The murine decorin. Complete cDNA cloning, genomic organization, chromosomal assignment, and expression during organogenesis and tissue differentiation

Decorin Inhibits Dermal Mesenchymal Cell Migration and Induces Scar Formation

Background

Variations in skin healing capacities are observed during different murine embryonic developmental stages. Through embryonic day 16 (E16), embryos are able to regenerate dermal architecture following flank skin wounding; however, after E17, wounds heal incompletely, inducing scar formation. The regenerative ability of the E16 fetal dermis depends on the migration of dermal mesenchymal cells. Decorin is a small molecule known to affect tissue tensile strength, cell phenotype, and tissue repair, including skin wound healing. In the current study, we evaluated the expression and roles of decorin in wound healing.

Methods

Surgical injury was induced at E16 and E17 in ICR mouse embryos. Decorin expression was evaluated in tissue samples from these embryos using immunohistochemistry and reverse transcription quantitative polymerase chain reaction. Cell migration assays were used to evaluate wound healing capability of separated dermal and fascial tissues.

Results

Our results showed that decorin exhibited distinct expression patterns during wound healing at E16 versus E17. Additionally, decorin expression altered cell migration in vitro. Dermal and fascial mesenchymal cells were found to exhibit distinct migration patterns concomitant with altered decorin expression. Specifically, decorin inhibited migration and favored scar formation.

Conclusion

Decorin expression may contribute to scar formation in the late stage of mouse embryos by inhibiting the migration of dermal mesenchymal cells.

Oncosuppressive roles of decorin through regulation of multiple receptors and diverse signaling pathways

Decorin is a stromal-derived prototype member of the small leucine-rich proteoglycan gene family. In addition to its functions as a regulator of collagen fibrillogenesis and TGF-β activity soluble decorin acts as a pan-receptor tyrosine kinase (RTK) inhibitor. Decorin binds to various RTKs including EGFR HER2 HGFR/Met VEGFR2 TLR and IGFR. Although the molecular mechanism for the action of decorin on these receptors is not entirely elucidated overall decorin evokes transient activation of these receptors with suppression of downstream signaling cascades culminating in growth inhibition followed by their physical downregulation via caveosomal internalization and degradation. In the case of Met decorin leads to decreased β-catenin signaling pathway and growth suppression. As most of these RTKs are responsible for providing a growth advantage to cancer cells the result of decorin treatment is oncosuppression. Another decorin-driven mechanism to restrict cancer growth and dissemination is by impeding angiogenesis via vascular endothelial growth factor receptor 2 (VEGFR2) and the concurrent activation of protracted endothelial cell autophagy. In this review we will dissect the multiple roles of decorin in cancer biology and its potential use as a next-generation protein-based adjuvant therapy to combat cancer.

Glycosaminoglycan Modification of Decorin Depends on MMP14 Activity and Regulates Collagen Assembly

Proper processing of collagens COL1 and COL6 is required for normal function of adipose tissue and skeletal muscle. Proteoglycan decorin (DCN) regulates collagen fiber formation. The amino-terminus of DCN is modified with an O-linked glycosaminoglycan (GAG), the function of which has remained unclear. Previously, non-glycanated DCN (ngDCN) was identified as a marker of adipose stromal cells. Here, we identify MMP14 as the metalloprotease that cleaves DCN to generate ngDCN. We demonstrate that mice ubiquitously lacking DCN GAG (ngDCN mice) have reduced matrix rigidity, enlarged adipocytes, fragile skin, as well as skeletal muscle hypotrophy, fibrosis, and dysfunction. Our results indicate that DCN deglycanation results in reduced intracellular DCN—collagen binding and increased production of truncated COL6 chains, leading to aberrant procollagen processing and extracellular localization. This study reveals that the GAG of DCN functions to regulate collagen assembly in adipose tissue and skeletal muscle and uncovers a new mechanism of matrix dysfunction in obesity and aging.

Peritoneal Proteoglycans: Much more than Ground Substance

Recent advances in the field of glycobiology have exposed a multitude of biological processes that are controlled or influenced by proteoglycans, in both physiological and pathological conditions ranging from early embryonic development, inflammation, and fibrosis to tumor invasion and metastasis. The first part of this article reviews the biosynthesis of proteoglycans and their multifunctional roles in health and disease; the second part of this review focuses on their putative roles in peritoneal homeostasis and peritoneal inflammation and fibrosis in the context of chronic peritoneal dialysis and peritonitis.

Borrelia burgdorferi adhere to blood vessels in the dura mater and are associated with increased meningeal T cells during murine disseminated borreliosis

Borrelia burgdorferi, the causative agent of Lyme disease, is a vector-borne bacterial infection that is transmitted through the bite of an infected tick. If not treated with antibiotics during the early stages of infection, disseminated infection can spread to the central nervous system (CNS). In non-human primates (NHPs) it has been demonstrated that the leptomeninges are among the tissues colonized by B. burgdorferi spirochetes. Although the NHP model parallels aspects of human borreliosis, a small rodent model would be ideal to study the trafficking of spirochetes and immune cells into the CNS. Here we show that during early and late disseminated infection, B. burgdorferi infects the meninges of intradermally infected mice, and is associated with concurrent increases in meningeal T cells. We found that the dura mater was consistently culture positive for spirochetes in transcardially perfused mice, independent of the strain of B. burgdorferi used. Within the dura mater, spirochetes were preferentially located in vascular regions, but were also present in perivascular, and extravascular regions, as late as 75 days post-infection. At the same end-point, we observed significant increases in the number of CD3+ T cells within the pia and dura mater, as compared to controls. Flow cytometric analysis of leukocytes isolated from the dura mater revealed that CD3+ cell populations were comprised of both CD4 and CD8 T cells. Overall, our data demonstrate that similarly to infection in peripheral tissues, spirochetes adhere to the dura mater during disseminated infection, and are associated with increases in the number of meningeal T cells. Collectively, our results demonstrate that there are aspects of B. burgdorferi meningeal infection that can be modelled in laboratory mice, suggesting that mice may be useful for elucidating mechanisms of meningeal pathogenesis by B. burgdorferi.

Absence of the dermatan sulfate chain of decorin does not affect mouse development

BACKGROUND

In vitro studies suggest that the multiple functions of decorin are related to both its core protein and its dermatan sulfate chain. To determine the contribution of the dermatan sulfate chain to the functional properties of decorin in vivo, a mutant mouse whose decorin lacked a dermatan sulfate chain was generated.

RESULTS

Homozygous mice expressing only the decorin core protein developed and grew in a similar manner to wild type mice. In both embryonic and postnatal mice, all connective tissues studied, including cartilage, skin and cornea, appeared to be normal upon histological examination, and their collagen fibrils were of normal diameter and organization. In addition, abdominal skin wounds healed in an identical manner in the mutant and wild type mice.

CONCLUSIONS

The absence of a dermatan sulfate chain on decorin does not appear to overtly influence its functional properties in vivo.

