Physical breakdown of CH4 hydrate under stress: a molecular dynamics simulation study

As a solid energy source, CH4 hydrate will inevitably break down physically as the result of geological movement or exploitation. Here, the molecular dynamics method was employed to simulate the uniaxial-deformation behavior of structure I (sI type) CH4 hydrate under stress. The stress increases regardless of whether the hydrate is stretched or squeezed, and other physical parameters also changed, such as hydrate cage numbers, order parameters, and the number of water molecules. A noticeable difference is observed between the two systems. Upon stretching, the stress immediately recovers to 0 GPa once the hydrate is completely stretched apart. During the squeeze process, the stress is ultimately not zero since solid and liquid are always in contact. When the hydrate is stretched apart, about 5% of water molecules change from solid to liquid, about 7.8% of CH4 molecules lose their shelter and become free due to the disintegration of water cages. While in the squeezing process, large cages (51262) are crushed more easily than small cages (512); in the end, about 93.5% of large cages and 73% of small cages are crushed, and approximately 87.5% CH4 is released from the cages. In mining CH4 hydrates, caution must be exercised, as if the hydrates break as a result of stress, a large release of CH4 may pose a security risk.

Acute effects of static stretching and proprioceptive neuromuscular facilitation on non-local range of movement

Acute effects of static stretching (SS) and proprioceptive neuromuscular facilitation (PNF) on local and non-local range of motion (ROM) were assessed in 29 participants. Three evaluations were performed one week apart: week-1 Control session (CS); weeks 2-3 either SS or PNF interventions (randomized). Dominant and non-dominant limbs, local (hamstring extensibility) and non-local ROMs (Shoulder extension-ShE) were collected at baseline (T0), immediately after (T1), and fifteen minutes post-intervention (T2). No differences were found between time-points during the CS. Local-ROM significantly increased (p=0.0002, ES=0.74 and 0.0079, 0.56, for dominant and non-dominant lower limbs, respectively) after both SS and PNF. No interaction between time and treatment was detected for ShE in both limbs. However, post-hoc analysis revealed a significant increase in dominant upper limb ShE between T0 and T1 only after SS (p=0.002; +6.5%). Acute bouts of SS and PNF can increase local-ROM, however, no clear effects were observed for non-local ROM.

Caveolae-associated cAMP/Ca2+-mediated mechano-chemical signal transduction in mouse atrial myocytes

Caveolae are tiny invaginations in the sarcolemma that buffer extra membrane and contribute to mechanical regulation of cellular function. While the role of caveolae in membrane mechanosensation has been studied predominantly in non-cardiomyocyte cells, caveolae contribution to cardiac mechanotransduction remains elusive. Here, we studied the role of caveolae in the regulation of Ca2+ signaling in atrial cardiomyocytes. In Langendorff-perfused mouse hearts, atrial pressure/volume overload stretched atrial myocytes and decreased caveolae density. In isolated cells, caveolae were disrupted through hypotonic challenge that induced a temporal (<10 min) augmentation of Ca2+ transients and caused a rise in Ca2+ spark activity. Similar changes in Ca2+ signaling were observed after chemical (methyl-β-cyclodextrin) and genetic ablation of caveolae in cardiac-specific conditional caveolin-3 knock-out mice. Acute disruption of caveolae, both mechanical and chemical, led to the elevation of cAMP level in the cell interior, and cAMP-mediated augmentation of protein kinase A (PKA)-phosphorylated ryanodine receptors (at Ser2030 and Ser2808). Caveolae-mediated stimulatory effects on Ca2+ signaling were abolished via inhibition of cAMP production by adenyl cyclase antagonists MDL12330 and SQ22536, or reduction of PKA activity by H-89. A compartmentalized mathematical model of mouse atrial myocytes linked the observed changes to a microdomain-specific decrease in phosphodiesterase activity, which disrupted cAMP signaling and augmented PKA activity. Our findings add a new dimension to cardiac mechanobiology and highlight caveolae-associated cAMP/PKA-mediated phosphorylation of Ca2+ handling proteins as a novel component of mechano-chemical feedback in atrial myocytes.

Impact of stretch on sarcomere length variability in isolated fully relaxed rat cardiac myocytes

The contractility of cardiac muscle is greatly affected by preload via the Frank-Starling mechanism (FSM). It is based on preload-dependent activation of sarcomeres-the elementary contractile units in muscle cells. Recent findings show a natural variability in sarcomere length (SL) in resting cardiomyocytes that, moreover, is altered in an actively contracting myocyte. SL variability may contribute to the FSM, but it remains unresolved whether the change in the SL variability is regulated by activation process per se or simply by changes in cell stretch, i.e., average SL. To separate the roles of activation and SL, we characterized SL variability in isolated, fully relaxed rat ventricular cardiomyocytes (n = 12) subjected to a longitudinal stretch with the carbon fiber (CF) technique. Each cell was tested in three states: without CF attachment (control, no preload), with CF attachment without stretch, and with CF attachment and ~ 10% stretch of initial SL. The cells were imaged by transmitted light microscopy to retrieve and analyze individual SL and SL variability off-line by multiple quantitative measures such as coefficient of variation or median absolute deviation. We found that CF attachment without stretch did not affect the extent of SL variability nor average SL. In stretched myocytes, the averaged SL significantly increased, while the SL variability remained unchanged. This result clearly indicates that the non-uniformity of individual SL is not sensitive to the average SL itself in fully relaxed myocytes. We conclude that SL variability per se does not contribute to the FSM in the heart.

Multiple pregnancies, the myometrium and the role of mechanical factors in the timing of labour

Multiple pregnancy remains a relatively common occurrence, but it is associated with increased risks of adverse outcomes for the mother and her babies and presents unique challenges to healthcare providers. This review will briefly discuss multiple pregnancies, their aetiology and their problems, including preterm birth, before reviewing the processes leading to normal labour onset and how they may be different in a multiple pregnancy. The mechanisms by which mechanical factors i.e., uterine distension or 'stretch' contribute to uterine excitability and the timing of labour onset will be the major focus, and how over distention may pre-dispose multiple pregnancies to preterm birth. This includes current thinking around the role of mechano (stretch) sensitive ion channels in the myometrium and changes to other important regulators of excitability and contraction which have been identified from studies using in vitro and in vivo models of uterine stretch. Physiological stimuli arising from the fetus(es) and placenta(s) will also be discussed. In reviewing what we know about the myometrium in multiple pregnancy in humans, the focus will be on twin pregnancy as it is the most common type of multiple pregnancy and has been the most studied.

Mechanical activation of lung epithelial cells through the ion channel Piezo1 activates the metalloproteinases ADAM10 and ADAM17 and promotes growth factor and adhesion molecule release

In the lung, pulmonary epithelial cells undergo mechanical stretching during ventilation. The associated cellular mechanoresponse is still poorly understood at the molecular level. Here, we demonstrate that activation of the mechanosensitive cation channel Piezo1 in a human epithelial cell line (H441) and in primary human lung epithelial cells induces the proteolytic activity of the metalloproteinases ADAM10 and ADAM17 at the plasma membrane. These ADAMs are known to convert cell surface expressed proteins into soluble and thereby play major roles in proliferation, barrier regulation and inflammation. We observed that chemical activation of Piezo1 promotes cleavage of substrates that are specific for either ADAM10 or ADAM17. Activation of Piezo1 also induced the synthesis and ADAM10/17-dependent release of the growth factor amphiregulin (AREG). In addition, junctional adhesion molecule A (JAM-A) was shed in an ADAM10/17-dependent manner resulting in a reduction of cell contacts. Stretching experiments combined with Piezo1 knockdown further demonstrated that mechanical activation promotes shedding via Piezo1. Most importantly, high pressure ventilation of murine lungs increased AREG and JAM-A release into the alveolar space, which was reduced by a Piezo1 inhibitor. Our study provides a novel link between stretch-induced Piezo1 activation and the activation of ADAM10 and ADAM17 in lung epithelium. This may help to understand acute respiratory distress syndrome (ARDS) which is induced by ventilation stress and goes along with perturbed epithelial permeability and release of growth factors.

Creation of myofascial pain syndrome-like muscle by artificial electrical stimulation and stretching treatment

BACKGROUND

Myofascial pain syndrome（MPS）is a common chronic pain disorder characterized by muscle hardness, low extensibility, restriction of range of motion (ROM)　and pain with trigger point (TP). Eccentric contraction has been used in past animal studies of MPS. However, clinical experience suggests that concentric contraction is also involved in MPS formation.

NEW METHODS

In this study, we adopted artificial electrical stimulation to create artificial concentric contraction (ACC) in rat gastrocnemius muscle. After ACC, muscle hardness, torsion and range of motion (ROM) were compared between before ACC, after ACC, and stretching group. To clarify the association with pain, the expression of pERK in DRG were analyzed.

COMPARISON TO EXISTING METHODS

Previous animal studies have created MPS models by inducing eccentric contractions in muscles. In this study, full tetanus contraction of the gastrocnemius muscle was achieved via tibial nerve stimulation. This method substituted muscle contraction due to abnormal excitation.

RESULTS

We found that artificial abnormal contraction (ACC) induced muscle hardness and ROM restriction. The pERK expression in DRG was increased by ACC. Analysis of muscle tissue sections revealed a meandeling structure in muscle fibers. The stretching treatment improved these indicators. These results were similar to feature of the MPS muscles.

