It is clear that the regulation of intestinal fat absorption
is critical to the energy balance of any animal. It is also clear from previous
research that the intestinal microbiota of an animal impacts its energy
balance. However, what is less clear is the role of the gut microbiota in
metabolism of dietary fat. Understanding this link may have advantageous implications
for fish health and nutrition and for aquaculture. Understanding the link
between microbiota and fat absorption may also have implications for human
health, in particular obesity and malnutrition.
In humans, dietary lipids supply 40-55% of the energy
requirements in the typical western diet. For vertebrates in general, dietary fats
come in the form of triglycerides. These are broken down into monoglycerides by
lipases in the GI tract and absorbed by enterocytes in the intestinal
epithelium. They are temporarily stored in the epithelium as Lipid Droplets before
progressing to other tissues such as the liver.
The majority of previous work linking gut microbiota and
metabolism focuses on microbial fermentation of otherwise indigestible carbohydrates
and lipids that allows the (usually mammalian) host to make use of alternative
energy sources, such as my post last term on microbe-assisted seaweed digestion.
However, this study uses zebrafish to investigate how microbiota regulates
lipid absorption. Specifically, they used fluorescently labelled fatty acids to
view how epithelial Lipid Droplet abundance differed between zebrafish with different
known microbiota, known as ‘gnotobiotic’ zebrafish.
Two fluorescent fatty acids were used, quantification of
epithelial fluorescence showed that both fatty acids were absorbed more
successfully in zebrafish containing a normal zebrafish microbiota compared to
zebrafish that were raised ‘germ-free’.
Higher lumenal fluorescence in germ-free fish suggests that the
microbiota plays a crucial role in absorption. Lipid Droplet number and size was
also shown to increase in zebrafish with a conventional microbiota. However,
these increases may not be due to increase absorption, but decreased ability to
subsequently shift fatty acids from the epithelium to other tissues, such as
the liver. They tested this and showed that the increase in epithelial Lipid
Droplet size and number was not due to impaired intestinal lipid export, nor
was it associated with ingestion rates, digestive organ size or differences in
digestive enzyme activity. They isolated microbiota as the one variable
responsible for increased fatty acid absorption and also increased export to
other tissues.
This study differs from previous studies in that it uses a
method that distinguishes between dietary and microbial produced fatty acids.
They can therefore say with certainty that microbiota composition affects the
absorption of dietary lipids, regardless of the fatty acids produced by the
microbiota. The mechanistic understanding of this interaction remains
incomplete, this study has only shown that it does happen, not how it happens. The
implications of this study could potentially be applied to aquaculture, manipulation
of fish gut microbiota via probiotics may allow increased efficiency of fatty
acid uptake, producing fish that are more nutritionally valuable for human
consumption. If applied to humans, greater understanding of our own microbiota
could lead to probiotics that manipulate fatty acid uptake for treatment of
disorders such as obesity and malnutrition.
Semova, I., Carten, J. D., Stombaugh, J., Mackey, L. C., Knight, R., Farber, S. A., & Rawls, J. F. (2012). Microbiota regulate intestinal absorption and metabolism of fatty acids in the zebrafish. Cell host & microbe, 12(3), 277-288.
No comments:
Post a Comment