Cellular Contraction Research Articles

Balance of Active, Passive, and Anatomical Cardiac Properties in Doxorubicin-Induced Heart Failure

Late-onset heart failure (HF) is a known side effect of doxorubicin chemotherapy. Typically, patients are diagnosed when already at an irreversible stage of HF, which allows few or no treatment options. Identifying the causes of compromised cardiac function in this patient group may improve early patient diagnosis and support treatment selection. To link doxorubicin-induced changes in cardiac cellular and tissue mechanical properties to overall cardiac function, we apply a multiscale biophysical biomechanics model of the heart to measure the plausibility of changes in model parameters representing the passive, active, or anatomical properties of the left ventricle for reproducing measured patient phenotypes. We create representative models of healthy controls (N = 10) and patients with HF induced by (N = 22) or unrelated to (N = 25) doxorubicin therapy. The model predicts that HF in the absence of doxorubicin is characterized by a 2- to 3-fold stiffness increase, decreased tension (0–20%), and ventricular dilation (of order 10–30%). HF due to doxorubicin was similar but showed stronger bias toward reduced active contraction (10–30%) and less dilation (0–20%). We find that changes in active, passive, and anatomical properties all play a role in doxorubicin-induced cardiotoxicity phenotypes. Differences in parameter changes between patient groups are consistent with doxorubicin cardiotoxicity having a greater dependence on reduced cellular contraction and less anatomical remodeling than HF not caused by doxorubicin.

Collective intercellular communication through ultra-fast hydrodynamic trigger waves.

The biophysical relationships between sensors and actuators1-5 have been fundamental to the development of complex life forms. Swimming organisms generate abundant flows that persist in aquatic environments6-13, and responding promptly to external stimuli is key to survival14-19. Here we present the discovery of 'hydrodynamic trigger waves' in cellular communities of the protist Spirostomum ambiguum that propagate-in a manner similar to a chain reaction20-22-hundreds of times faster than their swimming speed. By coiling its cytoskeleton, Spirostomum can contract its long body by 60% within milliseconds23, experiencing accelerations that can reach forces of 14g. We show that a single cellular contraction (the transmitter) generates long-ranged vortex flows at intermediate Reynolds numbers that can, in turn, trigger neighbouring cells (the receivers). To measure the sensitivity to hydrodynamic signals in these receiver cells, we present a high-throughput suction-flow device for probing mechanosensitive ion channels24 by back-calculating the microscopic forces on the cell membrane. We analyse and quantitatively model the ultra-fast hydrodynamic trigger waves in a universal framework of antenna and percolation theory25,26, and reveal a phase transition that requires a critical colony density to sustain collective communication. Our results suggest that this signalling could help to organize cohabiting communities over large distances and influence long-term behaviour through gene expression (comparable to quorum sensing16). In more immediate terms, because contractions release toxins27, synchronized discharges could facilitate the repulsion of large predators or immobilize large prey. We postulate that numerous aquatic organisms other than protists could coordinate their behaviour using variations of hydrodynamic trigger waves.

Histochemical Study of the Emergence of Apoptosis and Altered SYCP3 Protein Distribution During the First Spermatogenic Wave in Wistar Rats.

Apoptosis is a type of cell death responsible for maintaining tissue homeostasis that can occur in male gonads. The morphological and biochemical characteristics of apoptosis include cellular contraction, caspase activation, and DNA fragmentation. Dynamic processes of cell renewal and differentiation occur inside the seminiferous tubules, which are regulated by mitosis and meiosis, respectively. During meiosis, recombination is caused by assembly of the synaptonemal complex, which involves the participation of constitutive proteins, such as synaptonemal complex protein-3 (SYCP3). The present study evaluated germinal cell death in immature male rats and the distribution of the SYCP3 protein. Our results indicate that as germinal cells progress to the second meiotic stage, significant numbers of them are eliminated by apoptosis. We determined that the SYCP3 protein is not always incorporated into the structure of the synaptonemal complex but rather forms a nuclear cumulus near the inner nuclear membrane, causing many of these cells to undergo apoptosis. We propose that both the excess of the SYCP3 protein and its accumulation during the first meiotic division could contribute to the cell death of primary spermatocytes during the first spermatogenic wave in prepubertal Wistar rats. Anat Rec, 302:2082-2092, 2019. © 2019 American Association for Anatomy.

