The role of icariin in promoting autophagic repair of intervertebral disc nucleus pulposus cells via the PI3K-Akt-mTOR pathway

Background

The pathological mechanism of intervertebral disc degeneration (IVDD) is closely related to impaired autophagic function in nucleus pulposus (NP) cells. Icariin has demonstrated protective effects in osteoarthritis, but its role in autophagy regulation in IVDD remains unclear. It was to investigate impact of icariin on autophagic repair of intervertebral disc NP cells via PI3K/Akt/mTOR signaling pathway (SPW) and its dose-response relationship.

Methods

A rat model of IVDD was established using percutaneous annular puncture. Forty SD rats were rolled into sham surgery group (SG), model group (MG), and icariin-treated groups (low-dose (LDG): 10 mg/kg, medium-dose (MDG): 40 mg/kg, high-dose (HDG): 80 mg/kg). CCK-8 assay assessed cell proliferation. TEM showed autophagosome formation. The expression level (EL) of autophagy-related proteins and PI3K/Akt/mTOR SPW proteins was measured by Western blot. A PI3K/Akt/mTOR pathway-specific intervention experiment was conducted. The HDG+IGF-1 group was established as 80 mg/kg icariin administered by gavage plus daily intraperitoneal injection of the PI3K/Akt pathway agonist IGF-1 (100 μg/kg). The HDG+LY294002 group was constituted as 80 mg/kg icariin administered by gavage plus daily intraperitoneal injection of the PI3K inhibitor LY294002 (10 mg/kg).

Results

MG exhibited greatly reduced cell proliferation (P < 0.01), a decrease in the number of autophagosomes, accumulation of p62, and decreased EL of ATG5, Beclin-1, and p-ULK1/ULK1 versus SG. LC3-II/I ratio decreased, while PI3K p85, p-Akt/Akt, and p-mTOR/mTOR were markedly elevated (P < 0.01). After icariin intervention, HDG showed the most pronounced effects, notably outperforming the effects of LDG and MDG (P < 0.01). Pathway-specific intervention results demonstrated that compared with the HDG, autophagosome numbers were significantly reduced in the HDG+IGF-1 group (P < 0.01), whereas autophagosome numbers were significantly increased in the HDG+LY294002 group (P < 0.01). Relative to the HDG, the proliferation rate of NP cells at 24 h, 48 h, and 72 h was significantly decreased in the HDG+IGF-1 group (P < 0.01), while the proliferation rate at the same time points was significantly increased in the HDG+LY294002 group (P < 0.01).

Conclusion

Icariin can dose-dependently inhibit PI3K/Akt/mTOR SPW, promote autophagy and proliferation in NP cells, with the most marked effects observed at a dose of 80 mg/kg. This provides a new therapeutic strategy for IVDD.