Modulation of xylosyltransferase I expression provides a mechanism regulating glycosaminoglycan chain synthesis during cartilage destruction and repair

First Characterization of Human Dermal Fibroblasts Showing a Decreased Xylosyltransferase-I Expression Induced by the CRISPR/Cas9 System

BACKGROUND

Xylosyltransferases-I and II (XT-I and XT-II) catalyze the initial and rate limiting step of the proteoglycan (PG) biosynthesis and therefore have an import impact on the homeostasis of the extracellular matrix (ECM). The reason for the occurrence of two XT-isoforms in all higher organisms remains unknown and targeted genome-editing strategies could shed light on this issue.

METHODS

XT-I deficient neonatal normal human dermal fibroblasts were generated by using the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated proteins (Cas) 9 system. We analyzed if a reduced XT-I activity leads to abnormalities regarding ECM-composition, myofibroblast differentiation, cellular senescence and skeletal and cartilage tissue homeostasis.

RESULTS

We successfully introduced compound heterozygous deletions within exon 9 of the XYLT1 gene. Beside XYLT1, we detected altered gene-expression levels of further, inter alia ECM-related, genes. Our data further reveal a dramatically reduced XT-I protein activity. Abnormal myofibroblast-differentiation was demonstrated by elevated alpha-smooth muscle actin expression on both, mRNA- and protein level. In addition, wound-healing capability was slightly delayed. Furthermore, we observed an increased cellular-senescence of knockout cells and an altered expression of target genes knowing to be involved in skeletonization.

CONCLUSION

Our data show the tremendous relevance of the XT-I isoform concerning myofibroblast-differentiation and ECM-homeostasis as well as the pathophysiology of skeletal disorders.

Effect of Resveratrol on Serum Levels of Type II Collagen and Aggrecan in Patients with Knee Osteoarthritis: A Pilot Clinical Study

Treatment of knee osteoarthritis (OA) remains a challenging concern. Preclinical studies provided accumulating evidence on resveratrol efficacy in ameliorating degenerative articular damage. The present study was conducted to evaluate the effects of resveratrol as monotherapy on the serum level of type II collagen (Coll 2-1) and aggrecan in patients with knee osteoarthritis. The study was an open-labeled noncontrolled clinical trial. Resveratrol 500 mg/day in a single oral dose was given to the patients with knee osteoarthritis for 90 days. The serum levels of Coll-2-1, aggrecan, and biomarkers of inflammation were measured pre- and posttreatment. Hematological profiles and both hepatic and renal function markers were investigated at the baseline and at the end of the treatment for evaluating the tolerability and safety of resveratrol. Visual Analog Scale (VAS) for pain and Knee injury and Osteoarthritis Outcome Score (KOOS) for disease activity were clinically assessed monthly. Administration of 500 mg resveratrol for three months led to a nonsignificant decrease in the serum level of Coll 2-1 while a significant increase in aggrecan serum level. Resveratrol significantly improves pain score measured by VAS and KOOS after 30 days. Improvements in patients' activity and functional status were also evident at day 30 and kept on for three months which was reflected by KOOS subscale scores and with a significant improvement in all KOOS areas. In conclusion, oral administration of resveratrol as a monotherapy provides a remarkable improvement in the clinical status of the patients but has no significant effect on serum levels of Coll 2-1.

Fibronectin fragment inhibits xylosyltransferase-1 expression by regulating Sp1/Sp3- dependent transcription in articular chondrocytes

OBJECTIVE

We investigated the effects of 29-kDa amino-terminal fibronectin fragment (29-kDa FN-f) on xylosyltransferase-1 (XT-1), an essential anabolic enzyme that catalyzes the initial and rate-determining step in glycosaminoglycan chain synthesis, in human primary chondrocytes.

METHODS

Proteoglycan and XT-1 expression in cartilage tissue was analyzed using safranin O staining and immunohistochemistry. The effects of 29-kDa FN-f on XT-1 expression and its relevant signaling pathway were analyzed by quantitative real-time-PCR, immunoblotting, chromatin immunoprecipitation, and immunoprecipitation assays. The receptors for 29-kDa FN-f were investigated using small interference RNA and blocking antibodies.

RESULTS

The expression of XT-1 was significantly lower in human osteoarthritis cartilage than in normal cartilage. Intra-articular injection of 29-kDa FN-f reduced proteoglycan levels and XT-1 expression in murine cartilage. In addition, in 29-kDa FN-f-treated cells, XT-1 expression was significantly suppressed at both the mRNA and protein levels, modulated by the transcription factors specificity protein 1 (Sp1), Sp3, and activator protein 1 (AP-1). The 29-kDa FN-f suppressed the binding of Sp1 to the promoter region of XT-1 and enhanced the binding of Sp3 and AP-1. Inhibition of mitogen-activated protein kinase and nuclear factor kappa B signaling pathways restored the 29-kDa FN-f-inhibited XT-1 expression, along with the altered expression of Sp1 and Sp3. Blockading toll-like receptor 2 (TLR-2) and integrin α5β1 via siRNA and blocking antibodies revealed that the effects of 29-kDa FN-f on XT-1 expression were mediated through the TLR-2 and integrin α5β1 signaling pathways.

