Structural correlation between collagen VI microfibrils and collagen VI banded aggregates

Lift-out cryo-FIBSEM and cryo-ET reveal the ultrastructural landscape of extracellular matrix

The extracellular matrix (ECM) serves as a scaffold for cells and plays an essential role in regulating numerous cellular processes, including cell migration and proliferation. Due to limitations in specimen preparation for conventional room-temperature electron microscopy, we lack structural knowledge on how ECM components are secreted, remodeled, and interact with surrounding cells. We have developed a 3D-ECM platform compatible with sample thinning by cryo-focused ion beam milling, the lift-out extraction procedure, and cryo-electron tomography. Our workflow implements cell-derived matrices (CDMs) grown on EM grids, resulting in a versatile tool closely mimicking ECM environments. This allows us to visualize ECM for the first time in its hydrated, native context. Our data reveal an intricate network of extracellular fibers, their positioning relative to matrix-secreting cells, and previously unresolved structural entities. Our workflow and results add to the structural atlas of the ECM, providing novel insights into its secretion and assembly.

Dermal Fibroblasts as the Main Target for Skin Anti-Age Correction Using a Combination of Regenerative Medicine Methods

This article includes the data from current studies regarding the pathophysiological mechanisms of skin aging and the regenerative processes occurring in the epidermis and dermis at the molecular and cellular level, mainly, the key role of dermal fibroblasts in skin regeneration. Analyzing these data, the authors proposed the concept of skin anti-age therapy that is based on the correction of age-related skin changes by stimulating regenerative processes at the molecular and cellular level. The main target of the skin anti-age therapy is dermal fibroblasts (DFs). A variant of the cosmetological anti-age program using the combination of laser and cellular methods of regenerative medicine is presented in the paper. The program includes three stages of implementation and defines the tasks and methods of each stage. Thus, laser technologies allow one to remodel the collagen matrix and create favorable conditions for DFs functions, whereas the cultivated autologous dermal fibroblasts replenish the pool of mature DFs decreasing with age and are responsible for the synthesis of components of the dermal extracellular matrix. Finally, the use of autological platelet-rich plasma (PRP) enables to maintenance of the achieved results by stimulating DF function. It has been shown that growth factors/cytokines contained in α-granules of platelets injected into the skin bind to the corresponding transmembrane receptors on the surface of DFs and stimulate their synthetic activity. Thus, the consecutive, step-by-step application of the described methods of regenerative medicine amplifies the effect on the molecular and cellular aging processes and thereby allows one to optimize and prolong the clinical results of skin rejuvenation.

Collagen VI in the Musculoskeletal System

Collagen VI exerts several functions in the tissues in which it is expressed, including mechanical roles, cytoprotective functions with the inhibition of apoptosis and oxidative damage, and the promotion of tumor growth and progression by the regulation of cell differentiation and autophagic mechanisms. Mutations in the genes encoding collagen VI main chains, COL6A1, COL6A2 and COL6A3, are responsible for a spectrum of congenital muscular disorders, namely Ullrich congenital muscular dystrophy (UCMD), Bethlem myopathy (BM) and myosclerosis myopathy (MM), which show a variable combination of muscle wasting and weakness, joint contractures, distal laxity, and respiratory compromise. No effective therapeutic strategy is available so far for these diseases; moreover, the effects of collagen VI mutations on other tissues is poorly investigated. The aim of this review is to outline the role of collagen VI in the musculoskeletal system and to give an update about the tissue-specific functions revealed by studies on animal models and from patients' derived samples in order to fill the knowledge gap between scientists and the clinicians who daily manage patients affected by collagen VI-related myopathies.

Structural studies of elastic fibre and microfibrillar proteins

Elastic tissues owe their functional properties to the composition of their extracellular matrices, particularly the range of extracellular, multidomain extensible elastic fibre and microfibrillar proteins. These proteins include elastin, fibrillin, latent TGFβ binding proteins (LTBPs) and collagens, where their biophysical and biochemical properties not only give the matrix structural integrity, but also play a vital role in the mechanisms that underlie tissue homeostasis. Thus far structural information regarding the structure and hierarchical assembly of these molecules has been challenging and the resolution has been limited due to post-translational modification and their multidomain nature leading to flexibility, which together result in conformational and structural heterogeneity. In this review, we describe some of the matrix proteins found in elastic fibres and the new emerging techniques that can shed light on their structure and dynamic properties.

