Decorin binds near the C terminus of type I collagen

That's my story, and I'm sticking to it--an update on B. burgdorferi adhesins

Adhesion is the initial event in the establishment of any infection. Borrelia burgdorferi, the etiological agent of Lyme disease, possesses myriad proteins termed adhesins that facilitate contact with its vertebrate hosts. B. burgdorferi adheres to host tissues through interactions with host cells and extracellular matrix, as well as other molecules present in serum and extracellular fluids. These interactions, both general and specific, are critical in the establishment of infection. Modulation of borrelial adhesion to host tissues affects the microorganisms's ability to colonize, disseminate, and persist. In this review, we update the current knowledge on structure, function, and role in pathogenesis of these “sticky” B. burgdorferi infection-associated proteins.

Hen uterine gene expression profiling during eggshell formation reveals putative proteins involved in the supply of minerals or in the shell mineralization process

BACKGROUND

The chicken eggshell is a natural mechanical barrier to protect egg components from physical damage and microbial penetration. Its integrity and strength is critical for the development of the embryo or to ensure for consumers a table egg free of pathogens. This study compared global gene expression in laying hen uterus in the presence or absence of shell calcification in order to characterize gene products involved in the supply of minerals and / or the shell biomineralization process.

RESULTS

Microarrays were used to identify a repertoire of 302 over-expressed genes during shell calcification. GO terms enrichment was performed to provide a global interpretation of the functions of the over-expressed genes, and revealed that the most over-represented proteins are related to reproductive functions. Our analysis identified 16 gene products encoding proteins involved in mineral supply, and allowed updating of the general model describing uterine ion transporters during eggshell calcification. A list of 57 proteins potentially secreted into the uterine fluid to be active in the mineralization process was also established. They were classified according to their potential functions (biomineralization, proteoglycans, molecular chaperone, antimicrobials and proteases/antiproteases).

CONCLUSIONS

Our study provides detailed descriptions of genes and corresponding proteins over-expressed when the shell is mineralizing. Some of these proteins involved in the supply of minerals and influencing the shell fabric to protect the egg contents are potentially useful biological markers for the genetic improvement of eggshell quality.

Decreased decorin expression in the tumor microenvironment

Decorin is a small leucine-rich proteoglycan, synthesized and deposited by fibroblasts in the stroma where it binds to collagen I. It sequesters several growth factors and antagonizes numerous members of the receptor tyrosine kinase family. In experimental murine systems, it acted as a potent tumor suppressor. Examining the Human Protein Atlas online database of immunostained tissue samples we have surveyed decorin expression in silico in several different tumor types, comparing them with corresponding normal tissues. We found that decorin is abundantly secreted and deposited in normal connective tissue but its expression is consistently decreased in the tumor microenvironment. We developed a software to quantitate the difference in expression. The presence of two closely related proteoglycans in the newly formed tumor stroma indicated that the decreased decorin expression was not caused by the delay in proteoglycan deposition in the newly formed connective tissue surrounding the tumor.

Biophysical cues and cell behavior: the big impact of little things

The extracellular matrix is composed of a variety of proteins, polysaccharides, and glycosaminoglycans that self-assemble into a hierarchical order of nanometer- to micrometer-scale fibrils and fibers. The shapes, sizes, and elasticity present within this highly ordered meshwork regulate behaviors in most cell types. It has been well documented that cellular migration, proliferation, differentiation, and tissue development are all influenced by matrix geometries and compliance, but how these external biophysical cues are translated into activated intracellular signaling cascades remains poorly understood. Fortunately, technological improvements in artificial substrate fabrication have provided biologists with tools to test cellular interactions within controlled three-dimensional environments. Here, we review cellular responses to biophysical cues and discuss their clinical relevancy and application. We focus especially on integrative approaches that aim to first characterize the properties of specific extracellular matrices and then precisely fabricate biomimetic materials to elucidate how relevant cells respond to the individual biophysical cues present in their native tissues. Through these types of comprehensive studies, biologists have begun to understand and appreciate how exceedingly small features can have a significant impact on the regulation, development, and homeostasis of cells and tissues.

Matrikine and matricellular regulators of EGF receptor signaling on cancer cell migration and invasion

Cancer invasion is a complex process requiring, among other events, extensive remodeling of the extracellular matrix including deposition of pro-migratory and pro-proliferative moieties. In recent years, it has been described that while invading through matrices cancer cells can change shape and adapt their migration strategies depending on the microenvironmental context. Although intracellular signaling pathways governing the mesenchymal to amoeboid migration shift and vice versa have been mostly elucidated, the extracellular signals promoting these shifts are largely unknown. In this review, we summarize findings that point to matrikines that bind specifically to the EGF receptor as matricellular molecules that enable cancer cell migrational plasticity and promote invasion.

The concave face of decorin mediates reversible dimerization and collagen binding

Decorin, the prototypical small leucine-rich proteoglycan, binds to collagen and thereby regulates collagen assembly into fibrils. The crystal structure of the decorin core protein revealed a tight dimer formed by the association of two monomers via their concave faces (Scott, P. G., McEwan, P. A., Dodd, C. M., Bergmann, E. M., Bishop, P. N., and Bella, J. (2004) Proc. Natl. Acad. Sci. U.S.A. 101, 15633-15638). Whether decorin binds collagen as a dimer has been controversial. Using analytical ultracentrifugation, we determined a dissociation constant of 1.37 ± 0.30 μm for the mouse decorin dimer. Dimerization could be abolished by engineering glycosylation sites into the dimer interface; other interface mutants remained dimeric. The monomeric mutants were as stable as wild-type decorin in thermal unfolding experiments. Mutations on the concave face of decorin abolished collagen binding regardless of whether the mutant proteins retained the ability to dimerize or not. We conclude that the concave face of decorin mediates collagen binding and that the dimer therefore must dissociate to bind collagen.

A comparison of the behavioral and anatomical outcomes in sub-acute and chronic spinal cord injury models following treatment with human mesenchymal precursor cell transplantation and recombinant decorin

This study assessed the potential of highly purified (Stro-1(+)) human mesenchymal precursor cells (hMPCs) in combination with the anti-scarring protein decorin to repair the injured spinal cord (SC). Donor hMPCs isolated from spinal cord injury (SCI) patients were transplanted into athymic rats as a suspension graft, alone or after previous treatment with, core (decorin(core)) and proteoglycan (decorin(pro)) isoforms of purified human recombinant decorin. Decorin was delivered via mini-osmotic pumps for 14 days following sub-acute (7 day) or chronic (1 month) SCI. hMPCs were delivered to the spinal cord at 3 weeks or 6 weeks after the initial injury at T9 level. Behavioral and anatomical analysis in this study showed statistically significant improvement in functional recovery, tissue sparing and cyst volume reduction following hMPC therapy. The combination of decorin infusion followed by hMPC therapy did not improve these measured outcomes over the use of cell therapy alone, in either sub-acute or chronic SCI regimes. However, decorin infusion did improve tissue sparing, reduce spinal tissue cavitation and increase transplanted cell survivability as compared to controls. Immunohistochemical analysis of spinal cord sections revealed differences in glial, neuronal and extracellular matrix molecule expression within each experimental group. hMPC transplanted spinal cords showed the increased presence of serotonergic (5-HT) and sensory (CGRP) axonal growth within and surrounding transplanted hMPCs for up to 2 months; however, no evidence of hMPC transdifferentiation into neuronal or glial phenotypes. The number of hMPCs was dramatically reduced overall, and no transplanted cells were detected at 8 weeks post-injection using lentiviral GFP labeling and human nuclear antigen antibody labeling. The presence of recombinant decorin in the cell transplantation regimes delayed in part the loss of donor cells, with small numbers remaining at 2 months after transplantation. In vitro co-culture experiments with embryonic dorsal root ganglion explants revealed the growth promoting properties of hMPCs. Decorin did not increase axonal outgrowth from that achieved by hMPCs. We provide evidence for the first time that (Stro-1(+)) hMPCs provide: i) an advantageous source of allografts for stem cell transplantation for sub-acute and chronic spinal cord therapy, and (ii) a positive host microenvironment that promotes tissue sparing/repair that subsequently improves behavioral outcomes after SCI. This was not measurably improved by recombinant decorin treatment, but does provide important information for the future development and potential use of decorin in contusive SCI therapy.

