Thyroid hormone inhibits the proliferation of piglet Sertoli cell via PI3K signaling pathway

Thyroid disorders and male sexual dysfunction

Though early research suggested that thyroid hormones were not involved with the testes, male spermatogenesis, or erectile function, investigations on this topic over the past few decades have increased and shed new light. A literature review of studies conducted between 1963 and 2022 regarding male sexual dysfunction (SD) and thyroid disorders was performed to define the diagnostic consideration, pathophysiology, and management of SD secondary to thyroid dysregulation. This article provides evidence and interpretation of prior clinical and preclinical studies and contextualizes these studies for clinical practice. Clinical manifestations of SDs included erectile and ejaculatory dysfunction, impaired spermatogenesis, and disruption of the hypothalamic-pituitary-gonadal axis. Our aim of this communication was to perform a literature review detailing the impact of thyroid disorders on male SD. We hope to provide a framework for practicing urologists, endocrinologists, or general practitioners when evaluating patients with concurrent thyroid and male SD. It is important to recognize that thyroid disorders can be an important part of the pathophysiology of male SD in patients. Future research studies are needed to further elucidate the mechanisms involved.

Identification and Analysis of Genes Related to Testicular Size in 14-Day-Old Piglets

The RNA-Seq technology was used to screen the key genes that affect the early development of the testes of Duroc × Landrace × Yorkshire piglets, to determine the regulatory pathway and provide reference for subsequent reproductive performance research, breeding, and other production practices. This study selected 14-day-old Duroc × Landrace × Yorkshire piglets as the trial animals. Testes from piglets with similar weights and no pathological changes were divided into small testis (ST) and large testis (LT) groups, and the RNA-Seq screening of differentially expressed genes (DEGs) was performed to find candidate genes and regulatory pathways related to early testicular development. The results show that 570 DEGs were found in the ST and LT groups, with 281 upregulated and 289 downregulated. The DEGs were mainly enriched on 47 gene ontology (GO) functional items. The Kyoto encyclopedia of genes and genotypes (KEGG) enrichment analysis found that there were 44 significantly enriched KEGG signal pathways, and the regulation of testicular development mainly focused on the arachidonic acid metabolism, Wnt signaling pathway and GnRH secretion pathways. The PTGES, SFRP1, SPP1, PLA2G4E, KCNJ5, PTGS2, and HCN1 genes were found to be as closely related to the testicular development of these Duroc × Landrace × Yorkshire piglets, and the differential gene expression was consistent with the real-time quantitative reverse transcription PCR (real-time qRT-PCR) validation results. This study was validated by high-throughput sequencing analysis and real-time qRT-PCR, and showed that the PTGES, SFRP1, SPP1, PLA2G4E, KCNJ5, PTGS2, and HCN1 genes may be involved in the regulation of germ cell development, spermatogenesis and semen traits. These should be further studied as candidate genes for early testicular development and reproductive trait regulation in boars.

Effects of exposure to PM2.5 during pregnancy on the multigenerational reproductive outcomes of male mouse offspring and the role of Sertoli cells

There is a paucity of studies on the multigenerational reproductive toxicity of fine particle matter (PM2.5) exposure during pregnancy on male offspring and the underlying mechanisms. This study explored the effects of PM2.5 exposure during pregnancy on the spermatogenesis of three consecutive generations of male mouse offspring. We randomized pregnant C57BL/6 mice into the control group, the Quartz Fiber Membrane control group, and two experimental groups exposed to different concentrations of PM2.5 (4.8 and 43.2 mg/kg B.Wt.). Pregnant mice from experimental groups received intratracheal instillation of PM2.5 of different doses on a three-day basis until birth. F1 mature male offspring from PM2.5-exposed pregnant mice were mated with normal female C57BL/6 mice. Likewise, their F2 mature male followed the same to produce the F3 generation. The results showed that PM2.5 exposure during pregnancy led to decreased body and tail length, body weight, and survival rates, decreased sperm concentration and sperm motility, and increased sperm abnormality rates significantly in F1 male offspring. We barely observed significant impacts of PM2.5 on the birth number, survival rates, and index of testes in the F2 and F3 offspring. Further exploration showed that PM2.5 exposure during pregnancy caused the morphological abnormality of Sertoli cells, downregulated androgen receptor (AR) and connexin43, upregulated anti-Müllerian hormone (AMH), cytokeratin-18 (CK-18), caspase-3, and cleaved caspase-3, decreased thyroid-stimulating hormone (TSH) and testosterone (T), and increased triiodothyronine (T3) in F1 male mouse offspring. Overall, we hypothesize that PM2.5 exposure during pregnancy mainly negatively impacts spermatogenesis in the F1 offspring. The possible mechanism could be that PM2.5 exposure during pregnancy disrupts endocrine hormone release in the F1 generation, thereby influencing the maturation and proliferation of their Sertoli cells and hindering spermatogenesis. This study for the first time investigates the role of Sertoli cells in the reproductive toxicity of PM2.5 on offspring.

