Retinoic Acid Regulates Spermiogenesis Via Hoxb1 and Shh Signaling in Testicular Germ Cells.

Retinoic acid (RA) regulates all four major events in spermatogenesis; spermatogonial differentiation, meiotic entry, spermiogenesis, and spermiation. For the pre-meiotic phase, Sertoli cells are the source of RA and for the post-meiotic phase, pachytene spermatocytes are the source of RA. While the entire spermatogenic process is regulated by RA, how each of these phases is regulated by RA remains completely unknown. Homeobox B1 (Hoxb1) has two retinoic acid response elements (RARE) upstream and downstream of the gene. In this study, we investigated if RA facilitates spermatogenesis by its action on Hoxb1. The expressions of the Hoxb1 and Sonic hedgehog (Shh) genes were analyzed in the post-natal mouse testes and the testicular localizations of Hoxb1, Shh and Gli1 were analyzed by immunohistochemistry in the adult rat testis. To delineate the signaling mechanisms, Hoxb1 expression was altered in vitro and in vivo using retinoic acid and miR-361-3p. Finally, the levels of miR-361-3p and HOXB1 were analyzed in infertile human sperm samples. Hoxb1 and Shh gene expressions were found to be low in the testis of post-natal Swiss mice of 7, 14, 28, 35, and 60 days, after which the expressions of both spiked. Immunohistochemistry in the adult mouse testis showed the expressions of Hoxb1, Shh, and Gli1 in the elongating spermatids. Exposure of GC2 cells to RA and in vivo IP RA injection upregulated Hoxb1 and Shh signaling in the testis with increased expressions of Shh, Gli1, and Hdac1. Retinoic acid administration in Swiss mice compromised sperm production and reduced epididymal sperm count. The analysis of infertile human semen samples revealed an increased level of HOXB1 and a decreased level of miR-361-3p as compared to fertile controls. We conclude that retinoic acid regulates late stage of spermatogenesis (spermiogenesis) by affecting Hoxb1 and Shh signaling.

SPATA16 promoter hypermethylation and downregulation in male infertility.

Spermatogenesis associated 16 (SPATA16) gene plays an important role in acrosome formation. In this study, we analysed SPATA16 promoter methylation in 29 oligozoospermic infertile and 16 normozoospermic fertile sperm samples and in testicular biopsy from 16 non-obstructive azoospermic and 2 obstructive azoospermic individuals. Next, we analysed SPATA16 level in sperm from 8 oligozoospermic infertile, 6 normozoospermic fertile, 9 IVF failed normozoospermic and 10 IVF successful normozoospermic samples by immunoblotting. This was followed by the analysis of SPATA16 expression in testicular biopsy from azoospermic individuals (n = 8) in comparison to normozoospermic individuals (n = 2). Oligozoospermic infertile sperm samples showed significantly higher methylation in the SPATA16 promoter region. Similarly, testicular biopsy from azoospermic men also showed significantly higher level of DNA methylation. Sub-group analysis of infertile sperm and testicular biopsy samples showed a direct correlation between DNA methylation and the degree of spermatogenic impairment. Oligozoospermic infertile samples and IVF failed samples showed reduced SPATA16 expression in comparison to normozoospermic fertile and IVF successful samples, respectively. Human biopsy analysis showed a significant decrease in SPATA16 expression in hypospermatogenesis, maturation arrest and Sertoli cell only syndrome. In conclusion, hypermethylation in SPATA16 promoter shows a highly significant correlation with infertility, which is consistent with its down-regulation in infertility.