Age-related changes in human Leydig cell status.

STUDY QUESTION: What are the consequences of ageing on human Leydig cell number and hormonal function? SUMMARY ANSWER: Leydig cell number significantly decreases in parallel with INSL3 expression and Sertoli cell number in aged men, yet the in vitro Leydig cell androgenic potential does not appear to be compromised by advancing age. WHAT IS KNOWN ALREADY: There is extensive evidence that ageing is accompanied by decline in serum testosterone levels, a general involution of testis morphology and reduced spermatogenic function. A few studies have previously addressed single features of the human aged testis phenotype one at a time, but mostly in tissue from patients with prostate cancer. STUDY DESIGN, SIZE, DURATION: This comprehensive study examined testis morphology, Leydig cell and Sertoli cell number, steroidogenic enzyme expression, INSL3 expression and androgen secretion by testicular fragments in vitro. The majority of these endpoints were concomitantly evaluated in the same individuals that all displayed complete spermatogenesis. PARTICIPANTS/MATERIALS, SETTING, METHODS: Testis biopsies were obtained from 15 heart beating organ donors (age range: 19-85 years) and 24 patients (age range: 19-45 years) with complete spermatogenesis. Leydig cells and Sertoli cells were counted following identification by immunohistochemical staining of specific cell markers. Gene expression analysis of INSL3 and steroidogenic enzymes was carried out by qRT-PCR. Secretion of 17-OH-progesterone, dehydroepiandrosterone, androstenedione and testosterone by in vitro cultured testis fragments was measured by LC-MS/MS. All endpoints were analysed in relation to age. MAIN RESULTS AND THE ROLE OF CHANCE: Increasing age was negatively associated with Leydig cell number (R = -0.49; P < 0.01) and concomitantly with the Sertoli cell population size (R= -0.55; P < 0.001). A positive correlation (R = 0.57; P < 0.001) between Sertoli cell and Leydig cell numbers was detected at all ages, indicating that somatic cell attrition is a relevant cellular manifestation of human testis status during ageing. INSL3 mRNA expression (R= -0.52; P < 0.05) changed in parallel with Leydig cell number and age. Importantly, steroidogenic capacity of Leydig cells in cultured testis tissue fragments from young and old donors did not differ. Consistently, age did not influence the mRNA expression of steroidogenic enzymes. The described changes in Leydig cell phenotype with ageing are strengthened by the fact that the different age-related effects were mostly evaluated in tissue from the same men. LIMITATIONS, REASONS FOR CAUTION: In vitro androgen production analysis could not be correlated with in vivo hormone values of the organ donors. In addition, the number of samples was relatively small and there was scarce information about the concomitant presence of potential confounding variables. WIDER IMPLICATIONS OF THE FINDINGS: This study provides a novel insight into the effects of ageing on human Leydig cell status. The correlation between Leydig cell number and Sertoli cell number at any age implies a connection between these two cell types, which may be of particular relevance in understanding male reproductive disorders in the elderly. However aged Leydig cells do not lose their in vitro ability to produce androgens. Our data have implications in the understanding of the physiological role and regulation of intratesticular sex steroid levels during the complex process of ageing in humans. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by grants from Prin 2010 and 2017. The authors have no conflicts of interest. TRIAL REGISTRATION NUMBER: N/A.

The novel non-steroidal MR antagonist finerenone improves metabolic parameters in high-fat diet-fed mice and activates brown adipose tissue via AMPK-ATGL pathway.

Mineralocorticoid receptor antagonists (MRAs) are recommended for the treatment of heart failure and hypertension, mainly due to their natriuretic and anti-fibrotic mode of action. Rodent studies have shown that MRAs can prevent adverse metabolic consequences of obesity but an elucidation of underlying molecular mechanisms is missing. Here, we investigated metabolic effects of the novel non-steroidal MRA finerenone (FIN) in a mouse model of high-fat diet (HFD)-induced obesity and the signaling pathways activated by MR antagonism at level of interscapular brown adipose tissue (iBAT). C57BL/6J male mice were fed a normal diet or a HFD (with60% kcal from fat) containing or not FIN for 3 months. Metabolic parameters, adipose tissue morphology, gene and protein expression analysis were assessed. We also used brown adipocyte cultures (T37i cells) to investigate the effects of FIN-mediated MR antagonism upon lipid and mitochondrial metabolism. HFD + FIN-treated mice showed improved glucose tolerance together with increased multilocularity and higher expression of thermogenic markers at the level of iBAT, without differences in white adipose depots, suggesting an iBAT-specific effect of FIN. Mechanistically, FIN increased activation of AMP-activated protein kinase which, in turn, stimulated adipose triglyceride lipase activation, with subsequent increased expression of uncoupling protein-1 in brown adipocytes.

