Mis-expression of the Alzheimer’s disease associated gene Ankyrin causes memory loss and shortened lifespan in Drosophila

Abstract

Alzheimer's disease (AD) is the most common form of dementia and is characterized by the accumulation of extracellular amyloid beta (A) plaques and intracellular neurofibrillary tangles of hyperphosphorylated Tau, including the 4R0N isoform. Recent epigenome-wide association studies (EWAS) of AD have identified a number of loci that are differentially methylated in AD cortex. Indeed, hypermethylation of the Ankyrin 1 (ANK1) gene in AD has been reported in the cortex in numerous different post-mortem brain cohorts. Little is known about the normal function of ANK1 in the healthy brain, nor the role it may play in AD. We have generated Drosophila models to allow us to functionally characterize Drosophila Ank2, the ortholog of human ANK1. These models have targeted reduction in the expression of Ank2 in neurons. We find that Drosophila with reduced neuronal Ank2 expression have shortened lifespan, reduced locomotion, reduced memory and reduced neuronal excitability similar to flies overexpressing either human mutant APP (that leads to A42 production) and MAPT (that leads to 0N4R Tau). Therefore, we show that the mis-expression of Ank2 can drive disease relevant processes and phenocopy some features of AD and we propose targeting ANK1 may have therapeutic potential. This represents the first study to characterize a gene implicated in AD, which was nominated from EWAS. Author summary The majority (>95%) of Alzheimer's disease (AD) cases are sporadic, with their incidence attributed to common genetic mutations, epigenetic variation, aging and the environment. There is no cure for AD and only limited treatment options which only treat the symptoms of AD and only work in some people. Recent epigenome-wide association studies (EWAS) in AD have highlighted hypermethylation of the Ankyrin1 (ANK1) gene in AD cortex. Little is known of the normal role of the gene in the brain. Here, we have demonstrated that Drosophila with reduced neuronal expression of the Drosophila ortholog of human ANK1 (Ank2), can drive AD relevant processes including locomotor difficulties, memory loss and shortened lifespan similar to expression of human amyloid-Beta or tau mutant proteins. Furthermore, increasing Ank2 expression reversed the memory loss caused by expression of human amyloid-Beta or tau mutant proteins, suggesting that targeting ANK1 may have therapeutic potential. This represents the first study to characterize a gene implicated in AD, which was nominated from EWAS.

Identifying the function of methylated genes in Alzheimer’s disease to determine epigenetic signatures: a comprehensive bioinformatics analysis

“…Among the hubs, TOMM22 serve as the main receptor for accumulation of amyloid β (Aβ) peptides in AD (Hu et al, 2018). Previous studies showed that the gene ANK2 is involved in AD (Higham et al, 2018). Our analysis also detected RORA as a hub which is distinctively overexpressed in the hippocampus of AD brain (Acquaah-Mensah et al, 2015).…”

Changes in mitochondrial distribution occur at the axon initial segment in association with neurodegeneration inDrosophila

“…It is intriguing to speculate that altered tau funcCon could explain the differences in mitochondrial redistribuCon at the AIS between Cdk5α-KO and Ank2-L4 expression. Altering the acCvity of Cdk5, which is known to lead to the hyperphosphorylaCon of tau, causes mitochondrial redistribuCon into the AIS throughout the lifespan while expression of Ank2-L4, which is not known to directly cause changes in tau phosphorylaCon, only shows redistribuCon of mitochondria into the AIS at older ages when tau is known to undergo agedependent hyperphosphorylaCon (Higham et al, 2019;Pao & Tsai, 2021). It is conceivable, therefore, that impaired interacCons between tau and mitochondria may underlie the redistribuCon of mitochondria into the AIS, but more study will be required to determine if such a mechanism exists.…”

“…Specifically, it has been demonstrated that Cdk5α-KO in Drosophila causes AIS shrinkage or absence in MB neurons, followed by local swelling of the AIS and subsequent axonal degeneraCon (Spurrier et al, 2019;Trunova et al, 2011). Moreover, expressing a dominant-interfering fragment of the Drosophila neuronal ankyrin, Ank2-L4, induces similar structural disrupCon and shrinkage of the AIS, and this is also sufficient to cause axonal degeneraCon, neuron cell loss, and increased mortality (Higham et al, 2019;Jegla et al, 2016;Spurrier et al, 2019). GeneCc experiments, however, suggested that the mechanism of AIS disrupCon by Ank2-L4 expression is disCnct from that induced by Cdk5α-KO (Spurrier et al, 2019).…”

Ankyrin-R regulates fast-spiking interneuron excitability through perineuronal nets and Kv3.1b K+channels

“…A number of epigenome-wide association studies in Alzheimer's disease patients consistently report neuropathology-associated DNA hypermethylation of ANK1 (De Jager et al, 2014;Higham et al, 2019;Lunnon et al, 2014;Smith et al, 2019a;Smith et al, 2019b).…”

“…Loss of AnkR results in fragile erythrocyte membranes and hemolytic anemia (Lux et al, 1990). Intriguingly, case studies of patients with hereditary spherocytic anemia, caused by mutations in AnkR, report various neurological disturbances (Coetzer et al, 1988;McCann and Jacob, 1976;Miya et al, 2012), and a number of recent epigenome-wide association studies in Alzheimer's disease (AD) have consistently found neuropathology-associated DNA hypermethylation of ANK1 (ANK1 is the gene encoding AnkR) (De Jager et al, 2014;Gasparoni et al, 2018;Higham et al, 2019;Lunnon et al, 2014;Smith et al, 2019a;Smith et al, 2019b).…”