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Thulasisingh A, Kumar K, Yamunadevi B, Poojitha N, SuhailMadharHanif S, Kannaiyan S. Biodegradable packaging materials. Polym Bull (Berl) 2021. [DOI: 10.1007/s00289-021-03767-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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Siadat SM, Zamboulis DE, Thorpe CT, Ruberti JW, Connizzo BK. Tendon Extracellular Matrix Assembly, Maintenance and Dysregulation Throughout Life. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1348:45-103. [PMID: 34807415 DOI: 10.1007/978-3-030-80614-9_3] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
In his Lissner Award medal lecture in 2000, Stephen Cowin asked the question: "How is a tissue built?" It is not a new question, but it remains as relevant today as it did when it was asked 20 years ago. In fact, research on the organization and development of tissue structure has been a primary focus of tendon and ligament research for over two centuries. The tendon extracellular matrix (ECM) is critical to overall tissue function; it gives the tissue its unique mechanical properties, exhibiting complex non-linear responses, viscoelasticity and flow mechanisms, excellent energy storage and fatigue resistance. This matrix also creates a unique microenvironment for resident cells, allowing cells to maintain their phenotype and translate mechanical and chemical signals into biological responses. Importantly, this architecture is constantly remodeled by local cell populations in response to changing biochemical (systemic and local disease or injury) and mechanical (exercise, disuse, and overuse) stimuli. Here, we review the current understanding of matrix remodeling throughout life, focusing on formation and assembly during the postnatal period, maintenance and homeostasis during adulthood, and changes to homeostasis in natural aging. We also discuss advances in model systems and novel tools for studying collagen and non-collagenous matrix remodeling throughout life, and finally conclude by identifying key questions that have yet to be answered.
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Affiliation(s)
| | - Danae E Zamboulis
- Institute of Life Course and Medical Sciences, Faculty of Health and Life Sciences, University of Liverpool, Liverpool, UK
| | - Chavaunne T Thorpe
- Comparative Biomedical Sciences, The Royal Veterinary College, University of London, London, UK
| | - Jeffrey W Ruberti
- Department of Bioengineering, Northeastern University, Boston, MA, USA
| | - Brianne K Connizzo
- Department of Biomedical Engineering, Boston University, Boston, MA, USA.
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3
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Senadheera TR, Dave D, Shahidi F. Sea Cucumber Derived Type I Collagen: A Comprehensive Review. Mar Drugs 2020; 18:E471. [PMID: 32961970 PMCID: PMC7551324 DOI: 10.3390/md18090471] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Revised: 09/11/2020] [Accepted: 09/15/2020] [Indexed: 01/31/2023] Open
Abstract
Collagen is the major fibrillar protein in most living organisms. Among the different types of collagen, type I collagen is the most abundant one in tissues of marine invertebrates. Due to the health-related risk factors and religious constraints, use of mammalian derived collagen has been limited. This triggers the search for alternative sources of collagen for both food and non-food applications. In this regard, numerous studies have been conducted on maximizing the utilization of seafood processing by-products and address the need for collagen. However, less attention has been given to marine invertebrates and their by-products. The present review has focused on identifying sea cucumber as a potential source of collagen and discusses the general scope of collagen extraction, isolation, characterization, and physicochemical properties along with opportunities and challenges for utilizing marine-derived collagen.
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Affiliation(s)
- Tharindu R.L. Senadheera
- Department of Biochemistry, Memorial University of Newfoundland, St. John’s, NL A1B 3X9, Canada;
| | - Deepika Dave
- Department of Biochemistry, Memorial University of Newfoundland, St. John’s, NL A1B 3X9, Canada;
- Marine Bioprocessing Facility, Centre of Aquaculture and Seafood Development, Fisheries and Marine Institute, Memorial University of Newfoundland, St. John’s, NL A1C 5R3, Canada
| | - Fereidoon Shahidi
- Department of Biochemistry, Memorial University of Newfoundland, St. John’s, NL A1B 3X9, Canada;
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Lin J, Shi Y, Men Y, Wang X, Ye J, Zhang C. Mechanical Roles in Formation of Oriented Collagen Fibers. TISSUE ENGINEERING PART B-REVIEWS 2020; 26:116-128. [PMID: 31801418 DOI: 10.1089/ten.teb.2019.0243] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Collagen is a structural protein that is widely present in vertebrates, being usually distributed in tissues in the form of fibers. In living organisms, fibers are organized in different orientations in various tissues. As the structural base in connective tissue and load-bearing tissue, the orientation of collagen fibers plays an extremely important role in the mechanical properties and physiological and biochemical functions. The study on mechanics role in formation of oriented collagen fibers enables us to understand how discrete cells use limited molecular materials to create tissues with different structures, thereby promoting our understanding of the mechanism of tissue formation from scratch, from invisible to tangible. However, the current understanding of the mechanism of fiber orientation is still insufficient. In addition, existing fabrication methods of oriented fibers are varied and involve interdisciplinary study, and the achievements of each experiment are favorable to the construction and improvement of the fiber orientation theory. To this end, this review focuses on the preparation methods of oriented fibers and proposes a model explaining the formation process of oriented fibers in tendons based on the existing fiber theory. Impact statement As the structural base in connective tissue and load-bearing tissue, the orientation of collagen fibers plays an extremely important role in the mechanical properties and physiological and biochemical functions. However, the current understanding of the mechanism of fiber orientation is still insufficient, which is greatly responsible for the challenge of functional tissue repair and regeneration. Understanding the mechanism of fiber orientation can promote the successful application of fiber orientation scaffolds in tissue repair and regeneration, as well as providing an insight for the mechanism of tissue histomorphology.
