Low levels of Gαs and Ric8b in testicular sertoli cells may underlie restricted FSH action during infancy in primates

Understanding testicular single cell transcriptional atlas: from developmental complications to male infertility

Spermatogenesis is a multi-step biological process where mitotically active diploid (2n) spermatogonia differentiate into haploid (n) spermatozoa via regulated meiotic programming. The alarming rise in male infertility has become a global concern during the past decade thereby demanding an extensive profiling of testicular gene expression. Advancements in Next-Generation Sequencing (NGS) technologies have revolutionized our empathy towards complex biological events including spermatogenesis. However, despite multiple attempts made in the past to reveal the testicular transcriptional signature(s) either with bulk tissues or at the single-cell, level, comprehensive reviews on testicular transcriptomics and associated disorders are limited. Notably, technologies explicating the genome-wide gene expression patterns during various stages of spermatogenic progression provide the dynamic molecular landscape of testicular transcription. Our review discusses the advantages of single-cell RNA-sequencing (Sc-RNA-seq) over bulk RNA-seq concerning testicular tissues. Additionally, we highlight the cellular heterogeneity, spatial transcriptomics, dynamic gene expression and cell-to-cell interactions with distinct cell populations within the testes including germ cells (Gc), Sertoli cells (Sc), Peritubular cells (PTc), Leydig cells (Lc), etc. Furthermore, we provide a summary of key finding of single-cell transcriptomic studies that have shed light on developmental mechanisms implicated in testicular disorders and male infertility. These insights emphasize the pivotal roles of Sc-RNA-seq in advancing our knowledge regarding testicular transcriptional landscape and may serve as a potential resource to formulate future clinical interventions for male reproductive health.

The research progress on the impact of antibiotics on the male reproductive system

Antibiotics are extensively utilized in the livestock and poultry industry and can accumulate in animals and the environment, leading to potential health risks for humans via food and water consumption. Research on antibiotic toxicity, particularly their impact as endocrine disruptors on the male reproductive system, is still in its nascent stages. This review highlights the toxic effect of antibiotics on the male reproductive system, detailing the common routes of exposure and the detrimental impact and mechanisms of various antibiotic classes. Additionally, it discusses the protective role of food-derived active substances against the reproductive toxicity induced by antibiotics. This review aims to raise awareness about the reproductive toxicity of antibiotics in males and to outline the challenges that must be addressed in future research.

Etiology of Male Infertility: an Update

Spermatogenesis is a complex process of germ cell division and differentiation that involves extensive cross-talk between the developing germ cells and the somatic testicular cells. Defective endocrine signaling and/or intrinsic defects within the testes can adversely affect spermatogenic progression, leading to subfertility/infertility. In recent years, male infertility has been recognized as a global public health concern, and research over the last few decades has elucidated the complex etiology of male infertility. Congenital reproductive abnormalities, genetic mutations, and endocrine/metabolic dysfunction have been demonstrated to be involved in infertility/subfertility in males. Furthermore, acquired factors like exposure to environmental toxicants and lifestyle-related disorders such as illicit use of psychoactive drugs have been shown to adversely affect spermatogenesis. Despite the large body of available scientific literature on the etiology of male infertility, a substantial proportion of infertility cases are idiopathic in nature, with no known cause. The inability to treat such idiopathic cases stems from poor knowledge about the complex regulation of spermatogenesis. Emerging scientific evidence indicates that defective functioning of testicular Sertoli cells (Sc) may be an underlying cause of infertility/subfertility in males. Sc plays an indispensable role in regulating spermatogenesis, and impaired functional maturation of Sc has been shown to affect fertility in animal models as well as humans, suggesting abnormal Sc as a potential underlying cause of reproductive insufficiency/failure in such cases of unexplained infertility. This review summarizes the major causes of infertility/subfertility in males, with an emphasis on infertility due to dysregulated Sc function.

