# Gut dysbiosis induces the development of asthenozoospermia through butanoate metabolism

## TL;DR

This study shows that gut bacteria imbalances can lead to poor sperm motility by affecting butyrate metabolism, suggesting a gut-testis connection in male infertility.

## Contribution

The paper identifies gut dysbiosis and butyrate metabolism as novel factors in the development of asthenozoospermia.

## Key findings

- Men with asthenozoospermia had reduced butyrate-producing bacteria like Faecalibacterium prausnitzii.
- Fecal microbiota transplantation from patients caused impaired sperm motility and testicular abnormalities in mice.
- Butyrate metabolism was disrupted in both serum and testicular tissues of affected individuals and recipient mice.

## Abstract

Asthenozoospermia is a leading cause of male infertility with a rising incidence. While gut dysbiosis is implicated in metabolic disease, its role in asthenozoospermia pathogenesis remains unclear.

We conducted a case-control study comparing the fecal microbiomes of men with isolated asthenozoospermia (n=60) and healthy controls (n=60) using shotgun metagenomic sequencing. Causality was assessed by fecal microbiota transplantation (FMT) from patients or controls into germ-free male mice. Metabolic perturbations were profiled by untargeted serum metabolomics and targeted short-chain fatty acid (SCFA) quantification in humans, alongside untargeted testicular metabolomics and serum SCFAs in recipient mice.

Metagenomic analysis (LEfSe) identified species-level differences, with marked depletion of butyrate-producing taxa in asthenozoospermia, most notably the prototypical butyrate producer Faecalibacterium prausnitzii. The relative abundance of F. prausnitzii was significantly positively correlated with sperm motility and progressive motility, linking gut composition to sperm quality in asthenozoospermia. Untargeted serum metabolomics identified 39 differential metabolites; KEGG enrichment prioritized butanoate metabolism. Targeted SCFA profiling confirmed significantly lower serum butyrate in asthenozoospermia versus controls. In germ-free males, FMT with patient-derived microbiota reduced sperm motility and progressive motility and induced histopathological abnormalities, including decreased interstitial Leydig cells, loss and atrophy of select intratubular cells, and an increased proportion of abnormal seminiferous tubules. Following patient FMT, recipient mice exhibited significantly reduced serum butyrate; testicular metabolomics revealed distinct profiles with 140 key differential metabolites, again implicating butanoate metabolism. Mechanistically, reduced F. prausnitzii-derived butyrate might impair Leydig cell steroidogenesis via disrupted PPAR signaling.

Asthenozoospermia is associated with gut dysbiosis characterized by loss of butyrate-producing bacteria, systemic and testicular disturbances in butyrate metabolism, and microbiota-mediated transmission of impaired sperm quality. These findings implicate the gut-testis axis in asthenozoospermia pathogenesis and nominate butyrate metabolism as a potential therapeutic target.