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.

Subacute exposure to Roundup® changes steroidogenesis and gene expression of the glutathione-glutaredoxin system in rat ovaries: Implications for ovarian toxicity of this glyphosate-based herbicide

Studies have indicated that glyphosate induces endocrine disruption and may adversely affect the male reproductive system. However, evidence of its effects on ovarian function is poorly understood so far, making further studies necessary on the mechanisms of the glyphosate toxicity in the female reproductive system. The aim of this work was to evaluate the effect of a subacute exposure (28 days) to the glyphosate-based formulation Roundup® (1.05, 10.5 and 105 μg/kg b.w. of glyphosate) on steroidogenesis, oxidative stress, systems involved in cell redox control and histopathological parameters in rat ovaries. Hence we quantify plasma estradiol and progesterone by chemiluminescence; non-protein thiol levels, TBARS, superoxide dismutase and catalase activity by spectrophotometry; gene expression of steroidogenic enzymes and redox systems by real-time PCR; and ovarian follicles by optical microscopy. Our results demonstrated that oral exposure increased progesterone levels and the mRNA expression of 3β-hydroxysteroid dehydrogenase. Histopathological analysis revealed a decrease in the number of primary follicles and an increase in the number of corpus luteum in rats exposed to Roundup®. An imbalance of the oxidative status was also evidenced by decreasing the catalase activity at all groups exposed to the herbicide. Increased lipid peroxidation and gene expression of glutarredoxin and decreased of glutathione reductase were also observed. Our results indicate that Roundup® causes endocrine disruption of hormones related to female fertility and reproduction and changes the oxidative status by altering antioxidant activity, inducing lipid peroxidation, as well as changing the gene expression of the glutathione-glutarredoxin system in rat ovaries.

Calcifediol (25OH Vitamin D3) Deficiency: A Risk Factor from Early to Old Age

Vitamin D deficiency is the main cause of nutritional rickets in children and osteomalacia in adults. There is consensus that nutritional access to vitamin D can be estimated by measuring serum concentrations of 25OHD and vitamin D deficiency can thus be considered as calcifediol deficiency. However, the threshold for vitamin D/calcifediol sufficiency remains a matter of debate. Vitamin D/calcifediol deficiency has been associated with musculoskeletal effects but also multiple adverse extra-skeletal consequences. If these consequences improve or if they can be treated with vitamin D supplementation is still unclear. Observational studies suggest a higher infection risk in people with low calcifediol levels. There is also a consistent association between serum calcifediol and cardiovascular events and deaths, but large-scale, long-term intervention studies did not show any benefit on cardiovascular outcomes from supplementation, at least not in subjects without clear vitamin D deficiency. Cancer risk also did not change with vitamin D treatment, although there are some data that higher serum calcifediol is associated with longer survival in cancer patients. In pregnant women, vitamin D supplementation decreases the risk of pre-eclampsia, gestational diabetes mellitus, and low birth weight. Although preclinical studies showed that the vitamin D endocrine system plays a role in certain neural cells as well as brain structure and function, there is no evidence to support a beneficial effect of vitamin D in neurodegenerative diseases. Vitamin D supplementation may marginally affect overall mortality risk especially in elderly subjects with low serum calcifediol concentrations.

Insights into the perspective correlation between vitamin D and regulation of hormones: sex hormones and prolactin

Aim. Vitamin D is currently an exciting research target, besides its obvious role in calcium homeostasis and bone health, enormous work is being directed at examining the effects of this vitamin on various biological functions and pathological conditions.

Material and methods. The review of the literature and the analysis took about six months and was carried out through PubMed. This is a search engine opening mainly the MEDLINE database of trusted references. We called up all studies written in English that were published between the years 2004 to 2021 and that came through using the applied search terms, and analysed all those that met the criteria.

Results. The endocrine system with its many glands and hormones and their essential roles in the maintenance of normal body functioning cannot be far from interactions with vitamin D. Male and female sex hormones are no exceptions and many studies have investigated the correlations between these hormones and vitamin D. As such, direct and indirect relationships have been found between vitamin D, its receptors or one of its metabolising enzymes with sex hormones and the development of reproductive organs in males and females.

