A Novel Experimental Technique for Quantifying the Local Mechanical Environment of Skeletal Tissues

2007 ◽  
Author(s):  
Kristy T. S. Palomares ◽  
Gregory J. Miller ◽  
Louis C. Gerstenfeld ◽  
Thomas A. Einhorn ◽  
Elise F. Morgan
Keyword(s):  
Experimental Technique ◽  
Tissue Level ◽  
Biological Processes ◽  
Mechanical Stimuli ◽  
Mechanical Environment ◽  
Organ Level ◽  
Shear Motion ◽  
Healing Bone ◽  
Tissue Material

A growing body of evidence indicates that mechanical cues modulate the development and repair of skeletal tissues by regulating gene expression and tissue differentiation.[1–3] Further understanding of how the mechanical environment modulates these biological processes could be applied to enhance skeletal repair following injury or disease. Bone healing provides an excellent in vivo system for investigating cellular responses to mechanical stimuli, due to the recruitment of pluripotent, mechano-sensitive, mesenchymal stem cells. For example, recent studies have shown that bending and/or shear motion applied to a healing bone defect can result in cartilage rather than bone formation.[4,5] However, while different global (i.e. organ level) mechanical stimuli are known to result in different healing outcomes, the specific local (i.e. tissue level) stimuli that promote different tissue fates have yet to be established. Finite element analyses can provide estimates of these local stimuli, yet these analyses require many assumptions regarding tissue material properties and boundary conditions. Our overall goal in this study was to develop an experimental technique for quantifying the distributions of local strains that develop in skeletal tissues during mechanical loading.

Mechanotransduction in gastrointestinal smooth muscle cells: Role of mechanosensitive ion channels

2021 ◽  
Author(s):  
Vikram Joshi ◽  
Peter R Strege ◽  
Gianrico Farrugia ◽  
Arthur Beyder
Keyword(s):  
Smooth Muscle ◽  
Ion Channels ◽  
Smooth Muscle Cells ◽  
Muscle Cells ◽  
Tissue Level ◽  
Cytoskeletal Proteins ◽  
Cell Junction ◽  
Mechanical Stimuli ◽  
Junction Molecules

Mechanosensation, the ability to properly sense mechanical stimuli and transduce them into physiologic responses, is an essential determinant of gastrointestinal (GI) function. Abnormalities in this process result in highly prevalent GI functional and motility disorders. In the GI tract, several cell types sense mechanical forces and transduce them into electrical signals, which elicit specific cellular responses. Some mechanosensitive cells like sensory neurons act as specialized mechanosensitive cells that detect forces and transduce signals into tissue-level physiologic reactions. Non-specialized mechanosensitive cells like smooth muscle cells (SMCs) adjust their function in response to forces. Mechanosensitive cells utilize various mechanoreceptors and mechanotransducers. Mechanoreceptors detect and convert force into electrical and biochemical signals, and mechanotransducers amplify and direct mechanoreceptor responses. Mechanoreceptors and mechanotransducers include ion channels, specialized cytoskeletal proteins, cell junction molecules, and G-protein coupled receptors. SMCs are particularly important due to their role as final effectors for motor function. Myogenic reflex-the ability of smooth muscle to contract in response to stretch rapidly-is a critical smooth muscle function. Such rapid mechanotransduction responses rely on mechano-gated and -sensitive ion channels, which alter their ion pores' opening in response to force, allowing fast electrical and Ca2+ responses. Though GI SMCs express a variety of such ion channels, their identities remain unknown. Recent advancements in electrophysiological, genetic, in vivo imaging, and multi-omic technologies broaden our understanding of how SMC mechano-gated and -sensitive ion channels regulate GI functions. This review discusses GI SMC mechanosensitivity's current developments with a particular emphasis on mechano-gated and -sensitive ion channels.

scholarly journals Sost deficiency leads to reduced mechanical strains at the tibia midshaft in strain-matched in vivo loading experiments in mice

2018 ◽  
Vol 15 (141) ◽  
pp. 20180012 ◽  
Author(s):  
Laia Albiol ◽  
Myriam Cilla ◽  
David Pflanz ◽  
Ina Kramer ◽  
Michaela Kneissel ◽  
...  
Keyword(s):  
Bone Formation ◽  
Cortical Bone ◽  
Neutralizing Antibodies ◽  
Bone Geometry ◽  
Bone Adaptation ◽  
Mechanical Stimuli ◽  
Mineral Density ◽  
Littermate Control ◽  
Mechanical Environment

