Human sperm motility is downregulated by the AMPK activator A769662

Proteomic Landscape of Human Sperm in Patients with Different Spermatogenic Impairments

Although the proteome of sperm has been characterized, there is still a lack of high-throughput studies on dysregulated proteins in sperm from subfertile men, with only a few studies on the sperm proteome in asthenozoospermic and oligoasthenozoospermic men. Using liquid chromatography–mass spectrometry (LC-MS/MS) along with bioinformatics analyses, we investigated the proteomic landscape of sperm collected from subfertile men (n = 22), i.e., asthenozoospermic men (n = 13), oligoasthenozoospermic men (n = 9) and normozoospermic controls (n = 31). We identified 4412 proteins in human sperm. Out of these, 1336 differentially abundant proteins were identified in 70% of the samples. In subfertile men, 32 proteins showed a lower abundance level and 34 showed a higher abundance level when compared with normozoospermic men. Compared to normozoospermic controls, 95 and 8 proteins showed a lower abundance level, and 86 and 1 proteins showed a higher abundance level in asthenozoospermic and oligoasthenozoospermic men, respectively. Sperm motility and count were negatively correlated with 13 and 35 and positively correlated with 37 and 20 differentially abundant proteins in asthenozoospermic and oligoasthenozoospermic men, respectively. The combination of the proteins APCS, APOE, and FLOT1 discriminates subfertile males from normozoospermic controls with an AUC value of 0.95. Combined APOE and FN1 proteins discriminate asthenozoospermic men form controls with an AUC of 1, and combined RUVBL1 and TFKC oligoasthenozoospermic men with an AUC of 0.93. Using a proteomic approach, we revealed the proteomic landscape of sperm collected from asthenozoospermic or oligoasthenozoospermic men. Identified abundance changes of several specific proteins are likely to impact sperm function leading to subfertility. The data also provide evidence for the usefulness of specific proteins or protein combinations to support future diagnosis of male subfertility.

Obesity-induced oxidative stress and mitochondrial dysfunction negatively affect sperm quality

Obesity is a systemic metabolic disease that can induce male infertility or subfertility through oxidative stress. The aim of this study was to determine how obesity impairs sperm mitochondrial structural integrity and function, and reduces sperm quality in both overweight/obese men and mice on a high-fat diet (HFD). Mice fed the HFD demonstrated higher body weight and increased abdominal fat content than those fed the control diet. Such effects accompanied the decline in antioxidant enzymes, such as glutathione peroxidase (GPX) and catalase and superoxide dismutase (SOD) in testicular and epidydimal tissues. Moreover, malondialdehyde (MDA) content significantly increased in sera. Mature sperm in HFD mice demonstrated higher oxidative stress, including increased mitochondrial reactive oxygen species (ROS) levels and decreased protein expression of GPX1, which may impair mitochondrial structural integrity and reduce mitochondrial membrane potential (MMP) and ATP production. Moreover, cyclic AMPK phosphorylation status increased, whereas sperm motility declined in the HFD mice. Clinical studies demonstrated that being overweight/obese reduced SOD enzyme activity in the seminal plasma and increased ROS in sperm, accompanied by lower MMP and low-quality sperm. Furthermore, ATP content in the sperm was negatively correlated with increases in the BMI of all clinical subjects. In conclusion, our results suggest that excessive fat intake had similar disruptive effects on sperm mitochondrial structure and function, as well as oxidative stress levels in humans and mice, which in turn induced lower sperm motility. This agreement strengthens the notion that fat-induced increases in ROS and impaired mitochondrial function contribute to male subfertility.

Hydroxytyrosol and resveratrol improves kinetic and flow cytometric parameters of cryopreserved bull semen with low cryotolerance

