Cdc42 activity in Sertoli cells is essential for maintenance of spermatogenesis

Inactivation of JNK signalling results in polarity loss and cell senescence of Sertoli cell

As major somatic cells in the testis, Sertoli cell development is precisely regulated by numerous factors, and aberrant development of these cells is associated with male reproductive diseases. JNK signalling is evolutionarily conserved and involved in multiple critical biological processes. Here, we found that the double knockout of Jnk1 and Jnk2 resulted in aberrant localisation of Sertoli cells at early developmental stages, with most Sertoli cells being lost at later stages. Further studies revealed that the inactivation of JNK signalling caused polarity loss in Sertoli cells. In vitro-cultured Jnk1/2-DKO Sertoli cells exhibited a senescence-associated phenotype. Mechanistic studies demonstrate that JNK signalling is likely involved in establishing Sertoli cell polarity by regulating the expression of TGF-β2, mediated by c-Jun. The senescence of Sertoli cells in JNKs-deficient mice is caused by aberrant proteolysis of P27KIP1, mediated by c-Myc. This study demonstrates the role of JNK signalling in Sertoli cell development and functional maintenance, which may also represent an aetiology of male infertility in humans.

A Comparison of White and Yellow Seminal Plasma Phosphoproteomes Obtained from Turkey (Meleagris gallopavo) Semen

Seminal plasma is rich in proteins originating from various male reproductive organs. The phosphorylation of these proteins can significantly impact sperm motility, capacitation, and acrosome reaction. Phosphoproteomics identifies, catalogues, and characterizes phosphorylated proteins. The phosphoproteomic profiling of seminal plasma offers valuable insights into the molecular mechanisms that influence semen quality and male fertility. Thus, the aim of this study was a phosphoproteomic analysis of white and yellow turkey seminal plasma. The experimental material consisted of 100 ejaculates from BIG-6 turkeys between 39 and 42 weeks of age. The collected white and yellow turkey seminal plasmas were analyzed for total protein content; the activity of selected enzymes, i.e., alkaline phosphatase (ALP), acid phosphatase (ACP), superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT); and the content of reduced glutathione (GSH) and malondialdehyde (MDA). Phosphoproteins were isolated from white and yellow seminal fluids, and the resulting protein fractions were separated by SDS-PAGE and Western blotting. Phosphorylated residues were immunodetected, and the isolated phosphoproteins were identified (nano LC-MS/MS). Yellow seminal plasmas were characterized by higher levels of total protein, GSH, and MDA, as well as higher levels of ALP, ACP, and GPx activity. There were no significant differences in the activity of SOD and CAT. A total of 113 phosphoproteins were identified in turkey seminal fluids. The functional analysis demonstrated that these phosphoproteins were mainly involved in oocyte fertilization, organization and metabolism of the actin cytoskeleton, amplification of the intracellular signal transduction pathway, general regulation of transport, vesicular transport, proteome composition of individual cellular compartments, and the organization and localization of selected cellular components and macromolecules. Increased phosphorylation of the fractions containing proteins encoded by SPARC, PPIB, TRFE, QSOX1, PRDX1, PRDX6, and FASN genes in white plasmas and the proteins encoded by CKB, ORM2, APOA1, SSC5D, RAP1B, CDC42, FTH, and TTH genes in yellow plasmas was observed based on differences in the optical density of selected bands. The obtained results indicate that the phosphorylation profiles of turkey seminal plasma proteins vary depending on the type of ejaculate.

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.

Unveiling the roles of Sertoli cells lineage differentiation in reproductive development and disorders: a review

In mammals, gonadal somatic cell lineage differentiation determines the development of the bipotential gonad into either the ovary or testis. Sertoli cells, the only somatic cells in the spermatogenic tubules, support spermatogenesis during gonadal development. During embryonic Sertoli cell lineage differentiation, relevant genes, including WT1, GATA4, SRY, SOX9, AMH, PTGDS, SF1, and DMRT1, are expressed at specific times and in specific locations to ensure the correct differentiation of the embryo toward the male phenotype. The dysregulated development of Sertoli cells leads to gonadal malformations and male fertility disorders. Nevertheless, the molecular pathways underlying the embryonic origin of Sertoli cells remain elusive. By reviewing recent advances in research on embryonic Sertoli cell genesis and its key regulators, this review provides novel insights into sex determination in male mammals as well as the molecular mechanisms underlying the genealogical differentiation of Sertoli cells in the male reproductive ridge.