Sclerostin, a product of the Sost gene, is a Wnt-inhibitor and thus negatively regulates bone accrual. Canonical Wnt/β-catenin signalling is also known to be activated in mechanotransduction. Sclerostin neutralizing antibodies are being tested in ongoing clinical trials to target osteoporosis and osteogenesis imperfecta but their interaction with mechanical stimuli on bone formation remains unclear. Sost knockout (KO) mice were examined to gain insight into how long-term Sost deficiency alters the local mechanical environment within the bone. This knowledge is crucial as the strain environment regulates bone adaptation. We characterized the bone geometry at the tibial midshaft of young and adult Sost KO and age-matched littermate control (LC) mice using microcomputed tomography imaging. The cortical area and the minimal and maximal moment of inertia were higher in Sost KO than in LC mice, whereas no difference was detected in either the anterior–posterior or medio-lateral bone curvature. Differences observed between age-matched genotypes were greater in adult mice. We analysed the local mechanical environment in the bone using finite-element models (FEMs), which showed that strains in the tibiae of Sost KO mice are lower than in age-matched LC mice at the diaphyseal midshaft, a region commonly used to assess cortical bone formation and resorption. Our FEMs also suggested that tissue mineral density is only a minor contributor to the strain distribution in tibial cortical bone from Sost KO mice compared to bone geometry. Furthermore, they indicated that although strain gauging experiments matched strains at the gauge site, strains along the tibial length were not comparable between age-matched Sost KO and LC mice or between young and adult animals within the same genotype.

Modelling Dynamical Arterial Adaptations to Altered Chemo-Mechanical Environments

2008 ◽  
Author(s):  
Luca Cardamone ◽  
Arturo Valentin ◽  
Jay D. Humphrey
Keyword(s):  
Extracellular Matrix ◽  
Endothelial Cells ◽  
Smooth Muscle ◽  
Vascular Tone ◽  
Complex Dynamics ◽  
Cell Activity ◽  
Mechanical Stimuli ◽  
Mechanical Environment ◽  
Sense And Respond

Vascular smooth muscle cells (SMC), endothelial cells (EC), and fibroblasts exist in a dynamic mechanical environment and can sense and respond to mechanical stimuli in vivo (McKnight and Frangos [1]). It is becoming more and more clear that complex dynamics not only influences vascular tone but also SMC proliferation (see Dancu et al. [2]) and extracellular matrix turnover (Cummins et al. [3]) by stimulating cell activity.

Cyclic Mechanical Compression Increases Mineralization of Cell-Seeded Polymer Scaffolds In Vivo

2007 ◽  
Vol 129 (4) ◽  
pp. 531-539 ◽  
Author(s):  
Angel O. Duty ◽  
Megan E. Oest ◽  
Robert E. Guldberg
Keyword(s):  
Mechanical Stimulation ◽  
Bone Repair ◽  
Tissue Level ◽  
Interstitial Tissue ◽  
Mechanical Environment ◽  
Applied Loading ◽  
Polymeric Scaffold ◽  
Von Mises

Despite considerable documentation of the ability of normal bone to adapt to its mechanical environment, very little is known about the response of bone grafts or their substitutes to mechanical loading even though many bone defects are located in load-bearing sites. The goal of this research was to quantify the effects of controlled in vivo mechanical stimulation on the mineralization of a tissue-engineered bone replacement and identify the tissue level stresses and strains associated with the applied loading. A novel subcutaneous implant system was designed capable of intermittent cyclic compression of tissue-engineered constructs in vivo. Mesenchymal stem cell-seeded polymeric scaffolds with 8 weeks of in vitro preculture were placed within the loading system and implanted subcutaneously in male Fisher rats. Constructs were subjected to 2 weeks of loading (3 treatments per week for 30min each, 13.3N at 1Hz) and harvested after 6 weeks of in vivo growth for histological examination and quantification of mineral content. Mineralization significantly increased by approximately threefold in the loaded constructs. The finite element method was used to predict tissue level stresses and strains within the construct resulting from the applied in vivo load. The largest principal strains in the polymer were distributed about a modal value of −0.24% with strains in the interstitial space being about five times greater. Von Mises stresses in the polymer were distributed about a modal value of 1.6MPa, while stresses in the interstitial tissue were about three orders of magnitude smaller. This research demonstrates the ability of controlled in vivo mechanical stimulation to enhance mineralized matrix production on a polymeric scaffold seeded with osteogenic cells and suggests that interactions with the local mechanical environment should be considered in the design of constructs for functional bone repair.