Dichotomy of decorin activity on the insulin-like growth factor-I system

The stromal-specific proteoglycan decorin has emerged in recent years as a critical regulator of tumor initiation and progression. Decorin regulates the biology of various types of cancer by modulating the activity of several receptor tyrosine kinases coordinating growth, survival, migration, and angiogenesis. Decorin binds to surface receptors for epidermal growth factor and hepatocyte growth factor with high affinity, and negatively regulates their activity and signaling via robust internalization and eventual degradation. The insulin-like growth factor (IGF)-I system plays a critical role in the regulation of cell growth both in vivo and in vitro. The IGF-I receptor (IGF-IR) is also essential for cellular transformation, owing to its ability to enhance cell proliferation and protect cancer cells from apoptosis. Recent data have pointed to a role of decorin in regulating the IGF-I system in both nontransformed and transformed cells. Significantly, there is a surprising dichotomy in the mechanism of decorin action on IGF-IR signaling, which differs considerably between physiological and pathological cellular models. In this review, we summarize the current knowledge on decorin regulation of the IGF-I system in normal and transformed cells, and discuss possible decorin-based therapeutic approaches to target IGF-IR-driven tumors.

The regulatory roles of small leucine-rich proteoglycans in extracellular matrix assembly

Small leucine-rich proteoglycans (SLRPs) are involved in a variety of biological and pathological processes. This review focuses on their regulatory roles in matrix assembly. SLRPs have protein cores and hypervariable glycosylation with multivalent binding abilities. During development, differential interactions of SLRPs with other molecules result in tissue-specific spatial and temporal distributions. The changing expression patterns play a critical role in the regulation of tissue-specific matrix assembly and therefore tissue function. SLRPs play significant structural roles within extracellular matrices. In addition, they play regulatory roles in collagen fibril growth, fibril organization and extracellular matrix assembly. Moreover, they are involved in mediating cell-matrix interactions. Abnormal SLRP expression and/or structures result in dysfunctional extracellular matrices and pathophysiology. Altered expression of SLRPs has been found in many disease models, and structural deficiency also causes altered matrix assembly. SLRPs regulate assembly of the extracellular matrix, which defines the microenvironment, modulating both the extracellular matrix and cellular functions, with an impact on tissue function.

More than matrix: the multifaceted role of decorin in cancer

The small leucine-rich proteoglycan, decorin, has incrementally been shown to be a powerful inhibitor of growth in a wide variety of tumour cells, an effect specifically mediated by the interaction of decorin core protein with the epidermal growth factor receptor (EGFR) and other ErbB family proteins. Nowadays, this matrikine has become the main focus of various cancer studies. Decorin is an important component of the cellular microenvironment or extracellular matrix (ECM). Its interactions with matrix and cell membrane components have been implicated in many physiological and pathophysiological processes including matrix organisation, signal transduction, wound healing, cell migration, inhibition of metastasis, and angiogenesis. This review summarises recent findings on decorin's interactions and behaviour related to cancer. Highlighted are key functions of decorin such as interaction with cell surface receptors, as well as with ECM components, and the therapeutic potential of this multifunctional molecule.

Decorin protein core affects the global gene expression profile of the tumor microenvironment in a triple-negative orthotopic breast carcinoma xenograft model

Decorin, a member of the small leucine-rich proteoglycan gene family, exists and functions wholly within the tumor microenvironment to suppress tumorigenesis by directly targeting and antagonizing multiple receptor tyrosine kinases, such as the EGFR and Met. This leads to potent and sustained signal attenuation, growth arrest, and angiostasis. We thus sought to evaluate the tumoricidal benefits of systemic decorin on a triple-negative orthotopic breast carcinoma xenograft model. To this end, we employed a novel high-density mixed expression array capable of differentiating and simultaneously measuring gene signatures of both Mus musculus (stromal) and Homo sapiens (epithelial) tissue origins. We found that decorin protein core modulated the differential expression of 374 genes within the stromal compartment of the tumor xenograft. Further, our top gene ontology classes strongly suggests an unexpected and preferential role for decorin protein core to inhibit genes necessary for immunomodulatory responses while simultaneously inducing expression of those possessing cellular adhesion and tumor suppressive gene properties. Rigorous verification of the top scoring candidates led to the discovery of three genes heretofore unlinked to malignant breast cancer that were reproducibly found to be induced in several models of tumor stroma. Collectively, our data provide highly novel and unexpected stromal gene signatures as a direct function of systemic administration of decorin protein core and reveals a fundamental basis of action for decorin to modulate the tumor stroma as a biological mechanism for the ascribed anti-tumorigenic properties.

Decorin: a guardian from the matrix

Decorin, an archetypal member of the small leucine-rich proteoglycan gene family, has a broad binding repertoire that encompasses matrix structural components, such as collagens, and growth factors, particularly those that belong to the transforming growth factor-β ligand superfamily. Within the tumor microenvironment, stromal decorin has an inherent proclivity to directly bind and down-regulate several receptor tyrosine kinases, which are often overexpressed in cancer cells. The decorin interactome commands a powerful antitumorigenic signal by potently repressing and attenuating tumor cell proliferation, survival, migration, and angiogenesis. This collection of interacting molecules also regulates key downstream signaling processes indirectly via the sequestration of growth factors or directly via the antagonism of receptor tyrosine kinases. We propose that decorin can be considered a "guardian from the matrix" because of its innate ability to oppose pro-tumorigenic cues.

In vivo tendon engineering with skeletal muscle derived cells in a mouse model

Engineering a functional tendon with strong mechanical property remains an aim to be achieved for its eventual application. Both skeletal muscle and tendon are closely associated during their development and both can bear strong mechanical loading dynamically. This study explored the possibility of engineering stronger tendons with mouse skeletal muscle derived cells (MDCs) and with mouse tenocytes as a control. The results demonstrated that both MDCs and tenocytes shared the gene expression of growth differentiation factor-8 (GDF-8), collagens I, III, VI, scleraxis and tenomodulin, but with MyoD gene expression only in MDCs. Quantitatively, MDCs expressed higher levels of GDF-8, collagens III and VI (p < 0.05), whereas tenocytes expressed higher levels of collagen I, scleraxis and tenomodulin (p < 0.05). Interestingly, MDCs proliferated faster with more cells in S + G2/M phases than tenocytes (p < 0.05). After been seeded on polyglycolic acid (PGA) fibers, MDCs formed better quality engineered tendons with more mature collagen structure and thicker collagen fibrils as opposed to tenocyte engineered tendons. Biochemically, more collagen VI and decorin were produced in the former than in the later. Functionally, MDC engineered tendons exhibited stronger mechanical properties than tenocyte engineered tendons, including maximal load, stiffness, tensile strength and Young's modulus (p < 0.05). Furthermore, with the increase of implantation time, MDCs gradually lost their expression of myogenic molecules of MyoD and desmin and gained the expression of tenomodulin, a marker for tenocytes. Collectively, these results indicate that MDCs may serve as a desirable alternative cell source for engineering functional tendon tissue.

