From spermatogenesis to fertilisation: the role of melatonin on ram spermatozoa

This review presents recent findings on the effect of melatonin on ram spermatozoa. This hormone regulates seasonal reproduction in the ovine species through the hypothalamic-pituitary-gonadal axis, but it also exerts direct effects on spermatogenesis, seminal quality and fertility. In the testis, melatonin stimulates blood flow to this organ, but it also appears to be involved in the differentiation of spermatogonial stem cells and the secretion of testosterone through the MT1 and MT2 receptors. In the epididymis, this hormone modulates sperm maturation and the secretory activity of epidydimal epithelial cells. In addition, the antioxidant activity of melatonin may protect spermatozoa from oxidative damage during their formation in the testis and their maturation in the epididymis. After ejaculation, the melatonin present in seminal plasma may also protect sperm from oxidative damage and premature capacitation and may improve seminal quality. Finally, once the sperm begins its transit through the female genital tract, melatonin may modulate sperm capacitation. Thus, melatonin could have a bimodal activity in ram sperm capacitation, so high concentrations, such as those in seminal plasma, have a decapacitating effect. In contrast, low concentrations, such as those present in the female reproductive tract, may promote it, likely through interaction with MT2 receptors. In addition, melatonin could also be involved in chemotaxis and fertilisation, although further studies are needed to elucidate the specific role of melatonin in these processes. Finally, the effect of latitude and melatonin receptor gene polymorphisms in ram reproduction is also discussed.

New Insights of Target Therapy: Effects of Tyrosine Kinase Inhibitors on Male Gonadal Function: A Systematic Review

The number of cancer patients undergoing chronic treatment with target therapy is increasing. Although much is known about the toxicity of conventional anticancer therapies, evidence on the effects of tyrosine kinase inhibitors (TKIs) on fertility is still lacking. Therefore, this review was undertaken to evaluate the effects of TKIs on male gonadal function. A comprehensive search of PubMed and Scopus databases was conducted, focusing on the effects of TKIs on spermatogenesis and testicular endocrine function. We included animal studies, observational studies, and case reports published up to December 31, 2023. Identified articles were reviewed and analyzed to evaluate the impact of TKIs on the male gonad. Their long-term effects, the reversibility of the observed changes, and the underlying molecular mechanisms involved were recorded. The findings emerging on the effects of TKIs on male gonadal function are conflicting. Although specific TKIs (imatinib, gefitinib, sorafenib, sunitinib, quizartinib, dasatinib, and nilotinib) have been identified as potentially as potential interfering with spermatogenesis and hormone production, the extent and severity of these effects may vary from patient to patient and between different drugs within this drug class. Experimental studies on mouse models have suggested a potential interference with spermatogenesis. Evidence also suggests that TKIs affects the hypothalamic-pituitary-testicular axis, decreasing serum testosterone and gonadotropin levels. The effects of TKIs on male gonadal function highlight the need for personalized treatment choices. Potential fertility concerns can help minimize adverse effects and improve patient outcomes. Addressing the potential impact of TKIs on male fertility helps optimize cancer treatment and survival outcomes.

Effect of melatonin and nitric oxide on capacitation and apoptotic changes induced by epidermal growth factor in ram sperm

CONTEXT

Apart from the canonical cAMP-PKA pathway, ram sperm capacitation can be achieved by the MAPK ERK1/2 signalling cascade, activated by epidermal growth factor (EGF).

AIMS

This study aims to investigate the effect of melatonin and nitric oxide (NO·) on capacitation and apoptotic-like changes in EGF-capacitated ram spermatozoa.

METHODS

In vitro capacitation was induced by EGF in the absence or presence of melatonin (100pM or 1μM). Also, a NO· precursor, L-arginine, or a NOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), were added to capacitation media to study the interaction of NO· and melatonin during EGF-capacitation. Sperm functionality parameters (motility, viability, capacitation state), apoptotic markers (caspase activation and DNA damage), NO· levels, and phosphorylated c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (assessed by Western blot), were evaluated in swim-up and capacitated samples with EGF.

KEY RESULTS

NO· levels and the apoptotic-related markers were raised after EGF incubation. Melatonin had a bimodal role on sperm EGF-capacitation, preventing it at high concentration and promoting acrosome reaction at low concentration, but neither of the two concentrations prevented the increase in apoptotic-like markers or NO· levels. However, melatonin at 1μM prevented the activation of JNK.

