Basement membrane assembly

Laminin N-terminus α31 protein distribution in adult human tissues

Laminin N-terminus α31 (LaNt α31) is a netrin-like protein derived from alternative splicing of the laminin α3 gene. Although LaNt α31 has been demonstrated to influence corneal and skin epithelial cell function, its expression has not been investigated beyond these tissues. In this study, we used immunohistochemistry to characterise the distribution of this protein in a wide-array of human tissue sections in comparison to laminin α3. The data revealed widespread LaNt α31 expression. In epithelial tissue, LaNt α31 was present in the basal layer of the epidermis, throughout the epithelium of the digestive tract, and in much of the epithelium of the reproductive system. LaNt α31 was also found throughout the vasculature of most tissues, with enrichment in reticular-like fibres in the extracellular matrix surrounding large vessels. A similar matrix pattern was observed around the terminal ducts in the breast and around the alveolar epithelium in the lung, where basement membrane staining was also evident. Specific enrichment of LaNt α31 was identified in sub-populations of cells of the kidney, liver, pancreas, and spleen, with variations in intensity between different cell types in the collecting ducts and glomeruli of the kidney. Intriguingly, LaNt α31 immunoreactivity was also evident in neurons of the central nervous system, in the cerebellum, cerebral cortex, and spinal cord. Together these findings suggest that LaNt α31 may be functionally relevant in a wider range of tissue contexts than previously anticipated, and the data provides a valuable basis for investigation into this interesting protein.

Fibrogenesis in LAMA2-Related Muscular Dystrophy Is a Central Tenet of Disease Etiology

LAMA2-related congenital muscular dystrophy, also known as MDC1A, is caused by loss-of-function mutations in the alpha2 chain of Laminin-211. Loss of this protein interrupts the connection between the muscle cell and its extracellular environment and results in an aggressive, congenital-onset muscular dystrophy characterized by severe hypotonia, lack of independent ambulation, and early mortality driven by respiratory complications and/or failure to thrive. Of the pathomechanisms of MDC1A, the earliest and most prominent is widespread and rampant fibrosis. Here, we will discuss some of the key drivers of fibrosis including TGF-beta and renin–angiotensin system signaling and consequences of these pathways including myofibroblast transdifferentiation and matrix remodeling. We will also highlight some of the differences in fibrogenesis in congenital muscular dystrophy (CMD) with that seen in Duchenne muscular dystrophy (DMD). Finally, we will connect the key signaling pathways in the pathogenesis of MDC1A to the current status of the therapeutic approaches that have been tested in the preclinical models of MDC1A to treat fibrosis.

Identification and initial characterization of matrix metalloproteinases in the yellow fever mosquito, Aedes aegypti

Aedes aegypti is a major vector for arboviruses such as dengue, chikungunya and Zika viruses. During acquisition of a viremic bloodmeal, an arbovirus infects mosquito midgut cells before disseminating to secondary tissues, including the salivary glands. Once virus is released into the salivary ducts it can be transmitted to another vertebrate host. The midgut is surrounded by a basal lamina (BL) in the extracellular matrix, consisting of a proteinaceous mesh composed of collagen IV and laminin. BL pore size exclusion limit prevents virions from passing through. Thus, the BL probably requires remodelling via enzymatic activity to enable efficient virus dissemination. Matrix metalloproteinases (MMPs) are extracellular endopeptidases that are involved in remodelling of the extracellular matrix. Here, we describe and characterize the nine Ae. aegypti encoded MMPs, AeMMPs 1-9, which share common features with other invertebrate and vertebrate MMPs. Expression profiling in Ae. aegypti revealed that Aemmp4 and Aemmp6 were upregulated during metamorphosis, whereas expression of Aemmp1 and Aemmp2 increased during bloodmeal digestion. Aemmp1 expression was also upregulated in the presence of a bloodmeal containing chikungunya virus. Using polyclonal antibodies, AeMMP1 and AeMMP2 were specifically detected in tissues associated with the mosquito midgut.

Rethinking glomerular basement membrane thickening in diabetic nephropathy: adaptive or pathogenic?

Diabetic nephropathy (DN) is the leading cause of chronic kidney disease in the United States and is a major cause of cardiovascular disease and death. DN develops insidiously over a span of years before clinical manifestations, including microalbuminuria and declining glomerular filtration rate (GFR), are evident. During the clinically silent period, structural lesions develop, including glomerular basement membrane (GBM) thickening, mesangial expansion, and glomerulosclerosis. Once microalbuminuria is clinically apparent, structural lesions are often considerably advanced, and GFR decline may then proceed rapidly toward end-stage kidney disease. Given the current lack of sensitive biomarkers for detecting early DN, a shift in focus toward examining the cellular and molecular basis for the earliest structural change in DN, i.e., GBM thickening, may be warranted. Observed within one to two years following the onset of diabetes, GBM thickening precedes clinically evident albuminuria. In the mature glomerulus, the podocyte is likely key in modifying the GBM, synthesizing and assembling matrix components, both in physiological and pathological states. Podocytes also secrete matrix metalloproteinases, crucial mediators in extracellular matrix turnover. Studies have shown that the critical podocyte-GBM interface is disrupted in the diabetic milieu. Just as healthy podocytes are essential for maintaining the normal GBM structure and function, injured podocytes likely have a fundamental role in upsetting the balance between the GBM's synthetic and degradative pathways. This article will explore the biological significance of GBM thickening in DN by reviewing what is known about the GBM's formation, its maintenance during health, and its disruption in DN.

Type XIX collagen: A new partner in the interactions between tumor cells and their microenvironment

Type XIX collagen is a minor collagen that is associated with the basement membrane zone that belongs to the FACIT family (Fibril-Associated Collagens with Interrupted Triple helices). The FACIT family is composed of type IX, XII, XIV, XVI, XX, XXI, XXII and XIX collagens, which share many highly conserved structural motifs: a short NC1 domain, a thrombospondin-like N-terminal domain (TSPN), and numerous cysteine residues. The main role of FACITs is to ensure the integrity and stability of the extracellular matrix and its fibrillar collagen network by regulating the formation and size of the collagen fibrils. Type XIX collagen was discovered in a human rhabdomyosarcoma cell line. The collagen α1(XIX) chain is composed of 5 triple-helical domains (COL) interrupted by 6 non-triple-helical (NC) domains with a short, C-terminal, 19 amino acid non-collagenous domain (NC1). This collagen is involved in the differentiation of muscle cells, central nervous system development, and formation of the esophagus. Type XIX collagen is associated with the basement membrane zone, like type XVIII and XV collagens. Its short NC1(XIX) C-terminal domain inhibits the migration and invasion of melanoma cells. It also exerts a strong anti-angiogenic effect by inhibiting MMP-14 and VEGF expression. NC1(XIX) binding to αvβ3 integrin decreases the phosphorylation of proteins involved in the FAK (Focal Adhesion Kinase)/PI3K (PhosphoInositide 3-Kinase)/Akt (protein kinase B)/mTOR (Mammalian Target Of Rapamycin) pathway. On the other hand, NC1(XIX) induces an increase in GSK3β activity by decreasing its level of phosphorylation. The inhibition of this pathway could explain the anti-tumor properties of the NC1(XIX) domain.

