Detection of growth factors in the testis of roe deer (Capreolus capreolus)

Uncovering the Physiological Mechanisms Underlying the Roe Deer (Capreolus capreolus) Testicular Cycle: Analyses of Gelatinases and VEGF Patterns and Correlation with Testes Weight and Testosterone

Simple Summary

The roe deer (Capreolus capreolus) is a wild, small ruminant common in Europe and Asia with a peculiar reproductive cycle. The adult male shows a complete suspension of spermatozoa production during the winter that start again in spring with the peak of sexual activity in summer (July–August). The physiological mechanism underlying such a cycle is yet to be clarified. The work aimed at the analysis of some molecules, like gelatinases (MMP) and vascular growth factor, physiologically involved in tissue remodeling, in roe deer samples collected before (June–July) and after (August–September) the rutting period. Samples were provided by hunters of the Bologna Apennines area (Italy) according to the regional hunting plan. The result showed a post-rut reduction of testicular weight and testosterone, indicative of testes involution, correlated with an increase in pro-MMP2, the latent gelatinase capable of sustaining spermatogenesis once activated. It can be assumed that gelatinases are involved in the testicular cycle and start accumulating after the rutting period to be then activated in preparation of the next reproductive season inducing spermatozoa development and migration. Future studies on this pathway during all seasonal testicular cycles will provide more information about the interesting reproductive physiology of roe deer.

Abstract

The roe deer (Capreolus capreolus) represents a spontaneous model of testicular inactivation: During winter, bucks show a suspension of spermatogenesis that starts again in spring and peaks during the breeding season (July–August). The underlying mechanisms to the regulation of the cyclic testicular changes are still not fully clear but seem to be imputable to the spermatogenic cell line since other testicular cell populations remain stable without apoptotic phenomena. The aim of the study was to investigate apoptosis, gelatinases (MMP2 and 9), their inhibiting factors (TIMP 1-2), and two isoforms of vascular endothelial growth factor (VEGF121 and 165) with its receptors (VEGFR1-2) in testes collected during pre- and post-rut periods, and to correlate them with testicular weight (TW) and testosterone (TEST). Testes from 18 adult sexually mature bucks were collected in Bologna Apennines (Italy). Samples were weighed and parenchyma collected. Radioimmunoassay, real-time PCR, and zymography were performed. The results showed a post-rut decrease in TW and TEST and an increase in proMMP2, also highlighting a correlation between the gelatinases and the testicular functionality. The VEGF pattern did not show modifications nor correlation with TW and TEST. Overall, gelatinases and their inhibitors, described herein for the first time in roe deer testes, seem to play an important role in the testicular cycle.

Seasonal expressions of growth hormone receptor, insulin-like growth factor 1 and insulin-like growth factor 1 receptor in the scented glands of the muskrats (Ondatra zibethicus)

The growth hormone (GH)/insulin-like growth factor-1 (IGF-1) system plays an important role in regulating the cellular growth and organ development. The present study investigated the seasonal expressions of growth hormone receptor (GHR), IGF-1 and insulin-like growth factor 1 receptor (IGF-1R) in the scented glands of the muskrats. Morphological changes in the scented glands of the muskrats were observed significantly between the breeding and non-breeding seasons. Immunohistochemically, the expressions of GH, GHR, IGF-1 and IGF-1R were found in glandular cells and epithelial cells of the scented glands in both seasons. The protein and mRNA expression levels of GHR, IGF-1 and IGF-1R in the scented glands during the breeding season were noticeably higher than those of the non-breeding season. In parallel, the levels of GH and IGF-1 in the sera and scented glands were remarkably higher during the breeding season. In addition, small RNA sequencing showed that the predicted targets of the significantly changed hsa-miR-5100 and mmu-miR-6937-5p might regulate the expressions of Ghr, Igf-1 or Igf-1r. These results suggested that the morphological changes in the scented glands of the muskrats during the different seasons might be related to the expression levels of GHR, IGF-1 and IGF-1R. Meanwhile, GHR/IGF-1 system might regulate the scented glandular functions via endocrine or autocrine/paracrine manners.