CONCLUSIONS

The ACC caused by artificial electrical stimulation leads to the characteristic of MPS in rat gastrocnemius muscle. This ACC model can be one of the useful options for MPS analysis.

Eccentric muscle contractions: from single muscle fibre to whole muscle mechanics

Eccentric muscle loading encompasses several unique features compared to other types of contractions. These features include increased force, work, and performance at decreased oxygen consumption, reduced metabolic cost, improved energy efficiency, as well as decreased muscle activity. This review summarises explanatory approaches to long-standing questions in terms of muscular contraction dynamics and molecular and cellular mechanisms underlying eccentric muscle loading. Moreover, this article intends to underscore the functional link between sarcomeric components, emphasising the fundamental role of titin in skeletal muscle. The giant filament titin reveals versatile functions ranging from sarcomere organisation and maintenance, providing passive tension and elasticity, and operates as a mechanosensory and signalling platform. Structurally, titin consists of a viscoelastic spring segment that allows activation-dependent coupling to actin. This titin-actin interaction can explain linear force increases in active lengthening experiments in biological systems. A three-filament model of skeletal muscle force production (mediated by titin) is supposed to overcome significant deviations between experimental observations and predictions by the classic sliding-filament and cross-bridge theories. Taken together, this review intends to contribute to a more detailed understanding of overall muscle behaviour and force generation-from a microscopic sarcomere level to a macroscopic multi-joint muscle level-impacting muscle modelling, the understanding of muscle function, and disease.

Endocardial role in arrhythmias induced by acute ventricular stretch and the involvement of Purkinje fibres, in isolated rat hearts

Purkinje fibres (PFs) play an important role in some ventricular arrhythmias and acute ventricular stretch can evoke mechanically-induced arrhythmias. We tested whether PFs and specifically TRPM4 channels, play a role in these mechanically-induced arrhythmias. Pseudo-ECGs and left ventricular (LV) activation, measured by optical mapping, were recorded in isolated, Langendorff-perfused, rat hearts. The LV endocardial surface was irrigated with experimental agents, via an indwelling catheter. The number and period of ectopic activations was measured during LV lumen inflation via an indwelling fluid-filled balloon (100 μL added over 2 s, maintained for 38 s). Mechanically-induced arrhythmias occurred during balloon inflation: they were multifocal, maximal in the first 5 s and ceased within 20 s. Optical mapping revealed activation patterns indicating PF-mediated and ectopic focal sources. Irrigation of the LV lumen with Lugol solution (IK/I₂) for 10s reduced ectopics by 93% (n = 16, P < 0.001); with ablation of endocardial PFs confirmed by histology. Five min irrigation of the LV lumen with 50 μM 9-Phenanthrol, a blocker of TRPM4 channels, reduced ectopics by 39% (n = 15, P < 0.01). Immunohistochemistry confirmed that TRPM4 was more abundant in PFs than myocardium. Our results show that the endocardial surface plays an important role in these mechanically-induced ectopic activations. Ectopic activation patterns indicate a participation of PFs in these arrhythmias, with a potential involvement of TRPM4 channels, shown by the reduction of arrhythmias by 9-Phenanthrol.

Reduction in atrial and pulmonary vein stretch as a therapeutic target for prevention of atrial fibrillation

Atrial fibrillation (AF) is a common cardiac arrhythmia that is associated with increased mortality. Heart failure, hypertension, valvular disease, and obstructive sleep apnea are risk factors for incident AF. A common characteristic of these diseases is that they increase atrial wall stretch. Multiple experimental studies confirm a proarrhythmic effect of atrial stretch. Conversely, a reduction in stretch is antiarrhythmic. A therapeutic target for AF, therefore, lies in local reduction of atrial stretch. This review focuses on atrial stretch and its clinical associations in patients with AF and its downstream effects on electrophysiology. We discuss the possible application of targeted atrial stretch reduction in AF prevention. We conclude that a reduction in local atrial stretch should be considered an essential element in rhythm control.

The effect of Aqua Stretching exercises and Pilates on pain, function and spine posture in patients with ankylosing spondylitis: a randomized controlled trial

Background

Aqua Pilates and Aqua Stretch exercises are different and new methods for the rehabilitation of musculoskeletal disorders. This study aimed to compare the effectiveness of Aqua Stretch and Aqua Pilates interventions in the treatment of pain, function, and posture of the spine in ankylosing spondylitis (AS) patients.

Methods

Forty patients participated in this study who were randomly allocated into Aqua Stretch, aqua Pilates, and control. The experimental groups received four 60-min training sessions each week for six weeks. However, the control group had only its routine drug treatment (NSAIDs & Anti TNF). Pain with Visual Analog Scale (VAS), function with Bath Ankylosing Spondylitis Functional Index (BASFI) and 40-m walking test (MWT), quality of life with ankylosing spondylitis quality of life (ASQoL), and posture of the spine with the Spinal Mouse were evaluated. Evaluations were performed before and after the interventions. Repeated measure ANOVA was employed to determine the main and interaction effects.

Results

Aqua Stretch and Aqua Pilates had a significant effect on pain (Aqua-Pilates: P = 0.0001; Aqua-Stretch: P = 0.0001), BASFI (Aqua-Pilates: P = 0.01; Aqua-Stretch: P = 0.02), 40-MWT (Aqua-Pilates: P = 0.006; Aqua-Stretch: P = 0.0001) and ASQoL (Aqua-Pilates: P = 0.01; Aqua-Stretch: P = 0.001), spinal range of motion (ROM) (Aqua-Pilates: P = 0.0001; Aqua-Stretch: P = 0.0001) at a similar ratio. However, the control group did not present any improvement in these factors (P > 0.05). Moreover, the minimal clinically important difference (MCID) revealed that the Aqua Stretch group performed better than the Aqua Pilates group in terms of VAS, ASQOL, and 40-MWT factors.

Conclusions

Aqua Stretch and Aqua Pilates had statistically the same effect on improving pain, function, quality of life, and spinal ROM, while MCID results revealed that the Aqua Stretch group performed better than the Aqua Pilates in terms of VAS-ASQOL-40-MWT.

Trial registration It is notable that local ethics committee approval was obtained (IR.KUMS.REC.1399.1137), and the study was registered in Iranian Registry of Clinical Trials (IRCT; IRCT20190426043377N3; registered on 22/05/2021, https://fa.irct.ir/user/trial/56058/view) and patient recruitments were started on 06/07/2021.

Differential Regulation by Mechanical Stretch of the Expressions of Large-Conductance Ca2+-Activated K+ Channel and L-Type Voltage-Dependent Ca2+ Channel in Rat Uterine Smooth Muscle Cells

Large-conductance Ca²⁺-activated K⁺ (BK_Ca) channel and L-type voltage-dependent Ca²⁺ channel (L-VDCC) play important roles in regulating uterine contractility. The uterus stretch, occurring during pregnancy, is a critical factor to trigger uterine contraction. However, how mechanical stimuli impact the two channels remains unknown. Here we investigated the effects of exposure to mechanical stretches with varying magnitudes and durations on expressions of the two channels in rat uterine smooth muscle cells. Our results show that stretch down-regulates the BK_Ca channel expression but upregulates the L-VDCC expression. These findings are helpful to better understand the roles of L-VDCC and BK_Ca channel in stretch-triggered uterine contraction.

Mechanism of cell death of endothelial cells regulated by mechanical forces

Cell death of endothelial cells (ECs) is a common devastating consequence of various vascular-related diseases. Atherosclerosis, hypertension, sepsis, diabetes, cerebral ischemia and cardiac ischemia/reperfusion injury, and chronic kidney disease remain major causes of morbidity and mortality worldwide, in which ECs are constantly subjected to a great amount of dynamic changed mechanical forces including shear stress, extracellular matrix stiffness, mechanical stretch and microgravity. A thorough understanding of the regulatory mechanisms by which the mechanical forces controlled the cell deaths including apoptosis, autophagy, and pyroptosis is crucial for the development of new therapeutic strategies. In the present review, experimental and clinical data highlight that nutrient depletion, oxidative stress, tumor necrosis factor-α, high glucose, lipopolysaccharide, and homocysteine possess cytotoxic effects in many tissues and induce apoptosis of ECs, and that sphingosine-1-phosphate protects ECs. Nevertheless, EC apoptosis in the context of those artificial microenvironments could be enhanced, reduced or even reversed along with the alteration of patterns of shear stress. An appropriate level of autophagy diminishes EC apoptosis to some extent, in addition to supporting cell survival upon microenvironment challenges. The intervention of pyroptosis showed a profound effect on atherosclerosis. Further cell and animal studies are required to ascertain whether the alterations in the levels of cell deaths and their associated regulatory mechanisms happen at local lesion sites with considerable mechanical force changes, for preventing senescence and cell deaths in the vascular-related diseases.

