Immunohistochemical detection and distribution of the 1,25-dihydroxyvitamin D3 receptor in rat reproductive tissues

Relevance of vitamin D in reproduction

The steroid hormone vitamin D is historically recognized for its relevance to bone health and calcium homeostasis. Recent years have witnessed a shift in focus to non-skeletal benefits of vitamin D; in this latter context, an accruing body of literature attests to a relevance of vitamin D to reproductive physiology. This article reviews the existing data about the diverse and previously underappreciated roles for vitamin D in reproductive health. A large body of available literature suggests that vitamin D deficiency may be detrimental to reproductive biology. However, given that our appreciation of vitamin D's role in reproductive physiology is almost entirely shaped by 'associative' studies and that data based on prospective interventional trials are limited, these concepts remain predominantly conjectural. Exact mechanisms whereby vitamin D may participate in the regulation of reproductive physiology remain far from clear. This review underscores a need for appropriately designed intervention trials to address the existing knowledge gaps and to delineate the specific roles of vitamin D signaling in reproductive biology.

Non-genomic effects of vitamin D in human spermatozoa

The spectrum for vitamin D (VD) mediated effects has expanded in recent years. Activated VD (1,25(OH)(2)D(3)) binds to the VD receptor (VDR) and mediates non-genomic effects through the alternative ligand binding-pocket (VDR-ap) or regulates gene transcription through the genomic binding-pocket. VDR and VD-metabolizing enzymes are expressed in human testis, male reproductive tract and mature spermatozoa, and VD is considered important for male reproduction. Expression of the VD-inactivating enzyme CYP24A1 at the annulus of human spermatozoa distinguish normal and infertile men with high specificity, and CYP24A1 expression is positively correlated with all semen variables and suggested as a marker for both semen quality and VD responsiveness. Moreover, spermatozoa are transcriptionally silent and are therefore a unique model to study non-genomic effects. 1,25(OH)(2)D(3) induced a rapid increase in intracellular calcium concentration [Ca(2+)](i) in human spermatozoa. The [Ca(2+)](i) increase was abrogated by the non-genomic VDR antagonist 1β,25(OH)(2)D(3), while the specific agonist for VDR-ap (JN) increased [Ca(2+)](i) with similar kinetics as 1,25(OH)(2)D(3). The rise in [Ca(2+)](i) originated as a Ca(2+)-release from intracellular stores since inhibition of phospholipase-C diminished the 1,25(OH)(2)D(3) mediated Ca(2+) response, while suspending spermatozoa in a nominally Ca(2+)-free medium did not affect the VD mediated Ca(2+) rise. The spatio-temporal kinetics of the VD-response differed from the progesterone-mediated increase in [Ca(2+)](i) as the VD-mediated Ca(2+) rise was not observed in the tail region and was independent of extracellular Ca(2+). A functional role of the VD-mediated Ca(2+) increase was supported by showing that 1,25(OH)(2)D(3) increased sperm motility and induced the acrosome reaction in vitro.

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.

Research resource: whole transcriptome RNA sequencing detects multiple 1α,25-dihydroxyvitamin D(3)-sensitive metabolic pathways in developing zebrafish

The biological role of vitamin D receptors (VDR), which are abundantly expressed in developing zebrafish (Danio rerio) as early as 48 h after fertilization, and before the development of a mineralized skeleton and mature intestine and kidney, is unknown. We probed the role of VDR in developing zebrafish biology by examining changes in expression of RNA by whole transcriptome shotgun sequencing (RNA-seq) in fish treated with picomolar concentrations of the VDR ligand and hormonal form of vitamin D(3), 1α,25-dihydroxyvitamin D(3) [1α,25(OH)(2)D(3))].We observed significant changes in RNAs of transcription factors, leptin, peptide hormones, and RNAs encoding proteins of fatty acid, amino acid, xenobiotic metabolism, receptor-activator of NFκB ligand (RANKL), and calcitonin-like ligand receptor pathways. Early highly restricted, and subsequent massive changes in more than 10% of expressed cellular RNA were observed. At days post fertilization (dpf) 2 [24 h 1α,25(OH)(2)D(3)-treatment], only four RNAs were differentially expressed (hormone vs. vehicle). On dpf 4 (72 h treatment), 77 RNAs; on dpf 6 (120 h treatment) 1039 RNAs; and on dpf 7 (144 h treatment), 2407 RNAs were differentially expressed in response to 1α,25(OH)(2)D(3). Fewer RNAs (n = 481) were altered in dpf 7 larvae treated for 24 h with 1α,25(OH)(2)D(3) vs. those treated with hormone for 144 h. At dpf 7, in 1α,25(OH)(2)D(3)-treated larvae, pharyngeal cartilage was larger and mineralization was greater. Changes in expression of RNAs for transcription factors, peptide hormones, and RNAs encoding proteins integral to fatty acid, amino acid, leptin, calcitonin-like ligand receptor, RANKL, and xenobiotic metabolism pathways, demonstrate heretofore unrecognized mechanisms by which 1α,25(OH)(2)D(3) functions in vivo in developing eukaryotes.

