Background/Purpose:

Xylosyltransferase-1 (XT-1), encoded by xylt1 gene, is an essential anabolic enzyme to catalyze the initial and rate-determining step in glycosaminoglycan chain synthesis. The effect of fibronectin fragments (FN-fs), generated by proteolytic cleavage of FN and known as damage-associated molecular pattern (DAMP) molecules, on cartilage metabolism was poorly characterized. In this study we examined 29-kDa amino-terminal fibronectin fragment (29-kDa FN-f)-mediated XT-1 expression mechanism and its signaling pathway, determining the role of 29-kDa FN-f in cartilage matrix synthesis

Methods:

Human articular chondrocytes were enzymatically isolated from articular cartilage and cultured in monolayer. In 29-kDa FN-f-stimulated chondrocytes, the relative levels of mRNA and protein for XT-1 were analyzed by real-time quantitative reverse transcription-polymerase chain reaction and Western blot analysis, respectively. In order to investigate the effects of 29-kDa FN-f on XT-1, human chondrocytes were transfected with small interfering RNAs (siRNAs) targeting TLR-2.

Results:

The level of aggrecan and XT-1 in human osteoarthritis cartilage was significantly decreased compared to normal cartilage. XT-1 expression in cultured primary articluar chondrocytes showed a periodic oscillation in both mRNA and protein level. 29-kDa FN-f significantly suppressed the mRNA and protein levels of XT-1 at 14 h and 24 h, respectively. Inhibition of mitogen activated protein kinase and nuclear factor-κB signaling pathway restored 29-kDa FN-f-inhibited XT-1 expression. Knockdown of toll like receptor-2 (TLR-2) using small interference RNA revealed that the decrease of XT-1 expression by 29-kDa FN-f is mediated by TLR-2 signaling pathway. In addition, Sp3, a repressor of XT-1 promoter, was up-regulated by 29-kDa FN-f. Knockdown and overexpression experiments revealed that XT-1 expression was modulated by 29-kDa FN-f-stimulated Sp3 in primary articular chondrocytes

Conclusion:

These results demonstrated that 29-kDa FN-f plays a detrimental role in the regulation of cartilage extracellular matrix formation including XT-1 expression.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/expression-of-xylosyltransferase-1-is-modulated-by-fibronectin-fragment-in-human-articular-chondrocytes/