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2.
Inflamm Bowel Dis ; 30(2): 203-212, 2024 Feb 01.
Article in English | MEDLINE | ID: mdl-37061838

ABSTRACT

BACKGROUND: Patients with an ileal pouch-anal anastomosis (IPAA) can experience pouch inflammation postoperatively. The use of antitumor necrosis factor (anti-TNF) biologics may be associated with pouch inflammation, but limited data exist on the impact of multiple advanced therapies on development of subsequent pouch inflammation. The aim of this study was to assess for an association between preoperative use of multiple advanced therapies and risk of endoscopically detected inflammatory pouch diseases (EIPDs). METHODS: We performed a retrospective analysis of ulcerative colitis (UC) and indeterminate colitis (IBDU) patients who underwent an IPAA at a quaternary care center from January 2015 to December 2019. Patients were grouped based on number and type of preoperative drug exposures. The primary outcome was EIPD within 5 years of IPAA. RESULTS: Two hundred ninety-eight patients were included in this analysis. Most of these patients had UC (95.0%) and demonstrated pancolonic disease distribution (86.1%). The majority of patients were male (57.4%) and underwent surgery for medically refractory disease (79.2%). The overall median age at surgery was 38.6 years. Preoperatively, 68 patients were biologic/small molecule-naïve, 125 received anti-TNF agents only, and 105 received non-anti-TNF agents only or multiple classes. Ninety-one patients developed EIPD. There was no significant association between type (P = .38) or number (P = .58) of exposures and EIPD, but older individuals had a lower risk of EIPD (P = .001; hazard ratio, 0.972; 95% confidence interval, 0.956-0.989). CONCLUSION: Development of EIPD was not associated with number or type of preoperative advanced therapies.


Subject(s)
Colitis, Ulcerative , Colonic Pouches , Pouchitis , Proctocolectomy, Restorative , Humans , Male , Female , Adult , Retrospective Studies , Colonic Pouches/adverse effects , Pouchitis/complications , Tumor Necrosis Factor Inhibitors/therapeutic use , Proctocolectomy, Restorative/adverse effects , Colitis, Ulcerative/drug therapy , Colitis, Ulcerative/surgery , Colitis, Ulcerative/complications , Inflammation/complications
3.
J Gen Physiol ; 155(5)2023 05 01.
Article in English | MEDLINE | ID: mdl-37000171

ABSTRACT

The timing and magnitude of force generation by a muscle depend on complex interactions in a compliant, contractile filament lattice. Perturbations in these interactions can result in cardiac muscle diseases. In this study, we address the fundamental challenge of connecting the temporal features of cardiac twitches to underlying rate constants and their perturbations associated with genetic cardiomyopathies. Current state-of-the-art metrics for characterizing the mechanical consequence of cardiac muscle disease do not utilize information embedded in the complete time course of twitch force. We pair dimension reduction techniques and machine learning methods to classify underlying perturbations that shape the timing of twitch force. To do this, we created a large twitch dataset using a spatially explicit Monte Carlo model of muscle contraction. Uniquely, we modified the rate constants of this model in line with mouse models of cardiac muscle disease and varied mutation penetrance. Ultimately, the results of this study show that machine learning models combined with biologically informed dimension reduction techniques can yield excellent classification accuracy of underlying muscle perturbations.


Subject(s)
Muscle Contraction , Muscle, Skeletal , Mice , Animals , Muscle, Skeletal/physiology , Muscle Contraction/physiology , Mutation
4.
Front Physiol ; 14: 1126111, 2023.
Article in English | MEDLINE | ID: mdl-36960155

ABSTRACT

Mechanosignaling describes processes by which biomechanical stimuli are transduced into cellular responses. External biophysical forces can be transmitted via structural protein networks that span from the cellular membrane to the cytoskeleton and the nucleus, where they can regulate gene expression through a series of biomechanical and/or biochemical mechanosensitive mechanisms, including chromatin remodeling, translocation of transcriptional regulators, and epigenetic factors. Striated muscle cells, including cardiac and skeletal muscle myocytes, utilize these nuclear mechanosignaling mechanisms to respond to changes in their intracellular and extracellular mechanical environment and mediate gene expression and cell remodeling. In this brief review, we highlight and discuss recent experimental work focused on the pathway of biomechanical stimulus propagation at the nucleus-cytoskeleton interface of striated muscles, and the mechanisms by which these pathways regulate gene regulation, muscle structure, and function. Furthermore, we discuss nuclear protein mutations that affect mechanosignaling function in human and animal models of cardiomyopathy. Furthermore, current open questions and future challenges in investigating striated muscle nuclear mechanosignaling are further discussed.