Active contractile properties of fascia.

The ubiquitous network of fascial tissues in the human body is usually regarded as a passive contributor to musculoskeletal dynamics. This review aims to highlight the current understanding of fascial stiffness regulation. Notably the ability for active cellular contraction which may augment the stiffness of fascial tissues and thereby contribute to musculoskeletal dynamics. A related narrative literature search via PubMed and Google Scholar reveals a multitude of studies indicating that the intrafascial presence of myofibroblasts may enable these tissues to alter their stiffness. This contractile tissue behavior occurs not only in several pathological fibrotic contractures but has also been documented in normal fasciae. When viewed at time frames of seconds and minutes the force of such tissue contractions is not sufficient for exerting a significant effect on mechanical joint stability. However, when viewed in a time-window of several minutes and longer, such cellular contractions can impact motoneuronal coordination. In addition, over a time frame of days to months, this cellular activity can induce long-term and severe tissue contractures. These findings tend to question the common clear distinction between active tissues and passive tissues in musculoskeletal dynamics. Clin. Anat. 32:891-895, 2019. © 2019 Wiley Periodicals, Inc.

Fascia Is Able to Actively Contract and May Thereby Influence Musculoskeletal Dynamics: A Histochemical and Mechanographic Investigation.

Fascial tissues form a ubiquitous network throughout the whole body, which is usually regarded as a passive contributor to biomechanical behavior. We aimed to answer the question, whether fascia may possess the capacity for cellular contraction which, in turn, could play an active role in musculoskeletal mechanics. Human and rat fascial specimens from different body sites were investigated for the presence of myofibroblasts using immunohistochemical staining for α-smooth muscle actin (n = 31 donors, n = 20 animals). In addition, mechanographic force registrations were performed on isolated rat fascial tissues (n = 8 to n = 18), which had been exposed to pharmacological stimulants. The density of myofibroblasts was increased in the human lumbar fascia in comparison to fasciae from the two other regions examined in this study: fascia lata and plantar fascia [H(2) = 14.0, p < 0.01]. Mechanographic force measurements revealed contractions in response to stimulation by fetal bovine serum, the thromboxane A2 analog U46619, TGF-β1, and mepyramine, while challenge by botulinum toxin type C3–used as a Rho kinase inhibitor– provoked relaxation (p < 0.05). In contrast, fascial tissues were insensitive to angiotensin II and caffeine (p < 0.05). A positive correlation between myofibroblast density and contractile response was found (rs = 0.83, p < 0.001). The hypothetical application of the registered forces to human lumbar tissues predicts a potential impact below the threshold for mechanical spinal stability but strong enough to possibly alter motoneuronal coordination in the lumbar region. It is concluded that tension of myofascial tissue is actively regulated by myofibroblasts with the potential to impact active musculoskeletal dynamics.

PPARγ/ETV2 Regulate Endothelial‐to‐Mesenchymal Transition in the Hypoxia/Sugen Rat Model of Pulmonary Hypertension

