TKTL1: a new candidate gene in non-obstructive azoospermia.

RESEARCH QUESTION: What role does TKTL1 gene serve in human spermatogenesis and does its mutation trigger non-obstructive azoospermia (NOA)? DESIGN: The genetic background of NOA remains poorly explored. Recent studies using next generation sequencing techniques, however, have uncovered some NOA causative genes, including the TKTL1 gene. The aim of this study was to define the function of the TKTL1 gene in human spermatogenesis by inducing its overexpression in human testicular primary (hTP) cells, and verifying these results in male gonad tissue samples collected from patients with NOA determining the genes cluster regulated by TKTL1. RESULTS: Successful overexpression of the TKTL1 gene was achieved in hTP cells; the TKTL1 gene expression was significantly higher in genetically modified cells compared with both controls applied. RNA-sequencing was used to select 20 genes in which expression significantly differed in the modified hTP cells overexpressing TKTL1 gene compared with controls. Male gonad tissue samples collected from patients with NOA harbouring a mutation in the TKTL1 gene showed a significant downregulation in HERC5, CSF3, HES1 and HSPA1B genes, compared with patients with azoospermia without mutation in the TKTL1 gene (negative control) as well as control samples with normal spermatogenesis. This was in accordance with results obtained with hTP cells, as the overexpression of the TKTL1 gene correlated with an increased expression level of the mentioned genes compared with controls. CONCLUSIONS: The TKTL1 gene is likely involved in the regulation of gametogenesis affecting the proliferation and differentiation of germ cells at the early stage of spermatogenesis.