Extraction and isolation of mRNA from adult articular cartilage

Ca2+-Activated K+ Channels in Progenitor Cells of Musculoskeletal Tissues: A Narrative Review

Musculoskeletal disorders represent one of the main causes of disability worldwide, and their prevalence is predicted to increase in the coming decades. Stem cell therapy may be a promising option for the treatment of some of the musculoskeletal diseases. Although significant progress has been made in musculoskeletal stem cell research, osteoarthritis, the most-common musculoskeletal disorder, still lacks curative treatment. To fine-tune stem-cell-based therapy, it is necessary to focus on the underlying biological mechanisms. Ion channels and the bioelectric signals they generate control the proliferation, differentiation, and migration of musculoskeletal progenitor cells. Calcium- and voltage-activated potassium (KCa) channels are key players in cell physiology in cells of the musculoskeletal system. This review article focused on the big conductance (BK) KCa channels. The regulatory function of BK channels requires interactions with diverse sets of proteins that have different functions in tissue-resident stem cells. In this narrative review article, we discuss the main ion channels of musculoskeletal stem cells, with a focus on calcium-dependent potassium channels, especially on the large conductance BK channel. We review their expression and function in progenitor cell proliferation, differentiation, and migration and highlight gaps in current knowledge on their involvement in musculoskeletal diseases.

RNA Extraction from Cartilage: Issues, Methods, Tips

The increase in degenerative diseases involving articular cartilage has pushed research to focus on their pathogenesis and treatment, exploiting increasingly complex techniques. Gene expression analyses from tissue are representative of the in vivo situation, but the protocols to be applied to obtain a reliable analysis are not completely cleared through customs. Thus, RNA extraction from fresh samples and specifically from musculoskeletal tissue such as cartilage is still a challenging issue. The aim of the review is to provide an overview of the techniques described in the literature for RNA extraction, highlighting limits and possibilities. The research retrieved 65 papers suitable for the purposes. The results highlighted the great difficulty in comparing the different studies, both for the sources of tissue used and for the techniques employed, as well as the details about protocols. Few papers compared different RNA extraction methods or homogenization techniques; the case study reported by authors about RNA extraction from sheep cartilage has not found an analog in the literature, confirming the existence of a relevant blank on studies about RNA extraction from cartilage tissue. However, the state of the art depicted can be used as a starting point to improve and expand studies on this topic.

RNA Isolation from Articular Cartilage Tissue

Isolation of high-quality RNA directly from tissues is desirable to obtain precise information of in vivo gene expression profiles in cells embedded within their extracellular matrix (ECM). It is well known that purification of RNA from cartilage tissues is particularly challenging due to low cell (chondrocyte) content and its dense ECM rich in large negatively charged proteoglycans that can copurify with RNA. Older methodologies to purify RNA from cartilage involved the use of concentrated denaturing solutions containing guanidinium isothiocyanate followed by ultracentrifugation in cesium trifluoroacetate. Such ultracentrifugation approaches are rarely used now since the emergence of more user-friendly mini spin column chromatography kits. For this chapter, we tested and compared three methods to isolate RNA from immature murine articular (femoral head) cartilage and found that the combination of TRIzol® reagent and spin column chromatography (Norgen Total RNA Purification Kit) was the best approach to generate higher quality RNA. Here, the average RNA Integrity Number (RIN), as determined by Bioanalyzer technology, was 7.1. We then applied this method to attempt to isolate RNA directly from human articular cartilage harvested from three osteoarthritic (OA) knee joint specimens. As expected, the concentration and quality of RNA obtained differed between samples. However, from one specimen, we were able to isolate approximately 3 μg of total RNA (including small noncoding RNAs) from 100 mg of human OA cartilage with a RIN = 7.9. Despite the patient-to-patient variabilities that are known to exist between cartilage specimens from OA joints, we have demonstrated that it is possible to obtain reasonably high levels of RNA from human OA articular cartilage at a quality suitable for downstream analyses including microarray and RNA-Seq. A detailed description of our preferred RNA purification methodology, which can be used to isolate RNA from human, bovine, or rodent cartilage tissue, is provided in this chapter.

Optimisation of high-quality total ribonucleic acid isolation from cartilaginous tissues for real-time polymerase chain reaction analysis

Objectives

Studies which consider the molecular mechanisms of degeneration and regeneration of cartilaginous tissues are seriously hampered by problematic ribonucleic acid (RNA) isolations due to low cell density and the dense, proteoglycan-rich extracellular matrix of cartilage. Proteoglycans tend to co-purify with RNA, they can absorb the full spectrum of UV light and they are potent inhibitors of polymerase chain reaction (PCR). Therefore, the objective of the present study is to compare and optimise different homogenisation methods and RNA isolation kits for an array of cartilaginous tissues.

Materials and Methods

Tissue samples such as the nucleus pulposus (NP), annulus fibrosus (AF), articular cartilage (AC) and meniscus, were collected from goats and homogenised by either the MagNA Lyser or Freezer Mill. RNA of duplicate samples was subsequently isolated by either TRIzol (benchmark), or the RNeasy Lipid Tissue, RNeasy Fibrous Tissue, or Aurum Total RNA Fatty and Fibrous Tissue kits. RNA yield, purity, and integrity were determined and gene expression levels of type II collagen and aggrecan were measured by real-time PCR.

Results

No differences between the two homogenisation methods were found. RNA isolation using the RNeasy Fibrous and Lipid kits resulted in the purest RNA (A260/A280 ratio), whereas TRIzol isolations resulted in RNA that is not as pure, and show a larger difference in gene expression of duplicate samples compared with both RNeasy kits. The Aurum kit showed low reproducibility.

Conclusion

For the extraction of high-quality RNA from cartilaginous structures, we suggest homogenisation of the samples by the MagNA Lyser. For AC, NP and AF we recommend the RNeasy Fibrous kit, whereas for the meniscus the RNeasy Lipid kit is advised.

Cite this article: M. Peeters, C. L. Huang, L. A. Vonk, Z. F. Lu, R. A. Bank, M. N. Helder, B. Zandieh Doulabi. Optimisation of high-quality total ribonucleic acid isolation from cartilaginous tissues for real-time polymerase chain reaction analysis. Bone Joint Res 2016;5:560–568. DOI: 10.1302/2046-3758.511.BJR-2016-0033.R3.

Evaluation of different pulverisation methods for RNA extraction in squash fruit: lyophilisation, cryogenic mill and mortar grinding

INTRODUCTION

Quality and integrity of RNA are critical for transcription studies in plant molecular biology. In squash fruit and other high water content crops, the grinding of tissue with mortar and pestle in liquid nitrogen fails to produce a homogeneous and fine powered sample desirable to ensure a good penetration of the extraction reagent.

OBJECTIVE

To develop an improved pulverisation method to facilitate the homogenisation process of squash fruit tissue prior to RNA extraction without reducing quality and yield of the extracted RNA.

METHODOLOGY

Three methods of pulverisation, each followed by the same extraction protocol, were compared. The first approach consisted of the lyophilisation of the sample in order to remove the excess of water before grinding, the second one used a cryogenic mill and the control one a mortar grinding of frozen tissue. The quality of the isolated RNA was tested by carrying out a quantitative real time downstream amplification.

