miR-148a inhibits pro-inflammatory cytokines released by intervertebral disc cells by regulating the p38/MAPK pathway

The present study aimed to verify the expression and investigate the role of microRNA (miR)-148a in intervertebral disc degeneration (IDD) and explore the associated underlying mechanisms. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed to investigate levels of miR-148a in the peripheral blood mononuclear cells (PBMCs) of patients with IDD. To investigate the role of miR-148a in IDD, a stable miR-148a-overexpression/underexpression human nucleus pulposus (NP) cell line was generated by transfection with miR-148a mimic/inhibitor. Then, NP cells were treated with LPS (10 µM) to induce inflammation. The mRNA expression level of miR-148a in NP cells was determined by RT-qPCR and the expression levels of p38 and p-p38 were measured using western blotting. The mRNA expression and supernatant level of pro-inflammatory cytokines, tumor necrosis factor (TNF-α), interleukin (IL)-1β and IL-6, was evaluated by RT-qPCR and ELISA, respectively. The results indicated that miR-148a was significantly downregulated in the PBMCs of IDD patients compared with healthy controls. In vitro upregulation of miR-148a in LPS-stimulated NP cells, by transfection with miR-148a mimic, resulted in inhibition of p-p38 expression; however, inhibition of miR-148a led to overexpression of p-p38. Meanwhile, the production of pro-inflammatory cytokines (TNF-α, IL-1β and IL-6) was significantly reduced in miR-148a-overexpressing LPS-stimulated NP cells and significantly increased in miR-148a-underexpressing NP cells. In conclusion, miR-148a inhibits pro-inflammatory cytokines released by intervertebral disc cells via regulation of the p38/mitogen-activated protein kinase pathway.