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Affiliation(s)
- Jiexiang Lin
- Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control, National Demonstration Center for Experimental Mechanical and Electrical Engineering Education, School of Mechanical Engineering, Tianjin University of Technology, Tianjin, P.R. China
| | - Yanping Shi
- Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control, National Demonstration Center for Experimental Mechanical and Electrical Engineering Education, School of Mechanical Engineering, Tianjin University of Technology, Tianjin, P.R. China
| | - Yutao Men
- Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control, National Demonstration Center for Experimental Mechanical and Electrical Engineering Education, School of Mechanical Engineering, Tianjin University of Technology, Tianjin, P.R. China
| | - Xin Wang
- Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control, National Demonstration Center for Experimental Mechanical and Electrical Engineering Education, School of Mechanical Engineering, Tianjin University of Technology, Tianjin, P.R. China
| | - Jinduo Ye
- Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control, National Demonstration Center for Experimental Mechanical and Electrical Engineering Education, School of Mechanical Engineering, Tianjin University of Technology, Tianjin, P.R. China
| | - Chunqiu Zhang
- Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control, National Demonstration Center for Experimental Mechanical and Electrical Engineering Education, School of Mechanical Engineering, Tianjin University of Technology, Tianjin, P.R. China
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5
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Holmes DF, Lu Y, Starborg T, Kadler KE. Collagen Fibril Assembly and Function. Curr Top Dev Biol 2018; 130:107-142. [DOI: 10.1016/bs.ctdb.2018.02.004] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Kadler KE. Fell Muir Lecture: Collagen fibril formation in vitro and in vivo. Int J Exp Pathol 2017; 98:4-16. [PMID: 28508516 DOI: 10.1111/iep.12224] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2016] [Accepted: 01/21/2017] [Indexed: 12/29/2022] Open
Abstract
It is a great honour to be awarded the Fell Muir Prize for 2016 by the British Society of Matrix Biology. As recipient of the prize, I am taking the opportunity to write a minireview on collagen fibrillogenesis, which has been the focus of my research for 33 years. This is the process by which triple helical collagen molecules assemble into centimetre-long fibrils in the extracellular matrix of animals. The fibrils appeared a billion years ago at the dawn of multicellular animal life as the primary scaffold for tissue morphogenesis. The fibrils occur in exquisite three-dimensional architectures that match the physical demands of tissues, for example orthogonal lattices in cornea, basket weaves in skin and blood vessels, and parallel bundles in tendon, ligament and nerves. The question of how collagen fibrils are formed was posed at the end of the nineteenth century. Since then, we have learned about the structure of DNA and the peptide bond, understood how plants capture the sun's energy, cloned animals, discovered antibiotics and found ways of editing our genome in the pursuit of new cures for diseases. However, how cells generate tissues from collagen fibrils remains one of the big unsolved mysteries in biology. In this review, I will give a personal account of the topic and highlight some of the approaches that my research group are taking to find new insights.
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Affiliation(s)
- Karl E Kadler
- Faculty of Biology, Medicine and Health, Wellcome Trust Centre for Cell-Matrix Research, Manchester Academic Health Science Centre, University of Manchester, Manchester, UK
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Goh KL, Holmes DF. Collagenous Extracellular Matrix Biomaterials for Tissue Engineering: Lessons from the Common Sea Urchin Tissue. Int J Mol Sci 2017; 18:ijms18050901. [PMID: 28441344 PMCID: PMC5454814 DOI: 10.3390/ijms18050901] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Revised: 04/05/2017] [Accepted: 04/11/2017] [Indexed: 12/21/2022] Open
Abstract
Scaffolds for tissue engineering application may be made from a collagenous extracellular matrix (ECM) of connective tissues because the ECM can mimic the functions of the target tissue. The primary sources of collagenous ECM material are calf skin and bone. However, these sources are associated with the risk of having bovine spongiform encephalopathy or transmissible spongiform encephalopathy. Alternative sources for collagenous ECM materials may be derived from livestock, e.g., pigs, and from marine animals, e.g., sea urchins. Collagenous ECM of the sea urchin possesses structural features and mechanical properties that are similar to those of mammalian ones. However, even more intriguing is that some tissues such as the ligamentous catch apparatus can exhibit mutability, namely rapid reversible changes in the tissue mechanical properties. These tissues are known as mutable collagenous tissues (MCTs). The mutability of these tissues has been the subject of on-going investigations, covering the biochemistry, structural biology and mechanical properties of the collagenous components. Recent studies point to a nerve-control system for regulating the ECM macromolecules that are involved in the sliding action of collagen fibrils in the MCT. This review discusses the key attributes of the structure and function of the ECM of the sea urchin ligaments that are related to the fibril-fibril sliding action-the focus is on the respective components within the hierarchical architecture of the tissue. In this context, structure refers to size, shape and separation distance of the ECM components while function is associated with mechanical properties e.g., strength and stiffness. For simplicity, the components that address the different length scale from the largest to the smallest are as follows: collagen fibres, collagen fibrils, interfibrillar matrix and collagen molecules. Application of recent theories of stress transfer and fracture mechanisms in fibre reinforced composites to a wide variety of collagen reinforcing (non-mutable) connective tissue, has allowed us to draw general conclusions concerning the mechanical response of the MCT at specific mechanical states, namely the stiff and complaint states. The intent of this review is to provide the latest insights, as well as identify technical challenges and opportunities, that may be useful for developing methods for effective mechanical support when adapting decellularised connective tissues from the sea urchin for tissue engineering or for the design of a synthetic analogue.