Impact of endocrine disrupting chemicals and pharmaceuticals on Sertoli cell development and functions

Sertoli cells play essential roles in male reproduction, from supporting fetal testis development to nurturing male germ cells from fetal life to adulthood. Dysregulating Sertoli cell functions can have lifelong adverse effects by jeopardizing early processes such as testis organogenesis, and long-lasting processes such as spermatogenesis. Exposure to endocrine disrupting chemicals (EDCs) is recognized as contributing to the rising incidence of male reproductive disorders and decreasing sperm counts and quality in humans. Some drugs also act as endocrine disruptors by exerting off-target effects on endocrine tissues. However, the mechanisms of toxicity of these compounds on male reproduction at doses compatible with human exposure are still not fully resolved, especially in the case of mixtures, which remain understudied. This review presents first an overview of the mechanisms regulating Sertoli cell development, maintenance, and functions, and then surveys what is known on the impact of EDCs and drugs on immature Sertoli cells, including individual compounds and mixtures, and pinpointing at knowledge gaps. Performing more studies on the impact of mixtures of EDCs and drugs at all ages is crucial to fully understand the adverse outcomes these chemicals may induce on the reproductive system.

Integrated analysis of miRNA and mRNA expression profiles in testes of Landrace and Hezuo boars

Precocious puberty is closely related to testicular development and spermatogenesis, and there is increasing evidence that miRNAs are involved in regulation of testicular development and spermatogenesis. However, little is known about the regulation of microRNAs (miRNAs) during precocious maturation in Hezuo (HZ) boars. In this study, serum Testosterone (T), Estradiol (E₂), Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH) levels were detected in HZ and Landrace (LC) boars in the postnatal period at 30, 90, 120, 180, and 240 days, and the testes of HZ and LC boars at 30 and 120 days were used for histological observation. In addition, we performed small RNA-Seq to identify miRNA at sexual immaturity (30-days-old) and maturity (120-days-old) of HZ boar testis (using LC boar as control) to reveal the key miRNA in regulation of precocious puberty. Hormone assay results showed that high levels of T, E₂, FSH, and LH may be related to precocious sexual maturity of HZ boars, and that FSH may play an important function before sexual maturity. Histological observation showed that HZ boars developed earlier than LC boars and had reached sexual maturity at 120 days. Small RNA-Seq yielded a total of 359 exist miRNAs, 767 known miRNAs and 322 novel miRNAs in 12 samples; 549, 468, 133, and 247 differentially expressed (DE) miRNAs were identified between Ha vs. Hb, La vs. Lb, Ha vs. La, and Hb vs. Lb (log₂ fold change >1 and p < 0.05). Enrichment analysis showed that target genes of these DE miRNAs were enriched in many gene ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) signaling pathways (such as PI3K-Akt, Hippo and Rap1 signaling pathways) were related to testicular development and spermatogenesis. Further screening, some miRNAs (such as ssc-miR-29b, ssc-miR-199b, ssc-miR-383, ssc-miR-149, ssc-miR-615, and ssc-miR-370) were possibly associated with precocious puberty. These results provide new light on miRNA regulatory mechanisms involved in precocious puberty.

Bacterial Infections Affect Male Fertility: A Focus on the Oxidative Stress-Autophagy Axis

Numerous factors trigger male infertility, including lifestyle, the environment, health, medical resources and pathogenic microorganism infections. Bacterial infections of the male reproductive system can cause various reproductive diseases. Several male reproductive organs, such as the testicles, have unique immune functions that protect the germ cells from damage. In the reproductive system, immune cells can recognize the pathogen-associated molecular patterns carried by pathogenic microorganisms and activate the host's innate immune response. Furthermore, bacterial infections can lead to oxidative stress through multiple signaling pathways. Many studies have revealed that oxidative stress serves dual functions: moderate oxidative stress can help clear the invaders and maintain sperm motility, but excessive oxidative stress will induce host damage. Additionally, oxidative stress is always accompanied by autophagy which can also help maintain host homeostasis. Male reproductive system homeostasis disequilibrium can cause inflammation of the genitourinary system, influence spermatogenesis, and even lead to infertility. Here, we focus on the effect of oxidative stress and autophagy on bacterial infection in the male reproductive system, and we also explore the crosslink between oxidative stress and autophagy during this process.

