Glutathione-dependent defence mechanisms in isolated round spermatids from the rat

Antioxidant Intervention against Male Infertility: Time to Design Novel Strategies

Infertility is a highly prevalent condition, affecting 9-20% of couples worldwide. Among the identifiable causes, the male factor stands out in about half of infertile couples, representing a growing problem. Accordingly, there has been a decline in both global fertility rates and sperm counts in recent years. Remarkably, nearly 80% of cases of male infertility (MI) have no clinically identifiable aetiology. Among the mechanisms likely plausible to account for idiopathic cases, oxidative stress (OS) has currently been increasingly recognized as a key factor in MI, through phenomena such as mitochondrial dysfunction, lipid peroxidation, DNA damage and fragmentation and finally, sperm apoptosis. In addition, elevated reactive oxygen species (ROS) levels in semen are associated with worse reproductive outcomes. However, despite an increasing understanding on the role of OS in the pathophysiology of MI, therapeutic interventions based on antioxidants have not yet provided a consistent benefit for MI, and there is currently no clear consensus on the optimal antioxidant constituents or regimen. Therefore, there is currently no applicable antioxidant treatment against this problem. This review presents an approach aimed at designing an antioxidant strategy based on the particular biological properties of sperm and their relationships with OS.

Improved motility in the gastrointestinal tract of a postoperative ileus rat model with ilaprazole

Postoperative ileus (POI), a symptom that occurs after abdominal surgery, reduces gastrointestinal motility. Although its mechanism is unclear, POI symptoms are known to be caused by inflammation 6 to 72 h after surgery. As proton pump inhibitors exhibit protective effect against acute inflammation, the purpose of this study was to determine the effect of ilaprazole on a POI rat model. POI was induced in rats by abdominal surgery. Rats were divided into six groups: control: normal rat + 0.5% CMC-Na, vehicle: POI rat + 0.5% CMC-Na, mosapride: POI rat + mosapride 2 mg/kg, ilaprazole 1 mg/kg: POI rat + ilaprazole 1 mg/kg, ilaprazole 3 mg/kg: POI rat + ilaprazole 3 mg/kg, and ilaprazole 10 mg/kg: POI rat + ilaprazole 10 mg/kg. Gastrointestinal motility was confirmed by measuring gastric emptying (GE) and gastrointestinal transit (GIT). In the small intestine, inflammation was confirmed by measuring TNF-α and IL-1β; oxidative stress was confirmed by SOD, GSH, and MDA levels; and histological changes were observed by H&E staining. Based on the findings, GE and GIT were decreased in the vehicle group and improved in the ilaprazole 10 mg/kg group. In the ilaprazole 10 mg/kg group, TNF-α and IL-1β levels were decreased, SOD and GSH levels were increased, and MDA levels were decreased. Histological damage was also reduced in the ilaprazole-treated groups. These findings suggest that ilaprazole prevents the decrease in gastrointestinal motility, a major symptom of postoperative ileus, and reduces inflammation and oxidative stress.

Determination of histological, immunohistochemical and biochemical effects of acute and chronic grayanotoxin III administration in different doses in rats

Grayanotoxin (GTX)-III is a Na-channel neurotoxin. Grayanotoxins can be found in the nectar, pollen, and other plant parts of the Rhododendron genus plants from the Ericaceae family. It is widely believed that honey produced from these plants, which are concentrated in the Black Sea region, is traditionally characterized as enhancing sexual performance. It is thought that the effective factor is dose for this compound, which has both beneficial and toxic effects reported. Therefore, it is aimed to evaluate the histological, immunohistochemical, and biochemical effects of acute and chronic impact of GTX-III in different doses on testes tissue in this study. For this purpose, 100 Sprague-Dawley male rats were divided into 5 separate groups for acute and chronic research. While dose groups were (control, 0.1, 0.2, 0.4, ve 0.8 μg/kg/bw) for experimental groups, a single dose (i.p.) was administered for acute impact whereas the same doses were administered daily for 3 weeks to assess chronic effect. At the end of the experiment, Johnsen testicular biopsy scoring was performed on testicular tissue samples, seminiferous tubule diameters were measured, and apoptotic cells were evaluated by TUNEL method. Testosterone, LH, and FSH levels were measured by ELISA method in serum and tissue specimens. It was found that Johnsen score of acute doses was significantly lower than the control group, and the diameter of the seminiferous tubules decreased significantly in acute and chronic dose-administered groups compared to the control. Hemorrhage, epithelial shedding, irregularity in seminiferous epithelium, and vacuolization were observed in acute and chronic dose-administered groups, and increase in apoptotic cells was determined. Hormone levels varied depending on the dose. In conclusion, it was found that dose-dependent acute and chronic effects of GTX-III are different, and this factor should be taken into account in studies to be carried out due to the adverse effects of high doses.