CONCLUSION

These results demonstrate that 29-kDa FN-f negatively affects cartilage anabolism by regulating glycosaminoglycan formation through XT-1.

Glycosaminoglycan synthesis in the nucleus pulposus: Dysregulation and the pathogenesis of disc degeneration

Few human tissues have functions as closely linked to the composition of their extracellular matrices as the intervertebral disc. In fact, the hallmark of intervertebral disc degeneration, commonly accompanying low back and neck pain, is the progressive loss of extracellular matrix molecules - specifically the GAG-substituted proteoglycans. While this loss is often associated with increased extracellular catabolism via metalloproteinases and pro-inflammatory cytokines, there is strong evidence that disc degeneration is related to dysregulation of the enzymes involved in GAG biosynthesis. In this review, we discuss those environmental factors, unique to the disc, that control expression and function of XT-1, GlcAT-I, and ChSy/ChPF in the healthy and degenerative state. Additionally, we address the pathophysiology of aberrant GAG biosynthesis and highlight therapeutic strategies designed to augment the loss of extracellular matrix molecules that afflict the degenerative state.

Synthetic Xylosides: Probing the Glycosaminoglycan Biosynthetic Machinery for Biomedical Applications

Glycosaminoglycans (GAGs) are polysaccharides ubiquitously found on cell surfaces and in the extracellular matrix (ECM). They regulate numerous cellular signaling events involved in many developmental and pathophysiological processes. GAGs are composed of complex sequences of repeating disaccharide units, each of which can carry many different modifications. The tremendous structural variations account for their ability to bind many proteins and thus, for their numerous functions. Although the sequence of GAG biosynthetic events and the enzymes involved mostly were deduced a decade ago, the emergence of tissue or cell specific GAGs from a nontemplate driven process remains an enigma. Current knowledge favors the hypothesis that macromolecular assemblies of GAG biosynthetic enzymes termed "GAGOSOMEs" coordinate polymerization and fine structural modifications in the Golgi apparatus. Distinct GAG structures arise from the differential channeling of substrates through the Golgi apparatus to various GAGOSOMEs. As GAGs perform multiple regulatory roles, it is of great interest to develop molecular strategies to selectively interfere with GAG biosynthesis for therapeutic applications. In this Account, we assess our present knowledge on GAG biosynthesis, the manipulation of GAG biosynthesis using synthetic xylosides, and the unrealized potential of these xylosides in various biomedical applications. Synthetic xylosides are small molecules consisting of a xylose attached to an aglycone group, and they compete with endogenous proteins for precursors and biosynthetic enzymes to assemble GAGs. This competition reduces endogenous proteoglycan-bound GAGs while increasing xyloside-bound free GAGs, mostly chondroitin sulfate (CS) and less heparan sulfate (HS), resulting in a variety of biological consequences. To date, hundreds of xylosides have been published and the importance of the aglycone group in determining the structure of the primed GAG chains is well established. However, the structure-activity relationship has long been cryptic. Nonetheless, xylosides have been designed to increase HS priming, modified to inhibit endogenous GAG production without priming, and engineered to be more biologically relevant. Synthetic xylosides hold great promise in many biomedical applications and as therapeutics. They are small, orally bioavailable, easily excreted, and utilize the host cell biosynthetic machinery to assemble GAGs that are likely nonimmunogenic. Various xylosides have been shown, in different biological systems, to have anticoagulant effects, selectively kill tumor cells, abrogate angiogenic and metastatic pathways, promote angiogenesis and neuronal growth, and affect embryonic development. However, most of these studies utilized the commercially available one or two β-D-xylosides and focused on the impact of endogenous proteoglycan-bound GAG inhibition on biological activity. Nevertheless, the manipulation of cell behavior as a result of stabilizing growth factor signaling with xyloside-primed GAGs is also reckonable but underexplored. Recent advances in the use of molecular modeling and docking simulations to understand the structure-activity relationships of xylosides have opened up the possibility of a more rational aglycone design to achieve a desirable biological outcome through selective priming and inhibitory activities. We envision these advances will encourage more researchers to explore these fascinating xylosides, harness the GAG biosynthetic machinery for a wider range of biomedical applications, and accelerate the successful transition of xyloside-based therapeutics from bench to bedside.

