Perlecan maintains the integrity of cartilage and some basement membranes

Differentiation-induced loss of heparan sulfate in human exostosis derived chondrocytes

An exostosis or osteochondroma is an aberrant bony growth occurring next to the growth plate either as an isolated growth abnormality or as part of the Hereditary Multiple Exostosis (HME) syndrome. Mutations in either exostosin 1 (EXT1) or exostosin 2 (EXT2) gene cause the HME syndrome and also some isolated osteochondromas. The EXT1 and EXT2 genes are glycosyltransferases that function as hetero-oligomers in the Golgi to add repeating glycosaminoglycans (GAGs) to heparan sulfate (HS) chains. Previously, we demonstrated that HS is markedly diminished in the exostosis cartilage cap and that the HS proteoglycan, perlecan, has an abnormal distribution in these caps. The present studies were undertaken to evaluate which chondrocyte-specific functions are associated with diminished HS synthesis in human chondrocytes harboring either EXT1 or EXT2 mutations. Systematic evaluation of exostosis cartilage caps and chondrocytes, both in vitro and in vivo, suggests that chondrocyte-specific cell functions account for diminished HS levels. In addition, we provide evidence that perichondrial cells give rise to chondrocytes that clonally expand and develop into an exostosis. Undifferentiated EXT chondrocytes synthesized amounts of HS similar to control chondrocytes; however, EXT chondrocytes displayed very poor survival in vitro under conditions that promote normal chondrocyte differentiation with high efficiency. Collectively, these observations suggest that loss of one copy of either the EXT1 or EXT2 gene product compromises the perichondrial chondrocytes' ability to differentiate normally and to survive in a differentiated state in vitro. In vivo, these compromised responses may lead to abnormal chondrocyte growth, perhaps from a perichondrial stem cell reserve.

The role of the extracellular matrix in angiogenesis in malignant glioma tumors

Angiogenesis is a promising target for the development of effective strategies for the treatment of malignant brain tumors in that it has the potential to starve large tumors and prevent the regrowth of residual margins. Two critical steps in angiogenesis, the proliferation of activated endothelial cells and their migration into the perivascular space (sprouting), require adherence of the endothelial cells to the extracellular matrix (ECM). Thus, the availability of the appropriate ligands within the ECM contributes to the regulation of angiogenesis. In addition, several components of the ECM can act through other mechanisms to further promote angiogenesis or inhibit it. Current evidence suggests that the regulation of angiogenesis is a dynamic process in which the endothelial cells can promote angiogenesis by secreting proteases that remodel the ECM, tumor cells can further promote angiogenesis by secreting ECM components and actively remodeling their environment, and stromal cells may respond to angiogenesis associated with tumors and inflammatory reactions by secreting inhibitory molecules. Here, we provide a critical review of the protein and proteoglycan components of the ECM that have been implicated in angiogenesis with an emphasis on their role in promoting or inhibiting angiogenesis in brain tumors.

The role of proteomics in the assessment of premature rupture of fetal membranes

The presence and integrity of amniotic fluid is fundamental for the normal development of the human fetus during pregnancy. Its production rate changes throughout pregnancy and is mainly related to the functions of the different fetal, placental and amniotic compartments. Premature rupture of the membranes (PROM) occurs in about 5% of deliveries, with complications such as infection and preterm birth. The management of patients with PROM, regardless of gestational age, remains controversial, and it is therefore important to develop new biological tests in order to achieve accurate diagnoses by identifying the presence of specific amniotic fluid markers in vaginal environment. We recently showed the usefulness of amniotic fluid proteomics in identifying a series of peptides that were absent from the corresponding maternal plasma. Several peptides corresponded to fragments of plasma proteins. Two peptides, absent from plasma samples of pregnant women, were identified in amniotic fluid. They corresponded to the COOH-terminal parts of perlecan (SwissProt: P98160) and of agrin (SwissProt: O00468) protein cores, two major heparan sulfate proteoglycans of basement membranes. In this review we will discuss modern proteomic strategies that may improve the laboratory assessment of PROM, and will focus on some of the biochemical characteristics of agrin and perlecan fragments identified in amniotic fluid.

Compound genetic ablation of nidogen 1 and 2 causes basement membrane defects and perinatal lethality in mice

Nidogen 1 and 2 are basement membrane glycoproteins, and previous biochemical and functional studies indicate that they may play a crucial role in basement membrane assembly. While they show a divergent expression pattern in certain adult tissues, both have a similar distribution during development. Gene knockout studies in mice demonstrated that the loss of either isoform has no effect on basement membrane formation and organ development, suggesting complementary functions. Here, we show that this is indeed the case. Deficiency of both nidogens in mice resulted in perinatal lethality. Nidogen 1 and 2 do not appear to be crucial in establishing tissue architecture during organ development; instead, they are essential for late stages of lung development and for maintenance and/or integrity of cardiac tissue. These organ defects are not compatible with postnatal survival. Ultrastructural analysis suggests that the phenotypes directly result from basement membrane changes. However, despite the ubiquitous presence of nidogens in basement membranes, defects do not occur in all tissues or in all basement membranes, suggesting a varying spectrum of roles for nidogens in the basement membrane.

SPARC-like 1 regulates the terminal phase of radial glia-guided migration in the cerebral cortex

Differential adhesion between migrating neurons and transient radial glial fibers enables the deployment of neurons into appropriate layers in the developing cerebral cortex. The identity of radial glial signals that regulate the termination of migration remains unclear. Here, we identified a radial glial surface antigen, SPARC (secreted protein acidic and rich in cysteine)-like 1, distributed predominantly in radial glial fibers passing through the upper strata of the cortical plate (CP) where neurons end their migration. Neuronal migration and adhesion assays indicate that SPARC-like 1 functions to terminate neuronal migration by reducing the adhesivity of neurons at the top of the CP. Cortical neurons fail to achieve appropriate positions in the absence of SPARC-like 1 function in vivo. Together, these data suggest that antiadhesive signaling via SPARC-like 1 on radial glial cell surfaces may enable neurons to recognize the end of migration in the developing cerebral cortex.

Midmembranous vocal fold lamina propria proteoglycans across selected species

OBJECTIVES

We examined the proteoglycan (PG) and associated sulfated glycosaminoglycan (GAG) content of the midmembranous vocal fold lamina propria (LP) of humans, dogs, pigs, and ferrets.

METHODS

The LP PG levels were assessed indirectly by quantifying the associated sulfated GAGs, and immunohistochemical analyses of specific PGs and/or GAGs (PGs/GAGs) were conducted.