Transformed MDCK cells secrete elevated MMP1 that generates LAMA5 fragments promoting endothelial cell angiogenesis

Epithelial-mesenchymal transition (EMT) enhances the migration and invasion of cancer cells, and is regulated by various molecular mechanisms including extracellular matrix metalloproteinase (MMP) activity. Previously, we reported transformation of epithelial Madin-Darby canine kidney (MDCK) cells with oncogenic H-Ras (21D1 cells) induces EMT, and significantly elevates MMP1 expression. To explore the biological significance, in this study we characterized 21D1 cells with knocked-down MMP1 expression (21D1^−MMP1). MMP1 silencing diminished 21D1 cell migration, invasion and anchorage-independent growth in vitro. Additionally, 21D1^−MMP1 cells displayed reduced tumour volume when grown as in vivo subcutaneous xenografts in mice. Depletion of MMP1 lowered the ability of the cellular secretome (extracellular culture medium) to influence recipient cell behaviour. For example, supplementation with 21D1 secretome elevated cell migration of recipient fibroblasts, and enhanced endothelial cell angiogenesis (vessel length and branching). By contrast, 21D1^−MMP1 secretome was less potent in both functional assays. We reveal laminin subunit alpha-5 (LAMA5) as a novel biological substrate of MMP1, that generates internal and C-terminal proteolytic fragments in 21D1 secretome. Furthermore, antibody-based inhibition of integrin αvβ3 on endothelial cells nullified the angiogenic capability of 21D1 secretome. Therefore, we report this as a new VEGF-independent mechanism that oncogenic cells may employ to promote tumour angiogenesis.

The conserved ADAMTS-like protein lonely heart mediates matrix formation and cardiac tissue integrity

Here we report on the identification and functional characterization of the ADAMTS-like homolog lonely heart (loh) in Drosophila melanogaster. Loh displays all hallmarks of ADAMTSL proteins including several thrombospondin type 1 repeats (TSR1), and acts in concert with the collagen Pericardin (Prc). Loss of either loh or prc causes progressive cardiac damage peaking in the abolishment of heart function. We show that both proteins are integral components of the cardiac ECM mediating cellular adhesion between the cardiac tube and the pericardial cells. Loss of ECM integrity leads to an altered myo-fibrillar organization in cardiac cells massively influencing heart beat pattern. We show evidence that Loh acts as a secreted receptor for Prc and works as a crucial determinant to allow the formation of a cell and tissue specific ECM, while it does not influence the accumulation of other matrix proteins like Nidogen or Perlecan. Our findings demonstrate that the function of ADAMTS-like proteins is conserved throughout evolution and reveal a previously unknown interaction of these proteins with collagens.

Cellular adhesion and tissue integrity in multicellular organisms strongly depend on the molecular network of the extracellular matrix (ECM). The number, topology and function of ECM molecules are highly diverse in different species, or even in single matrices in one organism. In our study we focus on the protein class of ADAMTS-like proteins. We identified Lonely heart (Loh) a member of this protein family and describe its function using the cardiac system of Drosophila melanogaster as model. Loh constitutes a secreted protein that resides in the ECM of heart cells and mediates the adhesion between different cell types - the pericadial cells and the cardiomyocytes. Lack of Loh function induces the dissociation of these cells and consequently leads to a breakdown of heart function. We found evidence that the major function of Loh is to recruit the collagen Pericardin (Prc) to the ECM of the cells and allow the proper organization of Prc into a reticular matrix. Since the function of Loh homologous proteins in other systems is rather elusive, this work provides new important insights into the biology of cell adhesion, matrix formation and indicates that ADAMTS-like proteins might facilitate an evolutionary conserved function.

Effect of 17β-estradiol on adhesion of Mytilus galloprovincialis hemocytes to selected substrates. Role of alpha2 integrin subunit

The process of hemocyte adhesion to extracellular matrix (ECM) proteins plays a crucial role in cell immunity. In most of these interactions between ECM proteins and cells, integrins are involved. The results of the present study showed that incubation of Mytilus galloprovincialis hemocytes with 17β-estradiol caused significant increased adhesion of hemocytes to ECM proteins and specifically to laminin-1, collagen IV and oxidized collagen IV, in relation to control cells. The adhesion of hemocytes to oxidized collagen was significantly higher than to either collagen IV or to laminin-1. In accordance with this, inhibition of either NADPH oxidase or nitric oxide (NO) synthase attenuated 17β-estradiol effect on hemocyte adhesion, suggesting that the high levels of free radicals, produced after 17β-estradiol effect, could contribute to the high adhesion of hemocytes to laminin-1 and collagen IV. The implication of ROS was further confirmed by the use of the oxidant rotenone, which caused elevation of cell adhesion in relation to control and by the antioxidant NAC which attenuated 17β-estradiol effect. The mechanism of 17β-estradiol induced adhesion to laminin-1, collagen IV and oxidized collagen IV involves a large number of intracellular components, as Na+/H+ exchanger (NHE), all isoforms of protein kinase C (PKC), phosphatidylinositol-3-kinase (PI3K) and c-jun N-terminal kinase (JNK) as well as alpha2 integrin subunit. Maintenance of high cyclic adenosine-3'-5'-monophosphate (cAMP) levels caused non significant higher adhesion of hemocytes to ECM proteins in relation to control cells. Our results showed that 17β-estradiol caused a significant increase in α₂ integrin subunit levels, which was reduced after inhibition of NHE, PI3K, PKC, NO synthase, NADPH oxidase and JNK. In addition, our results showed that apart from 17β-estradiol, high cAMP and high ROS levels caused significantly higher induction of α₂ integrin subunit levels in relation to control. Our results imply a potential involvement of cAMP in immune responses of Mytilus hemocytes, which needs further investigation.

Skeletal muscle laminin and MDC1A: pathogenesis and treatment strategies

Laminin-211 is a cell-adhesion molecule that is strongly expressed in the basement membrane of skeletal muscle. By binding to the cell surface receptors dystroglycan and integrin α7β1, laminin-211 is believed to protect the muscle fiber from damage under the constant stress of contractions, and to influence signal transmission events. The importance of laminin-211 in skeletal muscle is evident from merosin-deficient congenital muscular dystrophy type 1A (MDC1A), in which absence of the α2 chain of laminin-211 leads to skeletal muscle dysfunction. MDC1A is the commonest form of congenital muscular dystrophy in the European population. Severe hypotonia, progressive muscle weakness and wasting, joint contractures and consequent impeded motion characterize this incurable disorder, which causes great difficulty in daily life and often leads to premature death. Mice with laminin α2 chain deficiency have analogous phenotypes, and are reliable models for studies of disease mechanisms and potential therapeutic approaches. In this review, we introduce laminin-211 and describe its structure, expression pattern in developing and adult muscle and its receptor interactions. We will also discuss the molecular pathogenesis of MDC1A and advances toward the development of treatment.