Morphological changes of telocytes in camel efferent ductules in response to seasonal variations during the reproductive cycle

Telocytes (TCs) are a distinct stromal cell type described in many organs. The present study investigated the existence of TCs within the efferent ductules in camel and the changes that occur in their morphology and activity during active and inactive reproductive seasons. TCs in the camel had a cell body and multiple telopodes (TPs), and most TCs had indented nuclei that exhibited prominent intranucleolar chromatin. TCs exhibited seasonal differences which were evaluated by histochemistry, immunohistochemistry (IHC), Transimition electron microscopy (TEM) and scanning electron microscopy (SEM). The presence of TCs in camel efferent ductules has been confirmed by CD34 positive immunostaing. In addition to the expression of the vascular endothelial growth factor (VEGF) which was stronger in the summer season. TCs exhibited stronger immunoreactivity for progesterone and oestrogen alpha receptors (ESR1) in the spring than in the summer. In addition, TCs showed strong positive immunostaining for both vimentin and androgen receptor (AR). Several ultrastructural changes were observed in TCs during the two seasons. TPs in the summer season had delicate ramifications whereas, in the spring, TPs displayed fine arborization and became more corrugated. TCs acquired signs of exaggerated secretory activities in the spring; TPs became expanded and packed with secretory vesicles. Thus, we conclude that, hormonal alterations during the reproductive cycle impact the morphology and secretory behavior of TCs.

Seasonal expression of insulin-like growth factor 1 (IGF-1), its receptor IGF-1R and klotho in testis and epididymis of the European bison (Bison bonasus, Linnaeus 1758)

The European bisons are the largest mammals of Europe that are still in danger of extinction. The species conservation is associated with their continuous reproduction, and bisons are characterized by the well-pronounced seasonality of reproductive processes. However, the exact mechanisms regulating their reproduction still remain unknown. Our previous studies indicated the involvement of some of the growth factors in the regulation of male seasonal reproductive activities in bison, showing expression patterns that seemed to be regulated by the length of the daylight. In the present study, using RT-PCR and Western blot approaches, we verified the expression and possible relationship between the insulin-like growth factor (IGF-1), its receptor (IGF-1R), and klotho in testis and epididymis of the European bison in pre- and post-reproductive periods, i.e., in June and in December. The observed expression of IGF-1 and IGF-1R mRNA in testis and epididymis was higher in June than in December. At the same time, klotho mRNA expression in both testis and epididymis did not differ between the analyzed seasons. However, along with the higher levels of IGF-1R protein observed in June, klotho protein levels for the membrane form and for the secrete form were higher in December than in June. Finally, the messenger and protein expression profiles presented herein indicate the importance of both the IGF-system and klotho in reproductive processes in the European bison, implying their involvement in the regulation of seasonal testicular activity in males of this threatened species.

Vascular endothelial growth factor (VEGF-A) and fibroblast growth factor (FGF-2) as potential regulators of seasonal reproductive processes in male European bison (Bison bonasus, Linnaeus 1758)

Growth factors: vascular endothelial growth factor A (VEGF-A) and fibroblast growth factor (FGF-2) were reported to affect normal physiological reproductive processes in human, domestic and free living animals. Moreover, some reports suggest that VEGF-A and FGF-2 may be directly involved in the control of the annual reproductive cycle of seasonally breeding animals but detailed knowledge is still missing. Our study aimed to demonstrate the expression of mRNA and protein for both factors in the tissues of testis and epididymis (caput, corpus, cauda) at different periods of the year (March, June, November, December) in European bison as a model of seasonally breeding animal. Results suggest, that VEGF-A expression was more pronounced in testis than in epididymis and the highest expression was noted in December and June. Surprisingly, the highest protein accumulation was observed in June at the same level in all tissues analyzed. On the other hand, the highest FGF-2 mRNA expression was noted in testis in June and in epididymis in March. However, no differences in protein expression of FGF-2 were found between analyzed groups. The results indicate that both factors are necessary for proper functioning of the reproductive system and their levels differ seasonally. Perhaps, it is linked to increased need of these factors in the testis as well as epididymis during preparation for the reproductive functions. Moreover, VEGF-A and FGF-2 not only may regulate reproductive functions by affecting vascularization and cell nutrition, but it also may be possible that they possess protective functions by stabilizing the reproductive cells. Therefore, obtained results provide new insight into mechanisms underlying seasonal breeding of the male European bison.

