Control of Sertoli cell metabolism by sex steroid hormones is mediated through modulation in glycolysis-related transporters and enzymes

Molecular insights into Sertoli cell function: how do metabolic disorders in childhood and adolescence affect spermatogonial fate?

Male infertility is a major public health concern globally with unknown etiology in approximately half of cases. The decline in total sperm count over the past four decades and the parallel increase in childhood obesity may suggest an association between these two conditions. Here, we review the molecular mechanisms through which obesity during childhood and adolescence may impair future testicular function. Several mechanisms occurring in obesity can interfere with the delicate metabolic processes taking place at the testicular level during childhood and adolescence, providing the molecular substrate to hypothesize a causal relationship between childhood obesity and the risk of low sperm counts in adulthood.

Low levels of serum LDH are associated with depression and suicide attempts

BACKGROUND

A huge body of evidence has signaled a correlation between adult depression and energy metabolism. The key links are the energy supply and substrates for brain energy metabolism and the crucial signaling molecule lactate. Nevertheless, the association between lactate metabolism and depression remains elusive.

OBJECTIVE

The primary objective of this study was to explore the difference in serum LDH levels between patients with major depressive disorder (MDD) and the normal population and to determine whether LDH can be employed as a predictor of suicide attempt (SA) in MDD patients.

METHODS

Serum LDH levels were measured in 232 patients with MDD and 110 healthy controls. Depressive symptoms were assessed using the 24-item Hamilton Depression Scale (HAMD-24). The data were collected and analyzed with SPSS 22.0.

RESULTS

The serum LDH level of the control group was (196.50 ± 34.40) U/L, while that of the MDD group was (177.94 ± 25.89) U/L (P < 0.001). Notably, the LDH level [(169.96 ± 25.31) U/L] in the SA group was significantly lower than that in the control and non-SA groups [(181.25 ± 25.47) U/L] (P < 0.01); There was no significant correlation with HAMD-24 score (P > 0.05). Collectively, this study demonstrated that a decrease in serum LDH levels is an independent risk factor for SA in MDD patients.

CONCLUSION

Our results imply that a decrease in LDH levels may be associated with MDD and suicidal behaviors. Early identification of suicide risk and evaluation of the prognosis of depression is critical.

TGF-β3 induces lactate production in Sertoli cell through inhibiting Notch pathway

BACKGROUNDS

In the testis, spermatocytes and spermatids rely on lactate produced by Sertoli cells (SCs) as energy source. TGF-β3 is one of the generally accepted paracrine regulatory factors of SC-created blood-testis barrier (BTB), yet its role in SC glycolysis and lactate production still remains unclear.

OBJECTIVES

To investigate the effect of TGF-β3 on glycolysis and lactate production in SCs and determine the role of Lgl2 and Notch signaling activity during this process.

MATERIALS AND METHODS

Primary cultured rat Sertoli cells and TM4 cells were treated with different concentrations of TGF-β3. In some experiments, cells were transfected with siRNA specifically targeting Lgl2 and then treated with TGF-β3 or DAPT. Lactate concentration, glucose and glutamine consumption in the culture medium, activity of PFK, LDH, and Gls, ATP level, oxygen consumption, extracellular acidification and mitochondrial respiration complex activity were detected using commercial kits. The protein level of Lgl2, LDH, MCT4, and activity of Akt, ERK, p38 MAPK, and Notch pathway were detected by Western blot. The stage-specific expression of Jagged1 was examined by immunohistochemistry and qPCR after LCM. Spermatogenesis in rat testis injected with recombinant Jagged1 (re-Jagged1) was observed by HE staining and lactate concentration in testis lysate was measured at different day point after re-Jagged1 treatment.

RESULTS

Significant enhancement of lactate concentration was detected in culture medium of both primary SCs and TM4 cells treated with TGF-β3 at 3 or 5 ng/ml. Besides, other parameters of glycolysis, i.e. glucose and Gln consumption, enzyme activity of PFK, LDH, and Gls, displayed different levels of increment in primary SCs and TM4 cells after TGF-β3 treatment. Mitochondria respiration of SCs was shown to decrease in response to TGF-β3. Lgl2, MCT4, activity of ERK and p38 MAPK were up-regulated, whereas Akt and Notch pathway activity were inhibited by TGF-β3. Silencing of Lgl2 in SCs affected lactate production and attenuated the above effects of TGF-β3 on SC glycolysis except for Gln consumption, Gls activity, and activity of Akt, ERK, and p38. DAPT treatment in SCs antagonized glycolysis suppression caused by Lgl2-silencing. In vivo analysis revealed a stage-specific expression of Jagged1 in contrary with TGF-β3. Activating Notch signaling by re-Jagged1 resulted in restorable hypospermatogenesis and lowered lactate level in rat testis.

CONCLUSION

TGF-β3 induces lactate production in Sertoli cell through upregulating Lgl2, which weakened the Notch signaling activity and intensified glycolysis in SCs. Thus, besides the known function of TGF-β3 as the BTB regulator, TGF-β3-Lgl2-Notch maybe considered as an important pathway controlling Sertoli cell glycolysis and spermatogenesis. This article is protected by copyright. All rights reserved.

Nuclear and Membrane Receptors for Sex Steroids Are Involved in the Regulation of Delta/Serrate/LAG-2 Proteins in Rodent Sertoli Cells

Delta/Serrate/LAG-2 (DSL) proteins, which serve as ligands for Notch receptors, mediate direct cell–cell interactions involved in the determination of cell fate and functioning. The present study aimed to explore the role of androgens and estrogens, and their receptors in the regulation of DSL proteins in Sertoli cells. To this end, primary rat Sertoli cells and TM4 Sertoli cell line were treated with either testosterone or 17β-estradiol and antagonists of their receptors. To confirm the role of particular receptors, knockdown experiments were performed. mRNA and protein expressions of Jagged1 (JAG1), Delta-like1 (DLL1), and Delta-like4 (DLL4) were analyzed using RT-qPCR, Western blot, and immunofluorescence. Testosterone caused downregulation of JAG1 and DLL1 expression, acting through membrane androgen receptor ZRT- and Irt-like protein 9 (ZIP9) or nuclear androgen receptor (AR), respectively. DLL4 was stimulated by testosterone in the manner independent of AR and ZIP9 in Sertoli cells. The expression of all studied DSL proteins was upregulated by 17β-estradiol. Estrogen action on JAG1 and DLL1 was mediated chiefly via estrogen receptor α (ERα), while DLL4 was controlled via estrogen receptor β (ERβ) and membrane G-protein-coupled estrogen receptor (GPER). To summarize, the co-operation of nuclear and membrane receptors for sex steroids controls DSL proteins in Sertoli cells, contributing to balanced Notch signaling activity in seminiferous epithelium.

What Does Androgen Receptor Signaling Pathway in Sertoli Cells During Normal Spermatogenesis Tell Us?