RESULTS

In the three situations considered, mean values for A(260) /A(280) indicated minimal interference by proteins and RNA quality indicator (RQI) values were considered appropriate for quantitative real-time polymerase chain reaction (qRT-PCR) amplification. Successful qRT-PCR amplifications were obtained with cDNA isolated with the three protocols.

CONCLUSION

Both apparatus can improve and facilitate the grinding step in the RNA extraction process in zucchini, resulting in isolated RNA of high quality and integrity as revealed by qRT-PCR downstream application. This is apparently the first time that a cryogenic mill has been used to prepare fruit samples for RNA extraction, thereby improving the sampling strategy because the fine powder obtained represents a homogeneous mix of the organ tissue.

Transcriptional profiling differences for articular cartilage and repair tissue in equine joint surface lesions

Background

Full-thickness articular cartilage lesions that reach to the subchondral bone yet are restricted to the chondral compartment usually fill with a fibrocartilage-like repair tissue which is structurally and biomechanically compromised relative to normal articular cartilage. The objective of this study was to evaluate transcriptional differences between chondrocytes of normal articular cartilage and repair tissue cells four months post-microfracture.

Methods

Bilateral one-cm² full-thickness defects were made in the articular surface of both distal femurs of four adult horses followed by subchondral microfracture. Four months postoperatively, repair tissue from the lesion site and grossly normal articular cartilage from within the same femorotibial joint were collected. Total RNA was isolated from the tissue samples, linearly amplified, and applied to a 9,413-probe set equine-specific cDNA microarray. Eight paired comparisons matched by limb and horse were made with a dye-swap experimental design with validation by histological analyses and quantitative real-time polymerase chain reaction (RT-qPCR).

Results

Statistical analyses revealed 3,327 (35.3%) differentially expressed probe sets. Expression of biomarkers typically associated with normal articular cartilage and fibrocartilage repair tissue corroborate earlier studies. Other changes in gene expression previously unassociated with cartilage repair were also revealed and validated by RT-qPCR.

Conclusion

The magnitude of divergence in transcriptional profiles between normal chondrocytes and the cells that populate repair tissue reveal substantial functional differences between these two cell populations. At the four-month postoperative time point, the relative deficiency within repair tissue of gene transcripts which typically define articular cartilage indicate that while cells occupying the lesion might be of mesenchymal origin, they have not recapitulated differentiation to the chondrogenic phenotype of normal articular chondrocytes.

Differential transcriptome analysis of intraarticular lesional vs intact cartilage reveals new candidate genes in osteoarthritis pathophysiology

OBJECTIVE

To elucidate disease-specific molecular changes in osteoarthritis (OA) by analyzing the differential gene expression profile of damaged vs intact cartilage areas within the same joint of patients with OA of the knee using a combination of a novel RNA extraction technique and whole-genome oligonucleotide arrays.

METHODS

The transcriptome of macroscopically affected vs intact articular cartilage as determined by visual assessment was analyzed using an optimized mill-based total RNA isolation directly from the tissue and high density synthetic oligonucleotide arrays. Articular cartilage samples were obtained from patients with OA of the knee. Expression of differentially regulated genes was validated by real-time quantitative polymerase chain reaction and immunohistochemistry.

RESULTS

The amount of RNA obtained by the optimized extraction procedure was at least 1 microg per 500 mg of cartilage and fulfilled the common quality requirements. After hybridization onto HG-U133 Plus 2.0 GeneChips (Affymetrix), 28.6-51.7% of the probe sets on the microarray showed a detectable signal above the signal threshold in the individual samples. A subset of 411 transcripts, which appeared to be differentially expressed, was obtained when applying predefined filtering criteria. Of these, six genes were found to be up-regulated in the affected cartilage of all patients, including insulin-like growth factor binding protein 3 (IGFBP-3), wnt-1-inducible signaling protein 1 (WISP-1), aquaporin 1 (AQP-1), delta/notch-like EGF-repeat containing transmembrane (DNER), decay accelerating factor (DAF), complement factor I (IF).

CONCLUSION

The optimized methodical approach reported here not only allows to determine area-specific gene expression profiles of intraindividually different low-RNA containing OA cartilage specimens. In addition, this study also revealed novel genes not yet reported to play a role in the pathophysiology of joint destruction in OA.

Regional quantification of cartilage type II collagen and aggrecan messenger RNA in joints with early experimental osteoarthritis

OBJECTIVE

Accurate assessment of chondrocyte metabolism is a potentially valuable indicator of cartilage health in osteoarthritis (OA). This study was conducted to explore the anabolic metabolism of chondrocytes early in the natural history of an experimental canine model of OA.

METHODS

Competitive reverse transcription-polymerase chain reaction was used to calculate the copy number of type II collagen and the messenger RNA (mRNA) levels of aggrecan core protein in articular cartilage samples obtained from different regions of the femorotibial joint 12 and 39 weeks after cruciate transection.

RESULTS

Gene expression of both type II collagen and aggrecan in cartilage samples obtained from experimental joints at both intervals after surgery was elevated significantly compared with that in samples from contralateral control joints. The number of mRNA copies per microgram of DNA of aggrecan exceeded that of type II collagen in control cartilage, but the copy number of type II collagen mRNA exceeded that of aggrecan in OA cartilage. Thus, the ratio of type II collagen-to-aggrecan mRNA copy number (normalized to DNA) was shown to be characteristically altered in cartilage with experimental OA.

CONCLUSION

Accurate assessment of multiple gene products in small samples of cartilage taken from focal areas of a joint can be used diagnostically for monitoring chondrocyte metabolism and possibly for staging at least the early phases of this joint disease.

Angiogenic cytokines in cartilage tumors

Pathologic neovascularization has been described in numerous types of cancers. The angiogenic cytokines vascular endothelial growth factor and basic fibroblast growth factor are thought to be the primary inducers of angiogenesis in these tumors. Hypoxia-inducible transcription factor is a nuclear transcription factor that promotes vascular endothelial growth factor expression. Prior studies have shown pathologic neovascularization in chondrosarcoma, which correlates with pathologic grade of the tumor. Angiogenic and nonangiogenic cartilage tumors were studied for expression of vascular endothelial growth factor, basic fibroblast growth factor and hypoxia-inducible transcription factors by immunohistochemistry and Northern blot analysis. Expression of vascular endothelial growth factor and hypoxia-inducible transcription factor were increased significantly in angiogenic tumors. Fibroblast growth factor expression was similar in angiogenic and nonangiogenic specimens. This may have implications for tumor grading and surgical decision-making, and potential treatment with antiangiogenesis chemotherapeutic agents.

PTEN mutation is rare in chondrosarcoma

Chondrosarcoma is the second most common primary malignant neoplasm of bone in adults, but the major genetic events involved in the progression of this often-fatal cancer remain to be elucidated. Loss of heterozygosity of chromosome 10q has been reported in 67% of chondrosarcoma. The tumor suppressor gene PTEN is located on chromosome 10q, specifically 10q23, raising the possibility that the loss of PTEN function is responsible for some chondrosarcomas. The authors examined 40 chondrosarcoma tumors and tumor-derived cell lines for alterations in PTEN. Only one mutation resulting in a truncated PTEN protein was detected, which was in a metastasized extraskeletal myxoid chondrosarcoma. Thus, mutated PTEN is an uncommon event in the development of chondrosarcoma. The high frequency of loss of heterozygosity on 10q suggests the presence of additional tumor suppressor genes at these loci.

