Nogo receptor impairs the clearance of fibril amyloid-β by microglia and accelerates Alzheimer's-like disease progression.

Alzheimer's disease (AD) is characterized by the progressive accumulation of β-amyloid (Aβ)-containing amyloid plaques, and microglia play a critical role in mediating Aβ clearance. Mounting evidence has confirmed that the ability of microglia in clearing Aβ decreased with aging and AD progress, but the underlying mechanisms are unclear. Previously, we have demonstrated that Nogo receptor (NgR), a receptor for three axon growth inhibitors associated with myelin, can decrease adhesion and migration of microglia to fibrils Aβ with aging. However, whether NgR expressed on microglia affect microglia phagocytosis of fibrils Aβ with aging remains unclear. Here, we found that aged but not young microglia showed increased NgR expression and decreased Aβ phagocytosis in APP/PS1 transgenic mice. NgR knockdown APP/PS1 mice showed simultaneous reduced amyloid burden and improved spatial learning and memory, which were associated with increased Aβ clearance. Importantly, Nogo-P4, an agonist of NgR, enhanced the protein level of p-Smad2/3, leading to a significant transcriptional inhibition of CD36 gene expression, which in turn decreased the microglial phagocytosis of Aβ. Moreover, ROCK accounted for Nogo-P4-induced activation of Smad2/3 signaling. Finally, the decreasing effect of NgR on microglial Aβ uptake was confirmed in a mouse model of intra-hippocampal fAβ injection. Our findings suggest that NgR may play an important role in the regulation of Aβ homeostasis, and has potential as a therapeutic target for AD.