tissue (ECT) comprised of cardiomyocytes (CM) and cardiac fibroblasts, derived from human-induced pluripotent stem cells (hiPSC). Control and atrial-like hiPSC-CM were produced using GiWi differentiation supplemented without and with 0.75 µM retinoic acid, respectively. ECTs were generated using hiPSC-cardiac fibroblasts and Day 30 hiPSC-CM combined in a fibrin matrix and molded via a FlexCell Tissue TrainTM system. ECTs were cultured for 30 days and evaluated for action potentials (AP) as well as mRNA and protein expression profiles. A subset of control ECTs were cyclically and incrementally stretched for 7 days up to 18% elongation. Stretch-induced changes were evaluated via transmission electron microscopy (TEM) and cell culture medium (LC-MS/MS). Atrial-like ECTs recapitulated various atrial phenotypes. They exhibit an atrial-like electrophysiology with a shorter AP duration and increased repolarization fraction (p<0.05). Atrial-like ECT show atrial-specific mRNA/protein expression, such as lower ventricular-like MYL2 and higher atrial-like MYL7 levels (p<0.05). They also demonstrate distinct contraction mechanics with faster kinetics (p<0.05) and decreased normalized contraction force, compared to control ECT. Cyclic stretch reduced cardiomyocyte membrane convolution index (estimating membrane tension) and caveolae membrane structure density (p<0.05). The latter was rescued via neutral sphingomyelinase inhibitor GW4869 (20 µM, p<0.05). LC-MS/MS of stretch-conditioned culture medium revealed decreases in relative sphingomyelins and phosphatidylcholines (p<0.05), ostensibly indicating membrane damage which was reversed by GW4869. Overall, our findings demonstrate retinoic acid-induced atrial-like phenotypes in hiPSC-CM are sustained in ECT form. We also introduce a novel ECT stretch protocol that recapitulates changes observed in animal models of heart pressure overload.

Is the Interpolated-Twitch Technique-Derived Voluntary Activation Just Neural? Novel Perspectives from Mechanomyographic Data.

Voluntary activation (VA) determined by interpolation-twitch technique could be affected by the characteristics of the in-series elastic components. To overcome this possible bias, a novel approach based on the mechanomyographic (MMG) signal to detect voluntary activation (VA MMG ) has been proposed. We examined the changes in VA and VA MMG after passive stretching to check the influence of neural and mechanical factors in the force output. Twenty-six healthy men underwent VA assessment using the interpolated-twitch technique before and after unilateral passive stretching of the plantarflexors (five 45-s on + 15-s off). In addition to the force signal, the MMG signal was detected on gastrocnemius medialis, gastrocnemius lateralis, and soleus. From the force and MMG signal analysis, VA and VA MMG were calculated in the stretched and contralateral nonstretched limbs. Joint passive stiffness was also defined. In the stretched limb, passive stretching increased dorsiflexion range (mean ± SD = +18% ± 10%, P < 0.001, ES = 1.54) but reduced joint passive stiffness (-22% ± 8%, P < 0.001, ES = -1.75), maximum voluntary contraction (-15% ± 7%, P < 0.001, ES = -0.87), VA (-7% ± 3%, P < 0.001, ES = -2.32), and VA MMG (~-5% ± 2%, P < 0.001, ES = -1.26/-1.14). In the contralateral nonstretched limb, passive stretching increased dorsiflexion range (+10% ± 6%, P < 0.001, ES = 0.80) but reduced joint passive stiffness (-3% ± 2%, P = 0.041, ES = -0.27), maximum voluntary contraction (-4% ± 3%, P = 0.035, ES = -0.24), VA (-4% ± 2%, P < 0.001, ES = -1.77), and VA MMG (~- 2% ± 1%, P < 0.05, ES = -0.54/-0.46). The stretch-induced changes in VA correlated with VA MMG ( R ranging from 0.447 to 0.583 considering all muscles) and with joint passive stiffness (stretched limb: R = 0.503; contralateral nonstretched limb: R = 0.530). VA output is overall influenced by both neural and mechanical factors, not distinguishable using the interpolated-twitch technique. VA MMG is a complementary index to assess the changes in VA not influenced by mechanical factors and to examine synergistic muscles.