Identification and Characterization of lncRNA and mRNA in Testes of Landrace and Hezuo Boars

Simple Summary

Precocious puberty is an excellent reproductive trait in domestic animals, which can generate higher breeding benefits in livestock production. However, regulators associated with this sexual maturation process remain largely unknown. Chinese Hezuo (HZ) boars are known for their early sexual maturity. In this work, the characteristics of precocious puberty in HZ pigs were confirmed by histological analysis, and some important long noncoding RNA (lncRNA) and mRNA were identified in the testes of immature (30-day-old) and mature (120-day-old) HZ boars, which could play a key role in precocious puberty. These results will provide a theoretical basis for further research on the regulatory mechanism of precocious puberty, which is important for accelerating the breeding process of highly fertile animals.

Abstract

Chinese HZ boars are typical plateau miniature boars characterized by precocious puberty, which is closely related to testicular development and spermatogenesis. Accumulating evidence indicates that lncRNA is involved in the testicular development and regulation of spermatogenesis. However, little is known about the lncRNA precocious regulation in testicular development and spermatogenesis on early sexual maturity of HZ boars. Thus, we investigated the expression and characterization of lncRNA and mRNA in 30-day-old and 120-day-old HZ boar testes using transcriptome to explore precocious puberty. Landrace (LC) boar was treated as the control. Histological analyses indicated that HZ boar underwent puberty development at an earlier stage than LC boar and had achieved sexual maturity at 120 days old. RNA-Seq yielded a total of 187 lncRNAs and 984 mRNAs; these molecules were identified as possible candidates for precocious puberty. GO terms and KEGG pathways enrichment analyses revealed that the differentially expressed lncRNA and their targeted genes were involved in metabolic pathways regulating testis development and spermatogenesis, such as the PI3K-Akt, TGF-beta and Wnt pathways. Further screening, some lncRNA (such as LOC102166140, LOC110259451, and MSTRG.15011.2), and mRNA (such as PDCL2, HSD17B4, SHCBP1L, CYP21A2, and SPATA3) were found to be possibly associated with precocious puberty, which would add to our understanding of the molecular regulatory mechanisms of precocious puberty. This study provided valuable information for further study of the role of lncRNA and mRNA in the process of precocious puberty.

miR-126 Controls the Apoptosis and Proliferation of Immature Porcine Sertoli Cells by Targeting the PIK3R2 Gene through the PI3K/AKT Signaling Pathway

Simple Summary

MicroRNAs (miRNAs) have been reported with potential regulatory roles in spermatogenesis. In the present study, we demonstrated that miR-126 can stimulate cell proliferation and restrain the apoptosis of immature porcine Sertoli cells by targeting the PIK3R2 gene. Through this process, miR-126 further activates the PI3K/AKT signaling pathway. These results indicated that miR-126, PIK3R2, and the PI3K/AKT signaling pathway might play pivotal regulatory roles in porcine spermatogenesis by deciding the destiny of immature Sertoli cells.

Abstract

The quantity of Sertoli cells in the adult testis decides the daily gamete formation, and accumulating evidence indicates that epigenetic factors regulate the proliferation of Sertoli cells. Research on the function and regulatory mechanism of microRNAs (miRNAs) in Sertoli cells has not been comprehensive yet, especially on domestic animals. In this article, we report that miR-126 controls the proliferation and apoptosis of immature porcine Sertoli cells based on previous studies. Our results confirmed that miR-126 elevation promotes cell cycle progression, cell proliferation and represses cell apoptosis; on the contrary, the inhibitory effects of miR-126 result in the opposite. The phosphoinositide-3-kinase regulatory subunit 2 (PIK3R2) gene, a member of the PI3K family, was verified as a direct target of miR-126 using the dual-luciferase reporter analysis. miR-126 negatively regulated the mRNA and protein expression level of PIK3R2 in immature porcine Sertoli cells. siRNA-induced PIK3R2 inhibition caused similar effects as miR-126 overexpression and eliminated the influences of miR-126 knockdown in immature porcine Sertoli cells. In addition, both miR-126 overexpression and PIK3R2 inhibition elevated the phosphorylation of PI3K and AKT, whereas the miR-126 knockdown demonstrated the contrary result. In short, miR-126 controls the proliferation and apoptosis of immature porcine Sertoli cells by targeting the PIK3R2 gene through the PI3K/AKT signaling pathway. The research supplies a theoretical and practical foundation for exploring the functional parts of miR-126 in swine sperm by defining the destiny of immature Sertoli cells.