Regulation of Gdnf expression by retinoic acid in Sertoli cells.

Glial cell line-derived neurotrophic factor (GDNF) and retinoic acid (RA) are two molecules crucial for the regulation of the spermatogonial compartment of the testis. During the cycle of the seminiferous epithelium, their relative concentration oscillates with lower GDNF levels in stages where RA levels are high. It has been recently shown that RA negatively regulates Gdnf expression but the mechanisms behind are so far unknown. Here, we show that RA directly downregulates Gdnf mRNA levels in primary murine Sertoli cells through binding of RARα to a novel DR5-RARE on Gdnf promoter. Pharmacological inhibition and chromatin immunoprecipitation-quantitative polymerase chain reaction analysis suggested that the underlying mechanism involved histone deacetylase activity and epigenetic repression of Gdnf promoter upon RA treatment.

Glucagon-like peptide-1 receptor is expressed in human and rodent testis.

BACKGROUND: The incretin hormone glucagon-like peptide-l (GLP-1) is an important regulator of post-prandial insulin secretion, acting through a G protein-coupled cell surface receptor (GLP-1R). In addition to its expression in pancreatic ß-cells, several studies suggested that GLP-1R is located in extra-pancreatic tissues. OBJECTIVES: In this study, we examined for the first time the testicular distribution of the GLP-1R, both in normal human and neoplastic testicular tissues as well as in rodent testis and rodent testicular cell lines. METHODS AND METHODS: The GLP-1R distribution in testicular section has been evaluated by immunohistochemistry, the specificity of IHC was validated by demonstrating a positive staining for GLP-1RmRNA by RISH technology. While GLP-1R expression in terms of protein was detected by western blot analysis, Moreover, mRNA levels were determined in human testis, in rodent Leydig, and Sertoli cell lines. RESULTS: Using immunohistochemistrya specific staining for GLP-1R was detected in Leydig cells. The specificity of IHC was validated by demonstrating a positive staining for GLP-1RmRNA only in these cell types. Species differences in the GLP-1R expression between humans and rodents were observed. Interestingly, a decreased expression of the receptor in rodent tumor Leydig cell line and an absence in human Leydig tumor samples was detected. DISCUSSION: It may be hypothesized that GLP-1R acts like an oncosuppressor in Leydig tumors. A role in regulation of hormone secretion by GLP-1 has been shown in other endocrine cells, therefore we hypothesized that GLP-1R is able to modulate somehow the Leydig cell function. CONCLUSION: In our findings, a careful evaluation of human testicular tissues and rodent testis revealed Leydig cells as a potential target for GLP-1. Collectively, an effect of GLP-1R in Leydig cell function may be presumed although future studies are needed to ascertain the GLP-1R's role both in normal and tumor Leydig cells.

Involvement of sperm acetylated histones and the nuclear isoform of Glutathione peroxidase 4 in fertilization.