RationalePulmonary hypertension (PH) is a chronic cardiopulmonary disorder that causes significant morbidity and mortality. Endothelial‐to‐mesenchymal transition(EndoMT) plays an important role in initiation and progression of PH, suggesting that EndoMT may be a novel and effective therapeutic target in PH. However, the molecular mechanisms regulating EndoMT and how they promote PH remains largely unknown. Our lab and others have established the importance of peroxisome proliferator‐activated receptor gamma (PPARγ) in PH. Our studies indicate that PPARγ regulates the transcription factor, ETS variant 2 (ETV2), which is in dispensable for cardiovascular system development and serves as a master regulator for endothelial cell generation and function. Thus, we hypothesize that the PPARγ/ETV2 axis regulates EndoMT in PH.MethodsMale Sprague Dawley rats received a single injection of Sugen 5416 (SU, 20 mg/kg) followed by exposure to 3 weeks of hypoxia (10% O2) or normoxia(NOR, 21% O2) followed an additional 2 weeks of NOR. Right ventricular systolic pressure (RVSP)and right ventricular hypertrophy (RVH) were measured to confirm PH. To further examine the functional significance of ETV2 in PH, we measured RVSP and RVH in ETV2+/− mice. Levels of EndoMT markers in lungs of HYP/SU rats or ETV2+/− mice were compared to NOR/SU rats or wild‐typemice using qRT‐PCR and Western blot analysis. An ETV2 promoter activity assay was used to determine if PPARγ transcriptionally regulates ETV2 expression. Further, to determine if PPARg or ETV2 signaling regulates the levels of EndoMT markers, PPARγ or ETV2 loss or gain of function strategies were employed. To model in vivo EndoMT in PH, induced‐EndoMT (i‐EndoMT) cells were induced by treating human pulmonaryartery endothelial cells (HPAECs) with IL1β, TNFα, and TGFβ, and then examined functional alterations using collagen cell contraction and wound healing assays.ResultsAs expected, HYP/SU treatment and ETV2+/− mice resulted in PH. HYP/SU treatment and ETV2+/− mice also increased lung levels of mesenchymal markers, including desmin, TGFβ1, SLUG, and αSMA. Luciferase‐promoter assays showed that PPARγ transcriptionally activates the ETV2 promoter. HPAECs lost cobblestone morphology to a more elongeted, spindle‐shaped myofibroblastic cell morphology, indication the activation of EndoMT. I‐EndoMT cells significantly enhanced basal cellular contraction and migratory response compared with HPAECs. Levels of PPARγ and ETV2 were decreased in i‐EndoMT cells whereas markers of EndoMT were increased. Importantly, knockdown of PPARγ or ETV2 in HPAEC increased levels of EndoMT markers whereas overexpression of PPARγ/ETV2 axis led to reduced expression of EndoMT markers.ConclusionsCollectively, these studies establish that the PPARγ/ETV2 axis contributes to regulation of EndoMT and maythere by participate in the pathogenesis of PH. These findings suggest novel molecular pathways involved in EndoMT and PH pathogenesis that merit further exploration.Support or Funding InformationNIH HL102167 (RLS and CMH), NIH HL119291 (CP), and NIH HL133053 (BYK).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Vascular‐targeted low dose photodynamic therapy stabilizes tumor vessels by modulating pericyte contractility

Vascular-targeted low-dose photodynamic therapy (L-PDT) was shown to improve chemotherapy distribution in malignant pleural tumors such as malignant pleural mesothelioma (MPM). However, the mechanisms triggered by L-PDT on the tumor vasculature are still debated. In pericyte and endothelial cell co-cultures, we show that pericytes exhibit enhanced sensitivity towards L-PDT compared to endothelial cells, displaying actin stress fibers and cellular contraction via Rho/ROCK kinase signaling myosin light chain and focal adhesion kinase phosphorylation (MLC-P, FAK-P). We then confirm, in two separate MPM models, in mice the phosphorylation of the MLC in pericytes specifically following L-PDT. Furthermore, while L-PDT does not affect tumor vascular density or diameter, we show that it enhances tumor vascular pericyte coverage, leads to a drop in tumor interstitial fluid pressure and enhances the transport of FITC-dextran throughout tumors. In conclusion, L-PDT has the potential to stabilize the tumor vascular bed which improves vascular transport. The mechanism described in the present study may help translate and optimize this approach in patients. Lasers Surg. Med. 51:550-561, 2019. © 2019 Wiley Periodicals, Inc.

Protease-activated receptor 2 activates CRAC-mediated Ca2+ influx to cause prostate smooth muscle contraction.