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.

HDAC3 promotes Sertoli cell maturation and maintains the blood-testis barrier dynamics

Germ cell development depends on the capacity of somatic Sertoli cells to undergo differentiation into a mature state and establish a germ cell-specific blood-testis barrier (BTB). The BTB structure confers an immunological barrier for meiotic and postmeiotic germ cells, and its dynamic permeability facilitates a transient movement of preleptotene spermatocytes through BTB to enter meiosis. However, the regulatory factors involved in Sertoli cell maturation and how BTB dynamics coordinate germ cell development remain unclear. Here, we found a histone deacetylase HDAC3 abundantly expresses in Sertoli cells and localizes in both cytoplasm and nucleus. Sertoli cell-specific Hdac3 knockout in mice causes infertility with compromised integrity of blood-testis barrier, leading to germ cells unable to traverse through BTB and an accumulation of preleptotene spermatocytes in juvenile testis. Mechanistically, nuclear HDAC3 regulates the expression program of Sertoli cell maturation genes, and cytoplasmic HDAC3 forms a complex with the gap junction protein Connexin 43 to modulate the BTB integrity and dynamics through regulating the distribution of tight junction proteins. Our findings identify HDAC3 as a critical regulator in promoting Sertoli cell maturation and maintaining the homeostasis of the blood-testis barrier.

A comprehensive review on signaling attributes of serine and serine metabolism in health and disease

Serine is a metabolite with ever-expanding metabolic and non-metabolic signaling attributes. By providing one‑carbon units for macromolecule biosynthesis and functional modifications, serine and serine metabolism largely impinge on cellular survival and function. Cancer cells frequently have a preference for serine metabolic reprogramming to create a conducive metabolic state for survival and aggressiveness, making intervention of cancer-associated rewiring of serine metabolism a promising therapeutic strategy for cancer treatment. Beyond providing methyl donors for methylation in modulation of innate immunity, serine metabolism generates formyl donors for mitochondrial tRNA formylation which is required for mitochondrial function. Interestingly, fully developed neurons lack the machinery for serine biosynthesis and rely heavily on astrocytic l-serine for production of d-serine to shape synaptic plasticity. Here, we recapitulate recent discoveries that address the medical significance of serine and serine metabolism in malignancies, mitochondrial-associated disorders, and neurodegenerative pathologies. Metabolic control and epigenetic- and posttranslational regulation of serine metabolism are also discussed. Given the metabolic similarities between cancer cells, neurons and germ cells, we further propose the relevance of serine metabolism in testicular homeostasis. Our work provides valuable hints for future investigations that will lead to a deeper understanding of serine and serine metabolism in cellular physiology and pathology.

Retinoic acid signaling in development and differentiation commitment and its regulatory topology

Retinoic acid (RA), the derivative of vitamin A/retinol, is a signaling molecule with important implications in health and disease. It is a well-known developmental morphogen that functions mainly through the transcriptional activity of nuclear RA receptors (RARs) and, uncommonly, through other nuclear receptors, including peroxisome proliferator-activated receptors. Intracellular RA is under spatiotemporally fine-tuned regulation by synthesis and degradation processes catalyzed by retinaldehyde dehydrogenases and P450 family enzymes, respectively. In addition to dictating the transcription architecture, RA also impinges on cell functioning through non-genomic mechanisms independent of RAR transcriptional activity. Although RA-based differentiation therapy has achieved impressive success in the treatment of hematologic malignancies, RA also has pro-tumor activity. Here, we highlight the relevance of RA signaling in cell-fate determination, neurogenesis, visual function, inflammatory responses and gametogenesis commitment. Genetic and post-translational modifications of RAR are also discussed. A better understanding of RA signaling will foster the development of precision medicine to improve the defects caused by deregulated RA signaling.

