Type VI collagen increases cell survival and prevents anti-beta 1 integrin-mediated apoptosis

Multi-Omics Profiles of Small Intestine Organoids in Reaction to Breast Milk and Different Infant Formula Preparations

Ensuring optimal infant nutrition is crucial for the health and development of children. Many infants aged 0-6 months are fed with infant formula rather than breast milk. Research on cancer cell lines and animal models is limited to examining the nutrition effects of formula and breast milk, as it does not comprehensively consider absorption, metabolism, and the health and social determinants of the infant and its physiology. Our study utilized small intestine organoids induced from human embryo stem cell (ESC) to compare the nutritional effects of breast milk from five donors during their postpartum lactation period of 1-6 months and three types of Stage 1 infant formulae from regular retail stores. Using transcriptomics and untargeted metabolomics approaches, we focused on the differences such as cell growth and development, cell junctions, and extracellular matrix. We also analyzed the roles of pathways including AMPK, Hippo, and Wnt, and identified key genes such as ALPI, SMAD3, TJP1, and WWTR1 for small intestine development. Through observational and in-vitro analysis, our study demonstrates ESC-derived organoids might be a promising model for exploring nutritional effects and underlying mechanisms.

The jam session between muscle stem cells and the extracellular matrix in the tissue microenvironment

Skeletal muscle requires a highly orchestrated coordination between multiple cell types and their microenvironment to exert its function and to maintain its homeostasis and regenerative capacity. Over the past decades, significant advances, including lineage tracing and single-cell RNA sequencing, have contributed to identifying multiple muscle resident cell populations participating in muscle maintenance and repair. Among these populations, muscle stem cells (MuSC), also known as satellite cells, in response to stress or injury, are able to proliferate, fuse, and form new myofibers to repair the damaged tissue. These cells reside adjacent to the myofiber and are surrounded by a specific and complex microenvironment, the stem cell niche. Major components of the niche are extracellular matrix (ECM) proteins, able to instruct MuSC behavior. However, during aging and muscle-associated diseases, muscle progressively loses its regenerative ability, in part due to a dysregulation of ECM components. This review provides an overview of the composition and importance of the MuSC microenvironment. We discuss relevant ECM proteins and how their mutations or dysregulation impact young and aged muscle tissue or contribute to diseases. Recent discoveries have improved our knowledge about the ECM composition of skeletal muscle, which has helped to mimic the architecture of the stem cell niche and improved the regenerative capacity of MuSC. Further understanding about extrinsic signals from the microenvironment controlling MuSC function and innovative technologies are still required to develop new therapies to improve muscle repair.

Type VI collagen α1 chain polypeptide in non-triple helical form is an alternative gene product of COL6A1

Expression of type IV collagen α1 chain in non-triple helical form, NTH α1(IV), is observed in cultured human cells, human placenta and rabbit tissues. Biological functions of NTH α1(IV) are most likely to be distinct from type IV collagen, since their biochemical characteristics are quite different. To explore the biological functions of NTH α1(IV), we prepared some anti-NTH α1(IV) antibodies. In the course of characterization of these antibodies, one antibody, #141, bound to a polypeptide of 140 kDa in size in addition to NTH α1(IV). In this study, we show evidence that the 140 kDa polypeptide is a novel non-triple helical polypeptide of type VI collagen α1 chain encoded by COL6A1, or NTH α1(VI). Expression of NTH α1(VI) is observed in supernatants of several human cancer cell lines, suggesting that the NTH α1(VI) might be involved in tumourigenesis. Reactivity with lectins indicates that sugar chains of NTH α1(VI) are different from those of the α1(VI) chain in triple helical form of type VI collagen, suggesting a synthetic mechanism and a mode of action of NTH α1(VI) is different from type VI collagen.

Low oxygen tension and macromolecular crowding accelerate extracellular matrix deposition in human corneal fibroblast culture

Development of implantable devices based on the principles of in vitro organogenesis has been hindered due to the prolonged time required to develop an implantable device. Herein we assessed the influence of serum concentration (0.5% and 10%), oxygen tension (0.5%, 2% and 20%) and macromolecular crowding (75 μg/ml carrageenan) in extracellular matrix deposition in human corneal fibroblast culture (3, 7 and 14 days). The highest extracellular matrix deposition was observed after 14 days in culture at 0.5% serum, 2% oxygen tension and 75 μg/ml carrageenan. These data indicate that low oxygen tension coupled with macromolecular crowding significantly accelerate the development of scaffold-free tissue-like modules. Copyright © 2016 John Wiley & Sons, Ltd.

A novel explanation of corneal clouding in a bone marrow transplant-treated patient with Hurler syndrome

One common complication of mucopolysaccharidosis I-Hurler (MPS1-H) is corneal clouding, which occurs despite current treatments, including bone marrow transplantation. Human corneas were obtained from a 14 year old subject with MPS1-H and visual disability from progressive corneal clouding despite a prior bone marrow transplant at age 2. This was compared to a cornea from a 17 year old donated to our eye bank after his accidental death. The corneas were analyzed microscopically after staining with Alcian blue, antibodies to collagen I, IV, VI, and α-smooth muscle actin. Differences in levels of expression of the indicated molecules were assessed. Corneas from Hurler and control mice were examined similarly to determine potential mechanistic overlap. The MPS1-H subject cornea showed elevations in mucopolysaccharide deposition. The MPS1-H and Hurler mice corneas showed increased and disorganized expression of collagen I and IV relative to the control corneas. The MPS1-H corneas also showed increased and disordered expression of collagen VI. Positive expression of α-smooth muscle actin indicated myofibroblast conversion within the MPS1-H cornea in both the patient and mutant mouse material compared to normal human and control mouse cornea. Increased deposition of collagens and smooth muscle actin correlate with corneal clouding, providing a potential mechanism for corneal clouding despite bone marrow transplantation in MPS1-H patients. It might be possible to prevent or slow the onset of corneal clouding by treating the cornea with drugs known to prevent myofibroblast conversion.