Androgen receptor signaling pathway is necessary to complete spermatogenesis in testes. Difference between androgen binding location in Sertoli cell classifies androgen receptor signaling pathway into classical signaling pathway and non-classical signaling pathway. As the only somatic cell type in seminiferous tubule, Sertoli cells are under androgen receptor signaling pathway regulation via androgen receptor located in cytoplasm and plasma membrane. Androgen receptor signaling pathway is able to regulate biological processes in Sertoli cells as well as germ cells surrounded between Sertoli cells. Our review will summarize the major discoveries of androgen receptor signaling pathway in Sertoli cells and the paracrine action on germ cells. Androgen receptor signaling pathway regulates Sertoli cell proliferation and maturation, as well as maintain the integrity of blood-testis barrier formed between Sertoli cells. Also, Spermatogonia stem cells achieve a balance between self-renewal and differentiation under androgen receptor signaling regulation. Meiotic and post-meiotic processes including Sertoli cell - Spermatid attachment and Spermatid development are guaranteed by androgen receptor signaling until the final sperm release. This review also includes one disease related to androgen receptor signaling dysfunction named as androgen insensitivity syndrome. As a step further ahead, this review may be conducive to develop therapies which can cure impaired androgen receptor signaling in Sertoli cells.

Inherited Metabolic Memory of High-fat Diet Impairs Testicular Fatty Acid Content and Sperm Parameters

Exposure to a high-fat diet (HFD) from early-life is associated with a testicular metabolic signature linked to abnormal sperm parameters up to two generations after exposure in mice. Hereby, we describe a testicular lipid signature associated with "inherited metabolic memory" of exposure to HFD, persisting up to two generations in mice. Diet-challenged mice (n = 36) were randomly fed after weaning with standard chow (CTRL); HFD for 200 days or transient HFD (HFD_t ) (60 days of HFD+140 days of standard chow). Subsequent generations (36 mice per generation) were fed with chow diet. Mice were euthanized 200 days post-weaning. Glucose homeostasis, serum hormones, testicular bioenergetics and antioxidant enzyme activity were evaluated. Testicular lipid-related metabolites and fatty acids were characterized by ¹ H-NMR and GC-MS. Sons of HFD display impaired choline metabolism, mitochondrial activity and antioxidant defenses, while grandsons show a shift in testicular ω3/ω6 ratio towards a pro-inflammatory environment. Grandsons of HFDt raise 3-hydroxybutyrate levels with possible implications to testicular insulin resistance. Sperm counts decrease in grandsons of HFD-exposed mice, regardless of the duration of exposure. HFD-induced "inherited metabolic memory" alters testicular fatty acid metabolism with consequences to sperm parameters up to two generations. This article is protected by copyright. All rights reserved.

PGAM1 regulates the glycolytic metabolism of SCs in tibetan sheep and its influence on the development of SCs

This study was to explore the regulation effect of PGAM1 on the proliferation, apoptosis and glycolysis pathway of Tibetan sheep Sertoli cells. In this paper, the reproductive organs of male Tibetan sheep before pre-puberty (3 months old), sexual maturity (1 year old) and adult (3 years old) were used as experimental materials. The complete CDS region sequence of PGAM1 gene was cloned for bioinformatics analysis, and had the closest relationship with Tibetan antelope. QRT-PCR, Western blot and immunohistochemical staining were used to detect the expression and localization of PGAM1 in the testis and epididymis tissues of Tibetan sheep at different growth and development stages at the transcription and translation levels. Then the Tibetan sheep primary Sertoli cells (SCs) were isolated to construct PGAM1 gene overexpression and interference vectors, and to transfect primary SCs so as to promote and inhibit PGAM1 gene expression; CCK-8 and flow cytometry were used to detect the proliferation effect of SCs;qRT-PCR technology was employed to detect the changes in the expression of genes related to cell proliferation and apoptosis. Different kits were used to detect pyruvate, lactic acid, ATP production and LDH activity during glycolysis, and to detect the changes in the expression of downstream genes in the glycolysis pathway. The results showed that the CDS region of Tibetan sheep PGAM1 gene was 765 bp in length, which can encode 254 amino acids; and the expression of PGAM1 protein in the testis and epididymis increased at 1Y group and 3Ygroup compared with 3 M group, and that the PGAM1 protein mainly existed in SCs and Leydig cells at different developmental stages. CCK-8 and flow cytometry test results found that compared with the empty vector group (pcDNA3.1(+)), the proliferation rate of the PGAM1 gene overexpression group (pcDNA3.1(+)-PGAM1) decreased. The mRNA expression of the cell proliferation related genes PCNA and Bcl2 was significantly decreased (P < 0.05), and the expression of apoptosis-related genes Bax and caspase3 was significantly increased (P < 0.05). The expression of downstream genes in the glycolysis pathway was significant increased (P < 0.05), pyruvate content, ATP content, lactic acid production and LDH activity increased significantly (P < 0.05). Compared with the interference control group (NC), the proliferation rate of the PGAM1 gene interference group (si-PGAM1) was weakened. The mRNA expression of the cell proliferation-related genes PCNA and Bcl2 was significantly increased (P < 0.05), and the expression of cell apoptosis related genes Bax and caspase3 was significantly decreased (P < 0.05). The expression of downstream genes in the glycolysis pathway was significantly reduced (P < 0.05), and the pyruvate content, ATP content, lactic acid production and LDH activity were significantly decreased (P < 0.05). The PGAM1 gene might regulate the glycolytic metabolism pathway and regulate the sperm formation and maturation process by affecting the proliferation and apoptosis of SCs. This result provides basic data for the study of the function of PGAM1 in sheep testicular development.

Impacts of Immunometabolism on Male Reproduction

The physiological process of male reproduction relies on the orchestration of neuroendocrine, immune, and energy metabolism. Spermatogenesis is controlled by the hypothalamic-pituitary-testicular (HPT) axis, which modulates the production of gonadal steroid hormones in the testes. The immune cells and cytokines in testes provide a protective microenvironment for the development and maturation of germ cells. The metabolic cellular responses and processes in testes provide energy production and biosynthetic precursors to regulate germ cell development and control testicular immunity and inflammation. The metabolism of immune cells is crucial for both inflammatory and anti-inflammatory responses, which supposes to affect the spermatogenesis in testes. In this review, the role of immunometabolism in male reproduction will be highlighted. Obesity, metabolic dysfunction, such as type 2 diabetes mellitus, are well documented to impact male fertility; thus, their impacts on the immune cells distributed in testes will also be discussed. Finally, the potential significance of the medicine targeting the specific metabolic intermediates or immune metabolism checkpoints to improve male reproduction will also be reassessed.

Sex hormones regulate lipid metabolism in adult Sertoli cells: A genome-wide study of estrogen and androgen receptor binding sites

Optimal functioning of Sertoli cells is crucial for spermatogenesis which is under tight regulation of sex hormones, estrogen and androgen. Adult rat Sertoli cells expresses estrogen receptor beta (ERβ) and androgen receptor (AR), both of which regulate gene transcription by binding to the DNA. The present study is aimed to acquire a genome-wide map of estrogen- and androgen-regulated genes in adult Sertoli cells. ChIP-Seq was performed for ERβ and AR in Sertoli cells under physiological conditions. 30,859 peaks in ERβ and 9,594 peaks in AR were identified with a fold enrichment >2 fold. Pathway analysis for the genes revealed metabolic pathways to be significantly enriched. Since Sertoli cells have supportive functions and provide energy substrates to germ cells during spermatogenesis, significantly enriched metabolic pathways were explored further. Peaks of the genes involved in lipid metabolism, like fatty acid, glyceride, leucine, and sphingosine metabolism were validated. Motif analysis confirmed the presence of estrogen- and androgen-response elements (EREs and AREs). Moreover, transcript levels of enzymes involved in the lipid metabolic pathways were significantly altered in cultured Sertoli cells treated with estrogen and androgen receptor agonists, demonstrating functional significance of these binding sites. This study elucidates a mechanism by which sex hormones regulate lipid metabolism in Sertoli cells by transcriptionally controlling the expression of these genes, thereby shedding light on the roles of these hormones in male fertility.