Cancer/testis antigen CSAGE is concurrently expressed with MAGE in chondrosarcoma

Differential display-polymerase chain reaction was used to compare gene expression between human chondrosarcoma cell lines and normal cartilage. A new gene, CSAGE, has been cloned and belongs to a gene family that includes the taxol resistance associated gene (TRAG)-3. CSAGE, like TRAG-3, does not confer resistance to taxol when transfected in vitro. Both genes have alternatively spliced variants. CSAGE and TRAG-3 are expressed in chondrosarcoma, melanoma, and cartilage and testis, but not in other normal tissues. TRAG-3 has been reported to be a cancer/testis antigen. Our results suggest that CSAGE belongs to the growing list of cancer/testis antigens as well. In all of the CSAGE positive samples, the melanoma antigen gene family was also expressed. This is the first report on the expression of cancer/testis antigens in chondrosarcoma.

Clusterin expression in adult human normal and osteoarthritic articular cartilage

OBJECTIVE

To characterize the expression pattern of clusterin in adult human normal and osteoarthritic cartilage.

METHODS

Clusterin mRNA expression in adult human normal and osteoarthritic cartilage was investigated by analysis of cDNA libraries, TaqMan quantitative RT-PCR, microarray and in situ hybridization.

RESULTS

Sequence analysis of ESTs from adult human normal and osteoarthritic cartilage cDNA libraries demonstrated that the abundance of clusterin in these libraries was equivalent to genes which have been more commonly associated with cartilage. To examine tissue distribution, TaqMan Quantitative PCR analysis was performed using RNA from a panel of individual normal tissues. Clusterin was expressed at significant levels in cartilage, brain, liver, and pancreas. The expression of clusterin mRNA was up-regulated in early osteoarthritic vs normal cartilage when analysed by microarray analysis. Using in situ hybridization, chondrocytes of normal cartilage expressed moderate levels of clusterin. Upper mid-zone chondrocytes in cartilage with early stages of osteoarthritic disease expressed high levels of clusterin mRNA. In advanced osteoarthritic cartilage, the overall expression of clusterin was reduced.

CONCLUSION

The induction of clusterin has been associated with a variety of disease states where it appears to provide a cytoprotective effect. The increased expression of clusterin mRNA in the early stages of osteoarthritis (OA) may reflect an attempt by the chondrocytes to protect and repair the tissue. In contrast, the decrease in clusterin mRNA in the advanced osteoarthritic cartilage accompanies the final degenerative stages of the disease. An understanding of the expression of clusterin in osteoarthritis may allow consideration of this protein as a marker for cartilage changes in this chronic degenerative condition.

Identification and initial characterization of 5000 expressed sequenced tags (ESTs) each from adult human normal and osteoarthritic cartilage cDNA libraries

OBJECTIVE

To prepare, sequence and analyse adult human cartilage cDNA libraries to study the gene expression pattern between normal and osteoarthritic cartilage.

METHODS

Poly A(+)RNA from adult human normal and osteoarthritic articular cartilage was isolated and used to prepare cDNA libraries. Approximately 5000 ESTs from each library were sequenced and analysed using bioinformatic tools. The expression of select genes was confirmed by Northern blot and in situ hybridization analysis.

RESULTS

Multiple gene families including several classical cartilage matrix protein encoding genes were identified. Approximately 28-40% of the genes sequenced from these libraries were novel, while half of the genes encoded known proteins and 4-6% of the genes encoded novel homologs of known proteins. Several known genes, whose expression has not been reported previously in cartilage, were also identified. We have confirmed the cartilage expression of three known (CTGF, CTGF-L and clusterin) and two novel homologs of known genes (PCPE-2 and Gal-Nac transferase) by Northern blot and in situ hybridization analysis.

CONCLUSION

This is the first report of the preparation and sequencing of cDNA libraries from adult human normal and osteoarthritic articular cartilage. Further analysis of genes identified from these libraries may provide molecular targets for diagnosis and/or treatment of osteoarthritis (OA).

Matrix metalloproteinase-1, -3, -13 and aggrecanase-1 and -2 are differentially expressed in experimental osteoarthritis

The aim of this study was to characterize the cellular phenotypes of articular cartilage and meniscus in rabbits with experimentally induced osteoarthritis (OA), by histological and molecular biological techniques. OA was induced by severing the anterior cruciate ligament of the knee and rabbits were killed 2, 4 or 9 weeks following surgery. Our histological observations show a progressive destruction of extracellular matrix in both tissues. To determine whether these morphological changes could be related to alterations in the regulation of gene expression for a subset of relevant molecules, levels of mRNA for proteinases and one inhibitor (MMP-1, -3 and -13, aggrecanase-1 and -2 and TIMP-1), matrix molecules and one chaperone (type II and X collagens, aggrecan, osteonectin, betaig-h3 and BiP) were assessed by reverse transcription-polymerase chain reaction. Our results indicate that for most markers expression profiles were similar in both tissues. In particular, matrix protein gene expression remained stable or varied little during progression of OA, suggesting a poor repair capacity of the tissues. MMP gene expression increased rapidly whereas aggrecanase gene expression remained stable. These findings suggest that differential regulation of mRNA levels of MMP-1, -3 and -13 on the one hand and aggrecanase-1 and -2 on the other, occurs during OA.

Isolation of RNA from small human articular cartilage specimens allows quantification of mRNA expression levels in local articular cartilage defects

Human adult cartilage is an inherently difficult tissue from which to isolate RNA. The RNA isolation techniques described so far have generally only been successfully applied to the isolation of RNA from larger amounts of cartilage. However, it is important to be able to analyse focal cartilage lesions in order to understand the local processes in the cartilage degeneration process. Therefore, we have developed a protocol for isolating RNA directly from as little as 10 mg wet weight of cartilage followed by quantitative PCR analysis. We were able to analyse the expression levels of several genes in parallel including aggrecan and type II collagen.

The amino-terminal part of PRELP binds to heparin and heparan sulfate

PRELP (proline, arginine-rich end leucine-rich repeat protein) is an extracellular matrix leucine-rich repeat protein. The amino-terminal region of PRELP differs from that of other leucine-rich repeat proteins in containing a high number of proline and arginine residues. The clustered proline and basic residues are conserved in rat, bovine, and human PRELP. Although the function of PRELP is not yet known, the clustered arginine residues suggest a heparan sulfate/heparin-binding capacity. We show here that PRELP indeed binds heparin and heparan sulfate. Truncated PRELP without the amino-terminal region does not bind heparin. The dissociation constant for the interaction of PRELP with heparin was determined by an in solution binding assay and by surface plasmon resonance analysis to be in the range of 10-30 nm. A 6-mer heparin oligosaccharide was the smallest size showing binding to PRELP. The binding increased with increasing length up to an 18-mer and depended on the degree of sulfation of heparin as well as heparan sulfate. Sulfate groups at all positions were shown to be of importance for the binding. Fibroblasts bind PRELP, and this interaction is inhibited with heparin, suggesting a function for PRELP as a linker between the matrix and cell surface proteoglycans.

