Transplanted XY germ cells produce spermatozoa in testes of XXY mice

X‑chromosome loss rescues Sertoli cell maturation and spermatogenesis in Klinefelter syndrome

Klinefelter syndrome (47,XXY) causes infertility with a testicular histology comprising two types of Sertoli cell-only tubules, representing mature and immature-like Sertoli cells, and occasionally focal spermatogenesis. Here, we show that the immature-like Sertoli cells highly expressed XIST and had two X-chromosomes, while the mature Sertoli cells lacked XIST expression and had only one X-chromosome. Sertoli cells supporting focal spermatogenesis also lacked XIST expression and the additional X-chromosome, while the spermatogonia expressed XIST despite having only one X-chromosome. XIST was expressed in Sertoli cells until puberty, where a gradual loss was observed. Our results suggest that a micro-mosaic loss of the additional X-chromosome is needed for Sertoli cells to mature and to allow focal spermatogenesis.

In vitro propagation of XXY human Klinefelter spermatogonial stem cells: A step towards new fertility opportunities

Klinefelter Syndrome (KS) is characterized by a masculine phenotype, supernumerary sex chromosomes (47, XXY), and impaired fertility due to loss of spermatogonial stem cells (SSCs). Early testicular cryopreservation could be an option for future fertility treatments in these patients, including SSCs transplantation or in vitro spermatogenesis. It is critically essential to adapt current in vitro SSCs propagation systems as a fertility option for KS patients. KS human testicular samples (13,15- and 17-year-old non-mosaic KS boys) were donated by patients enrolled in an experimental testicular tissue banking program. Testicular cells were isolated from cryopreserved tissue and propagated in long-term culture for 110 days. Cell-specific gene expression confirmed the presence of all four main cell types found in testes: Spermatogonia, Sertoli, Leydig, and Peritubular cells. A population of ZBTB16⁺ undifferentiated spermatogonia was identified throughout the culture using digital PCR. Flow cytometric analysis also detected an HLA^-/CD9⁺/CD49f⁺ population, indicating maintenance of a stem cell subpopulation among the spermatogonial cells. FISH staining for chromosomes X and Y showed most cells containing an XXY karyotype with a smaller number containing either XY or XX. Both XY and XX populations were able to be enriched by magnetic sorting for CD9 as a spermatogonia marker. Molecular karyotyping demonstrated genomic stability of the cultured cells, over time. Finally, single-cell RNAseq analysis confirmed transcription of ID4, TCN2, and NANOS 3 within a population of putative SSCs population. This is the first study showing successful isolation and long-term in vitro propagation of human KS testicular cells. These findings could inform the development of therapeutic fertility options for KS patients, either through in vitro spermatogenesis or transplantation of SSC, in vivo.

In Vitro Propagation of XXY Undifferentiated Mouse Spermatogonia: Model for Fertility Preservation in Klinefelter Syndrome Patients

Klinefelter syndrome (KS) is characterized by a masculine phenotype, supernumerary sex chromosomes (usually XXY), and spermatogonial stem cell (SSC) loss in their early life. Affecting 1 out of every 650 males born, KS is the most common genetic cause of male infertility, and new fertility preservation strategies are critically important for these patients. In this study, testes from 41, XXY prepubertal (3-day-old) mice were frozen-thawed. Isolated testicular cells were cultured and characterized by qPCR, digital PCR, and flow cytometry analyses. We demonstrated that SSCs survived and were able to be propagated with testicular somatic cells in culture for up to 120 days. DNA fluorescent in situ hybridization (FISH) showed the presence of XXY spermatogonia at the beginning of the culture and a variety of propagated XY, XX, and XXY spermatogonia at the end of the culture. These data provide the first evidence that an extra sex chromosome was lost during innate SSC culture, a crucial finding in treating KS patients for preserving and propagating SSCs for future sperm production, either in vitro or in vivo. This in vitro propagation system can be translated to clinical fertility preservation for KS patients.

The Evidence for Fertility Preservation in Pediatric Klinefelter Syndrome

Klinefelter syndrome (KS) is a common cause of non-obstructive azoospermia (NOA). Advances in fertility preservation (FP) techniques, such as the use of microdissection testicular sperm extraction (micro-TESE), have improved sperm retrieval rates (SRR) up to 40–50% in this population. Age has been suggested to have an impact on FP, postulating that sperm production may deteriorate over time due to germ cell loss. As such, sperm retrieval for patients with KS at a younger age has been proposed to further improve SRR; however, whether such practice pragmatically improves SRR is yet to be determined, and controversy remains with concerns over trauma caused by FP procedures on further impairment of testicular function. There has also been a debate on the ethics of performing FP procedures in the pediatric population. Optimizing FP for patients with KS invariably requires a holistic multidisciplinary approach. This review aimed to evaluate the latest evidence in performing FP in pediatric patients with KS, and discuss the controversy surrounding such practice. Hormonal changes in patients with KS during childhood and the use of hormonal manipulation to optimize SSR in this population have also been reviewed.

