5-Aminolevulinic acid suppresses the effector function of feline lymphocytes by reducing the mitochondrial membrane potential

5-Aminolevulinic acid (ALA) is an endogenous amino acid in mammalian cells; it is the first amino acid in the heme biosynthesis pathway occurring in the mitochondria. ALA possesses anti-inflammatory properties by inducing heme oxygenase (HO)-1 expression and releasing heme metabolites in humans and mice. We previously showed that ALA enhances the production of interferon-gamma (IFN-γ) and interleukin-17A in concanavalin A (ConA)-stimulated canine lymphocytes. However, the effects of ALA on feline lymphocytes remain to be investigated. In this study, we demonstrated that ALA-induced HO-1 expression and decreased IFN-γ production in ConA-stimulated feline lymphocytes. Comprehensive RNA sequencing analysis revealed that the Activating transcription factor 4 (ATF4) signaling pathway was inhibited by the addition of ALA. Moreover, we confirmed that ALA decreased ATF4 protein expression. Furthermore, the addition of ALA inhibited the phosphorylation levels of AKT and induced mitochondrial dysfunction in activated lymphocytes. Thus, ALA may suppress the effector function of feline lymphocytes via mitochondrial metabolism, thereby representing a novel mechanism in ALA research. RNA was extracted from feline peripheral blood lymphocytes (PBLs) treated as follows: control, ALA/SFC alone, ConA alone, and a combination of ALA/SFC and ConA for 24 h of incubation, followed by RNA sequencing.