Conclusion. This review summarises the research investigating the associations of vitamin D with sex hormones and reproductive organs in males and females, and thus may pave the road for future studies that will investigate the clinical significance of vitamin D in the management of reproductive system disorders. Despite some conflicting results about the relationship between VD and the effectiveness of the reproductive system, many studies confirm the presence of receptors for this vitamin in the reproductive system, and this supports the direct or indirect relationship between VD and prolactin or VD and testosterone through PO4 and Ca2+ homeostasis, or production of osteocalcin. Therefore, VD is positively associated with semen quality and androgen status. Furthermore, a direct relationship between VD and the production of progesterone, estrogen and estrone in human ovarian cells has been supported by many studies.

Seasonal Variations in Sex Steroids in a Young Male Population and Their Relationship with Plasma Levels of Vitamin D

Purpose

Vitamin D (VD) acts on sperm motility, capacitation and survival but its role in steroidogenesis is less clear. Aims: To analyze seasonal variations in sex steroids and VD in a healthy male population.

Materials and Methods

Twenty-nine healthy males, 34.0±4.8 years were included. Blood collection in winter (W) and summer (S) was performed to measure: 25OHD, total testosterone (TT), free testosterone (FT), estradiol (E2), luteinizing hormone (LH), and sex hormone binding globulin (SHBG). Testosterone/estradiol (T/E2) ratio was calculated.

Results

In W, lower levels of 25OHD: 18.8±7.2 ng/mL vs. 38.8±11.9 ng/mL (p<0.0001) and LH: 3.5±1.2 mU/mL vs. 3.9±1.5 mU/mL (p=0.05), and higher levels of TT: 501.9±157.7 ng/dL vs. 405.0±128.0 ng/dL (p=0.0003), FT: 11.8±4.1 ng/dL vs. 10.2±3.7 ng/dL (p=0.017), SHBG: 28.5±10.9 nmol/L vs. 23.6±7.9 nmol/L (p=0.002) and T/E2 ratio: 30.7±19.7 ng/dL/pg/mL vs. 17.3±3.6 ng/dL/pg/mL (p=0.0015) with no variation in E2 levels were observed. A positive correlation between 25OHD and E2 (r=0.28, p=0.04) and negative correlations between 25OHD and TT (r=−0.27, p=0.049), 25OHD and FT (r=−0.32, p=0.01), and 25OHD and T/E2 (r=−0.44, p=0.0008) were found.

Conclusions

In healthy young male population, seasonal variations were observed in 25OHD and LH levels (higher in S) and in TT, FT, SHBG levels, and T/E2 (higher in W). Lower values of TT and FT in S are accompanied by higher levels of LH, which rules out a central mechanism for lowering testosterone. 25OHD negatively correlated with TT, FT, and T/E2 and positively correlated with E2, suggesting a relationship between VD status and changes in gonadal steroids.

Proteomics analysis reveals the effect of 1α,25(OH)2VD3-glycosides on development of early testes in piglets

1α,25(OH)₂VD₃ is the most active form of VD3 in animals. It plays an important role in regulating mineral metabolism but also in reproduction. Testes are the main reproductive organs of male mammals. Our research aims to reveal the effect of 1α,25(OH)₂VD₃-glycosides on development of early testes in piglets. 140 weaned 21-day old piglets were selected. The piglets were randomly divided into four groups and were fed a commercial diet supplemented with 0, 1, 2 and 4 μg/kg of 1α,25(OH)₂VD₃, provided as 1α,25(OH)₂VD₃-glycosides. Sixty days after the start of the experiment, at piglet age 82 days, testes were harvested. The morphology and histology of early testicular development were assessed. In addition, the proteomic TMT/iTRAQ labelling technique was used to analyse the protein profile of the testes in each group. Western blotting was applied to verify the target of differentially abundant proteins (DAPs). The analysis of morphology and histology of testes showed that a certain concentration of 1α,25(OH)₂VD₃-glycosides had a positive and significant effect on testicular development. And the results of proteomics analysis showed that of the identified 132,715 peptides, 122,755 were unique peptides. 7852 proteins, of which 6573 proteins contain quantitative information. Screening for DAPs focused on proteins closely related to the regulation of testicular development such as steroid hormone synthesis, steroid biosynthesis, peroxisome and fatty acid metabolism pathways. These results indicated that 1α,25(OH)₂VD₃ is involved in the regulation of early testicular development in piglets. At the same time, these findings provide valuable information for the proteins involved in the regulation of testicular development, and help to better understand the mechanisms of 1α,25(OH)₂VD₃ in regulating the development of piglets’ testes.

