MicroRNA-26b promotes transition from Kit- to Kit+ mouse spermatogonia

The Role of microRNA in Spermatogenesis: Is There a Place for Fertility Preservation Innovation?

Oncological treatments have dramatically improved over the last decade, and as a result, survival rates for cancer patients have also improved. Quality of life, including concerns about fertility, has become a major focus for both oncologists and patients. While oncologic treatments are often highly effective at suppressing neoplastic growth, they are frequently associated with severe gonadotoxicity, leading to infertility. For male patients, the therapeutic option to preserve fertility is semen cryopreservation. In prepubertal patients, immature testicular tissue can be sampled and stored to allow post-cure transplantation of the tissue, immature germ cells, or in vitro spermatogenesis. However, experimental techniques have not yet been proven effective for restoring sperm production for these patients. MicroRNAs (miRNAs) have emerged as promising molecular markers and therapeutic tools in various diseases. These small regulatory RNAs possess the unique characteristic of having multiple gene targets. MiRNA-based therapeutics can, therefore, be used to modulate the expression of different genes involved in signaling pathways dysregulated by changes in the physiological environment (disease, temperature, ex vivo culture, pharmacological agents). This review discusses the possible role of miRNA as an innovative treatment option in male fertility preservation-restoration strategies and describes the diverse applications where these new therapeutic tools could serve as fertility protection agents.

Regulation of mammalian spermatogenesis by miRNAs

Male fertility requires the continual production of sperm by the process of spermatogenesis. This process requires the correct timing of regulatory signals to germ cells during each phase of their development. MicroRNAs (miRNAs) in germ cells and supporting Sertoli cells respond to regulatory signals and cause down- or upregulation of mRNAs and proteins required to produce proteins that act in various pathways to support spermatogenesis. The targets and functional consequences of altered miRNA expression in undifferentiated and differentiating spermatogonia, spermatocytes, spermatids and Sertoli cells are discussed. Mechanisms are reviewed by which miRNAs contribute to decisions that promote spermatogonia stem cell self-renewal versus differentiation, entry into and progression through meiosis, differentiation of spermatids, as well as the regulation of Sertoli cell proliferation and differentiation. Also discussed are miRNA actions providing the very first signals for the differentiation of spermatogonia stem cells in a non-human primate model of puberty initiation.

Differential microRNAs expression in seminal plasma of normospermic patients with different sperm DNA fragmentation indexes

Sperm DNA fragmentation index (SDF), as an important supplement to routine semen parameters, has been proposed to discriminate between fertile and infertile men, and predicts the outcomes of natural conception and in vitro fertilization. Unfortunately there are uncertainty and contradictory evidences regarding the importance of SDF. An important reason is the fact that significant and fundamental research about SDF is rare. This study was designed to characterize the microRNA (miRNA) expression profile in seminal plasma of normospermic patients with different SDF and their implications in human fertility. Using next-generation sequencing (NGS), a total of 897 human miRNAs were detected from 10 seminal plasma samples, out of which 431 differentially expressed miRNAs in 5 pairs of seminal plasma samples (each pair of seminal plasma samples obtained from the same male), with 14 miRNAs were identified in all the pairs. According to the fold change and expression level, 7 miRNAs including miR-374b-5p, miR-429, hsa-miR-26b-5p, miR-21-5p, miR-4257, miR-135b-5p and miR-134-5p were selected for further excavation. MiR-374b-5p and miR-26b-5p were significantly different in 3 sets of individual seminal plasma samples with different SDF from total 90 infertile patients (30 patients each set). Our results demonstrate that the profile of miR-374b and miR-26b with significantly decreased expression could be used as a first indication of increased SDF. And miR-374b and miR-26b could serve as adjunct biomarkers for the diagnosis of idiopathic infertile males.

Retinoic acid and microRNA

Retinoic acid (RA), the biologically active metabolite of vitamin A, regulates a vast spectrum of biological processes, such as cell differentiation, proliferation, apoptosis, and morphogenesis. microRNAs (miRNAs) play a crucial role in regulating gene expression by binding to messenger RNA (mRNA) which leads to mRNA degradation and/or translational repression. Like RA, miRNAs regulate multiple biological processes, including proliferation, differentiation, apoptosis, neurogenesis, tumorigenesis, and immunity. In fact, RA regulates the expression of many miRNAs to exert its biological functions. miRNA and RA regulatory networks have been studied in recent years. In this manuscript, we summarize literature that highlights the impact of miRNAs in RA-regulated molecular networks included in the PubMed.

Mechanisms regulating mammalian spermatogenesis and fertility recovery following germ cell depletion

Mammalian spermatogenesis is a highly complex multi-step process sustained by a population of mitotic germ cells with self-renewal potential known as spermatogonial stem cells (SSCs). The maintenance and regulation of SSC function are strictly dependent on a supportive niche that is composed of multiple cell types. A detailed appreciation of the molecular mechanisms underpinning SSC activity and fate is of fundamental importance for spermatogenesis and male fertility. However, different models of SSC identity and spermatogonial hierarchy have been proposed and recent studies indicate that cell populations supporting steady-state germline maintenance and regeneration following damage are distinct. Importantly, dynamic changes in niche properties may underlie the fate plasticity of spermatogonia evident during testis regeneration. While formation of spermatogenic colonies in germ-cell-depleted testis upon transplantation is a standard assay for SSCs, differentiation-primed spermatogonial fractions have transplantation potential and this assay provides readout of regenerative rather than steady-state stem cell capacity. The characterisation of spermatogonial populations with regenerative capacity is essential for the development of clinical applications aimed at restoring fertility in individuals following germline depletion by genotoxic treatments. This review will discuss regulatory mechanisms of SSCs in homeostatic and regenerative testis and the conservation of these mechanisms between rodent models and man.