Seminal extracellular vesicles from boar AI doses contain fertility-predictive protein and miRNA cargo and improve sperm physiology

This study demonstrates that extracellular vesicles isolated from boar artificial insemination doses retain structural integrity, carry fertility-predictive protein and miRNA signatures that distinguish high- and low-fertility boars, and functionally modulate sperm physiology to improve quality and reduce oxidative stress.

The Gist

Imagine you are a farmer trying to breed the best pigs. You have a team of boars (male pigs), and you want to know which ones are the "superstars" for making babies and which ones are just "average."

For years, scientists have looked at the sperm itself to make this judgment. But this new study suggests we've been ignoring the delivery truck that carries the sperm.

Here is the story of that delivery truck, explained simply.

The Problem: The "Diluted" Message

When farmers use artificial insemination, they take a tiny bit of semen from a boar and mix it with a huge amount of liquid (extender) to make enough doses for many farms. It's like taking a single drop of concentrated orange juice and filling a swimming pool with water.

The scientists realized that while they were carefully counting the sperm (the seeds), they were throwing away the Seminal Plasma (the juice). This plasma isn't just water; it's packed with tiny, invisible bubbles called Extracellular Vesicles (EVs). Think of these EVs as tiny, waterproof messenger drones flying around the sperm.

The Discovery: The Drones Carry the Real Secrets

The researchers took these "drones" from two groups of boars:

1. High-Fertility (HF): The superstars that produce lots of healthy piglets.
2. Reduced-Fertility (RF): The average guys that struggle to produce litters.

They opened up the drones to see what was inside. It was like comparing the cargo of a VIP delivery truck versus a broken-down one.

• The VIP Drones (HF): These carried "super-charged" cargo. They had proteins that act like construction workers helping sperm build strong armor (the acrosome) to penetrate the egg. They also carried "shielding" proteins that protect the sperm from rust (oxidative stress) and "instruction manuals" (miRNAs) that tell the sperm how to behave so they don't get tired too early.
• The Broken Drones (RF): These carried cargo that was a bit chaotic. They had proteins that might confuse the sperm or make them get "too excited" (prematurely capacitated) before they even reach the egg, causing them to burn out.

The Analogy: Imagine the sperm is a race car. The High-Fertility drones are carrying high-octane fuel, a fresh set of tires, and a GPS that says, "Drive straight to the finish line." The Reduced-Fertility drones are carrying a flat tire, a map to the wrong city, and a fuel leak.

The Experiment: Can We Fix the Broken Cars?

The most exciting part of the study was the "rescue mission."

The scientists took sperm from the "Reduced-Fertility" (average) boars. They washed away their original "bad" drones and replaced them with the "VIP" drones from the "High-Fertility" (superstar) boars.

The Result?
It worked! The average sperm suddenly started acting like superstars.

• They swam better.
• They stayed alive longer.
• They were less damaged by "rust" (oxidative stress).
• They kept their "armor" intact longer.

It was like taking a regular sedan, swapping its engine and GPS with parts from a Ferrari, and suddenly watching it win the race.

Why Does This Matter?

This study changes the game for pig farming (and potentially other livestock) in three big ways:

1. Better Predictors: Instead of just counting sperm, farmers can now look at the "drones" (EVs) in the semen. If the drones are carrying the right "VIP cargo," that boar is likely a superstar, even if the sperm count looks normal.
2. The "Magic Potion": We might be able to create a special additive for semen doses. If a farmer has a boar with average sperm, they could add these "VIP drones" to the mix to boost the sperm's performance, turning a "C-grade" boar into an "A-grade" one.
3. Understanding Life: It teaches us that sperm don't work alone. They need a support team (the plasma and its drones) to survive the journey and do their job.

The Bottom Line

This paper tells us that sperm are not just seeds; they are passengers. And the quality of their journey depends entirely on the "messenger drones" flying alongside them. By studying these tiny drones, we can predict which boars will be the best parents and even give the weaker ones a second chance to shine.

Technical Summary

1. Problem Statement

In the porcine industry, artificial insemination (AI) is the standard reproductive method. Commercial AI doses are highly diluted to standardize sperm concentration, a process that typically ignores the dilution of seminal plasma (SP) and its bioactive components. While SP is known to be crucial for sperm maturation and function, the specific role of Extracellular Vesicles (EVs) within these diluted doses remains poorly understood.

• The Gap: Current protocols focus solely on sperm count, potentially discarding or diluting critical molecular cargo (proteins and miRNAs) carried by EVs that regulate fertility.
• The Objective: To evaluate the structural integrity of EVs in commercial AI doses, characterize their protein and miRNA cargo in high-fertility (HF) vs. reduced-fertility (RF) boars, and determine if these EVs can functionally modulate sperm physiology in vitro.

2. Methodology

The study employed a multi-experimental approach using commercial Landrace boar semen doses classified as HF or RF based on farrowing rates and litter size (n=6 per group).

