P–538 Potential involvement of testicular extracellular vesicles in the paternal epigenetic inheritance of undesirable metabolic traits
Authors: Law T Y S , Choy H K K , Chan S Y , Fok E K L 
Published: August 2021

Abstract

Study question
Does high-fat diet alter the cargoes of testicular extracellular vesicles (tEVs) and thus modulate the sperm epigenome?

Summary answer
The properties and small RNA cargoes of tEVs and the sperm epigenome were significantly altered in mice fed with a high-fat diet.

What is known already
High-fat diet is known to alter spermatogenesis and sperm quality. Recent studies showed that the undesirable metabolic traits can be inherited to the next generation via paternal epigenetic inheritance. Hitherto, it has been shown that the extracellular vesicle, an important intercellular communication pathway, secreted by the epididymis conveys small RNA cargoes to sperms and mediate paternal epigenetic inheritance of metabolic traits. Surprisingly, although the sperm are first being produced in the testes, the potential contributions of testicular EVs (tEVs) in the sperm epigenome remain unexplored.

Study design, size, duration
It is a proof-of-concept study using mice as an experimental model. Thirty mice were raised for nine months, high-fat diet (HFD) and chow diet (SD) were treated on each half of the subject group starting from the sixth week until they were euthanized. Participants/materials, setting, methods: The study is conducted under laboratory settings. Sperm and tEVs were obtained from mice fed with HFD or SD. The uptake of tEVs by sperm was monitored by flow cytometry analysis using fluorescence-labelled tEVs. Physical properties of testicular EVs were examined by the transmission electron microscope. The small RNA cargoes were investigated by small RNA sequencing. The sperm epigenome was examined by real-time-qPCR.

Main results and the role of chance
Our results showed that sperm efficiently took up the tEVs in a dose-dependent manner, without compromising the sperm motility. Size of tEVs in HFD-fed mice (320.5 ± 99.83 nm) was significantly greater than that of SD-fed mice(251.9 ± 81.01 nm). RNA sequencing revealed a decrease in the percentage of miRNA in HFD tEVs. Eight miRNAs were differentially expressed in HFD tEVs.
Among them, real-time PCR results confirmed that miR–34b and c levels were significantly up-regulated in HFD tEVs, with a log2[Fold-change] of 0.46613 and 0.42935 respectively. Unexpectedly, the levels of both miR–34b and c were similar in HFD and SD epididymis, and were both down-regulated by about 2-fold in matured sperm of HFD-fed mice. To investigate the cause of discrepancy, we carried out flow cytometry analysis to measure the absorption efficiency of tEVs, which revealed a notable decrease in absorption efficiency of HFD tEVs (70.235 ± 4.864%) by sperms compared to that of SD tEVs (79.350 ± 4.012%).

Limitations, reasons for caution
Cauda sperm was used in the profiling of sperm epigenome where the contributions from the epididymosomes have not been compared. The study was conducted using mice models such that discrepancy may occur when applying to humans.
Wider implications of the findings: We revealed the alteration of tEVs in HFD-fed mice which may underlie the perturbation of spermatogenesis in HFD condition. We demonstrated the efficient uptake of tEVs by sperm which may be developed as a tool for the engineering of the sperm epigenome.

Trial registration number
Not applicable