Osteoarthritis (OA), the most prevalent aging-related joint disease, is characterized by insufficient extracellular matrix synthesis and articular cartilage degradation, mediated by several proteinases, including Adamts-5. miR-140 is one of a very limited number of noncoding microRNAs (miRNAs) specifically expressed in cartilage; however, its role in development and/or tissue maintenance is largely uncharacterized. To examine miR-140 function in tissue development and homeostasis, we generated a mouse line through a targeted deletion of miR-140. miR-140−/− mice manifested a mild skeletal phenotype with a short stature, although the structure of the articular joint cartilage appeared grossly normal in 1-mo-old miR-140−/− mice. Interestingly, miR-140−/− mice showed age-related OA-like changes characterized by proteoglycan loss and fibrillation of articular cartilage. Conversely, transgenic (TG) mice overexpressing miR-140 in cartilage were resistant to antigen-induced arthritis. OA-like changes in miR-140-deficient mice can be attributed, in part, to elevated Adamts-5 expression, regulated directly by miR-140. We show that miR-140 regulates cartilage development and homeostasis, and its loss contributes to the development of age-related OA-like changes.

Objective Several microRNA, which are ∼22‐nucleotide noncoding RNAs, exhibit tissue‐specific or developmental stage–specific expression patterns and are associated with human diseases. The objective of this study was to identify the expression pattern of microRNA‐146 (miR‐146) in synovial tissue from patients with rheumatoid arthritis (RA). Methods The expression of miR‐146 in synovial tissue from 5 patients with RA, 5 patients with osteoarthritis (OA), and 1 normal subject was analyzed by quantitative reverse transcription–polymerase chain reaction (RT‐PCR) and by in situ hybridization and immunohistochemistry of tissue sections. Induction of miR‐146 following stimulation with tumor necrosis factor α (TNFα) and interleukin‐1β (IL‐1β) of cultures of human rheumatoid arthritis synovial fibroblasts (RASFs) was examined by quantitative PCR and RT‐PCR. Results Mature miR‐146a and primary miR‐146a/b were highly expressed in RA synovial tissue, which also expressed TNFα, but the 2 microRNA were less highly expressed in OA and normal synovial tissue. In situ hybridization showed primary miR‐146a expression in cells of the superficial and sublining layers in synovial tissue from RA patients. Cells positive for miR‐146a were primarily CD68+ macrophages, but included several CD3+ T cell subsets and CD79a+ B cells. Expression of miR‐146a/b was markedly up‐regulated in RASFs after stimulation with TNFα and IL‐1β. Conclusion This study shows that miR‐146 is expressed in RA synovial tissue and that its expression is induced by stimulation with TNFα and IL‐1β. Further studies are required to elucidate the function of miR‐146 in these tissues.

Using deep sequencing (deepCAGE), the FANTOM4 study measured the genome-wide dynamics of transcription-start-site usage in the human monocytic cell line THP-1 throughout a time course of growth arrest and differentiation. Modeling the expression dynamics in terms of predicted cis-regulatory sites, we identified the key transcription regulators, their time-dependent activities and target genes. Systematic siRNA knockdown of 52 transcription factors confirmed the roles of individual factors in the regulatory network. Our results indicate that cellular states are constrained by complex networks involving both positive and negative regulatory interactions among substantial numbers of transcription factors and that no single transcription factor is both necessary and sufficient to drive the differentiation process.

Osteoarthritis (OA) is a chronic and highly prevalent degenerative joint disease. Approximately 40 million Americans are currently affected, and this number is predicted to increase to 60 million within the next 20 years as a result of population aging and an increase in life expectancy (1,2). Current treatment is limited to pain management, and disease-modifying therapies are not available in the late phase of the disease process, at which point joint replacement surgery is often indicated. OA has been associated with age-related loss of the homeostatic balance between degradation and repair mechanisms. Cartilage cellularity in OA is reduced by chondrocyte death, and remaining chondrocytes are activated by cytokines and growth factors to a catabolic and abnormal differentiation that leads to degradation

We describe a molecular switch based on the controlled methylation of nucleosome and the transcriptional cofactors, the CREB-binding proteins (CBP)/p300. The CBP/p300 methylation site is localized to an arginine residue that is essential for stabilizing the structure of the KIX domain, which mediates CREB recruitment. Methylation of KIX by coactivator-associated arginine methyltransferase 1 (CARM1) blocks CREB activation by disabling the interaction between KIX and the kinase inducible domain (KID) of CREB. Thus, CARM1 functions as a corepressor in cyclic adenosine monophosphate signaling pathway via its methyltransferase activity while acting as a coactivator for nuclear hormones. These results provide strong in vivo and in vitro evidence that histone methylation plays a key role in hormone-induced gene activation and define cofactor methylation as a new regulatory mechanism in hormone signaling.

