Elsevier

Behavioural Brain Research

Volume 334, 15 September 2017, Pages 50-54
Behavioural Brain Research

Short communications
Microbial regulation of hippocampal miRNA expression: Implications for transcription of kynurenine pathway enzymes

https://doi.org/10.1016/j.bbr.2017.07.026Get rights and content

Highlights

  • The gut microbiota influences gene expression in the hippocampus.

  • This influence may be linked with tryptophan metabolism.

  • Transcriptional changes are sex-dependant and may represent divergent molecular pathways between the brain and the gut.

Abstract

Increasing evidence points to a functional role of the enteric microbiota in brain development, function and behaviour including the regulation of transcriptional activity in the hippocampus. Changes in CNS miRNA expression may reflect the colonisation status of the gut. Given the pivotal impact of miRNAs on gene expression, our study was based on the hypothesis that gene expression would also be altered in the germ-free state in the hippocampus. We measured miRNAs in the hippocampus of Germ free (GF), conventional (C) and Germ free colonised (exGF) Swiss Webster mice. miRNAs were selected for follow up based on significant differences in expression between groups according to sex and colonisation status. The expression of miR-294-5p was increased in male germ free animals and was normalised following colonisation. Targets of the differentially expressed miRNAs were over-represented in the kynurenine pathway. We show that the microbiota modulates the expression of miRNAs associated with kynurenine pathway metabolism and, demonstrate that the gut microbiota regulates the expression of kynurenine pathway genes in the hippocampus. We also show a sex-specific role for the microbiota in the regulation of miR-294-5p expression in the hippocampus. The gut microbiota plays an important role in modulating small RNAs that influence hippocampal gene expression, a process critical to hippocampal development.

Section snippets

Sex and germ free status interact to alter the expression of miRNA’s

Microarray analysis was performed on hippocampi removed from both male and female conventional (CON), germ free (GF) and mice that had previously been germ free but were colonised (exGF) post-weaning (day 21), (Fig. 1A). Microarray analysis revealed that microbial colonisation status and sex affected the expression of hippocampal miRNAs (Fig. 1B). A two-way analysis of variance (ANOVA) analysis revealed a significant interaction between sex and colonisation status in 15 miRNAs (Table 2).

mir-294-5p expression in the hippocampus is regulated by the gut microbiota

To validate our microarray results, we performed qRT-PCR on hippocampal RNA from the same mice from the microarray experiment. Based on the results of the two-way ANOVA and using specific primers for 3 miRNAs mmu-miR-342-3p, mmu-miR-294-5p and mmu-miR-16-5p (Table 1), we found a significant increase in expression of miR-294-5p only in the hippocampus of male mice compared to conventionally raised male mice (Fig. 2C, p < 0.05). This increase in gene expression was reversed upon colonisation of

mir-294-5p targets the kynurenine pathway enzymes

Considering these results and the role the gut microbiota plays in other regions of the brain, we wanted to understand what genes were targeted by the miRNAs listed in Table 2, and what potential pathways they may be involved in. Specifically, we investigated if those miRNAs that displayed a significant interaction in relation to germ free status and sex (Table 2) were overrepresented in the tryptophan catabolic process to kynurenine pathway (GO: 0019441), as recent data from our group has

Funding

The APC Microbiome Institute is a research centre funded by Science Foundation Ireland, through the Irish Government’s National Development Plan Dr Clarke reported that his research is supported by Science Foundation Ireland (SFI) (grant number SFI/12/RC/2273) and by the Health Research Board (HRB) through Health Research Awards (grant number HRA-POR-2-14-647; GC). GC is supported by a NARSAD Young Investigator Grant from the Brain and Behaviour Research Foundation grant number (20771). Prof

Acknowledgements

We acknowledge the contribution of Ms Frances O’Brien and Patrick Fitzgerald in this study. This manuscript results in part from collaboration and network activities promoted under the frame of the international network GENIEUR (Genes in Irritable Bowel Syndrome Research Network Europe), which has been funded by the COST program (BM1106, www.GENIEUR.eu) and is currently supported by the European Society of Neurogastroenterology and Motility (ESNM, www.ESNM.eu). Eloisa Salvo-Romero received a

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