Developmentally regulated expression of type XV collagen correlates with abnormalities in Col15a1(-/-) mice

Rare disease research workflow using multilayer networks elucidates the molecular determinants of severity in Congenital Myasthenic Syndromes

Exploring the molecular basis of disease severity in rare disease scenarios is a challenging task provided the limitations on data availability. Causative genes have been described for Congenital Myasthenic Syndromes (CMS), a group of diverse minority neuromuscular junction (NMJ) disorders; yet a molecular explanation for the phenotypic severity differences remains unclear. Here, we present a workflow to explore the functional relationships between CMS causal genes and altered genes from each patient, based on multilayer network community detection analysis of complementary biomedical information provided by relevant data sources, namely protein-protein interactions, pathways and metabolomics. Our results show that CMS severity can be ascribed to the personalized impairment of extracellular matrix components and postsynaptic modulators of acetylcholine receptor (AChR) clustering. This work showcases how coupling multilayer network analysis with personalized -omics information provides molecular explanations to the varying severity of rare diseases; paving the way for sorting out similar cases in other rare diseases.

Lineage-specific differences and regulatory networks governing human chondrocyte development

To address large gaps in our understanding of the molecular regulation of articular and growth plate cartilage development in humans, we used our directed differentiation approach to generate these distinct cartilage tissues from human embryonic stem cells. The resulting transcriptomic profiles of hESC-derived articular and growth plate chondrocytes were similar to fetal epiphyseal and growth plate chondrocytes, with respect to genes both known and previously unknown to cartilage biology. With the goal to characterize the regulatory landscapes accompanying these respective transcriptomes, we mapped chromatin accessibility in hESC-derived chondrocyte lineages, and mouse embryonic chondrocytes, using ATAC-sequencing. Integration of the expression dataset with the differentially accessible genomic regions revealed lineage-specific gene regulatory networks. We validated functional interactions of two transcription factors (TFs) (RUNX2 in growth plate chondrocytes and RELA in articular chondrocytes) with their predicted genomic targets. The maps we provide thus represent a framework for probing regulatory interactions governing chondrocyte differentiation. This work constitutes a substantial step towards comprehensive and comparative molecular characterizations of distinct chondrogenic lineages and sheds new light on human cartilage development and biology.

Genetics and Molecular Basis of Congenital Heart Defects in Down Syndrome: Role of Extracellular Matrix Regulation

Down syndrome (DS), a complex disorder that is caused by the trisomy of chromosome 21 (Hsa21), is a major cause of congenital heart defects (CHD). Interestingly, only about 50% of individuals with Hsa21 trisomy manifest CHD. Here we review the genetic basis of CHD in DS, focusing on genes that regulate extracellular matrix (ECM) organization. The overexpression of Hsa21 genes likely underlies the molecular mechanisms that contribute to CHD, even though the genes responsible for CHD could only be located in a critical region of Hsa21. A role in causing CHD has been attributed not only to protein-coding Hsa21 genes, but also to genes on other chromosomes, as well as miRNAs and lncRNAs. It is likely that the contribution of more than one gene is required, and that the overexpression of Hsa21 genes acts in combination with other genetic events, such as specific mutations or polymorphisms, amplifying their effect. Moreover, a key function in determining alterations in cardiac morphogenesis might be played by ECM. A large number of genes encoding ECM proteins are overexpressed in trisomic human fetal hearts, and many of them appear to be under the control of a Hsa21 gene, the RUNX1 transcription factor.

Collagen fibrils and cell nuclei are entrapped within Randall's plaques but not in CaOx matrix overgrowth: A microscopic inquiry into Randall's plaque stone pathogenesis

Calcium oxalate (CaOx) stones can grow attached to the renal papillary calcification known as Randall's plaque. Although stone growth on Randall's plaque is a common phenomenon, this mechanism of stone formation is still poorly understood. The objective of this study was to investigate the microenvironment of mature Randall's plaque, explore its molecular composition and differentiate plaque from CaOx overgrowth using multimodal imaging on demineralized stone sections. Fluorescence imaging showed consistent differences in autofluorescence patterns between Randall's plaque and calcium oxalate overgrowth regions. Second harmonic generation imaging established the presence of collagen only in regions of decalcified Randall's plaque but not in regions of CaOx overgrowth matrix. Surprisingly, in these stone sections we observed cell nuclei with preserved morphology within regions of mature Randall's plaque. These conserved cells had variable expression of vimentin and CD45. The presence of nuclei in mature plaque indicates that mineralization is not necessarily associated with cell death. The markers identified suggest that some of the entrapped cells may be undergoing dedifferentiation or could emanate from a mesenchymal or immune origin. We propose that entrapped cells may play an important role in the growth and maintenance of Randall's plaque. Further characterization of these cells and thorough analyses of the mineralized stone forming renal papilla will be fundamental in understanding the pathogenesis of Randall's plaque and CaOx stone formation.

Mammary collagen is under reproductive control with implications for breast cancer

Mammographically-detected breast density impacts breast cancer risk and progression, and fibrillar collagen is a key component of breast density. However, physiologic factors influencing collagen production in the breast are poorly understood. In female rats, we analyzed gene expression of the most abundantly expressed mammary collagens and collagen-associated proteins across a pregnancy, lactation, and weaning cycle. We identified a triphasic pattern of collagen gene regulation and evidence for reproductive state-dependent composition. An initial phase of collagen deposition occurred during pregnancy, followed by an active phase of collagen suppression during lactation. The third phase of collagen regulation occurred during weaning-induced mammary gland involution, which was characterized by increased collagen deposition. Concomitant changes in collagen protein abundance were confirmed by Masson's trichrome staining, second harmonic generation (SHG) imaging, and mass spectrometry. We observed similar reproductive-state dependent collagen patterns in human breast tissue obtained from premenopausal women. SHG analysis also revealed structural variation in collagen across a reproductive cycle, with higher packing density and more collagen fibers arranged perpendicular to the mammary epithelium in the involuting rat mammary gland compared to nulliparous and lactating glands. Involution was also characterized by high expression of the collagen cross-linking enzyme lysyl oxidase, which was associated with increased levels of cross-linked collagen. Breast cancer relevance is suggested, as we found that breast cancer diagnosed in recently postpartum women displayed gene expression signatures of increased collagen deposition and crosslinking compared to breast cancers diagnosed in age-matched nulliparous women. Using publically available data sets, we found this involution-like, collagen gene signature correlated with poor progression-free survival in breast cancer patients overall and in younger women. In sum, these findings of physiologic collagen regulation in the normal mammary gland may provide insight into normal breast function, the etiology of breast density, and inform breast cancer risk and outcomes.