Silencing of miR-10b-5p alleviates the mechanical stretch-induced proliferation of HASMCs

MicroRNAs (miRNAs) are important mediators to human airway smooth muscle cells (HASMCs) phenotype remodeling and airway diseases. MicroRNA-10b-5p (miR-10b-5p) has been extensively studied in different fields. This study set out to probe into the effect of miR-10b-5p in cyclic mechanical stretch-induced apoptosis in HASMCs. The results showed that after 15 % deformation, 0.5 s stretching and 0.5 s cyclic mechanical stretching relaxation (0.5 Hz) occurred to HASMCs, miR-10b-5p showed up-regulation without inducing significant apoptosis. Moreover, the mRNA and protein expressions of FLT1 were reduced. Then, dual-luciferase reporter assay verified that FLT1 was targeted by miR-10b-5p, and miR-10b-5p silencing increased FLT1 expression, leading to a prolonged arrest of stretch-treated HASMCs at the G1/S stage, and increased cell apoptosis compared with control group. Furthermore, the activity of Caspase-3 was reinforced, and the ratio of Bcl-2 to Bax was markedly reduced after miR-10b-5p silencing. The current study proved that expression levels of p-PI3K and p-Akt in stretch-treated HASMCs of the inhibition group were significantly inhibited in comparison to those of the controls. The effects of miR-10b-5p overexpression are opposite to that of inhibition of miR-10b-5p in stretched HASMCs. In conclusion, this study showed that miR-10b-5p silencing could weaken the hypertrophy of HASMCs. MiR-10b-5p negatively regulated FLT1 expression, but positively regulated the PI3K/Akt pathway in HASMCs. By referring to other previous studies, we concluded that miR-10b-5p might be a potent target in the treatment of airway diseases.

What keeps us ticking? Sinoatrial node mechano-sensitivity: the grandfather clock of cardiac rhythm

The rhythmic and spontaneously generated electrical excitation that triggers the heartbeat originates in the sinoatrial node (SAN). SAN automaticity has been thoroughly investigated, which has uncovered fundamental mechanisms involved in cardiac pacemaking that are generally categorised into two interacting and overlapping systems: the 'membrane' and 'Ca²⁺ clock'. The principal focus of research has been on these two systems of oscillators, which have been studied primarily in single cells and isolated tissue, experimental preparations that do not consider mechanical factors present in the whole heart. SAN mechano-sensitivity has long been known to be a contributor to SAN pacemaking-both as a driver and regulator of automaticity-but its essential nature has been underappreciated. In this review, following a description of the traditional 'clocks' of SAN automaticity, we describe mechanisms of SAN mechano-sensitivity and its vital role for SAN function, making the argument that the 'mechanics oscillator' is, in fact, the 'grandfather clock' of cardiac rhythm.

Cellular mechanosignaling in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a vasculopathy characterized by sustained elevated pulmonary arterial pressures in which the pulmonary vasculature undergoes significant structural and functional remodeling. To better understand disease mechanisms, in this review article we highlight recent insights into the regulation of pulmonary arterial cells by mechanical cues associated with PAH. Specifically, the mechanobiology of pulmonary arterial endothelial cells (PAECs), smooth muscle cells (PASMCs) and adventitial fibroblasts (PAAFs) has been investigated in vivo, in vitro, and in silico. Increased pulmonary arterial pressure increases vessel wall stress and strain and endothelial fluid shear stress. These mechanical cues promote vasoconstriction and fibrosis that contribute further to hypertension and alter the mechanical milieu and regulation of pulmonary arterial cells.

Small conductance calcium activated K+ channel inhibitor decreases stretch induced vulnerability to atrial fibrillation

Background

Atrial dilation is an important risk factor for atrial fibrillation (AF) and animal studies have found that acute atrial dilation shortens the atrial effective refractory period (AERP) and increases the risk of AF. Stretch activated ion channels (SACs) and calcium channels play a role in this. The expression profile and calcium dependent activation makes the small conductance calcium activated K⁺ channel (K_Ca2.x) a candidate for coupling stretch induced increases in intracellular calcium through K⁺-efflux and thereby shortening of atrial refractoriness.

Objectives

We hypothesized that K_Ca2.x channel inhibitors can prevent the stretch induced shortening of AERP and protect the heart from AF.

Methods

The effect of K_Ca2 channel inhibitor (N-(pyridin-2-yl)-4-(pyridin-2-yl)thiazol-2-amine (ICA) 1 µM) was investigated using the isolated perfused rabbit heart preparation. To stretch the left atrium (LA) a balloon was inserted and inflated. AERP and action potential duration (APD) were recorded before and after atrial stretch. AF was induced by burst pacing the LA at different degrees of atrial stretch.

Results

Stretching of the LA by increasing the balloon pressure from 0 to 20 mmHg shortened the AERP by 8.6 ± 1 ms. In comparison, the K_Ca2 inhibitor ICA significantly attenuated the stretch induced shortening of AERP to 2.5 ± 1.1 ms. Total AF duration increased linearly with atrial balloon pressure. This relationship was not found in the presence of ICA. ICA lowered the incidence of AF induction and total AF duration.

Conclusion

The K_Ca2 channel inhibitor ICA attenuates the acute stretch induced shortening of AERP and decreases stretch induced vulnerability to AF.

Mechano-inflammatory sensitivity of ACE2: Implications for the regional distribution of SARS-CoV-2 injury in the lung

The coronavirus disease (COVID-19) caused by SARS-CoV-2 can result in severe injury to the lung. Computed tomography images have revealed that the virus preferentially affects the base of the lung, which experiences larger tidal stretches than the apex. We hypothesize that the expression of both the angiotensin converting enzyme-2 (ACE2) receptor for SARS-CoV-2 and the transmembrane serine protease 2 (TMPRSS2) are sensitive to regional cell stretch in the lung. To test this hypothesis, we stretched precision cut lung slices (PCLS) for 12 h with one of the following protocols: 1) unstretched (US); 2) low-stretch (LS), 5% peak-to-peak area strain mimicking the lung base; or 3) high-stretch (HS), the same peak-to-peak area strain superimposed on 10% static area stretch mimicking the lung apex. PCLS were additionally stretched in cigarette smoke extract (CSE) to mimic an acute inflammatory exposure. The expression of ACE2 was higher whereas that of TMPRSS2 was lower in the control samples following LS than HS. CSE-induced inflammation substantially altered the expression of ACE2 with higher levels following HS than LS. These results suggest that ACE2 and TMPRSS2 expression in lung cells is mechanosensitive, which could have implications for the spatial distribution of COVID-19-mediated lung injury and the increased risk for more severe disease in active smokers and patients with COPD.

Androgen receptor regulates the proliferation of myoblasts under appropriate or excessive stretch through IGF-1 receptor mediated p38 and ERK1/2 pathways

Background

Androgen receptor (AR) exerts important roles in exercise-induced alterations of muscle mass, in which the proliferation and differentiation of satellite cells or myoblasts are crucial. Our previous study in C2C12 myoblasts demonstrated that 15% (mimic appropriate exercise) and 20% (mimic excessive exercise) stretches promoted and inhibited the proliferation respectively; and AR played a crucial role in 15% stretch-induced pro-proliferation through IGF-1-modulated PI3K/Akt, p38 and ERK1/2 pathways, but AR’s role in stretches-modulated proliferation of general myoblasts, especially 20% stretch, remains unclear, and the mechanisms need to be further clarified.

Methods

Firstly, the discrepancy in proliferation and the above indicators between L6 (without AR) and C2C12 (with AR) myoblasts were compared under 15% or 20% stretch. Then the influences of transfection AR or exogenous IGF-1 treatment on proliferation and these indicators were detected in stretched L6 myoblasts.

Results

(1) Under un-stretched state, the proliferation of L6 was slower than C2C12 cells. Furthermore, AR knockdown in C2C12 myoblasts repressed, while AR overexpression in L6 myoblasts promoted the proliferation. (2) 15% stretch-induced increases in the proliferation and activities of p38 and ERK1/2 were lower in L6 than C2C12 cells; AR overexpression enhanced the proliferation of 15% stretched L6 cells accompanied with the increases of p38 and ERK1/2 activities. (3) 20% stretch-induced anti-proliferation and inhibition of p38 activity were severer in L6 than C2C12 myoblasts; AR overexpression reversed the anti-proliferation of 20% stretch and enhanced p38 activity in L6 myoblasts. (4) In stretched L6 myoblasts, AR overexpression increased IGF-1R level despite no detectable IGF-1; and recombinant IGF-1 increased the proliferation, the level of IGF-1R, and the activities of p38 and ERK1/2 in 15% stretched L6 myoblasts.

Conclusions

The study demonstrated AR's crucial roles in stretches-regulated proliferation of myoblasts, and increased AR fulfilled 15% stretch's pro-proliferation via activating IGF-1R- p38 and ERK1/2 pathways while decreased AR achieved 20% stretch's anti-proliferation via inhibiting IGF-1R- p38 pathway, which is useful to understand in depth the role and mechanisms of AR in appropriate exercise increasing while excessive exercise decreasing muscle mass.

Regional biomechanical and failure properties of healthy human ascending aorta and root

PURPOSE

Aortic dissection (AD) is a life-threatening event that occurs when the intimal entry tear propagates and separates inner from outer layers of the aorta. Diameter, the current criterion for aneurysm repair, is far from ideal and additional evidence to optimize clinical decision would be extremely beneficial. Biomechanical investigation of the regional failure properties of aortic tissue is essential to understand and proactively prevent AD. We previously studied biaxial mechanical properties of healthy human aorta. In this study, we investigated the regional failure properties of healthy human ascending aorta (AscAo) including sinuses of Valsalva (SOV), and sinotubular junction (STJ).

