Reversal of Injury-Induced Fibrosis and Anal Sphincter Muscle Dysfunction by sFRP2 in Rabbits

Anal sphincter injury is a major cause of anal incontinence (AI), and current treatments rarely restore anal sphincter muscle function. Secreted frizzled-related protein-2 (sFRP2) may promote muscle regeneration and reduce fibrosis, but its ability to reverse the established external anal sphincter (EAS) fibrosis and restore function is not known. This study examined whether sFRP2 promotes functional and structural recovery in a rabbit model of established EAS muscle fibrosis. Adult female rabbits underwent EAS myotomy and, six weeks later, received local injections of sFRP2 or saline. Anal canal pressure was recorded before injury, immediately after myotomy, six weeks post-injury, and every two weeks for six weeks following treatment. Myotomy significantly reduced anal canal pressure and induced fibrosis in the EAS muscle at 6 weeks. sFRP2 treatment restored anal canal pressure to near pre-injury levels within two weeks after sFRP2 injection, which remained elevated six weeks post-treatment, while saline-treated rabbits maintained low pressure. In the sFRP2 compared to saline treated animals, 1) histological analysis demonstrated significant increase in EAS muscle percent, 2) hydroxyproline assay showed reduced collagen content, 3) western blot analysis revealed increased expression of eMyHC, Myogenin, and active JNK, along with reduced Vimentin, TGF-β1, and nuclear active β-catenin, while Col1A1 and pSmad2/3 showed a downward trend, 4) proteomic analysis showed reduced fibrogenesis and TGF-β signaling, with activation of PCP-JNK, and striated muscle contraction pathways. These findings suggest that sFRP2 restores EAS muscle function and promotes muscle regeneration thus representing a potential novel therapy for the injury-induced anal sphincter dysfunction.