Vascular endothelial growth factor A is a putative paracrine regulator in seasonally controlled spermatogenesis: insights from a ruminant model, the roe deer

Vascular endothelial growth factor A (VEGFA) influences spermatogenesis, but its impact on seasonally regulated sperm production is still not fully understood. Thus, we investigated both expression levels and localisation of VEGFA and its receptors VEGFR1 and 2 in roe buck testis via real-time reverse transcription polymerase chain reaction and immunohistochemistry in relation to seasonal changes in the cellular composition of the testis. VEGFA was expressed by interstitial cells while its receptors were found on endothelial and perivascular cells. Inside the tubules, VEGFA was located in spermatogonia and spermatocytes, VEGFR1 was present on elongating spermatids and VEGFR2 on Sertoli cells. VEGFR1 mRNA was expressed tenfold lower than VEGFR2 and VEGF mRNAs. Relative VEGF and VEGFR2 expression (divided by the number of VEGFA and VEGFR2 expressing cells) showed an increase towards the rut (July/August) and a decrease thereafter. The results suggest involvement of VEGFA in the adjustment of vascular permeability as well as in spermiogenesis and the proliferation of spermatogonia.

Estrogens are involved in seasonal regulation of spermatogenesis and sperm maturation in roe deer (Capreolus capreolus)

Roe deer (a seasonal breeder, rut: July to August) is a well characterized model for studying the seasonal regulation of testicular activity. However, not much is known about the impact of estrogens on seasonally determined sperm production. We therefore explored the time and cell type specific expression of estrogen receptors and of enzymes involved in steroid biosynthesis in roe deer testicular parenchyma and in the epididymis. Every second month during the entire seasonal cycle five roe bucks were castrated (n=30). Estrogen receptor (ER) alpha, ERbeta and the enzymes P450Aromatase and P450C17 were localized immunohistochemically. The expression levels of ERalpha, ERbeta and P450Aromatase were evaluated by semi-quantitative Western blot. Contrary to the enzyme required for androgen production (P450C17), which is expectedly located only in the Leydig cells and shows an expression increase towards rutting season, a seasonal expression difference of the enzyme required for the conversion into oestradiol (P450Aromatase) is visible only in the epididymis. In the testis, ERalpha expression shows a striking dependency on tubular cell composition, and the single cell expression activity increases towards rut. This implicates that estrogens are directly involved in the regulation of spermatogenesis in the roe buck. In the epididymis, expression of ERalpha is seasonally determined particularly in the ductuli efferentes. ERbeta was detected throughout the year with no distinct dependency on season or the stages of germinative epithelium cycle. We conclude that estrogens in the roe buck influence the seasonally determined sperm production predominantly by the regulated expression of ERalpha.

Proprotein convertases: lessons from knockouts

The physiological role of the subtilisin/kexin-like proprotein convertases (PCs) in rodents has been examined through the use of knockout mice. This review will summarize the major in vivo defects that result from the disruption of the expression of their genes. This includes abnormal embryonic development, hormonal disorder, infertility, and/or modified lipid/sterol metabolism. Members of the PC family play a central role in the processing of various protein precursors ranging from hormones and growth factors to bacterial toxins and viral glycoproteins. Proteolysis occurring at basic residues is mediated by the basic amino acid-specific proprotein convertases, namely: PC1/3, PC2, furin, PACE4, PC4, PC5/6, and PC7. In contrast, proteolysis at nonbasic residues is performed by the subtilisin/kexin-like isozyme-1 (SKI-1/S1P) and the newly identified neural apoptosis-regulated convertase-1 (PCSK9/NARC-1). In addition to their requirement for many physiological processes, these enzymes are also involved in various pathologies such as cancer, obesity, diabetes, lipid disorders, infectious diseases, atherosclerosis and neurodegenerative diseases.