Chemo-Mechanical Energy Harvesters with Enhanced Intrinsic Electrochemical Capacitance in Carbon Nanotube Yarns.

Predicting and preventing disasters in difficult-to-access environments, such as oceans, requires self-powered monitoring devices. Since the need to periodically charge and replace batteries is an economic and environmental concern, energy harvesting from external stimuli to supply electricity to batteries is increasingly being considered. Especially, in aqueous environments including electrolytes, coiled carbon nanotube (CNT) yarn harvesters have been reported as an emerging approach for converting mechanical energy into electrical energy driven by large and reversible capacitance changes under stretching and releasing. To realize enhanced harvesting performance, experimental and computational approaches to optimize structural homogeneity and electrochemical accessible area in CNT yarns to maximize intrinsic electrochemical capacitance (IEC) and stretch-induced changes are presented here. Enhanced IEC further enables to decrease matching impedance for more energy efficient circuits with harvesters. In an ocean-like environment with a frequency from 0.1 to 1Hz, the proposed harvester demonstrates the highest volumetric power (1.6-10.45mW cm-3 ) of all mechanical harvesters reported in the literature to the knowledge of the authors. Additionally, a high electrical peak power of 540W kg-1 and energy conversion efficiency of 2.15% are obtained from torsional and tensile mechanical energy.

Active force generation contributes to the complexity of spontaneous activity and to the response to stretch of murine cardiomyocyte cultures.

Cardiomyocyte cultures exhibit spontaneous electrical and contractile activity, as in a natural cardiac pacemaker. In such preparations, beat rate variability exhibits features similar to those of heart rate variability in vivo. Mechanical deformations and forces feed back on the electrical properties of cardiomyocytes, but it is not fully elucidated how this mechano‐electrical interplay affects beating variability in such preparations. Using stretchable microelectrode arrays, we assessed the effects of the myosin inhibitor blebbistatin and the non‐selective stretch‐activated channel blocker streptomycin on beating variability and on the response of neonatal or fetal murine ventricular cell cultures against deformation. Spontaneous electrical activity was recorded without stretch and upon predefined deformation protocols (5% uniaxial and 2% equibiaxial strain, applied repeatedly for 1 min every 3 min). Without stretch, spontaneous activity originated from the edge of the preparations, and its site of origin switched frequently in a complex manner across the cultures. Blebbistatin did not change mean beat rate, but it decreased the spatial complexity of spontaneous activity. In contrast, streptomycin did not exert any manifest effects. During the deformation protocols, beat rate increased transiently upon stretch but, paradoxically, also upon release. Blebbistatin attenuated the response to stretch, whereas this response was not affected by streptomycin. Therefore, our data support the notion that in a spontaneously firing network of cardiomyocytes, active force generation, rather than stretch‐activated channels, is involved mechanistically in the complexity of the spatiotemporal patterns of spontaneous activity and in the stretch‐induced acceleration of beating. Key points Monolayer cultures of cardiac cells exhibit spontaneous electrical and contractile activity, as in a natural cardiac pacemaker. Beating variability in these preparations recapitulates the power‐law behaviour of heart rate variability in vivo. However, the effects of mechano‐electrical feedback on beating variability are not yet fully understood.Using stretchable microelectrode arrays, we examined the effects of the contraction uncoupler blebbistatin and the non‐specific stretch‐activated channel blocker streptomycin on beating variability and on stretch‐induced changes of beat rate.Without stretch, blebbistatin decreased the spatial complexity of beating variability, whereas streptomycin had no effects.Both stretch and release increased beat rate transiently; blebbistatin attenuated the increase of beat rate upon stretch, whereas streptomycin had no effects.Active force generation contributes to the complexity of spatiotemporal patterns of beating variability and to the increase of beat rate upon mechanical deformation. Our study contributes to the understanding of how mechano‐electrical feedback influences heart rate variability.