5.
Breast Cancer Res Treat ; 195(2): 153-160, 2022 Sep.
Article in English | MEDLINE | ID: mdl-35842521

ABSTRACT

PURPOSE: The United States Preventive Services Task Force recommends primary care physicians refer patients at high risk for BRCA1/2 mutations to genetic testing when appropriate. The objective of our study was to describe referrals for BRCA1/2 testing in a large integrated health system and to assess factors associated with referral. METHODS: This retrospective cohort study includes female patients between 18 and 50 years who had a primary care visit in the Cleveland Clinic Health System between 2010 and 2019. We used multivariable logistic regression to estimate differences in the odds of a woman being referred for BRCA1/2 testing by patient factors and referring physician specialty. We also assessed variation in referrals by physicians. RESULTS: Among 279,568 women, 5% were high risk. Of those, 22% were referred for testing. Black patients were significantly less likely to be referred than white patients (aOR 0.87; 95% CI 0.77, 0.98) and Jewish patients were more likely to be referred than non-Jewish patients (aOR 2.13; 95% CI 1.68, 2.70). Patients primarily managed by OB/GYN were significantly more likely to be referred than those cared for via Internal/Family Medicine (aOR 1.45; 95% CI 1.30, 1.61). Less than a quarter of primary care physicians ever referred a patient for testing. CONCLUSION: The majority of primary care patients at high risk for a BRCA1/2 mutation were not referred for testing, and over a decade, most physicians never referred a single patient. Internal/Family Medicine physicians, in particular, need support in identifying and referring women who could benefit from testing.


Subject(s)
Breast Neoplasms , Physicians, Primary Care , BRCA1 Protein/genetics , BRCA2 Protein , Breast Neoplasms/diagnosis , Breast Neoplasms/epidemiology , Breast Neoplasms/genetics , Female , Genes, BRCA1 , Genes, BRCA2 , Genetic Counseling , Genetic Predisposition to Disease , Genetic Testing , Humans , Referral and Consultation , Retrospective Studies , United States
6.
Int J Mol Sci ; 23(2)2022 Jan 14.
Article in English | MEDLINE | ID: mdl-35055055

ABSTRACT

Dilated cardiomyopathy (DCM) is a life-threatening form of heart disease that is typically characterized by progressive thinning of the ventricular walls, chamber dilation, and systolic dysfunction. Multiple mutations in the gene encoding filamin C (FLNC), an actin-binding cytoskeletal protein in cardiomyocytes, have been found in patients with DCM. However, the mechanisms that lead to contractile impairment and DCM in patients with FLNC variants are poorly understood. To determine how FLNC regulates systolic force transmission and DCM remodeling, we used an inducible, cardiac-specific FLNC-knockout (icKO) model to produce a rapid onset of DCM in adult mice. Loss of FLNC reduced systolic force development in single cardiomyocytes and isolated papillary muscles but did not affect twitch kinetics or calcium transients. Electron and immunofluorescence microscopy showed significant defects in Z-disk alignment in icKO mice and altered myofilament lattice geometry. Moreover, a loss of FLNC induces a softening myocyte cortex and structural adaptations at the subcellular level that contribute to disrupted longitudinal force production during contraction. Spatially explicit computational models showed that these structural defects could be explained by a loss of inter-myofibril elastic coupling at the Z-disk. Our work identifies FLNC as a key regulator of the multiscale ultrastructure of cardiomyocytes and therefore plays an important role in maintaining systolic mechanotransmission pathways, the dysfunction of which may be key in driving progressive DCM.


