Asthenozoospermia and membrane remodeling enzymes: a new role for phospholipase A2

Lipophilic phthalic acid esters impair human sperm acrosomal reaction through the likely inhibition of phospholipase A2-signaling pathway

Phthalic acid esters (PAEs) are recognized endocrine disruptors. Detection of PAEs in semen from idiopathic infertile males suggests possible direct mechanisms of sperm toxicity. In this study we aimed to correlate sperm function with semen levels of PAEs. Semen samples were obtained from 100 male patients attending the Unit of Andrology and Reproductive Medicine, University Hospital of Padova, (Italy), 22 of which having a recognized history of idiopathic infertility. Compared to fertile subjects, infertile patients showed reduced levels of acrosome reaction (AR), evaluated by CD46 staining upon progesterone (P4) triggering (p < 0.001). Subjects showing positive detection of PAEs in semen, evaluated by liquid chromatography-mass spectrometry (LC-MS), were significantly more represented in those reporting an history of infertility (13 out of 22), compared to fertile subjects (25 out of 78, P = 0.0266). In vitro sperm exposure to PAEs showed that lipophilic PAE representative Di-n-octyl phthalate (DNOP) had higher cell accumulation and inhibition of P4-induced AR than less lipophilic PAE representative Dibutyl phthalate (DBP). Computer-based binding analysis and fluorimetric inhibition assay, showed that both DNOP and DBP had similar Phospholipase-A2 (PLA₂) inhibitory activity (respectively: 3.98 nM and 5.52 nM). However, only DNOP showed a significant inhibition of PLA₂-mediated AR, triggered by A23187 calcium ionophore. Incubation with PLA₂-related product arachidonic acid restored AR. Our data are suggestive of a novel mechanistic model of PAEs interference on sperm function, through the inhibition of PLA₂-mediated signaling. According to this hypothesis, the inhibitory efficacy of the specific PAE is possibly linked to the corresponding cell accumulation.

What do secreted phospholipases A2 have to offer in combat against different viruses up to SARS-CoV-2?

Secreted phospholipases A2 (sPLA2s) form a widespread group of structurally-related enzymes that catalyse the hydrolysis of the sn-2 ester bond of glycerophospholipids to produce free fatty acids and lysophospholipids. In humans, nine catalytically active and two inactive sPLA2 proteins have been identified. These enzymes play diverse biological roles, including host defence against bacteria, parasites and viruses. Several of these endogenous sPLA2s may play a defensive role in viral infections, as they display in vitro antiviral activity by both direct and indirect mechanisms. However, endogenous sPLA2s may also exert an offensive and negative role, dampening the antiviral response or promoting inflammation in animal models of viral infection. Similarly, several exogenous sPLA2s, most of them from snake venoms and other animal venoms, possess in vitro antiviral activities. Thus, both endogenous and exogenous sPLA2s may be exploited for the development of new antiviral substances or as therapeutic targets for antagonistic drugs that may promote a more robust antiviral response. In this review, the antiviral versus proviral role of both endogenous and exogenous sPLA2s against various viruses including coronaviruses is presented. Based on the highlighted developments in this area of research, possible directions of future investigation are envisaged. One of them is also a possibility of exploiting sPLA2s as biological markers of the severity of the Covid-19 pandemic caused by SARS-CoV-2 infection.

Dysregulation of the Acrosome Formation Network by 8-oxoguanine (8-oxoG) in Infertile Sperm: A Case Report with Advanced Techniques