MicroRNA-125a-5p modulates the proliferation and apoptosis of TM4 Sertoli cells by targeting RAB3D and regulating the PI3K/AKT signaling pathway

Sertoli cells are cells that provide protection and nutrition for developing sperm. Each stage of sperm development occurs on the surface of Sertoli cells. MicroRNA (MiR)-125a-5p is involved in male reproduction. The current research aimed to probe the role of miR-125a-5p in Sertoli cell function. Functionally, miR-125a-5p knockdown facilitated Sertoli cell proliferation, while miR-125a-5p overexpression suppressed Sertoli cell proliferation, as evidenced by 5-ethynyl-20-deoxyuridine incorporation assay. Additionally, miR-125a-5p knockdown inhibited Sertoli cell apoptosis, while miR-125a-5p upregulation facilitated Sertoli cell apoptosis, as evidenced by flow cytometry analysis. Computationally, we identified four predicted mRNA targets of miR-125a-5p. Based on the results of luciferase reporter assay, miR-125a-5p was confirmed to bind to the predicted sequence in the Ras-related protein Rab-3D (RAB3D) 3'UTR. Rescue experiments showed that miR-125a-5p suppressed the proliferative ability of TM4 Sertoli cells and facilitated their apoptosis by targeting RAB3D. Finally, our data confirmed that miR-125a-5p and RAB3D modulated activation of the PI3K/AKT pathway. In conclusion, our data showed that miR-125a-5p regulated Sertoli cell proliferation and apoptosis by targeting RAB3D and regulating the PI3K/AKT pathway.

Proliferative and Apoptotic Pathways in the Testis of Quail Coturnix coturnix during the Seasonal Reproductive Cycle

Simple Summary

The quail Coturnix coturnix exhibits an annual cycle of testis size, sexual steroid production, and spermatogenesis. The testicular levels of both 17β-estradiol (E₂) and androgens are higher during the reproductive period compared to the non-reproductive period, suggesting that estrogens act in synergy with the androgens for the initiation of spermatogenesis. Therefore, the present study aimed to investigate the estrogen responsive system in quail testis in relation to the reproduction seasons, with a focus on the molecular pathways activated in both active and regressive quail testes. The results indicated that estrogens participated in the activation of mitotic and meiotic events during the reproductive period by activating the ERK1/2 and Akt-1 pathways. In the non-reproductive period, when the E₂/ERα levels are low, ERK1/2 and Akt-1 pathways remain inactive and apoptotic events occur. Our results suggest that the activation or inhibition of these molecular pathways plays a crucial role in the physiological switch “on/off” of the testicular activity in male quail during the seasonal reproductive cycle.

Abstract

The quail Coturnix coturnix is a seasonal breeding species, with the annual reproductive cycle of its testes comprising an activation phase and a regression phase. Our previous results have proven that the testicular levels of both 17β-estradiol (E₂) and androgens are higher during the reproductive period compared to the non-reproductive period, which led us to hypothesize that estrogens and androgens may act synergistically to initiate spermatogenesis. The present study was, therefore, aimed to investigate the estrogen responsive system in quail testis in relation to the reproduction seasonality, with a focus on the molecular pathways elicited in both active and regressive quail testes. Western blotting and immunohistochemistry analysis revealed that the expression of ERα, which is the predominant form of estrogen receptors in quail testis, was correlated with E₂ concentration, suggesting that increased levels of E₂-induced ERα could play a key role in the resumption of spermatogenesis during the reproductive period, when both PCNA and SYCP3, the mitotic and meiotic markers, respectively, were also increased. In the reproductive period we also found the activation of the ERK1/2 and Akt-1 kinase pathways and an increase in second messengers cAMP and cGMP levels. In the non-reproductive phase, when the E2/ERα levels were low, the inactivation of ERK1/2 and Akt-1 pathways favored apoptotic events due to an increase in the levels of Bax and cytochrome C, with a consequent regression of the gonad.

