Browsing by Subject "TENSION"

Sort by: Order: Results:

Now showing items 1-12 of 12
  • Lechuga, Susana; Cartagena-Rivera, Alexander X.; Khan, Afshin; Crawford, Bert; Narayanan, Vani; Conway, Daniel E.; Lehtimäki, Jaakko; Lappalainen, Pekka; Rieder, Florian; Longworth, Michelle S.; Ivanov, Andrei I. (2022)
    The actomyosin cytoskeleton serves as a key regulator of the integrity and remodeling of epithelial barriers by controlling assembly and functions of intercellular junctions and cell-matrix adhesions. Although biochemical mechanisms that regulate the activity of non-muscle myosin II (NM-II) in epithelial cells have been extensively investigated, little is known about assembly of the contractile myosin structures at the epithelial adhesion sites. UNC-45A is a cytoskeletal chaperone that is essential for proper folding of NM-II heavy chains and myofilament assembly. We found abundant expression of UNC-45A in human intestinal epithelial cell (IEC) lines and in the epithelial layer of the normal human colon. Interestingly, protein level of UNC-45A was decreased in colonic epithelium of patients with ulcerative colitis. CRISPR/Cas9-mediated knock-out of UNC-45A in HT-29cf8 and SK-CO15 IEC disrupted epithelial barrier integrity, impaired assembly of epithelial adherence and tight junctions and attenuated cell migration. Consistently, decreased UNC-45 expression increased permeability of the Drosophila gut in vivo. The mechanisms underlying barrier disruptive and anti-migratory effects of UNC-45A depletion involved disorganization of the actomyosin bundles at epithelial junctions and the migrating cell edge. Loss of UNC-45A also decreased contractile forces at apical junctions and matrix adhesions. Expression of deletion mutants revealed roles for the myosin binding domain of UNC-45A in controlling IEC junctions and motility. Our findings uncover a novel mechanism that regulates integrity and restitution of the intestinal epithelial barrier, which may be impaired during mucosal inflammation.
  • Ciuba, Katarzyna; Hawkes, William; Tojkander, Sari; Kogan, Konstantin; Engel, Ulrike; Iskratsch, Thomas; Lappalainen, Pekka (2018)
    Contractile actomyosin bundles, stress fibers, contribute to morphogenesis, migration, and mechanosensing of non-muscle cells. In addition to actin and non-muscle myosin II (NMII), stress fibers contain a large array of proteins that control their assembly, turnover, and contractility. Calponin-3 (Cnn3) is an actin-binding protein that associates with stress fibers. However, whether Cnn3 promotes stress fiber assembly, or serves as either a positive or negative regulator of their contractility has remained obscure. Here, we applied U2OS osteosarcoma cells as a model system to study the function of Cnn3. We show that Cnn3 localizes to both NMII-containing contractile ventral stress fibers and transverse arcs, as well as to non-contractile dorsal stress fibers that do not contain NMII. Fluorescencerecovery-after-photobleaching experiments revealed that Cnn3 is a dynamic component of stress fibers. Importantly, CRISPR/Cas9 knockout and RNAi knockdown studies demonstrated that Cnn3 is not essential for stress fiber assembly. However, Cnn3 depletion resulted in increased and uncoordinated contractility of stress fibers that often led to breakage of individual actomyosin bundles within the stress fiber network. Collectively these results provide evidence that Cnn3 is dispensable for the assembly of actomyosin bundles, but that it is required for controlling proper contractility of the stress fiber network.
  • Wickstroem, Sara A.; Niessen, Carien M. (2018)
    Biological patterns emerge through specialization of genetically identical cells to take up distinct fates according to their position within the organism. How initial symmetry is broken to give rise to these patterns remains an intriguing open question. Several theories of patterning have been proposed, most prominently Turing's reaction-diffusion model of a slowly diffusing activator and a fast diffusing inhibitor generating periodic patterns. Although these reaction-diffusion systems can generate diverse patterns, it is becoming increasingly evident that cell shape and tension anisotropies, mediated via cell-cell and/or cell-matrix contacts, also facilitate symmetry breaking and subsequent self-organized tissue patterning. This review will highlight recent studies that implicate local changes in adhesion and/or tension as key drivers of cell rearrangements. We will also discuss recent studies on the role of cadherin and integrin adhesive receptors in mediating and responding to local tissue tension asymmetries to coordinate cell fate, position and behavior essential for tissue self-organization and maintenance.