We previously demonstrated that the nuclear form of Glutathione peroxidase 4 (nGPx4) has a peculiar distribution in sperm head, being localized to nuclear matrix and acrosome and that sperm lacking nGPx4 are more prone to decondensation in vitro. In this study we have hypothesized that sperm retained acetylated histones and nGPx4 are implicated in paternal chromatin decondensation and male pronucleus formation at fertilization. Indeed, significant higher amounts of acetylated histone H4 and acetylated histone H3 were observed by both immunofluorescence and western blotting in nGPx4-KO sperm vs WT ones. In vitro fertilization of zona pellucida-deprived oocytes by WT sperm in the presence of trichostatin (TSA) also demonstrated that paternal histone acetylation was inversely related to the timing of sperm nucleus decondensation at fertilization. In contrast, TSA had no effect on nGPx4-KO sperm, indicating they had a maximal level of histone acetylation. Moreover the paternally imprinted gene Igf2/H19 was hypomethylated in KO sperm compared to WT ones. The lack of nGPx4 negatively affected male fertility, causing a marked decrease in total pups and pregnancies with delivery, a significant reduction in pronuclei (PN) embryos in in vitro fertilization assays and an approximately 2 h delay in egg fertilization in vivo. Because the zona pellucida binding and fusion to oolemma of nGPx4-KO and WT sperm were similar, the subfertility of nGPx4 sperm reflected a decreased sperm progression through egg cumulus/zona pellucida, pinpointing a defective acrosome in line with acrosomal nGPx4 localization. We conclude that paternal acetylated histones and acrosomal nGPx4 are directly involved in fertilization.

Spermatogonial kinetics in humans.

The human spermatogonial compartment is essential for daily production of millions of sperm. Despite this crucial role, the molecular signature, kinetic behavior and regulation of human spermatogonia are poorly understood. Using human testis biopsies with normal spermatogenesis and by studying marker protein expression, we have identified for the first time different subpopulations of spermatogonia. MAGE-A4 marks all spermatogonia, KIT marks all B spermatogonia and UCLH1 all Apale-dark (Ap-d) spermatogonia. We suggest that at the start of the spermatogenic lineage there are Ap-d spermatogonia that are GFRA1High, likely including the spermatogonial stem cells. Next, UTF1 becomes expressed, cells become quiescent and GFRA1 expression decreases. Finally, GFRA1 expression is lost and subsequently cells differentiate into B spermatogonia, losing UTF1 and acquiring KIT expression. Strikingly, most human Ap-d spermatogonia are out of the cell cycle and even differentiating type B spermatogonial proliferation is restricted. A novel scheme for human spermatogonial development is proposed that will facilitate further research in this field, the understanding of cases of infertility and the development of methods to increase sperm output.

Spermatogonial cells: mouse, monkey and man comparison.

In all mammals, spermatogonia are defined as constituting the mitotic compartment of spermatogenesis including stem, undifferentiated and differentiating cell types, possessing distinct morphological and molecular characteristics. Even though the real nature of the spermatogonial stem cell and its regulation is still debated the general consensus holds that in steady-state spermatogenesis the stem cell compartment needs to balance differentiation versus self-renewal. This review highlights current understanding of spermatogonial biology, the kinetics of amplification and the signals directing spermatogonial differentiation in mammals. The focus will be on relevant similarities and differences between rodents and non human and human primates.

Mutations Impairing GSK3-Mediated MAF Phosphorylation Cause Cataract, Deafness, Intellectual Disability, Seizures, and a Down Syndrome-like Facies.

Transcription factors operate in developmental processes to mediate inductive events and cell competence, and perturbation of their function or regulation can dramatically affect morphogenesis, organogenesis, and growth. We report that a narrow spectrum of amino-acid substitutions within the transactivation domain of the v-maf avian musculoaponeurotic fibrosarcoma oncogene homolog (MAF), a leucine zipper-containing transcription factor of the AP1 superfamily, profoundly affect development. Seven different de novo missense mutations involving conserved residues of the four GSK3 phosphorylation motifs were identified in eight unrelated individuals. The distinctive clinical phenotype, for which we propose the eponym Aymé-Gripp syndrome, is not limited to lens and eye defects as previously reported for MAF/Maf loss of function but includes sensorineural deafness, intellectual disability, seizures, brachycephaly, distinctive flat facial appearance, skeletal anomalies, mammary gland hypoplasia, and reduced growth. Disease-causing mutations were demonstrated to impair proper MAF phosphorylation, ubiquitination and proteasomal degradation, perturbed gene expression in primary skin fibroblasts, and induced neurodevelopmental defects in an in vivo model. Our findings nosologically and clinically delineate a previously poorly understood recognizable multisystem disorder, provide evidence for MAF governing a wider range of developmental programs than previously appreciated, and describe a novel instance of protein dosage effect severely perturbing development.

