n-3 polyunsaturated fatty acids ameliorate learning and memory abilities in APPPS1 mice by regulating microglial activation and polarization

To construct a model of Fat-1/APPPS1 transgenic mice and a cellular model of microglia and explore the improvement effect and underlying mechanism of n-3 polyunsaturated fatty acids (n-3 PUFAs) on the learning and memory abilities of APPPS1 mice by regulating microglial activation and polarization.

After the male mice with heterozygous Fat-1 genotype were mated with the female ones with heterozygous APPPS1 genotype, genetic identification was used to screen the male offspring with Fat-1/APPPS1 genotype. Then after the male wild-type (WT) mice and those with Fat-1, Fat-1/APPPS1, and APPPS1 genotypes were bred until 9 months old, their learning and memory abilities were evaluated with Morris water maze (MWM) test. In addition, gas chromatography-mass spectrometry (GC-MS) was performed to detect the concentration of PUFAs in the brain, and immunohistochemistry (IHC) was applied to detect the deposition of β-amyloid protein (Aβ) in the hippocampal regions. Moreover, immunofluorescence assay, qRT-PCR, and enzyme-linked immunosorbent assays (ELISA) were conducted to measure inflammation, and transcription and expression of Iba-1 (indicating the microglial activation) and CD86 and CD206 (indicating microglial polarization) in central nervous system (CNS). After pretreated with DHA+EPA (25 μmol/mL ∶25 μmol/mL), microglial model of inflammatory injury was established in immortalized mouse BV2 cells induced by LPS (1 μg/mL). Afterwards, immunofluorescence assay, qRT-PCR and Western blotting were used to detect inflammation and microglial activation and polarization.

Compared with the APPPS1 mice, endogenous n-3 PUFAs effectively improved the learning and memory disorders in Fat-1/APPPS1 ones (P<0.05), remarkably alleviated Aβ deposition in the hippocampal regions (P<0.05), evidently reduced CNS inflammation and microglial activation (P<0.05) and transformed the activated microglia from M1 to M2 (P<0.05). Furthermore, BV2 cells with DHA+EPA pretreatment obviously resisted LPS-induced cellular inflammation and induced activated ones from M1 to M2 (P<0.05).

n-3 PUFAs inhibit the microglial activation, regulate the microglial polarization from M1 to M2, reduce CNS inflammation, and thus alleviate learning and memory disorders in APPPS1 mice.