Single-Cell Transcriptomics Uncover Key Regulators of Skin Regeneration in Human Long-Term Mechanical Stretch-Mediated Expansion Therapy.

Tissue expansion is a commonly performed therapy to grow extra skin in vivo for reconstruction. While mechanical stretch-induced epidermal changes have been extensively studied in rodents and cell culture, little is known about the mechanobiology of the human epidermis in vivo. Here, we employed single-cell RNA sequencing to interrogate the changes in the human epidermis during long-term tissue expansion therapy in clinical settings. We also verified the main findings at the protein level by immunofluorescence analysis of independent clinical samples. Our data show that the expanding human skin epidermis maintained a cellular composition and lineage trajectory that are similar to its non-expanding neighbor, suggesting the cellular heterogeneity of long-term expanded samples differs from the early response to the expansion. Also, a decrease in proliferative cells due to the decayed regenerative competency was detected. On the other hand, profound transcriptional changes are detected for epidermal stem cells in the expanding skin versus their non-expanding peers. These include significantly enriched signatures of C-FOS, EMT, and mTOR pathways and upregulation of AREG and SERPINB2 genes. CellChat associated ligand-receptor pairs and signaling pathways were revealed. Together, our data present a single-cell atlas of human epidermal changes in long-term tissue expansion therapy, suggesting that transcriptional change in epidermal stem cells is the major mechanism underlying long-term human skin expansion therapy. We also identified novel therapeutic targets to promote human skin expansion efficiency in the future.

Changes in neural drive to calf muscles during steady submaximal contractions after repeated static stretches

Repeated static-stretching interventions consistently increase the range of motion about a joint and decrease total joint stiffness, but findings on the changes in muscle and connective-tissue properties are mixed. The influence of these stretch-induced changes on muscle function at submaximal forces is unknown. To address this gap in knowledge, the changes in neural drive to the plantar flexor muscles after a static-stretch intervention were estimated. Neural drive to the plantar flexor muscles during a low-force contraction increased after repeated static stretches. These findings suggest that adjustments in motor unit activity are necessary at low forces to accommodate reductions in the force-generating and transmission capabilities of the muscle-tendon unit after repeated static stretches of the calf muscles. Static stretching decreases stiffness about a joint, but its influence on muscle-tendon unit function and muscle activation is unclear. We investigated the influence of three static stretches on changes in neural drive to the plantar flexor muscles, both after a stretch intervention and after a set of maximal voluntary contractions (MVCs). Estimates of neural drive were obtained during submaximal isometric contractions by decomposing high-density electromyographic signals into the activity of individual motor units from medial gastrocnemius, lateral gastrocnemius and soleus. Motor units were matched across contractions and an estimate of neural drive to the plantar flexors was calculated by normalizing the cumulative spike train to the number of active motor units (normalized neural drive). Mean discharge rate increased after the stretch intervention during the 10% MVC task for all recorded motor units and those matched across conditions (all, P=0.0046; matched only, P=0.002), recruitment threshold decreased for motor units matched across contractions (P=0.022), and discharge rate at recruitment was elevated (P=0.004). Similarly, the estimate of normalized neural drive was significantly greater after the stretch intervention at 10% MVC torque (P=0.029), but not at 35% MVC torque. The adjustments in motor unit activity required to complete the 10% MVC task after stretch may have been partially attenuated by a set of plantar flexor MVCs. The increase in neural drive required to produce low plantar-flexion torques after repeated static stretches of the calf muscles suggests stretch-induced changes in muscle and connective tissue properties.

Ranolazine-Mediated Attenuation of Mechanoelectric Feedback in Atrial Myocyte Monolayers.