Expression Patterns of Extracellular Matrix Proteins during Posterior Commissure Development

Extracellular matrix (ECM) molecules are pivotal for central nervous system (CNS) development, facilitating cell migration, axonal growth, myelination, dendritic spine formation, and synaptic plasticity, among other processes. During axon guidance, the ECM not only acts as a permissive or non-permissive substrate for navigating axons, but also modulates the effects of classical guidance cues, such as netrin or Eph/ephrin family members. Despite being highly important, little is known about the expression of ECM molecules during CNS development. Therefore, this study assessed the molecular expression patterns of tenascin, HNK-1, laminin, fibronectin, perlecan, decorin, and osteopontin along chick embryo prosomere 1 during posterior commissure development. The posterior commissure is the first transversal axonal tract of the embryonic vertebrate brain. Located in the dorso-caudal portion of prosomere 1, posterior commissure axons primarily arise from the neurons of basal pretectal nuclei that run dorsally to the roof plate midline, where some turn toward the ipsilateral side. Expressional analysis of ECM molecules in this area these revealed to be highly arranged, and molecule interactions with axon fascicles suggested involvement in processes other than structural support. In particular, tenascin and the HNK-1 epitope extended in ventro-dorsal columns and enclosed axons during navigation to the roof plate. Laminin and osteopontin were expressed in the midline, very close to axons that at this point must decide between extending to the contralateral side or turning to the ipsilateral side. Finally, fibronectin, decorin, and perlecan appeared unrelated to axonal pathfinding in this region and were instead restricted to the external limiting membrane. In summary, the present report provides evidence for an intricate expression of different extracellular molecules that may cooperate in guiding posterior commissure axons.

Small leucine-rich repeat proteoglycans in corneal inflammation and wound healing

The small leucine rich repeat proteoglycans are major components of the cornea. Lumican, keratocan, decorin, biglycan and osteoglycin are present throughout the adult corneal stroma, and fibromodulin in the peripheral limbal area. In the cornea literature these proteoglycan have been reviewed as structural, collagen fibril-regulating proteins of the cornea. However, these proteoglycans are members of the leucine-rich-repeat superfamily, and share structural similarities with pathogen recognition toll-like receptors. Emerging studies are showing that these have a range of interactions with cell surface receptors, chemokines, growth factors and pathogen associated molecular patterns and are able to regulate host immune response, inflammation and wound healing. This review discusses what is known about their innate immune-related role directly in the cornea, and studies outside the field that find interesting links with innate immune and wound healing responses that are likely to be relevant to the ocular surface. In addition, the review discusses phenotypes of mice with targeted deletion of proteoglycan genes and genetic variants associated with human pathologies.

The interplay of extracellular matrix and microbiome in urothelial bladder cancer

Many pathological changes in solid tumours are caused by the accumulation of genetic mutations and epigenetic molecular alterations. In addition, tumour progression is profoundly influenced by the environment surrounding the transformed cells. The interplay between tumour cells and their microenvironment has been recognized as one of the key determinants of cancer development and is being extensively investigated. Data suggest that both the extracellular matrix and the microbiota represent microenvironments that contribute to the onset and progression of tumours. Through the introduction of omics technologies and pyrosequencing analyses, a detailed investigation of these two microenvironments is now possible. In urological research, assessment of their dysregulation has become increasingly important to provide diagnostic, prognostic and predictive biomarkers for urothelial bladder cancer. Understanding the roles of the extracellular matrix and microbiota, two key components of the urothelial mucosa, in the sequelae of pathogenic events that occur in the development and progression of urothelial carcinomas will be important to overcome the shortcomings in current bladder cancer treatment strategies.

Decorin as a multivalent therapeutic agent against cancer

Decorin is a prototypical small leucine-rich proteoglycan that epitomizes the multifunctional nature of this critical gene family. Soluble decorin engages multiple receptor tyrosine kinases within the target-rich environment of the tumor stroma and tumor parenchyma. Upon receptor binding, decorin initiates signaling pathways within endothelial cells downstream of VEGFR2 that ultimately culminate in a Peg3/Beclin 1/LC3-dependent autophagic program. Concomitant with autophagic induction, decorin blunts capillary morphogenesis and endothelial cell migration, thereby significantly compromising tumor angiogenesis. In parallel within the tumor proper, decorin binds multiple RTKs with high affinity, including Met, for a multitude of oncosuppressive functions including growth inhibition, tumor cell mitophagy, and angiostasis. Decorin is also pro-inflammatory by modulating macrophage function and cytokine secretion. Decorin suppresses tumorigenic growth, angiogenesis, and prevents metastatic lesions in a variety of in vitro and in vivo tumor models. Therefore, decorin would be an ideal therapeutic candidate for combating solid malignancies.

Decorin is an autophagy-inducible proteoglycan and is required for proper in vivo autophagy

We have recently discovered that soluble extracellular matrix constituents regulate autophagy via an outside-in signaling pathway. Decorin, a secreted proteoglycan, evokes autophagy in endothelial cells and mitophagy in breast carcinoma cells. However, it is not known whether decorin expression can be regulated by autophagic stimuli such as mTOR inhibition or nutrient deprivation. Thus, we tested whether pro-autophagic stimuli could affect decorin expression in mouse cardiac tissue and whether the absence of decorin could disrupt the in vivo autophagic response. We found that nutrient deprivation induced decorin at the mRNA and protein level in vivo and in vitro, a process regulated at the transcriptional level by inhibiting the canonical mTOR pathway. Moreover, Dcn-/- mice displayed an aberrant response to fasting compared to wild-type mice. Our study establishes a new role for an extracellular matrix proteoglycan and provides a mechanistic role for soluble decorin in regulating a fundamental intracellular catabolic process.

Microenvironmental Modulation of Decorin and Lumican in Temozolomide-Resistant Glioblastoma and Neuroblastoma Cancer Stem-Like Cells

The presence of cancer stem cells (CSCs) or tumor-initiating cells can lead to cancer recurrence in a permissive cell–microenvironment interplay, promoting invasion in glioblastoma (GBM) and neuroblastoma (NB). Extracellular matrix (ECM) small leucine-rich proteoglycans (SLRPs) play multiple roles in tissue homeostasis by remodeling the extracellular matrix (ECM) components and modulating intracellular signaling pathways. Due to their pan-inhibitory properties against receptor tyrosine kinases (RTKs), SLRPs are reported to exert anticancer effects in vitro and in vivo. However, their roles seem to be tissue-specific and they are also involved in cancer cell migration and drug resistance, paving the way to complex different scenarios. The aim of this study was to determine whether the SLRPs decorin (DCN) and lumican (LUM) are recruited in cell plasticity and microenvironmental adaptation of differentiated cancer cells induced towards stem-like phenotype. Floating neurospheres were generated by applying CSC enrichment medium (neural stem cell serum-free medium, NSC SFM) to the established SF-268 and SK-N-SH cancer cell lines, cellular models of GBM and NB, respectively. In both models, the time-dependent synergistic activation of DCN and LUM was observed. The highest DCN and LUM mRNA/protein expression was detected after cell exposure to NSC SFM for 8/12 days, considering these cells as SLRP-expressing (SLRP⁺) CSC-like. Ultrastructural imaging showed the cellular heterogeneity of both the GBM and NB neurospheres and identified the inner living cells. Parental cell lines of both GBM and NB grew only in soft agar + NSC SFM, whereas the secondary neurospheres (originated from SLRP⁺ t₈ CSC-like) showed lower proliferation rates than primary neurospheres. Interestingly, the SLRP⁺ CSC-like from the GBM and NB neurospheres were resistant to temozolomide (TMZ) at concentrations >750 μM. Our results suggest that GBM and NB CSC-like promote the activation of huge quantities of SLRP in response to CSC enrichment, simultaneously acquiring TMZ resistance, cellular heterogeneity, and a quiescent phenotype, suggesting a novel pivotal role for SLRP in drug resistance and cell plasticity of CSC-like, allowing cell survival and ECM/niche modulation potential.

