Altered LKB1/AMPK/TSC1/TSC2/mTOR signaling causes disruption of Sertoli cell polarity and spermatogenesis

Semen Cryopreservation to Expand Male Fertility in Cancer Patients: Intracase Evaluation of Semen Quality

To preserve male fertility after diagnosis of any kind of cancer, a prompt assessment of the semen quality and an appropriate semen cryopreservation must be performed before radio-chemotherapy starts. The present work aims to evaluate the semen parameters at diagnosis of different cancer patients before cryopreservation and after thawing. Testicular tumors and lymphomas are among the most common cancers in younger patients, and while chemotherapy significantly increases patients' survival, it can epigenetically alter the semen fluid, resulting in temporary or permanent infertility. We analyzed data from the database of the Gamete Cryopreservation Center (Annunziata Hospital, CS; Italy) in the period of 2011-2020 from a cohort of 254 cancer patients aged 18-56 years. The evaluation was performed in a blind manner and anonymously recovered; the main parameters referring to semen quality were assessed in accordance with the WHO guidelines and decision limits (6th edition; 2021). The cancer types were as follows: testis cancers (TC; n = 135; 53.1%), hematological cancers (HC; n = 76; 29.9%), and other types of cancer (OC; n = 43; 17%). Comparing TC vs. HC (P1) and vs. OC (P2), TC had the worst semen quality: sperm number/mL (P1 = 0.0014; P2 = 0.004), total motility (P1 = 0.02; P2 = 0.07), progressive motility (P1 = 0.04; P2 = 0.05), viability (P1 = 0.01; P2 = 0.02), and percentage of atypical morphology (P1 = 0.05; P2 = 0.03). After semen thawing, viability and progressive motility recovery lowered, accounting for 46.82% and 16.75%, respectively, in the whole cohort; similarly, in the subgroups ascribed to TC, they showed the lowest recovery. Strong correlation existed between pre- and post-cryopreservation viability and progressive motility in the whole cohort (p < 0.001) and in the TC subgroup (p < 0.05). All cancer subgroups, to significantly different extents, had semen findings below the WHO reference values, suggesting diverse sperm susceptibilities to different cancers and cryodamage. Cancer and associated treatments epigenetically affect patients' semen quality, meaning cryopreservation should be considered a useful personalized prerogative for any kind of cancer in a timely manner.

Defining Gene Function in Spermatogonial Stem Cells Through Conditional Knockout Approaches

Mammalian male fertility is maintained throughout life by a population of self-renewing mitotic germ cells known as spermatogonial stem cells (SSCs). Much of our current understanding regarding the molecular mechanisms underlying SSC activity is derived from studies using conditional knockout mouse models. Here, we provide a guide for the selection and use of mouse strains to develop conditional knockout models for the study of SSCs, as well as their precursors and differentiation-committed progeny. We describe Cre recombinase-expressing strains, breeding strategies to generate experimental groups, and treatment regimens for inducible knockout models and provide advice for verifying and improving conditional knockout efficiency. This resource can be beneficial to those aiming to develop conditional knockout models for the study of SSC development and postnatal function.

Genomic testing for copy number and single nucleotide variants in spermatogenic failure

PURPOSE

To identify clinically significant genomic copy number (CNV) and single nucleotide variants (SNV) in males with unexplained spermatogenic failure (SPGF).

MATERIALS AND METHODS

Peripheral blood DNA from 97/102 study participants diagnosed with oligozoospermia, severe oligozoospermia, or non-obstructive azoospermia (NOA) was analyzed for CNVs via array comparative genomic hybridization (aCGH) and SNVs using whole-exome sequencing (WES).

RESULTS

Of the 2544 CNVs identified in individuals with SPGF, > 90% were small, ranging from 0.6 to 75 kb. Thirty, clinically relevant genomic aberrations, were detected in 28 patients (~ 29%). These included likely diagnostic CNVs in 3/41 NOA patients (~ 7%): 1 hemizygous, intragenic TEX11 deletion, 1 hemizygous DDX53 full gene deletion, and 1 homozygous, intragenic STK11 deletion. High-level mosaicism for X chromosome disomy (~ 10% 46,XY and ~ 90% 47,XXY) was also identified in 3 of 41 NOA patients who previously tested normal with conventional karyotyping. The remaining 24 CNVs detected were heterozygous, autosomal recessive carrier variants. Follow-up WES analysis confirmed 8 of 27 (30%) CNVs (X chromosome disomy excluded). WES analysis additionally identified 13 significant SNVs and/or indels in 9 patients (~ 9%) including X-linked AR, KAL1, and NR0B1 variants.

CONCLUSION

Using a combined genome-wide aCGH/WES approach, we identified pathogenic and likely pathogenic SNVs and CNVs in 15 patients (15%) with unexplained SPGF. This value equals the detection rate of conventional testing for aneuploidies and is considerably higher than the prevalence of Y chromosome microdeletions. Our results underscore the importance of comprehensive genomic analysis in emerging diagnostic testing of complex conditions like male infertility.

The PI3K/AKT signaling pathway: How does it regulate development of Sertoli cells and spermatogenic cells?

The PI3K/AKT signaling pathway is one of the most crucial regulatory mechanisms in animal cells, which can mainly regulate proliferation, survival and anti-apoptosis in cell lines. In the seminiferous epithelium, most studies were concentrated on the role of PI3K/AKT signaling in immature Sertoli cells (SCs) and spermatogonia stem cells (SSCs). PI3K/AKT signaling can facilitate the proliferation and anti-apoptosis of immature Sertoli cells and spermatogenic cells. Besides, in mature Sertoli cells, this pathway can disintegrate the structure of the blood-testis barrier (BTB) via regulatory protein synthesis and the cytoskeleton of Sertoli cells. All of these effects can directly and indirectly maintain and promote spermatogenesis in male testis.

UHRF1 establishes crosstalk between somatic and germ cells in male reproduction

Sertoli cells (SCs) support and nourish germ cells (GCs) through their crosstalk during spermatogenesis. However, the underlying epigenetic mechanism that ensures SCs’ functions in this process remains unclear. Here, we report that UHRF1, a critical epigenetic regulator, is mainly expressed in human and mouse pre-mature SCs, and is essential for establishing Sertoli-Germ cell crosstalk. SC-specific UHRF1 knockout mice exhibit complete sterility with Sertoli cell (SC) proliferation and differentiation aberrance, blood-testis barrier (BTB) disruption, and immature germ cell (GC) sloughing. RNA sequencing and Whole Genome Bisulfite Sequencing (WGBS) revealed that many extracellular matrix (ECM)-related genes (e.g., Timp1, Trf, and Spp1) appeared upregulated with the DNA hypomethylation status in UHRF1-deficient SCs. Strikingly, overexpression of Timp1, Trf, and Spp1 in SCs in vitro and in vivo could phenocopy the SC-specific UHRF1-deficient mice. Our data demonstrated that UHRF1 regulates the transcriptional program of ECM-related genes in SCs and establishes SC-GC crosstalk.

Protein kinase A drives paracrine crisis and WNT4-dependent testis tumor in Carney complex

Large-cell calcifying Sertoli cell tumors (LCCSCTs) are among the most frequent lesions occurring in male Carney complex (CNC) patients. Although they constitute a key diagnostic criterion for this rare multiple neoplasia syndrome resulting from inactivating mutations of the tumor suppressor PRKAR1A, leading to unrepressed PKA activity, LCCSCT pathogenesis and origin remain elusive. Mouse models targeting Prkar1a inactivation in all somatic populations or separately in each cell type were generated to decipher the molecular and paracrine networks involved in the induction of CNC testis lesions. We demonstrate that the Prkar1a mutation was required in both stromal and Sertoli cells for the occurrence of LCCSCTs. Integrative analyses comparing transcriptomic, immunohistological data and phenotype of mutant mouse combinations led to the understanding of human LCCSCT pathogenesis and demonstrated PKA-induced paracrine molecular circuits in which the aberrant WNT4 signal production is a limiting step in shaping intratubular lesions and tumor expansion both in a mouse model and in human CNC testes.

