Male infertility in Sertoli cell‐only syndrome: An investigation of autosomal gene defects

Detection of AZF microdeletions and analysis of reproductive hormonal profiles in Hainan men undergoing assisted reproductive technology

BACKGROUND

Male infertility has become a global health problem, and genetic factors are one of the essential causes. Y chromosome microdeletion is the leading genetic factor cause of male infertility. The objective of this study is to investigate the correlation between male infertility and Y chromosome microdeletions in Hainan, the sole tropical island province of China.

METHODS

We analyzed the semen of 897 infertile men from Hainan in this study. Semen analysis was measured according to WHO criteria by professionals at the Department of Reproductive Medicine, the First Affiliated Hospital of Hainan Medical University, where samples were collected. Y chromosome AZF microdeletions were confirmed by detecting six STS markers using multiple polymerase chain reactions on peripheral blood DNA. The levels of reproductive hormones, including FSH, LH, PRL, T, and E2, were quantified using the enzyme-linked immunosorbent assay (ELISA).

RESULTS

The incidence of Y chromosome microdeletion in Hainan infertile men was 7.13%. The occurrence rate of Y chromosome microdeletion was 6.69% (34/508) in the oligozoospermia group and 7.71% (30/389) in the azoospermia group. The deletion of various types in the AZF subregion was observed in the group with azoospermia, whereas no AZFb deletion was detected in the oligozoospermia group. Among all patients with microdeletions, the deletion rate of the AZFc region was the higher at 68.75% (44 out of 64), followed by a deletion rate of 6.25% (4 out of 64) for the AZFa region and a deletion rate of 4.69% (3 out of 64) for the AZFb region. The deletion rate of the AZFa region was significantly higher in patients with azoospermia than in patients with oligozoospermia (0.51% vs. 0.39%, p < 0.001). In comparison, the deletion rate of the AZFc region was significantly higher in patients with oligozoospermia (3.08% vs. 6.30%, p < 0.001). Additionally, the AZFb + c subregion association deletion was observed in the highest proportion among all patients (0.89%, 8/897), followed by AZFa + b + c deletion (0.56%, 5/897), and exclusively occurred in patients with azoospermia. Hormone analysis revealed FSH (21.63 ± 2.01 U/L vs. 10.15 ± 0.96 U/L, p = 0.001), LH (8.96 ± 0.90 U/L vs. 4.58 ± 0.42 U/L, p < 0.001) and PRL (263.45 ± 21.84 mIU/L vs. 170.76 ± 17.10 mIU/L, p = 0.002) were significantly increased in azoospermia patients with microdeletions. Still, P and E2 levels were not significantly different between the two groups.

CONCLUSIONS

The incidence of AZF microdeletion can reach 7.13% in infertile men in Hainan province, and the deletion of the AZFc subregion is the highest. Although the Y chromosome microdeletion rate is distinct in different regions or populations, the regions mentioned above of the Y chromosome may serve an indispensable role in regulating spermatogenesis. The analysis of Y chromosome microdeletion plays a crucial role in the clinical assessment and diagnosis of male infertility.

RNF20 is required for male fertility through regulation of H2B ubiquitination in the Sertoli cells

BACKGROUND

Spermatogenesis depends on the supporting of the Sertoli cells and their communications with germ cells. However, the regulation of crosstalk between the Sertoli cells and germ cells remains unclear.

RESULTS

In this report, we used conditional knockout technology to generate the Sertoli cells-specific knockout of Rnf20 in mice. The Amh-Rnf20^-/- male mice were infertile owing to spermatogenic failure that mimic the Sertoli cell-only syndrome (SCOS) in humans. Knockout of Rnf20 resulted in the H2BK120ub loss in the Sertoli cells and impaired the transcription elongation of the Cldn11, a gene encoding a component of tight junction. Notably, RNF20 deficiency disrupted the cell adhesion, caused disorganization of the seminiferous tubules, and led to the apoptotic cell death of both spermatogonia and spermatocytes in the seminiferous tubules.

