NR1H4 and major depressive disorder: As key modulators of the microbiota-gut-brain axis, BAs can enter the systematic circulation and across the blood–brain barriers, and subsequently display neuroprotective potential against several neurological diseases by targeting endogenous receptors, such as Alzheimer’s disease (Wu et al., 2024), major depressive disorder (Sun et al., 2022), etc. Besides, NAFLD also affects the development of neurological diseases via BA signaling, while inflammatory and systematic metabolic disorders in the brain are regulated by FXR and TGR5 (Ren et al., 2022).