Adipose-Derived Mesenchymal Stem Cells Alleviate ᴅ-Galactose-Induced Testicular Injury by Activating the Keap1/Nrf2 Pathway and Suppressing NLRP3-Associated Pyroptosis

Objective: To evaluate whether human adipose-derived mesenchymal stem cells (ADSCs) protect against ᴅ-galactose (ᴅ-gal)-induced aging-like testicular injury and to investigate the involvement of the Keap1/Nrf2 pathway and NLRP3-associated pyroptosis. Methods: A mouse model of aging-like testicular injury was established by subcutaneous administration of ᴅ-gal for 8 weeks, followed by tail vein injection of ADSCs. Testicular morphology, blood–testis barrier (BTB) integrity, and senescence-associated markers (p16, p21) were assessed. In vitro, TM4 Sertoli cells were used to establish a senescence model and Tranwell co-cultured with ADSCs. Oxidative stress, inflammatory responses, and pyroptosis-related markers were evaluated using biochemical assays, immunofluorescence, Western blotting, and RT-qPCR. The involvement of the Keap1/Nrf2-NLRP3 axis was further examined using pharmacological inhibitors. Results: ADSC treatment significantly alleviated ᴅ-gal-induced testicular atrophy and histopathological injury, accompanied by reduced expression of the senescence markers p16 and p21 and partial restoration of BTB-related structures. ADSCs also attenuated oxidative stress, as evidenced by decreased ROS and MDA levels, increased SOD activity, and enhanced expression of Nrf2 and its downstream antioxidant targets, including HO-1 and NQO1. In parallel, ADSC administration suppressed NLRP3 activation, reduced caspase-1 cleavage, and lowered the expression of pro-inflammatory cytokines. In TM4 cells, inhibition of Nrf2 weakened the protective effects of ADSCs and was accompanied by reactivation of NLRP3-associated signaling, whereas inhibition of NLRP3 attenuated senescence- and inflammation-related changes without restoring Nrf2 activity. Conclusions: ADSCs alleviate ᴅ-gal-induced aging-like testicular injury, at least in part, by restoring redox balance, preserving BTB-associated structure, and suppressing NLRP3-associated pyroptosis through the Keap1/Nrf2 pathway. These findings suggest that ADSC-based therapy may represent a promising strategy for age-related male reproductive dysfunction, while further studies using genetic models and functional fertility endpoints are needed to confirm causality and translational relevance.