Reversal of autocrine and paracrine effects of interleukin 1 (IL-1) in human arthritis by type II IL-1 decoy receptor. Potential for pharmacological intervention

Interleukin 1 (IL-1), produced by both synovial cells and chondrocytes, plays a pivotal role in the pathogenesis of cartilage destruction in osteoarthritis (OA). We examined the specific expression and function of IL-1 receptor family-related genes in human joint tissues. Gene array analysis of human normal and OA-affected cartilage showed mRNA expression of IL-1 receptor accessory protein (IL-1RAcp) and IL-1 type I receptor (IL-1RI), but not IL-1 antagonist (IL-1ra) and IL-1 type II decoy receptor (IL-1RII). Similarly, human synovial and epithelial cells showed an absence of IL-1RII mRNA. Functional genomic analyses showed that soluble (s) IL-1RII, at picomolar concentrations, but not soluble TNF receptor:Fc, significantly inhibited IL-1beta-induced nitric oxide (NO) and/or prostaglandin E(2) production in chondrocytes, synovial and epithelial cells. In OA-affected cartilage, the IC(50) for inhibition of NO production by sIL-1RII was 2 log orders lower than that for sIL-1RI. Human chondrocytes that overexpressed IL-1RII were resistant to IL-1-induced IL-1beta mRNA accumulation and inhibition of proteoglycan synthesis. In osteoarthritis, deficient expression by chondrocytes of innate regulators or antagonists of IL-1 such as IL-1ra and IL-1RII (soluble or membrane form) may allow the catabolic effects of IL-1 to proceed unopposed. The sensitivity of IL-1 action to inhibition by sIL-1RII has therapeutic implications that could be directed toward correcting this unfavorable tissue(s) dependent imbalance.

Effective isolation of high-quality total RNA from human adult articular cartilage

The isolation of large quantities of good-quality RNA from human articular cartilage has been a long-standing problem for researchers working with human articular cartilage. In this paper we report a protocol which we have developed based on the Qiagen RNeasy procedure to produce high yields of purified, DNA-free RNA from normal and osteosteoarthritic human articular cartilage. The average yield of RNA was 8.39 microg/g (n = 59) for normal and 6.69 microg/g (n = 58) for osteoarthritic cartilage (average ratio OD 260/280 = 1.8-1.9). Quantitative PCR, cDNA array technology, and Northern blot analysis were used to verify the quality of the RNA.

Age-related effects of TGF-beta on proteoglycan synthesis in equine articular cartilage

The synthesis of proteoglycans was measured in normal equine articular cartilage of ages 9 months to 20 years and the effect of TGF-beta1 on this activity was investigated. The rate of incorporation of [(35)S]Na(2)SO(4) decreased with age as did the responsiveness of the tissue to the growth factor. The enhanced synthesis of proteoglycan induced at all ages by TGF-beta1 was down-regulated by IL-1 beta and retinoic acid. The expression of mRNA for TGF-beta1, 2, and 3 was also measured, and although the level of TGF-beta1 was highest at all ages, the expression of each growth factor decreased with age.

A comparison of various "housekeeping" probes for northern analysis of normal and osteoarthritic articular cartilage RNA

Several approaches are commonly used to normalize variations in RNA loading on Northern blots, including: ethidium bromide (EthBr) fluorescence of 18S or 28S rRNA or autoradiograms of radioactive probes hybridized with constitutively expressed RNAs such as elongation factor-1alpha (ELF), glyceraldehyde-3-phosphate dehydrogenase (G3PDH), actin, 18S or 28S rRNA, or others. However, in osteoarthritis (OA) the amount of total RNA changes significantly and none of these RNAs has been clearly demonstrated to be expressed at a constant level, so it is unclear if any of these approaches can be used reliably for normalizing RNA extracted from osteoarthritic cartilage. Total RNA was extracted from normal and osteoarthritic cartilage and assessed by EthBr fluorescence. RNA was then transferred to a nylon membrane hybridized with radioactive probes for ELF, G3PDH, Max, actin, and an oligo-dT probe. The autoradiographic signal across the six lanes of a gel was quantified by scanning densitometry. When compared on the basis of total RNA, the coefficient of variation was lowest for 28S ethidium bromide fluorescence and oligo-dT (approximately 7%), followed by 18S ethidium bromide fluorescence and G3PDH (approximately 13%). When these values were normalized to DNA concentration, the coefficient of variation exceeded 50% for all signals. Total RNA and the signals for 18S, 28S rRNA, and oligo-dT all correlated highly. These data indicate that osteoarthritic chondrocytes express similar ratios of mRNA to rRNA and mRNA to total RNA as do normal chondrocytes. Of all the "housekeeping" probes, G3PDH correlated best with the measurements of RNA. All of these "housekeeping" probes are expressed at greater levels by osteoarthritic chondrocytes when compared with normal chondrocytes. Thus, while G3PDH is satisfactory for evaluating the amount of RNA loaded, its level of expression is not the same in normal and osteoarthritic chondrocytes.

Differential expression of egr-1 in osteoarthritic compared to normal adult human articular cartilage

OBJECTIVE

The purpose of this study was to identify genes that are differentially expressed in normal versus osteoarthritic human articular cartilage as either potential novel therapeutic targets or diagnostic markers of this disease.

DESIGN

mRNA was isolated from histologically normal and osteoarthritic adult human articular cartilage. The Differential Display technique was employed which identified differentially expressed genes in the normal and diseased tissue. Northern and reverse Northern hybridization were used to confirm the gene expression pattern. Immunohistochemistry and in-situ hybridization were used to localize expression of Egr-1 protein and mRNA respectively in cartilage.

RESULTS

A transcription factor, early growth response protein-1 (Egr-1) was found to be down-regulated more than six-fold in multiple human OA cartilage samples when compared to normal tissue. Immunohistochemistry indicated that Egr-1 was expressed throughout normal adult cartilage, in deep-, mid- and superficial-zones. In contrast, in OA cartilage there was expression of Egr-1 mRNA and protein only in the chondrocytes undergoing cloning.

CONCLUSIONS

Egr-1 is differentially expressed in OA versus normal cartilage and because of its role in transcriptional activation and repression and regulation of proliferation, differentiation and apoptosis, Egr-1 may play an important role in the pathogenesis of OA. Up-regulation of Egr-1 may therefore provide a novel therapeutic approach for either the prevention or treatment of OA.