Vitamin D and fertility: a systematic review

BACKGROUND

Vitamin D has been well-known for its function in maintaining calcium and phosphorus homeostasis and promoting bone mineralization. There is some evidence that in addition to sex steroid hormones, the classic regulators of human reproduction, vitamin D also modulates reproductive processes in women and men.

AIM

The aim of this review was to assess the studies that evaluated the relationship between vitamin D and fertility in women and men as well as in animals.

METHODS

We performed a systematic literature search in Pubmed for relevant English language publications published until October 2011.

RESULTS AND DISCUSSION

The vitamin D receptor (VDR) and vitamin D metabolizing enzymes are found in reproductive tissues of women and men. Vdr knockout mice have significant gonadal insufficiency, decreased sperm count and motility, and histological abnormalities of testis, ovary and uterus. Moreover, we present evidence that vitamin D is involved in female reproduction including IVF outcome (clinical pregnancy rates) and polycystic ovary syndrome (PCOS). In PCOS women, low 25-hydroxyvitamin D (25(OH)D) levels are associated with obesity, metabolic, and endocrine disturbances and vitamin D supplementation might improve menstrual frequency and metabolic disturbances in those women. Moreover, vitamin D might influence steroidogenesis of sex hormones (estradiol and progesterone) in healthy women and high 25(OH)D levels might be associated with endometriosis. In men, vitamin D is positively associated with semen quality and androgen status. Moreover, vitamin D treatment might increase testosterone levels. Testiculopathic men show low CYP21R expression, low 25(OH)D levels, and osteoporosis despite normal testosterone levels.

Where is the vitamin D receptor?

The vitamin D receptor (VDR) is a member of the nuclear receptor superfamily and plays a central role in the biological actions of vitamin D. VDR regulates the expression of numerous genes involved in calcium/phosphate homeostasis, cellular proliferation and differentiation, and immune response, largely in a ligand-dependent manner. To understand the global function of the vitamin D system in physiopathological processes, great effort has been devoted to the detection of VDR in various tissues and cells, many of which have been identified as vitamin D targets. This review focuses on the tissue- and cell type-specific distribution of VDR throughout the body.

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.

Immunohistochemical staining of human sperm cells in smears from sexual assault cases

In the routine clinical examination of sexual assault victims, apart from documenting physical evidence of abuse, securing evidence, typically DNA from blood, semen, or saliva, is an important part of the process. Often the presence of semen is considered a most interesting piece of evidence. Not only does it often contain enough DNA for DNA profiling, but it also strongly indicates that an actual sexual act has taken place. The examination of smear slides obtained in sexual assault cases is a time-consuming task especially for the less trained and in cases where the smear only contains few sperm cells. In this work the goal was to develop a procedure to rapidly visualize human sperm cells in smear slides with the use of bright-field microscopy. Using SPERM HY-LITER™ by Independent Forensics, human sperm cells are visualized using a fluorescently labeled mouse antibody which significantly decreases the time used to screen smears. By further using an EnVision+ (DAKO) protocol, it was possible to create an immunohistochemical staining method to visualize sperm cells in bright-field microscopy with the same level of certainty as when using SPERM HY-LITER™.

Roosters affected by epididymal lithiasis present local alteration in vitamin D3, testosterone and estradiol levels as well as estrogen receptor 2 (β) expression

Epididymal lithiasis is a reproductive dysfunction of roosters that is associated with loss of fertility and is characterized by the formation of calcium stones in the lumen of the efferent ductules of the epididymal region. The efferent ductules of birds are responsible for the reabsorption of the fluid coming from the testis as well as luminal calcium. It has been hypothesized that the epididymal stone formation may be related to the impairment of local fluid or calcium homeostasis, which depends on hormones such as estradiol (E2). Therefore, this study aimed to investigate possible alterations in the expression of ERα (ESR1) and ERβ (ESR2) in the epididymal region of roosters affected by epididymal lithiasis. The study was performed by immunohistochemistry and western blotting assays. In addition, the concentrations of E2, vitamin D3, and testosterone, which are also key hormones in maintenance of calcium homeostasis, were determined in the plasma and epididymal region, by ELISA. It was observed that ESR2 expression is increased in all segments of the epididymal region of affected roosters, whereas ESR1 levels are not altered. Moreover, the hormone concentration profiles were changed, as in the epididymal region of roosters with lithiasis the E2levels were increased and vitamin D3 as well as testosterone concentrations were significantly decreased. These results suggest that a hormonal imbalance may be involved with the origin and progression of the epididymal lithiasis, possibly by affecting the local fluid or calcium homeostasis.

