Alzheimer’s Disease (AD), the most common form of dementia, is a progressive neurodegenerative disease most often characterized by initial memory impairment and cognitive decline that can ultimately affect behavior, speech, visuospatial orientation and the motor system. It’s the 6th leading cause of death in the US. The most common characteristics of AD are the abnormal accumulation of amyloid plaques and neurofibrillary tangles. The amyloid cascade hypothesis states that AD pathology is caused by the deposition of amyloid β. The formation of amyloid plaques is due to the incorrect cleavage of the amyloid precursor protein (APP) by 𝛾- secretase. The standard of care for AD patients has mainly focused on two classes of drugs: cholinesterase inhibitors and NMDA antagonists which only address disease symptoms. More recently, the FDA approved a drug, Aducanumab, that directly targets amyloid β to drive its clearance. This sparked debate on the validity of the amyloid cascade hypothesis providing a clear gap in understanding the role of amyloid clearance in AD.
Materials and Methods:: We use zebrafish (Danio Rerio) as a model organism to study various scales of amyloid clearance from molecular to organism. We created transgenic lines to study two clearance pathways: extracellularly by creating the following transgene Tg(huC:hAbeta42-mCherry);Tg(Kdrl:eGFP) which tags the amyloid in red and the vasculature in green fluorescent proteins. Intracellularly by creating the following transgene Tg(mpeg:membraneTurq) which tags the microglia in blue fluorescent protein.
Results, Conclusions, and Discussions:: Protein clearance extracellular pathway- Transgenic model of human amyloid β Tg(huC:hAbeta42-mCherry);Tg(Kdrl:eGFP) expressed in neurons aggregate in clusters in the zebrafish brain and interact with the brain vasculature. HuC drives expression of hAbeta42-mCherry in neurons, however, hbeta42-mCherry is also detected in the kidney. The presence of human amyloid β in the kidney is a result of its clearance from the brain through the vasculature.
With the established transgenic lines to study both extracellular and intracellular pathways for amyloid β, next steps will focus on quantifying the expression of amyloid in the brain and the kidney using fluorescence correlation spectroscopy (FCS), observing the interactions between microglia and amyloid using confocal microscopy, and studying drug efficacy for amyloid clearance.