Ageing affects chondroitin sulfates and their synthetic enzymes in the intervertebral disc

The depletion of chondroitin sulfates (CSs) within the intervertebral disc (IVD) during degenerative disc disease (DDD) results in a decrease in tissue hydration, a loss of fluid movement, cell apoptosis, a loss of nerve growth inhibition and ultimately, the loss of disc function. To date, little is known with regards to the structure and content of chondroitin sulfates (CSs) during IVD ageing. The behavior of glycosaminoglycans (GAGs), specifically CSs, as well as xylosyltransferase I (XT-I) and glucuronyltransferase I (GT-I), two key enzymes involved in CS synthesis as a primer of glycosaminoglycan (GAG) chain elongation and GAG synthesis in the nucleus pulposus (NP), respectively, were evaluated in a bovine ageing IVD model. Here, we showed significant changes in the composition of GAGs during the disc ageing process (6-month-old, 2-year-old and 8-year-old IVDs representing the immature to mature skeleton). The CS quantity and composition of annulus fibrosus (AF) and NP were determined. The expression of both XT-I and GT-I was detected using immunohistochemistry. A significant decrease in GAGs was observed during the ageing process. CSs are affected at both the structural and quantitative levels with important changes in sulfation observed upon maturity, which correlated with a decrease in the expression of both XT-I and GT-I. A progressive switch of the sulfation profile was noted in both NP and AF tissues from 6 months to 8 years. These changes give an appreciation of the potential impact of CSs on the disc biology and the development of therapeutic approaches for disc regeneration and repair.

Identification of genes differentially expressed in menstrual breakdown and repair

STUDY QUESTION

Does the changing molecular profile of the endometrium during menstruation correlate with the histological profile of menstruation.

SUMMARY ANSWER

We identified several genes not previously associated with menstruation; on Day 2 of menstruation (early-menstruation), processes related to inflammation are predominantly up-regulated and on Day 4 (late-menstruation), the endometrium is predominantly repairing and regenerating.

WHAT IS KNOWN ALREADY

Menstruation is induced by progesterone withdrawal at the end of the menstrual cycle and involves endometrial tissue breakdown, regeneration and repair. Perturbations in the regulation of menstruation may result in menstrual disorders including abnormal uterine bleeding.

STUDY DESIGN, SIZE DURATION

Endometrial samples were collected by Pipelle biopsy on Days 2 (n = 9), 3 (n = 9) or 4 (n = 6) of menstruation.

PARTICIPANTS/MATERIALS, SETTING, METHODS

RNA was extracted from endometrial biopsies and analysed by genome wide expression Illumina Sentrix Human HT12 arrays. Data were analysed using 'Remove Unwanted Variation-inverse (RUV-inv)'. Ingenuity pathway analysis (IPA) and the Database for Annotation, Visualization and Integrated Discovery (DAVID) v6.7 were used to identify canonical pathways, upstream regulators and functional gene clusters enriched between Days 2, 3 and 4 of menstruation. Selected individual genes were validated by quantitative PCR.

MAIN RESULTS AND THE ROLE OF CHANCE

Overall, 1753 genes were differentially expressed in one or more comparisons. Significant canonical pathways, gene clusters and upstream regulators enriched during menstrual bleeding included those associated with immune cell trafficking, inflammation, cell cycle regulation, extracellular remodelling and the complement and coagulation cascade. We provide the first evidence for a role for glutathione-mediated detoxification (glutathione-S-transferase mu 1 and 2; GSTM1 and GSTM2) during menstruation. The largest number of differentially expressed genes was between Days 2 and 4 of menstruation (n = 1176). We identified several genes not previously associated with menstruation including lipopolysaccharide binding protein, serpin peptidase inhibitor, clade B (ovalbumin), member 3 (SERPINB3) and -4 (SERPINB4), interleukin-17C (IL17C), V-set domain containing T-cell activation inhibitor 1 (VTCN1), proliferating cell nuclear antigen factor (KIAA0101/PAF), trefoil factor 3 (TFF3), laminin alpha 2 (LAMA2) and serine peptidase inhibitor, Kazal type 1 (SPINK1). Genes related to inflammatory processes were up-regulated on Day 2 (early-menstruation), and those associated with endometrial repair and regeneration were up-regulated on Day 4 (late-menstruation).

LIMITATIONS, REASONS FOR CAUTION

Participants presented with a variety of endometrial pathologies related to bleeding status and other menstrual characteristics. These variations may also have influenced the menstrual process.

WIDER IMPLICATIONS OF THE FINDINGS

The temporal molecular profile of menstruation presented in this study identifies a number of genes not previously associated with the menstrual process. Our findings provide valuable insight into the menstrual process and may present novel targets for therapeutic intervention in cases of endometrial dysfunction.

LARGE SCALE DATA

All microarray data have been deposited in the public data repository Gene Expression Omnibus (GSE86003).

STUDY FUNDING AND COMPETING INTERESTS

Funding for this work was provided by a National Health and Medical Research Council of Australia (NHMRC) Project Grant APP1008553 to M.H., P.R. and J.G. M.H. is supported by an NHMRC Practitioner Fellowship. P.P. is supported by a NHMRC Early Career Fellowship. The authors have no conflict of interest to declare.