Age-related changes in the epithelial and stromal compartments of the mammary gland in normocalcemic mice lacking the vitamin D3 receptor

The vitamin D₃ receptor (VDR) serves as a negative growth regulator during mammary gland development via suppression of branching morphogenesis during puberty and modulation of differentiation and apoptosis during pregnancy, lactation and involution. To assess the role of the VDR in the aging mammary gland, we utilized 12, 14, and 16 month old VDR knockout (KO) and wild type (WT) mice for assessment of integrity of the epithelial and stromal compartments, steroid hormone levels and signaling pathways. Our data indicate that VDR ablation is associated with ductal ectasia of the primary mammary ducts, loss of secondary and tertiary ductal branches and atrophy of the mammary fat pad. In association with loss of the white adipose tissue compartment, smooth muscle actin staining is increased in glands from VDR KO mice, suggesting a change in the stromal microenviroment. Activation of caspase-3 and increased Bax expression in mammary tissue of VDR KO mice suggests that enhanced apoptosis may contribute to loss of ductal branching. These morphological changes in the glands of VDR KO mice are associated with ovarian failure and reduced serum 17β-estradiol. VDR KO mice also exhibit progressive loss of adipose tissue stores, hypoleptinemia and increased metabolic rate with age. These developmental studies indicate that, under normocalcemic conditions, loss of VDR signaling is associated with age-related estrogen deficiency, disruption of epithelial ductal branching, abnormal energy expenditure and atrophy of the mammary adipose compartment.

Regulation of aromatase expression by 1α,25(OH)2 vitamin D3 in rat testicular cells

It is well known that the vitamin D endocrine system is involved in physiological and biochemical events in numerous tissues, especially gut, bone and kidney but also testis. Therefore, in this study the effect and mechanisms of action of 1α,25(OH)2 vitamin D3 (1,25D) on aromatase gene expression in immature rat Sertoli cells were evaluated. Vitamin D receptor transcripts were present in immature Sertoli cells as well as in adult testicular germ cells and somatic cells. The treatment of immature Sertoli cells with 100 nM 1,25D increased the amount of aromatase transcript, mainly in 30-day-old rats. The protein kinase A (PKA) blocker, H89, partially inhibited the 1,25D effect. The stimulation of aromatase gene expression in 30-day-old Sertoli cells by the agonist 1α,25(OH)2 lumisterol3, and the suppression of the 1,25D effect by the antagonists 1β,25(OH)2 vitamin D3 and (23S)-25-dehydro-1α (OH)-vitamin D3-26,23-lactone suggested, besides a genomic effect of 1,25D, the existence of non-genomic activation of the membrane-bound vitamin D receptor involving the PKA pathway.

Vitamin D receptor and vitamin D metabolizing enzymes are expressed in the human male reproductive tract

BACKGROUND

The vitamin D receptor (VDR) is expressed in human testis, and vitamin D (VD) has been suggested to affect survival and function of mature spermatozoa. Indeed, VDR knockout mice and VD deficient rats show decreased sperm counts and low fertility. However, the cellular response to VD is complex, since it is not solely dependent on VDR expression, but also on cellular uptake of circulating VD and presence and activity of VD metabolizing enzymes. Expression of VD metabolizing enzymes has not previously been investigated in human testis and male reproductive tract. Therefore, we performed a comprehensive analysis of the expression of VDR, VD activating (CYP2R1, CYP27A1, CYP27B1) and inactivating (CYP24A1) enzymes in the testis, epididymis, seminal vesicle (SV), prostate and spermatozoa.

METHODS

Tissue samples were obtained after orchiectomy (testis n = 13; epididymis n = 7), prostatectomy (prostate n = 5 and SVs n = 3) and semen samples obtained after ejaculation (n = 13). mRNA was detected with RT-PCR and expression of proteins was determined by immunohistochemistry.

RESULTS

VDR and VD metabolizing enzymes were concomitantly expressed in round and elongated spermatids, vesicles within the caput epididymis, and glandular epithelium of cauda epididymis, SV and prostate. The expression pattern in ejaculated spermatozoa varied, although, concomitant expression of VDR, CYP2R1, CYP27B1 and CYP24A1 was observed in neck and midpiece in a subpopulation of mature spermatozoa.

CONCLUSION

On the basis of the marked expression of VDR and the VD metabolizing enzymes in human testis, ejaculatory tract and mature spermatozoa, we suggest that VD is important for spermatogenesis and maturation of human spermatozoa.

Human male gamete endocrinology: 1alpha, 25-dihydroxyvitamin D3 (1,25(OH)2D3) regulates different aspects of human sperm biology and metabolism

BACKGROUND

A wider biological role of 1alpha,25-Dihydroxyvitamin D3 (1,25(OH)2D3), the active metabolite of vitamin D3, in tissues not primarily related to mineral metabolism was suggested. Recently, we evidenced the ultrastructural localization the 1,25(OH)2D3 receptor in the human sperm. However, the 1,25(OH)2D3 action in human male reproduction has not yet been clarified.