RESULTS

Sulfated GAGs constituted approximately (average +/- SEM) 14.7 +/- 2.1 microg per milligram of tissue total protein in the human LP--similar to levels in canine, porcine, and ferret LPs (p > .05). Immunohistochemical analysis identified versican, chondroitin 4- and 6-sulfate, and heparan sulfate in the LP extracellular matrix--PGs/GAGs previously believed to be localized only intracellularly and in the basement membrane. Observations of PG/GAG staining patterns resulted in identification of microstructurally based subdivisions of canine, porcine, and ferret LPs.

CONCLUSIONS

The sulfated GAG concentration in human LP was similar to that of dermis. In contrast to the interspecies similarity in LP sulfated GAG levels, immunohistochemical analysis indicated notable interspecies differences in specific PG/GAG distributions. Moreover, spatial variations in the presence of several PGs/GAGs were observed--variations that may be integral in maintaining normal LP physiology. Finally, the noted canine, porcine, and ferret LP subdivisions may yield insight into the adaptation of LP microstructure to the phonatory needs of each species.

Basement membrane proteoglycans: from cellar to ceiling

The biology of basement membrane proteoglycans extends far beyond the original notion of anionic filters. These complex molecules have dual roles as structural constituents of basement membranes and functional regulators of several growth-factor signalling pathways. As such, they are involved in angiogenesis and, consequently, in tumour progression and their partial or total absence causes several congenital defects that affect the musculoskeletal, cardiovascular and nervous systems. New findings indicate a potential functional coupling between the intricate make-up of basement membrane proteoglycans and their ability to control important biological processes.

Effects of fukutin deficiency in the developing mouse brain

The major pathological change in Fukuyama-type congenital muscular dystrophy brain is polymicrogyria. Pathological studies of Fukuyama-type congenital muscular dystrophy brain indicated that protrusion of neurons into the subarachnoid space through breaches in the glia limitans-basal lamina complex is a cardinal pathogenic process in this condition. It remains undetermined, however, whether the defect causing this abnormal migration resides in the migrating neurons or in the glia limitans-basal lamina complex. To elucidate the pathogenesis of brain abnormalities in Fukuyama-type congenital muscular dystrophy, we analyzed histologically and immunohistochemically the developing forebrain in fukutin-deficient chimeric mice and compared it with that in controls (n=4 in each group). In chimeric embryos, ectopia became apparent as early as embryonic day 14, and laminar organization became progressively distorted. The basal lamina of the cortical surface in chimeras showed defects at E14, coinciding with the earliest time point at which ectopia were detected. Immunohistochemical analysis of glycosylated alpha-dystroglycan showed progressive defects coincidental with the disruption of the basal lamina. Neuronal migration was not affected in chimeras, as determined by detection of bromodeoxyuridine-labeled neurons. Extension of radial glial fibers was intact in chimeras. Taken together, disruption of the basal lamina, caused by the loss of interaction between hypoglycosylated alpha-dystroglycan and its ligands, plays a key role in the pathogenesis of cortical dysplasia in Fukuyama-type congenital muscular dystrophy.

Perlecan displays variable spatial and temporal immunolocalisation patterns in the articular and growth plate cartilages of the ovine stifle joint

Perlecan is a modular heparan sulphate and/or chondroitin sulphate substituted proteoglycan of basement membrane, vascular tissues and cartilage. Perlecan acts as a low affinity co-receptor for fibroblast growth factors 1, 2, 7, 9, binds connective tissue growth factor and co-ordinates chondrogenesis, endochondral ossification and vascular remodelling during skeletal development; however, relatively little is known of its distribution in these tissues during ageing and development. The aim of the present study was to immunolocalise perlecan in the articular and epiphyseal growth plate cartilages of stifle joints in 2-day to 8-year-old pedigree merino sheep. Perlecan was prominent pericellularly in the stifle joint cartilages at all age points and also present in the inter-territorial matrix of the newborn to 19-month-old cartilage specimens. Aggrecan was part pericellular, but predominantly an extracellular proteoglycan. Perlecan was a prominent component of the long bone growth plates and displayed a pericellular as well as a strong ECM distribution pattern; this may indicate a so far unrecognised role for perlecan in the mineralisation of hypertrophic cartilage. A significant age dependant decline in cell number and perlecan levels was evident in the hyaline and growth plate cartilages. The prominent pericellular distribution of perlecan observed indicates potential roles in cell-matrix communication in cartilage, consistent with growth factor signalling, cellular proliferation and tissue development.

Identification of Direct Serum-response Factor Gene Targets during Me2SO-induced P19 Cardiac Cell Differentiation

Serum-response factor (SRF) is an obligatory transcription factor, required for the formation of vertebrate mesoderm leading to the origin of the cardiovascular system. Protein A-TEV-tagged chromatin immunoprecipitation technology was used to collect direct SRF-bound gene targets from pluripotent P19 cells, induced by Me2SO treatment into an enriched cardiac cell population. From 242 sequenced DNA fragments, we identified 188 genomic DNA fragments as potential direct SRF targets that contain CArG boxes and CArG-like boxes. Of the 92 contiguous genes that were identified, a subgroup of 43 SRF targets was then further validated by co-transfection assays with SRF. Expression patterns of representative candidate genes were compared with the LacZ reporter expression activity of the endogenous SRF gene. According to the Unigene data base, 84% of the SRF target candidates were expressed, at least, in the heart. In SRF null embryonic stem cells, 81% of these SRF target candidates were greatly affected by the absence of SRF. Among these SRF-regulated genes, Raf1, Map4k4, and Bicc1 have essential roles in mesoderm formation. The 12 regulated SRF target genes, Mapk10 (JNK3), Txnl2, Azi2, Tera, Sema3a, Lrp4, Actc1, Myl3, Hspg2, Pgm2, Hif3a, and Asb5, have been implicated in cardiovascular formation, and the Ski and Hes6 genes have roles in muscle differentiation. SRF target genes related to cell mitosis and cycle, E2f5, Npm1, Cenpb, Rbbp6, and Scyl1, expressed in the heart tissue were differentially regulated in SRF null ES cells.

Neuronal migration and the role of reelin during early development of the cerebral cortex

During development, neurons migrate to the cortex radially from periventricular germinative zones as well as tangentially from ganglionic eminences. The vast majority of cortical neurons settle radially in the cortical plate. Neuronal migration requires an exquisite regulation of leading edge extension, nuclear translocation (nucleokinesis), and retraction of trailing processes. During the past few years, several genes and proteins have been identified that are implicated in neuronal migration. Many have been characterized by reference to known mechanisms of neuronal and non-neuronal cell migration in culture; however, probably the most interesting have been identified by gene inactivation or modification in mice and by positional cloning of brain malformation genes in humans and mice. Although it is impossible to provide a fully integrated view, some patterns clearly emerge and are the subject of this article. Specific emphasis is placed on three aspects: first, the role of the actin treadmill, with cyclic formation of filopodial and lamellipodial extensions, in relation to surface events that occur at the leading edge of radially migrating neurons; second, the regulation of microtubule dynamics, which seems to play a key role in nucleokinesis; and third, the mechanisms by which the extracellular protein Reelin regulates neuronal positioning at the end of migration.