Testosterone regulates FGF-2 expression during testis maturation by an IRES-dependent translational mechanism

Spermatogenesis is a complex process involving cell proliferation, differentiation, and apoptosis. Fibroblast growth factor 2 (FGF-2) is involved in testicular function, but its role in spermatogenesis has not been fully documented. The control of FGF-2 expression particularly occurs at the translational level, by an internal ribosome entry site (IRES)-dependent mechanism driving the use of alternative initiation codons. To study IRES activity regulation in vivo, we have developed transgenic mice expressing a bicistronic construct coding for two luciferase genes. Here, we show that the FGF-2 IRES is age-dependently activated in mouse testis, whereas EMCV and c-myc IRESs are not. Real-time PCR confirms that this regulation is translational. By using immunohistological techniques, we demonstrate that FGF-2 IRES stimulation occurs in adult, but not in immature, type-A spermatogonias. This is correlated with activation of endogenous FGF-2 expression in spermatogonia; whereas FGF-2 mRNA transcription is known to decrease in adult testis. Interestingly, the FGF-2 IRES activation is triggered by testosterone and is partially inhibited by siRNA directed against the androgen receptor. Two-dimensional analysis of proteins bound to the FGF-2 mRNA 5'UTR after UV cross-linking reveals that testosterone treatment correlates with the binding of several proteins. These data suggest a paracrine loop where IRES-dependent FGF-2 expression, stimulated by Sertoli cells in response to testosterone produced by Leydig cells, would in turn activate Leydig function and testosterone production. In addition, nuclear FGF-2 isoforms could be involved in an intracrine function of FGF-2 in the start of spermatogenesis, mitosis, or meiosis initiation. This report demonstrates that mRNA translation regulation by an IRES-dependent mechanism participates in a physiological process.

The roe deer as a model for studying seasonal regulation of testis function

In mature male seasonal breeders, the circannual cycles of testicular growth and involution involve significant changes in structure and function of both the tubular and interstitial testicular compartment. Roe deer (Capreolus capreolus) are seasonal breeders with a short defined rutting season from mid-July to mid-August and represent a unique non-rodent model for studying testicular functions during the course of a complete reproductive cycle with naturally changing photoperiod. Germ cells and Sertoli cells of the seminiferous tubules and the interstitial Leydig cells all display significant morphological and physiological alterations during the seasonal changes. In contrast to the germ cell population, Sertoli and Leydig cells persist as a numerically constant cell population in the roe deer testis. This report emphasizes the intricate relationship between seasonal cellular differentiation, intratesticular growth factor networks and their impact on the functional dynamics during the seasonal changes in roe deer testis.

Analysis of fibroblast growth factor 2 (FGF2) gene transcription and protein distribution in the bovine testis

Several fibroblast growth factors (FGFs) are implicated in proliferation and differentiation of both somatic and germ cells during testicular development, as well as in spermatogenesis of adult testis. The expression of FGF2 was studied in the adult bovine testis using quantitative RT-PCR, RNA in situ hybridization, and immunohistochemistry. Quantitative RT-PCR revealed consistent levels of FGF2 mRNA in parenchymal samples of the bovine testis. In situ hybridization localized FGF2 transcripts only in a constant fraction of Leydig and Sertoli cells as well as in modified Sertoli cells of the terminal segments. Immunohistochemistry revealed (a) no FGF2 protein in Sertoli cells (b) moderate cytoplasmic staining in Leydig cells and spermatogonia and (c) strong nuclear and faint cytoplasmic staining in myofibroblasts, in epithelial cells of straight tubules and rete testis and in blood vessels. These observations indicate a pleiotropic effect of FGF2 on the control of spermatogenesis in a paracrine and/or autocrine manner.

