The Transcription Factor MEF2 Is a Novel Regulator of Gsta Gene Class in Mouse MA-10 Leydig Cells

Ethylene dimethanesulfonate effects on gene promoter activities related to the endocrine function of immortalized Leydig cell lines R2C and MA-10

Ethylene dimethanesulfonate (EDS) is a molecule with known selective cytotoxicity on adult Leydig cells. A single intraperitoneal injection in rats but not mice, leads to male androgen deprivation and infertility. In vitro studies using rat and mouse immortalized Leydig cell lines, showed similar effects of cell death promoted by EDS in rat cells as seen in vivo, and suggest that EDS affects gene transcription, which could firstly compromise steroidogenesis before the apoptosis process. Using gene reporter assay, this study aimed to investigate EDS effects on the promoter activity of genes important for endocrine function (Star, Insl3) and response to toxic agents (Gsta3) in immortalized Leydig cell lines (rat R2C and mouse MA-10 cells), as well as identify possible EDS-responsive elements in the Star gene promoter. EDS exposure of R2C and MA-10 Leydig cells increased Gsta3 promoter activity after 4 h of treatment and decreased Insl3 promoter activity only in R2C cells after 24 h of treatment. EDS also decreased Star promoter activity in both Leydig cell lines. Using R2C cells, the EDS-responsive region in the Star promoter was located between -400 and -195 bp. This suggests that this region and the associated transcription factors, which include MEF2, might be targeted by EDS. Additional somatic gonadal cell lines expressing Star were used and EDS did not affect Star promoter activity in DC3 granulosa cells while Star promoter activity was increased in MSC-1 Sertoli cells after 24 h of treatment. This study contributes to the knowledge regarding the mechanism of EDS action in Leydig cells, and in other gonadal cell lineages, and brings new light regarding the rats and mice differential susceptibility to EDS effects, in addition to providing new avenues for experimental approaches to better understand Leydig cell function and dynamics in different rodent species.

ERK5 Cooperates With MEF2C to Regulate Nr4a1 Transcription in MA-10 and MLTC-1 Leydig Cells

Leydig cells produce hormones required for the development and maintenance of sex characteristics and fertility in males. MEF2 transcription factors are important regulators of Leydig cell gene expression and steroidogenesis. ERK5 is an atypical member of the MAP kinase family that modulates transcription factor activity, either by direct phosphorylation or by acting as a transcriptional coactivator. While MEF2 and ERK5 are known to cooperate transcriptionally, the presence and role of ERK5 in Leydig cells remained unknown. Our goal was to determine whether ERK5 is present in Leydig cells and whether it cooperates with MEF2 to regulate gene expression. We found that ERK5 is present in Leydig cells in testicular tissue and immortalized cell lines. ERK5 knockdown in human chorionic gonadotrophin-treated MA-10 Leydig cells reduced steroidogenesis and decreased Star and Nr4a1 expression. Luciferase assays using a synthetic reporter plasmid containing 3 MEF2 elements revealed that ERK5 enhances MEF2-dependent promoter activation. Although ERK5 did not cooperate with MEF2 on the Star promoter in Leydig cell lines, we found that ERK5 and MEF2C do cooperate on the Nr4a1 promoter, which contains 2 adjacent MEF2 elements. Mutation of each MEF2 element in a short version of the Nr4a1 promoter significantly decreased the ERK5/MEF2C cooperation, indicating that both MEF2 elements need to be intact. The ERK5/MEF2C cooperation did not require phosphorylation of MEF2C on Ser387. Taken together, our data identify ERK5 as a new regulator of MEF2 activity in Leydig cells and provide potential new insights into mechanisms that regulate Leydig cell gene expression and function.

Constructing a seventeen-gene signature model for non-obstructive azoospermia based on integrated transcriptome analyses and WGCNA

BACKGROUND

Non-obstructive azoospermia (NOA) affects approximately 1% of the male population worldwide. The underlying mechanism and gene transcription remain unclear. This study aims to explore the potential pathogenesis for the detection and management of NOA.

METHODS

Based on four microarray datasets from the Gene Expression Omnibus database, integrated analysis and weighted correlation network analysis (WGCNA) were used to obtain the intersected common differentially expressed genes (DESs). Differential signaling pathways were identified via GO and GSVA-KEGG analyses. We constructed a seventeen-gene signature model using least absolute shrinkage and selection operation (LASSO) regression, and validated its efficacy in another two GEO datasets. Three patients with NOA and three patients with obstructive azoospermia were recruited. The mRNA levels of seven key genes were measured in testicular samples, and the gene expression profile was evaluated in the Human Protein Atlas (HPA) database.

