Upregulation of SLC38A2 by melatonin attenuates hippocampal ferroptosis in Alzheimer's disease.

BACKGROUND: Ferroptosis has been implicated in the pathogenesis of Alzheimer’s disease (AD), yet its upstream neuronal regulators remain unclear. This study investigated the mechanisms by which melatonin exerts neuroprotection, focusing on the glutamine transporter solute carrier family 38 member 2 (SLC38A2), which inhibits ferroptosis in AD. METHODS: AD models included C57BL/6 mice injected intracerebroventricularly with beta-amyloid (Aβ)1-42 oligomers, organotypic hippocampal slices treated with Aβ1-42 oligomers, and HT22 hippocampal neurons treated with hydrogen peroxide. Cognition and hippocampal pathology were assessed by open field test, Morris water maze (MWM), shuttle box tests, and histology. Cross-species multi-omics comprised single-cell RNA sequencing of human hippocampus, mouse spatial transcriptomics, human bulk RNA sequencing and proteomics. Protein changes were measured by immunohistochemistry, immunofluorescence and Western blotting. Biochemical assays quantified glutathione (GSH), malondialdehyde (MDA), iron, and reactive oxygen species (ROS). RESULTS: In Aβ1-42 oligomer-injected C57BL/6 mice, melatonin improved cognition in MWM and shuttle box tests without affecting locomotion, reduced hippocampal neuronal loss, and lowered Aβ/Tau/p-Tau. Single-cell RNA sequencing of human hippocampus and spatial transcriptomics in the mouse brain demonstrated pronounced ferroptosis in the AD hippocampal region. Integrative human proteomics, bulk RNA sequencing and spatial transcriptomics prioritized the downregulation of the glutamine-family amino-acid catabolic process and identified SLC38A2 as a key node. In vivo and in organotypic hippocampal slices, melatonin reversed the Aβ1-42 oligomer-induced ferroptosis signature. Immunohistochemistry, immunofluorescence, and Western blotting showed that melatonin upregulated SLC38A2 in the Aβ-treated hippocampus and slices. Functionally, shRNA-mediated SLC38A2 knockdown in HT22 neurons reduced GSH and glutathione peroxidase 4 (GPX4), increased iron and ROS, enhanced erastin-induced ferroptosis, and abolished the protective effect of melatonin. CONCLUSIONS: These findings identify SLC38A2 as a pivotal regulator of hippocampal ferroptosis and demonstrate that melatonin confers neuroprotection by stabilizing the SLC38A2-GSH-GPX4 axis, supporting SLC38A2 as a therapeutic target in AD.