Subject(s)
Biomarkers , Cardiomyopathy, Dilated/etiology , Cardiomyopathy, Dilated/metabolism , Filamins/deficiency , Genetic Predisposition to Disease , Myocytes, Cardiac/metabolism , Animals , Calcium/metabolism , Calcium Signaling , Cardiomyopathy, Dilated/diagnosis , Costameres/genetics , Costameres/metabolism , Disease Models, Animal , Female , Filamins/metabolism , Gene Expression , Genetic Association Studies , Male , Mice , Mice, Knockout , Models, Biological , Mutation , Myocardial Contraction/genetics
7.
J Mol Cell Cardiol ; 155: 112-124, 2021 06.
Article in English | MEDLINE | ID: mdl-33636222

ABSTRACT

One of the complexities of understanding the pathology of familial forms of cardiac diseases is the level of mutation incorporation in sarcomeres. Computational models of the sarcomere that are spatially explicit offer an approach to study aspects of mutational incorporation into myofilaments that are more challenging to get at experimentally. We studied two well characterized mutations of cardiac TnC, L48Q and I61Q, that decrease or increase the release rate of Ca2+ from cTnC, k-Ca, resulting in HCM and DCM respectively [1]. Expression of these mutations in transgenic mice was used to provide experimental data for incorporation of 30 and 50% (respectively) into sarcomeres. Here we demonstrate that fixed length twitch contractions of trabeculae from mice containing mutant differ from WT; L48Q trabeculae have slower relaxation while I61Q trabeculae have markedly reduced peak tension. Using our multiscale modelling approach [2] we were able to describe the tension transients of WT mouse myocardium. Tension transients for the mutant cTnCs were simulated with changes in k-Ca, measured experimentally for each cTnC mutant in whole troponin complex, a change in the affinity of cTnC for cTnI, and a reduction in the number of detached crossbridges available for binding. A major advantage of the multiscale explicit 3-D model is that it predicts the effects of variable mutation incorporation, and the effects of variations in mutation distribution within thin filaments in sarcomeres. Such effects are currently impossible to explore experimentally. We explored random and clustered distributions of mutant cTnCs in thin filaments, as well as distributions of individual thin filaments with only WT or mutant cTnCs present. The effects of variable amounts of incorporation and non-random distribution of mutant cTnCs are more marked for I61Q than L48Q cTnC. We conclude that this approach can be effective for study on mutations in multiple proteins of the sarcomere. SUMMARY: A challenge in experimental studies of diseases is accounting for the effect of variable mutation incorporation into myofilaments. Here we use a spatially explicit computational approach, informed by experimental data from transgenic mice expressing one of two mutations in cardiac Troponin C that increase or decrease calcium sensitivity. We demonstrate that the model can accurately describe twitch contractions for the data and go on to explore the effect of variable mutant incorporation and localization on simulated cardiac muscle twitches.


Subject(s)
Models, Biological , Mutation , Myocardial Contraction , Myofibrils/genetics , Myofibrils/metabolism , Troponin C/genetics , Algorithms , Alleles , Animals , Biomarkers , Calcium/metabolism , Humans , Mice , Mice, Transgenic , Models, Molecular , Myofibrils/chemistry , Protein Binding , Sarcomeres/metabolism , Structure-Activity Relationship , Troponin C/chemistry , Troponin I/genetics , Troponin I/metabolism
8.
Annu Rev Biophys ; 50: 373-400, 2021 05 06.
Article in English | MEDLINE | ID: mdl-33637009

ABSTRACT

Two groundbreaking papers published in 1954 laid out the theory of the mechanism of muscle contraction based on force-generating interactions between myofilaments in the sarcomere that cause filaments to slide past one another during muscle contraction. The succeeding decades of research in muscle physiology have revealed a unifying interest: to understand the multiscale processes-from atom to organ-that govern muscle function. Such an understanding would have profound consequences for a vast array of applications, from developing new biomimetic technologies to treating heart disease. However, connecting structural and functional properties that are relevant at one spatiotemporal scale to those that are relevant at other scales remains a great challenge. Through a lens of multiscale dynamics, we review in this article current and historical research in muscle physiology sparked by the sliding filament theory.