The nuclear form of glutathione peroxidase 4 colocalizes and directly interacts with protamines in the nuclear matrix during mouse sperm chromatin assembly.

The testis-specific nuclear form of Phospholipid Hydroperoxide Glutathione Peroxidase (nGPx4) is associated with the nuclear matrix during spermiogenesis and is implicated in sperm chromatin condensation. In this study, we have addressed the question whether nGPx4 directly interacts with protamines by transiently sharing a nuclear matrix localization. We first expressed tagged protamine 1-myc and protamine 2-V5 in HeLa and COS-1 cells and showed by both confocal microscopy and immunoblotting analyses that protamines were produced in vitro and colocalized correctly to the nucleus. Co-transfection experiments demonstrated that protamine 1 was physically associated with flag-nGPx4 specifically at the level of nuclear matrix. The peculiar presence of protamines together with nGPx4 in this subnuclear compartment was also confirmed in mouse elongated spermatids by immunofluorescence, suggesting that nGPx4 is a physiological component of a novel protein complex relevant to chromatin assembly in condensing haploid cells. Also, in epididymal sperm, nGPx4 and protamine 1 co-immunoprecipitated, indicating that nGPx4, although localized to a subnuclear compartment different from that of protamines, represents a constant link between nuclear matrix and chromatin in mammalian male gamete.

Novel stage classification of human spermatogenesis based on acrosome development.

To date, in the human seminiferous epithelium, only six associations of cell types have been distinguished, subdividing the epithelial cycle into six stages of very different duration. This hampers comparisons between studies on human and laboratory animals in which the cycle is usually subdivided into 12 stages. We now propose a new stage classification on basis of acrosomal development made visible by immunohistochemistry (IHC) for (pro)acrosin. IHC for acrosin gives results that are comparable to periodic acid Schiff staining. In the human too, we now distinguish 12 stages that differ from each other in duration by a factor of two at most. B spermatogonia are first apparent in stage I, preleptotene spermatocytes are formed in stage V, leptonema starts in stage VII, and spermiation takes place at the end of stage VI. A similar timing was previously observed in several monkeys. Stage identification by way of IHC for acrosin appeared possible for tissue fixed in formalin, Bouin fixative, diluted Bouin fixative, Cleland fluid, and modified Davidson fixative, indicating a wide applicability. In addition, it is also possible to distinguish the 12 stages in glutaraldehyde/osmium-tetroxide fixed/plastic embedded testis material without IHC for acrosin. The new stage classification will greatly facilitate research on human spermatogenesis and enable a much better comparison with results from work on experimental animals than hitherto possible. In addition, it will enable a highly focused approach to evaluate spermatogenic impairments, such as germ cell maturation arrests or defects, and to study details of germ cell differentiation.

The nuclear form of glutathione peroxidase 4 is associated with sperm nuclear matrix and is required for proper paternal chromatin decondensation at fertilization.

The nuclear isoform of the selenoprotein Phospholipid Hydroperoxide Glutathione Peroxidase (nGPx4) is expressed in haploid male germ cells, contains several cysteines and is able to oxidize protein thiols, besides glutathione. In this study we have investigated the subnuclear localization of this isoform in isolated mouse male germ cells at different steps of maturation. Immunoblotting and confocal microscopy analyses of subnuclear fractions showed that nGPx4 is localized to the nuclear matrix together with well known markers of this subnuclear compartment like lamin B and topoisomerase IIß at all stages of germ cell differentiation. The peculiar nGPx4 distribution was confirmed by both biochemical and morphological analyses of COS-1 cells overexpressing Flag-tagged nGPx4. To test the functional role of nGPx4 in the process of chromatin assembly, sperm isolated from the caput and the cauda epididymides of wild-type (WT) and genetically deficient in nGPx4 (nGPx4-KO) mice were analyzed in an in vitro chromatin decondensation assay. Results showed that sperm from nGPx4-KO mice were more prone to decondense than those from WT mice at all stages of epididymal maturation, providing conclusive evidence that nGPx4 is required for a correct sperm chromatin compaction. We next addressed the issue of whether the lack of nGPx4 impacts on early events occurring at fertilization. Indeed, in vitro fertilization experiments showed an acceleration of sperm chromatin dispersion in oocytes fertilized by nGpx4-KO sperm compared with control. Overall these data indicate that the absence of nGPx4 leads to sperm nuclear matrix/chromatin instability that may negatively affect the embryo development.