CONCLUSIONS

This study describes a Rnf20 knockout mouse model that recapitulates the Sertoli cell-only syndrome in humans and demonstrates that RNF20 is required for male fertility through regulation of H2B ubiquitination in the Sertoli cells.

Sertoli cell-only syndrome: advances, challenges, and perspectives in genetics and mechanisms

Male infertility can be caused by quantitative and/or qualitative abnormalities in spermatogenesis, which affects men's physical and mental health. Sertoli cell-only syndrome (SCOS) is the most severe histological phenotype of male infertility characterized by the depletion of germ cells with only Sertoli cells remaining in the seminiferous tubules. Most SCOS cases cannot be explained by the already known genetic causes including karyotype abnormalities and microdeletions of the Y chromosome. With the development of sequencing technology, studies on screening new genetic causes for SCOS are growing in recent years. Directly sequencing of target genes in sporadic cases and whole-exome sequencing applied in familial cases have identified several genes associated with SCOS. Analyses of the testicular transcriptome, proteome, and epigenetics in SCOS patients provide explanations regarding the molecular mechanisms of SCOS. In this review, we discuss the possible relationship between defective germline development and SCOS based on mouse models with SCO phenotype. We also summarize the advances and challenges in the exploration of genetic causes and mechanisms of SCOS. Knowing the genetic factors of SCOS offers a better understanding of SCO and human spermatogenesis, and it also has practical significance for improving diagnosis, making appropriate medical decisions, and genetic counseling. For therapeutic implications, SCOS research, along with the achievements in stem cell technologies and gene therapy, build the foundation to develop novel therapies for SCOS patients to produce functional spermatozoa, giving them hope to father children.

Mild androgen insensitivity syndrome: the current landscape

OBJECTIVE

Mild Androgen Insensitivity (MAIS) belongs to the Androgen Insensitivity Syndrome (AIS) spectrum, an X-linked genetic disease that is the most common cause of differences in sex development (DSD). Unfortunately, AIS studies mainly focus on the partial and the complete phenotype, and the mild phenotype (MAIS) has been barely reported. Our purpose is to explore the MAIS facets, clinical features, and molecular aspects.

METHODS

We collected all reported MAIS cases in the medical literature and presented them based on the phenotype and the molecular diagnosis.

RESULTS

We identified 49 different AR mutations in 69 individuals in the literature. We compared the AR mutations presented in MAIS individuals with AR mutations previously reported in other AIS phenotypes (CAIS and PAIS) regarding the type, location, genotype-phenotype correlation, and functional studies.

CONCLUSION

This review provides a landscape of the mild phenotype of AIS. Most MAIS patients present with male infertility. Therefore, AR gene sequencing should be considered during male infertility investigation, even in males with typically male external genitalia. In addition, MAIS can be part of other medical conditions, such as X-linked spinal and bulbar muscular atrophy (Kennedy's disease).

The Fate of Leydig Cells in Men with Spermatogenic Failure

The steroidogenic cells in the testicle, Leydig cells, located in the interstitial compartment, play a vital role in male reproductive tract development, maintenance of proper spermatogenesis, and overall male reproductive function. Therefore, their dysfunction can lead to all sorts of testicular pathologies. Spermatogenesis failure, manifested as azoospermia, is often associated with defective Leydig cell activity. Spermatogenic failure is the most severe form of male infertility, caused by disorders of the testicular parenchyma or testicular hormone imbalance. This review covers current progress in knowledge on Leydig cells origin, structure, and function, and focuses on recent advances in understanding how Leydig cells contribute to the impairment of spermatogenesis.

