A gene expression profile for endochondral bone formation: oligonucleotide microarrays establish novel connections between known genes and BMP-2-induced bone formation in mouse quadriceps

FGF7 as an essential mediator for the onset of ankylosing enthesitis related to psoriatic dermatitis

IL-17A plays an important role in the pathology of psoriasis and psoriatic arthritis (PsA). However, the pathogenic association between the skin and joint manifestations in PsA is not completely understood. In this study, we initially observed that IL-17A and FGF7 induced endochondral ossification in the mouse entheseal histoculture. Importantly, the responses of endochondral ossification by IL-17A stimulation were strongly inhibited by the treatment of a blocking antibody to FGF receptor 2IIIb, which is the receptor of FGF7, suggesting that FGF7 acts as a downstream factor of IL-17A in the endochondral ossification in the culture. Next, using the animal PsA model, the administration of an anti-FGF receptor 2IIIb antibody resulted in significant suppression of ankylosing enthesitis but not dermatitis. Collectively, our findings indicate that augmented IL-17A in PsA dermatitis induces the elevation of FGF7 levels in joint enthesis and results in a non-redundant role of FGF7 signaling in the development of ankylosing enthesitis in PsA.

ENO1 regulates IL-1β-induced chondrocyte inflammation, apoptosis and matrix degradation possibly through the potential binding to CRLF1

In this study, we aim to investigate the role of enolase 1 (ENO1) in osteoarthritis (OA) pathogenic process and to uncover the underlying mechanism. To this end, we used IL-1β to induce an in vitro OA‑like chondrocyte model in human immortalized chondrocyte C-28/I2 cells. We manipulated the expression of ENO1 and cytokine receptor-like factor 1 (CRLF1) in IL-1β-induced C-28/I2 cells using siRNA and/or overexpression and tested their effects on IL-1β-induced pathologies including cell viability, apoptosis and inflammatory cytokine levels (IL-6 and TNF-α), and the expression of extracellular matrix-related enzymes and major mediators in the NF-κB signaling pathway (p-p65, p65, p-IκBα and IκBα). We used co-immunoprecipitation and immunofluorescence imaging to study a possible binding between ENO1 and CRLF1. Our data showed that IL-1β induction elevated ENO1 and CRLF1 expression in C-28/I2 cells. Silencing ENO1 or CRLF1 inhibited the IL-1β-induced cell viability damage, apoptosis, inflammation, and extracellular matrix degradation. The inhibitory effect of silencing ENO1 was reversed by CRLF1 overexpression, suggesting a functional connection between ENO1 and CRLF1, which could be attributed to a binding between these two partners. Our study could help validate the role of ENO1 in OA pathogenies and identify novel therapeutic targets for OA treatment.

Directed differentiation of human iPSCs into mesenchymal lineages by optogenetic control of TGF-β signaling

In tissue development and homeostasis, transforming growth factor (TGF)-β signaling is finely coordinated by latent forms and matrix sequestration. Optogenetics can offer precise and dynamic control of cell signaling. We report the development of an optogenetic human induced pluripotent stem cell system for TGF-β signaling and demonstrate its utility in directing differentiation into the smooth muscle, tenogenic, and chondrogenic lineages. Light-activated TGF-β signaling resulted in expression of differentiation markers at levels close to those in soluble factor-treated cultures, with minimal phototoxicity. In a cartilage-bone model, light-patterned TGF-β gradients allowed the establishment of hyaline-like layer of cartilage tissue at the articular surface while attenuating with depth to enable hypertrophic induction at the osteochondral interface. By selectively activating TGF-β signaling in co-cultures of light-responsive and non-responsive cells, undifferentiated and differentiated cells were simultaneously maintained in a single culture with shared medium. This platform can enable patient-specific and spatiotemporally precise studies of cellular decision making.

Identification of proteins and N-glycosylation sites of knee cartilage in Kashin-Beck disease compared with osteoarthritis

The aim of this study was to identify crucial proteins and N-glycosylated sites in the pathological mechanism of Kashin-Beck disease (KBD) compared with osteoarthritis (OA). Nine KBD knee subjects and nine OA knee subjects were selected for the study. Quantitative proteomics and N-glycoproteomics data of KBD and OA were obtained by protein and N-glycoprotein enrichment and LC-MS/MS analysis. Differentially expressed proteins or N-glycosylation sites were examined with a comparative analysis between KBD and OA. Total 2205 proteins were identified in proteomic analysis, of which 375 were significantly different. Among these, 121 proteins were up-regulated and 254 were down-regulated. In N-glycoproteomic analysis, 278 different N-glycosylated sites that were related to 187 N-glycoproteins were identified. Proteins and their N-glycosylated sites are associated with KBD pathological process including ITGB1, LRP1, ANO6, COL1A1, MXRA5, DPP4, and CSPG4. CRLF1 and GLG1 are proposed to associate with both KBD and OA pathological processes. Key pathways in KBD vs. OA proteomic and N-glycoproteomic analysis contained extracellular matrix receptor interaction, focal adhesion, phagosome, protein digestion, and absorption. N-glycosylation may influence the pathological process by affecting the integrity of chondrocytes or cartilage. It regulated the intercellular signal transduction pathway, which contributes to cartilage destruction in KBD.

A disease-driver population within interstitial cells of human calcific aortic valves identified via single-cell and proteomic profiling

Cellular heterogeneity of aortic valves complicates the mechanistic evaluation of the calcification processes in calcific aortic valve disease (CAVD), and animal disease models are lacking. In this study, we identify a disease-driver population (DDP) within valvular interstitial cells (VICs). Through stepwise single-cell analysis, phenotype-guided omic profiling, and network-based analysis, we characterize the DDP fingerprint as CD44highCD29+CD59+CD73+CD45low and discover potential key regulators of human CAVD. These DDP-VICs demonstrate multi-lineage differentiation and osteogenic properties. Temporal proteomic profiling of DDP-VICs identifies potential targets for therapy, including MAOA and CTHRC1. In vitro loss-of-function experiments confirm our targets. Such a stepwise strategy may be advantageous for therapeutic target discovery in other disease contexts.

CRLF1 and CLCF1 in Development, Health and Disease

Cytokines and their receptors have a vital function in regulating various processes such as immune function, inflammation, haematopoiesis, cell growth and differentiation. The interaction between a cytokine and its specific receptor triggers intracellular signalling cascades that lead to altered gene expression in the target cell and consequent changes in its proliferation, differentiation, or activation. In this review, we highlight the role of the soluble type I cytokine receptor CRLF1 (cytokine receptor-like factor-1) and the Interleukin (IL)-6 cytokine CLCF1 (cardiotrophin-like cytokine factor 1) during development in physiological and pathological conditions with particular emphasis on Crisponi/cold-induced sweating syndrome (CS/CISS) and discuss new insights, challenges and possibilities arising from recent studies.

Influences of the IL-6 cytokine family on bone structure and function

The IL-6 family of cytokines comprises a large group of cytokines that all act via the formation of a signaling complex that includes the glycoprotein 130 (gp130) receptor. Despite this, many of these cytokines have unique roles that regulate the activity of bone forming osteoblasts, bone resorbing osteoclasts, bone-resident osteocytes, and cartilage cells (chondrocytes). These include specific functions in craniofacial development, longitudinal bone growth, and the maintenance of trabecular and cortical bone structure, and have been implicated in musculoskeletal pathologies such as craniosynostosis, osteoporosis, rheumatoid arthritis, osteoarthritis, and heterotopic ossifications. This review will work systematically through each member of this family and provide an overview and an update on the expression patterns and functions of each of these cytokines in the skeleton, as well as their negative feedback pathways, particularly suppressor of cytokine signaling 3 (SOCS3). The specific cytokines described are interleukin 6 (IL-6), interleukin 11 (IL-11), oncostatin M (OSM), leukemia inhibitory factor (LIF), cardiotrophin 1 (CT-1), ciliary neurotrophic factor (CNTF), cardiotrophin-like cytokine factor 1 (CLCF1), neuropoietin, humanin and interleukin 27 (IL-27).