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Affiliation(s)
- Kheng Lim Goh
- Newcastle University Singapore, SIT Building at Nanyang Polytechnic, 172A Ang Mo Kio Avenue 8 #05-01, Singapore 567739, Singapore.
- Newcastle University, School of Mechanical & Systems Engineering, Stephenson Building, Claremont Road, Newcastle upon Tyne NE1 7RU, UK.
| | - David F Holmes
- Manchester University, Wellcome Trust Centre for Cell Matrix Research, B.3016 Michael Smith Building, Faculty of Life Sciences, Oxford Road, Manchester M13 9PT, UK.
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Rutenberg AD, Brown AI, Kreplak L. Uniform spatial distribution of collagen fibril radii within tendon implies local activation of pC-collagen at individual fibrils. Phys Biol 2016; 13:046008. [PMID: 27559989 DOI: 10.1088/1478-3975/13/4/046008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Collagen fibril cross-sectional radii show no systematic variation between the interior and the periphery of fibril bundles, indicating an effectively constant rate of collagen incorporation into fibrils throughout the bundle. Such spatially homogeneous incorporation constrains the extracellular diffusion of collagen precursors from sources at the bundle boundary to sinks at the growing fibrils. With a coarse-grained diffusion equation we determine stringent bounds, using parameters extracted from published experimental measurements of tendon development. From the lack of new fibril formation after birth, we further require that the concentration of diffusing precursors stays below the critical concentration for fibril nucleation. We find that the combination of the diffusive bound, which requires larger concentrations to ensure homogeneous fibril radii, and lack of nucleation, which requires lower concentrations, is only marginally consistent with fully processed collagen using conservative bounds. More realistic bounds may leave no consistent concentrations. Therefore, we propose that unprocessed pC-collagen diffuses from the bundle periphery followed by local C-proteinase activity and subsequent collagen incorporation at each fibril. We suggest that C-proteinase is localized within bundles, at fibril surfaces, during radial fibrillar growth. The much greater critical concentration of pC-collagen, as compared to fully processed collagen, then provides broad consistency between homogeneous fibril radii and the lack of fibril nucleation during fibril growth.
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Affiliation(s)
- Andrew D Rutenberg
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, B3H 4R2, Canada
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Ahmadzadeh H, Freedman BR, Connizzo BK, Soslowsky LJ, Shenoy VB. Micromechanical poroelastic finite element and shear-lag models of tendon predict large strain dependent Poisson's ratios and fluid expulsion under tensile loading. Acta Biomater 2015; 22:83-91. [PMID: 25934322 PMCID: PMC4466068 DOI: 10.1016/j.actbio.2015.04.035] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Revised: 04/12/2015] [Accepted: 04/23/2015] [Indexed: 11/28/2022]
Abstract
As tendons are loaded, they reduce in volume and exude fluid to the surrounding medium. Experimental studies have shown that tendon stretching results in a Poisson's ratio greater than 0.5, with a maximum value at small strains followed by a nonlinear decay. Here we present a computational model that attributes this macroscopic observation to the microscopic mechanism of the load transfer between fibrils under stretch. We develop a finite element model based on the mechanical role of the interfibrillar-linking elements, such as thin fibrils that bridge the aligned fibrils or macromolecules such as glycosaminoglycans (GAGs) in the interfibrillar sliding and verify it with a theoretical shear-lag model. We showed the existence of a previously unappreciated structure-function mechanism whereby the Poisson's ratio in tendon is affected by the strain applied and interfibrillar-linker properties, and together these features predict tendon volume shrinkage under tensile loading. During loading, the interfibrillar-linkers pulled fibrils toward each other and squeezed the matrix, leading to the Poisson's ratio larger than 0.5 and fluid expulsion. In addition, the rotation of the interfibrillar-linkers with respect to the fibrils at large strains caused a reduction in the volume shrinkage and eventual nonlinear decay in Poisson's ratio at large strains. Our model also predicts a fluid flow that has a radial pattern toward the surrounding medium, with the larger fluid velocities in proportion to the interfibrillar sliding.
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Affiliation(s)
- Hossein Ahmadzadeh
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, USA
| | - Benjamin R Freedman
- McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA, USA
| | - Brianne K Connizzo
- McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA, USA
| | - Louis J Soslowsky
- McKay Orthopaedic Research Laboratory, University of Pennsylvania, Philadelphia, PA, USA
| | - Vivek B Shenoy
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, USA.
