Dysregulated miR-133a Mediates Loss of Type II Collagen by Directly Targeting Matrix Metalloproteinase 9 (MMP9) in Human Intervertebral Disc Degeneration.

ABSTRACT

STUDY DESIGN: A microRNA (miRNA) study using Solexa sequencing. OBJECTIVE: The purpose of this study was to identify intervertebral disc degeneration (IDD)-specific miRNA expression profile, and to validate its biological function. SUMMARY OF BACKGROUND DATA Accumulating evidence indicates that miRNAs play a critical role in IDD, but the role of specific miRNAs involved in this entity remains unclear. METHODS: MiRNA expression profile was determined in nucleus pulposus (NP) tissues from patients with IDD and controls, employing Solexa sequencing and quantitative real-time PCR (qRT-PCR). Biological functions of differential expression miRNAs were further investigated. Luciferase reporter assays and western blotting were performed to determine miRNA targets. RESULTS: We identified 31 miRNAs that were differentially expressed (22 upregulated and nine downregulated) in patients compared with controls. After qRT-PCR confirmation, miR-133a was significantly down-regulated in degenerative NP tissues. Moreover, its level was inversely correlated with grade of disc degeneration. Through gain- and loss-of-function studies, miR-133a was demonstrated to significantly promote type II collagen expression in NP cells. MMP9 was identified as a target of miR-133a. Knockdown of MMP9 induced effects on NP cells similar to those induced by miR-133a. Expression of MMP9 was inversely correlated with miR-133a expression in degenerative NP tissues. CONCLUSION: These results suggest that the downregulation of miR-133a induces type II collagen loss by directly targeting MMP9. Our findings also highlight miR-133a as a novel hopeful therapeutic target for IDD. LEVEL OF EVIDENCE 3.