METHODS AND RESULTS

By RT-PCR, Western blot and Immunofluorescence techniques, we demonstrated that human sperm expresses the 1,25(OH)2D3 receptor (VDR). Besides, 25(OH)D3-1 alpha-hydroxylase, evidenced by Western blot analysis, indicated that in sperm 1,25(OH)2D3 is locally produced, highlighting the potential for autocrine-paracrine responses. 1,25(OH)2D3 through VDR, increased intracellular Ca2+ levels, motility and acrosin activity revealing an unexpected significance of this hormone in the acquisition of fertilizing ability. In sperm, 1,25(OH)2D3 through VDR, reduces triglycerides content concomitantly to the increase of lipase activity. Rapid responses stimulated by 1,25(OH)2D3 have been observed on Akt, MAPK and GSK3 implying that this secosteroid is involved in different sperm signalling pathways.

CONCLUSION

Our data extended the role of 1,25(OH)2D3 beyond its conventional physiological actions, paving the way for novel therapeutic opportunities in the treatment of the male reproduction disorders.

Human sperm anatomy: ultrastructural localization of 1alpha,25-dihydroxyvitamin D receptor and its possible role in the human male gamete

Previous studies have suggested that 1alpha,25-dihydroxyvitamin D(3)[1,25(OH)(2)D(3)] has a role in reproductive function. Gonadal insufficiencies were observed as a result of 1,25(OH)(2)D(3) deficiency and in 1,25(OH)(2)D(3) receptor (VDR) null mutant mice. To study human sperm anatomy at the molecular level, we first evaluated the ultrastructural localization of VDR by immunogold electron microscopy using a monoclonal antibody against amino acids 344-424 of human VDR, in normozoospermic samples. Intriguingly, VDR was associated predominantly with the cell nucleus. In fact, it is known that VDR is a transcription factor, and that in vitamin-D-depleted animals, VDR is largely localized in the cell nucleus. To assess the significance of VDR in the male gamete, we investigated the role of 1,25(OH)(2)D(3)/VDR in sperm survival and capacitation. Our results revealed that the action of 1,25(OH)(2)D(3) depended on its concentration because although lower doses induced cholesterol efflux, protein phosphorylation and sperm survival, a higher concentration seemed to be ineffective or did not show an increased effect. These results increase our knowledge of human sperm anatomy at the molecular level and suggest that 1,25(OH)(2)D(3)/VDR may have an important role in sperm survival and the acquisition of fertilizing ability.

Role of 1alpha,25(OH)2 vitamin D3 on alpha-[1-(14)C]MeAIB accumulation in immature rat testis

1,25D3 is critical for the maintenance of normal reproduction since reduced fertility is observed in male rats on a vitamin D-deficient diet. Vitamin D-deficient male rats have incomplete spermatogenesis and degenerative testicular changes. In the present study we have examined the ionic involvement and intracellular messengers of the stimulatory effect of 1,25D3 on amino acid accumulation in immature rat testis. 1,25D3 stimulates amino acid accumulation from 10(-12) to 10(-6) M by increasing the slope to reach a maximum value at 10(-10) M, as compared to the control group. No effect was observed at a lower dose (10(-13) M). Time-course showed an increase on amino acid accumulation after 15, 30, and 60 min of incubation with 1,25D3 (10(-10) M). 1,25D3 stimulated amino acid accumulation in 11-day-old rat testis but not in testis that were 20 days old. Cycloheximide totally blocked the 1,25D3 action on amino acid accumulation. Furthermore, a localized elevation of cAMP increased the stimulatory effect of 1,25D3 and the blockage of PKA nullified the action of the hormone. In addition, 1,25D3 action on amino acid accumulation was also mediated by ionic pathways, since verapamil and apamine diminished the hormone effect. The stimulatory effect of 1,25D3 on amino acid accumulation is age-dependent and specific to this steroidal hormone since testosterone was not able to change amino acid accumulation in both ages studied. This study provides evidence for a dual effect for 1,25D3, pointing to a genomic effect that can be triggered by PKA, as well as to a rapid response involving Ca2+/K+ channels on the plasma membrane.

Expression and regulation of the vitamin D receptor in the zebrafish, Danio rerio

Vitamin D and vitamin D metabolites such as 25-hydroxyvitamin D and 1alpha,25-dihydroxyvitamin D [1alpha,25(OH)(2)D(3)] circulate in the serum of fish. The receptor for 1alpha,25(OH)(2)D(3) (VDR) has previously been cloned from fish intestine, and ligand binding assays have shown the presence of the VDR in the gills, intestine, and liver of fish. Using immunohistochemical methods with specific antibodies against the VDR, we now report that the VDR is widely expressed in tissues of the adult male and female zebrafish, Danio rerio, specifically in epithelial cells of gills, tubular cells of the kidney, and absorptive cells in the intestine. Additionally, the VDR is expressed in the skin, the olfactory organ, the retina, brain, and spinal cord. Sertoli cells of the testis, oocytes, acinar cells of the pancreas, hepatocytes, and bile duct epithelial cells express substantial amounts of the receptor. Osteoblast-like cells and chondrocytes also express VDR. Preimmune serum and antiserum preadsorbed with Danio VDR protein fails to detect VDR in the same tissues. The VDR is also present in the developing eye, brain, and otic vesicle of 48- and 96-h postfertilization zebrafish embryos. Parenteral administration of 1alpha,25(OH)(2)D(3) increases concentrations of VDR in intestinal epithelial cells but not in epithelial cells of the gills. Lithocholic acid, however, does not alter concentrations of VDR after parenteral administration. The data suggest that VDR is widely distributed in tissues of the zebrafish, D. rerio, and is likely to play important roles in epithelial transport, bone, and endocrine function. Furthermore, concentrations of the receptor seem to be regulated by its ligand, 1alpha,25-dihydroxyvitamin D but not by lithocholic acid. Zebrafish may serve as a useful model in which to assess the function of the VDR in diverse tissues.