The role of basement membranes in cardiac biology and disease

Basement membranes are highly specialised extracellular matrix structures that within the heart underlie endothelial cells and surround cardiomyocytes and vascular smooth muscle cells. They generate a dynamic and structurally supportive environment throughout cardiac development and maturation by providing physical anchorage to the underlying interstitium, structural support to the tissue, and by influencing cell behaviour and signalling. While this provides a strong link between basement membrane dysfunction and cardiac disease, the role of the basement membrane in cardiac biology remains under-researched and our understanding regarding the mechanistic interplay between basement membrane defects and their morphological and functional consequences remain important knowledge-gaps. In this review we bring together emerging understanding of basement membrane defects within the heart including in common cardiovascular pathologies such as contractile dysfunction and highlight some key questions that are now ready to be addressed.

The critical role of collagen VI in lung development and chronic lung disease

Type VI collagen (collagen VI) is an obligate extracellular matrix component found mainly in the basement membrane region of many mammalian tissues and organs, including skeletal muscle and throughout the respiratory system. Collagen VI is probably most recognized in medicine as the genetic cause of a spectrum of muscular dystrophies, including Ullrich Congenital Myopathy and Bethlem Myopathy. Collagen VI is thought to contribute to myopathy, at least in part, by mediating muscle fiber integrity by anchoring myoblasts to the muscle basement membrane. Interestingly, collagen VI myopathies present with restrictive respiratory insufficiency, thought to be due primarily to thoracic muscular weakening. Although it was recently recognized as one of the (if not the) most abundant collagens in the mammalian lung, there is a substantive knowledge gap concerning its role in respiratory system development and function. A few studies have suggested that collagen VI insufficiency is associated with airway epithelial cell survival and altered lung function. Our recent work suggested collagen VI may be a genomic risk factor for chronic lung disease in premature infants. Using this as motivation, we thoroughly assessed the role of collagen VI in lung development and in lung epithelial cell biology. Here, we describe the state-of-the-art for collagen VI cell and developmental biology within the respiratory system, and reveal its essential roles in normal developmental processes and airway epithelial cell phenotype and intracellular signaling.

Biopsy-Controlled Non-Invasive Quantification of Collagen Type VI in Kidney Transplant Recipients: A Post-Hoc Analysis of the MECANO Trial

The PRO-C6 assay, a reflection of collagen type VI synthesis, has been proposed as a non-invasive early biomarker of kidney fibrosis. We aimed to investigate cross-sectional and longitudinal associations between plasma and urine PRO-C6 and proven histological changes after kidney transplantation. The current study is a post-hoc analysis of 94 participants of the MECANO trial, a 24-month prospective, multicenter, open-label, randomized, controlled trial aimed at comparing everolimus-based vs. cyclosporine-based immunosuppression. PRO-C6 was measured in plasma and urine samples collected 6 and 24 months post-transplantation. Fibrosis was evaluated in biopsies collected at the same time points by Banff interstitial fibrosis/tubular atrophy (IF/TA) scoring and collagen staining (Picro Sirius Red; PSR); inflammation was evaluated by the tubulo-interstitial inflammation score (ti-score). Linear regression analyses were performed. Six-month plasma PRO-C6 was cross-sectionally associated with IF/TA score (Std. β = 0.34), and prospectively with 24-month IF/TA score and ti-score (Std. β = 0.24 and 0.23, respectively) (p < 0.05 for all). No significant associations were found between urine PRO-C6 and any of the biopsy findings. Fibrotic changes and urine PRO-C6 behaved differentially over time according to immunosuppressive therapy. These results are a first step towards non-invasive fibrosis detection after kidney transplantation by means of collagen VI synthesis measurement, and further research is required.

Tendon Extracellular Matrix Remodeling and Defective Cell Polarization in the Presence of Collagen VI Mutations

Mutations in collagen VI genes cause two major clinical myopathies, Bethlem myopathy (BM) and Ullrich congenital muscular dystrophy (UCMD), and the rarer myosclerosis myopathy. In addition to congenital muscle weakness, patients affected by collagen VI-related myopathies show axial and proximal joint contractures, and distal joint hypermobility, which suggest the involvement of tendon function. To gain further insight into the role of collagen VI in human tendon structure and function, we performed ultrastructural, biochemical, and RT-PCR analysis on tendon biopsies and on cell cultures derived from two patients affected with BM and UCMD. In vitro studies revealed striking alterations in the collagen VI network, associated with disruption of the collagen VI-NG2 (Collagen VI-neural/glial antigen 2) axis and defects in cell polarization and migration. The organization of extracellular matrix (ECM) components, as regards collagens I and XII, was also affected, along with an increase in the active form of metalloproteinase 2 (MMP2). In agreement with the in vitro alterations, tendon biopsies from collagen VI-related myopathy patients displayed striking changes in collagen fibril morphology and cell death. These data point to a critical role of collagen VI in tendon matrix organization and cell behavior. The remodeling of the tendon matrix may contribute to the muscle dysfunction observed in BM and UCMD patients.