BackgroundMechanical stretch increases Na+ inflow into myocytes, related to mechanisms including stretch-activated channels or Na+/H+ exchanger activation, involving Ca2+ increase that leads to changes in electrophysiological properties favoring arrhythmia induction. Ranolazine is an antianginal drug with confirmed beneficial effects against cardiac arrhythmias associated with the augmentation of INaL current and Ca2+ overload.ObjectiveThis study investigates the effects of mechanical stretch on activation patterns in atrial cell monolayers and its pharmacological response to ranolazine.MethodsConfluent HL-1 cells were cultured in silicone membrane plates and were stretched to 110% of original length. The characteristics of in vitro fibrillation (dominant frequency, regularity index, density of phase singularities, rotor meandering, and rotor curvature) were analyzed using optical mapping in order to study the mechanoelectric response to stretch under control conditions and ranolazine action.ResultsHL-1 cell stretch increased fibrillatory dominant frequency (3.65 ± 0.69 vs. 4.35 ± 0.74 Hz, p < 0.01) and activation complexity (1.97 ± 0.45 vs. 2.66 ± 0.58 PS/cm2, p < 0.01) under control conditions. These effects were related to stretch-induced changes affecting the reentrant patterns, comprising a decrease in rotor meandering (0.72 ± 0.12 vs. 0.62 ± 0.12 cm/s, p < 0.001) and an increase in wavefront curvature (4.90 ± 0.42 vs. 5.68 ± 0.40 rad/cm, p < 0.001). Ranolazine reduced stretch-induced effects, attenuating the activation rate increment (12.8% vs. 19.7%, p < 0.01) and maintaining activation complexity—both parameters being lower during stretch than under control conditions. Moreover, under baseline conditions, ranolazine slowed and regularized the activation patterns (3.04 ± 0.61 vs. 3.65 ± 0.69 Hz, p < 0.01).ConclusionRanolazine attenuates the modifications of activation patterns induced by mechanical stretch in atrial myocyte monolayers.

Neuromuscular versus Mechanical Stretch-induced Changes in Contralateral versus Ipsilateral Muscle.

Whether or not the homologous contralateral muscle (CM) undergoes stretch-induced force reduction as the stretched muscle (SM) is still unclear. The neuromuscular and mechanical factors underlying the force reduction in CM and SM were investigated. Twenty-one participants underwent unilateral knee extensors passive stretching. In both CM and SM, before, immediately after (POST), 5 (POST5), and 10 min (POST10) after passive stretching, maximum voluntary contraction (MVC), peak force (pF), and voluntary activation (VA) were measured. During MVC, the electromyographic and mechanomyographic root mean square (EMG RMS and MMG RMS, respectively) was calculated in rectus femoris, vastus lateralis, and vastus medialis, together with M-wave. The total electromechanical delay (EMD), divided in time delay (Δt) EMG-MMG and Δt MMG-F was calculated. In CM at POST, the decrease in MVC (-11%; 95% confidence interval [CI], -13 to -9; effect size [ES], -2.27) was accompanied by a fall in VA (-7%; 95% CI, -9 to -4; ES, -2.29), EMG RMS (range, -22% to -11%; ES, -3.92 to -2.25), MMG RMS (range, -10% to -8%; ES, -0.52 to -0.39) and an increase in Δt EMG-MMG (≈+10%; ES, 0.73 to 0.93). All changes returned to baseline at POST5. In SM, decrease in MVC (-19%; 95% CI, -24 to -18; ES, -3.08), pF (-25%; 95% CI, -28 to -22; ES, -4.90), VA (-10%; 95% CI, -11 to -9; ES, -5.71), EMG RMS (≈-33%; ES, -5.23 to -3.22) and rise in MMG RMS (range, +25% to +32%; ES, 4.21 to 4.98) and EMD (≈+28%; ES, 1.59 to 1.77) were observed at POST and persisted at POST10. No change in M-wave occurred. The contralateral central motor drive stretch-induced inhibition seems to account for the force reduction in CM. In SM, both central inhibition and mechanical factors concurred.

