Deficient expression of the gene coding for decorin in a lethal form of Marfan syndrome

SIRT1 protects against aortic dissection by regulating AP-1/decorin signaling-mediated PDCD4 activation

Medial degeneration of aorta wall is the principal feature of aortic dissection (AD). Sirtuin 1 (SIRT1) plays essential protective effect on many aortic-associated disease. However, it is still unclear whether SIRT1participates in the process of medial degeneration-mediated AD. The purpose of this study is to explore the association between SIRT1 and AD process. qRT-PCR was used to evaluate the transcriptional level of genes involved in study. Protein levels and acetylation detection were measured by Western blotting. The regulatory relations between AP-1 and decorin was assessed by luciferase reporter gene assay. Acute aortic dissection (AAD) mice model was constructed by feeding with β-aminopropionitrile monofumarate (BAPN). Haematoxylin and eosin (HE) and Mallory staining were performed for pathological analysis. In clinical aorta tissue of thoracic aortic dissection (TAD), the expression of SIRT1, activator protein 1 (AP-1) and decorin were in accordant trend. AP-1 expression which acts on Decorin promoter region is possibly regulated in a SIRT1-mediated deacetylation dependent manner. Resveratrol or SRT1720-initiated SIRT1 activation ameliorated BAPN-induced AAD symptoms accompanied by the activation of AP-1/decorin signaling and decorin-mediated programmed cell death 4 (PDCD4) expression by inhibiting miR-21 and miR-181b. These data suggest that SIRT1/AP-1/decorin signal cascades possibly play a part role in the process of AD. Our research demonstrate that activation of SIRT1 protects against AAD symptoms by enhancing AP-1-mediated decorin expression and downstream PDCD4 signaling pathway. Possibly, SIRT1 is served as a protective factor of AD and targeting SIRT1 therapy might be an attractive therapeutic approaches for AD treatment.

The small leucine-rich repeat proteoglycans in tissue repair and atherosclerosis

Proteoglycans consist of a protein core with one or more covalently attached glycosaminoglycan (GAG) side chains and have multiple roles in the initiation and progression of atherosclerosis. Here we discuss the potential and known functions of a group of small leucine-rich repeat proteoglycans (SLRPs) in atherosclerosis. We focus on five SLRPs, decorin, biglycan, lumican, fibromodulin and PRELP, because these have been detected in atherosclerotic plaques or demonstrated to have a role in animal models of atherosclerosis. Decorin and biglycan are modified post-translationally by substitution with chondroitin/dermatan sulphate GAGs, whereas lumican, fibromodulin and PRELP have keratan sulphate side chains, and the core proteins have leucine-rich repeat (LRR) motifs that are characteristic of the LRR superfamily. The chondroitin/dermatan sulphate GAG side chains have been implicated in lipid retention in atherosclerosis. The core proteins are discussed here in the context of (i) interactions with collagens and their implications in tissue integrity, fibrosis and wound repair and (ii) interactions with growth factors, cytokines, pathogen-associated molecular patterns and cell surface receptors that impact normal physiology and disease processes such as inflammation, innate immune responses and wound healing (i.e. processes that are all important in plaque development and progression). Thus, studies of these SLRPs in the context of wound healing are providing clues about their functions in early stages of atherosclerosis to plaque vulnerability and cardiovascular disease at later stages. Understanding of signal transduction pathways regulated by the core protein interactions is leading to novel roles and therapeutic potential for these proteins in wound repair and atherosclerosis.

Histone Deacetylase 3 Coordinates Deacetylase-independent Epigenetic Silencing of Transforming Growth Factor-β1 (TGF-β1) to Orchestrate Second Heart Field Development

About two-thirds of human congenital heart disease involves second heart field-derived structures. Histone-modifying enzymes, histone deacetylases (HDACs), regulate the epigenome; however, their functions within the second heart field remain elusive. Here we demonstrate that histone deacetylase 3 (HDAC3) orchestrates epigenetic silencing of Tgf-β1, a causative factor in congenital heart disease pathogenesis, in a deacetylase-independent manner to regulate development of second heart field-derived structures. In murine embryos lacking HDAC3 in the second heart field, increased TGF-β1 bioavailability is associated with ascending aortic dilatation, outflow tract malrotation, overriding aorta, double outlet right ventricle, aberrant semilunar valve development, bicuspid aortic valve, ventricular septal defects, and embryonic lethality. Activation of TGF-β signaling causes aberrant endothelial-to-mesenchymal transition and altered extracellular matrix homeostasis in HDAC3-null outflow tracts and semilunar valves, and pharmacological inhibition of TGF-β rescues these defects. HDAC3 recruits components of the PRC2 complex, methyltransferase EZH2, EED, and SUZ12, to the NCOR complex to enrich trimethylation of Lys-27 on histone H3 at the Tgf-β1 regulatory region and thereby maintains epigenetic silencing of Tgf-β1 specifically within the second heart field-derived mesenchyme. Wild-type HDAC3 or catalytically inactive HDAC3 expression rescues aberrant endothelial-to-mesenchymal transition and epigenetic silencing of Tgf-β1 in HDAC3-null outflow tracts and semilunar valves. These findings reveal that epigenetic dysregulation within the second heart field is a predisposing factor for congenital heart disease.