Prdm5 regulates collagen gene transcription by association with RNA polymerase II in developing bone

PRDM family members are transcriptional regulators involved in tissue specific differentiation. PRDM5 has been reported to predominantly repress transcription, but a characterization of its molecular functions in a relevant biological context is lacking. We demonstrate here that Prdm5 is highly expressed in developing bones; and, by genome-wide mapping of Prdm5 occupancy in pre-osteoblastic cells, we uncover a novel and unique role for Prdm5 in targeting all mouse collagen genes as well as several SLRP proteoglycan genes. In particular, we show that Prdm5 controls both Collagen I transcription and fibrillogenesis by binding inside the Col1a1 gene body and maintaining RNA polymerase II occupancy. In vivo, Prdm5 loss results in delayed ossification involving a pronounced impairment in the assembly of fibrillar collagens. Collectively, our results define a novel role for Prdm5 in sustaining the transcriptional program necessary to the proper assembly of osteoblastic extracellular matrix.

Osteoadherin accumulates in the predentin towards the mineralization front in the developing tooth

Background

Proteoglycans (PG) are known to be involved in the organization and assembly of the extracellular matrix (ECM) prior to mineral deposition. Osteoadherin (OSAD), a keratan sulphate PG is a member of the small leucine-rich (SLRP) family of PGs and unlike other SLRPs, OSAD expression is restricted to mineralized tissues. It is proposed to have a high affinity for hydroxyapatite and has been shown to be expressed by mature osteoblasts but its exact role remains to be elucidated.

Methodology/Principal Findings

We investigated the protein distribution of OSAD in the developing mouse tooth using immunohistochemistry and compared its expression with other SLRPs, biglycan (BGN), decorin (DCN) and fibromodulin (FMD). OSAD was found to be specifically localized in the predentin layer of the tooth and focused at the mineralization front. These studies were confirmed at the ultrastructural level using electron microscopy (iEM), where the distribution of immunogold labeled OSAD particles were quantified and significant amounts were found in the predentin, forming a gradient towards the mineralization front. In addition, iEM results revealed OSAD to lie in close association with collagen fibers, further suggesting an important role for OSAD in the organization of the ECM. The expression profile of mineralization-related SLRP genes by rat dental pulp cells exposed to mineralization inducing factors, showed an increase in all SLRP genes. Indeed, OSAD expression was significantly increased during the mineralization process, specifically following, matrix maturation, and finally mineral deposition. Alizarin Red S staining for calcium deposition showed clear bone-like nodules, which support matrix maturation and mineralization.

Conclusions

These studies provide new evidence for the role of OSAD in the mineralization process and its specific localization in the predentin layer accumulating at the mineralization front highlighting its role in tooth development.

Improvement of neural stem cell survival in collagen hydrogels by incorporating laminin-derived cell adhesive polypeptides

Cell transplantation is a potential methodology for the treatment of Parkinson's disease. However, the therapeutic effect is limited by poor viability of transplanted cells. To overcome this problem, we hypothesized that a dual step approach, whereby providing an adhesive substrate for transplanted cells and, at the same time, by preventing the infiltration of activated microglia into the site of transplantation promotes the cell survival. To establish above conditions, attempts were made to prepare 3-D matrices using collagen hydrogels that incorporated integrin-binding polypeptides derived from laminin-1. Tandem combinations of laminin globular domains as well as a single globular domain 3 were prepared using recombinant DNA technology as a fusion with hexahistidine and bound to metal chelated surfaces to screen for the adhesion and proliferation of neural stem cells (NSCs). In addition, a small peptide derived from laminin γ1 chain was prepared and heterodimerized with the globular domain-containing chimeric proteins to evaluate for the enhancement of integrin-mediated cell adhesion. As a result, a heterodimer consisting of the globular domain 3 of the laminin α1 chain and the peptide from the laminin γ1 chain was selected as the best candidate among the polypeptides studied here for the incorporation into a collagen hydrogel. It was shown that the survival of NSCs was indeed promoted in the collagen hydrogel incorporating the heterodimer compared to the pure collagen hydrogel.

Uterine dysfunction in biglycan and decorin deficient mice leads to dystocia during parturition

Cesarean birth rates are rising. Uterine dysfunction, the exact mechanism of which is unknown, is a common indication for Cesarean delivery. Biglycan and decorin are two small leucine-rich proteoglycans expressed in the extracellular matrix of reproductive tissues and muscle. Mice deficient in biglycan display a mild muscular dystrophy, and, along with mice deficient in decorin, are models of Ehlers-Danlos Syndrome, a connective tissue anomaly associated with uterine rupture. As a variant of Ehlers-Danlos Syndrome is caused by a genetic mutation resulting in abnormal biglycan and decorin secretion, we hypothesized that biglycan and decorin play a role in uterine function. Thus, we assessed wild-type, biglycan, decorin and double knockout pregnancies for timing of birth and uterine function. Uteri were harvested at embryonic days 12, 15 and 18. Nonpregnant uterine samples of the same genotypes were assessed for tissue failure rate and spontaneous and oxytocin-induced contractility. We discovered that biglycan/decorin mixed double-knockout dams displayed dystocia, were at increased risk of delayed labor onset, and showed increased tissue failure in a predominantly decorin-dependent manner. In vitro spontaneous uterine contractile amplitude and oxytocin-induced contractile force were decreased in all biglycan and decorin knockout genotypes compared to wild-type. Notably, we found no significant compensation between biglycan and decorin using quantitative real time PCR or immunohistochemistry. We conclude that the biglycan/decorin mixed double knockout mouse is a model of dystocia and delayed labor onset. Moreover, decorin is necessary for uterine function in a dose-dependent manner, while biglycan exhibits partial compensatory mechanisms in vivo. Thus, this model is poised for use as a model for testing novel targets for preventive or therapeutic manipulation of uterine dysfunction.

Alterations of overused supraspinatus tendon: a possible role of glycosaminoglycans and HARP/pleiotrophin in early tendon pathology

Supraspinatus tendon overuse injuries lead to significant pain and disability in athletes and workers. Despite the prevalence and high social cost of these injuries, the early pathological events are not well known. We analyzed the potential relation between glycosaminoglycan (GAG) composition and phenotypic cellular alteration using a rat model of rotator cuff overuse. Total sulfated GAGs increased after 4 weeks of overuse and remained elevated up to 16 weeks. GAG accumulation was preceded by up-regulation of decorin, versican, and aggrecan proteoglycans (PGs) mRNAs and proteins and biglycan PG mRNA after 2 weeks. At 2 weeks, collagen 1 transcript decreased whereas mRNAs for collagen 2, collagen 3, collagen 6, and the transcription factor Sox9 were increased. Protein levels of heparin affine regulatory peptide (HARP)/pleiotrophin, a cytokine known to regulate developmental chondrocyte formation, were enhanced especially at 4 weeks, without up-regulation of HARP/pleiotrophin mRNA. Further results suggest that the increased GAGs present in early lesions may sequester HARP/pleiotrophin, which could contribute to a loss of tenocyte's phenotype. All these modifications are characteristic of a shift towards the chondrocyte phenotype. Identification of these early changes in the extra-cellular matrix may help to prevent the progression of the pathology to more disabling, degenerative alterations.