Distribution of GFRA1-expressing spermatogonia in adult mouse testis.

In mice and other mammals, spermatogenesis is maintained by spermatogonial stem cells (SSCs), a cell population belonging to undifferentiated type A spermatogonia. In the accepted model of SSC self-renewal, Asingle (As) spermatogonia are the stem cells, whereas paired (Apaired (Apr)) and chained (Aaligned (Aal)) undifferentiated spermatogonia are committed to differentiation. This model has been recently challenged by evidence that As and chained (Apr and Aal), undifferentiated spermatogonia are heterogeneous in terms of gene expression and function. The expression profile of several markers, such as GFRA1 (the GDNF co-receptor), is heterogeneous among As, Apr and Aal spermatogonia. In this study, we have analysed and quantified the distribution of GFRA1-expressing cells within the different stages of the seminiferous epithelial cycle. We show that in all stages, GFRA1+ chained spermatogonia (Apr to Aal) are more numerous than GFRA1+ As spermatogonia. Numbers of chained GFRA1+ spermatogonia are sharply reduced in stages VII-VIII when Aal differentiate into A1 spermatogonia. GFRA1 expression is regulated by GDNF and in cultures of isolated seminiferous tubules, we found that GDNF expression and secretion by Sertoli cells is stage-dependent, being maximal in stages II-VI and decreasing thereafter. Using qRT-PCR analysis, we found that GDNF regulates the expression of genes such as Tex14, Sohlh1 and Kit (c-Kit) known to be involved in spermatogonial differentiation. Expression of Kit was upregulated by GDNF in a stage-specific manner. Our data indicate that GDNF, besides its crucial role in the self-renewal of stem cells also functions in the differentiation of chained undifferentiated spermatogonia.

The nuclear genes Mtfr1 and Dufd1 regulate mitochondrial dynamic and cellular respiration.

Dufd1 (DUF729 domain containing 1) is related to Mtfr1 (mitochondrial fission regulator 1), a gene involved in the regulation of antioxidant activity in the mouse testis. The present study was undertaken to better understand their role in regulating mitochondrial architecture and function in the mouse. We show that Dufd1 is expressed as a 2 kb mRNA and has a more specific tissue pattern compared to Mtfr1, with highest level of expression in testes, lower level in spleen, and negligible levels in other organs and/or tissues. In the male gonad, Dufd1 mRNA expression increases during postnatal development, similarly to Mtfr1. In situ hybridization and real-time PCR analyses show that Dufd1 is expressed in the seminiferous tubules by middle-late pachytene spermatocytes and spermatids. In transfected cells, the Dufd1-tagged protein is located in mitochondria, associated with the tips of mitochondrial tubules and to tubules constrictions, and induces mitochondrial fission although with a lesser efficiency than Mtfr1. We also found that both endogenous Dufd1 and Mtfr1 proteins are associated with membrane-enriched subcellular fractions, including mitochondria. Inhibition of Mtfr1 and/or Dufd1 expression, in a testicular germ cells line, severely impairs O(2) consumption and indicates that both genes are required for mitochondrial respiration. Accordingly, analysis of testes mitochondria from Mtfr1-deficient mice reveals severely reduced O(2) consumption and ATP synthesis compared to wt animals. These data show that, in murine testis, Dufd1 and Mtfr1 have redundant functions related to mitochondrial physiology and represent genes with a potential role in testicular function.

Identification of spermatogonial stem cell subsets by morphological analysis and prospective isolation.