A Novel Approach to Safer Glucocorticoid Receptor-Targeted Anti-lymphoma Therapy via REDD1 (Regulated in Development and DNA Damage 1) Inhibition

Glucocorticoids are widely used for therapy of hematologic malignancies. Unfortunately, chronic treatment with glucocorticoids commonly leads to adverse effects including skin and muscle atrophy and osteoporosis. We found recently that REDD1 (regulated in development and DNA damage 1) plays central role in steroid atrophy. Here, we tested whether REDD1 suppression makes glucocorticoid-based therapy of blood cancer safer. Unexpectedly, approximately 50% of top putative REDD1 inhibitors selected by bioinformatics screening of Library of Integrated Network-Based Cellular Signatures database (LINCS) were PI3K/Akt/mTOR inhibitors. We selected Wortmannin, LY294002, and AZD8055 for our studies and showed that they blocked basal and glucocorticoid-induced REDD1 expression. Moreover, all PI3K/mTOR/Akt inhibitors modified glucocorticoid receptor function shifting it toward therapeutically important transrepression. PI3K/Akt/mTOR inhibitors enhanced anti-lymphoma effects of Dexamethasone in vitro and in vivo, in lymphoma xenograft model. The therapeutic effects of PI3K inhibitor+Dexamethasone combinations ranged from cooperative to synergistic, especially in case of LY294002 and Rapamycin, used as a previously characterized reference REDD1 inhibitor. We found that coadministration of LY294002 or Rapamycin with Dexamethasone protected skin against Dexamethasone-induced atrophy, and normalized RANKL/OPG ratio indicating a reduction of Dexamethasone-induced osteoporosis. Together, our results provide foundation for further development of safer and more effective glucocorticoid-based combination therapy of hematologic malignancies using PI3K/Akt/mTOR inhibitors.

ATDC5 cells as a model of cartilage extracellular matrix neosynthesis, maturation and assembly

Fibrillar collagens and proteoglycans (PGs) are quantitatively the major constituents of extracellular matrices (ECM). They carry numerous crucial post-translational modifications (PTMs) that tune the resulting biomechanical properties of the corresponding tissues. The mechanisms determining these PTMs remain largely unknown, notably because available established cell lines do not recapitulate much of the complexity of the machineries involved. ATDC5 cells are a model of chondrogenesis widely used for decades, but it remains described mostly at histological and transcriptional levels. Here, we asked to what extent this model recapitulates the events of ECM synthesis and processing occurring in cartilage. Insulin-stimulated ATDC5 cells exhibit up- or down-regulation of more than one-hundred proteins, including a number of known participants in chondrogenesis and major markers thereof. However, they also lack several ECM components considered of significant, yet more subtle, function in cartilage. Still, they assemble the large PG aggrecan and type II collagen, both carrying most of their in vivo PTMs, into an ECM. Remarkably, collagen crosslinking is fully lysyl oxidase (LOX)-dependent. The ATDC5 model recapitulates critical aspects of the cartilage ECM-processing machinery and should be useful to decipher the mechanisms involved. Proteomics data are available via ProteomeXchange with identifier PXD014121. SIGNIFICANCE: The present work provides the first proteome characterization of the ATDC5 chondrogenesis model, which has been used for decades in the field of cartilage biology. The results demonstrate the up- and down-regulation of more than one hundred proteins. Overall, specific drawbacks of the model are pointed out, that will be important to take into consideration for future studies. However, major cartilage components are massively assembled into an extracellular matrix and carry most of their post-translational modifications occurring in cartilage tissue. Unlike other available established cell lines, the ATDC5 model recapitulates major aspects of cartilage biosynthesis and should be useful in investigating the mechanisms that regulate collagen maturation events.

Skeletal Toxicity of Coplanar Polychlorinated Biphenyl Congener 126 in the Rat Is Aryl Hydrocarbon Receptor Dependent

Epidemiological evidence links polychlorinated biphenyls (PCBs) to skeletal toxicity, however mechanisms whereby PCBs affect bone are poorly studied. In this study, coplanar PCB 126 (5 μmol/kg) or corn oil vehicle was administered to N = 5 and 6 male and female, wild type (WT) or AhR -/- rats via intraperitoneal injection. Animals were sacrificed after 4 weeks. Bone length was measured; bone morphology was assessed by microcomputed tomography and dynamic histomorphometry. Reduced bone length was the only genotype-specific effect and only observed in males (p < .05). WT rats exposed to PCB 126 had reduced serum calcium, and smaller bones with reduced tibial length, cortical area, and medullary area relative to vehicle controls (p < .05). Reduced bone formation rate observed in dynamic histomorphometry was consistent with inhibition of endosteal and periosteal bone growth. The effects of PCB 126 were abolished in AhR -/- rats. Gene expression in bone marrow and shaft were assessed by RNA sequencing. Approximately 75% of the PCB-regulated genes appeared AhR dependent with 89 genes significantly (p < .05) regulated by both PCB 126 and knockout of the AhR gene. Novel targets significantly induced by PCB 126 included Indian hedgehog (Ihh) and connective tissue growth factor (Ctgf/Ccn2), which regulate chondrocyte proliferation and differentiation in the bone growth plate and cell-matrix interactions. These data suggest the toxic effects of PCB 126 on bone are mediated by AhR, which has direct effects on the growth plate and indirect actions related to endocrine disruption. These studies clarify important mechanisms underlying skeletal toxicity of dioxin-like PCBs and highlight potential therapeutic targets.

Biomarkers for Early Stages of Johne's Disease Infection and Immunization in Goats

Background: Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) is the causative agent of Johne's disease, a chronic enteric infection of ruminants. Infection occurs within the first few months of life but remains subclinical for an average of 2-5 years. Current diagnostics to detect early subclinical infections lack diagnostic sensitivity, which hinders disease control resulting in significant economic losses to the dairy industry worldwide. The pathophysiology of early infection with M. paratuberculosis is still not well understood and represents a key hurdle toward the development of better diagnostics. Methods: The present study employed a large-scale RNA-Sequencing technology to better understand early stages of M. paratuberculosis infection and immunization. Specifically, gene expression profiles of peripheral blood mononuclear cells (PBMCs) from infected or vaccinated goats were compared to controls. Results: When compared to the naïve control goats, we identified a large number of transcripts (N = 226, 1018, 1714) that were differentially expressed in the M. paratuberculosis-infected goats, goats vaccinated with live attenuated or inactivated vaccines. There were also 1133 differentially expressed (DE) transcripts between vaccinated goats and infected ones. Bioinformatics evaluation of the DE genes indicated the regulation of a large number of genes with immunity and inflammatory functions including IL-18BP, IFN-γ, IL-17A, NOS2, LIPG, and IL-22. Interestingly, a large number of goat genes (N = 667) were regulated whether live or inactivated vaccine were used. Some of the regulated genes (e.g., IL-17A, IFN-γ) continued its unique transcriptional profile up to 12 months post-challenge. Conclusion: Overall, transcriptome analysis of infected and/or immunized goats identified potential targets for developing early diagnostics for Johne's disease and a potential approach to differentiate infected from vaccinated animals. A similar approach could be used to analyze later stages of Johne's disease or other chronic infections.

Cyclic Tensile Strain Can Play a Role in Directing both Intramembranous and Endochondral Ossification of Mesenchymal Stem Cells

Successfully regenerating damaged or diseased bone and other joint tissues will require a detailed understanding of how joint specific environmental cues regulate the fate of progenitor cells that are recruited or delivered to the site of injury. The goal of this study was to explore the role of cyclic tensile strain (CTS) in regulating the initiation of mesenchymal stem cell/multipotent stromal cell (MSC) differentiation, and specifically their progression along the endochondral pathway. To this end, we first explored the influence of CTS on the differentiation of MSCs in the absence of any specific growth factor, and secondly, we examined the influence of the long-term application of this mechanical stimulus on markers of endochondral ossification in MSCs maintained in chondrogenic culture conditions. A custom bioreactor was developed to apply uniaxial tensile deformation to bone marrow-derived MSCs encapsulated within physiological relevant 3D fibrin hydrogels. Mechanical loading, applied in the absence of soluble differentiation factors, was found to enhance the expression of both tenogenic (COL1A1) and osteogenic markers (BMP2, RUNX2, and ALPL), while suppressing markers of adipogenesis. No evidence of chondrogenesis was observed, suggesting that CTS can play a role in initiating direct intramembranous ossification. During long-term culture in the presence of a chondrogenic growth factor, CTS was shown to induce MSC re-organization and alignment, increase proteoglycan and collagen production, and to enhance the expression of markers associated with endochondral ossification (BMP2, RUNX2, ALPL, OPN, and COL10A1) in a strain magnitude-dependent manner. Taken together, these findings indicate that tensile loading may play a key role in promoting both intramembranous and endochondral ossification of MSCs in a context-dependent manner. In both cases, this loading-induced promotion of osteogenesis was correlated with an increase in the expression of the osteogenic growth factor BMP2. The results of this study demonstrate the potent role that extrinsic mechanical loading plays in guiding stem cell fate, which must be carefully considered when designing cell and tissue-engineering therapies if they are to realize their clinical potential.