12q21.2q22 deletion: a new patient

Interstitial deletions of long arm of chromosome 12 are rare, and the interstitial deletion 12q21.1q22 has been reported to the best of our knowledge in only four patients. Comparing the patients reported, a characteristic phenotypic pattern (facial features like prominent forehead, short and upturned nose, low set ears, and ectodermal abnormalities) can be identified. It has been suggested to be considered a deletion syndrome [Klein et al., (2005); Am J Med Genet 138:349-354]. We report on a 34-month-old girl, who was referred to our clinic at 6 months of age, presenting at birth with axial hypotonia, enlarged anterior fontanel, ventriculomegaly, dysmorphic facies (prominent forehead, sparse hair and eyebrows, short palpebral fissures), failure to thrive and development delay. Her cytogenetic study showed an interstitial deletion of the long arm of chromosome 12: 46,XX,del(12)(q21.1q22) redefined by array comparative genomic hybridization. We compare and review our patient with the four previously reported cases, plus one with a deletion with an overlap of the chromosomal region and phenotypic similarities. As far as we know our patient is the fourth reported with this cytogenetic abnormality. This additional report allows us to support a genotype-phenotype correlation for this chromosomal abnormality.

Proteoglycan form and function: A comprehensive nomenclature of proteoglycans

We provide a comprehensive classification of the proteoglycan gene families and respective protein cores. This updated nomenclature is based on three criteria: Cellular and subcellular location, overall gene/protein homology, and the utilization of specific protein modules within their respective protein cores. These three signatures were utilized to design four major classes of proteoglycans with distinct forms and functions: the intracellular, cell-surface, pericellular and extracellular proteoglycans. The proposed nomenclature encompasses forty-three distinct proteoglycan-encoding genes and many alternatively-spliced variants. The biological functions of these four proteoglycan families are critically assessed in development, cancer and angiogenesis, and in various acquired and genetic diseases where their expression is aberrant.

A decorin-deficient matrix affects skin chondroitin/dermatan sulfate levels and keratinocyte function

Decorin is a small leucine-rich proteoglycan harboring a single glycosaminoglycan chain, which, in skin, is mainly composed of dermatan sulfate (DS). Mutant mice with targeted disruption of the decorin gene (Dcn(-/-)) exhibit an abnormal collagen architecture in the dermis and reduced tensile strength, collectively leading to a skin fragility phenotype. Notably, Ehlers-Danlos patients with mutations in enzymes involved in the biosynthesis of DS display a similar phenotype, and recent studies indicate that DS is involved in growth factor binding and signaling. To determine the impact of the loss of DS-decorin in the dermis, we analyzed the glycosaminoglycan content of Dcn(-/-) and wild-type mouse skin. The total amount of chondroitin/dermatan sulfate (CS/DS) was increased in the Dcn(-/-) skin, but was overall less sulfated with a significant reduction in bisulfated ΔDiS2,X (X=4 or 6) disaccharide units, due to the reduced expression of uronyl 2-O sulfotransferase (Ust). With increasing age, sulfation declined; however, Dcn(-/-) CS/DS was constantly undersulfated vis-à-vis wild-type. Functionally, we found altered fibroblast growth factor (Fgf)-7 and -2 binding due to changes in the micro-heterogeneity of skin Dcn(-/-) CS/DS. To better delineate the role of decorin, we used a 3D Dcn(-/-) fibroblast cell culture model. We found that the CS/DS extracts of wild-type and Dcn(-/-) fibroblasts were similar to the skin sugars, and this correlated with the lack of uronyl 2-O sulfotransferase in the Dcn(-/-) fibroblasts. Moreover, Ffg7 binding to total CS/DS was attenuated in the Dcn(-/-) samples. Surprisingly, wild-type CS/DS significantly reduced the binding of Fgf7 to keratinocytes in a concentration dependent manner unlike the Dcn(-/-) CS/DS that only affected the binding at higher concentrations. Although binding to cell-surfaces was quite similar at higher concentrations, keratinocyte proliferation was differentially affected. Higher concentration of Dcn(-/-) CS/DS induced proliferation in contrast to wild-type CS/DS. 3D co-cultures of fibroblasts and keratinocytes showed that, unlike Dcn(-/-) CS/DS, wild-type CS/DS promoted differentiation of keratinocytes. Collectively, our results provide novel mechanistic explanations for the reported defects in wound healing in Dcn(-/-) mice and possibly Ehlers-Danlos patients. Moreover, the lack of decorin-derived DS and an altered CS/DS composition differentially influence keratinocyte behavior.

Lack of decorin expression by human bladder cancer cells offers new tools in the therapy of urothelial malignancies

Decorin, a multifunctional small leucine-rich extracellular matrix proteoglycan, has been shown to possess potent antitumour activity. However, there is some uncertainty whether different cancer cells express decorin in addition to non-malignant stromal cells. In this study we clarified decorin expression by human bladder cancer cells both in vivo and in vitro. In addition, the effect of adenovirus-mediated decorin expression on human bladder cancer cells in vitro was examined. We first demonstrated using the publicly available GeneSapiens databank that decorin gene expression is present in both normal and malignant human bladder tissues. However, when we applied in situ hybridization with digoxigenin-labeled RNA probes for decorin on human bladder carcinoma tissue samples derived from a large radical cystectomy patient cohort (n = 199), we unambiguously demonstrated that invasive and non-invasive bladder carcinoma cells completely lack decorin mRNA. The cancer cells were also negative for decorin immunoreactivity. Instead, decorin expression was localized solely to original non-malignant stromal areas of bladder tissue. In accordance with the aforementioned results, human bladder cancer cells in vitro were also negative for decorin expression as shown by RT-qPCR analyses. The lack of decorin expression by bladder cancer cells was shown not to be due to the methylation of the proximal promoter region of the decorin gene. When bladder cancer cells were transfected with a decorin adenoviral vector, their proliferation was significantly decreased. In conclusion, we have shown that human bladder cancer cells are totally devoid of decorin expression. We have also shown that adenovirus-mediated decorin gene transduction of human bladder cancer cell lines markedly inhibits their proliferation. Thus, decorin gene delivery offers new potential therapeutic tools in urothelial malignancies.

Intracellularly-retained decorin lacking the C-terminal ear repeat causes ER stress: a cell-based etiological mechanism for congenital stromal corneal dystrophy

Decorin, a small leucine-rich proteoglycan (SLRP), is involved in the pathophysiology of human congenital stromal corneal dystrophy (CSCD). This disease is characterized by corneal opacities and vision impairment. In reported cases, the human gene encoding decorin contains point mutations in exon 10, generating a truncated form of decorin lacking the C-terminal 33 amino acid residues. We have previously described a transgenic mouse model carrying a similar mutation in the decorin gene that leads to an ocular phenotype characterized by corneal opacities identical to CSCD in humans. We have also identified abnormal synthesis and secretion of various SLRPs in mutant mouse corneas. In the present study, we found that mutant C-terminal truncated decorin was retained in the cytoplasm of mouse keratocytes in vivo and of transfected human embryonic kidney cells. This resulted in endoplasmic reticulum stress and an unfolded protein response. Thus, we propose a novel cell-based mechanism underlying CSCD in which a truncated SLRP protein core is retained intracellularly, its accumulation triggering endoplasmic reticulum stress that results in abnormal SLRP synthesis and secretion, which ultimately affects stromal structure and corneal transparency.