Subject(s)
Muscle Contraction/physiology , Actin Cytoskeleton , Animals , Humans , Myofibrils/physiology , Myosins/physiology , Sarcomeres/physiology
9.
J Biomater Sci Polym Ed ; 32(4): 454-476, 2021 03.
Article in English | MEDLINE | ID: mdl-33091329

ABSTRACT

This paper reports on the hybrid process we have used for producing hierarchical scaffolds made of poly(lactic-co-glycolic) acid (PLGA) and nanohydroxyapatite (nHA), analyzes their internal structures via scanning electron microscopy, and presents the results of our in vitro proliferation of MC3T3-E1 cells and alkaline phosphatase activity (ALP) for 0 and 21 days. These scaffolds were produced by combining additive manufacturing (AM) and thermally induced phase separation (TIPS) techniques. Slow cooling at a rate of 1.5 °C/min during the TIPS process was used to enable a uniform temperature throughout the scaffolds, and therefore, a relatively uniform pore size range. We produced ten different scaffold compositions and topologies in this study. These scaffolds had macrochannels with diameters of ∼300 µm, ∼380 µm, and ∼460 µm, generated by the extraction of embedded porous 3D-plotted polyethylene glycol (PEG) matrices. The other experimental factors included different TIPS temperatures (-20 °C, -10 °C, and 0 °C), as well as varying PLGA concentrations (8%, 10%, and 12% w/v) and nHA content (0%, 10%, and 20% w/w). Our results indicated that almost all these macro/microporous scaffolds supported cell growth over the period of 21 days. Nevertheless, significant differences were observed among some scaffolds in terms of their support of cell proliferation and differentiation. This paper presents the results of our in vitro cell culture for 0 and 21 days. Our optimal scaffold with a porosity of ∼90%, a modulus of ∼5.2 MPa, and a nHA content of 20% showed a cell adhesion of ∼29% on day 0 and maintained cell proliferation and ALP activity over the 21-day in vitro culture. Hence, the use of additive manufacturing and designed experiments to optimize the scaffold fabrication parameters resulted in superior mechanical properties that most other studies using TIPS.


Subject(s)
Tissue Engineering , Tissue Scaffolds , Cell Adhesion , Cell Differentiation , Porosity
10.
JCI Insight ; 5(20)2020 10 15.
Article in English | MEDLINE | ID: mdl-32931484

ABSTRACT

Dilated cardiomyopathy (DCM) is often associated with sarcomere protein mutations that confer reduced myofilament tension-generating capacity. We demonstrated that cardiac twitch tension-time integrals can be targeted and tuned to prevent DCM remodeling in hearts with contractile dysfunction. We employed a transgenic murine model of DCM caused by the D230N-tropomyosin (Tm) mutation and designed a sarcomere-based intervention specifically targeting the twitch tension-time integral of D230N-Tm hearts using multiscale computational models of intramolecular and intermolecular interactions in the thin filament and cell-level contractile simulations. Our models predicted that increasing the calcium sensitivity of thin filament activation using the cardiac troponin C (cTnC) variant L48Q can sufficiently augment twitch tension-time integrals of D230N-Tm hearts. Indeed, cardiac muscle isolated from double-transgenic hearts expressing D230N-Tm and L48Q cTnC had increased calcium sensitivity of tension development and increased twitch tension-time integrals compared with preparations from hearts with D230N-Tm alone. Longitudinal echocardiographic measurements revealed that DTG hearts retained normal cardiac morphology and function, whereas D230N-Tm hearts developed progressive DCM. We present a computational and experimental framework for targeting molecular mechanisms governing the twitch tension of cardiomyopathic hearts to counteract putative mechanical drivers of adverse remodeling and open possibilities for tension-based treatments of genetic cardiomyopathies.