RESULTS

In total, 388 upregulated and 795 downregulated common DEGs were identified between the NOA and control groups. ATPase activity, tubulin binding, microtubule binding, and metabolism- and immune-associated signaling pathways were significantly enriched. A seventeen-gene signature predictive model was constructed, and receiver operating characteristic (ROC) analysis showed that the area under the curve (AUC) values were 1.000 (training group), 0.901 (testing group), and 0.940 (validation set). The AUCs of seven key genes (REC8, CPS1, DHX57, RRS1, GSTA4, SI, and COX7B) were all > 0.8 in both the testing group and the validation set. The qRT-PCR results showed that consistent with the sequencing data, the mRNA levels of RRS1, GSTA4, and COX7B were upregulated, while CPS1, DHX57, and SI were downregulated in NOA. Four genes (CPS1, DHX57, RRS1, and SI) showed significant differences. Expression data from the HPA database showed the localization characteristics and trajectories of seven key genes in spermatogenic cells, Sertoli cells, and Leydig cells.

CONCLUSIONS

Our findings suggest a novel seventeen-gene signature model with a favorable predictive power, and identify seven key genes with potential as NOA-associated marker genes. Our study provides a new perspective for exploring the underlying pathological mechanism in male infertility.

Tension force causes cell cycle arrest at G2/M phase in osteocyte-like cell line MLO-Y4

Bone remodelling is the process of bone resorption and formation, necessary to maintain bone structure or for adaptation to new conditions. Mechanical loadings, such as exercise, weight bearing and orthodontic force, play important roles in bone remodelling. During the remodelling process, osteocytes play crucial roles as mechanosensors to regulate osteoblasts and osteoclasts. However, the precise molecular mechanisms by which the mechanical stimuli affect the function of osteocytes remain unclear. In the present study, we analysed viability, cell cycle distribution and gene expression pattern of murine osteocyte-like MLO-Y4 cells exposed to tension force (TF). Cells were subjected to TF with 18% elongation at 6 cycles/min for 24 h using Flexcer Strain Unit (FX-3000). We found that TF stimulation induced cell cycle arrest at G2/M phase but not cell death in MLO-Y4 cells. Differentially expressed genes (DEGs) between TF-stimulated and unstimulated cells were identified by microarray analysis, and a marked increase in glutathione-S-transferase α (GSTA) family gene expression was observed in TF-stimulated cells. Enrichment analysis for the DEGs revealed that Gene Ontology (GO) terms and Kyoto Encyclopedia Genes and Genomes (KEGG) pathways related to the stress response were significantly enriched among the upregulated genes following TF. Consistent with these results, the production of reactive oxygen species (ROS) was elevated in TF-stimulated cells. Activation of the tumour suppressor p53, and upregulation of its downstream target GADD45A, were also observed in the stimulated cells. As GADD45A has been implicated in the promotion of G2/M cell cycle arrest, these observations may suggest that TF stress leads to G2/M arrest at least in part in a p53-dependent manner.

Differential Response of Transcription Factors to Activated Kinases in Steroidogenic and Non-Steroidogenic Cells

Hormone-induced Leydig cell steroidogenesis requires rapid changes in gene expression in response to various hormones, cytokines, and growth factors. These proteins act by binding to their receptors on the surface of Leydig cells leading to activation of multiple intracellular signaling cascades, downstream of which are several kinases, including protein kinase A (PKA), Ca2+/calmodulin-dependent protein kinase I (CAMKI), and extracellular signal-regulated protein kinase 1 and 2 (ERK1/2). These kinases participate in hormone-induced steroidogenesis by phosphorylating numerous proteins including transcription factors leading to increased steroidogenic gene expression. How these various kinases and transcription factors come together to appropriately induce steroidogenic gene expression in response to specific stimuli remains poorly understood. In the present work, we compared the effect of PKA, CAMKI and ERK1/2 on the transactivation potential of 15 transcription factors belonging to 5 distinct families on the activity of the Star gene promoter. We not only validated known cooperation between kinases and transcription factors, but we also identified novel cooperations that have not yet been before reported. Some transcription factors were found to respond to all three kinases, whereas others were only activated by one specific kinase. Differential responses were also observed within a family of transcription factors. The diverse response to kinases provides flexibility to ensure proper genomic response of steroidogenic cells to different stimuli.

COUP-TFII interacts and functionally cooperates with GATA4 to regulate Amhr2 transcription in mouse MA-10 Leydig cells

BACKGROUND

Leydig cells produce testosterone and insulin-like 3, two hormones essential for male sex differentiation and reproductive function. The orphan nuclear receptor COUP-TFII and the zinc finger factor GATA4 are two transcription factors involved in Leydig cell differentiation, gene expression and function.

OBJECTIVES

Several Leydig cell gene promoters contain binding motifs for both GATA factors and nuclear receptors. The goal of present study is to determine whether GATA4 and COUP-TFII cooperate to regulate gene expression in Leydig cells.