Deletion of the sclerotome-enriched lncRNA PEAT augments ribosomal protein expression

To define a complete catalog of the genes that are activated during mouse sclerotome formation, we sequenced RNA from embryonic mouse tissue directed to form sclerotome in culture. In addition to well-known early markers of sclerotome, such as Pax1, Pax9, and the Bapx2/Nkx3-2 homolog Nkx3-1, the long-noncoding RNA PEAT (Pax1 enhancer antisense transcript) was induced in sclerotome-directed samples. Strikingly, PEAT is located just upstream of the Pax1 gene. Using CRISPR/Cas9, we generated a mouse line bearing a complete deletion of the PEAT-transcribed unit. RNA-seq on PEAT mutant embryos showed that loss of PEAT modestly increases bone morphogenetic protein target gene expression and also elevates the expression of a large subset of ribosomal protein mRNAs.

Bone Morphogenetic Proteins and Their Receptors in the Eye

The human genome encodes at least 42 different members of the transforming growth factor-β superfamily of growth factors. Bone morphogenetic proteins (BMPs) are the largest subfamily of proteins within the transforming growth factor-β superfamily and are involved in numerous cellular functions including development, morphogenesis, cell proliferation, apoptosis, and extracellular matrix synthesis. This article first reviews BMPs and BMP receptors, BMP signaling pathways, and mechanisms controlling BMP signaling. Second, we review BMP and BMP receptor expression during embryonic ocular development/ differentiation and in adult ocular tissues. Lastly, future research directions with respect to BMP, BMP receptors, and ocular tissues are suggested.

[An updated review of 1p36 deletion (monosomy) syndrome]

The Monosomy 1p36 deletion syndrome is part of the group of diseases known as Rare Diseases. The objective of the present work is to review the characteristics of Monosomy 1p36 deletion syndrome. The monosomy 1p36 deletion syndrome phenotype includes: dysmorphic craniofacial features; large anterior fontanelle, unibrow, deep-set eyes, epicanthus, wide nasal root/bridge, mandible hypoplasia, abnormal location of the pinna, philtrum and pointed chin; neurological alterations: seizures and hydrocephalus (in some cases). Cerebral malformations: ventricular hypertrophy, increased subarachnoid space, morphological alterations of corpus callosum, cortical atrophy, delays in myelinisation, periventricular leukomalacia and periventricular heterotopia. These alterations produce intellectual disability and delays in motor growth, communication skills, language, social and adaptive behaviour. It is Hearing and vision impairments are also observed in subjects with this syndrome, as well as alterations of cardiac, endocrine and urinary systems and alterations at skin and skeletal level.

CONCLUSIONS

Approximately 100 cases have been documented since 1981. This rare disease is the most common subtelomeric-micro-deletion syndrome. In situ hybridization with fluorescence (FISH) and array-comparative genomic hybridization (CGH-array) are at present the two best diagnostic techniques. There is currently no effective medical treatment for this disease.

1p36 deletion syndrome: an update

Deletions of chromosome 1p36 affect approximately 1 in 5,000 newborns and are the most common terminal deletions in humans. Medical problems commonly caused by terminal deletions of 1p36 include developmental delay, intellectual disability, seizures, vision problems, hearing loss, short stature, distinctive facial features, brain anomalies, orofacial clefting, congenital heart defects, cardiomyopathy, and renal anomalies. Although 1p36 deletion syndrome is considered clinically recognizable, there is significant phenotypic variation among affected individuals. This variation is due, at least in part, to the genetic heterogeneity seen in 1p36 deletions which include terminal and interstitial deletions of varying lengths located throughout the 30 Mb of DNA that comprise chromosome 1p36. Array-based copy number variant analysis can easily identify genomic regions of 1p36 that are deleted in an affected individual. However, predicting the phenotype of an individual based solely on the location and extent of their 1p36 deletion remains a challenge since most of the genes that contribute to 1p36-related phenotypes have yet to be identified. In addition, haploinsufficiency of more than one gene may contribute to some phenotypes. In this article, we review recent successes in the effort to map and identify the genes and genomic regions that contribute to specific 1p36-related phenotypes. In particular, we highlight evidence implicating MMP23B, GABRD, SKI, PRDM16, KCNAB2, RERE, UBE4B, CASZ1, PDPN, SPEN, ECE1, HSPG2, and LUZP1 in various 1p36 deletion phenotypes.

MMP and TIMP temporal gene expression during osteocytogenesis

Osteocytes within bone differentiate from osteoblast precursors which reside in a mineralised extracellular matrix (ECM). Fully differentiated osteocytes are critical for bone development and function but the factors that regulate this differentiation process are unknown. The enzymes primarily responsible for ECM remodelling are matrix metalloproteinases (MMP); however, the expression and role of MMPs during osteocytogenesis is undefined. Here we used MLO-A5 cells to determine the temporal gene expressions of the MMP family and their endogenous inhibitors--tissue inhibitors of metalloproteinases (TIMPs) during osteocytogenesis. RT-qPCR revealed expression of 14 Mmps and 3 Timps in MLO-A5 cells. Mmp2, Mmp23 and Mmp28 were decreased concurrent with mineralisation onset (P < 0.05*). Mmp14 and Mmp19 mRNAs were also significantly increased at day 3 (P < 0.05*) before returning to baseline levels at day 6. Decreased expressions of Timp1, Timp2 and Timp3 mRNA were observed by day 6 compared to day 0 (P < 0.05*). To examine whether these changes are linked to osteocytogenesis, we determined Mmp/Timp mRNA expressions in mineralisation-limited conditions. RT-qPCR revealed that the previously observed decreases in Mmp2, Mmp23 and Mmp28 were not observed in these mineralisation-limited cultures, therefore closely linking these MMPs with osteocyte differentiation. Similarly, we found differential expression of Timp1, Timp2 and Timp3 mRNA in mineralisation-restricted cultures (P < 0.05*). In conclusion, we have identified several members of the MMP/TIMP families as regulators of ECM remodelling necessary for the acquisition of the osteocyte phenotype.

Microarray meta-analysis identifies evolutionarily conserved BMP signaling targets in developing long bones

In vertebrates, BMP signaling has been demonstrated to be sufficient for bone formation in several tissue contexts. This suggests that genes necessary for bone formation are expressed in a BMP signaling dependent manner. However, till date no gene has been reported to be expressed in a BMP signaling dependent manner in bone. Our aim was to identify such genes. On searching the literature we found that several microarray experiments have been conducted where the transcriptome of osteogenic cells in absence and presence of BMP signaling activation have been compared. However, till date, there is no evidence to suggest that any of the genes found to be upregulated in presence of BMP signaling in these microarray analyses is indeed a target of BMP signaling in bone. We wanted to utilize this publicly available information to identify candidate BMP signaling target genes in vivo. We performed a meta-analysis of six such comparable microarray datasets. This analysis and subsequent experiments led to the identification of five targets of BMP signaling in bone that are conserved both in mouse and chick. Of these Lox, Klf10 and Gpr97 are likely to be direct transcriptional targets of BMP signaling pathway. Dpysl3, is a novel BMP signaling target identified in our study. Our data demonstrate that Dpysl3 is important for osteogenic differentiation of mesenchymal cells and is involved in cell secretion. We have demonstrated that the expression of Dpysl3 is co-operatively regulated by BMP signaling and Runx2. Based on our experimental data, in silico analysis of the putative promoter-enhancer regions of Bmp target genes and existing literature, we hypothesize that BMP signaling collaborates with multiple signaling pathways to regulate the expression of a unique set of genes involved in endochondral ossification.

