Gut microbiota composition correlates with PBMC microRNA expression following maximal exercise testing in endurance athletes.

Introduction: MicroRNAs (miRNAs) are key post-transcriptional regulators that also take part in immune responses and recovery processes following exercise. While both gut microbiota composition and peripheral blood mononuclear cell (PBMC)-derived miRNAs are known to be influenced by endurance training, potential correlations between these two systems in athletes remain largely unexplored. Objective: This study aimed to investigate correlations between gut microbiota composition and PBMC miRNA expression following a maximal exercise stress test in endurance athletes. Methods: Fifty-eight participants (22 runners, 18 cyclists, and 18 controls) underwent maximal exercise testing, with blood samples collected pre- and post-maximal exercise stress test for small RNA sequencing of PBMCs. Baseline fecal samples were analyzed via 16S rRNA gene sequencing to characterize gut microbiota. Expression data of PBMC miRNAs and microbial taxonomic profiles were integrated to assess potential correlations. Results: Thirteen significant correlations (|r| = 0.41-0.51, p < 0.005) were identified between gut bacterial taxa known to produce short-chain fatty acids (SCFAs)-including Conclusion: This is the first study demonstrating an association between resting gut microbiota composition and PBMC miRNA expression following maximal exercise stress test in endurance athletes. These findings raise the possibility of a complex association between gut microbial composition and PBMC miRNA expression in response to exercise. While causality cannot be inferred, the observed correlations suggest a candidate microbiota-miRNA that warrants further investigation in the context of exercise-induced immune regulation and recovery in athletes.