Protease‐activated receptor 2 (PAR2) is a G‐protein‐coupled receptor that contributes to prostate fibrosis and lower urinary tract symptoms (LUTS). In addition to fibrosis, aberrant smooth muscle tone in the prostate has been hypothesized to play a role. We therefore examined PAR2 expression in primary human prostate smooth muscle cells (PSMC) and studied the downstream signaling effects of PAR2 activation. Signaling pathways involved in the process were assessed using the PAR2 activating peptide SLIGKV‐NH2. We show that PAR2 is expressed in PSMC and that PAR2 activation mediates a biphasic elevation in intracellular Ca2+ and phosphorylation of myosin light chain 20 (MLC20), causing cellular contraction as assessed in a gel contraction assay. Intracellular Ca2+ flux was inhibited by a phosphoinositide hydrolysis inhibitor, U73122, showing a requirement for phospholipase C β (PLCβ) activation. PSMC expressed mRNA for L‐type voltage dependent Ca2+ channels (VDCC) as well as Ca2+ release activated channels (CRAC), a hitherto unreported finding. Secondary intracellular Ca2+ oscillations were abrogated only by BTP2, the CRAC channel inhibitor, but not by nifedipine, an inhibitor of VDCC. These data suggest that, PAR2 activation and subsequent Ca2+ entry through CRAC channels are important mechanisms in prostate smooth muscle contraction.

Correlation analysis between cellular contraction and MAPK activation

Correlation analysis between cellular contraction and MAPK activation

Actomyosin contractility modulates Wnt signaling through adherens junction stability.

Actomyosin contractility can influence the canonical Wnt signaling pathway in processes like mesoderm differentiation and tissue stiffness during tumorigenesis. We identified that increased nonmuscle myosin II activation and cellular contraction inhibited Wnt target gene transcription in developing Drosophila imaginal disks. Genetic interactions studies were used to show that this effect was due to myosin-induced accumulation of cortical F-actin resulting in clustering and accumulation of E-cadherin to the adherens junctions. This results in E-cadherin titrating any available β-catenin, the Wnt pathway transcriptional coactivator, to the adherens junctions in order to maintain cell–cell adhesion under contraction. We show that decreased levels of cytoplasmic β-catenin result in insufficient nuclear translocation for full Wnt target gene transcription. Previous studies have identified some of these interactions, but we present a thorough analysis using the wing disk epithelium to show the consequences of modulating myosin phosphatase. Our work elucidates a mechanism in which the dynamic promotion of actomyosin contractility refines patterning of Wnt transcription during development and maintenance of epithelial tissue in organisms.

Abstract 16799: Decellularized Cardiac Extracellular Matrix Increases Cardiomyocyte Elongation and Contractility

Background: Cardiomyocyte elongation has been linked to enhanced myofilament organization, which contributes to overall cell contractility and functionality. While tissue scaffolds have been engineered to induce cell elongation using topographical cues, decellularized cardiac extracellular matrix (dECM) bioscaffolds are known to be bioactive and retain native cues for cell organization and regeneration, including the alignment of stem cells. However, the effects of the native extracellular matrix on cardiomyocyte elongation and contractility are still unknown. Hypothesis: We hypothesized that dECM increases elongation and contractility of neonatal rat ventricular cardiomyocytes (NRVCMs) versus engineered collagen constructs, resulting in physiologically-relevant, scalable tissues for cardiovascular tissue engineering. Methods and Results: Adult rat hearts were harvested and perfusion-decellularized through the coronary vasculature under constant pressure. Hearts were sectioned on a vibratome transversally to create 300 μm-thick rings of the left ventricle. Collagen (type 1) rings of the same size as the dECM rings were made by using rat tail collagen (2.0 mg/ml). Ten million NRVCMs were isolated, purified, and injected into the left ventricle of dECM or collagen rings (n=12 each). Cell survival, distribution, elongation, and alignment were evaluated after 14 days by using immunofluorescence and confocal microscopy. The dECM significantly increased nuclear elongation (major to minor axis ratio of 1.585 for cells in dECM vs. 1.37 in collagen, n=6 each, p&lt;0.01). Microscopic contractions were observed in dECM as early as day 3 (n=3). The number of spontaneous contractions of cells in dECM (n=5) was significantly greater than that in collagen (n=3) (p&lt;0.01), as observed by atomic force microscopy. Conclusion: In conclusion, dECM increased cellular elongation and contraction frequency of neonatal rat ventricular cardiomyocytes, suggesting the presence of tissue-specific cues in the extracellular environment of cardiomyocytes is beneficial for tissue function. Studies utilizing human stem-cell derived cardiomyocytes are underway to verify the organizational, functional, and physiologic properties of recellularized dECM.