Proteomic and phosphoproteomic profiles of Sertoli cells in buffalo

Sertoli cells provide nutrients and support for germ cell differentiation and maintain a stable microenvironment for spermatogenesis. Comprehensive identification of Sertoli cellular proteins is important in understanding spermatogenesis. In this study, we performed an integrative analysis of the proteome and phosphoproteome to explore the role of Sertoli cells in spermatogenesis. A total of 2912 and 753 proteins were identified from the proteome and phosphoproteome in Sertoli cells, respectively; 438 proteins were common to the proteome and phosphoproteome. Data are available via ProteomeXchange with identifier PXD024984. In the proteome, ACTG1, ACTB, ACTA2, MYH9 were the most abundant proteins. Gene Ontology (GO) analysis indicated that most of the proteins were involved in the processes of localization, biosynthesis, gene expression, and transport. In addition, some of the proteins related to Sertoli cell functions were also enriched. In the phosphoproteome, most of the proteins were involved in gene expression and the RNA metabolic process; the pathways mainly involved the spliceosome, mitogen-activated protein kinase signaling pathway, focal adhesion, and tight junctions. The pleckstrin homology-like domain is the most highly enriched protein domain in phosphoproteins. Cyclin-dependent kinases and protein kinases C were found to be highly active kinases in the kinase-substrate network analysis. Ten proteins most closely related to network stability were found in the analysis of the network interactions of proteins identified jointly in the phosphoproteome and proteome. Through immunohistochemistry and immunofluorescence verification of vimentin, it was found that there were localization differences between phosphorylated and non-phosphorylated vimentin in testicular tissue. This study is the first in-depth proteomic and phosphoproteomic analysis of buffalo testicular Sertoli cells. The results provide insight into the role of Sertoli cells in spermatogenesis and provide clues for further study of male reproduction.

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.

miR-222 Suppresses Immature Porcine Sertoli Cell Growth by Targeting the GRB10 Gene Through Inactivating the PI3K/AKT Signaling Pathway

Sertoli cells are central and essential coordinators of spermatogenesis. Accumulating evidence has demonstrated that miRNAs participate in the regulation of Sertoli cell growth. However, the functions and the regulatory mechanisms of miRNAs in Sertoli cells of domestic animals remain largely unknown. Here we report that miR-222 overexpression repressed cell cycle progression and proliferation and promoted the apoptosis of immature porcine Sertoli cells, whereas miR-222 inhibition resulted in the opposite result. miR-222 directly targeted the 3′-UTR of the GRB10 gene and inhibited its mRNA abundance. An siRNA-induced GRB10 knockdown showed similar effects as did miR-222 overexpression on cell proliferation and apoptosis and further attenuated the role of miR-222 inhibition. Furthermore, both miR-222 overexpression and GRB10 inhibition repressed the phosphorylation of PI3K and AKT, the key elements of the PI3K/AKT signaling pathway, whereas GRB10 inhibition offsets the effects of the miR-222 knockdown. Overall, we concluded that miR-222 suppresses immature porcine Sertoli cell growth by targeting the GRB10 gene through inactivation of the PI3K/AKT signaling pathway. This study provides novel insights into the epigenetic regulation of porcine spermatogenesis by determining the fate of Sertoli cells.

Hypothyroidism induced by postnatal PTU (6-n-propyl-2-thiouracil) treatment decreases Sertoli cell number and spermatogenic efficiency in sexually mature pigs

Studies with 6-n-propyl-2-thiouracil (PTU) in laboratory rodents have shown that transient neonatal hypothyroidism leads to increased Sertoli cell (SC) number, testis size and sperm production. However, scarce and inconclusive data are available for farm animals. In the present study, Piau pigs received PTU in a gel capsule containing 8 mg/kg of body weight for 14 weeks starting from the first week of age, whereas control animals received only the vehicle. Blood samples were collected during the experimental period for hormonal evaluation in the serum. The animals were orchiectomized at adulthood and had their testes used for histomorphometric analysis. Indicating that the PTU concentration used was effective in promoting hypothyroidism, PTU-treated pigs showed a 30% lower body weight and reduced thyroxine levels (p < 0.05) during the treatment period. At adulthood, the body weight was similar in both groups but, surprisingly, PTU-treated pigs showed 30% lower testis weight (p < 0.05). In general, treated pigs presented increased follicle-stimulating hormone levels, whereas testosterone levels tended to be lower from 9 to 23 weeks of age. No significant differences were observed for estradiol, Leydig cell volume and number, tubular diameter, SC number per gram of testis, SC efficiency and meiotic index. However, seminiferous tubule occupancy, total tubular length, SC number per testis, and daily sperm production per testis and per gram of testis (DSP/g/T) were significantly lower (p < 0.05) in PTU-treated pigs. Therefore, in contrast to laboratory rodents, our results showed that SC proliferation and DSP/g/T (spermatogenic efficiency) in Piau pigs is diminished by postnatal PTU treatment.