Estradiol ameliorates metformin-inhibited Sertoli cell proliferation via AMPK/TSC2/mTOR signaling pathway

Metformin is a commonly used for treating type 2 diabetes and it acts on a variety of organs including the male reproductive system. 17β-estradiol plays an important role in Sertoli cell (SC) proliferation which determines the germ cell development and spermatogenesis. The aim of this study is to investigate the effect of metformin on immature chicken SC proliferation and the potential mechanisms by which 17β-estradiol regulate this process. Results showed that metformin significantly inhibited SC proliferation, whereas 17β-estradiol weakened the inhibitory effects of metformin on SC viability, cell growth, and cell cycle progression. SC proliferation-inhibiting effect of metformin exposure was regulated by decreasing adenosine triphosphate level and respiratory enzyme activity in the mitochondria; this process was possibly mediated by the adenosine monophosphate-activated protein kinase (AMPK)/tuberous sclerosis complex 2 (TSC2)/mammalian target of rapamycin (mTOR) signaling pathway, which was regulated by the down-expressed miR-1764 and by the decreased antioxidant enzyme activity and excessive reactive oxygen species generation. In addition, SCs transfected with the miR-1764 agomir led to an improvement of proliferation capacity through down-regulating AMPKα2 level, which further decreased TSC2 expression and induced mTOR activation. However, the anti-proliferative effect of miR-1764 antagomir can be alleviated by 17β-estradiol treatment via the up-expression of miR-1764 in transfected SCs. Our findings suggest appropriate dose of exogenous 17β-estradiol treatment can ameliorate the inhibitory effect of metformin on SC proliferation via the regulation of AMPK/TSC2/mTOR signaling pathway, this might reduce the risk of poor male fertility caused by the abuse of anti-diabetic agents.

MiR-181a Promotes Spermatogenesis by Targeting the S6K1 Pathway

Approximately 15% of couples suffer from infertility worldwide, and male factors contribute to about 30% of total sterility cases. However, there is little progress in treatments due to the obscured understanding of underlying mechanisms. Recently microRNAs have emerged as a key player in the process of spermatogenesis. Expression profiling of miR-181a was carried out in murine testes and spermatocyte culture system. In vitro cellular and biochemical assays were used to examine the effect of miR-181a and identify its target S6K1, as well as elucidate the function with chemical inhibitor of S6K1. Human testis samples analysis was employed to validate the findings. miR-181a level was upregulated during mouse spermatogenesis and knockdown of miR-181a attenuated the cell proliferation and G1/S arrest and increased the level of S6K1, which was identified as a downstream target of miR-181a. Overexpression of S6K1 also led to growth arrest of spermatocytes while inhibitor of S6K1 rescued the miR-181a knockdown-mediated cell proliferation defect. In human testis samples of azoospermia patients, low level of miR-181a was correlated with defects in the spermatogenic process. miR-181a is identified as a new regulator and high level of miR-181a contributes to spermatogenesis via targeting S6K1.

Bisphenol S perturbs Sertoli cell junctions in male rats via alterations in cytoskeletal organization mediated by an imbalance between mTORC1 and mTORC2

Bisphenol S (BPS) is now used as an alternative of bisphenol A (BPA), but has been implicated in male reproductive dysfunction-including diminished sperm number and quality and altered hormonal concentrations. However, the mechanisms of action subserving these effects remains unclear. In the present study, BPS at doses of 50 mg/kg bw and 100 mg/kg bw caused defects in the integrity of the blood-testis barrier (BTB) and apical ectoplasmic specialization (ES), and we also delineated an underlying molecular mechanism of action. BPS induced F-actin and α-tubulin disorganization in seminiferous tubules, which in turn led to the truncation of actin filaments and microtubules. Additionally, BPS was found to perturb the expression of the actin-binding proteins Arp3 and Eps8, which are critical for the organization of the actin filaments. mTORC1 and mTORC2 manifest opposing roles in Sertoli cell junctional function, and we demonstrated that mTORC1/rpS6/Akt/MMP9 signaling was increased and that mTORC2/rictor activity was also attenuated. In summary, we showed that BPS-induced disruption of the BTB and apical ES perturbed normal spermatogenic function that was mediated by mTORC1 and mTORC2. The imbalance in mTORC1 and mTORC2, in turn, altered the expression of actin-binding proteins, resulting in the impairment of F-actin and MT organization, and inhibited the expression of junctional proteins at the BTB and apical ES.

Human Hsp90 cochaperones: perspectives on tissue-specific expression and identification of cochaperones with similar in vivo functions

The Hsp90 molecular chaperone is required for the function of hundreds of different cellular proteins. Hsp90 and a cohort of interacting proteins called cochaperones interact with clients in an ATP-dependent cycle. Cochaperone functions include targeting clients to Hsp90, regulating Hsp90 ATPase activity, and/or promoting Hsp90 conformational changes as it progresses through the cycle. Over the last 20 years, the list of cochaperones identified in human cells has grown from the initial six identified in complex with steroid hormone receptors and protein kinases to about fifty different cochaperones found in Hsp90-client complexes. These cochaperones may be placed into three groups based on shared Hsp90 interaction domains. Available evidence indicates that cochaperones vary in client specificity, abundance, and tissue distribution. Many of the cochaperones have critical roles in regulation of cancer and neurodegeneration. A more limited set of cochaperones have cellular functions that may be limited to tissues such as muscle and testis. It is likely that a small set of cochaperones are part of the core Hsp90 machinery required for the folding of a wide range of clients. The presence of more selective cochaperones may allow greater control of Hsp90 activities across different tissues or during development.

Roles of AMP-Activated Protein Kinase (AMPK) in Mammalian Reproduction

Reproduction is an energy demanding function and only take place in case of sufficient available energy status in mammals. Metabolic diseases such as anorexia nervosa are clinically associated with reduced fertility. AMP-activated protein kinase (AMPK), as a major regulator of cellular energy homeostasis, is activated in limited energy reserves to ensure the orderly progress of various physiological activities. In recent years, mounting evidence shows that AMPK is involved in the regulation of reproductive function through multiple mechanisms. AMPK is likely to be a metabolic sensor integrating central and peripheral signals. In this review, we aim to explore the preclinical studies published in the last decade that investigate the role of AMP-activated protein kinase in the reproductive field, and its role as a target for drug therapy of reproductive system-related diseases. We also emphasized the emerging roles of AMPK in transcriptional regulation of reproduction processes and metabolisms, which are tightly related to the energy state and fertility of an organism.

The dynamics and regulation of microfilament during spermatogenesis

Spermatogenesis is a highly complex physiological process which contains spermatogonia proliferation, spermatocyte meiosis and spermatid morphogenesis. In the past decade, actin binding proteins and signaling pathways which are critical for regulating the actin cytoskeleton in testis had been found. In this review, we summarized 5 actin-binding proteins that have been proven to play important roles in the seminiferous epithelium. Lack of them perturbs spermatids polarity and the transport of spermatids. The loss of Arp2/3 complex, Formin1, Eps8, Palladin and Plastin3 cause sperm release failure suggesting their irreplaceable role in spermatogenesis. Actin regulation relies on multiple signal pathways. The PI3K/Akt signaling pathway positively regulate the mTOR pathway to promote actin reorganization in seminiferous epithelium. Conversely, TSC1/TSC2 complex, the upstream of mTOR, is activated by the LKB1/AMPK pathway to inhibit cell proliferation, differentiation and migration. The increasing researches focus on the function of actin binding proteins (ABPs), however, their collaborative regulation of actin patterns and potential regulatory signaling networks remains unclear. We reviewed ABPs that play important roles in mammalian spermatogenesis and signal pathways involved in the regulation of microfilaments. We suggest that more relevant studies should be performed in the future.