Physical map and characterization of transcripts in the candidate interval for familial chondrocalcinosis at chromosome 5p15.1

The gene for familial chondrocalcinosis (MIM 118600; gene symbol CCAL2) has been localized to a 0.8-cM interval on the short arm of chromosome 5, between the polymorphic microsatellite markers D5S416 and D5S2114. We have undertaken the physical and transcript mapping of this interval, as well as regions telomeric to the interval, in an attempt to define ultimately the gene for this disorder. The physical map is composed of YAC, BAC, PAC, and cosmid resources and spans a physical distance of approximately 0.3 Mb. Using cDNA selection, we have identified eight novel transcripts in and around the interval; two of the selected transcripts reside in the candidate interval. We have also more precisely placed several expressed sequence tags (ESTs) that were previously mapped by radiation hybrid analysis and were reported to reside in or near the candidate interval. Two of the ESTs analyzed overlap with the selected cDNAs that reside in the candidate interval. All of the selected cDNAs are expressed partial transcripts, as determined by Northern blot analysis, and using RT-PCR analysis, we have determined that the cDNAs that reside in the candidate interval are expressed in cartilage and synovium, tissues that are presumably relevant to the chondrocalcinosis phenotype.

Down-regulation of chondrocyte aggrecan and type-II collagen gene expression correlates with increases in static compression magnitude and duration

The goal of this study was to examine the simultaneous effects of mechanical compression of chondrocytes on mRNA expression and macromolecular synthesis of aggrecan and type-II collagen. Bovine cartilage explants were exposed to different magnitudes and durations of applied mechanical compression, and levels of aggrecan and type-IIa collagen mRNA normalized to glyceraldehyde-3-phosphate dehydrogenase were measured and quantified by Northern blot analysis. Synthesis of aggrecan and type-II collagen protein was measured by radiolabel incorporation of [35S]sulfate and [3H]proline into macromolecules. The results showed a dose-dependent decrease in mRNA levels for aggrecan and type-II collagen, with increasing compression relative to physiological cut thickness applied for 24 hours. Radiolabel incorporation into glycosaminoglycans and collagen also decreased with increasing compression in a dose-related manner similar to the changes seen in mRNA expression. The modulation of aggrecan and type-II collagen mRNA and protein synthesis were dependent on the duration of the compression. Aggrecan and type-II collagen mRNA expression increased during the initial 0.5 hours of static compression; however, 4-24 hours after compression was applied total mRNA levels had significantly decreased. The synthesis of aggrecan and collagen protein decreased more rapidly than did mRNA levels after the application of a step compression. Together, these results suggest that mechanical compression rapidly alters chondrocyte aggrecan and type-II collagen gene expression on application of load. However, our results indicate that the observed decreases in biosynthesis may not be related solely to changes in mRNA expression. The mechanisms by which mechanical forces affect different segments of the biosynthetic pathways remain to be determined.

Cynomolgus monkey (Macaca fascicularis) cathepsin K: cloning, expression, purification, and activation

Methodology for the production of recombinant active cynomolgus monkey (Macaca fascicularis) cathepsin K (EC 3.4.22.38) was elucidated. The cDNA encoding the cathepsin K was cloned from female M. cynomolgus monkey mRNA. The deduced amino acid sequence of M. cynomolgus preprocathepsin K from the cDNA sequence showed 94.2% identity to human preprocathepsin K. Sequence differences occurred only in the prepro- domains; the mature domains were identical. The recombinant M. cynomolgus cathepsin K was expressed as a secreted proenzyme using baculovirus-infected SF21 insect cells having the predicted N-terminus (LYPEEILDTH ellipsis ), indicating proper cleavage of the secretion sequence. Purified monkey procathepsin K was activated under autocatalytic conditions at pH 4.0. The mature enzyme was composed of mixture of enzymes having N-termini of Gly113 and Arg114. The molecular weight was determined to be 23,668.3 Da by MALDI-TOF-MS which is consistent with the absence of carbohydrate on the mature enzyme. These results indicate that monkey procathepsin K is able to autoactivate and produces a mature enzyme which is identical to that of human cathepsin K. Since the sequence of monkey and human mature cathepsin K are identical and the in vitro activation mechanisms appear to be indistinguishable, monkeys are predicted to be a good animal model for evaluating cathepsin K inhibitors in vivo as therapeutic agents for diseases characterized by excessive bone loss, such as osteoporosis.

Terminal differentiation of chondrocytes is arrested at distinct stages identified by their expression repertoire of marker genes

During endochondral bone formation, cells in the emerging cartilaginous model transit through a cascade of several chondrocyte differentiation stages, each characterized by a specific expression repertoire of matrix macromolecules, until, as a final step, the hypertrophic cartilage is replaced by bone. In many permanent cartilage tissues, however, late differentiation of chondrocytes does not occur, due to negative regulation by the environment of the cells. Here, addressing the reason for the difference between chondrocyte fates in the chicken embryo sternum, cells from the caudal and cranial part were cultured separately in serum-free agarose gels with complements defined earlier that either permit or prevent hypertrophic development. Total RNA was extracted using a novel protocol adapted to agarose cultures, and the temporal changes in developmental stage-specific mRNA expression were monitored by Northern hybridization and phosphor image analysis. Kinetic studies of the mRNA accumulation not only showed significant differences between the expression patterns of cranial and caudal cultures after recovery, but also revealed two checkpoints of chondrocyte differentiation in keeping with cartilage development in vivo. Terminal differentiation of caudal chondrocytes is blocked at the late proliferative stage (stage Ib), while the cranial cells can undergo hypertrophic development spontaneously. The differentiation of cranial chondrocytes is reversible, since they can re-assume an early proliferative (stage Ia) phenotype under the influence of insulin, fibroblast growth factor-2 and transforming growth factor-beta in combination. Thus, the expression pattern in the latter culture resembles that of articular chondrocytes. We also provide evidence that the capacities of caudal and sternal chondrocytes to progress from the late proliferative (stage Ib) to hypertrophic stage (stage II) correlate with their differing abilities to express the Indian hedgehog gene.

Cloning and deduced amino acid sequence of a novel cartilage protein (CILP) identifies a proform including a nucleotide pyrophosphohydrolase

The cDNA cloning and expression in vitro and in eukaryotic cells of a novel protein isolated from human articular cartilage, cartilage intermediate layer protein (CILP) is described. A single 4. 2-kilobase mRNA detected in human articular cartilage encodes a polypeptide of 1184 amino acids with a calculated molecular mass of 132.5 kDa. The protein has a putative signal peptide of 21 amino acids, and is a proform of two polypeptides. The amino-terminal half corresponds to CILP (molecular mass of 78.5 kDa, not including post-translational modifications) and the carboxyl-terminal half corresponds to a protein homologous to a porcine nucleotide pyrophosphohydrolase, NTPPHase (molecular mass of 51.8 kDa, not including post-translational modifications). CILP has 30 cysteines and six putative N-glycosylation sites. The human homolog of porcine NTPPHase described here contains 10 cysteine residues and two putative N-glycosylation sites. In the precursor protein the NTPPHase region is immediately preceded by a tetrapeptide conforming to a furin proteinase cleavage consensus sequence. Expression of the full-length cDNA in a cell-free translation system and in COS-7 or EBNA cells indicates that the precursor protein is synthesized as a single polypeptide chain that is processed, possibly by a furin-like protease, into two polypeptides upon or preceding secretion.

Differential splicing of type II procollagen mRNA in canine retina

Canine retina expressed two forms of Type II procollagen mRNA, IIA and IIB, due to alternate splicing of exon 2 at the N-propeptide region. The N-propeptide region of Type II procollagen showed a high degree of homology with human, approximately 96% both at the nucleotide and the amino acid levels. Expression of IIA and IIB forms of Type II procollagen from early stage of development to adult life suggests the important role of both forms for the development as well as maintenance of the ocular structure.