Responses of bladder smooth muscle to the stretch go through extracellular signal-regulated kinase (ERK)/p90 ribosomal S6 protein kinase (p90RSK)/Nuclear factor-κB (NF-κB) Pathway.

The present study was designed to study changes and its potential mechanisms in human bladder smooth muscle subjected to stretch. Bioinformatics analyses including differential expression analysis, overrepresentation enrichment analysis, principal component analysis, and weighted gene coexpression network analysis were used to analyze a microarray dataset (GSE47080) of partial bladder outlet obstruction (pBOO) in rat to find the potential changes of gene expressions. Bladder from pBOO model and human bladder smooth muscle cells (HBSMCs) subjected to sustained prolonged stretch were collected for Western blot analysis, real-time polymerase chain reaction, and fluorescence analysis to verify the changes of gene expressions and preliminarily study the potential role of signaling pathway regulation in treatment of pBOO. The bioinformatics analysis showed that chronic obstruction activated mitogen-activated protein kinase pathway and changed cytoskeleton structure in bladder smooth muscle. In in vivo experiments in mice, pBOO was verified by cystometry. Partial BOO activated the extracellular signal-regulated kinase (ERK)/p90 ribosomal S6 protein kinase (p90RSK)/nuclear factor-κB (NF-κB) signaling pathway in DM. The messenger RNA (mRNA) expressions of contractile phenotypic proteins increased after pBOO. In in vitro experiments of HBSMCs, mechanical stretch activated ERK/p90RSK/NF-κB in HBSMCs in a time-dependent manner. The mRNA expressions of α-smooth muscle actin and SM22 also increased and filamentous actin (F-actin) polymerization was enhanced as well. Inhibition of ERK/p90RSK/NF-κB pathway reversed mechanical stretch-induced changes of contractile phenotypic expression and F-action polymerization. Continuous stretch increases expressions of contractile phenotypic proteins and promotes the polymerization of F-actin. This process partially goes through ERK/p90RSK/NF-κB pathway.

Effects of cyclic stretch-induced mechanical changes of the cell nucleus on the ultraviolet radiation resistance of cells

Effects of cyclic stretch-induced mechanical changes of the cell nucleus on the ultraviolet radiation resistance of cells

Effects of the Inhibition of Late Sodium Current by GS967 on Stretch-Induced Changes in Cardiac Electrophysiology.

Mechanical stretch increases sodium and calcium entry into myocytes and activates the late sodium current. GS967, a triazolopyridine derivative, is a sodium channel blocker with preferential effects on the late sodium current. The present study evaluates whether GS967 inhibits or modulates the arrhythmogenic electrophysiological effects of myocardial stretch. Atrial and ventricular refractoriness and ventricular fibrillation modifications induced by acute stretch were studied in Langendorff-perfused rabbit hearts (n = 28) using epicardial multiple electrodes and high-resolution mapping techniques under control conditions and during the perfusion of GS967 at different concentrations (0.03, 0.1, and 0.3μM). On comparing ventricular refractoriness, conduction velocity and wavelength obtained before stretch had no significant changes under each GS967 concentration while atrial refractoriness increased under GS967 0.3μM. Under GS967, the stretch-induced changes were attenuated, and no significant differences were observed between before and during stretch. GS967 0.3μM diminished the normal stretch-induced changes resulting in longer (less shortened) atrial refractoriness (138±26ms vs 95±9ms; p < 0.01), ventricular refractoriness (155±18ms vs 124±16 ms; p < 0.01) and increments in spectral concentration (23±5% vs 17±2%; p < 0.01), the fifth percentile of ventricular activation intervals (46±8ms vs 31±3ms; p < 0.05), and wavelength of ventricular fibrillation (2.5±0.5cm vs 1.7±0.3cm; p < 0.05) during stretch. The stretch-induced increments in dominant frequency during ventricular fibrillation (control = 38%, 0.03μM = 33%, 0.1μM = 33%, 0.3μM = 14%; p < 0.01) and the stretch-induced increments in arrhythmia complexity index (control = 62%, 0.03μM = 41%, 0.1μM = 32%, 0.3μM = 16%; p < 0.05) progressively decreased on increasing the GS967 concentration. GS967 attenuates stretch-induced changes in cardiac electrophysiology.