Domain structure and function of matrix metalloprotease 23 (MMP23): role in potassium channel trafficking

MMP23 is a member of the matrix metalloprotease family of zinc- and calcium-dependent endopeptidases, which are involved in a wide variety of cellular functions. Its catalytic domain displays a high degree of structural homology with those of other metalloproteases, but its atypical domain architecture suggests that it may possess unique functional properties. The N-terminal MMP23 pro-domain contains a type-II transmembrane domain that anchors the protein to the plasma membrane and lacks the cysteine-switch motif that is required to maintain other MMPs in a latent state during passage to the cell surface. Instead of the C-terminal hemopexin domain common to other MMPs, MMP23 contains a small toxin-like domain (TxD) and an immunoglobulin-like cell adhesion molecule (IgCAM) domain. The MMP23 pro-domain can trap Kv1.3 but not closely-related Kv1.2 channels in the endoplasmic reticulum, preventing their passage to the cell surface, while the TxD can bind to the channel pore and block the passage of potassium ions. The MMP23 C-terminal IgCAM domain displays some similarity to Ig-like C2-type domains found in IgCAMs of the immunoglobulin superfamily, which are known to mediate protein-protein and protein-lipid interactions. MMP23 and Kv1.3 are co-expressed in a variety of tissues and together are implicated in diseases including cancer and inflammatory disorders. Further studies are required to elucidate the mechanism of action of this unique member of the MMP family.

Modeling clear cell sarcomagenesis in the mouse: cell of origin differentiation state impacts tumor characteristics

Clear cell sarcoma (CCS) of tendons and aponeuroses is a deadly soft-tissue malignancy resembling melanoma, with a predilection for young adults. EWS-ATF1, the fusion product of a balanced chromosomal translocation between chromosomes 22 and 12, is considered the definitional feature of the tumor. Conditional expression of the EWS-ATF1 human cDNA in the mouse generates CCS-like tumors with 100% penetrance. Tumors, developed through varied means of initiating expression of the fusion oncogene, model human CCS morphologically, immunohistochemically, and by genome-wide expression profiling. We also demonstrate that although fusion oncogene expression in later stages of differentiation can transform mesenchymal progenitor cells and generate tumors resembling CCS generally, expression in cells retaining stem cell markers permits the full melanoma-related phenotype.

Intracellular trafficking of the KV1.3 potassium channel is regulated by the prodomain of a matrix metalloprotease

Matrix metalloproteases (MMPs) are endopeptidases that regulate diverse biological processes. Synthesized as zymogens, MMPs become active after removal of their prodomains. Much is known about the metalloprotease activity of these enzymes, but noncanonical functions are poorly defined, and functions of the prodomains have been largely ignored. Here we report a novel metalloprotease-independent, channel-modulating function for the prodomain of MMP23 (MMP23-PD). Whole-cell patch clamping and confocal microscopy, coupled with deletion analysis, demonstrate that MMP23-PD suppresses the voltage-gated potassium channel KV1.3, but not the closely related KV1.2 channel, by trapping the channel intracellularly. Studies with KV1.2-1.3 chimeras suggest that MMP23-PD requires the presence of the KV1.3 region from the S5 trans-membrane segment to the C terminus to modulate KV1.3 channel function. NMR studies of MMP23-PD reveal a single, kinked trans-membrane α-helix, joined by a short linker to a juxtamembrane α-helix, which is associated with the surface of the membrane and protected from exchange with the solvent. The topological similarity of MMP23-PD to KCNE1, KCNE2, and KCNE4 proteins that trap KV1.3, KV1.4, KV3.3, and KV3.4 channels early in the secretory pathway suggests a shared mechanism of channel regulation. MMP23 and KV1.3 expression is enhanced and overlapping in colorectal cancers where the interaction of the two proteins could affect cell function.

Role of cytokine receptor-like factor 1 in hepatic stellate cells and fibrosis

AIM

To elucidate the role of cytokine receptor-like factor 1 (CRLF1) in hepatic stellate cells and liver fibrosis.

METHODS

Rat hepatic stellate cells (HSCs) were isolated by Nykodenz gradient centrifugation and activated by culturing in vitro. Differentially expressed genes in quiescent and culture activated HSCs were identified using microarrays. Injections of carbon tetrachloride (CCl(4)) for 4 wk were employed to induce liver fibrosis. The degree of fibrosis was assessed by Sirius red staining. Adenovirus expressing CRLF1 was injected through tail vein into mice to achieve overexpression of CRLF1 in the liver. The same adenovirus was used to overexpress CRLF1 in quiescent HSCs cultured in vitro. Expression of CRLF1, CLCF1 and ciliary neurotrophic factor receptor (CNTFR) in hepatic stellate cells and fibrotic livers was analyzed by semi-quantitative reverse transcription-polymerase chain reaction and Western blotting. Expression of profibrotic cytokines and collagens was analyzed by the same method.

RESULTS

CRLF1 is a secreted cytokine with unknown function. Human mutations suggested a role in development of autonomous nervous system and a role of CRLF1 in immune response was implied by its similarity to interleukin (IL)-6. Here we show that expression of CRLF1 was undetectable in quiescent HSCs and was highly upregulated in activated HSCs. Likewise, expression of CRLF1 was very low in normal livers, but was highly upregulated in fibrotic livers, where its expression correlated with the degree of fibrosis. A cofactor of CLRF1, cardiotrophin-like cytokine factor 1 (CLCF1), and the receptor which binds CRLF1/CLCF1 dimer, the CNTFR, were expressed to similar levels in quiescent and activated HSCs and in normal and fibrotic livers, indicating a constitutive expression. Overexpression of CLRF1 alone in the normal liver did not stimulate expression of profibrotic cytokines, suggesting that the factor itself is not pro-inflammatory. Ectopic expression in quiescent HSCs, however, retarded their activation into myofibroblasts and specifically decreased expression of type III collagen. Inhibition of type III collagen expression by CRLF1 was also seen in the whole liver. Our results suggest that CLRF1 is the only component of the CRLF1/CLCF1/CNTFR signaling system that is inducible by a profibrotic stimulus and that activation of this system by CLRF1 may regulate expression of type III collagen in fibrosis.

CONCLUSION

By regulating activation of HSCs and expression of type III collagen, CRLF1 may have an ability to change the composition of extracellular matrix in fibrosis.

Effect of host sex and sex hormones on muscle-derived stem cell-mediated bone formation and defect healing

Muscle-derived stem cells (MDSCs) are known to exhibit sexual dimorphism, by donor sex, of osteogenic, chondrogenic, and myogenic differentiation potential in vitro. Moreover, host sex differences in the myogenic capacity of MDSCs in vivo are also observed. This study investigated the role of host sex and host sex hormones in MDSC-mediated bone formation and healing. Using unaltered male, castrated male, unaltered female, and ovariectomized female mice, both MDSC-mediated ectopic bone formation and cranial defect healing were examined. Male hosts, whether unaltered or castrated, form significantly larger volumes of MDSC-mediated ectopic bone than female hosts (either unaltered or ovariectomized), and no differences in ectopic bone volume were found between hosts of the same sex. In a cranial defect healing model, similar results were found-unaltered and castrated male hosts display larger volumes of bone formed when compared with unaltered and ovariectomized female hosts. However, in this healing model, some volume differences were found between hosts of the same sex. In both models, these differences were attributed to varying rates of endochondral bone formation in male and female hosts.

Changes in matrix protein biochemistry and the expression of mRNA encoding matrix proteins and metalloproteinases in posterior tibialis tendinopathy

OBJECTIVES

Adult-acquired flat foot secondary to a dysfunctional posterior tibialis tendon (PTT) is often treated by surgical transfer of the flexor digitorum longus tendon (FDLT). In this study, the authors compared normal PTT, stage II dysfunctional PTT and replacement FDLT, aiming to define changes in collagen modification, glycosaminoglycan (GAG) and the expression of matrix and metalloproteinase mRNA.