Subject(s)
Calcium Signaling/genetics , Cardiomyopathy, Dilated/genetics , Heart/growth & development , Troponin C/genetics , Amino Acid Substitution/genetics , Animals , Calcium/metabolism , Cardiomyopathy, Dilated/metabolism , Cardiomyopathy, Dilated/pathology , Heart/physiopathology , Humans , Mice , Mice, Transgenic , Mutation/genetics , Myocardial Contraction/genetics , Myocardium/metabolism , Myocardium/pathology , Myofibrils/genetics , Myofibrils/pathology , Sarcomeres/genetics , Sarcomeres/pathology
11.
Insects ; 11(6)2020 May 28.
Article in English | MEDLINE | ID: mdl-32481519

ABSTRACT

The immunological strategies employed by insects to overcome infection vary with the type of infection and may change with experience. We investigated how a bacterial infection in the hemocoel of the African malaria mosquito, Anopheles gambiae, prepares the immune system to face a subsequent bacterial infection. For this, adult female mosquitoes were separated into three groups-unmanipulated, injured, or infected with Escherichia coli-and five days later all the mosquitoes were infected with a different strain of E. coli. We found that an injury or a bacterial infection early in life enhances the ability of mosquitoes to kill bacteria later in life. This protection results in higher mosquito survival and is associated with an increased hemocyte density, altered phagocytic activity by individual hemocytes, and the increased expression of nitric oxide synthase and perhaps prophenoloxidase 6. Protection from a second infection likely occurs because of heightened immune awareness due to an already existing infection instead of memory arising from an earlier, cured infection. This study highlights the dynamic nature of the mosquito immune response and how one infection prepares mosquitoes to survive a subsequent infection.

12.
Proc Natl Acad Sci U S A ; 117(25): 14066-14072, 2020 06 23.
Article in English | MEDLINE | ID: mdl-32522882

ABSTRACT

Many attractive jobs in today's world require people to take on new challenges and figure out how to master them. As with any challenging goal, this involves systematic strategy use. Here we ask: Why are some people more likely to take a strategic stance toward their goals, and can this tendency be cultivated? To address these questions, we introduce the idea of a domain-general "strategic mindset." This mindset involves asking oneself strategy-eliciting questions, such as "What can I do to help myself?", "How else can I do this?", or "Is there a way to do this even better?", in the face of challenges or insufficient progress. In three studies (n = 864), people who scored higher on (or were primed with) a strategic mindset reported using more metacognitive strategies; in turn, they obtained higher college grade point averages (GPAs) (Study 1); reported greater progress toward their professional, educational, health, and fitness goals (Study 2); and responded to a challenging timed laboratory task by practicing it more and performing it faster (Study 3). We differentiated a strategic mindset from general self-efficacy, self-control, grit, and growth mindsets and showed that it explained unique variance in people's use of metacognitive strategies. These findings suggest that being strategic entails more than just having specific metacognitive skills-it appears to also entail an orientation toward seeking and employing them.


Subject(s)
Achievement , Goals , Metacognition/classification , Academic Performance , Female , Humans , Male , Self Efficacy , Young Adult
13.
J Physiol ; 598(2): 331-345, 2020 01.
Article in English | MEDLINE | ID: mdl-31786814

ABSTRACT

KEY POINTS: Fast sarcomere-level mechanics in contracting intact fibres from frog skeletal muscle reveal an I-band spring with an undamped stiffness 100 times larger than the known static stiffness. This undamped stiffness remains constant in the range of sarcomere length 2.7-3.1 µm, showing the ability of the I-band spring to adapt its length to the width of the I-band. The stiffness and tunability of the I-band spring implicate titin as a force contributor that, during contraction, allows weaker half-sarcomeres to equilibrate with in-series stronger half-sarcomeres, preventing the development of sarcomere length inhomogeneity. This work opens new possibilities for the detailed in situ description of the structural-functional basis of muscle dysfunctions related to mutations or site-directed mutagenesis in titin that alter the I-band stiffness. ABSTRACT: Force and shortening in the muscle sarcomere are due to myosin motors from thick filaments pulling nearby actin filaments toward the sarcomere centre. Thousands of serially linked sarcomeres in muscle make the shortening (and the shortening speed) macroscopic, while the intrinsic instability of in-series force generators is likely prevented by the cytoskeletal protein titin that connects the thick filament with the sarcomere end, working as an I-band spring that accounts for the rise of passive force with sarcomere length (SL). However, current estimates of titin stiffness, deduced from the passive force-SL relation and single molecule mechanics, are much smaller than what is required to avoid the development of large inhomogeneities among sarcomeres. In this work, using 4 kHz stiffness measurements on a population of sarcomeres selected along an intact fibre isolated from frog skeletal muscle contracting at different SLs (temperature 4°C), we measure the undamped stiffness of an I-band spring that at SL > 2.7 µm attains a maximum constant value of ∼6 pN nm-1 per half-thick filament, two orders of magnitude larger than expected from titin-related passive force. We conclude that a titin-like dynamic spring in the I-band, made by an undamped elastic element in-series with damped elastic elements, adapts its length to the SL with kinetics that provide force balancing among serially linked sarcomeres during contraction. In this way, the I-band spring plays a fundamental role in preventing the development of SL inhomogeneity.