The Molecular Mechanism of Sex Hormones on Sertoli Cell Development and Proliferation

Sustaining and maintaining the intricate process of spermatogenesis is liable upon hormones and growth factors acting through endocrine and paracrine pathways. The Sertoli cells (SCs) are the major somatic cells present in the seminiferous tubules and are considered to be the main regulators of spermatogenesis. As each Sertoli cell supports a specific number of germ cells, thus, the final number of Sertoli cells determines the sperm production capacity. Similarly, sex hormones are also major regulators of spermatogenesis and they can determine the proliferation of Sertoli cells. In the present review, we have critically and comprehensively discussed the role of sex hormones and some other factors that are involved in Sertoli cell proliferation, differentiation and maturation. Furthermore, we have also presented a model of Sertoli cell development based upon the recent advancement in the field of reproduction. Hence, our review article provides a general overview regarding the sex hormonal pathways governing Sertoli cell proliferation and development.

Monocarboxylate Transporters (SLC16): Function, Regulation, and Role in Health and Disease

The solute carrier family 16 (SLC16) is comprised of 14 members of the monocarboxylate transporter (MCT) family that play an essential role in the transport of important cell nutrients and for cellular metabolism and pH regulation. MCTs 1-4 have been extensively studied and are involved in the proton-dependent transport of L-lactate, pyruvate, short-chain fatty acids, and monocarboxylate drugs in a wide variety of tissues. MCTs 1 and 4 are overexpressed in a number of cancers, and current investigations have focused on transporter inhibition as a novel therapeutic strategy in cancers. MCT1 has also been used in strategies aimed at enhancing drug absorption due to its high expression in the intestine. Other MCT isoforms are less well characterized, but ongoing studies indicate that MCT6 transports xenobiotics such as bumetanide, nateglinide, and probenecid, whereas MCT7 has been characterized as a transporter of ketone bodies. MCT8 and MCT10 transport thyroid hormones, and recently, MCT9 has been characterized as a carnitine efflux transporter and MCT12 as a creatine transporter. Expressed at the blood brain barrier, MCT8 mutations have been associated with an X-linked intellectual disability, known as Allan-Herndon-Dudley syndrome. Many MCT isoforms are associated with hormone, lipid, and glucose homeostasis, and recent research has focused on their potential roles in disease, with MCTs representing promising novel therapeutic targets. This review will provide a summary of the current literature focusing on the characterization, function, and regulation of the MCT family isoforms and on their roles in drug disposition and in health and disease. SIGNIFICANCE STATEMENT: The 14-member solute carrier family 16 of monocarboxylate transporters (MCTs) plays a fundamental role in maintaining intracellular concentrations of a broad range of important endogenous molecules in health and disease. MCTs 1, 2, and 4 (L-lactate transporters) are overexpressed in cancers and represent a novel therapeutic target in cancer. Recent studies have highlighted the importance of MCTs in glucose, lipid, and hormone homeostasis, including MCT8 in thyroid hormone brain uptake, MCT12 in carnitine transport, and MCT11 in type 2 diabetes.

Down regulating PHGDH affects the lactate production of sertoli cells in varicocele

BACKGROUND

Although varicocele is considered to be one of the leading causes of male infertility, the precise mechanism underlying how varicocele leads to male infertility is not completely understood. We found the lactate concentration on the varicocele side of the patients was decreased compare with peripheral venous blood. In the testicles, the lactate produced by the sertoli cells through the glycolysis pathway provides most of the energy needed for spermatogenesis, the reduction of lactate will affect spermatogenesis. The objective of this study was to investigate the mechanism of this abnormal energy metabolism phenomenon in varicocele.

METHODS

In this study, we collected the testicular tissue from patients with varicocele, the glycolysis related proteins PHGDH was identified by iTRAQ proteomics technology. Experimental rat varicocele model was constructed according to our new clip technique, the mRNA and protein expression levels of PHGDH were examined with qRT-PCR and Western blotting. We constructed a sertoli cell of PHGDH down-regulation model, and then detected the glucose consumption, LDH activities and lactate production in the sertoli cells. Western blot was conducted to investigate the effects of PHGDH on the expression of phosphoserine phosphatase (PSPH) and Pyruvate kinase M2 (PKM2). Flow cytometry was used to detect the cell apoptosis and cell cycle in sertoli cells.

RESULTS

The results showed that testicular protein PHGDH was down-regulated in patients with varicocele and in experimental rat varicocele model. Down-regulation of PHGDH in sertoli cells significantly decreased the glucose consumption, LDH activities and lactate production in the sertoli cells, indicating that the low expression of PHGDH ultimately led to a decrease in lactate production by affecting the glycolysis. The Western blot results showed that the down-regulation of PHGDH significantly reduced the expression of pathway protein PSPH and PKM2, leading to the reduction of lactate production. Moreover, PHGDH knockdown can promote apoptosis and inhibit cell cycle to affect cell growth.

CONCLUSIONS

Overall, we conformed that varicocele lead to the decreasing of testis lactate production. Down-regulation of PHGDH in sertoli cells may mediate the process of abnormal glucose metabolism. Our study provide new insight into the mechanisms underlying metabolism-associated male infertility and suggests a novel therapeutic target for male infertility.

Role of pyroglutamylated RFamide peptide43 in germ cell dynamics in mice testes in relation to energy metabolism

QRFP is a neuropeptide that regulates glucose homeostasis and increases insulin sensitivity in tissues. We have previously shown that QRFP and its receptor (GPR103) are predominantly expressed in germ cells and Sertoli cells, respectively, in mice testes. In the present study, we report that QRFP caused an increase in PCNA and a decrease in p27Kip1 expressions in the testis under both in vivo and ex vivo conditions. Besides, via an in vivo study, cell cycle analysis by FACS showed an increase in 2C cells and a decrease in 1C cells. QRFP also induced expression of GDNF and phosphorylation of Akt and ERK-1/2. Together these results suggest that QRFP has a proliferative effect on germ cells in mice testes, since it caused a proportional increase in the mitotic activity and the number of spermatogonial cells. Further, observations of increased expressions of STAT-3 and Neurog3 in treated mice suggest that QRFP treatment regulates priming of undifferentiated spermatogonia to undergo differentiation, while a decrease in c-Kit expression indicate that spermatogonia at this time point are in an undifferentiated state. In addition, QRFP administration also caused an increase in intratesticular levels of glucose and lactate, and in LDH activity accompanied by increased expressions of GLUT-3 and LDH-C in the testis. Also, the phosphorylation of IR-β and expressions of p-Akt and p-mTOR were increased under ex vivo conditions in testicular tissue. In conclusion, our findings suggest that QRFP treatment caused proliferation of germ cells independently from the hypothalamic-pituitary axis via regulation of testicular energy metabolism.

Effect of clomiphene citrate treatment on the Sertoli cells of dysmetabolic obese men with low testosterone levels

BACKGROUND

Clomiphene citrate (CC) has been shown to restore the hypothalamic-pituitary-gonadal (HPG) axis by increasing testosterone (T) levels to physiological levels in patients with dysmetabolic conditions such as obesity, metabolic syndrome and type 2 diabetes mellitus (T2DM). However, the data are unclear regarding the effects on Sertoli cell (SC) function.

AIM

To study SC function by assessing Inhibin B (IB) and anti-Mullerian hormone (AMH) levels at baseline and after 3 months of CC treatment.

