MicroRNA-7 Regulates The Role Of IL-1?-induced Nucleus Pulposus Extracellular Matrix Degeneration

The precise role of interleukin-1 beta(IL-1?)-induced extracellular matrix degeneration in the pathogenesis of intervertebral disc degeneration(IDD) is currently unknown. Recent evidence has revealed that microRNAs(miRNAs) are associated with IDD, but their function in the extracellular matrix degradation of nucleus pulposus(NP) tissues is also poorly understood. The aim of this study was to evaluate the expression and functional role of mi R-7 in IL-1?-induced disc degeneration. The expression level of mi R-7 was investigated in degenerative NP tissues and in IL-1?-induced NP cells using quantitative reverse transcription-polymerase chain reaction amplification analysis. A dual-luciferase reporter assay and western blotting were then utilized to determine whether GDF5 is a target of miR-7. Finally, mRNA and protein levels of known matrix components and of matrix degradation enzymes were determined to elucidate the function of miR-7 in IL-1?-induced disc degeneration. In this study, we found that miR-7 is highly expressed in human degenerative NP tissues and in IL-1? stimulated NP cells compared to normal controls.We also determined that GDF5 was a target of miR-7. A Mi R-7 mimic down-regulated both GDF5 mRNA and protein expression levels, whereas a miR-7inhibitor up-regulated GDF5 expression. Luciferase reporter assays confirmed that miR-7 directly targeted GDF5. Functional analysis showed that the overexpression of miR-7 significantly aggravated the IL-1?-induced down-regulation of type II collagen and aggrecan expression and up-regulation of MMP-13 and ADAMTS4 expression,whereas inhibition of mi R-7 function by antagomir-7 reversed NP cell homeostasis in response to IL-1?. Additionally, the reversal of IL-1?-induced NP extra-cellular matrix(ECM) degeneration by miR-7 silencing was attenuated by GDF5 siRNA.These findings suggest that miR-7 contributes to an impaired ECM in intervertebral discs through targeting GDF5 and miR-7 might therefore represent a novel therapeutic target for the prevention of IDD.