Gulp1 regulates chondrocyte growth arrest and differentiation via the TGF-ß/SMAD2/3 pathway.

Chondrocyte differentiation is crucial for cartilage formation. However, the complex processes and mechanisms coordinating chondrocyte proliferation and differentiation remain incompletely understood. Here, we report a novel function of the adaptor protein Gulp1 in chondrocyte differentiation. Gulp1 expression is upregulated during chondrogenic differentiation. Gulp1 knockdown in chondrogenic ATDC5 cells reduces the expression of chondrogenic and hypertrophic marker genes during differentiation. Furthermore, Gulp1 knockdown impairs cell growth arrest during chondrocyte differentiation and reduces the expression of the cyclin-dependent kinase inhibitor p21. The activation of the TGF-ß/SMAD2/3 pathway, which is associated with p21 expression in chondrocytes, is impaired in Gulp1 knockdown cells. Collectively, these results demonstrate that Gulp1 contributes to cell growth arrest and chondrocyte differentiation by modulating the TGF-ß/SMAD2/3 pathway.

Periostin is a novel histological biomarker for the diagnosis of chondroid tumor.

BACKGROUND: The chondroid tumor is generally classified into three types, enchondroma, low-grade chondrosarcoma, and high-grade chondrosarcoma. A histological evaluation of a biopsy sample is the best predictor of the clinical course in most patients with carcinomas or sarcomas. Sometimes serological or molecular markers are used as prediction markers, but there has been no reliable marker for chondroid tumor diagnosis. Clinical and radiological, but not histological features, are still used in the diagnosis and staging of chondroid tumors. During a histopathological diagnosis, it has been difficult to distinguish between benign enchondroma and low-grade chondrosarcoma. To allow for more accurate treatments, new histological biomarkers for the differential diagnosis are needed. METHODS: Twenty-eight cases of enchondromas and thirty-three cases of low-grade chondrosarcoma were selected. Thirteen cases of non-tumorous cartilage were used for the control group, who underwent artificial joint surgery for degenerative arthritis. Surgically removed tissue specimens were formalin-fixed paraffin-embedded and hematoxylin and eosin (H&E) and immunohistochemistry (IHC) stains were performed. RESULTS: Periostin was expressed in chondroid tumors but not in the normal cartilage. Periostin was observed via immunostaining in the cytoplasm but not in the extracellular matrix of enchondroma tissue, and was observed in the cytoplasm and extracellular matrix of low-grade chondrosarcoma. The sensitivity and specificity of these stains were 93.9% and 96.4%, respectively. CONCLUSIONS: Based on these results, we suggest that periostin could be used as a novel prognostic marker to distinguish between enchondroma and low-grade chondrosarcoma.

CFL2 is an essential mediator for myogenic differentiation in C2C12 myoblasts.

CFL2, a skeletal muscle-specific member of the actin depolymerizing factor/cofilin protein family, is known to be involved in the regulation of actin filament dynamics. Although the impact of CFL2 has been studied in human myopathy, its functional contribution to myogenic differentiation, in terms of its effects on cell proliferation, cell cycle, and myogenic factor modulation, remains largely unknown. Here, we report that CFL2 is required for the myogenic differentiation of C2C12 myoblasts by regulating proliferation and myogenic transcription factors expressions. CFL2 expression was induced during myogenic progression, and its knockdown by siRNA in myoblasts enhanced phalloidin staining, indicating increased filamentous actin formation. Interestingly, CFL2 depletion stimulated cell proliferation and induced a cell cycle shift from G0/G1 to G2/M phases, which are known to inhibit progenitor cell differentiation. CFL2 knockdown markedly downregulated the protein expressions of myogenic transcription factors (MyoD, MyoG, and MEF2C) and thereby impaired the differentiation and myotube formation of C2C12 myoblasts. Collectively, this study highlights the roles played by CFL2 on cell cycle progression and proliferation and suggests a novel regulatory mechanism of myogenic differentiation mediated by CFL2.

C1q and TNF related protein 1 regulates expression of inflammatory genes in vascular smooth muscle cells.

BACKGROUND: C1q and TNF related protein 1 (C1QTNF1) is known to be associated with coronary artery diseases. However, the molecular function of C1QTNF1 on the vascular smooth muscles remains to be investigated. OBJECTIVE: This study was therefore undertaken to investigate the effect of C1QTNF1 on gene expression of human smooth muscle cells and to reveal potential molecular mechanisms mediated by C1QTNF1. METHODS: Vascular smooth muscle cells were incubated with recombinant C1QTNF1 for 16 h, followed by determining any change in mRNA expressions by Affymetrix genechip. Gene ontology (GO), KEGG pathway, and protein-protein interaction (PPI) network were analyzed in differentially expressed genes. In addition, validation of microarray data was performed using quantitative real-time PCR. RESULTS: The mRNA expressions of annotated 74 genes were significantly altered after incubation with recombinant C1QTNF1; 41 genes were up-regulated and 33 down-regulated. The differentially expressed genes were enriched in biological processes and KEGG pathways associated with inflammatory responses. In the PPI network analysis, IL-6, CCL2, and ICAM1 were identified as potential key genes with relatively high degree. The cluster analysis in the PPI network identified a significant module composed of upregulated genes, such as IL-6, CCL2, NFKBIA, SOD2, and ICAM1. The quantitative real-time PCR results of potential key genes were consistent with microarray data. CONCLUSION: The results in the present study provide insights on the effects of C1QTNF1 on gene expression of smooth muscle cells. We believe our findings will help to elucidate the molecular mechanisms regarding the functions of C1QTNF1 on smooth muscle cells in inflammatory diseases.