To observe the effect of acupuncture at the acupoint pair “Houxi” (SI3) and “Huantiao” (GB30) on the phosphatidylinositol-3 kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway and autophagy of nucleus pulposus cells in a rat model of intervertebral disc degeneration (IDD), so as to explore its underlying mechanism in delaying IDD.

A total of 36 male SD rats were randomly assigned to sham operation, model and acupoint pair groups, with 12 rats in each group. The IDD model was established by annulus fibrosus puncture. After modeling, rats of the acupoint pair group received acupuncture stimulation of bilateral SI3 and GB30, with the acupuncture needles retained for 20 min, once daily for 14 consecutive days. Before and after modeling and after the intervention, the mechanical withdrawal reflex threshold (mechanic pain threshold) of the right foot was measured using VonFrey filaments, and the thermal pain threshold measured by using a thermal pain tester. The morphological characteristics of the intervertebral disc tissue were observed by H.E. staining. The contents of type Ⅱ collagen (Collagen Ⅱ), Aggrecan, matrix metalloproteinase 3 (MMP3), matrix metalloproteinase 13 (MMP13), and transcription factor sex-determining region Y-box protein 9 (SOX9) in the nucleus pulposus tissue were detected by ELISA. The mRNA relative expression levels of SOX9 and MMP13 in the nucleus pulposus tissue were detected by real-time fluorescence quantitative PCR. The positive expression of microtubule-associated protein 1 light chain 3 (LC3) in the nucleus pulposus tissue was detected by immunofluorescence staining. The expression levels of PI3K/AKT/mTOR signaling pathway-related proteins and LC3-Ⅱ, Beclin1, and chaperone 1 (p62) in the nucleus pulposus tissue were detected by Western blot.

After modeling, in contrast to the sham operation group, the model group showed a striking decrease in the mechanical and thermal pain thresholds on day 7 and 14, contents of Aggrecan, collagen Ⅱ and SOX9, and the expression levels of SOX9 mRNA and p62 protein, ratios of p-PI3K/PI3K, p-AKT/AKT, and p-mTOR/mTOR in the nucleus pulposus tissue (P<0.001, P<0.01), and a notable increase in the contents of MMP3 and MMP13, and MMP13 mRNA expression level, LC3 immunofluorescence intensity, and protein expressions of LC3-Ⅱ and Beclin 1 (P<0.001). Under light microscope, the nucleus pulposus cells in the model group was relatively small in the number and discorded in the distribution, with a large number of vacuoles and chaotic matrix arrangement, and the lumbar intervertebral discs showed obvious degeneration, and decrease in the height. In comparison with the model group, both the decrease and increase of the indexes mentioned above were all reversed in the acupoint pair group (P<0.001, P<0.01, P<0.05). The results of H.E. stain displayed that in the acupoint pair group, the arrangement of the nucleus pulposus cells was more regular, and the number of vacuoles was reduced.

Acupuncture of acupoint pair SI3 and GB30 can mitigate pain and regulate the autophagy process of lumbar intervertebral disc nucleus cells, reduce the degree of degradation of cytoplasmic matrix, and thereby delay the progression of IDD, which may be associated with its function in activating PI3K/AKT/mTOR signaling pathway in IDD rats.