New insights into CFTR modulation in reproduction: testicular microenvironment imbalance leads to over-activated caspase signalling in spermatogenesis and adversely affects fertility

Abstract

Cystic fibrosis transmembrane conductance regulator (CFTR) is a prominent chloride channel that governs mucous secretion in multiple organs, including the reproductive tract. According to earlier reports, defective CFTR results in infertility due to congenital bilateral absence of the vas deferens (CBAVD). However, obstruction in the vas deferens is not the only reason CFTR deficiency causes male infertility. The mechanism underlying the loss of mature sperm owing to CFTR deficiency remains elusive. This study aimed to assess the role of CFTR in spermatogenesis, for which 6- and 8-week-old male mice with Cftr+/+, Cftr+/-, and Cftr-/- genotypes were chosen. Furthermore, we assessed the correlation between CFTR deficiency and delayed development of the reproductive system, anomalous apoptosis activation in spermatogenesis, and ionic alterations of the testis lumen. The results demonstrated that the growth of Cftr-/- mice were delayed, with underweight reproductive organs and mild hypospermatogenesis. CFTR depletion destabilizes spermatogenesis by producing abnormal sperm and triggers activation of the Bax/Bcl-2 ratio in Cftr-/- and Cftr+/-mice, causing caspase-mediated irreversible intrinsic apoptosis. Stage-specific apoptosis in germ cells targeted the sexually mature mice, and the testis microenvironment affirmed that ion concentrations influence sperm capacitation. The blood pH determines apoptosis induction, as CFTR is a bicarbonate transporter. In conclusion, Cftr-/- mice were infertile because CFTR deficiency generated an ionic imbalance in the testis lumen, leading to Bax expression and Bcl-2 blockage, which triggered caspases or further activation of voltage-dependent anion-selective channel 1 (VDAC1). Cumulatively, cytochrome C was released due to altered mitochondrial membrane potential. Eventually, anomalous up-regulated apoptosis activation affected spermatogenesis, thus rendering the Cftr-/- male mice infertile. The results supplied new insights into CFTR modulation in reproduction: an imbalanced testicular microenvironment due to CFTR deficiency affects spermatogenesis and fertility in mice through the overactivation of spermatocyte caspase signalling, thus driving us to focus on updated treatments for CFTR deficiency-caused infertility.