The role of GnRH in Tibetan male sheep and goat reproduction

The hypothalamic-pituitary-gonadal (HPG) axis connects the hypothalamus, pituitary gland, and gonads. The regulation of reproductive processes includes integrating various factors from structural functions and environmental conditions in the HPG axis, with the outcome indication of these processes being the pulsatile secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus. These factors include feed consumption and nutritional condition, sex steroids, season/photoperiod, pheromones, age, and stress. GnRH pulsatile secretion affects the pattern of gonadotropin secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which then regulates both endocrine function and gamete maturation in the gonads. This regulates gonadotropins and testosterone (T) production. There is evidence that in males, GnRH participates in a variety of host behavioural and physiological processes such as the release of reproductive hormones, progression of spermatogenesis and sperm function, aggressive behaviour, and physiological metabolism. GnRH activates receptors expressed on Leydig cells and Sertoli cells, respectively to stimulate T secretion and spermatogenesis in the testis. Photoperiod affects the reproductive system of the hypothalamic-pituitary axis via rhythmic diurnal melatonin secretion. Increased release of melatonin promotes sexual activity, GnRH production, LH stimulation, and T production. This induces testicular functions, spermatogenesis, and puberty. GnRH reduces the release of LH by the pituitary through the cascade effect and decreases plasma concentration of T. Gut microbiota maintain sex steroid homeostasis and may induce reduction in reproduction productivity. Recently, findings of kisspeptin-neurokinin-dynorphin neuronal network in the brain have resulted in fast advances in how GnRH secretion is controlled. Emerging studies have also indicated that other neuropeptide analogues could be used in control reproduction procedures in various goat and sheep breeds. The Tibetan male sheep and goats reproduce on a seasonal basis and have high reproductive performance. This is a review for the role of GnRH in Tibetan male sheep and goats reproduction. This is intended to enhance reproductive knowledge for understanding the key roles of GnRH relating to male reproductive efficiency of Tibetan sheep or goats.

Long-acting recombinant human follicle-stimulating hormone (SAFA-FSH) enhances spermatogenesis

INTRODUCTION

Administration of follicle-stimulating hormone (FSH) has been recommended to stimulate spermatogenesis in infertile men with hypogonadotropic hypogonadism, whose sperm counts do not respond to human chorionic gonadotropin alone. However, FSH has a short serum half-life requiring frequent administration to maintain its therapeutic efficacy. To improve its pharmacokinetic properties, we developed a unique albumin-binder technology, termed "anti-serum albumin Fab-associated" (SAFA) technology. We tested the feasibility of applying SAFA technology to create long-acting FSH as a therapeutic candidate for patients with hypogonadotropic hypogonadism.

METHODS

SAFA-FSH was produced using a Chinese hamster ovary expression system. To confirm the biological function, the production of cyclic AMP and phosphorylation of ERK and CREB were measured in TM4-FSHR cells. The effect of gonadotropin-releasing hormone agonists on spermatogenesis in a hypogonadal rat model was investigated.

RESULTS

In in vitro experiments, SAFA-FSH treatment increased the production of cyclic AMP and increased the phosphorylation of ERK and CREB in a dose-dependent manner. In animal experiments, sperm production was not restored by human chorionic gonadotropin treatment alone, but was restored after additional recombinant FSH treatment thrice per week or once every 5 days. Sperm production was restored even after additional SAFA-FSH treatment at intervals of once every 5 or 10 days.

DISCUSSION

Long-acting FSH with bioactivity was successfully created using SAFA technology. These data support further development of SAFA-FSH in a clinical setting, potentially representing an important advancement in the treatment of patients with hypogonadotropic hypogonadism.