Estradiol and 1α,25(OH)2 vitamin D3 share plasma membrane downstream signal transduction through calcium influx and genomic activation in immature rat testis

The aim of this study was to investigate the rapid response pathway and gene and protein expression profiles of the rat testis in response to estradiol (E₂) and 1α,25(OH)₂ vitamin D₃ (1,25-D₃), to understand how they mediate their effects on the first spermatogenic wave. To do this, we compared the effects of 1,25-D₃ and E₂ on ⁴⁵calcium(Ca²⁺) uptake and the involvement of estrogen receptors (ESR) in their rapid responses. Additionally, we studied the downstream signal transduction effects of 1,25-D₃ and E₂ on cyclin A1/B1 and cellular cycle protein expression. As previously observed for 1,25-D₃, E₂ also increased ⁴⁵Ca²⁺ uptake in immature rat testes via voltage-dependent Ca²⁺ channels, Ca²⁺-dependent chloride channels and via the activation of protein kinase C, protein kinase A and mitogen-activated protein kinase kinase (MEK). Elevated aromatase expression by testes was observed in the presence of 1,25-D₃ and both hormones decreased ESR mRNA expression. Furthermore, 1,25-D₃ and E₂ diminished cyclin A1 mRNA expression, but E₂ did not affect cyclin B1 mRNA levels. Consistent with these findings, the immunocontent of cyclin A1 and B1 in the testes was also increased by 1,25-D₃ and E₂. 1,25-D₃ increased expressions of the p16 and p53 proteins, supporting the anti-proliferative and pro-apoptotic properties of 1,25-D_3, while E₂ also augmented p16. Data indicate that both hormones trigger rapid responses at the plasma membrane that may control the expression of gene and proteins related to cell cycle regulation, and thereby modulate spermatogenesis.

Developmental vitamin D deficiency increases foetal exposure to testosterone

Background

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders which are more common in males. The ‘prenatal sex steroid’ hypothesis links excessive sex-steroid exposure during foetal life with the behavioural differences observed in ASD. However, the reason why sex steroid exposure may be excessive remains unclear. Epidemiological studies have identified several environmental risk factors associated with ASD, including developmental vitamin D (DVD) deficiency. We have demonstrated in an animal model that DVD-deficiency is associated with a hyper-inflammatory response in placentas from male but not female foetuses. Vitamin D also regulates the expression of several steroidogenic enzymes in vitro. Therefore using this animal model, we have examined whether DVD-deficiency leads to increased sex-steroid levels in both the maternal and foetal compartments.

Methods

Female rats are fed a vitamin D deficient diet from 6 weeks before mating until tissue collection at embryonic day 18. We examined the levels of testosterone, androstenedione and corticosterone in maternal plasma, foetal brains and amniotic fluid. We further examined gene expressions of steroidogenic enzymes and DNA methylation of aromatase promoters in foetal brains as a potential molecular mechanism regulating testosterone expression.

Results

We show that DVD-deficiency increases testosterone levels in maternal blood. We also show elevated levels of testosterone and androstenedione in the amniotic fluid of female but not male DVD-deficient foetuses. Testosterone levels were also elevated in DVD-deficient male brains. Vitamin D, like other steroid-related hormones, regulates gene expression via methylation. Therefore we examined whether the significant elevation in testosterone in male brains was due to such a potential gene-silencing mechanism. We show that the promoter of aromatase was hyper-methylated compared to male controls.

Limitations

A reduction in aromatase, in addition to causing excessive testosterone, could also lead to a reduction in estradiol which was not examined here.

Conclusions

This study is the first to show how an epidemiologically established environmental risk factor for ASD may selectively elevate testosterone in male embryonic brains. These findings provide further mechanistic support for the prenatal sex steroid theory of ASD.