CONCLUSIONS

NO· metabolism does not seem to modulate the apoptosis-like events in ram spermatozoa. Melatonin at 1μM prevents ram sperm capacitation induced by EGF independently from nitric oxide metabolism, and it could be exerted by limiting the JNK mitogen-activated protein kinase (MAPK) activation.

IMPLICATIONS

This study improvesour understanding of the biochemical mechanisms involved in sperm capacitation, and ultimately, fertility.

cDNA cloning, expression and bioinformatical analysis of Tssk genes in tree shrews

Tree shrews are more closely related to primate animals than rodents in many aspects. In addition, they also possess several advantageous characteristics including small body size, high brain-to-body mass ratio, low cost of feeding and maintenance, short reproductive cycle and life span, which make them promising novel laboratory animals to replace more precious larger primate animals. Testis-specific serine/threonine kinase (Tssk) plays important roles in spermatogenesis and/or the regulation of sperm function. However, studies on Tssk in tree shrews have not been reported yet. In the present study, the full-length sequences of five members of the Tssk family in tree shrews were cloned and their CDS region sequences were analyzed by basic bioinformatics. The phylogenetic tree and prokaryotic protein expression system of Tssk gene of tree shrews were constructed. The mRNA expressions of Tssk genes in 11 tissues/organs from tree shrews were studied. The results showed that: 1. the length of the CDS region of tree shrew Tssk gene for Tssk1B, Tssk2, Tssk3 (variant X1 / X2), Tssk4 (variant X1 / X2) and Tssk6 is 1080bp, 1077bp, 867 / 807bp, 1014 / 984bp, 822bp, respectively, encoding 359, 358, 288/268, 337/327 and 273 amino acids, respectively; the cloned sequences of Tssk genes have been submitted to GenBank with the following accession numbers: KX091161(Tssk1B), KX091162(Tssk2), KX091163(Tssk3 variant X1)/KX091164(Tssk3 variant X2), KX091165(Tssk4variant X1)/KX091166(Tssk4variant X2), KX091160(Tssk6). 2. All tree shrew Tssk proteins distribute in cytoplasm, indicating that they are hydrophilic and non-secretory proteins, with multiple phosphorylation sites of serine and/or threonine. In addition, they are all mixed proteins with similar tertiary structures sharing a highly conserved functional domain of S_TKc (Serine/Threonine protein kinases, catalytic domain). 3.The molecular phylogenetic tree of five Tssk genes in tree shrews indicates that they are neither rodent nor primate animal, but are closely related to primate animals. 4. Five members of the Tssk recombinant proteins in tree shrews were successfully obtained using the constructed prokaryotic protein expression system. 5. Five Tssk genes are specifically expressed in the testis and/or sperm of tree shrews. Additionally, small amount of Tssk1B was expressed in several tissues other than testis and sperm. Limited mRNA levels of Tssk2 and Tssk4 were expressed in the brain, while mRNA of Tssk3 or Tssk6 could only be detected in the testis and sperm. This study will provide fundamental data on reproductive biology of tree shrews, which paves a way for further studying Tssk's biological function in this novel model animal.

FAK regulates actin polymerization during sperm capacitation via the ERK2/GEF-H1/RhoA signaling pathway

Actin polymerization is a crucial process during sperm capacitation. We have recently described the participation of FAK during actin polymerization in guinea pig spermatozoa. However, the mechanism by which FAK mediates these processes is unknown. Our previous data have shown that MAPK1 (hereafter referred to as ERK2) is activated during the first minutes of capacitation, and inhibition of ERK2 blocked actin polymerization and the acrosome reaction. In this current study, we found that FAK is involved in ERK2 activation - as FAK was phosphorylated at tyrosine residue 925 and bound to Grb2 - and that inhibition of FAK results in a significant decrease of ERK2 activation. We also confirmed the presence of Rho guanine nucleotide exchange factor 2 (ARHGEF2, hereafter referred to as GEF-H1), which is able to associate with RhoA during capacitation. RhoA activation and its participation in actin polymerization were also analyzed. Inhibition of FAK or ERK1/2 impeded GEF-H1 phosphorylation, RhoA activation, and the association between GEF-H1 and RhoA. Finally, we observed the presence of fibronectin on the sperm surface, its role in sperm-sperm interaction as well as participation of β-integrin in the activation of ERK2. Our results show that the signaling pathway downstream of fibronectin, via integrin, FAK, Grb2, MEK1/2, ERK2, GEF-H1 and RhoA regulates the actin polymerization associated with spermatozoa capacitation.

Factors and pathways involved in capacitation: how are they regulated?