Possible dual role of decorin in abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is characterized by chronic inflammation, which leads to pathological remodeling of the extracellular matrix. Decorin, a small leucine-rich repeat proteoglycan, has been suggested to regulate inflammation and stabilize the extracellular matrix. Therefore, the present study investigated the role of decorin in the pathogenesis of AAA. Decorin was localized in the aortic adventitia under normal conditions in both mice and humans. AAA was induced in mice using CaCl2 treatment. Initially, decorin protein levels decreased, but as AAA progressed decorin levels increased in all layers. Local administration of exogenous decorin prevented the development of CaCl2-induced AAA. However, decorin was highly expressed in the degenerative lesions of human AAA walls, and this expression positively correlated with matrix metalloproteinase (MMP)-9 expression. In cell culture experiments, the addition of decorin inhibited secretion of MMP-9 in vascular smooth muscle cells, but had the opposite effect in macrophages. The results suggest that decorin plays a dual role in AAA. Adventitial decorin in normal aorta may protect against the development of AAA, but macrophages expressing decorin in AAA walls may facilitate the progression of AAA by up-regulating MMP-9 secretion.

Pathogenesis of mitral valve disease in mucopolysaccharidosis VII dogs

Mucopolysaccharidosis VII (MPS VII) is due to the deficient activity of β-glucuronidase (GUSB) and results in the accumulation of glycosaminoglycans (GAGs) in lysosomes and multisystemic disease with cardiovascular manifestations. The goal here was to determine the pathogenesis of mitral valve (MV) disease in MPS VII dogs. Untreated MPS VII dogs had a marked reduction in the histochemical signal for structurally-intact collagen in the MV at 6 months of age, when mitral regurgitation had developed. Electron microscopy demonstrated that collagen fibrils were of normal diameter, but failed to align into large parallel arrays. mRNA analysis demonstrated a modest reduction in the expression of genes that encode collagen or collagen-associated proteins such as the proteoglycan decorin which helps collagen fibrils assemble, and a marked increase for genes that encode proteases such as cathepsins. Indeed, enzyme activity for cathepsin B (CtsB) was 19-fold normal. MPS VII dogs that received neonatal intravenous injection of a gamma retroviral vector had an improved signal for structurally-intact collagen, and reduced CtsB activity relative to that seen in untreated MPS VII dogs. We conclude that MR in untreated MPS VII dogs was likely due to abnormalities in MV collagen structure. This could be due to upregulation of enzymes that degrade collagen or collagen-associated proteins, to the accumulation of GAGs that compete with proteoglycans such as decorin for binding to collagen, or to other causes. Further delineation of the etiology of abnormal collagen structure may lead to treatments that improve biomechanical properties of the MV and other tissues.

ADAMTS-1 and ADAMTS-4 levels are elevated in thoracic aortic aneurysms and dissections

BACKGROUND

ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) is a recently identified family of extracellular metalloproteinases that has been shown to participate in tissue destruction. We hypothesized that ADAMTS-1 and ADAMTS-4 expression is increased in aortic tissues from patients with thoracic aortic aneurysms and dissections.

METHODS

We examined ADAMTS-1 and ADAMTS-4 expression in human descending thoracic aortic aneurysms (n = 14), chronic descending thoracic aortic dissections (n = 16), and descending thoracic aortas from age-matched control organ donors (n = 12). In these tissues, we also evaluated the degradation of versican, a proteoglycan substrate of ADAMTS-1 and ADAMTS-4. In cultured macrophages, we examined whether ADAMTS-4 functions in macrophage infiltration by using a transwell assay.

RESULTS

ADAMTS-1 and ADAMTS-4 protein and mRNA expression was significantly higher in thoracic aortic aneurysm and dissection tissues than in control aortic tissues. Double immunofluorescence staining showed the expression of ADAMTS-1 and ADAMTS-4 in smooth muscle cells and macrophages. Consistent with the upregulation of ADAMTS-1 and ADAMTS-4 in thoracic aortic aneurysm and dissection tissues, versican was degraded significantly more in these tissues than in control aortic tissues. In cultured macrophages, transforming growth factor-β increased ADAMTS-4 protein levels and induced macrophage invasion, and the knockdown of ADAMTS-4 reduced cell invasion.

CONCLUSIONS

Increased expression of ADAMTS proteins may promote thoracic aortic aneurysm progression by degrading versican and facilitating macrophage invasion.

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 in atherosclerosis

Atherosclerotic cardiovascular disease is a major cause of morbidity and mortality in the Western world. Despite tremendous strides in understandings its pathogenesis, it still remains a challenge because of gaps in our understanding of its initiation, progression and complications leading to the clinical syndromes of angina, acute coronary syndrome, cerebrovascular disease and peripheral vascular disease. Recent studies have provided impetus on the shift from models of atherosclerosis based on cellular interactions to models where the important role of extracellular matrix is recognized. Proteoglycans, especially those belonging to the small leucine-rich proteoglycan family of which decorin is a representative example, have come under close scrutiny for their role in atherogenesis. There is evidence from in vitro and in vivo animal models as well as humans to suggest an important role of decorin in attenuating progression of atherosclerosis. Decorin distribution in different blood vessels has been shown to inversely correlate with the tendency to develop atherosclerosis. Decorin seems to interact closely with different cellular components of the plaque milieu, thereby suggesting its role in influencing atherogenesis at different steps. Here we review the current understanding of the role of decorin in the pathogenesis of atherosclerosis.

