The impact of polyphenols on chondrocyte growth and survival: a preliminary report

Background: Imbalances in the functional binding of fibroblast growth factors (FGFs) to their receptors (FGFRs) have consequences for cell proliferation and differentiation that in chondrocytes may lead to degraded cartilage. The toxic, proinflammatory, and oxidative response of cytokines and FGFs can be mitigated by dietary polyphenols. Objective: We explored the possible effects of polyphenols in the management of osteoarticular diseases using a model based on the transduction of a mutated human FGFR3 (G380R) in murine chondrocytes. This mutation is present in most cases of skeletal dysplasia and is responsible for the overexpression of FGFR3 that, in the presence of its ligand, FGF9, results in toxic effects leading to altered cellular growth. Design: Different combinations of dietary polyphenols derived from plant extracts were assayed in FGFR3 (G380R) mutated murine chondrocytes, exploring cell survival, chloride efflux, extracellular matrix (ECM) generation, and grade of activation of mitogen-activated protein kinases. Results: Bioactive compounds from Hibiscus sabdariffa reversed the toxic effects of FGF9 and restored normal growth, suggesting a probable translation to clinical requests in humans. Indeed, these compounds activated the intracellular chloride efflux, increased ECM generation, and stimulated cell proliferation. The inhibition of mitogen-activated protein kinase phosphorylation was interpreted as the main mechanism governing these beneficial effects. Conclusions: These findings support the rationale behind the encouragement of the development of drugs that repress the overexpression of FGFRs and suggest the dietary incorporation of supplementary nutrients in the management of degraded cartilage.The authors are grateful for the constant support provided by the Hospital Universitari de Sant Joan and the Universitat Rovira i Virgili. Salvador Fernández-Arroyo is the recipient of a Sara Borrell grant (CD12/00672) from the Instituto de Salud Carlos III, Madrid, Spain. The authors also thank the Andalusian Regional Government Council of Innovation and Science for the Excellence Project P11-CTS-7625 and Generalitat Valenciana for the project PROMETEO/2012/007. This work was also supported by projects of the Fundación Areces and the Fundación MAGAR

Transient dimerization and interaction with ergic-53 occur in the Fibroblast Growth Factor Receptor 3 early secretory pathway

The fibroblast growth factor receptor 3 (FGFR3) secretory pathway includes N-linked glycosylation in the endoplasmic reticulum where a stringent quality control system ensures that only correctly folded receptor reaches the cell surface from where mature-functional FGFR3 signals upon ligand-mediated dimerization. We have previously shown that the increased kinase activity associated with FGFR3 bearing the thanatophoric dysplasia type II (TDII) mutation hampers its maturation, enabling the receptor to signal from the endoplasmic reticulum. Here we investigate if this biosynthetic disturbance could be explained by premature dimerization of the receptor. Our observations show that a limited fraction of the immature high-mannose, mutant receptor dimerizes in the early secretory pathway, as does the immature wild type FGFR3. In contrast, the mature fully glycosylated wild type receptor reaches the cell surface as monomer suggesting that dimerization is a transient event. The kinase activity of mutant FGFR3 is not required for dimerization to occur, although it increases dimerization efficiency. Furthermore, mutant FGFR3 trans-phosphorylates the immature wild type receptor indicating that dimerization occurs in the endoplasmic reticulum. Visualization of protein interaction inside the secretory pathway confirms receptor dimerization. In addition, it shows that both wild type and TDII FGFR3 interact with the mannose-specific lectin ERGIC-53. We conclude that transient dimerization is an obligatory step in FGFR3 biosynthesis acting as a pre-assembly quality control mechanism. Furthermore, the TDII/ERGIC-53 complex formation may function as a checkpoint for FGFR3 sorting downstream the endoplasmic reticulum. These findings have implications for understanding the pathogenesis of FGFR3-related disorders