8-Hydroxyguanine (8-oxoG) is the most common oxidative DNA lesion and unrepaired 8-oxoG is associated with DNA fragmentation in sperm. However, the molecular effects of 8-oxoG on spermatogenesis are not entirely understood. Here, we identified one infertile bull (C14) due to asthenoteratozoospermia. We compared the global concentration of 8-oxoG by reverse-phase liquid chromatography/mass spectrometry (RP-LC/MS), the genomic distribution of 8-oxoG by next-generation sequencing (OG-seq), and the expression of sperm proteins by 2-dimensional polyacrylamide gel electrophoresis followed by peptide mass fingerprinting (2D-PAGE/PMF) in the sperm of C14 with those of a fertile bull (C13). We found that the average levels of 8-oxoG in C13 and C14 sperm were 0.027% and 0.044% of the total dG and it was significantly greater in infertile sperm DNA (p = 0.0028). Over 81% of the 8-oxoG loci were distributed around the transcription start site (TSS) and 165 genes harboring 8-oxoG were exclusive to infertile sperm. Functional enrichment and network analysis revealed that the Golgi apparatus was significantly enriched with the products from 8-oxoG genes of infertile sperm (q = 2.2 × 10-7). Proteomic analysis verified that acrosome-related proteins, including acrosin-binding protein (ACRBP), were downregulated in infertile sperm. These preliminary results suggest that 8-oxoG formation during spermatogenesis dysregulated the acrosome-related gene network, causing structural and functional defects of sperm and leading to infertility.

Role of isoprostanes in human male infertility

One of the major causes of defective sperm function is oxidative stress, which limits the fertilizing potential of these cells as the result of collateral damage to proteins and lipids in the sperm plasma membrane. On this point, a derangement of both generation and neutralization of reactive oxygen species (ROS) is a recognized cause of male infertility. Antioxidant protection in sperm has been widely investigated, as well as the sperm composition of fatty acids (FA), which represents the preferred substrate for ROS, most frequently linked to the disease-related infertility. Isoprostanes are compounds derived from free radical-mediated oxidation of FAs. As such, they are considered an index of lipid oxidative damage and lipid mediators. This article discusses the role of isoprostanes as relevant factors both to sperm FA composition and sperm membrane integrity. Additionally, isoprostane's influence on sperm quality is reviewed. With reference to male reproductive dysfunction, increasing evidence indicates isoprostanes, detectable in biological fluids or sperm membrane, as the specific index of 1) exposure to chemical etiological agents, 2) oxidative damage, 3) reduced antioxidant response, and 4) sperm immaturity.

ABBREVIATIONS

OS: oxidative stress; ROS: reactive oxygen species; PUFAs: polyunsaturated fatty acids; ARA: arachidonic acid, F₂-IsoPs; F₂-isoprostanes, PLA₂: phospholipase A₂; NADPH: nicotinamide adenine dinucleotide phosphate; IVF: in vitro fertilization.

Transcriptome profiling of porcine testis tissue reveals genes related to sperm hyperactive motility

BACKGROUND

Sperm hyperactive motility has previously been shown to influence litter size in pigs, but little is known about the underlying biological mechanisms. The aim of this study was to use RNA sequencing to investigate gene expression differences in testis tissue from Landrace and Duroc boars with high and low levels of sperm hyperactive motility. Boars with divergent phenotypes were selected based on their sperm hyperactivity values at the day of ejaculation (day 0) (contrasts (i) and (ii) for Landrace and Duroc, respectively) and on their change in hyperactivity between day 0 and after 96 h liquid storage at 18 °C (contrast (iii)).

RESULTS

RNA sequencing was used to measure gene expression in testis. In Landrace boars, 3219 genes were differentially expressed for contrast (i), whereas 102 genes were differentially expressed for contrast (iii). Forty-one differentially expressed genes were identified in both contrasts, suggesting a functional role of these genes in hyperactivity regardless of storage. Zinc finger DNLZ was the most up-regulated gene in contrasts (i) and (iii), whereas the most significant differentially expressed gene for the two contrasts were ADP ribosylation factor ARFGAP1 and solute carrier SLC40A1, respectively. For Duroc (contrast (ii)), the clustering of boars based on their gene expression data did not reflect their difference in sperm hyperactivity phenotypes. No results were therefore obtained for this breed. A case-control analysis of variants identified in the Landrace RNA sequencing data showed that SNPs in NEU3, CHRDL2 and HMCN1 might be important for sperm hyperactivity.

CONCLUSIONS

Differentially expressed genes were identified in Landrace boars with high and low levels of sperm hyperactivity at the day of ejaculate collection and high and low change in hyperactivity after 96 h of sperm storage. The results point towards important candidate genes, biochemical pathways and sequence variants underlying sperm hyperactivity in pigs.

