Background Peritoneal fibrosis is the most common cause of peritoneal dialysis (PD) ultrafiltration failure. Osteopontin (OPN) plays a pro-fibrotic role in other organs, but its role in peritoneal dialysis-related fibrosis has not been confirmed.

Objective To confirm that OPN promotes the development of peritoneal fibrosis in PD.

Methods Human peritoneal mesothelial cells were stimulated with 1.25 μg/mL, 2.5 μg/mL, and 5 μg/mL OPN in vitro, and the morphology of mesothelial cells was observed. Mouse macrophages were cultured in vitro and stimulated with 0.5 μg/mL Lipopolysaccharide (LPS) and the expression of OPN was detected. Three siRNA sequences were screened, and the selected sequences were used to synthesize in vivo siRNA. Twenty mice were randomly divided into saline control group, peritoneal dialysis control group, siRNA vector control group and siRNA experimental group. The modeling method was as follows: 100 mL/kg normal saline was injected into the mice in the normal saline group once a day; In the peritoneal dialysis control group, 100 mL/kg peritoneal dialysate containing 4.25% glucose was injected into the peritoneal cavity once a day. The siRNA carrier group and the siRNA experimental group were injected with 100 mL/kg of peritoneal dialysate containing 4.25% glucose daily, and at the same time, the empty carrier of 5 nmol in vivo siRNA or the siRNA in vivo was dissolved into the peritoneal dialysate for intraperitoneal injection, once every 3 days. All animal models were constructed for 4 weeks. The right parietal peritoneum of mice was collected, and the peritoneal thickness, subcutaneous collagen fiber area and number of microvessels were measured by pathological section. The expression of α-SMA and e-cadherin were detected by WB and α-SAM staining was performed by immunohistochemistry to evaluate the degree of peritoneal fibrosis.

Results After the addition of exogenous OPN, human peritoneal mesothelial cells arranged disorderly, and the cell shape became elongated and extended into angular shape, showing mesenchymal-like changes. The expression of OPN increased in macrophages after LPS-stimulated (P ＜ 0.05). The expression of osteopontin was inhibited after siRNA transfection, and the decrease of osteopontin was more significant after si-002 addition (P ＜ 0.05). In the peritoneal dialysis control group, the expression of OPN in macrophages was confirmed by immunofluorescence co-staining with CD68 and OPN. Compared with the PD control group, the siRNA experimental group had a significant reduction in the thickness of the peritoneum (P ＜ 0.05), the number of subcutaneous microvessels (P ＜ 0.05), and area of collagen deposition (P ＜ 0.05). The expression of α-SMA was decreased and the expression of E-cadherin was increased in the parietal peritoneum (P ＜ 0.05).

Conclusion Inhibition of the expression of osteopontin can alleviate peritoneal dialysis-related fibrosis.