Mitochondrial regulation during male germ cell development

Mechanistic Insights into 1,2-bis(2,4,6-tribromophenoxy)ethane-Induced Male Reproductive Toxicity in Zebrafish

The novel brominated flame retardant, 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), has increasingly been detected in environmental and biota samples. However, limited information is available regarding its toxicity, especially at environmentally relevant concentrations. In the present study, adult male zebrafish were exposed to varying concentrations of BTBPE (0, 0.01, 0.1, 1, and 10 μg/L) for 28 days. The results demonstrated underperformance in mating behavior and reproductive success of male zebrafish when paired with unexposed females. Additionally, a decline in sperm quality was confirmed in BTBPE-exposed male zebrafish, characterized by decreased total motility, decreased progressive motility, and increased morphological malformations. To elucidate the underlying mechanism, an integrated proteomic and phosphoproteomic analysis was performed, revealing a predominant impact on mitochondrial functions at the protein level and a universal response across different cellular compartments at the phosphorylation level. Ultrastructural damage, increased expression of apoptosis-inducing factor, and disordered respiratory chain confirmed the involvement of mitochondrial impairment in zebrafish testes. These findings not only provide valuable insights for future evaluations of the potential risks posed by BTBPE and similar chemicals but also underscore the need for further research into the impact of mitochondrial dysfunction on reproductive health.

BdTTLL3B-mediated polyglycylation is involved in the spermatogenesis in Bactrocera dorsalis

Polyglycylation is a post-translational modification that generates glycine side chains in the C-terminal domains of both α- and β-tubulins. To date, the patterns and significance of polyglycylation across insect species remain largely unknown. The TTLL3B was thought to be a polyglycylase and be essential for polyglycylation in dipteran insects. In this study, the TTLL3B of Bactrocera dorsalis (BdTTLL3B) was identified and characterized. The BdTTLL3B expressed remarkably higher in adult males, especially in testes. The spatio-temporal patterns of polyglycylation were consistent with that of BdTTLL3B. Along with spermatogenesis, the intensity of polyglycylation was enhanced steadily and concentrated in elongated flagella. The expression of recombinant BdTTLL3B in Hela cells, which are genetically deficient in polyglycylation, catalyzed intracellular polyglycylation, validating the identity of BdTTLL3B as a polyglycylase. Knockout of BdTTLL3B significantly suppressed polyglycylation in testes and impaired male fertility, probably due to abnormal morphology of mitochondrial derivatives and over-accumulation of paracrystalline. Taken together, these findings indicated that the BdTTLL3B-mediated polyglycylation is involved in the spermatogenesis and play an important role in fertility of adult B. dorsalis. Therefore, the BdTTLL3B can be considered as a candidate target gene for the management of B. dorsalis, such as developing gene silencing/knockout-based sterile insect technology (SIT).

Mitochondrial Differentiation during Spermatogenesis: Lessons from Drosophila melanogaster

Numerous diseases can arise as a consequence of mitochondrial malfunction. Hence, there is a significant focus on studying the role of mitochondria in cancer, ageing, neurodegenerative diseases, and the field of developmental biology. Mitochondria could exist as discrete organelles in the cell; however, they have the ability to fuse, resulting in the formation of interconnected reticular structures. The dynamic changes between these forms correlate with mitochondrial function and mitochondrial health, and consequently, there is a significant scientific interest in uncovering the specific molecular constituents that govern these transitions. Moreover, the specialized mitochondria display a wide array of variable morphologies in their cristae formations. These inner mitochondrial structures are closely associated with the specific functions performed by the mitochondria. In multiple cases, the presence of mitochondrial dysfunction has been linked to male sterility, as it has been observed to cause a range of abnormal spermatogenesis and sperm phenotypes in different species. This review aims to elucidate the dynamic alterations and functions of mitochondria in germ cell development during the spermatogenesis of Drosophila melanogaster.

