Global comparative transcriptome analysis of cartilage formation in vivo

<p>Abstract</p> <p>Background</p> <p>During vertebrate embryogenesis the initial stages of bone formation by endochondral ossification involve the aggregation and proliferation of mesenchymal cells into condensations. Continued growth of the condensations and differentiation of the mesenchymal cells into chondrocytes results in the formation of cartilage templates, or anlagen, which prefigure the shape of the future bones. The chondrocytes in the anlagen further differentiate by undergoing a complex sequence of maturation and hypertrophy, and are eventually replaced by mineralized bone. Regulation of the onset of chondrogenesis is incompletely understood, and would be informed by comprehensive analyses of <it>in vivo </it>gene expression.</p> <p>Results</p> <p>Tibial and fibular pre-condensed mesenchyme was microdissected from mouse hind limbs at 11.5 dpc, and the corresponding condensations at 12.5 dpc and cartilage anlagen at 13.5 dpc. Total RNA was isolated, and cRNA generated by linear amplification was interrogated using mouse whole genome microarrays. Differential expression was validated by quantitative PCR for <it>Agc1</it>, <it>Bmp8a</it>, <it>Col2a1</it>, <it>Fgfr4</it>, <it>Foxa3</it>, <it>Gdf5</it>, <it>Klf2</it>, <it>Klf4</it>, <it>Lepre1</it>, <it>Ncad</it>, <it>Sox11</it>, and <it>Trpv4</it>. Further, independent validation of the microarray data was achieved by <it>in situ </it>hybridization to analyse the expression of <it>Lepre1</it>, <it>Pcdh8</it>, <it>Sox11</it>, and <it>Trpv4 </it>from 11.5 dpc to 13.5 dpc during mouse hind limb development. We found significant differential expression of 931 genes during these early stages of chondrogenesis. Of these, 380 genes were down-regulated and 551 up-regulated. Our studies characterized the expression pattern of gene families previously associated with chondrogenesis, such as adhesion molecules, secreted signalling molecules, transcription factors, and extracellular matrix components. Gene ontology approaches identified 892 differentially expressed genes not previously identified during the initiation of chondrogenesis. These included several <it>Bmp, Gdf, Wnt, Sox and Fox </it>family members.</p> <p>Conclusion</p> <p>These data represent the first global gene expression profiling analysis of chondrogenic tissues during <it>in vivo </it>development. They identify genes for further study on their functional roles in chondrogenesis, and provide a comprehensive and important resource for future studies on cartilage development and disease.</p

Deficiency of annexins A5 and A6 induces complex changes in the transcriptome of growth plate cartilage but does not inhibit the induction of mineralization

Initiation of mineralization during endochondral ossification is a multistep process and has been assumed to correlate with specific interactions of annexins A5 and A6 and collagens. However, skeletal development appears to be normal in mice deficient for either A5 or A6, and the highly conserved structures led to the assumption that A5 and A6 may fulfill redundant functions. We have now generated mice deficient of both proteins. These mice were viable and fertile and showed no obvious abnormalities. Assessment of skeletal elements using histologic, ultrastructural, and peripheral quantitative computed tomographic methods revealed that mineralization and development of the skeleton were not significantly affected in mutant mice. Otherwise, global gene expression analysis showed subtle changes at the transcriptome level of genes involved in cell growth and intermediate metabolism. These results indicate that annexins A5 and A6 may not represent the essential annexins that promote mineralization in vivo

S100A8 and S100A9 in experimental osteoarthritis

INTRODUCTION: The objective was to evaluate the changes in S100A8 S100A9, and their complex (S100A8/S100A9) in cartilage during the onset of osteoarthritis (OA) as opposed to inflammatory arthritis. METHODS: S100A8 and S100A9 protein localization were determined in antigen-induced inflammatory arthritis in mice, mouse femoral head cartilage explants stimulated with interleukin-1 (IL-1), and in surgically-induced OA in mice. Microarray expression profiling of all S100 proteins in cartilage was evaluated at different times after initiation of degradation in femoral head explant cultures stimulated with IL-1 and surgically-induced OA. The effect of S100A8, S100A9 or the complex on the expression of aggrecan (Acan), collagen II (Col2a1), disintegrin and metalloproteases with thrombospondin motifs (Adamts1, Adamts 4 &Adamts 5), matrix metalloproteases (Mmp1, Mmp3, Mmp13 &Mmp14) and tissue inhibitors of metalloproteinases (Timp1, Timp2 &Timp3), by primary adult ovine articular chondrocytes was determined using real time quantitative reverse transcription polymerase chain reaction (qRT-PCR). RESULTS: Stimulation with IL-1 increased chondrocyte S100a8 and S100a9 mRNA and protein levels. There was increased chondrocyte mRNA expression of S100a8 and S100a9 in early but not late mouse OA. However, loss of the S100A8 staining in chondrocytes occurred as mouse OA progressed, in contrast to the positive reactivity for both S100A8 and S100A9 in chondrocytes in inflammatory arthritis in mice. Homodimeric S100A8 and S100A9, but not the heterodimeric complex, significantly upregulated chondrocyte Adamts1, Adamts4 and Adamts 5, Mmp1, Mmp3 and Mmp13 gene expression, while collagen II and aggrecan mRNAs were significantly decreased. CONCLUSIONS: Chondrocyte derived S100A8 and S100A9 may have a sustained role in cartilage degradation in inflammatory arthritis. In contrast, while these proteins may have a role in initiating early cartilage degradation in OA by upregulating MMPs and aggrecanases, their reduced expression in late stages of OA suggests they do not have an ongoing role in cartilage degradation in this non-inflammatory arthropathy

Identification of TGFβ-related genes regulated in murine osteoarthritis and chondrocyte hypertrophy by comparison of multiple microarray datasets

Objective: Osteoarthritis (OA) is a joint disease characterized by progressive degeneration of articular cartilage. Some features of OA, including chondrocyte hypertrophy and focal calcification of articular cartilage, resemble the endochondral ossification processes. Alterations in transforming growth factor β (TGFβ) signaling have been associated with OA as well as with chondrocyte hypertrophy. Our aim was to identify novel candidate genes implicated in chondrocyte hypertrophy during OA pathogenesis by determining which TGFβ-related genes are regulated during murine OA and endochondral ossification. Methods: A list of 580 TGFβ-related genes, including TGFβ signaling pathway components and TGFβ-target genes, was generated. Regulation of these TGFβ-related genes was a

Fluorescent immunohistochemistry of articular cartilage.

<p>Collagen II (A, B) and collagen VI (C, D) protein localization was unaffected by RNA<i>later</i>/EDTA, pH 5.2 decalcification (B, D) compared to conventional EDTA decalcification (A, C). Using both methods collagen II can be seen in both the pericellular and extracellular matrix, while collagen VI is predominantly localized to the pericellular matrix. DAPI was used as a nuclear stain. Scale bars = 50 µm.</p

<i>In situ</i> hybridization for <i>Prg4</i> and <i>Col2a1</i>.

<p>Cryosections from tibia decalcified with EDTA (A,B) or RNA<i>later</i>/EDTA at pH5.2 (C–F) were hybridized with DIG-labeled <i>Prg4</i> antisense (A,C) or sense (B,D) RNA probes, and against ³⁵S-labeled <i>Col2a1</i> antisense (E) or sense (F) RNA probes for <i>Col2a1</i>. Arrows show representative regions of target gene mRNA expression. Scale bars = 100 µm (A–D), 10 µm (E, F).</p