Overexpression of Follistatin in the Mouse Epididymis Disrupts Fluid Resorption and Sperm Transit in Testicular Excurrent Ducts1

Abstract

Activin is a well-established modulator of male and female reproduction that stimulates the synthesis and secretion of follicle-stimulating hormone. Nonpituitary effects of activin have also been reported, although the paracrine actions of this growth factor in several reproductive tissues are not well understood. To identify the paracrine functions of activin during mammary gland morphogenesis and tumor progression, we produced transgenic mice that overexpress follistatin (FST), an intrinsic inhibitor of activin, under control of the mouse mammary tumor virus (MMTV) promoter. Although the MMTV-Fst mice were constructed to assess the role of activin in females, expression of the transgene was also observed in the testes and epididymides of males. While all 17 transgenic founder males exhibited copulatory behavior and produced vaginal plugs in females, only one produced live offspring. In contrast, transgenic females were fertile, permitting expansion of transgenic mouse lines. Light and transmission electron microscopic examination of the transgenic testes and epididymides revealed impairment of fluid resorption and sperm transit in the efferent ducts and initial segment of the epididymis, as indicated by accumulation of fluid and sperm stasis. Consequently, a variety of degenerative lesions were observed in the seminiferous epithelium, such as vacuolation and early stages of mineralization and fibrosis. Sperm collected from the caudae epididymidis of MMTV-Fst males had detached heads and were immotile. Together, these data reveal that activin signaling is essential for normal testicular excurrent duct function and that its blockade impairs fertility. These results also suggest that selective inhibitors of activin signaling may provide a useful approach for the development of male contraceptives without compromising androgen synthesis and actions.

Identification of New Epididymal Luminal Fluid Proteins Involved in Sperm Maturation in Infertile Rats Treated by Dutasteride Using iTRAQ

“…Among the seven proteins that were significantly down-regulated by dutasteride in the epididymal luminal fluids, there were three β-defensins (Defb2, Defb18 and Defb39) that may be involved in sperm maturation and male fertility [9,19,20,21]. As for the 16 up-regulated proteins, there were eight proteins participating in material and energy metabolism, such as St6galnac2 and Ckmt1b, which could influence sperm motility and maturation when passed through the epididymal lumen.…”

“…Androgens affect fluid balance in the epididymis by regulating anion transport across the epithelium and modulate the epididymal expression of specific channels that mediate water transport in many tissues [21]. From our iTRAQ results, dutasteride could significantly up-regulate the expression of proteins such as S100b, S100a11, and Crip1 which are associated with anion transport in epididymal fluids, possibly resulting in metal ion binding and transportation disorders in the epididymal microenvironment.…”

The Immunophysiology of Male Reproduction

“…In transgenic mice that overexpress the activin-binding protein, follistatin, fluid resorption and sperm transport in the efferent ducts and proximal epididymis is impaired, suggesting a role for endogenous activin in the control of fluid dynamics. 792 Furthermore, activin A has been shown to induce SRD5α in genital fibroblasts, 793 and the caput epididymis is the site of highest expression of this enzyme, indicating that activin A may regulate androgen activity in the epididymis.…”

Disruption of estrogen receptor signaling and similar pathways in the efferent ductules and initial segment of the epididymis

“…However, many of these appear to either decrease ESR1 activity 97,[123][124][125] or inhibit ESR1 associated pathways. 77,126,127 Surprisingly, the knockout of two genes regulated by ESR1, Slc9a3 and Car2, produced normal epithelial morphology in the efferent ductules, while exhibiting luminal dilations of the ductules and rete testes that were greater than those observed in the Esr1KO.…”

“…Species and time dependent; correlated with tubular dilation; must examine over time; ranges from normal to mild to severe; rete testis proximity may be more severe; may lead to atrophy 88,89,124,125,147,156 Atrophy of seminiferous tubules b Must examine after long-term effects; not all tubules will show equal effects; may be unilateral 88,89,125 INDUCTION OF SPERM GRANULOMA Potential Efferent Ductule Effects Histopathological Complications Luminal compaction of sperm Dose and time dependent; not all ductules will show equal effects; proportional to dosage; may be unilateral; could miss observation in histology section 4,130,134,135,171 Neutrophilic granulocyte inflammation Dose and time dependent; not all ductules will show equal effects; may subside with the onset of fibrosis 4,130,134,135 Fibrosis Must examine after long-term effects; may require serial sections Recanalization Must examine after long-term effects; may require serial sections 135,241,242 Potential Testicular Effects Testis weight increase b Species and time dependent; this can be transient; correlated with tubular dilation; may be unilateral; must examine over time 4,130,131 Rete testis lumen dilated Depends on location of occlusion and species; proportional to dosage; may be unilateral 129,[223][224][225] Seminiferous tubular lumen dilated Depends on location of occlusion and species; proportional to dosage; may be unilateral 129,[223][224][225] Atrophy of seminiferous tubules collapsed lumen with no sperm, stain more intensely but lack the typical number of lysosomes in their cytoplasm. In larger mammals, such as the dog, bull and man, the blind-ending ductules are capable of accumulating stagnant sperm, dilating in size...…”