Expression of the (V+C)- fibronectin isoform is tightly linked to the presence of a cartilaginous matrix

Fibronectin is encoded by a single gene, but heterogeneity is introduced by alternative splicing of the pre-mRNA. An unique splice variant, designated (V+C)-, which deletes nucleotides encoding the V, III-15 and I-10 segments, has been identified in articular cartilage. In this study, a ribonuclease protection assay was used to quantitate expression of the (V+C)- isoform in eight canine cartilaginous tissues and in chondrocytes cultured as monolayers or in alginate beads. The (V+C)- fibronectin isoform was detected in all cartilaginous tissues examined, ranging from a low of 11% of steady-state fibronectin mRNA in the nucleus pulposus to 71% in the rib. An age dependent increase, from 18% in the epiphyseal cartilage of a newborn to 54% in the articular cartilage of dogs over 10 months of age, was observed. The ubiquitous presence of this isoform in cartilaginous tissues and its absence in all non-cartilaginous tissues examined to date is consistent with a very strong association of the (V+C)- fibronectin isoform with the cartilaginous phenotype. Results from a ribonuclease protection assay using a probe extending into the V region from III-14 were combined with the quantitative information about (V+C)- fibronection expression to develop an over-all profile of splicing within the V region in cartilage. Monolayer culture of articular chondrocytes altered fibronectin splicing patterns. The (V+C)- isoform was rapidly lost and ED-A(+) fibronectin was induced. Three-dimensional culture in alginate beads prevented induction of ED-A(+) fibronection, but failed to sustain expression of the (V+C)- isoform. Thus, some matrix component or structure, lost in cell culture, may be essential to maintain expression of the (V+C)- isoform. The possible relationship of changing patterns of fibronectin isoforms in cultured chondrocytes to maintenance of the differentiated phenotype is discussed.

Expression of type X collagen and matrix calcification in three-dimensional cultures of immortalized temperature-sensitive chondrocytes derived from adult human articular cartilage

Chondrocytes isolated from normal adult human articular cartilage were infected with a retroviral vector encoding a temperature-sensitive mutant of the simian virus 40 large tumor antigen and a linked geneticin (G418)-resistance marker. G418-resistant colonies were then isolated, ring-cloned, and expanded in serum-containing media. Several immortalized chondrocyte cell lines were established from the clones that survived, some of which have been maintained in continuous culture for over 2 years. Despite serial subcultures and maintenance as monolayers, these cells retain expression of markers specific for cells of the lineage, namely type II collagen and aggrecan, detected immunocytochemically. We also examined the phenotype of three of these immortalized cell lines (designated HAC [human articular chondrocyte]) using a pellet culture system, and in this report, we present evidence that a prototype of these lines (HAC-F cells) expresses markers normally associated with hypertrophic chondrocytes. When HAC-F cells were cultivated in centrifuge tubes, for periods of up to 63 days, at 39 degrees C with mild and intermittent centrifugation they continued to express both lineage markers; total type II collagen/pellet remained stable, whereas there was a temporal decrease in cartilage-specific glycosaminoglycans content. In addition, in the presence of ascorbate but in the absence of a phosphate donor or inorganic phosphate supplement, the cells also begin to express a hypertrophic phenotype characterized by type X collagen synthesis and extensive mineralization of the extracellular matrix in late stage cultures. The mRNA encoding type X collagen was detected in the cell pellets by reverse transcriptase polymerase chain reaction as early as day 2, and anti-type X collagen immunoreactivity was subsequently localized in the matrix. The mineral was characterized by energy-dispersive X-ray microanalysis as containing calcium (Ca) and phosphorus (P) with a Ca:P peak height ratio close to that of mineralized bone tissue. The unexpected phenotype of this human chondrocyte cell line provides an interesting opportunity for studying chondrocyte maturation in vitro.

p53 mutations in chondrosarcoma

Chondrosarcoma is a primary bone tumor that has several different grades and variants. We evaluated 48 chondrosarcomas for p53 overexpression and p53 mutations. p53 expression was evaluated with immunohistochemistry using monoclonal antibodies PAb421, PAb1801, and PAb240. p53 mutations were identified with single-strand conformational polymorphism (SSCP) and DNA sequencing in selected cases. Immunohistochemistry revealed nuclear staining with PAb421 and PAb1801 in the spindle cell portion of one dedifferentiated chondrosarcoma. SSCP analysis was abnormal only in the case with positive immunostaining and localized the mutation to exons 7 and 8. DNA sequence analysis identified a point mutation of G to C in codon 276, resulting in an amino acid substitution of proline for alanine. This point mutation has been reported previously in other tumors but not in chondrosarcoma. Assimilation of our results with previous studies suggests that p53 mutations are present in a minority of chondrosarcomas but when present, are in higher grade chondrosarcomas and their variants.

Matrix metalloproteinase MMP-19 (RASI-1) is expressed on the surface of activated peripheral blood mononuclear cells and is detected as an autoantigen in rheumatoid arthritis

In order to characterize the autoimmune response participating in the pathogenesis of rheumatoid arthritis (RA) a cDNA expression library constructed from mRNAs which had been isolated from the inflamed synovium of an RA patients was screened with autologous IgG autoantibodies. This led to the identification of gene rasi-1 which encodes a protein showing sequence identity with the zinc-binding matrix metalloproteinase MMP-19. MMP-19 is detected on the surface of activated PBMCs, TH1 lymphocytes, and Jurkat T lymphoma cells. It exhibits gelatinolytic activity and is recognized by autoantibodies in 26% and, respectively, 33% of sera collected from RA patients and systemic lupus erythematosus (SLE) patients. The novel autoantigen MMP-19 thus could play a role in the pathological processes participating in RA-associated joint tissue destruction.

Utilization of a recombinant substrate rAgg1 to study the biochemical properties of aggrecanase in cell culture systems

This paper describes the first report of the production and use of an artificial recombinant protein substrate to study "aggrecanase" activity. The substrate (rAgg1) is composed of the complete interglobular domain (IGD) of human aggrecan flanked by the "marker" sequences FLAGTM at the amino terminus and the human immunoglobulin G1 constant region at the carboxyl terminus. The expressed protein occurs as large multimolecular aggregates (>120 kDa) that, upon reduction, consist of a major isoform of 72 kDa (containing the IGD) and a minor 39-kDa species that through alternative splicing has had the IGD deleted. Using this recombinant substrate we developed a novel agarose cell culture system containing either rat chondrosarcoma or bovine chondrocytes that could be used in studies of the biochemical characterization of aggrecanase activities. These studies showed the following. (i) rAgg1 is a suitable substrate for aggrecanase proteolysis. (ii) Aggrecanase activity was specifically induced by exposing chondrocytes to retinoic acid. (iii) A considerable time period was required to synthesize and/or activate aggrecanase, with considerable differences in that found in rat chondrosarcoma versus bovine chondrocyte culture systems. (iv) Aggrecanase cleavage of the aggrecan IGD does not require the presence of the G1 or G2 globular domains or keratan sulfate post-translational modification in the IGD. (v) Aggrecanase is a diffusible activity that does not require association with the chondrocyte plasma membrane or immediate pericellular matrix for its action.