Cytosolic phospholipase A2 and F2 isoprostanes are involved in semen quality and human infertility-A study on leucocytospermia, varicocele and idiopathic infertility

Phospholipase A₂ (PLA₂ ) is involved in eicosanoid release, and F₂ -isoprostanes (F₂ -IsoPs), as free radical-generated eicosanoids released by PLA₂ , are indicators of oxidative stress in different human conditions. This study investigated the interplay between cytosolic PLA₂ (cPLA₂ ), F₂ -IsoPs and sperm features in male infertility, when the involvement of oxidative stress has been reported. Semen evaluation was performed following WHO guidelines, sperm ultrastructure was detected by transmission electron microscopy indicating a fertility index, and the percentages of sperm immaturity, apoptosis and necrosis. In sperm cells and seminal plasma, cPLA₂ levels were determined by immunological method, whereas F₂ -IsoPs by mass spectrometry. Sperm concentration, morphology, vitality and fertility index values were significantly lower in infertile groups compared with fertile men. An increase in sperm apoptosis and necrosis (p < .01), apoptosis (p < .01) and immaturity (p < .001) was detected in leucocytospermia, idiopathic infertility and varicocele, respectively. Seminal cPLA₂ showed the highest value in varicocele group (p < .05), whereas seminal F₂ -IsoPs increased in varicocele (p < .001) and leucocytospermia (p < .05) groups. In the whole population, F₂ -IsoP and cPLA₂ levels were positively correlated (p < .05). On the contrary, F₂ -IsoPs and cPLA₂ were not significantly different when investigated in sperm cells. Our data indicate that fatty acid oxidation/metabolism plays a role in different male reproductive pathological conditions.

Intracellular localisation of platelet-activating factor during mammalian embryo development in vitro: a comparison of cattle, mouse and human

Platelet-activating factor (PAF) is a well-known marker for embryo quality and viability. For the first time, we describe an intracellular localisation of PAF in oocytes and embryos of cattle, mice and humans. We showed that PAF is represented in the nucleus, a signal that was lost upon nuclear envelope breakdown. This process was confirmed by treating the embryos with nocodazole, a spindle-disrupting agent that, as such, arrests the embryo in mitosis, and by microinjecting a PAF-specific antibody in bovine MII oocytes. The latter resulted in the absence of nuclear PAF in the pronuclei of the zygote and reduced further developmental potential. Previous research indicates that PAF is released and taken up from the culture medium by preimplantation embryos invitro, in which bovine serum albumin (BSA) serves as a crucial carrier molecule. In the present study we demonstrated that nuclear PAF does not originate from an extracellular source because embryos cultured in polyvinylpyrrolidone or BSA showed similar levels of PAF in their nuclei. Instead, our experiments indicate that cytosolic phospholipase A2 (cPLA2) is likely to be involved in the intracellular production of PAF, because treatment with arachidonyl trifluoromethyl ketone (AACOCF3), a specific cPLA2 inhibitor, clearly lowered PAF levels in the nuclei of bovine embryos.

Progesterone-induced Acrosome Exocytosis Requires Sequential Involvement of Calcium-independent Phospholipase A2β (iPLA2β) and Group X Secreted Phospholipase A2 (sPLA2)

Phospholipase A2 (PLA2) activity has been shown to be involved in the sperm acrosome reaction (AR), but the molecular identity of PLA2 isoforms has remained elusive. Here, we have tested the role of two intracellular (iPLA2β and cytosolic PLA2α) and one secreted (group X) PLA2s in spontaneous and progesterone (P4)-induced AR by using a set of specific inhibitors and knock-out mice. iPLA2β is critical for spontaneous AR, whereas both iPLA2β and group X secreted PLA2 are involved in P4-induced AR. Cytosolic PLA2α is dispensable in both types of AR. P4-induced AR spreads over 30 min in the mouse, and kinetic analyses suggest the presence of different sperm subpopulations, using distinct PLA2 pathways to achieve AR. At low P4 concentration (2 μm), sperm undergoing early AR (0-5 min post-P4) rely on iPLA2β, whereas sperm undergoing late AR (20-30 min post-P4) rely on group X secreted PLA2. Moreover, the role of PLA2s in AR depends on P4 concentration, with the PLA2s being key actors at low physiological P4 concentrations (≤2 μm) but not at higher P4 concentrations (~10 μm).