Co-expression of CYP27B1 enzyme with the 1.5kb CYP27B1 promoter-luciferase transgene in the mouse

The renal enzyme 25-hydroxyvitamin D 1alpha-hydroxylase (CYP27B1), responsible for the synthesis of circulating. 1,25-dihydroxyvitamin D (1,25D), is also expressed in a number of non-renal tissues. The regulation of CYP27B1 expression by the short flanking promoter outside the kidney is, however, largely unknown. We have used a transgenic mice expressing the 1.5kb promoter of the human CYP27B1 gene fused to the firefly luciferase gene in order to investigate tissue-specific CYP27B1 expression. These transgenic animals demonstrated co-localised luciferase and endogenous CYP27B1 expression in kidney proximal convoluted tubular cells. Strong co-expression of luciferase and CYP27B1 also occurred in neurons and Purkinje cells of the cerebellum and in Leydig and Sertoli cells of the testes. Other tissues to exhibit CYP27B1-promoter directed luciferase activity included lung, prostate, trabecular bone and jejunum as well as the choroid epithelium. The tissue specific changes in luciferase activity were age-related. These findings demonstrate that the proximal 1.5kb 5' flanking region of the CYP27B1 gene directs the expression of CYP27B1 in a number of known and novel tissues in a specific manner.

Distribution of vitamin D3 receptor in the epididymal region of roosters (Gallus domesticus) is cell and segment specific

Vitamin D3 is a steroid hormone well known by its role in maintaining calcium homeostasis, however this hormone may also participate in other biological functions, including control of reproductive processes. The vitamin D3 action is mediated by the vitamin D3 receptor (VDR). VDR is widely distributed in the rodent reproductive tract, however the occurrence of VDR and the role of the vitamin D3 in the avian reproductive tract remain unknown. The aim of the present study was to investigate the expression and cellular distribution of VDR in the epididymal region of roosters. VDR expression was investigated by Western blotting analysis and the tissue distribution of the receptor was determined by immunohistochemistry. The Western blotting assay revealed a major VDR protein band of 61kDa in the epididymal region of rooster. Nuclear VDR expression was found in all segments of the epididymal region, namely rete testis, efferent ductules, connecting ducts and epididymal ducts. Nonciliated cells of the distal efferent ductules showed the highest levels of VDR expression, followed by the proximal efferent ductules and rete testis. The connecting and epididymal ducts showed less intense VDR immunostaining. The differential VDR expression in the epididymal region segments reveals that several extratesticular ducts may be target for vitamin D3 action and suggests that vitamin D3 may have a regional-specific function, such as calcium transport, that is modulated through VDR activity.

The effects of postmenopausal Vitamin D treatment on vaginal atrophy

OBJECTIVES

To evaluate the efficacy of Vitamin D for relieving vaginal atrophy.

METHODS

In our cross-sectional study, 60 eligible women were consecutively identified among patients who were followed in physical medicine and rehabilitation's outpatient clinic, during the period March June 2001. The sample consisted of 30 postmenopausal women on 1,25-dihydroxy Vitamin D (calcitriol) treatment, 30 postmenopausal women taking neither hormone replacement nor osteoporosis treatment. Vaginal atrophy was determined by symptoms, physical examination and maturation index (MI).

RESULTS

The mean physical findings score in Vitamin D treatment (VDT) group was significantly lower than the mean physical findings score in the group without treatment. Symptom scores were lower in both groups and there was not significantly difference between two groups. As maturation indices: in VDT group, superficial cells proportion was significantly higher and basal, parabasal cells proportion was lower than in the group without treatment.

CONCLUSION

The results of current study seem to indicate that vaginal tissue may be a new target organ for therapeutically applied Vitamin D analogues.

Immunohistochemical detection of 1,25-dihydroxyvitamin D receptor in rat vaginal epithelium

OBJECTIVE

To determine the distribution of 1,25-dihydroxyvitamin D receptor (VDR) in rat vaginal epithelium during the estrus cycle and in ovariectomized rats.

DESIGN

Animal study performed in two groups of rats. The expression of VDR was examined in the first group during the estrous cycle and in the second group after ovariectomy.