Toward positional cloning of thecurly tailgene

BACKGROUND

The curly tail (ct) mutant mouse is one of the best-studied mouse models of spina bifida. The ct mutation has been localized to distal chromosome 4 in two independent studies and was recently postulated to be in the Grhl-3 gene.

METHODS

A recombinant BALB/c-ct strain was generated and used to precisely map the ct gene.

RESULTS

We report the absence of gross chromosomal abnormalities and the precise mapping of the ct gene to a 3-Mb region at 135 Mb (66 cM) from the centromere, closely linked to the polymorphic microsatellite marker D4Mit148. Candidate genes, Idb3, Wnt4, Cdc42, and perlecan, all localized in the critical region, were studied by sequence and expression analyses. Our data indicate that these genes in all probability do not account for the ct phenotype. In addition, our expression data do not provide strong evidence that Grhl-3 is indeed the ct gene.

CONCLUSIONS

The ct gene has not yet been identified. A total of 29 candidate genes remain present in the critical region. Refined mapping studies need to be performed to further narrow the region and additional candidate genes need to be examined. Supplementary material for this article can be found on the Birth Defects Research (Part A) website (http://www.mrw.interscience.wiley.com/suppmat/1542-0752/suppmat/2005/73/tables_S3-S6.doc).

Microfibrils at basement membrane zones interact with perlecan via fibrillin-1

Mutational defects in fibrillin-rich microfibrils give rise to a number of heritable connective tissue disorders, generally termed microfibrillopathies. To understand the pathogenesis of these microfibrillopathies, it is important to elucidate the supramolecular composition of microfibrils and their interaction properties with extracellular matrix components. Here we demonstrate that the proteoglycan perlecan is an associated component of microfibrils typically close to basement membrane zones. Double immunofluorescence studies demonstrate colocalization of fibrillin-1, the major backbone component of microfibrils, with perlecan in fibroblast cultures as well as in dermal and ocular tissues. Double immunogold labeling further confirms colocalization of perlecan to microfibrils in various tissues at the ultrastructural level. Extraction studies revealed that perlecan is not covalently associated with microfibrils. High affinity interactions between fibrillin-1 and perlecan were found by kinetic binding studies with dissociation constants in the low nanomolar range. A detailed mapping study of the interaction epitopes by solid phase binding assays primarily revealed interactions of perlecan domains I and II with a central region of fibrillin-1. Analysis of perlecan null embryos showed less microfibrils at the dermal-epidermal junction as compared with wild-type littermates. The data presented indicate a functional significance for perlecan in anchoring microfibrils to basement membranes and in the biogenesis of microfibrils.

Heparan sulfates in skeletal muscle development and physiology

Recent years have seen an emerging interest in the composition of the skeletal muscle extracellular matrix (ECM) and in the developmental and physiological roles of its constituents. Many cell surface-associated and ECM-embedded molecules occur in highly organized spatiotemporal patterns, suggesting important roles in the development and functioning of skeletal muscle. Glycans are historically underrepresented in the study of skeletal muscle ECM, even though studies from up to 30 years ago have demonstrated specific carbohydrates and glycoproteins to be concentrated in neuromuscular junctions (NMJs). Changes in glycan profile and distribution during myogenesis and synaptogenesis hint at an active involvement of glycoconjugates in muscle development. A modest amount of literature involves glycoconjugates in muscle ion housekeeping, but a recent surge of evidence indicates that glycosylation defects are causal for many congenital (neuro)muscular disorders, rendering glycosylation essential for skeletal muscle integrity. In this review, we focus on a single class of ECM-resident glycans and their emerging roles in muscle development, physiology, and pathology: heparan sulfate proteoglycans (HSPGs), notably their heparan sulfate (HS) moiety.

Matrix revolutions: ‘tails’ of basement-membrane components with angiostatic functions

Angiogenesis, the creation of neovasculature from native blood vessels, is a prerequisite for many physiological and pathological processes. Recently, C-terminal tail fragments of several basement-membrane proteins such as endostatin, tumstatin and endorepellin have been shown to inhibit angiogenesis. Although there seems to be little or no homology among them, a common theme is that these fragments modulate endothelial cells by distinct interactions with integrins and activate distinct intracellular signaling cascades that often lead to disruption of the actin cytoskeleton. In this article, we focus on recent advances regarding the mechanism of action of these angiostatic fragments and the emerging concept of similarities among them, with the underlying premise that appreciating these similarities might lead to improved therapeutics.

When sugars guide axons: insights from heparan sulphate proteoglycan mutants

Although there have previously been hints that heparan sulphate proteoglycans (HSPGs) are important for axon guidance, as they are for many other biological processes, there has been little in vivo evidence for interaction with known axon-guidance pathways. Genetic analyses of fly, mouse, nematode and zebrafish mutants now confirm the role of HSPGs in axon guidance and are beginning to show that they might have a key role in modulating the action of axon-guidance ligands and receptors.

BMP-1/Tolloid-like metalloproteases process endorepellin, the angiostatic C-terminal fragment of perlecan

Endorepellin, the C-terminal domain of the heparan sulfate proteoglycan perlecan, possesses angiostatic activity. The terminal laminin-like globular (LG3) domain of endorepellin appears to possess most of the biological activity on endothelial cells. LG3 protein has been detected in the urine of patients with end-stage renal disease and in the amniotic fluid of pregnant women with premature rupture of fetal membranes. These findings suggest that proteolytic processing of endorepellin and the generation of LG3 might have biological significance. In this study, we have identified specific enzymes of the bone morphogenetic protein-1 (BMP-1)/Tolloid family of metalloproteases that cleave LG3 from recombinant endorepellin at the physiologically relevant site and that cleave LG3 from endogenous perlecan in cultured mouse and human cells. The BMP-1/Tolloid family of metalloproteases is thereby implicated in the processing of a major basement membrane proteoglycan and in the liberation of an anti-angiogenic factor. Using molecular modeling, site-directed mutagenesis and angiogenic assays, we further demonstrate that LG3 activity requires specific amino acids involved in Ca(2+) coordination.