Serpina3n attenuates granzyme B-mediated decorin cleavage and rupture in a murine model of aortic aneurysm

Granzyme B (GZMB) is a proapoptotic serine protease that is released by cytotoxic lymphocytes. However, GZMB can also be produced by other cell types and is capable of cleaving extracellular matrix (ECM) proteins. GZMB contributes to abdominal aortic aneurysm (AAA) through an extracellular, perforin-independent mechanism involving ECM cleavage. The murine serine protease inhibitor, Serpina3n (SA3N), is an extracellular inhibitor of GZMB. In the present study, administration of SA3N was assessed using a mouse Angiotensin II-induced AAA model. Mice were injected with SA3N (0–120 μg/kg) before pump implantation. A significant dose-dependent reduction in the frequency of aortic rupture and death was observed in mice that received SA3N treatment compared with controls. Reduced degradation of the proteoglycan decorin was observed while collagen density was increased in the aortas of mice receiving SA3N treatment compared with controls. In vitro studies confirmed that decorin, which regulates collagen spacing and fibrillogenesis, is cleaved by GZMB and that its cleavage can be prevented by SA3N. In conclusion, SA3N inhibits GZMB-mediated decorin degradation leading to enhanced collagen remodelling and reinforcement of the adventitia, thereby reducing the overall rate of rupture and death in a mouse model of AAA.

Pathway analysis of differentially expressed genes in patients with acute aortic dissection

Background

Acute aortic dissection (AAD) is a life-threatening condition with high mortality and a relatively unclarified pathophysiological mechanism. Although differentially expressed genes in AAD have been recognized, interactions between these genes remain poorly defined. This study was conducted to gain a better understanding of the molecular mechanisms underlying AAD and to support the future development of a clinical test for monitoring patients at high risk.

Materials and Methods

Aortic tissue was collected from 19 patients with AAD (mean age 61.7 ± 13.1 years), and from eight other patients (mean age 32.9 ± 12.2 years) who carried the mutated gene for Marfan syndrome (MS). Six patients (mean age 56.7 ± 12.3 years) served as the control group. The PIQOR^TM Immunology microarray with 1076 probes in quadruplicates was utilized; the differentially expressed genes were analysed in a MedScan search using Pathway Assist software. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and protein analysis were performed.

Results

Interactions of MS fibrillin-1 (FBN1) in the MedScan pathway analysis showed four genes, fibulin-1 (FBLN1), fibulin-2 (FBLN2), decorin (DCN) and microfibrillar associated protein 5 (MFAP5), which were differentially expressed in all tissue from AAD. The validation of these genes by qRT-PCR revealed a minimum of three-fold downregulation of FBLN1 (0.5 ± 0.4 vs. 6.1 ± 2.3 fold, p = 0.003) and of DCN (2.5 ± 1.0 vs. 8.5 ± 4.7 fold, p = 0.04) in AAD compared to MS and control samples.

Conclusions

Downregulation of fibrillin-1 (FBN1) may weaken extracellular components in the aorta and/or interfer with the transmission of cellular signals and eventually cause AAD. Additional research on these four identified genes can be a starting point to develop a diagnostic tool.

Decorin-mediated regulation of fibrillin-1 in the kidney involves the insulin-like growth factor-I receptor and Mammalian target of rapamycin

Decorin, a small leucine-rich proteoglycan, affects the synthesis of the elastic fiber component fibrillin-1 in the kidney via hitherto unknown mechanisms. Here, we show that decorin binds to and induces phosphorylation of insulin-like growth factor-I (IGF-I) receptor in renal fibroblasts. Inhibition of the IGF-I receptor tyrosine kinase and its downstream target phosphoinositide-3 kinase prevented decorin-mediated synthesis of fibrillin-1. Furthermore, decorin induced phosphorylation of phosphoinositide-dependent kinase 1, protein kinase B/Akt, mammalian target of rapamycin (mTOR), and p70 S6 kinase. Accordingly, the enhanced synthesis of fibrillin-1 was blocked by rapamycin, an inhibitor of mTOR. Notably, IGF-I, which signals through the same pathway, also stimulated fibrillin-1 synthesis. Systemic administration of rapamycin to mice subjected to unilateral ureteral obstruction, a model of renal fibrosis and increased fibrillin-1 synthesis, markedly reduced the number of interstitial fibroblasts and fibrillin-1 deposition. In streptozotocin-induced diabetes, IGF-I receptor was up-regulated in the kidneys from decorin-null mice. However, this could not compensate for the decorin deficiency, resulting ultimately in decreased fibrillin-1 content. This study provides evidence for the involvement of decorin and the IGF-I receptor/mTOR/p70 S6 kinase signaling pathway in the translational regulation of fibrillin-1.

Decorina e Condroitim sulfato na remodelação da matriz extracelular do línquen escleroso vulvar