Proteolytic degradation of heat shock protein A2 occurs in response to oxidative stress in male germ cells of the mouse

STUDY QUESTION

Does oxidative stress compromise the protein expression of heat shock protein A2 (HSPA2) in the developing germ cells of the mouse testis?

SUMMARY ANSWER

Oxidative stress leads to the modification of HSPA2 by the lipid aldehyde 4-hydroxynonenal (4HNE) and initiates its degradation via the ubiquitin-proteasome system.

WHAT IS KNOWN ALREADY

Previous work has revealed a deficiency in HSPA2 protein expression within the spermatozoa of infertile men that have failed fertilization in a clinical setting. While the biological basis of this reduction in HSPA2 remains to be established, we have recently shown that the HSPA2 expressed in the spermatozoa of normozoospermic individuals is highly susceptible to adduction, a form of post-translational modification, by the lipid aldehyde 4HNE that has been causally linked to the degradation of its substrates. This modification of HSPA2 by 4HNE adduction dramatically reduced human sperm-egg interaction in vitro. Moreover, studies in a mouse model offer compelling evidence that the co-chaperone BCL2-associated athanogene 6 (BAG6) plays a key role in regulating the stability of HSPA2 in the testis, by preventing its ubiquitination and subsequent proteolytic degradation.

STUDY DESIGN, SIZE, DURATION

Dose-dependent studies were used to establish a 4HNE-treatment regime for primary culture(s) of male mouse germ cells. The influence of 4HNE on HSPA2 protein stability was subsequently assessed in treated germ cells. Additionally, sperm lysates from infertile patients with established zona pellucida recognition defects were examined for the presence of 4HNE and ubiquitin adducts. A minimum of three biological replicates were performed to test statistical significance.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Oxidative stress was induced in pachytene spermatocytes and round spermatids isolated from the mouse testis, as well as a GC-2 cell line, using 50-200 µM 4HNE or hydrogen peroxide (H2O2), and the expression of HSPA2 was monitored via immunocytochemistry and immunoblotting approaches. Using the GC-2 cell line as a model, the ubiquitination and degradation of HSPA2 was assessed using immunoprecipitation techniques and pharmacological inhibition of proteasomal and lysosomal degradation pathways. Finally, the interaction between BAG6 and HSPA2 was examined in response to 4HNE exposure via proximity ligation assays.

MAIN RESULTS AND THE ROLE OF CHANCE

HSPA2 protein levels were significantly reduced compared with controls after 4HNE treatment of round spermatids (P < 0.01) and GC-2 cells (P < 0.001) but not pachytene spermatocytes. Using GC-2 cells as a model, HSPA2 was shown to be both adducted by 4HNE and targeted for ubiquitination in response to cellular oxidative stress. Inhibition of the proteasome with MG132 prevented HSPA2 degradation after 4HNE treatment indicating that the degradation of HSPA2 is likely to occur via a proteasomal pathway. Moreover, our assessment of proteasome activity provided evidence that 4HNE treatment can significantly increase the proteasome activity of GC-2 cells (P < 0.05 versus control). Finally, 4HNE exposure to GC-2 cells resulted in the dissociation of HSPA2 from its regulatory co-chaperone BAG6, a key mediator of HSPA2 stability in male germ cells.

LIMITATIONS, REASONS FOR CAUTION

While these experiments were performed using a mouse germ cell-model system, our analyses of patient sperm lysate imply that these mechanisms are conserved between mouse and human germ cells.

WIDER IMPLICATIONS OF THE FINDINGS

This study suggests a causative link between non-enzymatic post-translational modifications and the relative levels of HSPA2 in the spermatozoa of a specific sub-class of infertile males. In doing so, this work enhances our understanding of failed sperm-egg recognition and may assist in the development of targeted antioxidant-based approaches for ameliorating the production of cytotoxic lipid aldehydes in the testis in an attempt to prevent this form of infertility.

