In this study, the authors examined the catabolic cascade in osteoarthritis (OA). OA is primarily characterized by cartilage degeneration, is caused by an imbalance between anabolic and catabolic factors. The authors investigated the role of zinc (Zn(2+)) homeostasis, Zn(2+) transporters, and Zn(2+)-dependent transcription factors in OA pathogenesis. Among Zn(2+) transporters, the Zn(2+) importer ZIP8 was specifically upregulated in OA cartilage of humans and mice, resulting in increased levels of intracellular Zn(2+) in chondrocytes. ZIP8- mediated Zn(2+) influx upregulated the expression of matrix-degrading enzymes (MMP3, MMP9, MMP12, MMP13, and ADAMTS5) in chondrocytes. Ectopic expression of ZIP8 in mouse cartilage tissue caused OA cartilage destruction, whereas Zip8 knockout suppressed surgically induced OA pathogenesis, with concomitant modulation of Zn(2+) influx and matrix-degrading enzymes. Furthermore, MTF1 was identified as an essential transcription factor in mediating Zn(2+)/ZIP8-induced catabolic factor expression, and genetic modulation of Mtf1 in mice altered OA pathogenesis. The authors conclude that the zinc-ZIP8-MTF1 axis is an essential catabolic regulator of OA pathogenesis. This could have potential implications when translated into the clinical setting. Cell. February 2014. PMID: 24529376.