Sperm mitochondria dysfunction in response to testicular cancer

Testicular cancer is the most common form of cancer in young men of reproductive age and its incidence is increasing globally. With the currently successful treatment and 95% survival rate, there is a need for deeper understanding of testicular cancer-related infertility. Most patients with testicular cancer experience semen abnormalities prior to cancer therapy. However, the exact mechanism of the effect of testicular cancer on sperm anomalies is not known. Mitochondria are organelles that play a crucial role in both tumorigenesis and spermatogenesis and their malfunction may be an important factor resulting in sperm abnormalities in testicular cancer patients. Within the scope of this review, we will discuss current knowledge of testicular cancer-related alterations in the ATP production pathway, a possible pathophysiological switch from oxidative phosphorylation (OXPHOS) to glycolysis, as well as the role of oxidative stress promoting sperm dysfunction. In this regard, the review provides a summary of the impact of testicular cancer on sperm quality as a possible consequence of impaired mitochondrial function including the energy metabolic pathways that are known to be altered in the sperm of testicular cancer patients.

Photoperiod-regulated mitophagy in the germ cells of Brandt's voles (Lasiopodomys brandtii)

Photoperiod is a pivotal factor in affecting testicular function and spermatogenesis in seasonal-breeding animals. Mitophagy is essential for spermatogenesis, but its association with seasonal photoperiods has not been studied extensively. To explore this, we exposed male Brandt's voles (Lasiopodomys brandtii) to long-photoperiod (LP, 16 h/day) and short-photoperiod (SP, 8 h/day) conditions from their embryonic stages. Our results indicated that testis weight, volume, and relative testes weight were all significantly increased in LP compared to SP. Additionally, blood testosterone levels were markedly higher in LP than SP. Histological examination revealed that seminiferous diameter and epithelium thickness were greater in LP, with an increased abundance of germ cell types and cell numbers compared to SP. RT-qPCR analysis showed that mitophagy-promoting genes, such as Pink1, Prkn, Tomm7, Mnf2, Lc3, Optn, Gabarap, and Nbr1 were all upregulated in LP. Fluorescence in situ hybridization indicated that Pink1 expression was present in spermatogonia in SP, while in LP, Pink1 expression extended to almost all germ cell types with significantly higher mean optical density. Prkn expression was found in all germ cell types in both LP and SP, with a significantly higher mean optical density of 10-week-old LP males. Transmission electron microscopy showed normal mitochondrial morphology with clear membranes in SP, while the LP group had reduced cristae in mitochondria and damaged mitochondria undergoing autophagy. This study suggests that mitophagy may be involved in the photoperiodic spermatogenesis in Brandt's voles, providing insights into the role of photoperiod in seasonal reproduction in wild animals.

The mitochondrial protease PARL is required for spermatogenesis

Mitochondrial function plays an important role in the maintenance of male fertility. However, the mechanisms underlying mitochondrial defect-related infertility remain mostly unclear. Here we show that a deficiency of PARL (Parl-/-), a mitochondrial protease, causes complete arrest of spermatogenesis during meiosis I. PARL deficiency led to severe downregulation of proteins of respiratory chain complex IV in testes that did not occur in other tested organs, causing a deficit in complex IV activity and ATP production. Furthermore, Parl-/- testes showed an almost complete loss of HSD17B3, a protein of the sER responsible for the last step in testosterone synthesis. While testosterone production appeared to be restored by overexpression of HSD17B12, loss of the canonical testosterone synthesis led to an upregulation of luteinizing hormone (LH) and of LH-regulated responses. These results suggest an important impact of the downstream regulation of mitochondrial defects that manifest in a cell-type-specific manner and extend beyond mitochondria.

A landscape of mouse mitochondrial small non-coding RNAs

Small non-coding RNAs (ncRNAs), particularly miRNAs, play key roles in a plethora of biological processes both in health and disease. Although largely operative in the cytoplasm, emerging data indicate their shuttling in different subcellular compartments. Given the central role of mitochondria in cellular homeostasis, here we systematically profiled their small ncRNAs content across mouse tissues that largely rely on mitochondria functioning. The ubiquitous presence of piRNAs in mitochondria (mitopiRNA) of somatic tissues is reported for the first time, supporting the idea of a strong and general connection between mitochondria biology and piRNA pathways. Then, we found groups of tissue-shared and tissue-specific mitochondrial miRNAs (mitomiRs), potentially related to the "basic" or "cell context dependent" biology of mitochondria. Overall, this large data platform will be useful to deepen the knowledge about small ncRNAs processing and their governed regulatory networks contributing to mitochondria functions.