miR-130a promotes immature porcine Sertoli cell growth by activating SMAD5 through the TGF-β-PI3K/AKT signaling pathway

Sertoli cells play vital roles in normal spermatogenesis, and microRNAs (miRNAs) participate in regulating Sertoli cell development. However, the functions and mechanisms of action of most identified miRNAs in porcine Sertoli cells remain largely unknown. Herein, we primarily explored the regulatory roles of miR-130a in immature porcine Sertoli cells using EdU-based high-content screening assay. The results demonstrated that 27 miRNAs have potential roles in the promotion of immature porcine Sertoli cell proliferation, and miR-130a was identified as a promising candidate. miR-130a promoted cell cycle progression and cell proliferation, whereas it impeded cell apoptosis in immature porcine Sertoli cells. It also contributed to Sertoli cell proliferation and testis development in vivo. A TMT-based proteomics approach revealed that miR-130a regulated the expression of 91 proteins and multiple pathways, including the TGF-β and PI3K/AKT signaling. miR-130a did not directly target the 3'-UTR of SMAD5; however, it increased SMAD5 phosphorylation. Moreover, miR-130a enhanced TGF-β signaling by activating SMAD5 protein, and TGF-β signaling further activated the PI3K/AKT signaling pathway to promote cell proliferation and inhibit cell apoptosis in porcine immature Sertoli cells. Collectively, miR-130a promoted immature porcine Sertoli cell growth by activating SMAD5 through the TGF-β-PI3K/AKT signaling pathway. This study, therefore, provides novel insights into the effects of miR-130a on porcine spermatogenesis through the regulation of immature Sertoli cell proliferation and apoptosis.

3, 3', 5-Triiodo-L-thyronine affects polarity proteins of bovine Sertoli cells via WT1/non-canonical Wnt signaling pathway

To determine the role of 3, 3', 5-triiodo-L thyroxine (T3) in the differentiation of Sertoli cells (SCs) and the factors influencing maturity via the Wilms' tumor 1 (WT1)/non-canonical Wnt signaling pathway, high purity SCs were isolated from newborn calves' testes and cultured in vitro. The SCs were stimulated with T3, and co-treated with short interference (si) RNA to knockdown endogenous WT1 and non-canonical Wnt signalling inhibitor Wnt-c59. Our results suggested that the addition of different concentrations (0, 25, 50, and 100 nM) of T3 in the culture medium changed the expression of KRT-18 (SCs immature marker) and accelerated the differentiation of SCs. T3 (100 nM) treatment induced up-regulated expression of WT1 over time (p < 0.05), while the expression of polarity proteins (Par3, Par6b, and E-cadherin) and Wnt4 were affected to varying degrees (p < 0.05). SCs were treated simultaneously with T3 + Wnt-c59 and T3 + WT1 siRNA, and the results showed that T3 could affect the expression of polarity proteins via WT1/non-canonical Wnt signaling pathway. These data put together indicate that T3 plays a dependent role in the induction of bovine SCs differentiation via WT1/non-canonical Wnt signaling pathway in vitro. This study proposes for the first time that WT1 is a major target for T3.

Multiple signaling pathways in Sertoli cells: recent findings in spermatogenesis

The functions of Sertoli cells in spermatogenesis have attracted much more attention recently. Normal spermatogenesis depends on Sertoli cells, mainly due to their influence on nutrient supply, maintenance of cell junctions, and support for germ cells' mitosis and meiosis. Accumulating evidence in the past decade has highlighted the dominant functions of the MAPK, AMPK, and TGF-β/Smad signaling pathways during spermatogenesis. Among these pathways, the MAPK signaling pathway regulates dynamics of tight junctions and adherens junctions, proliferation and meiosis of germ cells, proliferation and lactate production of Sertoli cells; the AMPK and the TGF-β/Smad signaling pathways both affect dynamics of tight junctions and adherens junctions, as well as the proliferation of Sertoli cells. The AMPK signaling pathway also regulates lactate supply. These signaling pathways combine to form a complex regulatory network for spermatogenesis. In testicular tumors or infertile patients, the activities of these signaling pathways in Sertoli cells are abnormal. Clarifying the mechanisms of signaling pathways in Sertoli cells on spermatogenesis provides new insights into the physiological functions of Sertoli cells in male reproduction, and also serves as a pre-requisite to identify potential therapeutic targets in abnormal spermatogenesis including testicular tumor and male infertility.