The Effects of UVB and Vitamin D on Decreasing Risk of Colorectal Cancer Incidence and Mortality: A Review of the Epidemiology, Clinical Trials, and Mechanisms

The solar ultraviolet B-vitamin D-cancer hypothesis was first suggested in 1980 based on a geographical ecological study. Since then, several ecological and observational studies, as well as researches of mechanisms have supported the hypothesis. Also, the association between vitamin D condition and cancer risk has been assessed in a number of epidemiologic studies, while data from interventional studies remain scant. In regard of cancer locations, the body of evidence is most substantial for colorectal cancer, for which support comes from studies of 25(OH)D, vitamin D intake, and region of residence in a sunny weather. Collectively evidence demonstrates that vitamin D has a potent and beneficial effect at antagonizing and blocking several mitogenic mechanisms related to tumorigenesis. Taken together with the epidemiological studies and limited clinical trials, individuals may need to consider elevating 25(OH)D levels via sun exposure and/or vitamin D supplementation to decrease risk of colorectal cancer, in addition to standard care, treat cancer.

Acute effect of bisphenol A: Signaling pathways on calcium influx in immature rat testes

We investigated the acute effect of low concentrations of BPA on calcium influx and the mechanism of action of BPA in this rapid response in the rat testis. BPA increased calcium influx at 1 pM and 1 nM at 300 s of incubation, in a similar manner to that of estradiol. At 1 pM, BPA stimulated calcium influx independently of classical estrogen receptors, consistent with a G-protein coupled receptor. This effect also involves the modulation of ionic channels, such as K⁺, TRPV1 and Cl^- channels. Furthermore, BPA is able to modulate calcium from intracellular storages by inhibiting SERCA and activating IP₃ receptor/Ca²⁺ channels at the endoplasmic reticulum and activate kinase proteins, such as PKA and PKC. The rapid responses of BPA on calcium influx could, in turn, trigger a cross talk by MEK and p38^MAPK activation and also mediate genomic responses.

Reproductive endocrinology of vitamin D

Vitamin D is a versatile hormone with several functions beyond its well-established role in maintenance of skeletal health and calcium homeostasis. The effects of vitamin D are mediated by the vitamin D receptor, which is expressed together with the vitamin D metabolizing enzymes in the reproductive tissues. The reproductive organs are therefore responsive to and able to metabolize vitamin D locally. The exact role remains to be clarified but several studies have suggested a link between vitamin D and production/release of reproductive hormones into circulation, which will be the main focus of this review. Current evidence is primarily based on small human association studies and rodent models. This highlights the need for randomized clinical trials, but also functional animal and human in vitro studies, and larger, prospective cohort studies are warranted. Given the high number of men and women suffering from reproductive problems and abnormal endocrinology research addressing the role of vitamin D in reproductive endocrinology may be of clinical importance.

The role of vitamin D in male fertility: A focus on the testis

In the last decade, vitamin D has emerged as a pleiotropic molecule with a multitude of autocrine, paracrine and endocrine functions, mediated by classical genomic as well as non-classical non-genomic actions, on multiple target organs and systems. The expression of vitamin D receptor and vitamin D metabolizing enzymes in male reproductive system, particularly in the testis, suggests the occurrence of vitamin D synthesis and regulation as well as function in the testis. The role of vitamin D in the modulation of testis functions, including hormone production and spermatogenesis, has been investigated in animals and humans. Experimental studies support a beneficial effect of vitamin D on male fertility, by modulating hormone production through genomic and non-genomic actions, and, particularly, by improving semen quality essentially through non-genomic actions. However, clinical studies in humans are controversial. Indeed, vitamin D seems to contribute to the modulation of the bioavailable rather than total testosterone. Moreover, although an increased prevalence or risk for testosterone deficiency was reported in men with vitamin D deficiency in observational studies, the majority of interventional studies demonstrated the lack of effect of vitamin D supplementation on circulating levels of testosterone. The most consistent effect of vitamin D was reported on semen quality. Indeed, vitamin D was shown to be positively associated to sperm motility, and to exert direct actions on spermatozoa, including non-genomic driven modulation of intracellular calcium homeostasis and activation of molecular pathways involved in sperm motility, capacitation and acrosome reaction. The current review provides a summary of current knowledge on the role of vitamin D in male fertility, by reporting clinical and experimental studies in humans and animals addressing the relationship between vitamin D and testis function.

