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Schoenenberger MS, Halfter W, Ferrand A, Halfter K, Tzankov A, Scholl HPN, Henrich PB, Monnier CA. The biophysical and compositional properties of human basement membranes. FEBS J 2024; 291:477-488. [PMID: 37984833 DOI: 10.1111/febs.17007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Revised: 10/14/2023] [Accepted: 11/16/2023] [Indexed: 11/22/2023]
Abstract
Basement membranes are among the most widespread, non-cellular functional materials in metazoan organisms. Despite this ubiquity, the links between their compositional and biophysical properties are often difficult to establish due to their thin and delicate nature. In this article, we examine these features on a molecular level by combining results from proteomics, elastic, and nanomechanical analyses across a selection of human basement membranes. Comparing results between these different membranes connects certain compositional attributes to distinct nanomechanical signatures and further demonstrates to what extent water defines these properties. In all, these data underline BMs as stiff yet highly elastic connective tissue layers and highlight how the interplay between composition, mechanics and hydration yields such exceptionally adaptable materials.
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Affiliation(s)
| | - Willi Halfter
- Department of Ophthalmology, University of Basel, Switzerland
| | - Alexia Ferrand
- Imaging Core Facility, Biozentrum of the University of Basel, Switzerland
| | - Kathrin Halfter
- Munich Cancer Registry, Institute of Medical Informatics, Biometry and Epidemiology, Maximilian University Munich, Germany
| | - Alexandar Tzankov
- Histopathology and Autopsy, Institute of Medical Genetics and Pathology, University Hospital and University of Basel, Switzerland
| | - Hendrik P N Scholl
- Department of Ophthalmology, University of Basel, Switzerland
- Institute of Molecular and Clinical Ophthalmology Basel (IOB), Switzerland
| | - Paul Bernhard Henrich
- Department of Ophthalmology, University of Basel, Switzerland
- Università della Svizzera Italiana, Lugano, Switzerland
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Lansdell TA, Chambers LC, Dorrance AM. Endothelial Cells and the Cerebral Circulation. Compr Physiol 2022; 12:3449-3508. [PMID: 35766836 DOI: 10.1002/cphy.c210015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Endothelial cells form the innermost layer of all blood vessels and are the only vascular component that remains throughout all vascular segments. The cerebral vasculature has several unique properties not found in the peripheral circulation; this requires that the cerebral endothelium be considered as a unique entity. Cerebral endothelial cells perform several functions vital for brain health. The cerebral vasculature is responsible for protecting the brain from external threats carried in the blood. The endothelial cells are central to this requirement as they form the basis of the blood-brain barrier. The endothelium also regulates fibrinolysis, thrombosis, platelet activation, vascular permeability, metabolism, catabolism, inflammation, and white cell trafficking. Endothelial cells regulate the changes in vascular structure caused by angiogenesis and artery remodeling. Further, the endothelium contributes to vascular tone, allowing proper perfusion of the brain which has high energy demands and no energy stores. In this article, we discuss the basic anatomy and physiology of the cerebral endothelium. Where appropriate, we discuss the detrimental effects of high blood pressure on the cerebral endothelium and the contribution of cerebrovascular disease endothelial dysfunction and dementia. © 2022 American Physiological Society. Compr Physiol 12:3449-3508, 2022.
