Biallelic mutations in spermatogenesis and centriole-associated 1 like (SPATC1L) cause acephalic spermatozoa syndrome and male infertility

Genetic Causes of Qualitative Sperm Defects: A Narrative Review of Clinical Evidence

Several genes are implicated in spermatogenesis and fertility regulation, and these genes are presently being analysed in clinical practice due to their involvement in male factor infertility (MFI). However, there are still few genetic analyses that are currently recommended for use in clinical practice. In this manuscript, we reviewed the genetic causes of qualitative sperm defects. We distinguished between alterations causing reduced sperm motility (asthenozoospermia) and alterations causing changes in the typical morphology of sperm (teratozoospermia). In detail, the genetic causes of reduced sperm motility may be found in the alteration of genes associated with sperm mitochondrial DNA, mitochondrial proteins, ion transport and channels, and flagellar proteins. On the other hand, the genetic causes of changes in typical sperm morphology are related to conditions with a strong genetic basis, such as macrozoospermia, globozoospermia, and acephalic spermatozoa syndrome. We tried to distinguish alterations approved for routine clinical application from those still unsupported by adequate clinical studies. The most important aspect of the study was related to the correct identification of subjects to be tested and the correct application of genetic tests based on clear clinical data. The correct application of available genetic tests in a scenario where reduced sperm motility and changes in sperm morphology have been observed enables the delivery of a defined diagnosis and plays an important role in clinical decision-making. Finally, clarifying the genetic causes of MFI might, in future, contribute to reducing the proportion of so-called idiopathic MFI, which might indeed be defined as a subtype of MFI whose cause has not yet been revealed.

ROS-induced oxidative stress is a major contributor to sperm cryoinjury

STUDY QUESTION

What is the mechanism behind cryoinjury in human sperm, particularly concerning the interplay between reactive oxygen species (ROS) and autophagy, and how does it subsequently affect sperm fate?

SUMMARY ANSWER

The freeze-thaw operation induces oxidative stress by generating abundant ROS, which impairs sperm motility and activates autophagy, ultimately guiding the sperm toward programmed cell death such as apoptosis and necrosis, as well as triggering premature capacitation.

WHAT IS KNOWN ALREADY

Both ROS-induced oxidative stress and autophagy are thought to exert an influence on the quality of frozen-thawed sperm.

STUDY DESIGN, SIZE, DURATION

Overall, 84 semen specimens were collected from young healthy fertile males, with careful quality evaluation. The specimens were split into three groups to investigate the ROS-induced cryoinjury: normal control without any treatment, sperm treated with 0.5 mM hydrogen peroxide (H2O2) for 1 h, and sperm thawed following cryopreservation. Samples from 48 individuals underwent computer-assisted human sperm analysis (CASA) to evaluate sperm quality in response to the treatments. Semen samples from three donors were analyzed for changes in the sperm proteome after H2O2 treatment, and another set of samples from three donors were analyzed for changes following the freeze-thaw process. The other 30 samples were used for fluorescence-staining and western blotting.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Sperm motility parameters, including progressive motility (PR %) and total motility (PR + NP %), were evaluated using the CASA system on a minimum of 200 spermatozoa. The proteomic profiles were determined with label-free mass spectrometry (MS/MS) and protein identification was performed via ion search against the NCBI human database. Subsequently, comprehensive bioinformatics was applied to detect significant proteomic changes and functional enrichment. Fluorescence-staining and western blot analyses were also conducted to confirm the proteomic changes on selected key proteins. The ROS level was measured using 2',7'-dichlorodihydrofluorescein diacetate labeling and the abundance of bioactive mitochondria was determined by evaluating the inner mitochondrial membrane potential (MMP) level. Molecular behaviors of sequestosome-1 (p62 or SQSTM1) and microtubule-associated proteins 1A/1B light chain 3 (LC3) were monitored to evaluate the state of apoptosis in human sperm. Fluorescent probes oxazole yellow (YO-PRO-1) and propidium iodide (PI) were utilized to monitor programmed cell death, namely apoptosis and necrosis. Additionally, gradient concentrations of antioxidant coenzyme Q10 (CoQ10) were introduced to suppress ROS impacts on sperm.