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10
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Kalson NS, Lu Y, Taylor SH, Starborg T, Holmes DF, Kadler KE. A structure-based extracellular matrix expansion mechanism of fibrous tissue growth. eLife 2015; 4. [PMID: 25992598 PMCID: PMC4438642 DOI: 10.7554/elife.05958] [Citation(s) in RCA: 89] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Accepted: 04/22/2015] [Indexed: 01/01/2023] Open
Abstract
Embryonic growth occurs predominately by an increase in cell number; little is known about growth mechanisms later in development when fibrous tissues account for the bulk of adult vertebrate mass. We present a model for fibrous tissue growth based on 3D-electron microscopy of mouse tendon. We show that the number of collagen fibrils increases during embryonic development and then remains constant during postnatal growth. Embryonic growth was explained predominately by increases in fibril number and length. Postnatal growth arose predominately from increases in fibril length and diameter. A helical crimp structure was established in embryogenesis, and persisted postnatally. The data support a model where the shape and size of tendon is determined by the number and position of embryonic fibroblasts. The collagen fibrils that these cells synthesise provide a template for postnatal growth by structure-based matrix expansion. The model has important implications for growth of other fibrous tissues and fibrosis. DOI:http://dx.doi.org/10.7554/eLife.05958.001 Young animals are able to grow in a way that allows them to maintain roughly the same shape until they reach their adult size. The growth of embryos is driven by increases in cell size and number, but it is less clear how the body grows after birth. By this point, many of the cells in the body are part of tendons and other fibrous tissues, where they are surrounded by a mesh of fibres made of collagen and other proteins. These fibres provide strength to the tissue, but may also restrict its ability to grow. Tendons connect muscles to bones. They contain fibres of collagen that run along their length, which enables them to cope with very strong pulling forces. Kalson et al. used electron microscopy to generate highly detailed three-dimensional models of mouse tendons at three stages: in the embryo, at birth and six weeks later. The experiments identified two stages in tendon development. During the first stage, the number of cells and fibres across the tendon is determined in the embryo. The fibres also slightly expand in diameter and form regular waves called crimps that are important for the structural strength of the tendon. The second stage happens after birth, during which the number of cells and fibres remains constant, but the tendons continue to grow because the fibres increase in diameter and length. The cells also move to form towers of cells running along the tendon. From these observations, Kalson et al. propose that the numbers and locations of the cells and collagen fibres that determine the shape and size of tendons are established in the embryo. The collagen fibres create a framework for the continued growth of the tendon after birth. Future challenges are to understand how the number and the arrangement of cells in the tendon is determined before the collagen fibres are made, and how these cells control the number of collagen fibres that form. DOI:http://dx.doi.org/10.7554/eLife.05958.002
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Affiliation(s)
- Nicholas S Kalson
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Yinhui Lu
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Susan H Taylor
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Tobias Starborg
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - David F Holmes
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Karl E Kadler
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
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Nonmuscle myosin II powered transport of newly formed collagen fibrils at the plasma membrane. Proc Natl Acad Sci U S A 2013; 110:E4743-52. [PMID: 24248360 DOI: 10.1073/pnas.1314348110] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Collagen fibrils can exceed thousands of microns in length and are therefore the longest, largest, and most size-pleomorphic protein polymers in vertebrates; thus, knowing how cells transport collagen fibrils is essential for a more complete understanding of protein transport and its role in tissue morphogenesis. Here, we identified newly formed collagen fibrils being transported at the surface of embryonic tendon cells in vivo by using serial block face-scanning electron microscopy of the cell-matrix interface. Newly formed fibrils ranged in length from ~1 to ~30 µm. The shortest (1-10 µm) occurred in intracellular fibricarriers; the longest (~30 µm) occurred in plasma membrane fibripositors. Fibrils and fibripositors were reduced in numbers when collagen secretion was blocked. ImmunoEM showed the absence of lysosomal-associated membrane protein 2 on fibricarriers and fibripositors and there was no effect of leupeptin on fibricarrier or fibripositor number and size, suggesting that fibricarriers and fibripositors are not part of a fibril degradation pathway. Blebbistatin decreased fibricarrier number and increased fibripositor length; thus, nonmuscle myosin II (NMII) powers the transport of these compartments. Inhibition of dynamin-dependent endocytosis with dynasore blocked fibricarrier formation and caused accumulation of fibrils in fibripositors. Data from fluid-phase HRP electron tomography showed that fibricarriers could originate at the plasma membrane. We propose that NMII-powered transport of newly formed collagen fibrils at the plasma membrane is fundamental to the development of collagen fibril-rich tissues. A NMII-dependent cell-force model is presented as the basis for the creation and dynamics of fibripositor structures.
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Starborg T, Kalson NS, Lu Y, Mironov A, Cootes TF, Holmes DF, Kadler KE. Using transmission electron microscopy and 3View to determine collagen fibril size and three-dimensional organization. Nat Protoc 2013; 8:1433-48. [PMID: 23807286 DOI: 10.1038/nprot.2013.086] [Citation(s) in RCA: 175] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Collagen fibrils are the major tensile element in vertebrate tissues, in which they occur as ordered bundles in the extracellular matrix. Abnormal fibril assembly and organization results in scarring, fibrosis, poor wound healing and connective tissue diseases. Transmission electron microscopy (TEM) is used to assess the formation of the fibrils, predominantly by measuring fibril diameter. Here we describe a protocol for measuring fibril diameter as well as fibril volume fraction, mean fibril length, fibril cross-sectional shape and fibril 3D organization, all of which are major determinants of tissue function. Serial-section TEM (ssTEM) has been used to visualize fibril 3D organization in vivo. However, serial block face-scanning electron microscopy (SBF-SEM) has emerged as a time-efficient alternative to ssTEM. The protocol described below is suitable for preparing tissues for TEM and SBF-SEM (by 3View). We describe how to use 3View for studying collagen fibril organization in vivo and show how to find and track individual fibrils. The overall time scale is ~8 d from isolating the tissue to having a 3D image stack.