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Affiliation(s)
- Theresa A Lansdell
- Department of Pharmacology and Toxicology, College of Osteopathic Medicine, Michigan State University, East Lansing, MI, 48824, USA
| | - Laura C Chambers
- Department of Pharmacology and Toxicology, College of Osteopathic Medicine, Michigan State University, East Lansing, MI, 48824, USA
| | - Anne M Dorrance
- Department of Pharmacology and Toxicology, College of Osteopathic Medicine, Michigan State University, East Lansing, MI, 48824, USA
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Abstract
Located at the interface of the circulation system and the CNS, the basement membrane (BM) is well positioned to regulate blood-brain barrier (BBB) integrity. Given the important roles of BBB in the development and progression of various neurological disorders, the BM has been hypothesized to contribute to the pathogenesis of these diseases. After stroke, a cerebrovascular disease caused by rupture (hemorrhagic) or occlusion (ischemic) of cerebral blood vessels, the BM undergoes constant remodeling to modulate disease progression. Although an association between BM dissolution and stroke is observed, how each individual BM component changes after stroke and how these components contribute to stroke pathogenesis are mostly unclear. In this review, I first briefly introduce the composition of the BM in the brain. Next, the functions of the BM and its major components in BBB maintenance under homeostatic conditions are summarized. Furthermore, the roles of the BM and its major components in the pathogenesis of hemorrhagic and ischemic stroke are discussed. Last, unsolved questions and potential future directions are described. This review aims to provide a comprehensive reference for future studies, stimulate the formation of new ideas, and promote the generation of new genetic tools in the field of BM/stroke research.
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Affiliation(s)
- Yao Yao
- Yao Yao, Department of Pharmaceutical and Biomedical Sciences, University of Georgia, 340 Pharmacy South Building, 250 West Green Street, Athens, GA 30602, USA.
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Xu L, Nirwane A, Yao Y. Basement membrane and blood-brain barrier. Stroke Vasc Neurol 2018; 4:78-82. [PMID: 31338215 PMCID: PMC6613871 DOI: 10.1136/svn-2018-000198] [Citation(s) in RCA: 158] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2018] [Accepted: 11/16/2018] [Indexed: 12/24/2022] Open
Abstract
The blood–brain barrier (BBB) is a highly complex and dynamic structure, mainly composed of brain microvascular endothelial cells, pericytes, astrocytes and the basement membrane (BM). The vast majority of BBB research focuses on its cellular constituents. Its non-cellular component, the BM, on the other hand, is largely understudied due to its intrinsic complexity and the lack of research tools. In this review, we focus on the role of the BM in BBB integrity. We first briefly introduce the biochemical composition and structure of the BM. Next, the biological functions of major components of the BM in BBB formation and maintenance are discussed. Our goal is to provide a concise overview on how the BM contributes to BBB integrity.
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Affiliation(s)
- Lingling Xu
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, Georgia, USA
| | - Abhijit Nirwane
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, Georgia, USA
| | - Yao Yao
- Department of Pharmaceutical and Biomedical Sciences, University of Georgia, Athens, Georgia, USA
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Effect of Supercoiling on the Mechanical and Permeability Properties of Model Collagen IV Networks. Ann Biomed Eng 2014; 43:1695-705. [PMID: 25408357 DOI: 10.1007/s10439-014-1187-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2014] [Accepted: 11/11/2014] [Indexed: 11/27/2022]
Abstract
Collagen IV networks in the glomerular basement membrane (GBM) are essential for the maintenance and regulation of blood filtration in the kidneys. The GBM contains two different types of collagen IV networks: [α1(IV)]2α2(IV) and α3(IV)α4(IV)α5(IV), the latter of which has a higher number of supercoils (two or more collagens coiling around each other). To investigate the effects of supercoiling on the mechanical and permeability properties of collagen IV networks, we generated model collagen IV networks in the GBM and reconnected them to create different levels of supercoiling. We found that supercoiling greatly increases the stiffness of collagen IV networks but only minimally decreases the permeability. Also, doubling the amount of supercoils in a network had a bigger effect than doubling the stiffness of the supercoils. Our results suggest that the formation of supercoils is a specialized mechanism by the GBM that provides with a network stiff and strong enough to withstand the high hydrostatic pressures of filtration, yet porous enough that filtration is not hindered. Clinically, understanding the effects of supercoiling gives us insight into the mechanisms of GBM failure in some disease states where the normal collagen IV structure is disrupted.