RESULTS

A total of 430 intact tissue samples were harvested from 19 healthy donors whose hearts were excluded from heart transplantation. The donors had mean age of 51 ± 11.7 years and nearly equal gender distribution. Samples were excised from aortic regions and subregions at defined locations. Tissue strips were subjected to either biaxial or uniaxial failure testing. Wall thickness varied regionally being thickest at AscAo (2.08 ± 0.66 mm) and thinnest at SOV (1.46 ± 0.31 mm). Biaxial testing demonstrated hyperplastic behavior of aortic tissues. Posterior and lateral STJ subregions were found to be stiffer than anterior and medial subregions in both circumferential and longitudinal directions. Failure stresses were significantly higher in the circumferential than longitudinal directions in each subregion of AscAo, STJ, and SOV. Longitudinal failure stresses were significantly greater in AscAo than those in STJ or SOV. Longitudinal failure stresses in AscAo were much smaller anteriorly than posteriorly, and medially than laterally.

CONCLUSIONS

The finding of weakest region at the sinotubular junction along the longitudinal direction corroborates clinical observations of that region being commonly involved as the initial site of intimal tear in aortic dissections. Failure stretch ratios correlated to elastic modulus at each region. Furthermore, strong correlation was seen between STJ failure stresses and elastic modulus at physiological pressure along both circumferential and longitudinal directions. Correlating in-vivo aortic elastic modulus based on in-vivo imaging with experimentally determined elastic modulus at physiological pressure and failure stresses may potentially provide valuable information regarding aortic wall strength. Better understanding of aortic biomechanics in normal physiologic and aneurysmal pathologic states may aid in determining risk factors for predicting dissection in patient-specific fashion.

Evaluation of the first annular pulley stretch effect under isometric contraction of the flexor tendon in healthy volunteers and trigger finger patients using ultrasonography

Background

Isometric exercises for a flexed finger have been reported to be effective for treating trigger finger as the flexor tendon widens the space under the first annular (A1) pulley towards the palmar destination during the exercise. This study aimed to evaluate the structural changes during the A1 pulley stretch in healthy volunteers and patients with trigger finger using ultrasonography.

Methods

We enrolled 25 male and 14 female patients (39 middle fingers). The thickness of the subcutaneous tissue (parameter a), A1 pulley (parameter b), and the flexor tendon (parameter c) and the distance between the dorsal surface of the flexor tendon and the palmar surface of the metacarpal head (parameter d) were measured using ultrasonography of the metacarpophalangeal joint of the middle finger flexed at 45° at rest (pattern A) and under isometric contraction of the flexor tendon against an extension force of the proximal interphalangeal joint (pattern B).

Results

The average differences between patterns A and B in the healthy volunteers were 0.29 mm (parameter a; P = 0.02), 0.017 mm (parameter b; P = 0.63), 0.16 (parameter c; P = 0.26), and 0.41 (parameter d; P = 0.004), and those in patients with trigger finger were 0.22 mm (parameter a; P = 0.23), 0.019 mm (parameter b; P = 0.85), 0.03 mm (parameter c; P = 0.82), and 0.78 mm (parameter d; P < 0.001). The distance between the dorsal side of the A1 pulley and the palmar surface of the metacarpal head was also significantly increased by 0.57 mm (8.2%) in healthy volunteers (P < 0.001) and 0.81 mm (11%) in patients with trigger finger (P < 0.001).

Conclusions

In this study, the space under the A1 pulley was expanded under isometric contraction of the flexor tendon. These findings support the effectiveness of pulley stretch exercises for the trigger finger condition.

Functional and electron-microscopic changes after differential traction injury in the sciatic nerve of a rat

Background

During maxillofacial trauma or oral cancer surgery, peripheral nerve might be damaged by traction injury. The purpose of this study was to evaluate functional and histomorphometric changes after traction nerve injury in the sciatic nerve of a rat model.

Methods

A total of 24 Sprague-Dawley rats were equally divided into three groups: unstretched (sham/control, group A), stretched with 0.7N (group B) and 1.5N (group C). Traction injury was performed for 10 min in B and C groups. Functional recovery of the sciatic nerve was evaluated by walking track analysis, toe spread test, and pinprick test 2 weeks after injury. The weight of gastrocnemius muscles of both sides was measured to evaluate weight ratio (ipsilateral/contralateral). Total number of axons, axon fiber size, myelin thickness, G-ratio, axon number/mm², diameter of fiber, changes of longitudinal width, and formation of the edema and hematoma were evaluated by transmission electron microscopy.

Results

The sciatic function indexes were −11.48±4.0, −15.11±14.84, and −49.12±35.42 for groups A, B, and C, respectively. Pinprick test showed 3.0, 2.86±0.38, and 1.38±0.52 for A, B, and group C. Muscle weight ratios were 0.98±0.13 for group A, 0.70±0.10 for group B, and 0.54±0.05 for group C. There were significant differences in toe spread test, pinprick test, and muscle weight ratio between control group and experimental group (p<0.001). In the experimental group, fiber number, fiber size, G-ratio, fiber number/mm², myelin thickness, diameter of fiber, and longitudinal width were decreased with statistical significance.

Conclusion

The present study demonstrated that the nerve traction injury in the rat sciatic nerve damaged the motor and sensory function and axonal integrity. The amount of functional nerve damage was proportional to the amount of traction power and dependent on the initial tensile strengths (0.7N and 1.5N).

Stretch-induced sarcoplasmic reticulum calcium leak is causatively associated with atrial fibrillation in pressure-overloaded hearts

AIMS

Despite numerous reports documenting an important role of hypertension in the development of atrial fibrillation (AF), the detailed mechanism underlying the pathological process remains incompletely understood. Here, we aim to test the hypothesis that diastolic sarcoplasmic reticulum (SR) Ca2+ leak in atrial myocytes, induced by mechanical stretch due to elevated pressure in the left atrium (LA), plays an essential role in the AF development in pressure-overloaded hearts.

METHODS AND RESULTS

Isolated mouse atrial myocytes subjected to acute axial stretch displayed an immediate elevation of SR Ca2+ leak. Using a mouse model of transverse aortic constriction (TAC), the relation between stretch, SR Ca2+ leak, and AF susceptibility was further tested. At 36 h post-TAC, SR Ca2+ leak in cardiomyocytes from the LA (with haemodynamic stress), but not right atrium (without haemodynamic stress), significantly increased, which was further elevated at 4 weeks post-TAC. Accordingly, AF susceptibility to atrial burst pacing in the 4-week TAC mice were also significantly increased, which was unaffected by inhibition of atrial fibrosis or inflammation via deletion of galectin-3. Western blotting revealed that type 2 ryanodine receptor (RyR2) in left atrial myocytes of TAC mice was oxidized due to activation and up-regulation of Nox2 and Nox4. Direct rescue of dysfunctional RyR2 with dantrolene or rycal S107 reduced diastolic SR Ca2+ leak in left atrial myocytes and prevented atrial burst pacing stimulated AF.

CONCLUSION

Our study demonstrated for the first time the increased SR Ca2+ leak mediated by enhanced oxidative stress in left atrial myocytes that is causatively associated with higher AF susceptibility in pressure-overloaded hearts.

Stretch and poke stimulation for characterizing mechanically activated ion channels

Quantitative functional characterization of mechanically activated ion channels is most commonly achieved by a combination of patch-clamp electrophysiology and stimulation by stretch (or pressure-clamp) and poke (or cell-indentation). A variety of stretch and poke protocols can be used to make measurements of many ion channel properties, including channel number, unitary conductance, ion selectivity, stimulus threshold and sensitivity, stimulus adaptation, and gating kinetics (activation, deactivation, inactivation, recovery from inactivation). Here, we review the general methods of stretch and poke stimulation and discuss the advantages and disadvantages of each. We use the vertebrate mechanically activated ion channel Piezo1 to explain equipment components and calibration, demonstrate experimental protocols and data analyses, and discuss underlying concepts and mechanistic interpretations.

Acute effects of dynamic stretching on neuromechanical properties: an interaction between stretching, contraction, and movement

PURPOSE

The present study aimed to investigate the acute effects of dynamic stretching on neurophysiological and mechanical properties of plantar flexor muscles and to test the hypothesis that dynamic stretching resulted from an interaction between stretching, movement, and contraction.

METHODS

The dynamic stretching conditioning activity (DS) was compared to static stretching (SS), passive cyclic stretching (PCS), isometric contractions (IC), static stretching followed by isometric contractions (SSIC), and control (CO) conditions. Stretching amplitude (DS, SS, PCS and SSIC), contraction intensity (DS, IC and SSIC) and duration (all 6 conditions) were matched. Thirteen volunteers were included. Passive torque, fascicle length, and stiffness were evaluated from a dynamometer and ultrasonography during passive dorsiflexion. Neuromuscular electrical stimulation was used to investigate contractile properties [peak twitch torque (PTT), and rate of torque development (RTD)] and muscle voluntary activation (%VA). Gastrocnemius lateralis electromyographic activity (GL EMG/Mwave) was obtained during maximal voluntary contraction. All of these parameters were measured immediately before and 10 s after each experimental condition.