MAIN RESULTS AND THE ROLE OF CHANCE

The CASA analysis revealed a significant decrease in sperm motility for both the H2O2-treatment and freeze-thaw groups. Fluorescence staining showed that high ROS levels were produced in the treated sperm and the MMPs were largely reduced. The introduction of CoQ10 at concentrations of 20 and 30 μM resulted in a significant rescue of progressive motility (P < 0.05). The result suggested that excessive ROS could be the major cause of sperm motility impairment, likely by damaging mitochondrial energy generation. Autophagy was significantly activated in sperm when they were under oxidative stress, as evidenced by the upregulation of p62 and the increased conversion of LC3 as well as the upregulation of several autophagy-related proteins, such as charged multivesicular body protein 2a, mitochondrial import receptor subunit TOM22 homolog, and WD repeat domain phosphoinositide-interacting protein 2. Additionally, fluorescent staining indicated the occurrence of apoptosis and necrosis in both H2O2-treated sperm and post-thaw sperm. The cell death process can be suppressed when CoQ10 is introduced, which consolidates the view that ROS could be the major contributor to sperm cryoinjury. The freeze-thaw process could also initiate sperm premature capacitation, demonstrated by the prominent increase in tyrosine phosphorylated proteins, verified with anti-phosphotyrosine antibody and immunofluorescence assays. The upregulation of capacitation-related proteins, such as hyaluronidase 3 and Folate receptor alpha, supported this finding.

LARGE SCALE DATA

The data underlying this article are available in the article and its online supplementary material.

LIMITATIONS, REASONS FOR CAUTION

The semen samples were obtained exclusively from young, healthy, and fertile males with progressive motility exceeding 60%, which might overemphasize the positive effects while possibly neglecting the negative impacts of cryoinjury. Additionally, the H2O2 treatment conditions in this study may not precisely mimic the oxidative stress experienced by sperm after thawing from cryopreservation, potentially resulting in the omission of certain molecular alterations.

WIDER IMPLICATIONS OF THE FINDINGS

This study provides substantial proteomic data for a comprehensive and deeper understanding of the impact of cryopreservation on sperm quality. It will facilitate the design of optimal protocols for utilizing cryopreserved sperm to improve applications, such as ART, and help resolve various adverse situations caused by chemotherapy, radiotherapy, and surgery.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from the Major Innovation Project of Research Institute of National Health Commission (#2022GJZD01-3) and the National Key R&D Program of China (#2018YFC1003600). All authors declare no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

The evolution of centriole degradation in mouse sperm

Centrioles are subcellular organelles found at the cilia base with an evolutionarily conserved structure and a shock absorber-like function. In sperm, centrioles are found at the flagellum base and are essential for embryo development in basal animals. Yet, sperm centrioles have evolved diverse forms, sometimes acting like a transmission system, as in cattle, and sometimes becoming dispensable, as in house mice. How the essential sperm centriole evolved to become dispensable in some organisms is unclear. Here, we test the hypothesis that this transition occurred through a cascade of evolutionary changes to the proteins, structure, and function of sperm centrioles and was possibly driven by sperm competition. We found that the final steps in this cascade are associated with a change in the primary structure of the centriolar inner scaffold protein FAM161A in rodents. This information provides the first insight into the molecular mechanisms and adaptive evolution underlying a major evolutionary transition within the internal structure of the mammalian sperm neck.