The roles of UVB and vitamin D in reducing risk of cancer incidence and mortality: A review of the epidemiology, clinical trials, and mechanisms

Global cancer incidence and mortality rates are high and increasing. Thus, it is imperative to find novel solutions to preventing cancer incidence and treating it at an affordable yet efficacious manner. The solar UVB-vitamin D-cancer hypothesis was first proposed in 1980 based on a geographical ecological study. Since then, numerous ecological and observational studies as well as studies of mechanisms have provided support for the hypothesis. However, observational studies have not provided consistent support, in part due to using a single blood draw from any season to use for serum 25-hydroxyvitamin D [25(OH)D] concentration in prospective studies with long follow-up times. Case-controls studies, in which blood is drawn near time of diagnosis, and prospective studies in which blood is drawn in the sunnier half of the year, are more likely to find significant inverse relations between 25(OH)D and cancer incidence. Three vitamin D plus calcium clinical trials have found significant reduction in all-cancer incidence. This paper reviews the evidence for vitamin D in reducing incidence of and increasing survival from breast, colorectal, lung, ovarian, pancreatic, and prostate cancer. The epidemiological evidence provides strong support for all of these types of cancer except for non-aggressive prostate cancer. Studies of the cellular mechanisms of vitamin D action in different cancer cell types, strongly indicate that vitamin D can exert protective and anti-tumorigenic activities that would retard cellular transformation, hyperplasia and cancer progression. Based on the scientific evidence reviewed in this paper, individuals and health providers can consider increasing 25(OH)D concentrations through sensible sun exposure and/or vitamin D supplementation to reduce risk of and, in conjunction with standard care, treat cancer. Public health acceptance of vitamin D for cancer prevention and treatment requires stronger support from vitamin D clinical trials.

Interactions between oestrogen and 1α,25(OH)2-vitamin D3 signalling and their roles in spermatogenesis and spermatozoa functions

Oestrogens and 1α,25(OH)₂-vitamin D₃ (1,25-D₃) are steroids that can provide effects by binding to their receptors localised in the cytoplasm and in the nucleus or the plasma membrane respectively inducing genomic and non-genomic effects. As confirmed notably by invalidation of the genes, coding for their receptors as tested with mice with in vivo and in vitro treatments, oestrogens and 1,25-D₃ are regulators of spermatogenesis. Moreover, some functions of ejaculated spermatozoa as viability, DNA integrity, motility, capacitation, acrosome reaction and fertilizing ability are targets for these hormones. The studies conducted on their mechanisms of action, even though not completely elicited, have allowed the demonstration of putative interactions between their signalling pathways that are worth examining more closely. The present review focuses on the elements regulated by oestrogens and 1,25-D₃ in the testis and spermatozoa as well as the interactions between the signalling pathways of both hormones.

A time-course regulatory and kinetic expression study of steroid metabolizing enzymes by calcitriol in primary cultured human placental cells

1,25-dihydroxivitamin D₃ (calcitriol), is a secoesteroid involved in several placental functions. In particular, we and others showed that calcitriol regulates peptides, proteins, cytokines and hormones production in human trophoblastic cells. On the other hand, calcitriol modifies the activity and expression of some steroidogenic enzymes, a process that is considered tissue-specific. However, the effects of calcitriol on the expression of enzymes involved in the synthesis of sex steroids in placental tissue have not yet been entirely studied. The aim of the present study was to investigate the effects of calcitriol upon gene expression of several steroid enzymes such as cytochrome P450scc (CYP11A1), type 1 3β-hydroxysteroid dehydrogenase(3β-HSDI), 17β-HSD3, 17α-hydroxylase/17,20 lyase (CYP17A1) and aromatase (CYP19A1) in primary cultures of human placental cells. Cell cultures were performed using placentas obtained immediately after delivery by caesarean section from normotensive healthy women and calcitriol effects were evaluated, at level of transcription, by qPCR. The results showed that: 1) from basal expression values of the five genes studied, 3β-HSDI was the most expressed gene (P<0.05); 2) basal expression of all enzymes was significantly higher in cultured syncytiotrophoblast than in cytotrophoblasts (P<0.05); 3) the presence of calcitriol in cultured trophoblast cells generally resulted in a stimulatory effect of CYP11A1, CYP19A1 and 17β-HSD3 gene expression at 3h of treatment whereas 3β-HSDI was induced at 6h (P<0.05). However, a time-dependent variable was also observed; 4) protein expression of CYP11A1 and 3β-HSDI were not modified significantly by calcitriol, however that of CYP19A1 was regulated in similar fashion as gene expression. In conclusion, calcitriol affected in a time-dependent manner the expression of steroids metabolizing enzymes in human placental cell cultures.