Expression profile of microRNAs in the testes of patients with Klinefelter syndrome

Klinefelter syndrome (KS) is the most common sex chromosome aneuploidy. A distinctive characteristic of KS is oligozoospermia. Despite multiple studies that have described the natural history of the degenerative process of germ cells in patients with KS, the molecular mechanisms that initiate this process are not well characterized. MicroRNA (miRNA)-mediated post-transcriptional control mechanisms have been increasingly recognized as important regulators of spermatogenesis; however, only a few studies have evaluated the role of miRNAs in the gonadal failure of these patients. Here, we describe a differential expression profile for the miRNAs in testicular tissue samples taken from KS patients. We analysed testicular tissue samples from 4 KS patients and 5 control patients (obstructive azoospermia) through next-generation sequencing, which can provide information about the mechanisms involved in the degeneration of germ cells. A distinctive differential expression profile was identified for 166 miRNAs in the KS patients: 66 were upregulated, and 100 were downregulated. An interactome analysis was performed for 7 of the upregulated and the 20 downregulated miRNAs. The results showed that the target genes are involved in the development, proliferation, and differentiation processes of spermatogenesis, which may explain their role in the development of infertility. This is the first report of a miRNA expression profile generated from testicular tissue samples of KS patients.

Germ cell loss in Klinefelter syndrome: When and why?

Klinefelter syndrome (KS) is a quite common disorder with an incidence of 1-2 in 1,000 new-born males. Most patients are diagnosed in the light of a clinical checkup when consulting a fertility clinic with an unfulfilled child wish. Infertility in KS patients is caused by a massive germ cell loss, leading to azoospermia in more than 90% of the adult patients. Most seminiferous tubules in the adult KS testis are degenerated or hyalinized and testicular fibrosis can be observed, starting from puberty. However, focal spermatogenesis can be found in the testis of some patients. This offers the opportunity to extract spermatozoa from the testis by testicular sperm extraction (TESE). Nevertheless, TESE is only successful in about half of the KS adults seeking to father children. The reason for the germ cell loss remains unclear. To date, it is still debated whether the testicular tissue changes and the germ cell loss seen in KS is directly caused by an altered X-linked gene expression, the altered somatic environment, or a deficiency in the germ cells. In this review, we provide an overview of the current knowledge about the germ cell loss in KS patients.

TEX11 modulates germ cell proliferation by competing with estrogen receptor β for the binding to HPIP

Klinefelter syndrome (KS), characterized by the presence of more than one X-chromosome in men, is a major genetic cause of male infertility. Germ cell degeneration in KS patients is thought to be the consequences of overexpression of some genes on the X-chromosome. However, the identity of these genes and the underlying mechanisms remain unclear. Testis-expressed 11 (TEX11) is an X-chromosome-encoded germ-cell-specific protein that is expressed most abundantly in spermatogonia and early spermatocytes in the testes. In our search for TEX11-interacting partners using the yeast two-hybrid system, we identified hematopoietic pre-B cell leukemia transcription factor-interacting protein (HPIP), which anchors estrogen receptors (ER) to the cytoskeleton and modulates their functions. We found that mouse spermatogonial stem cells expressed Tex11, Hpip, and Esr2 but not Esr1. In cultured cells, TEX11 competed with ERβ for binding to HPIP. Upon treatment with 17β-estradiol or an ERβ agonist diarylpropionitrile, TEX11 promoted the nuclear translocation of ERβ and enhanced its transcriptional activities. On the other hand, TEX11 suppressed the nongenomic activities of ERβ in the cytoplasm, as indicated by reduced phosphorylation of AKT and ERK signaling molecules. Overexpression of TEX11 in mouse germ-cell-derived GC-1 and GC-2 cells suppressed the cell proliferation and the expression of cFos, Ccnd1, and Ccnb1 that were stimulated by 17β-estradiol or diarylpropionitrile and elevated the expression level of the proapoptotic Bax gene. The negative effect of TEX11 on cell proliferation suggests that increased expression of TEX11 in the germ cells may partially contribute to the spermatogenic defect observed in KS patients.