Induction of Toll-Like Receptor 9 Signaling as a Method for Ameliorating Alzheimer's Disease-Related Pathology

The pathogenesis of Alzheimer's disease (AD) is thought to be related to the accumulation of amyloid beta (A beta) in amyloid deposits and toxic oligomeric species. Immunomodulation is emerging as an effective means of shifting the equilibrium from A beta accumulation to clearance; however, excessive cell mediated inflammation and cerebral microhemorrhages are two forms of toxicity which can occur with this approach. Vaccination studies have so far mainly targeted the adaptive immune system. In the present study, we have stimulated the innate immune system via the Toll-like receptor 9 (TLR9) with cytosine-guanosine-containing DNA oligodeoxynucleotides in Tg2576 AD model transgenic mice. This treatment produced a 66% and 80% reduction in the cortical (p = 0.0001) and vascular (p = 0.0039) amyloid burden, respectively, compared with nontreated AD mice. This was in association with significant reductions in A beta 42, A beta 40, and A beta oligomer levels. We also show that treated Tg mice performed similarly to wild-type mice on a radial arm maze. Our data suggest that stimulation of innate immunity via TLR9 is highly effective at reducing the parenchymal and vascular amyloid burden, along with A beta oligomers, without apparent toxicity.