New insights into the role of mTORC1 in male fertility in zebrafish

Mechanistic target of rapamycin complex 1 (mTORC1) plays crucial roles in male fertility. In mammals, deregulation of mTORC1 led to disordered spermatogonia proliferation and spermatogenesis, which eventually caused infertility in males. However, its roles in male fertility of non-mammalian species remain unclarified. In the present study, it was found that treatment of rapamycin, an mTORC1 inhibitor, resulted in infertility with decreased milt production and sperm motility in zebrafish. However, it is surprising to find that spermatogenesis was normal in these fish. All types of germ cells were found and the proliferation of spermatogonia and spermatocyte were normal. These results suggested that maturation of sperm may be impaired in males treated with rapamycin. Increased apoptosis was found surrounding the lumen containing spermatozoa, implicating a loss of Sertoli cells in testes treated with rapamycin. Moreover, LH/hCG mediated up-regulation of steroidogenic genes was abolished. The expression of npr and ar induced by LH/hCG was also blocked, which further suppressed the signaling of progestin and androgen. Collectively, mTORC1 maintains male fertility via different mechanisms in fish and mammals. mTORC1 is dispensable for spermatogenesis in zebrafish, but possibly supports the maintenance of Sertoli cells and mediates the signaling of hormones, which are crucial for sperm maturation.

Maternal energy insufficiency affects testicular development of the offspring in a swine model

We determined the effects of insufficient maternal energy on testicular development in offspring in a swine model. Thirty-six sows were divided into control (CON) and low-energy diet (LE) groups during gestation. We observed that the number of Sertoli, germ, and Leydig cells in the offspring of the CON group were significantly higher than those in the LE group at 28 and 120 d after birth. Furthermore, the percentage of apoptotic testis cells was significantly higher in the offspring of the LE group than in the CON group. Transcriptome analysis of differentially expressed mRNAs and long noncoding RNAs in offspring testes indicated that these RNAs were mainly involved in lipid metabolism, apoptosis, cell proliferation, and some pivotal regulatory pathways. Results revealed that AMPK-PI3K-mTOR, MAPK, and oxidative phosphorylation signaling pathways play an important role in mediating the programming effect of insufficient maternal energy on testicular development, and that this effect occurs mainly at an early stage in life. mRNA and protein expression analyses confirmed the importance of certain signaling pathways in the regulation of testicular development. This study provides insights into the influence and possible mechanism underlying the effect of inadequate maternal energy intake on testicular development in the offspring.

Melatonin suppresses milk fat synthesis by inhibiting the mTOR signaling pathway via the MT1 receptor in bovine mammary epithelial cells

Milk fat content is an important criterion for assessing milk quality and is one of the main target traits of dairy cattle breeding. Recent studies have shown the importance of melatonin in regulating lipid metabolism, but the potential effects of melatonin on milk fat synthesis in bovine mammary epithelial cells (BMECs) remain unclear. Here, we showed that melatonin supplementation at 10 μmol/L significantly downregulated the mRNA expression of lipid metabolism-related genes and resulted in lower lipid droplet formation and triglyceride accumulation. Moreover, melatonin significantly upregulated melatonin receptor subtype melatonin receptor 1a (MT1) gene expression, and the negative effects of melatonin on milk fat synthesis were reversed by treatment with the nonselective MT1/melatonin receptor subtype melatonin receptor 1b (MT2) antagonist. However, a selective MT2 antagonist did not modify the negative effects of melatonin on milk fat synthesis. In addition, KEGG analysis revealed that melatonin inhibition of milk fat synthesis may occur via the mTOR signaling pathway. Further analysis revealed that melatonin significantly suppressed the activation of the mTOR pathway by restricting the phosphorylation of mTOR, 4E-BP1, and p70S6K, and the inhibition of melatonin on milk fat synthesis was reversed by mTOR activator MHY1485 in BMECs. Furthermore, in vivo experiments in Holstein dairy cows showed that exogenous melatonin significantly decreased milk fat concentration. Our data from in vitro and in vivo studies revealed that melatonin suppresses milk fat synthesis by inhibiting the mTOR signaling pathway via the MT1 receptor in BMECs. These findings lay a foundation to identify a new potential means for melatonin to modulate the fat content of raw milk in Holstein dairy cows.

A germline-specific role for the mTORC2 component Rictor in maintaining spermatogonial differentiation and intercellular adhesion in mouse testis

STUDY QUESTION

What is the physiological role of Rictor in spermatogenic cells?

SUMMARY ANSWER

Germline expression of Rictor regulates spermatogonial differentiation and has an essential role in coordinating germ cells and Sertoli cells in maintaining intact cell-cell adhesion dynamics and cytoskeleton-based architecture in the seminiferous epithelium.

WHAT IS KNOWN ALREADY

The mechanistic target of rapamycin (mTOR) resides in its functions as the catalytic subunits of the structurally and functionally distinct mTORC1 and mTORC2 complexes. In the mammalian testis, mTORC1 regulates spermatogonial stem cell self-renewal and differentiation, whereas mTORC2 is required for Sertoli cell function. In contrast to mTORC1, mTORC2 has been much less well studied. Rictor is a distinct component of the mTORC2 complex.

STUDY DESIGN, SIZE, DURATION

We investigated the effects of germ cell-specific ablation of Rictor on testicular development by using a mouse model of germline-specific ablation of Rictor.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We analyzed the in-vivo functions of Rictor through different methods including histology, immunofluorescent staining, chromosome spreads, blood-testis barrier (BTB) integrity assays and RNA sequencing.

MAIN RESULTS AND THE ROLE OF CHANCE

Mutant mice did not show a defect in meiotic synapsis or recombination, but exhibited compromised spermatogonial differentiation potential, disorganized cell-cell junctions, impaired BTB dynamics and defective spermiogenesis. Concomitantly, RNA-seq profiling revealed that many genes involved in adhesion and migration were expressed inappropriately.

LARGE SCALE DATA

RNA-seq data are published in the SRA database (PRJNA419273).

LIMITATIONS REASONS FOR CAUTION

A detailed analysis of the mechanisms underlying the phenotype needs further investigations.

WIDER IMPLICATIONS OF THE FINDINGS

Our work provides previously unidentified in-vivo evidence that germline expression of Rictor plays a role in maintaining spermatogonial differentiation and cell-cell adhesion. These findings are important for understanding the regulation of spermatogenesis and have clinical implications for the effect of mTOR inhibitors on human fertility.

STUDY FUNDING AND COMPETING INTEREST(S)

This study was supported by National Key R&D Program of China (2016YFA0500902), National Natural Science Foundation of China (31471228 and 31771653), Jiangsu Science Foundation for Distinguished Young Scholars (BK20150047), and Natural Science Foundation of Jiangsu Province (BK20140897, 14KJA180005 and 14KJB310004) to K.Z. The authors declare no competing or financial interests.

Metformin-induced endocrine disruption and oxidative stress of Oryzias latipes on two-generational condition

Metformin has been treated for diabetes (type 2). Nowadays, this compound is frequently found in ambient water, influent/effluent of a wastewater treatment plant. To evaluate the metformin aquatic toxicity under a multi-generational exposure regimen, we exposed Oryzias latipes to metformin for two generations (133 d) and investigated its adverse effects. In the F0 generation, metformin significantly elevated gene expression for cytochrome P450 19a (CYP19a) and estrogen receptor α (ERα) in male fish; in female fish, the treatment decreased gene expression of vitellogenin (VTG2) and ERβ1, suggesting endocrine disruption (one-way ANOVA, p <  0.05). Intersex occurrence of F0 female fish were found in a concentration-dependent manner, whereas no significant changes in fecundity and hatching rate were observed (p <  0.05). Metformin increased the reactive oxygen species (ROS) content, and decreased the glutathione (GSH) content in F0 male fish compared with those of the control (one-way ANOVA, p >  0.05). In F0 female fish, metformin increased catalase activity compared with that of the control (p >  0.05). The results demonstrated that metformin leads to oxidative stress and two-generation endocrine disruption in O. latipes. These results may be useful for better understanding metformin toxicity mechanism.

