Testicular piRNA Analysis Identified Dysregulated piRNAs in Non-obstructive Azoospermia

Male infertility has remained idiopathic in a remarkable proportion of all cases. Gonadal expression of PIWI-interacting RNAs (piRNAs) has been shown to be vital to normal spermatogenesis, as they are expressed in almost all types of testicular germ cells. These molecules and their related Piwi proteins strictly regulate transposable elements' activity and gene expression. We aimed to identify dysregulated piRNAs in idiopathic non-obstructive azoospermic (NOA) testis by global expression analysis. Testis tissue samples from 18 azoospermic patients (ten NOA and eight OA) were studied by small RNA sequencing. To validate high-throughput sequencing data, quantitative real-time polymerase chain reactions for two differentially altered piRNAs were performed. Bioinformatics analyses were undertaken to identify pathways affected by piRNA dysregulation. In the NOA group, 1328 piRNAs were identified to be differentially expressed, of which 1322 were downregulated and 6 were upregulated. Bioinformatics analysis corroborated the involvement of dysregulated piRNA in spermatogenesis. We also identified 64 clusters of differentially expressed piRNAs, of which 42 clusters had a minimum of ten absolute piRNA hits. Our study suggests that piRNAs show significant dysregulation in infertility. Their target genes play a role in their self-biogenesis, probably by regulating their own production through a feedback mechanism. The downregulated piRNAs may find value as biomarkers for the presence of spermatozoa in the testis of azoospermic individuals, while the upregulated piRNAs are great candidates for further investigation of their precise functions in spermatogenesis.