Cell cycle specificity of spermatogenic cell apoptosis in rats with experimental varicocele

Varicocele has been implicated as a factor responsible for infertility. Many researchers have shown that varicocele causes spermatogenic dysfunction and abnormal germ cell apoptosis. However, the effects of varicocele on the cell cycle and the mechanism of germ cell apoptosis have not been fully defined. Spermatogenic dysfunction in varicocele testes may be related partly to abnormal apoptosis.

Methods Forty Sprague-Dawley male rats were randomly divided into two groups: sham-operated group (SOG) and experimental left varicocele (ELV) group. Experimental varicocele was induced by partial ligation of the left renal vein in rats. After 90 days, two flow cytometric methods, PI staining and annexin V/PI labeling assays, were used to analyze the cell cycle and cell cycle specificity of spermatogenic cell apoptosis.

The weight of the left testicle in SOG and ELV was 1.527 +/- 0.071 g and 1.223 +/- 0.136 g, respectively, indicating a lower left testicle weight in ELV than in SOG (p < 0.05). Many changes were observed in ELV. Seminiferous tubules shrunk, spermatogenic epithelium became thinner and many spermatogenic cells dropped into the tubules. Furthermore, we found that the cell cycle was arrested at the phase of spermatogonium. Compared with SOG, the proportion of cells in G0/G1 phase increased from 60.632 +/- 5.144% to 74.128 +/- 17.067% (p < 0.05), and the proportion of cells in S phase decreased from 13.853 +/- 2.796% to 7.905 +/- 5.314% in ELV (p < 0.05). Compared with SOG, the apoptosis index (A) increased from 4.345 +/- 0.554% to 14.583 +/- 3% (p < 0.05) in ELV. In ELV, apoptotic cells were mainly in G0/G1 and G2/M phases, and A1 (A1: Apoptosis index of G0/G1 phase) and A3 (Apoptosis index of G2/M phase) increased to 8.343 +/- 1.605% and 5.648 +/- 1.685%, respectively (p < 0.05).

Spermatogenesis is arrested in G0/G1 phase in experimental left varicocele. The apoptosis of spermatogenic cells by a varicocele may be induced in G0/G1 and G2/M phases of the cell cycle. Apoptosis of germ cells with DNA damage may be the principal method through which the testis eliminates arrested germ cells.