Autophagy regulation and protein kinase activity of PIK3C3 controls sertoli cell polarity through its negative regulation on SCIN (scinderin)

Sertoli cells are highly polarized testicular cells that provide a nurturing environment for germ cell development and maturation during spermatogenesis. The class III phosphatidylinositol 3-kinase (PtdIns3K) plays core roles in macroautophagy in various cell types; however, its role in Sertoli cells remains unclear. Here, we generated a mouse line in which the gene encoding the catalytic subunit, Pik3c3, was specifically deleted in Sertoli cells (cKO) and found that after one round of normal spermatogenesis, the cKO mice quickly became infertile and showed disruption of Sertoli cell polarity and impaired spermiogenesis. Subsequent proteomics and phosphoproteomics analyses enriched the F-actin cytoskeleton network involved in the disorganized Sertoli-cell structure in cKO testis which we identified a significant increase of the F-actin negative regulator SCIN (scinderin) and the reduced phosphorylation of HDAC6, an α-tubulin deacetylase. Our results further demonstrated that the accumulation of SCIN in cKO Sertoli cells caused the disorder and disassembly of the F-actin cytoskeleton, which was related to the failure of SCIN degradation through the autophagy-lysosome pathway. Additionally, we found that the phosphorylation of HDAC6 at site S59 by PIK3C3 was essential for its degradation through the ubiquitin-proteasome pathway. As a result, the HDAC6 that accumulated in cKO Sertoli cells deacetylated SCIN at site K189 and led to a disorganized F-actin cytoskeleton. Taken together, our findings elucidate a new mechanism for PIK3C3 in maintaining the polarity of Sertoli cells, in which both its autophagy regulation or protein kinase activities are required for the stabilization of the actin cytoskeleton.Abbreviations: ACTB: actin, beta; AR: androgen receptor; ATG14: autophagy related 14; BafA1: bafilomycin A1; BECN1: beclin 1, autophagy related; BTB: blood-testis barrier; CASP3: caspase 3; CDC42: cell division cycle 42; CDH2: cadherin 2; CHX: cycloheximide; CTNNA1: catenin (cadherin associated protein), alpha 1; CYP11A1: cytochrome P450, family 11, subfamily A, polypeptide 1; EBSS: Earle's balanced salt solution; ES: ectoplasmic specialization; FITC: fluorescein isothiocyanate; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GCNA: germ cell nuclear acidic protein; GJA1: gap junction protein, alpha 1; H2AX: H2A.X variant histone; HDAC6: histone deacetylase 6; KIT: KIT proto-oncogene, receptor tyrosine kinase; LAMP1: lysosomal associated membrane protein 1; MAP3K5: mitogen-activated protein kinase kinase kinase 5; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; OCLN: occludin; PIK3C3: phosphatidylinositol 3-kinase catalytic subunit type 3; PIK3R4: phosphoinositide-3-kinase regulatory subunit 4; PNA: arachis hypogaea lectin; RAC1: Rac family small GTPase 1; SCIN: scinderin; SQSTM1/p62: sequestosome 1; SSC: spermatogonia stem cell; STK11: serine/threonine kinase 11; TJP1: tight junction protein 1; TubA: tubastatin A; TUBB3: tubulin beta 3 class III; TUNEL: TdT-mediated dUTP nick-end labeling; UB: ubiquitin; UVRAG: UV radiation resistance associated gene; VIM: vimentin; WT1: WT1 transcription factor; ZBTB16: zinc finger and BTB domain containing 16.