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Li Y, Zhu Y, Yu H, Chen L, Liu Y. Topographic characterization and protein quantification of esophageal basement membrane for scaffold design reference in tissue engineering. J Biomed Mater Res B Appl Biomater 2011; 100:265-73. [DOI: 10.1002/jbm.b.31949] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2011] [Revised: 06/05/2011] [Accepted: 07/05/2011] [Indexed: 11/06/2022]
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Powell TA, Amini R, Oltean A, Barnett VA, Dorfman KD, Segal Y, Barocas VH. Elasticity of the porcine lens capsule as measured by osmotic swelling. J Biomech Eng 2011; 132:091008. [PMID: 20815642 DOI: 10.1115/1.4002024] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
As an alternative to purely mechanical methods, optical tracking of passive osmotic swelling was used to assess mechanical properties of the porcine lens capsule. A simple model was developed accounting for the permeability of the lens fiber cells and capsule to water, the concentration of fixed charges in the fiber cells, and the capsule's resistance to the swelling of fiber cells. Fitting the model solution to experimental data provided an estimate of the elastic modulus of the lens capsule under the assumption of linear isotropic elasticity. The calculated elastic modulus at a fixed charge density of 20 mol m(-3) was 2.0+/-0.5 MPa (mean+/-95% confidence interval; n=15) for 0.1% saline solution, 0.64+/-0.3 MPa (n=10) for 0.2% saline solution, and 0.28+/-0.5 MPa (n=6) for 0.5% saline solution. These values are comparable to previously reported moduli of elasticity for the porcine lens capsule at small strains (<10%), and the slight increase with hypotonicity is consistent with the nonlinear mechanical behavior of the lens capsule. Although limited by being a single measurement on a heterogeneous tissue, osmotic swelling provides a quantitative assessment of the stiffness of the lens capsule without requiring dissection or manipulation of the lens. Thus, the new method could be useful for small animal models.
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Affiliation(s)
- Tracy A Powell
- Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, USA
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Liliensiek SJ, Nealey P, Murphy CJ. Characterization of endothelial basement membrane nanotopography in rhesus macaque as a guide for vessel tissue engineering. Tissue Eng Part A 2009; 15:2643-51. [PMID: 19207042 DOI: 10.1089/ten.tea.2008.0284] [Citation(s) in RCA: 109] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Basement membranes have many features that greatly influence vascular endothelial cell function, including a complex three-dimensional topography. As a first step in the design and development of vascular prosthetics, we undertook a thorough characterization of the topographic features of endothelial vascular basement membranes utilizing transmission electron microscopy and scanning electron microscopy. Specifically, we quantitatively analyzed the topographic features present in the aorta, carotid, saphenous, and inferior vena cava vessels in the rhesus macaque. Our results indicate that vascular basement membranes are composed of a complex meshwork consisting of pores and fibers in the submicron (100-1000 nm) and nanoscale (1-100 nm) range, consistent with what has previously been reported in basement membranes of other tissues. We found significant differences (p<0.05) in basement membrane thickness and pore and fiber diameter depending on the location and physical properties of the vessel. These results have relevance to our fundamental understanding of vascular endothelial cell-matrix interactions in health and disease, evolving strategies in cell and tissue engineering and the design of cardiovascular prosthetic devices.