Lineage restriction of human hepatic stem cells to mature fates is made efficient by tissue-specific biomatrix scaffolds

Current protocols for differentiation of stem cells make use of multiple treatments of soluble signals and/or matrix factors and result typically in partial differentiation to mature cells with under- or overexpression of adult tissue-specific genes. We developed a strategy for rapid and efficient differentiation of stem cells using substrata of biomatrix scaffolds, tissue-specific extracts enriched in extracellular matrix, and associated growth factors and cytokines, in combination with a serum-free, hormonally defined medium (HDM) tailored for the adult cell type of interest. Biomatrix scaffolds were prepared by a novel, four-step perfusion decellularization protocol using conditions designed to keep all collagen types insoluble. The scaffolds maintained native histology, patent vasculatures, and ≈1% of the tissue's proteins but >95% of its collagens, most of the tissue's collagen-associated matrix components, and physiological levels of matrix-bound growth factors and cytokines. Collagens increased from almost undetectable levels to >15% of the scaffold's proteins with the remainder including laminins, fibronectins, elastin, nidogen/entactin, proteoglycans, and matrix-bound cytokines and growth factors in patterns that correlate with histology. Human hepatic stem cells (hHpSCs), seeded onto liver biomatrix scaffolds and in an HDM tailored for adult liver cells, lost stem cell markers and differentiated to mature, functional parenchymal cells in ≈1 week, remaining viable and with stable mature cell phenotypes for more than 8 weeks.

CONCLUSION

Biomatrix scaffolds can be used for biological and pharmaceutical studies of lineage-restricted stem cells, for maintenance of mature cells, and, in the future, for implantable, vascularized engineered tissues or organs.

Matrix-independent stimulation of human tubular epithelial cell migration by Rho kinase inhibitors

Proximal tubular epithelial cells differ from other epithelial cells in the expression of N-cadherin as major adherens junction protein instead of E-cadherin. Migration of proximal epithelial cells (HKC-8) was analyzed by scratch wounding and by a barrier assay, which allowed determination of migration velocity on different extracellular matrices. Migration velocity was about threefold higher on fibronectin compared to collagen IV. The differential migration velocity was reflected by the orientation of F-actin stress fibers. TGF-beta activated secretion of fibronectin and thus increased migration on collagen IV, but did not further promote migration on fibronectin. Pharmacological inhibition of Rho kinases (ROCKs) by Y-27632, hydroxyfasudil and H-1152, or siRNA against ROCKs significantly increased migration velocity independently of the extracellular matrix. Cells at the migration front showed long filopodia, which could not be mimicked by overexpression of consitutively active Cdc42, indicative of a more complex regulation of F-actin structures. N-cadherin was reorganized from tight zipper-like structures into loosened cell-cell contacts upon incubation with Y-27632, but HKC-8 cells still migrated as cohort. Migration through single cell pores in a modified Boyden chamber assay was also stimulated by ROCK inhibitors. ROCK inhibitors enhanced migration of primary cultures of renal tubular cells which consisted of proximal and distal tubular cells expressing N-cadherin and E-cadherin, respectively. There was no indication of a switch in cadherin expression in these cells or a preferential migration of N-cadherin expressing cells. Pharmacologic inhibition of ROCKs may thus favor repair processes in renal tubules by increasing the migratory capacity of tubular epithelial cells.

Solute partitioning and filtration by extracellular matrices

The physiology of glomerular filtration remains mechanistically obscure despite its importance in disease. The correspondence between proteinuria and foot process effacement suggests podocytes as the locus of the filtration barrier. If so, retained macromolecules ought to accumulate at the filtration barrier, an effect called concentration polarization. Literature data indicate macromolecule concentrations decrease from subendothelial to subepithelial glomerular basement membrane (GBM), as would be expected if the GBM were itself the filter. The objective of this study was to obtain insights into the possible role of the GBM in protein retention by performing fundamental experimental and theoretical studies on the properties of three model gels. Solute partitioning and filtration through thin gels of a commercially available laminin-rich extracellular matrix, Matrigel, were measured using a polydisperse polysaccharide tracer molecule, Ficoll 70. Solute partitioning into laminin gels and lens basement membrane (LBM) were measured using Ficoll 70. A novel model of a laminin gel was numerically simulated, as well as a mixed structure-random-fiber model for LBM. Experimental partitioning was predicted by numerical simulations. Sieving coefficients through thin gels of Matrigel were size dependent and strongly flux dependent. The observed flux dependence arose from compression of the gel in response to the applied pressure. Gel compression may alter solute partitioning into extracellular matrix at physiologic pressures present in the glomerular capillary. This suggests a physical mechanism coupling podocyte structure to permeability characteristics of the GBM.

Osteoconductive carriers for integrated bone repair

Successful bone repair is judged in achieving restitution of space and mechanical integrity, and in regaining function. When the biology or anatomy are insufficient to attain a full repair, therapeutic use of graft material has been used to omit compliance features such as strain tolerance, reduced stiffness, and attenuated strength, and instead promote primary or membranous-type bone formation within the physical approximation of a graft material. The challenge of most conductive materials is that they emerge from a static platform and in placement force the living system to adapt to placement, dimension, different properties, and eventually are only successful in degradation and replacement, or in integration. The synergy and interdependency between adhesion, ECM, and proteolysis are important concepts that must be understood to engineer scaffolds capable of holding up to standards which are more than cell decoration. Moreover, the reactive specificity to loading, degradation, therapeutic delivery during absorption remains a key aim of both academic and industrial designs. Achieving conductivity comes with challenges of best fit integration, delivery, and in integrated modeling. The more liquid is the delivery, the more modular the components, and adaptive the matrix to meeting the intended application, the more likely that the conductivity will not be excluded by the morphology of the injury site. Considerations for osteoconductive materials for bone repair and replacement have developed conceptually and advanced parallel with a better understanding of not only bone biology but of materials science. First models of material replacements utilized a reductionist-constructionist logic; define the constituents of the material in terms of its morphology and chemical composition, and then engineer material with similar content and properties as a means of accommodating a replacement. Unfortunately for biologic systems, empiric formulation is insufficient to promote adequate integration in a timely fashion. Future matrices will need to translate their biological surfaces as more than a scaffold to be decorated with cells. Conductivity will be improved by formulations that enhance function, further extended from understanding what composition best suits cell attachment, and be adopted by conveniences of delivery that meet those criteria.

Self-assembling Peptides: From Bio-inspired Materials to Bone Regeneration

In recent years, the development of new biomaterials with specifications for tissue and organ functional requirements—such as proper biological, structural, and biomechanical properties as well as designed control for biodegradation and therapeutic drug-release capacity—is the main aim of many academic and industrial programs. Hence, the concept of molecular self-assembly is the driving force for the development of new biomaterials that support the growth and functional differentiation of cells and tissues in a controlled manner. The discovery, properties, and development of self-assembling peptides to be used as three-dimensional (3D) scaffolds based on their similarity (in structure and mechanical features) to extracellular matrices are described. Self-assembling peptides can be used for in vitro applications for cell 3D culture as well as in vivo for tissue regeneration such as bone and optical nerve repair, as well as for drug delivery of mediators to improve therapy, as in the case of myocardial infarction. Finally, the use of self-assembling materials in combination with a bioengineering platform is proposed to assist functional bone regeneration in cases of larger bone defects, including exposed fractures due to trauma and spinal disorders dealing with high loadings, as well as replacement of big bone structures due to tumors.