Puerarin improves busulfan-induced disruption of spermatogenesis by inhibiting MAPK pathways

Male infertility is a global concern, with a noticeable increase in the decline of spermatogenesis and sperm quality. However, there are limited clinically effective treatments available. This study aimed to investigate the potential effectiveness of puerarin in treating male infertility, which leads to gonadal changes. The results obtained from various analyses such as CASA, immunofluorescence, DIFF-Quick, hematoxylin and eosin (H&E), and periodic acid-Schiff (PAS) staining demonstrated that puerarin supplementation significantly alleviated the busulfan-induced reduction in spermatogenesis and sperm quality in both young and adult mice. Furthermore, puerarin exhibited a marked improvement in the damage caused by busulfan to the architecture of seminiferous tubules, causal epididymis, blood-testicular barrier (BTB), as well as spermatogonia and Sertoli cells. Similarly, puerarin significantly reduced the levels of total antioxidant capacity (T-AOC), malondialdehyde (MDA), and caspase-3 in the testes of busulfan-induced mice, as determined by microplate reader analysis. Additionally, RNA-seq data, RT-qPCR, and western blotting revealed that puerarin restored the abnormal gene expressions induced by busulfan to nearly healthy levels. Notably, puerarin significantly reversed the impact of busulfan on the expression of marker genes involved in spermatogenesis and oxidative stress. Moreover, puerarin suppressed the phosphorylation of p38, ERK1/2, and JNK in the testes, as observed through testicular analysis. Consequently, this study concludes that puerarin may serve as a potential alternative for treating busulfan-induced damage to male fertility by inactivating the testicular MAPK pathways. These findings may pave the way for the use of puerarin in addressing chemotherapy- or other factors-induced male infertility in humans.

Cytoskeletal orchestration of glucose uptake in Sertoli cell to support efferocytosis of apoptotic germ cells

Efferocytosis of non-viable germ cells by Sertoli cells (SCs) constitutes a sentinel for testis homeostasis, yet how SCs signal for the metabolic and cytoskeletal adaption to this energetically costly process remains unexplored. Spectrin is membrane-associated periodic skeleton assembled into an actin-spectrin-based cytoskeletal structure with an interaction with glucose transporter Glut1. The contribution of spectrin to glucose uptake and efferocytosis is unknown. In this study, we identified a cross-regulation between glucose metabolism and efferocytosis in SCs. Pharmacological or genetic inhibition of glucose uptake or glycolysis compromises efferocytosis activity. We further found that βII-spectrin is a hitherto unappreciated regulator of glucose metabolism and cytoskeletal architecture. βII-spectrin deficiency impairs glucose uptake and lactate production in SCs. Moreover, a defective assembly of cytoskeleton and a loss of blood-testis barrier integrity are also featured by SCs deficient in βII-spectrin. The disruption in glucose metabolism and cytoskeletal organization synergistically lead to a defective efferocytosis. In vivo siRNA-mediated targeting of βII-spectrin in testis causes an obvious morphological aberration in seminiferous epithelium with the presence of exfoliated germ cells and multinucleated giant cells. Importantly, a decrease in expression of αII/βII-spectrin was observed in testes of Adjudin-induced infertility model. By exploring the functional relevance of βII-spectrin to the metabolic and cytoskeletal regulation of efferocytosis, our study proposes a potential link between βII-spectrin deregulation and male infertility.

Role of a small GTPase Cdc42 in aging and age-related diseases

A small GTPase, Cdc42 is evolutionarily one of the most ancient members of the Rho family, which is ubiquitously expressed and involved in a wide range of fundamental cellular functions. The crucial role of Cdc42 includes regulation of the actin cytoskeleton, cell polarity, morphology and migration, endocytosis and exocytosis, cell cycle, and proliferation in many different cell types. Many studies have provided compelling yet contradicting evidence that Cdc42 dysregulation plays an important role in cellular and tissue aging. Furthermore, Cdc42 is a critical factor in the development and progression of aging-related pathologies, such as neurodegenerative and cardiovascular disorders, diabetes type 2, and aging-related disorders of the joints and bones, and the inhibition of the Cdc42 demonstrates potentially significant therapeutic and anti-aging effects in animal models of aging and disease. However, regulation of Cdc42 expression and activity is very complex and depends on many factors, such as the origin and complexity of the tissues, hormonal status, etc. Therefore, this review is focused on current advances in understanding the underlying cellular and molecular mechanisms associated with Cdc42 activity and regulation of senescence in different cell types since they may provide a foundation for novel therapeutic strategies and targeted drugs to reverse the aging process and treat aging-associated disorders.

