Effect of Faecalibacterium prausnitzii on intestinal barrier function and immune homeostasis : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nutritional Science, Massey University, Manawatū, New Zealand
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Date
2017
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Massey University
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Abstract
Various gastrointestinal (GI) diseases, for example inflammatory bowel disease, are linked
to impaired barrier function, chronic inflammation and dysbiosis of the resident
microbiota. Faecalibacterium prausnitzii, an abundant obligate anaerobe of the healthy
human microbiota, has reduced abundance in the GI tract of people with these diseases,
and has been suggested to exert beneficial effects. Only a few studies have investigated its
mechanisms of action, partly due to the difficulty of co-culturing live obligate anaerobes
with oxygen-requiring human cells. The novel apical anaerobic co-culture model used in
this study allows this co-culture through the separation of anaerobic and aerobic
compartments. This model was used to investigate the effects of live F. prausnitzii (strains
A2-165, ATCC 27768 and HTF-F) on intestinal barrier integrity, measured by transepithelial
electrical resistance (TEER) of the intestinal epithelial cell line Caco-2, and on
immune homeostasis, specifically on Toll-like receptor (TLR) activation. Method
development was required to adapt these assays to the novel model and to optimise the
growth of F. prausnitzii co-cultured with Caco-2 cells and TLR-expressing cell lines while
maintaining their viabilities. Firstly, the optimised co-culture conditions were used to
determine the effect of the three F. prausnitzii strains on barrier integrity of healthy and
tumour necrosis factor alpha (TNF-α) treated Caco-2 cells. Live and growing F. prausnitzii
did not alter the TEER across healthy Caco-2 cells. However, under TNF-α mediated
inflammatory conditions, dead F. prausnitzii decreased TEER, whereas live bacteria
maintained TEER. Secondly, the TLR activation assay was adapted to be carried out in the
novel model. Using the adapted assay conditions it was determined that live F. prausnitzii
induced greater TLR2 and TLR2/6 activation than dead F. prausnitzii. Collectively, these
results indicate greater immuno-stimulatory effects of live F. prausnitzii, via TLR2
activation, and this effect is potentially linked to its barrier maintaining properties, because
previous research showed enhancement of barrier integrity induced by TLR2 signalling.
This new knowledge contributes to the understanding of how F. prausnitzii may maintain
immune homeostasis in the GI tract. Unravelling the biological mechanisms used by
prevalent species of the human microbiota, such as F. prausnitzii, will ultimately allow
better comprehension of microbial regulation of GI function.
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Keywords
Intestines, Microbiology, Gastrointestinal mucosa, Immune system, Homeostasis, Research Subject Categories::MEDICINE::Microbiology, immunology, infectious diseases