The selective retinoic acid receptor-α agonist AM580 fails to control autoimmune neuroinflammation

Environmental cues provided by products from the diet,gut microbiota metabolism,and exposure to sunlight are sensed by specific receptors that drive a specific genomic profile in immune cells and influence the outcome of multiple sclerosis(MS),an autoimmune disease of the central nervous system(CNS),1 which affects approximately 2.3 million people worldwide.2 Among these receptors,the ligand-activated transcription factor retinoic acid receptorα(RAR-α)senses retinoic acid and other ligands to promote the transcription of genes that have retinoic acid receptor elements in their promoter region.3 Supplementation with all-trans retinoic acid(ATRA),a metabolite of vitamin A,ameliorates inflammation in MS and the corresponding animal model,experimental autoimmune encephalomyelitis(EAE),by shifting the balance between Th17/regulatory T cells(Tregs)and inducing tolerogenic dendritic cells.4,5 To overcome the weaknesses associated with ATRA agonists,e.g.,instability,poor bioavailability and nonselective binding to a broad range of retinoid receptors,a variety of synthetic agonists specifically targeting RAR have been developed.6 One of them,AM80,inhibits Th17 cells and suppress acute neuroinflammation;however,continuous AM80 treatment is ineffective,most likely because AM80 also inhibits Tregs and IL-10 production.6 AM580,a stable benzoic derivative of retinoic acid and a selective RAR-αagonist,has been recently shown to significantly reduce the production of Th1 cytokines but promote Th2 cytokines in human PBMCs7 and to inhibit microglial activation,thus acting beneficially in Alzheimer’s disease treatment.8 In addition,AM580 protects retinal cells against diabetes-induced apoptosis by inducing neurotrophic factors.9 However,whether it has a protective effect on neuroinflammation is unknown.