SETTING

University animal laboratory.

ANIMAL(S)

Balb/c female rats.

INTERVENTION(S)

Vaginas were removed and processed for immunohistochemical analysis.

MAIN OUTCOME MEASURE(S)

We recorded the localization, distribution, and expression of VDR in vaginal epithelium during the rat estrus cycle and in ovariectomized rats.

RESULT(S)

In cyclic rats, VDR was detected in basal and suprabasal cells during all of the cycle periods. In apical cells, VDR was positive in diestrus and estrus but negative in proestrous. In ovariectomized rats, VDR was not detected in any layers of vaginal epithelium.

CONCLUSION(S)

In vaginal epithelium, the presence of VDR was shown by using immunohistochemical techniques. During the estrous cycle, VDR has an important role in the proliferation and differentiation of vaginal squamous epithelium that is similar to the effects of estrogen.

p27(Kip1) stabilization and G(1) arrest by 1,25-dihydroxyvitamin D(3) in ovarian cancer cells mediated through down-regulation of cyclin E/cyclin-dependent kinase 2 and Skp1-Cullin-F-box protein/Skp2 ubiquitin ligase

p27(Kip1) (p27) is a tumor suppressor whose stability is controlled by proteasome-mediated degradation, a process directed in part by cyclin-dependent kinase 2 (CDK2)-mediated phosphorylation of p27 at Thr(187) and its subsequent interaction with the Skp1-Cullin-F-box protein/Skp2 (Skp2) ubiquitin ligase. The present study shows that 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) arrests ovarian cancer cells in G(1) by stabilizing the p27 protein. 1,25(OH)(2)D(3) initiates a chain of events by decreasing the amounts of cyclin E and cyclin E-associated CDK2 activity. As a result, p27 phosphorylation at Thr(187) and consequently the interaction with Skp2 are decreased. 1,25(OH)(2)D(3) also increases p27 stability by decreasing the abundance of Skp2. It is the combined effect of 1,25(OH)(2)D(3) on both the CDK2-dependent phosphorylation of p27, and thus its affinity for Skp2, and Skp2 expression that dramatically increases the stability of the p27 protein. Similar to its effects in ovarian cancer cells, 1,25(OH)(2)D(3) induces p27 accumulation in wild type mouse embryo fibroblasts and arrests wild type but not p27-null mouse embryo fibroblasts in G(1). Stable expression of Skp2 in OVCAR3 cells diminishes the G(1) arrest and decreases the growth response to 1,25(OH)(2)D(3). Taken together, the results of this study identify p27 as the key mediator of 1,25(OH)(2)D(3)-induced growth suppression in G(1) and show that the hormone achieves this by decreasing the activity of CDK2 and reducing the abundance of Skp2, which act together to degrade p27.

G2/M arrest by 1,25-dihydroxyvitamin D3 in ovarian cancer cells mediated through the induction of GADD45 via an exonic enhancer

1,25-Dihydroxyvitamin D3 suppresses the growth of multiple human cancer cell lines by inhibiting cell cycle progression and inducing cell death. The present study showed that 1,25-dihydroxyvitamin D3 causes cell cycle arrest at the G2/M transition through p53-independent induction of GADD45 in ovarian cancer cells. Detailed analyses have established GADD45 as a primary target gene for 1,25-dihydroxyvitamin D3. A DR3-type vitamin D response element was identified in the fourth exon of GADD45 that forms a complex with the vitamin D receptor.retinoid X receptor heterodimer in electrophoresis mobility shift assays and mediates the dose-dependent induction of luciferase activity by 1,25-dihydroxyvitamin D3 in reporter assays. Chromatin immunoprecipitation assays have shown that the vitamin D receptor is recruited in a ligand-dependent manner to the exonic enhancer but not to the GADD45 promoter regions. In ovarian cancer cells expressing GADD45 antisense cDNA or GADD45-null mouse embryo fibroblasts, 1,25-dihydroxyvitamin D3 failed to induce G2/M arrest. Taken together, these results identify GADD45 as an important mediator for the tumor-suppressing activity of 1,25-dihydroxyvitamin D3 in human ovarian cancer cells.

Hormonal replacement therapy in an animal model with chronic renal failure and ovariectomy: biochemical and densitometric study

BACKGROUND

In spite of estrogen replacement therapy being extensively used in clinical and experimental studies without renal impairment, there are no long-term studies concerning estrogen replacement in chronic renal failure.

METHODS

In this experimental study, six groups of nephrectomized and ovariectomized animals were treated with different doses of 17beta-estradiol, alone or in combination with calcitriol, to evaluate the effect of these treatments on bone metabolism.

RESULTS

Biochemical results showed that estrogen alone did not have any effect neither on calcium nor on PTH serum levels. By contrast, in the groups treated with calcitriol, the levels of serum calcium were significantly higher, and the levels of iPTH were significantly lower than those observed in the control group. Animals receiving the combined treatment with estrogen and calcitriol showed the greater gain in uterus weight and a better bone mineral density at the lumbar site and the proximal and distal tibia sites.