There is considerable interest in breeding programs to "rescue" semen with poor post-thaw fertility from bulls known as "bad freezers". We hypothesized that there may be an interaction between the post-thaw recovery of sperm and the efficacy of antioxidant addition to extenders. The current study assesses the effects of antioxidant additives hydroxytyrosol (HT) and resveratrol (RSV) on the post-thaw semen parameters in two groups of bulls classified as either high or low cryotolerant (i.e., "good" and "bad" freezers). Semen samples were collected from 40 bulls and processed in the extenders containing different concentrations of HT (experiment 1; 0, 25 and 50 µM) and RSV (experiment 2; 0.0, 0.01, 0.1 and 1 mM). In experiment 1, bulls in the low cryotolerance group had a significant improvement in post-thaw recovery at 25 µM and 50 µM (P < 0.05). These improvements were observed in motility and several cellular parameters. However, post-thaw semen quality in the high cryotolerance group was not significantly affected by the HT addition. In experiment 2, although RSV did not have any positive impact in high cryotolerance group, post-thaw recovery in the low cryotolerance bulls was significantly improved in 0.1 mM RSV. Oxidative stress markers in either high or low cryotolerance groups were not significantly changed by RSV addition (P > 0.05). It can be concluded that addition of optimized concentrations of HT and RSV to the extender could be a strategy for improving the post-thaw semen, especially in bulls with high genetic merit but low initial cryotolerance.

The Activated AMPK/mTORC2 Signaling Pathway Associated with Oxidative Stress in Seminal Plasma Contributes to Idiopathic Asthenozoospermia

Asthenozoospermia is a common form of abnormal sperm quality in idiopathic male infertility. While most sperm-mediated causes have been investigated in detail, the significance of seminal plasma has been neglected. Herein, we aimed to investigate the possible pathogenic factors leading to decreased sperm motility based on seminal plasma. Semen was collected from normo- (NOR, n = 70), idiopathic oligo- (OLI, n = 57), and idiopathic asthenozoospermic (AST, n = 53) patients. Using attenuated total reflection-Fourier transform infrared coupled with chemometrics, distinct differences in the biochemical compositions of nucleic acids, protein structure (amides I, II, and III), lipids, and carbohydrates in seminal plasma of AST were observed when compared to NOR and OLI. Compared with NOR and OLI, the levels of peptide aggregation, protein phosphorylation, unsaturated fatty acid, and lipid to protein ratio were significantly increased in AST; however, the level of lipid saturation was significantly decreased in seminal plasma of AST. Compared with NOR, the levels of ROS, MDA, 8-iso-prostaglandin F2α (8-isoPGF2α), and the ratio of phospho-AMPKα/AMPKα1 were significantly increased in AST; however, the levels of SOD, glutathione S-transferase (GSTs), protein carbonyl derivative (PC), and the ratio of phospho-Rictor/Rictor were significantly decreased in seminal plasma of AST. Changes of the AMPK/mTORC2 signaling in the seminal microenvironment possibly induce abnormal glucose and lipid metabolism, which impairs energy production. Oxidative stress potentially damages seminal plasma lipids and proteins, which in turn leads to impaired sperm structure and function. These findings provide evidence that the changes in seminal plasma compositions, oxidative stress, and activation of the AMPK/mTORC2 signaling contribute to the development of asthenozoospermia.

A comparative study between curcumin and curcumin nanoemulsion on high-fat, high-fructose diet-induced impaired spermatogenesis in rats

Objectives

Curcumin is a promising nutraceutical with reported diverse therapeutic properties, but of limited oral bioavailability. The current manuscript investigates the role of encapsulation of curcumin in nanoemulsion form in counteracting the adverse effect of chronic ingestion of a high-fat high-fructose diet (HFHF) by juvenile male rats regarding testicular abnormalities and declined spermatogenesis.

Methods

Curcumin nanoemulsion was administered orally to Wistar rats at a dose of 5 or 10 mg/kg and compared with curcumin powder, followed by a pharmacological and histological assessment.

Key findings

Results demonstrated that curcumin nanoemulsion was superior to curcumin powder, particularly in enhancing the percentage progressive motility of spermatozoa, normalization of essential and non-essential amino acids in semen, normalization of serum leptin and testosterone levels, as well as normalization of oxidative and nitrosative parameters. It was also proven to reduce testicular DNA fragmentation, while elevating testicular cellular energy. In addition, curcumin nanoemulsion administered at a dose of 10 mg/kg induced the highest level of spermatogenesis, delineated by histological examination of the seminiferous tubules.

Conclusions

It can be concluded that curcumin nanoemulsion administered at a dose of 10 mg/kg successfully ameliorates the adverse effects of a HFHF on spermatogenesis.

