Metformin enhances external urethral sphincter integrity and restores continence via AMPK activation in a rat model of stress urinary incontinence

Background Stress urinary incontinence (SUI) is primarily caused by structural and functional damage to the external urethral sphincter (EUS). In previous studies, metformin, a known AMP-activated protein kinase (AMPK) activator, has shown repair effects after skeletal muscle injury. This study explored its therapeutic effect and molecular mechanisms in SUI associated with EUS injury. Methods The SUI model was established by double vaginal dilation. Rats were assigned to sham, vehicle-treated, or metformin-treated (200 mg/kg/day, oral) groups. Urodynamic testing was performed after 7 and 14 days. Subsequently, EUS tissues were isolated for histological (hematoxylin and eosin [H&E], Masson's), apoptotic (TUNEL), ultrastructural (transmission electron microscopy [TEM]), and molecular analyses. Finally, C2C12 myotubes cells were treated with varying concentrations of metformin to evaluate the expression of phosphorylated AMPK (p-AMPK) and MYH1/2, which are markers of skeletal muscle fiber type and regeneration. Results Abdominal leak point pressure (ALPP) and bladder leak point pressure (BLPP) decreased after double vaginal dilation, suggesting that SUI was established. After treatment for 7 and 14 days, respectively, metformin significantly increased ALPP and BLPP ( p < 0.05) without affecting maximum bladder capacity ( p > 0.05). Masson's staining and TEM revealed that metformin improved disorganized EUS architecture. Further, Western blot analysis demonstrated that metformin increased the expression of MYH1/2 and p-AMPK in vivo and in vitro. Meanwhile TUNEL assay showed that metformin treatment reduced apoptotic cells in the EUS from SUI rats. Conclusions These results indicate that metformin enhances EUS repair to improve SUI via activating the AMPK signaling pathway. These findings provide new insights into therapeutic strategies for SUI.