Subject(s)
Connectin/physiology , Muscle Contraction , Muscle, Skeletal/physiology , Sarcomeres/physiology , Animals , Anura , In Vitro Techniques
14.
Curr Opin Biomed Eng ; 11: 35-44, 2019 Sep.
Article in English | MEDLINE | ID: mdl-31886450

ABSTRACT

Myocardial hypertrophy is the result of sustained perturbations to the mechanical and/or neurohormonal homeostasis of cardiac cells and is driven by integrated, multiscale biophysical and biochemical processes that are currently not well defined. In this brief review, we highlight recent computational and experimental models of cardiac hypertrophy that span mechanisms from the molecular level to the tissue level. Specifically, we focus on: (i) molecular-level models of the structural dynamics of sarcomere proteins in hypertrophic hearts, (ii) cellular-level models of excitation-contraction coupling and mechanosensitive signaling in disease-state myocytes, and (iii) organ-level models of myocardial growth kinematics and predictors thereof. Finally, we discuss how spanning these scales and combining multiple experimental/computational models will provide new information about the processes governing hypertrophy and potential methods to prevent or reverse them.

15.
Proc Natl Acad Sci U S A ; 116(23): 11502-11507, 2019 06 04.
Article in English | MEDLINE | ID: mdl-31110001

ABSTRACT

The naturally occurring nucleotide 2-deoxy-adenosine 5'-triphosphate (dATP) can be used by cardiac muscle as an alternative energy substrate for myosin chemomechanical activity. We and others have previously shown that dATP increases contractile force in normal hearts and models of depressed systolic function, but the structural basis of these effects has remained unresolved. In this work, we combine multiple techniques to provide structural and functional information at the angstrom-nanometer and millisecond time scales, demonstrating the ability to make both structural measurements and quantitative kinetic estimates of weak actin-myosin interactions that underpin sarcomere dynamics. Exploiting dATP as a molecular probe, we assess how small changes in myosin structure translate to electrostatic-based changes in sarcomere function to augment contractility in cardiac muscle. Through Brownian dynamics simulation and computational structural analysis, we found that deoxy-hydrolysis products [2-deoxy-adenosine 5'-diphosphate (dADP) and inorganic phosphate (Pi)] bound to prepowerstroke myosin induce an allosteric restructuring of the actin-binding surface on myosin to increase the rate of cross-bridge formation. We then show experimentally that this predicted effect translates into increased electrostatic interactions between actin and cardiac myosin in vitro. Finally, using small-angle X-ray diffraction analysis of sarcomere structure, we demonstrate that the proposed increased electrostatic affinity of myosin for actin causes a disruption of the resting conformation of myosin motors, resulting in their repositioning toward the thin filament before activation. The dATP-mediated structural alterations in myosin reported here may provide insight into an improved criterion for the design or selection of small molecules to be developed as therapeutic agents to treat systolic dysfunction.