Defining cell-matrix combination products in the era of pluripotency

Human pluripotent stem (hPS) cells provide an attractive opportunity for the manufacture of a wide array of therapeutic cell types. The challenges to commercialization include the thousand-fold diversity of cell types emerging from hPS cells and the associated difficulties in validating processes to reliably generate cells with precise identity and purity. Improved methods of controlling the dosage and migration of hPS-derived cells in solid tissues are also needed. To directly address these issues, we clonally expanded proliferating lineages of cells that were intermediate in regard to their state of differentiation between hPS and terminally differentiated cells. These cells called monoclonal embryonic progenitors (hEP), are expandable mortal lineages with diverse site-specific homeobox gene expression and multipotentiality. In this review, we discuss methods of generating combination products wherein the fate space of precisely identified monoclonal hEP cells is mapped by differentiating the cells in vitro in HyStem-3D bead arrays in the presence of diverse growth factors. This combination of discovery processes has the potential to translate directly into cell-matrix formulations that can be used to generate pre-clinical data leading to human clinical trials and potentially new medical therapies.

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.

An isoform of decorin is a resistin receptor on the surface of adipose progenitor cells

Adipose stromal cells (ASCs) serve as mesenchymal progenitors in white adipose tissue (WAT). Intercellular interactions involving ASCs have remained obscure. By merging phage display technology with fluorescence-activated cell sorting (FACS), we screened a combinatorial library for peptides that target mouse ASCs in vivo. We isolated peptide CSWKYWFGEC that specifically homes to ASCs, used it as bait to purify the corresponding ASC surface receptor, and identified it as a previously unreported cleavage product of decorin (DCN) lacking the glycanation site (termed ΔDCN). We demonstrate that ΔDCN is differentially expressed on ASC surface. In a screen for ΔDCN-binding proteins, we identified resistin, an adipokine for which the receptor has been unknown. Expression of ΔDCN in 3T3-L1 cells promoted proliferation and migration but suppressed lipid accumulation upon adipogenesis induction, which was resistin dependent. We conclude that ΔDCN serves as a functional receptor of resistin in adipocyte progenitors and may regulate WAT expansion.

Proteoglycans in health and disease: novel regulatory signaling mechanisms evoked by the small leucine-rich proteoglycans

The small leucine-rich proteoglycans (SLRPs) are involved in many aspects of mammalian biology, both in health and disease. They are now being recognized as key signaling molecules with an expanding repertoire of molecular interactions affecting not only growth factors, but also various receptors involved in controlling cell growth, morphogenesis and immunity. The complexity of SLRP signaling and the multitude of affected signaling pathways can be reconciled with a hierarchical affinity-based interaction of various SLRPs in a cell- and tissue-specific context. Here, we review this interacting network, describe new relationships of the SLRPs with tyrosine kinase and Toll-like receptors and critically assess their roles in cancer and innate immunity.

Binding characteristics of the osteoarthritis-associated protein asporin

Asporin is an extracellular matrix (ECM) protein that regulates cartilage matrix gene expression and cartilage formation by modulating the transforming growth factor-beta (TGF-beta) signaling pathway. Our previous studies have indicated that asporin binds to TGF-beta1 directly and inhibits TGF-beta1-mediated expression of cartilage matrix genes. However, it is still unknown how asporin interacts with TGF-beta1 and influences its activity. Using competition assays, we determined that amino acids 159-205 of asporin mediate its interaction with TGF-beta1 and effectively repress TGF-beta1-induced cartilage matrix gene expression. Asporin also has a binding ability to type II collagen in vitro, but its binding pattern is different from that of TGF-beta1. In contrast with previous in vivo findings, asporin did not affect the interaction between TGF-beta1 and the TGF-beta type II receptor (TbetaRII) by itself or in the presence of type II collagen in vitro. However, in the presence of heparin/heparan sulfate, asporin inhibits the interaction between TGF-beta and TbetaRII in vitro. These findings suggest that asporin is one of the important cartilage matrix proteins that binds to the ECM and TGF-beta1 and thereby modulates interactions between TGF-beta and its signaling receptors.

The bladder extracellular matrix. Part I: architecture, development and disease

From the earliest studies with epithelial cells implanted into detrusor muscle to later experiments on smooth muscle in defined collagen gels, cell niche and extracellular matrix (ECM) have been clearly shown to orchestrate cellular behavior and fate whether quiescent, migratory, or proliferative. Normal matrix can revert transformed cells to quiescence, and damaged matrix can trigger malignancy or dedifferentiation. ECM influence in disease, development, healing and regeneration has been demonstrated in many other fields of study, but a thorough examination of the roles of ECM in bladder cell activity has not yet been undertaken. Structural ECM proteins, in concert with adhesive proteins, provide crucial structural support to the bladder. Both structural and nonstructural components of the bladder have major effects on smooth muscle function, through effects on matrix rigidity and signaling through ECM receptors. While many ECM components and receptors identified in the bladder have specific known functions in the vascular smooth musculature, their function in the bladder is often less well defined. In cancer and obstructive disease, the ECM has a critical role in pathogenesis. The challenge in these settings will be to find therapies that prevent hyperproliferation and encourage proper differentiation, through an understanding of matrix effects on cell biology and susceptibility to therapeutics.

A central role for decorin during vertebrate convergent extension

Decorin, an archetypal member of the small leucine-rich proteoglycan gene family, regulates collagen fibrillogenesis and cell growth. To further explore its biological function, we examined the role of Decorin during zebrafish development. Zebrafish Decorin is a chondroitin sulfate proteoglycan that exhibits a high degree of conservation with its mammalian counterpart and displays a unique spatiotemporal expression pattern. Morpholino-mediated knockdown of zebrafish decorin identified a developmental role during medial-lateral convergence and anterior-posterior extension of the body plan, as well as in craniofacial cartilage formation. decorin morphants displayed a pronounced shortening of the head-to-tail axis as well as compression, flattening, and extension of the jaw cartilages. The morphant phenotype was efficiently rescued by zebrafish decorin mRNA. Unexpectedly, microinjection of excess zebrafish decorin mRNA or proteoglycan/protein core into one-cell stage embryos caused cyclopia. The morphant and overexpression phenotype represent a convergent extension defect. Our results indicate a central function for Decorin during early embryogenesis.

