miR-654-5p inhibits autophagy by targeting ATG7 via mTOR signaling in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common chronic disease characterized by the loss of extracellular matrix (ECM) in the nucleus pulposus (NP). Accumulating evidence has revealed that abnormal expression of microRNAs (miRs) is closely associated with IDD development. The present study aimed to investigate the precise role and possible mechanism underlying the effects of miR-654-5p in the pathogenesis of IDD. NP cells were isolated from patients with IDD. Monodansylcadaverine staining was conducted to reveal cell autophagy, while western blotting was performed to detect the expression of ECM-related proteins in NP cells. Luciferase reporter and RNA immunoprecipitation assays were conducted to identify the binding between RNAs. The results demonstrated that miR-654-5p was significantly upregulated in degenerated NP tissues from patients with IDD and high miR-654-5p expression was positively associated with disc degeneration grade. Functional assays suggested that miR-654-5p facilitated ECM degradation by increasing the expression levels of MMP-3, MMP-9 and MMP-13, as well as decreasing collagen I, collagen II, SOX9 and aggrecan expression by inhibiting autophagy. Furthermore, autophagy-related gene 7 (ATG7) was verified as a direct downstream target gene of miR-654-5p. miR-654-5p could bind to the 3′ untranslated region of ATG7 to inhibit its mRNA expression and further reduce its translation. Notably, ATG7 knockdown abrogated the effects of the miR-654-5p inhibitor on ECM degradation and autophagy regulation. Furthermore, miR-654-5p inhibited autophagy in NP cells by increasing the protein expression levels of phosphorylated (p)-PI3K, p-AKT and p-mTOR in an ATG7-dependent manner. In conclusion, the results of the present study revealed that miR-654-5p may enhance ECM degradation via inhibition of autophagy by targeting ATG7 to activate the PI3K/AKT/mTOR signaling pathway. These findings may provide novel insights into the treatment of IDD.