RESULTS

Peak twitch torque, RTD, %VA, GL EMG/Mwave remained unaltered, while passive torque was significantly reduced after DS (- 8.14 ± 2.21%). SS decreased GL EMG/Mwave (- 7.83 ± 12.01%) and passive torque (- 2.16 ± 7.25%). PCS decreased PTT (- 3.40 ± 6.03%), RTD (- 2.96 ± 5.16%), and passive torque (- 2.16 ± 2.05%). IC decreased passive torque (- 7.72 ± 1.97%) and enhanced PTT (+ 5.77 ± 5.19%) and RTD (+ 7.36 ± 8.35%). However, SSIC attenuated PTT and RTD improvements as compared to IC.

CONCLUSION

These results suggested that dynamic stretching is multi-component and would result from an interaction between stretching, contraction, and movement.

Stretch-excitation correlation in the toad heart

The activation sequence of the ventricular myocardium in ectotherms is a matter of debate. We studied the correlation between the ventricular activation sequence and the pattern of local stretches in 13 toads (Bufo bufo). Epicardial potential mapping was done with a 56-lead sock array. Activation times were determined as dV/dt (min) in each lead. Initial epicardial foci of activation were found on the left side of the ventricular base, whereas regions on the apex and the right side of the base demonstrated late activation. Video recordings (50 frames s-1) showed that the median presystolic stretch in left-side ventricular regions was greater than that in right-side regions [4.70% (interquartile range 3.25-8.85%) versus 1.45% (interquartile range 0.38-3.05%), P=0.028, respectively]. Intracardiac bolus injection elicited ventricular activation with a similar sequence and duration. Thus, ventricular areas of earliest activation were associated with greater presystolic stretch, implying the existence of a stretch-excitation relationship in ectotherm hearts.

A methodological nine-step process to bioengineer heart muscle tissue

Research in the field of heart muscle tissue engineering is focused on the fabrication of heart muscle tissue which can be utilized to repair, replace and/or augment functionality of damaged and/or diseased tissue. In the simplest embodiment, bioengineering heart muscle tissue constructs involves culture of cardiomyocytes within natural or synthetic scaffolds. Functional integration of the cells with the scaffold and subsequent remodeling lead to the formation of 3D heart muscle tissue and physiological cues like mechanical stretch, electrical stimulation and perfusion are necessary to guide tissue maturation and development. Potential applications for bioengineered heart muscle include use as grafts to repair or replace damaged tissue, as models for basic research and as tools for high-throughput screening of pharmacological agents. In this article, we provide a methodological process to bioengineer functional 3D heart muscle tissue and discuss state of the art and potential challenges in each of the nine-step tissue fabrication process.

Both the resistance training session and the static stretching after exercise does not affect the pectoralis major stiffness of well-trained men

Previous evidence suggests the intense resistance training session can increase the muscle hardness, while stretching protocols with high intensity and volume can decrease it. However, it remains unknown the effects of an exercise and a less intensive stretching maneuver on muscle stiffness of well-trained men. Herein we (i) analyze the acute effects of heavy bench press exercise on the pectoralis major muscle shear modulus of well-trained men and (ii) assess the effectiveness of a 1-min stretching maneuver applied on this muscle after the exercise using shear wave elastography. Fourteen participants performed three sets of bench press from 8 to 13 repetitions maximum. Immediately after the exercise, their right shoulder was passively stretched for 1 min (stretched side) while their left arm stayed relaxed along the side of the body (control side). Elastographic images were acquired for the pectoralis major mid-region of both sides before the exercise, immediately after the intervention and after 5 min of rest. Our results revealed that both the bench press exercise and the static stretching does not affect the pectoralis major shear modulus of well-trained men. Conversely, the shear modulus significantly decreased at 5 min after intervention with respect to immediately after, for both the stretched (from 5.52 to 4.29 kPa) and the control sides (from 5.87 to 4.56 kPa). Therefore, both resistance training session and 1-min static stretching were not sufficient to significantly change the pectoralis major muscle stiffness of well-trained men.

Suppressing ROS generation by apocynin inhibited cyclic stretch-induced inflammatory reaction in HPDLCs via a caspase-1 dependent pathway

It has been reported that cyclic stretch could induce inflammatory reaction in human periodontal ligament cells (HPDLCs). Though reactive oxygen species (ROS) has been reported to be involved in pathogen-induced periodontal inflammatory reaction, its role in the force-related periodontal diseases has not been well clarified. This study inspected the role of ROS in the cyclic stretch-induced inflammatory reaction in HPDLCs and studied the inhibitory effect of antioxidant apocynin on this inflammatory reaction. Results confirmed that cyclic stretch induced inflammatory reaction and production of ROS in HPDLCs. This inflammatory reaction was inhibited by apocynin through blocking the production of ROS. The cyclic stretch also induced the expression of caspase-1 and NLRP3 inflammasome, which could also be inhibited by apocynin. Moreover, the cyclic stretch-induced inflammatory reaction was inhibited by caspase-1 inhibitor. Collectively, it is the first time that increased intracellular ROS was proved to play as an intermediate signal in the cyclic stretch-induced inflammatory reaction in HPDLCs, via a caspase-1-dependent pathway. The inhibitory effect of apocynin on the cyclic stretch-induced inflammatory reaction in HPDLCs shows the potential of antioxidants in the treatment of force-related periodontal inflammatory diseases.

A survey of pathways for mechano-electric coupling in the atria

Mechano-electric coupling (MEC) in atrial tissue has received sparse investigation to date, despite the well-known association between chronic atrial dilation and atrial fibrillation (AF). Of note, no fewer than six different mechanisms pertaining to stretch-activated channels, cellular capacitance and geometric effects have been identified in the literature as potential players. In this mini review, we briefly survey each of these pathways to MEC. We then perform computational simulations using single cell and tissue models in presence of various stretch regimes and MEC pathways. This allows us to assess the relative significance of each pathway in determining action potential duration, conduction velocity and rotor stability. For chronic atrial stretch, we find that stretch-induced alterations in membrane capacitance decrease conduction velocity and increase action potential duration, in agreement with experimental findings. In the presence of time-dependent passive atrial stretch, stretch-activated channels play the largest role, leading to after-depolarizations and rotor hypermeandering. These findings suggest that physiological atrial stretches, such as passive stretch during the atrial reservoir phase, may play an important part in the mechanisms of atrial arrhythmogenesis.

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Passive strains caused by ventricular contraction need to be considered when incorporating mechano-electro feedback in atrial electrophysiology models.

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In chronic stretch, stretch-induced capacitance changes dominate.

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Chronic stretch leads to an increase in action potential duration and a reduction in conduction velocity, consistent with experimental studies.

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In the presence of passive stretch, stretch-activated channels can induce delayed after-depolarisations and lead to rotor hypermeandering.

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Mechano-electro feedback is thus likely to have implications for the genesis and maintenance of atrial arrhythmias.

Enhanced BMP-2/BMP-4 ratio in patients with peripheral spondyloarthritis and in cytokine- and stretch-stimulated mouse chondrocytes

Background

Excessive bone formation in the entheses is one of the features of peripheral spondyloarthritis (SpA). Complex pathological mechanisms connecting inflammation, mechanical stress, and ossification are probably involved. We focused on bone morphogenetic protein (BMP)-2, -4, and -7 as possible mediators of this process.

Methods

BMP-2, -4, and -7 concentration was measured by ELISA in synovial fluids (SFs) of SpA (n = 56) and osteoarthritic (n = 21) patients. Mouse organotypic ankle cultures were challenged by a pro-inflammatory cocktail. Mouse primary chondrocytes, osteoblasts, or tenocytes were treated with TNF-α, interleukin (IL)-17, or IL-22 and/or subjected to cyclic stretch, or with recombinant BMP-2 or -4.

Results

In SpA SFs, if BMP-7 was barely detectable, BMP-2 concentration was higher and BMP-4 was lower than in osteoarthritic samples, so that BMP-2/BMP-4 ratio augmented 6.5 folds (p < 0.001). In SpA patients, TNF-α, IL-6, and IL-17 levels correlated this ratio (n = 21). Bmp-2/Bmp-4 ratio was similarly enhanced by cytokine treatment in explant and cell cultures, at mRNA level. In particular, simultaneous application of TNF-α and cyclical stretch induced a 30-fold increase of the Bmp-2/Bmp-4 ratio in chondrocytes (p = 0.027). Blockade of prostaglandin E₂ and IL-6 production had almost no effect on the stretch-induced regulation of Bmp-2 or -4. Osteoinductive effects of BMP-4, and to a lesser extend BMP-2, were identified on cultured chondrocytes and tenocytes.

Conclusions

Our results first settle that BMP factors are locally deregulated in the SpA joint. An unexpected decrease in BMP-4 could be associated to an increase in BMP-2, possibly in response to mechanical and/or cytokine stimulations.