METHODS

Normal PTTs were obtained from patients with no history of tendon problems. Samples of dysfunctional PTT and replacement FDLT tissue were obtained from patients undergoing surgical reconstruction. Tissue samples were analysed for total collagen and GAG, pentosidine and collagen cross-links. Total RNA was assayed for mRNA encoding matrix proteins and metalloproteinases, using real-time reverse transcription PCR. Differences between clinical groups were assessed using non-parametric statistics.

RESULTS

Dysfunctional PTT contained higher levels of GAG and lower levels of pentosidine than normal PTT or FDLT. In contrast, collagen in FDLT contained fewer ketoimine and more aldimine cross-links than either normal or dysfunctional PTT. mRNA encoding types I and III collagens, aggrecan, biglycan, matrix metalloproteinase (MMP)-2, -13 and -23, and a disintegrin and metalloproteinase (ADAM)-12L each showed increased levels in dysfunctional PTT compared with either normal PTT or (except MMP-13) FDLT. In contrast, MMP-3 and ADAM with thrombospondin domain (ADAMTS)-5 mRNA were lower in both dysfunctional PTT and FDLT than in normal PTT, while ADAMTS-1 mRNA was lower in dysfunctional PTT than in FDLT.

CONCLUSIONS

Stage II dysfunctional PTT shows biochemical and molecular changes consistent with a chronic remodelling of the extracellular matrix, rather than rupture, while the replacement FDLT resembles normal PTT in many, but not all, parameters.

Molecular characterization of porcine MMP19 and MMP23B genes and its association with immune traits

MMP19 and MMP23B belong to the Matrix metalloproteases (MMPs) family, which are zinc-binding endopeptidases that are capable of degrading various components of the extracellular matrix. They are thought to play important roles in embryonic development, reproduction and tissue remodeling, as well as in cell proliferation, differentiation, migration, angiogenesis, apoptosis and host defense. However, they are poorly understood in pigs. Here, we obtained the full length coding region sequence and genomic sequence of the porcine MMP19 and MMP23B genes and analyzed their genomic structures. The deduced amino acid sequence shares similar precursor protein domains with human and mouse MMP19 and MMP23B protein, respectively. Using IMpRH panel, MMP19 was mapped to SSC5p12-q11 (closely linked to microsatellite DK) and MMP23B was mapped to SSC8q11-q12 (linked to microsatellite Sw2521). Quantitative real-time PCR showed that MMP19 was abundantly expressed in the liver, while MMP23B was strongly expressed in the ovarian and heart. Furthermore, both genes were all expressed increasingly in prenatal skeletal muscle during development. Three SNPs were detected by sequencing and PCR-RFLP methods, and association analysis indicated that C203T at exon 5 of MMP19 has a significant association with the blood parameters WBC (G/L) and IgG2 (mg/mL) (P<0.05), SNP C131T at exon 3 of MMP23B is significantly associated with the blood parameters HGB (g/L) and MCH (P<0.05), and A150G in exon 4 has no significant association with the economic traits in pigs.

Systems genetics analysis of mouse chondrocyte differentiation

One of the goals of systems genetics is the reconstruction of gene networks that underlie key processes in development and disease. To identify cartilage gene networks that play an important role in bone development, we used a systems genetics approach that integrated microarray gene expression profiles from cartilage and bone phenotypic data from two sets of recombinant inbred strains. Microarray profiles generated from isolated chondrocytes were used to generate weighted gene coexpression networks. This analysis resulted in the identification of subnetworks (modules) of coexpressed genes that then were examined for relationships with bone geometry and density. One module exhibited significant correlation with femur length (r = 0.416), anteroposterior diameter (r = 0.418), mediolateral diameter (r = 0.576), and bone mineral density (r = 0.475). Highly connected genes (n = 28) from this and other modules were tested in vitro using prechondrocyte ATDC5 cells and RNA interference. Five of the 28 genes were found to play a role in chondrocyte differentiation. Two of these, Hspd1 and Cdkn1a, were known previously to function in chondrocyte development, whereas the other three, Bhlhb9, Cugbp1, and Spcs3, are novel genes. Our integrative analysis provided a systems-level view of cartilage development and identified genes that may be involved in bone development.

New Strategies for the Next Generation of Matrix-Metalloproteinase Inhibitors: Selectively Targeting Membrane-Anchored MMPs with Therapeutic Antibodies

MMP intervention strategies have met with limited clinical success due to severe toxicities. In particular, treatment with broad-spectrum MMP-inhibitors (MMPIs) caused musculoskeletal pain and inflammation. Selectivity may be essential for realizing the clinical potential of MMPIs. Here we review discoveries pinpointing membrane-bound MMPs as mediators of mechanisms underlying cancer and inflammation and as possible therapeutic targets for prevention/treatment of these diseases. We discuss strategies to target these therapeutic proteases using highly selective inhibitory agents (i.e., human blocking antibodies) against individual membrane-bound MMPs.

Differential gene expression profiling of metalloproteinases and their inhibitors: a comparison between bovine intervertebral disc nucleus pulposus cells and articular chondrocytes

STUDY DESIGN

A comparative in vitro metalloproteinases and their inhibitors gene expression profile.

OBJECTIVE

To obtain a complete expression profile of matrix metalloproteinases (MMPs), family of proteases with a disintegrin and metalloproteinase domain with thrombospondin motifs (ADAMTS), and tissue inhibitors of metalloproteinases (TIMPs) in bovine adult nucleus pulposus (NP) cells and to compare this profile with the expression profile obtained from bovine adult articular chondrocytes cultured under identical conditions.

SUMMARY OF BACKGROUND DATA

The cells of the NP resemble articular chondrocytes morphologically but produce a matrix which, though consisting of similar components, has very different biomechanical properties. No specific markers for NP cells have yet been identified; they can be distinguished from chondrocytes only by differences in gene expression. Here we compare profiles of gene expression of metalloproteinases and their inhibitors between NP cells and chondrocytes to improve understanding of the differences between these cell types.

METHODS

NP cells and articular chondrocytes were harvested respectively from bovine caudal discs and the articular cartilage of metacarpal-phalangeal joints of 18- to 24-month-old steers. These cells were cultured under identical conditions for 96 hours in alginate beads. Expression levels of MMPs, ADAMTSs, and TIMPs were detected by real-time RT-PCR.

RESULTS

Gene profiling demonstrated distinct differences between levels of MMPs, ADAMTSs, and TIMPs produced by chondrocytes and NP cells. In particular, NP cells expressed considerably more MMP-2 and MMP-14 than chondrocytes, and expression of ADAMTS-1,-2,-17 and TIMP-1 was also higher. However, expression of MMP-1,-3,-7,-8,-10,-11,-13,-16,-19,-20,-21,-23,-24,-28, ADAMTS-4,-5,-6,-14,-18,-19, and TIMP-3 was lower in NP cells than in chondrocytes. Chondrocytes but not NP cells expressed MMP12 and MMP27; this difference is a potential marker for distinguishing between NP cells and chondrocytes.

CONCLUSION

Because culture conditions and animal age were identical, differences in metalloproteinase and inhibitor expression between NP cells and chondrocytes were intrinsic to cell phenotype and not induced by differences in the in situ extracellular environment.

Cytokine receptor-like factor 1 is highly expressed in damaged human knee osteoarthritic cartilage and involved in osteoarthritis downstream of TGF-beta

Osteoarthritis (OA) is the most prevalent joint disease and is characterized by pain and functional loss of the joint. However, the pathogenic mechanism of OA remains unclear, and no drug therapy for preventing its progress has been established. To identify genes related to the progress of OA, the gene expression profiles of paired intact and damaged cartilage obtained from OA patients undergoing joint substitution were compared using oligo microarrays. Using functional categorization combined with gene ontology and a statistical analysis, five genes were found to be highly expressed in damaged cartilage (HBEGF, ASUS, CRLF1, LOX, CDA), whereas three genes were highly expressed in intact tissues (CHST2, PTPRD, CPAN6). Among these genes, the upregulated expression of CRLF1 was reconfirmed using real-time PCR, and the in vivo expression of CRLF1 was detected in clusters of chondrocytes and fibrocartilage-like cells in damaged OA cartilages using in situ hybridization. In vitro, the transcriptional level of CRLF1 was positively regulated by TGF-beta1 in the mouse chondrogenic cell line ATDC5. Additionally, the CRLF1/CLC complex promoted the proliferation of ATDC5 cells and suppressed the expression level of aggrecan and type II collagen. Our data suggest that the CRLF1/CLC complex disrupts cartilage homeostasis and promotes the progress of OA by enhancing the proliferation of chondrocytes and suppressing the production of cartilage matrix. A component of the complex, CRLF1, may be useful as a biomarker of OA; and the corresponding receptor is a potential new drug target for OA.