Variants in COL6A3 gene influence susceptibility to esophageal cancer in the Chinese population

Esophageal cancer (EC) is a frequent malignant tumor in our world, and has a highly morbidity and mortality. It was reported that genetic factors play vital roles in its pathogenesis. Here, we performed a case - control study to evaluate the COL6A3 genetic variants and EC risk in a Chinese Han cohort. All subjects were genotyped with the Agena MassARRAY platform. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by logistic regression after adjusting age and gender. We found that rs6720283 (G > A) allele had significantly enhanced EC risk (OR = 1.32, 95% CI = 1.11 alculate p = 0.002). Stratified analysis was performed by gender, age, alcohol drinking, BMI, TNM stage and lymph node metastasis, the results showed that rs7436, rs115510139 and rs6720283 were significantly associated with the risk of EC in different groups (all p < 0.05). Besides, no statistical significant was found between the COL6A3 gene polymorphisms and clinicopathological parameters such as TNM stage and lymph node metastasis among EC patients (p > 0.05). In conclusions, our study found that COL6A3 variants were associated with risk of EC in the Chinese population.

Rho-associated protein kinase inhibitor induced morphological changes in type VI collagen in the human trabecular meshwork

Aims

To investigate morphological changes in type VI collagen in the human trabecular meshwork associated with the rho kinase inhibitor ripasudil.

Methods

This cross-sectional study evaluated the effects of ripasudil eye drop administration (RA) or no ripasudil eye drop administration (NRA) in patients with primary open-angle glaucoma (POAG; age range 60–80 years) who underwent conventional outflow reconstruction between December 2015 and September 2016 at Tokai University Hachioji Hospital. The juxtacanalicular tissue was removed and imaged using transmission electron microscopy. Type VI collagen comprises cross-banded aggregates with transverse bands 30 nm apart repeating every 105 nm. The transverse bands are called the outer rod-like region (ORR) and the intervals are called the inner rod-like region (IRR). The waveform intensity in the type VI collagen was analysed in electron micrographs using Fourier transformation to detect the IRR and ORR borders.

Results

Ten eyes of 10 patients were included (n=5/group). The baseline characteristics did not differ significantly between groups. ORR width was significantly smaller in the RA group (37.85±3.43 nm) than in the NRA group (50.62±5.23 nm, p<0.05), whereas IRR width was significantly greater in the RA group (70.68±10.84 nm) than in the NRA group (58.19±5.34 nm, p<0.05). Morphological changes in the type VI collagen total width tended to correlate with the duration of ripasudil administration (r=0.9, p=0.08).

Conclusions

Ripasudil administration in patients with POAG induced morphological changes in type VI collagen. Patients with POAG administered RA had a significantly smaller ORR width and a significantly greater IRR width than patients with POAG not administered RA.

COL6A3-derived endotrophin links reciprocal interactions among hepatic cells in the pathology of chronic liver disease

Extracellular matrix dysregulation is associated with chronic liver disease. CollagenVI-alpha3 chain (COL6A3) is a biomarker for hepatic fibrosis and poor prognosis of hepatocellular carcinoma (HCC), but its function in liver pathology remains unknown. High levels of COL6A3 and its cleaved product, endotrophin (ETP) in tumor-neighboring regions are strongly associated with poor prognosis in HCC patients. Here, we report that the high levels of ETP in injured hepatocytes induce JNK-dependent hepatocyte apoptosis and activate nonparenchymal cells to lead further activation of hepatic inflammation, fibrosis, and apoptosis. Nevertheless ETP per se showed limited phenotypic changes in normal liver tissues. Furthermore, inhibition of ETP activity by utilizing neutralizing antibodies efficiently suppressed the pathological consequences in chronic liver diseases. Our results implicate ETP mechanistically as a crucial mediator in reciprocal interactions among various hepatic cell populations in the pathogenesis of chronic liver disease, and it could be a promising therapeutic target particularly in individuals with high local levels of COL6A3. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Decellularized tongue tissue as an in vitro model for studying tongue cancer and tongue regeneration