[Research advances in pathomechanism and treatment of joint contracture]

Joint contracture is one of the common musculoskeletal disorders. It has seriously disturbed patients' activities of daily living in various aspects. The pathogenesis of it is eager to explore to distinct degree. Nowadays the thickeness and fibrosis of joint capsular is redarded as the major reason to joint contracture. It is reported that excessive fibroblasts and myofibroblasts activity, collagen hyperplasia, and extracellular matrix (ECM) deposition in these fibrotic condtions lead to the contracture. In addition, upregulators of myofibroblast and collagen synthesis, transforming growth factor-beta 1 (TGF-β1), and connective tissue growth factor (CTGF) were shown to be increased. Altered levels of cytokines were also thought to play a role in this process as elevated levelsof tumor necrosis factor-α(TNF-α), matrix metalloproteinases(MMPs) and abnormal distribution tissue inhibitors of MMPs(TIMPs) were demonstrated in contracted capsules. At present, the methods for clinical treatment of joint contracture mainly include two major categories:stretching therapy, physical factor therapy, exercise therapy, botulinum toxin injection and other non-surgical treatments, arthroscopic lysis, open lysis, and other surgical treatments. Surgical treatment is performed when non-surgical treatment is difficult to achieve further improvement. It has a good effect on mild to moderate joint contracture, but it is difficult to completely restore joint activity for serious joint contracture. Although clinical treatment methods are diverse, the clinical effects are staggered and the effectiveness of their treatment is controversial. Joint contracture is an important challenge faced by orthopedics and rehabilitation physicians, therapists and patients. The review summarized the pathogenesisand treatment of joint contracture and provided a theoretical basis for clinical diagnosis and treatment.

Mechanical on-off gates for regulation of drug release in cutaneous or musculoskeletal tissue repairs

Drug release synchronized with tissue motion is attractive to cutaneous or musculoskeletal tissue injury repair. Here, we have developed a method of regulating drug release by mechanical on-off gates for potential treatment of repeated injury in these tissues. The mechanical gates consisted of a multilayer structure: A brittle outmost layer adhered to an elastic middle layer, which wrapped an inmost drug carrier to form the composite multilayer structure. When it was stretched, cracks appeared as mechanical gates due to mechanical performance difference between the outmost layer and the middle layer, leading to the drug release. When the external force disappeared, it recovered to stop the drug release. The controlled drug release would therefore be achieved by changing the status (opening or closure) of mechanical gates through applying this on-off mechanical stretching. A prototype based on the composite multilayer structure of adhesive coating and electrospinning technique realized the controlled release of drug and effectively repaired the incision. More types of composite multilayer structures for mechanical drug release were expected to meet curing requirement in cutaneous or musculoskeletal tissues.

In vivo paracrine effects of ATP-induced urothelial acetylcholine in the rat urinary bladder

Mechanical stretch of the urothelium induces the release of ATP that activates bladder afferent nerves. In the rat urinary bladder, ATP is also a contractile co-transmitter in the parasympathetic innervation. In isolated preparations, ATP evokes a urothelial release of acetylcholine that substantially contributes to ATP-evoked contractile responses. Currently we aimed to further examine the interactions of ATP and acetylcholine in the rat urinary bladder in two in vivo models. In the whole bladder preparation, atropine reduced ATP-evoked responses by about 50% in intact but denervated bladders, while atropine had no effect after denudation of the urothelium. In a split bladder preparation, reflex-evoked responses of the contralateral half were studied by applying stimuli (agonists or stretch) to the ipsilateral half. Topical administration of ATP and methacholine as well as of stretch induced contralateral reflex-evoked contractions. While topical administration of atropine ipsilaterally reduced the ATP- and stretch-induced contralateral contractions by 27 and 39%, respectively, the P2X purinoceptor antagonist PPADS reduced them by 74 and 84%. In contrary, the muscarinic M2-(M4)-selective receptor antagonist methoctramine increased the responses by 38% (ATP) and 75% (stretch). Pirenzepine (M1-selective antagonist) had no effect on the reflex. In vitro, in the absence of the reflex, methoctramine did not affect the ATP-induced responses. It is concluded that urothelial ATP potently induces the micturition reflex and stimulates urothelial release of acetylcholine. Acetylcholine subsequently acts on afferents and on the detrusor muscle. While muscarinic M2 and/or M4 receptors in the sensory innervation exert inhibitory modulation, muscarinic M3 receptors cause excitation.

Whole-body vibration and stretching enhances dorsiflexion range of motion in individuals with chronic ankle instability

OBJECTIVE

The purpose of this study was to determine if WBV performed concurrently with static stretching was more effective than static stretching alone to increase dorsiflexion ROM (DFROM) in individuals with chronic ankle instability (CAI).

DESIGN

Controlled laboratory study.

PARTICIPANTS

Thirty-nine participants with CAI (history of ankle sprain, a feeling of "giving way" during activity, and a qualifying Foot and Ankle Ability Measure Ankle score) were divided into 3 groups (normative (N), static stretch (SS), and static stretch with vibration (SV)). Participants stretched the triceps surae 4 days/wk for 3 wks. Vibration was imposed at 34 Hz and 1.8 mm.

MAIN OUTCOME MEASURES

DFROM was assessed in a straight and bent-leg position.

RESULTS

No differences were detected at any time in the N or SS group, however SS did exhibit large effect sizes with 95% confidence intervals (CI) that did not cross zero from baseline to 3 weeks for both measures. The SV group demonstrated increased DFROM from baseline for both time points and a large effect size with 95% CI that did not cross zero from post tx-1 to post tx-2.

CONCLUSIONS

Static stretching with WBV increases DFROM in participants with CAI more effectively than static stretching alone.

Effects of a titin mutation on force enhancement and force depression in mouse soleus muscles

The active isometric force produced by muscles varies with muscle length in accordance with the force-length relationship. Compared with isometric contractions at the same final length, force increases after active lengthening (force enhancement) and decreases after active shortening (force depression). In addition to cross-bridges, titin has been suggested to contribute to force enhancement and depression. Although titin is too compliant in passive muscles to contribute to active tension at short sarcomere lengths on the ascending limb and plateau of the force-length relationship, recent evidence suggests that activation increases titin stiffness. To test the hypothesis that titin plays a role in force enhancement and depression, we investigated isovelocity stretching and shortening in active and passive wild-type and mdm (muscular dystrophy with myositis) soleus muscles. Skeletal muscles from mdm mice have a small deletion in the N2A region of titin and show no increase in titin stiffness during active stretch. We found that: (1) force enhancement and depression were reduced in mdm soleus compared with wild-type muscles relative to passive force after stretch or shortening to the same final length; (2) force enhancement and force depression increased with amplitude of stretch across all activation levels in wild-type muscles; and (3) maximum shortening velocity of wild-type and mdm muscles estimated from isovelocity experiments was similar, although active stress was reduced in mdm compared with wild-type muscles. The results of this study suggest a role for titin in force enhancement and depression, which contribute importantly to muscle force during natural movements.

Functionality of Mozzarella cheese analogues prepared using varying protein sources as influenced by refrigerated storage

The functional properties (shredability, meltability, fat leakage, stretchability) of Mozzarella Cheese Analogue (MCA) prepared using acid casein (ACMCA), rennet casein (RCMCA) and their admixture (ARCMCA) were monitored with those of Natural Mozzarella Cheese (NMC) during refrigerated storage. The shredability of analogues was superior over such attribute of NMC. The MCAs had good shredability up to 28 days, while that of NMC started deteriorating from 21 days onwards. The meltability of both NMC and MCAs improved with advancement of storage; the extent of increase in meltability during span of 35 days period was 2.65, 2.85, 2.78 and 2.63 for NMC, ACMCA, RCMCA and ARCMCA respectively. The stretch value of the MCAs exhibited an increase up to 21 days of refrigerated storage followed by decline up to 35 days, whereas NMC exhibited a linear increase in stretch value with advancement of storage till 35 days. There was a steady decline in the fat leakage in case of any of the MCAs with advancement in storage period; the difference in the values of fat leakage up to 35 days was to the tune of 1.50 cm2, 1.39 cm2 and 1.43 cm2 for ACMCA, RCMCA and ARCMCA respectively. Conversely, NMC exhibited linear increase in fat leakage with progressive storage up to 35 days. It is concluded that MCAs had better functional stability as compared to NMC during refrigerated storage. Amongst MCAs, ARCMCA performed better in terms of baking qualities than those prepared using AC or RC alone. MCAs had better storage stability as compared to NMC.

The effect of adding TENS to stretch on improvement of ankle range of motion in inactive patients in intensive care units: a pilot trial

Background

Patients hospitalized in intensive care units (ICUs) are susceptible to joint contracture and diminished range of motion. This is due to immobility as well as other underlying factors such as brain damage. Joint contracture causes functional disorders thereby diminishing the quality of life of patients following the intensive care period. Recent studies have introduced transcutaneous electrical nerve stimulation (TENS) as a new method for preventing and treating joint contracture. This study was performed to determine the effect of adding TENS to stretch on the range of ankle motion in patients hospitalized in ICUs.

Methods

Thirty-six patients admitted to the ICU ward of the hospital who were not able to move their legs voluntarily were assigned randomly into experimental (n = 18) and control (n = 18) groups. The intervention group received TENS along with manual stretch in the ankle three times a week for 2 weeks. The control group only received stretch in the ankle for the same time. The extent of dorsiflexion and plantar flexion of the ankle was measured using a standard goniometer. Both groups were evaluated before and one and 2 weeks after the intervention. The obtained data were analyzed by SPSS 21 through analysis of covariance and repeated measures ANOVA tests.

