Moderate Intensity Exercise Training in Combination with L-Carnitine Ameliorates The Varicocele-Suppressed Self-Renewal; Implication on Gdnf/C-ret/Gfrɑ1 Complex Signaling in Rats.

OBJECTIVE: For the first time, this study aimed to investigate the potential protective effects of L-carnitine and moderate-intensity exercise training (MIET), both individually and in combination, against varicocele (VCL)-induced impairment of spermatogonial stem cell (SSC) self-renewal. MATERIALS AND METHODS: In this experimental study, a total of 36 male Wistar rats (200 ± 20 g) were divided into the following groups: control, VCL (3-month and 5-month), and treatment groups receiving either Lcarnitine (100 mg/kg/day, orally) or MIET for two months, starting three months after VCL induction. After three months of VCL induction, the condition was confirmed by measuring serum testosterone levels and sperm count. The animals in the treatment groups were then subjected to L-carnitine, MIET, or their combination for an additional two months. The expression of key markers involved in SSC self-renewal, including glial cell line-derived neurotrophic factor (Gdnf), its receptors C-ret and Gfrα1, and target genes Etv5 and Bcl6b, was assessed and compared between groups. RESULTS: The VCL-sole groups exhibited significant reductions in serum testosterone, sperm counts, and the numbers of Gdnf+, Gfrα1+, and C-ret+ spermatogonia and spermatocytes compared to controls (P=0.001). Lcarnitine and MIET, both individually and in combination, significantly increased Gdnf, Gfrα1, and C-ret expression at mRNA and protein levels, enhanced the numbers of Gdnf+, Gfrα1+, C-ret+, Etv5+, Bcl6b+, and Nanog+ cells per seminiferous tubule, and improved SSC repopulation index (RI). CONCLUSION: MIET, particularly in combination with L-carnitine, enhances SSC self-renewal by upregulating the Gdnf/C-ret/Gfrα1 signaling pathway and activating downstream target genes, such as Etv5 and Bcl6b.