Heparan sulfate proteoglycans undergo differential expression alterations in right sided colorectal cancer, depending on their metastatic character

Background

Heparan sulfate proteoglycans (HSPGs) are complex molecules involved in the growth, invasion and metastatic properties of cancerous cells. This study analyses the alterations in the expression patterns of these molecules in right sided colorectal cancer (CRC), both metastatic and non-metastatic.

Methods

Twenty right sided CRCs were studied. A transcriptomic approach was used, employing qPCR to analyze both the expression of the enzymes involved in heparan sulfate (HS) chains biosynthesis, as well as the proteoglycan core proteins. Since some of these proteoglycans can also carry chondroitin sulfate (CS) chains, we include the study of the genes involved in the biosynthesis of these glycosaminoglycans. Immunohistochemical techniques were also used to analyze tissue expression of particular genes showing significant expression differences, of potential interest.

Results

Changes in proteoglycan core proteins differ depending on their location; those located intracellularly or in the extracellular matrix show very similar alteration patterns, while those located on the cell surface vary greatly depending on the nature of the tumor: glypicans 1, 3, 6 and betaglycan are affected in the non-metastatic tumors, whereas in the metastatic, only glypican-1 and syndecan-1 are modified, the latter showing opposing alterations in levels of RNA and of protein, suggesting post-transcriptional regulation in these tumors. Furthermore, in non-metastatic tumors, polymerization of glycosaminoglycan chains is modified, particularly affecting the synthesis of the tetrasaccharide linker and the initiation and elongation of CS chains, HS chains being less affected. Regarding the enzymes responsible for the modificaton of the HS chains, alterations were only found in non-metastatic tumors, affecting N-sulfation and the isoforms HS6ST1, HS3ST3B and HS3ST5. In contrast, synthesis of the CS chains suggests changes in epimerization and sulfation of the C4 and C2 in both types of tumor.

Conclusions

Right sided CRCs show alterations in the expression of HSPGs, including the expression of the cell surface core proteins, many glycosiltransferases and some enzymes that modify the HS chains depending on the metastatic nature of the tumor, resulting more affected in non-metastatic ones. However, matrix proteoglycans and enzymes involved in CS fine structure synthesis are extensively modified independetly of the presence of lymph node metastasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1724-9) contains supplementary material, which is available to authorized users.

Xylosyltransferase-1 expression is refractory to inhibition by the inflammatory cytokines tumor necrosis factor α and IL-1β in nucleus pulposus cells: novel regulation by AP-1, Sp1, and Sp3

We investigated whether expression of xylosyltransferase-1 (XT-1), a key enzyme in glycosaminoglycan biosynthesis, is responsive to disk degeneration and to inhibition by the inflammatory cytokines tumor necrosis factor α and IL-1β in nucleus pulposus (NP) cells. Analysis of human NP tissues showed that XT-1 expression is unaffected by degeneration severity; XT-1 and Jun, Fos, and Sp1 mRNA were positively correlated. Cytokines failed to inhibit XT-1 promoter activity and expression. However, cytokines decreased activity of XT-1 promoters containing deletion and mutation of the -730/-723 bp AP-1 motif, prompting us to investigate the role of AP-1 and Sp1/Sp3 in the regulation of XT-1 in healthy NP cells. Overexpression and suppression of AP-1 modulated XT-1 promoter activity. Likewise, treatment with the Sp1 inhibitors WP631 and mithramycin A or cotransfection with the plasmid DN-Sp1 decreased XT-1 promoter activity. Inhibitors of AP-1 and Sp1 and stable knockdown of Sp1 and Sp3 resulted in decreased XT-1 expression in NP cells. Genomic chromatin immunoprecipitation analysis showed AP-1 binding to motifs located at -730/-723 bp and -684/-677 bp and Sp1 binding to -227/-217 bp and -124/-114 bp in XT-1 promoter. These results suggest that XT-1 expression is refractory to the disease process and to inhibition by inflammatory cytokines and that signaling through AP-1, Sp1, and Sp3 is important in the maintenance of XT-1 levels in NP cells.