LARGE SCALE DATA

Not applicable.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Health and Medical Research Council of Australia (APP1101953). The authors have no competing interests to declare.

Genes, Proteins, and Biological Pathways Preventing Chromothripsis

The highly complex structural genome variations chromothripsis, chromoanasynthesis, and chromoplexy are subsumed under the term chromoanagenesis, which means chromosome rebirth. Precipitated by numerous DNA double-strand breaks, they differ in number of and distances between breakpoints, associated copy number variations, order and orientation of segments, and flanking sequences at joining points. Results from patients with the autosomal dominant cancer susceptibility disorder Li-Fraumeni syndrome implicated somatic TP53 mutations in chromothripsis. TP53 participates in the G2/M phase checkpoint, halting cell cycling after premature chromosome compaction during the second half of the S phase, thus preventing chromosome shattering. By experimental TP53 ablation and micronucleus induction, one or a few isolated chromosomes underwent desynchronized replication and chromothripsis. Secondly, chromothripsis occurred after experimental induction of telomere crisis after which dicentric chromosomes sustained TREX1-mediated resolution of chromosome bridges and kataegis. Third, DNA polymerase Polθ-dependent chromothripsis has been documented. Finally, a family with chromothripsis after L1 element-dependent retrotransposition and Alu/Alu homologous recombination has been reported. Human chromosomal instability syndromes share defects in responses to DNA double-strand breaks, characteristic cell cycle perturbations, elevated rates of micronucleus formation, premature chromosome compaction, and apoptosis. They are also associated with elevated susceptibility to malignant disease, such as medulloblastomas and gliomas in ataxia-telangiectasia, leukemia and lymphoma in Bloom syndrome, and osteosarcoma and soft tissue sarcoma in Werner syndrome. The latter syndrome is characterized by a premature aging-like progressive decline of mesenchymal tissues. In all thus far studied cases, constitutional chromothripsis occurred in the male germline and male patients with defects in the double-strand break response genes ATM, MRE11, BLM, LIG4, WRN, and Ku70 show impaired fertility. Conceivably, chromothripsis may, in a stochastic rather than deterministic way, be implicated in germline structural variation, malignant disease, premature aging, genome mosaicism in somatic tissues, and male infertility.

Mechanisms of Origin, Phenotypic Effects and Diagnostic Implications of Complex Chromosome Rearrangements

Complex chromosome rearrangements (CCRs) are currently defined as structural genome variations that involve more than 2 chromosome breaks and result in exchanges of chromosomal segments. They are thought to be extremely rare, but their detection rate is rising because of improvements in molecular cytogenetic technology. Their population frequency is also underestimated, since many CCRs may not elicit a phenotypic effect. CCRs may be the result of fork stalling and template switching, microhomology-mediated break-induced repair, breakage-fusion-bridge cycles, or chromothripsis. Patients with chromosomal instability syndromes show elevated rates of CCRs due to impaired DNA double-strand break responses during meiosis. Therefore, the putative functions of the proteins encoded by ATM, BLM, WRN, ATR, MRE11, NBS1, and RAD51 in preventing CCRs are discussed. CCRs may exert a pathogenic effect by either (1) gene dosage-dependent mechanisms, e.g. haploinsufficiency, (2) mechanisms based on disruption of the genomic architecture, such that genes, parts of genes or regulatory elements are truncated, fused or relocated and thus their interactions disturbed - these mechanisms will predominantly affect gene expression - or (3) mixed mutation mechanisms in which a CCR on one chromosome is combined with a different type of mutation on the other chromosome. Such inferred mechanisms of pathogenicity need corroboration by mRNA sequencing. Also, future studies with in vitro models, such as inducible pluripotent stem cells from patients with CCRs, and transgenic model organisms should substantiate current inferences regarding putative pathogenic effects of CCRs. The ramifications of the growing body of information on CCRs for clinical and experimental genetics and future treatment modalities are briefly illustrated with 2 cases, one of which suggests KDM4C (JMJD2C) as a novel candidate gene for mental retardation.

