Impact of 5'-AMP-activated protein kinase (AMPK) on Epithelial Sodium Channels (ENaCs) in human sperm

Hyperpolarization is associated with decreased intracellular Na⁺ concentration through the closure of the epithelial Na⁺ channels (ENaCs) during capacitation. 5'-AMP-activated protein kinase (AMPK) is involved in the regulation of Na⁺ transport by reducing ENaC-β abundance in the plasma membrane in somatic cells. However, it is not known whether AMPK acts on ENaCs in sperm. The aim of the present study was to analyze the role of AMPK activation in the regulation of ENaC and to examine its relationship with capacitation-associated hyperpolarization of human sperm. Human sperm were treated with AICAR (AMPK activator) in non-capacitating and capacitating conditions. AMPK activity and ENaC-β concentration were evaluated by ELISA. Flow cytometry was used to measure tyrosine phosphorylation, hyperpolarization, intracellular Na⁺ concentration and acrosome reaction. Immunofluorescence staining was carried out to analyze the distribution of ENaC-β and CD46 in sperm. We found that induction of capacitation triggered AMPK phosphorylation. AMPK activation by AICAR increased tyrosine phosphorylation. AICAR decreased ENaC-β levels, mainly localized at the principal-piece of the flagellum, resulting in lower intracellular Na⁺ concentration and increased hyperpolarization of the plasma membrane. Altogether, these data provide evidence that AMPK activation is involved in capacitation-associated hyperpolarization by reducing ENaC abundance in human sperm.