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Affiliation(s)
- Sara J Liliensiek
- Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA. sjlilien@.wisc.edu
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Suprastructures of extracellular matrices: paradigms of functions controlled by aggregates rather than molecules. Cell Tissue Res 2009; 339:7-18. [DOI: 10.1007/s00441-009-0864-0] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2009] [Accepted: 08/11/2009] [Indexed: 01/17/2023]
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McKee KK, Harrison D, Capizzi S, Yurchenco PD. Role of Laminin Terminal Globular Domains in Basement Membrane Assembly. J Biol Chem 2007; 282:21437-47. [PMID: 17517882 DOI: 10.1074/jbc.m702963200] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Laminins contribute to basement membrane assembly through interactions of their N- and C-terminal globular domains. To further analyze this process, recombinant laminin-111 heterotrimers with deletions and point mutations were generated by recombinant expression and evaluated for their ability to self-assemble, interact with nidogen-1 and type IV collagen, and form extracellular matrices on cultured Schwann cells by immunofluorescence and electron microscopy. Wild-type laminin and laminin without LG domains polymerized in contrast to laminins with deleted alpha1-, beta1-, or gamma1-LN domains or with duplicated beta1- or alpha1-LN domains. Laminins with a full complement of LN and LG domains accumulated on cell surfaces substantially above those lacking either LN or LG domains and formed a lamina densa. Accumulation of type IV collagen onto the cell surface was found to require laminin with separate contributions arising from the presence of laminin LN domains, nidogen-1, and the nidogen-binding site in laminin. Collectively, the data support the hypothesis that basement membrane assembly depends on laminin self-assembly through formation of alpha-, beta-, and gamma-LN domain complexes and LG-mediated cell surface anchorage. Furthermore, type IV collagen recruitment into the laminin extracellular matrices appears to be mediated through a nidogen bridge with a lesser contribution arising from a direct interaction with laminin.
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Affiliation(s)
- Karen K McKee
- Department of Pathology and Laboratory Medicine, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA
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12
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Abstract
In recent years, the basement membrane (BM)--a specialized form of extracellular matrix (ECM)--has been recognized as an important regulator of cell behaviour, rather than just a structural feature of tissues. The BM mediates tissue compartmentalization and sends signals to epithelial cells about the external microenvironment. The BM is also an important structural and functional component of blood vessels, constituting an extracellular microenvironment sensor for endothelial cells and pericytes. Vascular BM components have recently been found to be involved in the regulation of tumour angiogenesis, making them attractive candidate targets for potential cancer therapies.
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Affiliation(s)
- Raghu Kalluri
- Center for Matrix Biology, Department of Medicine, Dana 514, Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Avenue, Boston, Massachusetts 02215, USA.
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Teixeira AI, Abrams GA, Bertics PJ, Murphy CJ, Nealey PF. Epithelial contact guidance on well-defined micro- and nanostructured substrates. J Cell Sci 2003; 116:1881-92. [PMID: 12692189 PMCID: PMC1885893 DOI: 10.1242/jcs.00383] [Citation(s) in RCA: 632] [Impact Index Per Article: 30.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human corneal basement membrane has a rich felt-like surface topography with feature dimensions between 20 nm and 200 nm. On the basis of these findings, we designed lithographically defined substrates to investigate whether nanotopography is a relevant stimulus for human corneal epithelial cells. We found that cells elongated and aligned along patterns of grooves and ridges with feature dimensions as small as 70 nm, whereas on smooth substrates, cells were mostly round. The percentage of aligned cells was constant on substrate tomographies with lateral dimensions ranging from the nano- to the micronscale, and increased with groove depth. The presence of serum in the culture medium resulted in a larger percentage of cells aligning along the topographic patterns than when no serum was added to the basal medium. When present, actin microfilaments and focal adhesions were aligned along the substrate topographies. The width of the focal adhesions was determined by the width of the ridges in the underlying substrate. This work documents that biologic length-scale topographic features that model features encountered in the native basement membrane can profoundly affect epithelial cell behavior.
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Affiliation(s)
- Ana I Teixeira
- Department of Chemical Engineering, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA
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Abstract
The laminins are a family of glycoproteins that provide an integral part of the structural scaffolding of basement membranes in almost every animal tissue. Each laminin is a heterotrimer assembled from alpha, beta, and gamma chain subunits, secreted and incorporated into cell-associated extracellular matrices. The laminins can self-assemble, bind to other matrix macromolecules, and have unique and shared cell interactions mediated by integrins, dystroglycan, and other receptors. Through these interactions, laminins critically contribute to cell differentiation, cell shape and movement, maintenance of tissue phenotypes, and promotion of tissue survival. Recent advances in the characterization of genetic disruptions in humans, mice, nematodes and flies have revealed developmental roles for the different laminin subunits in diverse cell types, affecting differentiation from blastocyst formation to the post-natal period. These genetic defects have challenged some of the previous concepts about basement membranes and have shed new light on the diversity and complexity of laminin functions as well as established the molecular basis of several human diseases.