Redox regulation of human sperm function: from the physiological control of sperm capacitation to the etiology of infertility and DNA damage in the germ line

Defective sperm function is the largest single defined cause of human infertility and one of the major reasons we are witnessing an exponential increase in the uptake of assisted conception therapy in the developed world. A major characteristic of defective human spermatozoa is the presence of large amounts of DNA damage, which is, in turn, associated with reduced fertility, increased rates of miscarriage, and an enhanced risk of disease in the offspring. This DNA damage is largely oxidative and is closely associated with defects in spermiogenesis. To explain the origins of this DNA damage, we postulate that spermiogenesis is disrupted by oxidative stress, leading to the creation of defective gametes with poorly remodeled chromatin that are particularly susceptible to free radical attack. To compound the problem, these defective cells have a tendency to undergo an unusual truncated form of apoptosis associated with high amounts of superoxide generation by the sperm mitochondria. This leads to significant oxidative DNA damage that eventually culminates in the DNA fragmentation we see in infertile patients. In light of the significance of oxidative stress in the etiology of defective sperm function, a variety of antioxidant therapies are now being assessed for their therapeutic potential.

Apoptosis in the germ line

Apoptosis is a critical process for regulating both the size and the quality of the male and female germ lines. In this review, we examine the importance of this process during embryonic development in establishing the pool of spermatogonial stem cells and primordial follicles that will ultimately define male and female fertility. We also consider the importance of apoptosis in controlling the number and quality of germ cells that eventually determine reproductive success. The biochemical details of the apoptotic process as it affects germ cells in the mature gonad still await resolution, as do the stimuli that persuade these cells to commit to a pathway that leads to cell death. Our ability to understand and ultimately control the reproductive potential of male and female mammals depends upon a deeper understanding of these fundamental processes.

Leukocytes and oxidative stress: dilemma for sperm function and male fertility

Spermatozoa are constantly exposed to the interphase between oxidation through high amounts of reactive oxygen species (ROS) and leukocytes, and reduction by means of scavengers and antioxidants. Considering the very special functions as being the only cells with such high polarization and exerting their functions outside the body, even in a different individual, the female genital tract, the membranes of these cells are chemically composed of an extraordinary high amount of polyunsaturated fatty acids. This in turn, renders them very susceptible to oxidative stress, which is defined as an imbalance between oxidation and reduction towards the oxidative status. As a result, ROS deriving from both leukocytes and the male germ cells themselves cause a process called 'lipid peroxidation' and other damages to the sperm cell. On the other hand, a certain limited amount of ROS is essential in order to trigger vital physiological reactions in cells, including capacitation or the acrosome reaction in sperm. The treatment of patients with antioxidants to compensate the oxidative status caused by oxidative stress is highly debated as uncontrolled antioxidative treatment might derail the system towards the reduced status, which is also unphysiological and can even induce cancer. This paradox is called the 'antioxidant paradox'. Therefore, a proper andrological diagnostic work-up, including the evaluation of ROS levels and the antioxidant capacity of the semen, has to be carried out beforehand, aimed at keeping the fine balance between oxidation and scavenging of vital amounts of ROS.

Multiple glutathione S-transferase isoforms are present on male germ cell plasma membrane

Phase II detoxification enzymes, the glutathione S-transferases (GSTs) of 24 kDa are known to be cytosolic enzymes. This study shows that multiple GST isoforms that are 24 kDa in size are present on the extracellular side of the plasma membrane of rat male germ cells. The GST activity of male germ cell plasma membranes is several folds higher than somatic cell plasma membrane GST activity. Isoform composition of the germ cell plasma membrane and the cytosolic pool differ, GSTM5 and GSTPi being absent on the plasma membranes. The molecular masses of the common isoforms are comparable between the two pools and both pools show GST and glutathione peroxidase activity.

Influence of age, hormones and germ cells on glutathione S-transferase activity in cultured Sertoli cells

Glutathione S-transferase (GSH-S-T) activity was measured, using 1-Cl-2,4-dinitrobenzene as substrate, in Sertoli cell cultures obtained from rats aged 10, 18, and 26 days. The GSH-S-T activity showed a significant increase with age of the Sertoli cell donor. When cultures were treated with hypotonic solution, in order to eliminate residual contaminating germ cells, the age dependent increase in enzyme activity was less pronounced. FSH, but not testosterone, increased enzyme activity in all cultures. Addition of freshly isolated germ cells (mainly pachytene spermatocytes) to hypotonic-treated Sertoli cell monolayers enhanced GSH-S-T activity at all ages. It is concluded that GSH-S-T activity can be measured in cultured Sertoli cells during the period of onset of spermatogenesis (10-26 days). This enzyme activity is dependent on age of the Sertoli cell donor and is influenced by FSH and germ cells. Since GSH-S-Ts are actively engaged in cell detoxificative functions through conjugation of xenobiotics with glutathione, the present findings suggest that this enzyme may have a relevant protective role during the critical period when spermatogenesis is being established.

