Down-Regulation of Acyloxyacyl Hydrolase Expression in Alzheimer's Disease Impairs LPS Detoxification and Contributes to Brain Pro-Inflammatory Signaling.

Lipopolysaccharides (LPSs) are potent pro-inflammatory neurotoxins abundant in the gut microbiome and originate primarily from Gram-negative bacteria, such as Escherichia coli. LPS levels increase with brain aging and accumulate around neurons in Alzheimer's disease (AD) brains. Microbiome-generated LPS and other endotoxins cross gut barriers, enter systemic circulation, and translocate across the blood-brain barrier into vascularized brain regions. These processes are exacerbated by aging and neurovascular diseases. Although pro-homeostatic systems mitigate LPS effects, these defenses can fail. This study provides the first evidence that acyloxyacyl hydrolase (AOAH; EC 3.1.1.77), a microglia-enriched LPS detoxifying enzyme, shows reduced expression in AD brain tissue. Analysis of AD patient brains revealed reduced AOAH messenger RNA (mRNA) levels, accompanied by elevated expression of microRNA (hsa-miR-450b-5p), an inflammation regulator. Furthermore, luciferase reporter assays demonstrated that miR-450b-5p specifically targets the AOAH 3'-UTR, leading to a dose-dependent suppression of reporter activity. Also, in vitro experiments on human neuronal glial (HNG) cells further confirmed down-regulation of AOAH expression at protein levels by miR-450b-5p. These findings suggest miR-450b-5p-mediated AOAH deficiency drives LPS-associated neurotoxicity and inflammatory neurodegeneration in AD.