Decorin-mediated inhibition of proliferation and migration of the human trophoblast via different tyrosine kinase receptors

Decorin (DCN), a decidua-derived TGFbeta-binding proteoglycan, negatively regulates proliferation, migration, and invasiveness of human extravillous trophoblast (EVT) cells in a TGFbeta-independent manner. The present study examined underlying mechanisms, in particular possible roles of epidermal growth factor receptor (EGFR), IGF receptor (IGFR)-I, and vascular endothelial growth factor receptor (VEGFR)-2. EVT cell sprouting from first-trimester chorionic villus explants in the presence or absence of TGFbeta-neutralizing antibody was inhibited with DCN, suggesting its negative regulatory role in situ. Inhibition of migration of the human EVT cell line HTR-8/SVneo in transwells undercoated with fibronectin was stronger when cells were briefly preincubated with DCN at 4 C (known to retard dissociation of receptor-ligand complex) than at 37 C, suggesting possible DCN action by cell membrane binding. Pretreatment of cells with an IGFR-I blocking agent, but not two EGFR blocking agents or a VEGFR blocking agent, significantly abrogated migration inhibitory effects of DCN, suggesting the involvement of IGFR-I but not EGFR or VEGFR in migration inhibition by DCN. On the other hand, pretreatment with either of the EGFR blocking agents, or the VEGFR blocking agent but not the IGFR-I blocking agent, blocked proliferation inhibitory effects of DCN, indicating the roles of EGFR and VEGFR, but not IGFR-I in antiproliferative action of DCN. EVT cells expressed EGFR, IGFR-I, and VEGFR-2. IGFR-I and VEGF-R2 were phosphorylated in the presence of their natural ligands as well as DCN, and these events were blocked by pretreatment with respective receptor blocking agents indicating DCN-mediated activation of these receptors. In conclusion, DCN effects on EVT cells are mediated selectively by multiple tyrosine kinase receptors.

Abundantly expressed genes in pig adipose tissue: an expressed sequence tag approach

Adipose tissue plays a critical role in metabolism, storage, and release of fatty acids in mammals. Construction of a full-length cDNA library is an effective way to understand the functional expression of genes in adipose tissue, and in addition, novel genes for further research can be found in the library. In this study, adipose tissue RNA was extracted from three 18-mo-old Lee-Sung pigs. The mRNA was isolated, reverse transcribed, and used to construct a cDNA library. After transformation, 2,880 clones were selected and sequenced. Cluster analysis was performed, and the assembled contig of each cluster was subjected to search against DNA sequences in the nucleotide databases (NCBINR/TIGRGI). These sequences were clustered into 1,527 unique sequences; 80% of the sequences were categorized as known genes, and 20% of the sequences were categorized as unknown genes. In this adipose tissue cDNA library, approximately 16% of the genes contained full-length sequences with start and stop codons. Gene ontology analysis was performed to indicate the possible functions of these genes. Genes associated with mitochondrial function were abundant and represented 10% of the total. Several fatty acid transport genes and stearoyl coenzyme A desaturase were among the most abundant genes expressed. Tissue distribution of several abundant genes was analyzed by northern analysis, and many of these genes were transcribed in porcine adipose tissue in high copy number. Our full-length sequence data and tissue distribution data can be used to decipher the functional roles exhibited by the adipocyte under various perturbations via endocrine, environmental, genetic, nutritional, pharmacological, or physiological manipulations.

Expression and Regulation of the Osteoarthritis-associated Protein Asporin

Asporin (ASPN) is a small leucine-rich proteoglycan that is involved in pathological processes of osteoarthritis. Previously, we showed that asporin can inhibit transforming growth factor-beta1 (TGF-beta1)-mediated expression of cartilage matrix genes and chondrogenesis in vitro (Kizawa, H., Kou, I., Iida, A., Sudo, A., Miyamoto, Y., Fukuda, A., Mabuchi, A., Kotani, A., Kawakami, A., Yamamoto, S., Uchida, A., Nakamura, K., Notoya, K., Nakamura, Y., and Ikegawa, S. (2005) Nat. Genet. 37, 138-144). However, details about regulation of asporin itself are not yet known. Here, we examined ASPN expression in skeletal tissue and potential regulation of ASPN by TGF-beta. In situ hybridization revealed the presence of ASPN mRNA in the perichondrium/periosteum of long bones, but its absence in articular cartilage and growth plates. Immunohistochemical analysis also showed ASPN protein expression predominantly in the perichondrium/periosteum. TGF-beta1 induced endogenous ASPN mRNA expression over time in vitro, and this induction was suppressed by the TGF-beta type I receptor kinase inhibitor SB431542. Inhibition of Smad3 significantly reduced TGF-beta1-induced ASPN expression, whereas overexpression of Smad3 augmented the induction. Characterization of the human ASPN promoter region revealed a region from -126 to -82 that is sufficient for full promoter activity; however, TGF-beta1 failed to increase activity through the ASPN promoter. Our findings indicate that TGF-beta1 induces ASPN through Smad3 but that this induction is indirect.

Bladder defense molecules, urothelial differentiation, urinary biomarkers, and interstitial cystitis

It has long been recognized that interstitial cystitis (IC) is a disease of the urothelium. In this article, we review the results of published studies and present new data concerning the precise role of the bladder epithelium in IC. We discuss bladder defenses against both the penetration of urinary solutes and bacterial adherence, and we present new information about the proteoglycans that are present on the normal bladder. Previously published results and new data presented here support the conclusion that IC involves an aberrant differentiation program in the bladder urothelium that leads to altered synthesis of several proteoglycans, cell adhesion and tight junction proteins, and bacterial defense molecules such as GP51. These findings lend support to the rationale for glycosaminoglycan replacement therapy for the treatment of patients with IC.

The cleavage of biglycan by aggrecanases

OBJECTIVE

Aggrecanase-1 [a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4] and aggrecanase-2 (ADAMTS-5) have been named for their ability to degrade the proteoglycan aggrecan. While this may be the preferred substrate for these enzymes, they are also able to degrade other proteins. The aim of this work was to determine whether the aggrecanases could degrade biglycan and decorin.

METHODS

Biglycan, decorin and aggrecan were purified from human and bovine cartilage and subjected to degradation by recombinant aggrecanase-1 or aggrecanase-2. In vitro degradation was assessed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS/PAGE) and immunoblotting, and the cleavage site in biglycan was determined by N-terminal amino acid sequencing. SDS/PAGE and immunoblotting were also used to assess in situ degradation in both normal and arthritic human articular cartilage.

RESULTS

Both aggrecanase-1 and aggrecanase-2 are able to cleave bovine and human biglycan at a site within their central leucine-rich repeat regions. Cleavage occurs at an asparagine-cysteine bond within the fifth leucine-rich repeat. In contrast, the closely related proteoglycan decorin is not a substrate for the aggrecanases. Analysis of human articular cartilage from osteoarthritic (OA) and rheumatoid arthritic (RA) joints showed that a biglycan degradation product of equivalent size is present in the extracellular matrix. No equivalent degradation product was, however, detectable in normal adult human articular cartilage.

CONCLUSION

Biglycan, which is structurally unrelated to aggrecan, can act as a substrate for aggrecanase-1 and aggrecanase-2, and these proteinases may account for at least part of the biglycan degradation that is present in arthritic cartilage.