Collagens VI and XII form complexes mediating osteoblast interactions during osteogenesis

Bone formation is precisely regulated by cell-cell communication in osteoblasts. We have previously demonstrated that genetic deletion of Col6a1 or Col12a1 impairs osteoblast connections and/or communication in mice, resulting in bone mass reduction and bone fragility. Mutations of the genes encoding collagen VI cause Ullrich congenital muscular dystrophy (UCMD) and Bethlem myopathy (BM), which have overlapping phenotypes involving connective tissue and muscle. Recent studies have identified COL12A1 gene mutations in patients with UCMD- and BM-like disorders harboring no COL6 mutations, indicating the shared functions of these collagens in connective tissue homeostasis. The purpose of this investigation has been to test the hypothesis that collagens VI and XII have coordinate regulatory role(s) during bone formation. We analyzed the localization of collagens VI and XII relative to primary osteoblasts during osteogenesis. Immunofluorescence analysis demonstrated that collagens VI and XII colocalized in matrix bridges between adjacent cells during periods when osteoblasts were establishing cell-cell connections. Quantification of cells harboring collagen bridges demonstrated that matrix bridges were composed of collagens VI and XII but not collagen I. Interestingly, matrix bridge formation was impaired in osteoblasts deficient in either Col6a1 or Col12a1, suggesting that both collagens were indispensable for matrix bridge formation. These data demonstrate, for the first time, a functional relationship between collagens VI and XII during osteogenesis and indicate that a complex containing collagens VI and XII is essential for the formation of a communicating cellular network during bone formation.

Ullrich congenital muscular dystrophy: clinicopathological features, natural history and pathomechanism(s)

Collagen VI is widely distributed throughout extracellular matrices (ECMs) in various tissues. In skeletal muscle, collagen VI is particularly concentrated in and adjacent to basement membranes of myofibers. Ullrich congenital muscular dystrophy (UCMD) is caused by mutations in either COL6A1, COL6A2 or COL6A3 gene, thereby leading to collagen VI deficiency in the ECM. It is known to occur through either recessive or dominant genetic mechanism, the latter most typically by de novo mutations. UCMD is well defined by the clinicopathological hallmarks including distal hyperlaxity, proximal joint contractures, protruding calcanei, scoliosis and respiratory insufficiency. Recent reports have depicted the robust natural history of UCMD; that is, loss of ambulation by early teenage years, rapid decline in respiratory function by 10 years of age and early-onset, rapidly progressive scoliosis. Muscle pathology is characterised by prominent interstitial fibrosis disproportionate to the relative paucity of necrotic and regenerating fibres. To date, treatment for patients is supportive for symptoms such as joint contractures, respiratory failure and scoliosis. There have been clinical trials based on the theory of mitochondrion-mediated myofiber apoptosis or impaired autophagy. Furthermore, the fact that collagen VI producing cells in skeletal muscle are interstitial mesenchymal cells can support proof of concept for stem cell-based therapy.

TAF4 inactivation reveals the 3 dimensional growth promoting activities of collagen 6A3

Collagen 6A3 (Col6a3), a component of extracellular matrix, is often up-regulated in tumours and is believed to play a pro-oncogenic role. However the mechanisms of its tumorigenic activity are poorly understood. We show here that Col6a3 is highly expressed in densely growing mouse embryonic fibroblasts (MEFs). In MEFs where the TAF4 subunit of general transcription factor IID (TFIID) has been inactivated, elevated Col6a3 expression prevents contact inhibition promoting their 3 dimensional growth as foci and fibrospheres. Analyses of gene expression in densely growing Taf4^−/− MEFs revealed repression of the Hippo pathway and activation of Wnt signalling. The Hippo activator Kibra/Wwc1 is repressed under dense conditions in Taf4^−/− MEFs, leading to nuclear accumulation of the proliferation factor YAP1 in the cells forming 3D foci. At the same time, Wnt9a is activated and the Sfrp2 antagonist of Wnt signalling is repressed. Surprisingly, treatment of Taf4^−/− MEFs with all-trans retinoic acid (ATRA) restores contact inhibition suppressing 3D growth. ATRA represses Col6a3 expression independently of TAF4 expression and Col6a3 silencing is sufficient to restore contact inhibition in Taf4^−/− MEFs and to suppress 3D growth by reactivating Kibra expression to induce Hippo signalling and by inducing Sfrp2 expression to antagonize Wnt signalling. All together, these results reveal a critical role for Col6a3 in regulating both Hippo and Wnt signalling to promote 3D growth, and show that the TFIID subunit TAF4 is essential to restrain the growth promoting properties of Col6a3. Our data provide new insight into the role of extra cellular matrix components in regulating cell growth.

