Cartilage dyshomeostasis contributes to osteoarthritis (OA) pathogenesis, and tumor necrosis factor (TNF)-α has critical role in this process by driving inflammatory cascades and cartilage degradation. However, the negative regulation of TNF-α-mediated signaling remains undefined. In a recent study, scientists demonstrate the crucial role of miR-145 in the modulation of TNF-α-mediated signaling and cartilage matrix degradation.

MicroRNA (miRNA) expression profiles of TNF-α-stimulated chondrocytes showed that miR-145 expression was rapidly downregulated by TNF-α. Moreover, miR-145 was directly repressed by p65 and was negatively correlated with TNF-α secretion during OA progression. Further, it was found that miR-145 directly targeted mitogen-activated protein kinase kinase 4 (MKK4) and broadly restrained the production of several TNF-α-triggered matrix-degrading enzymes (MMP-3, MMP-13, and Adamts-5). Mechanistic studies unveiled that miR-145 negatively regulated TNF-α-mediated JNK and p38 activation, as well as the nuclear accumulation of p-c-Jun and p-ATF2, by inhibiting MKK4 phosphorylation, eventually resulting in the alteration of catabolic genes transcription. Indeed, p-ATF2 interacted with the promoter of Mmp-13, whereas p-c-Jun bound to promoters of Mmp-3 and Adamts-5. MKK4 was significantly elevated in OA cartilage. Eliminating MKK4 by short hairpin RNA resulted in obviously decreased matrix-degrading enzymes production, JNK and p38 inactivation, and an inhibition of cartilage degradation. On the contrary, MKK4 overexpression enhanced TNF-α-mediated signaling activation and transcription of downstream catabolic genes, and consequently worsened cartilage degradation. Moreover, intra-articular (IA) injection of miR-145 agonist to rat with surgery-induced OA alleviated cartilage destruction.

Altogether, this research elucidates a novel regulatory mechanism underlying TNF-α-triggered cartilage degradation and demonstrates the potential utility of miR-145 and MKK4 as therapy targets for OA.

Expression level of miR-145 in TNF-α-stimulated chondrocytes and OA cartilage

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G. Hu; X. Zhao, C. Wang, Y. Geng, J. Zhao et al. (2017) MicroRNA-145 attenuates TNF-[alpha]-driven cartilage matrix degradation in osteoarthritis via direct suppression of MKK4 Cell Death and Disease Vol. 8 doi: 10.1038/cddis.2017.522 [article]

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