Exploration of the relationship between gut microbiota and fecal microRNAs in patients with major depressive disorder.

Microbiota-gut-brain axis signaling plays a pivotal role in mood disorders. The communication between the host and the gut microbiota may involve complex regulatory networks. Previous evidence showed that host-fecal microRNAs (miRNAs) interactions partly shaped gut microbiota composition. We hypothesized that some miRNAs are correlated with specific bacteria in the fecal samples in patients with major depressive disorder (MDD), and these miRNAs would show enrichment in pathways associated with MDD. MDD patients and healthy controls were recruited to collect fecal samples. We performed 16S ribosome RNA sequence using the Illumina MiSeq sequencers and analysis of 798 fecal miRNAs using the nCounter Human-v2 miRNA Panel in 20 subjects. We calculated the Spearman correlation coefficient for bacteria abundance and miRNA expressions, and analyzed the predicted miRNA pathways by enrichment analysis with false-discovery correction (FDR). A total of 270 genera and 798 miRNAs were detected in the fecal samples. Seven genera (Anaerostipes, Bacteroides, Bifidobacterium, Clostridium, Collinsella, Dialister, and Roseburia) had fold changes greater than one and were present in over 90% of all fecal samples. In particular, Bacteroides and Dialister significantly differed between the MDD and control groups (p-value < 0.05). The correlation coefficients between the seven genera and miRNAs in patients with MDD showed 48 pairs of positive correlations and 36 negative correlations (p-value < 0.01). For miRNA predicted functions, there were 57 predicted pathways with a p-value < 0.001, including MDD-associated pathways, axon guidance, circadian rhythm, dopaminergic synapse, focal adhesion, long-term potentiation, and neurotrophin signaling pathway. In the current pilot study, our findings suggest specific genera highly correlated with the predicted miRNA functions, which might provide clues for the interaction between host factors and gut microbiota via the microbiota-gut-brain axis. Follow-up studies with larger sample sizes and refined experimental design are essential to dissect the roles between gut microbiota and miRNAs for depression.