Subject(s)
Actins/metabolism , Adenosine Triphosphate/metabolism , Cardiac Myosins/metabolism , Deoxyadenine Nucleotides/metabolism , Actin Cytoskeleton/metabolism , Adenosine Diphosphate/metabolism , Animals , Kinetics , Male , Muscle Contraction/physiology , Myocardium/metabolism , Protein Binding/physiology , Rats , Rats, Inbred F344 , Sarcomeres/metabolism , Static Electricity
16.
J Gen Physiol ; 151(1): 53-65, 2019 01 07.
Article in English | MEDLINE | ID: mdl-30510036

ABSTRACT

When striated (skeletal and cardiac) muscle is in its relaxed state, myosin motors are packed in helical tracks on the surface of the thick filament, folded toward the center of the sarcomere, and unable to bind actin or hydrolyze ATP (OFF state). This raises the question of whatthe mechanism is that integrates the Ca2+-dependent thin filament activation, making myosin heads available for interaction with actin. Here we test the interdependency of the thin and thick filament regulatory mechanisms in intact trabeculae from the rat heart. We record the x-ray diffraction signals that mark the state of the thick filament during inotropic interventions (increase in sarcomere length from 1.95 to 2.25 µm and addition of 10-7 M isoprenaline), which potentiate the twitch force developed by an electrically paced trabecula by up to twofold. During diastole, none of the signals related to the OFF state of the thick filament are significantly affected by these interventions, except the intensity of both myosin-binding protein C- and troponin-related meridional reflections, which reduce by 20% in the presence of isoprenaline. These results indicate that recruitment of myosin motors from their OFF state occurs independently and downstream from thin filament activation. This is in agreement with the recently discovered mechanism based on thick filament mechanosensing in which the number of motors available for interaction with actin rapidly adapts to the stress on the thick filament and thus to the loading conditions of the contraction. The gain of this positive feedback may be modulated by both sarcomere length and the degree of phosphorylation of myosin-binding protein C.


Subject(s)
Diastole/physiology , Myocardium/metabolism , Myosins/metabolism , Actins/metabolism , Animals , Calcium/metabolism , Male , Muscle Contraction/physiology , Muscle, Skeletal/metabolism , Phosphorylation/physiology , Rats , Rats, Wistar , Sarcomeres/metabolism
17.
Sports Health ; 10(5): 469, 2018.
Article in English | MEDLINE | ID: mdl-30153101
18.
Integr Comp Biol ; 58(2): 186-193, 2018 08 01.
Article in English | MEDLINE | ID: mdl-29897447

ABSTRACT

In striated muscle, the giant protein titin spans the entire length of a half-sarcomere and extends from the backbone of the thick filament, reversibly attaches to the thin filaments, and anchors to the dense protein network of the z-disk capping the end of the half-sarcomere. However, little is known about the relationship between the basic mechanical properties of titin and muscle contractility. Here, we build upon our previous multi-filament, spatially explicit computational model of the half-sarcomere by incorporating the nonlinear mechanics of titin filaments in the I-band. We vary parameters of the nonlinearity to understand the effects of titin stiffness on contraction dynamics and efficiency. We do so by simulating isometric contraction for a range of sarcomere lengths (SLs; 1.6-3.25 µm). Intermediate values of titin stiffness accurately reproduce the passive force-SL relation for skeletal muscle. The maximum force-SL relation is not affected by titin for SL≤2.5 µm. However, as titin stiffness increases, maximum force for the four thick filament system at SL = 3.0 µm significantly decreases from 103.2 ± 2 to 58.8 ± 1 pN. Additionally, by monitoring ATP consumption, we measure contraction efficiency as a function of titin stiffness. We find that at SL = 3.0 µm, efficiency significantly decreases from 13.9 ± 0.4 to 7.0 ± 0.3 pN/ATP when increasing titin stiffness, with little or no effect below 2.5 µm. Taken together, our results suggest that, despite an increase in the fraction of motors bound to actin along the descending limb when titin is stiffer, the force-generating capacity of the motors is reduced. These results suggest that titin stiffness has the potential to affect contractile efficiency.