In-Situ Deformation of the Aortic Valve Interstitial Cell Nucleus Under Diastolic Loading

2007 ◽  
Vol 129 (6) ◽  
pp. 880-889 ◽  
Author(s):  
Hsiao-Ying Shadow Huang ◽  
Jun Liao ◽  
Michael S. Sacks
Keyword(s):  
Aortic Valve ◽  
Collagen Fiber ◽  
Structural Integrity ◽  
Tissue Level ◽  
Fe Model ◽  
Mechanical Stimuli ◽  
Fiber Alignment ◽  
Collagen Fiber Alignment

Within the aortic valve (AV) leaflet resides a population of interstitial cells (AVICs), which serve to maintain tissue structural integrity via protein synthesis and enzymatic degradation. AVICs are typically characterized as myofibroblasts, exhibit phenotypic plasticity, and may play an important role in valve pathophysiology. While it is known that AVICs can respond to mechanical stimuli in vitro, the level of in vivo AVIC deformation and its relation to local collagen fiber reorientation during the cardiac cycle remain unknown. In the present study, the deformation of AVICs was investigated using porcine AV glutaraldehyde fixed under 0–90mmHg transvalvular pressures. The resulting change in nuclear aspect ratio (NAR) was used as an index of overall cellular strain, and dependencies on spatial location and pressure loading levels quantified. Local collagen fiber alignment in the same valves was also quantified using small angle light scattering. A tissue-level finite element (FE) model of an AVIC embedded in the AV extracellular matrix was also used explore the relation between AV tissue- and cellular-level deformations. Results indicated large, consistent increases in AVIC NAR with transvalvular pressure (e.g., from mean of 1.8 at 0mmHg to a mean of 4.8 at 90mmHg), as well as pronounced layer specific dependencies. Associated changes in collagen fiber alignment indicated that little AVIC deformation occurs with the large amount of fiber straightening for pressures below ∼1mmHg, followed by substantial increases in AVIC NAR from 4mmHgto90mmHg. While the tissue-level FE model was able to capture the qualitative response, it also underpredicted the extent of AVIC deformation. This result suggested that additional micromechanical and fiber-compaction effects occur at high pressure levels. The results of this study form the basis of understanding transvalvular pressure-mediated mechanotransduction within the native AV and first time quantitative data correlating AVIC nuclei deformation with AV tissue microstructure and deformation.

Differences in Transmural Pressure and Axial Loading Ex Vivo Affect Arterial Remodeling and Material Properties

2009 ◽  
Vol 131 (10) ◽  
Author(s):  
Amanda R. Lawrence ◽  
Keith J. Gooch
Keyword(s):  
Mechanical Properties ◽  
Ex Vivo ◽  
Axial Stress ◽  
Axial Loading ◽  
Transmural Pressure ◽  
Mechanical Stimuli ◽  
Axial Stretch ◽  
Mechanical Environment ◽  
Artery Geometry

Arterial axial strains, present in the in vivo environment, often become reduced due to either bypass grafting or the normal aging process. Since the prevalence of hypertension increases with aging, arteries are often exposed to both decreased axial stretch and increased transmural pressure. The combined effects of these mechanical stimuli on the mechanical properties of vessels have not previously been determined. Porcine carotid arteries were cultured for 9 days at normal and reduced axial stretch ratios in the presence of normotensive and hypertensive transmural pressures using ex vivo perfusion techniques. Measurements of the amount of axial stress were obtained through longitudinal tension tests while inflation-deflation test results were used to determine circumferential stresses and incremental moduli. Macroscopic changes in artery geometry and zero-stress state opening angles were measured. Arteries cultured ex vivo remodeled in response to the mechanical environment, resulting in changes in arterial dimensions of up to ∼25% and changes in zero-stress opening angles of up to ∼55°. While pressure primarily affected circumferential remodeling and axial stretch primarily affected axial remodeling, there were clear examples of interactions between these mechanical stimuli. Culture with hypertensive pressure, especially when coupled with reduced axial loading, resulted in a rightward shift in the pressure-diameter relationship relative to arteries cultured with normotensive pressure. The observed differences in the pressure-diameter curves for cultured arteries were due to changes in artery geometry and, in some cases, changes in the arteries’ intrinsic mechanical properties. Relative to freshly isolated arteries, arteries cultured under mechanical conditions similar to in vivo conditions were stiffer, suggesting that aspects of the ex vivo culture other than the mechanical environment also influenced changes in the arteries’ mechanical properties. These results confirm the well-known importance of transmural pressure with regard to arterial wall mechanics while highlighting additional roles for axial stretch in determining mechanical behavior.

scholarly journals Influence of the Mechanical Environment on the Regeneration of Osteochondral Defects

