Study Of Germ Cell Apoptosis In Testis Of Hyperlipidemic Mice

Objectives To investigate the effects of hyperlipidemia on testicular germ cell apoptosis and involved mechanisms. Methods 12 ApoE-knockout C57BL/6J male mice were randomly divided into two dietary groups: group 1 fed high-fat diet(Hyperlipidemic group), and group 2 fed high-fat diet with the addition of melatonin(MT) [1mg/(kg·d)](MT group). 6 ApoE wild-type C57BL/6J male mice fed normal diet,served as controls. After 12 weeks, the levels of CHO and LDL-c in the sera was tested and the testis tissues were examined by pathologic methods. The serum lipid profiles were detected by enzymatic determination in all groups. The testis was embedded in paraffin, sectioned, and stained with hematoxylin and eosin (HE). Ultrastructural changes were observed under transmission electron microscope(TCM). Germ cell apoptosis was assessed by means of the teminal deoxynucleotidyl transferase-mediated dUTP nick end labeling(TUNEL) method. Expressions of Bcl-2 and Bax proteins in the testis were detected by avidin-biotin-complex (ABC) immunohistochemical staining and computerized image analysis. Results①The high-fat diet led to a significant increase in serum CHO and LDL-c in ApoE-knockout mice compared with control group; No significant increase in serum CHO was noticed in ApoE-knockout mice fed a high-fat diet and also received melatonin.②The testis of hyperlipidemic mice exhibited obvious pathological change: basement membrane of seminiferous tubule was not complete; the layers of spermatogenic cells decreased, and the gap increased. The testicular histology in MT group was relatively normal.③A series of ultrastructural changes were found in the hyperlipidemic group, mainly as follows: most mitochondria(Mi) exhibited swelling, vacuole degeneration, rough endoplasmic reticulum(rER) expanded and showed degranulation. Abnormal structure with high electron density was found in cytoplasm of germ cells. Vacuolization and tight sediment were observed in cytoplasm of Sertoli cells. Basement membrane thickened and winkled. The number of Mi and lipid droplets decreased obviously, and Mi also exhibited vacuole degeneration and rER expanded in Leydig cell. Mi exhibited vacuole degeneration and rER was degranulated in endothelial cells of continuous capillary. No significant degenerative changes in ultra-structure were found in MT group.④Germ cell apoptosis was detected in the testis of all groups. There was significant increase of germ cell apoptosis rate in hyperlipidemic mice compared with control group and MT group.⑤Bcl-2 and Bax expressed in the testis of all group. Bcl-2 expressed mainly in cytoplasm of spermatocyte and spermatoblast, and Bax localised in cytoplasm of spermatogonia, spermatocyte, Sertoli cell and nuclei of round spermatoblast. The expressions of Bcl-2 significantly down-regulated and Bax up-regulated in hyperlipidemic group compared with control group. The increased Bcl-2 expressions and decreased Bax expressions were observed in the testis MT group compared with the hyperlipidemic group. Conclusion Enhanced germ cell apoptosis occurred in hyperlipidemic mice, which may indicate the main mechanisms involved in hyperlipidemia-induced testis damage. Bcl-2 and Bax play a role in germ cell apoptosis in hyperlipidemic mice. Melatonin's ability to prevent testicular damage induced by hyperlipidemia was documented.