Targeting a tumor-specific laminin domain critical for human carcinogenesis

Laminin-332 is critical for squamous cell carcinoma (SCC) tumorigenesis, but targeting it for cancer therapy has been unachievable due to key role of laminin-332 in promoting tissue integrity. Here, we show that a portion of laminin-332, termed G45, which is proteolytically removed and absent in normal tissues, is prominently expressed in most human SCC tumors and plays an important role in human SCC tumorigenesis. Primary human keratinocytes lacking G45 (DeltaG45) showed alterations of basal receptor organization, impaired matrix deposition, and increased migration. After SCC transformation, the absence of G45 domain in DeltaG45 cells was associated with deficient extracellular signal-regulated kinase and phosphotidylinositol 3-kinase (PI3K) pathway activation, impaired invasion, deficient metalloproteinase activity, and absent tumorgenicity in vivo. Expression of G45 or activated PI3K subunit in DeltaG45 cells reversed these abnormalities. G45 antibody treatment induced SCC tumor apoptosis, decreased SCC tumor proliferation, and markedly impaired human SCC tumorigenesis in vivo without affecting normal tissue adhesion. These results show a remarkable selectivity of expression and function for laminin-332 G45 in human SCC tumorigenesis and implicate it as a specific target for anticancer therapy.

Interaction of extracellular matrix protein 1 with extracellular matrix components: ECM1 is a basement membrane protein of the skin

The extracellular matrix protein 1 (ECM1) is a secreted glycoprotein, which plays an important role in the structural and functional biology of the skin as demonstrated by the identification of loss-of-function mutations in ECM1 as cause of the genodermatosis lipoid proteinosis, characterized by reduplication of the skin basement membrane and hyalinization of the underlying dermis. To search for binding partner(s) of ECM1, we tested the in vitro binding activity of ECM1a, a major isoform of four ECM1 splice variants, to different skin extracellular matrix proteins (such as laminin 332, collagen type IV, and fibronectin) and polysaccharides (such as hyaluronan, heparin, and chondroitin sulfate A) with solid-phase binding assay. We demonstrated that ECM1a utilizes different regions to bind to a variety of extracellular matrix components. Ultrastructurally, ECM1 is a basement membrane protein in human skin and is part of network-like suprastructures containing perlecan, collagen type IV, and laminin 332 as constituents. Furthermore, ECM1a enhanced the binding of collagen IV to laminin 332 dose-dependently, showing its involvement in the dermal-epidermal junction and interstitial dermis and making the functional link to the pathophysiology of lipoid proteinosis. To our knowledge, this is previously unreported.

The basement membrane microenvironment directs the normalization and survival of bioengineered human skin equivalents

Epithelial-mesenchymal interactions promote the morphogenesis and homeostasis of human skin. However, the role of the basement membrane (BM) during this process is not well-understood. To directly study how BM proteins influence epidermal differentiation, survival and growth, we developed novel 3D human skin equivalents (HSEs). These tissues were generated by growing keratinocytes at an air-liquid interface on polycarbonate membranes coated with individual matrix proteins (Type I Collagen, Type IV Collagen or fibronectin) that were placed on contracted Type I Collagen gels populated with dermal fibroblasts. We found that only keratinocytes grown on membranes coated with the BM protein Type IV Collagen showed optimal tissue architecture that was similar to control tissues grown on de-epidermalized dermis (AlloDerm) that contained intact BM. In contrast, tissues grown on proteins not found in BM, such as fibronectin and Type I Collagen, demonstrated aberrant tissue architecture that was linked to a significant elevation in apoptosis and lower levels of proliferation of basal keratinocytes. While all tissues demonstrated a normalized, linear pattern of deposition of laminin 5, tissues grown on Type IV Collagen showed elevated expression of alpha6 integrin, Type IV Collagen and Type VII Collagen, suggesting induction of BM organization. Keratinocyte differentiation (Keratin 1 and filaggrin) was not dependent on the presence of BM proteins. Thus, Type IV Collagen acts as a critical microenvironmental factor in the BM that is needed to sustain keratinocyte growth and survival and to optimize epithelial architecture.

The effect of functionalized self-assembling peptide scaffolds on human aortic endothelial cell function

A class of designed self-assembling peptide nanofiber scaffolds with more than 99% water content has been shown to be a good biological material for cell culture. Here, we report the functionalization of one of these peptide scaffolds, RAD16-I (AcN-RADARADARADARADA-CONH2), by direct solid phase synthesis extension at the amino terminal with three short-sequence motifs. These motifs are present in two major protein components of the basement membrane, laminin 1 (YIGSR, RYVVLPR) and collagen IV (TAGSCLRKFSTM). These motifs have been previously shown to promote specific biological activities including endothelial cell adhesion, spreading, and tubular formation. Therefore, the generic functionalized peptide developed was AcN-X-GG-RADARADARADARADA-CONH2 with each motif represented by "X". We show in this work that these tailor-made peptide scaffolds enhance the formation of confluent cell monolayers of human aortic endothelial cells (HAEC) in culture. Moreover, additional assays designed to evaluate endothelial cell function showed that HAEC monolayers obtained on these scaffolds not only maintained LDL uptake activity but also enhanced nitric oxide release and elevated laminin 1 and collagen IV deposition. These results suggest that this new scaffold provide a better physiological substrate for endothelial cell culture and suggest its further application for biomedical research, cancer biology and regenerative biology.

The subendothelial extracellular matrix modulates NF-kappaB activation by flow: a potential role in atherosclerosis

Atherosclerotic plaque forms in regions of the vasculature exposed to disturbed flow. NF-κB activation by fluid flow, leading to expression of target genes such as E-selectin, ICAM-1, and VCAM-1, may regulate early monocyte recruitment and fatty streak formation. Flow-induced NF-κB activation is downstream of conformational activation of integrins, resulting in new integrin binding to the subendothelial extracellular matrix and signaling. Therefore, we examined the involvement of the extracellular matrix in this process. Whereas endothelial cells plated on fibronectin or fibrinogen activate NF-κB in response to flow, cells on collagen or laminin do not. In vivo, fibronectin and fibrinogen are deposited at atherosclerosis-prone sites before other signs of atherosclerosis. Ligation of integrin α2β1 on collagen prevents flow-induced NF-κB activation through a p38-dependent pathway that is activated locally at adhesion sites. Furthermore, altering the extracellular matrix to promote p38 activation in cells on fibronectin suppresses NF-κB activation, suggesting a novel therapeutic strategy for treating atherosclerosis.