Annexin A2 mediates secretion of collagen VI, pulmonary elasticity and apoptosis of bronchial epithelial cells

The annexins are an evolutionarily conserved family of phospholipid-binding proteins of largely unknown function. We observed that the AnxA2(-/-) lung basement membrane specifically lacks collagen VI (COL6), and postulated that ANXA2 directs bronchial epithelial cell secretion of COL6, an unusually large multimeric protein. COL6 serves to anchor cells to basement membranes and, unlike other collagens, undergoes multimerization prior to secretion. Here, we show that AnxA2(-/-) mice have reduced exercise tolerance with impaired lung tissue elasticity, which was phenocopied in Col6a1(-/-) mice. In vitro, AnxA2(-/-) fibroblasts retained COL6 within intracellular vesicles and adhered poorly to their matrix unless ANXA2 expression was restored. In vivo, AnxA2(-/-) bronchial epithelial cells underwent apoptosis and disadhesion. Immunoprecipitation and immunoelectron microscopy revealed that ANXA2 associates with COL6 and the SNARE proteins SNAP-23 and VAMP2 at secretory vesicle membranes of bronchial epithelial cells, and that absence of ANXA2 leads to retention of COL6 in a late-Golgi, VAMP2-positive compartment. These results define a new role for ANXA2 in the COL6 secretion pathway, and further show that this pathway establishes cell-matrix interactions that underlie normal pulmonary function and epithelial cell survival.

Alterations in junctional proteins, inflammatory mediators and extracellular matrix molecules in eosinophilic esophagitis

Eosinophilic esophagitis (EoE), an inflammatory atopic disease of the esophagus, causes massive eosinophil infiltration, basal cell hyperplasia, and sub-epithelial fibrosis. To elucidate cellular and molecular factors involved in esophageal tissue damage and remodeling, we examined pinch biopsies from EoE and normal pediatric patients. An inflammation gene array confirmed that eotaxin-3, its receptor CCR3 and interleukins IL-13 and IL-5 were upregulated. An extracellular matrix (ECM) gene array revealed upregulation of CD44 & CD54, and of ECM proteases (ADAMTS1 & MMP14). A cytokine antibody array showed a marked decrease in IL-1α and IL-1 receptor antagonist and an increase in eotaxin-2 and epidermal growth factor. Western analysis indicated reduced expression of intercellular junction proteins, E-cadherin and claudin-1 and increased expression of occludin and vimentin. We have identified a number of novel genes and proteins whose expression is altered in EoE. These findings provide new insights into the molecular mechanisms of the disease.

Collagen XIV is important for growth and structural integrity of the myocardium

Collagen XIV is a fibril-associated collagen with an interrupted triple helix (FACIT). Previous studies have shown that this collagen type regulates early stages of fibrillogenesis in connective tissues of high mechanical demand. Mice null for Collagen XIV are viable, however formation of the interstitial collagen network is defective in tendons and skin leading to reduced biomechanical function. The assembly of a tightly regulated collagen network is also required in the heart, not only for structural support but also for controlling cellular processes. Collagen XIV is highly expressed in the embryonic heart, notably within the cardiac interstitium of the developing myocardium, however its role has not been elucidated. To test this, we examined cardiac phenotypes in embryonic and adult mice devoid of Collagen XIV. From as early as E11.5, Col14a1(-/-) mice exhibit significant perturbations in mRNA levels of many other collagen types and remodeling enzymes (MMPs, TIMPs) within the ventricular myocardium. By post natal stages, collagen fibril organization is in disarray and the adult heart displays defects in ventricular morphogenesis. In addition to the extracellular matrix, Col14a1(-/-) mice exhibit increased cardiomyocyte proliferation at post natal, but not E11.5 stages, leading to increased cell number, yet cell size is decreased by 3 months of age. In contrast to myocytes, the number of cardiac fibroblasts is reduced after birth associated with increased apoptosis. As a result of these molecular and cellular changes during embryonic development and post natal maturation, cardiac function is diminished in Col14a1(-/-) mice from 3 months of age; associated with dilation in the absence of hypertrophy, and reduced ejection fraction. Further, Col14a1 deficiency leads to a greater increase in left ventricular wall thickening in response to pathological pressure overload compared to wild type animals. Collectively, these studies identify a new role for type XIV collagen in the formation of the cardiac interstitium during embryonic development, and highlight the importance of the collagen network for myocardial cell survival, and function of the working myocardium after birth.

Extracellular matrix remodelling properties of human fibrocytes

The fibrocytes are thought to serve as a source of newly deposited collagens I and III during reparative processes and in certain fibrotic disorders, but their matrix remodelling properties are incompletely understood. We evaluated their ability to produce several extracellular matrix (ECM) components, in comparison with fibroblasts, and to participate in collagen turnover. The collagen gene expression profile of fibrocytes differed from that of fibroblasts because fibrocytes constitutively expressed relatively high levels of the mRNA encoding collagen VI and significantly lower levels of the mRNA encoding collagens I, III and V. The proteoglycan (PG) gene expression profile was also different in fibrocytes and fibroblasts because fibrocytes constitutively expressed the mRNA encoding perlecan and versican at relatively high levels and the mRNA encoding biglycan and decorin at low and very low levels, respectively. Moreover, fibrocytes expressed the mRNA for hyaluronan synthase 2 at higher level than fibroblasts. Significant differences between the two cell populations were also demonstrated by metabolic labelling and analysis of the secreted collagenous proteins, PGs and hyaluronan. Fibrocytes constitutively expressed the scavenger receptors CD163 and CD204 as well as the mannose receptors CD206 and Endo180, and internalized and degraded collagen fragments through an Endo180-mediated mechanism. The results of this study demonstrate that human fibrocytes exhibit ECM remodelling properties previously unexplored, including the ability to participate in collagen turnover. The observed differences in collagen and PG expression profile between fibrocytes and fibroblasts suggest that fibrocytes may predominantly have a matrix-stabilizing function.