Identification of microRNAs for regulating adenosine monophosphate-activated protein kinase expression in immature boar Sertoli cells in vitro

Adenosine monophosphate-activated protein kinase (AMPK) plays a key role in cellular energy homeostasis and cell proliferation. MicroRNAs (miRNAs) function as posttranscriptional regulators of gene expression in biological processes. It is unclear to whether miRNAs are involved in AMPK-regulated Sertoli cell (SC) proliferation. To further understand the regulation of miRNAs in the immature boar SC proliferation, 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) was added to activate AMPK. By an Illumina small RNA deep sequencing, we obtained sequences and relative expression levels of 272 known mature miRNAs, among which 9 miRNAs were significantly upregulated whereas 16 miRNAs were downregulated following the AICAR treatment. The results identified 38 conserved miRNAs, with 8 significantly downregulated miRNAs whereas no upregulated miRNAs. Gene Ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses suggested that miR-1285 was involved in many activities and pathways associated with cell proliferation via targeting on AMPKα2. We validated that AICAR significantly downregulated miR-1285 level in SCs. Transfection of miR-1285 mimic increased the SC viability and cell cycle progression but reduced AMPKα2 mRNA and protein levels, indicating that miR-1285 is involved in the immature boar SC proliferation via downregulating AMPKα2 expression.

AMPK Function in Mammalian Spermatozoa

AMP-activated protein kinase AMPK regulates cellular energy by controlling metabolism through the inhibition of anabolic pathways and the simultaneous stimulation of catabolic pathways. Given its central regulator role in cell metabolism, AMPK activity and its regulation have been the focus of relevant investigations, although only a few studies have focused on the AMPK function in the control of spermatozoa's ability to fertilize. This review summarizes the known cellular roles of AMPK that have been identified in mammalian spermatozoa. The involvement of AMPK activity is described in terms of the main physiological functions of mature spermatozoa, particularly in the regulation of suitable sperm motility adapted to the fluctuating extracellular medium, maintenance of the integrity of sperm membranes, and the mitochondrial membrane potential. In addition, the intracellular signaling pathways leading to AMPK activation in mammalian spermatozoa are reviewed. We also discuss the role of AMPK in assisted reproduction techniques, particularly during semen cryopreservation and preservation (at 17 °C). Finally, we reinforce the idea of AMPK as a key signaling kinase in spermatozoa that acts as an essential linker/bridge between metabolism energy and sperm's ability to fertilize.

MicroRNA-7450 regulates non-thermal plasma-induced chicken Sertoli cell apoptosis via adenosine monophosphate-activated protein kinase activation

Non-thermal plasma treatment is an emerging innovative technique with a wide range of biological applications. This study was conducted to investigate the effect of a non-thermal dielectric barrier discharge plasma technique on immature chicken Sertoli cell (SC) viability and the regulatory role of microRNA (miR)-7450. Results showed that plasma treatment increased SC apoptosis in a time- and dose-dependent manner. Plasma-induced SC apoptosis possibly resulted from the excess production of reactive oxygen species via the suppression of antioxidant defense systems and decreased cellular energy metabolism through the inhibition of adenosine triphosphate (ATP) release and respiratory enzyme activity in the mitochondria. In addition, plasma treatment downregulated miR-7450 expression and activated adenosine monophosphate-activated protein kinase α (AMPKα), which further inhibited mammalian target of rapamycin (mTOR) phosphorylation in SCs. A single-stranded synthetic miR-7450 antagomir disrupted mitochondrial membrane potential and decreased ATP level and mTOR phosphorylation by targeting the activation of AMPKα, which resulted in significant increases in SC lethality. A double-stranded synthetic miR-7450 agomir produced opposite effects on these parameters and ameliorated plasma-mediated apoptotic effects on SCs. Our findings suggest that miR-7450 is involved in the regulation of plasma-induced SC apoptosis through the activation of AMPKα and the further inhibition of mTOR signaling pathway.

Differentially expressed novel alternatively spliced transcript variant of tumor suppressor Stk11 gene in mouse

Serine/threonine kinase 11 (STK11) is a protein kinase that is encoded by Stk11 gene located on chromosome 19 and 10 in humans and mouse respectively. It acts as a master kinase of adenine monophosphate-activated protein kinase (AMPK) pathway that coordinates the regulation of cellular energy metabolism and cell division. STK11 exerts effect by activating more than 14 kinases including AMPK and AMPK-related kinases. It is also known to regulate cell polarity and acts as tumor suppressor. Alternative splicing of pre-mRNA is a mechanism which results in multiple transcript variants of a single gene. In human, two STK11 isoforms have been reported, an alternatively spliced isoform which has variation at its C-terminal and mostly expressed in testis (LKB1_S). Another isoform exhibiting oncogenic properties lacks few residues at its N-terminal (ΔN-LKB1). In the present study, we report the identification of a new transcript variant Stk11N which is generated through alternative splicing. The new variant was found to have differential and tissue specific expression at Postnatal-7 and adult stages of mouse. As compared to the known variant Stk11C, the conceptually translated amino acid sequences of the new variant differ from exon-E2 onwards. In silico post translational studies of the new and published variant show similarity in some of the properties while differ in properties like nuclear export signals, phosphorylation, glycosylation, etc. Thus, alternative splicing of Stk11 gene generating new variant with heterogeneous properties suggests for complex regulation of these variants in controlling the AMPK pathway and other functions.

Influences of different dietary energy level on sheep testicular development associated with AMPK/ULK1/autophagy pathway

Energy balance is an important feature for spermatozoa production in the testis. The 5'-AMP-activated protein kinase (AMPK) is a sensor of cell energy, has been implicated as a mediator between gonadal function and energy balance. Herein, we intended to determine the physiological effects of AMPK on testicular development in feed energy restricted and compensated pre-pubertal rams. Lambs had restricted feeding for 2 months and then provided compensatory feeding for another 3 months. Feed levels were 100%(control), 15% and 30% of energy restriction (ER) diets, respectively. The results showed that lambs fed the 30% ER diet had significantly lower testicular weight (P < .05) and spermatids number in the seminiferous tubules, but there were no differences between control and 15% ER groups. Meanwhile, 15% ER and 30% ER diets induced testis autophagy and apoptosis through activating AMPK-ULK1(ULK1, Unc-51 like autophagy activating kinase) signal pathway with characterization of increased Beclin-1 and Light chain 3-Ⅱ/Light chain 3-Ⅰ (LC3-II/LC3-I) ratio, up-regulated the ratio of pro-apoptotic Bcl-2-associated X protein (BAX) and anti-apoptotic B-cell lymphoma 2 (Bcl-2), as well as activated AMPK, phosphorylated AMPK(p-AMPK) and ULK1. Furthermore, a compensation of these parameters occurred when the lambs were re-fed with normal energy requirement after restriction. Taken together, dietary energy levels influence testicular development through autophagy and apoptosis interplay mediated by AMPK-ULK1 signal pathway, which also indicates the important role of the actions of AMPK in the testis homeostasis.

[Rictor/mTORC2 regulates blood-testis barrier and spermatogenesis in mice]

OBJECTIVE

To investigate the role of Rictor/mTORC2 in the formation of blood testis barrier (BTB), testicular development, and spermatogenesis.