Tadalafil attenuates hypotonicity-induced Ca2+ influx via TRPV2 and TRPV4 in primary rat bladder urothelial cell cultures.

To investigate the localization of phosphodiesterase 5 (PDE5) and the molecular mechanism underlying the effect of the PDE5 inhibitor tadalafil in signal transduction in the bladder urothelium. PDE5 expression in rat bladder tissues and cultured primary rat bladder urothelial cells was evaluated using immunochemistry and western blot assays. Ca2+ influx in cells exposed to isotonic solution, hypotonic solution, a selective transient receptor potential vanilloid 2 (TRPV2) channel agonist (cannabidiol), a selective TRPV4 channel agonist (GSK1016790A), a TRP cation channel melastatin 7 (TRPM7) channel agonist (PIP2), or a purinergic receptor agonist (ATP) in the presence or absence of 10 µM tadalafil was evaluated using calcium imaging techniques. We also evaluated stretch-induced changes in ATP concentration in the mouse bladder in the presence or absence of 100 µM tadalafil. Immunochemistry and western blot analyses demonstrated that PDE5 is abundantly expressed in the bladder urothelium and in primary rat urothelial cells. Ca2+ influx induced by hypotonic stimulation, GSK1016790A, or cannabidiol was significantly inhibited by tadalafil, whereas ATP-induced Ca2+ influx was unaffected by tadalafil. PIP2 did not induce Ca2+ influx. ATP release in tadalafil-pretreated bladders significantly decreased compared to control bladders. Tadalafil attenuates Ca2+ influx via TRPV4 and TRPV2, and inhibits ATP release in the bladder urothelium. These findings indicate that tadalafil functions as an inhibitor of urothelial signal transduction.

Acute effects of static stretching on passive stiffness and postural balance in healthy, elderly men

ABSTRACTObjectives: This study aimed to examine the acute effects of straight-leg raise (SLR) static stretching on passive stiffness and postural balance in healthy, elderly men. An additional aim of this study was to examine the relationships between stiffness and balance at baseline (prior to stretching) and the relationships between the stretch-induced changes in these variables.Methods: Eleven elderly men (age = 69 ± 6 years; height = 177 ± 7 cm; mass = 83 ± 13 kg) underwent postural balance and passive stiffness assessments before and after: 1) a stretching treatment consisting of four, 15-s SLR static stretches performed by the primary investigator and 2) a control treatment consisting of no static stretching. Passive stiffness was calculated from the slopes of the initial (phase 1) and final (phase 2) portions of the angle–torque curve. Unilateral postural balance was assessed on the right leg using a commercially designed balance testing device, which provides a measurement of static stability based on the overall stability index (OSI).Results: The slope coefficients and OSI values decreased from pre- to post-treatment for the stretching intervention (P = 0.015 and 0.018, respectively); however, there were no changes for the control (P = 0.654 and 0.920). For the stretching intervention, a significant positive relationship was observed between OSI and the slope coefficient of phase 1 at baseline (r = 0.619; P = 0.042). A significant positive relationship was also observed between the stretched-induced changes in OSI and the slope coefficient of phase 1 (r = 0.731; P = 0.011). No relationship was observed between OSI and the slope coefficient of phase 2 at baseline (r = 0.262; P = 0.437) nor was there a relationship between the changes in these variables (r = 0.419; P = 0.200).Conclusion: A short, practical bout of SLR static stretching may be an effective intervention for reducing passive stiffness and improving postural balance in healthy, elderly men.