Identification of genomic imbalances (CNVs as well as LOH) in sertoli cell only syndrome cases through cytoscan microarray

Sertoli cell only syndrome (SCOS) is characterized by complete absence of germ cells in seminiferous tubules of testis. SCOS is multifactorial but genetic factors play a major role in pathogenesis of the disorder with idiopathic origin. Genetic factors majorly include sex chromosomal aneuploidy and Yq Microdeletion. But a large number of cases are still idiopathic. The study aimed to evaluate the genomic imbalances (CNVs and LOH) in idiopathic SCOS patients. The study is based on 28 apparent idiopathic SCOS cases and 10 controls. Molecular cytogenetic techniques viz., FISH, STS-Multiplex PCR and Affymetrix cytoscan microarray (750 K) were used. The microarray screened whole genomic imbalances in DNA from peripheral blood of 25 cases (excluded Klinefelter syndrome patients) and testicular FNAC sample of 2 cases. High FSH and low Inhibin B were observed in cases as compared to control controls groups. Four cases of sex chromosomal abnormality (i.e., three non-mosaic 47, XXY males and one non-mosaic 46, XX male) as well as four cases of Yq microdeletion (i.e., three cases with AZFc deletion and one case with complete AZFa, b and c deletion) were identified. Microarray detected unbalanced translocation of two segments of Y-chromosome i.e., Yp11.31-p11.2 (~4.o mb region, involving SRY) and Yp11.2 (~2.5 mb region) on X-chromosome in XX male. Also, loss of segment on same X-chromosome involving PAR1 region was identified. We have identified both autosomal and sex chromosomal CNVs (recurrent as well as private) involving candidate genes like SYCE1, ZFPM2, SRPK1, DAZ1, BPY2, HSFY1, VCY1 etc. All these CNVs are possibly associated with SCOS pathogenesis. CNVs identified in cases were already reported as pathogenic variant in clinical database DECIPHER. Microarray also detected many LOH (all autosomal, >3.0 mb size) that covered genes with spermatogenesis related function. The mechanism of action of LOH in pathogenesis of SCOS still remains unravelled. CNVs and LOH related to spermatogenesis identified from two different sample types (blood vs. testicular tissue) were discordant. This study should be extended for larger cohort of patients.

TRIM71 Deficiency Causes Germ Cell Loss During Mouse Embryogenesis and Is Associated With Human Male Infertility

Mutations affecting the germline can result in infertility or the generation of germ cell tumors (GCT), highlighting the need to identify and characterize the genes controlling germ cell development. The RNA-binding protein and E3 ubiquitin ligase TRIM71 is essential for embryogenesis, and its expression has been reported in GCT and adult mouse testes. To investigate the role of TRIM71 in mammalian germ cell embryonic development, we generated a germline-specific conditional Trim71 knockout mouse (cKO) using the early primordial germ cell (PGC) marker Nanos3 as a Cre-recombinase driver. cKO mice are infertile, with male mice displaying a Sertoli cell-only (SCO) phenotype which in humans is defined as a specific subtype of non-obstructive azoospermia characterized by the absence of germ cells in the seminiferous tubules. Infertility in male Trim71 cKO mice originates during embryogenesis, as the SCO phenotype was already apparent in neonatal mice. The in vitro differentiation of mouse embryonic stem cells (ESCs) into PGC-like cells (PGCLCs) revealed reduced numbers of PGCLCs in Trim71-deficient cells. Furthermore, TCam-2 cells, a human GCT-derived seminoma cell line which was used as an in vitro model for PGCs, showed proliferation defects upon TRIM71 knockdown. Additionally, in vitro growth competition assays, as well as proliferation assays with wild type and CRISPR/Cas9-generated TRIM71 mutant NCCIT cells showed that TRIM71 also promotes proliferation in this malignant GCT-derived non-seminoma cell line. Importantly, the PGC-specific markers BLIMP1 and NANOS3 were consistently downregulated in Trim71 KO PGCLCs, TRIM71 knockdown TCam-2 cells and TRIM71 mutant NCCIT cells. These data collectively support a role for TRIM71 in PGC development. Last, via exome sequencing analysis, we identified several TRIM71 variants in a cohort of infertile men, including a loss-of-function variant in a patient with an SCO phenotype. Altogether, our work reveals for the first time an association of TRIM71 deficiency with human male infertility, and uncovers further developmental roles for TRIM71 in the germline during mouse embryogenesis.