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Affiliation(s)
- Tobias Starborg
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester, UK
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14
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Ribeiro AR, Barbaglio A, Oliveira MJ, Ribeiro CC, Wilkie IC, Candia Carnevali MD, Barbosa MA. Matrix metalloproteinases in a sea urchin ligament with adaptable mechanical properties. PLoS One 2012; 7:e49016. [PMID: 23173042 PMCID: PMC3500250 DOI: 10.1371/journal.pone.0049016] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Accepted: 10/09/2012] [Indexed: 11/18/2022] Open
Abstract
Mutable collagenous tissues (MCTs) of echinoderms show reversible changes in tensile properties (mutability) that are initiated and modulated by the nervous system via the activities of cells known as juxtaligamental cells. The molecular mechanism underpinning this mechanical adaptability has still to be elucidated. Adaptable connective tissues are also present in mammals, most notably in the uterine cervix, in which changes in stiffness result partly from changes in the balance between matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). There have been no attempts to assess the potential involvement of MMPs in the echinoderm mutability phenomenon, apart from studies dealing with a process whose relationship to the latter is uncertain. In this investigation we used the compass depressor ligaments (CDLs) of the sea-urchin Paracentrotus lividus. The effect of a synthetic MMP inhibitor - galardin - on the biomechanical properties of CDLs in different mechanical states (“standard”, “compliant” and “stiff”) was evaluated by dynamic mechanical analysis, and the presence of MMPs in normal and galardin-treated CDLs was determined semi-quantitatively by gelatin zymography. Galardin reversibly increased the stiffness and storage modulus of CDLs in all three states, although its effect was significantly lower in stiff than in standard or compliant CDLs. Gelatin zymography revealed a progressive increase in total gelatinolytic activity between the compliant, standard and stiff states, which was possibly due primarily to higher molecular weight components resulting from the inhibition and degradation of MMPs. Galardin caused no change in the gelatinolytic activity of stiff CDLs, a pronounced and statistically significant reduction in that of standard CDLs, and a pronounced, but not statistically significant, reduction in that of compliant CDLs. Our results provide evidence that MMPs may contribute to the variable tensility of the CDLs, in the light of which we provide an updated hypothesis for the regulatory mechanism controlling MCT mutability.
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Affiliation(s)
- Ana R. Ribeiro
- INEB- Instituto de Engenharia Biomédica, NEWTherapies Group, Universidade do Porto, Porto, Portugal
- FEUP- Faculdade de Engenharia da Universidade do Porto, Departamento de Engenharia Metalúrgica e de Materiais, Porto, Portugal
- * E-mail: (ARR); (MAB)
| | - Alice Barbaglio
- Life Sciences Department, University of Milan, Milano, Italy
| | - Maria J. Oliveira
- INEB- Instituto de Engenharia Biomédica, NEWTherapies Group, Universidade do Porto, Porto, Portugal
- FMUP- Faculdade de Medicina da Universidade do Porto, Porto, Portugal
| | - Cristina C. Ribeiro
- INEB- Instituto de Engenharia Biomédica, NEWTherapies Group, Universidade do Porto, Porto, Portugal
- ISEP-Instituto Superior de Engenharia do Porto, Departamento de Física, Porto, Portugal
| | - Iain C. Wilkie
- Department of Biological and Biomedical Sciences, Glasgow Caledonian University, Glasgow, Scotland
| | | | - Mário A. Barbosa
- INEB- Instituto de Engenharia Biomédica, NEWTherapies Group, Universidade do Porto, Porto, Portugal
- FEUP- Faculdade de Engenharia da Universidade do Porto, Departamento de Engenharia Metalúrgica e de Materiais, Porto, Portugal
- ICBAS- Instituto de Ciências Biomédicas Abel Salazar, Universidade do Porto, Porto, Portugal
- * E-mail: (ARR); (MAB)
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15
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Ribeiro AR, Barbaglio A, Benedetto CD, Ribeiro CC, Wilkie IC, Carnevali MDC, Barbosa MA. New insights into mutable collagenous tissue: correlations between the microstructure and mechanical state of a sea-urchin ligament. PLoS One 2011; 6:e24822. [PMID: 21935473 PMCID: PMC3173489 DOI: 10.1371/journal.pone.0024822] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2011] [Accepted: 08/18/2011] [Indexed: 11/18/2022] Open
Abstract
The mutable collagenous tissue (MCT) of echinoderms has the ability to undergo rapid and reversible changes in passive mechanical properties that are initiated and modulated by the nervous system. Since the mechanism of MCT mutability is poorly understood, the aim of this work was to provide a detailed morphological analysis of a typical mutable collagenous structure in its different mechanical states. The model studied was the compass depressor ligament (CDL) of a sea urchin (Paracentrotus lividus), which was characterized in different functional states mimicking MCT mutability. Transmission electron microscopy, histochemistry, cryo-scanning electron microscopy, focused ion beam/scanning electron microscopy, and field emission gun-environmental scanning electron microscopy were used to visualize CDLs at the micro- and nano-scales. This investigation has revealed previously unreported differences in both extracellular and cellular constituents, expanding the current knowledge of the relationship between the organization of the CDL and its mechanical state. Scanning electron microscopies in particular provided a three-dimensional overview of CDL architecture at the micro- and nano-scales, and clarified the micro-organization of the ECM components that are involved in mutability. Further evidence that the juxtaligamental cells are the effectors of these changes in mechanical properties was provided by a correlation between their cytology and the tensile state of the CDLs.
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Affiliation(s)
- Ana R Ribeiro
- Instituto de Engenharia Biomédica, Biomaterials Division, NEWTherapies Group, Universidade do Porto, Porto, Portugal.