Subsynovial connective tissue is sensitive to surgical interventions in a rabbit model of carpal tunnel syndrome

The most common histological finding in carpal tunnel syndrome (CTS) is non-inflammatory fibrosis and thickening of the subsynovial connective tissue (SSCT) in the tunnel. While the cause of SSCT fibrosis and the relationship of SSCT fibrosis and CTS are unknown, one hypothesis is that SSCT injury causes fibrosis, and that the fibrosis then leads to CTS. We investigated the sensitivity of the SSCT to injuries. Two types of surgical interventions were performed in a rabbit model: A skin incision with tendon laceration and SSCT stretching sufficient to damage the SSCT, and skin incision alone. Twelve weeks after surgery, the rabbit carpal tunnel tissues were studied with immunochemistry for TGF-β receptors 1, 2, and 3, collagen III, and collagen VI. All TGF-β receptors were expressed. The percentages of the TGF-β receptors' expressions were less in the control SSCT fibroblasts than in the fibroblasts from rabbits with surgical interventions. The surgical interventions did not result in any alteration of collagen III expression. However, both surgical interventions resulted in a significant decrease in collagen VI expression compared to the control group. The two surgical interventions achieved similar expression of TGF-β receptors and collagens. Our results provide evidence that the SSCT is sensitive to surgical interventions, even when these are modest. Since SSCT fibrosis is a hallmark of CTS, these data also suggest that such fibrosis could result from relatively minor trauma.

ColVI myopathies: where do we stand, where do we go?

Collagen VI myopathies, caused by mutations in the genes encoding collagen type VI (ColVI), represent a clinical continuum with Ullrich congenital muscular dystrophy (UCMD) and Bethlem myopathy (BM) at each end of the spectrum, and less well-defined intermediate phenotypes in between. ColVI myopathies also share common features with other disorders associated with prominent muscle contractures, making differential diagnosis difficult. This group of disorders, under-recognized for a long time, has aroused much interest over the past decade, with important advances made in understanding its molecular pathogenesis. Indeed, numerous mutations have now been reported in the COL6A1, COL6A2 and COL6A3 genes, a large proportion of which are de novo and exert dominant-negative effects. Genotype-phenotype correlations have also started to emerge, which reflect the various pathogenic mechanisms at play in these disorders: dominant de novo exon splicing that enables the synthesis and secretion of mutant tetramers and homozygous nonsense mutations that lead to premature termination of translation and complete loss of function are associated with early-onset, severe phenotypes. In this review, we present the current state of diagnosis and research in the field of ColVI myopathies. The past decade has provided significant advances, with the identification of altered cellular functions in animal models of ColVI myopathies and in patient samples. In particular, mitochondrial dysfunction and a defect in the autophagic clearance system of skeletal muscle have recently been reported, thereby opening potential therapeutic avenues.

A proteomic approach for identification and localization of the pericellular components of chondrocytes

Although the pericellular matrix (PCM) plays a central role in the communication between chondrocytes and extracellular matrix, its composition is largely unknown. In this study, the PCM was investigated with a proteomic approach using chondrons, which are enzymatically isolated constructs including the chondrocyte and its surrounding PCM. Chondrons and chondrocytes alone were isolated from human articular cartilage. Proteins extracted from chondrons and chondrocytes were used for two-dimensional electrophoresis. Protein spots were quantitatively compared between chondron and chondrocyte gels. Cellular proteins, which had similar density between chondron and chondrocyte gels, did not proceed for analysis. Since chondrons only differ from chondrocytes in association of the PCM, protein spots in the chondron gels that had higher quantity than that in the chondrocyte gels were selected as candidates of the PCM components and processed for mass spectrometry. Among 15 identified peptides, several were fragments of the three type VI collagen chains (α-1, α-2, and α-3). Other identified PCM proteins included triosephosphate isomerase, transforming growth factor-β induced protein, peroxiredoxin-4, ADAM (A disintegrin and metalloproteinases) 28, and latent-transforming growth factor beta-binding protein-2. These PCM components were verified with immunohisto(cyto)chemistry for localization in the PCM region of articular cartilage. The abundance of type VI collagen in the PCM emphasizes its importance to the microenvironment of chondrocytes. Several proteins were localized in the PCM of chondrocytes for the first time and that warrants further investigation for their functions in cartilage biology.

The protective role of the pericellular matrix in chondrocyte apoptosis

INTRODUCTION

This study was designed to quantify the role of the pericellular matrix (PCM) in chondrocyte apoptosis using chondrons, which are a cartilage functional unit including a chondrocyte and its associated PCM.

METHODS

Chondrocytes and chondrons were enzymatically isolated from human articular cartilage and exposed to monosodium iodoacetate (MIA) and staurosporine for apoptosis induction. Chondrons were defined by the presence of type VI collagen, a basic component of the PCM. Apoptosis of chondrocytes and chondrons was measured with annexin V binding by flow cytometry and verified with terminal dUTP nick end-labeling staining. In a separate experiment, isolated chondrocytes were treated with soluble type VI collagen, before or after apoptosis induction with MIA, and cell death was measured by the activity of LDH and terminal dUTP nick end-labeling staining.

RESULTS

Chondrocytes treated with MIA incurred 27% cell death, compared with 12% in chondrons. On treating with MIA, 9% of chondrocytes underwent apoptosis, compared with only 1.6% of chondrons. Similarly, staurosporine induced 13% apoptosis in chondrocytes, whereas it was 3% in chondrons. Preincubation of type VI collagen effectively prevented chondrocytes from MIA-induced cell death. After apoptosis was induced with MIA, however, treatment with type VI collagen failed to rescue chondrocytes from death.

CONCLUSION

The PCM, a native microenvironment of chondrocytes, protects chondrocytes from apoptosis. Type VI collagen is a functional component of the PCM that contributes to the survival of chondrocytes.