Perlecan immunolocalizes to perichondrial vessels and canals in human fetal cartilaginous primordia in early vascular and matrix remodeling events associated with diarthrodial joint development

The aim of this study was to ascertain how perlecan was localized in human fetal cartilaginous joint rudiment tissues. Perlecan was immunolocalized in human fetal (12-14-week-old) toe, finger, knee, elbow, shoulder, and hip joint rudiments using a monoclonal antibody to domain-1 of perlecan (MAb A76). Perlecan had a widespread distribution in the cartilaginous joint rudiments and growth plates and was also prominent in a network of convoluted hairpin loop-type vessels at the presumptive articulating surfaces of joints. Perlecan was also present in small perichondrial venules and arterioles along the shaft of the developing long bones, small blood vessels in the synovial lining and joint capsules, and in distinctive arrangements of cartilage canals in the knee, elbow, shoulder, and hip joint rudiments. Perlecan was notably absent from CD-31-positive metaphyseal vessels in the hip, knee, shoulder, and fingers. These vessels may have a role in the nutrition of the expanding cell populations in these developing joint tissues and in the establishment of the secondary centers of ossification in the long bones, which is essential for endochondral ossification.

ENU induced mutations causing congenital cardiovascular anomalies

We used non-invasive high frequency ultrasound to screen N-ethyl-N-nitrosourea mutagenized mouse fetuses for congenital cardiovascular anomalies. We ultrasound scanned 7546 mouse fetuses from 262 mutagenized families, and identified 124 families with cardiovascular defects. Represented were most of the major congenital cardiovascular anomalies seen clinically. The ENU-induced mutations in several families were mapped using polymorphic microsatellite DNA markers. One family with forelimb anomalies and ventricular septal defects, phenotypes similar to Holt-Oram syndrome, and one family with transposition of the great arteries and heart situs anomalies were mapped to different regions of mouse chromosome 4. A third mutation causing persistent truncus arteriosus and craniofacial defects, phenotypes reminiscent of DiGeorge syndrome, was mapped to mouse chromosome 2. We note that mouse chromosomes 4 and 2 do not contain Tbx5 or Tbx1, genes previously linked to Holt-Oram and DiGeorge syndromes, respectively. In two other families, the ENU-induced mutation was identified--Sema3CL605P was associated with persistent truncus arteriosus with interrupted aortic arch, and the Gja1W45X connexin43 mutation caused conotruncal malformation and coronary aneurysms. Although our screen was designed as a recessive screen, a number of the mutations showed cardiovascular phenotypes in both heterozygote and homozygote animals. These studies show the efficacy of ENU mutagenesis and high-throughput ultrasound phenotyping in recovering mutations causing a wide spectrum of congenital heart defects. These ENU-induced mutations hold promise in yielding new insights into the genetic basis for human congenital heart disease.

alpha3beta1 integrin modulates neuronal migration and placement during early stages of cerebral cortical development

We show that alpha3 integrin mutation disrupts distinct aspects of neuronal migration and placement in the cerebral cortex. The preplate develops normally in alpha3 integrin mutant mice. However, time lapse imaging of migrating neurons in embryonic cortical slices indicates retarded radial and tangential migration of neurons, but not ventricular zone-directed migration. Examination of the actin cytoskeleton of alpha3 integrin mutant cortical cells reveals aberrant actin cytoskeletal dynamics at the leading edges. Deficits are also evident in the ability of developing neurons to probe their cellular environment with filopodial and lamellipodial activity. Calbindin or calretinin positive upper layer neurons as well as the deep layer neurons of alpha3 integrin mutant mice expressing EGFP were misplaced. These results suggest that alpha3beta1 integrin deficiency impairs distinct patterns of neuronal migration and placement through dysregulated actin dynamics and defective ability to search and respond to migration modulating cues in the developing cortex.

Perlecan in late stages of osteoarthritis of the human knee joint

OBJECTIVE

Disturbances of the proteoglycan metabolism play an essential role in the pathology of osteoarthritis. The extracellular matrix proteoglycan, perlecan, has lately been identified as a cell biological factor in cartilage development and maintenance. We investigated the tissue distribution of perlecan, the relation between the level of the protein and its mRNA and which type of cell, type 1 chondrocytes or elongated secretory type 2 cells, produces perlecan in late stages of osteoarthritis.

METHODS

In 10 patients suffering from late-stage osteoarthritis tissue samples taken from a macroscopically intact area and the area adjacent to the main cartilage defect were investigated. We performed quantitative immunogold histochemistry and in situ hybridization in vivo and determined the level of perlecan mRNA with the help of real-time RT-PCR in native cartilage tissue and in cultured cells.

RESULTS

In vivo, an increased level of perlecan protein was found in the area adjacent to the main defect. A 45% rise in the level of perlecan mRNA secreted by elongated secretory type 2 cells in comparison to type 1 chondrocytes was detected. Type 2 cells also translated the highest levels of perlecan to be deposited mainly in the pericellular matrix, and also in the interterritorial matrix in late stages of osteoarthritis. Also in vitro, type 2 cells showed a 50% higher level of mRNA for perlecan.

CONCLUSION

We found evidence that perlecan is involved in the pathogenesis of late stages of osteoarthritis. The levels of perlecan protein and mRNA are up-regulated especially by the elongated secretory type 2 cells in the area adjacent to the main cartilage defect. This might be seen as an attempt on the part of the cartilage tissue to stabilize the extracellular matrix.

Testican-1, an inhibitor of pro-MMP-2 activation, is expressed in cartilage

OBJECTIVE

Recently, testican-1 has been described to be an inhibitor of MT1-MMP and MT3-MMP mediated pro-MMP-2 activation. As MT1-MMP mediated pro-MMP-2 activation is of significance for cartilage destruction in osteoarthritis, we studied the expression and localization of testican-1 in human articular cartilage.

METHODS

Cartilage samples from the medial and lateral tibia plateau were obtained from osteoarthritic patients who underwent joint replacements, and were graded histomorphologically by Mankin score. Testican-1 expression was assessed in RNA isolated directly from cartilage as well as in freshly isolated chondrocytes by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantified by real-time RT-PCR. Testican-1 protein was localized by immunohistochemistry in human osteoarthritic cartilage samples, in human fetal knee joint, and in knees from mice.

RESULTS

Testican-1 mRNA could be detected in cartilage and in freshly isolated chondrocytes both from moderately and from severely damaged osteoarthritic cartilage. In the same donor, expression in chondrocytes from more severely affected regions was decreased compared with chondrocytes from less affected regions. By immunolocalization, testican-1 protein could be detected in chondrocytes predominantly of the superficial and transitional zones. Matrix staining in these zones was greatly reduced in samples from more severely affected osteoarthritic cartilage. A similar distribution was found in the articular cartilage of knees from 7-week-old mice. In addition to articular cartilage, testican-1 was also present in growth plate cartilage.

CONCLUSIONS

Testican-1 is a component of cartilage, both of the joint and of the growth plate. Given its activity as an inhibitor of MT1-MMP mediated pro-MMP-2 activation, it is reasonable to speculate that it participates in the regulation of matrix turnover in cartilage.

