MRP4 transporter is involved in the acquisition of human sperm's fertilizing ability

Cyclic AMP (cAMP) regulates multiple aspects of sperm function essential for attaining fertilizing ability; therefore, its intracellular levels must be tightly controlled to ensure proper signaling dynamics. In recent years, multidrug resistance-associated protein 4 (MRP4) has emerged as a novel regulator of cAMP homeostasis by facilitating its efflux. Previous studies from our laboratory have identified MRP4 in mammalian sperm and demonstrated its role in capacitation-associated events in murine and bovine species. However, its relevance in human sperm remains unknown. Our study demonstrates a functional MRP4 in human sperm, as its pharmacological inhibition led to a rapid (5 min) intracellular cAMP accumulation and a subsequent decrease in extracellular levels (30 min) under capacitating conditions, as assessed by radio binding protein assay. At the biological level, MRP4 inhibition resulted in a decrease in tyrosine phosphorylation at 360 min of capacitation. Membrane hyperpolarization was also affected, diminishing the induced acrosome reaction. Moreover, a significant reduction in intracellular Ca2+ levels was observed, leading to a significant decrease in progressive and total motility, as well as an inhibition of hyperactivation. In addition, our results indicated that the decrease in Ca2+ levels was due to impaired CatSper channel activity upon MRP4 inhibition. These findings suggest that MRP4-mediated cAMP efflux is essential for proper sperm function, playing a critical role in maintaining nucleotide homeostasis, which is a key determinant in the regulation of human sperm capacitation.