The decellularization of tissues or organs provides an efficient strategy for preparing functional scaffolds for tissue engineering. The microstructures of native extracellular matrices and biochemical compositions retained in the decellularized matrices provide tissue-specific microenvironments for anchoring cells. Here, we report the tongue extracellular matrix (TEM), which showed favorable cytocompatibility for normal tongue-derived cells and tongue squamous cell carcinoma (TSCC) cells under static or stirring culture conditions. Our results show that TEM retained tongue-specific integrated microstructures and abundant matrix components, which offer mechanical support and spatial signals for regulating cell behavior and function. Reconstructed TSCC by TEM presented characteristics resembling clinical TSCC histopathology, suggesting the possibility for TSCC research. In addition, TEM might be capable of guiding tongue-derived cells to the niche, benefiting cell survival, proliferation and differentiation.

STATEMENT OF SIGNIFICANCE

In this study, we prepared decellularized tongue extracellular matrix (TEM) and evaluated the possibility for tongue squamous cell carcinoma (TSCC) research and tongue regeneration. TEM has six irreplaceable advantages: (1) tongue-specific intricate structures of TEM, which offer mechanical support for the cells; (2) abundant matrix components and spatial signals benefiting for cell attachment, survival, differentiation, and long-term viability of the highly functional phenotypes of tongue cells or TSCC cells; (3) reconstructed TSCC by TEM exhibited tumor heterogeneity, extremely resembling clinical TSCC histopathology; (4) ideal model to evaluate TSCC movement mode; (5) guiding tongue-derived cells to the site-appropriate niche; and (6) the possibility for static or stirred cell culture. These properties might be considered in TSCC research or tongue regeneration.

Defining the hierarchical organisation of collagen VI microfibrils at nanometre to micrometre length scales

Extracellular matrix microfibrils are critical components of connective tissues with a wide range of mechanical and cellular signalling functions. Collagen VI is a heteromeric network-forming collagen which is expressed in tissues such as skin, lung, blood vessels and articular cartilage where it anchors cells into the matrix allowing for transduction of biochemical and mechanical signals. It is not understood how collagen VI is arranged into microfibrils or how these microfibrils are arranged into tissues. Therefore we have characterised the hierarchical organisation of collagen VI across multiple length scales. The frozen hydrated nanostructure of purified collagen VI microfibrils was reconstructed using cryo-TEM. The bead region has a compact hollow head and flexible tail regions linked by the collagenous interbead region. Serial block face SEM imaging coupled with electron tomography of the pericellular matrix (PCM) of murine articular cartilage revealed that the PCM has a meshwork-like organisation formed from globular densities ∼30nm in diameter. These approaches can characterise structures spanning nanometer to millimeter length scales to define the nanostructure of individual collagen VI microfibrils and the micro-structural organisation of these fibrils within tissues to help in the future design of better mimetics for tissue engineering.

STATEMENT OF SIGNIFICANCE

Cartilage is a connective tissue rich in extracellular matrix molecules and is tough and compressive to cushion the bones of joints. However, in adults cartilage is poorly repaired after injury and so this is an important target for tissue engineering. Many connective tissues contain collagen VI, which forms microfibrils and networks but we understand very little about these assemblies or the tissue structures they form. Therefore, we have use complementary imaging techniques to image collagen VI microfibrils from the nano-scale to the micro-scale in order to understand the structure and the assemblies it forms. These findings will help to inform the future design of scaffolds to mimic connective tissues in regenerative medicine applications.