Deletion of Col15a1 Modulates the Tumour Extracellular Matrix and Leads to Increased Tumour Growth in the MMTV-PyMT Mouse Mammary Carcinoma Model

Basement membrane (BM) zone-associated collagen XV (ColXV) has been shown to suppress the malignancy of tumour cells, and its restin domain can inhibit angiogenesis. In human breast cancer, as well as in many other human carcinomas, ColXV is lost from the epithelial BM zone prior to tumour invasion. Here, we addressed the roles of ColXV in breast carcinogenesis using the transgenic MMTV-PyMT mouse mammary carcinoma model. We show here for the first time that the inactivation of Col15a1 in mice leads to changes in the fibrillar tumour matrix and to increased mammary tumour growth. ColXV is expressed by myoepithelial and endothelial cells in mammary tumours and is lost from the ductal BM along with the loss of the myoepithelial layer during cancer progression while persisting in blood vessels and capillaries, even in invasive tumours. However, despite the absence of anti-angiogenic restin domain, neovascularisation was reduced rather than increased in the ColXV-deficient mammary tumours compared to controls. We also show that, in robust tumour cell transplantation models or in a chemical-induced fibrosarcoma model, the inactivation of Col15a1 does not affect tumour growth or angiogenesis. In conclusion, our results support the proposed tumour suppressor function of ColXV in mammary carcinogenesis and reveal diverse roles of this collagen in different cancer types.

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.

Relapse of pathological angiogenesis: functional role of the basement membrane and potential treatment strategies

Blinding eye diseases such as corneal neovascularization, proliferative diabetic retinopathy, and age-related macular degeneration are driven by pathological angiogenesis. In cancer, angiogenesis is key for tumor growth and metastasis. Current antiangiogenic treatments applied clinically interfere with the VEGF signaling pathway-the main angiogenic pathway-to inhibit angiogenesis. These treatments are, however, only partially effective in regressing new pathologic vessels, and the disease relapses following cessation of treatment. Moreover, the relapse of pathological angiogenesis can be rapid, aggressive and more difficult to treat than angiogenesis in the initial phase. The manner in which relapse occurs is poorly understood; however, recent studies have begun to shed light on the mechanisms underlying the revascularization process. Hypotheses have been generated to explain the rapid angiogenic relapse and increased resistance of relapsed disease to treatment. In this context, the present review summarizes knowledge of the various mechanisms of disease relapse gained from different experimental models of pathological angiogenesis. In addition, the basement membrane-a remnant of regressed vessels-is examined in detail to discuss its potential role in disease relapse. Finally, approaches for gaining a better understanding of the relapse process are discussed, including prospects for the management of relapse in the context of disease.

Collagen XV, a multifaceted multiplexin present across tissues and species

Type XV collagen is a non-fibrillar collagen that is associated with basement membranes and belongs to the multiplexin subset of the collagen superfamily. Collagen XV was initially studied because of its sequence homology with collagen XVIII/endostatin whose anti-angiogenic and anti-tumorigenic properties were subjects of wide interest in the past years. But during the last fifteen years, collagen XV has gained growing attention with increasing number of studies that have attributed new functions to this widely distributed collagen/proteoglycan hybrid molecule. Despite the cumulative evidence of its functional pleiotropy and its evolutionary conserved function, no review compiling the current state of the art about collagen XV is currently available. Here, we thus provide the first comprehensive view of the knowledge gathered so far on the molecular structure, tissue distribution and functions of collagen XV in development, tissue homeostasis and disease with an evolutionary perspective. We hope that our review will open new roads for promising research on collagen XV in the coming years.

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Type XV collagen belongs to the multiplexin subset of the collagen superfamily.

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It is evolutionarily conserved collagen and associated with basement membranes.

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This collagen/proteoglycan hybrid molecule contains an anti-angiogenic restin domain.

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It has important functions in the cardiovascular and the neuromuscular systems.

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Its expression is dysregulated in various diseases including cancers.

Extracellular Matrix in Regulation of Contractile System in Cardiomyocytes

The contractile apparatus of cardiomyocytes is considered to be a stable system. However, it undergoes strong rearrangements during heart development as cells progress from their non-muscle precursors. Long-term culturing of mature cardiomyocytes is also accompanied by the reorganization of their contractile apparatus with the conversion of typical myofibrils into structures of non-muscle type. Processes of heart development as well as cell adaptation to culture conditions in cardiomyocytes both involve extracellular matrix changes, which appear to be crucial for the maturation of contractile apparatus. The aim of this review is to analyze the role of extracellular matrix in the regulation of contractile system dynamics in cardiomyocytes. Here, the remodeling of actin contractile structures and the expression of actin isoforms in cardiomyocytes during differentiation and adaptation to the culture system are described along with the extracellular matrix alterations. The data supporting the regulation of actin dynamics by extracellular matrix are highlighted and the possible mechanisms of such regulation are discussed.

Transcriptome Profiling of Primary Skin Fibroblasts Reveal Distinct Molecular Features Between PLOD1- and FKBP14-Kyphoscoliotic Ehlers-Danlos Syndrome

Kyphoscoliotic Ehlers-Danlos Syndrome (kEDS) is a rare genetic heterogeneous disease clinically characterized by congenital muscle hypotonia, kyphoscoliosis, and joint hypermobility. kEDS is caused by biallelic pathogenic variants in either PLOD1 or FKBP14. PLOD1 encodes the lysyl hydroxylase 1 enzyme responsible for hydroxylating lysyl residues in the collagen helix, which undergo glycosylation and form crosslinks in the extracellular matrix thus contributing to collagen fibril strength. FKBP14 encodes a peptidyl-prolyl cis-trans isomerase that catalyzes collagen folding and acts as a chaperone for types III, VI, and X collagen. Despite genetic heterogeneity, affected patients with mutations in either PLOD1 or FKBP14 are clinically indistinguishable. We aim to better understand the pathomechanism of kEDS to characterize distinguishing and overlapping molecular features underlying PLOD1-kEDS and FKBP14-kEDS, and to identify novel molecular targets that may expand treatment strategies. Transcriptome profiling by RNA sequencing of patient-derived skin fibroblasts revealed differential expression of genes encoding extracellular matrix components that are unique between PLOD1-kEDS and FKBP14-kEDS. Furthermore, we identified genes involved in inner ear development, vascular remodeling, endoplasmic reticulum (ER) stress, and protein trafficking that were differentially expressed in patient fibroblasts compared to controls. Overall, our study presents the first transcriptomics data in kEDS revealing distinct molecular features between PLOD1-kEDS and FKBP14-kEDS, and serves as a tool to better understand the disease.

