Gene therapy for Alzheimer's disease targeting CD33 reduces amyloid beta accumulation and neuroinflammation.

Neuroinflammation is a key contributor to the pathology of Alzheimer's disease (AD). CD33 (Siglec-3) is a transmembrane sialic acid-binding receptor on the surface of microglial cells. CD33 is upregulated on microglial cells from post-mortem AD patient brains, and high levels of CD33 inhibit uptake and clearance of amyloid beta (Aß) in microglial cell cultures. Furthermore, knockout of CD33 reduces amyloid plaque burden in mouse models of AD. Here, we tested whether a gene therapy strategy to reduce CD33 on microglia in AD could decrease Aß plaque load. Intracerebroventricular injection of an adeno-associated virus (AAV) vector-based system encoding an artificial microRNA targeting CD33 (miRCD33) into APP/PS1 mice reduced CD33 mRNA and TBS-soluble Aß40 and Aß42 levels in brain extracts. Treatment of APP/PS1 mice with miRCD33 vector at an early age (2 months) was more effective at reducing Aß plaque burden than intervening at later times (8 months). Furthermore, early intervention downregulated several microglial receptor transcripts (e.g. CD11c, CD47 and CD36) and pro-inflammatory activation genes (e.g. Tlr4 and Il1b). Marked reductions in the chemokine Ccl2 and the pro-inflammatory cytokine Tnfα were observed at the protein level in the brain of APP/PS1 mice treated with miRCD33 vector. Overall, our data indicate that CD33 is a viable target for AAV-based knockdown strategies to reduce AD pathology. One Sentence Summary: A gene therapy approach for Alzheimer's disease using adeno-associated virus vector-based knockdown of CD33 reduced amyloid beta accumulation and neuroinflammation.

Cromolyn Reduces Levels of the Alzheimer's Disease-Associated Amyloid ß-Protein by Promoting Microglial Phagocytosis.

Amyloid-beta protein (Aß) deposition is a pathological hallmark of Alzheimer's disease (AD). Aß deposition triggers both pro-neuroinflammatory microglial activation and neurofibrillary tangle formation. Cromolyn sodium is an asthma therapeutic agent previously shown to reduce Aß levels in transgenic AD mouse brains after one-week of treatment. Here, we further explored these effects as well as the mechanism of action of cromolyn, alone, and in combination with ibuprofen in APPSwedish-expressing Tg2576 mice. Mice were treated for 3 months starting at 5 months of age, when the earliest stages of ß-amyloid deposition begin. Cromolyn, alone, or in combination with ibuprofen, almost completely abolished longer insoluble Aß species, i.e. Aß40 and Aß42, but increased insoluble Aß38 levels. In addition to its anti-aggregation effects on Aß, cromolyn, alone, or plus ibuprofen, but not ibuprofen alone, increased microglial recruitment to, and phagocytosis of ß-amyloid deposits in AD mice. Cromolyn also promoted Aß42 uptake in microglial cell-based assays. Collectively, our data reveal robust effects of cromolyn, alone, or in combination with ibuprofen, in reducing aggregation-prone Aß levels and inducing a neuroprotective microglial activation state favoring Aß phagocytosis versus a pro-neuroinflammatory state. These findings support the use of cromolyn, alone, or with ibuprofen, as a potential AD therapeutic.