Genome diversity and instability in human germ cells and preimplantation embryos

Genome diversity is essential for evolution and is of fundamental importance to human health. Generating genome diversity requires phases of DNA damage and repair that can cause genome instability. Humans have a high incidence of de novo congenital disorders compared to other organisms. Recent access to eggs, sperm and preimplantation embryos is revealing unprecedented rates of genome instability that may result in infertility and de novo mutations that cause genomic imbalance in at least 70% of conceptions. The error type and incidence of de novo mutations differ during developmental stages and are influenced by differences in male and female meiosis. In females, DNA repair is a critical factor that determines fertility and reproductive lifespan. In males, aberrant meiotic recombination causes infertility, embryonic failure and pregnancy loss. Evidence suggest germ cells are remarkably diverse in the type of genome instability that they display and the DNA damage responses they deploy. Additionally, the initial embryonic cell cycles are characterized by a high degree of genome instability that cause congenital disorders and may limit the use of CRISPR-Cas9 for heritable genome editing.

Sertoli cell-only syndrome: etiology and clinical management

Almost 50% of infertility cases are due to male factors, and spermatogenesis failure is one of the most severe forms of male infertility. Sertoli cell-only syndrome (SCOS) also known as germ cell aplasia is characterized by azoospermia in which the seminiferous tubules of testicular biopsy are lined only with Sertoli cells. The definitive diagnosis of SCOS is by diagnostic testicular biopsy. Although SCOS may be a result of Klinefelter syndrome, most of the SCOS men have a normal karyotype. Along with genetic aberrations, signaling pathways and endocrine processes might be major factors in the development of SCOS. Sperm retrieval and intracytoplasmic sperm injection (ICSI) are available treatments for SCOS. However, some SCOS patients do not have therapeutic options to help them having a biological child. This review aims to summarize our present knowledge about SCOS and to highlight the importance of future researches in the diagnosis and treatment of this disorder.

Mapping molecular pathways for embryonic Sertoli cells derivation based on differentiation model of mouse embryonic stem cells

Background

Embryonic Sertoli cells (eSCs) have been known for playing important roles in male reproductive development system. In current studies, eSCs were mainly generated from induced intermediate mesoderm. The deriving mechanism of eSCs has been unclear so far. Therefore, this work was aimed to reveal the molecular pathways during derivation of eSCs.

Methods

In this scenario, a differentiation model from mouse embryonic stem cells (mESCs) to eSCs was established through spatiotemporal control of 5 key factors, Wilms tumor 1 homolog (Wt1), GATA binding protein 4 (Gata4), nuclear receptor subfamily 5, group A, member 1 (Nr5a1, i.e., Sf1), SRY (sex determining region Y)-box 9 (Sox9), doublesex, and mab-3 related transcription factor 1 (Dmrt1). To investigate the molecular mechanism, these key factors were respectively manipulated through a light-switchable (light-on) system, tetracycline-switchable (Tet-on) system, and CRISPR/Cas9 knock out (KO) system.

Results

Via the established approach, some embryonic Sertoli-like cells (eSLCs) were induced from mESCs and formed ring-like or tubular-like structures. The key factors were respectively manipulated and revealed their roles in the derivation of these eSLCs. Based on these results, some molecular pathways were mapped during the development of coelomic epithelial somatic cells to eSCs.

Conclusions

This differentiation model provided a high controllability of some key factors and brought a novel insight into the deriving mechanism of Sertoli cells.

Supplementary information

accompanies this paper at 10.1186/s13287-020-01600-2.

Generation of an iPSC line (HUSTi002-A) from fibroblasts of a patient with Sertoli cell-only syndrome carrying c.731_732delAT in PIWIL2 gene

Sertoli cell-only syndrome (SCOS) is a severe phenotype of male infertility; autosomal gene defects are thought to be the causes for this disease. The iPSC line generated from a SCOS patient carrying a mutation in PIWIL2 gene expresses pluripotent markers, has a normal karyotype and the mutation c.731_732delAT in PIWIL2 gene and is able to differentiate into three germ layers. This cell line will help to study the pathogenesis of SCOS, and the roles of PIWIL2 in human germ cells development and spermatogenesis.