Ultrafast epithelial contractions provide insights into contraction speed limits and tissue integrity

By definition of multicellularity, all animals need to keep their cells attached and intact, despite internal and external forces. Cohesion between epithelial cells provides this key feature. To better understand fundamental limits of this cohesion, we study the epithelium mechanics of an ultrathin (∼25 μm) primitive marine animal Trichoplax adhaerens, composed essentially of two flat epithelial layers. With no known extracellular matrix and no nerves or muscles, T. adhaerens has been claimed to be the "simplest known living animal," yet is still capable of coordinated locomotion and behavior. Here we report the discovery of the fastest epithelial cellular contractions known in any metazoan, to be found in T. adhaerens dorsal epithelium (50% shrinkage of apical cell area within one second, at least an order of magnitude faster than other known examples). Live imaging reveals emergent contractile patterns that are mostly sporadic single-cell events, but also include propagating contraction waves across the tissue. We show that cell contraction speed can be explained by current models of nonmuscle actin-myosin bundles without load, while the tissue architecture and unique mechanical properties are softening the tissue, minimizing the load on a contracting cell. We propose a hypothesis, in which the physiological role of the contraction dynamics is to resist external stresses while avoiding tissue rupture ("active cohesion"), a concept that can be further applied to engineering of active materials.

ER-Mitochondria Microdomains in Cardiac Ischemia-Reperfusion Injury: A Fresh Perspective.

The mitochondrial and endoplasmic reticulum (ER) homeostasis is pivotal to the maintenance of an array of physiological processes. The physical contact and association between ER and mitochondria, known as the ER–mitochondria microdomains or mitochondria-associated ER membrane (MAM), temporally and spatially regulates the mitochondria/ER structure and function. More evidence suggests a role for MAMs in energy production, cellular contraction and mobility, and normal extracellular signal transmission. In pathological states, such as cardiac ischemia–reperfusion (I/R injury), this ER–mitochondria microdomains may act to participate in the cellular redox imbalance, ER stress, mitochondrial injury, energy deletion, and programmed cell death. From a therapeutic perspective, a better understanding of the cellular and molecular mechanisms of the pathogenic ER–mitochondria contact should help to identify potential therapeutic target for cardiac I/R injury and other cardiovascular diseases and also pave the road to new treatment modalities pertinent for the treatment of reperfusion damage in clinical practice. This review will mainly focus on the possible signaling pathways involved in the regulation of the ER–mitochondria contact. In particular, we will summarize the downstream signaling modalities influenced by ER–mitochondria microdomains, for example, mitochondrial fission, mitophagy, calcium balance, oxidative stress, and programmed cell death in details.

Myosin-1c promotes E-cadherin tension and force-dependent recruitment of α-actinin to the epithelial cell junction.

Actomyosin II contractility in epithelial cell plays an essential role in tension-dependent adhesion strengthening. One key unsettling question is how cellular contraction transmits force to the nascent cell-cell adhesion when there is no stable attachment between the nascent adhesion complex and actin filament. Here, we show that myosin-1c is localized to the lateral membrane of polarized epithelial cells and facilitates the coupling between actin and cell-cell adhesion. Knockdown of myosin-1c compromised the integrity of the lateral membrane, reduced the generation of tension at E-cadherin, decreased the strength of cell-cell cohesion in an epithelial cell monolayer and prevented force-dependent recruitment of junctional α-actinin. Application of exogenous force to cell-cell adhesions in a myosin-1c-knockdown cell monolayer fully rescued the localization defect of α-actinin, indicating that junction mechanoregulation remains intact in myosin-1c-depleted cells. Our study identifies a role of myosin-1c in force transmission at the lateral cell-cell interface and underscores a non-junctional contribution to tension-dependent junction regulation.

Vascular differentiation from pluripotent stem cells in 3-D auxetic scaffolds.