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16
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Growth of collagen fibril seeds from embryonic tendon: fractured fibril ends nucleate new tip growth. J Mol Biol 2010; 399:9-16. [PMID: 20385142 PMCID: PMC2887488 DOI: 10.1016/j.jmb.2010.04.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2009] [Revised: 03/31/2010] [Accepted: 04/02/2010] [Indexed: 11/22/2022]
Abstract
Collagen fibrils are the principal tensile element of vertebrate tissues where they occur in the extracellular matrix as spatially organised arrays. A major challenge is to understand how the mechanisms of nucleation, growth and remodelling yield fibrils of tissue-specific diameter and length. Here we have developed a seeding system whereby collagen fibrils were isolated from avian embryonic tendon and added to purified collagen solution, in order to characterise fibril surface nucleation and growth mechanisms. Fragmentation of tendon in liquid nitrogen followed by Dounce homogenisation generated fibril length fragments. Most (>94%) of the fractured ends of fibrils, which show an abrupt square profile, were found to act as nucleation sites for further growth by molecular accretion. The mechanism of this nucleation and growth process was investigated by transmission electron microscopy, atomic force microscopy and scanning transmission electron microscopy mass mapping. Typically, a single growth spur occurred on the N-terminal end of seed fibrils whilst twin spurs frequently formed on the C-terminal end before merging into a single tip projection. The surface nucleation and growth process generated a smoothly tapered tip that achieved maximum diameter when the axial extension reached approximately 13 mum. Lateral growth also occurred along the entire length of all seed fibrils that contained tip projections. The data support a model of collagen fibril growth in which the broken ends of fibrils are nucleation sites for propagation in opposite axial directions. The observed fibril growth behaviour has direct relevance to tendon matrix remodelling and repair processes that might involve rupture of collagen fibrils.
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Starborg T, Lu Y, Kadler KE, Holmes DF. Electron microscopy of collagen fibril structure in vitro and in vivo including three-dimensional reconstruction. Methods Cell Biol 2008; 88:319-45. [PMID: 18617041 DOI: 10.1016/s0091-679x(08)00417-2] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Tissue development in multicellular animals relies on the ability of cells to synthesize an extracellular matrix (ECM) containing spatially organized collagen fibrils, whose length greatly exceeds that of individual cells. The importance of the correct regulation of fibril deposition is exemplified in diseases such as osteogenesis imperfecta (caused by mutations in collagen genes), fibrosis (caused by ectopic accumulation of collagen), and cardiovascular disease (which involves cells and macromolecules binding to collagen in the vessel wall). Much is known about the molecular biology of collagens but less is known about collagen fibril structure and how the fibrils are formed (fibrillogenesis). This is explained in part by the fact that the fibrils are noncrystalline, extensively cross-linked, and very large, which makes them refractory to study by conventional biochemical and high-resolution structure-determination techniques. Electron microscopy has become established as the method of choice for studying collagen fibril structure and assembly. This article describes the electron microscopic methods most often used in studying collagen fibril assembly and structure.
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Affiliation(s)
- Tobias Starborg
- Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, United Kingdom
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18
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Stress transfer in collagen fibrils reinforcing connective tissues: effects of collagen fibril slenderness and relative stiffness. J Theor Biol 2006; 245:305-11. [PMID: 17123548 DOI: 10.1016/j.jtbi.2006.10.008] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2006] [Revised: 09/25/2006] [Accepted: 10/10/2006] [Indexed: 11/17/2022]
Abstract
Unlike engineering fibre composite materials which comprise of fibres that are uniform cylindrical in shape, collagen fibrils reinforcing the proteoglycan-rich (PG) gel in the extra-cellular matrices (ECMs) of connective tissues are taper-ended (paraboloidal in shape). In an earlier paper we have discussed how taper of a fibril leads to an axial stress up-take which differs from that of a uniform cylindrical fibre and implications for fibril fracture. The present paper focuses on the influence of fibre aspect ratio, q (slenderness), and Young's modulus (stiffness), relative to that of the gel phase, E(R), on the magnitude of the axial tensile stresses generated within a fibril and wider implications on failure at tissue level. Fibre composite models were evaluated using finite element (FE) and mathematical analyses. When the applied force is low, there is elastic stress transfer between the PG gel and a fibril. FE modelling shows that the stress in a fibril increases with E(R) and q. At higher applied forces, there is plastic stress transfer. Mathematical modelling predicts that the stress in a fibril increases linearly with q. For small q values, fibrils may be regarded as fillers with little ability to provide tensile reinforcement. Large q values lead to high stress in a fibril. Such high stresses are beneficial provided they do not exceed the fracture stress of collagen. Modulus difference regulates the strain energy release density, u, for interfacial rupture; large E(R) not only leads to high stress in a fibril but also insures against interfacial rupture by raising the value of u.
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Goh K, Meakin J, Aspden R, Hukins D. Influence of fibril taper on the function of collagen to reinforce extracellular matrix. Proc Biol Sci 2006; 272:1979-83. [PMID: 16191606 PMCID: PMC1559877 DOI: 10.1098/rspb.2005.3173] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Collagen fibrils provide tensile reinforcement for extracellular matrix. In at least some tissues, the fibrils have a paraboloidal taper at their ends. The purpose of this paper is to determine the implications of this taper for the function of collagen fibrils. When a tissue is subjected to low mechanical forces, stress will be transferred to the fibrils elastically. This process was modelled using finite element analysis because there is no analytical theory for elastic stress transfer to a non-cylindrical fibril. When the tissue is subjected to higher mechanical forces, stress will be transferred plastically. This process was modelled analytically. For both elastic and plastic stress transfer, a paraboloidal taper leads to a more uniform distribution of axial tensile stress along the fibril than would be generated if it were cylindrical. The tapered fibril requires half the volume of collagen than a cylindrical fibril of the same length and the stress is shared more evenly along its length. It is also less likely to fracture than a cylindrical fibril of the same length in a tissue subjected to the same mechanical force.
