Investigation of GSTK1 and GSTT1 expression in rat testis and epididymis during postnatal development

The testis and epididymis are crucial components of the male reproductive system, becoming functional during the postnatal development process through complex cellular differentiation and hormonal regulations. Throughout these processes, the production of reactive oxygen species increases, elevating the potential for oxidative stress. Glutathione S-transferases (GSTs) are an important part of the antioxidant defense system that counteracts this condition by conjugating reduced glutathione with harmful compounds, thereby neutralizing them. Changes in the expression of GSTK1 and GSTT1 isoenzymesmay be associated with male infertility by affecting sperm quality, DNA integrity, and hormonal balance. In this study, the cellular localization and expression patterns of GSTK1 and GSTT1 isoenzymes were evaluated in the testis and epididymis (initial segment, caput, corpus, and cauda) tissues of rats during postnatal development (neonatal: 5th day, infantile: 20th day, peripubertal: 50th day, late pubertal: 70th day). Expression levels were determined using the immunohistochemical method. Besides semiquantitative scoring, a quantitative analysis was performed. Limited GSTK1 immunoreactivity was observed only in gonocytes in the testis tissue during the neonatal period, while Sertoli and Leydig cells were found to be negative. During the infantile period, positivity was detected in spermatocytes and Leydig cells. The highest levels were seen in primary spermatocytes during the peripubertal period, with expression remaining at lower levels in other germ cells and Sertoli cells. In the late pubertal period, the intensity in primary spermatocytes was maintained, while limited levels continued in other cell types. In the epididymal epithelium, the increase became more pronounced with age, with the maximum value detected in the cauda segment during the late pubertal period. In the quantitative analysis for the testis, the highest value was obtained during the late pubertal period. Strong GSTT1positivity was found only in Leydig cells in the testis during the neonatal period, while germ cells and Sertoli cells were evaluated as negative. During the infantile period, the high expression in Leydig cells was maintained, and low-level positivity emerged in spermatogonium, spermatocytes, and Sertoli cells. Expression in Leydig cells continued during the peripubertal and late pubertal periods, with low levels observed in germ cells. In the epididymal epithelium, GSTT1 expression, which was low in the neonatal period, increased from the infantile period onwards, and the highest levels were detected in the cauda segment during the peripubertal and late pubertal periods. In the quantitative analysis for the testis, the highest value was observed during the peripubertal and late pubertal periods. In conclusion, GSTK1 is more concentrated in germ cells, particularly primary spermatocytes, and the distal segment of the epididymis, while GSTT1 is predominantly expressed in Leydig cells and the epididymal epithelium. The findings indicate that antioxidant defense mechanisms differentiate in a cell-type and region-specific manner during postnatal development and that both enzymes undertake complementary roles in the control of oxidative stress.