Collagens XV and XVIII show different expression and localisation in cutaneous squamous cell carcinoma: type XV appears in tumor stroma, while XVIII becomes upregulated in tumor cells and lost from microvessels

As the second most common skin malignancy, cutaneous squamous cell carcinoma (cSCC) is an increasing health concern, while its pathogenesis at molecular level remains largely unknown. We studied the expression and localisation of two homologous basement membrane (BM) collagens, types XV and XVIII, at different stages of cSCC. These collagens are involved in angiogenesis and tumorigenesis, but their role in cancer development is incompletely understood. Quantitative RT-PCR analysis revealed upregulation of collagen XVIII, but not collagen XV, in primary cSCC cells in comparison with normal human epidermal keratinocytes. In addition, the Ha-ras-transformed invasive cell line II-4 expressed high levels of collagen XVIII mRNA, indicating upregulation in the course of malignant transformation. Immunohistochemical analyses of a large human tissue microarray material showed that collagen XVIII is expressed by tumor cells from grade 1 onwards, while keratinocytes in normal skin and in premalignant lesions showed negative staining for it. Collagen XV appeared instead as deposits in the tumor stroma. Our findings in human cSCCs and in mouse cSCCs from the DMBA-TPA skin carcinogenesis model showed that collagen XVIII, but not collagen XV or the BM markers collagen IV or laminin, was selectively reduced in the tumor vasculature, and this decrease associated significantly with cancer progression. Our results demonstrate that collagens XV and XVIII are expressed in different sites of cSCC and may contribute in a distinct manner to processes related to cSCC tumorigenesis, identifying these collagens as potential biomarkers in the disease.

Different gene knockout/transgenic mouse models manifesting persistent fetal vasculature: Are integrins to blame for this pathological condition?

Persistent fetal vasculature (PFV) occurs as a result of a failure of fetal vasculature to undergo normal programmed involution. During development, before the formation of retinal vessels, the lens and the inner retina are nourished by the hyaloid vasculature. Hyaloid vessels extend from the optic nerve and run through the vitreous to encapsulate the lens. As fetal retinal vessels develop, hyaloid vasculature naturally regresses. Failure of regression of the hyaloid artery has been shown to lead to severe congenital pathologies. Studies on childhood blindness and visual impairment in the United States have shown that PFV accounts for 4.8% of total blindness. Although PFV is a serious developmental disease affecting the normal visual development pathway, the exact regulatory mechanism responsible for the regression of the hyaloid artery is still unknown. In this review, we have summarized the cellular defects associated with different knockout models that manifest features of persistent fetal vasculature. Based on similar cellular defects observed in different knockouts (KO)s such as altered migration, increased proliferation and decreased apoptosis and, the known role of integrins in the regulation of these cellular behaviors, we propose here that integrins may play a significant role in the pathophysiology of persistent fetal vasculature disease.

Mineralization Effect of Hyaluronan on Dental Pulp Cells via CD44

INTRODUCTION

CD44 is a cell-surface glycoprotein involved in various cellular functions. Recent studies have suggested that CD44 is involved in early mineralization of odontoblasts. Hyaluronic acid (HA) is the principal ligand for receptor CD44. Whether and how HA regulated the mineralization process of dental pulp cells were investigated.

METHODS

The effects of high-molecular-weight HA on differentiation and mineral deposition of dental pulp cells were tested by using alkaline phosphatase (ALP) activity assay and alizarin red S staining. Osteogenesis real-time polymerase chain reaction array, quantitative polymerase chain reaction, and Western blotting were performed to identify downstream molecules involved in the mineralization induction of HA. CD44 was knocked down and examined to confirm whether the mineralization effect of HA was mediated by receptor CD44. Immunohistochemistry was used to understand the localization patterns of CD44 and the identified downstream proteins in vivo.

RESULTS

Pulse treatment of HA enhanced ALP activity and mineral deposition in dental pulp cells. Tissue-nonspecific ALP, bone morphogenetic protein 7 (BMP7), and type XV collagen (Col15A1) were upregulated via the HA-CD44 pathway in vitro. Immunohistochemistry of tooth sections showed that the staining pattern of BMP7 was very similar to that of CD44.

CONCLUSIONS

Results of this study indicated that high-molecular-weight HA enhanced early mineralization of dental pulp cells mediated via CD44. The process involved important mineralization-associated molecules including tissue-nonspecific ALP, BMP7, and Col15A1. The findings may help develop new strategies in regenerative endodontics.

Comparative Characterization of Vaginal Cells Derived From Premenopausal Women With and Without Severe Pelvic Organ Prolapse

BACKGROUND

This study tested a hypothesis that primary human vaginal cells derived from tissue of premenopausal women with severe pelvic organ prolapse (POP-HVCs) would display differential functional characteristics as compared to vaginal cells derived from asymptomatic women with normal pelvic floor support (control-HVCs).

METHODS

Vaginal tissue biopsies were collected from premenopausal patients with POP (n = 8) and asymptomatic controls (n = 7) during vaginal hysterectomy or repair. Primary vaginal cells were isolated by enzymatic digestion and characterized by immunocytochemistry. Cell attachment and proliferation on different matrices (collagen I, collagen II, collagen IV, fibronectin, laminin, tenascin, and vitronectin) were compared between POP-HVCs and control-HVCs. RNA was extracted, and the expression of 84 genes was screened using Human Extracellular Matrix and Adhesion Molecules RT(2) Profiler PCR array. The expression of selected genes was verified by quantitative reverse transcription-polymerase chain reaction.

RESULTS

(1) Control-HVCs attached to collagen IV more efficiently than POP-HVCs; (2) control-HVCs and POP-HVCs show a similar proliferation rate when plated on proNectin and collagen I; (3) when seeded on collagen I, resting POP-HVCs expressed significantly (P < .05) increased transcript levels of collagen VII, multiple matrix metalloproteinases (MMP3, MMP7, MMP10, MMP12, MMP13, and MMP14), integrins (ITGA1, ITGA4, ITGA6, ITGA8, ITGB1, ITGB2, and ITGB3), and cell adhesion molecules as compared to control-HVCs. Collagen XV and tissue inhibitors of MMPs (TIMP1 and TIMP2) as well as genes involved in the biogenesis and maturation of collagen and elastin fibers (LOX, LOXL1-LOXL3, BMP1, and ADAMTS2) were significantly downregulated in POP-HVCs versus control-HVCs (P < .05).