MATERIALS AND METHODS

This is an ancillary study of a cross-over, randomised, double-blind, placebo-controlled trial performed to evaluate androgen response to CC treatment in dysmetabolic obese subjects with low T levels treated with metformin. We evaluated SC function by assessing IB and AMH levels at baseline and after 3 months of each treatment in ten dysmetabolic obese subjects with low T levels. In all subjects, the influence of the clinical characteristics, metabolic and hormonal baseline parameters on SC and Leydig (LC) function, evaluated respectively with AMH, IB, follicle-stimulating hormone (FSH) and T levels, was tested.

RESULTS

No significant changes were observed for IB and AMH concentrations after each treatment period. Whereas T and oestradiol (E2) levels were shown to be significantly higher in the CC plus metformin phase (CC/Met) only. No clinical, metabolic or hormonal parameters showed significant effects on serum AMH at baseline or after treatments. However, baseline T, dihydrotestosterone (DHT) and E2 positively affected IB levels during CC/Met therapy (P = .003, P = .038 and P = .049, respectively). Baseline leptin and FSH had a negative (P = 031) and positive (P = .048) respectively role on T levels during CC/Met, as they were statistically significant compared to the placebo period (Plac/Met).

CONCLUSION

Unlike the LC activity, CC was unable to influence SC function, as shown by the lack of IB and AMH serum modifications, thus suggesting an intrinsic nonreversible defect of SC cells in patients with dysmetabolic conditions.

Exogenous oestradiol benzoate induces male mice azoospermia through modulation of oxidative stress and testicular metabolic cooperation

In most cases, exogenous oestradiol benzoate (EB) inhibits spermatogenesis, however, the mechanism underlying this process has not been fully elucidated. The present study investigated the effect of EB on redox equilibrium and glycometabolism in mouse testes. Male Kunming mice were divided into 3 groups and injected with 0, 5 and 10 mg/kg EB, respectively. Histological analysis revealed no sperm and far fewer spermatogenic cells in the testes of EB‑treated mice. Additionally, transmission electron microscopy revealed that mitochondria in Sertoli cells were transformed to vacuoles with irregular cristae in the EB‑treated group. EB also significantly decreased the activities and mRNA expression of catalase, superoxide dismutase, and glutathione peroxidase and increased the activity of nitric oxide synthase and nitric oxide concentration in the testes compared with the control. These results indicated that oxidative damage was caused by EB treatment. With regard to glycometabolism, ATP content and activities of hexokinase and pyruvate kinase were significantly reduced in the EB‑treated group. Although glucose and pyruvate concentrations were significantly increased by EB treatment, levels of lactate, the main energy source of spermatogenic cells, were unchanged. Monocarboxylate transporter 2 (MCT2) and MCT4, which are responsible for lactate transportation, were downregulated by EB. In conclusion, the results of the present study indicated that azoospermia induced by EB in male mice was associated with oxidative damage and the disorder of testicular metabolic cooperation.

The hypothalamic neuropeptide orexin A- a possible regulator in glucose homeostasis and germ cell kinetics in adult mice testes

Orexin A (OXA), a hypothalamic neuropeptide, regulates food intake, sleep-wake cycle and energy balance by binding to its receptor (OX1R). Apart from brain, OXA and OX1R are also present in peripheral organs including reproductive tissues. Mammalian reproduction depends on uptake and proper utilization of glucose in the testes. This study, therefore, examined role of OXA/OX1R system in regulation of glucose homeostasis in adult mouse testis under in vivo and ex vivo conditions. Binding of OXA to OX1R was blocked using an OX1R antagonist, SB-334867. Mice were given a single bilateral intratesticular injection of the antagonist at doses of 4 and 12μg/mouse and sacrificed 24 h post-injection. In order to understand the direct role of OXA in testes of adult mice, an ex vivo experiment was performed where binding of OXA to OX1R in the testis was blocked by using the same OX1R antagonist. The antagonist treatment affected testicular glucose and lactate concentration with concomitant down-regulation in the expression of glucose transporters 3 and 8. A decreased activity in lactate dehydrogenase enzyme and imbalance between germ cell survival and proliferation were also noted in testes in treated mice. The results of ex vivo study supported the results obtained from in vivo study. The findings thus suggest involvement of OXA/OX1R system in regulation of testicular glucose homeostasis and germ cell kinetics in adult mice.

Molecular Mechanisms and Signaling Pathways Involved in the Nutritional Support of Spermatogenesis by Sertoli Cells

Sertoli cells play a central role in spermatogenesis. They maintain the blood-testis barrier, an essential feature of seminiferous tubules which creates the proper environment for the occurrence of the spermatogenesis. However, this confinement renders germ cells almost exclusively dependent on Sertoli cells' nursing function and support. Throughout spermatogenesis, differentiating sperm cells become more specialized, and their biochemical machinery is insufficient to meet their metabolic demands. Although the needs are not the same at all differentiation stages, Sertoli cells are able to satisfy their needs. In order to maintain the seminiferous tubule energetic homeostasis, Sertoli cells react in response to several metabolic stimuli, through signaling cascades. The AMP-activated kinase, sensitive to the global energetic status; the hypoxia-inducible factors, sensitive to oxygen concentration; and the peroxisome proliferator-activated receptors, sensitive to fatty acid availability, are pathways already described in Sertoli cells. These cells' metabolism also reflects the whole-body metabolic dynamics. Metabolic diseases, including obesity and type II diabetes mellitus, induce changes that, both directly and indirectly, affect Sertoli cell function and, ultimately, (dys)function in male reproductive health. Insulin resistance, increased estrogen synthesis, vascular disease, and pubic fat accumulation are examples of metabolic-related conditions that affect male fertility potential. On the other hand, malnutrition can also induce negative effects on male sexual function. In this chapter, we review the molecular mechanisms associated with the nutritional state and male sexual (dys)function and the central role played by the Sertoli cells.

Direct regulation of genes involved in sperm release by estrogen and androgen through their receptors and coregulators

Steroid hormones, estrogen and androgen, control transcription in various reproductive and non-reproductive tissues. Both hormones are known to be important for control of sperm release from the seminiferous epithelium (spermiation), a process characterized by extensive remodeling of actin filaments and endocytosis. Earlier studies with an estrogen (E2)-induced rat model of spermiation failure revealed genes involved in actin remodeling (Arpc1b and Evl) and endocytosis (Picalm, Eea1, and Stx5a) to be differentially regulated. Further, among these genes, Arpc1b and Evl were found to be estrogen-responsive whereas Eea1 and Stx5a were androgen-responsive and Picalm was responsive to both hormones in seminiferous tubule cultures. Yet, the mechanism by which these genes are regulated by estrogen and androgen in the testis was unclear. Here, we report the presence of a functional estrogen response element (ERE) upstream of Arpc1b and Evl genes and androgen response element (ARE) upstream of Picalm, Eea1, and Stx5a genes. Chromatin immunoprecipitation in control versus E2-treated testes revealed significant changes in estrogen receptor beta (ERβ) recruitment along with coregulators to the EREs upstream of Arpc1b and Evl genes and androgen receptor (AR) at AREs upstream of Picalm, Eea1, and Stx5a genes. Enrichment patterns of these EREs/AREs with coregulators, activating and repressing histone modifications along with RNA polymerase II recruitment, correlated with the observed expression patterns of these genes upon E2 treatment. Taken together, our results reveal direct targets of estrogen and androgen in the testes and provide insights into transcriptional control of sperm release by the two steroid hormones.

