Persistent Amyloidosis following Suppression of Aβ Production in a Transgenic Model of Alzheimer Disease

Abstract

BackgroundThe proteases (secretases) that cleave amyloid-β (Aβ) peptide from the amyloid precursor protein (APP) have been the focus of considerable investigation in the development of treatments for Alzheimer disease. The prediction has been that reducing Aβ production in the brain, even after the onset of clinical symptoms and the development of associated pathology, will facilitate the repair of damaged tissue and removal of amyloid lesions. However, no long-term studies using animal models of amyloid pathology have yet been performed to test this hypothesis.Methods and FindingsWe have generated a transgenic mouse model that genetically mimics the arrest of Aβ production expected from treatment with secretase inhibitors. These mice overexpress mutant APP from a vector that can be regulated by doxycycline. Under normal conditions, high-level expression of APP quickly induces fulminant amyloid pathology. We show that doxycycline administration inhibits transgenic APP expression by greater than 95% and reduces Aβ production to levels found in nontransgenic mice. Suppression of transgenic Aβ synthesis in this model abruptly halts the progression of amyloid pathology. However, formation and disaggregation of amyloid deposits appear to be in disequilibrium as the plaques require far longer to disperse than to assemble. Mice in which APP synthesis was suppressed for as long as 6 mo after the formation of Aβ deposits retain a considerable amyloid load, with little sign of active clearance.ConclusionThis study demonstrates that amyloid lesions in transgenic mice are highly stable structures in vivo that are slow to disaggregate. Our findings suggest that arresting Aβ production in patients with Alzheimer disease should halt the progression of pathology, but that early treatment may be imperative, as it appears that amyloid deposits, once formed, will require additional intervention to clear.

Methylene Blue Modulates β-Secretase, Reverses Cerebral Amyloidosis, and Improves Cognition in Transgenic Mice

“…Brain A␤ and A␤ 1-42 species were detected by a three-step extraction protocol (30,31). Briefly, brains were homogenized using TissueLyser LT (Qiagen, Valencia, CA; two times for 1 min at 50 Hz) in TBS solution containing protease inhibitor mixture (Sigma) and centrifuged at 18,800 ϫ g for 60 min at 4°C, and supernatants were removed (representing the TBS-soluble fraction).…”

Tannic Acid Is a Natural β-Secretase Inhibitor That Prevents Cognitive Impairment and Mitigates Alzheimer-like Pathology in Transgenic Mice

“…Briefly, BACE1 enzyme was incubated with various concentrations of TA ( ELISA-We separately quantified A␤ and A␤ 1-42 in brain homogenates and cultured SweAPP N2a cell supernatants by sandwich ELISAs. Brain A␤ and A␤ 1-42 species were detected by a three-step extraction protocol according to previously published methods (46,47). Briefly, we homogenized brains using TissueLyser LT (Qiagen, Valencia, CA; two times for 1 min at 50 Hz) in TBS solution containing protease inhibitor mixture (Sigma), centrifuged homogenates at 18,800 ϫ g for 60 min at 4°C, and removed the supernatants (TBS-soluble fraction).…”

Amyloid Plaque and Neurofibrillary Tangle Pathology in a Regulatable Mouse Model of Alzheimer's Disease

“…Moreover, it was previously shown in a regulatable APP SWE/IND model, that plaques are extremely stable structures that remained in the brain during a 6-month period of almost complete transgene suppression. 36 However, the effects of transgene suppression on A␤ plaque deposition and memory retention remain to be determined.…”