Analysis of Long Non-Coding RNA and mRNA Expression Profiling in Immature and Mature Bovine (Bos taurus) Testes

Testis development and spermatogenesis are strictly regulated by numbers of genes and non-coding genes. However, long non-coding RNAs (lncRNAs) as key regulators in multitudinous biological processes have not been systematically identified in bovine testes during sexual maturation. In this study, we comprehensively analyzed lncRNA and mRNA expression profiling of six bovine testes at 3 days after birth and 13 months by RNA sequencing. 23,735 lncRNAs and 22,118 mRNAs were identified, in which 540 lncRNAs (P-value < 0.05) and 3,525 mRNAs (P-adjust < 0.05) were significantly differentially expressed (DE) between two stages. Correspondingly, the results of RT-qPCR analysis showed well correlation with the transcriptome data. Moreover, GO and KEGG enrichment analyses showed that DE genes and target genes of DE lncRNAs were enriched in spermatogenesis. Furthermore, we constructed lncRNA–gene interaction networks; consequently, 15 DE lncRNAs and 12 cis-target genes were involved. The target genes (SPATA16, TCF21, ZPBP, PACRG, ATP8B3, COMP, ACE, and OSBP2) were found associated with bovine sexual maturation. In addition, the expression of lncRNAs and cis-target genes was detected in bovine Leydig cells, Sertoli cells, and spermatogonia. Our study identified and analyzed lncRNAs and mRNAs in testis tissues, suggesting that lncRNAs may regulate testis development and spermatogenesis. Our findings provided new insights for further investigation of biological function in bovine lncRNA.

Thyroid hormone (T3) is involved in inhibiting the proliferation of newborn calf Sertoli cells via the PI3K/Akt signaling pathway in vitro

The experiment was designed to study the effects of Thyroid hormone (T₃) on the proliferation and differentiation of newborn calf Sertoli cells (SCs) to provide a theoretical and practical basis for increased testicular semen production. In this experiment, the cck8 method was used to detect the effects of different concentrations of T₃ on the proliferation rate of newborn calf SCs. qPCR and Western Blot methods were used to explore the effects of T3 on the proliferation and differentiation of calves SCs and whether T₃ through Wnt/β-catenin and PI3K/Akt pathways can regulate the proliferation and differentiation of SCs. We found that dosage (T₃) and time correlated with proliferation inhibition of SC. T₃ inhibited the proliferation of SC by down-regulating cyclinD1, upregulating p21Cip, p27Kip1, and other cell-cycle factors. By up-regulating AR and down-regulating KRT-18, T3 promoted the maturated differentiation of SC. T₃ could not affect the expression of β-catenin in SC of newborn calf, indicating that T₃ may not regulate SCs proliferation through the Wnt pathway. T3 also negatively regulated the gene expression and protein levels of some genes in the PI3K/Akt signaling pathway. We concluded that T₃ inhibited newborn calf SCs proliferation through the PI3K/Akt signaling pathway and possibly promoted their differentiation.

Enhanced sperm production in bulls following transient induction of hypothyroidism during prepubertal development

Male reproductive capacity is a critical component of cattle production and the majority of genetic gain is made via selective utilization of gametes from desirable sires. Thus, strategies that enhance sperm production increase the availability of elite genetics for use in improving production characteristics of populations on a worldwide scale. In all mammals, the amount of sperm produced is strongly correlated to the number of Sertoli cells in testes. Studies with rodents showed that the size of the Sertoli cell population is set during prepubertal development via signaling from thyroid hormones. Here, we devised a strategy to increase Sertoli cell number in bulls via induction of a transient hypothyroidic state just prior to and extending beyond the period of Sertoli cell proliferation that we found to normally cease between 4.5 and 5 mo of age. In adulthood, these bulls produced a significantly greater number of sperm compared to age-matched controls and their testes contained nearly 2 times more Sertoli cells. Importantly, sperm motility, morphology, fertilizing ability, and viability after cryopreservation were found to be no different for treated bulls compared to untreated control bulls. This strategy of transient induction of hypothyroidism during a defined period of prepubertal development in bulls could prove to be an efficacious approach for enhancing daily sperm production in genetically desirable sires that will, in turn, provide an avenue for improving the efficiency of commercial cattle production.