Neonatal hypothyroidism affects testicular glucose homeostasis through increased oxidative stress in prepubertal mice: effects on GLUT3, GLUT8 and Cx43

Thyroid hormones (THs) play an important role in maintaining the link between metabolism and reproduction and the altered THs status is associated with induction of oxidative stress in various organs like brain, heart, liver and testis. Further, reactive oxygen species play a pivotal role in regulation of glucose homeostasis in several organs, and glucose utilization by Leydig cells is essential for testosterone biosynthesis and thus is largely dependent on glucose transporter 8 (GLUT8). Glucose uptake by Sertoli cells is mediated through glucose transporter 3 (GLUT3) under the influence of THs to meet energy requirement of developing germ cells. THs also modulate level of gap junctional protein such as connexin 43 (Cx43), a potential regulator of cell proliferation and apoptosis in the seminiferous epithelium. Although the role of transient neonatal hypothyroidism in adult testis in terms of testosterone production is well documented, the effect of THs deficiency in early developmental period and its role in testicular glucose homeostasis and oxidative stress with reference to Cx43 in immature mice remain unknown. Therefore, the present study was conducted to evaluate the effect of neonatal hypothyroidism on testicular glucose homeostasis and oxidative stress at postnatal days (PND) 21 and 28 in relation to GLUT3, GLUT8 and Cx43. Hypothyroidism induced by 6-propyl-2-thiouracil (PTU) markedly decreased testicular glucose level with considerable reduction in expression level of GLUT3 and GLUT8. Likewise, lactate dehydrogenase (LDH) activity and intratesticular concentration of lactate were also decreased in hypothyroid mice. There was also a rise in germ cell apoptosis with increased expression of caspase-3 in PTU-treated mice. Further, neonatal hypothyroidism affected germ cell proliferation with decreased expression of proliferating cell nuclear antigen (PCNA) and Cx43. In conclusion, our results suggest that neonatal hypothyroidism alters testicular glucose homeostasis via increased oxidative stress in prepubertal mice, thereby affecting germ cell survival and proliferation.

Testis Transcriptome Modulation in Klinefelter Patients with Hypospermatogenesis

The main genetic cause of male infertility is represented by the Klinefelter Syndrome (KS), a condition accounting for 3% of all cases of infertility and up to15% of cases of azoospermia. KS is generally characterized by azoospermia; approximately 10% of cases have severe oligozoospermia. Among these, the 30-40% of patients show hypospermatogenesis. The mechanisms leading to adult testis dysfunctions are not completely understood. A microarray transcriptome analysis was performed on testis biopsies obtained from three KS patients with hypospermatogenesis and three control subjects. KS testis showed a differential up- and down-regulation of 303 and 747 transcripts, respectively, as compared to controls. The majority of down-regulated transcripts were involved in spermiogenesis failure and testis morphological defects, whereas up-regulated genes were responsible for testis apoptotic processes. Functional analysis of the transcriptionally altered genes indicated a deregulation in cell death, germ cell function and morphology as well as blood-testis-barrier maintenance and Leydig cells activity. These data support a complex scenario in which spermatogenic impairment is the result of functional and morphological alterations in both germinal and somatic components of KS testis. These findings could represent the basis for evaluating new markers of KS spermatogenesis and potential targets of therapeutic intervention to preserve residual spermatogenesis.

Effects of Elevated β-Estradiol Levels on the Functional Morphology of the Testis - New Insights

Elevated estradiol levels are correlated with male infertility. Causes of hyperestrogenism include diseases of the adrenal cortex, testis or medications affecting the hypothalamus-pituitary-gonadal axis. The aim of our study was to elucidate the effects of estradiol treatment on testicular cellular morphology and function, with reference to the treatment regimen received. Testes samples (n = 9) were obtained post-orchiectomy from male-to-female transsexuals within the age range of 26–52 years. Each patient had a minimum of 1–6 years estradiol treatment. For comparison, additional samples were obtained from microscopically unaltered testicular tissue surrounding tumors (n = 7). The tissues obtained were investigated by stereomicroscopy, histochemistry, scanning electron microscopy (SEM) and immunohistochemistry. Our studies revealed that estradiol treatment significantly decreased the diameter of the seminiferous tubules (p < 0.05) and induced fatty degeneration in the surrounding connective tissue. An increase in collagen fiber synthesis in the extracellular matrix (ECM) surrounding the seminiferous tubules was also induced. Spermatogenesis was impaired resulting in mainly spermatogonia being present. Sertoli cells revealed diminished expression of estrogen receptor alpha (ERα). Both Sertoli and Leydig cells showed morphological alterations and glycoprotein accumulations. These results demonstrate that increased estradiol levels drastically impact the human testis.

Ghrelin acts as energy status sensor of male reproduction by modulating Sertoli cells glycolytic metabolism and mitochondrial bioenergetics

Ghrelin is a growth hormone-releasing peptide that has been suggested to interfere with spermatogenesis, though the underling mechanisms remain unknown. We studied the effect of ghrelin in human Sertoli cells (hSCs) metabolic phenotype. For that, hSCs were exposed to increasing concentrations of ghrelin (20, 100 and 500 pM) mimicking the levels reported in obese, normal weight, and severely undernourished individuals. The metabolite production/consumption was determined. The protein levels of key glycolysis-related transporters and enzymes were assessed. The lactate dehydrogenase (LDH) activity was measured. Mitochondrial complexes protein levels and mitochondria membrane potential were also measured. We showed that hSCs express the growth hormone secretagogue receptor. At the concentration present in the plasma of normal weight men, ghrelin caused a decrease of glucose consumption and mitochondrial membrane potential in hSCs, though LDH activity and lactate production remained unchanged, illustrating an alteration of glycolytic flux efficiency. Exposure of hSCs to levels of ghrelin found in the plasma of severely undernourished individuals decreased pyruvate consumption and mitochondrial complex III protein expression. All concentrations of ghrelin decreased alanine and acetate production by hSCs. Notably, the effects of ghrelin levels found in severely undernourished individuals were more pronounced in hSCs metabolic phenotype highlighting the importance of a proper eating behavior to maintain male reproductive potential. In conclusion, ghrelin acts as an energy status sensor for hSCs in a dose-dependent manner, showing an inverse association with the production of lactate, thus controlling the nutritional support of spermatogenesis.

Adjudin--A Male Contraceptive with Other Biological Activities

BACKGROUND

Adjudin has been explored as a male contraceptive for the last 15 years since its initial synthesis in the late 1990s. More than 50 papers have been published and listed in PubMed in which its mechanism that induces exfoliation of germ cells from the seminiferous epithelium, such as its effects on actin microfilaments at the apical ES (ectoplasmic specialization, a testis-specific actin-rich anchoring junction) has been delineated.

OBJECTIVE

Recent studies have demonstrated that, besides its activity to induce germ cell exfoliation from the seminiferous epithelium to cause reversible infertility in male rodents, adjudin possesses other biological activities, which include anti-cancer, anti-inflammation in the brain, and anti-ototoxicity induced by gentamicin in rodents. Results of these findings likely spark the interest of investigators to explore other medical use of this and other indazole-based compounds, possibly mediated by the signaling pathway(s) in the mitochondria of mammalian cells following treatment with adjudin. In this review, we carefully evaluate these recent findings.

METHODS

Papers published and listed at www.pubmed.org and patents pertinent to adjudin and its related compounds were searched. Findings were reviewed and critically evaluated, and summarized herein.