Nephrocan, a novel member of the small leucine-rich repeat protein family, is an inhibitor of transforming growth factor-beta signaling

In a search of new, small leucine-rich repeat proteoglycan/protein (SLRP) family members, a novel gene, nephrocan (NPN), has been identified. The gene consists of three exons, and based on the deduced amino acid sequence, NPN has 17 leucine-rich repeat motifs and unique cysteine-rich clusters both in the N and C termini, indicating that this gene belongs to a new class of SLRP family. NPN mRNA was predominantly expressed in kidney in adult mice, and during mouse embryogenesis, the expression was markedly increased in 11-day-old embryos at a time when early kidney development takes place. In the adult mouse kidney, NPN protein was located in distal tubules and collecting ducts. When NPN was overexpressed in cell culture, the protein was detected in the cultured medium, and upon treatment with N-glycosidase F, the molecular mass was lowered by approximately 14 kDa, indicating that NPN is a secreted N-glycosylated protein. Furthermore, transforming growth factor-beta (TGF-beta)-responsive 3TP promoter luciferase activity was down-regulated, and TGF-beta-induced Smad3 phosphorylation was also inhibited by NPN, suggesting that NPN suppresses TGF-beta/Smad signaling. Taken together, NPN is a novel member of the SLRP family that may play important roles in kidney development and pathophysiology by functioning as an endogenous inhibitor of TGF-beta signaling.

Activation of genes for growth factor and cytokine pathways late in chondrogenic differentiation of ATDC5 cells

The mouse embryonal carcinoma cell line ATDC5 provides an excellent model system for chondrogenesis in vitro. To understand better the molecular mechanisms of endochondral bone formation, we investigated gene expression profiles during the differentiation course of ATDC5 cells, using an in-house microarray harboring full-length-enriched cDNAs. For 28 days following chondrogenic induction, 507 genes were up- or down-regulated at least 1.5-fold. These genes were classified into five clusters based on their expression patterns. Genes for growth factor and cytokine pathways were significantly enriched in the cluster characterized by increases in expression during late stages of chondrocyte differentiation. mRNAs for decorin and osteoglycin, which have been shown to bind to transforming growth factors-beta and bone morphogenetic proteins, respectively, were found in this cluster and were detected in hypertrophic chondrocytes of developing mouse bones by in situ hybridization analysis. Taken together with assigned functions of individual genes in the cluster, interdigitated interaction between a number of intercellular signaling molecules is likely to take place in the late chondrogenic stage for autocrine and paracrine regulation among chondrocytes, as well as for chemoattraction and stimulation of progenitor cells of other lineages.

Structural change in decorin with skin aging

Decorin, the main proteoglycan in skin, has a small size with a core protein of approximately 40kDa and one chondroitin sulfate/dermatan sulfate glycosaminoglycan (GAG) chain. The main function of decorin is to regulate the collagen matrix assembly. Decorin is distributed along collagen fibrils with the core protein and the decorin GAG chain controls the distance between the collagen fibrils. Reducing the length of the decorin GAG chain reduces the distance between the collagen fibrils. Age-related changes in decorin are apparent in the GAG chain in respect to the molecular size and sulfate position but not in the core protein. Structural changes in the decorin GAG chain may be involved in changes in collagen matrix assembly during the aging process.

Imprinted genes in the placenta – A review

Imprinted genes are expressed monoallelically depending on their parental origin. High expression of the majority of imprinted genes tested to date has been demonstrated in extraembryonic tissues; placenta and yolk sac. Several mouse models where specific imprinted genes have been disrupted demonstrate that fetal and placental growth may be regulated by imprinted genes, in which paternally expressed genes enhance, and maternally expressed genes restrain, growth. We review the current information on, and suggest possible functional roles for, imprinted genes in placental development.

Pre-B cell leukemia transcription factor (PBX) proteins are important mediators for retinoic acid-dependent endodermal and neuronal differentiation of mouse embryonal carcinoma P19 cells

Pre-B cell leukemia transcription factors (PBXs) act as cofactors in the transcriptional regulation mediated by Homeobox proteins during embryonic development and cellular differentition. PBX1 protein is expressed throughout murine embryonic development, and its deletion in mice disrupts chondrogenesis. PBX protein levels are also increased in mouse embryonal carcinoma P19 cells during retinoic acid (RA)-induced differentiation. To elucidate the role of PBX proteins in this process, we stably overexpressed PBX1b antisense mRNA in P19 cells (PBX1b-AS cells). PBX1b-AS cells did not differentiate to neuronal or endodermal cells following treatment with RA suggesting PBX proteins are required for both processes. Furthermore we demonstrated that PBX proteins regulate the RA-dependent induction in the mRNA levels of bone morphogenetic protein 4 (BMP4) and Decorin (DCN) in P19 cells using both PBX1b-AS cells and PBX1 small interfering RNA. Chromatin immunoprecipitation assays further demonstrated that PBX proteins directly bind to the promoter of Bmp4 and Dcn in vivo in a RA-dependent fashion. In addition, type I and type II BMP receptor mRNA levels were also increased in P19 cells following RA treatment; however, this was PBX-independent. Taken together these data demonstrate that PBX proteins are required for RA-induced differentiation of P19 cells and that PBX proteins regulate the expression of BMP4 and DCN during this differentiation process.

Biochemical and biomechanical analysis of tendons of caged and penned chickens

Chickens were divided into two groups, one caged and the other penned. Superficial digital flexor tendons from penned chickens showed greater tensile strength, withstanding a greater strain before rupture than tendons from caged chickens. The tensile region of tendons from penned chickens showed more swelling in acetic acid and a higher hydroxyproline concentration compared with caged chickens, indicating the presence of large collagen amounts in the former. The tensile region of penned chickens presented higher glycosaminoglycan concentrations than the same region of caged chickens. For both groups, the predominant glycosaminoglycan in the compression regions was chondroitin sulfate, whereas dermatan sulfate was found in the tensile regions. N-terminal analysis identified the small proteoglycans fibromodulin and decorin. SDS-PAGE indicated that decorin was present in all regions and fibromodulin was mainly observed in the tensile region. These results indicate that an external condition, in this case the area available for locomotion, might influence the synthesis of extracellular matrix components and the mechanical properties of the tendon.

Gene expression profiling reveals multiple novel intrinsic and extrinsic factors associated with axonal regeneration failure

In contrast to the regeneration-competent peripheral nervous system (PNS), lesions of nerve tracts within the central nervous system (CNS) lead to chronically impaired neuronal connections. We have analysed changes in gene expression patterns occurring as a consequence of postcommissural fornix transection at a time when spontaneous axonal growth has ceased at the lesion site. This was done in order to describe both extrinsic and intrinsic determinants of regeneration failure. Using a genomic approach we have identified a number of so far undetected factors such as bamacan and semaphorin 6B, which relate to chronic axonal growth arrest and therefore are promising candidates for lesion-induced axonal growth inhibitors. In addition, we observed that within the subiculum, where the fornix axons originate, neuronal Oct-6 was induced and NG2 was down-regulated, indicating that axotomized neurons as well as glial cells react at the level of gene expression to remote axotomy.

Intratracheal gene transfer of decorin reduces subpleural fibroproliferation induced by bleomycin

Decorin, a small leucin-rich proteoglycan, is a negative regulator of transforming growth factor-beta, but the antifibrotic effect of decorin gene transfer has not been examined in a mouse model of usual interstitial pneumonia (UIP). We constructed a replication-defective recombinant adenovirus harboring human decorin gene (AdCMV.DC) and administered 1 x l0(9) plaque-forming units of AdCMV.DC intratracheally or intravenously to C57BL/6 mice with intraperitoneal injection of bleomycin, which induces a subpleural fibroproliferation, mimicking UIP, by day 28. Only intratracheal administration of AdCMV.DC increased decorin mRNA expression in the lung and decreased the hydroxyproline content augmented in bleomycin-induced pulmonary fibrosis (1.13 +/- 0.02 to 0.96 +/- 0.02, P = 0.006). In contrast, intravenous administration of AdCMV.DC increased the decorin expression only in the liver, but not in the lung, and without reducing lung fibrosis. These results indicate that adenoviral decorin gene transfer is effective only by direct administration to fibrosing lungs.

