The inflammation-induced pathological chaperones ACT and apo-E are necessary catalysts of Alzheimer amyloid formation.
Biochemical, genetic, and epidemiological evidence indicates that inflammation is an essential part of the pathogenesis of Alzheimer's disease. Over the last decade, we and others have focused on the mechanism by which specific inflammatory molecules contribute to the Alzheimer pathogenic pathway. In particular, we have learned that several acute phase/inflammatory molecules, specifically alpha(1)-antichymotrypsin (ACT) and apolipoprotein E (apoE) that are overproduced in the AD brain can promote the formation of, and are associated with, the neurotoxic amyloid deposits that are a key pathological hallmark of the disease. Because both of these proteins bind to the Abeta peptide and catalyze its polymerization into amyloid filaments, they have been termed "pathological chaperones".ACT, and, to a lesser extent, apoE are greatly overproduced only in areas of the AD brain that are prone to amyloid formation. This restriction suggests a local inflammatory reaction may underlie the regional specificity of amyloid deposition by inducing the production of pathological chaperones. The data that will be discussed indicate that ACT over-expression is caused by the activation of ACT mRNA synthesis in astrocytes in response to increased production of the inflammatory cytokine IL-1. IL-1 is released from microglia that become activated by pre-amyloid seeds of Abeta. Recently, this inflammatory cascade has been extended to include the amyloid precursor protein (APP), for IL-1 also upregulates the production of APP in astrocytes, but at the translational rather that the transcriptional level. Thus many of the key elements of the Alzheimer's disease pathogenic pathway are products of a local inflammatory reaction in the brain. Further support for a mechanistic role of inflammation in the Alzheimer's disease pathogenic pathway has been provided by genetic studies, which have associated an increased risk of developing AD with specific polymorphisms in the apoE, ACT, and the IL-1 genes. Most recently, transgenic mouse models of AD have demonstrated that ACT and apoE are amyloid promoters/pathological chaperones in vivo whose contribution is necessary for both amyloid formation and for amyloid-associated cognitive decline and memory loss. The importance of these findings is that they help to place inflammation at the center of the pathogenic pathway to Alzheimer's disease and identify specific steps in the pathway that may be amenable to therapeutic intervention.