Genes expressed in the human trabecular meshwork during pressure-induced homeostatic response

Physiological pressure inside the eye is maintained by a resistance mechanism provided by the trabecular meshwork tissue. In most cases, prolonged, elevated pressure leads to an eye pathology characterized by retinal ganglion cell (RGC) degeneration, optic nerve damage, and non-remedial blindness. We are investigating the regulation of trabecular meshwork genes in response to elevated pressure. Using perfused organ cultures from postmortem human donors, we have previously demonstrated the presence of a homeostatic mechanism at 2-4 days of pressure insult (Borrás et al. 2002, Invest Ophthalmol Vis Sci 43:33-40). Here, we sought to identify trabecular meshwork genes whose expression was altered during this homeostatic period. By macroarray hybridization, we compared the expression profiles of high-pressure (HP) and normal-pressure (NP) treated eyes from the same individual (n = 3 pairs). Our results identified 40 upregulated and 14 downregulated genes. The highest proportion of upregulated genes encoded proteins involved in signal transduction (32%). Among the potentially relevant genes, PIP 5K1C, VIP, tropomodulin, and MMP2 encoded mediators known to influence outflow resistance. Others encoded functions which are new for the trabecular meshwork, but which are intrinsic to unrelated tissues. These new mechanisms appear as they could be of benefit for trabecular meshwork function. Matrix Gla protein (MGP), perlecan, osteomodulin, and osteoblast-specific factor are essential in cartilage and bone physiology whereas spectrin and ICAM4 are specific for blood cells and crucial in maintaining their shape and adhesion. In addition, MGP transcripts were stimulated by extracellular calcium and downregulated by TGF-beta1. We propose that MGP might be an important player in the adaptive homeostatic mechanism by contributing to maintain a softer trabecular meshwork tissue and facilitate aqueous humor outflow.

Matrix remodeling during endochondral ossification

Endochondral ossification, the process by which most of the skeleton is formed, is a powerful system for studying various aspects of the biological response to degraded extracellular matrix (ECM). In addition, the dependence of endochondral ossification upon neovascularization and continuous ECM remodeling provides a good model for studying the role of the matrix metalloproteases (MMPs) not only as simple effectors of ECM degradation but also as regulators of active signal-inducers for the initiation of endochondral ossification. The daunting task of elucidating their specific role during endochondral ossification has been facilitated by the development of mice deficient for various members of this family. Here, we discuss the ECM and its remodeling as one level of molecular regulation for the process of endochondral ossification, with special attention to the MMPs.

Regulation of ureteric bud branching morphogenesis by sulfated proteoglycans in the developing kidney

Glycosaminoglycans in the form of heparan sulfate proteoglycans (HSPG) and chondroitin sulfate proteoglycans (CSPG) are required for normal kidney organogenesis. The specific roles of HSPGs and CSPGs on ureteric bud (UB) branching morphogenesis are unclear, and past reports have obtained differing results. Here we employ in vitro systems, including isolated UB culture, to clarify the roles of HSPGs and CSPGs on this process. Microarray analysis revealed that many proteoglycan core proteins change during kidney development (syndecan-1,2,4, glypican-1,2,3, versican, decorin, biglycan). Moreover, syndecan-1, syndecan-4, glypican-3, and versican are differentially expressed during isolated UB culture, while decorin is dynamically regulated in cultured isolated metanephric mesenchyme (MM). Biochemical analysis indicated that while both heparan sulfate (HS) and chondroitin sulfate (CS) are present, CS accounts for approximately 75% of the glycosaminoglycans (GAG) in the embryonic kidney. Selective perturbation of HS in whole kidney rudiments and in the isolated UB resulted in a significant reduction in the number of UB branch tips, while CS perturbation has much less impressive effects on branching morphogenesis. Disruption of endogenous HS sulfation with chlorate resulted in diminished FGF2 binding and proliferation, which markedly altered kidney area but did not have a statistically significant effect on patterning of the ureteric tree. Furthermore, perturbation of GAGs did not have a detectable effect on FGFR2 expression or epithelial marker localization, suggesting the expression of these molecules is largely independent of HS function. Taken together, the data suggests that nonselective perturbation of HSPG function results in a general proliferation defect; selective perturbation of specific core proteins and/or GAG microstructure may result in branching pattern defects. Despite CS being the major GAG synthesized in the whole developing kidney, it appears to play a lesser role in UB branching; however, CS is likely to be integral to other developmental processes during nephrogenesis, possibly involving the MM. A model is presented of how, together with growth factors, heterogeneity of proteoglycan core proteins and glycosaminoglycan sulfation act as a switching mechanism to regulate different stages of the branching process. In this model, specific growth factor-HSPG combinations play key roles in the transitioning between stages and their maintenance.

Assembly and tissue functions of early embryonic laminins and netrins

Vertebrate laminins and netrins share N-terminal domain structure, but appear to be only distantly related. Both families can be divided into different subfamilies on the basis of structural considerations. Recent observations suggest that specific laminin and netrin members have developmental functions that are highly conserved across species. Vertebrate laminin-1 (alpha1beta1gamma1) and laminin-10 (alpha5beta1gamma1), like the two Caenorhabditis elegans laminins, are embryonically expressed and are essential for basement membrane assembly. Basement membrane assembly is a cooperative process in which laminins polymerize through their LN domains and anchor to the cell surface through their G domains; this leads to cell signaling through integrins and dystroglycan (and possibly other receptors) recruited to the adherent laminin. Netrins may associate with this network through heterotypic LN domain interactions. Vertebrate netrin-1, like invertebrate UNC-6/netrins, is well known as an extracellular guidance cue that directs axon migration towards or away from the ventral midline. It also regulates cell adhesions and migrations, probably as a basement membrane component. Although sharing structural features, these two vertebrate protein families are quite distinct, having both retained members that mediate the ancestral developmental functions.

Premature aggregation of type IV collagen and early lethality in lysyl hydroxylase 3 null mice

Collagens carry hydroxylysine residues that act as attachment sites for carbohydrate units and are important for the stability of crosslinks but have been regarded as nonessential for vertebrate survival. We generated mice with targeted inactivation of the gene for one of the three lysyl hydroxylase isoenzymes, LH3. The null embryos developed seemingly normally until embryonic day 8.5, but development was then retarded, with death around embryonic day 9.5. Electron microscopy (EM) revealed fragmentation of basement membranes (BMs), and immuno-EM detected type IV collagen within the dilated endoplasmic reticulum and in extracellular aggregates, but the typical BM staining was absent. Amorphous intracellular and extracellular particles were also seen by collagen IV immunofluorescence. SDS/PAGE analysis demonstrated increased mobilities of the type IV collagen chains, consistent with the absence of hydroxylysine residues and carbohydrates linked to them. These results demonstrate that LH3 is indispensable for biosynthesis of type IV collagen and for BM stability during early development and that loss of LH3's functions leads to embryonic lethality. We propose that the premature aggregation of collagen IV is due to the absence of the hydroxylysine-linked carbohydrates, which thus play an essential role in its supramolecular assembly.