Sperm acrosomal released proteome reveals MDH and VDAC3 from mitochondria are involved in acrosome formation during spermatogenesis in Eriocheir sinensis

Acrosome is inextricably related to membranous organelles. The origin of acrosome is still controversial, one reason is that limited articles were reported about the proteomic analysis of the acrosome. Mitochondrial proteins were found exist in the acrosome, nevertheless, only limited attention has been paid to the function of mitochondrial proteins in the acrosome formation. Eriocheir sinensis sperm has a large acrosome, which makes it an ideal model to study acrosome formation. Here, we firstly compared the rate of acrosome reaction induced by the calcium ionophore A23187 and ionomycin. The rate of acrosome reaction induced by ionomycin is higher (95.8%) than A23187 (58.7%). Morphological changes were observed using light, confocal and transmission electron microscopy. Further more, proteins released during the acrosome reaction as induced by ionomycin were collected for LC-MS/MS analysis. A total of 945 proteins, including malate dehydrogenase (MDH) and voltage-dependent anion channel 3 (VDAC3), were identified in the acrosomal released proteome. The number of proteins from mitochondria (17.57%) was higher compared with endoplasmic reituculum (1.59%) and lysosomes (1.8%). To investigate the functions of target mitochondrial proteins during spermatogenesis, poly-antibodies of MDH in E. sinensis were prepared. The characteristics, further analyzed using immunofluorescence, of two mitochondrial proteins during acrosome formation showed that MDH and VDAC3 were independently involved in the formation of acrosomal membrane. These findings illustrate the acrosomal released proteome and provide important data resource for understanding the relationship between mitochondria and the acrosome in Decapoda crustacean.

Morphology, Histology, and Transcriptome Analysis of Gonadal Development in Octopus minor (Sasaki, 1920)

Octopus minor is an economically important species, but little is known about the histological pattern and regulatory mechanisms during gonadal development. In this study, we investigated the annual changes in total body weight (TW), gonad somatic index (GSI), gonadal histological features, and transcriptome of O. minor. The results indicated that both females and males showed a similar TW trend. The GSI peaked in June in females, while it remained constant at around 3% in males. Nine and four histological stages were observed in ovaries and testes, respectively. Our field sampling results implied that O. minor might have overwintering periods for both eggs and larvae. Transcriptome analysis revealed that a total of 1095 and 2468 genes were significantly expressed during ovarian and testicular development, separately. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis displayed that 126 GO terms and 5 KEGG pathways were significantly enriched in the ovarian group of advanced vitellogenic oocytes vs vitellogenic oocytes (AVO vs VO). The pathways "Ribosomal", "Cell cycle", and "Progesterone-mediated oocyte maturation" were predicted to promote yolk deposition. Additionally, the testicular comparison group of spent vs mature (Spent vs Mature) showed significant enrichment in 674 GO terms and 13 KEGG pathways, suggesting that energy metabolism and cell repair pathways may be involved in the spermatogenesis process. This work revealed the development process of the gonads and shed light on the potential regulatory pathways of O. minor, providing novel insights and laying a molecular basis for artificial breeding.

Functions and mechanism of noncoding RNA in regulation and differentiation of male mammalian reproduction

Noncoding RNAs (ncRNAs) are active regulators of a wide range of biological and physiological processes, including the majority of mammalian reproductive events. Knowledge of the biological activities of ncRNAs in the context of mammalian reproduction will allow for a more comprehensive and comparative understanding of male sterility and fertility. In this review, we describe recent advances in ncRNA-mediated control of mammalian reproduction and emphasize the importance of ncRNAs in several aspects of mammalian reproduction, such as germ cell biogenesis and reproductive organ activity. Furthermore, we focus on gene expression regulatory feedback loops including hormones and ncRNA expression to better understand germ cell commitment and reproductive organ function. Finally, this study shows the role of ncRNAs in male reproductive failure and provides suggestions for further research.