Testosterone-induced changes in testicular antioxidant system

In order to investigate the role of testosterone propionate (TP) on the antioxidant system of the rat testis, lipid peroxidation (LPX) and activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) of the testis of testosterone-treated and control rats were compared. The results indicate that TP administration to intact adult rats resulted in a significant decline in protein content of various subcellular fractions. This is accompanied with significant elevation in LPX levels of various subcellular fractions suggesting induction of oxidative stress. Activities of three enzymes related to the metabolism of superoxide radical (SOD) and hydrogen peroxide (CAT and GPx) of testis, were found to be significantly decreased in response to TP treatment. The role of testosterone in regulating testicular spermatogenesis through oxidative stress is discussed.

Identification of a unique mu-class glutathione S-transferase in mouse spermatogenic cells

The fibrous sheath is a major cytoskeletal structure in the principal piece of the mammalian sperm flagellum. Two peptide sequences obtained from a tryptic digest of mouse fibrous sheath proteins exhibited high homology with mu-class glutathione S-transferases (GSTs). Using a DNA probe amplified from degenerate polymerase chain reaction (PCR) primers predicted from these two peptide sequences, a approximately 1.1 kb cDNA clone for fibrous sheath component 2 (Fsc2) was isolated which had 84% nucleic acid and 89% amino acid sequence identity with a previously reported mu-class human GST gene (hGSTM3; Campbell et al., 1990: J Biol Chem 265:4188-9193). Sequences corresponding to those of the two fibrous sheath peptides were present in the protein encoded by the Fsc2 cDNA. Northern analysis with the full length Fsc2 cDNA detected a approximately 1.1 kb mRNA in 12 of 15 somatic tissues examined, as well as in testis and isolated spermatogenic cells. However, 5'(nt--96 to 12) or 3'(nt 637 to 808) Fsc2 probes, containing mostly noncoding sequences, detected a approximately 1.1 kb mRNA abundant in testis and isolated spermatogenic cells, but absent or present at low levels in somatic tissues. Northern analysis with RNA from testes of mice of different postnatal ages and purified spermatogenic cell populations indicated that this transcript is first present during the meiotic phase of germ cell development. These results suggest that a previously unreported mu-class GST gene (mGSTM5.) is expressed at a specific time during the development of spermatogenic cells in the mouse. Immunoblot analysis indicated that a mu-class GST protein is associated with the fibrous sheath, suggesting that it becomes an integral part of the mouse sperm cytoskeleton.

Antioxidant system in rat testicular cells

The activity of the enzymes involved in the antioxidant defence--superoxide dismutase (SOD), glutathione peroxidase (GPx), reductase (GR), S-transferase (GST)--as well as the glutathione (GSH) levels were measured in different rat testicular cell populations. A differential distribution of these components among testicular cell types was clearly observed. Sertoli and peritubular cells had elevated SOD and GSH-dependent enzyme activities associated with a high GSH content. Compared with the somatic cells, pachytene spermatocytes (PS) and round spermatids (RS) presented a different antioxidant system characterized by higher SOD activity and GSH content associated with very low GSH-dependent enzyme activity. Spermatozoa exhibited the same enzymatic system as PS and RS but were devoid of GSH. Interstitial tissue displayed high GSH content, moderate SOD and GSH-related enzyme activity except for GPx which was very elevated. It is concluded that the different categories of testicular cells probably display a highly variable susceptibility to oxidative stress.

Glutathione therapy for male infertility

Eleven infertile men were treated with glutathione (600 mg/day IM) for 2 months. The patients were suffering from dyspermia associated with various andrological pathologies. Standard semen and computer analyses of sperm motility were carried out before treatment and after 30 and 60 days of therapy. Glutathione exerted significant effect on sperm motility patterns. Glutathione appears to have a therapeutic effect on some andrological pathologies causing male infertility.