Potassium channel modulation by a toxin domain in matrix metalloprotease 23

Peptide toxins found in a wide array of venoms block K(+) channels, causing profound physiological and pathological effects. Here we describe the first functional K(+) channel-blocking toxin domain in a mammalian protein. MMP23 (matrix metalloprotease 23) contains a domain (MMP23(TxD)) that is evolutionarily related to peptide toxins from sea anemones. MMP23(TxD) shows close structural similarity to the sea anemone toxins BgK and ShK. Moreover, this domain blocks K(+) channels in the nanomolar to low micromolar range (Kv1.6 > Kv1.3 > Kv1.1 = Kv3.2 > Kv1.4, in decreasing order of potency) while sparing other K(+) channels (Kv1.2, Kv1.5, Kv1.7, and KCa3.1). Full-length MMP23 suppresses K(+) channels by co-localizing with and trapping MMP23(TxD)-sensitive channels in the ER. Our results provide clues to the structure and function of the vast family of proteins that contain domains related to sea anemone toxins. Evolutionary pressure to maintain a channel-modulatory function may contribute to the conservation of this domain throughout the plant and animal kingdoms.

rhBMP-2 modulation of gene expression in infected segmental bone defects

The osteoinductive capability of BMPs appears diminished in the setting of acute infection. We applied rhBMP-2 to a segmental defect in a rat femur and measured the expression of key bone formation genes in the presence of acute infection. Types I and II collagen, osteocalcin, and BMP Type II receptor mRNA expression were characterized in 72 Sprague-Dawley rats, which received either bovine collagen carrier with 200 mug rhBMP-2 plus Staphylococcus aureus, carrier with bacteria only, carrier with rhBMP-2 only, or carrier alone. Six animals from each group were euthanized at 1, 2, and 4 weeks. Total RNA was isolated and extracted, and mRNA was determined by real-time comparative quantitative PCR. Infected defects had little expression of collagen I and II and osteocalcin mRNAs, while BMP receptor II expression with infection was greater than carrier-only controls at weeks 2 and 4. Notably, all four genes were upregulated in infected defects in the presence of rhBMP-2. Thus, in a clinical setting with a high risk of infection and nonunion, such as a compound fracture with bone loss, rhBMP-2 may increase the rate and extent of bone formation. Even if infection does occur, rhBMP-2 may allow a quicker overall recovery time.

Menin expression modulates mesenchymal cell commitment to the myogenic and osteogenic lineages

Menin plays an established role in the differentiation of mesenchymal cells to the osteogenic lineage. Conversely, whether Menin influences the commitment of mesenschymal cells to the myogenic lineage, despite expression in the developing somite was previously unclear. We observed that Menin is down-regulated in C2C12 and C3H10T1/2 mesenchymal cells when muscle differentiation is induced. Moreover, maintenance of Menin expression by constitutive ectopic expression inhibited muscle cell differentiation. Reduction of Menin expression by siRNA technology results in precocious muscle differentiation and concomitantly attenuates BMP-2 induced osteogenesis. Reduced Menin expression antagonizes BMP-2 and TGF-beta1 mediated inhibition of myogenesis. Furthermore, Menin was found to directly interact with and potentiate the transactivation properties of Smad3 in response to TGF-beta1. Finally in concert with these observations, tissue-specific inactivation of Men1 in Pax3-expressing somite precursor cells leads to a patterning defect of rib formation and increased muscle mass in the intercostal region. These data invoke a pivotal role for Menin in the competence of mesenchymal cells to respond to TGF-beta1 and BMP-2 signals. Thus, by modulating cytokine responsiveness Menin functions to alter the balance of multipotent mesenchymal cell commitment to the osteogenic or myogenic lineages.

Bone morphogenetic proteins in tissue engineering: the road from the laboratory to the clinic, part I (basic concepts)

Discovered in 1965, bone morphogenetic proteins (BMPs) are a group of cytokines from the transforming growth factor-beta (TGFbeta) superfamily with significant roles in bone and cartilage formation. BMPs are used as powerful osteoinductive components of diverse tissue-engineering products for the healing of bone. Several BMPs with different physiological roles have been identified in humans. The purpose of this review is to cover the biological function of the main members of BMP family, the latest research on BMPs signalling pathways and advances in the production of recombinant BMPs for tissue engineering purposes.

Transcriptional profiling of putative human epithelial stem cells

Background

Human interfollicular epidermis is sustained by the proliferation of stem cells and their progeny, transient amplifying cells. Molecular characterization of these two cell populations is essential for better understanding of self renewal, differentiation and mechanisms of skin pathogenesis. The purpose of this study was to obtain gene expression profiles of alpha 6⁺/MHCI⁺, transient amplifying cells and alpha 6⁺/MHCI^-, putative stem cells, and to compare them with existing data bases of gene expression profiles of hair follicle stem cells. The expression of Major Histocompatibility Complex (MHC) class I, previously shown to be absent in stem cells in several tissues, and alpha 6 integrin were used to isolate MHCI positive basal cells, and MHCI low/negative basal cells.

Results

Transcriptional profiles of the two cell populations were determined and comparisons made with published data for hair follicle stem cell gene expression profiles. We demonstrate that presumptive interfollicular stem cells, alpha 6⁺/MHCI^- cells, are enriched in messenger RNAs encoding surface receptors, cell adhesion molecules, extracellular matrix proteins, transcripts encoding members of IFN-alpha family proteins and components of IFN signaling, but contain lower levels of transcripts encoding proteins which take part in energy metabolism, cell cycle, ribosome biosynthesis, splicing, protein translation, degradation, DNA replication, repair, and chromosome remodeling. Furthermore, our data indicate that the cell signaling pathways Notch1 and NF-κB are downregulated/inhibited in MHC negative basal cells.

Conclusion

This study demonstrates that alpha 6⁺/MHCI^- cells have additional characteristics attributed to stem cells. Moreover, the transcription profile of alpha 6⁺/MHCI^- cells shows similarities to transcription profiles of mouse hair follicle bulge cells known to be enriched for stem cells. Collectively, our data suggests that alpha 6⁺/MHCI^- cells may be enriched for stem cells. This study is the first comprehensive gene expression profile of putative human epithelial stem cells and their progeny that were isolated directly from neonatal foreskin tissue. Our study is important for understanding self renewal and differentiation of epidermal stem cells, and for elucidating signaling pathways involved in those processes. The generated data base may serve those working with other human epithelial tissue progenitors.

Osteogenic gene regulation and relative acceleration of healing by adenoviral-mediated transfer of human BMP-2 or -6 in equine osteotomy and ostectomy models

This study evaluated healing of equine metatarsal osteotomies and ostectomies in response to percutaneous injection of adenoviral (Ad) bone morphogenetic protein (BMP)-2, Ad-BMP-6, or beta-galactosidase protein vector control (Ad-LacZ) administered 14 days after surgery. Radiographic and quantitative computed tomographic assessment of bone formation indicated greater and earlier mineralized callus in both the osteotomies and ostectomies of the metatarsi injected with Ad-BMP-2 or Ad-BMP-6. Peak torque to failure and torsional stiffness were greater in osteotomies treated with Ad-BMP-2 than Ad-BMP-6, and both Ad-BMP-2- and Ad-BMP-6-treated osteotomies were greater than Ad-LacZ or untreated osteotomies. Gene expression of ostectomy mineralized callus 8 weeks after surgery indicated upregulation of genes related to osteogenesis compared to intact metatarsal bone. Expression of transforming growth factor beta-1, cathepsin H, and gelsolin-like capping protein were greater in Ad-BMP-2- and Ad-BMP-6-treated callus compared to Ad-LacZ-treated or untreated callus. Evidence of tissue biodistribution of adenovirus in distant organs was not identified by quantitative PCR, despite increased serum antiadenoviral vector antibody. This study demonstrated a greater relative potency of Ad-BMP-2 over Ad-BMP-6 in accelerating osteotomy healing when administered in this regimen, although both genes were effective at increasing bone at both osteotomy and ostectomy sites.

