piRNA-46403 Promotes Sertoli Cell Ferroptosis via Disrupting m5C-dependent USP18 mRNA Stabilization in Varicocele-mediated Infertility.

Varicocele (VC) represents a primary etiology of male infertility, yet the epigenetic landscapes and molecular triggers driving VC-associated spermatogenic failure remain largely enigmatic. Herein, it is demonstrated that Sertoli cell ferroptosis is a critical pathological feature of VC, and its pharmacological inhibition effectively rescues VC-induced reproductive impairment in vivo. Through small RNA sequencing of clinical testicular tissues, piRNA-46403 is identified as a significantly upregulated mediator in VC patients with asthenospermia. Functionally, piRNA-46403 is shown to orchestrate Sertoli cell ferroptosis, whereas its silencing attenuates spermatogonial apoptosis and restores spermatogenic function. Mechanistically, piRNA-46403 acts as a molecular decoy that binds to the RNA-binding protein YBX1. This interaction disrupts the binding of YBX1 to m5C-modified USP18 mRNA, thereby reducing USP18 mRNA stability and triggering ferroptosis. These findings elucidate a novel piRNA-46403/YBX1/m5C-modified USP18 regulatory axis in the male reproductive system and position piRNA-46403 as a promising therapeutic target for mitigating VC-mediated infertility.