Exogenous Albumin Is Crucial for Pig Sperm to Elicit In Vitro Capacitation Whereas Bicarbonate Only Modulates Its Efficiency

Bicarbonate and BSA increase the capacitation pattern and acrosomal exocytosis in boar sperm after 120 min of incubation

Sperm capacitation is a crucial step towards the acquisition of fertilizing capacity. Despite the attempts to mimic the in vivo situation, there is still a lack of standardization in vitro techniques. Bicarbonate and serum albumin (BSA) are routinely used, although controversial results are reported regarding the optimal concentration of each compound. In addition, whether caffeine is needed on in vitro capacitation media in boar sperm remains to be elucidated. Here, 18 boar commercial artificial insemination doses were used to test different concentrations of bicarbonate (19, 37 or 56 mM) in experiment 1, BSA (1.5, 3, 4.5 mg/mL) in experiment 2 and the presence or absence of caffeine (5.15 mM) experiment 3. We analysed at 0, 30 and 120 min of incubation at 38.5°C, 5% CO2 : Total motility (TMOT), membrane integrity (VIAB), acrosomal exocytosis (rAcro; H33342/PI/PNA), capacitation status (chlortetracycline staining CTC) and mitochondrial membrane potential (JC-1). The higher concentrations of bicarbonate (37 and 56 mM) decreased TM and VIAB (p < .01) but increased rAcro (p < .01) after 120 min of incubation compared to the fresh control. In contrast, only the BSA concentration of 3 mg/mL reduced the VIAB at 120 min, but all the concentrations tested increased the average of JC-1 and decreased TM (p < .01) throughout incubation compared to the fresh control. Finally, in experiment 3, when boar sperm were incubated in the capacitating media with bicarbonate, BSA and with or without caffeine, the capacitated pattern measured by the CTC technique and rAcro increased after 120 min of incubation (p < .01) compared to fresh control, either in the presence or in the absence of caffeine. In summary, our results suggested that the combination of capacitating components, like bicarbonate and BSA, contributed to increasing the proportion of capacitated boar spermatozoa, mitochondrial membrane potential as well as acrosomal exocytosis. However, caffeine did not significantly influence in vitro sperm capacitation in this species.

Relationship between biochemical parameters and paraoxonase 1 activity of boar seminal plasma and semen quality

The aim of this study was to examine the biochemical components and the parameters of antioxidant protection in the seminal plasma (SP) of boars, as well as their relationship with semen quality parameters. Thirty-six boars were included in the study, whose ejaculates were divided into two groups: Group I (good quality semen, > 70% progressively motile sperm, < 20% spermatozoa with abnormal morphology, n = 16), and Group II (poor quality semen, < 70% progressively motile sperm, > 20% spermatozoa with abnormal morphology, n = 20). Significantly higher concentrations of ionized calcium (iCa), total cholesterol (TC), lactate-dehydrogenase (LDH) activity, as well as significantly higher values ​​of antioxidant protection parameters: thiol groups (-SH), paraoxonase 1 (PON1), and total antioxidant capacity (TAC) ) were found in the good quality semen, while higher phosphorus (P) concentrations and increased alkaline-phosphatase (ALP) activity were found in the semen of poor quality. A negative correlation of total and progressive sperm motility with P and ALP was found in all examined semen samples, while a positive correlation was found with PON1 and TAC. The percentage of fast sperm cells positively correlated with iCa, chlorine (Cl), lactate, LDH and TAC, while a negative correlation was found with P, magnesium (Mg) and the enzyme creatine-kinase (CK). The percentage of immobile sperm positively correlated with P and ALP, and negatively correlated with TC, CK, PON1 and TAC. Elevated values ​​of PON1 and TAC in SP and a positive correlation with sperm motility indicate the possible use of these parameters as sensitive biomarkers of boar semen quality. To the best of our knowledge there are no published data on association between PON1 activity and boar semen quality.

Understanding Sperm Quality for Improved Reproductive Performance

The assessment of semen quality is used to identify factors that influence sperm performance and diagnose male infertility [...].

Hexane fraction of Prunus japonica thunb. Seed extract enhances boar sperm motility via CatSper ion channel

Introduction

Mammalian sperm motility is facilitated by flagellar beating, which depends on active ion movement through ion channels and their regulation. Prunus japonica Thunb., also known as oriental bush cherry, is a widely used traditional medicinal plant. However, its significance in improving fertility and sperm quality has not been fully elucidated yet. One of our previous reports revealed that P. japonica seed extract (PJE) can improve human sperm motility through intracellular pH modulation.