METHODS

Amh Cre positive mice homozygous for rictor loxP with Sertoli cell specific deletion of rictor were obtained by cross breeding Amh Cre mice with rictor loxP mice. The histology of the reproductive organs, seminiferous tubules and epididymis of the transgenic mice was observed with HE staining. The cell subgroups of the germ cells in the seminiferous tubule were detected by flow cytometry with propidium iodide labeling. The expression levels of Ki 67 and separase were detected with immunofluorescence assay, and the expression levels of BTB associated proteins were detected with immunofluorescence and Western blotting.

RESULTS

Compared with the control (Amh Cre^-, rictor^loxP/loxP or rictor^loxP/-) mice, the mice with Sertoli cell specific rictor deletion showed significantly decreased testicular weight and epididymis weight (P<0.05), significantly increased diploid cells (P<0.01), and decreased haploid cells (P<0.01) but comparable tetraploid cells and similar expression levels of Ki 67 and separase. The mice with rictor knockout also showed aberrant localization of BTB associated proteins, which were scattered over the whole seminiferous epithelium, but the expression levels of the protein remained stable.

CONCLUSION

Rictor in testicular Sertoli cells is essential for maintaining BTB integrity and function and ensuring normal spermatogenesis in mice.

LKB1 as a Tumor Suppressor in Uterine Cancer: Mouse Models and Translational Studies

The LKB1 tumor suppressor was identified in 1998 as the gene mutated in the Peutz-Jeghers Syndrome (PJS), a hereditary cancer predisposition characterized by gastrointestinal polyposis and a high incidence of cancers, particularly carcinomas, at a variety of anatomic sites including the gastrointestinal tract, lung, and female reproductive tract. Women with PJS have a high incidence of carcinomas of the uterine corpus (endometrium) and cervix. The LKB1 gene is also somatically mutated in human cancers arising at these sites. Work in mouse models has highlighted the potency of LKB1 as an endometrial tumor suppressor and its distinctive roles in driving invasive and metastatic growth. These in vivo models represent tractable experimental systems for the discovery of underlying biological principles and molecular processes regulated by LKB1 in the context of tumorigenesis and also serve as useful preclinical model systems for experimental therapeutics. Here we review LKB1's known roles in mTOR signaling, metabolism, and cell polarity, with an emphasis on human pathology and mouse models relevant to uterine carcinogenesis, including cancers of the uterine corpus and cervix.

Utrophin Compensates dystrophin Loss during Mouse Spermatogenesis

Duchenne muscular dystrophy (DMD) is an X-linked genetic disorder resulting from mutations in the dystrophin gene. The mdx/utrn^−/− mouse, lacking in both dystrophin and its autosomal homologue utrophin, is commonly used to model the clinical symptoms of DMD. Interestingly, these mice are infertile but the mechanisms underlying this phenomenon remain unclear. Using dystrophin deficient mdx mouse and utrophin haplodeficient mdx/utrn^+/− mouse models, we demonstrate the contribution of Dp427 (full-length dystrophin) and utrophin to testis and epididymis development, as well as spermatogenesis. We show that Dp427 deficiency disturbed the balance between proliferation and apoptosis of germ cells during spermatogenesis, which was further disrupted with utrophin haplodeficiency, deciphering a compensatory role of utrophin for dystrophin in the male reproductive system. In the spermatozoa, we have found a compensatory response of utrophin to dystrophin deficiency - namely the upregulation and relocation of utrophin to the flagellar midpiece. This study demonstrates the contribution of Dp427 and utrophin in male fertility, suggesting a potential pathology in DMD patients.

Drosophila LKB1 is required for the assembly of the polarized actin structure that allows spermatid individualization

In mammals, a testis-specific isoform of the protein kinase LKB1 is required for spermiogenesis, but its exact function and specificity are not known. Human LKB1 rescues the functions of Drosophila Lkb1 essential for viability, but these males are sterile, revealing a new function for this genes in fly. We also identified a testis-specific transcript generated by an alternative promoter and that only differs by a longer 5'UTR. We show that dLKB1 is required in the germline for the formation of the actin cone, the polarized structure that allows spermatid individualization and cytoplasm excess extrusion during spermiogenesis. Three of the nine LKB1 classical targets in the Drosophila genome (AMPK, NUAK and KP78b) are required for proper spermiogenesis, but later than dLKB1. dLkb1 mutant phenotype is reminiscent of that of myosin V mutants, and both proteins show a dynamic localization profile before actin cone formation. Together, these data highlight a new dLKB1 function and suggest that dLKB1 posttranscriptional regulation in testis and involvement in spermatid morphogenesis are evolutionarily conserved features.

Genome-wide analysis of long non-coding RNAs and their role in postnatal porcine testis development

A comprehensive and systematic understanding of the roles of lncRNAs in the postnatal development of the pig testis has still not been achieved. In the present study, we obtained more than one billion clean reads and identified 15,528 lncRNA transcripts; these transcripts included 5032 known and 10,496 novel porcine lncRNA transcripts and corresponded to 10,041 lncRNA genes. Pairwise comparisons identified 449 known and 324 novel lncRNAs that showed differential expression patterns. GO and KEGG pathway enrichment analyses revealed that the targeted genes were involved in metabolic pathways regulating testis development and spermatogenesis, such as the TGF-beta pathway, the PI3K-Akt pathway, the Wnt/β-catenin pathway, and the AMPK pathway. Using this information, we predicted some lncRNAs and coding gene pairs were predicted that may function in testis development and spermatogenesis; these are listed in detail. This study has provided the most comprehensive catalog to date of lncRNAs in the postnatal pig testis and will aid our understanding of their functional roles in testis development and spermatogenesis.

Ptbp2 Controls an Alternative Splicing Network Required for Cell Communication during Spermatogenesis

Alternative splicing has essential roles in development. Remarkably, spermatogenic cells express more alternatively spliced RNAs compared to most whole tissues; however, regulation of these RNAs remains unclear. Here, we characterize the alternative splicing landscape during spermatogenesis and reveal an essential function for the RNA-binding protein Ptbp2 in this highly regulated developmental program. We found that Ptbp2 controls a network of genes involved in cell adhesion, migration, and polarity, suggesting that splicing regulation by Ptbp2 is critical for germ cell communication with Sertoli cells (multifunctional somatic cells necessary for spermatogenesis). Indeed, Ptbp2 ablation in germ cells resulted in disorganization of the filamentous actin (F-actin) cytoskeleton in Sertoli cells, indicating that alternative splicing regulation is necessary for cellular crosstalk during germ cell development. Collectively, the data delineate an alternative splicing regulatory network essential for spermatogenesis, the splicing factor that controls it, and its biological importance in germ-Sertoli communication.

Impact of 5'-amp-activated Protein Kinase on Male Gonad and Spermatozoa Functions

As we already know, the male reproductive system requires less energetic investment than the female one. Nevertheless, energy balance is an important feature for spermatozoa production in the testis and for spermatozoa properties after ejaculation. The 5'-AMP-activated protein kinase, AMPK, is a sensor of cell energy, that regulates many metabolic pathways and that has been recently shown to control spermatozoa quality and functions. It is indeed involved in the regulation of spermatozoa quality through its action on the proliferation of testicular somatic cells (Sertoli and Leydig), on spermatozoa motility and acrosome reaction. It also favors spermatozoa quality through the management of lipid peroxidation and antioxidant enzymes. I review here the most recent data available on the roles of AMPK in vertebrate spermatozoa functions.

Emerging Role for Mammalian Target of Rapamycin in Male Fertility

Male fertility is modulated by environmental, endocrine, paracrine, and metabolic cues. Mammalian target of rapamycin (mTOR) coordinates many cellular events in response to those signals. Here, we discuss how the mTOR pathway integrates and mediates signals throughout the male reproductive system, acting as a central player in the control of spermatogenesis.