Superinduction of cyclooxygenase-2 activity in human osteoarthritis-affected cartilage. Influence of nitric oxide

Cartilage specimens from osteoarthritis (OA)-affected patients spontaneously released PGE2 at 48 h in ex vivo culture at levels at least 50-fold higher than in normal cartilage and 18-fold higher than in normal cartilage + cytokines + endotoxin. The superinduction of PGE2 production coincides with the upregulation of cyclooxygenase-2 (COX-2) in OA-affected cartilage. Production of both nitric oxide (NO) and PGE2 by OA cartilage explants is regulated at the level of transcription and translation. Dexamethasone inhibited only the spontaneously released PGE2 production, and not NO, in OA-affected cartilage. The NO synthase inhibitor HN(G)-monomethyl-L-arginine monoacetate inhibited OA cartilage NO production by > 90%, but augmented significantly (twofold) the spontaneous production of PGE2 in the same explants. Similarly, addition of exogenous NO donors to OA cartilage significantly inhibited PGE2 production. Cytokine + endotoxin stimulation of OA explants increased PGE2 production above the spontaneous release. Addition of L-NMMA further augmented cytokine-induced PGE2 production by at least fourfold. Inhibition of PGE2 by COX-2 inhibitors (dexamethasone or indomethacin) or addition of exogenous PGE2 did not significantly affect the spontaneous NO production. These data indicate that human OA-affected cartilage in ex vivo conditions shows (a) superinduction of PGE2 due to upregulation of COX-2, and (b) spontaneous release of NO that acts as an autacoid to attenuate the production of the COX-2 products such as PGE2. These studies, together with others, also suggest that PGE2 may be differentially regulated in normal and OA-affected chondrocytes.

Gene expression of type II collagens in chondro-osteophytes in experimental osteoarthritis

The formation of chondro-osteophytes in osteoarthritic joints is a unique example of adult neochondrogenesis that bears some similarities to growth plate elongation and fracture callus formation. This study uses in situ hybridization histochemistry to define the molecular phenotype of cells in active chondro-osteophytes. Chondro-osteophytes are composed of fibrocytes and osteoblasts that express type I procollagen mRNA, mesenchymal prechondrochytes that express type IIA procollagen mRNA, and maturing chondrocytes that express type IIB procollagen mRNA. Based on the spatial pattern of gene expression and cytomorphology, the neochondrogenesis associated with chondro-osteophyte formation closely resembles that of healing fracture callus.

Quantification of aggrecan and link-protein mRNA in human articular cartilage of different ages by competitive reverse transcriptase-PCR

A competitive reverse transcriptase-PCR (RT-PCR) assay has been developed for the quantification of particular mRNA species in human articular cartilage. Competitor RNA species were synthesized that differed from the amplified target sequence only by the central insertion of an EcoRI restriction site. By using known amounts of synthetic target and competitor RNA, it was shown that competitor RNA molecules designed in this way are reverse-transcribed and amplified with equal efficiency to the target of interest. Furthermore quantification could be performed during the plateau phase of the PCR, which was necessary when using ethidium bromide fluorescence as a detection system. The inhibition of aggrecan and link-protein mRNA expression by interleukin 1 or tumour necrosis factor in monolayers of human articular chondrocytes quantified by this competitive RT-PCR method compared favourably with Northern hybridization studies. The main advantage of this technique is that it can be used to quantify levels of mRNA with RNA extracted directly from 100 mg wet weight of human articular cartilage. Age-related changes in aggrecan and link-protein mRNA were therefore quantified in human articular cartilage directly after dissection from the joint. The concentration of link-protein mRNA was higher in immature cartilage than in mature cartilage when expressed relative to the amount of glyceraldehyde-3-phosphate dehydrogenase mRNA, but no age-related changes were observed in aggrecan mRNA expression. The ratio of aggrecan to link-protein mRNA was higher in mature cartilage than in immature tissue. These age-related differences in the molecular stoichiometry of aggrecan and link-protein mRNA might have implications with respect to the regulation of the formation and the stability of the proteoglycan aggregates in cartilage.

Expression of biglycan, decorin and fibromodulin in the hypertrophic phase of experimental osteoarthritis

This study sought to assess the relative levels of the mRNAs of the core proteins of the small proteoglycans (PGs) biglycan, decorin and fibromodulin in the hypertrophic phase of the early osteoarthritis (OA) that follows joint injury. Experimental OA was induced in eight dogs by transection of the anterior cruciate ligament. Articular cartilage was harvested from each joint, the total RNA was extracted and the concentration of DNA in the cartilage was measured. The relative levels of mRNA for biglycan, decorin and fibromodulin were assessed by northern blot analyses. An increase in cartilage mass with no increase in DNA concentration confirmed that the joints were in the hypertrophic phase that follows joint injury. The total RNA per microgram of DNA was increased 2.5 times. Compared with control cartilage, the mRNA levels in osteoarthritic cartilage, when normalized to the concentration of DNA, were increased 3.9 times for biglycan, 1.2 times for decorin and 2.4 times for fibromodulin. Because these small PGs affect collagen fibrillogenesis in vitro, their discoordinate metabolism may contribute to the abnormal collagen formation and deposition that occurs in OA and to the ultimate failure of the articular cartilage.

Fibronectin mRNA splice variant in articular cartilage lacks bases encoding the V, III-15, and I-10 protein segments

Fibronectin is an extracellular matrix glycoprotein encoded by a single gene. Alternative RNA splicing has been reported at three sites, ED (extra type III domain)-A, ED-B, and the variable or V region. Articular cartilage fibronectin monomers are rarely (ED-A)+, but approximately 25% are (ED-B)+. RNA gel electrophoresis and Northern blot analysis identified two (ED-B)+ and two (ED-B)- fibronectin transcripts in cartilage, each pair differing by approximately 750 bases. This difference results from a previously unreported RNA splicing pattern that eliminates not only the V region but also nucleotides encoding protein segments III-15 and I-10. This new splice variant, which we designate (V+C)-, represents the majority of fibronectin transcripts in equine, canine, and rabbit articular cartilage but is absent in the liver. Reverse transcriptase-polymerase chain reaction analyses of 11 additional equine tissues failed to detect the (V+C)- splice variant, except for very low levels in lymph node, bone, aorta, and skin. Furthermore, chondrocytes grown in monolayer culture maintain high levels of fibronectin expression but stop expressing (V+C)- transcripts over time. The tissue-specific expression pattern of this novel fibronectin isoform suggests that it may have an important function in the matrix organization of cartilage.