CONCLUSIONS

Resting primary POP-HVCs in vitro show altered cellular characteristics as compared to control-HVCs, which may influence their dynamic responses to external mechanical or hormonal stimuli.

Endostatin's emerging roles in angiogenesis, lymphangiogenesis, disease, and clinical applications

BACKGROUND

Angiogenesis is the process of neovascularization from pre-existing vasculature and is involved in various physiological and pathological processes. Inhibitors of angiogenesis, administered either as individual drugs or in combination with other chemotherapy, have been shown to benefit patients with various cancers. Endostatin, a 20-kDa C-terminal fragment of type XVIII collagen, is one of the most potent inhibitors of angiogenesis.

SCOPE OF REVIEW

We discuss the biology behind endostatin in the context of its endogenous production, the various receptors to which it binds, and the mechanisms by which it acts. We focus on its inhibitory role in angiogenesis, lymphangiogenesis, and cancer metastasis. We also present emerging clinical applications for endostatin and its potential as a therapeutic agent in the form a short peptide.

MAJOR CONCLUSIONS

The delicate balance between pro- and anti-angiogenic factors can be modulated to result in physiological wound healing or pathological tumor metastasis. Research in the last decade has emphasized an emerging clinical potential for endostatin as a biomarker and as a therapeutic short peptide. Moreover, elevated or depressed endostatin levels in diseased states may help explain the pathophysiological mechanisms of the particular disease.

GENERAL SIGNIFICANCE

Endostatin was once sought after as the 'be all and end all' for cancer treatment; however, research throughout the last decade has made it apparent that endostatin's effects are complex and involve multiple mechanisms. A better understanding of newly discovered mechanisms and clinical applications still has the potential to lead to future advances in the use of endostatin in the clinic.

Portal myofibroblasts promote vascular remodeling underlying cirrhosis formation through the release of microparticles

Liver fibrosis expanding from portal tracts and vascular remodeling are determinant factors in the progression of liver diseases to cirrhosis. In the present study, we examined the potential contribution of portal myofibroblasts (PMFs) to the vascular changes leading to cirrhosis. The analyses of liver cells based on the transcriptome of rat PMFs, compared to hepatic stellate cell HSC-derived myofibroblasts in culture, identified collagen, type XV, alpha 1 (COL15A1) as a marker of PMFs. Normal liver contained rare COL15A1-immunoreactive cells adjacent to the bile ducts and canals of Hering in the portal area. A marked increase in COL15A1 expression occurred together with that of the endothelial marker, von Willebrand factor, in human and rat liver tissue, at advanced stages of fibrosis caused by either biliary or hepatocellular injury. In cirrhotic liver, COL15A1-expressing PMFs adopted a perivascular distribution outlining vascular capillaries proximal to reactive ductules, within large fibrotic septa. The effect of PMFs on endothelial cells (ECs) was evaluated by in vitro and in vivo angiogenesis assays. PMF-conditioned medium increased the migration and tubulogenesis of liver ECs as well as human umbilical vein ECs and triggered angiogenesis within Matrigel plugs in mice. In coculture, PMFs developed intercellular junctions with ECs and enhanced the formation of vascular structures. PMFs released vascular endothelial growth factor (VEGF)A-containing microparticles, which activated VEGF receptor 2 in ECs and largely mediated their proangiogenic effect. Cholangiocytes potentiated the angiogenic properties of PMFs by increasing VEGFA expression and microparticle shedding in these cells.

CONCLUSION

PMFs are key cells in hepatic vascular remodeling. They signal to ECs through VEGFA-laden microparticles and act as mural cells for newly formed vessels, driving scar progression from portal tracts into the parenchyma.

LGL1 modulates proliferation, apoptosis, and migration of human fetal lung fibroblasts

Rapid growth and formation of new gas exchange units (alveogenesis) are hallmarks of the perinatal lung. Bronchopulmonary dysplasia (BPD), common in very premature infants, is characterized by premature arrest of alveogenesis. Mesenchymal cells (fibroblasts) regulate both lung branching and alveogenesis through mesenchymal-epithelial interactions. Temporal or spatial deficiency of late-gestation lung 1/cysteine-rich secretory protein LD2 (LGL1/CRISPLD2), expressed in and secreted by lung fibroblasts, can impair both lung branching and alveogenesis (LGL1 denotes late gestation lung 1 protein; LGL1 denotes the human gene; Lgl1 denotes the mouse/rat gene). Absence of Lgl1 is embryonic lethal. Lgl1 levels are dramatically reduced in oxygen toxicity rat models of BPD, and heterozygous Lgl1(+/-) mice exhibit features resembling human BPD. To explore the role of LGL1 in mesenchymal-epithelial interactions in developing lung, we developed a doxycycline (DOX)-inducible RNA-mediated LGL1 knockdown cellular model in human fetal lung fibroblasts (MRC5(LGL1KD)). We assessed the impact of LGL1 on cell proliferation, cell migration, apoptosis, and wound healing. DOX-induced MRC5(LGL1KD) suppressed cell growth and increased apoptosis of annexin V(+) staining cells and caspase 3/7 activity. LGL1-conditioned medium increased migration of fetal rat primary lung epithelial cells and human airway epithelial cells. Impaired healing by MRC5(LGL1KD) cells of a wound model was attenuated by addition of LGL1-conditioned medium. Suppression of LGL1 was associated with dysregulation of extracellular matrix genes (downregulated MMP1, ColXVα1, and ELASTIN) and proapoptosis genes (upregulated BAD, BAK, CASP2, and TNFRSF1B) and inhibition of 44/42MAPK phosphorylation. Our findings define a role for LGL1 in fibroblast expansion and migration, epithelial cell migration, and mesenchymal-epithelial signaling, key processes in fetal lung development.

The Role of Collagens in Peripheral Nerve Myelination and Function

In the peripheral nervous system, myelin is formed by Schwann cells, which are surrounded by a basal lamina. Extracellular matrix (ECM) molecules in the basal lamina play an important role in regulating Schwann cell functions, including adhesion, survival, spreading, and myelination, as well as in supporting neurite outgrowth. Collagens are a major component of ECM molecules, which include 28 types that differ in structure and function. A growing body of evidence suggests that collagens are key components of peripheral nerves, where they not only provide a structural support but also affect cell behavior by triggering intracellular signals. In this review, we will summarize the main properties of collagen family, discuss the role of extensively studied collagen types (collagens IV, V, VI, and XV) in Schwann cell function and myelination, and provide a detailed overview of the recent advances with respect to these collagens in peripheral nerve function.