2021 ◽  
Vol 9 ◽  
Author(s):  
Sarah Davis ◽  
Marta Roldo ◽  
Gordon Blunn ◽  
Gianluca Tozzi ◽  
Tosca Roncada
Keyword(s):  
Articular Cartilage ◽  
Subchondral Bone ◽  
Structural Integrity ◽  
Mechanical Performance ◽  
Cartilage Damage ◽  
Mechanical Stimuli ◽  
Osteochondral Defects ◽  
Mechanical Environment ◽  
Nature Restoration

Articular cartilage is a highly specialised connective tissue of diarthrodial joints which provides a smooth, lubricated surface for joint articulation and plays a crucial role in the transmission of loads. In vivo cartilage is subjected to mechanical stimuli that are essential for cartilage development and the maintenance of a chondrocytic phenotype. Cartilage damage caused by traumatic injuries, ageing, or degradative diseases leads to impaired loading resistance and progressive degeneration of both the articular cartilage and the underlying subchondral bone. Since the tissue has limited self-repairing capacity due its avascular nature, restoration of its mechanical properties is still a major challenge. Tissue engineering techniques have the potential to heal osteochondral defects using a combination of stem cells, growth factors, and biomaterials that could produce a biomechanically functional tissue, representative of native hyaline cartilage. However, current clinical approaches fail to repair full-thickness defects that include the underlying subchondral bone. Moreover, when tested in vivo, current tissue-engineered grafts show limited capacity to regenerate the damaged tissue due to poor integration with host cartilage and the failure to retain structural integrity after insertion, resulting in reduced mechanical function. The aim of this review is to examine the optimal characteristics of osteochondral scaffolds. Additionally, an overview on the latest biomaterials potentially able to replicate the natural mechanical environment of articular cartilage and their role in maintaining mechanical cues to drive chondrogenesis will be detailed, as well as the overall mechanical performance of grafts engineered using different technologies.

scholarly journals In vivo interactome profiling by enzyme‐catalyzed proximity labeling

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yangfan Xu ◽  
Xianqun Fan ◽  
Yang Hu
Keyword(s):  
State Of The Art ◽  
Catalytic Efficiency ◽  
Biological Processes ◽  
Protein Protein Interaction ◽  
Current State ◽  
Protein Interactome ◽  
Potential Applications ◽  
Protein Protein Interaction Networks ◽  
Temporal And Spatial

AbstractEnzyme-catalyzed proximity labeling (PL) combined with mass spectrometry (MS) has emerged as a revolutionary approach to reveal the protein-protein interaction networks, dissect complex biological processes, and characterize the subcellular proteome in a more physiological setting than before. The enzymatic tags are being upgraded to improve temporal and spatial resolution and obtain faster catalytic dynamics and higher catalytic efficiency. In vivo application of PL integrated with other state of the art techniques has recently been adapted in live animals and plants, allowing questions to be addressed that were previously inaccessible. It is timely to summarize the current state of PL-dependent interactome studies and their potential applications. We will focus on in vivo uses of newer versions of PL and highlight critical considerations for successful in vivo PL experiments that will provide novel insights into the protein interactome in the context of human diseases.

scholarly journals Massively parallel in vivo CRISPR screening identifies RNF20/40 as epigenetic regulators of cardiomyocyte maturation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Nathan J. VanDusen ◽  
Julianna Y. Lee ◽  
Weiliang Gu ◽  
Catalina E. Butler ◽  
Isha Sethi ◽  
...  
Keyword(s):  
Gene Expression ◽  
Genetic Screen ◽  
Forward Genetics ◽  
Epigenetic Mark ◽  
Biological Processes ◽  
Dynamic Changes ◽  
Forward Genetic Screen ◽  
High Resource ◽  
Organ Systems

AbstractThe forward genetic screen is a powerful, unbiased method to gain insights into biological processes, yet this approach has infrequently been used in vivo in mammals because of high resource demands. Here, we use in vivo somatic Cas9 mutagenesis to perform an in vivo forward genetic screen in mice to identify regulators of cardiomyocyte (CM) maturation, the coordinated changes in phenotype and gene expression that occur in neonatal CMs. We discover and validate a number of transcriptional regulators of this process. Among these are RNF20 and RNF40, which form a complex that monoubiquitinates H2B on lysine 120. Mechanistic studies indicate that this epigenetic mark controls dynamic changes in gene expression required for CM maturation. These insights into CM maturation will inform efforts in cardiac regenerative medicine. More broadly, our approach will enable unbiased forward genetics across mammalian organ systems.

Sign in / Sign up

Export Citation Format

Share Document