Mohawk (Mkx) is a member of the Three Amino acid Loop Extension superclass of atypical homeobox genes that is expressed in developing tendons. To investigate the in vivo functions of Mkx, we generated Mkx −/− mice. These mice had hypoplastic tendons throughout the body. Despite the reduction in tendon mass, the cell number in tail tendon fiber bundles was similar between wild-type and Mkx −/− mice. We also observed small collagen fibril diameters and a down-regulation of type I collagen in Mkx −/− tendons. These data indicate that Mkx plays a critical role in tendon differentiation by regulating type I collagen production in tendon cells.T endons are dense, fibrous connective tissues that connect muscle to bone, transmitting the forces that allow for body movement (1). Tendon damage from overuse or degeneration due to aging is a common clinical problem because damaged tendon tissue heals very slowly and rarely recovers completely (2). The establishment of new therapies, such as regenerative medicine, for injured tendons has been delayed by a limited understanding of tendon biology (1, 3).Tendons are composed primarily of collagen fibrils that cross-link to each other to form fibers (4). A small number of tendon cells reside between parallel chains of these fibrils and synthesize the specific ECM that contains collagens and proteoglycans (4, 5). The elasticity of tendons is provided by the large amount of collagen, predominantly type I collagen and small amounts of other collagens, including types III, IV, V, and VI (4, 6-9). The proteoglycans found in tendons, including decorin, fibromodulin, biglycan, and lumican, act to lubricate and organize collagen fiber bundles (4, 5). Targeted disruption of these proteoglycans in mice leads to abnormal collagen fibrils in tendons (3, 10-13). Tendon disruptions have also been described in patients with defects in collagen production, such as Ehlers-Danlos Syndrome, in which the type I collagen gene is mutated (14). These studies indicate that the ability of tendon cells to produce ECM is important for tendon formation.Recently, it was reported that Scleraxis (Scx), a basic helix-loophelix (bHLH) transcription factor expressed in the tendon progenitors and cells of all tendon tissues (15, 16), is essential for tendon differentiation. Scx knockout mice show severe disruption of force-transmitting tendons, although ligaments, which are tissues connecting bone to bone that closely resemble tendons in their components, and short-range anchoring tendons are not affected (17). It was also reported that Scx positively regulates the expression of type I collagen, a main ECM component of tendons (18). However, the type I collagen does not completely disappear from the tendons of Scx knockout mice (17), suggesting the presence of other regulatory factors for type I collagen. The tendon differentiation mechanisms remain largely unknown, with Scx being the only known transcription factor regulating tendon differentiation.Mohawk (Mkx; also known as Irxl1) is the sole member of a newly c...

The transcriptional activation by SRY-type high mobility group box 9 (SOX9) and the transforming growth factor ␤ (TGF-␤) signals are necessary for chondrogenic differentiation. We have previously shown that CREB-binding protein (CBP/p300) act as an important SOX9 co-activator during chondrogenesis. In the present study, we investigated the relationship between TGF-␤-dependent Smad2/3 signaling pathways and the SOX9-CBP/p300 transcriptional complex at the early stage of chondrogenesis. Overexpressed Smad3 strongly induced the primary chondrogenesis of human mesenchymal stem cells. In addition, Smad3 enhanced the transcriptional activity of SOX9 and the expression of ␣1(II) collagen gene (COL2A1), and small interference RNA against Smad3 (si-Smad3) inhibited them. We observed that Smad2/3 associated with Sox9 in a TGF-␤-dependent manner and formed the transcriptional complexes with SOX9 on the enhancer region of COL2A1. Interestingly, the association between Sox9 and CBP/p300 was increased by Smad3 overexpression and was suppressed by si-Smad3. Our findings indicate that Smad3 has a stronger potential to stimulate the SOX9-dependent transcriptional activity by modulating the interaction between SOX9 and CBP/ p300, rather than Smad2. This study suggests that the Smad3 pathway presents a key role for the SOX9-dependent transcriptional activation in primary chondrogenesis.

Introduction Recent findings suggest that articular cartilage contains mesenchymal progenitor cells. The aim of this study was to examine the distribution of stem cell markers (Notch-1, Stro-1 and VCAM-1) and of molecules that modulate progenitor differentiation (Notch-1 and Sox9) in normal adult human articular cartilage and in osteoarthritis (OA) cartilage.