Abstract
Summary Statement
The deletion of gangliosides enhanced OA development by elevating MMP-13 and ADAMTS-5 expression and accelerating chondrocyte apoptosis. Gangliosides possibly play suppressive roles in IL-1α-induced inflammatory signaling cascades.
Introduction
We have previously reported that glycosphingolipids (GSLs) play chondroprotective roles in the cartilage degradation process [1]. Gangliosides, one of the series of GSLs, are known to be important in intercellular signal transduction and cell-to-cell recognition [2]. Therefore, we hypothesised that gangliosides are important in cartilage metabolisms among the GSLs species. The purpose of this study was to determine the functional role of gangliosides in the development of OA in murine models.
Materials & Methods
We adopted systemic GM3 synthase deficient mice (GM3S−/−) which lack most of the gangliosides [3], and wild-type C57BL/6 mice as controls (WT). We applied instability-induced OA model (transecting the medial collateral ligament and removing the cranial half of the medial meniscus [4]) and age-associated OA model (following up to 15 months) with these mice. We also applied IL-1α-induced OA model with femoral head cartilage explants ex vivo. Histological evaluation and quantification of released proteoglycan (PG), secreted MMP-13, and NO in the cultured media were performed. In vitro experiments with chondrocytes extracted from articular cartilages of both genotypes (GM3S−/−, WT) were also performed to check the mRNA expression of cartilage degrading enzymes (MMP-13, ADAMTS-5). To test the functional roles of gangliosides, transient GM3S transfection was applied to WT chondrocytes and quantification of MMP-13 and ADAMTS-5 expression was performed.
Results
Both age-associated and instability-induced OA models showed cartilage degradation in GM3S−/− mice were significantly more severe than WT mice. The results of IL-1α-induced OA model showed gangliosides deletion enhanced chondrocyte apoptosis and accelerated cartilage degradation. Femoral heads from GM3S−/− showed significantly higher concentration of MMP-13 and NO in the cultured media than those from WT. In vitro experiments revealed that ganglioside deletion enhanced MMP-13 and ADAMTS-5 expression in the chondrocytes stimulated with IL-1α. The expression of these enzymes was significantly suppressed by overexpressed GM3S in WT chondrocytes.
Discussion/Conclusion
The deletion of gangliosides enhanced OA development by elevating MMP-13 and ADAMTS-5 expression and accelerating chondrocyte apoptosis. The results of this study raised the possibility that gangliosides, synthesised mainly from GM3, would play crucial roles in maintaining cartilage homeostasis among the GSLs species. Moreover, the result of overexpression experiment indicated that gangliosides play suppressive roles in IL-1α-triggered inflammatory signaling cascades. Although further studies are required to confirm our speculation, gangliosides may be the target molecules of a novel and effective strategy for the treatment of OA.