The primary structure of a basic leucine-rich repeat protein, PRELP, found in connective tissues

We have determined the primary structure of a connective tissue matrix protein from the nucleotide sequence of a clone isolated from a human articular chondrocyte cDNA library. The major part of the amino acid sequence has also been determined by direct protein sequencing. The translated primary sequence corresponds to 382 amino acid residues, including a 20-residue signal peptide. The molecular mass of the mature protein is 41,646 Da. The main part of the protein consists of 10 leucine-rich repeats ranging in length from 20 to 26 residues, with asparagine at position 10 (B-type). The N-terminal part is unusual in that it is basic and rich in arginine and proline. There are four potential N-linked glycosylation sites present. In three of these sites, post-translational modifications are likely to be present since Asn was not found by direct protein sequencing. The amino- and carboxyl-terminal parts contain four and two cysteine residues, respectively, probably forming disulfide bonds by analogy with the other members of this family. The protein shows highest identity (36%) to fibromodulin and 33% to bovine lumican, two other leucine-rich repeat connective tissue proteins. Northern blot analysis showed the presence of an approximately 3.8-kilobase mRNA in different types of bovine cartilage and cultured osteoblasts, whereas RNAs isolated from bovine kidney, skin, spleen, thymus, and trabecular bone and rat calvaria were negative. Human articular chondrocyte and rat chondrosarcoma cell RNAs contained an additional mRNA of approximately 1.6 and 1.8 kilobases, respectively.

Effects of tenidap on canine experimental osteoarthritis. I. Morphologic and metalloprotease analysis

OBJECTIVE

To examine the effects of tenidap and diclofenac on osteoarthritic lesions and metalloprotease activity in experimental osteoarthritis (OA).

METHODS

The anterior cruciate ligament of the right stifle joint of 25 mongrel dogs was sectioned by a stab wound. Seven dogs received no treatment, 6 were treated with oral omeprazole (20 mg/day), another 6 were treated with diclofenac (0.25 mg/kg/twice daily) plus omeprazole (20 mg/day), and 6 received oral tenidap (3 mg/kg/twice daily) plus omeprazole (20 mg/day). The dogs received medication for 8 weeks; all dogs were killed at the end of this period. Eight normal dogs were used as controls. Lesions were evaluated macroscopically for the incidence and size of osteophytes and the area and grade of cartilage erosions on the condyles and plateaus, along with histologic evaluation of the severity of the cartilage lesions and synovial inflammation. Stromelysin and collagenase activities and the collagenase messenger RNA (mRNA) level were measured in cartilage and synovial membrane.

RESULTS

Compared with the untreated or omeprazole-treated OA groups, the dogs treated with tenidap exhibited significant reduction in the incidence (P < or = 0.001) and size (P < or = 0.0001) of osteophytes. Tenidap also significantly decreased the size and grade of cartilage macroscopic lesions, as well as the histologic severity of cartilage lesions on both condyles and plateaus. The histologic severity of synovial inflammatory reaction was also significantly reduced (P < or = 0.003) in the tenidap group. Tenidap markedly decreased stromelysin and collagenase activity in both cartilage (stromelysin P < or = 0.003; collagenase P < or = 0.01) and synovial membrane (stromelysin P < or = 0.003; collagenase P < or = 0.005). Moreover, tenidap also decreased the collagenase mRNA level in cartilage (P < or = 0.005) and synovial membrane (P < or = 0.002). Diclofenac slightly reduced the incidence and size of osteophytes and cartilage lesions, but these changes were not statistically significant. Diclofenac had no effect on the severity of synovial inflammation, metalloprotease activity, or collagenase expression.

CONCLUSION

This study showed that tenidap had a more potent anti-osteoarthritic effect than diclofenac in this model. The effect of the drug in suppressing metalloprotease synthesis, a process known to play a major role in the pathophysiology of osteoarthritic lesions, may explain its mechanism of action.

Isolation, characterization, and primary structure of a calcium-binding 63-kDa bone protein

A novel noncollagenous protein of the mineralized matrix of bovine bone was isolated by ion exchange and gel permeation chromatography. The apparent M(r) of the protein is 63,000 as determined by SDS-polyacrylamide gel electrophoresis. The protein is a rather minor constituent in bone and could not be detected in other connective tissues by enzyme-linked immunosorbent assay of guanidine HCl extracts. The 63-kDa protein was detected in the osteoid and around the osteocytes upon immuno-histochemical staining of bovine compact bone. The sequence of the 63-kDa protein was deduced from cDNA clones isolated from a rat calvaria lambda gt11 expression library. The protein contains two centrally located EF-hand Ca(2+)-binding domains. Seven heptad repeats are present indicating the ability of the protein for coiled-coil interactions. Ability to bind calcium was confirmed by 45Ca2+ binding to protein blotted onto nitrocellulose membrane. The protein was synthesized in calvaria explants as detected by immunoprecipitation of radiolabeled protein from the culture medium. Although the protein can be detected in biochemical amounts in bone only, varying amounts of mRNA for this protein were detected in several rat tissues by RNase protection assay with highest levels in rat calvaria. This extracellular protein corresponds to a mouse protein called nucleobindin.

Discoordinate gene expression of aggrecan and type II collagen in experimental osteoarthritis

OBJECTIVE

To quantify the gene expression of aggrecan core protein and type II collagen in an experimental animal model of osteoarthritis (OA).

METHODS

Total RNA was extracted from the articular cartilage of unoperated knee joints and from OA joints produced by anterior cruciate ligament transection. The relative amounts of type II collagen and aggrecan core protein messenger RNA (mRNA) were evaluated by Northern blot analysis.

RESULTS

Total RNA was elevated 2.5 times, aggrecan mRNA was elevated 2 times, and type II collagen mRNA was elevated 8 times, in OA knees compared to unoperated controls.

CONCLUSION

Chondrocytes are activated metabolically in response to joint injury. Discoordinate gene expression of aggrecan and type II collagen is characteristic of early experimental OA, and we speculate that it may contribute to its pathogenesis.

Alternative splicing of ED-A and ED-B sequences of fibronectin pre-mRNA differs in chondrocytes from different cartilaginous tissues and can be modulated by biological factors

The alternative splicing of the ED-A and ED-B segments of fibronectin pre-mRNA was examined in epiphyseal, costal, and meniscal cartilage from 3-week-old beagles and in nasal, tracheal, articular, and meniscal cartilage from 1- and 2-year-old Labrador retrievers. In contrast to the 100% expression of ED-B(+) mRNA that has been reported for embryonic chick cartilage (Bennett, V.D., Pallante, K.M., and Adams, S.K. (1991) J. Biol. Chem. 266, 5918-5924), all cartilages studied expressed both the ED-B(+) and ED-B(-) forms of fibronectin mRNA with the exception of the trachea, in which expression was 100% ED-B(-). Of all cartilages studied, only the meniscus had detectable levels of ED-A(+) mRNA. Placing articular cartilage chondrocytes in primary monolayer culture dramatically up-regulated the expression of ED-A(+) mRNA to 25% of the total, and this expression was further increased by the addition of transforming growth factor beta 1 or fucoidan to the culture medium. The expression of ED-B(+) mRNA remained at about 18% in the cultured chondrocytes and was not further affected by either transforming growth factor beta 1 or fucoidan. In contrast, dibutyryl cyclic adenosine monophosphate decreased the relative expression of both the ED-A(+) and ED-B(+) forms of fibronectin pre-mRNA. We concluded that the expression of ED-B(+) fibronectin remains relatively high in chondrocytes from cartilaginous canine tissues (15-35%) with the exception of the trachea, in contrast to the less than 10% expression of ED-B(+) fibronectin reported for other non-fetal tissues.