Collagen XV: exploring its structure and role within the tumor microenvironment

The extracellular matrix (ECM) is a critical component of stroma-to-cell interactions that subsequently activate intracellular signaling cascades, many of which are associated with tumor invasion and metastasis. The ECM contains a wide range of proteins with multiple functions, including cytokines, cleaved cell-surface receptors, secreted epithelial cell proteins, and structural scaffolding. Fibrillar collagens, abundant in the normal ECM, surround cellular structures and provide structural integrity. However during the initial stages of invasive cancers, the ECM is among the first compartments to be compromised. Also present in the normal ECM is the nonfibrillar collagen XV, which is seen in the basement membrane zone but is lost prior to tumor metastasis in several organs. In contrast, the tumor microenvironment often exhibits increased synthesis of fibrillar collagen I and collagen IV, which are associated with fibrosis. The unique localization of collagen XV and its disappearance prior to tumor invasion suggests a fundamental role in maintaining basement membrane integrity and preventing the migration of tumor cells across this barrier. This review examines the structure of collagen XV, its functional domains, and its involvement in cell-surface receptor-mediated signaling pathways, thus providing further insight into its critical role in the suppression of malignancy.

Multiplexin promotes heart but not aorta morphogenesis by polarized enhancement of slit/robo activity at the heart lumen

The Drosophila heart tube represents a structure that similarly to vertebrates' primary heart tube exhibits a large lumen; the mechanisms promoting heart tube morphology in both Drosophila and vertebrates are poorly understood. We identified Multiplexin (Mp), the Drosophila orthologue of mammalian Collagen-XV/XVIII, and the only structural heart-specific protein described so far in Drosophila, as necessary and sufficient for shaping the heart tube lumen, but not that of the aorta. Mp is expressed specifically at the stage of heart tube closure, in a polarized fashion, uniquely along the cardioblasts luminal membrane, and its absence results in an extremely small heart tube lumen. Importantly, Mp forms a protein complex with Slit, and interacts genetically with both slit and robo in the formation of the heart tube. Overexpression of Mp in cardioblasts promotes a large heart lumen in a Slit-dependent manner. Moreover, Mp alters Slit distribution, and promotes the formation of multiple Slit endocytic vesicles, similarly to the effect of overexpression of Robo in these cells. Our data are consistent with Mp-dependent enhancement of Slit/Robo activity and signaling, presumably by affecting Slit protein stabilization, specifically at the lumen side of the heart tube. This activity results with a Slit-dependent, local reduction of F-actin levels at the heart luminal membrane, necessary for forming the large heart tube lumen. Consequently, lack of Mp results in decreased diastolic capacity, leading to reduced heart contractility, as measured in live fly hearts. In summary, these findings show that the polarized localization of Mp controls the direction, timing, and presumably the extent of Slit/Robo activity and signaling at the luminal membrane of the heart cardioblasts. This regulation is essential for the morphogenetic changes that sculpt the heart tube in Drosophila, and possibly in forming the vertebrates primary heart tube.

Glia unglued: how signals from the extracellular matrix regulate the development of myelinating glia

The health and function of the nervous system relies on glial cells that ensheath neuronal axons with a specialized plasma membrane termed myelin. The molecular mechanisms by which glial cells target and enwrap axons with myelin are only beginning to be elucidated, yet several studies have implicated extracellular matrix proteins and their receptors as being important extrinsic regulators. This review provides an overview of the extracellular matrix proteins and their receptors that regulate multiple steps in the cellular development of Schwann cells and oligodendrocytes, the myelinating glia of the PNS and CNS, respectively, as well as in the construction and maintenance of the myelin sheath itself. The first part describes the relevant cellular events that are influenced by particular extracellular matrix proteins and receptors, including laminins, collagens, integrins, and dystroglycan. The second part describes the signaling pathways and effector molecules that have been demonstrated to be downstream of Schwann cell and oligodendroglial extracellular matrix receptors, including FAK, small Rho GTPases, ILK, and the PI3K/Akt pathway, and the roles that have been ascribed to these signaling mediators. Throughout, we emphasize the concept of extracellular matrix proteins as environmental sensors that act to integrate, or match, cellular responses, in particular to those downstream of growth factors, to appropriate matrix attachment.

Models for studies of proteoglycans in kidney pathophysiology

Proteoglycans (PGs) impact many aspects of kidney health and disease. Models that permit genetic dissection of PG core protein and glycosaminoglycan (GAG) function have been instrumental to understanding their roles in the kidney. Matrix-associated PGs do not serve critical structural roles in the organ, nor do they contribute significantly to the glomerular barrier under normal conditions, but their abnormal expression influences fibrosis, inflammation, and progression of kidney disease. Most core proteins are dispensable for nephrogenesis (glypican-3 being an exception) and for maintenance of function in adult life, but their loss alters susceptibility to experimental kidney injury. In contrast, kidney development is exquisitely sensitive to GAG expression and fine structure as evidenced by the severe phenotypes of mutants for genes involved in GAG biosynthesis. This article reviews PG expression in normal kidney and the abnormalities caused by their disruption in mice and man.

Extracellular matrix and heart development

The extracellular matrix (ECM) of the developing heart contains numerous molecules that form a dynamic environment that plays an active and crucial role in the regulation of cellular events. ECM molecules found in the heart include hyaluronan, fibronectin, fibrillin, proteoglycans, and collagens. Tight regulation of the spatiotemporal expression, and the proteolytic processing of ECM components by proteases including members of the ADAMTS family, is essential for normal cardiac development. Perturbation of the expression of genes involved in matrix composition and remodeling can interfere with a myriad of events involved in the formation of the four-chambered heart and result in prenatal lethality or cardiac malformations as seen in humans with congenital heart disease. In this review, we summarize what is known about the specific importance of some of the components of the ECM in relation to the cardiovascular development.