  • Huethorst, Eline; Mortensen, Peter; Simitev, Radostin D; Gao, Hao; Pohjolainen, Lotta; Talman, Virpi; Ruskoaho, Heikki; Burton, Francis L; Gadegaard, Nikolaj; Smith, Godfrey L (2022)
    Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) in monolayers interact mechanically via cell-cell and cell-substrate adhesion. Spatiotemporal features of contraction were analysed in hiPSC-CM monolayers (1) attached to glass or plastic (Young's modulus (E) >1 GPa), (2) detached (substrate-free) and (3) attached to a flexible collagen hydrogel (E = 22 kPa). The effects of isoprenaline on contraction were compared between rigid and flexible substrates. To clarify the underlying mechanisms, further gene expression and computational studies were performed. HiPSC-CM monolayers exhibited multiphasic contractile profiles on rigid surfaces in contrast to hydrogels, substrate-free cultures or single cells where only simple twitch-like time-courses were observed. Isoprenaline did not change the contraction profile on either surface, but its lusitropic and chronotropic effects were greater in hydrogel compared with glass. There was no significant difference between stiff and flexible substrates in regard to expression of the stress-activated genes NPPA and NPPB. A computational model of cell clusters demonstrated similar complex contractile interactions on stiff substrates as a consequence of cell-to-cell functional heterogeneity. Rigid biomaterial surfaces give rise to unphysiological, multiphasic contractions in hi PSC-CM monolayers. Flexible substrates are necessary for normal twitch-like contractility kinetics and interpretation of inotropic interventions.
  • Dekoninck, Sophie; Hannezo, Edouard; Sifrim, Alejandro; Miroshnikova, Yekaterina A.; Aragona, Mariaceleste; Malfait, Milan; Gargouri, Souhir; de Neunheuser, Charlotte; Dubois, Christine; Voet, Thierry; Wickström, Sara A.; Simons, Benjamin D.; Blanpain, Cédric (2020)
    Summary During embryonic and postnatal development, organs and tissues grow steadily to achieve their final size at the end of puberty. However, little is known about the cellular dynamics that mediate postnatal growth. By combining in vivo clonal lineage tracing, proliferation kinetics, single-cell transcriptomics, and in vitro micro-pattern experiments, we resolved the cellular dynamics taking place during postnatal skin epidermis expansion. Our data revealed that harmonious growth is engineered by a single population of developmental progenitors presenting a fixed fate imbalance of self-renewing divisions with an ever-decreasing proliferation rate. Single-cell RNA sequencing revealed that epidermal developmental progenitors form a more uniform population compared with adult stem and progenitor cells. Finally, we found that the spatial pattern of cell division orientation is dictated locally by the underlying collagen fiber orientation. Our results uncover a simple design principle of organ growth where progenitors and differentiated cells expand in harmony with their surrounding tissues.
  • Rentola, Raisa R.; Skrifvars, Markus B.; Heinonen, Erkki; Häggblom, Tom; Hästbacka, Johanna (2020)
    Background Controlling arterial carbon dioxide is paramount in mechanically ventilated patients, and an accurate and continuous noninvasive monitoring method would optimize management in dynamic situations. In this study, we validated and further refined formulas for estimating partial pressure of carbon dioxide with respiratory gas and pulse oximetry data in mechanically ventilated cardiac arrest patients. Methods A total of 4741 data sets were collected retrospectively from 233 resuscitated patients undergoing therapeutic hypothermia. The original formula used to analyze the data is PaCO2-est1 = PETCO2 + k[(PIO2 - PETCO2) - PaO2]. To achieve better accuracy, we further modified the formula to PaCO2-est2 = k(1)*PETCO2 + k(2)*(PIO2 - PETCO2) + k(3)*(100-SpO(2)). The coefficients were determined by identifying the minimal difference between the measured and calculated arterial carbon dioxide values in a development set. The accuracy of these two methods was compared with the estimation of the partial pressure of carbon dioxide using end-tidal carbon dioxide. Results With PaCO2-est1, the mean difference between the partial pressure of carbon dioxide, and the estimated carbon dioxide was 0.08 kPa (SE +/- 0.003); with PaCO2-est2 the difference was 0.036 kPa (SE +/- 0.009). The mean difference between the partial pressure of carbon dioxide and end-tidal carbon dioxide was 0.72 kPa (SE +/- 0.01). In a mixed linear model, there was a significant difference between the estimation using end-tidal carbon dioxide and PaCO2-est1 (P <.001) and PaCO2-est2 (P <.001) respectively. Conclusions This novel formula appears to provide an accurate, continuous, and noninvasive estimation of arterial carbon dioxide.