Molecular Mechanisms and Signaling Pathways Involved in Sertoli Cell Proliferation

Sertoli cells are somatic cells present in seminiferous tubules which have essential roles in regulating spermatogenesis. Considering that each Sertoli cell is able to support a limited number of germ cells, the final number of Sertoli cells reached during the proliferative period determines sperm production capacity. Only immature Sertoli cells, which have not established the blood-testis barrier, proliferate. A number of hormonal cues regulate Sertoli cell proliferation. Among them, FSH, the insulin family of growth factors, activin, and cytokines action must be highlighted. It has been demonstrated that cAMP/PKA, ERK1/2, PI3K/Akt, and mTORC1/p70SK6 pathways are the main signal transduction pathways involved in Sertoli cell proliferation. Additionally, c-Myc and hypoxia inducible factor are transcription factors which participate in the induction by FSH of various genes of relevance in cell cycle progression. Cessation of proliferation is a pre-requisite to Sertoli cell maturation accompanied by the establishment of the blood-testis barrier. With respect to this barrier, the participation of androgens, estrogens, thyroid hormones, retinoic acid and opioids has been reported. Additionally, two central enzymes that are involved in sensing cell energy status have been associated with the suppression of Sertoli cell proliferation, namely AMPK and Sirtuin 1 (SIRT1). Among the molecular mechanisms involved in the cessation of proliferation and in the maturation of Sertoli cells, it is worth mentioning the up-regulation of the cell cycle inhibitors p21Cip1, p27Kip, and p19INK4, and of the gap junction protein connexin 43. A decrease in Sertoli cell proliferation due to administration of certain therapeutic drugs and exposure to xenobiotic agents before puberty has been experimentally demonstrated. This review focuses on the hormones, locally produced factors, signal transduction pathways, and molecular mechanisms controlling Sertoli cell proliferation and maturation. The comprehension of how the final number of Sertoli cells in adulthood is established constitutes a pre-requisite to understand the underlying causes responsible for the progressive decrease in sperm production that has been observed during the last 50 years in humans.

Insights into leptin signaling and male reproductive health: the missing link between overweight and subfertility?

Obesity stands as one of the greatest healthcare challenges of the 21st century. Obesity in reproductive-age men is ever more frequent and is reaching upsetting levels. At the same time, fertility has taken an inverse direction and is decreasing, leading to an increased demand for fertility treatments. In half of infertile couples, there is a male factor alone or combined with a female factor. Furthermore, male fertility parameters such as sperm count and concentration went on a downward spiral during the last few decades and are now approaching the minimum levels established to achieve successful fertilization. Hence, the hypothesis that obesity and deleterious effects in male reproductive health, as reflected in deterioration of sperm parameters, are somehow related is tempting. Most often, overweight and obese individuals present leptin levels directly proportional to the increased fat mass. Leptin, besides the well-described central hypothalamic effects, also acts in several peripheral organs, including the testes, thus highlighting a possible regulatory role in male reproductive function. In the last years, research focusing on leptin effects in male reproductive function has unveiled additional roles and molecular mechanisms of action for this hormone at the testicular level. Herein, we summarize the novel molecular signals linking metabolism and male reproductive function with a focus on leptin signaling, mitochondria and relevant pathways for the nutritional support of spermatogenesis.

Thyroid Hormone Deiodination and Action in the Gonads

Alterations in thyroid hormone (TH) status during developmental or adult age are associated with abnormal gonadal development and function in human and animal models. In the developing testis, aberrant levels of TH action lead to disruptions in cell proliferation and differentiation, ultimately influencing testicular size, spermatogenesis, steroidogenesis and male fertility. Recent work is increasingly identifying the systems and signaling pathways in gonadal cells that are affected by TH, as well as delineating the major factors that determine TH signaling in gonadal tissue. The TH receptor alpha, the monocarboxylate transporter 8 and the type 3 deiodinase appear to be major contributors to the timely regulation of TH action in the developing testis.

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.