Steroid Receptors and Aromatase Gene Expression in Different Brain Areas of Copulating and Sexually Sluggish Male Rats

INTRODUCTION

Sexually sluggish (SS) males have been identified in several species of mammals including rats. These animals take more than 30 minutes to ejaculate; they do not ejaculate or do so inconsistently despite being tested repeatedly with sexually receptive females. Different brain areas and hormones play an important role in the control of male sexual behavior.

AIMS

Determine gene expression for the androgen receptor (AR), the estrogen receptor alpha (ERα), the progesterone receptor (PR), and the aromatase enzyme (ARO), in brain regions important in the control of male sexual behavior including the medial preoptic area (MPOA), the amygdala (AMG), the olfactory bulb (OB), and, as a control, the cortex (CTX) of copulating (C) and SS male rats.

METHODS

Males that ejaculated within 30 minutes in three tests with receptive females were included in the C group, while those males that ejaculated in one or none of the four tests were included in the SS group. RNA was isolated 1 week after the last test of sexual behavior, and cDNA was synthesized from the brain areas listed above.

MAIN OUTCOMES MEASURES

Expression of the AR, ERα, PR, and ARO genes was determined by quantitative polymerase chain reaction (qPCR). Cyclophilin A (CycA) and tyrosine 3-monooxygenase-tryptophan activation protein zeta (Ywhaz) were housekeeping genes used to determine relative gene expression with the 2(-ΔΔCt) method.

RESULTS

The expression of mRNA for AR and ARO increased in the MPOA of SS males. ARO mRNA was increased in the AMG of SS males. In the OB, ERα mRNA was increased and AR mRNA reduced in SS males.

CONCLUSION

These results indicate SS and C males show differences in gene expression within brain regions controlling sexual behavior.

The vitamin D receptor localization and mRNA expression in ram testis and epididymis

The objectives of present study were to investigate the presence of vitamin D receptor (VDR) in testis and epididymis of ram by polymerase chain reaction (PCR), to locate VDR in testis and epididymis by immunohistochemistry and to compare difference of VDR expression between testis and epididymis before and after sexual maturation by Real time-PCR and Western blot. The results showed that VDR exists in the testis and epididymis of ram while VDR protein in testis and epididymis was localized in Leydig cells, spermatogonial stem cells, spermatocytes, Sertoli cells and principal cells. For the adult ram, the amounts of VDR mRNA and VDR protein were less (p < 0.01) in testis than compared with caput, corpus and cauda epididymis. For prepubertal ram, the result showed the same trend (p < 0.01). However, the expression levels of VDR mRNA and VDR protein in caput, corpus, cauda epididymis and testis showed no significant difference (p > 0.05) between adult and prepubertal. In conclusion, VDR exists in testis and epididymis of ram, suggesting 1α,25-(OH)(2)VD(3) may play a role in ram reproduction.

Functional Importance of 1α,25(OH)2-Vitamin D3 and the Identification of Its Nongenomic and Genomic Signaling Pathways in the Testis

The 1α,25(OH)2-vitamin D3 (1,25-D3) is known by its classic effects on Ca2+ metabolism and regulation of cellular proliferation and differentiation. The hormone 1,25-D3 acts in the testis through nongenomic and genomic events being implicated in the success of spermatogenesis in rats and in human being. The aim of this review was to highlight the effect and intracellular pathways of 1,25-D3 to modulate the spermatogenesis. The pivotal role of 1,25-D3 in male reproduction is reinforced by the presence of VDR and 1α-hydroxylase in reproductive tract. Also, the marked expression of VDR and the VD metabolizing enzymes in human testis, ejaculatory tract, and mature spermatozoa implicates the 1,25-D3 in spermatogenesis and maturation of human spermatozoa. Among genomic events, 1,25-D3 influences the expression of calcium binding protein and stimulates aromatase gene expression through a nongenomic activation of the membrane-bound VDR receptor involving the PKA pathway in the testis. Also, 1,25-D3 stimulates amino acid transport and exocytosis in testis by nongenomic events coupled to ionic currents triggered at plasma membrane. All together, the demonstration that 1,25-D3 regulates both Sertoli cell and sperm function may be useful for the study and development of new therapeutic strategies for the male reproductive disorders.