Decorin antagonizes the angiogenic network: concurrent inhibition of Met, hypoxia inducible factor 1α, vascular endothelial growth factor A, and induction of thrombospondin-1 and TIMP3

Decorin, a small leucine-rich proteoglycan, inhibits tumor growth by antagonizing multiple receptor tyrosine kinases including EGFR and Met. Here, we investigated decorin during normoxic angiogenic signaling. An angiogenic PCR array revealed a profound decorin-evoked transcriptional inhibition of pro-angiogenic genes, such as HIF1A. Decorin evoked a reduction of hypoxia inducible factor (HIF)-1α and vascular endothelial growth factor A (VEGFA) in MDA-231 breast carcinoma cells expressing constitutively-active HIF-1α. Suppression of Met with decorin or siRNA evoked a similar reduction of VEGFA by attenuating downstream β-catenin signaling. These data establish a noncanonical role for β-catenin in regulating VEGFA expression. We found that exogenous decorin induced expression of thrombospondin-1 and TIMP3, two powerful angiostatic agents. In contrast, decorin suppressed both the expression and enzymatic activity of matrix metalloprotease (MMP)-9 and MMP-2, two pro-angiogenic proteases. Our data establish a novel duality for decorin as a suppressor of tumor angiogenesis under normoxia by simultaneously down-regulating potent pro-angiogenic factors and inducing endogenous anti-angiogenic agents.

The retinoic acid-induced up-regulation of insulin-like growth factor 1 and 2 is associated with prolidase-dependent collagen synthesis in UVA-irradiated human dermal equivalents

BACKGROUND

Ultraviolet (UV) A irradiation causes the degeneration of extracellular matrix in the skin dermis, mainly due to disrupted collagen homeostasis, resulting in the photo-aging of human skin. All-trans retinoic acid (ATRA) improves photo-aged human skin in vivo.

OBJECTIVES

Although the effects of ATRA on collagen synthesis and MMP regulation are well known, the effects of ATRA on other collagen homeostasis-associated genes have not been elucidated. This study was aimed to study the factors that are pharmacologically associated with the effect of ATRA on collagen homeostasis.

METHODS

The gene transcription profile of collagen homeostasis-associated genes was systematically evaluated in three-dimensional human dermal equivalents (HDEs) following UVA-irradiation and/or ATRA treatment.

RESULTS

In addition to the expected changes in MMPs and collagen synthesis in HDEs in response to ATRA, prolidase, an important enzyme in the recycling of proline and hydroxyproline from degraded collagen molecules, was significantly decreased by UVA irradiation, and its down-regulation was antagonized by ATRA. Transfection with a prolidase-specific siRNA led to a significant decrease in procollagen synthesis in human fibroblasts. ATRA inhibited the UVA irradiation-induced decrease in prolidase activity through an insulin-like growth factor (IGF) receptor signaling pathway in HDEs. ARTA increased IGF1 and IGF2 production in HDEs, and neutralizing IGFs with anti-IGF antibodies abolished the effect of ATRA on proliase activity.

CONCLUSIONS

These data demonstrate that ATRA regulates prolidase activity in HDEs via IGF receptor signaling, suggesting one of the pharmacological mechanisms by which improves photo-aged human skin.

Pathophysiological mechanisms of autosomal dominant congenital stromal corneal dystrophy: C-terminal-truncated decorin results in abnormal matrix assembly and altered expression of small leucine-rich proteoglycans

Autosomal-dominant congenital stromal corneal dystrophy (CSCD) is a human genetic disease characterized by corneal opacities beginning shortly after birth. It is linked to a frameshift mutation in decorin, resulting in a C-terminal truncation lacking 33 amino acids that includes the "ear" repeat, a feature specific for small leucine-rich proteoglycans. Our goals are to elucidate the roles of the mutant decorin in CSCD pathophysiology and to decipher the mechanism whereby mutant decorin affects matrix assembly. A novel animal model that recapitulates human CSCD was generated. This transgenic mouse model targets expression of truncated decorin to keratocytes, thereby mimicking the human frameshift mutation. Mutant mice expressed both wild-type and mutant decorin. Corneal opacities were found throughout, with increased severity toward the posterior stroma. The architecture of the lamellae was disrupted with relatively normal lamellae separated by regions of abnormal fibril organization. Within abnormal zones, the interfibrillar spacing and the fibril diameters were increased. Truncated decorin negatively affected the expression of endogenous decorin, biglycan, lumican, and keratocan and positively affected fibromodulin. Our results provide a mechanistic explanation for the generation of corneal opacities in CSCD. Thus, truncated decorin acts in a dominant-negative manner to interfere dually with matrix assembly and binding to receptor tyrosine kinases, thereby causing abnormal expression of endogenous small leucine-rich proteoglycans leading to structural abnormalities within the cornea and vision loss.

Biominerals--hierarchical nanocomposites: the example of bone

Many organisms incorporate inorganic solids in their tissues to enhance their functional, primarily mechanical, properties. These mineralized tissues, also called biominerals, are unique organo-mineral nanocomposites, organized at several hierarchical levels, from nano- to macroscale. Unlike man-made composite materials, which often are simple physical blends of their components, the organic and inorganic phases in biominerals interface at the molecular level. Although these tissues are made of relatively weak components under ambient conditions, their hierarchical structural organization and intimate interactions between different elements lead to superior mechanical properties. Understanding basic principles of formation, structure, and functional properties of these tissues might lead to novel bioinspired strategies for material design and better treatments for diseases of the mineralized tissues. This review focuses on general principles of structural organization, formation, and functional properties of biominerals on the example the bone tissues.

Proteoglycans in cancer biology, tumour microenvironment and angiogenesis

Proteoglycans, key molecular effectors of cell surface and pericellular microenvironments, perform multiple functions in cancer and angiogenesis by virtue of their polyhedric nature and their ability to interact with both ligands and receptors that regulate neoplastic growth and neovascularization. Some proteoglycans such as perlecan, have pro- and anti-angiogenic activities, whereas other proteoglycans, such as syndecans and glypicans, can also directly affect cancer growth by modulating key signalling pathways. The bioactivity of these proteoglycans is further modulated by several classes of enzymes within the tumour microenvironment: (i) sheddases that cleave transmembrane or cell-associated syndecans and glypicans, (ii) various proteinases that cleave the protein core of pericellular proteoglycans and (iii) heparanases and endosulfatases which modify the structure and bioactivity of various heparan sulphate proteoglycans and their bound growth factors. In contrast, some of the small leucine-rich proteoglycans, such as decorin and lumican, act as tumour repressors by physically antagonizing receptor tyrosine kinases including the epidermal growth factor and the Met receptors or integrin receptors thereby evoking anti-survival and pro-apoptotic pathways. In this review we will critically assess the expanding repertoire of molecular interactions attributed to various proteoglycans and will discuss novel proteoglycan functions modulating cancer progression, invasion and metastasis and how these factors regulate the tumour microenvironment.

Decorin modulates collagen I-stimulated, but not fibronectin-stimulated, migration of C2C12 myoblasts

Extracellular matrix factors, specifically fibronectin and collagen I, are essential for structural support during muscle regeneration. Decorin has been identified as an anti-fibrotic agent with binding sites located on both fibronectin and collagen I. Upon injury, activated myoblasts are required to migrate through the extracellular matrix factors deposited by the myofibroblasts to facilitate skeletal muscle regeneration. In this study we looked at the effects decorin on fibronectin- and collagen I-stimulated myoblast migration. Dose response studies demonstrated 10 μg/ml, 5 μg/ml and 25 μg/ml as the optimal stimulatory concentrations of decorin (1.2 fold increase), fibronectin (3.5 fold increase) and collagen I (2.4 fold increase), when compared with control respectively. A synergistic effect was identified when decorin and collagen I were added in combination; this effect was not evident when decorin was added with fibronectin. The effects of these factors on the ROCK signalling pathway were also analyzed. ROCK-2 was identified as the key Rho-activated kinase isoform involved in migration, due to its higher expression levels and localisation to focal points within migrating C2C12 myoblasts. Decorin and collagen I in combination stimulated an increase in the number of ROCK-2 localized focal points when compared with control, decorin and collagen I added separately. Fibronectin did not show any increase in ROCK-2 focal points when compared with control. These results show for the first time that decorin can modify collagen I-stimulated, but not fibronectin-stimulated myoblast migration in vitro. Furthermore, the synergistic, rather than additive, effect observed suggests a direct modification of collagen I signalling by decorin mediated, at least in part, by ROCK-2 rather than ROCK-1.