FUNDAMENTOS: O líquen escleroso (LS) apresenta zona de hialinização do colágeno na derme superior característica, que persiste pouco definida do ponto de vista morfológico e cujo significado permanece sem explicação. Já se pôde demonstrar que no LS há profundas modificações da matriz extracelular (MEC), com acúmulo de proteínas colagênicas e de glicosaminoglicanos sulfatados na região hialina. OBJETIVOS: Caracterizar morfologicamente a presença nessa zona de decorina e condroitim sulfato que, ao interagir com as fibrilas colágenas, entre outras proteínas matriciais, poderiam contribuir para essa peculiar apresentação da MEC. MÉTODOS: 31 casos de LS vulvar foram subdivididos segundo a gradação histológica de Hewitt e analisados por imuno-histoquímica utilizando anticorpos contra decorina e condroitim sulfato revelados pela diaminobenzidina. Esses resultados foram comparados aos do grupo controle constituído por fragmentos de retalhos cutâneos excisados durante cirurgias corretivas da região vulvoperineal. RESULTADOS: Ocorreu predomínio da decorina quando a matriz apresentava um aspecto frouxo/edematoso, e o condroitim sulfato foi mais evidente quando a MEC assumia um padrão compacto, parecendo que ambos contribuem para o aspecto hialino, porém em fases diferentes da patogenia dessa doença. CONCLUSÕES: A seqüência observada na síntese desses proteoglicanos/glicosaminoglicanos levou à suposição de que a decorina seja um possível marcador precoce do LS vulvar e de que o condroitim sulfato possa estar relacionado à contenção da alteração matricial no nível da derme média.

How genetic is school myopia?

Myopia is of diverse aetiology. A small proportion of myopia is clearly familial, generally early in onset and of high level, with defined chromosomal localisations and in some cases, causal genetic mutations. However, in economically developed societies, most myopia appears during childhood, particularly during the school years. The chromosomal localisations characterised so far for high familial myopia do not seem to be relevant to school myopia. Family correlations in refractive error and axial length are consistent with a genetic contribution to variations in school myopia, but potentially confound shared genes and shared environments. High heritability values are obtained from twin studies, but rest on contestable assumptions, and require further critical analysis, particularly in view of the low heritability values obtained from parent-offspring correlations where there has been rapid environmental change between generations. Since heritability is a population-specific parameter, the values obtained on twins cannot be extrapolated to define the genetic contribution to variation in the general population. In addition, high heritability sets no limit to the potential for environmentally induced change. There is in fact strong evidence for rapid, environmentally induced change in the prevalence of myopia, associated with increased education and urbanisation. These environmental impacts have been found in all major branches of the human family, defined in modern molecular terms, with the exception of the Pacific Islanders, where the evidence is too limited to draw conclusions. The idea that populations of East Asian origin have an intrinsically higher prevalence of myopia is not supported by the very low prevalence reported for them in rural areas, and by the high prevalence of myopia reported for Indians in Singapore. A propensity to develop myopia in "myopigenic" environments thus appears to be a common human characteristic. Overall, while there may be a small genetic contribution to school myopia, detectable under conditions of low environmental variation, environmental change appears to be the major factor increasing the prevalence of myopia around the world. There is, moreover, little evidence to support the idea that individuals or populations differ in their susceptibility to environmental risk factors.

Regulation of fibrillin-1 by biglycan and decorin is important for tissue preservation in the kidney during pressure-induced injury

There is growing evidence that the two small leucine-rich proteoglycans biglycan and decorin regulate the assembly of connective tissues and alter cell behavior during development and pathological processes. In this study, we have used an experimental animal model of unilateral ureteral ligation and mice deficient in either biglycan or decorin. We discovered that pressure-induced injury to the wild-type kidneys led to overexpression of decorin, biglycan, fibrillin-1, and fibrillin-2. In contrast, in biglycan-deficient kidneys the overexpression of fibrillin-1 was markedly attenuated and this was associated with cystic dilatation of Bowman's capsule and proximal tubules. Notably, we found that in ligated kidneys from decorin-null mice, fibrillin-1 expression was initially enhanced to the same extent as in wild-type animals. However, long-term obstruction resulted in down-regulation of fibrillin-1 and concurrent cystic dilatation of Bowman's capsule in 33% of kidneys at 5 months after obstruction. In all of the genotypes, no differences in fibrillin-2 expression were observed. These in vivo data correlated with a significant induction of fibrillin-1 expression in renal fibroblasts and mesangial cells by recombinant biglycan and decorin. Our results indicate a novel role for decorin and biglycan during pressure-induced renal injury by stimulating fibrillin-1 expression.

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.

Deficiency of the decorin core protein in the variant form of Ehlers-Danlos syndrome with chronic skin ulcer

Decorin belongs to a family of small leucine-rich dermatan sulfate proteoglycans that are involved in the control of matrix organization and cell growth. Here, we described a patient whose skin glycosaminoglycans showed extremely decreased amount of dermatan sulfate compared with a normal control skin. This patient presented clinical features of Ehlers-Danlos syndrome with a chronic skin ulcer. Western blotting revealed that the deficiency of dermatan sulfate was due to the defect of decorin core protein. Beta-xyloside, an initiator of dermatan sulfate glycosaminoglycan chain elongation, enhanced the synthesis of dermatan sulfate in the fibroblasts of the patient to a similar extent to that of control. This result indicated that the enzymes for the elogation of dermatan sulfate side chains were normal. Northern blotting demonstrated remarkable reduction of decorin mRNA level, while biglycan mRNA level was concomitantly increased and procollagen alpha1(I) mRNA level was normal. cDNA and exons sequencing analysis showed there was no mutation in decorin gene of the patient. IL-1beta stimulated decorin expression to about 140% in control fibroblasts while about 110% in patient fibroblasts. On the other hand, TGF-beta1 resulted in 40% reductions of decorin expression in both control and patient fibroblasts. These data suggested that reduced decorin expression of fibroblasts from the patient of Ehlers-Danlos syndrome may be due to abnormalities in the regulatory regions, which is responsible for the IL-1beta stimulation.