Tendinopathy--from basic science to treatment

Chronic tendon pathology (tendinopathy), although common, is difficult to treat. Tendons possess a highly organized fibrillar matrix, consisting of type I collagen and various 'minor' collagens, proteoglycans and glycoproteins. The tendon matrix is maintained by the resident tenocytes, and there is evidence of a continuous process of matrix remodeling, although the rate of turnover varies at different sites. A change in remodeling activity is associated with the onset of tendinopathy. Major molecular changes include increased expression of type III collagen, fibronectin, tenascin C, aggrecan and biglycan. These changes are consistent with repair, but they might also be an adaptive response to changes in mechanical loading. Repeated minor strain is thought to be the major precipitating factor in tendinopathy, although further work is required to determine whether it is mechanical overstimulation or understimulation that leads to the change in tenocyte activity. Metalloproteinase enzymes have an important role in the tendon matrix, being responsible for the degradation of collagen and proteoglycan in both healthy patients and those with disease. Metalloproteinases that show increased expression in painful tendinopathy include ADAM (a disintegrin and metalloproteinase)-12 and MMP (matrix metalloproteinase)-23. The role of these enzymes in tendon pathology is unknown, and further work is required to identify novel and specific molecular targets for therapy.

Molecular profile of peripheral blood mononuclear cells from patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory arthritis. Currently, diagnosis of RA may take several weeks, and factors used to predict a poor prognosis are not always reliable. Gene expression in RA may consist of a unique signature. Gene expression analysis has been applied to synovial tissue to define molecularly distinct forms of RA; however, expression analysis of tissue taken from a synovial joint is invasive and clinically impractical. Recent studies have demonstrated that unique gene expression changes can be identified in peripheral blood mononuclear cells (PBMCs) from patients with cancer, multiple sclerosis, and lupus. To identify RA disease-related genes, we performed a global gene expression analysis. RNA from PBMCs of 9 RA patients and 13 normal volunteers was analyzed on an oligonucleotide array. Compared with normal PBMCs, 330 transcripts were differentially expressed in RA. The differentially regulated genes belong to diverse functional classes and include genes involved in calcium binding, chaperones, cytokines, transcription, translation, signal transduction, extracellular matrix, integral to plasma membrane, integral to intracellular membrane, mitochondrial, ribosomal, structural, enzymes, and proteases. A k-nearest neighbor analysis identified 29 transcripts that were preferentially expressed in RA. Ten genes with increased expression in RA PBMCs compared with controls mapped to a RA susceptibility locus, 6p21.3. These results suggest that analysis of RA PBMCs at the molecular level may provide a set of candidate genes that could yield an easily accessible gene signature to aid in early diagnosis and treatment.

β-Catenin Signaling Pathway Is Crucial for Bone Morphogenetic Protein 2 to Induce New Bone Formation

Endochondral ossification is recapitulated during bone morphogenetic protein (BMP)-induced ectopic bone formation. Although BMP and beta-catenin have been investigated in bone development and in mesenchymal cells, how they interact in this process is not clear. We implanted recombinant BMP-2 into the muscle of mice to investigate the effect of beta-catenin signaling on BMP-induced in vivo endochondral bone formation. BMP-2 induced expression of several Wnt ligands and their receptors and also activated beta-catenin-mediated T cell factor-dependent transcriptional activity. An adenovirus expressing Dickkopf-1 (Dkk-1, an inhibitor of canonical Wnt pathway) inhibited beta-catenin signaling and endochondral bone formation. Interestingly, Dkk-1 inhibited both chondrogenesis and osteogenesis. Likewise, mice expressing conditional beta-catenin null alleles also displayed an inhibition of BMP-induced chondrogenesis and osteogenesis. This is in contrast to studies of embryonic skeletogenesis, which demonstrate that beta-catenin is required for osteogenesis but is dispensable for chondrogenesis. These findings suggest that embryonic development pathways are not always recapitulated during post-natal regenerative processes, and the biochemical pathways utilized to regulate cell differentiation may be different. During in vivo ectopic bone formation, BMP-2 induces beta-catenin-mediated signaling through Wnt ligands, and beta-catenin is required for both chondrogenesis and osteogenesis.

Advanced molecular profiling in vivo detects novel function of dickkopf-3 in the regulation of bone formation

A bioinformatics-based analysis of endochondral bone formation model detected several genes upregulated in this process. Among these genes the dickkopf homolog 3 (Dkk3) was upregulated and further studies showed that its expression affects in vitro and in vivo osteogenesis. This study indicates a possible role of Dkk3 in regulating bone formation.

INTRODUCTION

Endochondral bone formation is a complex biological process involving numerous chondrogenic, osteogenic, and angiogenic proteins, only some of which have been well studied. Additional key genes may have important roles as well. We hypothesized that to identify key genes and signaling pathways crucial for bone formation, a comprehensive gene discovery strategy should be applied to an established in vivo model of osteogenesis.

MATERIALS AND METHODS

We used in vivo implanted C3H10T1/2 cells that had been genetically engineered to express human bone morphogenetic protein-2 (BMP2) in a tetracycline-regulated system that controls osteogenic differentiation. Oligonucleotide microarray data from the implants (n = 4 repeats) was analyzed using coupled two-way clustering (CTWC) and statistical methods. For studying the effects of dickkopf homolog 3 (Dkk3) in chondrogenesis and osteogenesis, C3H10T1/2 mesenchymal progenitors were used.

RESULTS

The CTWC revealed temporal expression of Dkk3 with other chondrogenesis-, osteogenesis-, and Wnt-related genes. Quantitative RT-PCR confirmed the expression of Dkk3 in the implants. C3H10T1/2 cells that expressed Dkk3 in the presence of BMP2 displayed lower levels of alkaline phosphatase and collagen I mRNA expression than control C3H10T1/2 cells that did not express Dkk3. Interestingly, the levels of collagen II mRNA expression, Alcian blue staining, and glucose aminoglycans (GAGs) production were not influenced by Dkk3 expression. In vivo microCT and bioluminescence imaging revealed that co-expression of Dkk3 and BMP2 by implanted C3H10T1/2 cells induced the formation of significantly lower quantities of bone than cells expressing only BMP2.

CONCLUSIONS

A bioinformatics analysis enabled the identification of Dkk3 as a pivotal gene with a novel function in endochondral bone formation. Our results showed that Dkk3 might have inhibitory effects on osteogenesis, but no effect on chondrogenesis, indicating that Dkk3 plays a regulatory role in endochondral bone formation. Further mechanistic studies are required to reveal the mechanism of action of Dkk3 in endochondral bone formation.

Molecular genetic studies of gene identification for osteoporosis: a 2004 update

This review summarizes comprehensively the most important and representative molecular genetics studies of gene identification for osteoporosis published up to the end of December 2004. It is intended to constitute a sequential update of our previously published review covering the available data up to the end of 2002. Evidence from candidate gene association studies and genome-wide linkage studies in humans, as well as quantitative trait locus mapping animal models are reviewed separately. Studies of transgenic and knockout mice models relevant to osteoporosis are summarized. An important extension of this update is incorporation of functional genomic studies (including DNA microarrays and proteomics) on osteogenesis and osteoporosis, in light of the rapid advances and the promising prospects of the field. Comments are made on the most notable findings and representative studies for their potential influence and implications on our present understanding of genetics of osteoporosis. The format adopted by this review should be ideal for accommodating future new advances and studies.

