Germ cell depletion in recipient testis has adverse effects on spermatogenesis in orthotopically transplanted testis pieces via retinoic acid insufficiency.

Germ cell depletion in recipient testes is indispensable for successful transplantation of spermatogonial stem cells. However, we found that such treatment had an adverse effect on spermatogenesis of orthotopically transplanted donor testis tissues. In the donor tissue, the frequency of stimulated by retinoic acid (RA) 8 (STRA8) expression was reduced in germ cells, suggesting that RA signalling indispensable for spermatogenesis was attenuated in germ cell-depleted recipient testes. In this context, germ cell depletion diminished expression of testicular Aldh1a2, which is responsible for testicular RA synthesis, while Cyp26b1, which is responsible for testicular RA metabolism, was still expressed even after germ cell depletion, suggesting an alteration of the RA synthesis/metabolism ratio. These observations suggested that RA insufficiency was one of the causes of the defective donor spermatogenesis. Indeed, repetitive RA administrations significantly improved donor spermatogenesis to produce fertile offspring without any side effects. These findings may contribute to improving fertility preservation techniques for males, especially to prevent iatrogenic infertility induced by chemotherapy in prepubertal cancer patients.

Long-term exposure of xenoestrogens with environmental relevant concentrations disrupted spermatogenesis of zebrafish through altering sex hormone balance, stimulating germ cell proliferation, meiosis and enhancing apoptosis.

Environmental estrogens are capable of interfering with the spermatogenesis and fertility of fish. However in natural waters, these chemicals are more likely to occur as a combination rather than a single stressor. Whether and how the mixture of xenoestrogens with environmental relevant concentrations may affect fish spermatogenesis remains largely unknown. In this study, male zebrafish adults were administered to 17alpha-ethinylestradiol (EE2) and a mixture of xenoestrogens (Mix (E2, EE2, DES, 4-t-OP, 4-NP and BPA)), with the estrogenic potency equivalent to EE2. After a 60-day exposures, elevated mRNA levels of vitellogenin 1 (vtg1) and estrogen receptor 1 (esr1) in the liver of fish in both treated groups were observed. Moreover, the plasma level of E2 declined significantly in the Mix group and the ratio of 11-KT/E2 was significantly elevated in both treated groups. Consistently, the mRNA level of P450 side-chain cleavage (scc) in the EE2 group and ovarian type aromatase (cyp19a1a) in the Mix group was significantly suppressed. In addition, decreased gonadosomatic index and sperm count in the fish of Mix group were present. Furthermore, increased number of the proliferating germ cells (such as spermatogonia and spermatocytes) was observed in the fish of both groups, suggesting a stimulated germ cell proliferation and meiosis. Accordingly, both exposures significantly up-regulated the mRNA levels of genes in mitosis (cyclinb1) and meiosis (cyp26a1 in EE2 group, aldh1a2, cyp26a1, sycp3 and spo11 in Mix). In addition, decreased number of spermatozoa and increased number of TUNEL-positive signals were present in the testis of fish in the Mix group, indicating an enhanced apoptosis. Further analyses demonstrated the significant elevated expressions of tnfrsf1a and the ratio of tnfrsf1a/tnfrsf1b in the Mix group, suggesting an elevated apoptosis in the testis of fish in the Mix group via extrinsic pathway. The present study greatly extends our understanding of the underlying mechanisms of the reproductive toxicity of xenoestrogens on fish.