Corneal collagen-its role in maintaining corneal shape and transparency

Corneal collagen has a number of properties that allow it to fulfil its role as the main structural component within the tissue. Fibrils are narrow, uniform in diameter and precisely organised. These properties are vital to maintain transparency and to provide the biomechanical prerequisites necessary to sustain shape and provide strength. This review describes the structure and arrangement of corneal collagen from the nanoscopic to the macroscopic level, and how this relates to the maintenance of the form and transparency of the cornea.

Metabolic dysregulation and adipose tissue fibrosis: role of collagen VI

Adipocytes are embedded in a unique extracellular matrix whose main function is to provide mechanical support, in addition to participating in a variety of signaling events. During adipose tissue expansion, the extracellular matrix requires remodeling to accommodate adipocyte growth. Here, we demonstrate a general upregulation of several extracellular matrix components in adipose tissue in the diabetic state, therefore implicating "adipose tissue fibrosis" as a hallmark of metabolically challenged adipocytes. Collagen VI is a highly enriched extracellular matrix component of adipose tissue. The absence of collagen VI results in the uninhibited expansion of individual adipocytes and is paradoxically associated with substantial improvements in whole-body energy homeostasis, both with high-fat diet exposure and in the ob/ob background. Collectively, our data suggest that weakening the extracellular scaffold of adipocytes enables their stress-free expansion during states of positive energy balance, which is consequently associated with an improved inflammatory profile. Therefore, the disproportionate accumulation of extracellular matrix components in adipose tissue may not be merely an epiphenomenon of metabolically challenging conditions but may also directly contribute to a failure to expand adipose tissue mass during states of excess caloric intake.

Predominant fiber atrophy and fiber type disproportion in early ullrich disease

Ullrich disease (congenital muscular dystrophy type Ullrich, UCMD) is a severe congenital disorder of muscle caused by recessive and dominant mutations in the three genes that encode the alpha-chains of collagen type VI. Little is known about the early pathogenesis of this myopathy. The aim of this study was to investigate early histological changes in muscle of patients with molecularly confirmed UCMD. Muscle biopsies were analyzed from 8 UCMD patients ranging in age from 6 to 30 months. Type I fiber atrophy and predominance were seen early, together with a widening of the fiber diameter spectrum, whereas no dystrophic features were apparent. A subpopulation of more severely atrophic type I fibers was apparent subsequently, including one biopsy that fulfilled the formal diagnostic criteria of histopathological fiber type disproportion (FTD). Thus, early in the disease, UCMD presents as a non-dystrophic myopathy with predominant fiber atrophy. Collagen VI mutations also qualify as a cause of fiber type disproportion.

Production of type VI collagen by human macrophages: a new dimension in macrophage functional heterogeneity

Macrophages derived from human blood monocytes perform many tasks related to tissue injury and repair. The main effect of macrophages on the extracellular matrix is considered to be destructive in nature, because macrophages secrete metalloproteinases and ingest foreign material as part of the remodeling process that occurs in wound healing and other pathological conditions. However, macrophages also contribute to the extracellular matrix and hence to tissue stabilization both indirectly, by inducing other cells to proliferate and to release matrix components, and directly, by secreting components of the extracellular matrix such as fibronectin and type VIII collagen, as we have recently shown. We now report that monocytes and macrophages express virtually all known collagen and collagen-related mRNAs. Furthermore, macrophages secrete type VI collagen protein abundantly, depending upon their mode of activation, stage of differentiation, and cell density. The primary function of type VI collagen secreted by macrophages appears to be modulation of cell-cell and cell-matrix interactions. We suggest that the production of type VI collagen is a marker for a nondestructive, matrix-conserving macrophage phenotype that could profoundly influence physiological and pathophysiological conditions in vivo.

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.

Development of a hemicornea from human primary cell cultures for pharmacotoxicology testing

We report the reconstruction and characterization of a hemicornea (epithelialized stroma), using primary human cells, for use in research and as an alternative to the use of animals in pharmacotoxicology testing. To create a stromal equivalent, keratocytes from human corneas were cultured in collagen-glycosaminoglycan-chitosan foams. Limbal stem cell-derived epithelial cells were seeded on top of these, giving rise to hemi-corneas. The epithelium appeared morphologically similar to its physiological counterpart, as shown by the basal cell expression of p63 isoforms including, in some cases, the stem cell marker p63DeltaNalpha, and the expression of keratin 3 and 14-3-3sigma in the upper cell layers. In addition, the cuboidal basal epithelial cells were anchored to a basement membrane containing collagen IV, laminin 5, and hemidesmosomes. In the stromal part, the keratocytes colonized the porous scaffold, formed a network of interconnecting cells, and synthesized an ultrastructurally organized extracellular matrix (ECM) containing collagen types I, V, and VI. Electron microscopy showed the newly synthesized collagen fibrils to have characteristic periodic striations, with diameters and interfibril spacings similar to those found in natural corneas. Compared to existing models for corneal pharmacotoxicology testing, this new model more closely approaches physiological conditions by including the inducing effects of mesenchyme and cell-matrix interactions on epithelial cell morphogenesis.

Collagen VI related muscle disorders

Mutations in the genes encoding collagen VI (COL6A1, COL6A2, and COL6A3) cause Bethlem myopathy (BM) and Ullrich congenital muscular dystrophy (UCMD), two conditions which were previously believed to be completely separate entities. BM is a relatively mild dominantly inherited disorder characterised by proximal weakness and distal joint contractures. UCMD was originally described as an autosomal recessive condition causing severe muscle weakness with proximal joint contractures and distal hyperlaxity. Here we review the clinical phenotypes of BM and UCMD and their diagnosis and management, and provide an overview of the current knowledge of the pathogenesis of collagen VI related disorders.