Vitamin D and male reproduction

Vitamin D is a versatile signalling molecule with a well-established role in the regulation of calcium homeostasis and bone health. The spectrum of vitamin D target organs has expanded and the reproductive role of vitamin D is highlighted by expression of the vitamin D receptor (VDR) and enzymes that metabolize vitamin D in testis, male reproductive tract and human spermatozoa. The expression levels of VDR and CYP24A1 in human spermatozoa serve as positive predictive markers of semen quality, and VDR mediates a nongenomic increase in intracellular calcium concentration that induces sperm motility. Interestingly, functional animal models show that vitamin D is important for estrogen signalling and sperm motility, while cross-sectional studies support the positive association between serum 25-hydroxyvitamin D level and sperm motility in both fertile and infertile men. Expression of VDR and enzymes that metabolize vitamin D in fetal testis indicates a yet unknown role during development, which may be extrapolated from invasive testicular germ cell tumours where 1α,25-dihydroxyvitamin D induces a mesodermal differentiation of the pluripotent testicular cancer cells. Taken together, vitamin D signalling has a positive effect on semen quality, increases estrogen responsiveness and differentiates germ cell tumours. Future studies are needed to determine when 1α,25-dihydroxyvitamin D acts in a paracrine manner and whether systemic changes, which are subject to pharmacological modulation, could influence male reproductive function.

Characterization of the testicular, epididymal and endocrine phenotypes in the Leuven Vdr-deficient mouse model: targeting estrogen signalling

Vitamin D is a key factor for calcium and bone homeostasis, but signalling through the vitamin D receptor (VDR) seems also to be important for testicular function. To test the functional role of vitamin D signalling we examined the male reproductive system of the Leuven Vdr-ablated (Vdr(-/-)) mice, previously established as a model for hereditary vitamin D-resistant rickets. We investigated reproductive hormones, changes in gene expression and histological phenotype of eleven Vdr(-/-), eight Vdr(+/-) and nine Vdr(+/+) mice. Testicular and epididymal histology were grossly normal in Vdr(-/-) mice. Accordingly, no differences were found in serum concentrations of testosterone, estradiol, LH, and FSH or testicular expression of Cyp19a1, Ersα, Cyp17a1, Star, Insl3, Inhbb, and Amh. However, a significantly lower ERβ expression was found in testis of Vdr(+/-) and Vdr(-/-) mice, conversely epididymal expressions of ERα and the estrogen-target gene Aqp9 were higher. In conclusion, vitamin D seems dispensable for murine spermatogenesis and sex hormone production, but aberrant estrogen-signalling may elicit some of the VDR-mediated effects on male reproduction.

Integrin participates in the effect of thyroxine on plasma membrane in immature rat testis

BACKGROUND

The secretory activity of Sertoli cells (SC) is dependent on ion channel functions and protein synthesis and is critical to ongoing spermatogenesis. The aim of this study was to investigate the mechanism of action associated with a non-metabolizable amino acid [14C]-MeAIB (alpha-(methyl-amino)isobutyric acid) accumulation stimulated by T4 and the role of the integrin receptor in this event, and also to clarify whether the T4 effect on MeAIB accumulation and on Ca2+ influx culminates in cell secretion.

METHODS

We have studied the rapid and plasma membrane initiated effects of T4 by using 45Ca2+ uptake and [45C]-MeAIB accumulation assays, respectively. Thymidine incorporation into DNA was used to monitor nuclear activity and quinacrine to analyze the secretory activity on SC.

RESULTS

The stimulation of MeAIB accumulation byT4 appears to be mediated by the integrin receptor in the plasma membrane since tetrac and RGD peptide were able to nullify the effect of this hormone. In addition, T4 increases extracellular Ca2+ uptake and Ca2+ from intracellular stocks to enhance nuclear activity, but this genomic action seems not to influence SC secretion mediated by T4. Also, the cytoskeleton and CIC-3 chloride channel contribute to the membrane-associated responses of SC.

