n = 6 blank control group was created. The mice in the control group were fed regular food and gavaged with normal saline daily. The mice in the control group were given a high-fat diet and 1 mg/kg of letrozole via gavage for 21 days to establish a PCOS model of insulin resistance and hyperandrogenism. The mice, after successful modeling, were randomly divided into PCOS group and metformin group (n = 6). During the treatment period, the control group continued to be fed with normal feed and given normal saline; the PCOS group was fed with continuous high-fat feed and given letrozole (1 mg/kg/day) by intragastric administration, and the metformin group was given metformin by intragastric administration (200 mg/kg/day). After 30 days of treatment, the experimental mice were euthanized, serum was collected, one mouse ovary was collected for histological examination, and the other was stored in a -80 refrigerator for molecular biology experimental research.

All animal protocols were approved by the Animal Care and Use Committee of TaizhouHospital, affiliated to Zhejiang University (Taizhou, China). Twenty-four 2-month-old male Wistar rats weighing 190-220 g were purchased from the Experimental Animal Center of Basi Medicine, Zhejiang Chinese Medical University. The animals were reared under a 12 h light/12 h dark cycle at a relative humidity of 55 ± 5% and temperature of 23 ± 2 , with unrestricted access to food and water. All animals were acclimatized to laboratory conditions for 1 week before the experiments and were randomly divided into four groups: control group (CG, n = 6); LCZ696 group (LCZ, n = 6); DOX group (DOX, n = 6); and DOX + LCZ696 group (DOX + LCZ, n = 6). The CG received saline solution by gavage for 6 weeks (2 mL/day), while the treatment groups received DOX (Cat. HY-15142A, MedChemExpress, USA), LCZ696 (Cat. HY-18204A, MedChemExpress, USA), or DOX + LCZ696. DOX was administered at a dose of 2.5 mg/kg once a week for 6 weeks via tailvein injection. LCZ696 (60 mg/kg/day) was administered by gavage for 6 weeks. Body weight was measured weekly.

8-10 weeks old male mice were placed in prone position and anesthetized with isoflurane inhalation. The 1.5 cm-long longitudinal incision was made in 2 mm from the posterior midline. The superior and inferior articular processes, supraspinous ligament and interspinous ligament of the L4-L5 lumbar vertebrae were removed to construct LSI, which would induce IVDD. After the operation, the mice were placed in a warm environment.

Forty male BALB/cnude mice (4 weeks old, 15-16 g) were purchased from the Shanghai Laboratory Animal Center (Shanghai, China) and divided into eight groups. Cells (1.0 x 10⁶) were subcutaneously injected into the leftaxillaof nude mice.