The role of apoptosis in neuromuscular diseases and prospects for anti-apoptosis therapy

Although genetic mutations that are responsible for most of the inherited neuromuscular diseases have been identified, the molecular and cellular mechanisms that cause muscle and nerve depletion are not well understood and therapies are lacking. Histological studies of many neuromuscular diseases indicated that loss of motor-nerve and/or skeletal-muscle function might be due to excessive cell death by apoptosis. Recent studies have confirmed this possibility by showing that pathology in mouse models of amyotrophic lateral sclerosis, congenital muscular dystrophy, oculopharyngeal muscular dystrophy and collagen-VI deficiency, but not Duchenne muscular dystrophy, is significantly ameliorated by genetic or pharmacological interventions that have been designed to inhibit apoptosis. Thus, apoptosis greatly contributes to pathology in mouse models of several neuromuscular diseases, and appropriate anti-apoptosis therapy might therefore be beneficial for the corresponding human diseases.

Type VI collagen induces cardiac myofibroblast differentiation: implications for postinfarction remodeling

Cardiac fibroblast (CF) proliferation and differentiation into hypersecretory myofibroblasts can lead to excessive extracellular matrix (ECM) production and cardiac fibrosis. In turn, the ECM produced can potentially activate CFs via distinct feedback mechanisms. To assess how specific ECM components influence CF activation, isolated CFs were plated on specific collagen substrates (type I, III, and VI collagens) before functional assays were carried out. The type VI collagen substrate potently induced myofibroblast differentiation but had little effect on CF proliferation. Conversely, the type I and III collagen substrates did not affect differentiation but caused significant induction of proliferation (type I, 240.7 +/- 10.3%, and type III, 271.7 +/- 21.8% of basal). Type I collagen activated ERK1/2, whereas type III collagen did not. Treatment of CFs with angiotensin II, a potent mitogen of CFs, enhanced the growth observed on types I and III collagen but not on the type VI collagen substrate. Using an in vivo model of myocardial infarction (MI), we measured changes in type VI collagen expression and myofibroblast differentiation after post-MI remodeling. Concurrent elevations in type VI collagen and myofibroblast content were evident in the infarcted myocardium 20-wk post-MI. Overall, types I and III collagen stimulate CF proliferation, whereas type VI collagen plays a potentially novel role in cardiac remodeling through facilitation of myofibroblast differentiation.

Adipocyte-derived collagen VI affects early mammary tumor progression in vivo, demonstrating a critical interaction in the tumor/stroma microenvironment

The interactions of transformed cells with the surrounding stromal cells are of importance for tumor progression and metastasis. The relevance of adipocyte-derived factors to breast cancer cell survival and growth is well established. However, it remains unknown which specific adipocyte-derived factors are most critical in this process. Collagen VI is abundantly expressed in adipocytes. Collagen(-/-) mice in the background of the mouse mammary tumor virus/polyoma virus middle T oncogene (MMTV-PyMT) mammary cancer model demonstrate dramatically reduced rates of early hyperplasia and primary tumor growth. Collagen VI promotes its growth-stimulatory and pro-survival effects in part by signaling through the NG2/chondroitin sulfate proteoglycan receptor expressed on the surface of malignant ductal epithelial cells to sequentially activate Akt and beta-catenin and stabilize cyclin D1. Levels of the carboxyterminal domain of collagen VIalpha3, a proteolytic product of the full-length molecule, are dramatically upregulated in murine and human breast cancer lesions. The same fragment exerts potent growth-stimulatory effects on MCF-7 cells in vitro. Therefore, adipocytes play a vital role in defining the ECM environment for normal and tumor-derived ductal epithelial cells and contribute significantly to tumor growth at early stages through secretion and processing of collagen VI.

SREBP contributes to induction of collagen VI transcription by serum starvation

Collagen VI is a main extracellular matrix protein whose mutation is linked to myopathic diseases. In myoblasts and other cell types, collagen VI gene transcription peaks during cell-cycle exit that precedes differentiation, upon serum withdrawal or confluence. To get insight into this transcriptional regulation, we characterized a growth arrest responsive region (GARR) in the Col6a1 promoter responsible for this effect. In this work, we identify sterol regulatory element binding protein (SREBP) as a GARR binding protein and provide evidence that SREBP contributes to induction of Col6a1 transcription in serum free conditions. Furthermore, our data unveil a previously unexpected link between extracellular matrix production and LDL signaling.

Mitochondrial dysfunction and apoptosis in myopathic mice with collagen VI deficiency

Collagen VI is an extracellular matrix protein that forms a microfilamentous network in skeletal muscles and other organs. Inherited mutations in genes encoding collagen VI in humans cause two muscle diseases, Bethlem myopathy and Ullrich congenital muscular dystrophy. We previously generated collagen VI-deficient (Col6a1-/-) mice and showed that they have a muscle phenotype that strongly resembles Bethlem myopathy. The pathophysiological defects and mechanisms leading to the myopathic disorder were not known. Here we show that Col6a1-/- muscles have a loss of contractile strength associated with ultrastructural alterations of sarcoplasmic reticulum (SR) and mitochondria and spontaneous apoptosis. We found a latent mitochondrial dysfunction in myofibers of Col6a1-/- mice on incubation with the selective F1F(O)-ATPase inhibitor oligomycin, which caused mitochondrial depolarization, Ca2+ deregulation and increased apoptosis. These defects were reversible, as they could be normalized by plating Col6a1-/- myofibers on collagen VI or by addition of cyclosporin A (CsA), the inhibitor of mitochondrial permeability transition pore (PTP). Treatment of Col6a1-/- mice with CsA rescued the muscle ultrastructural defects and markedly decreased the number of apoptotic nuclei in vivo. These findings indicate that collagen VI myopathies have an unexpected mitochondrial pathogenesis that could be exploited for therapeutic intervention.