CONCLUSION

The combination of estrogen and calcitriol is the most effective therapy to prevent bone mass loss in animals with chronic renal failure and estrogen deprivation.

In situ detection of 1,25-dihydroxyvitamin D3 receptor in human skeletal muscle tissue

Growing evidence suggests that intracellular vitamin D receptors are present in skeletal muscle tissue mediating vitamin D hormone response. The aim of the work reported here was to investigate the in situ expression of 1,25-dihydroxyvitamin D3 receptor in human skeletal muscle tissue. Intraoperative periarticular muscle biopsies were taken from 20 female orthopaedic patients (17 middle-aged and elderly patients receiving total hip arthroplasty due to osteoarthritis of the hip or an osteoporotic hip fracture and 3 young patients who received back surgery). The immunohistological distribution of the vitamin D3 receptor was investigated using a monoclonal rat antibody to the receptor (Clone Nr. 9A7). The receptor-positive nuclei were quantified by counting 500 nuclei per biopsy. Strong intranuclear immunostaining of the vitamin D receptor was detected in human muscle cells. Biopsies of hip patients had significantly fewer receptor-positive nuclei compared to those of back surgery patients (Mann-Whitney U-test: p = 0.0025). VDR expression (number of antigen-positive nuclei) was significantly correlated with age (coefficient of correlation = 0.46; p = 0.005), but not with 25-hydroxyvitamin D or 1,25-dihydroxyvitamin D levels. The data clearly demonstrate presence of nuclear 1,25-dihydroxyvitamin D3 receptor in human skeletal muscle. To our knowledge this is the first in situ detection of the receptor in human skeletal muscle. The difference in the expression of the receptor between hip and spinal muscle biopsies might be explained by age or location. Further research is needed in order to evaluate whether vitamin D3 receptor expression in human skeletal muscle is age-dependent and varies between different muscles.

Androgen receptor and vitamin D receptor in human ovarian cancer: growth stimulation and inhibition by ligands

The data suggest that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and androgens are essential for regulation of growth and differentiation in, e.g., human reproductive tissues. We investigated the possible cross-talk between 1,25(OH)2D3 and androgens in the human ovarian cancer cell line OVCAR-3. Our data demonstrate that 1,25(OH)2D3 and androgen (dihydrotestosterone, DHT) regulate the growth of OVCAR-3 cells. Nine days' treatment of OVCAR-3 cells with 100 nM DHT resulted in 48% stimulation of growth, whereas growth inhibition (73%) was observed after treatment with 100 nM 1,25(OH)2D3. The combination of 1,25(OH)2D3 and DHT showed that 1,25(OH)2D3 clearly reduces the growth-stimulatory effect of DHT on OVCAR-3 cells. Moreover, Western blot analysis revealed that these cells contain receptors for 1,25(OH)2D3 (VDR) and androgen (AR). Expression of VDR and AR was up-regulated by their cognate ligands. Up-regulation of AR by 1,25(OH)2D3 and of VDR by DHT provides evidence of cross-talk between 2 signaling pathways in OVCAR-3 cells. We also studied the immuno-histochemical distribution of VDRs and ARs in rat ovaries and human ovarian cancer cases. In rat ovaries, VDRs were observed mainly in granulosa and theca cells and ARs in granulosa cells and surface epithelium. In the human ovarian cancer cases studied, 43% were VDR-positive and 64% AR-positive. Combining the results suggests that the growth of ovarian tissue might be regulated by 1,25(OH)2D3 and androgen.

Hormone-dependent translocation of vitamin D receptors is linked to transactivation

Vitamin D receptor (VDR) acts as a transcription factor mediating genomic actions of calcitriol. Our earlier studies suggested that calcitriol induces translocation of cytoplasmic VDR, but the physiologic relevance of this finding remained uncertain. Previous studies demonstrated that the activation function 2 domain (AF-2) plays an essential role in VDR transactivation. To elucidate hormone-dependent VDR translocation and its role, we constructed green fluorescent protein (GFP) chimeras with full-length VDR (VDR-GFP), AF-2-truncated VDR (AF-2del-VDR-GFP), and ligand-binding domain (LBD)-truncated VDR (LBDdel-VDR-GFP). COS-7 cells were transiently transfected with these constructs. Western blot analysis, fluorescent microscopy, and transactivation assays showed that the generated chimeras are expressed and fluoresce and that VDR-GFP is transcriptionally active. After hormone treatment, cytoplasmic VDR-GFP translocated to the nucleus in a concentration-, time-, temperature-, and analog-specific manner. Hormone dose-response relationships for translocation and for transactivation were similar. Truncation of LBD and truncation of AF-2 each abolished hormone-dependent translocation and transactivation. Our data confirm a hormone-dependent VDR translocation, demonstrate that an intact AF-2 domain is required for this translocation, and indicate that translocation is part of the receptor activation process.