Lack of collagen XV impairs peripheral nerve maturation and, when combined with laminin-411 deficiency, leads to basement membrane abnormalities and sensorimotor dysfunction

Although the Schwann cell basement membrane (BM) is required for normal Schwann cell terminal differentiation, the role of BM-associated collagens in peripheral nerve maturation is poorly understood. Collagen XV is a BM zone component strongly expressed in peripheral nerves, and we show that its absence in mice leads to loosely packed axons in C-fibers and polyaxonal myelination. The simultaneous lack of collagen XV and another peripheral nerve component affecting myelination, laminin α4, leads to severely impaired radial sorting and myelination, and the maturation of the nerve is permanently compromised, contrasting with the slow repair observed in Lama4-/- single knock-out mice. Moreover, the Col15a1-/-;Lama4-/- double knock-out (DKO) mice initially lack C-fibers and, even over 1 year of age have only a few, abnormal C-fibers. The Lama4-/- knock-out results in motor and tactile sensory impairment, which is exacerbated by a simultaneous Col15a1-/- knock-out, whereas sensitivity to heat-induced pain is increased in the DKO mice. Lack of collagen XV results in slower sensory nerve conduction, whereas the Lama4-/- and DKO mice exhibit increased sensory nerve action potentials and decreased compound muscle action potentials; x-ray diffraction revealed less mature myelin in the sciatic nerves of the latter than in controls. Ultrastructural analyses revealed changes in the Schwann cell BM in all three mutants, ranging from severe (DKO) to nearly normal (Col15a1-/-). Collagen XV thus contributes to peripheral nerve maturation and C-fiber formation, and its simultaneous deletion from neural BM zones with laminin α4 leads to a DKO phenotype distinct from those of both single knock-outs.

Collagen XV Is Necessary for Modeling of the Extracellular Matrix and Its Deficiency Predisposes to Cardiomyopathy

Rationale:

The extracellular matrix (ECM) is a major determinant of the structural integrity and functional properties of the myocardium in common pathological conditions, and changes in vasculature contribute to cardiac dysfunction. Collagen (Col) XV is preferentially expressed in the ECM of cardiac muscle and microvessels.

Objective:

We aimed to characterize the ECM, cardiovascular function and responses to elevated cardiovascular load in mice lacking Col XV ( Col15a1 −/− ) to define its functional role in the vasculature and in age- and hypertension-associated myocardial remodeling.

Methods and Results:

Cardiac structure and vasculature were analyzed by light and electron microscopy. Cardiac function, intraarterial blood pressure, microhemodynamics, and gene expression profiles were studied using echocardiography, telemetry, intravital microscopy, and PCR, respectively. Experimental hypertension was induced with angiotensin II or with a nitric oxide synthesis inhibitor. Under basal conditions, lack of Col XV resulted in increased permeability and impaired microvascular hemodynamics, distinct early-onset and age-dependent defects in heart structure and function, a poorly organized fibrillar collagen matrix with marked interstitial deposition of nonfibrillar protein aggregates, increased tissue stiffness, and irregularly organized cardiomyocytes. In response to experimental hypertension, Col15a1 gene expression was increased in the left ventricle of wild-type mice, and mRNA expression of natriuretic peptides (ANP and BNP) and ECM modeling were abnormal in Col15a1 −/− mice.

Conclusions:

Col XV is necessary for ECM organization in the heart, and for the structure and functions of microvessels. Col XV deficiency leads to a complex cardiac phenotype and predisposes the subject to pathological responses under cardiac stress.

Gene array profile identifies collagen type XV as a novel human osteoblast-secreted matrix protein

Bone marrow stromal cells (MSCs) and osteoblasts are the two main non-haematopoietic cellular components of human bone tissue. To identify novel osteoblast-related molecules, we performed a gene expression profiling analysis comparing MSCs and osteoblasts isolated from the same donors. Genes differentially overexpressed in osteoblasts were mainly related to the negative control of cell proliferation, pro-apoptotic processes, protein metabolism and bone remodelling. Notably, we also identified the collagen XV (COL15A1) gene as the most up-regulated gene in osteoblasts compared with MSCs, previously described as being expressed in the basement membrane in other cell types. The expression of collagen type XV was confirmed at the protein level on isolated osteoblasts and we demonstrated that it significantly increases during the osteogenic differentiation of MSCs in vitro and that free ionised extracellular calcium significantly down-modulates its expression. Moreover, light and electron microscopy showed that collagen type XV is expressed in bone tissue biopsies mainly by working osteoblasts forming new bone tissue or lining bone trabeculae. To our knowledge, these data represent the first evidence of the expression of collagen type XV in human osteoblasts, a calcium-regulated protein which correlates to a specific functional state of these cells.

Collagen XV, a novel factor in zebrafish notochord differentiation and muscle development

Muscle cells are surrounded by extracellular matrix, the components of which play an important role in signalling mechanisms involved in their development. In mice, loss of collagen XV, a component of basement membranes expressed primarily in skeletal muscles, results in a mild skeletal myopathy. We have determined the complete zebrafish collagen XV primary sequence and analysed its expression and function in embryogenesis. During the segmentation period, expression of the Col15a1 gene is mainly found in the notochord and its protein product is deposited exclusively in the peri-notochordal basement membrane. Morpholino mediated knock-down of Col15a1 causes defects in notochord differentiation and in fast and slow muscle formation as shown by persistence of axial mesodermal marker gene expression, disorganization of the peri-notochodal basement membrane and myofibrils, and a U-shape myotome. In addition, the number of medial fast-twitch muscle fibers was substantially increased, suggesting that the signalling by notochord derived Hh proteins is enhanced by loss of collagen XV. Consistent with this, there is a concomitant expansion of patched-1 expression in the myotome of morphant embryos. Together, these results indicate that collagen XV is required for notochord differentiation and muscle development in the zebrafish embryo and that it interplays with Shh signalling.

Gene expression in human keloids is altered from dermal to chondrocytic and osteogenic lineage

Keloids are a dermal fibrotic disease whose etiology remains totally unknown and for which there is no successful treatment. Here, we employed cDNA microarray analysis to examine gene expression in keloid lesions and control skin. We found that 32 genes among the 9000 tested were strongly up-regulated in keloid lesions, of which 21 were confirmed by Northern blotting. These included at least seven chondrocyte/osteoblast marker genes, and RT-PCR analysis revealed that transcription factors specific for these genes, SOX9 and CBFA1, were induced. Immunostaining and in situ hybridization further supported that these markers are expressed in keloid lesions. Intriguingly, scleraxis, a transcription factor known as a marker of tendons and ligaments, was also induced in keloid fibroblasts. We propose that reprogramming of gene expression or disordered differentiation from a dermal pattern to that of a chondrocytic/osteogenic lineage, probably closer to that of tendon/ligament lineage, may be involved in the etiology of keloids.