Tendon Extracellular Matrix Alterations in Ullrich Congenital Muscular Dystrophy

Collagen VI (COLVI) is a non-fibrillar collagen expressed in skeletal muscle and most connective tissues. Mutations in COLVI genes cause two major clinical forms, Bethlem myopathy and Ullrich congenital muscular dystrophy (UCMD). In addition to congenital muscle weakness, patients affected by COLVI myopathies show axial and proximal joint contractures and distal joint hypermobility, which suggest the involvement of the tendon function. We examined a peroneal tendon biopsy and tenocyte culture of a 15-year-old patient affected by UCMD with compound heterozygous COL6A2 mutations. In patient’s tendon biopsy, we found striking morphological alterations of tendon fibrils, consisting in irregular profiles and reduced mean diameter. The organization of the pericellular matrix of tenocytes, the primary site of collagen fibril assembly, was severely affected, as determined by immunoelectron microscopy, which showed an abnormal accumulation of COLVI and altered distribution of collagen I (COLI) and fibronectin (FBN). In patient’s tenocyte culture, COLVI web formation and cell surface association were severely impaired; large aggregates of COLVI, which matched with COLI labeling, were frequently detected in the extracellular matrix. In addition, metalloproteinase MMP-2, an extracellular matrix-regulating enzyme, was increased in the conditioned medium of patient’s tenocytes, as determined by gelatin zymography and western blot. Altogether, these data indicate that COLVI deficiency may influence the organization of UCMD tendon matrix, resulting in dysfunctional fibrillogenesis. The alterations of tendon matrix may contribute to the complex pathogenesis of COLVI related myopathies.

From nano to macro: studying the hierarchical structure of the corneal extracellular matrix

In this review, we discuss current methods for studying ocular extracellular matrix (ECM) assembly from the 'nano' to the 'macro' levels of hierarchical organization. Since collagen is the major structural protein in the eye, providing mechanical strength and controlling ocular shape, the methods presented focus on understanding the molecular assembly of collagen at the nanometre level using X-ray scattering through to the millimetre to centimetre level using non-linear optical (NLO) imaging of second harmonic generated (SHG) signals. Three-dimensional analysis of ECM structure is also discussed, including electron tomography, serial block face scanning electron microscopy (SBF-SEM) and digital image reconstruction. Techniques to detect non-collagenous structural components of the ECM are also presented, and these include immunoelectron microscopy and staining with cationic dyes. Together, these various approaches are providing new insights into the structural blueprint of the ocular ECM, and in particular that of the cornea, which impacts upon our current understanding of the control of corneal shape, pathogenic mechanisms underlying ectatic disorders of the cornea and the potential for corneal tissue engineering.

Collagen VI at a glance

Collagen VI represents a remarkable extracellular matrix molecule, and in the past few years, studies of this molecule have revealed its involvement in a wide range of tissues and pathological conditions. In addition to its complex multi-step pathway of biosynthesis and assembly that leads to the formation of a characteristic and distinctive network of beaded microfilaments in the extracellular matrix, collagen VI exerts several key roles in different tissues. These range from unique biomechanical roles to cytoprotective functions in different cells, including myofibers, chondrocytes, neurons, fibroblasts and cardiomyocytes. Indeed, collagen VI has been shown to exert a surprisingly broad range of cytoprotective effects, which include counteracting apoptosis and oxidative damage, favoring tumor growth and progression, regulating autophagy and cell differentiation, and even contributing to the maintenance of stemness. In this Cell Science at a Glance article and the accompanying poster, we present the current knowledge of collagen VI, and in particular, discuss its relevance in stemness and in preserving the mechanical properties of tissues, as well as its links with human disorders.

Influence of ranibizumab treatment on the extracellular matrix in patients with neovascular age-related macular degeneration

BACKGROUND

We know the influence of the intravitreal anti-vascular endothelial growth factor (VEGF) injections on the choroidal neovascularization in the course of exudative age-related macular degeneration (AMD). However, the influence of the ranibizumab therapy in question on the extracellular matrix (ECM) remains unknown. We aimed to estimate the influence of Lucentis intravitreal injections on the gene expression of structural components of the extracellular matrix in patients with neovascular AMD.

MATERIAL AND METHODS

Patients with subfoveal localization of neovascularization in AMD, which was clinically active and observed using optical coherence tomography, were treated with ranibizumab (0.5 mg/0.05 mL) in accordance with the PrONTO scheme. Total RNA was extracted from peripheral blood mononuclear cells, and an oligonucleotide microarray technique enabled comparison of the expression level of genes encoding collagens, elastin, and laminins in AMD patients compared to control subjects.

RESULTS

After 3 intravitreal injections of ranibizumab (Lucentis), COL1A1 and COL6A1 genes showed increased expression, whereas decreased expression mainly occurred for the following genes: COL4A5, COL11A1, OL4A6C, LAMB4, and LAMC2.