Fibroblast and prostate tumor cell cross-talk: fibroblast differentiation, TGF-β, and extracellular matrix down-regulation

Growth and survival of tumors at a site of metastasis involve interactions with stromal cells in the surrounding environment. Stromal cells aid tumor cell growth by producing cytokines as well as by modifying the environment surrounding the tumor through modulation of the extracellular matrix (ECM). Small leucine-rich proteoglycans (SLRPs) are biologically active components of the ECM which can be altered in the stroma surrounding tumors. The influence tumor cells have on stromal cells has been well elucidated. However, little is understood about the effect metastatic cancer cells have on the cell biology and behavior of the local stromal cells. Our data reveal a significant down-regulation in the expression of ECM components such as collagens I, II, III, and IV, and the SLRPs, decorin, biglycan, lumican, and fibromodulin in stromal cells when grown in the presence of two metastatic prostate cancer cell lines PC3 and DU145. Interestingly, TGF-β down-regulation was observed in stromal cells, as well as actin depolymerization and increased vimentin and α5β1 integrin expression. MT1-MMP expression was upregulated and localized in stromal cell protrusions which extended into the ECM. Moreover, enhanced stromal cell migration was observed after cross-talk with metastatic prostate tumor cells. Xenografting metastatic prostate cancer cells together with "activated" stromal cells led to increased tumorigenicity of the prostate cancer cells. Our findings suggest that metastatic prostate cancer cells create a metastatic niche by altering the phenotype of local stromal cells, leading to changes in the ECM.

Spatiotemporal distribution of chondroitin sulfate proteoglycans in the developing mouse retina and optic nerve

The aim of the present study was to determine the distribution of chondroitin sulfate proteoglycans in the mouse retina and optic nerve of the prenatal and postnatal mouse by immunohistochemistry. At embryonic day (E) 18, chondroitin-4-sulfate (C4S), chondroitin-6-sulfate (C6S) and biglycan were detected in the retina and optic nerve. However, aggrecan was seen in the retina but not in the optic nerve. At postnatal day (P) 7, aggrecan and biglycan were clearly observed in the optic nerve, inner nuclear layer and ganglion cell layer and diffuse in the outer retina. C4S diffusely distributed in the retina and optic nerve, but C6S was mainly confined to the photoreceptor layer and optic nerve sheath. At P42, biglycan showed diffuse distribution in the retina and optic nerve with intense staining in nerve-fiber rich layers. Aggrecan showed weak staining at the inner plexiform layer with higher density in the outer and inner nuclear layers, outer plexiform layer and ganglion cell layer. Both C4S and C6S were detected in the optic nerve and retina, but C6S showed strong immunostaining in the photoreceptor layer. The distributions of these proteoglycans with respect of time course during development of the retina and optic nerve suggest that they may have unique or overlapping roles in development and maintenance of the retina and optic nerve.

The effect of age and spontaneous exercise on the biomechanical and biochemical properties of chicken superficial digital flexor tendon

The aim of this study was to evaluate if spontaneous (nonforced active) exercise and age (maturation process) alter the biomechanical and biochemical properties of superficial digital flexor tendon. Chickens aged 1, 5, and 8 months were divided into two groups: caged and penned. The caged group was reared in an area of 0.5 m(2) (3 animals/cage), while the penned group was reared in an area of 60 m(2) (3 animals/area). For biochemical analysis, the tendon was divided into tensile and compressive regions for quantification of hydroxyproline and glycosaminoglycan content. Biomechanical properties were analyzed from tensile tests of intact tendons. The biomechanical measurements were taken at maximum load and maximum stress. In both the caged and penned groups, maximum load and energy absorption increased with maturation; however, the elastic modulus, maximum stress, and maximum strain did not increase with maturation. Exercise resulted in a higher load, stress, and elastic modulus in the fifth month. Collagen content increased with age in the penned group and with exercise in the fifth and eighth months. Exercise results in a higher expression of glycosaminoglycans in young tendons compared to mature tendons. Thus, low-intensity mechanical stimuli promote the synthesis and possible rearrangement of molecules in immature tendons, whereas inactivity leads to deleterious effects on the material properties (maximum stress and elastic modulus) during growth and maturation.

Decorin transfection suppresses profibrogenic genes and myofibroblast formation in human corneal fibroblasts

Decorin, a small leucine-rich proteoglycan, is a natural inhibitor of transforming growth factor beta (TGFbeta). Myofibroblast and haze formation in the cornea have been attributed to TGFbeta hyperactivity released from corneal epithelium following injury to eye. This study tested the hypothesis that decorin-gene transfer inhibits TGFbeta-driven myofibroblast and haze formation in the cornea. Human corneal fibroblast (HSF) cultures generated from donor human corneas were used. Decorin cDNA was cloned into mammalian expression vector. Restriction enzyme analysis and DNA sequencing confirmed the nucleotide sequence of generated vector construct. The decorin gene cloned into mammalian expression vector was introduced into HSF with lipofectamine transfection kit. Expression of decorin in selected clones was characterized with RT-PCR, immunocytochemistry and western blotting. Phage contrast microscopy and trypan blue exclusion assay evaluated the effects of decorin-gene transfer on HSF phenotype and viability, respectively. Real-time PCR, western blot and immunocytochemistry were used to analyze inhibitory effects of decorin-gene transfer on TGFbeta-induced myofibroblast formation by measuring differential expression of alpha smooth muscle actin (SMA), a myofibroblast marker, mRNA and protein expression. Analysis of variance (ANOVA) and the Bonferroni-Dunn adjustment for repeated measures were used for statistical analysis. Our data indicate that decorin-gene transfer into HSF do not alter cellular phenotype or viability. Decorin over-expressing HSF clones grown in the presence of TGFbeta1 under serum-free conditions showed a statistically significant 80-83% decrease in SMA expression (p value < 0.01) compared to naked-vector transfected clones or un-transfected HSF controls. Decorin-transfected, naked-vector transfected and un-transfected HSF grown in the absence of TGFbeta1 showed no or extremely low expression of SMA. Furthermore, decorin over-expression did not affect HSF phenotype and decreased TGFbeta-induced RNA levels of profibrogenic genes such as fibronectin, collagen type I, III, and IV that play important role in stromal matrix modulation and corneal wound healing. The results of study suggest that decorin-gene transfer effectively prevents TGFbeta-driven transformation of keratocyte and corneal fibroblast to myofibroblasts. We postulate that decorin-gene therapy can be used to treat corneal haze in vivo.