MATERIALS AND METHODS

The transcriptomes from GATA4- and COUP-TFII-depleted MA-10 Leydig cells were analyzed using bioinformatic tools. Functional cooperation between GATA4 and COUP-TFII, and other related family members, was assessed by transient transfections in Leydig (MA-10 and MLTC-1) and fibroblast (CV-1) cell lines on several gene promoters. Recruitment of GATA4 and COUP-TFII to gene promoters was investigated by chromatin immunoprecipitation. Co-immunoprecipitation was used to determine whether GATA4 and COUP-TFII interact in MA-10 Leydig cells.

RESULTS

Transcriptomic analyses of GATA4- and COUP-TFII-depleted MA-10 Leydig cells revealed 44 commonly regulated genes including the anti-Müllerian hormone receptor (Amhr2) gene. GATA4 and COUP-TFII independently activated the Amhr2 promoter, and their combination led to a stronger activation. A GC-rich element, located in the proximal Amhr2 promoter was found to be essential for GATA4- and COUP-TFII-dependent activation as well as for the COUP-TFII/GATA4 cooperation. COUP-TFII and GATA4 directly interacted in MA-10 Leydig cell extracts. Chromatin immunoprecipitation revealed that GATA4 and COUP-TFII are recruited to the proximal Amhr2 promoter, which contains binding sites for both factors in addition to the GC-rich element. Cooperation between COUP-TFII and GATA6, but not GATA1 and GATA3, was also observed.

DISCUSSION AND CONCLUSION

Our results establish the importance of a physical and functional cooperation between COUP-TFII/GATA4 in the regulation of gene expression in MA-10 Leydig cells, and more specifically the Amhr2 gene. This article is protected by copyright. All rights reserved.

Transcription Factors in the Regulation of Leydig Cell Gene Expression and Function

Cell differentiation and acquisition of specialized functions are inherent steps in events that lead to normal tissue development and function. These processes require accurate temporal, tissue, and cell-specific activation or repression of gene transcription. This is achieved by complex interactions between transcription factors that form a unique combinatorial code in each specialized cell type and in response to different physiological signals. Transcription factors typically act by binding to short, nucleotide-specific DNA sequences located in the promoter region of target genes. In males, Leydig cells play a crucial role in sex differentiation, health, and reproductive function from embryonic life to adulthood. To better understand the molecular mechanisms regulating Leydig cell differentiation and function, several transcription factors important to Leydig cells have been identified, including some previously unknown to this specialized cell type. This mini review summarizes the current knowledge on transcription factors in fetal and adult Leydig cells, describing their roles and mechanisms of action.

Identification of novel genes and pathways regulated by the orphan nuclear receptor COUP-TFII in mouse MA-10 Leydig cells†

In males, Leydig cells are the main producers of testosterone and insulin-like 3 (INSL3), two hormones essential for sex differentiation and reproductive functions. Chicken ovalbumin upstream promoter-transcription factors I (COUP-TFI/NR2F1) and COUP-TFII (NR2F2) belong to the steroid/thyroid hormone nuclear receptor superfamily of transcription factors. In the testis, COUP-TFII is expressed and plays a role in the differentiation of cells committed to give rise to fully functional steroidogenic adult Leydig cells. Steroid production has also been shown to be diminished in COUP-TFII-depleted Leydig cells, indicating an important functional role in steroidogenesis. Until now, only a handful of target genes have been identified for COUP-TFII in Leydig cells. To provide new information into the mechanism of action of COUP-TFII in Leydig cells, we performed microarray analyses of COUP-TFII-depleted MA-10 Leydig cells. We identified 262 differentially expressed genes in COUP-TFII-depleted MA-10 cells. Many of the differentially expressed genes are known to be involved in lipid biosynthesis, lipid metabolism, male gonad development, and steroidogenesis. We validated the microarray data for a subset of the modulated genes by RT-qPCR. Downregulated genes included Hsd3b1, Cyp11a1, Prlr, Shp/Nr0b2, Fdx1, Scarb1, Inha and Gsta3. Finally, analysis of the Gsta3 and Inha gene promoters showed that at least two of the downregulated genes are potentially new direct targets for COUP-TFII. These data provide new evidence that further strengthens the important nature of COUP-TFII in steroidogenesis, androgen homeostasis, cellular defense, and differentiation in mouse Leydig cells.