Impaired angiogenesis, delayed wound healing and retarded tumor growth in perlecan heparan sulfate-deficient mice

Perlecan, a modular proteoglycan carrying primary heparan sulfate (HS) side chains, is a major component of blood vessel basement membranes. It sequesters growth factors such as fibroblast growth factor 2 (FGF-2) and regulates the ligand-receptor interactions on the cell surface, and thus it has been implicated in the control of angiogenesis. Both stimulatory and inhibitory effects of perlecan on FGF-2 signaling have been reported. To understand the in vivo function of HS carried by perlecan, the perlecan gene heparan sulfate proteoglycan 2 (Hspg2) was mutated in mouse by gene targeting. The HS at the NH(2) terminus of perlecan was removed while the core protein remained intact. Perlecan HS-deficient (Hspg2(Delta3/Delta3)) mice survived embryonic development and were apparently healthy as adults. However, mutant mice exhibited significantly delayed wound healing, retarded FGF-2-induced tumor growth, and defective angiogenesis. In the mouse corneal angiogenesis model, FGF-2-induced neovascularization was significantly impaired in Hspg2(Delta3/Delta3) mutant mice. Our results suggest that HS in perlecan positively regulates the angiogenesis in vivo.

Endorepellin causes endothelial cell disassembly of actin cytoskeleton and focal adhesions through alpha2beta1 integrin

Endorepellin, the COOH-terminal domain of the heparan sulfate proteoglycan perlecan, inhibits several aspects of angiogenesis. We provide evidence for a novel biological axis that links a soluble fragment of perlecan protein core to the major cell surface receptor for collagen I, α2β1 integrin, and provide an initial investigation of the intracellular signaling events that lead to endorepellin antiangiogenic activity. The interaction between endorepellin and α2β1 integrin triggers a unique signaling pathway that causes an increase in the second messenger cAMP; activation of two proximal kinases, protein kinase A and focal adhesion kinase; transient activation of p38 mitogen-activated protein kinase and heat shock protein 27, followed by a rapid down-regulation of the latter two proteins; and ultimately disassembly of actin stress fibers and focal adhesions. The end result is a profound block of endothelial cell migration and angiogenesis. Because perlecan is present in both endothelial and smooth muscle cell basement membranes, proteolytic activity during the initial stages of angiogenesis could liberate antiangiogenic fragments from blood vessels' walls, including endorepellin.

A bit of give and take: the relationship between the extracellular matrix and the developing chondrocyte

The extracellular matrix (ECM), once thought to be a static structural component of tissues, is now known to play a complex and dynamic role in a variety of cellular functions in a number of diverse tissues. A significant body of literature attests to the ability of the ECM to communicate both spatial and temporal information to adherent cells, thereby directing cell behavior via interactions between the ECM and cell-surface receptors. Moreover, volumes of experimental data show that a great deal of communication travels in the opposite direction, from the cell to the ECM, allowing for regulation of the cues transmitted by the ECM. As such, the ECM, with respect to its components and their organization, is not a fixed reflection of the state the local microenvironment in which a cell finds itself at a particular time, but rather is able to respond to and effect changes in its local microenvironment. As an example of the developmental consequences of ECM interactions, this review gives an overview of the 'give and take' relationship between the ECM and the cells of the developing skeletal elements, in particular, the chondrocyte.

Dystroglycan in skin and cutaneous cells: beta-subunit is shed from the cell surface

In skin, hemidesmosomal protein complexes attach the epidermis to the dermis and are critical for stable connection of the basal epithelial cell cytoskeleton with the basement membrane (BM). In muscle, a similar supramolecular aggregate, the dystrophin glycoprotein complex links the inside of muscle cells with the BM. A component of the muscle complex, dystroglycan (DG), also occurs in epithelia. In this study, we characterized the expression and biochemical properties of authentic and recombinant DG in human skin and cutaneous cells in vitro. We show that DG is present at the epidermal BM zone, and it is produced by both keratinocytes and fibroblasts in vitro. The biosynthetic precursor is efficiently processed to the alpha- and beta-DG subunits; and, in addition, a distinct extracellular segment of the transmembranous beta-subunit is shed from the cell surface by metalloproteinases. Shedding of the beta-subunit releases the alpha-subunit from the DG complex on the cell surface into the extracellular space. The shedding is enhanced by IL-1beta and phorbol esters, and inhibited by metalloproteinase inhibitors. Deficiency of perlecan, a major ligand of alpha-DG, enhanced shedding suggesting that lack of a binding partner destabilizes the epithelial DG complex and makes it accessible to proteolytic processing.

Trophoblast-uterine interactions at implantation

Implantation of the embryo in the uterus is a critical and complex event and its failure is widely considered an impediment to improved success in assisted reproduction. Depending on whether placentation is invasive or superficial (epitheliochorial), the embryo may interact transiently or undergo a prolonged adhesive interaction with the uterine epithelium. Numerous candidate interactions have been identified, and there is good progress on identifying gene networks required for early placentation. However no molecular mechanisms for the epithelial phase are yet firmly established in any species. It is noteworthy that gene ablation in mice has so far failed to identify obligatory initial molecular events.

Serglycin is essential for maturation of mast cell secretory granule

To address the biological function of the scarcely studied intracellular proteoglycans, we targeted the gene for serglycin (SG), the only known committed intracellular proteoglycan. SG-/- mice developed normally and were fertile, but their mast cells (MCs) were severely affected. In peritoneum there was a complete absence of normal granulated MCs. Furthermore, peritoneal cells and ear tissue from SG-/- animals were devoid of the various MC-specific proteases. However, mRNA for the proteases was present in SG+/+, SG+/-, and SG-/- tissues, indicating that SG is essential for the storage, but not expression, of the MC proteases. Experiments, in which the differentiation of bone marrow stem cells into mature MCs was followed, showed that secretory granule maturation was compromised in SG-/- cells. Moreover, SG+/+ and SG+/- cells, but not SG-/- cells, synthesized proteoglycans of high anionic charge density. Taken together, we demonstrate a key role for SG proteoglycan in MC function.

The remodelled tracheal basement membrane zone of infant rhesus monkeys after 6 months of recovery

BACKGROUND

In previous studies, we showed that repeated exposure to (1) house dust mite allergen (HDMA) (Dermatophagoides farinae) caused thickening of the basement membrane zone (BMZ) and (2) HDMA+ozone (O3) caused depletion of BMZ perlecan and atypical development of BMZ collagen (irregular thin areas<2.0 microm in width).

OBJECTIVE

The purpose of this study was to determine if these remodelling changes were reversible after 6 months of recovery.