Differential Expression of Collagen Types XVIII/Endostatin and XV in Normal, Keratoconus, and Scarred Human Corneas

PURPOSE

This study was designed to clarify the expression of 2 closely related collagen (Col) types XVIII and XV, and the proteolytically derived endostatin fragment of ColXVIII in normal, keratoconus, and scarred human corneas.

METHODS

Immunohistochemistry, in situ hybridization, immunoelectron microscopy, and Western immunoblotting were used for human corneal samples obtained from penetrating keratoplasty.

RESULTS

In the normal cornea, ColXVIII was immunolocalized to the corneal and conjunctival epithelial basement membrane (EBM), Descemet s membrane, and the limbal and conjunctival capillaries. Immunoreaction for endostatin was otherwise similar, but it also was present in corneal epithelial cells. Western immunoblotting showed that normal cornea contains several endostatin fragments ranging from 20 to 100 kDa. ColXV was present in the EBM of the limbus and conjunctiva, but not in EBM of the clear cornea. In situ hybridization revealed that corneal basal epithelial cells were responsible for the synthesis of ColXVIII mRNA. Keratoconus cases were characterized by an irregular EBM immunoreactivity for ColXVIII and endostatin and patchy immunoreactivity beneath EBM. In scarred corneas, highly increased immunoreactivity for ColXVIII, endostatin, and ColXV was present within stroma.

CONCLUSIONS

The results indicate that ColXVIII and ColXV are differentially expressed in normal human corneas. Constant expression of ColXVIII by corneal EBM suggests that it is an important structural molecule. Aberrant expression of ColXVIII, endostatin, and ColXV in keratoconus and scarred corneas emphasizes the active role these molecules in the wound healing process.

Endogenous stimulators and inhibitors of angiogenesis in gastrointestinal cancers: basic science to clinical application

Progression of cancer is dependent on acquisition of vascular networks within the tumor. Tumor angiogenesis is dependent on up-regulation of angiogenesis stimulators to overcome the endogenous anti-angiogenic barrier. Such disruption of angiogenesis balance to favor neovascularization is a key step for progression of tumor growth and metastasis. In this regard, the vascular basement membrane and the extracellular matrix have been found to be rich sources of angiogenesis stimulators and inhibitors that become bioavailable on proteolysis of the matrix by tumor microenvironment-related enzymes. In this review the subgroup of endogenous angiogenesis stimulators and inhibitors is discussed, and their mechanism of action during tumor angiogenesis is evaluated. The role in regulating tumor growth and the possibility of using them as prognostic markers for human gastrointestinal cancers is discussed. Furthermore, we specifically address the role of vascular endothelial growth factor in human gastrointestinal cancers and discuss the development and use of bevacizumab (Avastin; anti-vascular endothelial growth factor antibody [Genentech, CA]) in the treatment of colorectal and other gastrointestinal cancers.

Organ-specific collagen expression: implications for renal disease

Chronic kidney disease is characterized by progressive accumulation of extracellular matrix and scarring, leading to the loss of kidney function. Excess deposition of the collagen family of proteins is the hallmark of kidney fibrosis. In this review, we survey the collagens that are associated with renal disease and we highlight the use of a transgenic approach to identify cis-acting sequences in the collagen type I promoter which are capable of directing collagen type I expression specifically in the kidney. Ultimately it may be possible to use this approach to halt the accumulation of collagen selectively in this organ.

Abnormal maturation of the retinal vasculature in type XVIII collagen/endostatin deficient mice and changes in retinal glial cells due to lack of collagen types XV and XVIII

Type XVIII collagen is important in the early phase of retinal vascular development and for the regression of the primary vasculature in the vitreous body after birth. We show here that the retina in Col18a1-/- mice becomes densely vascularized by anomalous anastomoses from the persistent hyaloid vasculature by day 10 after birth. In situ hybridizations revealed normal VEGF mRNA expression, but the phenotype of collagen XVIII deficient mice closely resembled that of mice expressing VEGF120 and VEGF188 isoforms only, suggesting that type XVIII collagen may be involved in VEGF function. Type XVIII collagen was found to be indispensable for angiogenesis in the eye, as also oxygen-induced neovascularization was less intense than normal in the Col18a1-/- mice. We observed a marked increase in the amount of retinal astrocytes in the Col18a1-/- mice. Whereas the retinal vessels of wild-type mice are covered by astrocytes and the regressing, thin hyaloid vessels are devoid of astrocytes, the retinal vessels in the Col18a1-/- mice were similarly covered by astrocytes but not the persistent hyaloid vessels in the vitreous body. Interestingly, double null mice lacking type XVIII collagen and its homologue type XV collagen had the persistent hyaloid vessels covered by astrocytes, including the parts located in the vitreous body. We thus hypothesize that type XV collagen is a regulator of glial cell recruitment around vessels and that type XVIII collagen regulates their proliferation.

Non-heparan sulfate-binding interactions of endostatin/collagen XVIII in murine development

Knobloch syndrome is characterized by a congenital generalized eye disease and cranial defect. Pathogenic mutations preferentially lead to a deletion or functional alteration of collagen XVIII's most C-terminal endostatin domain. Endostatin can be released from collagen XVIII and is a potent inhibitor of angiogenesis and tumor growth. We show differential expression of binding partners for endostatin, vascular endothelial growth factor (VEGF), and the collagen XV endostatin homologue in murine embryonal development using a set of alkaline phosphatase fusion proteins. Consistent with the human phenotype, vascular mesenchyme in the developing eye was identified as endostatin's primary target. While endostatin predominantly bound to blood vessels, the VEGF164 affinity probe labeled nonvascular tissues such as forebrain, hindbrain, the optic nerve, and the surface ectoderm of the future cornea. Strikingly increased staining specificity was observed with a non-heparin/heparan sulfate-binding endostatin probe. In contrast, elimination of the heparan sulfate binding site from VEGF led to complete loss of binding. The collagen XV endostatin homologue showed a highly restricted binding pattern. Oligomerization with endogenous endostatin was ruled out by use of collagen XVIII knockout mice. Our data provide strong evidence that collagen XVIII's C-terminal endostatin domain harbors a prominent tissue-binding site and that binding can occur in the absence of heparan sulfates in situ.

The contribution of vascular basement membranes and extracellular matrix to the mechanics of tumor angiogenesis

The goal of this review is to highlight the contribution of extracellular matrix and vascular basement membranes to the regulation of angiogenesis and tumor progression. Here we present a new concept that vascular basement membrane influences endothelial cells and possibly other cell types in a solid state assembled form, and also in a degraded solution state form. Depending on the structural integrity, composition and exposure of cryptic sites, the vascular basement membrane proteome exerts functional influences on proliferating and resting endothelial cells. This review provides the reader with an appreciation of this newly evolved concept in the area of vascular biology.

