Characterization of A Novel Mouse Model Expressing Human 82-kDa Choline Acetyltransferase: Potential Role in Physiological and Pathological Aging
Abstract
Choline acetyltransferase (ChAT), the acetylcholine synthesizing enzyme, is an important cholinergic marker whose levels/activity are reduced in aging and Alzheimer’s disease (AD). In humans, the M-transcript produces two ChAT isoforms, 69-kDa and 82-kDa ChAT, with preferential subcellular localization in the cytoplasm and nucleus, respectively. Under conditions of cellular stress, including aging and AD, 82-kDa ChAT is aberrantly mis-placed to the cytoplasm. The function of nuclear ChAT is unknown, but studies indicate a role in stress, via regulation of gene expression and hint to a role in neuronal vulnerability. In this regard, our laboratory has generated a novel transgenic mouse model expressing 82-kDa ChAT which is not endogenously expressed in rodents. The overall objective of this study is to understand the role of 82-kDa ChAT under physiological and pathological conditions. We aim to phenotype this new mouse model and elucidate any potential implications of this nuclear protein on aging and AD. Using qPCR, RNAscope and immunohistochemical analysis, we were able to demonstrate 82-kDa ChAT mRNA and protein expression in basal forebrain neurons of our mouse model with age/pathology-dependent subcellular distribution similar to human necropsy brains. The nuclear 82-kDa ChAT expression in wild type mice led to alterations in genes related to the aging process, with subtle improvements in age related cognitive deficits and inflammation. Similarly, its expression in AD mice (APPNL-G-F) altered the expression of several genes and proteins linked to amyloid-beta (Aβ) clearance and inflammation accompanied by enhanced cognitive behavior, reduced amyloidosis, and gliosis. These beneficial effects were inversely proportional to age and plaque load, two factors that seemed to impact the subcellular distribution of 82-kDa ChAT, aberrantly shifting it from the nucleus to the cytoplasm. In conclusion, this thesis characterizes a novel transgenic mouse model expressing the primate-specific nuclear ChAT isoform and provides the first application of this model in studying the impact of 82-kDa ChAT on AD highlighting its potential neuroprotective role. These mice will be valuable in understanding the function of 82-kDa ChAT and its role in the selective cholinergic susceptibility observed in aging and neurodegenerative diseases featuring cholinergic deficits.