Background data: microRNAs (miRNAs) are short ∼22 nucleotide RNA sequences that regulate messengerRNA translation. miRNAs have shown to play a role in synthesis of inflammatory mediators. Since inflammation play a role in intervertebral disk (IVD) degeneration, the objective was to isolate miRNA from human lumbar intervertebral disks and subsequently characterize the difference in miRNA expression between the annulus fibrosus (AF) and nucleus pulposus (NP).
Methods: Fourteen patients undergoing anterior interbody fusion for degenerative disk disease of the lumbar spine were included. During surgery biopsies from the intervertebral disks were obtained and immediately placed in RNAlater. The RNAlater was decanted and the samples frozen at -80˚C until RNA extraction. This was performed using the Trizol method. Global miRNA expression analysis was performed using the Affymetrix GeneChip® miRNA array.
Results: We developed a method allowing the extraction of miRNA from human intervertebral disks usually yielding 1-4 µg of total RNA pr. 100 mg of disk. Twenty-seven miRNAs had a higher expression in the AF and 10 had the highest expression in the NP. Among the top 15 signaling pathways most likely to be controlled by these miRNAs were the transforming growth factor β (TGFβ), platelet-derived growth factor (PDGF), insulin-like growth factor (IGF) epidermal growth factor (EGF), and actin cytoskeletal pathway.
Conclusion: We have demonstrated the presence of miRNA in the human IVD. The miRNA expression differs from muscle tissue and there are differences between the miRNA expressed in the NP and AF. The miRNAs identified control signaling pathways important for maintenance of the IVD. Future studies may determine the importance of miRNA in the development of IVD disease.