Mice deficient in small leucine-rich proteoglycans: novel in vivo models for osteoporosis, osteoarthritis, Ehlers-Danlos syndrome, muscular dystrophy, and corneal diseases

Small leucine-rich proteoglycans (SLRPs) are extracellular molecules that bind to TGFbetas and collagens and other matrix molecules. In vitro, SLRPs were shown to regulate collagen fibrillogenesis, a process essential in development, tissue repair, and metastasis. To better understand their functions in vivo, mice deficient in one or two of the four most prominent and widely expressed SLRPs (biglycan, decorin, fibromodulin, and lumican) were recently generated. All four SLRP deficiencies result in the formation of abnormal collagen fibrils. Taken together, the collagen phenotypes demonstrate a cooperative, sequential, timely orchestrated action of the SLRPs that altogether shape the architecture and mechanical properties of the collagen matrix. In addition, SLRP-deficient mice develop a wide array of diseases (osteoporosis, osteoarthritis, muscular dystrophy, Ehlers-Danlos syndrome, and corneal diseases), most of them resulting primarily from an abnormal collagen fibrillogenesis. The development of these diseases by SLRP-deficient mice suggests that mutations in SLRPs may be part of undiagnosed predisposing genetic factors for these diseases. Although the distinct phenotypes developed by the different singly deficient mice point to distinct in vivo function for each SLRP, the analysis of the double-deficient mice also demonstrates the existence of rescuing/compensation mechanisms, indicating some functional overlap within the SLRP family.

Decorin suppresses tumor cell-mediated angiogenesis

The progressive growth of most neoplasms is dependent upon the establishment of new blood vessels, a process regulated by tumor-secreted factors and matrix proteins. We examined the in vitro and in vivo angiogenic ability of conditioned media obtained from fibrosarcoma, carcinoma, and osteosarcoma cells and their decorin-transfected counterparts. Human endothelial cells were investigated in vitro by evaluating three essential steps of angiogenesis: migration, attachment, and differentiation. On the whole, wild-type tumor cell-secretions enhanced endothelial cell attachment, migration, and differentiation, whereas their decorin-expressing forms inhibited these processes. Similarly, decorin-containing media suppressed endothelial cell sprouting in an ex vivo aortic ring assay. Since angiogenesis is an important component of tumor expansion, the growth rate of these cells as tumor xenografts was examined by implantation in nude mice. In vivo, the decorin-expressing tumor xenografts grew at markedly lower rates and showed a significant suppression of neovascularization. Immunohistochemical, Northern and Western blot analyses indicated that the decorin-expressing cells produced vascular endothelial growth factor (VEGF) at markedly reduced rates vis-á-vis their wild-type counterparts. Specificity of this process was confirmed by experiments where addition of recombinant decorin to the wild-type tumor cells caused 80-95% suppression of VEGF mRNA and protein. These results provide a novel mechanism of action for decorin, and indicate that decorin could adversely affect in vivo tumor growth by suppressing the endogenous tumor cell production of a powerful angiogenic stimulus.

Asb4, Ata3, and Dcn are novel imprinted genes identified by high-throughput screening using RIKEN cDNA microarray

Genes differentially expressed between parthenogenetic and androgenetic embryos are candidates for the identification of imprinted genes, which are expressed specifically from the maternal or paternal allele. To search for genes differentially expressed between parthenogenetic and androgenetic embryos, we used the RIKEN full-length enriched mouse cDNA microarray. The 25 candidates obtained included 8 known imprinted genes (such as IgfII, Snrpn, and Neuronatin) and 3 new ones--Asb4 (ankyrin repeat and SOCS box-containing protein 4), Ata3 (amino acid transport system A3), and Decorin--which were confirmed by using normal diploid embryos from the reciprocal F1 crosses of B6 and JF1 mice. The 25 candidates also included genes that showed no imprinting-associated expression in normal diploid embryos. We describe a feasible high-throughput method of screening for novel imprinted genes by using the RIKEN cDNA microarray.

WISP-1 binds to decorin and biglycan

Wnt-1-induced secreted protein 1 (WISP-1) is a member of the CCN (connective tissue growth factor, Cyr61, NOV) family of growth factors. Structural and experimental evidence suggests that CCN family member activities are modulated by their interaction with sulfated glycoconjugates. To elucidate the mechanism of action for WISP-1, we characterized the specificity of its tissue and cellular interaction and identified binding factors. WISP-1 binding was restricted to the stroma of colon tumors and to cells with a fibroblastic phenotype. By using a solid phase assay, we showed that human skin fibroblast conditioned media contained WISP-1 binding factors. Competitive inhibition with different glycosaminoglycans and treatment with glycosaminoglycan lyases and proteases demonstrated that binding to the conditioned media was mediated by dermatan sulfate proteoglycans. Mass spectrometric analysis identified the isolated binding factors as decorin and biglycan. Decorin and biglycan interacted directly with WISP-1 and inhibited its binding to components in the conditioned media. Similarly, WISP-1 interaction with human skin fibroblasts was inhibited by dermatan sulfate, decorin, and biglycan or by treatment of the cell surface with dermatan sulfate-specific lyases. Together these results demonstrate that decorin and biglycan are WISP-1 binding factors that can mediate and modulate its interaction with the surface of fibroblasts. We propose that this specific interaction plays a role in the regulation of WISP-1 function.

A composite element binding the vitamin D receptor and the retinoic X receptor alpha mediates the transforming growth factor-beta inhibition of decorin gene expression in articular chondrocytes

Decorin, a small leucine-rich proteoglycan may play an important role in the attempt of cartilage repair initiated by chondrocytes in early stages of osteoarthritis, through its ability to bind collagen fibrils and growth factors such as transforming growth factor-beta (TGF-beta). We previously demonstrated that TGF-beta decreased decorin mRNA steady state levels in articular chondrocytes (Demoor, M., Rédini, F., Boittin, M., and Pujol, J.-P. (1998) Biochim. Biophys. Acta 1398, 179-191). Here, we investigated the effect of TGF-beta on decorin gene expression in both primary cultures of articular chondrocytes and chondrocytes dedifferentiated by serial passages. Transient transfection of cells with plasmid constructs of the decorin promoter linked to the luciferase reporter gene revealed transcriptional repression by TGF-beta, in fully differentiated as well as dedifferentiated chondrocytes. Experiments with 5'-deleted constructs allowed characterization of a TGF-beta-responsive element in the shortest construct (base pairs (bp) -155/+269). DNase I footprinting analysis delineated a negative TGF-beta-responsive region between -140 and -111 bp in the decorin proximal promoter. Gel retardation assays demonstrated that TGF-beta modulates decorin gene expression through transcription factors, the nature and mode of action of which depend on the differentiation state of the chondrocytes; two DNA-protein complexes were formed in the region -144/-127 bp with nuclear extracts from primary chondrocytes, whereas a higher mobility complex was observed in the -127/-111 bp region for dedifferentiated cells. Antibodies against vitamin D and retinoic acid receptors used in supershift experiments showed that these nuclear receptors are involved in the regulation of decorin gene expression in articular chondrocytes.