A rare ring chromosome 21 abnormality is associated with azoospermia in two different phenotypically normal cases

Azoospermia can be diagnosed with spermiogram analysis, and karyotyping is the golden standard to explain the etiology. In this study, we investigated two male cases with azoospermia and male infertility for chromosomal abnormalities. Their phenotypes and physical and hormonal examinations were both normal. In karyotyping G-banding and NOR staining, a rare ring chromosome 21 abnormality was detected in the cases and no microdeletion in chromosome Y. Ring abnormality, deletion size, and deleted regions were shown with subtelomeric FISH (.ish r(21)(p13q22.3?)(D21S1446-)) and array CGH analyses. Due to the findings, bioinformatics, protein, and pathway analyses were done to detect a candidate gene through common genes in two cases' deleted regions or ring chromosome 21.

The Transformation of the Centrosome into the Basal Body: Similarities and Dissimilarities between Somatic and Male Germ Cells and Their Relevance for Male Fertility

The sperm flagellum is essential for the transport of the genetic material toward the oocyte and thus the transmission of the genetic information to the next generation. During the haploid phase of spermatogenesis, i.e., spermiogenesis, a morphological and molecular restructuring of the male germ cell, the round spermatid, takes place that includes the silencing and compaction of the nucleus, the formation of the acrosomal vesicle from the Golgi apparatus, the formation of the sperm tail, and, finally, the shedding of excessive cytoplasm. Sperm tail formation starts in the round spermatid stage when the pair of centrioles moves toward the posterior pole of the nucleus. The sperm tail, eventually, becomes located opposed to the acrosomal vesicle, which develops at the anterior pole of the nucleus. The centriole pair tightly attaches to the nucleus, forming a nuclear membrane indentation. An articular structure is formed around the centriole pair known as the connecting piece, situated in the neck region and linking the sperm head to the tail, also named the head-to-tail coupling apparatus or, in short, HTCA. Finally, the sperm tail grows out from the distal centriole that is now transformed into the basal body of the flagellum. However, a centriole pair is found in nearly all cells of the body. In somatic cells, it accumulates a large mass of proteins, the pericentriolar material (PCM), that together constitute the centrosome, which is the main microtubule-organizing center of the cell, essential not only for the structuring of the cytoskeleton and the overall cellular organization but also for mitotic spindle formation and chromosome segregation. However, in post-mitotic (G1 or G0) cells, the centrosome is transformed into the basal body. In this case, one of the centrioles, which is always the oldest or mother centriole, grows the axoneme of a cilium. Most cells of the body carry a single cilium known as the primary cilium that serves as an antenna sensing the cell's environment. Besides, specialized cells develop multiple motile cilia differing in substructure from the immotile primary cilia that are essential in moving fluids or cargos over the cellular surface. Impairment of cilia formation causes numerous severe syndromes that are collectively subsumed as ciliopathies. This comparative overview serves to illustrate the molecular mechanisms of basal body formation, their similarities, and dissimilarities, in somatic versus male germ cells, by discussing the involved proteins/genes and their expression, localization, and function. The review, thus, aimed to provide a deeper knowledge of the molecular players that is essential for the expansion of clinical diagnostics and treatment of male fertility disorders.

Pathogenic Variants in ACTRT1 Cause Acephalic Spermatozoa Syndrome

Acephalic spermatozoa syndrome is a rare type of teratozoospermia, but its pathogenesis is largely unknown. Here, we performed whole-exome sequencing for 34 patients with acephalic spermatozoa syndrome and identified pathogenic variants in the X-linked gene, ACTRT1, in two patients. Sanger sequencing confirmed the pathogenic variants of ACTRT1 in the patients. Both pathogenic variants of ACTRT1 were highly conserved, and in silico analysis revealed that they were deleterious and rare. Actrt1-knockout mice exhibited a similar acephalic spermatozoa phenotype. Therefore, we speculated that mutations in ACTRT1 account for acephalic spermatozoa syndrome. Moreover, the patients in this study conceived their children through artificial insemination. This study provides further insights for clinicians and researchers regarding the genetic etiology and therapeutic strategies for acephalic spermatozoa patients with pathogenic variants in ACTRT1.