BACKGROUND: The purpose of our study was to determine the functional role of microRNA (miR)-16 in chronic inflammatory pain and to disclose its underlying molecular mechanism.

MATERIAL AND METHODS: Inflammatory pain was induced by injection of complete Freund’s adjuvant (CFA) to Wistar rats. The pWPXL-miR-16, PcDNA3.1- Ras-related protein (RAB23), and/or SB203580 were delivered intrathecally to the rats. Behavioral tests were detected at 0 h, 4 h, 1 d, 4 d, 7 d, and 14 d after CFA injection. After behavioral tests, L4–L6 dorsal spinal cord were obtained and the levels of miR-16, RAB23, and phosphorylation of p38 (p-p38) were evaluated by quantitative real-time PCR (qRT-PCR). In addition, luciferase reporter assay was performed to explore whether RAB23 was a target of miR-16, and qRT-PCR and Western blotting were used to confirm the regulation between RAB23 and miR-16.

RESULTS: The level of miR-16 was significantly decreased in the CFA-induced inflammatory pain. Intrathecal injection of miR-16 alleviates pain response and raised pain threshold. The level of RAB23 was significantly increased in the pain model, and intrathecal injection of RAB23 aggravated pain response. Luciferase reporter assay confirmed that RAB23 was a direct target of miR-16, and RAB23 was negatively regulated by miR-16. In addition, we found that simultaneous administration of SB203580 and miR-16 further alleviates pain response compared to only administration of miR-16.

CONCLUSIONS: Our findings suggest that miR-16 relieves chronic inflammatory pain by targeting RAB23 and inhibiting p38 MAPK activation.

Keywords: HEK293 Cells, Hyperalgesia - genetics, Inflammation - complications, Pain - metabolism, Pain Threshold, Phosphorylation, Rats, Wistar, p38 Mitogen-Activated Protein Kinases - metabolism, rab GTP-Binding Proteins - metabolism