Oral administration of melatonin modulates macrophage polarization via modulating the Vegf signaling pathway and ameliorates Alzheimer's disease in APP/PS1 mice.

Alzheimer's disease (AD) is a neurodegenerative disorder with a global prevalence, currently lacking effective treatments and posing a major public health challenge due to the burden it places on healthcare systems while affecting millions of people. Melatonin is a hormone with considerable potential for treating various neurodegenerative disorders, including AD. The mechanisms responsible for melatonin's therapeutic benefits in Alzheimer's disease (AD) require further elucidation. This study was designed to investigate the mechanisms by which melatonin exerts its effects in APP/PS1 mice. The Morris water maze was used to assess the performance of melatonin-treated APP/PS1 mice. Haematoxylin&Eosin and Nissl staining were conducted to observe the integrity of hippocampal neurons. Transcriptomic sequencing of hippocampal tissue was performed to identify differentially expressed genes, which were subjected to Gene Ontology (GO) term and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. Immunofluorescence analysis was used to detect the levels of Cd16, Cd32, Cd68 and Cd206 in APP/PS1 mice. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR), immunoblotting, and immunohistochemistry were employed to validate the relative expression of Vegf, Flt1, and Kdr proteins. In the Morris water maze, melatonin-treated APP/PS1 mice demonstrated a marked increase in platform crossings. Improved neuronal integrity in the hippocampus was observed through Haematoxylin&Eosin and Nissl staining. Transcriptomic sequencing of hippocampal tissue revealed 295 differentially expressed genes, which were significantly associated with 1091 GO terms and 30 KEGG pathways. Immunofluorescence analysis indicated that melatonin treatment notably reduced Cd16 and Cd32 levels while elevating Cd68 and Cd206 in APP/PS1 mice. Subsequent analyses via RT-qPCR, immunoblotting, and immunohistochemistry validated the increased relative expression of Vegf, Flt1, and Kdr proteins. Melatonin attenuates AD pathogenesis in APP/PS1 mice by promoting macrophage polarization via the Vegf signaling pathway, revealing a novel mechanism for AD prevention and treatment.