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

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