Revisiting the gonadotropic regulation of mammalian spermatogenesis: evolving lessons during the past decade

Spermatogenesis is a multi-step process of male germ cell (Gc) division and differentiation which occurs in the seminiferous tubules of the testes under the regulation of gonadotropins - Follicle Stimulating Hormone (FSH) and Luteinising hormone (LH). It is a highly coordinated event regulated by the surrounding somatic testicular cells such as the Sertoli cells (Sc), Leydig cells (Lc), and Peritubular myoid cells (PTc). FSH targets Sc and supports the expansion and differentiation of pre-meiotic Gc, whereas, LH operates via Lc to produce Testosterone (T), the testicular androgen. T acts on all somatic cells e.g.- Lc, PTc and Sc, and promotes the blood-testis barrier (BTB) formation, completion of Gc meiosis, and spermiation. Studies with hypophysectomised or chemically ablated animal models and hypogonadal (hpg) mice supplemented with gonadotropins to genetically manipulated mouse models have revealed the selective and synergistic role(s) of hormones in regulating male fertility. We here have briefly summarized the present concept of hormonal control of spermatogenesis in rodents and primates. We also have highlighted some of the key critical questions yet to be answered in the field of male reproductive health which might have potential implications for infertility and contraceptive research in the future.

The function of nuclear hormone receptor 4A signaling in the human reproductive system: A review

AIM

This review aims to summarize the research focused upon the functions of nuclear hormone receptor 4A (NR4A) in the human reproductive system. The research questions addressed are to decipher what role the NR4A subfamily plays in the regulation of the human reproductive system and effects upon fertility issues through regulation of the expression of the NR4A subfamily.

METHODS

The electronic database PubMed was searched for studies published before November 2021. Keywords included "NR4A," "trophoblast," "decidualization," "folliculogenesis," "estrogen," "pregnancy," "Leydig cells," "fertility," and "reproductive." Relevant references from retrieved manuscripts and review articles were also searched manually.

RESULTS

NR4A subfamily are involved in trophoblast differentiation, endometrial decidualization, embryo adhesion, secretion of related hormones, and regulation of spontaneous term labor. Besides, many studies have provided strong evidence that they play critical roles in spermatogenesis. Furthermore, Multiple mechanisms can affect the expression of NR4As. Broadly, NR4A family receptors affect the human reproductive system in multiple ways.

CONCLUSIONS

Further research is needed to specifically dissect the functions and regulatory mechanisms of these receptors and their pharmaceutical antagonists and agonists. The connection between the NR4A subfamily and a variety of reproductive disorders needs to be proven experimentally such that further examination of human tissue is required to assess the role of these receptors in human reproductive diseases.

Follicle-stimulating hormone-mediated decline in miR-92a-3p expression in pubertal mice Sertoli cells is crucial for germ cell differentiation and fertility

Sertoli cells (Sc) are the sole target of follicle-stimulating hormone (FSH) in the testis and attain functional maturation post-birth to significantly augment germ cell (Gc) division and differentiation at puberty. Despite having an operational microRNA (miRNA) machinery, limited information is available on miRNA-mediated regulation of Sc maturation and male fertility. We have shown before that miR-92a-3p levels decline in pubertal rat Sc. In response to FSH treatment, the expressions of FSH Receptor, Claudin11 and Klf4 were found to be elevated in pubertal rat Sc coinciding with our finding of FSH-induced decline in miR-92a-3p levels. To investigate the association of miR-92a-3p and spermatogenesis, we generated transgenic mice where such pubertal decline of miR-92a-3p was prevented by its overexpression in pubertal Sc under proximal Rhox5 promoter, which is known to be activated specifically at puberty, in Sc. Our in vivo observations provided substantial evidence that FSH-induced decline in miR-92a-3p expression during Sc maturation acts as an essential prerequisite for the pubertal onset of spermatogenesis. Elevated expression of miR-92a-3p in post-pubertal testes results into functionally compromised Sc, leading to impairment of the blood-testis barrier formation and apoptosis of pre-meiotic Gc, ultimately culminating into infertility. Collectively, our data suggest that regulation of miR-92a-3p expression is crucial for Sc-mediated induction of active spermatogenesis at puberty and regulation of male fertility.

