The effect of estrogen administration in vivo on the elemental composition of the intraluminal fluids of the seminiferous tubules, rete testis, and epididymis of the rat

Calcium and vitamin D homoeostasis in male fertility

Calcium and vitamin D have well-established roles in maintaining calcium balance and bone health. Decades of research in human subjects and animals have revealed that calcium and vitamin D also have effects on many other organs including male reproductive organs. The presence of calcium-sensing receptor, vitamin D receptor, vitamin D activating and inactivating enzymes and calcium channels in the testes, male reproductive tract and human spermatozoa suggests that vitamin D and calcium may modify male reproductive function. Functional animal models have shown that vitamin D deficiency in male rodents leads to a decrease in successful mating and fewer pregnancies, often caused by impaired sperm motility and poor sperm morphology. Human studies have to a lesser extent validated these findings; however, newer studies suggest a positive effect of vitamin D supplementation on semen quality in cases with vitamin D deficiency, which highlights the need for initiatives to prevent vitamin D deficiency. Calcium channels in male reproductive organs and spermatozoa contribute to the regulation of sperm motility and capacitation, both essential for successful fertilisation, which supports a need to avoid calcium deficiency. Studies have demonstrated that vitamin D, as a regulator of calcium homoeostasis, influences calcium influx in the testis and spermatozoa. Emerging evidence suggests a potential link between vitamin D deficiency and male infertility, although further investigation is needed to establish a definitive causal relationship. Understanding the interplay between vitamin D, calcium and male reproductive health may open new avenues for improving fertility outcomes in men.

The Calcium-Sensing Receptor Is Essential for Calcium and Bicarbonate Sensitivity in Human Spermatozoa

CONTEXT

The calcium-sensing receptor (CaSR) is essential to maintain a stable calcium concentration in serum. Spermatozoa are exposed to immense changes in concentrations of CaSR ligands such as calcium, magnesium, and spermine during epididymal maturation, in the ejaculate, and in the female reproductive environment. However, the role of CaSR in human spermatozoa is unknown.

OBJECTIVE

This work aimed to investigate the role of CaSR in human spermatozoa.

METHODS

We identified CaSR in human spermatozoa and characterized the response to CaSR agonists on intracellular calcium, acrosome reaction, and 3',5'-cyclic adenosine 5'-monophosphate (cAMP) in spermatozoa from men with either loss-of-function or gain-of-function mutations in CASR and healthy donors.

RESULTS

CaSR is expressed in human spermatozoa and is essential for sensing extracellular free ionized calcium (Ca2+) and Mg2+. Activators of CaSR augmented the effect of sperm-activating signals such as the response to HCO3- and the acrosome reaction, whereas spermatozoa from men with a loss-of-function mutation in CASR had a diminished response to HCO3-, lower progesterone-mediated calcium influx, and were less likely to undergo the acrosome reaction in response to progesterone or Ca2+. CaSR activation increased cAMP through soluble adenylyl cyclase (sAC) activity and increased calcium influx through CatSper. Moreover, external Ca2+ or Mg2+ was indispensable for HCO3- activation of sAC. Two male patients with a CASR loss-of-function mutation in exon 3 presented with normal sperm counts and motility, whereas a patient with a loss-of-function mutation in exon 7 had low sperm count, motility, and morphology.

CONCLUSION

CaSR is important for the sensing of Ca2+, Mg2+, and HCO3- in spermatozoa, and loss-of-function may impair male sperm function.