Spermatogenesis is maintained by a pool of spermatogonial stem cells (SSCs). Analyses of the molecular profile of SSCs have revealed the existence of subsets, indicating that the stem cell population is more heterogeneous than previously believed. However, SSC subsets are poorly characterized. In rodents, the first steps in spermatogenesis have been extensively investigated, both under physiological conditions and during the regenerative phase that follows germ cell damage. In the widely accepted model, the SSCs are type Asingle (As) spermatogonia. Here, we tested the hypothesis that As spermatogonia are phenotypically heterogeneous by analyzing glial cell line-derived neurotrophic factor (GDNF) family receptor alpha1 (GFRA1) expression in whole-mounted seminiferous tubules, via cytofluorimetric analysis and in vivo colonogenic assays. GFRA1 is a coreceptor for GDNF, a Sertoli cell-derived factor essential for SSC self-renewal and proliferation. Morphometric analysis demonstrated that 10% of As spermatogonia did not express GFRA1 but were colonogenic, as shown by germ cell transplantation assay. In contrast, cells selected for GFRA1 expression were not colonogenic in vivo. In human testes, GFRA1 was also heterogeneously expressed in Adark and in Apale spermatogonia, the earliest spermatogonia. In vivo 5-bromo-2'-deoxyuridine administration showed that both GFRA1(+) and GFRA1(-) As spermatogonia were engaged in the cell cycle, a finding supported by the lack of long-term label-retaining As spermatogonia. GFRA1 expression was asymmetric in 5% of paired cells, suggesting that As subsets may be generated by asymmetric cell division. Our data support the hypothesis of the existence of SSC subsets and reveal a previously unrecognized heterogeneity in the expression profile of As spermatogonia in vivo.

Selenium, a key element in spermatogenesis and male fertility.

Selenium is essential for normal spermatogenesis of mammals and its critical role is mainly mediated by two selenoproteins, namely phospholipid hydroperoxide glutathione peroxidase (PHGPx/GPx4) and Selenoprotein P. PHGPx/GPx4 is the major selenoprotein expressed by germ cells in the testis, having multiple functions and representing the pivotal link between selenium, sperm quality and male fertility. Selenoprotein P is a plasma protein that is required for selenium supply to the testis. In the last years, nutritional studies and experimental animal models lacking/overexpressing a specific PHGPx isoform and selenoprotein P have highly expanded our understanding on how the male reproductive system depends on selenium. The focus of this review, is to report and discuss the most relevant and recent findings in this field. Clinical data have pointed to a correlation between abnormal PHGPx content in sperm and disturbance of human male fertility. However, additional evidence is still required to draw any definitive conclusions about therapeutical strategies for improving fertility by selenium administration.

Impaired expression of genes coding for reactive oxygen species scavenging enzymes in testes of Mtfr1/Chppr-deficient mice.

Mtfr1/Chppr is a nuclear gene coding for a mitochondrial protein capable of inducing fission of this organelle in a sequence-specific manner. Here we show that in mice, Mtfr1/Chppr is ubiquitously expressed and displays the highest level of expression in pubertal and adult testes and in particular in spermatids and Leydig cells. To investigate Mtfr1 function in vivo, we analyzed homozygous mice null for this gene obtained through a gene trap approach. We show that these mice fail to express Mtfr1 and that in their testes several genes coding for enzymes involved in the defense against oxidative stress are downregulated. Among these, we studied in particular glutathione peroxidase 3 and show its expression in selected testis cell types. Furthermore, we demonstrate oxidative DNA damage specifically in testes of Mtfr1-deficient mice likely resulting from a reduced antioxidant activity. As a whole, these data suggest that Mtfr1 protects the male gonads against oxidative stress.

Mice overexpressing the mitochondrial phospholipid hydroperoxide glutathione peroxidase in male germ cells show abnormal spermatogenesis and reduced fertility.