Declining levels of miR-382-3p at puberty trigger the onset of spermatogenesis

A major change in the transcriptome of testicular Sertoli cells (Scs) at the onset of puberty enables them to induce robust spermatogenesis. Through comprehensive literature mining, we generated a list of genes crucial for Sc functioning and computationally predicted the microRNAs regulating them. Differential expression analysis of microRNAs in infant and pubertal rat Scs showed that miR-382-3p levels decline significantly in pubertal Scs. Interestingly, miR-382-3p was found to regulate genes like Ar and Wt1, which are crucial for functional competence of Scs. We generated a transgenic (Tg) mouse model in which pubertal decline of miR-382-3p was prevented by its overexpression in pubertal Scs. Elevated miR-382-3p restricted the functional maturation of Scs at puberty, leading to infertility. Prevention of decline in miR-382-3p expression in pubertal Scs was responsible for defective blood-testis barrier (BTB) formation, severe testicular defects, low epididymal sperm counts and loss of fertility in these mice. This provided substantial evidence that decline in levels of miR-382-3p at puberty is the essential trigger for onset of robust spermatogenesis at puberty. Hence, sustained high levels of miR-382-3p in pubertal Scs could be one of the underlying causes of idiopathic male infertility and should be considered for diagnosis and treatment of infertility.

FSH mediated cAMP signalling upregulates the expression of Gα subunits in pubertal rat Sertoli cells

Follicle Stimulating Hormone (FSH) acts via FSH-Receptor (FSH-R) by employing cAMP as the dominant secondary messenger in testicular Sertoli cells (Sc) to support spermatogenesis. Binding of FSH to FSH-R, results the recruitment of the intracellular GTP binding proteins, either stimulatory Gαs or inhibitory Gαi that in turn regulate cAMP production in Sc. The cytosolic concentration of cAMP being generated by FSH-R thereafter critically determines the downstream fate of the FSH signalling. The pleiotropic action of FSH due to differential cAMP output during functional maturation of Sc has been well studied. However, the developmental and cellular regulation of the Gα proteins associated with FSH-R is poorly understood in Sc. In the present study, we report the differential transcriptional modulation of the Gα subunit genes by FSH mediated cAMP signalling in neonatal and pubertal rat Sc. Our data suggested that unlike in neonatal Sc, both the basal and FSH/forskolin induced expression of Gαs, Gαi-1, Gαi-2 and Gαi-3 transcripts was significantly (p < 0.05) up-regulated in pubertal Sc. Further investigations involving treatment of Sc with selective Gαi inhibitor pertussis toxin, confirmed the elevated expression of Gi subunits in pubertal Sc. Collectively our results indicated that the high level of Gαi subunits serves as a negative regulator to optimize cAMP production in pubertal Sc.

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.

Toxicologic Pathology Forum*: Opinion on Sexual Maturity and Fertility Assessment in Long-tailed Macaques ( Macaca fascicularis) in Nonclinical Safety Studies

If nonhuman primates represent the only relevant species for nonclinical safety evaluation of biotechnology-derived products, male and female fertility effects can be assessed in repeat dose toxicity studies given that sexually mature monkeys are used. This opinion piece provides recommendations for determining sexual maturity and when/how fertility assessments should be conducted in the cynomolgus monkey. Male sexual maturity should be proven by presence of sperm in a semen sample, female sexual maturity by at least two consecutive menstrual bleedings. As per regulatory guidance, default parameters for an indirect assessment of fertility in both sexes are reproductive organ weight and histopathology. Beyond default parameters, daily vaginal swabs are recommended for females, and for males, it is recommended to include blood collections (for potential analysis of reproductive hormones), testis volume sonography, and collection of frozen testis samples at necropsy. Only if there is a cause for concern, blood collection for potential reproductive hormone analysis should be conducted in females and semen analysis in males. In principle, adverse reproductive effects can be detected within 4 weeks of test article administration, depending on study design and reproductive end point chosen. Therefore, there are options for addressing reproductive toxicity aspects with studies of less than 3 months dosing duration. *This is an opinion article submitted to the Toxicologic Pathology Forum. It represents the views of the authors. It does not constitute an official position of the Society of Toxicologic Pathology, British Society of Toxicological Pathology, or European Society of Toxicologic Pathology, and the views expressed might not reflect the best practices recommended by these Societies. This article should not be construed to represent the policies, positions, or opinions of their respective organizations, employers, or regulatory agencies.

