Exploring glucagon-like peptide 1-secreting L-cells as signal transducers in the microbiota-gut-brain signalling pathways

Background: Communication across the microbiota-gut-brain axis is integral to homeostatic functions throughout the body. However, the mechanisms behind this communication network have yet to be fully elucidated. There is mounting evidence that bacterially secreted metabolites, such as short-chain fatty acids (SCFAs) or poly-unsaturated fatty acids (PUFAs) including conjugated linoleic acid (CLA), may mediate this cross talk. Although CLA is present in the diet, recommended bioactive doses are unobtainable from the western diet. As such, bacterial producers of CLA such as Bifidobacterium breve NCFB 2258 have been investigated for their numerous health benefits. L-cells are located at the intersection of the gut barrier, and the host endocrine and neural systems. As such, these cells may act as signal transducing cells by releasing GLP-1 basolaterally following stimulation by nutritional, microbial, or liver products in the gut lumen, with effects observed in both the gastrointestinal tract and the brain. Their role in the microbiota-gut-brain axis is under investigation in this study. I aim to explore the mechanisms by which B. breve NCFB 2258 alters GLP-1 secretion from a human GLP-1 secreting L-cell model. Methods: Immunofluorescent imaging was used to examine the expression of direct and indirect receptor targets for B. breve NCFB 2258 secretions in a human model of L-cells. Through calcium imaging, I explored cellular activation of NCI-H716 cells in response to B. breve NCFB 2258 secretions, and ELISA was used to determine the effects of B. breve NCFB 2258 products on the secretion of GLP-1 from NCI-H716 cells. Results: Although exposure to PUFA-containing B. breve NCFB 2258 secretions did not result in GLP-1 secretion from NCI-H716 cells following a 2-hour incubation, acute exposure to B. breve NCFB 2258 secretions increased intracellular calcium and nuclear c-Fos expression. Exposure to B. breve NCFB 2258 supernatants altered PUFA-receptor expression and localisation. Furthermore, inhibition of FFAR4 blocked the alterations in c-Fos expression evoked by B. breve NCFB 2258 secretions, and inhibition of both FFAR4 and PPARα blocked B. breve NCFB 2258 secretion-evoked calcium signalling. Interestingly, exposure of cells to B. breve supernatants in the presence of IL-6R antagonist resulted in significant GLP-1 secretion. Conclusion: Our work has shown that B. breve NCFB 2258 secretions stimulate human-derived NCI-H716 cells through both FFAR4 and PPARα receptors and influences the expression of several direct and indirect receptor targets of PUFAs. Altogether, although I have illuminated a novel aspect of B. breve NCFB 2258 secretion induced signalling in a model of L-cells, further research is required to completely understand the mechanism underpinning this stimulation and the larger impacts this may have on intestinal cross-barrier signalling in the microbiota-gut-brain axis.

Grantor dc:publisher

University College Cork

Year dc:date.issued

2026

Author dc:creator

• O'Connor, Clíona

Advisors dc:contributor.advisor

• O'Malley, Dervla
• Rae, Mark

• Microbiota-gut-brain axis
• GLP-1
• Bifidobacterium breve NCFB 2258
• Poly-unsaturated fatty acid
• Conjugated linoleic acid
• L-cell
• Cross-barrier signalling
• FFAR4
• PPARα
• Gut barrier
• Microbiota

Statement dc:rights

• © 2026, Clíona O'Connor.

Licence dc:rights.uri

• https://creativecommons.org/licenses/by-nc-sa/4.0/

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10468/18907

OAI identifier oai:identifier

oai:cora.ucc.ie:10468/18907