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Affiliation(s)
- K.L Goh
- School of Optometry & Vision Sciences, Cardiff UniversityRedwood Building, King Edward VII Avenue, Cardiff CF10 3NB, UK
| | - J.R Meakin
- Department of Biomedical Physics & Bioengineering, University of AberdeenForesterhill, Aberdeen AB25 2ZD, UK
| | - R.M Aspden
- Department of Orthopaedic Surgery, University of AberdeenForesterhill, Aberdeen AB25 2ZD, UK
| | - D.W.L Hukins
- School of Engineering, Mechanical Engineering, University of BirminghamEdgbaston, Birmingham B15 2TT, UK
- Author for correspondence ()
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Gudo M. An evolutionary scenario for the origin of pentaradial echinoderms-implications from the hydraulic principles of form determination. Acta Biotheor 2005; 53:191-216. [PMID: 16329008 DOI: 10.1007/s10441-005-2528-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2004] [Revised: 12/04/2004] [Accepted: 01/19/2005] [Indexed: 10/25/2022]
Abstract
The early evolutionary history of echinoderms was reconstructed on the basis of structural-functional considerations and application of the quasi-engineering approach of 'Konstruktions-Morphologie'. According to the presented evolutionary scenario, a bilaterally symmetrical ancestor, such as an enteropneust-like organism, became gradually modified into a pentaradial echinoderm by passing through an intermediate pterobranch-like stage. The arms of a pentaradial echinoderm are identified as hydraulic outgrowths from the central coelomic cavity of the bilateral ancestor which developed due to a shortening of the body in length but widening in the diameter. The resulting pentaradial symmetry is a consequence of mechanical laws that dictate minimal contact surface areas among hydraulic pneumatic entities. These developed in the coelomic cavity (metacoel) in the bilaterally symmetrical ancestor, when from the already U-shaped mesentery with the intestinal tract two additional U-shaped bows developed directly or subsequently. During the subsequent development tensile chords of the mesentery 'sewed' the gut with the body wall first in three and secondly in five 'seams'. During the direct development five 'seams' between tensile chords and body wall developed straightly. These internal tensile chords subdivide the body coelom into five hydraulic subsystems ('pneus'), which eventually arrange in a pentaradial pattern. The body could then enlarge only between the tensile chords, which means that five hydraulic bulges developed. These bulges initially supported the tentacles and finally each of them enclosed the tentacle until only the feather-like appendages of the tentacles projected over the surface. The tentacles with their feathers were transformed into the ambulacral system, and the bulges become the arms. These morphological transformations were accompanied and partly determined by specific histological modifications, such as the development of mutable connective tissues and skeletal elements that fused to ossicles and provided shape stabilization in form of a calcareous skeleton in the body wall. The organism resulted was an ancestral echinoderm ('Ur-Echinoderm') with an enlarged metacoel, stabilized by hydraulic pressure working against a capsule of mutable connective tissue, skeletal elements and longitudinal muscles. In regard to these reconstructions, the body structure of echinoderms can be understood as a hydraulic skeletal capsule.
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Affiliation(s)
- Michael Gudo
- Morphisto-Evolutions-forschung und Anwendung GmbH, Senckenberganlage 25, 60325, Frankfurt am Main, Germany.
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Wilkie IC. Mutable collagenous tissue: overview and biotechnological perspective. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2005; 39:221-50. [PMID: 17152700 DOI: 10.1007/3-540-27683-1_10] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
The mutable collagenous tissue (MCT) of echinoderms can undergo extreme changes in passive mechanical properties within a timescale of less than 1 s to a few minutes, involving a mechanism that is under direct neural control and coordinated with the activities of muscles. MCT occurs at a variety of anatomical locations in all echinoderm classes, is involved in every investigated echinoderm autotomy mechanism, and provides a mechanism for the energy-sparing maintenance of posture. It is therefore crucially important for the biology of extant echinoderms. This chapter summarises current knowledge of the physiology and organisation of MCT, with particular attention being given to its molecular organisation and the molecular mechanism of mutability. The biotechnological potential of MCT is discussed. It is argued that MCT could be a source of, or inspiration for, (1) new pharmacological agents and strategies designed to manipulate therapeutically connective tissue mechanical properties and (2) new composite materials with biomedical applications.
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Affiliation(s)
- I C Wilkie
- Department of Biological and Biomedical Sciences, Glasgow Caledonian University, 70 Cowcaddens Road, Glasgow G4 OBA, Scotland, UK.
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22
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Tettamanti G, Grimaldi A, Congiu T, Perletti G, Raspanti M, Valvassori R, de Eguileor M. Collagen reorganization in leech wound healing. Biol Cell 2005; 97:557-68. [PMID: 15898949 DOI: 10.1042/bc20040085] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
BACKGROUND INFORMATION Leeches respond to surgical lesions with the same sequence of events as that described for wound healing in vertebrates, where collagen is important for the development of tensions in healing wounds, functioning as an extracellular scaffold for accurate regeneration of the structures disrupted by surgical or traumatic actions. RESULTS In surgically lesioned leeches, newly synthesized collagen is arranged in hierarchical structures. Fibrils can be packed and shaped to form cords or tubular structures, thus acting as an extracellular scaffold that directs and organizes the outgrowth of new vessels and the migration of immune cells towards lesioned tissues. In these animals, the general architecture of collagen fibrils, generated during tissue regeneration, shows similarities to both the structural pattern of collagen bundles and assembly processes observed in several vertebrate systems (fish scales, amphibian skin and human cornea). CONCLUSIONS The production of extracellular matrix during wound healing in leeches is a surprising example of conservation of an extremely close relationship between the structure and function of molecular structures. It could be hypothesized that collagen structures, characterized not only by a striking structural complexity, but also by multifunctional purposes, are anatomical systems highly conserved throughout evolution.