Mechanisms of primordial follicle activation and new pregnancy opportunity for premature ovarian failure patients

Primordial follicles are the starting point of follicular development and the basic functional unit of female reproduction. Primordial follicles are formed around birth, and most of the primordial follicles then enter a dormant state. Since primordial follicles are limited in number and can't be renewed, dormant primordial follicles cannot be reversed once they enter the growing state. Thus, the orderly occurrence of primordial follicles selective activation directly affects the rate of follicle consumption and thus determines the length of female reproductive lifespan. Studies have found that appropriately inhibiting the activation rate of primordial follicles can effectively slow down the rate of follicle consumption, maintain fertility and delay ovarian aging. Based on the known mechanisms of primordial follicle activation, primordial follicle in vitro activation (IVA) technique has been clinically developed. IVA can help patients with premature ovarian failure, middle-aged infertile women, or infertile women due to gynecological surgery treatment to solve infertility problems. The study of the mechanism of selective activation of primordial follicles can contribute to the development of more efficient and safe IVA techniques. In this paper, recent mechanisms of primordial follicle activation and its clinical application are reviewed.

Postnatal exposure to low-dose tetrabromobisphenol A increases the susceptibility of mammal testes to chemical-induced spermatogenic stress in adulthood

There is increasing data showing that some environmental chemicals can increase susceptibility to follow-up stress or injuries, possibly thereby contributing to certain clinical and subclinical diseases. Previous studies reported that tetrabromobisphenol A (TBBPA), one of the most used brominated flame retardants, exerted little male reproductive toxicity in terms of conventional endpoints but affected testis development and thereby caused testicular alterations at the molecular and cellular levels. Here, we aimed to reveal whether developmental exposure to TBBPA can increase testicular susceptibility to follow-up stress in adulthood. For this purpose, newborn mice were exposed to 50 or 500 μg/kg/d TBBPA for 56 days to confirm adverse effects on testes, followed by a single intraperitoneal injection of 3 mg/kg busulfan (BSF) to induce spermatogenic stress. Four weeks after BSF injection, TBBPA-treated mice exhibited severe pathological alterations, including reduced testis weight, damaged testicular histological structure, declined sperm count, apoptosis of spermatogenic cells, while no remarkable damage was observed in mice without historical exposure to TBBPA. These results demonstrate that historical exposure to TBBPA, either 50 or 500 µg/kg/d, increased the susceptibility of mouse testes to BSF-induced spermatogenic stress, resulting in severe adverse reproductive outcomes. Further analysis indicates that TBBPA-caused microtubule and microfilament damage, along with spermatogonia and spermatocyte reduction, could contributed to the increased susceptibility of testes, suggesting that these non-conventional reproductive lesions caused by chemicals should not be ignored. This is the first study to investigate the reproductive hazard of chemicals from the perspective of testicular susceptibility to stress, thereby opening a new avenue to identify environmental chemicals possibly contributing to male infertility and subfertility.

Whole Exome Sequencing and In Silico Analysis of Human Sertoli in Patients with Non-Obstructive Azoospermia