In mammals, fertilization occurs via a comprehensive progression of events. Freshly ejaculated sperm have yet to acquire progressive motility or fertilization ability. They must first undergo a series of biochemical and physiological changes, collectively known as capacitation. Capacitation is a significant prerequisite to fertilization. During the process of capacitation, changes in membrane properties, intracellular ion concentration and the activities of enzymes, together with other protein modifications, induce multiple signaling events and pathways in defined media in vitro or in the female reproductive tract in vivo. These, in turn, stimulate the acrosome reaction and prepare spermatozoa for penetration of the egg zona pellucida prior to fertilization. In the present review, we conclude all mainstream factors and pathways regulate capacitation and highlight their crosstalk. We also summarize the relationship between capacitation and assisted reproductive technology or human disease. In the end, we sum up the open questions and future avenues in this field.

Second messengers, steroids and signaling cascades: Crosstalk in sperm development and function

Signaling cascades control numerous aspects of sperm physiology, ranging from creation to fertilization. Novel aspects of several kinases and their influence on sperm development will be discussed in the first section and cover proliferation, chromatin remodeling and morphology. In the second section, protein kinases (A, B and C) that affect sperm function and their regulation by second messengers, cyclic-AMP and phosphoinositides, as well as steroids will be featured. Key areas of integration will be presented on the topics of sperm motility, capacitation, acrosome reaction and fertilization.

Involvement of epidermal growth factor receptors and mitogen-activated protein kinase in progestin-induction of sperm hypermotility in Atlantic croaker through membrane progestin receptor-alpha

The intracellular pathways mediating rapid, nongenomic progestin stimulation of sperm motility remain unclear. The role of epidermal growth factor receptors (Egfr and ErbB2) and mitogen-activated protein kinase (Mapk) in membrane progestin receptor-alpha (mPRα)-mediated progestin stimulation of sperm hypermotility was examined in a teleost, Atlantic croaker. Inhibition of upstream regulators of Egfr, intracellular tyrosine kinase (Src) with PP2, and matrix metalloproteinase (MMP) with Ilomastat, abolished progestin-initiated sperm hypermotility by 17,20β,21-trihydroxy-4-pregnen-3-one (20β-S; 20 nM) and a specific mPRα agonist, Org OD 02-0 (20 nM). Pretreatment of croaker sperm with EGFR inhibitors, AG1478 (5 μM) and RG13022 (50 μM), the ErbB2 inhibitor, AG879 (5 nM), or the MEK1/2 inhibitor, U0126 (500 nM) blocked progestin stimulation of sperm motility. Levels of phosphorylated extracellular-related kinase 1 and 2 (P-Erk1/2) were increased after 20β-S treatment. These results demonstrate that progestin-mediated hypermotility via mPRα in croaker sperm involves activation of the Egfr, ErbB2 and Mapk pathways.

Signalling Events and Associated Pathways Related to the Mammalian Sperm Capacitation

Capacitation is a biological phenomenon occurring prior to fertilization and is a multiple event process. Many physiological and biochemical changes takes place during the process; these changes are related to lipid composition of membrane, intracellular modulation of ion concentration, protein phosphorylation, sperm movement and membrane permeability. These events occur when the sperm is exposed to the new environment of ion concentration in the female reproductive tract. Ions such as bicarbonate and calcium facilitate capacitation by activating adenylyl cyclase, thus initiating protein kinase A (PKA) signalling cascade. Extracellular-regulated kinase pathway is activated by ligand binding to the membrane receptors and intracellular activation by reactive oxygen species (ROS). Activation of these pathways leads to the phosphorylation of different proteins, which is associated with events such as capacitation, hyperactivation and acrosome reaction that are essential for successful fertilization. Extensive studies were carried out on protein phosphorylation in relation to capacitation, but its role still remains ambiguous.