METHODS

Rhesus monkeys were exposed to a regimen of HDMA and or O3 or filtered air (FA) for 6 months. After the exposure protocol was completed FA and O3 groups were allowed to recover in FA for 6 months. The HDMA and HDMA+O3 exposure groups recovered in a modified environment. They were re-exposed to HDMA aerosol for 2 h at monthly intervals during recovery in order to maintain sensitization for pulmonary function testing. To detect structural changes in the BMZ, collagen I and perlecan immunoreactivity were measured and compared to data from the previous papers.

RESULTS

The remodelled HDMA group had a significantly thicker BMZ and after 6 months of recovery the width had not regressed. In the remodelled BMZ of the HDMA+O3 group, perlecan had returned to the BMZ after 6 months of the recovery protocol, and the thin, irregular, collagen BMZ had been resolved.

CONCLUSION

In summary, this study has shown that: (1) The width of the remodelled HDMA BMZ did not regress during a recovery protocol that included a sensitizing dose of HDMA. (2) The atypical collagen BMZ in the HDMA+O3 BMZ was resolved in the absence of O3. (3) Depletion of perlecan from the BMZ by O3 was reversed by recovery in the absence of O3.

Regulation of angiogenesis by extracellular matrix

During angiogenesis, endothelial cell growth, migration, and tube formation are regulated by pro- and anti-angiogenic factors, matrix-degrading proteases, and cell-extracellular matrix interactions. Temporal and spatial regulation of extracellular matrix remodeling events allows for local changes in net matrix deposition or degradation, which in turn contributes to control of cell growth, migration, and differentiation during different stages of angiogenesis. Remodeling of the extracellular matrix can have either pro- or anti-angiogenic effects. Extracellular matrix remodeling by proteases promotes cell migration, a critical event in the formation of new vessels. Matrix-bound growth factors released by proteases and/or by angiogenic factors promote angiogenesis by enhancing endothelial migration and growth. Extracellular matrix molecules, such as thrombospondin-1 and -2, and proteolytic fragments of matrix molecules, such as endostatin, can exert anti-angiogenic effects by inhibiting endothelial cell proliferation, migration and tube formation. In contrast, other matrix molecules promote endothelial cell growth and morphogenesis, and/or stabilize nascent blood vessels. Hence, extracellular matrix molecules and extracellular matrix remodelling events play a key role in regulating angiogenesis.

Perlecan and Syndecan-4 in Uterine Tissues during the Early Pregnancy in Mice

PROBLEM

During early pregnancy in mice, there is recruitment of specific immune cells, remodeling of the endometrium, cell differentiation and synthesis of new molecules.

METHOD OF STUDY

Immunohistochemistry was used to determine the distribution of perlecan and syndecan-4 in the uteri before and after embryo implantation.

RESULTS

During pre-implantation, perlecan was identified in basement membranes and extracellular spaces of the endometrial stroma. In contrast, expression of syndecan-4 was quite weak. In the peri-implantation period, perlecan remained in the basement membranes, and it was no longer observed in the stroma and it was identified in the embryonic cells. On day 4 of pregnancy, syndecan-4 increased in the fibroblasts of the subepithelial stroma. After implantation, syndecan-4 was pronounced in pre-decidual and mature decidual cells.

CONCLUSIONS

The coordinate balance between the pre- and post-implantation periods suggests a role of these two molecules in the adaptive modification of the uterine microenvironment to receive and implant the embryo.

Perlecan and its immunoglobulin like domain IV are abundant in vitreous and serum of the chick embryo

Perlecan is a highly conserved heparan sulfate proteoglycan in cartilage and basement membranes. We identified chick perlecan and a 90 KD perlecan fragment in vivo using a newly generated monoclonal antibody. Chick perlecan is, like its human and mouse homologue, a hybrid heparan sulfate/chondroitin sulfate proteoglycan with a core protein of 400 KD. Analysis of the 90 KD fragment by Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) and Capillary LC nano Electrospray Ionization tandem MS (LC nano ESI MS/MS) showed that it belonged to domain IV of the perlecan core protein. We found that full-length perlecan and its domain IV fragment are abundant in embryonic vitreous body and serum. Their expression in vitreous and serum is greatly down-regulated shortly after hatching of the chick. We speculate that the abundance of perlecan in the embryonic circulation and vitreous reflects the ongoing formation of new BMs in the expanding vascular system and the growing retina. In addition, we found that perlecan as a substrate does not support, rather inhibits neurite outgrowth.

Laminin: the crux of basement membrane assembly

Laminin-1 is emerging as the key molecule in early embryonic basement membrane assembly. Here we review recent insights into its functions gained from the synergistic application of genetic and structural methods.

Collagen IV is essential for basement membrane stability but dispensable for initiation of its assembly during early development

Basement membranes are specialized extracellular matrices consisting of tissue-specific organizations of multiple matrix molecules and serve as structural barriers as well as substrates for cellular interactions. The network of collagen IV is thought to define the scaffold integrating other components such as, laminins, nidogens or perlecan, into highly organized supramolecular architectures. To analyze the functional roles of the major collagen IV isoform alpha1(IV)(2)alpha2(IV) for basement membrane assembly and embryonic development, we generated a null allele of the Col4a1/2 locus in mice, thereby ablating both alpha-chains. Unexpectedly, embryos developed up to E9.5 at the expected Mendelian ratio and showed a variable degree of growth retardation. Basement membrane proteins were deposited and assembled at expected sites in mutant embryos, indicating that this isoform is dispensable for matrix deposition and assembly during early development. However, lethality occurred between E10.5-E11.5, because of structural deficiencies in the basement membranes and finally by failure of the integrity of Reichert's membrane. These data demonstrate for the first time that collagen IV is fundamental for the maintenance of integrity and function of basement membranes under conditions of increasing mechanical demands, but dispensable for deposition and initial assembly of components. Taken together with other basement membrane protein knockouts, these data suggest that laminin is sufficient for basement membrane-like matrices during early development, but at later stages the specific composition of components including collagen IV defines integrity, stability and functionality.

Distinctive Expression Patterns of Heparan Sulfate O-Sulfotransferases and Regional Differences in Heparan Sulfate Structure in Chick Limb Buds

The skeletal tissue development and patterning in chick limb buds are known to be under the spacio-temporal control of various heparin-binding cell growth factors such as fibroblast growth factors and bone morphogenetic proteins. Different structural regions on heparan sulfate (HS) chains of proteoglycans could be implicated in regional differences in the binding capacities of these cell growth factors, by which they could selectively interact with targeted cells and regulate their signaling in those processes. In this study we first demonstrated by cDNA cloning that one heparan sulfate 2-O-sulfotransferase (HS2ST) and two isoforms of heparan sulfate 6-O-sulfotransferase (HS6ST-1 and -2) occurred in chick embryos and had different substrate specificities each other. We next showed by whole mount in situ hybridization that the HS6ST-1 and HS6ST-2 transcripts were preferentially localized to the anterior proximal region and at the posterior proximal region of the limb bud, respectively, whereas the HS2ST transcript was distributed rather uniformly throughout the bud. Analyses of the structures of HS from different regions of the wing buds have shown variation in that 6-O-sulfated residues are more abundant in the proximal than distal region, whereas iduronosyl 6-O-sulfated residues are abundant in the anterior proximal region and glucuronosyl 6-O-sulfated residues in the posterior proximal region. These results suggest that HS with different sulfation patterns created with multiple sulfotransferase activities provides an appropriate extracellular environment for morphogenetic signal transduction.