Differential expression of proteoglycans biglycan and decorin during neointima formation after stent implantation in normal and atherosclerotic rabbit aortas

Proteoglycans decorin and biglycan, which bind to TGF-beta, are thought to participate in regulation of extracellular matrix accumulation in arterial intimal hyperplasia. To investigate the correlation of these proteoglycans with the cellular localization and phenotypic modulation of smooth muscle cells (SMCs), we analyzed the spatial and chronological distribution of these proteoglycans and two cytokines, TGF-beta and IL-1beta, in the process of neointima formation after stent implantation in the aortas of rabbits fed a high-cholesterol diet (atherosclerotic group) or a regular diet (control group). We implanted metallic stents in the rabbit aortas and harvested the aortas 4-56 days later for immunohistochemical and mRNA in situ hybridization analyses. In the control group, TGF-beta and biglycan expression was in correspondence with the chronology and localization of embryonic SMCs. In the atherosclerotic group, TGF-beta and biglycan expression was sustained throughout the experimental period, which was in accord with the prolonged expression of embryonic SMCs. Decorin, which did not occur in neointima in the control group, appeared in the atherosclerotic aortas in the confined area of vascular SMCs surrounding the macrophages around the stent wire. These results indicate that biglycan and decorin kinetics during neointima formation after arterial injury are distinct, despite their similar construction; biglycan synthesis correlates with embryonic SMCs.

A regulatory role of fibroblast growth factor in the expression of decorin, biglycan, betaglycan and syndecan in osteoblasts from patients with Crouzon's syndrome

Bone development is controlled by the autocrine and/or paracrine effects of regulatory molecules. We previously showed that the phenotype of fibroblasts obtained from patients affected by Crouzon's syndrome, an autosomal dominant disease characterized by pathological skull bone development, differed from that of normal cells and was regulated by interleukin treatments. The changes in the relative concentrations of extracellular macromolecules (glycosaminoglycans-GAG, collagen and fibronectin) were associated with abnormal interleukin secretion that affected the microenvironment where the osteogenic processes take place. Mutations in human fibroblast growth factor receptors are now thought to be involved in Crouzon's syndrome. Since coactivation of interleukins and basic fibroblast growth factor (bFGF) is probably implicated in morphogenetic and osteogenic processes and heparan sulphate proteoglycans have a critical role in regulating bFGF activity, the phenotypes of normal and Crouzon osteoblasts were studied and the effects of bFGF on the expression of bFGF, procollagen alpha1 (I), and proteoglycan (PG) genes for biglycan, decorin, betaglycan and syndecan analyzed. Specific human cDNA probes were used to screen the relative levels of mRNA by Northern analysis. Spontaneous or bFGF-modulated release of interleukins was also assayed. The bFGF gene transcript was detected only in Crouzon osteoblasts. We showed for the first time that Crouzon osteoblasts, despite a mutation in the FGF receptor, still responded to exogenous bFGE In fact, the growth factor induced changes in the GAG profile and in the levels of mRNA coding for PG and procollagen alpha1 (I) and down-regulated heparan sulfate GAG chains. ELISA showed that bFGF-induced interleukin secretion differed in normal and Crouzon osteoblasts. The observed differences in PG core protein, procollagen alpha1 (I) and bFGF could be associated with the Crouzon bone phenotype and also should provide further understanding on the molecular basis of the diseased state of bone.

Leucine-rich repeat glycoproteins of the extracellular matrix

The extracellular matrix plays an integral role in the pivotal processes of development, tissue repair, and metastasis by regulating cell proliferation, differentiation, adhesion, and migration. This review is focused on a family of related glycoproteins represented by at least one member in all specialized extracellular matrices. This family currently comprises nine members grouped together on the basis of their presence in the extracellular matrix and by virtue of a leucine-rich repeat motif that dominates the structure of the core protein. It is likely that most, if not all the members of this group exist as proteoglycans in some tissues, and thus have been termed the Small Leucine-Rich Proteoglycan family, or SLRPs. The leucine-rich repeat (LRR) is usually present in tandem array and has been described in an increasing number of proteins, giving rise to a LRR-superfamily. The LRR domain of the SLRP family is unique within the superfamily in that it is flanked by cysteine clusters, and the 24 amino acid consensus for SLRP members is x-x-I/V/L-x-x-x-x-F/P/L-x-x-L/P-x-x-L-x-x-L/I-x-L-x-x-N-x-I/L, where x is any amino acid. Enormous progress has been made in describing the membership, structure and localization of this family, and recently new insight has emerged into the putative function of these molecules not just as modulators of matrix assembly but also on their intriguing role in regulating cell growth, adhesion, and migration. Determination of membership, structure and putative function of this fascinating class of molecules is summarized in this review.

Transforming growth factor-beta reverses deficient expression of type (I) collagen in cultured fibroblasts of a patient with metageria

Metageria is a generalized form of acrogeria belonging to the group of premature aging syndromes and is characterized by loss of subcutaneous fat, thinning of the dermis, multiple teleangiectasias and mottled hyperpigmentation. The skin changes present suggest that an altered formation of extracellular matrix might be involved in the pathogenesis of this disease. Fibroblasts obtained from the skin of a patient with this disease revealed a marked reduction of type I collagen expression to about 20% of control levels both at the mRNA and protein level. In addition decreased decorin but unchanged type IV collagen and fibronectin mRNA levels were found. Similar although less pronounced changes were observed in fibroblasts obtained from the sister of this patient showing skin changes compatible with acrogeria. To further analyze the deficient expression of type I collagen run on analysis was performed revealing a decrease of transcription of type I collagen. Incubation of the cells with transforming growth factor-beta, a strong inducer of type I collagen and extracellular matrix formation, restored type I collagen expression both at the mRNA and protein level to amounts comparable with normal skin fibroblasts. These results are consistent with a defect in type I collagen transcription that is readily reversed after incubation with transforming growth factor beta. The deficient synthesis of type I collagen and decorin by dermal fibroblasts might thus contribute to an altered formation of the extracellular matrix resulting in the poikilodermic skin changes observed in this patient.