Subject(s)
Connectin/physiology , Energy Metabolism , Muscle, Striated/physiology , Animals , Biomechanical Phenomena , Computer Simulation , Humans , Models, Biological
19.
J Mol Cell Cardiol ; 118: 147-158, 2018 05.
Article in English | MEDLINE | ID: mdl-29604261

ABSTRACT

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) grown in engineered heart tissue (EHT) can be used for drug screening, disease modeling, and heart repair. However, the immaturity of hiPSC-CMs currently limits their use. Because mechanical loading increases during development and facilitates cardiac maturation, we hypothesized that afterload would promote maturation of EHTs. To test this we developed a system in which EHTs are suspended between a rigid post and a flexible one, whose resistance to contraction can be modulated by applying braces of varying length. These braces allow us to adjust afterload conditions over two orders of magnitude by increasing the flexible post resistance from 0.09 up to 9.2 µN/µm. After three weeks in culture, optical tracking of post deflections revealed that auxotonic twitch forces increased in correlation with the degree of afterload, whereas twitch velocities decreased with afterload. Consequently, the power and work of the EHTs were maximal under intermediate afterloads. When studied isometrically, the inotropy of EHTs increased with afterload up to an intermediate resistance (0.45 µN/µm) and then plateaued. Applied afterload increased sarcomere length, cardiomyocyte area and elongation, which are hallmarks of maturation. Furthermore, progressively increasing the level of afterload led to improved calcium handling, increased expression of several key markers of cardiac maturation, including a shift from fetal to adult ventricular myosin heavy chain isoforms. However, at the highest afterload condition, markers of pathological hypertrophy and fibrosis were also upregulated, although the bulk tissue stiffness remained the same for all levels of applied afterload tested. Together, our results indicate that application of moderate afterloads can substantially improve the maturation of hiPSC-CMs in EHTs, while high afterload conditions may mimic certain aspects of human cardiac pathology resulting from elevated mechanical overload.


Subject(s)
Cell Differentiation , Heart/physiology , Induced Pluripotent Stem Cells/cytology , Myocytes, Cardiac/cytology , Stress, Mechanical , Tissue Engineering/methods , Calcium/metabolism , Cardiomegaly/genetics , Cardiomegaly/pathology , Cell Line , Gene Expression Regulation , Humans , Induced Pluripotent Stem Cells/ultrastructure , Isometric Contraction , Kinetics , Myocytes, Cardiac/ultrastructure
20.
J Sci Food Agric ; 98(10): 3706-3714, 2018 Aug.
Article in English | MEDLINE | ID: mdl-29315589

ABSTRACT

BACKGROUND: Red raspberries are a delicate and highly perishable fruit with a fragile pulp tissue. In this study we used vacuum impregnation (VI) methods to incorporate pectin and calcium chloride into whole red raspberries to improve their firmness. Specifically, we impregnated low methoxyl pectin (LMP) at 10 g of pectin kg-1 of solution and calcium chloride (CaCl2 ·2H2 O) at 30 g calcium kg-1 of pectin, and on the other side pectin methylesterase (PME) at 10 g of enzyme kg-1 of solution, and (CaCl2 ·2H2 O) at 10 g of calcium kg-1 of solution, into whole red raspberries. We tested three vacuum levels 33.9, 50.8, and 67.8 kPa, three vacuum impregnation times 2, 7, and 15 min, and two temperatures, 20 and 40 °C, during VI treatment. Maximum force (FM ) and gradient (GC3 ) were evaluated to assess raspberry firmness. RESULTS: A vacuum level of 50.8 kPa, processing time of 7 min, and a LMP and calcium infusion at 20 °C resulted in the firmest fruit compared to the other treatments. At these VI treatment conditions, FM and GC3 values of red raspberries obtained were 28 N, and 8.4 N mm-1 , respectively. CONCLUSION: The optimal VI conditions identified in this study can be used to improve firmness and structural integrity of red raspberries by infusion of LMP and calcium. Findings on vacuum-impregnated red raspberries may be used to develop dehydrofrozen berries for incorporation into bakery and dairy products. © 2018 Society of Chemical Industry.


Subject(s)
Food Preservation/methods , Rubus/chemistry , Calcium Chloride/analysis , Food Preservation/instrumentation , Fruit/chemistry , Hardness , Pectins/analysis , Vacuum
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