RESULTS

Adjudin is a novel compound that possesses anti-spermatogenetic activity. Furthermore, it possesses anti-cancer, anti-inflammation, anti-neurodegeneration, and anti-ototoxicity activities based on studies using different in vitro and in vivo models.

CONCLUSION

Studies on adjudin should be expanded to better understand its biological activities so that it can become a useful drug for treatment of other ailments besides serving as a male contraceptive.

Accumulation of Palmitoylcarnitine and Its Effect on Pro-Inflammatory Pathways and Calcium Influx in Prostate Cancer

BACKGROUND

Acylcarnitines are intermediates of fatty acid oxidation and accumulate as a consequence of the metabolic dysfunction resulting from the insufficient integration between β-oxidation and the tricarboxylic acid (TCA) cycle. The aim of this study was to investigate whether acylcarnitines accumulate in prostate cancer tissue, and whether their biological actions could be similar to those of dihydrotestosterone (DHT), a structurally related compound associated with cancer development.

METHODS

Levels of palmitoylcarnitine (palcar), a C16:00 acylcarnitine, were measured in prostate tissue using LC-MS/MS. The effect of palcar on inflammatory cytokines and calcium (Ca(2+) ) influx was investigated in in vitro models of prostate cancer.

RESULTS

We observed a significantly higher level of palcar in prostate cancerous tissue compared to benign tissue. High levels of palcar have been associated with increased gene expression and secretion of the pro-inflammatory cytokine IL-6 in cancerous PC3 cells, compared to normal PNT1A cells. Furthermore, we found that high levels of palcar induced a rapid Ca(2+) influx in PC3 cells, but not in DU145, BPH-1, or PNT1A cells. This pattern of Ca(2+) influx was also observed in response to DHT. Through the use of whole genome arrays we demonstrated that PNT1A cells exposed to palcar or DHT have a similar biological response.

CONCLUSIONS

This study suggests that palcar might act as a potential mediator for prostate cancer progression through its effect on (i) pro-inflammatory pathways, (ii) Ca(2+) influx, and (iii) DHT-like effects. Further studies need to be undertaken to explore whether this class of compounds has different biological functions at physiological and pathological levels. Prostate 76:1326-1337, 2016. © 2016 The Authors. The Prostate published by Wiley Periodicals, Inc.

2-hydroxyoestradiol and 2-methoxyoestradiol, two endogenous oestradiol metabolites, induce DNA fragmentation in Sertoli cells

Elevated intratesticular levels of hydroxyoestradiols and methoxyoestradiols, two classes of endogenous oestradiol metabolites, have been associated with male infertility. The aim of this study was to explore the effects of 2-hydroxyoestradiol (2OHE₂ ), 4-hydroxyoestradiol (4OHE₂ ), 2-methoxyoestradiol (2ME₂ ) and 4-methoxyoestradiol (4ME₂ ) on Sertoli cell viability. For this, TM4 cells were incubated with different concentrations of these metabolites for 24 h to then evaluate the viability and DNA integrity by MTS and TUNEL assay respectively. The participation of classical oestrogen receptors and the involvement of oxidative stress and apoptotic mechanisms were also evaluated co-incubating TM4 cells with these estradiol metabolites and with the drugs ICI182780, N-acetylcysteine and Z-VAD-FMK respectively. Only high concentrations of 2OHE₂ and 2ME₂ decreased cell viability inducing DNA fragmentation. In addition, ICI182780 did not block the effect of 2OHE₂ and 2ME₂ , while N-Acetylcysteine and Z-VAD-FMK only blocked the effect of 2OHE₂ . Moreover, 2OHE₂ but not 2ME₂ induced PARP and caspase-3 cleavage. Finally, lower 2OHE₂ and 2ME₂ concentrations (0.01-0.1-1.0 μmol l^-1 ) decreased Sertoli cell viability 48 h post-treatment. Our results support the hypothesis that elevated intratesticular 2OHE₂ or 2ME₂ concentrations could be related to male infertility since 2OHE₂ by apoptosis and 2ME₂ by undetermined mechanisms induce DNA fragmentation in Sertoli cells.

Testicular lactate content is compromised in men with Klinefelter Syndrome

Klinefelter syndrome (KS) is the most common genetic cause of human infertility, but the mechanism(s) responsible for its phenotype remain largely unknown. KS is associated with alterations in body composition and with a higher risk of developing metabolic diseases. We therefore hypothesized that KS men seeking fertility treatment possess an altered testicular metabolism profile that may hamper the nutritional support of spermatogenesis. Testicular biopsies from control (46, XY) (n = 6) and KS (47, XXY) (n = 6) individuals were collected and analyzed by proton high-resolution magic-angle spinning nuclear magnetic resonance spectroscopy. The mRNA and protein expression of crucial glycolysis-associated enzymes and transporters were evaluated in parallel by quantitative PCR and Western blot, respectively. Our data revealed altered regulation of glucose transporters (GLUT1 and GLUT3); phosphofructokinase 1, liver isoform (PFKL); and lactate dehydrogenase A (LDHA) expression in the testis of KS patients. Moreover, we detected a severe reduction in lactate and creatine accumulation within testicular tissue from KS men. The aberrant levels of the biomarkers detected in testicular biopsies of KS men may therefore be associated with the infertility phenotypes presented by these men. Mol. Reprod. Dev. 83: 208-216, 2016. © 2015 Wiley Periodicals, Inc.

Mammalian target of rapamycin controls glucose consumption and redox balance in human Sertoli cells

OBJECTIVE

To study the role of mammalian target of rapamycin (mTOR) in the regulation of human Sertoli cell (hSC) metabolism, mitochondrial activity, and oxidative stress.

DESIGN

Experimental study.

SETTING

University research center and private assisted reproductive technology centers.

PATIENT(S)

Six men with anejaculation (psychological, vascular, neurologic) and conserved spermatogenesis.

INTERVENTION(S)

Testicular biopsies were used from patients under treatment for recovery of male gametes. Primary hSCs cultures were established from each biopsy and divided into a control group and one treated with rapamycin, the inhibitor of mTOR, for 24 hours.

MAIN OUTCOME MEASURE(S)

Cytotoxicity of hSCs to rapamycin was evaluated by sulforhodamine B assay. The glycolytic profile of hSCs was assessed by proton nuclear magnetic resonance and by studying protein expression of key glycolysis-related transporters and enzymes. Expression of mitochondrial complexes and citrate synthase activity were determined. Protein carbonylation, nitration, lipid peroxidation, and sulfhydryl protein group contents were quantified. The mTOR signaling pathway was studied.

RESULT(S)

Rapamycin increased glucose consumption by hSCs, maintaining lactate production. Alanine production by rapamycin-exposed hSCs was affected, resulting in an unbalanced intracellular redox state. Rapamycin-exposed hSCs had decreased expression of mitochondrial complex III and increased lipid peroxidation, whereas other oxidative stress markers were unaltered. Treatment of hSCs with rapamycin down-regulated phospho-mTOR (Ser-2448) levels, illustrating an effective partial inhibition of mTORC1. Protein levels of downstream signaling molecule p-4E-BP1 were not altered, suggesting that during treatment it became rephosphorylated.

CONCLUSION(S)

We show that mTOR regulates the nutritional support of spermatogenesis by hSCs and redox balance in these cells.