CONCLUSIONS

Anti-VEGF local therapy influences the gene expression of structural components of the ECM as measured from blood samples. The loading dose of ranibizumab for the retina changes the expression of collagen and laminin genes, but does not influence the expression of the elastin gene.

Different collagen types define two types of idiopathic epiretinal membranes

AIMS

To identify differences in extracellular matrix contents between idiopathic epiretinal membranes (IEM) of cellophane macular reflex (CMRM) or preretinal macular fibrosis (PMFM) type.

METHODS AND RESULTS

Idiopathic epiretinal membranes were analysed by light and quantitative transmission electron microscopy, immunohistochemistry and Western blotting. Substantial differences between CMRM and PMFM were observed regarding the nature of extracellular fibrils. In CMRM the fibrils were thin, with diameters between 6 and 15 nm. Between the fibrils, aggregates of long-spacing collagen were observed. In PMFM the diameters of fibrils measured either 18-26 or 36-56 nm. Using immunogold electron microscopy, 6-15 nm fibrils in CMRM were labelled for collagen type VI, while the fibrils in PMFM remained unstained. Using Western blotting and immunohistochemistry, a strong signal for collagen type VI was observed in all CMRM, while immunoreactivity was weak or absent in PMFM. In contrast, PMFM showed immunoreactivity for collagen types I and II, which was weak or absent in CMRM. Both types of membranes showed immunoreactivity for collagen types III and IV, laminin and fibronectin with similar intensity.

CONCLUSION

The presence of high amounts of collagen type VI in CMRM and the relative absence of collagen types I and II is the major structural difference to PMFM.

The architecture of the cornea and structural basis of its transparency

The cornea is the transparent connective tissue window at the front of the eye. In the extracellular matrix of the corneal stroma, hybrid type I/V collagen fibrils are remarkably uniform in diameter at approximately 30 nm and are regularly arranged into a pseudolattice. Fibrils are believed to be kept at defined distances by the influence of proteoglycans. Light entering the cornea is scattered by the collagen fibrils, but their spatial distribution is such that the scattered light interferes destructively in all directions except from the forward direction. In this way, light travels forward through the cornea to reach the retina. In this chapter, we will review the macromolecular components of the corneal stroma, the way they are organized into a stacked lamellar array, and how this organization guarantees corneal transparency.

Ultrastructure of inclusion bodies in annulus cells in the degenerating human intervertebral disc

The rough endoplasmic reticulum (rER) of the cell has an architectural editing function that checks whether protein structure and three-dimensional assembly have occurred properly prior to export of newly synthesized material out of the cell. If these have been faulty, the material is retained within the rER as an inclusion body. Inclusion bodies have been identified previously in chondrocytes and osteoblasts in chondrodysplasias and osteogenesis imperfecta. Inclusion bodies in intervertebral disc cells, however, have only recently been recognized. Our objectives were to use transmission electron microscopy to analyze more fully inclusion bodies in the annulus pulposus and to study the extracellular matrix (ECM) surrounding cells containing inclusion bodies. ECM frequently encapsulated cells with inclusion bodies, and commonly contained prominent banded aggregates of Type VI collagen. Inclusion body material had several morphologies, including relatively smooth, homogeneous material, or a rougher, less homogeneous feature. Such findings expand our knowledge of the fine structure of the human disc cell and ECM during disc degeneration, and indicate the potential utility of ultrastructural identification of discs with intracellular inclusion bodies as a screening method for molecular studies directed toward identification of defective gene products in degenerating discs.

ECM macromolecules: height-mapping and nano-mechanics using atomic force microscopy

The atomic force microscope (AFM) may be used to collect quantitative height data from extracellular matrix molecules and macro-molecular assemblies adsorbed to a wide range of solid substrates. The advantages of atomic force microscopy include rapid specimen preparation, which does not rely on chemical fixation, dehydration or heavy-metal staining, and sub-nanometre resolution imaging with a high signal-noise ratio. In combination with complimentary techniques such as molecular combing and by exploiting the ability to act as a force spectrometer, the AFM can provide valuable information on the nano-mechanical properties of extracellular matrix components.

Gene expression of types I, II, and VI collagen, aggrecan, and chondroitin-6-sulfotransferase in the human annulus: in situ hybridization findings

BACKGROUND CONTEXT

Within each lamellar bundle in the annulus, disc cells produce a complex and sophisticated architectural organization which acts to meet the unique biomechanical needs of the disc. How cells coordinate expression of genes throughout the disc is an important but as yet poorly understood process. For the annulus, such coordination probably involves cell-cell communication as well as growth factor and mechanoreceptor signaling to appropriately maintain the disc extracellular matrix (ECM) for the prevention of annular tears.