Results

In both groups, the increase in the ankle range of motion parameters was significant over time (means ranged over 44–48 for plantar flexion and means ranged over 5–11 for dorsiflexion, P < 0.001 for all of time points). The increase in ankle plantar and dorsiflexion in experimental group was significantly more than control group (mean between-group differences ranged over 1.35–3.57 within 95% CI of 1.04 to 4.01, P < 0.001).

Conclusion

Adding TENS to stretch may provide more improvement in ankle dorsiflexion and plantar flexion.

Trial registration

Trial registration: This study was registered in the Iranian Clinical Trial Center with the code IRCT2017010814333N64, registered 20 January 2017.

Familial Left Ventricular Non-Compaction Is Associated With a Rare p.V407I Variant in Bone Morphogenetic Protein 10

BACKGROUND

Left ventricular non-compaction (LVNC) is a heritable cardiomyopathy characterized by hypertrabeculation, inter-trabecular recesses and thin compact myocardium, but the genetic basis and mechanisms remain unclear. This study identified novel LVNC-associated mutations inNOTCH-dependent genes and investigated their mutational effects.Methods and Results:High-resolution melting screening was performed in 230 individuals with LVNC, followed by whole exome and Sanger sequencing of available family members. Dimerization of bone morphogenetic protein 10 (BMP10) and its binding to BMP receptors (BMPRs) were evaluated. Cellular differentiation, proliferation and tolerance to mechanical stretch were assessed in H9C2 cardiomyoblasts, expressing wild-type (WT) or mutant BMP10 delivered by adenoviral vectors. Rare variants, p.W143*-NRG1and p.V407I-BMP10, were identified in 2 unrelated probands and their affected family members. Although dimerization of mutant V407I-BMP10 was preserved like WT-BMP10, V407I-BMP10 pulled BMPR1a and BMPR2 receptors more weakly compared with WT-BMP10. On comparative gene expression and siRNA analysis, expressed BMPR1a and BMPR2 receptors were responsive to BMP10 treatment in H9C2 cardiomyoblasts. Expression of V407I-BMP10 resulted in a significantly lower rate of proliferation in H9C2 cells compared with WT-BMP10. Cyclic stretch resulted in destruction and death of V407I-BMP10 cells.

CONCLUSIONS

The W143*-NRG1and V470I-BMP10variants are associated with LVNC. Impaired BMPR-binding ability, perturbed proliferation and differentiation processes and intolerance to stretch in V407I-BMP10 mutant cardiomyoblasts may underlie myocardial non-compaction.

Mucosa-Dependent, Stretch-Sensitive Spontaneous Activity in Seminal Vesicle

Seminal vesicles (SVs), a pair of male accessory glands, contract upon sympathetic nerve excitation during ejaculation while developing spontaneous phasic constrictions in the inter-ejaculatory storage phase. Recently, the fundamental role of the mucosa in generating spontaneous activity in SV of the guinea pig has been revealed. Stretching the mucosa-intact but not mucosa-denuded SV smooth muscle evokes spontaneous phasic contractions arising from action potential firing triggered by electrical slow waves and associated Ca²⁺ flashes. These spontaneous events primarily depend on sarco-endoplasmic reticulum (SR/ER) Ca²⁺ handling linked with the opening of Ca²⁺-activated chloride channels (CaCCs) resulting in the generation of slow waves. Slow waves in mucosa-intact SV smooth muscle are abolished upon blockade of gap junctions, suggesting that seminal smooth muscle cells are driven by cells distributed in the mucosa. In the SV mucosal preparations dissected free from the smooth muscle layer, a population of cells located just beneath the epithelium develop spontaneous Ca²⁺ transients relying on SR/ER Ca²⁺ handling. In the lamina propria of the SV mucosa, vimentin-immunoreactive interstitial cells including platelet-derived growth factor receptor α (PDGFRα)-immunoreactive cells are distributed, while known pacemaker cells in other smooth muscle tissues, e.g. c-Kit-positive interstitial cells or α-smooth muscle actin-positive atypical smooth muscle cells, are absent. The spontaneously-active subepithelial cells appear to drive spontaneous activity in SV smooth muscle either by sending depolarizing signals or by releasing humoral substances. Interstitial cells in the lamina propria may act as intermediaries of signal transmission from the subepithelial cells to the smooth muscle cells.

Accelerated construction of an in vitro model of human periodontal ligament tissue: vacuum plasma combined with fibronectin coating and a polydimethylsiloxane matrix

Tying shape memory wires to crowded teeth causes the wires to deform according to the dental arch. This deformation results in a resilient force that is delivered to the tooth. The appropriate amount of force can activate the osteogenetic and osteoclastic ability of the periodontal ligament (PDL) and the tooth can be moved. This is the biological basis of orthodontic treatment. To achieve further insight into the mechanisms underlying orthodontic treatment, we examined whether accelerated construction of an in vitro human PDL fibroblast (HPdLF) stretching model can be achieved by combining fibronectin coating and vacuum plasma treatment with polydimethylsiloxane (PDMS) cell-culture chambers. Each chamber was randomly assigned to a no-surface modification (NN), fibronectin coating (FN), vacuum plasma treatment (PN), or vacuum plasma treatment followed by a fibronectin coating (PF) treatment protocol. The physical and chemical features and ability to promote cellular proliferation of the PDMS chamber surfaces were evaluated. Cellular adhesion of four materials were evaluated and two best-proliferated groups were considered as better model-constructing surfaces and used in subsequent experiments and used in subsequent experiments. HPdLFs were cultured on these two kinds of chambers without stretching for 3 days, then with stretching for 7 days. Time-course gene expression cellular morphology were evaluated. Chambers in the PN group had high wettability and surface component changes. The FN and PF chambers had high cellular proliferation ability. They were selected into subsequent experiments. After 3 days of culturing HPdLFs on the PF and PN chambers, the cells in the PF chambers had significantly higher levels of runt-related transcription factor 2 (Runx-2) and osteocalcin (OCN) gene expression compared with the cells in the PN chambers. After cyclic stretch application to the cells in the PN and PF chambers, expression of the type-3 collagen (COL-3) gene in PF group continued to increase for 7 days and was significantly higher than that in the PN group from day 5 onwards. The HPdLFs in the PF group showed parallel alignment from days 3 to 7 after imposition of cyclic stretch, while those in the PN group aligned in parallel from day 5 on. Our results suggested that applying a fibronectin coating to a PDMS chamber after plasma treatment can accelerate establishment of an in vitro PDL stretching model.

p38-MAP Kinase Negatively Regulates the Slow Force Response to Stretch in Rat Myocardium through the Up-Regulation of Dual Specificity Phosphatase 6 (DUSP6)

BACKGROUND/AIMS

Myocardial stretch increases cardiac force in two consecutive phases: The first one due to Frank-Starling mechanism, followed by the gradually developed slow force response (SFR). The latter is the mechanical counterpart of an autocrine/paracrine mechanism involving the release of angiotensin II (Ang II) and endothelin (ET) leading to Na⁺/H⁺ exchanger 1 (NHE-1) phosphorylation and activation. Since previous evidence indicates that p38-MAP kinase (p38-MAPK) negatively regulates the Ang II-induced NHE1 activation in vascular smooth muscle and the positive inotropic effect of ET in the heart, we hypothesized that this kinase might modulate the magnitude of the SFR to stretch.

METHODS

Experiments were performed in isolated rat papillary muscles subjected to sudden stretch from 92 to 98% of its maximal length, in the absence or presence of the p38-MAPK inhibitor SB202190, or its inactive analogous SB202474. Western blot technique was used to determine phosphorylation level of p38-MAPK, ERK1/2, p90RSK and NHE-1 (previously immunoprecipitated with NHE-1 polyclonal antibody). Dual specificity phosphatase 6 (DUSP6) expression was evaluated by RT-PCR and western blot. Additionally, the Na⁺-dependent intracellular pH recovery from an ammonium prepulse-induced acid load was used to asses NHE-1 activity.

RESULTS

The SFR was larger under p38-MAPK inhibition (SB202190), effect that was not observed in the presence of an inactive analogous (SB202474). Myocardial stretch activated p38-MAPK, while pre-treatment with SB202190 precluded this effect. Inhibition of p38-MAPK increased stretched-induced NHE-1 phosphorylation and activity, key event in the SFR development. Consistently, p38-MAPK inhibition promoted a greater increase in ERK1/2-p90RSK phosphorylation/activation after myocardial stretch, effect that may certainly be responsible for the observed increase in NHE-1 phosphorylation under this condition. Myocardial stretch induced up-regulation of the DUSP6, which specifically dephosphorylates ERK1/2, effect that was blunted by SB202190.

CONCLUSION

Taken together, our data support the notion that p38-MAPK activation after myocardial stretch restricts the SFR by limiting ERK1/2-p90RSK phosphorylation, and consequently NHE-1 phosphorylation/activity, through a mechanism that involves DUSP6 up-regulation.