Dehydroepiandrosterone and 7-oxo-dehydroepiandrosterone in male reproductive health: Implications of differential regulation of human Sertoli cells metabolic profile

Dehydroepiandrosterone (DHEA) is a precursor of androgen synthesis whose action is partially exerted through its metabolites. 7-Oxo-dehydroepiandrosterone (7-oxo-DHEA) is a common DHEA metabolite, non-convertible to androgens, which constitutes a promising therapeutic strategy for multiple conditions. Sertoli cells (SCs) are responsible for the support of spermatogenesis, having unique metabolic characteristics strongly modulated by androgens. Consequently, disruptions in androgen synthesis compromise SCs function and hence male fertility. We aimed to evaluate the effects of DHEA and 7-oxo-DHEA in human SCs (hSCs) metabolism and oxidative profile. To do so, hSCs were exposed to increasing concentrations of DHEA and 7-oxo-DHEA (0.025, 1 and 50 μM) that revealed to be non-cytotoxic in these experimental conditions. We measured hSCs metabolites consumption/production by (1)H NMR, the protein expression levels of key players of the glycolytic pathway by Western blot as well as the levels of carbonyl groups, nitration and lipid peroxidation by Slot blot. The obtained data demonstrated that 7-oxo-DHEA is a more potent metabolic modulator than DHEA since it increased hSCs glycolytic flux. DHEA seem to redirect hSCs metabolism to the Krebs cycle, while 7-oxo-DHEA has some inhibitory effect in this path. The highest 7-oxo-DHEA concentrations (1 and 50 μM) also increased lactate production, which is of extreme relevance for the successful progression of spermatogenesis in vivo. None of these steroids altered the intracellular oxidative profile of hSCs, illustrating that, at the concentrations used they do not have pro- nor antioxidant actions in hSCs. Our study represents a further step in the establishment of safe doses of DHEA and 7-oxo-DHEA to hSCs, supporting its possible use in hormonal and non-hormonal therapies against male reproductive problems.

The potential for chemical mixtures from the environment to enable the cancer hallmark of sustained proliferative signalling

The aim of this work is to review current knowledge relating the established cancer hallmark, sustained cell proliferation to the existence of chemicals present as low dose mixtures in the environment. Normal cell proliferation is under tight control, i.e. cells respond to a signal to proliferate, and although most cells continue to proliferate into adult life, the multiplication ceases once the stimulatory signal disappears or if the cells are exposed to growth inhibitory signals. Under such circumstances, normal cells remain quiescent until they are stimulated to resume further proliferation. In contrast, tumour cells are unable to halt proliferation, either when subjected to growth inhibitory signals or in the absence of growth stimulatory signals. Environmental chemicals with carcinogenic potential may cause sustained cell proliferation by interfering with some cell proliferation control mechanisms committing cells to an indefinite proliferative span.

Metabolic fingerprints in testicular biopsies from type 1 diabetic patients

Diabetes mellitus (DM) is a metabolic disease that has grown to pandemic proportions. Recent reports have highlighted the effect of DM on male reproductive function. Here, we hypothesize that testicular metabolism is altered in type 1 diabetic (T1D) men seeking fertility treatment. We propose to determine some metabolic fingerprints in testicular biopsies of diabetic patients. For that, testicular tissue from five normal and five type 1 diabetic men was analyzed by high-resolution magic-angle spinning (HR-MAS) nuclear magnetic resonance (NMR) spectroscopy. mRNA and protein expression of glucose transporters and glycolysis-related enzymes were also evaluated. Our results show that testes from diabetic men presented decreased levels of lactate, alanine, citrate and creatine. The mRNA levels of glucose transporter 1 (GLUT1) and phosphofructokinase 1 (PFK1) were decreased in testes from diabetic men but only GLUT3 presented decreased mRNA and protein levels. Lactate dehydrogenase (LDH) and glutamate pyruvate transaminase (GPT) protein levels were also found to be decreased in testes from diabetic men. Overall, our results show that T1D alters glycolysis-related transporters and enzymes, compromising lactate content in the testes. Moreover, testicular creatine content was severely depressed in T1D men. Since lactate and creatine are essential for germ cells development and support, the data discussed here open new insights into the molecular mechanism by which DM promotes subfertility/infertility in human males.

Androgens enhance the glycolytic metabolism and lactate export in prostate cancer cells by modulating the expression of GLUT1, GLUT3, PFK, LDH and MCT4 genes

PURPOSE

The present study aims to investigate the role of androgens in controlling the glycolytic metabolism and lactate efflux in prostate cancer (PCa) cells.

METHODS

Androgen-responsive LNCaP cells were treated with 5α-dihydrotestosterone (DHT, 10 nM) for 12-48 h, and their glycolytic metabolism, lactate production and viability were analyzed. Intracellular and extracellular levels of glucose and lactate were determined spectrophotometrically, and the expression of glucose transporters (GLUT1/GLUT3), phosphofructokinase 1, lactate dehydrogenase (LDH) and monocarboxylate transporter (MCT4) was analyzed by real-time PCR and Western blot. The enzymatic activity of LDH was determined by means of a colorimetric assay. Experiments were reproduced in androgen-non-responsive DU145 and PC3 cells.

RESULTS

Androgens stimulated glucose consumption in LNCaP cells by increasing the expression of GLUT3, GLUT1 and PFK, which was underpinned by increased cell viability. Accordingly, lactate production by LNCaP cells was enhanced upon DHT stimulation as evidenced by the increased levels of lactate found in cell culture medium. Although LDH enzymatic activity decreased in LNCaP cells treated with DHT, the expression of MCT4 was significantly increased with androgenic treatment, which sustains the increase on lactate export. Glucose consumption and the expression of GLUTs and PFK remained unchanged in DHT-treated DU145 and PC3 cells.

CONCLUSIONS

The results obtained establish androgens as modulators of glycolytic metabolism in PCa cells by stimulating glucose consumption, as well as the production and export of lactate, which may represent a crucial issue-driven prostate tumor development. These findings also highlight the importance of PCa therapies targeting AR and metabolism-related proteins.

Testicular Metabolic Reprogramming in Neonatal Streptozotocin-Induced Type 2 Diabetic Rats Impairs Glycolytic Flux and Promotes Glycogen Synthesis

Defects in testicular metabolism are directly implicated with male infertility, but most of the mechanisms associated with type 2 diabetes- (T2DM) induced male infertility remain unknown. We aimed to evaluate the effects of T2DM on testicular glucose metabolism by using a neonatal-streptozotocin- (n-STZ) T2DM animal model. Plasma and testicular hormonal levels were evaluated using specific kits. mRNA and protein expression levels were assessed by real-time PCR and Western Blot, respectively. Testicular metabolic profile was assessed by (1)H-NMR spectroscopy. T2DM rats showed increased glycemic levels, impaired glucose tolerance and hyperinsulinemia. Both testicular and serum testosterone levels were decreased, whereas those of 17β-estradiol were not altered. Testicular glycolytic flux was not favored in testicles of T2DM rats, since, despite the increased expression of both glucose transporters 1 and 3 and the enzyme phosphofructokinase 1, lactate dehydrogenase activity was severely decreased contributing to lower testicular lactate content. However, T2DM enhanced testicular glycogen accumulation, by modulating the availability of the precursors for its synthesis. T2DM also affected the reproductive sperm parameters. Taken together these results indicate that T2DM is able to reprogram testicular metabolism by enhancing alternative metabolic pathways, particularly glycogen synthesis, and such alterations are associated with impaired sperm parameters.