Non-obstructive azoospermia (NOA) is a serious cause of male infertility. The Sertoli cell responds to androgens and takes on roles supporting spermatogenesis, which may cause infertility. This work aims to enhance the genetic diagnosis of NOA via the discovery of new and hub genes implicated in human NOA and to better assess the odds of successful sperm extraction according to the individual’s genotype. Whole exome sequencing (WES) was done on three NOA patients to find key genes involved in NOA. We evaluated genome-wide transcripts (about 50,000 transcripts) by microarray between the Sertoli of non-obstructive azoospermia and normal cells. The microarray analysis of three human cases with different non-obstructive azoospermia revealed that 32 genes were upregulated, and the expressions of 113 genes were downregulated versus the normal case. For this purpose, Enrich Shiny GO, STRING, and Cytoscape online evaluations were applied to predict the functional and molecular interactions of proteins and then recognize the master pathways. The functional enrichment analysis demonstrated that the biological process (BP) terms “inositol lipid-mediated signaling”, “positive regulation of transcription by RNA polymerase II”, and “positive regulation of DNA-templated transcription” significantly changed in upregulated differentially expressed genes (DEGs). The BP investigation of downregulated DEGs highlighted “mitotic cytokinesis”, “regulation of protein-containing complex assembly”, “cytoskeleton-dependent cytokinesis”, and the “peptide metabolic process”. Overrepresented molecular function (MF) terms in upregulated DEGs included “ubiquitin-specific protease binding”, “protease binding”, “phosphatidylinositol trisphosphate phosphatase activity”, and “clathrin light chain binding”. Interestingly, the MF analysis of the downregulated DEGs revealed overexpression in “ATPase inhibitor activity”, “glutathione transferase activity”, and “ATPase regulator activity”. Our findings suggest that these genes and their interacting hub proteins could help determine the pathophysiologies of germ cell abnormalities and infertility.

Sertoli cell survival and barrier function are regulated by miR-181c/d-Pafah1b1 axis during mammalian spermatogenesis

Sertoli cells contribute to the formation of the blood-testis barrier (BTB), which is necessary for normal spermatogenesis. Recently, microRNAs (miRNAs) have emerged as posttranscriptional regulatory elements in BTB function during spermatogenesis. Our previous study has shown that miR-181c or miR-181d (miR-181c/d) is highly expressed in testes from boars at 60 days old compared with at 180 days old. Herein, we found that overexpression of miR-181c/d via miR-181c/d mimics in murine Sertoli cells (SCs) or through injecting miR-181c/d-overexpressing lentivirus in murine testes perturbs BTB function by altering BTB-associated protein distribution at the Sertoli cell-cell interface and F-actin organization, but this in vivo perturbation disappears approximately 6 weeks after the final treatment. We also found that miR-181c/d represses Sertoli cell proliferation and promotes its apoptosis. Moreover, miR-181c/d regulates Sertoli cell survival and barrier function by targeting platelet-activating factor acetylhydrolase 1b regulatory subunit 1 (Pafah1b1) gene. Furthermore, miR-181c/d suppresses PAFAH1B1 expression, reduces the complex of PAFAH1B1 with IQ motif-containing GTPase activating protein 1, and inhibits CDC42/PAK1/LIMK1/Cofilin pathway which is required for F-actin stabilization. In total, our results reveal the regulatory axis of miR-181c/d-Pafah1b1 in cell survival and barrier function of Sertoli cells and provide additional insights into miRNA functions in mammalian spermatogenesis.

Smtnl2 regulates apoptotic germ cell clearance and lactate metabolism in mouse Sertoli cells

Smtnl2 is an epithelial Smoothelin that binds to actin filaments and is crucial for epithelial morphogenesis. We examined the role of Smtnl2 in Sertoli cells, which undergo dynamic cytoskeleton reorganization to phagocytose apoptotic germ cells, a process known as efferocytosis. We observed Smtnl2 expression in primary mouse Sertoli cells and the 15P1 Sertoli cell line. Smtnl2 expression increased in 15P1 cells committing efferocytosis. Smtnl2-deficient Sertoli cells exhibited defective ability to engulf apoptotic germ cells and importantly, the phenomenon occurred in the setting of an unaffected maturation of phagosome. We demonstrated that Smtnl2 regulates the engulfment process through the function of branched actin nucleation protein ARP3, an actin assembly dictator. Intriguingly, a shift in glucose metabolism that restricts lactate production in Sertoli cells was induced upon Smtnl2 depletion, leading to the activation of downstream AMPK and AKT signaling. Using an in vivo RNAi approach, we found that silencing of Smtnl2 in testis triggers an obvious disruption in cytoskeleton architecture and blood-testis barrier integrity across seminiferous epithelium, causing the detachment of massive germ cells from their nest, as evidenced by their exfoliation into the lumen. Overall, our study identifies Smtnl2 as a determinant for Sertoli cells' functioning in supporting spermatogenesis.