MEF-2 isoforms' (A-D) roles in development and tumorigenesis

Myocyte enhancer factor (MEF)-2 plays a critical role in proliferation, differentiation, and development of various cell types in a tissue specific manner. Four isoforms of MEF-2 (A-D) differentially participate in controlling the cell fate during the developmental phases of cardiac, muscle, vascular, immune and skeletal systems. Through their associations with various cellular factors MEF-2 isoforms can trigger alterations in complex protein networks and modulate various stages of cellular differentiation, proliferation, survival and apoptosis. The role of the MEF-2 family of transcription factors in the development has been investigated in various cell types, and the evolving alterations in this family of transcription factors have resulted in a diverse and wide spectrum of disease phenotypes, ranging from cancer to infection. This review provides a comprehensive account on MEF-2 isoforms (A-D) from their respective localization, signaling, role in development and tumorigenesis as well as their association with histone deacetylases (HDACs), which can be exploited for therapeutic intervention.

MEF2 signaling and human diseases

The members of myocyte Enhancer Factor 2 (MEF2) protein family was previously believed to function in the development of heart and muscle. Recent reports indicate that they are also closely associated with development and progression of many human diseases. Although their role in cancer biology is well established, the molecular mechanisms underlying their action is yet largely unknown. MEF2 family is closely associated with various signaling pathways, including Ca²⁺ signaling, MAP kinase signaling, Wnt signaling, PI3K/Akt signaling, etc. microRNAs also contribute to regulate the activities of MEF2. In this review, we summarize the known molecular mechanism by which MEF2 family contribute to human diseases.

Ca2+/Calmodulin-Dependent Protein Kinase II and Androgen Signaling Pathways Modulate MEF2 Activity in Testosterone-Induced Cardiac Myocyte Hypertrophy

Testosterone is known to induce cardiac hypertrophy through androgen receptor (AR)-dependent and -independent pathways, but the molecular underpinnings of the androgen action remain poorly understood. Previous work has shown that Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and myocyte-enhancer factor 2 (MEF2) play key roles in promoting cardiac myocyte growth. In order to gain mechanistic insights into the action of androgens on the heart, we investigated how testosterone affects CaMKII and MEF2 in cardiac myocyte hypertrophy by performing studies on cultured rat cardiac myocytes and hearts obtained from adult male orchiectomized (ORX) rats. In cardiac myocytes, MEF2 activity was monitored using a luciferase reporter plasmid, and the effects of CaMKII and AR signaling pathways on MEF2C were examined by using siRNAs and pharmacological inhibitors targeting these two pathways. In the in vivo studies, ORX rats were randomly assigned to groups that were administered vehicle or testosterone (125 mg⋅kg^-1⋅week^-1) for 5 weeks, and plasma testosterone concentrations were determined using ELISA. Cardiac hypertrophy was evaluated by measuring well-characterized hypertrophy markers. Moreover, western blotting was used to assess CaMKII and phospholamban (PLN) phosphorylation, and MEF2C and AR protein levels in extracts of left-ventricle tissue from control and testosterone-treated ORX rats. Whereas testosterone treatment increased the phosphorylation levels of CaMKII (Thr286) and phospholambam (PLN) (Thr17) in cardiac myocytes in a time- and concentration-dependent manner, testosterone-induced MEF2 activity and cardiac myocyte hypertrophy were prevented upon inhibition of CaMKII, MEF2C, and AR signaling pathways. Notably, in the hypertrophied hearts obtained from testosterone-administered ORX rats, both CaMKII and PLN phosphorylation levels and AR and MEF2 protein levels were increased. Thus, this study presents the first evidence indicating that testosterone activates MEF2 through CaMKII and AR signaling. Our findings suggest that an orchestrated mechanism of action involving signal transduction and transcription pathways underlies testosterone-induced cardiac myocyte hypertrophy.

Development, function and fate of fetal Leydig cells

During fetal testis development, fetal Leydig cells (FLCs) are found to be originated from multiple progenitor cells. FLC specification and function are under tight regulation of specific genes and signaling proteins. Furthermore, Sertoli cells play a crucial role to regulate FLC differentiation during fetal testis development. FLC progenitor- and FLC-produced biomolecules are also involved in the differentiation and activity of rodent FLCs. The main function of FLCs is to produce androgens to masculinize XY embryos. However, FLCs are capable of producing androstenedione but not testosterone due to the lack of 17β-HSD (17β-hydroxysteroid dehydrogenase), but fetal Sertoli cells express 17β-HSD which thus transforms androstenedione to testosterone in the fetal testis. On the other hand, FLCs produce activin A to regulate Sertoli cell proliferation, and Sertoli cells in turn modulate testis cord expansion. It is now generally accepted that adult Leydig cells (ALCs) gradually replace FLCs during postnatal development to produce testosterone to support spermatogenesis as FLCs undergo degeneration in neonatal and pre-pubertal testes. However, based on studies using genetic tracing mouse models, FLCs are found to persist in adult testes, making up ∼20% of total Leydig cells. In this review, we evaluate the latest findings regarding the development, function and fate of FLCs during fetal and adult testis development.