Consumption of lactic acid bacteria (LAB)—found in foods such as milk, yogurt, and sauerkraut—is known to have beneficial health effects, but why these bacteria are beneficial to humans is still not well-understood. In a paper published in PLOS Genetics, scientists report the discovery of one way that lactic acid interacts with our bodies. According to the study, humans and other great apes possess a receptor on their cells that detects metabolites from bacteria found in fermented food and triggers immune cell migration.
The study was done by researchers at the University of Leipzig. The study focused on GPCRs belonging to the family of hydroxycarboxylic acid receptors (HCAR). Most animals have two types of this receptor, but an evolutionary reconstruction of this receptor revealed humans and great apes have three. The team found that a metabolite released by lactic acid bacteria, called D-phenyllactic acid, binds strongly to this additional third receptor.
When D-phenyllactic acid binds to the third HCA receptor, signaling occurs to monocytes in the immune system. Functional and phylogenetic evidence presented by the researchers suggests ingestion of LAB-fermented food likely posed a positive selective pressure to maintain the third HCAR, allowing continued consumption of foods that are starting to decay.
"We are convinced that this receptor very likely mediates some beneficial and anti-inflammatory effects of lactic acid bacteria in humans," says author Claudia Stäubert. "That is why we believe it could serve as a potential drug target to treat inflammatory diseases."
Image: D-phenyllactic acid is absorbed from lactic acid bacteria fermented food (e.g. Sauerkraut) and induces HCA3-dependent migration in human monocytes. Future studies need to address how HCA3 activation by lactic acid bacteria-derived metabolites modulates immune function and energy storage. Image courtesy of Claudia Stäubert.