Genetic Ablation of Na,K-ATPase alpha 4 Results in Sperm Energetic Defects

The Na,K-ATPase alpha 4 isoform (NKA alpha 4) is expressed specifically in the male germ cells of the testes and is particularly abundant in mature spermatozoa. Genetic deletion of NKA alpha 4 in mice (NKA alpha 4 KO mice) results in complete infertility of male, but not female mice. The reduced fecundity of NKA alpha 4 KO male mice is due to a series of defects, including a severe impairment in total and hyperactive sperm motility. In this work, we show that deletion of NKA alpha 4 also leads to major defects in sperm metabolism and energetics. Thus, compared to wild-type sperm, sperm from NKA alpha 4 KO mice display a significant reduction in the extracellular acidification rate (ECAR), indicative of impaired glycolytic flux. In addition, mitochondrial function is disrupted in sperm lacking NKA alpha 4, as indicated by a reduction in the mitochondrial membrane potential and lower oxygen consumption rate (OCR). Moreover, the ratio between the oxidized and reduced forms of nicotinamide adenine dinucleotide (NAD/NADH) is increased in NKA alpha 4 KO sperm, indicating a shift in the cellular redox state. These metabolic changes are associated with augmented reactive oxygen species (ROS) production and increased lipid peroxidation in NKA alpha 4 KO sperm. Altogether, these findings reveal a novel link between NKA alpha 4 activity and sperm energetics, highlighting the essential role of this ion transporter in sperm physiology.