Mitochondrial defects caused by PARL deficiency lead to arrested spermatogenesis and ferroptosis

Impaired spermatogenesis and male infertility are common manifestations associated with mitochondrial diseases, yet the underlying mechanisms linking these conditions remain elusive. In this study, we demonstrate that mice deficient for the mitochondrial intra-membrane rhomboid protease PARL, a recently reported model of the mitochondrial encephalopathy Leigh syndrome, develop early testicular atrophy caused by a complete arrest of spermatogenesis during meiotic prophase I, followed by degeneration and death of arrested spermatocytes. This process is independent of neurodegeneration. Interestingly, genetic modifications of PINK1, PGAM5, and TTC19 - three major substrates of PARL with important roles in mitochondrial homeostasis - fail to reproduce or modify this severe phenotype, indicating that the spermatogenic arrest arises from distinct molecular pathways. We further observed severe abnormalities in mitochondrial ultrastructure in PARL-deficient spermatocytes, along with prominent electron transfer chain defects, disrupted coenzyme Q (CoQ) biosynthesis, and metabolic rewiring. These mitochondrial defects are associated with a germ cell-specific decrease in GPX4 expression leading arrested spermatocytes to ferroptosis - a regulated cell death modality characterized by uncontrolled lipid peroxidation. Our results suggest that mitochondrial defects induced by PARL depletion act as an initiating trigger for ferroptosis in primary spermatocytes through simultaneous effects on GPX4 and CoQ - two major inhibitors of ferroptosis. These findings shed new light on the potential role of ferroptosis in the pathogenesis of mitochondrial diseases and male infertility warranting further investigation.

Cryopreservation Induces Acetylation of Metabolism-Related Proteins in Boar Sperm

Cryodamage affects the normal physiological functions and survivability of boar sperm during cryopreservation. Lysine acetylation is thought to be an important regulatory mechanism in sperm functions. However, little is known about protein acetylation and its effects on cryotolerance or cryodamage in boar sperm. In this study, the characterization and protein acetylation dynamics of boar sperm during cryopreservation were determined using liquid chromatography-mass spectrometry (LC-MS). A total of 1440 proteins were identified out of 4705 modified proteins, and 2764 quantifiable sites were elucidated. Among the differentially modified sites, 1252 were found to be upregulated compared to 172 downregulated sites in fresh and frozen sperms. Gene ontology indicated that these differentially modified proteins are involved in metabolic processes and catalytic and antioxidant activities, which are involved in pyruvate metabolism, phosphorylation and lysine degradation. In addition, the present study demonstrated that the mRNA and protein expressions of SIRT5, IDH2, MDH2 and LDHC, associated with sperm quality parameters, are downregulated after cryopreservation. In conclusion, cryopreservation induces the acetylation and deacetylation of energy metabolism-related proteins, which may contribute to the post-thawed boar sperm quality parameters.

Impacts of disinfection byproduct exposures on male reproductive health: Current evidence, possible mechanisms and future needs

Disinfection byproducts (DBPs) are a class of ubiquitous chemicals in drinking water and inevitably result in widespread human exposures. Potentially adverse health effects of DBP exposures, including reproductive and developmental outcomes, have been increasing public concerns. Several reviews have focused on the adverse pregnancy outcomes of DBPs. This review summarized current evidence on male reproduction health upon exposure to DBPs from toxicological and epidemiological literature. Based on existing experimental studies, there are sufficient evidence showing that haloacetic acids (HAAs) are male reproductive toxicants, including reduced epididymal weight, decreased semen parameters and sperm protein 22, and declined testosterone levels. However, epidemiological evidence remains insufficient to support a link of DBP exposures with adverse male reproductive outcomes, despite that blood and urinary DBP biomarkers are associated with decreased semen quality. Eight potential mechanisms, including germ/somatic cell dysfunction, oxidative stress, genotoxicity, inflammation, endocrine hormones, folate metabolism, epigenetic alterations, and gut microbiota, are likely involved in male reproductive toxicity of DBPs. We also identified knowledge gaps in toxicological and epidemiological studies to enhance future needs.

A Germline-Specific Regulator of Mitochondrial Fusion is Required for Maintenance and Differentiation of Germline Stem and Progenitor Cells

Maintenance and differentiation of germline stem and progenitor cells (GSPCs) is important for sexual reproduction. Here, the authors identify zebrafish pld6 as a novel germline-specific gene by cross-analyzing different RNA sequencing results, and find that pld6 knockout mutants develop exclusively into infertile males. In pld6 mutants, GSPCs fail to differentiate and undergo apoptosis, leading to masculinization and infertility. Mitochondrial fusion in pld6-depleted GSPCs is severely impaired, and the mutants exhibit defects in piRNA biogenesis and transposon suppression. Overall, this work uncovers zebrafish Pld6 as a novel germline-specific regulator of mitochondrial fusion, and highlights its essential role in the maintenance and differentiation of GSPCs as well as gonadal development and gametogenesis.