Glycosyltransferases and glycosaminoglycans in bleomycin and transforming growth factor-β1-induced pulmonary fibrosis

Glycosaminoglycan (GAG) chains of proteoglycans (PGs) play important roles in fibrosis through cell-matrix interactions and growth factor binding in the extracellular matrix. We investigated the expression and regulation of PG core protein (versican) and key enzymes (xylosyltransferase [XT]-I, β1,3-glucuronosyltransferase [GlcAT]-I, chondroitin-4-sulfotransferase [C4ST]) implicated in synthesis and sulfation of GAGs in bleomycin (BLM) and adenovirus-transforming growth factor (TGF)-β1-induced lung fibrosis in rats. We also studied the role of GlcAT-I or TGF-β1 and the signaling pathways regulating PG-GAG production in primary lung fibroblasts isolated from saline- or BLM-instilled rats. The mRNA for XT-I, GlcAT-I, C4ST, and versican was increased in the lung 14 days after BLM injury. In vitro studies indicate that fibrotic lung fibroblasts (FLFs) expressed more XT-I, C4ST, and chondroitin sulfate (CS)-GAGs than did normal lung fibroblasts at baseline. TGF-β1 enhanced the expression of XT-I, C4ST-I, and versican in normal lung fibroblasts, whereas SB203580 or SB431542, by targeting p38 mitogen-activated protein kinase or TGF-β type-1 receptor/activin receptor-like kinase 5, respectively, attenuated the response to both TGF-β1 and FLFs on PG-GAG expression. Neutralizing anti-TGF-β1 antibody abrogated FLF-conditioned medium-stimulated expression of XT-I, GlcAT-I, versican, and CS-GAG. Forced expression of TGF-β1 in vivo enhanced versican, XT-I, GlcAT-I, and C4ST-I expression and PG-GAG deposition in rat lungs. Finally, induced expression of GlcAT-I gene in rat lung fibroblasts increased GAG synthesis by these cells. Together, our results provide new insights into the basis for increased PG-GAG deposition in lung fibrosis; inhibition of TGF-β1-mediated or fibrosis-induced PG-GAG production by activin receptor-like kinase 5/p38 inhibitors may contribute to antifibrotic activity.

Effect of Angelica sinensis Polysaccharides on Osteoarthritis In Vivo and In Vitro: A Possible Mechanism to Promote Proteoglycans Synthesis

This study investigated the effect of Angelica sinensis polysaccharides (APS-3c) on rat osteoarthritis (OA) model in vivo and rat interleukin-1-beta- (IL-1β-) stimulated chondrocytes in vitro. APS-3c was administrated into rat OA knee joints and had protective effects on rat OA cartilage in vivo. Primary rat articular chondrocytes were cotreated with APS-3c and IL-1β   in vitro. 2~50 μg/mL APS-3c had no effect on chondrocytes viability, whereas it increased the proteoglycans (PGs) synthesis inhibited by IL-1β. Microarray analysis showed that the significant changes were concentrated in the genes which were involved in PGs synthesis. RT-PCR confirmed that treatment with APS-3c increased the mRNA expression of aggrecan and glycosyltransferases (GTs) inhibited by IL-1β but did not affect the mRNA expression of matrix-degrading enzymes. These results indicate that APS-3c can improve PGs synthesis of chondrocytes on rat OA model in vivo and IL-1β-stimulated chondrocytes in vitro, which is due to the promotion of the expression of aggrecan and GTs involved in PGs synthesis but not the inhibition of the expression of matrix-degrading enzymes. Our findings suggest the clinical relevance of APS-3c in the prospective of future alternative medical treatment for OA.

The effect of glucosamine sulfate on the proliferative potential and glycosaminoglycan synthesis of nucleus pulposus intervertebral disc cells

STUDY DESIGN

On the basis of the similarities in the structure of cartilage and intervertebral disc and on the property of glucosamine of being the building block for the construction of proteoglycan aggregates, we investigated the compound's role in the proliferation of nucleus pulposus cells under iso- and hyperosmotic conditions, the putative activation of signaling cascades, and the induction of glycosaminoglycan production.

OBJECTIVE

We examined the mode of action of glucosamine in nucleus pulposus cells.

SUMMARY OF BACKGROUND DATA

Glucosamine that naturally occurs in cartilage tissues has been widely used for treating osteoarthritis, but its role in nucleus pulposus cells is largely unknown.

METHODS

The effect of glucosamine sulfate on the viability and proliferation of nucleus pulposus cells was assessed by the microculture tetrazolium test (MTT) assay, direct cell counting, and tritiated thymidine incorporation. Changes in the expression and phosphorylation profile of selected proteins were estimated by Western analysis. Glycosaminoglycan production was measured using the Blyscan assay.

RESULTS

We showed that glucosamine sulfate up to 1 mM did not influence the viability, proliferation rate, or novel DNA synthesis of nucleus pulposus cells in the presence or absence of elevated osmolality but induced the transient phosphorylation of p38 mitogen-activated protein kinase. The highest concentration used (10 mM) negatively affected cellular proliferation and resulted in deactivation of extracellular signal-regulated kinases and c-Jun N-terminal kinases. Interestingly, these effects resulted from an additional hyperosmotic stress provoked by glucosamine alone. Finally, we found that a long-term incubation with glucosamine leads to an increase in the glycosaminoglycan content of nucleus pulposus cells.