Influence of FGF23 and Klotho on male reproduction: Systemic vs direct effects

Currently, no treatment exists to improve semen quality in most infertile men. Here, we demonstrate systemic and direct effects of Fibroblast growth factor 23 (FGF23) and Klotho, which normally regulate vitamin D and mineral homeostasis, on testicular function. Direct effects are plausible because KLOTHO is expressed in both germ cells and spermatozoa and forms with FGFR1 a specific receptor for the bone-derived hormone FGF23. Treatment with FGF23 increased testicular weight in wild-type mice, while mice with global loss of either FGF23 or Klotho had low testicular weight, reduced sperm count, and sperm motility. Mice with germ cell-specific Klotho (gcKL) deficiency neither had a change in sperm count nor sperm motility. However, a tendency toward fewer pregnancies was detected, and significantly fewer Klotho heterozygous pups originated from gcKL knockdown mice than would be expected by mendelian inheritance. Moreover, gcKL mice had a molecular phenotype with higher testicular expression of Slc34a2 and Trpv5 than wild-type littermates, which suggests a regulatory role for testicular phosphate and calcium homeostasis. KLOTHO and FGFR1 were also expressed in human germ cells and spermatozoa, and FGF23 treatment augmented the calcium response to progesterone in human spermatozoa. Moreover, cross-sectional data revealed that infertile men with the highest serum Klotho levels had significantly higher serum Inhibin B and total sperm count than men with the lowest serum Klotho concentrations. In conclusion, this translational study suggests that FGF23 and Klotho influence gonadal function and testicular mineral ion homeostasis both directly and indirectly through systemic changes in vitamin D and mineral homeostasis.

Functional expression of G protein-coupled receptor 30 in immature rat epididymal epithelium

The aim of this study is to investigate the functional role of G protein-coupled receptor 30 (GPR30) in the epididymis. We found that GPR30 is expressed in the epithelium of the immature rat epididymis and is involved in chloride secretion into the caudal epididymis lumen. The short-circuit current (Isc) experiments showed that in primary cultured caudal epididymis epithelium, activation of GPR30 by its specific agonist G1 induced a mono-phasic current increase, and G15, the specific antagonist of GPR30, could completely inhibit the current induced by G1. The G1-induced Isc was largely blocked by application of the non-specific chloride channel inhibitor diphenylamine-dicarboxylic acid (DPC), or by the cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor CFTR_inh-172 , suggesting that the current was mainly mediated through CFTR. In addition, after stimulating GPR30 by G1, the intracellular concentration of cAMP in the epithelium was significantly increased, indicating that the cAMP signal pathway is involved and could be responsible for the CFTR activation. Finally, to further investigate the function of GPR30 in vivo, G15 was administrated into rats subcutaneously. The osmotic pressure of the micro perfusion solution from epididymis was measured and the sperms were collected. Results showed that there was an osmotic pressure increase of the perfusion solution from G15 treated rats. When the GPR30 was inhibited by G15 endogenously, the motility of sperms decreased. Our data demonstrated that GPR30 is involved in the formation of caudal epididymis fluid micro-environment thus affecting sperm motility.

Development of apical blebbing in the boar epididymis

Microvesicles are of increasing interest in biology as part of normal function of numerous systems; from the immune system (T cell activation) to implantation of the embryo (invasion of the trophoblasts) and sperm maturation (protein transfer in the epididymis). Yet, the mechanisms involved in the appearance of apical blebbing from healthy cells as part of their normal function remain understudied. Microvesicles are produced via one of two pathways: exocytosis or apical blebbing also termed ectocytosis. This work quantifies the histological appearance of apical blebbing in the porcine epididymis during development and examines the role of endogenous estrogens in regulating this blebbing. Apical blebbing appears at puberty and increases in a linear manner into sexual maturity suggesting that this blebbing is a mature phenotype. Endogenous estrogen levels were reduced with an aromatase inhibitor but such a reduction did not affect apical blebbing in treated animals compared with their vehicle-treated littermates. Epididymal production of apical blebs is a secretion mechanism of functionally mature principal cells regulated by factors other than estradiol.

In vitro expression of androgen and estrogen receptors in prepubertal and adult rat epididymis

Androgens and estrogens regulate epididymal function but the mechanisms by which these hormones act is not fully understood. Epididymal culture systems have been described but none of these identify if AR, ERα and ERβ are expressed concurrently under identical culture conditions. Presumably, the actions of androgens and estrogens require their receptors and our results demonstrate for the first time that rat epididymal cell cultures express AR, ERα and ERβ protein under identical culture conditions. Furthermore, we demonstrate that the expression of these receptors in vitro mirrors normal in vivo expression patterns, a key finding for past and future studies. An epididymal culture system that maintains expression of androgen and estrogen receptors will allow for future investigations into the regulation and function of the epididymis. Previous studies showing prepubertal expression of ERα, did not find ERα expression in adult animals, making our study the first to demonstrate both prepubertal and adult expression of ERα. Additionally, species differences have been suggested to exist with regards to epididymal expression of ERα. Our results are the first to experimentally compare ERα expression in two different rat species and show that expression is similar between the two species. The expression of ERα and ERβ protein prior to puberty and into adulthood provides further supports for the hypothesis that the epididymis may be influenced by estrogens, in addition to androgens, during development and mature function.

