Selection of High-Quality Spermatozoa May Be Promoted by Activated Vitamin D in the Woman.

CONTEXT: The vitamin D receptor (VDR) and enzymes involved in activation (CYP2R1, CYP27B1) and inactivation (CYP24A1) of vitamin D are expressed in ovary, testes, and spermatozoa.

OBJECTIVE

Determine responsiveness to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] in spermatozoa from normal and infertile men, and identify the site of exposure and how 1,25(OH)2D3 influences sperm function.

DESIGN

Spermatozoa expressing VDR, CYP2R1, CYP27B1, and CYP24A1 were analyzed in normal and infertile men. 25-Hydroxyvitamin D (25-OHD), 24,25-dihydroxyvitamin D [24,25(OH)2D3], and 1,25(OH)2D3 were measured in serum, seminal fluid, cervical secretions, and ovarian follicular fluid. 1,25(OH)2D3 was tested on human spermatozoa.

SETTING

Tertiary center for fertility.

PARTICIPANTS

Protein expression in spermatozoa and semen quality were assessed in 230 infertile and 114 healthy men. Vitamin D metabolites were measured in fluids from 245 men and 13 women, while 74 oocytes and 17 semen donors were used for sperm-function tests.

MAIN OUTCOME MEASURES: VDR and CYP24A1 expressions in spermatozoa, fluid concentrations of 25-OHD, 24,25(OH)2D3, and 1,25(OH)2D3, and 1,25(OH)2D3-induced effects on intracellular calcium concentration ([Ca2+]i) and sperm-oocyte binding in vitro.

RESULTS

VDR and CYP24A1 were expressed in a >2-fold higher fraction of spermatozoa from normal than infertile men (P < 0.01). Concentrations of 25-OHD, 24,25(OH)2D, and 1,25(OH)2D3 were undetectable in seminal fluid but high in ovarian follicular fluid. Follicular concentrations of 1,25(OH)2D3 induced a modest increase in [Ca2+]i and sperm-oocyte binding in vitro (P < 0.05).

CONCLUSION

Presence of VDR and CYP24A1 mainly in spermatozoa of higher quality supports that 1,25(OH)2D3 available in the female reproductive tract may promote selection of the best gametes for fertilization.