Rotavirus enterotoxin NSP4 binds to the extracellular matrix proteins laminin-beta3 and fibronectin

Rotavirus is the most important cause of viral gastroenteritis and dehydrating diarrhea in young children. Rotavirus nonstructural protein 4 (NSP4) is an enterotoxin that was identified as an important agent in symptomatic rotavirus infection. To identify cellular proteins that interact with NSP4, a two-hybrid technique with Saccharomyces cerevisiae was used. NSP4 cDNA, derived from the human rotavirus strain Wa, was cloned into the yeast shuttle vector pGBKT7. An intestinal cDNA library derived from Caco-2 cells cloned into the yeast shuttle vector pGAD10 was screened for proteins that interact with NSP4. Protein interactions were confirmed in vivo by coimmunoprecipitation and immunohistochemical colocalization. After two-hybrid library screening, we repeatedly isolated cDNAs encoding the extracellular matrix (ECM) protein laminin-beta3 (amino acids [aa] 274 to 878) and a cDNA encoding the ECM protein fibronectin (aa 1755 to 1884). Using deletion mutants of NSP4, we mapped the region of interaction with the ECM proteins between aa 87 and 145. Deletion analysis of laminin-beta3 indicated that the region comprising aa 726 to 875 of laminin-beta3 interacts with NSP4. Interaction of NSP4 with either laminin-beta3 or fibronectin was confirmed by coimmunoprecipitation. NSP4 was present in infected enterocytes and in the basement membrane (BM) of infected neonatal mice and colocalized with laminin-beta3, indicating a physiological interaction. In conclusion, two-hybrid screening with NSP4 yielded two potential target proteins, laminin-beta3 and fibronectin, interacting with the enterotoxin NSP4. The release of NSP4 from the basal side of infected epithelial cells and the subsequent binding to ECM proteins localized at the BM may signify a new mechanism by which rotavirus disease is established.

Integrins and extracellular matrix in animal models

Integrins are a family of transmembrane receptors that mediate interactions of cells with extracellular matrix (ECM) constituents and cell surface counter receptors. Each integrin mediates interactions with specific sets of ligands and regulates distinct aspects of cellular function including attachment to and organization of ECM assemblies, cell migration, proliferation and survival, and mechanical force transmission. Integrins exert their versatile functions by establishing a transmembrane link between the cell exterior and the cytoskeleton, and by activating intracellular second messenger systems. In addition, cellular signals can modulate integrin activity and ligand interactions, enabling transduction of information from the inside of the cell to the outside. Many of the basic functions of integrins and their ECM ligands have been uncovered by studying them biochemically or with cells in culture. Integrin and ECM functions have also been determined genetically, defining their essential roles in the organism. The ongoing challenge is to integrate cell biological, biochemical, and genetical evidence into a coherent picture. I will discuss here genetic findings, focusing on the murine system, that have shed light on the developmental functions of integrins and their ECM ligands. Where suitable information is available, I will relate the genetical finding to results obtained with cell biological and biochemical approaches.

Recognition of the N-terminal modules of thrombospondin-1 and thrombospondin-2 by alpha6beta1 integrin

In addition to its recognition by alpha3beta1 and alpha4beta1 integrins, the N-terminal pentraxin module of thrombospondin-1 is a ligand for alpha6beta1 integrin. alpha6beta1 integrin mediates adhesion of human microvascular endothelial and HT-1080 fibrosarcoma cells to immobilized thrombospondin-1 and recombinant N-terminal regions of thrombospondin-1 and thrombospondin-2. alpha6beta1 also mediates chemotaxis of microvascular cells to thrombospondin-1 and thrombospondin-2. Using synthetic peptides, LALERKDHSG was identified as an alpha6beta1-binding sequence in thrombospondin-1. This peptide inhibited alpha6beta1-dependent cell adhesion to thrombospondin-1, thrombospondin-2, and the E8 fragment of murine laminin-1. The Glu residue in this peptide was required for activity, and the corresponding residue (Glu90) in the N-terminal module of thrombospondin-1 was required for its recognition by alpha6beta1, but not by alpha4beta1. alpha6beta1 was also expressed in human umbilical vein endothelial cells; but in these cells, only certain agonists could activate the integrin to recognize thrombospondins. Selective activation of alpha6beta1 integrin in microvascular endothelial cells by the anti-beta1 antibody TS2/16 therefore accounts for their adhesion responses to thrombospondins and explains the distinct functions of alpha4beta1 and alpha6beta1 integrins as thrombospondin receptors in microvascular and large vessel endothelial cells.

Anopheles gambiae collagen IV genes: cloning, phylogeny and midgut expression associated with blood feeding and Plasmodium infection

A prerequisite for understanding the role that mosquito midgut extracellular matrix molecules play in malaria parasite development is proper isolation and characterisation of the genes coding for components of the basal lamina. Here we have identified genes coding for alpha1 and alpha2 chains of collagen IV from the major malaria vector, Anopheles gambiae. Conserved sequences in the terminal NC1 domain were used to obtain partial gene sequences of this functional region, and full sequence was isolated from a pupal cDNA library. In a DNA-derived phylogeny, the alpha1 and alpha2 chains cluster with dipteran orthologs, and the alpha2 is ancestral. The expression of collagen alpha1(IV) peaked during the pupal stage of mosquito development, and was expressed continuously in the adult female following a blood meal with a further rise detected in older mosquitoes. Collagen alpha1(IV) is also upregulated when the early oocyst of Plasmodium yoelii was developing within the mosquito midgut and may contribute to a larger wound healing response. A model describing the expression of basal lamina proteins during oocyst development is presented, and we hypothesise that the development of new basal lamina between the oocyst and midgut epithelium is akin to a wound healing process.

Analysis of microenvironmental factors contributing to basement membrane assembly and normalized epidermal phenotype

To understand further the role of the dynamic interplay between keratinocytes and stromal components in the regulation of the growth, differentiation, morphogenesis, and basement membrane assembly of human stratified squamous epithelium, we have generated novel, three-dimensional organotypic cultures in which skin keratinocytes were grown in the absence or presence of pre-existing basement membrane components and/or dermal fibroblasts. We found that keratinocytes cultured in the presence of pre-existing basement membrane components and dermal fibroblasts for 9 d showed rapid assembly of basement membrane, as seen by a nearly complete lamina densa, hemidesmosomes, and the polarized, linear distribution of laminin 5 and a6 integrin subunit. Basement membrane assembly was somewhat delayed in the absence of dermal fibroblasts, but did occur at discrete nucleation sites when pre-existing basement membrane components were present. No basement membrane developed in the absence of pre-existing basement membrane components, even in the presence of dermal fibroblasts. Bromodeoxyuridine incorporation studies showed that early keratinocyte growth was independent of mesenchymal support, but by 14 d, both fibroblasts and assembled basement membrane were required to sustain growth. Normalization of keratinocyte differentiation was independent of both dermal fibroblasts and structured basement membrane. These results indicated that epithelial and mesenchymal components play a coordinated role in the generation of structured basement membrane and in the regulation of normalized epithelial growth and tissue architecture in an in vitro model of human skin.