Identification of a bimodal regulatory element encompassing a canonical AP-1 binding site in the proximal promoter region of the human decorin gene

We have previously described a tumor necrosis factor alpha (TNF-alpha) response element, located between residues -188 and -140 of the human decorin promoter, that mediates the inhibitory effect of TNF-alpha on decorin gene expression (Mauviel, A., Santra, M., Chen, Y.-Q., Uitto, J., and Iozzo, R. V. (1995) J. Biol. Chem. 270, 11692-11700). In this report, we demonstrate that interleukin 1 (IL-1), a pleiotropic cytokine that shares a wide variety of biological properties with TNF-alpha, uses the same cis element to up-regulate decorin gene expression. Specifically, IL-1 enhances the expression of the human decorin gene, and this effect is mediated by activation of the corresponding promoter, as shown in transient cell transfection experiments using decorin promoter-chloramphenicol acetyl transferase reporter gene constructs. Additional transfection experiments with various 5'-deletion promoter-chloramphenicol acetyltransferase constructs demonstrate that both the inhibitory effect of TNF-alpha and the stimulatory effect of IL-1 are mediated by a 48-base pair segment of the promoter, between residues -188 and -140. This region, which contains a canonical AP-1 binding site, TGAGTCA, allows an antagonistic effect of these two cytokines on the decorin promoter activity. When cloned upstream of the thymidine kinase promoter, this promoter fragment requires the AP-1 sequence to be responsive to IL-1. Supershift assays with various AP-1 antibodies identified c-Jun, Jun-B, and Fra-1 as components of the complex binding to the decorin promoter. Overexpression of c-jun, an oncogene encoding the c-Jun/AP-1 transcription factor, reduces the basal activity of both decorin and -188/-140 thymidine kinase promoter constructs. In contrast, blockage of c-jun expression with an antisense c-jun construct potentiates the stimulatory effect of IL-1 and reverses the response to TNF-alpha. These data indicate that the region between residues -188 and -140 of the human decorin promoter functions as a bimodal regulatory element and allows transcriptional repression by c-Jun/AP-1 complexes.

Delineation of the Marfan phenotype associated with mutations in exons 23-32 of the FBN1 gene

Marfan syndrome is a dominantly inherited connective tissue disorder with a wide range of phenotypic severity. The condition is the result of mutations in FBN1, a large gene composed of 65 exons encoding the fibrillin-1 protein. While mutations causing classic manifestations of Marfan syndrome have been identified throughout the FBN1 gene, the six previously characterized mutations resulting in the severe, perinatal lethal form of Marfan syndrome have clustered in exons 24-32 of the gene. We screened 8 patients with either neonatal Marfan syndrome or severe cardiovascular complications of Marfan syndrome for mutations in this region of the gene. Using intron-based exon-specific primers, we amplified exons 23-32 from genomic DNAs, screened these fragments by single-stranded conformational polymorphism analysis, and sequenced indicated exons. This analysis documented mutations in exons 25-27 of the FBN1 gene in 6 of these patients. These results, taken together with previously published FBN1 mutations in this region, further define the phenotype associated with mutations in exons 24-32 of the FBN1 gene, information important for the development of possible diagnostic tests and genetic counseling.

The bone mineral status of patients with Marfan syndrome

Osteopenia at the hip and low total body calcium content have been reported in women with Marfan syndrome. Using dual X-ray absorptiometry (DXA), we evaluated the lumbar spine L2-L4 and proximal femur bone mineral density (BMD,/cm2) in 32 women and 16 children with Marfan syndrome. The women were 38 +/- 10 (SD) years old (23-58 years); their mean height was 178.7 +/- 8 cm. The children (9 boys and girls were 9.9-17.5 years old. Children were tall for their ages but of normal weight. All subjects were moderately active, without previous nontraumatic fracture. In the women, BMD was reduced at L2-L4, femoral neck (fnk), trochanter (tr), and intertrochanter (intr) (p < 0.0001-0.006), compared with age-predicted values. Z scores for L2-L4 and for the fnk, tr, and intr, were -0.59 +/- 1.06,-1.25 +/- 0.99,-1.03 +/- 0.91, respectively. The average hip axis length (HAL) of 11.5 +/- 0.093 cm was at the 80th percentile for women. No significant change was observed in 1 year follow-up BMD measurements in 13 women (fnk = -0.23 +/- 2.3%/year; L2-L4 = -0.43 +/- 1.57%/year). In Marfan children, BMD correlated with age, height, and pubertal development. Femoral neck BMG was reduced (Z = -0.74 +/- 1.22,p < 0.05) with a nonsignificant trend toward decreased BMD at L2-L4 (Z = 33 +/- 1.48). Resorption markers in Marfan women were normal and did not correlate with bone status. We conclude that women with Marfan syndrome have both axial and peripheral osteopenia as well as an increased HAL. This combination of findings likely increases substantially their long-term risk for hip fracture. Presence of osteopenia in Marfan children indicates that the skeletal deficits of Marfan syndrome may reflect inadequate bone acquisition.