Proteome-wide identification of palmitoylated proteins in mouse testis

The reversible lipid modification, S-palmitoylation, plays regulatory roles in various physiological processes, e.g., neuronal plasticity and organs development; however, the roles of palmitoylation engaged in testis have yet remained unexplored. Here, we used combined approaches of palm-proteomics, informatics and quantitative PCR to systematically analyze the expression of key enzymes related to protein palmitoylation and identify proteome-wide palmitoylated proteins during the processes of spermatogenesis. Specifically, different timepoints were chosen to collect samples to cover the initiation of meiosis (postnatal, P12), the appearance of the first batch of sperm (P36) and fully fertile status (P60) in mouse. Interestingly, our results showed that only a few enzymes related to protein palmitoylation are highly expressed at later stages (from P36 to P60), rather than in the earlier phase of testis development (P12). To focus on the molecular event of spermatogenesis, we examined the palm-proteomics of testes in P36 and P60 mouse. In total, we identified 4,883 palmitoylated proteins, among which 3,310 proteins match the published palmitoyl-proteome datasets and 1,573 proteins were firstly identified as palmitoylated proteins in this study. Informatics analysis suggested that palmitoylation is involved in events of protein transport, metabolic process, protein folding and cell adhesion, etc. Importantly, further analysis revealed that several networks of palmitoylated proteins are closely associated with sperm morphology and motility. Together, our study laid a solid ground for understanding the roles of protein palmitoylation in spermatogenesis for future studies.

Cell-Cell Interaction-Mediated Signaling in the Testis Induces Reproductive Dysfunction—Lesson from the Toxicant/Pharmaceutical Models

Emerging evidence has shown that cell-cell interactions between testicular cells, in particular at the Sertoli cell-cell and Sertoli-germ cell interface, are crucial to support spermatogenesis. The unique ultrastructures that support cell-cell interactions in the testis are the basal ES (ectoplasmic specialization) and the apical ES. The basal ES is found between adjacent Sertoli cells near the basement membrane that also constitute the blood-testis barrier (BTB). The apical ES is restrictively expressed at the Sertoli-spermatid contact site in the apical (adluminal) compartment of the seminiferous epithelium. These ultrastructures are present in both rodent and human testes, but the majority of studies found in the literature were done in rodent testes. As such, our discussion herein, unless otherwise specified, is focused on studies in testes of adult rats. Studies have shown that the testicular cell-cell interactions crucial to support spermatogenesis are mediated through distinctive signaling proteins and pathways, most notably involving FAK, Akt1/2 and Cdc42 GTPase. Thus, manipulation of some of these signaling proteins, such as FAK, through the use of phosphomimetic mutants for overexpression in Sertoli cell epithelium in vitro or in the testis in vivo, making FAK either constitutively active or inactive, we can modify the outcome of spermatogenesis. For instance, using the toxicant-induced Sertoli cell or testis injury in rats as study models, we can either block or rescue toxicant-induced infertility through overexpression of p-FAK-Y397 or p-FAK-Y407 (and their mutants), including the use of specific activator(s) of the involved signaling proteins against pAkt1/2. These findings thus illustrate that a potential therapeutic approach can be developed to manage toxicant-induced male reproductive dysfunction. In this review, we critically evaluate these recent findings, highlighting the direction for future investigations by bringing the laboratory-based research through a translation path to clinical investigations.

Sertoli Cell-Germ Cell Interactions Within the Niche: Paracrine and Juxtacrine Molecular Communications

Male germ cell development depends on multiple biological events that combine epigenetic reprogramming, cell cycle regulation, and cell migration in a spatio-temporal manner. Sertoli cells are a crucial component of the spermatogonial stem cell niche and provide essential growth factors and chemokines to developing germ cells. This review focuses mainly on the activation of master regulators of the niche in Sertoli cells and their targets, as well as on novel molecular mechanisms underlying the regulation of growth and differentiation factors such as GDNF and retinoic acid by NOTCH signaling and other pathways.