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Affiliation(s)
- Gianluca Tettamanti
- Department of Structural and Functional Biology, University of Insubria, Via J.H. Dunant 3, 21100 Varese, Italy
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Kadler K. Matrix loading: assembly of extracellular matrix collagen fibrils during embryogenesis. ACTA ACUST UNITED AC 2004; 72:1-11. [PMID: 15054900 DOI: 10.1002/bdrc.20002] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Nothing in biology stimulates the imagination like the development of a single fertilized egg into a newborn child. Consequently, a major focus of biomedical research is aimed at understanding cell differentiation, proliferation, and specialization during child health and human development. However, the fact that the increase in size and shape of the growing embryo has as much to do with the extracellular matrix (ECM) as with the cells themselves, is largely overlooked. Cells in developing tissues are surrounded by a fiber-composite ECM that transmits mechanical stimuli, maintains the shape of developing tissues, and functions as a scaffold for cell migration and attachment. The major structural element of the ECM is the collagen fibril. The fibrils, which are indeterminate in length, are arranged in different tissues in exquisite supramolecular architectures, including parallel bundles, orthogonal lamellae, and concentric weaves. This article reviews our current understanding of the synthesis and assembly of collagen fibrils, and discusses challenging questions about how cells assemble an organized ECM during embryogenesis.
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Affiliation(s)
- Karl Kadler
- Wellcome Trust Centre for Cell-Matrix Research, School of Biological Sciences, University of Manchester, Manchester, United Kingdom.
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Abstract
Changes in supramolecular assembly of matrix, specifically collagen, have important functional consequences, especially for tissues requiring high mechanical strength. Thus modulation of collagen assembly could be used as a therapeutic intervention or to control the development of tissue-engineered constructs containing natural matrix. Quantitative methods that monitor such effects currently are lacking. Using live cultured cells, we developed a convenient way either to visualize by fluorescence microscopy or to measure directly, using a high throughput fluorescence assay, the supramolecular assembly of FITC-labeled collagen monomers. The wide applicability of this assay was confirmed by testing the assay using two major collagen sources, rat tail and bovine skin, and vascular smooth muscle cells from two different origins, mouse aorta and human saphenous vein. We further determined that treatments that interfere with the function of the cytoskeleton modulate collagen assembly. Use of positive and negative regulators of lysyl-oxidase indicated that while the assay does not require active production of endogenous collagen, it can be used to monitor the incorporation of such de novo synthesized collagen into labeled fibrils. Thus we have designed a novel quantitative assay that can monitor assembly of exogenous and endogenous collagen by live cells and reveal the effects of various interventions upon this process.
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Affiliation(s)
- Chad Johnson
- Division of Cardiology, Emory University School of Medicine, 1639 Pierce Drive, Atlanta, Georgia 30322, USA
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Trotter JA. Structure-function considerations of muscle-tendon junctions. Comp Biochem Physiol A Mol Integr Physiol 2002; 133:1127-33. [PMID: 12485696 DOI: 10.1016/s1095-6433(02)00213-1] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Skeletal muscle cells transmit force across the cell membrane to the extracellular matrix and ultimately to tendons. Force transmission may occur both along the lateral surfaces of muscle fibers and at their ends. Forces within muscles may follow the path of greatest resistance. Sites of force transmission are morphologically and compositionally specialized for this function. They are also specialized to provide stress-information that feeds into the synthetic programs of the muscle cell. A detailed analysis of the structures and functions of muscle-tendon junctions is essential to a comprehensive understanding of the way in which muscles and their connective tissues are controlled to move joints and to respond to mechanical stresses.
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Affiliation(s)
- John A Trotter
- Department of Cell Biology and Physiology, University of New Mexico School of Medicine, Albuquerque, NM 87131, USA.
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Kadler KE, Holmes DF, Graham H, Starborg T. Tip-mediated fusion involving unipolar collagen fibrils accounts for rapid fibril elongation, the occurrence of fibrillar branched networks in skin and the paucity of collagen fibril ends in vertebrates. Matrix Biol 2000; 19:359-65. [PMID: 10963997 DOI: 10.1016/s0945-053x(00)00082-2] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Collagen fibrils are the principal source of mechanical strength of connective tissues such as tendon, skin, cornea, cartilage and bone. The ability of these tissues to withstand tensile forces is directly attributable to the length and diameter of the fibrils, and to interactions between individual fibrils. Although electron microscopy studies have provided information on fibril diameters, little is known about the length of fibrils in tissue and how fibrils interact with each other. The question of fibril length has been difficult to address because fibril ends are rarely observed in cross-sections of tissue. The paucity of fibril ends, or tips, has led to controversy about how long individual fibrils might be and how the fibrils grow in length and diameter. This review describes recent discoveries that are relevant to these questions. We now know that vertebrate collagen fibrils are synthesised as short (1-3 microm) early fibrils that fuse end-to-end in young tissues to generate very long fibrils. The diameter of the final fibril is determined by the diameter of the collagen early fibrils. During a late stage of tissue assembly fibril tips fuse to fibril shafts to generate branched networks. Of direct relevance to fibril fusion is the fact that collagen fibrils can be unipolar or bipolar, depending on the orientation of collagen molecules in the fibril. Fusion relies on: (1) specific molecular interactions at the carboxyl terminal ends of unipolar collagen fibrils; and (2) the insulator function of small proteoglycans to shield the surfaces of fibrils from inappropriate fusion reactions. The fusion of tips to shafts to produce branched networks of collagen fibrils is an elegant mechanism to increase the mechanical strength of tissues and provides an explanation for the paucity of fibril tips in older tissue.
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Affiliation(s)
- K E Kadler
- Wellcome Trust Centre for Cell-Matrix Research, School of Biological Sciences, University of Manchester, Stopford Building 2.205, Oxford Road, M13 9PT, Manchester, UK.
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