• EV Isolation and Characterization:

  • EVs were isolated from highly diluted AI doses using a combination of differential centrifugation, ultrafiltration (100 kDa), and Size Exclusion Chromatography (SEC).
  • Validation: EVs were characterized according to MISEV2023 guidelines using:
    • Nanoparticle Tracking Analysis (NTA): For size and concentration.
    • Transmission Electron Microscopy (TEM): For morphology.
    • Western Blot & Flow Cytometry: To confirm positive markers (ALIX, CD63, CD81, Hsp70) and exclude contaminants (Albumin, Calnexin).

• Omics Profiling (Experiments 1 & 2):

  • Proteomics: Data-Dependent Acquisition (DDA) and Data-Independent Acquisition (DIA) mass spectrometry (nano-LC-MS/MS) were used to identify Differentially Expressed Proteins (DEPs) in EVs.
  • Transcriptomics: Small RNA sequencing was performed on three compartments: EVs, free seminal plasma, and spermatozoa to identify Differentially Expressed miRNAs (DEMs). Bioinformatics included alignment to the Sus scrofa genome, target prediction, and Gene Ontology (GO)/KEGG pathway enrichment.

• Functional Coincubation (Experiment 3):

  • Sperm from RF males were pooled and coincubated with EVs derived from either HF or RF males at two concentrations (1X and 2X).
  • Samples were incubated at 38°C for up to 24 hours to mimic the female genital tract.
  • Assessment: Sperm quality was evaluated at multiple time points (0, 1, 3, 6, 12, 24h) using:
    • CASA: Motility and kinematics.
    • Flow Cytometry: Viability, acrosome integrity, mitochondrial activity/oxidation, membrane fluidity (capacitation status), and total oxidative stress.

3. Key Contributions and Results

A. Structural Integrity of EVs in AI Doses

• EVs isolated from commercial AI doses retained their structural integrity (cup-shaped morphology) and specific protein markers (CD63, CD81, Hsp70, ALIX) despite high dilution.
• No significant differences were found in EV concentration or size distribution between HF and RF groups, indicating that dilution does not selectively remove EVs based on fertility status.

B. Molecular Cargo Differences (Proteomics & Transcriptomics)

• Proteomics: 108 DEPs were identified.
  • HF EVs: Enriched in proteins related to sperm-egg recognition (Acrosin, ACR), vesicle transport, cytoskeletal regulation (CCT3, CCT7, CNN3), and metabolism. These proteins support fertilization and proper capacitation timing.
  • RF EVs: Enriched in proteins linked to premature capacitation and reduced fertility, such as Actin (ACTB), Toll-like receptor 2 (TLR2), and Dickkopf-related protein 1 (DKK1).
• Transcriptomics:
  • EVs: 80 DEMs identified (59 upregulated in HF, 21 in RF). HF EVs contained miRNAs targeting genes involved in embryo development, immune modulation, and membrane regulation.
  • Compartmentalization: A significant finding was the inverse expression of shared miRNAs between EVs and free seminal plasma. For example, miR-127 was upregulated in RF EVs but upregulated in HF free plasma, suggesting compartment-specific regulation and protection of EV cargo from RNases.
  • Novel miRNAs: Several novel Sus scrofa miRNAs were identified with high homology to human reproductive miRNAs (e.g., miR-203a-3p, miR-33a-5p), linking them to embryo implantation and cholesterol efflux.

C. Functional Impact on Sperm Physiology

• Motility: RF EVs significantly increased total and progressive motility in RF sperm, suggesting a "compatibility" effect where RF EVs provide specific cues for RF sperm.
• Viability & Oxidative Stress: HF EVs demonstrated superior protective capabilities:
  • Increased the percentage of live sperm with intact acrosomes.
  • Enhanced mitochondrial activity and reduced mitochondrial oxidation.
  • Significantly lowered total cellular oxidative stress (DHE staining).
• Capacitation: EVs modulated the timing of capacitation. HF EVs helped maintain sperm in a non-capacitated state (preventing premature acrosome reaction) for longer periods, a critical factor for in vivo fertility.

4. Significance and Implications

• Biomarker Potential: The study establishes that the protein and miRNA cargo of seminal EVs serves as a robust, non-invasive biomarker for predicting boar fertility, superior to current sperm concentration-based metrics.
• Functional Modulators: EVs are not passive transporters but active modulators of sperm physiology. HF EVs can rescue sperm quality parameters (viability, oxidative stress) in low-fertility samples.
• Industry Application: These findings suggest that optimizing AI doses by preserving or supplementing specific EV cargo (rather than just sperm count) could significantly improve reproductive efficiency in swine production.
• Scientific Insight: The discovery of inverse miRNA expression between EVs and free plasma highlights a sophisticated regulatory mechanism where EVs protect specific transcripts from degradation, ensuring targeted delivery to sperm cells.

In conclusion, this research validates the utility of seminal EVs as both diagnostic tools for fertility assessment and therapeutic agents to enhance sperm quality in livestock production.