  • Toddie-Moore, Daniel J.; Montanari, Martti P.; Tran, Ngan Vi; Brik, Evgeniy M.; Antson, Hanna; Salazar-Ciudad, Isaac; Shimmi, Osamu (2022)
    Developmental patterning is thought to be regulated by conserved signalling pathways. Initial patterns are often broad before refining to only those cells that commit to a particular fate. However, the mechanisms by which pattern refinement takes place remain to be addressed. Using the posterior crossvein (PCV) of the Drosophila pupal wing as a model, into which bone morphogenetic protein (BMP) ligand is extracellularly transported to instruct vein patterning, we investigate how pattern refinement is regulated. We found that BMP signalling induces apical enrichment of Myosin II in developing crossvein cells to regulate apical constriction. Live imaging of cellular behaviour indicates that changes in cell shape are dynamic and transient, only being maintained in those cells that retain vein fate competence after refinement. Disrupting cell shape changes throughout the PCV inhibits pattern refinement. In contrast, disrupting cell shape in only a subset of vein cells can result in a loss of BMP signalling. We propose that mechano-chemical feedback leads to competition for the developmental signal which plays a critical role in pattern refinement.
  • Kumpulainen, Kristiina; Kajamaa, Anu; Rajala, Antti (Springer, 2019)
    Perspectives in cultural-historical research
    Making and design environments, often referred to as makerspaces, have aroused recent educational interest. These environments typically consist of spaces that support interest-driven engagement in hands-on creative activities with a range of digital artefacts. Although a variety of benefits from participating in making and design activities have been proposed, we currently have limited understanding of students’ learning experiences in makerspaces situated in schools. Following Hedegaards’ conceptualisations, we investigate motive-demand dynamics in students’ social activity in a school-based digital making and design environment, ‘The FUSE Studio’. We highlight our findings via vignettes selected from 65 h of video recordings of 94 students (aged between 9 and 12 years old) carrying out activities; the recordings were collected intermittently from an elective course over one semester. Our study illustrates how the students’ learning experiences were shaped through tension-laden interplay between the motives and demands of their activity situated across personal, relational and institutional contexts. The findings make visible how established ways of working and being at school interacted and came into tension with the students’ motive orientations, thereby limiting and at times transforming the social context of their learning. Our work also demonstrates how the analysis of motive-demand dynamics offers one useful conceptual tool to unpack students’ learning experiences in novel learning environments.
  • Liu, Lizhi; Pan, Dingyi; Chen, Sheng; Martikainen, Maria-Viola; Kårlund, Anna; Ke, Jing; Pulkkinen, Herkko; Ruhanen, Hanna; Roponen, Marjut; Käkelä, Reijo; Xu, Wujun; Wang, Jie; Lehto, Vesa-Pekka (2022)
    Cell membrane (CM) coating technology is increasingly being applied in nanomedicine, but the entire coating procedure including adsorption, rupture, and fusion is not completely understood. Previously, we showed that the majority of biomimetic nanoparticles (NPs) were only partially coated, but the mechanism underlying this partial coating remains unclear, which hinders the further improvement of the coating technique. Here, we show that partial coating is an intermediate state due to the adsorption of CM fragments or CM vesicles, the latter of which could eventually be ruptured under external force. Such partial coating is difficult to self-repair to achieve full coating due to the limited membrane fluidity. Building on our understanding of the detailed coating process, we develop a general approach for fixing the partial CM coating: external phospholipid is introduced as a helper to increase CM fluidity, promoting the final fusion of lipid patches. The NPs coated with this approach have a high ratio of full coating (similar to 23%) and exhibit enhanced tumor targeting ability in comparison to the NPs coated traditionally (full coating ratio of similar to 6%). Our results provide a mechanistic basis for fixing partial CM coating towards enhancing tumor accumulation.
  • Rahikainen, Rolle; Öhman, Tiina; Turkki, Paula; Varjosalo, Markku; Hytönen, Vesa P. (2019)
    Talin protein is one of the key components in integrin-mediated adhesion complexes. Talins transmit mechanical forces between beta-integrin and actin, and regulate adhesion complex composition and signaling through the force-regulated unfolding of talin rod domain. Using modified talin proteins, we demonstrate that these functions contribute to different cellular processes and can be dissected. The transmission of mechanical forces regulates adhesion complex composition and phosphotyrosine signaling even in the absence of the mechanically regulated talin rod subdomains. However, the presence of the rod subdomains and their mechanical activation are required for the reinforcement of the adhesion complex, cell polarization and migration. Talin rod domain unfolding was also found to be essential for the generation of cellular signaling anisotropy, since both insufficient and excess activity of the rod domain severely inhibited cell polarization. Utilizing proteomics tools, we identified adhesome components that are recruited and activated either in a talin rod-dependent manner or independently of the rod subdomains. This study clarifies the division of roles between the force-regulated unfolding of a talin protein (talin 1) and its function as a physical linker between integrins and the cytoskeleton.