A catalogue of gene expression in the developing kidney

BACKGROUND

Although many genes with important function in kidney morphogenesis have been described, it is clear that many more remain to be discovered. Microarrays allow a more global analysis of the genetic basis of kidney organogenesis.

METHODS

In this study, Affymetrix U74Av2 microarrays, with over 12,000 genes represented, were used in conjunction with robust target microamplification techniques to define the gene expression profiles of the developing mouse kidney.

RESULTS

Microdissected murine ureteric bud and metanephric mesenchyme as well as total kidneys at embryonic day E11.5, E12.5, E13.5, E16.5, and adult were examined. This work identified, for example, 3847 genes expressed in the E12.5 kidney. Stringent comparison of the E12.5 versus adult recognized 428 genes with significantly elevated expression in the embryonic kidney. These genes fell into several functional categories, including transcription factor, growth factor, signal transduction, cell cycle, and others. In contrast, surprisingly few differences were found in the gene expression profiles of the ureteric bud and metanephric mesenchyme, with many of the differences clearly associated with the more epithelial character of the bud. In situ hybridizations were used to confirm and extend microarray-predicted expression patterns in the developing kidney. For three genes, Cdrap, Tgfbi, and Col15a1, we observed strikingly similar expression in the developing kidneys and lungs, which both undergo branching morphogenesis.

CONCLUSION

The results provide a gene discovery function, identifying large numbers of genes not previously associated with kidney development. This study extends developing kidney microarray analysis to the powerful genetic system of the mouse and establishes a baseline for future examination of the many available mutants. This work creates a catalogue of the gene expression states of the developing mouse kidney and its microdissected subcomponents.

Knobloch syndrome: novel mutations in COL18A1, evidence for genetic heterogeneity, and a functionally impaired polymorphism in endostatin

Knobloch syndrome (KNO) is an autosomal recessive disorder characterized by high myopia, vitreoretinal degeneration with retinal detachment, and congenital encephalocele. Pathogenic mutations in the COL18A1 gene on 21q22.3 were recently identified in KNO families. Analysis of two unrelated KNO families from Hungary and New Zealand allowed us to confirm the involvement of COL18A1 in the pathogenesis of KNO and to demonstrate the existence of genetic heterogeneity. Two COL18A1 mutations were identified in the Hungarian family: a 1-bp insertion causing a frameshift and a premature in-frame stop codon and an amino acid substitution. This missense variant is located in a conserved amino acid of endostatin, a cleavage product of the carboxy-terminal domain of collagen alpha 1 XVIII. D1437N (D104N in endostatin) likely represents a pathogenic mutation, as we show that the endostatin N104 mutant is impaired in its affinity towards laminin. Linkage to the COL18A1 locus was excluded in the New Zealand family, providing evidence for the existence of a second KNO locus. We named the second unmapped locus for Knobloch syndrome KNO2. Mutation analysis excluded COL15A1, a member of the multiplexin collagen subfamily similar to COL18A1, as being responsible for KNO2.

Global gene expression profiles during acute pathogen-induced pulmonary inflammation reveal divergent roles for Th1 and Th2 responses in tissue repair

T helper 1 responses are typically proinflammatory, while Th2 responses have been considered regulatory. Interestingly, Th2 responses characterize a number of pulmonary diseases, many of which terminate in tissue remodeling and fibrosis. We developed a mouse model using Schistosoma mansoni eggs and cytokine-deficient mice to induce highly polarized Th1- or Th2-type inflammation in the lung. In this study, we examined the pathology and cytokine profiles in Th1- and Th2-polarized environments and used oligonucleotide microarray analysis to decipher the genes responsible for these effects. We further elaborated on the results using IL-10- and IL-13-deficient mice because these cytokines are believed to be the central regulators of Th2-associated pathology. We found that the Th1-polarized mice developed small granulomas with less fibrosis while expressing genes characteristic of tissue damage. Th2-polarized mice, in contrast, formed large granulomas with massive collagen deposition and up-regulated genes associated with wound healing, specifically, arginase, collagens, matrix metalloproteinases (MMPs), and tissue inhibitors of MMP. In addition, several members of the chitinase-like family were up-regulated in the lung following egg challenge. We also developed a method of defining the net collagen deposition using the expression profiles of several collagen, MMP, and tissue inhibitors of MMP genes. We found that Th1-polarized mice did not elaborate collagens or MMPs and therefore did not have a significant capacity for repair in this model. Thus, Th1-mediated inflammation is characterized by tissue damage, while Th2 directs wound healing and fibrosis.

Double knockout mice reveal a lack of major functional compensation between collagens XV and XVIII

Generation of double knockout mice for collagen types XV and XVIII indicated surprisingly that the mice are viable and do not suffer from any new major defects. Although the two collagens are closely related molecules sharing similarities in tissue expression, we conclude that their biological roles are essentially separate, that of type XV in muscle and type XVIII in the eye. Detailed comparisons of the null mice eyes indicated that type XV collagen seems to be involved in the tunica vasculosa lentis regression process, whereas type XVIII is in the regression of vasa hyaloidea propria, and only minor compensatory effects could be detected. Furthermore, the essential role of type XVIII collagen in the eye is highlighted by the occurrence of this collagen in the epithelial basement membranes of the iris and the ciliary body and in the inner limiting membrane of the retina, sites lacking type XV.

Basement membranes: structure, assembly and role in tumour angiogenesis

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.

New functional roles for non-collagenous domains of basement membrane collagens

Collagens IV, XV and XVIII are major components of various basement membranes. In addition to the collagen-specific triple helix, these collagens are characterized by the presence of several non-collagenous domains. It is clear now that these ubiquitous collagen molecules are involved in more subtle and sophisticated functions than just the molecular architecture of basement membranes, particularly in the context of extracellular matrix degradation. Degradation of the basement membrane collagens occurs during numerous physiological and pathological processes such as embryonic development or tumorigenesis and generates collagen fragments. These fragments are involved in the regulation of functions differing from those of their original intact molecules. The non-collagenous C-terminal fragment NC1 of collagen IV, XV and XVIII have been recently highlighted in the literature because of their potential in reducing angiogenesis and tumorigenesis, but it is clear that their biological functions are not limited to these processes. Proteolytic release of soluble NC1 fragments stimulates migration, proliferation, apoptosis or survival of different cell types and suppresses various morphogenetic events.