Emerging Role of Plasma Membranes in Vascular Endothelial Mechanosensing

Vascular endothelial cells (ECs) maintain circulatory system homeostasis by changing their functions in response to changes in hemodynamic forces, including shear stress and stretching. However, it is unclear how ECs sense changes in shear stress and stretching and transduce these changes into intracellular biochemical signals. The plasma membranes of ECs have recently been shown to respond to shear stress and stretching differently by rapidly changing their lipid order, fluidity, and cholesterol content. Such changes in the membranes' physical properties trigger the activation of membrane receptors and cell responses specific to each type of force. Artificial lipid-bilayer membranes show similar changes in lipid order in response to shear stress and stretching, indicating that they are physical phenomena rather than biological reactions. These findings suggest that the plasma membranes of ECs act as mechanosensors; in response to mechanical forces, they first alter their physical properties, modifying the conformation and function of membrane proteins, which then activates downstream signaling pathways. This new appreciation of plasma membranes as mechanosensors could help to explain the distinctive features of mechanotransduction in ECs involving shear stress and stretching, which activate a variety of membrane proteins and multiple signal transduction pathways almost simultaneously.

Cyclic stretch enhances reorientation and differentiation of 3-D culture model of human airway smooth muscle

Activation of airway smooth muscle (ASM) cells plays a central role in the pathophysiology of asthma. Because ASM is an important therapeutic target in asthma, it is beneficial to develop bioengineered ASM models available for assessing physiological and biophysical properties of ASM cells. In the physiological condition in vivo, ASM cells are surrounded by extracellular matrix (ECM) and exposed to mechanical stresses such as cyclic stretch. We utilized a 3-D culture model of human ASM cells embedded in type-I collagen gel. We further examined the effects of cyclic mechanical stretch, which mimics tidal breathing, on cell orientation and expression of contractile proteins of ASM cells within the 3-D gel. ASM cells in type-I collagen exhibited a tissue-like structure with actin stress fiber formation and intracellular Ca²⁺ mobilization in response to methacholine. Uniaxial cyclic stretching enhanced alignment of nuclei and actin stress fibers of ASM cells. Moreover, expression of mRNAs for contractile proteins such as α-smooth muscle actin, calponin, myosin heavy chain 11, and transgelin of stretched ASM cells was significantly higher than that under the static condition. Our findings suggest that mechanical force and interaction with ECM affects development of the ASM tissue-like construct and differentiation to the contractile phenotype in a 3-D culture model.

Post-injury stretch promotes recovery in a rat model of muscle damage induced by lengthening contractions

We investigated the cellular mechanisms and therapeutic effect of post-injury stretch on the recovery process from muscle injury induced by lengthening contractions (LC). One day after LC, a single 15-min bout of muscle stretch was applied at an intensity of 3 mNm. The maximal isometric torque was measured before and at 2-21 days after LC. The myofiber size was analyzed at 21 days after LC. Developmental myosin heavy chain-immunoreactive (dMHC-ir) cells, a marker of regenerating myofibers, were observed in the early recovery stage (2-5 days after LC). We observed that LC-induced injury markedly decreased isometric torque and myofiber size, which recovered faster in rats that underwent stretch than in rats that did not. Regenerating myofiber with dMHC-ir cells was observed earlier in rats that underwent stretch. These results indicate that post-injury stretch may facilitate the regeneration and early formation of new myofibers, thereby promoting structural and functional recovery from LC-induced muscle injury.

The inhibitory effect of rosmarinic acid on overexpression of NCX1 and stretch- induced arrhythmias after acute myocardial infarction in rats

The incidence of arrhythmias is the main cause of high mortality after myocardial infarction (AMI). The aim of the present study was to determine whether the rosmarinic acid (RA) could reduce the stretch-induced arrhythmias (SIAs) related to overexpression of NCX1 after AMI. Adult male Sprague-Dawley rats were randomly allocated into six groups: Sham, MI (100 mg/kg of isoproterenol (Iso), subcutaneously, on two consecutive days), RA (30 mg/kg, orally, 14 days), and RA (10, 15 and 30 mg/kg, 14 days) + I. MI induction was performed on the 13th and 14th days of the study period. Forty-eight hours after the first injection of Iso, the parameters of hypertrophy, plasma levels of malondialdehyde (MDA) and lipid profile were evaluated. Using Langendorff apparatus, the isolated hearts were transiently stretched for 5 s with three different end-diastolic volumes (ΔV1to3 = 0.05, 0.1 and 0.2 mL). Cardiac function parameters were measured for 30 s, and ventricular arrhythmias were recorded for 3 min after each stretch. Finally, the levels of cardiac troponin-I and NCX1 mRNA expression were examined. The rats of MI group showed a significant increase in hypertrophy index, MDA, triglyceride and cholesterol (P < 0.001). Additionally, a marked impairment in cardiac parameters, an increase in the rates of SIAs and NCX1 expression, and a decrease in troponin-I (P < 0.001) were observed. RA at three doses especially 15 mg/kg strongly improved almost all the mentioned factors (P < 0.001). Our results confirm that RA pretreatment could prevent hypertrophia, arrhythmia and cardiac dysfunction following AMI which is associated with inhibition of lipid peroxidation and overexpression of NCX1.

Role of TREK-1 channel

Quiescence of myometrium contractile activity allows uterine expansion to accommodate the growing fetus and prevents preterm labor particularly during excessive uterine stretch in multiple pregnancy. However, the mechanisms regulating uterine response to stretch are unclear. We tested the hypothesis that prolonged uterine stretch is associated with decreased myometrium contractile activity via activation of TWIK-related K⁺ channel (TREK-1). Pregnant women at different gestational age (preterm and term) and uterine stretch (singleton and twin pregnancy) were studied, and uterine strips were isolated for measurement of contractile activity and TREK-1 channel expression/activity. Both oxytocin- and KCl-induced contraction were reduced in term vs preterm pregnancy and in twin vs singleton pregnancy. Oxytocin contraction was reduced in uterine segments exposed to 8 g stretch compared to control tissues under 2 g basal tension. TREK-1 mRNA expression and protein levels were augmented in Singleton-Term vs Singleton-Preterm, and in uterine strips exposed to 8 g stretch. The TREK-1 activator arachidonic acid reduced oxytocin contraction in preterm and term, singleton and twin pregnant uterus. The TREK-1 blocker l-methionine enhanced oxytocin contraction in Singleton-Term and twin pregnant uterus, and reversed the decreases in contraction in uterine strips exposed to prolonged stretch. Carboprost-induced uterine contraction was also reduced by arachidonic acid and enhanced by l-methionine. Thus, myometrium contraction decreases with gestational age and uterine expansion in twin pregnancy. The results suggest that prolonged stretch enhances the expression/activity of TREK-1 channel, leading to decreased myometrium contractile activity and maintained healthy term pregnancy particularly in multiple pregnancy.

TRPC3 participates in angiotensin II type 1 receptor-dependent stress-induced slow increase in intracellular Ca2+ concentration in mouse cardiomyocytes

When a cardiac muscle is held in a stretched position, its [Ca2+] transient increases slowly over several minutes in a process known as stress-induced slow increase in intracellular Ca2+ concentration ([Ca2+]i) (SSC). Transient receptor potential canonical (TRPC) 3 forms a non-selective cation channel regulated by the angiotensin II type 1 receptor (AT1R). In this study, we investigated the role of TRPC3 in the SSC. Isolated mouse ventricular myocytes were electrically stimulated and subjected to sustained stretch. An AT1R blocker, a phospholipase C inhibitor, and a TRPC3 inhibitor suppressed the SSC. These inhibitors also abolished the observed SSC-like slow increase in [Ca2+]i induced by angiotensin II, instead of stretch. Furthermore, the SSC was not observed in TRPC3 knockout mice. Simulation and immunohistochemical studies suggest that sarcolemmal TRPC3 is responsible for the SSC. These results indicate that sarcolemmal TRPC3, regulated by AT1R, causes the SSC.

Mechanotransduction in Blood and Lymphatic Vascular Development and Disease

The blood and lymphatic vasculatures are hierarchical networks of vessels, which constantly transport fluids and, therefore, are exposed to a variety of mechanical forces. Considering the role of mechanotransduction is key for fully understanding how these vascular systems develop, function, and how vascular pathologies evolve. During embryonic development, for example, initiation of blood flow is essential for early vascular remodeling, and increased interstitial fluid pressure as well as initiation of lymph flow is needed for proper development and maturation of the lymphatic vasculature. In this review, we introduce specific mechanical forces that affect both the blood and lymphatic vasculatures, including longitudinal and circumferential stretch, as well as shear stress. In addition, we provide an overview of the role of mechanotransduction during atherosclerosis and secondary lymphedema, which both trigger tissue fibrosis.

Functional properties of Mozzarella cheese for its end use application

Cheese is an extremely versatile food product that has a wide range of flavor, textures and end uses. The vast majority of cheese is eaten not by itself, but as part of another food. As an ingredient in foods, cheese is required to exhibit functional characteristics in the raw as well as cooked forms. Melting, stretching, free-oil formation, elasticity and browning are the functional properties considered to be significant for Mozzarella cheese. When a cheese is destined for its end use, some of its unique characteristics play a significant role in the products acceptability. For instance pH of cheese determines the cheese structure which in turn decides the cheese shredability and meltability properties. The residual galactose content in cheese mass determines the propensity of cheese to brown during baking. Development of 'tailor-made cheese' involves focusing on manipulation of such unique traits of cheese in order to obtain the desired characteristics for its end use application suiting the varied consumer's whims and wishes. This comprehensive review paper will provide an insight to the cheese maker regarding the factors determining the functional properties of cheese and also for the pizza manufacturers to decide which age of cheese to be used which will perform well in baking applications.