LINCRNA-P21 IS REGULATED BY CYCLIC MECHANICAL STRETCH AND UPREGULATED IN AORTIC ANEURYSMS

Emerging evidence suggests that long noncoding RNAs (lncRNAs) may represent a cellular hub for coordination of cellular processes involved in cardiovascular health and disease. Alterations in the characteristics of vascular smooth muscle cells, triggered largely by mechanical stress, play a critical role in the pathophysiology of vascular diseases. We hypothesized that lncRNAs are involved in the pathogenesis of mechanical stretch-induced changes in human aortic smooth muscle cells (HASMCs). HASMCs were subjected to 20% elongation (1 Hz) for 24 h (Flexcell® FX4000™). Total RNA was extracted with TRIzol. LncRNAs were profiled using the Arraystar Human LncRNA Microarray V3.0. Human aneurysmal and non-aneurysmal aortic samples were collected from patients undergoing aortic arch repair and coronary artery bypass grafting, respectively. Aneurysmal and non-aneurysmal samples were also collected from the aorta of ApoE-/- mice after 4-week infusion of angiotensin II and saline, respectively. Gene expression was quantified via qRT-PCR. For knockdown studies, siLincRNA-p21 and scrambled control were transfected into HASMCs at 10 nM and 5nM final concentration, respectively, using Dharmafect 2 (Dharmacon). Apoptosis was assessed using Annexin V/PI double staining. Of the 30,586 human lncRNAs screened, 580 were differentially expressed (P < 0.05) in the stretched vs. static group. Human long intergenic non-coding RNA-p21 (lincRNA-p21) was significantly upregulated in stretched HASMCs (N = 3, P < 0.05) and human aneurysmal samples (N = 10, P < 0.05). The murine ortholog of lincRNA-p21 was upregulated in aortic tissues from angiotensin-II-infused ApoE-/- mice (N = 3, P < 0.05). Upon silencing of lincRNA-p21 in stretched HASMCs, there was a decrease in total apoptosis (N = 3, P < 0.05) and expression of the p53-downstream genes Bax, Puma, Noxa, and Mdm2 (N = 3, P < 0.05). Our data provides the first transcriptome profile of stretched HASMCs and implicates lincRNA-p21 as a mechanoresponsive regulator of aneurysm formation in mice and humans. This data provides novel insights into the regulatory switches governing aberrant VSMC remodeling, which may have importance in the pathogenesis of aneurysms and hypertension.

Kinetics of Mechanical Stretch-Induced Nitric Oxide Production in Rat Ventricular Cardiac Myocytes.

Discrete mechanical stretch of isolated spontaneously contracting cardiac myocytes was employed to examine the kinetics of NO production in these cells. NO oscillations were detected with fluorescent dye 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate. The mechanisms underlying stretch-induced changes in NO concentration remain unclear and further studies are needed to evaluate the role of NO oscillation in the regulation of cardiomyocyte function.

Fingerprint of long non-coding RNA regulated by cyclic mechanical stretch in human aortic smooth muscle cells: implications for hypertension.

Emerging evidence suggests that long non-coding RNAs (lncRNAs) represent a cellular hub coordinating various cellular processes that are critical in health and disease. Mechanical stress triggers changes in vascular smooth muscle cells (VSMCs) that in turn contribute to pathophysiological changes within the vasculature. We sought to evaluate the role that lncRNAs play in mechanical stretch-induced alterations of human aortic smooth muscle cells (HASMCs). RNA (lncRNA and mRNA) samples isolated from HASMCs that had been subjected to 10 or 20% elongation (1Hz) for 24h were profiled with the Arraystar Human LncRNA Microarray V3.0. LncRNA expression was quantified in parallel via qRT-PCR. Of the 30,586 human lncRNAs screened, 580 were differentially expressed (DE, P<0.05) in stretched HASMCs. Amongst the 26,109 protein-coding transcripts evaluated, 25 of those DE were associated with 25 of the aforementioned DE lncRNAs (P<0.05). Subsequent Kyoto Encyclopedia of Genes and Genomes analysis revealed that the DE mRNAs were largely associated with the tumor necrosis factor signaling pathway and inflammation. Gene Ontology analysis indicated that the DE mRNAs were associated with cell differentiation, stress response, and response to external stimuli. We describe the first transcriptome profile of stretch-induced changes in HASMCs and provide novel insights into the regulatory switches that may be fundamental in governing aberrant VSMC remodeling.

