Intraperitoneal injection of IFN-γ restores microglial autophagy, promotes amyloid-β clearance and improves cognition in APP/PS1 mice

Autophagy is a major self-degradative process that maintains cellular homeostasis and function in mammalian cells. Autophagic dysfunction occurs in the early pathogenesis of Alzheimer's disease (AD) and directly regulates amyloid-beta (A beta) metabolism. Although it has been proven that the cytokine IFN-gamma enhances autophagy in macrophage cell lines, whether the signaling cascade is implicated in A beta degradation in AD mouse models remains to be elucidated. Here, we found that 9 days of the intraperitoneal administration of IFN-gamma significantly increased the LC3II/I ratio and decreased the level of p62 in APP/PS1 mice, an AD mouse model. In vitro, IFN-gamma protected BV2 cells from A beta toxicity by upregulating the expressions of Atg7 and Atg5 and the LC3II/I ratio, whereas these protective effects were ablated by interference with Atg5 expression. Moreover, IFN-gamma enhanced autophagic flux, probably through suppressing the AKT/mTOR pathway both in vivo and in vitro. Importantly, using intravital two-photon microscopy and fluorescence staining, we found that microglia interacted with exogenous IFN-gamma and A beta, and surrounded A beta in APP/PS1;CX3CR1-GFP(+/-) mice. In addition, IFN-gamma treatment decreased the A beta plaque load in the cortex and hippocampus and rescued cognitive deficits in APP/PS1 mice. Our data suggest a possible mechanism by which the peripheral injection of IFN-gamma restores microglial autophagy to induce the phagocytosis of cerebral A beta, which represents a potential therapeutic approach for the use of exogenous IFN-gamma in AD.