CONCLUSION

Glucosamine sulfate was not found to reverse the high osmolality-mediated delay of proliferation in nucleus pulposus cells needed for the maintenance of the tissue's homeostasis. In addition, glycosaminoglycan synthesis stimulated by glucosamine provides a possible promising clinical role for treating disc degenerative disorders.

Regulation of xylosyltransferase I gene expression by interleukin 1β in human primary chondrocyte cells: mechanism and impact on proteoglycan synthesis

Xylosyltransferase I (XT-I) is an essential enzyme of proteoglycan (PG) biosynthesis pathway catalyzing the initial and rate-limiting step in glycosaminoglycan chain assembly. It plays a critical role in the regulation of PG synthesis in cartilage; however, little is known about underlying mechanism. Here, we provide evidence that, in human primary chondrocytes, IL-1β regulates XT-I gene expression into an early phase of induction and a late phase of down-regulation. Based on promoter deletions, the region up to -850 bp was defined as a major element of XT-I gene displaying both constitutive and IL-1β-regulated promoter activity. Point mutation and signaling analyses revealed that IL-1β-induced promoter activity is achieved through AP-1 response elements and mediated by SAP/JNK and p38 signaling pathways. Transactivation and chromatin immunoprecipitation assays indicated that AP-1 is a potent transactivator of XT-I promoter and that IL-1β-induced activity is mediated through increased recruitment of AP-1 to the promoter. Finally, we show that Sp3 is a repressor of XT-I promoter and bring evidence that the repressive effect of IL-1β during the late phase is mediated through Sp3 recruitment to the promoter. This suggests that modulation of Sp3 in cartilage could prevent IL-1β inhibition of PG synthesis and limit tissue degradation.

Incomplete elongation of the chondroitin sulfate linkage region on aggrecan and response to interleukin-1β

Aggrecan is the prominent proteoglycan in cartilage and is modified with approximately 100 chondroitin sulfate (CS) chains through a tetrasaccharide linkage structure. In osteoarthritis (OA), the viscoelastic properties of cartilage are compromised on both the quantity and integrity of aggrecan core protein expressed as well as reduced overall CS chain length. Herein, we postulated that chronic low-level inflammation may also contribute to OA progression by promoting regulatory mechanisms in early CS biosynthesis that yield incomplete linkage structures on aggrecan. To test this idea, chondrocytes extracted from human tali were cultured in alginate beads and challenged with 5 ng/mL IL-1β as a model for chronic inflammation leading to OA progression. Novel mass spectrometry-based methods were devised to detect and quantify partially elongated linkage structures relative to control cultures. The total mole fraction of unelongated xylose residues per aggrecan was significantly less (p = 0.03) after IL-1β treatment compared to control cultures, with unelongated xylose residues constituting between 6% and 12% of the fraction of total CS measured. A portion (<1%) of the partially elongated linkage structures was found to be either phosphorylated or sulfated. These results establish quantitative mass spectrometry as a very sensitive and effective platform for evaluating truncated proteoglycan linkage structures. Our observations using this method suggest a possible role for aberrant linkage structure elongation in OA progression.

Serum xylosyltransferase 1 level increases during early posttraumatic osteoarthritis in mice with high bone forming potential

Increased proteoglycan (PG) synthesis is essential for the stimulation of cartilage repair processes that take place during the reversible phase of osteoarthritis (OA). In articular cartilage, xylosyltransferase 1 (Xylt1) is the key enzyme that initiates glycosaminoglycan (GAG) chain synthesis by transferring the first sugar residue to the PG core protein. Biological activity of PGs is closely linked to GAG biosynthesis since their polyanionic nature directly contributes to the proper hydration and elastic properties of the cartilage tissue present at the articular interface. The aim of this study was to investigate whether variations in the level of Xylt1 present in serum can be used to predict OA disease progression. The influence of bone forming activity on the systemic release of this enzyme was addressed by experimentally-inducing OA in mice of two different genetic backgrounds that were previously characterized for their distinct bone metabolism: C57BL/6J (B6, high bone remodelers) or C3H/HeJ (C3H, high bone formers). Serum was collected after medial meniscectomy or sham surgeries in young adult mice of these two strains over a period of 3.5months at which point knee histopathology was assessed. A significant increase in serum Xylt1 levels observed shortly after meniscectomy positively correlated with severe cartilage damage evaluated by histological assessment at later time points in mice of the C3H background. In contrast, no temporal regulation of Xylt1 level was found between meniscectomies and control surgeries in B6 mice, which developed OA at a slower rate. Additionally, longitudinal evaluation of the serum levels of other markers of cartilage/bone metabolism (C1,2C, osteocalcin) did not reveal any association with late knee damages. Our results strongly support the idea that serum Xylt1 has a clinical value for monitoring risk of OA progression in young adults with high bone forming potential. Ultimately, the understanding of posttraumatic mechanisms regulating PG synthesis and their modification by GAG will be essential so that interventions that stimulate cartilage regrowth can be undertaken prior to irreversible destruction of the joint tissue. This article is part of a Special Issue entitled "Osteoarthritis".