Improving the post-thaw quality of rooster semen using the extender supplemented with resveratrol

Avian spermatozoa are highly susceptible to reactive oxygen species (ROS) produced during the cryopreservation. The aim of the current study was to investigate the antioxidant effects of resveratrol (RSV) during rooster semen cryopreservation. Changes in expression of AMP-activated protein kinase as a possible mechanism behind the beneficial effects of resveratrol were also evaluated. Semen samples were collected from ten Ross broiler breeders (52-wk) using abdominal massage, then divided into 4 equal aliquots and cryopreserved in Beltsville extender that contained different concentrations (0 µM, 0.01µM, 0.1µM, and 1µM) of RSV. higher percentage (P < 0.05) of total motility and membrane integrity was observed in RSV-0.1 compared to the other frozen groups. Moreover, higher percentage of sperm mitochondrial activity was observed in the RSV-0.01 and RSV-0.1 compared to the frozen control (P < 0.05). The lowest percentage of apoptotic like changes was found in the RSV-0.1 in comparison to the other groups (P < 0.05). RSV-0.01 and RSV-1 groups produced the lowest levels of H2O2 and O2- compared to the other frozen groups, respectively. Malondialdehyde (MDA) concentration, velocity average path (VAP), and linearity (LIN) were not affected by different concentrations of RSV (P > 0.05). We observed a dose-dependent increase in AMP-activated protein kinase expression in groups exposed to RSV. Thus, RSV-1 increased AMP-activated protein kinase phosphorylation but had no positive effects on post thaw sperm parameters. Our findings suggest that RSV-0.1 improve thawed sperm functions, and these effects might be mediated through activation of AMP-activated protein kinase.

In vitro exposure to metformin activates human spermatozoa at therapeutically relevant concentrations

BACKGROUND

Metformin, a drug used to treat type 2 diabetes, has gained attention for its multiple therapeutic applications. However, little is known about its effects on human sperm function at therapeutically relevant concentration.

OBJECTIVES

The aim of this study was to elucidate the in vitro actions of metformin on human sperm function and explore the underlying mechanism of any effects.

MATERIALS AND METHODS

Human ejaculated spermatozoa were treated with therapeutically relevant concentrations (0.25, 5, 10, 20, 40, and 80 µM) of metformin in vitro. Fertilization-essential functions of spermatozoa were examined, including viability, motility, capacitation, acrosome reaction, hyperactivation, and penetration ability. The signaling pathways mediated by 5'-AMP-activated protein kinase (AMPK), intracellular calcium concentration ([Ca²⁺ ]_i ), and tyrosine phosphorylation of spermatozoa were also measured.

RESULTS

Although metformin did not affect sperm viability, motility, and [Ca²⁺ ]_i , it significantly increased the percentages of capacitated spermatozoa, acrosomal-reacted spermatozoa, and hyperactivated spermatozoa as well as penetration ability of human spermatozoa at the concentrations of 40 and 80 µM (P < .05). These concentrations of metformin also elevated the levels of phosphorylated AMPK and tyrosine phosphorylation in human spermatozoa. In addition, activation of AMPK by A769662 (an AMPK activator) had similar effects to metformin on human spermatozoa, while inhibition of AMPK by Compound C (an AMPK inhibitor) suppressed the enhancement of metformin on human spermatozoa.

CONCLUSION

Our findings indicate that metformin activates human sperm function through an AMPK-related mechanism which increases tyrosine phosphorylation at therapeutically relevant concentrations, thereby suggesting its improvement on human sperm function when treating subfertile males of type 2 diabetes.

Metformin inhibits human spermatozoa motility and signalling pathways mediated by protein kinase A and tyrosine phosphorylation without affecting mitochondrial function

