Purpose: PIWI-interacting RNA (piRNA) is a sub-group of small RNAs about 30 nucleotides length which specifically expressed in mammalian germ cells. Although piRNAs play pivotal roles in spermatogenesis regulation, little is known in the testicular tissues of infertile men. To explore whether piRNA profile could serve as a biomarker for male infertility diagnosis in a clinic, in this study, we systematically investigated the expression profile of piRNAs in testicular tissues from the patients with non-obstructive azoospermia (NOA) between successful and unsuccessful sperm retrieval before micro-dissection testicular sperm extraction (micro-TESE).
Methods: The differential expression levels of piRNAs were evaluated using small RNA-Seq method. Ontologic analyses were performed to determine the presence of enriched biological processes.
Results: A total of 18,324 Homo sapiens piRNAs were identified by small RNA-Seq from NOA patient testicular tissues; among them, 959 piRNAs were significantly altered between successful and unsuccessful sperm retrieval groups, of which 951 testicular piRNAs were significantly downregulated and 8 piRNAs were upregulated in NOA patients with unsuccessful sperm retrieval (USR) groups compared to those with successful sperm retrieval (SSR) groups, respectively. Unexpectedly, 553 testicular piRNAs were found completely absent in USR but showing abundant in SSR, which suggests that those piRNAs might serve as a biomarker for micro-TESE application. A total of 20 significantly differential piRNAs (hsa-piR-20830, hsa-piR-4731, hsa-piR-6254, hsa-piR-419, hsa-piR-7152, hsa-piR-7548, hsa-piR-14195, hsa-piR-5026, hsa-piR-11482, hsa-piR-17765, hsa-piR-17102, hsa-piR-4484, hsa-piR-17260, hsa-piR-17098, hsa-piR-20511, hsa-piR-5802, hsa-piR-19121, hsa-piR-2510, hsa-piR-4745, hsa-piR-11873) were selected to further validate the RNA-Seq data by quantitative real-time polymerase chain reaction. In addition, bioinformatic analyses revealed that those altered piRNAs were involved in many important biological pathways, including apoptosis, cell proliferation, and differentiation.
Conclusions: Our results demonstrate that testicular tissues from NOA patients with successful and unsuccessful spermatozoa retrieval exhibit differential piRNA profiles. This study provides a useful resource to further elucidate the regulatory role of piRNAs in spermatogenesis and provides a profound clue to identify useful biomarkers for predicting residual spermatogenic loci in NOA patients during assisted reproductive treatment.
Keywords: Infertility; Non-obstructive azoospermia; Spermatogenesis; piRNA.