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.

Laminin assembles into separate basement membrane and fibrillar matrices in Schwann cells

Laminins are important for Schwann cell basement membrane assembly and axonal function. In this study, we found that exogenous laminin-1, like neuromuscular laminins-2/4, formed two distinct extracellular matrices on Schwann cell surfaces, each facilitated by laminin polymerization. Assembly of one, a densely-distributed reticular matrix, was accompanied by a redistribution of cell-surface dystroglycan and cytoskeletal utrophin into matrix-receptor-cytoskeletal complexes. The other, a fibrillar matrix,accumulated in separate zones associated with pre-existing β1-integrin arrays. The laminin-1 fragment E3 (LG-modules 4-5), which binds dystroglycan and heparin, inhibited reticular-matrix formation. By contrast,β1-integrin blocking antibody (Ha2/5) prevented fibrillar assembly. Ultrastructural analysis revealed that laminin treatment induced the formation of a linear electron-dense extracellular matrix (lamina densa)separated from plasma membrane by a narrow lucent zone (lamina lucida). This structure was considerably reduced with non-polymerizing laminin, fully blocked by E3, and unaffected by Ha2/5. Although it formed in the absence of type IV collagen, it was nonetheless able to incorporate this collagen. Finally, cell competency to bind laminin and form a basement membrane was passage-dependent. We postulate that laminin induces the assembly of a basement membrane on competent cell surfaces probably mediated by anchorage through LG 4-5. Upon binding, laminin interacts with dystroglycan,mobilizes utrophin, and assembles a `nascent' basement membrane, independent of integrin, that is completed by incorporation of type IV collagen. However,the fibrillar β1-integrin dependent matrix is unlikely to be precursor to basement membrane.

Rac1 orientates epithelial apical polarity through effects on basolateral laminin assembly

Cellular polarization involves the generation of asymmetry along an intracellular axis. In a multicellular tissue, the asymmetry of individual cells must conform to the overlying architecture of the tissue. However, the mechanisms that couple cellular polarization to tissue morphogenesis are poorly understood. Here, we report that orientation of apical polarity in developing Madin-Darby canine kidney (MDCK) epithelial cysts requires the small GTPase Rac1 and the basement membrane component laminin. Dominant-negative Rac1 alters the supramolecular assembly of endogenous MDCK laminin and causes a striking inversion of apical polarity. Exogenous laminin is recruited to the surface of these cysts and rescues apical polarity. These findings implicate Rac1-mediated laminin assembly in apical pole orientation. By linking apical orientation to generation of the basement membrane, epithelial cells ensure the coordination of polarity with tissue architecture.

Proteoglycan arrays in the cochlear basement membrane

Indirect immunofluorescence and transmission electron microscopy were used to investigate the composition and assembly of proteoglycans in the basement membranes of the spiral limbus, basilar membrane, spiral ligament, Reissner's membrane, myelinated nerve fibers, and blood capillaries of the spiral ligament and stria vascularis in the chinchilla cochlea. Four types of basement membrane components: laminin, entactin/nidogen, type IV collagen and heparan sulfate proteoglycans were immunolocalized in all basement membranes in association with heparan sulfate proteoglycans. beta 1 and alpha 1 integrin subunits were also detected along these basement membranes. The concentration of the basement membrane-associated proteins and integrin subunits differed according to the adjacent cell type. Electron microscopy showed that all basement membranes, with exception of those of stria vascularis, consist of two layers: lamina lucida and lamina densa. In the stria vascularis only a homogeneous lamina densa was observed. Cuprolinic blue treatment revealed heterogeneity in the ultrastructure and arrangement of proteoglycans in the cochlear basement membranes. Proteoglycans of the subepithelial basement membrane in the spiral limbus and spiral ligament formed quasi-regular, linear arrays within the lamina lucida, or were located at both sides of the lamina densa in the basilar membrane and Reissner's membrane. In the basement membranes of nerve fibers, and capillaries in the spiral ligament and stria vascularis, proteoglycans were scattered throughout these basement membranes, but showed different concentration and ultrastructural appearance, which may be related to different filtration and mechanical properties. In the basilar membrane, PGs were located above and below the lamina densa. An additional layer of PGs below the lamina densa may function as increased mechanical support of organ of Corti by its interaction with underlying fibrillar collagen layer. In the stria vascularis capillaries, PGs were stained considerably less with Cuprolinic blue and were scattered through the lamina densa of the basement membrane compared to capillaries of spiral ligament. This observation is compatible with a higher permeability of the strial capillaries.

The dystroglycan complex is necessary for stabilization of acetylcholine receptor clusters at neuromuscular junctions and formation of the synaptic basement membrane

The dystrophin-associated protein (DAP) complex spans the sarcolemmal membrane linking the cytoskeleton to the basement membrane surrounding each myofiber. Defects in the DAP complex have been linked previously to a variety of muscular dystrophies. Other evidence points to a role for the DAP complex in formation of nerve-muscle synapses. We show that myotubes differentiated from dystroglycan-/- embryonic stem cells are responsive to agrin, but produce acetylcholine receptor (AChR) clusters which are two to three times larger in area, about half as dense, and significantly less stable than those on dystroglycan+/+ myotubes. AChRs at neuromuscular junctions are similarly affected in dystroglycan-deficient chimeric mice and there is a coordinate increase in nerve terminal size at these junctions. In culture and in vivo the absence of dystroglycan disrupts the localization to AChR clusters of laminin, perlecan, and acetylcholinesterase (AChE), but not rapsyn or agrin. Treatment of myotubes in culture with laminin induces AChR clusters on dystroglycan+/+, but not -/- myotubes. These results suggest that dystroglycan is essential for the assembly of a synaptic basement membrane, most notably by localizing AChE through its binding to perlecan. In addition, they suggest that dystroglycan functions in the organization and stabilization of AChR clusters, which appear to be mediated through its binding of laminin.

Binding of the renal epithelial cell line LLC-PK1 to laminin is regulated by protein kinase C

The alpha6beta1 integrin heterodimer has been implicated in the mediation of renal epithelial cell binding to laminin, and it has been suggested that this binding is important for renal morphogenesis and development. Studies of nonrenal cells have suggested that the functional activity of alpha6beta1 integrin is regulated by protein kinase C (PKC) activity. In this study, the binding of a renal epithelial cell line, LLC-PK1, to laminin was characterized and the role of PKC activity in the modulation of binding was investigated. LLC-PK1 cells bound to laminin-coated surfaces in a time- and laminin concentration-dependent manner. Binding was strongly inhibited by anti-beta1 integrin antibodies and by anti-alpha6 integrin antibodies. Antibodies against alpha2 integrin and a3 integrin had little inhibitory effect. Cells bound to both whole laminin and laminin fragment E8, i.e., the fragment to which the alpha6beta1 integrin heterodimer binds. Exposure of cells to PKC activators for as little as 2 h enhanced cell binding to laminin approximately twofold, in a protein synthesis-dependent manner. PKC inhibitors antagonized this effect. PKC-stimulated binding was also inhibited by anti-beta1 integrin and anti-alpha6 integrin antibodies. PKC activation did not alter expression of beta1 integrin subunits at the cell surface after short time periods (2 to 4 h), but expression was increased after longer time periods (24 h). These results indicate that the renal epithelial cell line LLC-PK1 binds to laminin via the alpha6betal integrin heterodimer and binding is enhanced by PKC activation. The PKC-mediated enhancement of binding requires protein synthesis and is mediated in part by activation of surface alpha6beta1 integrin.