Mammalian target of rapamycin (mTOR): a central regulator of male fertility?

Mammalian target of rapamycin (mTOR) is a central regulator of cellular metabolic phenotype and is involved in virtually all aspects of cellular function. It integrates not only nutrient and energy-sensing pathways but also actin cytoskeleton organization, in response to environmental cues including growth factors and cellular energy levels. These events are pivotal for spermatogenesis and determine the reproductive potential of males. Yet, the molecular mechanisms by which mTOR signaling acts in male reproductive system remain a matter of debate. Here, we review the current knowledge on physiological and molecular events mediated by mTOR in testis and testicular cells. In recent years, mTOR inhibition has been explored as a prime strategy to develop novel therapeutic approaches to treat cancer, cardiovascular disease, autoimmunity, and metabolic disorders. However, the physiological consequences of mTOR dysregulation and inhibition to male reproductive potential are still not fully understood. Compelling evidence suggests that mTOR is an arising regulator of male fertility and better understanding of this atypical protein kinase coordinated action in testis will provide insightful information concerning its biological significance in other tissues/organs. We also discuss why a new generation of mTOR inhibitors aiming to be used in clinical practice may also need to include an integrative view on the effects in male reproductive system.

Control of Germline Stem Cell Lineages by Diet and Physiology

Tight coupling of reproduction to environmental factors and physiological status is key to long-term species survival. In particular, highly conserved pathways modulate germline stem cell lineages according to nutrient availability. This chapter focuses on recent in vivo studies in genetic model organisms that shed light on how diet-dependent signals control the proliferation, maintenance, and survival of adult germline stem cells and their progeny. These signaling pathways can operate intrinsically in the germ line, modulate the niche, or act through intermediate organs to influence stem cells and their differentiating progeny. In addition to illustrating the extent of dietary regulation of reproduction, findings from these studies have implications for fertility during aging or disease states.

4-Nonylphenol induces autophagy and attenuates mTOR-p70S6K/4EBP1 signaling by modulating AMPK activation in Sertoli cells

The estrogenic chemical 4-nonylphenol (NP) is known to impair testicular devolopment and spermatogenesis in rodents. The objective of this study was to explore the effects of NP on autophagy induction and AMPK-mTOR signaling pathway in Sertoli cells (SCs), which are the "nursemaid cells" for meiosis of spermatocytes. In this study we exposed 7-week-old male rats to NP by intra-peritoneal injection at 0, 20, 50 or 100mg/kg body weight/2days for 20 consecutive days. Our results showed that exposure to NP dose-dependently induces the formation of autophagosomes in SCs, increases the expression of Beclin-1, the conversion of LC3-I to LC3-II and the mRNA expression of Atg3, Atg5, Atg7 and Atg12 in testis, and these effects are concomitant with the activation of AMPK, and the suppression of TSC2-mTOR-p70S6K/4EBP1 signaling cascade in testis. Furthermore, 10μM Compound C or AMPKα1 siRNA pre-treatment effectively attenuated autophagy and reversed AMPK-mTOR-p70S6K/4EBP1 signaling in NP-treated SCs. Co-treatment with 1mM AICAR remarkably strengthened NP-induced autophagy and mTOR inhibition in SCs. Together, these data suggest that NP stimulates Sertoli cell autophagy and inhibits mTOR-p70S6K/4EBP1 activity through AMPK activation, which is the potential mechanism responsible for the regulation of testis function and differentiation following NP exposure.

Formaldehyde exposure inhibits the expression of mammalian target of rapamycin in rat testis

Formaldehyde (FA), a ubiquitous environmental pollutant, has long been suspected of causing adverse male reproductive effects. However, the molecular and cellular mechanisms underlying this phenomenon remain elusive. The overall aim of this study is to clarify the role of mammalian target of rapamycin (mTOR) in male reproductive injuries induced by FA exposure, by which we can further understand the molecular mechanism of FA male reproductive toxicity. In this study, immunohistochemistry, Western blotting, and reverse transcription polymerase chain reaction analysis were used to detect the expression of mTOR molecule in testicular tissues. We found that FA exposure inhibits the expression of mTOR in a dose-dependent manner. Combined with our earlier finding, we found the decreasing expression of mTOR in testicular tissue were consistent with the changes of testicular structure and autophagy levels. In summary, our data suggested that mTOR molecule might be involved in male reproductive injuries induced by FA exposure.

mTOR Regulates Gap Junction Alpha-1 Protein Trafficking in Sertoli Cells and Is Required for the Maintenance of Spermatogenesis in Mice

The mammalian target of rapamycin (Mtor) gene encodes a serine/threonine kinase that acts as a master regulator of processes as diverse as cell growth, protein synthesis, cytoskeleton reorganization, and cell survival. In the testis, physiological roles for Mtor have been proposed in perinatal Sertoli cell proliferation and blood-testis barrier (BTB) remodeling during spermatogenesis, but no in vivo studies of Mtor function have been reported. Here, we used a conditional knockout approach to target Mtor in Sertoli cells. The resulting Mtor(flox/flox); Amhr2(cre/+) mice were characterized by progressive, adult-onset testicular atrophy associated with disorganization of the seminiferous epithelium, loss of Sertoli cell polarity, increased germ cell apoptosis, premature release of germ cells, decreased epididymal sperm counts, increased sperm abnormalities, and infertility. Histopathologic analysis and quantification of the expression of stage-specific markers showed a specific loss of pachytene spermatocytes and spermatids. Although the BTB and the ectoplasmic specializations did not appear to be altered in Mtor(flox/flox);Amhr2(cre/+) mice, a dramatic redistribution of gap junction alpha-1 (GJA1) was detected in their Sertoli cells. Phosphorylation of GJA1 at Ser373, which is associated with its internalization, was increased in the testes of Mtor(flox/flox); Amhr2(cre/+) mice, as was the expression and phosphorylation of AKT, which phosphorylates GJA1 at this site. Together, these results indicate that Mtor expression in Sertoli cells is required for the maintenance of spermatogenesis and the progression of germ cell development through the pachytene spermatocyte stage. One mechanism of mTOR action may be to regulate gap junction dynamics by inhibiting AKT, thereby decreasing GJA1 phosphorylation and internalization. mTOR regulates gap junction alpha-1 protein distribution in Sertoli cells and is necessary for progression through the pachytene spermatocyte stage.

Copy number analysis of whole-genome data using BIC-seq2 and its application to detection of cancer susceptibility variants

Whole-genome sequencing data allow detection of copy number variation (CNV) at high resolution. However, estimation based on read coverage along the genome suffers from bias due to GC content and other factors. Here, we develop an algorithm called BIC-seq2 that combines normalization of the data at the nucleotide level and Bayesian information criterion-based segmentation to detect both somatic and germline CNVs accurately. Analysis of simulation data showed that this method outperforms existing methods. We apply this algorithm to low coverage whole-genome sequencing data from peripheral blood of nearly a thousand patients across eleven cancer types in The Cancer Genome Atlas (TCGA) to identify cancer-predisposing CNV regions. We confirm known regions and discover new ones including those covering KMT2C, GOLPH3, ERBB2 and PLAG1. Analysis of colorectal cancer genomes in particular reveals novel recurrent CNVs including deletions at two chromatin-remodeling genes RERE and NPM2. This method will be useful to many researchers interested in profiling CNVs from whole-genome sequencing data.