A white paper on Phospholipid Hydroperoxide Glutathione Peroxidase (GPx4) forty years later

The purification of a protein inhibiting lipid peroxidation led to the discovery of the selenoperoxidase GPx4 forty years ago. Thus, the evidence of the enzymatic activity was reached after identifying the biological effect and unambiguously defined the relationship between the biological function and the enzymatic activity. In the syllogism where GPx4 inhibits lipid peroxidation and its inhibition is lethal, cell death is operated by lipid peroxidation. Based on this rationale, this form of cell death emerged as regulated iron-enforced oxygen toxicity and was named ferroptosis in 2012. In the last decades, we learned that reduction of lipid hydroperoxides is indispensable and, in cooperation with prooxidant systems, controls the critical steady state of lipid peroxidation. This concept defined the GPx4 reaction as both the target for possible anti-cancer therapy and if insufficient, as cause of degenerative diseases. We know the reaction mechanism, but the details of the interaction at the membrane cytosol interface are still poorly defined. We know the gene structure, but the knowledge about expression control is still limited. The same holds true for post-transcriptional modifications. Reverse genetics indicate that GPx4 has a role in inflammation, immunity, and differentiation, but the observations emerging from these studies need a more specifically addressed biochemical evidence. Finally, the role of GPx4 in spermatogenesis disclosed an area unconnected to lipid peroxidation. In its mitochondrial and nuclear form, the peroxidase catalyzes the oxidation of protein thiols in two specific aspects of sperm maturation: stabilization of the mid-piece and chromatin compaction. Thus, although available evidence converges to the notion that GPx4 activity is vital due to the inhibition of lipid peroxidation, it is reasonable to foresee other unknown aspects of the GPx4 reaction to be disclosed.

Multiple roles played by the mitochondrial citrate carrier in cellular metabolism and physiology

The citrate carrier (CIC) is an integral protein of the inner mitochondrial membrane which catalyzes the efflux of mitochondrial citrate (or other tricarboxylates) in exchange with a cytosolic anion represented by a tricarboxylate or a dicarboxylate or phosphoenolpyruvate. In this way, the CIC provides the cytosol with citrate which is involved in many metabolic reactions. Several studies have been carried out over the years on the structure, function and regulation of this metabolite carrier protein both in mammals and in many other organisms. A lot of data on the characteristics of this protein have therefore accumulated over time thereby leading to a complex framework of metabolic and physiological implications connected to the CIC function. In this review, we critically analyze these data starting from the multiple roles played by the mitochondrial CIC in many cellular processes and then examining the regulation of its activity in different nutritional and hormonal states. Finally, the metabolic significance of the citrate flux, mediated by the CIC, across distinct subcellular compartments is also discussed.

Condensed Mitochondria Assemble Into the Acrosomal Matrix During Spermiogenesis

Mammalian spermatogenesis is associated with the transient appearance of condensed mitochondria, a singularity of germ cells with unknown function. Using proteomic analysis, respirometry, and electron microscopy with tomography, we studied the development of condensed mitochondria. Condensed mitochondria arose from orthodox mitochondria during meiosis by progressive contraction of the matrix space, which was accompanied by an initial expansion and a subsequent reduction of the surface area of the inner membrane. Compared to orthodox mitochondria, condensed mitochondria respired more actively, had a higher concentration of respiratory enzymes and supercomplexes, and contained more proteins involved in protein import and expression. After the completion of meiosis, the abundance of condensed mitochondria declined, which coincided with the onset of the biogenesis of acrosomes. Immuno-electron microscopy and the analysis of sub-cellular fractions suggested that condensed mitochondria or their fragments were translocated into the lumen of the acrosome. Thus, it seems condensed mitochondria are formed from orthodox mitochondria by extensive transformations in order to support the formation of the acrosomal matrix.