Changes in epithelial cell turnover and extracellular matrix in human small intestine after TPN

BACKGROUND

The atrophy and architectural remodeling of the jejunal mucosa arising in adults receiving total parenteral nutrition (TPN) has been suggested to originate from a disturbance in tissue homeostasis. The present study aims at examining (1) whether there are differences in proliferation and apoptosis of epithelial cells between enterally and parenterally nourished patients and (2) whether the distribution pattern of extracellular matrix (ECM) proteins known to influence cell turnover along the the crypt-villus axis is changed after TPN.

METHODS

The mitotic frequency and the proliferation index [using an antibody against Ki-67 antigen (MIB 1)] were determined on epoxy semithin and paraffin sections, respectively. Morphological techniques and the TUNEL assay were applied to detect apoptotic events. Immunolocalization of collagen IV, laminin, fibronectin, tenascin, and collagen VI was performed on cryosections.

RESULTS

After TPN the cell renewal was significantly enhanced, while epithelial cell death was drastically reduced. The comparison of TPN and EN patients revealed differences in the distribution patterns of the ECM proteins laminin, fibronectin, and tenascin along the crypt-villus axis. Moreover, after TPN an increased expression of collagen types IV and VI was observed.

CONCLUSIONS

TPN in human adults is associated with alterations in epithelial cell turnover and changes in expression and/or localization of ECM proteins. Thus, the inverted route of nutrient supply in patients might modify environmental tissue conditions, which may influence the interactions between intestinal epithelial cells and the extracellular matrix.

Different apoptotic responses and patterns in adhering and floating neoplastic cell cultures: effects of microtubule antagonists

The relationship between apoptotic progression and cell cycle perturbation induced by microtubule-destabilising (vinblastine, Colcemid) and -stabilising (taxol) drugs was studied in two mesenchyme-derived neoplastic cell lines, growing as suspension (Jurkat) and monolayer (SGS/3A) culture, by morphocytochemical and biochemical approaches. The same kind of drug induced different effects on the cell kinetics (proliferation, polyploidisation, death) of the two cell lines. In floating cells, the drugs appeared more effective during the S phase, while in adherent cells they were more effective during the G2/M phase. Moreover two distinct neoplasia-associated apoptotic phenotypes emerged: the first pattern was the typical one and was found in cells with a low transition through the S/G2 phase (Jurkat), and the second one was mainly characterised by a cell death derived from micronucleated and mitotic cells, as a consequence of a low transition through the M/G1 phase (SGS/3A). Our data show that the machinery required for the trigger and progression of apoptosis is present in every cell cycle phase, also in conditions of karyological alterations (aneugenic micronucleations). On the other hand, a different sensitivity of the two microtubular components (interphasic network and mitotic spindle) appears to be related to the anchorage-dependence or -independence during the cell growth disturbances after exposure to antimicrotubular drugs.

Matrix-mediated cellular rejuvenation

Biomaterial surface morphology and chemistry influence cell responses mediated via signaling cascades that regulate a wide range of metabolic processes. These responses may range from changes in surface adhesion and remodeling of the extracellular matrix to activation of cytokine, cytoskeletal and other biochemical pathways regulating or modulating cellular morphology and function. The present study has focused on collagen Type I, a key extracellular matrix protein, and its potential impact on the process of cellular aging. This study was undertaken for several reasons. First, several investigators reported that growth of cells on a collagen matrix markedly enhanced the resistance of cells to stresses. Second, a large body of accumulated data strongly indicated a relationship between the potential to respond to stresses and cellular aging with the former strongly influencing the rate of the latter. Finally, it has been recently demonstrated that in aged cells one of the key aging-related processes previously considered irreversible, attenuation of the expression of a major stress response protein, Hsp70, can be reversed. This fact together with a probable regulatory role of the stress response potential in cellular aging suggested a possibility that the cellular aging process as a whole can be altered. Indeed, in the present study, growth on a denatured collagen matrices reversed in aged cells not only the attenuation of Hsp70 expression but also other aging-related processes, such as beta-galactosidase expression, increase in protein oxidation and changes in cell morphology. Moreover, it appeared to reduce the rate of aging in young cells. Understanding the nature of collagen matrix-mediated cellular rejuvenation might suggest approaches for interfering with organismic aging. Some immediate applications include cell rejuvenation for purposes of cloning and reduction of the rate of aging during expansion of stem cells for purposes of tissue engineering.

The alpha5beta1 integrin provides matrix survival signals for normal and osteoarthritic human articular chondrocytes in vitro

OBJECTIVE

Chondrocyte cell death may play an important role in the development of arthritis. The goal of the present study was to evaluate the role of the extracellular matrix (ECM) in promoting chondrocyte survival via signals through the integrin family of ECM receptors.

METHODS

Chondrocytes were isolated by sequential enzymatic digestion from normal ankle cartilage of organ donors and from osteoarthritic (OA) knee tissue obtained from patients undergoing total knee replacement. Cell survival in monolayer and in suspension culture was measured using fluorescent labels after treatment with specific integrin-blocking antibodies and echistatin, a disintegrin peptide. A quantitative enzyme-linked immunosorbent assay for histone-associated DNA fragments and morphologic evaluation by electron microscopy were used to evaluate apoptosis.