Testosterone augments FSH signaling by upregulating the expression and activity of FSH-Receptor in Pubertal Primate Sertoli cells

The synergistic actions of Testosterone (T) and FSH via testicular Sertoli cells (Sc) regulate male fertility. We have previously reported that the actions of these hormones (T and FSH) in infant monkey testes are restricted only to the expansion of Sc and spermatogonial cells. The robust differentiation of male Germ cells (Gc) occurs after pubertal maturation of testis. The present study was aimed to investigate the molecular basis of the synergy between T and FSH action in pubertal primate (Macaca mulatta) Sc. Using primary Sc culture, we here have demonstrated that T (but not FSH) downregulated AMH and Inhibin-β-B (INHBB) mRNAs in pubertal Sc. We also found that, prolonged stimulation of T in pubertal Sc significantly elevated the expression of genes involved in FSH signaling pathway like FSH-Receptor (FSHR), GNAS and RIC8B, and this was associated with a rise in cAMP production. T also augmented FSH induced expression of genes like SCF, GDNF, ABP and Transferrin (TF) in pubertal Sc. We therefore conclude that T acts in synergy with FSH signaling in pubertal Sc. Such a coordinated network of hormonal signaling in Sc may facilitate the timely onset of the first spermatogenic wave in pubertal primates and is responsible for quantitatively and qualitatively normal spermatogenesis.

Efficacy of curcumin for age-associated cognitive decline: a narrative review of preclinical and clinical studies

Processes such as aberrant redox signaling and chronic low-grade systemic inflammation have been reported to modulate age-associated pathologies such as cognitive impairment. Curcumin, the primary therapeutic component of the Indian spice, Turmeric (Curcuma longa), has long been known for its strong anti-inflammatory and antioxidant activity attributable to its unique molecular structure. Recently, an interest in this polyphenol as a cognitive therapeutic for the elderly has emerged. The purpose of this paper is to critically review preclinical and clinical studies that have evaluated the efficacy of curcumin in ameliorating and preventing age-associated cognitive decline and address the translational progress of preclinical to clinical efficacy. PubMed, semantic scholar, and Google scholar searches were used for preclinical studies; and clinicaltrials.gov , the Australian and New Zealand clinical trials registry, and PubMed search were used to select relevant completed clinical studies. Results from preclinical studies consistently demonstrate curcumin and its analogues to be efficacious for various aspects of cognitive impairment and processes that contribute to age-associated cognitive impairment. Results of published clinical studies, while mixed, continue to show promise for curcumin's use as a therapeutic for cognitive decline but overall remain inconclusive at this time. Both in vitro and in vivo studies have found that curcumin can significantly decrease oxidative stress, systemic inflammation, and obstruct pathways that activate transcription factors that augment these processes. Future clinical studies would benefit from including evaluation of peripheral and cerebrospinal fluid biomarkers of dementia and behavioral markers of cognitive decline, as well as targeting the appropriate population.

Defective Wnt3 expression by testicular Sertoli cells compromise male fertility

Testicular Sertoli cells make a niche for the division and differentiation of germ cells. Sertoli cells respond to increased follicle-stimulating hormone (FSH) and testosterone (T) levels at the onset of puberty by producing paracrine factors which affect germ cells and trigger robust onset of spermatogenesis. Such paracrine support to germ cells is absent during infancy, despite Sertoli cells being exposed to high FSH and T within the infant testis. This situation is similar to certain cases of male idiopathic infertility where post-pubertal Sertoli cells fail to support germ cell division and differentiation in spite of endogenous or exogenous hormonal support. Defective Sertoli cells in such individuals may fail to express the full complement of their paracrine repertoire. Identification and supplementation with such factors may overcome Sertoli cells deficiencies and help trigger quantitatively and qualitatively normal differentiation of germ cells. To this end, we compared the transcriptome of FSH- and T-treated infant and pubertal monkey Sertoli cells by DNA microarray. Expression of Wnt3, a morphogen of the Wnt/β-catenin pathway, was higher in pubertal Sertoli cells relative to infant Sertoli cells. Transgenic mice were generated by us in which Wnt3 expression was curtailed specifically in post-pubertal Sertoli cells by shRNA. Subfertility and oligozoospermia were noticed in such animals with low Wnt3 expression in post-pubertal Sertoli cells along with diminished expression of Connexin43, a gap-junctional molecule essential for germ cell development. We report that the FSH- and T-targetedf Wnt3 governs Sertoli cell-mediated regulation of spermatogenesis and hence is crucial for fertility.

