Writing in the journal Nature Communications, the team of German researchers note that while it is known that the make-up of our gut microbiome can have a distinct effect on health, it is not the intestinal bacteria themselves but rather their metabolites which affect the immune system and therefore have a knock-on effect on autoimmune diseases such as rheumatoid arthritis.
Led by Dr Mario Zaiss, the team from Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) reveal that recent mouse data suggests a healthy diet rich in fibre is capable of changing intestinal bacteria in such a way that more short-chained fatty acids, in particular propionate, are formed.
Furthermore, they found that when higher concentration of short-chained fatty acids (SCFA), for example in bone marrow, propionate caused a reduction in the number of bone-degrading cells.
This resulted in a considerable slowing of bone degradation, they said.
“We were able to show that a bacteria-friendly diet has an anti-inflammatory effect, as well as a positive effect on bone density,” said Zaiss.
The study shows that SCFA are regulators of important bone cells known as osteoclasts and therefore bone mass.
Zaiss and his colleagues reported that treatment of mice with SCFA - as well as feeding with a high-fibre diet - significantly increased bone mass and prevented postmenopausal and inflammation-induced bone loss.
Mechanistically, the team said that the SCFA’s propionate and butyrate prompted metabolic reprogramming of osteoclasts, which resulted in downregulation of essential osteoclast genes like TRAF6 and NFATc1.
“Here we show a hitherto undiscovered role of SCFA on bone homeostasis,” said the team. “Our data suggest that microbial homeostasis in the gut associated with adequate production of SCFA is an important regulatory element in determining bone composition in mice.”
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Microbiome or metabolites?
The German team note that the exact way in which our intestinal bacteria and the immune system communicate remains unclear – while researchers are also unsure of exactly what can cause, or how to create, a positive effect on the our gut bacteria.
However, as a result of the new study, they suggest that benefits on bone density and autoimmune conditions may not come directly from particular microbial species per se - rather from the composition of secreted microbial metabolites, in particular SCFA, which appear to link gut and bone homeostasis.
“Our findings offer a promising approach for developing innovative therapies for inflammatory joint diseases as well as for treating osteoporosis, which is often suffered by women after the menopause,” said Zaiss. “We are not able to give any specific recommendations for a bacteria-friendly diet at the moment, but eating muesli every morning as well as enough fruit and vegetables throughout the day helps to maintain a rich variety of bacterial species.”
Source: Nature Communications
Volume 9, Article number: 55, doi: 10.1038/s41467-017-02490-4
“Short-chain fatty acids regulate systemic bone mass and protect from pathological bone loss”
Authors: Sébastien Lucas, et al