Animal. 2016 Nov 10:1-9. [Epub ahead of print]
- 1Institute
of Nutritional Physiology 'Oskar Kellner',Leibniz Institute for Farm
Animal Biology (FBN),Wilhelm-Stahl-Allee 2,18196 Dummerstorf,Germany.
Abstract
Data
on nutrient sensing by free fatty acid receptors (FFAR1, FFAR2, FFAR3,
FFAR4) and hydroxycarboxylic acid receptors (HCAR1, HCAR2) are
increasing for human or rodent models. Both receptor families link
intestinal fermentation by the microbiota and energy metabolism with
cellular responses. Therefore, this finding provides a link that is
independent of the only function of the fermentation products as energy
substrates. For example, these reactions are associated with insulin
secretion, regulation of lipolysis, adipose tissue differentiation and
innate immune responses. In farm animals, the available data on both
receptor families from the intestine and other tissues increase.
However, currently, the data are primarily linked with the distribution
of receptor messenger RNAs (mRNAs) and more rarely with proteins.
Functional data on the importance of these receptors in farm animal
species is not abundant and is often associated with the immune system.
In certain farm animal species, the receptors were cloned and ligand
binding was characterised. In chicken, only one FFAR2 was recently
identified using genome analysis, which is contradictory to a study
using an FFAR1 small interfering RNA. The chicken FFAR2 is composed of
more than 20 paralogs. No data on HCAR1 or HCAR2 exist in this species.
Currently, in pigs,
most available data are on the mRNA distribution within intestine.
However, no FFAR1 expression has been shown in this organ to date. In
addition to FFAR2, an orthologue (FFAR2-like) with the highest abundance
in intestine has been reported. The data on HCAR1 and HCAR2 in pigs
is scarce. In ruminants, most of the currently available information on
receptor distribution is linked to mRNA data and shows the expression,
for example, in mammary gland and adipose tissue. However, some protein
data on FFAR2 and FFAR1 protein has been reported and functional data
availability is slowly increasing. The receptor mRNAs of HCAR1 and HCAR2
are expressed in bovine. The HCAR2 protein has been demonstrated in
certain tissues, such as liver and fat. Because of the physiological
importance of both receptor families in human life science, more studies
that analyse the physiological significance of both receptor families
in animal science may be performed within the next several years.
KEYWORDS:
farm animal species; fatty acids; free fatty acid receptors; hydroxycarboxylic acid receptors; β-hydroxybutyric acid