Aim of the study

The present study was designed to investigate the effects of PJE on boar spermatozoa and potential underlying mechanisms.

Materials and methods

Sperm motility changes were examined using a computer-assisted sperm analysis (CASA) system under both capacitated and non-capacitated conditions. Intracellular calcium concentration was measured using either confocal microscopy or a fluorescent microplate reader with Fluo-4AM calcium fluorescent dye. Sperm capacitation-related proteins were analyzed using western blotting.

Results

A significant increase in rapid motility, velocity, and linear displacement of sperm was observed in PJE-treated capacitated boar sperm, whereas the effect was insignificant in the non-capacitated counterparts. Intracellular calcium levels were significantly elevated upon PJE treatment (20-100 μg/L) in a concentration-dependent manner. The increase in intracellular calcium levels was inhibited when the sperm were treated with a CatSper (cation channel of sperm) channel inhibitor, 10 μM Mibefradil, indicating the involvement of the ion channel in the PJE modulatory mechanism. In addition, western blotting revealed an increased level of protein phosphorylation (p-tyrosine and p-PKA), which is a hallmark of sperm capacitation.

Conclusions

PJE treatment resulted in a combination of increased motility, intracellular calcium concentration, and capacitation, thereby indicating its potential to ameliorate sperm motility parameters and induce capacitation of boar spermatozoa as a result of intracellular calcium elevation via the CatSper channel. Our observations further elaborate ion channel-related underlying mechanisms and show putative implications of the seed extract of traditionally used P. japonica Thunb. in ameliorating sperm quality.

Bicarbonate-Triggered In Vitro Capacitation of Boar Spermatozoa Conveys an Increased Relative Abundance of the Canonical Transient Receptor Potential Cation (TRPC) Channels 3, 4, 6 and 7 and of CatSper-γ Subunit mRNA Transcripts

Simple Summary

The detection of sub-fertile boars has been a difficult task, and despite their prevalence being low, its impact is very significant because it implies economic drawbacks for artificial insemination (AI) centers and farms. Unfortunately, some crucial reproductive processes fall beyond the routine analysis performed in the porcine model, such as sperm capacitation, which is a necessary event for fertilization. A synergistic action of bicarbonate (HCO₃⁻) with calcium (Ca²⁺) is needed to achieve capacitation. The transport of Ca²⁺ is mediated by CatSper channels and Canonical Transient Potential Channels (TRPC). We quantified mRNA transcripts of different subunits of CatSper (β, γ and δ) and TRPC (1, 3, 4, 6 and 7) before and after in vitro capacitation by HCO₃⁻ ions. Our results showed that in vitro capacitation using HCO₃⁻ increases the relative abundance of mRNA transcripts of almost all subunits of Ca²⁺ channels, except CatSper-δ and TRPC1, which were significantly reduced. More studies are needed to elucidate the specific roles of the TRPC channels at a physiological and functional level.

Abstract

Sperm capacitation is a stepwise complex biochemical process towards fertilization. It includes a crucial early calcium (Ca²⁺) transport mediated by CatSper channels and Canonical Transient Potential Channels (TRPC). We studied the relative abundance of mRNA transcripts changes of the CatSper β, γ and δ subunits and TRPC-channels 1, 3, 4, 6 and 7 in pig spermatozoa, after triggering in vitro capacitation by bicarbonate ions at levels present in vivo at the fertilization site. For this purpose, we analyzedfive5 ejaculate pools (from three fertile adult boars) before (control-fresh samples) and after in vitro exposure to capacitation conditions (37 mM NaHCO₃, 2.25 mM CaCl₂, 2 mM caffeine, 0.5% bovine serum albumin and 310 mM lactose) at 38 °C, 5% CO₂ for 30 min. In vitro capacitation using bicarbonate elicits an increase in the relative abundance of mRNA transcripts of almost all studied Ca²⁺ channels, except CatSper-δ and TRPC1 (significantly reduced). These findings open new avenues of research to identify the specific role of each channel in boar sperm capacitation and elucidate the physiological meaning of the changes on sperm mRNA cargo.