CONCLUSIONS

T4 integrin receptor activation ultimately determines the plasma membrane responses on amino acid transport in SC, but it is not involved in calcium influx, cell secretion or the nuclear effect of the hormone.

GENERAL SIGNIFICANCE

The integrin receptor activation by T4 may take a role in plasma membrane processes involved in the male reproductive system.

Vitamin D metabolism, sex hormones, and male reproductive function

The spectrum of vitamin D (VD)-mediated effects has expanded in recent years, and VD is now recognized as a versatile signaling molecule rather than being solely a regulator of bone health and calcium homeostasis. One of the recently identified target areas of VD is male reproductive function. The VD receptor (VDR) and the VD metabolizing enzyme expression studies documented the presence of this system in the testes, mature spermatozoa, and ejaculatory tract, suggesting that both systemic and local VD metabolism may influence male reproductive function. However, it is still debated which cell is the main VD target in the testis and to what extent VD is important for sex hormone production and function of spermatozoa. This review summarizes descriptive studies on testicular VD metabolism and spatial distribution of VDR and the VD metabolizing enzymes in the mammalian testes and discusses mechanistic and association studies conducted in animals and humans. The reviewed evidence suggests some effects of VD on estrogen and testosterone biosynthesis and implicates involvement of both systemic and local VD metabolism in the regulation of male fertility potential.

1α,25(OH)2-Vitamin D3 stimulates rapid plasma membrane calcium influx via MAPK activation in immature rat Sertoli cells

It was characterized that the rapid response to 1α,25(OH)(2)-vitamin D(3) (1,25D(3)) on (45)Ca(2+) influx in rat Sertoli cells was mediated by voltage-dependent Ca(2+) channels (VDCCs), PKC, ERK1/2 and p38 MAPK pathways. In primary culture of 10 day-old rat Sertoli cells as well as in the whole testis, the time-course of (45)Ca(2+) influx did not change significantly in basal conditions. However, 1,25D(3) showed stimulatory effect on (45)Ca(2+) influx from 10(-15) to 10(-8) M after 60 s of incubation. The maximum effect was around 140% at 10(-12) M on purified Sertoli cells showing a steady state on (45)Ca(2+) influx between 10(-11) and 10(-9) M. Under this experimental condition, 1,25D(3) stimulated (45)Ca(2+) influx from 73% to 106% and no effect was observed at 10(-16), 10(-8) and 10(-7) M in whole testis. VDCC activities are mandatory for a full and complete stimulatory effect of 1,25D(3) in these approaches. K(+) and Cl(-) channels also are strongly involved in this rapid response coordinated by 1,25D(3). The participation of some selected kinases, points to PKC and ERK1/2 upstream activity to p38 MAPK activation suggesting an intracellular cross-talk between rapid (45)Ca(2+) influx and nuclear events. In addition, the comparative effect of microtubule disassembles and ClC-3 channel blocker on (45)Ca(2+) influx provides evidence of secretory activity of Sertoli cells triggered by 1,25D(3). Our results suggest that 1,25D(3) activates p38 MAPK and reorganizes microtubules, involving Ca(2+), PKC and ERK1/2 as upstream regulators and that extracellular Ca(2+) have a central role to rapidly start hormone-induced gene transcription and/or the secretory activity of Sertoli cell.

Teasing out the role of aromatase in the healthy and diseased testis

Scientific discoveries over the past decade have shifted the stereotypical view of androgens as male hormones and estrogens as female hormones. It is now recognized that a delicate balance of both androgens and estrogens, a process controlled by aromatase, is fundamental for normal testicular development and fertility. While the site-specific actions of these two classes of steroids within the testis are becoming better documented, the role and regulation of estrogen biosynthesis by aromatase within the testis remains unclear. The majority of data comes from a wide range of animal species, particularly genetically modified mouse models; aromatase knockout (ArKO) and overexpressing (AROM(+)), with limited information on humans, however the existence of congenital aromatase mutations has provided some insight into its effects on individual parameters of the testis. This review dissects out the localization and activity of aromatase in the healthy and diseased testis, addresses the cellular insult to the testis that occurs in its absence and over abundance and proposes potential molecular mechanisms of aromatase regulation in the testis.