Transcriptional regulation of decorin gene expression. Induction by quiescence and repression by tumor necrosis factor-alpha

Decorin, a leucine-rich proteoglycan with ubiquitous tissue distribution, may play essential biological roles during inflammation and cancer growth through its ability to bind extracellular matrix constituents and growth factors. In this study, we demonstrate that decorin gene expression is greatly enhanced after normal diploid fibroblasts reach confluency and cease to proliferate. Elevation of decorin mRNA steady state levels was maintained for up to 16 days postconfluency. In vitro transcription analyses indicated enhanced transcriptional activity in quiescent fibroblasts when compared to cells harvested in their logarithmic phase of growth. This phenotypic trait was reversed by the exogenous addition of tumor necrosis factor-alpha (TNF-alpha). Furthermore, transforming growth factor-beta (TGF-beta) down-regulated decorin gene expression in an additive manner with TNF-alpha. Transient cell transfection assays using plasmid constructs harboring the decorin promoter linked to the chloramphenicol acetyltransferase reporter gene demonstrated a dose-dependent transcriptional repression by TNF-alpha. These findings were further corroborated by in vitro transcription experiments using nuclear extracts from control and TNF-alpha-treated quiescent fibroblasts. In contrast, the decorin promoter constructs failed to respond to TGF-beta, thus suggesting either post-transcriptional regulation by this growth factor or lack of TGF-beta-responsive elements. Further experiments with 5' deletion constructs showed two TNF-alpha response elements, one residing within the 5'-untranslated region (exon Ib), the other one between residues -188 and -140 of the decorin promoter. Collectively, our results indicate that TNF-alpha, through its ability to transcriptionally inhibit decorin gene expression in growth-arrested cells, may be a key modulator of the biological functions of this proteoglycan.

Small proteoglycans

In this review the structure and functions of two non-related proteoglycan families are discussed. One family represents a group of extracellular matrix macromolecules characterized by core proteins with leucine-rich repeat motifs. Within this family special attention is given to those members which carry chondroitin or dermatan sulfate glycosaminoglycan chains. The second family is characterized by repeat sequences of serine and glycine. Their members are products of a single core protein gene and are characteristic constituents of secondary vesicles in cells of the haematopoietic lineage.

The molecular basis of Marfan syndrome

The Marfan syndrome is an inherited, autosomal dominant disorder that affects the skeletal, ocular, and cardiovascular systems. Recent biochemical and genetic studies have demonstrated that this deadly genetic disorder arises from defects in the connective tissue protein fibrillin. Fibrillin is a component of microfibrils, structures found in the extracellular matrices of most tissues, including those affected in Marfan patients. The appearance of microfibrils in the matrix produced by Marfan patient fibroblasts is different from that of normal cells. Genetic linkage between the fibrillin gene and the Marfan phenotype has been established and the gene mapped to the same chromosomal position as the disease locus. In several instances, the disease has been associated with mutations in the fibrillin gene, confirming that defects in fibrillin cause the Marfan syndrome.

Platelet-derived growth factor and transforming growth factor-beta 1 differentially affect the synthesis of biglycan and decorin by monkey arterial smooth muscle cells

Platelet-derived growth factor (PDGF) and transforming growth factor-beta 1 (TGF-beta 1), two growth-regulatory peptides with opposite effects on arterial smooth muscle cell (ASMC) proliferation, were examined for their influence on the synthesis of two small chondroitin sulfate/dermatan sulfate proteoglycans (CS/DS PGs) called biglycan and decorin. Quiescent ASMCs treated with either PDGF or TGF-beta 1 for 24 hours increased [35S]sulfate incorporation into biglycan 3.3- and 2.9-fold, respectively, whereas the incorporation of [35S]sulfate into decorin was not significantly affected. Treatment with TGF-beta 1 but not PDGF more than doubled the steady-state level of messenger RNA (mRNA) transcripts hybridizing to a complementary DNA (cDNA) encoding biglycan. Both growth factors had little or no effect on steady-state levels of mRNA transcripts hybridizing to a decorin cDNA. Incorporation of [35S]sulfate into biglycan glycosaminoglycan (GAG) was maximal by 12 to 18 hours after either PDGF or TGF-beta 1 addition. Both PDGF and TGF-beta 1 increased the molecular sizes of biglycan and decorin. This increase was a result of the synthesis of longer GAG chains substituted on the core proteins of both PGs. PDGF but not TGF-beta 1 led to an increase of more than twofold in the ratio of 6'- to 4'-sulfated disaccharides in these newly synthesized GAG chains. These results indicate that PDGF and TGF-beta 1 have specific but different effects on the synthesis of small CS/DS PGs by monkey ASMCs in culture.

Small proteoglycans

In this review the structure and functions of two non-related proteoglycan families are discussed. One family represents a group of extracellular matrix macromolecules characterized by core proteins with leucine-rich repeat motifs. Within this family special attention is given to those members which carry chondroitin or dermatan sulfate glycosaminoglycan chains. The second family is characterized by repeat sequences of serine and glycine. Their members are products of a single core protein gene and are characteristic constituents of secretory vesicles in cells of the haematopoietic lineage.

