Melatonin Protects Mouse Type A Spermatogonial Stem Cells against Oxidative Stress via The Mitochondrial Thioredoxin System.

Objective: Mitochondrial oxidative stress is an important factor in infertility. The mitochondrial thioredoxin system plays an important role in this condition. N-acetyl-5-methoxy tryptamine (melatonin) plays a role in reducing oxidative stress and apoptosis in spermatogonial stem cells (SSCs). In this study, we explore the probable protective effects of melatonin on the mitochondrial thioredoxin system [thioredoxin 2 (Trx2)/Txnip] in SSCs under oxidative stress.

Materials and methods: In this experimental study, SSCs were co-cultured two-dimensionally (2D) with Sertoli cells in DMEM culture medium that contained 10% fetal bovine serum (FBS), 1% antibiotics, and 10 ng/ml glial cell-derived neurotrophic factor (GDNF) for 30 days. The cultured cells were subsequently divided into four groups: control; melatonin (250 μM, 24 hours); melatonin (250 μM, 24 hours)+hydrogen peroxide (H₂O₂, 50 μM, 24 hours); and H₂O₂ (50 μM, 24 hours). Intracellular reactive oxygen species (ROS) production was determined by flow cytometry. Malondialdehyde (MDA) levels were measured by Fluorometry. The expressions of apoptotic and antioxidant genes and nuclear factor erythroid 2-related factor 2 (Nrf2), Trx2, and nicotinamide nucleotide transhydrogenase (NNT) proteins were determined by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. Adenosine triphosphate (ATP) levels were measured by fluorometry.

Results: Melatonin reduced H2O2-induced ROS levels and apoptosis in the SSCs. Melatonin also increased mRNA expression of Nrf2, Trx2, NNT, Sirtuin 3 (Sirt3), and decreased mRNA expression of Txnip, and increased protein expressions of Nrf2, Trx2, NNT thereby increasing activity of the mitochondrial thioredoxin system. In addition, melatonin increased ATP levels.

Conclusion: Melatonin increased Trx2 expression through the Nrf2 pathway. This study suggests that melatonin may protect SSCs from oxidative stress in diseases related to infertility.