Age-dependent effects in fathead minnows from the anti-diabetic drug metformin

The anti-diabetic drug metformin is thought to be the pharmaceutical most deposited into the aquatic environment by mass at up to 6tons per year from individual WWTPs in urban areas. Recent studies have shown that exposure to 40ug/L of metformin increased the relative expression of the egg yolk precursor protein vitellogenin in adult male fathead minnows (Pimephales promelas) (FHM). For this study, the expression of several other genes involved in estrogen biosynthesis, clearance and downstream effects were assessed in FHM after treatment to three concentrations of metformin, to better understand the estrogenic effects of metformin on FHM. In contrast to the previous study, although upward trends were observed, metformin failed to significantly alter the expression of VTG, ERα, GnRH3, and CYP3A126 in adult male FHM. However, a concentration-dependent response to metformin was observed in younger 80-90day juvenile FHM. A 17.7-, 22-, and 22-fold increase in the relative expression of VTG mRNA in juvenile FHM exposed to 1, 10, and 100μg/L as compared to the control was observed. There was also a 3.3-, 4.7-, and 5.5-fold increase in GnRH3 in juvenile FHM exposed to 1, 10, and 100μg/L as compared to the control. Similarly, a 14-, 16-, and 24-fold increase in the relative expression of CYP3A126 mRNA was measured in juvenile FHM exposed to 1, 10 and 100μg/L metformin as compared to the control. These results indicate that juvenile FHM were more susceptible to the estrogenic effects of metformin during a 7-d exposure than older, sexually mature male FHM.

[AMPK, regulator of sperm energy and functions]

The 5'-AMP-activated protein kinase, AMPK, is a key protein kinase in the metabolism of the cell that regulates many metabolic pathways. The involvement of cell metabolism in sperm ability to fertilize is well established, but only a few studies have focused on the role of AMPK in the control of male fertility. This article summarizes the known role of AMPK in this area. AMPK is involved in the regulation of sperm quality by its action on the proliferation of Sertoli cells. AMPK also directly controls the quality of sperm by its involvement in the regulation of motility and acrosome reaction. It is also involved in the management of lipid peroxidation and gametes antioxidant enzymes. Thus, AMPK appears as a key signaling protein for sperm and male fertility control.

Specific deletion of AMP-activated protein kinase (α1AMPK) in mouse Sertoli cells modifies germ cell quality

The AMP-activated protein kinase (AMPK) is an important regulator of cellular energy homeostasis which plays a role in fertility. Complete disruption of the AMPK catalytic subunit α1 gene (α1AMPK KO) in male mice results in a decrease in litter size which is associated with the production of altered sperm morphology and motility. Because of the importance of Sertoli cells in the formation of germ cells, we have chosen to selectively disrupt α1AMPK only in the Sertoli cells in mice (Sc-α1AMPK-KO mice). Specific deletion of the α1AMPK gene in Sertoli cells resulted in a 25% reduction in male fertility associated with abnormal spermatozoa with a thin head. No clear alterations in testis morphology or modification in the number of Sertoli cells in vivo were observed, but a dysregulation in energy metabolism in Sertoli cells occurred. We have reported an increase in lactate production, in lipid droplets, and a reduction in ATP production in Sc-α1AMPK-KO Sertoli cells. These perturbations were associated with lower expression of mitochondrial markers (cytochrome c and PGC1-α). In addition another metabolic sensor, the deacetylase SIRT1, had a reduction in expression which is correlated with a decline in deacetylase activity. Finally, expression and localization of junctions forming the blood-testis barrier between Sertoli cells themselves and with germ cells were deregulated in Sc-α1AMPK-KO. In conclusion, these results suggest that dysregulation of the energy sensing machinery exclusively through disruption of α1AMPK in Sertoli cells translates to a reduction in the quality of germ cells and fertility.

Targeted Disruption of miR-17-92 Impairs Mouse Spermatogenesis by Activating mTOR Signaling Pathway

The miR-17-92 cluster and its 6 different mature microRNAs, including miR-17, miR-18a, miR-19a, miR-20a, miR-19b-1, and miR-92a, play important roles in embryo development, immune system, kidney and heart development, adipose differentiation, aging, and tumorigenicity. Currently, increasing evidence indicates that some members of miR-17-92 cluster may be critical players in spermatogenesis, including miR-17, miR-18a, and miR-20a. However, the roles and underlying mechanisms of miR-17-92 in spermatogenesis remain largely unknown. Our results showed that the targeted disruption of miR-17-92 in the testes of adult mice resulted in severe testicular atrophy, empty seminiferous tubules, and depressed sperm production. This phenotype is partly because of the reduced number of spermatogonia and spermatogonial stem cells, and the significantly increased germ cell apoptosis in the testes of miR-17-92-deficient mice. In addition, overactivation of the mammalian target of rapamycin signaling pathway and upregulation of the pro-apoptotic protein Bim, Stat3, c-Kit, and Socs3 were also observed in miR-17-92-deficient mouse testes, which might be, at least partially if not all, responsible for the aforementioned phenotypic changes in mutant testes. Taken together, these findings suggest that miR-17-92 is essential for normal spermatogenesis in mice.

Regulation of microtubule (MT)-based cytoskeleton in the seminiferous epithelium during spermatogenesis

In rodents and humans, testicular cells, similar to other mammalian cells, are supported by actin-, microtubule (MT)- and intermediate filament-based cytoskeletons. Although the cytoskeletal network of the testis serves an important role in regulating spermatogenesis during the epithelial cycle, most of the published findings in the literature are limited to studies that only visualize these cytoskeletons in the seminiferous epithelium. Few focus on the underlying molecular mechanism that regulates their organization in the epithelium in response to changes in the stages of the epithelial cycle. Functional studies in the last decade have begun to focus on the role of binding proteins that regulate these cytoskeletons, with some interesting findings rapidly emerging in the field. Since the actin- and intermediate filament-based cytoskeletons have been recently reviewed, herein we focus on the MT-based cytoskeleton for two reasons. First, besides serving as a structural support cytoskeleton, MTs are known to serve as the track to support and facilitate the transport of germ cells, such as preleptotene spermatocytes connected in clones and elongating/elongated spermatids during spermiogenesis, across the blood-testis barrier (BTB) and the adluminal compartment, respectively, during spermatogenesis. While these cellular events are crucial to the completion of spermatogenesis, they have been largely ignored in the past. Second, MT-based cytoskeleton is working in concert with the actin-based cytoskeleton to provide structural support for the transport of intracellular organelles across the cell cytosol, such as endosome-based vesicles, and phagosomes, which contain residual bodies detached from spermatids, to maintain the cellular homeostasis in the seminiferous epithelium. We critically evaluate some recent published findings herein to support a hypothesis regarding the role of MT in conferring germ cell transport in the seminiferous epithelium.

The Rapamycin-Sensitive Complex of Mammalian Target of Rapamycin Is Essential to Maintain Male Fertility

The mammalian target of rapamycin complex 1 (mTORC1) inhibitor rapamycin and its analogs are being increasingly used in solid-organ transplantation. A commonly reported side effect is male subfertility to infertility, yet the precise mechanisms of mTOR interference with male fertility remain obscure. With the use of a conditional mouse genetic approach we demonstrate that deficiency of mTORC1 in the epithelial derivatives of the Wolffian duct is sufficient to cause male infertility. Analysis of spermatozoa from Raptor fl/fl*KspCre mice revealed an overall decreased motility pattern. Both epididymis and seminal vesicles displayed extensive organ regression with increasing age. Histologic and ultrastructural analyses demonstrated increased amounts of destroyed and absorbed spermatozoa in different segments of the epididymis. Mechanistically, genetic and pharmacologic mTORC1 inhibition was associated with an impaired cellular metabolism and a disturbed protein secretion of epididymal epithelial cells. Collectively, our data highlight the role of mTORC1 to preserve the function of the epididymis, ductus deferens, and the seminal vesicles. We thus reveal unexpected new insights into the frequently observed mTORC1 inhibitor side effect of male infertility in transplant recipients.