Amelogenin-collagen interactions regulate calcium phosphate mineralization in vitro

Collagen and amelogenin are two major extracellular organic matrix proteins of dentin and enamel, the mineralized tissues comprising a tooth crown. They both are present at the dentin-enamel boundary (DEB), a remarkably robust interface holding dentin and enamel together. It is believed that interactions of dentin and enamel protein assemblies regulate growth and structural organization of mineral crystals at the DEB, leading to a continuum at the molecular level between dentin and enamel organic and mineral phases. To gain insight into the mechanisms of the DEB formation and structural basis of its mechanical resiliency we have studied the interactions between collagen fibrils, amelogenin assemblies, and forming mineral in vitro, using electron microscopy. Our data indicate that collagen fibrils guide assembly of amelogenin into elongated chain or filament-like structures oriented along the long axes of the fibrils. We also show that the interactions between collagen fibrils and amelogenin-calcium phosphate mineral complexes lead to oriented deposition of elongated amorphous mineral particles along the fibril axes, triggering mineralization of the bulk of collagen fibril. The resulting structure was similar to the mineralized collagen fibrils found at the DEB, with arrays of smaller well organized crystals inside the collagen fibrils and bundles of larger crystals on the outside of the fibrils. These data suggest that interactions between collagen and amelogenin might play an important role in the formation of the DEB providing structural continuity between dentin and enamel.

Glucuronic acid and phosphoserine act as mineralization mediators of collagen I based biomimetic substrates

Glucuronic acid (GlcA) and phosphoserine (pS) carrying acidic functional groups were used as model molecules for glycosaminoglycans and phosphoproteins, respectively to mimic effects of native biomolecules and influence the mineralization behaviour of collagen I. Collagen substrates modified with GlcA showed a stable interaction between GlcA and collagen fibrils. Substrates were mineralized using the electrochemically assisted deposition (ECAD) in a Ca(2+)/H( x )PO (4) ((3-x)) electrolyte at physiological pH and temperature. During mineralization of collagen-GlcA matrices, crystalline hydroxyapatite (HA) formed earlier with increasing GlcA content of the collagen matrix, while the addition of pS to the electrolyte succeeded in inhibiting the transformation of preformed amorphous calcium phosphate (ACP) to HA. The lower density of the resulting mineralization and the coalesced aggregates formed at a certain pS concentration suggest an interaction between calcium and the phosphate groups of pS involving the formation of complexes. Combining GlcA-modified collagen and pS-modified electrolyte showed dose-dependent cooperative effects.

The role of small leucine-rich proteoglycans in collagen fibrillogenesis

Small leucine-rich proteoglycans/proteins (SLRPs) are associated with collagen fibril formation, and therefore important for the proper formation of extracellular matrices. SLRPs are differentially expressed in tissues and during pathological conditions, contributing to the development of connective tissue properties. The binding of SLRPs to collagens have recently been characterized, and may give some clues to the significance of these interactions. In this mini review, we summarize published work in this field, and propose several mechanisms for how SLRPs can control collagen matrix structure and function. SLRPs appear to influence collagen cross-linking patterns. We also propose that the SLRP-collagen interactions can assist in the process of juxtaposing the collagen monomers by steric hindrance or by directly connecting two collagen monomers during the fibril growth.

The matricellular functions of small leucine-rich proteoglycans (SLRPs)

The small leucine-rich proteoglycans (SLRPs) are biologically active components of the extracellular matrix (ECM), consisting of a protein core with leucine rich-repeat (LRR) motifs covalently linked to glycosaminoglycan (GAG) side chains. The diversity in composition resulting from the various combinations of protein cores substituted with one or more GAG chains along with their pericellular localization enables SLRPs to interact with a host of different cell surface receptors, cytokines, growth factors, and other ECM components, leading to modulation of cellular functions. SLRPs are capable of binding to: (i) different types of collagens, thereby regulating fibril assembly, organization, and degradation; (ii) Toll-like receptors (TLRs), complement C1q, and tumor necrosis factor-alpha (TNFalpha), regulating innate immunity and inflammation; (iii) epidermal growth factor receptor (EGF-R), insulin-like growth factor receptor (IGF-IR), and c-Met, influencing cellular proliferation, survival, adhesion, migration, tumor growth and metastasis as well as synthesis of other ECM components; (iv) low-density lipoprotein receptor-related protein (LRP-1) and TGF-beta, modulating cytokine activity and fibrogenesis; and (v) growth factors such as bone morphogenic protein (BMP-4) and Wnt-I-induced secreted protein-1 (WISP-1), controlling cell proliferation and differentiation. Thus, the ability of SLRPs, as ECM components, to directly or indirectly regulate cell-matrix crosstalk, resulting in the modulation of various biological processes, aptly qualifies these compounds as matricellular proteins.

Asporin competes with decorin for collagen binding, binds calcium and promotes osteoblast collagen mineralization

The interactions of the ECM (extracellular matrix) protein asporin with ECM components have previously not been investigated. Here, we show that asporin binds collagen type I. This binding is inhibited by recombinant asporin fragment LRR (leucine-rich repeat) 10-12 and by full-length decorin, but not by biglycan. We demonstrate that the polyaspartate domain binds calcium and regulates hydroxyapatite formation in vitro. In the presence of asporin, the number of collagen nodules, and mRNA of osteoblastic markers Osterix and Runx2, were increased. Moreover, decorin or the collagen-binding asporin fragment LRR 10-12 inhibited the pro-osteoblastic activity of full-length asporin. Our results suggest that asporin and decorin compete for binding to collagen and that the polyaspartate in asporin directly regulates collagen mineralization. Therefore asporin has a role in osteoblast-driven collagen biomineralization activity. We also show that asporin can be expressed in Escherichia coli (Rosetta-gami) with correctly positioned cysteine bridges, and a similar system can possibly be used for the expression of other SLRPs (small LRR proteoglycans/proteins).

High xylosyltransferase activity in children and during mineralization of osteoblast-like SAOS-2 cells

Skeletal growth and tissue remodelling processes are characterized by an elevated collagen and proteoglycan biosynthesis. The xylosyltransferases I and II are the rate-limiting step enzymes in proteoglycan biosynthesis and serum xylosyltransferase (XT) activity has been shown to be a biomarker for the actual proteoglycan biosynthesis rate. Here, XT, alkaline phosphatase (ALP), bone ALP (BALP) activities were measured in 133 juvenile Caucasians. Serum XT activities in juveniles were elevated and significantly correlated with ALP and BALP. In an osteoblast-like cell model using SAOS-2 cells mineralization and bone nodule formation were induced and XT-I, XT-II and ALP were monitored. Induction of mineralization in SAOS-2 cells resulted in a long-term increase of XT-I mRNA and enzyme activity, which could be paralleled with elevated ALP activity. In addition, HGH and IGF-I treatment of SAOS-2 cells led to an increased expression of XT-I and ALP. These results point to skeletal growth and tissue remodeling as a cause of the high XT activity in children.

Decorin modulates collagen matrix assembly and mineralization

Decorin (DCN) is one of the major matrix proteoglycans in bone. To investigate the role of DCN in matrix mineralization, the expression of DCN in MC3T3-E1 (MC) cell cultures and the phenotypes of MC-derived clones expressing higher (sense; S-DCN) or lower (antisense; AS-DCN) levels of DCN were characterized. DCN expression was significantly decreased as the mineralized nodules were formed and expanded in vitro. In S-DCN clones, in vitro matrix mineralization was inhibited, whereas in AS-DCN clones, mineralization was accelerated. At the microscopic level, collagen fibers in S-DCN clones were thinner while those of AS-DCN clones were thicker and lacked directionality compared to the controls. At the ultrastructural level, the collagen fibrils in S-DCN clones were markedly thinner, whereas those of AS-DCN clones were larger and irregular in shape. The results from Fourier transform infrared spectroscopy analysis demonstrated that in AS-DCN cultures the mineral content was greater but the crystallinity of mineral was poorer than that of the controls at early stage of mineralization. The in vivo transplantation assay demonstrated that no mineralized matrices were formed in S-DCN transplants, whereas they were readily detected in AS-DCN transplants at 3 weeks of transplantation. The areas of bone-like matrices in AS-DCN transplants were significantly greater than the controls at 3 weeks but became comparable at 5 weeks. The bone-like matrices in AS-DCN transplants exhibited woven bone-like non-lamellar structure while the lamellar bone-like structure was evident in the control transplants. These results suggest that DCN regulates matrix mineralization by modulating collagen assembly.