Crosstalk between FSH and relaxin at the end of the proliferative stage of rat Sertoli cells

Follicle-stimulating hormone (FSH) stimulates the proliferation of immature Sertoli cells through the activation of PI3K/AKT/mTORC1 and MEK/ERK1/2 pathways. Mature Sertoli cells stop proliferating and respond to FSH by stimulating cAMP production. To gain insight into possible mechanisms involved in this switch as well as the impact of paracrine factors that stimulate cell proliferation, we analyzed the effects of FSH and relaxin on intracellular signaling pathways involved with proliferation and differentiation in Sertoli cells from 15-day-old rats, which are close to the transition between the two stages. FSH stimulated ³H-thymidine incorporation and cyclin D1 expression, changes associated with proliferation. In contrast, FSH inhibited AKT and ERK1/2 phosphorylation, activated cAMP production and induced changes in several cell cycle genes that were compatible with differentiation. Relaxin also stimulated ³H-thymidine incorporation but increased phosphorylation of ERK1/2 and AKT. When both hormones were added simultaneously, relaxin attenuated FSH-mediated inhibition of ERK1/2 and AKT phosphorylation and FSH-mediated activation of cAMP production. FSH but not relaxin increased CREB phosphorylation, and relaxin but not FSH shifted NF-κB expression from the cytoplasm to the nucleus. Relaxin did not inhibit the effects of FSH on inhibin α and Bcl2 expression. We propose that at this time of Sertoli cell development, FSH starts to direct cells to differentiation through activation of cAMP/CREB and inhibition of ERK1/2 and AKT pathways. Relaxin counteracts FSH signaling through the inhibition of cAMP and activation of ERK1/2, AKT and NF-κB, but does not block the differentiation process triggered by FSH.

A Study of Differential Expression of Testicular Genes in Various Reproductive Phases of Hemidactylus flaviviridis (Wall Lizard) to Derive Their Association with Onset of Spermatogenesis and Its Relevance to Mammals

Testis of Hemidactylus flaviviridis, commonly known as Indian wall lizard, displays a lack of cellular and metabolic activity in regressed phase of testis during non-breeding season of the year. Retracted Sertoli cells (Sc), fibroid myoid cells and pre-meiotic resting spermatogonia are observed in such testis. This situation is akin to certain forms of infertility in men where hormone supplementation fails to generate sperm despite the presence of Sc and germ cells (Gc) in testis. In testis of lizard, spermatogenesis is reinitiated upon increased level of hormones during appropriate season (phase of recrudescence). Study of genes associated with generation of sperm, from regressed adult testis in lizard, may provide valuable information for understanding certain forms of male idiopathic infertility. Subtractive hybridization using testicular RNA obtained from the regressed and active phases of lizard reproductive cycle led to identify eight partial mRNA sequences that showed sequence homology with mice genes. We further evaluated the gene expression prolife by real-time PCR in three different reproductive phases of H. flaviviridis: regressed (pre-meiotic), recrudescent (meiotic) and active (post meiotic), for comparison with the corresponding testicular phases found in testis of 5 days (pre-meiotic), 20 days (meiotic) and 60 days (post-meiotic) old mouse. This is the first report where genes associated with progression of spermatogenesis during active phase, which follows a regressed state of adult testis, were identified in lizard and found to be conserved in mouse. Six important genes, Hk1, Nme5, Akap4, Arih1, Rassf7 and Tubb4b were found to be strictly associated with active spermatogenesis in both mouse and lizard. Factors interfering with the expression of any of these genes may potentially abrogate the process of spermatogenesis leading to infertility. Such information may shed light on unknown causes of idiopathic male infertility.