D- and L-Lactate enhance intestinal barrier function via activation of an apical HCAR1/Gαi pathway in a human colonic epithelial cell model

The stereoisomers of lactate, L- and D- are not only metabolic substrates but also signalling molecules, capable of activating and signalling through its G protein-coupled receptor, Hydroxycarboxylic acid receptor 1 (HCAR1). These stereoisomers are both produced by the gut microbiota at millimolar concentrations creating a physiological environment for lactate-sensing unique to the gut yet, poorly understood. Here we identify a role for D-/L-lactate on intestinal barrier function. A human colonic epithelial cell model, Caco2, activated Gαi signalling in response to both L- and D-lactate, although L-lactate exhibited a more potent and rapid Gαi signal profile. When differentiated, apically but not basally treated D-/L-lactate enhanced tight junctions and reduced cell permeability, consistent with the apical localization of HCAR1. This improved barrier function occurred in a Gαi-dependent manner. In addition, apical lactate rescued the reduced intestinal barrier function induced by lipopolysaccharides. This work highlights the potential for D-/L-lactate supplementation in improving gut health.