Cytokine-like 1 Knock-out Mice (Cytl1−/−) Show Normal Cartilage and Bone Development but Exhibit Augmented Osteoarthritic Cartilage Destruction

Abstract

We have shown that cytokine-like 1 (Cytl1) is a novel autocrine regulatory factor that regulates chondrogenesis of mouse mesenchymal cells (Kim, J. S., Ryoo, Z. Y., and Chun, J. S. (2007) J. Biol. Chem. 282, 29359 -29367). In this previous work, we found that Cytl1 expression was very low in mesenchymal cells, increased dramatically during chondrogenesis, and decreased during hypertrophic maturation, both in vivo and in vitro. Moreover, exogenous addition or ectopic expression of Cytl1 caused chondrogenic differentiation of mouse limb bud mesenchymal cells. In the current study, we generated a Cytl1 knockout (Cytl1 ؊/؊ ) mouse to investigate the in vivo role of Cytl1. Although a number of regulatory factors have been identified, the precise regulatory mechanisms underlying chondrogenesis and cartilage and bone development remain to be elucidated. In permanent cartilage tissue, cartilage homeostasis is maintained by chondrocytes, which are a cell type unique to cartilage tissue. Cartilage homeostasis is disrupted in osteoarthritis (OA), leading to eventual cartilage destruction. OA is a progressive and degenerative disorder of the joint primarily characterized by articular cartilage destruction. A variety of potential OA-causing mechanisms have been proposed (5-7). Biophysical and biochemical factors, such as mechanical stress and proinflammatory cytokines, respectively, are responsible for disruption of cartilage homeostasis and initiation of the catabolic pathway. This, in turn, activates intracellular pathways in chondrocytes that lead to the production of pro-inflammatory cytokines, inflammation, degradation of the ECM by matrixdegrading enzymes, and cessation of ECM synthesis via dedifferentiation and apoptosis of chondrocytes (5-7). Deletion of theWe have previously shown that cytokine-like 1 (Cytl1) is a novel autocrine regulatory factor involved in chondrogenesis of mouse mesenchymal cells in vitro (8). CYTL1 was originally cloned as a functionally unknown cytokine candidate from human bone marrow and cord blood mononuclear cells bearing the CD34 surface marker (9). The CYTL1 protein contains four ␣-helices and six conserved cysteine residues, which may form intra-disulfide bonds to yield a globular structure, a common structural characteristic of cytokines. CYTL1 also contains an N-terminal secretory signal peptide, and its secretion is associated with post-translational modifications, although the nature of these modifications remains to be established (8

Cytokine-like 1 Chemoattracts Monocytes/Macrophages via CCR2

“…However, CCL2 could also reportedly inhibit development of colitis and colorectal cancer by exerting inhibitory effects on lymphocytes in disease models in mice (45). A study by Chun and colleagues (11) reported that Cytl1 2/2 mice were more sensitive to osteoarthritic cartilage destruction, which indicated that CYTL1 might have an anti-inflammatory effect. Indeed, Chao et al (12) demonstrated that CYTL1 could significantly reduce acute joint inflammation in a murine arthritis model and block expression of several key inflammatory genes such as IL-1b and IL-6 in mice.…”

“…Chun and colleagues (10,11) determined that Cytl1 2/2 mice were more sensitive to osteoarthritic cartilage destruction. Chao et al (12) demonstrated that CYTL1 could significantly prevent inflammatory arthritis.…”

Dkk‐1 expression in chondrocytes inhibits experimental osteoarthritic cartilage destruction in mice

“…Dkk-2 expression in Col2a1-Dkk2-transgenic mice was also decreased after DMM surgery, but Dkk-2 expression still remained at a relatively high level compared with that in WT mice ( Figures 5B and C). We have previously shown that type II collagen expression is decreased in OA cartilage destruction caused by DMM surgery (32), suggesting that the promoter activity of Col2a1 in transgenic mice may be reduced in DMM-induced OA cartilage destruction. Therefore, the decrease of Dkk-2 expression in trans- Dkk-1 INHIBITS EXPERIMENTAL OAgenic mice may be due to the nature of the Col2a1 promoter and enhancer that we used to generate transgenic mice.…”

Misexpression of Dickkopf-1 in endothelial cells, but not in chondrocytes or hypertrophic chondrocytes, causes defects in endochondral ossification

“…(18) PCR primers and conditions are shown in Supplemental Table 1. Cartilage and skeletal staining, histological analysis, immunohistochemistry, and immunofluorescence microscopy Cartilage and skeletons of whole-mouse embryos or postnatal mice, and mineralized zones in developing bone were stained with alcian blue, alizarin red, and von Kossa. (19) The lengths of bone and mineralized zones were measured using the AxioVision microscope image analysis program (Carl Zeiss, Jena, Germany). CD31, Vegf, Mmp9, Dkk1, Dkk2, and RANKL (receptor activator of nuclear factor kB ligand) in cartilage or bone sections were detected by immunofluorescence microscopy or immunohistochemical staining.…”