Non-enzymatic glycation of type I collagen diminishes collagen-proteoglycan binding and weakens cell adhesion

Non-enzymatic glycation of type I collagen occurs in aging and diabetes, and may affect collagen solubility, charge, polymerization, and intermolecular interactions. Proteoglycans(1) (PGs) bind type I collagen and are proposed to regulate fibril assembly, function, and cell-collagen interactions. Moreover, on the collagen fibril a keratan sulfate (KS) PG binding region overlaps with preferred collagen glycation sites. Thus, we examined the effect of collagen modified by simple glycation on PG-collagen interactions. By affinity coelectrophoresis (ACE), we found reduced affinities of heparin and KSPGs for glycated but not normal collagen, whereas the dermatan sulfate (DS)PGs decorin and biglycan bound similarly to both, and that the affinity of heparin for normal collagen decreased with increasing pH. Circular dichroism (CD) spectroscopy revealed normal and glycated collagens to assume triple helical conformations, but heparin addition caused precipitation and decreased triple helical content-effects that were more marked with glycated collagen. A spectrophotometric assay revealed slower polymerization of glycated collagen. However, ultrastructural analyses indicated that fibrils assembled from normal and glycated collagen exhibited normal periodicity, and had similar structures and comparable diameter distributions. B-cells expressing the cell surface heparan sulfate PG syndecan-1 adhered well to normal but not glycated collagen, and endothelial cell migration was delayed on glycated collagen. We speculate that glycation diminishes the electrostatic interactions between type I collagen and PGs, and may interfere with core protein-collagen associations for KSPGs but not DSPGs. Therefore in vivo, collagen glycation may weaken PG-collagen interactions, thereby disrupting matrix integrity and cell-collagen interactions, adhesion, and migration.

Cleft Palate Cells Can Regenerate a Palatal Mucosa in vitro

Cleft palate repair leaves full-thickness mucosal defects on the palate. Healing might be improved by implantation of a mucosal substitute. However, the genetic and phenotypic deviations of cleft palate cells may hamper tissue engineering. The aim of this study was to construct mucosal substitutes from cleft palate cells, and to compare these with substitutes from normal palatal cells, and with native palatal mucosa. Biopsies from the palatal mucosa of eight children with cleft palate and eight age-matched control individuals were taken. Three biopsies of both groups were processed for (immuno)histochemistry; 5 were used to culture mucosal substitutes. Histology showed that the substitutes from cleft-palate and non-cleft-palate cells were comparable, but the number of cell layers was less than in native palatal mucosa. All epithelial layers in native palatal mucosa and mucosal substitutes expressed the cytokeratins 5, 10, and 16, and the proliferation marker Ki67. Heparan sulphate and decorin were present in the basal membrane and the underlying connective tissue, respectively. We conclude that mucosal cells from children with cleft palate can regenerate an oral mucosa in vitro.

Glycosaminoglycans show a specific periodic interaction with type I collagen fibrils

Current wisdom on intermolecular interactions in the extracellular matrix assumes that small proteoglycans bind collagen fibrils on highly specific sites via their protein core, while their carbohydrate chains interact with each other in the interfibrillar space. The present study used high-resolution scanning electron microscopy to analyse the interaction of two small leucine-rich proteoglycans and several glycosaminoglycan chains with type I collagen fibrils obtained in vitro in a controlled, cell-free environment. Our results show that most ligands directly influence the collagen fibril size and shape, and their aggregation into thicker bundles. All chondroitin sulphate/dermatan sulphate glycosaminoglycans we tested, except chondroitin 4-sulphate, bound to the fibril surface in a highly specific way and, even in the absence of any protein core, formed regular, periodic interfibrillar links resembling those of the intact proteoglycan. Only intact decorin, however, was able to organize collagen fibrils into fibres compact enough to mimic in vitro the superfibrillar organization of natural tissues. Our data indicate that multiple interaction patterns may exist in vivo, may explain why decorin- or biglycan-knockout organisms show milder effects than can be expected, and may lead to the development of better, simpler engineered biomaterials.

Effect of NKISK on tendon lengthening: an in vivo model for various clinically applicable dosing regimens

One proposed mechanism of tendon lengthening is the "sliding fibril" hypothesis, in which tendons lengthen through the sliding of discontinuous fibrils after release of decorin-fibronectin interfibrillar bonds. The pentapeptide NKISK has been reported to inhibit the binding of decorin, a proteoglycan on the surface of collagen fibrils, to fibronectin, a tissue adhesion molecule, which are thought to play a role in interfibrillar binding. Prior investigations have demonstrated that NKISK produces in vivo tendon lengthening. This study investigates the effect of potential clinically applicable NKISK injection regimens in an in vivo model. One hundred and thirteen male Sprague-Dawley rats were divided into 15 different treatment groups, each receiving percutaneous patellar tendon injections of NKISK, QKTSK (a "nonsense" pentapeptide), or PBS of varying volumes, concentrations, and injection schedules. Following sacrifice, the patellar tendon lengths were measured in all groups, and biomechanical testing was performed with comparisons made to the contralateral, untreated control limbs. Tendon lengthening was significantly greater (p < or = 0.05) in nearly all NKISK-treated tendons as compared to PBS- and QKTSK-treated tendons and was dose-dependent. Measured lengthening was less in rats whose sacrifice was delayed following the final injection of NKISK, which likely indicates recontraction of lengthened tendons, but they remained significantly longer than the controls. Biomechanical testing did not reveal significant differences in ultimate load, modulus, stiffness, or displacement. This study demonstrates that NKISK given in clinically plausible dosing regimens produces dose-dependent tendon lengthening in an in vivo setting with minimal effects on the mechanical properties of the treated tendons.

Decorin regulates endothelial cell motility on collagen I through activation of insulin-like growth factor I receptor and modulation of alpha2beta1 integrin activity

The proteoglycan decorin is expressed by sprouting but not quiescent endothelial cells, and angiogenesis is dysregulated in its absence. Previously, we have shown that decorin core protein can bind to and activate insulin-like growth factor-I receptor (IGF-IR) in endothelial cells. In this study, we show that decorin promotes alpha2beta1 integrin-dependent endothelial cell adhesion and migration on fibrillar collagen type I. We provide evidence that decorin modulates cell-matrix interaction in this context by stimulating cytoskeletal and focal adhesion reorganization through activation of the IGF-IR and the small GTPase Rac. Further, the glycosaminoglycan moiety of decorin interacts with alpha2beta1, but not alpha1beta1 integrin, at a site distinct from the collagen I-binding A-domain, to allosterically modulate collagen I-binding activity of the integrin. We propose that induction of decorin expression in angiogenic, as opposed to quiescent, endothelial cells promotes a motile phenotype in an interstitial collagen I-rich environment by both signaling through IGF-IR and influencing alpha2beta1 integrin activity.

High expression of osteoglycin decreases the metastatic capability of mouse hepatocarcinoma Hca-F cells to lymph nodes

Osteoglycin, one of the matrix molecules, belongs to the small leucine-rich proteoglycan gene family and might play important roles in cell growth and differentiation and in pathological processes such as fibrosis and cancer growth. In this study, a eukaryotic expression plasmid pIRESpuro3 osteoglycin(+) was constructed and transfected into mouse hepatocarcinoma Hca-F cells to evaluate the contribution of osteoglycin to the malignant behavior of Hca-F. It was found that Hca-F cells transfected with pIRESpuro3 osteoglycin(+) showed significantly decreased potential for both migration and invasion. Furthermore, Hca-F cells transfected with osteoglycin showed decreased metastatic potential to peripheral lymph nodes. However, proliferation potential and adhesive capacity of Hca-F cells to different protein substrates were not influenced by osteoglycin transfection. In summary, high expression of osteoglycin decreases the metastatic capability of Hca-F to lymph nodes.

