Nano-elemental imaging reveals zinc and calcium redistribution in human sperm during capacitation and hyperactivation

To characterize the redistribution patterns of zinc and calcium ions during human sperm capacitation and to investigate their roles in sperm maturation and fertilization.

In vitro experimental study using synchrotron-based x-ray fluorescence microscopy and complementary immunohistochemistry to assess elemental changes during different capacitation stages at nanometric spatial resolution.

Semen samples collected from healthy donors, evaluated according to World Health Organization guidelines.

None.

Nanometric distribution and quantification of zinc and calcium in different sperm region (head, midpiece, tail, and centriole) during different stages of capacitation.

The x-ray fluorescence mapping allowed to evaluate the nanometric redistribution of zinc and calcium in human sperm during capacitation. Distinct "zinc signatures" were observed during different capacitation stages, with zinc initially abundant throughout the cell, later concentrating in the midpiece after capacitation, and further decreasing during acrosomal exocytosis. A persistent presence of zinc-rich areas at the centriole was also observed, which likely helps maintain the integrity of the head and midpiece. Concurrently, increased calcium levels in the flagellum during capacitation suggest potentially linked dynamics between zinc efflux and calcium influx. These findings provide new insight into elemental dynamics underlying sperm maturation and fertilization potential.

A deeper understanding of male fertility may be achieved by elucidating the multifaceted role of zinc in sperm function, particularly its interaction with calcium signaling pathways. By considering both the biochemical and ionic mechanisms alongside the physical aspects of sperm activity, a more precise assessment of sperm functionality becomes possible.