Xylosyltransferase-I regulates glycosaminoglycan synthesis during the pathogenic process of human osteoarthritis

Loss of glycosaminoglycan (GAG) chains of proteoglycans (PGs) is an early event of osteoarthritis (OA) resulting in cartilage degradation that has been previously demonstrated in both huma and experimental OA models. However, the mechanism of GAG loss and the role of xylosyltransferase-I (XT-I) that initiates GAG biosynthesis onto PG molecules in the pathogenic process of human OA are unknown. In this study, we have characterized XT-I expression and activity together with GAG synthesis in human OA cartilage obtained from different regions of the same joint, defined as "normal", "late-stage" or adjacent to "late-stage". The results showed that GAG synthesis and content increased in cartilage from areas flanking OA lesions compared to cartilage from macroscopically "normal" unaffected regions, while decreased in "late-stage" OA cartilage lesions. This increase in anabolic state was associated with a marked upregulation of XT-I expression and activity in cartilage "next to lesion" while a decrease in the "late-stage" OA cartilage. Importantly, XT-I inhibition by shRNA or forced-expression with a pCMV-XT-I construct correlated with the modulation of GAG anabolism in human cartilage explants. The observation that XT-I gene expression was down-regulated by IL-1β and up-regulated by TGF-β1 indicates that these cytokines may play a role in regulating GAG content in human OA. Noteworthy, expression of IL-1β receptor (IL-1R1) was down-regulated whereas that of TGF-β1 was up-regulated in early OA cartilage. Theses observations may account for upregulation of XT-I and sustained GAG synthesis prior to the development of cartilage lesions during the pathogenic process of OA.

Injectable perlecan domain 1-hyaluronan microgels potentiate the cartilage repair effect of BMP2 in a murine model of early osteoarthritis

The goal of this study was to use bioengineered injectable microgels to enhance the action of bone morphogenetic protein 2 (BMP2) and stimulate cartilage matrix repair in a reversible animal model of osteoarthritis (OA). A module of perlecan (PlnD1) bearing heparan sulfate (HS) chains was covalently immobilized to hyaluronic acid (HA) microgels for the controlled release of BMP2 in vivo. Articular cartilage damage was induced in mice using a reversible model of experimental OA and was treated by intra-articular injection of PlnD1-HA particles with BMP2 bound to HS. Control injections consisted of BMP2-free PlnD1-HA particles, HA particles, free BMP2 or saline. Knees dissected following these injections were analyzed using histological, immunostaining and gene expression approaches. Our results show that knees treated with PlnD1-HA/BMP2 had lesser OA-like damage compared to control knees. In addition, the PlnD1-HA/BMP2-treated knees had higher mRNA levels encoding for type II collagen, proteoglycans and xylosyltransferase 1, a rate-limiting anabolic enzyme involved in the biosynthesis of glycosaminoglycan chains, relative to control knees (PlnD1-HA). This finding was paralleled by enhanced levels of aggrecan in the articular cartilage of PlnD1-HA/BMP2-treated knees. Additionally, decreases in the mRNA levels encoding for cartilage-degrading enzymes and type X collagen were seen relative to controls. In conclusion, PlnD1-HA microgels constitute a formulation improvement compared to HA for efficient in vivo delivery and stimulation of proteoglycan and cartilage matrix synthesis in mouse articular cartilage. Ultimately, PlnD1-HA/BMP2 may serve as an injectable therapeutic agent for slowing or inhibiting the onset of OA after knee injury.

Biological aspects of early osteoarthritis

PURPOSE

Early OA primarily affects articular cartilage and involves the entire joint, including the subchondral bone, synovial membrane, menisci and periarticular structures. The aim of this review is to highlight the molecular basis and histopathological features of early OA.

METHODS

Selective review of literature.

RESULTS

Risk factors for developing early OA include, but are not limited to, a genetic predisposition, mechanical factors such as axial malalignment, and aging. In early OA, the articular cartilage surface is progressively becoming discontinuous, showing fibrillation and vertical fissures that extend not deeper than into the mid-zone of the articular cartilage, reflective of OARSI grades 1.0-3.0. Early changes in the subchondral bone comprise a progressive increase in subchondral plate and subarticular spongiosa thickness. Early OA affects not only the articular cartilage and the subchondral bone but also other structures of the joint, such as the menisci, the synovial membrane, the joint capsule, ligaments, muscles and the infrapatellar fat pad. Genetic markers or marker combinations may become useful in the future to identify early OA and patients at risk.

CONCLUSION

The high socioeconomic impact of OA suggests that a better insight into the mechanisms of early OA may be a key to develop more targeted reconstructive therapies at this first stage of the disease.

LEVEL OF EVIDENCE

Systematic review, Level II.