To investigate the physiological effects of mitochondrial phospholipid hydroperoxide glutathione peroxidase (mPHGPx) overexpression during early male germ cell differentiation, we have generated transgenic mice bearing the rat mPhgpx coding sequence driven by the mouse synaptonemal complex protein 1 promoter, allowing the transgene to be specifically activated in the testis from the zygotene to diplotene stages of the first meiotic division. Northern/Western blotting and immunocytochemical analyses of endogenous mPHGPx expression during spermatogenesis showed a low enzyme level in middle-late pachytene spermatocytes, but not in earlier meiotic stages, and a significant increase in mPHGPx content in round spermatids. The histological and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling analysis of transgenic testes revealed a number of spermatogenetic defects, including primary spermatocyte apoptosis, haploid cell loss, and seminiferous epithelium disorganization. In line with these features, adult transgenic male mice also displayed a reduction in fertility. Results obtained in this study suggest that mPHGPx expression is tightly regulated in pachytene spermatocytes, with any spatial-temporal increase in mPHGPx expression resulting in damage to spermatogenesis and eventual loss of haploid cells. Present findings in the mouse may be of interest to human male fertility.

PHGPx in spermatogenesis: how many functions?

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is a unique intracellular enzyme that directly reduces lipid hydroperoxides in membranes and has the ability to use protein thiol groups as donor substrates. Three isoforms of PHGPx have so far been identified, namely, a mitochondrial, a cytosolic and a nuclear variant. This article is focused on recent evidence demonstrating that (1) mitochondrial and nuclear PHGPx isoforms display a different pattern of expression during male germ cell differentiation; (2) different PHGPx isoforms play specific and independent functions during sperm maturation. The data are discussed in light of the idea that PHGPx is a moonlighting protein, changing roles depending on the intracellular localization, expression in a specific cell type and different partners which it interacts with.

Regulatory role of BMP2 and BMP7 in spermatogonia and Sertoli cell proliferation in the immature mouse.

AIM: The aim of this study was to determine the action of bone morphogenetic proteins (BMPs) on testicular cell proliferation during early postnatal life, a definite developmental time at which crucial changes in germ cell and Sertoli cell maturation occur. METHODS: We investigated the effect of BMP2 and BMP7, two factors which belong to the relatively distant decapentaplegic (DPP) and 60 A classes of the large BMP family, upon spermatogonial and Sertoli cell proliferation, and we examined the expression of activin/BMP type II and type I receptors. We used in vitro cultured testis fragments from 7-day-old mice, highly purified populations of somatic and germ cells and total testes from mice of different ages. Cell proliferation was assessed by BrdU labelling and [3H]-thymidine incorporation. Ribonuclease protection assays and Northern blotting were performed to analyse receptor expression. RESULTS AND CONCLUSIONS: We have demonstrated a stimulatory action of BMP2 and BMP7 in spermatogonia and Sertoli cell proliferation respectively. ActRIIB is the type II receptor expressed most in spermatogonia, whereas Sertoli cells specifically expressed BMPRIIB, in addition to ActRIIB. By contrast, the presence of ActRIIA was undetectable in either germ or somatic cells. The type I receptors ActRIA, ActRIB and BMPRIA were all found in both cell types, indicating that the observed effect of BMP2 and BMP7 on testicular cell proliferation may be mediated by a number of combinatorial interactions in the receptor complexes. These findings suggest that BMPs are involved in physiological paracrine signalling during the first wave of spermatogenesis.

Ryanodine receptors are expressed and functionally active in mouse spermatogenic cells and their inhibition interferes with spermatogonial differentiation.

Ryanodine receptors (RyRs) are intracellular calcium release channels that are highly expressed in striated muscle and neurons but are also detected in several non-excitable cells. We have studied the expression of the three RyR isoforms in male germ cells at different stages of maturation by western blot and RT-PCR. RyR1 was expressed in spermatogonia, pachytene spermatocytes and round spermatids whereas RyR2 was found only in 5- to 10-day-old testis but not in germ cells. RyR3 was not revealed at the protein level, although its mRNA was detected in mixed populations of germ cells. Caffeine, a known agonist of RyRs, was able to induce release of Ca(2+) from intracellular stores in spermatogonia, pachytene spermatocytes and round spermatids, but not spermatozoa. Treatment with high doses of ryanodine, which are known to block RyR channel activity, reduced spermatogonial proliferation and induced meiosis in in vitro organ cultures of testis from 7-day-old mice. In conclusion, the results presented here indicate that RyRs are present in germ cells and that calcium mobilization through RyR channels could participate to the regulation of male germ maturation.