Metformin and male reproduction: effects on Sertoli cell metabolism

BACKGROUND AND PURPOSE

Metformin is commonly used to treat type 2 diabetes (T2D). While new clinical applications have been ascribed to metformin, including treatment of anovulatory infertility, its effects on male reproduction have not been investigated. The Sertoli cell (SC) is crucial for germ cell development, exerting metabolic control of spermatogenesis, therefore, we investigated the effects of metformin on SC metabolism.

EXPERIMENTAL APPROACH

Rat SCs were cultured in the absence and presence of metformin (5, 50 and 500 μM). mRNA and protein levels of glucose transporters (GLUT1 and GLUT3), phosphofructokinase 1 (PFK 1), lactate dehydrogenase (LDH) and monocarboxylate transporter 4 (MCT4) were determined by quantitative PCR and Western blot respectively. LDH activity was assessed and metabolite production/consumption determined by (1) H-NMR.

KEY RESULTS

Metformin (50 μM) decreased mRNA and protein levels of GLUT1, GLUT3, MCT4 and PFK 1 but did not affect LDH mRNA or protein levels. However, although glucose consumption was maintained in metformin-treated cells, LDH activity, lactate and alanine production were increased, indicating an enhanced glycolytic flux. No metabolic cytotoxicity was detected in SCs exposed to supra-pharmacological concentration of metformin.

CONCLUSIONS AND IMPLICATIONS

Our results indicate that metformin: (i) decreases mRNA and protein levels of glycolysis-related transporters in SCs but increases their activity; and (ii) stimulates alanine production, which induces antioxidant activity and maintains the NADH/NAD(+) equilibrium. The increased lactate in metformin-treated SCs provides nutritional support and has an anti-apoptotic effect in developing germ cells. Thus, metformin can be considered as a suitable antidiabetic drug for male patients of reproductive age with T2D.

Melatonin alters the glycolytic profile of Sertoli cells: implications for male fertility

Melatonin co-operates with insulin in the regulation of glucose homeostasis. Within the testis, glucose metabolism in the somatic Sertoli cells (SCs) is pivotal for spermatogenesis. Since the effects of melatonin on male reproductive physiology remain largely unknown, we hypothesized that melatonin may affect spermatogenesis by modulating SC metabolism, interacting with insulin. To test our hypothesis, rat SCs were maintained in culture for 24 h in the presence of insulin, melatonin or both and metabolite production/consumption was determined by proton nuclear magnetic resonance ((1)H-NMR). Protein levels of glucose transporters (GLUT1 and GLUT3), phosphofructokinase 1, lactate dehydrogenase (LDH) and monocarboxylate transporter 4 were determined by western blot. LDH activity was also assessed. SCs treated with melatonin showed an increase in glucose consumption via modulation of GLUT1 levels, but decreased LDH protein expression and activity, which resulted in lower lactate production. Moreover, SCs exposed to melatonin produced and accumulated less acetate than insulin-exposed cells. The combined treatment (insulin plus melatonin) increased acetate production by SCs, but intracellular acetate content remained lower than in insulin exposed cells. Finally, the intracellular redox state, as reflected by intracellular lactate/alanine ratio, was maintained at control levels in SCs by melatonin exposure (i.e. melatonin, alone or with insulin, increased the lactate/alanine ratio versus cells treated with insulin). Furthermore, SCs exposed to insulin plus melatonin produced more lactate and maintained the protein levels of some glycolysis-related enzymes and transporters at control levels. These findings illustrate that melatonin regulates SCs metabolism, and thus may affect spermatogenesis. Since lactate produced by SCs provides nutritional support and has an anti-apoptotic effect in developing germ cells, melatonin supplementation may be an effective therapy for diabetic male individuals facing subfertility/infertility.

The Warburg effect revisited--lesson from the Sertoli cell

Otto Warburg observed that cancerous cells prefer fermentative instead of oxidative metabolism of glucose, although the former is in theory less efficient. Since Warburg's pioneering works, special attention has been given to this difference in cell metabolism. The Warburg effect has been implicated in cell transformation, immortalization, and proliferation during tumorigenesis. Cancer cells display enhanced glycolytic activity, which is correlated with high proliferation, and thus, glycolysis appears to be an excellent candidate to target cancer cells. Nevertheless, little attention has been given to noncancerous cells that exhibit a "Warburg-like" metabolism with slight, but perhaps crucial, alterations that may provide new directions to develop new and effective anticancer therapies. Within the testis, the somatic Sertoli cell (SC) presents several common metabolic features analogous to cancer cells, and a clear "Warburg-like" metabolism. Nevertheless, SCs actively proliferate only during a specific time period, ceasing to divide in most species after puberty, when they become terminally differentiated. The special metabolic features of SC, as well as progression from the immature but proliferative state, to the mature nonproliferative state, where a high glycolytic activity is maintained, make these cells unique and a good model to discuss new perspectives on the Warburg effect. Herein we provide new insight on how the somatic SC may be a source of new and exciting information concerning the Warburg effect and cell proliferation.

Effect of white tea (Camellia sinensis (L.)) extract in the glycolytic profile of Sertoli cell

PURPOSE

Many health benefits have been attributed to tea (Camellia sinensis (L.)), and tea infusions are used as dietary agent and included in food supplements. Herein, we report the effect of a white tea (WTEA) extract in Sertoli cell (SC) metabolism. The SC is responsible for the nutritional support of the developing germ cells.

METHODS

An aqueous WTEA extract was prepared and analyzed by (1)H-NMR. Rat SCs were cultured with or without the WTEA extract. mRNA and protein levels of glucose transporters (GLUT1 and GLUT3), phosphofructokinase, lactate dehydrogenase (LDH) and monocarboxylate transporter 4 were determined by qPCR and western blot. LDH activity was assessed and metabolite production/consumption determined by (1)H-NMR.

RESULTS

WTEA-exposed SCs presented decreased protein and mRNA levels of GLUT1 and decreased glucose uptake. However, intracellular LDH activity was increased and SC lactate production was stimulated by the presence of the WTEA extract. Interestingly, alanine production was also found to be stimulated in WTEA extract-exposed SCs.

CONCLUSION

WTEA extract altered the glycolytic profile of cultured SCs, stimulating lactate production. Since lactate is used as metabolic substrate and has an anti-apoptotic effect in the developing germ cells, the supplementation with WTEA extract may be advantageous to improve male reproductive health.

Insulin deprivation decreases caspase-dependent apoptotic signaling in cultured rat sertoli cells

Insulin is essential for the regulation of glucose homeostasis. Insulin dysfunction occurs in several pathologies, such as diabetes mellitus, which is associated with fertility problems. Somatic Sertoli cells (SCs) not only metabolize glucose to lactate, which is the central energy source used by developing germ cells, but also determine the germ cell population size. If a deregulation in SCs apoptosis occurs, it will affect germ cells, compromising spermatogenesis. As SCs apoptotic signaling is a hormonally regulated process, we hypothesized that the lack of insulin could lead to alterations in apoptotic signaling. Therefore, we examined the effect of insulin deprivation on several markers of apoptotic signaling in cultured rat SCs. We determined mRNA and protein expression of apoptotic markers as well as caspase-3 activity. SCs cultured in insulin deprivation demonstrated a significant decrease on mRNA levels of p53, Bax, caspase-9, and caspase-3 followed by a significant increase of Bax and decrease of caspase-9 protein levels relatively to the control. Caspase-3 activity was also decreased in SCs cultured in insulin deprivation conditions. Our results show that insulin deprivation decreases caspase-dependent apoptotic signaling in cultured rat SCs evidencing a possible mechanism by which lack of insulin can affect spermatogenesis and fertility.