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Affiliation(s)
- H Colognato
- Department of Pathology & Laboratory Medicine, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
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Fujisato T, Tomihata K, Tabata Y, Iwamoto Y, Burczak K, Ikada Y. Cross-linking of amniotic membranes. JOURNAL OF BIOMATERIALS SCIENCE. POLYMER EDITION 2000; 10:1171-81. [PMID: 10606034 DOI: 10.1163/156856299x00829] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Human amniotic membrane was cross-linked with chemical and radiation methods to investigate the effect of cross-linking on its physicochemical and biodegradation properties. Radiation cross-linking was performed with gamma-ray and electron beam while chemical cross-linking was with glutaraldehyde (GA). Both gamma-ray and electron beam irradiation decreased the tensile strength and elongation at break of the amniotic membrane with an increase in the irradiation dose, whereas GA cross-linking had no effect on the tensile properties. This is probably due to the scission of collagen chains through irradiation. No significant change was observed on the water content of cross-linked amniotic membranes for any of the crosslinking methods and in marked contrast with cross-linking of a gelatin membrane. A permeation study revealed that protein permeation through the amniotic membrane was not influenced by the GA concentration at cross-linking. These findings are ascribed to the structure characteristic of the amniotic membrane. The membrane is composed of a fibrous mesh structure from an assemblage of collagen fibers. It is possible that cross-linking takes place in the interior of the fiber assembly without impairing the mesh structure, resulting in no change of the water content and protein permeability. In vitro degradation of cross-linked amniotic membranes revealed that radiation cross-linking appeared to be much less effective than GA cross-linking in retarding the degradation, probably because of low cross-linking densities. GA-cross-linked amniotic membranes were degraded more slowly as the GA concentration at cross-linking increased. When the GA-cross-linked amniotic membrane was subcutaneously implanted in the rat, the tissue response was mild, similar to that of the non-cross-linked native membrane.
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Affiliation(s)
- T Fujisato
- Institute for Frontier Medical Sciences, Kyoto University, Japan
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Abrams GA, Schaus SS, Goodman SL, Nealey PF, Murphy CJ. Nanoscale topography of the corneal epithelial basement membrane and Descemet's membrane of the human. Cornea 2000; 19:57-64. [PMID: 10632010 DOI: 10.1097/00003226-200001000-00012] [Citation(s) in RCA: 143] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE Quantitatively define and compare the nanoscale topography of the corneal epithelial basement membrane (anterior basement membrane) and Descemet's membrane (posterior basement membrane) of the human. METHODS Human corneas not suitable for transplantation were obtained from the Wisconsin Eye Bank. The corneas were placed in 2.5 mM EDTA for 2.5 h or 30 min. for removal of the epithelium or endothelium, respectively. After removal of the overlying cells, specimens were fixed in 2% glutaraldehyde and either examined in this state by atomic force microscopy only or dehydrated through an ethanol series and prepared for transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). RESULTS The subepithelial and subendothelial basement membrane surfaces have a similar appearance that consists of an interwoven meshwork of fibers and pores. Topographic feature sizes were found to be in the nanometer size range with the epithelial basement membrane features larger and less densely packed than Descemet's membrane features. The topographic features are fractile in nature and increase surface area for cell contact. CONCLUSION With the use of the TEM, SEM, and AFM, a detailed description of the surface topography of corneal epithelial basement membrane and Descemet's membrane of the human cornea are provided. The significance of differences in corneal basement membrane topography may reflect differences in function of the overlying cells or may be related to differences in cell migration and turnover patterns between the epithelium and endothelium.