Expression and localization of growth factors and their receptors in the mammalian testis. Part I: Fibroblast growth factors and insulin-like growth factors

It is now well established that normal development and function of testis are mediated by endocrine and paracrine pathways including hormones, growth factors and cytokines as well as by direct cell-to-cell contacts depending on tight, adhering and gap junctions. In the last two decades, several growth factors were identified in the testis of various mammalian species. Growth factors are shown to promote cell proliferation, regulate tissue differentiation, and modulate organogenesis. Interestingly, most of these peptides are expressed not only in the adult mammalian testis during spermatogenesis but also during testicular morphogenesis in prenatal and postnatal life. Our study was launched to provide an overview of the expression, localization, and putative physiological roles of growth factors and their receptors in the mammalian testis. The growth factors considered in this part of our review are fibroblast growth factors and insulin-like growth factors. These factors are found in testicular cells in prenatal, postnatal, and adult animals and are implicated in the regulation of important testicular activities including testicular cord morphogenesis, modulation of testicular hormone secretion and control of spermatogenesis.

Gene expression in the spermatogenically inactive "dark" and maturing "light" testicular tissues of the prepubertal colt

In the testis of the 1.5-year-old horse, spermatogenesis initiates locally in grossly light, central areas that contrast with grossly dark, peripheral areas that are as yet inactive in spermatogenesis. Gene expression was compared between "light" and "dark" tissues of 1.5-year-old horse testes to identify mechanisms important to the initiation of spermatogenesis. Microarrays containing human cDNAs were used to assess expression levels of 9132 genes simultaneously in matched pairs of dark and light testis tissues from 3 prepubertal colts. In all 3 analyses, dysferlin (DYS), down-regulated in ovarian cancer 1 (DOC1), and Golgi apparatus protein 1 (GLG1) genes were preferentially expressed in dark tissues, while outer dense fiber of sperm tails (ODF2) and phosphodiesterase 3B (PDE3B) genes were more highly expressed in light testis tissue (>1.7 balanced difference value, Incyte GEM tools software). Expression levels of 88 additional genes appeared to be different between dark and light tissues in 2 of the 3 microarray analyses. The preferential expression of DYS, DOC1, ODF2, and PDE3B genes in dark or light testis tissues was confirmed on Northern blots and localized to cell types by in situ hybridization. Future studies to determine the role of genes regulated during the initiation of spermatogenesis may aid in elucidating molecular mechanisms during this critical time as well as in identifying new therapies for enhancing male fertility.

Seasonal changes of spermatogonial proliferation in roe deer, demonstrated by flow cytometric analysis of c-kit receptor, in relation to follicle-stimulating hormone, luteinizing hormone, and testosterone

The roe deer (Capreolus capreolus) is a seasonal breeder. The cyclic changes between totally arrested and highly activated spermatogenesis offer an ideal model to study basic mechanisms of spermatogenesis. In this study, we demonstrated, to our knowledge for the first time, c-kit receptor-positive cells in the testis of roe deer. They were immunohistologically identified mainly as spermatogonia. Analysis of the amount of those cells by flow cytometry shows a distinct seasonal pattern, with pronounced differences between cells in the diploid state and in the G2/M phase of mitosis. The specific seasonal pattern of spermatogonial proliferation results in the increased relative abundance of spermatogonia as well as in their increased total number per testis in November and December. This suggests that cell divisions continue on a level sufficient to accumulate spermatogonia during winter. The serum concentrations of LH and FSH showed a peak in spring; testosterone showed a maximum concentration during the rut (July/August). The peak of both gonadotropins seems to precede the period of stimulated spermatogonial proliferation in spring. The testosterone peak coincides with maximal meiotic intensity in August. The results suggest the importance of testosterone for sperm production, and they provide a basis for detailed investigations of regulatory factors of the proliferation of spermatogonia.