Auxetic scaffolds, that is, scaffolds that can display negative Poisson's ratio, have unique physical properties and can expand transversally when axially strained or contract under compression. Auxetic materials have been used for bioprostheses and artery stents due to the enhanced compressive strength and shear stiffness. In vascular tissue engineering, auxetic scaffolds allow the widening of blood vessels when blood flows through (creating compressive stress) to prevent the blockage. However, the influence of auxetic materials on the cellular fate decision in local environment is unclear. In this study, auxetic polyurethane foams were used to support vascular differentiation from pluripotent stem cells. The expression of alkaline phosphatase, Oct-4, and Nanog was lower after 4days of differentiation for the cells grown in auxetic scaffolds. Higher expression of vascular markers CD31 and VE-cadherin was observed for the cells from auxetic scaffolds compared with those from the scaffolds before auxetic conversion. Little influence on the expression of cardiac marker α-actinin was observed. The vascular cells secreted extracellular matrix proteins vitronectin and laminin and expressed membrane-bound matrix metalloproteinase 9. The examination of Yes-associated protein expression indicated more cytoplasmic retention in the cells from auxetic scaffolds compared with those from regular scaffolds, suggesting that the auxetic scaffolds may affect cellular contraction. This study demonstrates a novel 3-D culture based on auxetic scaffolds for vascular differentiation and provides a platform to study the influence of biophysical microenvironments on differentiation of pluripotent stem cells. The outcome of this study has implications for regenerative medicine and drug discovery.

Sodium tanshinone IIA sulfonate promotes endothelial integrity via regulating VE-cadherin dynamics and RhoA/ROCK-mediated cellular contractility and prevents atorvastatin-induced intracerebral hemorrhage in zebrafish

Impaired vascular integrity leads to serious cerebral vascular diseases such as intracerebral hemorrhage (ICH). In addition, high-dose statin therapy is suggested to cause increased ICH risk due to unclear effects of general inhibition of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) on the vascular system. Here we evaluated the protective effects of sodium tanshinone IIA sulfonate (STS), which has high efficacy and safety in clinical studies of ischemic stroke, by using atorvastatin (Ator) induced ICH zebrafish embryos and human umbilical vein endothelial cells (HUVECs). By using double transgenic Tg(fli1a:EGFP)y1 & Tg(gata1a:dsRed)sd2 zebrafish, we demonstrated that STS effectively reduced the occurrence and area of hemorrhage induced by Ator in zebrafish and restored impairment in motor function. We further demonstrated that Ator-induced disruption in VE-cadherin (VEC)-containing cell-cell adherens junctions (AJs) in HUVECs by enhancing Src-induced VEC internalization and RhoA/ROCK-mediated cellular contraction. STS inhibited Ator-induced Src activation and subsequent VEC internalization and actin depolymerization near cell borders, reducing lesions between neighboring cells and increasing barrier functions. STS also inhibited the Ator-induced RhoA/ROCK-mediated cellular contraction by regulating downstream LIMK/cofilin and MYPT1/MLC phosphatase signaling. These results showed that STS significantly promoted the stability of cell junctions and vascular integrity. Moreover, we observed that regulations of both Src and RhoA/ROCK are required for the maintenance of vascular integrity, and Src inhibitor (PP2) or ROCK inhibitors (fasudil and H1152) alone could not reduce the occurrence Ator-induced ICH. Taken together, we investigated the underlying mechanisms of Ator-induced endothelial instability, and provided scientific evidences of STS as potential ICH therapeutics by promoting vascular integrity.

Suppression of TGF\u03b2-mediated conversion of endothelial cells and fibroblasts into cancer associated (myo)fibroblasts via HDAC inhibition

BackgroundCancer-associated fibroblasts (CAFs) support tumour progression and invasion, and they secrete abundant extracellular matrix (ECM) that may shield tumour cells from immune checkpoint or kinase inhibitors. Targeting CAFs using drugs that revert their differentiation, or inhibit their tumour-supportive functions, has been considered as an anti-cancer strategy.MethodsWe have used human and murine cell culture models, atomic force microscopy (AFM), microarray analyses, CAF/tumour cell spheroid co-cultures and transgenic fibroblast reporter mice to study how targeting HDACs using small molecule inhibitors or siRNAs re-directs CAF differentiation and function in vitro and in vivo.ResultsFrom a small molecule screen, we identified Scriptaid, a selective inhibitor of HDACs 1/3/8, as a repressor of TGFβ-mediated CAF differentiation. Scriptaid inhibits ECM secretion, reduces cellular contraction and stiffness, and impairs collective cell invasion in CAF/tumour cell spheroid co-cultures. Scriptaid also reduces CAF abundance and delays tumour growth in vivo.ConclusionsScriptaid is a well-tolerated and effective HDACi that reverses many of the functional and phenotypic properties of CAFs. Impeding or reversing CAF activation/function by altering the cellular epigenetic regulatory machinery could control tumour growth and invasion, and be beneficial in combination with additional therapies that target cancer cells or immune cells directly.