Evidence that distinct states of the integrin alpha6beta1 interact with laminin and an ADAM

Integrins can exist in different functional states with low or high binding capacity for particular ligands. We previously provided evidence that the integrin alpha6beta1, on mouse eggs and on alpha6-transfected cells, interacted with the disintegrin domain of the sperm surface protein ADAM 2 (fertilin beta). In the present study we tested the hypothesis that different states of alpha6beta1 interact with fertilin and laminin, an extracellular matrix ligand for alpha6beta1. Using alpha6-transfected cells we found that treatments (e.g., with phorbol myristate acetate or MnCl2) that increased adhesion to laminin inhibited sperm binding. Conversely, treatments that inhibited laminin adhesion increased sperm binding. Next, we compared the ability of fluorescent beads coated with either fertilin beta or with the laminin E8 fragment to bind to eggs. In Ca2+-containing media, fertilin beta beads bound to eggs via an interaction mediated by the disintegrin loop of fertilin beta and by the alpha6 integrin subunit. In Ca2+-containing media, laminin E8 beads did not bind to eggs. Treatment of eggs with phorbol myristate acetate or with the actin disrupting agent, latrunculin A, inhibited fertilin bead binding, but did not induce laminin E8 bead binding. Treatment of eggs with Mn2+ dramatically increased laminin E8 bead binding, and inhibited fertilin bead binding. Our results provide the first evidence that different states of an integrin (alpha6beta1) can interact with an extracellular matrix ligand (laminin) or a membrane-anchored cell surface ligand (ADAM 2).

Cross-linking of osteopontin by tissue transglutaminase increases its collagen binding properties

Osteopontin, a major noncollagenous bone protein, is an in vitro and in vivo substrate of tissue transglutaminase, which catalyzes formation of cross-linked protein aggregates. The roles of the enzyme and the polymeric osteopontin are presently not fully understood. In this study we provide evidence that transglutaminase treatment significantly increases the binding of osteopontin to collagen. This was tested with an enzyme-linked immunosorbent assay. The results also show that this increased interaction is clearly calcium-dependent and specific to osteopontin. In dot blot overlay assay 1 microgram of collagen type I was able to bind 420 ng of in vitro prepared and purified polymeric osteopontin and only 83 ng of monomeric osteopontin, indicating that the transglutaminase treatment introduces a 5-fold amount of osteopontin onto collagen. Assays using a reversed situation showed that the collagen binding of the polymeric form of osteopontin appears to be dependent on its conformation in solution. Circular dichroism analysis of monomeric and polymeric osteopontin indicated that transglutaminase treatment induces a conformational change in osteopontin, probably exposing motives relevant to its interactions with other extracellular molecules. This altered collagen binding property of osteopontin may have relevance to its biological functions in tissue repair, bone remodeling, and collagen fibrillogenesis.

Glomerular basement membrane. Identification of a novel disulfide-cross-linked network of alpha3, alpha4, and alpha5 chains of type IV collagen and its implications for the pathogenesis of Alport syndrome

Glomerular basement membrane (GBM) plays a crucial function in the ultrafiltration of blood plasma by the kidney. This function is impaired in Alport syndrome, a hereditary disorder that is caused by mutations in the gene encoding type IV collagen, but it is not known how the mutations lead to a defective GBM. In the present study, the supramolecular organization of type IV collagen of GBM was investigated. This was accomplished by using pseudolysin (EC 3.4.24.26) digestion to excise truncated triple-helical protomers for structural studies. Two distinct sets of truncated protomers were solubilized, one at 4 degrees C and the other at 25 degrees C, and their chain composition was determined by use of monoclonal antibodies. The 4 degrees C protomers comprise the alpha1(IV) and alpha2(IV) chains, whereas the 25 degrees C protomers comprised mainly alpha3(IV), alpha4(IV), and alpha5(IV) chains along with some alpha1(IV) and alpha2(IV) chains. The structure of the 25 degrees C protomers was examined by electron microscopy and was found to be characterized by a network containing loops and supercoiled triple helices, which are stabilized by disulfide cross-links between alpha3(IV), alpha4(IV), and alpha5(IV) chains. These results establish a conceptual framework to explain several features of the GBM abnormalities of Alport syndrome. In particular, the alpha3(IV). alpha4(IV).alpha5(IV) network, involving a covalent linkage between these chains, suggests a molecular basis for the conundrum in which mutations in the gene encoding the alpha5(IV) chain cause defective assembly of not only alpha5(IV) chain but also the alpha3(IV) and alpha4(IV) chains in the GBM of patients with Alport syndrome.

Self-assembly of laminin isoforms

The alpha, beta, and gamma subunits of basement membrane laminins can combine into different heterotrimeric molecules with either three full short arms (e.g. laminins-1-4), or molecules containing one (laminins-6-9) or more (laminin-5) short arm truncations. Laminin-1 (alpha1beta1gamma1), self-assembles through a calcium-dependent thermal gelation requiring binding interactions between N-terminal short arm domains, forming a meshwork polymer thought to contribute to basement membrane architecture (Yurchenco, P. D., and Cheng, Y. S. (1993) J. Biol. Chem. 268, 17286-17299). However, it has been unclear whether other isoforms share this property, and if so, which ones. To begin to address this, we evaluated laminin-2 (alpha2beta1gamma1), laminin-4 (alpha2beta2gamma1), laminin-5 (alpha3Abeta3gamma2), and laminin-6 (alpha3Abeta1gamma1). The first two isoforms were found to self-aggregate in a concentration- and temperature-dependent manner and a close self-assembly relationship among laminins-1, -2, and -4 were demonstrated by: (a) polymerization of all three proteins was inhibited by EDTA and laminin-1 short arm fragments, (b) polymerization of laminin-1 was inhibited by fragments of laminins-2 and -4, (c) laminin-2 and, to a lesser degree, laminin-4, even well below their own critical concentration, co-aggregated with laminin-1, evidence for co-polymerization. Laminin-5, on the other hand, neither polymerized nor co-polymerized with laminin-1. Laminin-6 failed to co-aggregate with laminin-1 at all concentrations evaluated, evidence for a lack of a related self-assembly activity. The data support the hypothesis that all three short arms are required for self-assembly and suggest that the short arm domain structure of laminin isoforms affect their architecture-forming properties in basement membranes.