Effect of a nonsteroidal antiandrogen, flutamide on intraluminal acidification in rat testis and epididymis

Flutamide, a pure antiandrogen was administered to intact adult male rats to study the effect of altered availability of hormones on in situ pH, PCO2 and bicarbonate concentration ([HCO3-]) of seminiferous tubules, proximal caput, middle caput, middle corpus, and proximal cauda epididymidis. The weights of the epididymis and ventral prostate as well as the plasma testosterone level showed antiandrogenic effects of flutamide. Relative to controls, flutamide elevated significantly in situ pH in proximal caput, middle caput, middle corpus and proximal cauda epididymidis but not in seminiferous tubules. In situ PCO2 values in the above segments, after flutamide, were indistinguishable from controls and from each other but all values remained significantly higher than systemic arterial blood PCO2. Flutamide treatment did not change the [HCO3-] in systemic arterial blood or seminiferous tubules but increased markedly the values in proximal caput and middle caput. The results of the present studies support the view that luminal acidification in the rat epididymis is under androgen control and may be important for sperm maturation and storage.

Enzymohistochemical and immunohistochemical study of the human efferent ducts

An enzymohistochemical and immunohistochemical study of the efferent ducts was performed in normal adult men. The epithelium consists of two types of columnar cells: principal cells (PCs) and ciliated cells (CCs), and is surrounded by a lamina propria (LP) with cells arranged circularly (LPCs). Enzymohistochemical study revealed more intense activity of succinic dehydrogenase, NADP, and ATPase in the CCs than in the PCs. The LPCs also showed an intense reaction for NADP and ATPase. Acid phosphatase activity was only intense in the apical cytoplasm of PCs. Immunohistochemical study revealed that antibodies to oestradiol receptor-related protein (ER-D5) immunostained the PCs and CCs intensely and the LPCs weakly. AE1/AE3 antibodies (which stain keratins nos. 1-8 and 14, 15 and 19) immunostained the PCs intensely, but was negative in both CCs and LPCs. Antibodies to keratin Ks.4.62 (which stain keratin no. 19) immunostained PCs and CCs but not LPCs. Epithelial membrane antigen antibodies (EMA) immunostained the adluminal surface and apical cytoplasm of PCs. Anti-vimentin antibodies immunostained the cytoplasm of PCs and CCs weakly as well as isolated cells in the LP. Antibodies to desmin immunostained most LPCs. Antibodies to collagen IV immunostained the basal lamina and many extracellular spaces in the LP, mainly around the LPCs. The differences between the enzymohistochemical and immunohistochemical patterns of the efferent ducts and those of the epididymis may help to explain functional differences along the epididymis.

No evidence for aromatization of [3H]testosterone in oestrogen receptor containing cells of the epididymis

Oestrogen receptors are found in the principal cells of the caput and in apical and clear cells of the epididymis of the mouse. The distribution pattern of oestrogen receptors is different from that of androgen receptors and suggests a physiological role for oestrogens in the epididymis. We examined by competition experiments and thaw-mount autoradiography to see whether aromatization of [3H]testosterone is the source of oestrogens in the epididymis. After injection of [3H]testosterone we found the same labeling pattern as after non-aromatizable [3H]dihydrotestosterone. In particular, apical and clear cells showed a low or no nuclear concentration of radioactivity as with [3H]dihydrotestosterone. Competition with oestradiol had no effect on the binding pattern of [3H]testosterone in the epididymis in contrast to its effects in the brain of the same animals. Competition with dihydrotestosterone abolished labeling in contrast to the brain, where no effect was observed. Thus no aromatization of [3H]testosterone to oestrogens but conversion to dihydrotestosterone seems to occur in the epididymis.