Muscle mechanoreflex activation via passive calf stretch causes renal vasoconstriction in healthy humans.

Reflex renal vasoconstriction occurs during exercise, and renal vasoconstriction in response to upper-limb muscle mechanoreflex activation has been documented. However, the renal vasoconstrictor response to muscle mechanoreflex activation originating from lower limbs, with and without local metabolite accumulation, has not been assessed. Eleven healthy young subjects (26 ± 1 yr; 5 men) underwent two trials involving 3-min passive calf muscle stretch (mechanoreflex) during 7.5-min lower-limb circulatory occlusion (CO). In one trial, 1.5-min 70% maximal voluntary contraction isometric calf exercise preceded CO to accumulate metabolites during CO and stretch (mechanoreflex and metaboreflex; 70% trial). A control trial involved no exercise before CO (mechanoreflex alone; 0% trial). Beat-to-beat renal blood flow velocity (RBFV; Doppler ultrasound), mean arterial blood pressure (MAP; photoplethysmographic finger cuff), and heart rate (electrocardiogram) were recorded. Renal vascular resistance (RVR), an index of renal vasoconstriction, was calculated as MAP/RBFV. All baseline cardiovascular variables were similar between trials. Stretch increased RVR and decreased RBFV in both trials (change from CO with stretch: RVR - 0% trial = Δ 10 ± 2%, 70% trial = Δ 7 ± 3%; RBFV - 0% trial = Δ -3.8 ± 1.1 cm/s, 70% trial = Δ -2.7 ± 1.5 cm/s; P < 0.05 for RVR and RBFV). These stretch-induced changes were of similar magnitudes in both trials, e.g., with and without local metabolite accumulation, as well as when thromboxane production was inhibited. These findings suggest that muscle mechanoreflex activation via passive calf stretch causes renal vasoconstriction, with and without muscle metaboreflex activation, in healthy humans.

Systems Mechanobiology of Cardiac Myocytes

Cardiac myocytes are sensitive to specific and distinct mechanical stimuli. We examined the effect of the major axis of biaxial mechanical stretch on cardiac myocyte gene expression and reconstructed a stretch signaling model to identify pathways and transcription factors regulating these responses. Neonatal cardiac myocytes were cultured on a micropatterned substrate, and the primary stretch axis was applied either parallel or transverse to the myofibril direction. RNA sequencing (RNA-Seq) after acute myocyte stretch showed a more robust response to longitudinal than to transverse stretch. After 30 minutes of stretch, 53 and 168 genes were significantly up- or down-regulated by transverse or longitudinal stretch, respectively. After 4 hours, the number of differentially expressed genes increased to 795 with longitudinal stretch but only 35 with transverse stretch. Genes regulated by both stretches showed significant enrichment of transcription factor activity and protein kinase activity, whereas longitudinal but not transverse stretch specifically activated genes involved in sarcomere organization and cytoskeletal protein binding. Network analysis using logic-based signaling model constructed from published data identified serum response factor (SRF) and myocyte enhancer factor-2 (MEF2) as critical regulators of longitudinal stretch-induced changes mediated by protein kinase C (PKC). cAMP response element-binding protein (CREB) was found to be activated by both longitudinal and transverse stretch. Inhibitor experiments were used to validate these model predictions. Cardiac myocytes activate different pathways in response to transverse and longitudinal mechanical strain; these responses may underlie differential whole organ responses to pressure versus volume overload.