Transcriptome analysis of fetal metatarsal long bones by microarray, as a model for endochondral bone formation

Endochondral bone formation is orchestrated by mesenchymal cell condensation to form cartilage anlagen, which act as a template for bone formation and eventual mineralization. The current study performed gene expression analysis to examine pre- and post-mineralization stages (E15 and E19) of endochondral bone formation, using fetal metatarsal long bones as a model. An extensive number of genes were differentially expressed, with 543 transcripts found to have at least 2-fold up-regulation and 742 with a greater than 2-fold down-regulation. A bioinformatics approach was adopted based on gene ontology groups, and this identified genes associated with the regulation of signaling and skeletal development, cartilage replacement by bone, and matrix degradation and turnover. Transcripts linked to skeletal patterning, including Hoxd genes 10-12, Gli2 and Noggin were considerably down-regulated at E19. Whereas genes associated with bone matrix formation and turnover, ACP5, MMP-13, bone sialoprotein, osteopontin, dentin matrix protein-1 and MMP-9 all were distinctly up-regulated at this later time point. This approach to studying the formation of the primary ossification center provides a unique picture of the developmental dynamics involved in the molecular and biochemical processes during this intricately regulated process.

Characterization of human fetal osteoblasts by microarray analysis following stimulation with 58S bioactive gel-glass ionic dissolution products

Bioactive glasses dissolve upon immersion in culture medium, releasing their constitutive ions in solution. There is evidence suggesting that these ionic dissolution products influence osteoblast-specific processes. Here, we investigated the effect of 58S sol-gel-derived bioactive glass (60 mol % SiO2, 36 mol % CaO, 4 mol % P2O5) dissolution products on primary osteoblasts derived from human fetal long bone explant cultures (hFOBs). We used U133A human genome GeneChip oligonucleotide arrays to examine 22,283 transcripts and variants, which represent over 18,000 well-substantiated human genes. Hybridization of samples (biotinylated cRNA) derived from monolayer cultures of hFOBs on the arrays revealed that 10,571 transcripts were expressed by these cells, with high confidence. These included transcripts representing osteoblast-related genes coding for growth factors and their associated molecules or receptors, protein components of the extracellular matrix (ECM), enzymes involved in degradation of the ECM, transcription factors, and other important osteoblast-associated markers. A 24-h treatment with a single dosage of ionic products of sol-gel 58S dissolution induced the differential expression of a number of genes, including IL-6 signal transducer/gp130, ISGF-3/STAT1, HIF-1 responsive RTP801, ERK1 p44 MAPK (MAPK3), MAPKAPK2, IGF-I and IGFBP-5. The over 2-fold up-regulation of gp130 and MAPK3 and down-regulation of IGF-I were confirmed by real-time RT-PCR analysis. These data suggest that 58S ionic dissolution products possibly mediate the bioactive effect of 58S through components of the IGF system and MAPK signaling pathways.

The Wnt antagonist secreted frizzled-related protein-1 controls osteoblast and osteocyte apoptosis

Mechanisms controlling human bone formation remain to be fully elucidated. We have used differential display-polymerase chain reaction analysis to characterize osteogenic pathways in conditionally immortalized human osteoblasts (HOBs) representing distinct stages of differentiation. We identified 82 differentially expressed messages and found that the Wnt antagonist secreted frizzled-related protein (sFRP)-1 was the most highly regulated of these. Transient transfection of HOBs with sFRP-1 suppressed canonical Wnt signaling by 70% confirming its antagonistic function in these cells. Basal sFRP-1 mRNA levels increased 24-fold during HOB differentiation from pre-osteoblasts to pre-osteocytes, and then declined in mature osteocytes. This expression pattern correlated with levels of cellular viability such that the pre-osteocytes, which had the highest levels of sFRP-1 mRNA, also had the highest rate of cell death. Basal sFRP-1 mRNA levels also increased 29-fold when primary human mesenchymal stem cells were differentiated to osteoblasts supporting the developmental regulation of the gene. Expression of sFRP-1 mRNA was induced 38-fold following prostaglandin E2 (PGE2) treatment of pre-osteoblasts and mature osteoblasts that had low basal message levels. In contrast, sFRP-1 expression was down-regulated by as much as 80% following transforming growth factor (TGF)-beta1 treatment of pre-osteocytes that had high basal mRNA levels. Consistent with this, treatment of pre-osteoblasts and mature osteoblasts with PGE(2) increased apoptosis threefold, while treatment of pre-osteocytes with TGF-beta1 decreased cell death by 50%. Likewise, over-expression of sFRP-1 in HOBs accelerated the rate of cell death threefold. These results establish sFRP-1 as an important negative regulator of human osteoblast and osteocyte survival.

Expression profiling of metalloproteinases and tissue inhibitors of metalloproteinases in normal and degenerate human achilles tendon

OBJECTIVE

To profile the messenger RNA (mRNA) expression for the 23 known genes of matrix metalloproteinases (MMPs), 19 genes of ADAMTS, 4 genes of tissue inhibitors of metalloproteinases (TIMPs), and ADAM genes 8, 10, 12, and 17 in normal, painful, and ruptured Achilles tendons.

METHODS

Tendon samples were obtained from cadavers or from patients undergoing surgical procedures to treat chronic painful tendinopathy or ruptured tendon. Total RNA was extracted and mRNA expression was analyzed by quantitative real-time reverse transcription-polymerase chain reaction, normalized to 18S ribosomal RNA.

RESULTS

In comparing expression of all genes, the normal, painful, and ruptured Achilles tendon groups each had a distinct mRNA expression signature. Three mRNA were not detected and 14 showed no significant difference in expression levels between the groups. Statistically significant (P < 0.05) differences in mRNA expression, when adjusted for age, included lower levels of MMPs 3 and 10 and TIMP-3 and higher levels of ADAM-12 and MMP-23 in painful compared with normal tendons, and lower levels of MMPs 3 and 7 and TIMPs 2, 3, and 4 and higher levels of ADAMs 8 and 12, MMPs 1, 9, 19, and 25, and TIMP-1 in ruptured compared with normal tendons.

CONCLUSION

The distinct mRNA profile of each tendon group suggests differences in extracellular proteolytic activity, which would affect the production and remodeling of the tendon extracellular matrix. Some proteolytic activities are implicated in the maintenance of normal tendon, while chronically painful tendons and ruptured tendons are shown to be distinct groups. These data will provide a foundation for further study of the role and activity of many of these enzymes that underlie the pathologic processes in the tendon.

BMP receptor signaling: transcriptional targets, regulation of signals, and signaling cross-talk

Bone morphogenetic proteins (BMPs), members of the transforming growth factor-beta (TGF-beta) superfamily, bind to two different serine/threonine kinase receptors, and mediate their signals through Smad-dependent and Smad-independent pathways. Receptor regulated-Smad (R-Smad) proteins specific for the BMP pathways interact with various proteins, including transcription factor Runx, and transmit specific signals in target cells. The recent development of DNA microarray techniques has allowed us to identify many BMP target genes. BMP signaling is modulated by various molecules, including inhibitory Smads (I-Smads). Moreover, recent findings have revealed that BMP pathways interact with other signaling pathways, and such signaling cross-talk plays pivotal roles in growth and differentiation of target cells.

Comparative analysis of gene expression profiles in intact and damaged regions of human osteoarthritic cartilage

OBJECTIVE

To analyze the differences in gene expression profiles of chondrocytes in intact and damaged regions of cartilage from the same knee joint of patients with osteoarthritis (OA) of the knee.

METHODS

We compared messenger RNA expression profiles in regions of intact and damaged cartilage (classified according to the Mankin scale) obtained from patients with knee OA. Five pairs of intact and damaged regions of OA cartilage were evaluated by oligonucleotide array analysis using a double in vitro transcription amplification technique. The microarray data were confirmed by real-time quantitative polymerase chain reaction (PCR) amplification and were compared with previously published data.

RESULTS

About 1,500 transcripts, which corresponded to 8% of the expressed transcripts, showed > or = 2-fold differences in expression between the cartilage tissue pairs. Approximately 10% of these transcripts (n = 151) were commonly expressed in the 5 patient samples. Accordingly, 114 genes (35 genes expressed in intact > damaged; 79 genes expressed in intact < damaged) were selected. The expression of some genes related to the wound-healing process, including cell proliferation and interstitial collagen synthesis, was higher in damaged regions than in intact regions, similar to the findings for genes that inhibit matrix degradation. Comparisons of the real-time quantitative PCR data with the previously reported data support the validity of our microarray data.

CONCLUSION

Differences between intact and damaged regions of OA cartilage exhibited a similar pattern among the 5 patients examined, indicating the presence of common mechanisms that contribute to cartilage destruction. Elucidation of this mechanism is important for the development of effective treatments for OA.