An epididymis-specific β-defensin is important for the initiation of sperm maturation

Abstract

Although the role of the epididymis, a male accessory sex organ, in sperm maturation has been established for nearly four decades, the maturation process itself has not been linked to a specific molecule of epididymal origin. Here we show that Bin1b, a rat epididymis-specific beta-defensin with antimicrobial activity, can bind to the sperm head in different regions of the epididymis with varied binding patterns. In addition, Bin1b-expressing cells, either of epididymal origin or from a Bin1b-transfected cell line, can induce progressive sperm motility in immotile immature sperm. This induction of motility is mediated by the Bin1b-induced uptake of Ca(2+), a mechanism that has a less prominent role in maintaining motility in mature sperm. In vivo antisense experiments show that suppressed expression of Bin1b results in reduced binding of Bin1b to caput sperm and in considerable attenuation of sperm motility and progressive movement. Thus, beta-defensin is important for the acquisition of sperm motility and the initiation of sperm maturation.

Identification, characterization, and evolution of a primate β-defensin gene cluster

“…40 Figure 3 Expression of novel human b-defensin genes in different tissues. Total RNAs isolated from human (1) parotid glands, (2) thyroid, (3) breast, (4) lungs, (5) liver, (6) spleen, (7) kidney, (8) colon, (9) adrenal, (10) ovary, (11) seminal vesicle, (12) cauda, (13) corpus, (14) caput, (15) prostate, and (16) testis were used for RT-PCR analysis. PPIA was amplified as a control to check the quality and quantity of the template.…”

“…We demonstrate that, similar to other bdefensins, 3,4,11 the expression of these novel 20q defensins is restricted to the testis and epididymis. DEFB118 location on sperm, 25 DEFB126 involvement in the capacitation process, 13 the Bin1b role in sperm motility and maturation, 14 taken together with the male tract specific expression and differential regional expression of the 20q defensins provide evidence that these bdefensins have evolved to perform reproduction-specific tasks, combining immunity and fertility in their functional repertoires. In addition, the male organs may require more elaborate protection against pathogens than other organ systems.…”

“…3,4,11 In addition, the b-defensin-like epididymal protein (EP2)/sperm-associated antigen 11 (SPAG11) isoforms are also predominantly expressed in the male reproductive tract. 12 Recent studies specifically implicate b-defensins in pivotal roles in reproductive biology including ESP13.2/DEFB126 in sperm capacitation 13 and Bin1b/EP2E in sperm maturation, 14 thereby redefining our concepts concerning the multifunctional roles of b-defensins.…”

mBin1b transgenic mice show enhanced resistance to epididymal infection by bacteria challenge

“…2 Approximately 4,000 cauda epididymal sperms were analyzed for each assay, and six mice were used in each group.…”

“…Bin1b has been reported to function in the initiation of sperm maturation. 2 However, the in vivo antimicrobial activities of Bin1b have not been elucidated.…”