Fibulin-5 protects the extracellular matrix of chondrocytes by inhibiting the Wnt/ß-catenin signaling pathway and relieves osteoarthritis.

OBJECTIVE: Osteoarthritis (OA) is a common disease in the elderly and seriously affects the quality of life of patients. The purpose of this study was to explore the protective effect of Fibulin-5 on articular chondrocytes and its mechanism of action. PATIENTS AND METHODS: Articular cartilage tissues from patients with OA and normal people were selected and tested for differences in Fibulin-5 expression. In addition, human chondrocytes were cultured, and the effects of Fibulin-5 on the extracellular matrix (ECM) of chondrocytes and the level of inflammation were examined by means of cell transfection and cytokine intervention. SKL2001, an agonist of the Wnt/ß-catenin signaling pathway, was used to validate the mechanism of action of Fibulin-5 to protect chondrocytes. RESULTS: Fibulin-5 was lowly expressed in the cartilage tissue of patients with OA. Overexpression of Fibulin-5 significantly increased the expressions of ECM collagen II and aggrecan in chondrocytes, while decreasing the expressions of MMP-3 and MMP-13. In addition, Fibulin-5 reduced IL-1ß-induced inflammation of chondrocytes, as well as expressions of IL-6, IL-8, and TNF-α. Overexpression of Fibulin-5 also reduced the activity of Wnt/ß-catenin signaling pathway, and activation of Wnt/ß-catenin signaling pathway attenuated the protective effects of Fibulin-5 on the ECM of chondrocytes. CONCLUSIONS: Fibulin-5 can protect the ECM of chondrocytes and reduce the inflammatory response of chondrocytes by inhibiting the Wnt/ß-catenin signaling pathway.

Distinct leukemia phenotypes in transgenic mice and different corepressor interactions generated by promyelocytic leukemia variant fusion genes PLZF-RARalpha and NPM-RARalpha.

Acute promyelocytic leukemia (APL) is characterized by a specific chromosome translocation involving RARalpha and one of four fusion partners: PML, PLZF, NPM, and NuMA genes. To study the leukemogenic potential of the fusion genes in vivo, we generated transgenic mice with PLZF-RARalpha and NPM-RARalpha. PLZF-RARalpha transgenic animals developed chronic myeloid leukemia-like phenotypes at an early stage of life (within 3 months in five of six mice), whereas three NPM-RARalpha transgenic mice showed a spectrum of phenotypes from typical APL to chronic myeloid leukemia relatively late in life (from 12 to 15 months). In contrast to bone marrow cells from PLZF-RARalpha transgenic mice, those from NPM-RARalpha transgenic mice could be induced to differentiate by all-trans-retinoic acid (ATRA). We also studied RARE binding properties and interactions between nuclear corepressor SMRT and various fusion proteins in response to ATRA. Dissociation of SMRT from different receptors was observed at ATRA concentrations of 0.01 microM, 0.1 microM, and 1.0 microM for RARalpha-RXRalpha, NPM-RARalpha, and PML-RARalpha, respectively, but not observed for PLZF-RARalpha even in the presence of 10 microM ATRA. We also determined the expression of the tissue factor gene in transgenic mice, which was detected only in bone marrow cells of mice expressing the fusion genes. These data clearly establish the leukemogenic role of PLZF-RARalpha and NPM-RARalpha and the importance of fusion receptor/corepressor interactions in the pathogenesis as well as in determining different clinical phenotypes of APL.