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Affiliation(s)
- G A Abrams
- Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin at Madison, 53706, USA
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Kocsis K, Hyttinen M, Helminen HJ, Aydelotte MB, Módis L. Combination of digital image analysis and polarization microscopy: theoretical considerations and experimental data. Microsc Res Tech 1998; 43:511-7. [PMID: 9880165 DOI: 10.1002/(sici)1097-0029(19981215)43:6<511::aid-jemt4>3.0.co;2-a] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The potentialities of polarization microscopy has been greatly increased by using specific stains for selective enhancement of the optical anisotropy of a macromolecular constituent of cells and tissues. Such stainings have proved to be especially useful in exploring the spatial orientation pattern of the extracellular matrix components. The retardation value, which characterizes quantitatively the degree of submicroscopic orientation, can be measured traditionally with a compensator plate. This technique, however, is time-consuming and greatly dependent on visual judgment. Several attempts have been made to combine digital image analysis and polarization microscopy to improve the measuring technique in unstained structures. In this paper, we summarize theoretical considerations and experimental data to show the advantages and limitations of this methodological approach when using stained and birefringent specimens. The technique we are suggesting is the measurement of the light intensity using a 12 bit cCCD camera attached to a polarized light microscope and digital image analysis system. The theoretical basis is given by the Fresnel equation describing the relationship between light intensity and retardation value. According to this, there is a sin2 function between the light intensity and the retardation value. The same relationship of these two parameters was observed in our experiments on the birefringent extracellular matrix around chondrocytes grown in agarose gel and interterritorial and territorial matrix of canine articular cartilage stained with picrosirius red. Our results suggest that the retardation values can be calculated directly from the light intensity values if the retardation value is lower than lambda/2.
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Affiliation(s)
- K Kocsis
- Department of Anatomy, Histology and Embryology, University Medical School, Debrecen, Hungary
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Ruben GC. Vertical Pt-C replication for TEM, a revolution in imaging non-periodic macromolecules, biological gels and low-density polymer networks. Micron 1998; 29:359-96. [PMID: 9842722 DOI: 10.1016/s0968-4328(98)00003-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Vertical replication for TEM is ideal for studying non-periodic specimens from 0.7 to 3 nm, a resolution mid-range difficult to attain by any other technique. This paper discusses the importance of vertical replication, its methods and hardware for high-resolution TEM. Evidence from diverse published research will demonstrate vertical replication's versatility in imaging the molecular level normally unattainable in freeze-dried polymers, polyethylene tribological wear on surfaces, low-density polymer networks or biological gels. Vertical platinum-carbon (Pt-C) replication minimizes the horizontal movement of Pt-C on a surface. Surface objects are symmetrically enlarged by a vertically deposited Pt-C film. To estimate real size in replicas, 16-25 particles or filaments need to be measured in calibrated transmission electron microscopy (TEM) images and reduced by a value less than the Pt-C film thickness measured with a quartz monitor. Continuous, vertically deposited Pt-C films are formed on mica at a deposition thickness of around 1.0 nm and on silver at a thickness of 0.4-0.5 nm. The distance between helical turns in poly(1-tetradecene sulfone) of 0.7 nm is the highest resolution achieved with vertical replication. Two polysulfones freeze-dried and vertically replicated on mica contained structures are predicted by indirect physical chemical methods to be present in solution. Polymer chains are fully Pt-C coated, with no uncoated gaps along chains. Some side-chains on the extended non-helical poly(1-tetradecene sulfone) are also detected. To estimate the real chain width, polymer chains measured in images are reduced by the Pt-C film thickness minus 0.5 nm. The polymer chain widths estimated from molecular models are in the same range of widths as those measured using the image size correction method. Also, it is possible to distinguish random coil proteins (chain width of around 0.5 nm) from an alpha-helix (chain diameter of about 1 nm) in vertically replicated samples on silver substrates. In the future, subnanometer resolutions below 0.7 nm should be possible. The resolution of vertical replication depends on the thickness of a continuous, amorphous Pt-C film. That thin, continuous 0.4-0.5 nm Pt-C films on silver substrates can be made suggests that a point-to-point resolution limit of around 0.28 nm in TEM may ultimately be approachable with replication.