Metformin is a leading antidiabetic drug that is used worldwide in the treatment of diabetes mellitus. This biguanide exerts metabolic and pleiotropic effects in somatic cells, although its invitro actions on human spermatozoa remain unknown. The present study investigated the effects of metformin on human sperm function. Human spermatozoa were incubated in the presence or absence of 10mM metformin for 8 or 20h, and motility was measured by computer-aided sperm analysis (CASA); other parameters were evaluated by flow cytometry. Metformin significantly reduced the percentage of motile, progressive and rapid spermatozoa and significantly decreased sperm velocity. Metformin did not affect viability, mitochondrial membrane potential (MMP) or mitochondrial superoxide anion generation of human spermatozoa at any time studied. However, metformin clearly inhibited the protein kinase (PK) A pathway and protein tyrosine phosphorylation at 8 and 20h, key regulatory pathways for correct sperm function. In summary, metformin treatment of human spermatozoa had a detrimental effect on motility and inhibited essential sperm signalling pathways, namely PKA and protein tyrosine phosphorylation, without affecting physiological parameters (viability, MMP, mitochondrial superoxide anion generation). Given the growing clinical use of metformin in different pathologies in addition to diabetes, this study highlights an adverse effect of metformin on spermatozoa and its relevance in terms of human fertility in patients who potentially could be treated with metformin in the future.

New insights in the AMPK regulation in chicken spermatozoa: Role of direct AMPK activator and relationship between AMPK and PKA pathways

Energy balance is an important feature for spermatozoa functions. The 5'-AMP-activated protein kinase (AMPK), a sensor of cell energy, has been implicated as a mediator between spermatozoa functions and energy balance. We recently identified and localized the AMPK protein in chicken spermatozoa and showed that its activation with non-specific activators significantly modified spermatozoa quality. The aim of the present study was to determine more directly the role of AMPK activation induced by the specific activator A-769662 and the interaction between AMPK and another pathway, the protein kinase A (PKA) signaling pathway in bird spermatozoa. The results showed that A-769662 induced at the low dose 50 μM an increase in spermatozoa motility, viability, and acrosome reaction through AMPK activation. Furthermore, phospho-Thr172-AMPK levels were greatly decreased by the PKA inhibitor H89 that also decreased spermatozoa quality. The inhibitory action of H89 was also efficient on A-769662 AMPK phosphorylation. We conclude that AMPK activity in bird spermatozoa is stimulated by low dose of A-769662 with consequent increase in spermatozoa quality, and that AMPK is upstream regulated by PKA pathway in this model.

The in vitro effects of gibberellin on human sperm motility

Gibberellin, a plant growth regulator, is widely used to increase the shelf life and quality of fruits and vegetables. In this study, human semen samples were exposed to different concentrations of gibberellin, which reduced spermatozoa motility in vitro. Gibberellin exposure also increased levels of reactive oxygen species and the protein levels of apoptosis markers in human sperm. Gibberellin inhibited the activity of Na+/K+-adenosine triphosphatase (ATPase) and Ca2+-ATPase, which maintain the stability of ions inside and outside the membranes of spermatozoa. Moreover, gibberellin exposure suppressed adenosine triphosphate production and reduced the protein levels of adenosine triphosphate synthases, which may have induced the protein expression of adenosine 5'-monophosphate-activated protein kinase (AMPK) and its phosphorylated form. These results suggest that gibberellin reduces human sperm motility in vitro by increasing reactive oxygen species levels and reducing ATPase activity, which may upregulate AMPK and consequently reduce the fertilization potential of spermatozoa.

AMPK Function in Mammalian Spermatozoa

AMP-activated protein kinase AMPK regulates cellular energy by controlling metabolism through the inhibition of anabolic pathways and the simultaneous stimulation of catabolic pathways. Given its central regulator role in cell metabolism, AMPK activity and its regulation have been the focus of relevant investigations, although only a few studies have focused on the AMPK function in the control of spermatozoa's ability to fertilize. This review summarizes the known cellular roles of AMPK that have been identified in mammalian spermatozoa. The involvement of AMPK activity is described in terms of the main physiological functions of mature spermatozoa, particularly in the regulation of suitable sperm motility adapted to the fluctuating extracellular medium, maintenance of the integrity of sperm membranes, and the mitochondrial membrane potential. In addition, the intracellular signaling pathways leading to AMPK activation in mammalian spermatozoa are reviewed. We also discuss the role of AMPK in assisted reproduction techniques, particularly during semen cryopreservation and preservation (at 17 °C). Finally, we reinforce the idea of AMPK as a key signaling kinase in spermatozoa that acts as an essential linker/bridge between metabolism energy and sperm's ability to fertilize.