A survey of DICER1 hotspot mutations in ovarian and testicular sex cord-stromal tumors

Sertoli-Leydig cell tumors are characterized by the presence of somatic DICER1 hotspot mutations. In this study, we sought to define the association between DICER1 hotspot mutations and different morphologic subtypes of ovarian Sertoli-Leydig cell tumors. Furthermore, we aimed to assess whether DICER1 hotspot mutations occur in other ovarian sex cord-stromal tumors, testicular sex cord-stromal tumors, or other female genital tract tumors with rhabdomyosarcomatous differentiation. We subjected a series of ovarian Sertoli-Leydig cell tumors (n=32), Sertoli cell tumors (n=5) and gynandroblastomas (n=5), testicular sex cord-stromal tumors (n=15) and a diverse group of female genital tract tumors with rhabdomyosarcomatous morphology (n=10) to DICER1 hotspot mutation analysis using Sanger sequencing. We also tested two gynandroblastomas for the presence of FOXL2 hotspot mutations (p.C134W; c.402C>G). Twenty of 32 (63%) Sertoli-Leydig cell tumors harbored a DICER1 hotspot mutation, of which 80% had the p.E1705K mutation. No association was found between DICER1 mutation status and the presence of heterologous or retiform differentiation in Sertoli-Leydig cell tumors. DICER1 mutations were found at similar frequencies in gynandroblastoma (2/5; 40%) and ovarian Sertoli cell tumors (5/8; 63%; P>0.1), and all mutated tumors harbored a p.E1705K mutation. DICER1 hotspot mutations were also identified in a single cervical rhabdomyosarcoma and in the rhabdomyosarcomatous component of a uterine carcinosarcoma. No DICER1 mutations were detected in testicular sex cord-stromal tumors. Two DICER1 wild-type gynandroblastomas harbored a p.C134W FOXL2 hotspot mutation in both tumor components. In this study we confirmed that DICER1 hotspot mutations occur in over half of ovarian Sertoli-Leydig cell tumors, and are unrelated to tumor differentiation. We also widened the spectrum of ovarian sex cord-stromal tumors with sertoliform differentiation, in which DICER1 mutations are known to occur, to include Sertoli cell tumors and gynandroblastomas. Our results suggest that DICER1 mutations may not have a role in testicular sex cord-stromal tumorigenesis.

Rictor Regulates Spermatogenesis by Controlling Sertoli Cell Cytoskeletal Organization and Cell Polarity in the Mouse Testis

Maintenance of cell polarity is essential for Sertoli cell and blood-testis barrier (BTB) function and spermatogenesis; however, the signaling mechanisms that regulate the integrity of the cytoskeleton and polarity of Sertoli cells are not fully understood. Here, we demonstrate that rapamycin-insensitive component of target of rapamycin (TOR) (Rictor), a core component of mechanistic TOR complex 2 (mTORC2), was expressed in the seminiferous epithelium during testicular development, and was down-regulated in a cadmium chloride-induced BTB damage model. We then conditionally deleted the Rictor gene in Sertoli cells and mutant mice exhibited azoospermia and were sterile as early as 3 months old. Further study revealed that Rictor may regulate actin organization via both mTORC2-dependent and mTORC2-independent mechanisms, in which the small GTPase, ras-related C3 botulinum toxin substrate 1, and phosphorylation of the actin filament regulatory protein, Paxillin, are involved, respectively. Loss of Rictor in Sertoli cells perturbed actin dynamics and caused microtubule disarrangement, both of which accumulatively disrupted Sertoli cell polarity and BTB integrity, accompanied by testicular developmental defects, spermiogenic arrest and excessive germ cell loss in mutant mice. Together, these findings establish the importance of Rictor/mTORC2 signaling in Sertoli cell function and spermatogenesis through the maintenance of Sertoli cell cytoskeletal dynamics, BTB integrity, and cell polarity.

AMPK: a master energy regulator for gonadal function

From C. elegans to mammals (including humans), nutrition and energy metabolism significantly influence reproduction. At the cellular level, some detectors of energy status indicate whether energy reserves are abundant (obesity), or poor (diet restriction). One of these detectors is AMPK (5′ AMP-activated protein kinase), a protein kinase activated by ATP deficiency but also by several natural substances such as polyphenols or synthetic molecules like metformin, used in the treatment of insulin resistance. AMPK is expressed in muscle and liver, but also in the ovary and testis. This review focuses on the main effects of AMPK identified in gonadal cells. We describe the role of AMPK in gonadal steroidogenesis, in proliferation and survival of somatic gonadal cells and in the maturation of oocytes or spermatozoa. We discuss also the role of AMPK in germ and somatic cell interactions within the cumulus-oocyte complex and in the blood testis barrier. Finally, the interface in the gonad between AMPK and modification of metabolism is reported and discussion about the role of AMPK on fertility, in regards to the treatment of infertility associated with insulin resistance (male obesity, polycystic ovary syndrome).

mTOR is involved in 17β-estradiol-induced, cultured immature boar Sertoli cell proliferation via regulating the expression of SKP2, CCND1, and CCNE1

Mammalian target of rapamycin (mTOR) is known to be involved in mammalian cell proliferation, while S-phase kinase-associated protein 2 (SKP2) plays a vital role in the cell cycle. Within the testis, estrogen also plays an important role in Sertoli cell proliferation, although it is not clear how. The present study asked if mTOR is involved in 17β-estradiol-dependent Sertoli cell proliferation. We specifically assessed if extracellular signal-regulated kinase 1/2 (ERK1/2) and/or phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) exert convergent effects toward the activation of mTOR signaling, and if this signaling regulates the expression of SKP2 through retinoblastoma (RB) and early mitotic inhibitor 1 (EMI1) protein and on CCNE1 and CCND1 mRNA levels. Treatment with 17β-estradiol for 15-90 min activated mTOR, with mTOR phosphorylation peaking after 30 min. U0126 (5 μM), a specific inhibitor of (MEK1/2), and 10-DEBC (2 μM), a selective inhibitor of AKT, both significantly reduced 17β-estradiol-induced phosphorylation of mTOR. Rapamycin suppressed 17β-estradiol-induced Sertoli cell proliferation, appearing to act by reducing the abundance of SKP2, CCND1, and CCNE1 mRNA as well as RB and EMI1 protein. These data indicated that 17β-estradiol enhances Sertoli cell proliferation via mTOR activation, which involves both ERK1/2 and PI3K/AKT signaling. Activated mTOR subsequently increases SKP2 mRNA and protein expression by enhancing the expression of CCND1 and CCNE1, and inhibits SKP2 protein degradation by increasing EMI1 abundance.

Distinct germline progenitor subsets defined through Tsc2-mTORC1 signaling

Adult tissue maintenance is often dependent on resident stem cells; however, the phenotypic and functional heterogeneity existing within this self-renewing population is poorly understood. Here, we define distinct subsets of undifferentiated spermatogonia (spermatogonial progenitor cells; SPCs) by differential response to hyperactivation of mTORC1, a key growth-promoting pathway. We find that conditional deletion of the mTORC1 inhibitor Tsc2 throughout the SPC pool using Vasa-Cre promotes differentiation at the expense of self-renewal and leads to germline degeneration. Surprisingly, Tsc2 ablation within a subset of SPCs using Stra8-Cre did not compromise SPC function. SPC activity also appeared unaffected by Amh-Cre-mediated Tsc2 deletion within somatic cells of the niche. Importantly, we find that differentiation-prone SPCs have elevated mTORC1 activity when compared to SPCs with high self-renewal potential. Moreover, SPCs insensitive to Tsc2 deletion are preferentially associated with mTORC1-active committed progenitor fractions. We therefore delineate SPC subsets based on differential mTORC1 activity and correlated sensitivity to Tsc2 deletion. We propose that mTORC1 is a key regulator of SPC fate and defines phenotypically distinct SPC subpopulations with varying propensities for self-renewal and differentiation.