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Affiliation(s)
- G C Ruben
- Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA.
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Ruben GC. Quantification of particle sizes with metal replication under standard freeze-etching conditions: a gold ball standard for calibrating shadow widths was used to measure freeze-etched globular proteins. Microsc Res Tech 1995; 32:312-29. [PMID: 8573781 DOI: 10.1002/jemt.1070320406] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The real size of platinum-carbon (Pt-C) replicated particles is not directly equivalent to either its metal-coated diameter or its shadow width. This paper describes two indirect methods, shadow widths and coated particle diameters, for determining a particle's actual size beneath a Pt-C replication film. Both produce equivalent measurements using the same standardized conditions: 2.3 nm Pt-C films deposited at a 45 degree angle on an approximately -100 degrees C surface in a 10(-6) torr vacuum. For the first method, gold balls nucleated in a partial pressure of helium and deposited on flat indirect carbon films (root mean square roughness of 0.8 nm) on 400 mesh grids were used as test particles for calibrating shadow widths as a function of particle size. The gold ball test specimens were replicated, and a distribution of Pt-C shadow widths orthogonal to the Pt-C deposition direction was measured and averaged for gold balls 1.5 +/- 0.25 nm, 2.0 +/- 0.25 nm, etc. The diameter of each gold ball was measured within the Pt-C film along with its shadow width because the Pt-C did not obscure or adhere well to the gold. The shadow width distributions for each gold size do not differ significantly from log normal. Two proteins, the lactose repressor and the mitochondrial ATPase, F1, were also used as replication test objects. Negative staining of both proteins was conducted to measure their average diameters. In the second method, a distribution of Pt-C-coated lac repressor diameters perpendicular to the shadow direction was measured. The Pt-C film thickness measured on the quartz crystal monitor was subtracted from the average metal-coated protein diameter to obtain the lac repressor's diameter. The Pt-C-coated particle diameter distributions also did not differ significantly from log normal. While doing this work it was discovered that outgassing the Pt-C electron gun greatly affected Pt-C film granularity: 19 sec produced a high contrast, granular Pt-C film, whereas 120 sec yielded a low contrast, less granular Pt-C film. Both gold balls and protein particles were subjected in separate experiments to either 19 or 120 sec of outgassing of the Pt-C gun prior to Pt-C replication. Outgassing had a profound effect on the average size of the Pt-C shadow widths on both gold and protein particles. The Pt-C gun outgassing procedure also determined the smallest replicated particle that could be resolved. The frequency of some smaller gold ball sizes detected after replication was reduced disproportionately with 19 sec vs. 120 sec outgassing. However, Pt-C gun outgassing did not affect the average measured diameter of the Pt-C-coated protein particles. The "geometric assumption" that each metal-coated particle creates a shadow width the same size as the metal-coated particle diameter was tested using a globular protein. Pt-C replication of protein particles at a 45 degree and 20 degree angle could not confirm the geometric assumption because an average shadow width was always significantly larger than its average Pt-C-coated particle diameter. A model for how the large shadow widths are formed is presented. Gold balls were also replicated at a 45 degree angle with current high resolution conditions at a substrate temperature of -185 degrees C, and the results of these replicas were compared to the results reported here at approximately -100 degrees C.
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Affiliation(s)
- G C Ruben
- Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA
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21
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Affiliation(s)
- P D Yurchenco
- Department of Pathology, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA
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