ERK1/2 mediates sperm acrosome reaction through elevation of intracellular calcium concentration

Mammalian sperm acquire fertilization capacity after residing in the female reproductive tract for a few hours in a process called capacitation. Only capacitated sperm can bind the zona pellucida (ZP) of the egg and undergo the acrosome reaction, a process that allows penetration and fertilization. Extracellular signal regulated kinase (ERK1/2) mediates signalling in many cell types, however its role in sperm function is largely unknown. Here we show that ERK1/2 is highly phosphorylated/activated after a short incubation of mouse sperm under capacitation conditions and that this phosphorylation is reduced after longer incubation. Further phosphorylation was observed upon addition of crude extract of egg ZP or epidermal growth factor (EGF). The mitogen-activated ERK-kinase (MEK) inhibitor U0126 abolished ERK1/2 phosphorylation, in vitro fertilization rate and the acrosome reaction induced by ZP or EGF but not by the Ca2+-ionophore A23187. Moreover, inhibition of ERK1/2 along the capacitation process diminished almost completely the sperm's ability to go through the acrosome reaction, while inhibition at the end of capacitation attenuated the acrosome reaction rate by only 45%. The fact that the acrosome reaction, induced by the Ca2+ -ionophore A23187, was not inhibited by U0126 suggests that ERK1/2 mediates the acrosome reaction by activating Ca2+ transport into the cell. Direct determination of intracellular [Ca2+] revealed that Ca2+ influx induced by EGF or ZP was completely blocked by U0126. Thus, it has been established that the increase in ERK1/2 phosphorylation/activation in response to ZP or by activation of the EGF receptor (EGFR) by EGF, is a key event for intracellular Ca2+ elevation and the subsequent occurrence of the acrosome reaction.

Overexpression of TDRP1 gene in swine testis cell and its global transcriptome analysis

The testis development-related protein-1 (TDRP1) gene was first isolated in spermatogenic cells of testis, and was related to the spermatogenesis and reproduction traits in mammals. This study was performed to further analyze the function of the pig TDRP1 gene by microarray screening of the TDRP1-overexpressed swine testis (ST) cell. After transfection of the recombinant pcDNA3.1-TDRP1 vector into the ST cell, the expression of the TDRP1 gene continued to increase at 12, 24, and 36 h post-transfection, and then decreased at 48 h, as indicated by both the fluorescence signal and quantitative PCR. Microarray screening revealed 529 upregulated and 1086 downregulated genes in TDRP1-overexpressed ST cells at 24 h post-transfection (TD-24) versus untransfected control (TD-blank), and 764 upregulated and 858 downregulated genes at 36 h post-transfection (TD-36) versus TD-blank, as well as 720 upregulated and 375 downregulated genes in TD-36 versus TD-24. As far as three contrasts were totally considered, 29 common genes were identified, including 17 upregulated genes and 12 downregulated ones. Further, Kyoto encyclopedia of genes and genomes prediction analysis indicated that some of these 29 differently expressed genes were involved in a number of biological pathways. Among the 17 upregulated genes, the PMAIP1 gene was significantly enriched in the p53 signaling pathway, and the others were the DDIT3 gene in the mitogen-activated protein kinases (MAPK) signaling pathway, the PPP1R3C gene in the insulin signaling pathway, as well as the GADD45A gene in the p53 signaling pathway, MAPK signaling pathway, and the cell cycle. Among the 12 downregulated genes, the SFRP4 gene was significantly enriched in the Wnt signaling pathway. This study indicated that the TDRP1 gene regulated PMAIP1, GADD45A, DDIT3, and PPP1R3C expression, and these genes involving p53, MAPK, insulin, and Wnt signaling pathways are related to spermatogenesis or reproduction in pig.

Cellular functions regulated by phosphorylation of EGFR on Tyr845

The Src gene product (Src) and the epidermal growth factor receptor (EGFR) are prototypes of oncogene products and function primarily as a cytoplasmic non-receptor tyrosine kinase and a transmembrane receptor tyrosine kinase, respectively. The identification of Src and EGFR, and the subsequent extensive investigations of these proteins have long provided cutting edge research in cancer and other molecular and cellular biological studies. In 1995, we reported that the human epidermoid carcinoma cells, A431, contain a small fraction of Src and EGFR in which these two kinase were in physical association with each other, and that Src phosphorylates EGFR on tyrosine 845 (Y845) in the Src-EGFR complex. Y845 of EGFR is located in the activation segment of the kinase domain, where many protein kinases contain kinase-activating autophosphorylation sites (e.g., cAMP-dependent protein kinase, Src family kinases, transmembrane receptor type tyrosine kinases) or trans-phosphorylation sites (e.g., cyclin-dependent protein kinase, mitogen-activated protein kinase, Akt protein kinase). A number of studies have demonstrated that Y845 phosphorylation serves an important role in cancer as well as normal cells. Here we compile the experimental facts involving Src phosphorylation of EGFR on Y845, by which cell proliferation, cell cycle control, mitochondrial regulation of cell metabolism, gamete activation and other cellular functions are regulated. We also discuss the physiological relevance, as well as structural insights of the Y845 phosphorylation.