PURPOSE

To determine the percentage and patterns of gene expression for types I, II, and VI collagen, aggrecan, and chondroitin-6-sulfotransferase in the human annulus.

STUDY DESIGN/SETTING

Human annulus specimens were obtained from surgical subjects and a control donor in a study approved by the authors' Human Subjects Institutional Review Board.

PATIENT SAMPLE

Four Thompson grade II, three grade III, and four grade IV annulus specimens were evaluated with in situ hybridization to determine gene expression.

OUTCOME MEASURES

The percentages of cells in the human annulus expressing type I, II, and VI collagen, aggrecan, and chondroitin-6-sulfotransferase.

METHODS

In situ hybridization, a technique with high temporal and spatial resolution, was used to detect gene expression of types I, II, and VI collagen, aggrecan, and chondroitin-6 sulfotransferase in cells in adjacent sections of annulus from discs with Thompson grades of II, III, and IV.

RESULTS

Overall, 30.8% of cells expressed aggrecan, 38.4% type I collagen, 45.6% type II collagen, 48.1% type VI collagen, and 57.7% chondroitin-6-sulfotransferase. An important finding was that adjacent cells could be expressing, or not expressing, the gene of interest. These data could not have been gained from other global molecular techniques such as microarray analysis or reverse transcription polymerase chain reaction (RT-PCR). Information on gene expression by individual disc cells is important to better understand disc matrix homeostasis, the pathogenesis of disc degeneration, and to formulate potential biologic therapies for disc degeneration.

CONCLUSIONS

This in situ hybridization study revealed the important finding that adjacent cells differ in their gene expression patterns for specific genes. Factors that could contribute to this difference in adjacent cell gene expression include cellular heterogeneity within the annulus, the presence of senescent cells with altered gene expression, and/or loss of coordinated disc cell function as a result of disruption of cell-cell communication.

Extracellular matrix in the trabecular meshwork

The extracellular matrix (ECM) of the trabecular meshwork (TM) is thought to be important in regulating intraocular pressure (IOP) in both normal and glaucomatous eyes. IOP is regulated primarily by a fluid resistance to aqueous humor outflow. However, neither the exact site nor the identity of the normal resistance to aqueous humor outflow has been established. Whether the site and nature of the increased outflow resistance, which is associated with open-angle glaucoma, is the same or different from the normal resistance is also unclear. The ECMs of the TM beams, juxtacanalicular region (JCT) and Schlemm's canal (SC) inner wall are comprised of fibrillar and non-fibrillar collagens, elastin-containing microfibrils, matricellular and structural organizing proteins, glycosaminoglycans (GAGs) and proteoglycans. Both basement membranes and stromal ECM are present in the TM beams and JCT region. Cell adhesion proteins, cell surface ECM receptors and associated binding proteins are also present in the beams, JCT and SC inner wall region. The outflow pathway ECM is relatively dynamic, undergoing constant turnover and remodeling. Regulated changes in enzymes responsible for ECM degradation and biosynthetic replacement are observed. IOP homeostasis, triggered by pressure changes or mechanical stretching of the TM, appears to involve ECM turnover. Several cytokines, growth factors and drugs, which affect the outflow resistance, change ECM component expression, mRNA alternative splicing, cellular cytoskeletal organization or all of these. Changes in ECM associated with open-angle glaucoma have been identified.

Morphologic complexity of the pericellular matrix in the annulus of the human intervertebral disc

The pericellular region of the extracellular matrix (ECM) contains collagens, proteoglycans and other noncollagenous matrix proteins. Although such specialized pericellular ECM has been well studied in articular cartilage, little is known about the pericellular matrix in the disc. In the study reported here, pericellular matrix was studied in annulus tissue from 52 subjects ranging in age from 17-74 years. In aging/degenerating intervertebral discs, cells were identified that formed a distinctive cocoon of encircling pericellular ECM. Immunohistochemical studies identified types I, II, III and VI collagen in these pericellular sites with diverse morphological features. Similar types of changes in the pericellular matrix were observed in both surgical specimens and control donor discs. Results indicate the need for future studies to address why such specialized matrix regions form around certain disc cells and to determine the consequences of these unusual matrix regions on annular lamellar organization and function.