Transforming growth factor beta1-regulated xylosyltransferase I activity in human cardiac fibroblasts and its impact for myocardial remodeling

In cardiac fibrosis remodeling of the failing myocardium is associated with a complex reorganization of the extracellular matrix (ECM). Xylosyltransferase I and Xylosyltransferase II (XT-I and XT-II) are the key enzymes in proteoglycan biosynthesis, which are an important fraction of the ECM. XT-I was shown to be a measure for the proteoglycan biosynthesis rate and a biochemical fibrosis marker. Here, we investigated the XT-I and XT-II expression in cardiac fibroblasts and in patients with dilated cardiomyopathy and compared our findings with nonfailing donor hearts. We analyzed XT-I and XT-II expression and the glycosaminoglycan (GAG) content in human cardiac fibroblasts incubated with transforming growth factor (TGF)-beta(1) or exposed to cyclic mechanical stretch. In vitro and in vivo no significant changes in the XT-II expression were detected. For XT-I we found an increased expression in parallel with an elevated chondroitin sulfate-GAG content after incubation with TGF-beta(1) and after mechanical stretch. XT-I expression and subsequently increased levels of GAGs could be reduced with neutralizing anti-TGF-beta(1) antibodies or by specific inhibition of the activin receptor-like kinase 5 or the p38 mitogen-activated protein kinase pathway. Usage of XT-I small interfering RNA could specifically block the increased XT-I expression under mechanical stress and resulted in a significantly reduced chondroitin sulfate-GAG content. In the left and right ventricular samples of dilated cardiomyopathy patients, our data show increased amounts of XT-I mRNA compared with nonfailing controls. Patients had raised levels of XT-I enzyme activity and an elevated proteoglycan content. Myocardial remodeling is characterized by increased XT-I expression and enhanced proteoglycan deposition. TGF-beta(1) and mechanical stress induce XT-I expression in cardiac fibroblasts and have impact for ECM remodeling in the dilated heart. Specific blocking of XT-I expression confirmed that XT-I catalyzes a rate-limiting step during fibrotic GAG biosynthesis.

Modulation of glycosaminoglycan levels in tree shrew sclera during lens-induced myopia development and recovery

PURPOSE

In juvenile tree shrews, positioning a negative-power lens in front of an eye produces a hyperopic shift in refractive state and causes a compensatory increase in axial length over several days so that the eye is myopic when the lens is removed. During negative lens compensation, the scleral extracellular matrix is remodeled. A biomechanical property of the sclera, creep rate, increases; during recovery from induced myopia, the creep rate decreases below normal levels. Changes in glycosaminoglycan (GAG) levels, including those of hyaluronan, may participate in these changes in creep rate and, in turn, participate in controlling the axial length and refractive state. This study investigated the unsulfated and sulfated GAG composition of the sclera during compensation for a -5 diopter (D) lens and during recovery.

METHODS

Capillary electrophoresis was used to assess the relative levels (ng/mg dry scleral weight) of unsulfated GAGs (hyaluronan [HA] and chondroitin [C0S]), sulfated GAGs (chondroitin-4-sulfate [C4S], chondroitin-6-sulfate [C6S], and dermatan sulfate [DS]) in the sclera of groups of tree shrews (n = 5 per group) that wore a monocular -5 D lens for 1, 2, 4, or 11 days or had 11 days of -5 D lens wear followed by 1, 2, or 4 days of recovery from lens wear. The fellow eye served as an untreated control. Groups of normal and plano lens-treated animals provided age-matched values.

RESULTS

Expressed as a fraction of dry weight, levels of HA were lower after 1, 4, and 11 days of -5 D lens wear. Levels of C0S, C6S, and C4S were significantly lower after 4 and 11 days of lens wear. After 1 and 2 days of recovery, GAG levels in the treated eyes were not significantly different from those in control eyes. After 4 recovery days, HA levels were lower, but the levels of all other GAGs were not different in the recovering and control eyes. Some binocular changes also occurred.

CONCLUSIONS

The rapid differential decrease in HA levels during negative lens compensation and the absence of any difference after just 1 day of recovery suggest that HA levels may play a previously unrecognized early role in regulating the biomechanical property (creep rate) of the sclera. The reduced levels of the other GAGs, which occur when creep rate is at its peak elevation, and their rapid return to normal after 1 day of recovery suggest that they may also participate in regulating this biomechanical property of the sclera.

The decorin sequence SYIRIADTNIT binds collagen type I

Decorin belongs to the small leucine-rich repeat proteoglycan family, interacts with fibrillar collagens, and regulates the assembly, structure, and biomechanical properties of connective tissues. The decorin-collagen type I-binding region is located in leucine-rich repeats 5-6. Site-directed mutagenesis of this 54-residue-long collagen-binding sequence identifies Arg-207 and Asp-210 in leucine-rich repeat 6 as crucial for the binding to collagen. The synthetic peptide SYIRIADTNIT, which includes Arg-207 and Asp-210, inhibits the binding of full-length recombinant decorin to collagen in vitro. These collagen-binding amino acids are exposed on the exterior of the beta-sheet-loop structure of the leucine-rich repeat. This resembles the location of interacting residues in other leucine-rich repeat proteins.

Consortium for osteogenesis imperfecta mutations in the helical domain of type I collagen: regions rich in lethal mutations align with collagen binding sites for integrins and proteoglycans

Osteogenesis imperfecta (OI) is a generalized disorder of connective tissue characterized by fragile bones and easy susceptibility to fracture. Most cases of OI are caused by mutations in type I collagen. We have identified and assembled structural mutations in type I collagen genes (COL1A1 and COL1A2, encoding the proalpha1(I) and proalpha2(I) chains, respectively) that result in OI. Quantitative defects causing type I OI were not included. Of these 832 independent mutations, 682 result in substitution for glycine residues in the triple helical domain of the encoded protein and 150 alter splice sites. Distinct genotype-phenotype relationships emerge for each chain. One-third of the mutations that result in glycine substitutions in alpha1(I) are lethal, especially when the substituting residues are charged or have a branched side chain. Substitutions in the first 200 residues are nonlethal and have variable outcome thereafter, unrelated to folding or helix stability domains. Two exclusively lethal regions (helix positions 691-823 and 910-964) align with major ligand binding regions (MLBRs), suggesting crucial interactions of collagen monomers or fibrils with integrins, matrix metalloproteinases (MMPs), fibronectin, and cartilage oligomeric matrix protein (COMP). Mutations in COL1A2 are predominantly nonlethal (80%). Lethal substitutions are located in eight regularly spaced clusters along the chain, supporting a regional model. The lethal regions align with proteoglycan binding sites along the fibril, suggesting a role in fibril-matrix interactions. Recurrences at the same site in alpha2(I) are generally concordant for outcome, unlike alpha1(I). Splice site mutations comprise 20% of helical mutations identified in OI patients, and may lead to exon skipping, intron inclusion, or the activation of cryptic splice sites. Splice site mutations in COL1A1 are rarely lethal; they often lead to frameshifts and the mild type I phenotype. In alpha2(I), lethal exon skipping events are located in the carboxyl half of the chain. Our data on genotype-phenotype relationships indicate that the two collagen chains play very different roles in matrix integrity and that phenotype depends on intracellular and extracellular events.