The Interaction of BMP2-Induced Defect Healing in Rat and Fixator Stiffness Modulates Matrix Alignment and Contraction.

ABSTRACTSuccessful fracture healing requires a tight interplay between mechanical and biological cues. In vitro studies illustrated that mechanical loading modulates bone morphogenetic protein (BMP) signaling. However, in the early phases of large bone defect regeneration in vivo, the underlying mechanisms leading to this mechanosensation remained unknown. We investigated the interaction of BMP2 stimulation and mechanical boundary conditions in a rat critical‐sized femoral defect model (5 mm) stabilized with three distinctly different external fixator stiffness. Defects were treated with 5 μg rhBMP2 loaded on an absorbable collagen sponge. Early matrix alignment was monitored by second‐harmonic generation imaging. Bony bridging of defects and successive healing was monitored by histology at day 7 and day 14 as well as in vivo microCT at days 10, 21, and 42 post‐operation. Femora harvested at day 42 were characterized mechanically assessing torsional load to failure ex vivo. At tissue level, differences between groups were visible at day 14 with manifest bone formation in the microCT. Histologically, we observed prolonged chondrogenesis upon flexible fixation, whereas osteogenesis started earlier after rigid and semirigid fixation. At later time points, there was a boost of bone tissue formation upon flexible fixation, whereas other groups already displayed signs of tissue maturation. Based on gene expression profiling, we analyzed the mechanobiological interplay. Already at day 3, these analyses revealed differences in expression pattern, specifically of genes involved in extracellular matrix formation. Gene regulation correlating with fixator stiffness was pronounced at day 7 comprising genes related to immunological processes and cellular contraction. The influence of loading on matrix contraction was further investigated and confirmed in a 3D bioreactor. Taken together, we demonstrate an early onset of mechanical conditions influencing BMP2‐induced defect healing and shed light on gene regulatory networks associated with extracellular matrix organization and contraction that seemed to directly impact healing outcomes. © 2018 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Exercise training and pulmonary arterial hypertension: A review of the cardiac benefits

Summary Aims Patients of pulmonary arterial hypertension (PAH) exhibit reduced functional capacity and exercise tolerance. Despite the evidences that exercise training is beneficial to this population, it is still being tested whether regular physical exercise can mitigate the complications of PAH. The aim of this review was to point out the cardiac functional and structural adaptations to exercise training in animal models of PAH, and highlight the cellular and molecular mechanisms underlying the benefits of exercise to individuals with PAH. News A systematic review of original articles published in PubMed and ScienceDirect databases was conducted by two independent researchers. Relevant information on animal model, exercise protocol, cardiac functional and structural adaptations was extracted and discussed. The results show that in rats with monocrotaline-induced PAH (50–60 mg/kg body weight), the predominant model used, aerobic continuous (treadmill running) and intermittent (voluntary wheel running) exercise training of moderate intensity, performed either prior or during the development of PAH, promote benefits to the myocardium. Moreover, the articles reveal that the cardiac function (i.e. restoration of right ventricle systolic and diastolic pressure, AT/ET ratio, TAPSE and cardiomyocyte contractility) and structure (i.e. reduced hypertrophy and fibrosis; improved profile of proteins related to cellular contraction and inflammatory response) are enhanced by exercise training. Furthermore, these exercise adaptations result in augmented exercise capacity and survival of animals with PAH. Conclusion Regular aerobic exercise of moderate intensity promotes cellular and molecular adaptations that improve myocardial function and structure along with increased exercise tolerance and survival.

Cellular Contraction can Drive Rapid Epithelial Flows

Cellular Contraction can Drive Rapid Epithelial Flows