An unusual patient with the neonatal Marfan phenotype and mitochondrial complex I deficiency

We report the case of a 16-month-old male with the neonatal appearance of Marfan syndrome (NMS), with dolichocephaly, a long midface, deep-set eyes, arachnodactyly, dislocated lenses and carciovascular abnormalities. The presence of persistent lactic acidosis led to studies which disclosed mitochondrial complex I deficiency. We speculate that this unusual association may be due to the combination of an inherited mutation affecting complex I activity along with a de novo mutation disrupting the corresponding locus and an adjacent NMS locus on the homologous autosome. The possibility that the phenotype observed in this patient is directly due to the mitochondrial defect cannot be excluded.

Deficiencies of fibrillin and decorin in fibroblast cultures of a patient with neonatal Marfan syndrome

Changes in the structure and metabolism of fibrillin, a microfibril associated protein, can result in classical Marfan syndrome, and reduced expression of decorin, a small extracellular chondroitin sulphate/dermatan sulphate proteoglycan, has been observed in fibroblasts of a patient with neonatally lethal Marfan syndrome. We have studied the synthesis of fibrillin and decorin in cultured fibroblasts of a further sporadic patient with neonatally lethal Marfan syndrome. Fibrillin immunoreactivity in the extracellular matrix of the patient's fibroblasts was markedly reduced, and the fibrillar pattern was absent, in spite of normal amounts of fibrillin mRNA. Decorin mRNA, synthesis, and immunoreactivity in the matrix were also reduced. The results indicate involvement of both fibrillin and decorin in the pathogenesis of neonatal Marfan syndrome in this patient, but do not indicate which is the primary defect. We speculate, however, that a structural defect of fibrillin leads to diminished incorporation of the protein into the extracellular matrix, and that underexpression of decorin is secondary to the primary fibrillin defect. Combined deficiency of fibrillin and decorin may be the cause of the severe clinical phenotype.

Genetic analysis of proteoglycan structure, function and metabolism

Significant progress has been made in understanding the structure, function, and metabolism of proteoglycans. Many of the advances derive from the application of recombinant DNA methodology to their core proteins and from the characterization of animal cell mutants altered in glycosaminoglycan synthesis.

Enhanced sulfated-proteoglycan core protein synthesis by incubation of rabbit chondrocytes with recombinant transforming growth factor-beta 1

Rabbit articular chondrocytes were incubated with recombinant transforming-growth-factor-beta 1 (rhTGF-beta 1) and its effect on newly synthesized proteoglycan measured. rhTGF-beta 1 stimulated proteoglycan synthesis at a concentration as low as 5 ng/ml without further increases in radiosulfate incorporation up to 50 ng/ml. The quantitative increase in radiosulfate incorporation in rh-TGF-beta 1-treated chondrocytes was greater in the cell-associated culture compartment than in the medium compartment. rhTGF-beta 1 promoted an increased proteoglycan retention in the cell-associated compartment as evidenced by an increase in the t1/2 of retention from 8 h to 11 h. Specific enhanced synthesis of [35S]-methionine-labeled core proteins was seen in rh-TGF-beta 1-treated chondrocytes. rh-TGF-beta 1 increased the synthesis of the 2 core proteins derived from hydrodynamically large proteoglycans. They possessed apparent molecular weights of greater than 480 kD and 390 kD after 3-5% acrylamide gel electrophoresis. A compartmental analysis revealed that the cell-associated culture compartment contained only the larger of the 2 core proteins derived from large proteoglycans. Two other core proteins with apparent molecular weights 52 kD and 46 kD were also stimulated by rhTGF-beta 1. These results indicated that TGF-beta probably plays a significant role in stimulating proteoglycan core protein synthesis in articular chondrocytes and therefore may be an important growth factor in the restoration of cartilage extracellular matrix after injury.

Extracellular matrix molecules and their receptors: an overview with special emphasis on periodontal tissues

Knowledge of extracellular matrix molecules and their cell receptors has increased exponentially during the last 2 decades. It is now known that the structure and function of each tissue is based on specific combinations of matrix molecules. The major constituents of the extracellular matrix are collagens, proteoglycans, and adhesive glycoproteins. The rapid development of biochemical, molecular biological, and immunological research has revealed a lot of interesting details pertaining to these molecules. Several new collagen types have been discovered. In addition to being responsible for the strength and form of tissues, each collagen type has specific sequences providing them with special features such as flexibility and the ability to interact with other matrix molecules and cells. Proteoglycans are another large group of matrix molecules with a variety of functions. Proteoglycans play an important role in tissue resilience and filtering. Some proteoglycans have a capacity to specifically bind other matrix molecules and growth factors, while others act as matrix receptors on the cell surface. An important part of regulation of the cell behavior is played by adhesive glycoproteins belonging to the fibronectin and laminin families. Several isoforms of fibronectin and laminin that result from alternative RNA splicing serve specific functions such as controlling the attachment, migration, and synthetic activity of cells. A major group of cell receptors for cell-matrix and cell-cell interactions is termed integrins. The integrins are cell surface proteins composed of two polypeptides whose structure dictates the specificity of each receptor. The cytoplasmic domain of the integrins interacts with cytoskeletal elements within the cell, and thereby relays the information from the extracellular space into the protein synthesis machinery. The expression of the integrins is controlled by the extracellular matrix and growth factors, most notably TGF beta. During periodontal diseases several aspects of the cell-matrix interactions may be disturbed. Therefore, an understanding of the special features of the extracellular matrix and their receptors in periodontal tissues is a prerequisite for developing new approaches to the prevention and treatment of periodontal diseases.