Expression pattern and gene characterization of asporin. a newly discovered member of the leucine-rich repeat protein family

We have discovered a new member of the class I small leucine-rich repeat proteoglycan (SLRP) family which is distinct from the other class I SLRPs since it possesses a unique stretch of aspartate residues at its N terminus. For this reason, we called the molecule asporin. The deduced amino acid sequence is about 50% identical (and 70% similar) to decorin and biglycan. However, asporin does not contain a serine/glycine dipeptide sequence required for the assembly of O-linked glycosaminoglycans and is probably not a proteoglycan. The tissue expression of asporin partially overlaps with the expression of decorin and biglycan. During mouse embryonic development, asporin mRNA expression was detected primarily in the skeleton and other specialized connective tissues; very little asporin message was detected in the major parenchymal organs. The mouse asporin gene structure is similar to that of biglycan and decorin with 8 exons. The asporin gene is localized to human chromosome 9q22-9q21.3 where asporin is part of a SLRP gene cluster that includes extracellular matrix protein 2, osteoadherin, and osteoglycin. Further analysis shows that, with the exception of biglycan, all known SLRP genes reside in three gene clusters.

A comparison of the expression pattern of five genes of the family of small leucine-rich proteoglycans during mouse development

For five members of the family of the small leucine-rich proteoglycans (SLRPs), the expression pattern during fetal development was analyzed. RNA in situ hybridization on whole body sections of mouse embryos was performed for biglycan (Bgn), decorin (Dcn), fibromodulin (Fmod), chondroadherin (Chad), and lumican (Lum). Special attention was given to the question of whether these patterns coincide only with sites of collagen secretion in connective tissue during tissue modeling or if expression can be observed at specific sites of organ differentiation also. In general, Fmod, Lum, and Bgn are expressed at sites of cartilage and bone formation and interstitial tissue deposition; Chad is expressed only at sites of cartilage; and Dcn is expressed only at sites of interstitial tissue deposition. However, there are some distinct developmental stages where no collagen secretion is known to occur. For example, this applies for the expression of Fmod in the forming somites of stage 9.5 postconception (p.c.), for Dcn and Lum in later stage embryos in the pituitary gland and dorsal root ganglia, and for Bgn and Dcn during differentiation in the kidney. These studies provide further evidence for a role of these molecules during connective tissue organization but also for an involvement at specific sites of organ differentiation.

Bone morphogenetic protein-1 processes probiglycan

Bone morphogenetic protein-1 (BMP-1) is a metalloprotease that plays important roles in regulating the deposition of fibrous extracellular matrix in vertebrates, including provision of the procollagen C-proteinase activity that processes the major fibrillar collagens I-III. Biglycan, a small leucine-rich proteoglycan, is a nonfibrillar extracellular matrix component with functions that include the positive regulation of bone formation. Biglycan is synthesized as a precursor with an NH(2)-terminal propeptide that is cleaved to yield the mature form found in vertebrate tissues. Here, we show that BMP-1 cleaves probiglycan at a single site, removing the propeptide and producing a biglycan molecule with an NH(2) terminus identical to that of the mature form found in tissues. BMP-1-related proteases mammalian Tolloid and mammalian Tolloid-like 1 (mTLL-1) are shown to have low but detectable levels of probiglycan-cleaving activity. Comparison shows that wild type mouse embryo fibroblasts (MEFs) produce only fully processed biglycan, whereas MEFs derived from embryos homozygous null for the Bmp1 gene, which encodes both BMP-1 and mammalian Tolloid, produce predominantly unprocessed probiglycan, and MEFs homozygous null for both the Bmp1 gene and the mTLL-1 gene Tll1 produce only unprocessed probiglycan. Thus, all detectable probiglycan-processing activity in MEFs is accounted for by the products of these two genes.

Expression of the small leucine-rich proteoglycan osteoadherin/osteomodulin in human dental pulp and developing rat teeth

Because the extracellular matrices of dentin and bone are composed mainly of type I collagen, their characteristics are determined by the nature of noncollagenous proteins (NCPs). Among these NCPs, some proteoglycans (PGs) belong to the small leucine-rich proteoglycans (SLRPs). Recently, osteoadherin (OSAD) has been described as a new member of this family, that is expressed by mature bovine osteoblasts. Here, we report the expression of OSAD messenger RNA (mRNA) in human dental tissues and during the development of rat molars, using in situ hybridization. For this purpose, we constructed a probe for OSAD mRNA transcripts from human odontoblast cells cultured in vitro. Our results indicate that the mature human odontoblasts overexpress the OSAD gene as compared with cells present in the pulp core. In rat developing molars, mRNA transcripts were first detected in alveolar bone in 19-day-old embryos. At the same age, no signal was detected in any cell of the first molar. In more mature teeth (newborn and 2-day-old rats), OSAD expression starts in the polarized odontoblasts and increases in the secretory and mature odontoblasts, respectively. Interestingly, a similar pattern of expression was observed in the ameloblast layer responsible for the deposition of enamel mineralized matrix. Together, these results lead us to speculate that OSAD may be implicated in biomineralization processes.

Expression of the keratan sulfate proteoglycans lumican, keratocan and osteoglycin/mimecan during chick corneal development

The corneal proteoglycans belong to the Leu-rich proteoglycan (LRP) gene family and contain chondroitin/dermatan (CS/DS) or keratan sulfate (KS) chains. These proteoglycans play a critical role in generating and maintaining a transparent matrix within the corneal stroma. Decorin which has CS/DS chains and lumican which has KS chains, were first to be identified in the cornea. Two other corneal KS proteoglycans (KSPGs), keratocan and osteoglycin/mimecan were recently identified in bovine corneas. We cloned and sequenced chick osteoglycin/mimecan and found it to contain a stretch of 60 amino acids that showed no identity to the presumed mammalian homolog. The 177 base pair DNA coding for this unique sequence shows 47% identity to an 189 base pair sequence between exons 4 and 5 of the bovine osteoglycin/mimecan gene. This indicates that this cDNA represents an alternatively spliced form of osteoglycin/mimecan containing a unique N-terminal sequence. The expression of each of the three corneal KSPGs in the developing and mature chick cornea was investigated by competitive PCR and immuno-biochemical analysis of corneal extracts. Competitive PCR was used to determine the message levels for chick lumican, keratocan and osteoglycin in embryonic day 9, 12, 15, 18 and adult corneas. Results showed that lumican mRNA fluctuated during development but remained at a relatively high level while keratocan and osteoglycin message levels declined steadily from day 9 to adult. Additionally, lumican mRNA was present at higher levels, during all stages of corneal development, than keratocan and at much higher levels than osteoglycin. Antibodies shown to be specific for each KSPG were used to characterize proteoglycans isolated from embryonic and adult chick corneas. KSPGs from embryonic corneas eluted 1-2 fractions earlier on Q-Sepharose than KSPG from adult corneas. Additionally, Western blot analysis showed that embryonic KSPGs were more keratanase-resistant, endo-beta-galactosidase sensitive than adult KSPGs. The results of this study indicate an alteration in sulfation or the fine structure of the glycosaminoglycan chains occurs during corneal maturation for the 3 KSPGs.