Perlecan Functions in Chondrogenesis: Insights from in vitro and in vivo Models

Perlecan is a large heparan sulfate proteoglycan that is typically found in basal lamina of adult and embryonic tissues. Recent studies have demonstrated that perlecan accumulates impressively during cartilage development and is maintained as the major heparan sulfate proteoglycan of adult cartilage. In vertebrates, perlecan mutations result in skeletal defects. Moreover, in vitro studies indicate that perlecan can stimulate early stages of cartilage differentiation and cooperate with chondrogenic growth factors to promote this process. This short article will summarize these results and propose a model for perlecan function that incorporates these genetic and cell biological findings.

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.

Heparan sulfate proteoglycans are increased during skeletal muscle regeneration: requirement of syndecan-3 for successful fiber formation

Skeletal muscle regeneration is a highly complex and regulated process that involves muscle precursor proliferation and differentiation and probably requires the participation of heparin binding growth factors such as FGFs, HGF and TGFβ. Heparan sulfate proteoglycans, key components of cell-surfaces and ECM, modulate growth factor activities and influence cell growth and differentiation. Their expression in forming muscle masses during development and in cell culture, suggest their participation in the regulation of myogenesis. In the present study, heparan sulfate proteoglycan expression in skeletal muscle regeneration induced by barium chloride injection was evaluated. Expression of muscle differentiation markers and neuromuscular junction (NMJ) components was characterized. Immunoblots with anti-Δ-heparan sulfate antibody showed that four major species - perlecan, glypican, syndecan-3 and syndecan-4 - were transiently up-regulated. The first three were detected at the surface or basement membranes of newly formed myotubes by specific indirect immunofluorescence. Syndecan-3, a satellite cell marker, showed the earliest and most significant increase. Experiments involving myoblast grafting into regenerating muscle showed that C2C12 cell clones, with inhibited syndecan-3 expression resulting from antisense transfection, presented a normal proliferation rate but an impaired capacity to fuse and form skeletal muscle fibers. These data constitute the first in vivo evidence suggesting the requirement of a specific heparan sulfate proteoglycan for successful skeletal muscle regeneration.

Heparan sulfate proteoglycans: Coordinators of multiple signaling pathways during chondrogenesis

Heparan sulfate proteoglycans are abundantly expressed in the pericellular matrix of both developing and mature cartilage. Increasing evidence indicates that the action of numerous chondroregulatory molecules depends on these proteoglycans. This review summarizes the current understanding of the interactions of heparan sulfate chains of cartilage proteoglycans with both soluble and nonsoluble ligands during the process of chondrogenesis. In addition, the consequences of mutating genes encoding heparan sulfate biosynthetic enzymes or heparan sulfate proteoglycan core proteins on cartilage development are discussed.

Basement membrane assembly, stability and activities observed through a developmental lens

Basement membranes are cell surface associated extracellular matrices containing laminins, type IV collagens, nidogens, perlecan, agrin, and other macromolecules. Biochemical and ultrastructural studies have suggested that basement membrane assembly and integrity is provided through multiple component interactions consisting of self-polymerizations, inter-component binding, and cell surface adhesions. Mutagenesis in vertebrate embryos and embryoid bodies have led to revisions of this model, providing evidence that laminins are essential for the formation of an initial polymeric scaffold of cell-attached matrix which matures in stability, ligand diversity, and functional complexity as additional matrix components are integrated into the scaffold. These studies also demonstrate that basement membrane components differentially promote cell polarization, organize and compartmentalize developing tissues, and maintain adult tissue function.

Perlecan and tumor angiogenesis

Perlecan is a major heparan sulfate proteoglycan (HSPG) of basement membranes (BMs) and connective tissues. The core protein of perlecan is divided into five domains based on sequence homology to other known proteins. Commonly, the N-terminal domain I of mammalian perlecan is substituted with three HS chains that can bind a number of matrix molecules, cytokines, and growth factors. Perlecan is essential for metazoan life, as shown by genetic manipulations of nematodes, insects, and mice. There are also known human mutations that can be lethal. In vertebrates, new functions of perlecan emerged with the acquisition of a closed vascular system and skeletal connective tissues. Many of perlecan's functions may be related to the binding and presentation of growth factors to high-affinity tyrosine kinase (TK) receptors. Data are accumulating, as discussed here, that similar growth factor-mediated processes may have unwanted promoting effects on tumor cell proliferation and tumor angiogenesis. Understanding of these attributes at the molecular level may offer opportunities for therapeutic intervention.

Perlecan-induced suppression of smooth muscle cell proliferation is mediated through increased activity of the tumor suppressor PTEN

We were interested in the elucidation of the interaction between the heparan sulfate proteoglycan, perlecan, and PTEN in the regulation of vascular smooth muscle cell (SMC) growth. We verified serum-stimulated DNA synthesis, and Akt and FAK phosphorylation were significantly reduced in SMCs overexpressing wild-type PTEN. Our previous studies showed perlecan is a potent inhibitor of serum-stimulated SMC growth. We report in the present study, compared with SMCs plated on fibronectin, serum-stimulated SMCs plated on perlecan exhibited increased PTEN activity, decreased FAK and Akt activities, and high levels of p27, consistent with SMC growth arrest. Adenoviral-mediated overexpression of constitutively active Akt reversed perlecan-induced SMC growth arrest while morpholino antisense-mediated loss of endogenous PTEN resulted in increased growth and phosphorylation of FAK and Akt of SMCs on perlecan. Immunohistochemical and Western analyses of balloon-injured rat carotid artery tissues showed a transient increase in phosphoPTEN (inactive) after injury, correlating to high rates of neointimal cell replication; phosphoPTEN was largely limited to actively replicating SMCs. Similarly, in the developing rat aorta, we found increased PTEN activity associated with increased perlecan deposition and decreased SMC replication rates. However, significantly decreased PTEN activity was detected in aortas of perlecan-deficient mouse embryos, consistent with SMC hyperplasia observed in these animals, compared with E17.5 heterozygous controls that produce abundant amounts of perlecan at this developmental time point. Our data show PTEN is a potent endogenously produced inhibitor of SMC growth and increased PTEN activity mediates perlecan-induced suppression of SMC proliferation.