  • Jakkula, Pekka; Reinikainen, Matti; Hästbacka, Johanna; Pettilä, Ville; Loisa, Pekka; Karlsson, Sari; Laru-Sompa, Raili; Bendel, Stepani; Oksanen, Tuomas; Birkelund, Thomas; Tiainen, Marjaana; Toppila, Jussi; Hakkarainen, Antti; Skrifvars, Markus B.; COMACARE Study Grp (2017)
    Background: Arterial carbon dioxide tension (PaCO2), oxygen tension (PaO2), and mean arterial pressure (MAP) are modifiable factors that affect cerebral blood flow (CBF), cerebral oxygen delivery, and potentially the course of brain injury after cardiac arrest. No evidence regarding optimal treatment targets exists. Methods: The Carbon dioxide, Oxygen, and Mean arterial pressure After Cardiac Arrest and REsuscitation (COMACARE) trial is a pilot multi-center randomized controlled trial (RCT) assessing the feasibility of targeting low-or high-normal PaCO2, PaO2, and MAP in comatose, mechanically ventilated patients after out-of-hospital cardiac arrest (OHCA), as well as its effect on brain injury markers. Using a 23 factorial design, participants are randomized upon admission to an intensive care unit into one of eight groups with various combinations of PaCO2, PaO2, and MAP target levels for 36 h after admission. The primary outcome is neuron-specific enolase (NSE) serum concentration at 48 h after cardiac arrest. The main feasibility outcome is the between-group differences in PaCO2, PaO2, and MAP during the 36 h after ICU admission. Secondary outcomes include serum concentrations of NSE, S100 protein, and cardiac troponin at 24, 48, and 72 h after cardiac arrest; cerebral oxygenation, measured with near-infrared spectroscopy (NIRS); potential differences in epileptic activity, monitored via continuous electroencephalogram (EEG); and neurological outcomes at six months after cardiac arrest. Discussion: The trial began in March 2016 and participant recruitment has begun in all seven study sites as of March 2017. Currently, 115 of the total of 120 patients have been included. When completed, the results of this trial will provide preliminary clinical evidence regarding the feasibility of targeting low-or high-normal PaCO2, PaO2, and MAP values and its effect on developing brain injury, brain oxygenation, and epileptic seizures after cardiac arrest. The results of this trial will be used to evaluate whether a larger RCT on this subject is justified.
  • Nelskylä, Annika; Nurmi, Jouni; Jousi, Milla; Schramko, Alexey; Mervaala, Eero; Ristagno, Giuseppe; Skrifvars, Markus (2017)
    Background and aim: We hypothesised that the use of 50% compared to 100% oxygen maintains cerebral oxygenation and ameliorates the disturbance of cardiac mitochondrial respiration during cardiopulmonary resuscitation (CPR). Methods: Ventricular fibrillation (VF) was induced electrically in anaesthetised healthy adult pigs and left untreated for seven minutes followed by randomisation to manual ventilation with 50% or 100% oxygen and mechanical chest compressions (LUCAS (R)). Defibrillation was performed at thirteen minutes and repeated if necessary every two minutes with 1 mg intravenous adrenaline. Cerebral oxygenation was measured with near-infrared spectroscopy (rSO(2), INVOS (TM) 5100C Cerebral Oximeter) and with a probe (NEUROVENT-PTO, RAUMEDIC) in the frontal brain cortex (PbO2). Heart biopsies were obtained 20 min after the return of spontaneous circulation (ROSC) with an analysis of mitochondrial respiration (OROBOROS Instruments Corp., Innsbruck, Austria), and compared to four control animals without VF and CPR. Brain rSO(2) and PbO2 were log transformed and analysed with a mixed linear model and mitochondrial respiration with an analysis of variance. Results: Of the twenty pigs, one had a breach of protocol and was excluded, leaving nine pigs in the 50% group and ten in the 100% group. Return of spontaneous circulation (ROSC) was achieved in six pigs in the 50% group and eight in the 100% group. The rSO(2) (p = 0.007) was lower with FiO(2) 50%, but the PbO2 was not (p = 0.93). After ROSC there were significant interactions between time and FiO(2) regarding both rSO(2) (p = 0.001) and PbO2 (p = 0.004). Compared to the controls, mitochondrial respiration was decreased, with adenosine diphosphate (ADP) levels of 57 (17) pmol s(-1) mg(-1) compared to 92 (23) pmol s(-1) mg(-1) (p = 0.008), but there was no difference between different oxygen fractions (p = 0.79). Conclusions: The use of 50% oxygen during CPR results in lower cerebral oximetry values compared to 100% oxygen but there is no difference in brain tissue oxygen. Cardiac arrest disturbs cardiac mitochondrial respiration, but it is not alleviated with the use of 50% compared to 100% oxygen (Ethical and hospital approvals ESAVI/1077/04.10.07/2016 and HUS/215/2016, 7 30.3.2016, Funding Helsinki University and others). (C) 2017 Elsevier B.V. All rights reserved.