Distribution of 1,25-dihydroxyvitamin D3 receptor immunoreactivity in the rat brain and spinal cord

A complete mapping study on the 1,25-dihydroxyvitamin D3 receptor immunoreactivity within the rat central nervous system was performed with a monoclonal and a polyclonal antibody. Specific immunostaining was observed within both nuclear and cytoplasmic compartments of a variety of cells in the cerebellum, mesopontine area, diencephalon, cortex, spinal cord, and limbic system. Both monoclonal and polyclonal antibodies provided similar staining patterns. The monoclonal antibody stained distinct domains within the nuclei of all and the cytoplasm of specific neuronal cell types, like motor neurons, Purkinje cells, and pyramidal cells of the cortex more clearly than the polyclonal antibody. The expression of vitamin D3 receptor in the rat central nervous system was confirmed by in situ hybridisation. The widespread distribution of vitamin D3 receptor in distinct portions of the sensory, motor, and limbic brain systems suggests multiple functional properties of 1,25-dihydroxyvitamin D3 in the central nervous system.

1,25-Dihydroxyvitamin D3 receptors in the central nervous system of the rat embryo

We have mapped areas within the central nervous system (CNS) of the developing fetal rat which immunostain for the 1,25-dihydroxyvitamin D3 receptor (VDR). The VDR was detected from days 12 to 21 of gestation throughout the CNS; immunostaining was particularly intense in the neuroepithelium and within the differentiating fields of various areas of the brain. Cells within the spinal cord, dorsal root, and other ganglia exhibited positive staining for the VDR. The intensity of staining for the VDR diminished or disappeared in the neuroepithelium throughout the CNS during the later days of development, while in the differentiating fields single VDR immunoreactive cells were observed. The presence of the VDR in the CNS was confirmed by in situ hybridization and RNA-based polymerase chain reaction methods with di-deoxy sequencing of the resultant DNA product. These results support the hypothesis that 1, 25-dihydroxyvitamin D3, through interactions with the VDR, may play a role in the development of the CNS.

Localization of 1,25-dihydroxyvitamin D3 receptor (VDR) expression in human prostate

1,25-dihydroxyvitamin D3 (1,25(OH)2D3) has been found to have a variety of physiological functions, including effects on growth and differentiation in normal and malignant cells. The antiproliferative effects of 1,25(OH)2D3 are reported to be mediated through the genomic signaling pathway by binding to a specific high affinity receptor protein, the 1,25-dihydroxyvitamin D3 receptor (VDR). VDR has been localized in a variety of tissues, but little is known about VDR distribution in human prostate. In this study, we raised an antibody against a synthetic peptide corresponding to amino acids 10-24 of human vitamin D receptor. The sequence selected for immunization is identical in human, rat and mouse VDR. Based on this antibody, we developed an immunohistochemical method suitable for studying VDR expression in paraffin-embedded tissue. The immunohistochemical staining was verified using classical target organs for vitamin D (kidney, intestine, skin). With this method, we studied VDR localization on paraffin-embedded human prostatic tissue obtained from 8 patients undergoing radical prostatectomy for urinary bladder cancer and demonstrate VDR expression in the secretory epithelial and few stromal cells of human prostate. The nuclear staining in the secretory epithelial cells was concentrated near the nuclear membrane and in discrete foci in the nucleoplasm. This suggests that effects of 1,25-dihydroxyvitamin D3 are mediated through VDR in these cells. Moreover our result indicates that there are strong variations in VDR expression between prostatic samples.

Selectivity of a C-terminal peptide antiserum for different DNA-binding states of the vitamin D receptor

Antisera against peptides from the extreme N- and C-terminal regions of the VDR were evaluated. The N-terminal antiserum Ab192 functioned as a general-purpose antibody, being able to supershift the rhVDR in heterodimeric or homodimeric binding complexes in the EMSA, and detect both recombinant and native forms of the receptor on Western blots. The C-terminal antiserum, Ab195, also identified the receptor on Western blots, but in contrast, it displayed differential sensitivity to the conditions employed in the EMSA. In the presence of 1,25(OH)2D3, rhVDR, rhRXR alpha, and nonspecific DNA, Ab195 produced a weak supershift of the heterodimer complex in the EMSA. Significantly, omission of hormone from the binding buffer resulted in a complete shift of the bound complex with the antiserum. A complete supershift was also observed if only the nonspecific DNA was removed. Together these results indicate antiserum sensitivity to the ligand status in the rhVDR C-terminus as part of a DNA-bound heterodimer complex. Inclusion of 9-cis RA resulted in a modest increase in the amount of shifted product relative to 1,25(OH)2D3 alone. Finally, Ab195 completely supershifted the rhVDR homodimer binding complex under all tested conditions, including those analogous to where it was largely ineffective in shifting the heterodimer. Thus, Ab195 is sensitive to the ligand binding status of the VDR, discriminates heterodimer and homodimer binding interactions, and should provide an additional tool for exploring conformational changes induced in the receptor.