RESULTS

Freshly isolated chondrocytes died when plated in serum-free media at low density on poly-L-lysine, but showed >95% survival on fibronectin (FN). A monoclonal blocking antibody to the alpha5-integrin subunit (FN receptor) significantly inhibited survival on FN, whereas control antibodies had no effect. Likewise, treatment of freshly isolated chondrocytes in serum-free alginate-suspension culture with the alpha5-blocking antibody resulted in cell death in a dose-dependent manner, with 20 microg/ml of the antibody reducing normal chondrocyte survival to 20% of that in controls, and OA chondrocyte survival to 23% of that in controls. Antibody inhibition of alphav and alpha1 integrins or treatment with echistatin did not cause cell death. Addition of insulin-like growth factor 1 (IGF-1; 100 ng/ ml) was not able to improve survival of alpha5-antibody-treated cells. However, treatment with 10% fetal bovine serum improved normal chondrocyte survival to 98% (a 5.1-fold increase) and OA chondrocyte survival to 64% (a 2.8-fold increase). Cell death due to alpha5 inhibition was associated with apoptosis.

CONCLUSION

These results demonstrate that chondrocyte survival signals are transmitted via the alpha5beta1 FN receptor. Inhibition of matrix survival signals mediated by alpha5beta1 also inhibits the ability of IGF-1 to promote survival, suggesting that IGF-1-mediated survival signaling may require a cosignal from alpha5beta1.

Collagen VI deficiency affects the organization of fibronectin in the extracellular matrix of cultured fibroblasts

Fibronectin is one of the main components of the extracellular matrix and associates with a variety of other matrix molecules including collagens. We demonstrate that the absence of secreted type VI collagen in cultured primary fibroblasts affects the arrangement of fibronectin in the extracellular matrix. We observed a fine network of collagen VI filaments and fibronectin fibrils in the extracellular matrix of normal murine and human fibroblasts. The two microfibrillar systems did not colocalize, but were interconnected at some discrete sites which could be revealed by immunoelectron microscopy. Direct interaction between collagen VI and fibronectin was also demonstrated by far western assay. When primary fibroblasts from Col6a1 null mutant mice were cultured, collagen VI was not detected in the extracellular matrix and a different pattern of fibronectin organization was observed, with fibrils running parallel to the long axis of the cells. Similarly, an abnormal fibronectin deposition was observed in fibroblasts from a patient affected by Bethlem myopathy, where collagen VI secretion was drastically reduced. The same pattern was also observed in normal fibroblasts after in vivo perturbation of collagen VI-fibronectin interaction with the 3C4 anti-collagen VI monoclonal antibody. Competition experiments with soluble peptides indicated that the organization of fibronectin in the extracellular matrix was impaired by added soluble collagen VI, but not by its triple helical (pepsin-resistant) fragments. These results indicate that collagen VI mediates the three-dimensional organization of fibronectin in the extracellular matrix of cultured fibroblasts.

Soluble collagen VI drives serum-starved fibroblasts through S phase and prevents apoptosis via down-regulation of Bax

We previously showed that soluble, pepsin-solubilized collagen VI increases de novo DNA synthesis in serum-starved HT1080 and 3T3 fibroblasts up to 100-fold compared with soluble collagen I, reaching 80% of the stimulation caused by 10% fetal calf serum. Here we show that collagen VI also inhibits apoptotic cell death in serum-starved cells as evidenced by morphological criteria, DNA laddering, complementary apoptosis assays (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, enzyme-linked immunosorbent assay, and fluorescence-activated cell sorting), and quantification of apoptosis-regulating proteins. In the presence of starving medium alone or collagen I, the proapoptotic Bax was up-regulated 2-2.5-fold, compared with soluble collagen VI and fetal calf serum, whereas levels of the antiapoptotic Bcl-2 protein remained unaffected. In accordance with its potent stimulation of DNA synthesis, soluble collagen VI carries serum-starved HT1080 and Balb 3T3 fibroblasts through G(2) as shown by fluorescence-activated cell sorting analysis, whereas cells exposed to medium and collagen I where arrested at G(1)-S. This was accompanied by a 2-3-fold increase in cyclin A, B, and D1 protein expression. Collagen VI-induced inhibition of apoptotic cell death may be operative during embryogenesis, wound healing, and fibrosis when elevated tissue and blood levels of collagen VI are observed, thus initiating a feedback loop of mesenchymal cell activation and proliferation.

Collagens and atherosclerosis

Smooth muscle cells in the atherosclerotic lesions of diseased arteries produce new extracellular matrix, largely collagenous in nature, which is responsible in part for the occlusion of the vessel lumen by the atherosclerotic plaque. These smooth muscle cells express a different phenotype, responsive to growth factors, to that of the differentiated, nondividing contractile cell in the media. Specific collagens may be involved in the regulation of phenotype and in the migration of the cells to the site of lesion growth. Collagens may also be involved in the calcification of lesions, in the retention of low-density lipoprotein in the vessel wall and in smooth muscle cell survival. Glycation of collagen may promote atherogenesis. Effects as summarized in this short review, are not always, at first sight, consistent. The following points should be kept in mind, though, when considering the response of a cell to collagen. Any effect may be governed not just by the identity of the collagen type as such but by its state of polymerization: monomeric collagen, for instance, whether in solution or immobilized on plastic, may express different effects to the same collagen type when presented in its native polymerized state, e.g., as fibers. The precise identity of the cell and its location may be important: SMCs in secondary culture may not necessarily respond to any given collagen exactly as SMCs within the lesion or possess precisely the same properties, albeit both types are regarded as expressing the same (synthetic) phenotype. Effects may not necessarily be directly attributable to collagen, but to some other matrix constituent bound to collagen.