Developmental expression of perlecan during murine embryogenesis

Perlecan is a modular heparan sulfate proteoglycan that is an intrinsic constituent of all basement membranes and extracellular matrices. Because of its strategic position and unique structure, perlecan has been implicated in modulating the activity of various growth factors required for normal development and tissue homeostasis. To gain insights into the potential function of perlecan in vivo, we examined the spatiotemporal distribution of its mRNA and protein core during murine embryogenesis. We utilized a new affinity-purified antibody that recognizes specifically the protein core of perlecan together with an in situ RT-PCR approach to perform a systematic analysis of perlecan expression and deposition during murine ontogeny. Perlecan appeared early (E10.5) in tissues of vasculogenesis including heart, pericardium, and major blood vessels. Its early expression coincided with the development of the cardiovascular system. Subsequently (E11-13), the greatest deposition of perlecan occurred within the developing cartilage, especially the cartilage undergoing endochondral ossification, where it remained elevated throughout all the developmental stages, and up to adulthood. Interestingly, the mRNA levels of perlecan were always higher in all the vascularized tissues, principally within endothelial cells, while chondrocytes displayed relatively low mRNA levels. This suggests a higher biosynthesis and turnover rates in the blood vessels vis-à-vis those of cartilaginous and other mesenchymal tissues. During later stages of development (E13-17.5) perlecan mRNA levels progressively increased and its expression correlated with the onset of tissue differentiation of various parenchymal organs including the developing kidneys, lungs, liver, spleen, and gastrointestinal tract. The central nervous system showed no perlecan expression with the exception of the calvaria and choroid plexus. Collectively, the results indicate that perlecan may play crucial roles not only in vasculogenesis but also in the maturation and maintenance of differentiated tissues, including cartilage.

Oxidized LDL binding to a macrophage-secreted extracellular matrix

Extracellular matrix (ECM), which was shown to be secreted by arterial wall cells, is a major part of the atherosclerotic lesion. ECM can contribute to low density lipoprotein (LDL) retention which can then lead to macrophage foam cell formation, the hallmark of early atherogenesis. The present study demonstrated that in addition to the known ability of endothelial cells and smooth muscle cells to produce ECM, macrophages can also secrete an ECM layer. The macrophage derived ECM was shown to contain the proteoglycans chondroitin sulfate, heparan sulfate and dermatan sulfate. Macrophage derived ECM can bind native LDL, as well as oxidized LDL (3 fold more than native LDL), and this binding is significantly increased in the presence of lipoprotein lipase. Glycosaminoglycans from the ECM (mainly chondroitin sulfate and heparan sulfate) participate in the binding of Ox-LDL to the macrophage derived ECM. These observations suggest that ECM is produced also by macrophages, and it can contribute to a specific and local delivery of atherogenic LDL to macrophages, leading to cellular cholesterol accumulation and foam cell formation.

Seminiferous tubule basement membrane. Composition and organization of type IV collagen chains, and the linkage of alpha3(IV) and alpha5(IV) chains

Seminiferous tubule basement membrane (STBM) plays an important role in spermatogenesis. In the present study, the composition and structural organization of type IV collagen of bovine STBM was investigated. STBM was found to be composed of all six alpha-chains of type IV collagen based upon immunocytochemical and biochemical analysis. The content of alpha3(IV) chain (40%) and the alpha4(IV) chain (18%) was substantially higher than in any other basement membrane collagen. The supramolecular structure of the six alpha(IV) chains was investigated using pseudolysin (EC 3.4.24.26) digestion to excise triple-helical molecules, subsequent collagenase digestion to produce NC1 hexamers and antibody affinity chromatography to resolve populations of NC1 hexamers. The hexamers, which reflect specific arrangements of alpha(IV) chains, were characterized for their alpha(IV) chain composition using high performance liquid chromatography, two-dimensional electrophoresis, and immunoblotting with alpha(IV) chain-specific antibodies. Three major hexamer populations were found that represent the classical network of the alpha1(IV) and alpha2(IV) chains and two novel networks, one composed of the alpha1(IV)-alpha6(IV) chains and the other composed of the alpha3(IV)-alpha6(IV) chains. The results establish a structural linkage between the alpha3(IV) and alpha5(IV) chains, suggesting a molecular basis for the conundrum in which mutations in the gene encoding the alpha5(IV) chain cause defective assembly of the alpha3(IV) chain in the glomerular basement membrane of patients with Alport syndrome.

Immunohistochemical localization of extracellular matrix components in human breast tumours with special reference to PG-M/versican

Immunohistochemical localization of the large proteoglycan, PG-M/versican, was studied in 36 breast tumours, including infiltrating ductal carcinomas, benign tumours and fibrocystic diseases. The relation between the proteoglycan and the other extracellular matrix components was also investigated. In the carcinoma tissues, the interstitial elements of the 'specific stroma', consisting of fibroblastic cells and fine fibrils, were reactive to antibody 2B1, which specifically recognizes the large proteoglycan, PG-M/versican. In the peripheral invasive areas of infiltrating ductal carcinoma, the most intense 2B1-positive reaction was visualized in mesenchymal tissues between carcinoma cells clumps and the surrounding tissues, where hyaluronic acid could be demonstrated histochemically. The 2B1-positive elements were not reactive to antibody 6B6, which specifically recognizes small proteoglycan. In the central sclerotic areas, where antibody 6B6 was reactive, a 2B1-positive reaction was detected only in elastosis masses, which also bound antibodies to type IV collagen and laminin, and to some extent antibody raised against chondroitin 6-sulphate proteoglycan. Elastic tissues of blood vessel walls and perivascular elements became reactive to antibody 2B1 when they were involved in carcinoma invasion. The present results have shown that PG-M/versican was localized in the proliferating interstitial tissues, in particular in hyaluronic acid-rich portions, in association with carcinoma cell growth, and also that PG-M/versican accumulated in vascular and perivascular elastic tissues involved in carcinoma invasion. The biological significance of PG-M/versican was briefly discussed.

Expression of laminin and type IV collagen by basement membrane-producing EHS tumors in streptozotocin-induced diabetic mice: in vivo modulation by low-molecular-weight heparin fragments

The biosynthesis of basement membrane components in Engelberth Holm Swarm-bearing mice with or without streptozotocin-induced diabetes and the effect of low-molecular-weight heparin derivatives (CY222, Sanofi Recherche/Institut Choay) on the relative rates of these synthetic activities were studied. In diabetic mice, the laminin mRNA level increased, whereas type IV collagen mRNA decreased. In vivo treatment with heparin fragments decreased the mRNA level of laminin to control values without altering the mRNA level of collagen IV. Biosynthetic studies with radiolabeled precursors ([3H]-proline for collagen and [35S]-methionine for laminin) confirmed these results. Laminin protein biosynthesis increased in diabetic mice. Treatment with CY222 corrected this alteration. Our results suggested an increased labeling of polymeric forms of collagen IV in diabetic mice. In addition, we showed that biosynthesis of acid-extractable collagen IV decreased in diabetic mice and that CY222 treatment corrected this disturbance. These experiments suggest that low-molecular-weight heparin fragments CY222 can modulate the biosynthesis of extracellular matrix macromolecules altered in diabetic animals by different pathways, including pretranslational and posttranslational steps.