Allergen-induced airway remodeling in brown norway rats: structural and metabolic changes in glycosaminoglycans

Increased proteoglycan (PG) deposition is a feature of airway remodeling in asthma. Glycosaminoglycans (GAGs) mediate many of the biological and mechanical properties of PGs by providing docking sites through their carbohydrate chains to bioactive ligands; therefore, it is imperative to define structural and metabolic changes of GAGs in asthma. Using a Brown Norway (BN) ovalbumin (OVA)-sensitized and -challenged rat model to induce airway remodeling, we found excessive deposition of chondroitin/dermatan (CS/DS)-, heparan (HS), and keratan (KS) sulfate GAGs in the airways and bronchoalveolar lavage cells of OVA-challenged rats. Disaccharide composition of CS/DS of OVA-challenged rats was significantly different compared with saline-treated (SAL) control rats, with increased levels of 0-, 6-, and 4-sulfated disaccharides. Increases in the amount and a change in the proportion of CS/DS versus HS GAGs were noted in OVA-challenged rats. The higher content and sulfation of CS/DS disaccharides was reflected by the increased expression of xylosyltransferase-I, β1,3-glucuronosyltransferase-I, chondroitin-4, and chondroitin-6 sulfotransferase genes and protein expression of xylosyltransferase-I and β1,3-glucuronosyltransferase-I in OVA-challenged rats. Genes encoding the core proteins of the CS/DS and KS-containing PGs, such as versican, biglycan, decorin, and lumican, were overexpressed in OVA-challenged rats. Our results suggest that GAG biosynthetic enzymes may be involved in the altered expression of GAGs in the airways and are potential targets for inhibiting excess PG-GAG deposition and the airway remodeling process in asthma.

Identification and characterization of the human xylosyltransferase I gene promoter region

Human xylosyltransferase I catalyzes the initial and rate-limiting step in the biosynthesis of glycosaminoglycans and proteoglycans. Furthermore, this enzyme has been shown to play a major role in the physiological development of bone and cartilage as well as in pathophysiological processes such as systemic sclerosis, dilated cardiomyopathy, or fibrosis. Here, we report for the first time the identification and characterization of the XYLT1 gene promoter region and important transcription factors involved in its regulation. Members of the activator protein 1 (AP-1) and specificity protein 1 (Sp1) family of transcription factors are necessary for the transcriptional regulation of the XYLT1 gene, which was proven by curcumin, tanshinone IIA, mithramycin A, and short interference RNA treatment. A stepwise 5' and 3' deletion of the predicted GC-rich promoter region, which lacks a TATA and/or CAAT box, revealed that a 531-bp core promoter element is able to drive the transcription on a basal level. A binding site for transcription factors of the AP-1 family, which is essential for full promoter activity, was identified by site-directed mutagenesis located 730 bp 5' of the translation initiation site. The ability of this site to bind members of the AP-1 family was further verified by electrophoretic mobility shift assays. A promoter element containing this binding site was able to drive the transcription to about 79-fold above control in SW1353 chondrosarcoma cells. Our findings provide a first insight into the regulation of the XYLT1 gene and may contribute to understanding the processes taking place during extracellular matrix formation and remodeling in health and disease.

Epigenetics: methylation-associated repression of heparan sulfate 3-O-sulfotransferase gene expression contributes to the invasive phenotype of H-EMC-SS chondrosarcoma cells

Heparan sulfate proteoglycans (HSPGs), strategically located at the cell-tissue-organ interface, regulate major biological processes, including cell proliferation, migration, and adhesion. These vital functions are compromised in tumors, due, in part, to alterations in heparan sulfate (HS) expression and structure. How these modifications occur is largely unknown. Here, we investigated whether epigenetic abnormalities involving aberrant DNA methylation affect HS biosynthetic enzymes in cancer cells. Analysis of the methylation status of glycosyltransferase and sulfotransferase genes in H-HEMC-SS chondrosarcoma cells showed a typical hypermethylation profile of 3-OST sulfotransferase genes. Exposure of chondrosarcoma cells to 5-aza-2'-deoxycytidine (5-Aza-dc), a DNA-methyltransferase inhibitor, up-regulated expression of 3-OST1, 3-OST2, and 3-OST3A mRNAs, indicating that aberrant methylation affects transcription of these genes. Furthermore, HS expression was restored on 5-Aza-dc treatment or reintroduction of 3-OST expression, as shown by indirect immunofluorescence microscopy and/or analysis of HS chains by anion-exchange and gel-filtration chromatography. Notably, 5-Aza-dc treatment of HEMC cells or expression of 3-OST3A cDNA reduced their proliferative and invading properties and augmented adhesion of chondrosarcoma cells. These results provide the first evidence for specific epigenetic regulation of 3-OST genes resulting in altered HSPG sulfation and point to a defect of HS-3-O-sulfation as a factor in cancer progression.