Restoration of Olfactory Memory in Drosophila Overexpressing Human Alzheimer’s Disease Associated Tau by Manipulation of L-Type Ca2+ Channels

Abstract

The cellular underpinnings of memory deficits in Alzheimer’s disease (AD) are poorly understood. We utilized the tractable neural circuits sub-serving memory in Drosophila to investigate the role of impaired Ca2+ handling in memory deficits caused by expression of human 0N4R isoform of tau which is associated with AD. Expression of tau in mushroom body neuropils, or a subset of mushroom body output neurons, led to impaired memory. By using the Ca2+ reporter GCaMP6f, we observed changes in Ca2+ signaling when tau was expressed in these neurons, an effect that could be blocked by the L-type Ca2+ channel antagonist nimodipine or reversed by RNAi knock-down of the L-type channel gene. The L-type Ca2+ channel itself is required for memory formation, however, RNAi knock-down of the L-type Ca2+ channel in neurons overexpressing human tau resulted in flies whose memory is restored to levels equivalent to wild-type. Expression data suggest that Drosophila L-type Ca2+ channel mRNA levels are increased upon tau expression in neurons, thus contributing to the effects observed on memory and intracellular Ca2+ homeostasis. Together, our Ca2+ imaging and memory experiments suggest that expression of the 0N4R isoform of human tau increases the number of L-type Ca2+ channels in the membrane resulting in changes in neuronal excitability that can be ameliorated by RNAi knockdown or pharmacological blockade of L-type Ca2+ channels. This highlights a role for L-type Ca2+ channels in tauopathy and their potential as a therapeutic target for AD.

DYRK1a Inhibitor Mediated Rescue of Drosophila Models of Alzheimer’s Disease-Down Syndrome Phenotypes

“…Another hallmark of DS and AD is learning and memory difficulties ( Querfurth and LaFerl a, 2010 ; Ballard et al, 2016 ). Therefore, to compare the effects of the different neurotoxic genes we measured 1 h memory using the olfactory shock assay, with mnb, Tau, and Aβ42 having previously been shown to reduce learning and memory in flies ( Tejedor et al, 1995 ; Iijima et al, 2004 ; Papanikolopoulou and Skoulakis, 2015 ; Higham et al, 2019a ; Higham et al, 2019b ). In this task the flies were exposed to two consecutive odours with the first odour being delivered at the same time as a mild foot shock, and the second odour without shock.…”

“…In this task the flies were exposed to two consecutive odours with the first odour being delivered at the same time as a mild foot shock, and the second odour without shock. After an hour, the flies are taken to a choice point of a T-maze with one arm containing the odour previously paired with shock and the other the non-shocked odour, the flies show learning and memory by avoiding the odour previously paired with shock ( Higham et al, 2019a ; Higham et al, 2019b ). For the flies participate in the assay they need to be able to smell and react to shock normally.…”

“…In Drosophila , neuronal overexpression of different human APP products [including human tandem oligomerising secreted Aβ42 ( Chen et al, 2014a )] and mutants cause degeneration of the photoreceptor neurons of the fly eye, shortened lifespan, change in neuronal excitability as well as movement, circadian, sleep, and learning deficits ( Iijima et al, 2004 ; Chiang et al, 2010 ; Spere tta et al, 2012 ; Chen et al, 2014a ; Blake et al, 2015 ; Ping et al, 2015 ; Tabuchi et al, 2015 ; Higham et al, 2019a ). Likewise, neuronal overexpression of AD-associated human Tau isoforms also result in degeneration of the photoreceptor neurons, central brain neurodegeneration, shortened lifespan, movement, changes in neuronal excitability, circadian rhythm, sleep, and learning defects ( Wittmann et al, 2001 ; Folwell et al, 2010 ; Iijima-Ando and Iijima, 2010 ; Kosmidis et al, 2010 ; Beharry et al, 2013 ; Papanikolopoulou and Skoulakis, 2015 ; Sealey et al, 2017 ; Higham et al, 2019a ; Higham et al, 2019b ; Buhl et al, 2019 ; Lowe et al, 2019 ).…”

Animal Models of Neurodegenerative Disease: Recent Advances in Fly Highlight Innovative Approaches to Drug Discovery

“…Some D. melanogaster models of PD are able to mimic loss of olfaction seen in patients (Poddighe et al, 2013 ). Olfactory conditioning has been used to show rescue in AD-associated memory deficits induced by tau pathology and could be used to validate therapeutic potential of candidate compounds in a similar application (Higham et al, 2019 ).…”

Lighting Up Ca2+ Dynamics in Animal Models

“…As an example, Drosophila AD models have been generated, and neuronal Ca 2+ homeostasis has been evaluated using different approaches, e.g., loading the chemical indicator fura-2 in dissociated neurons [150,151] or imaging the whole brain of adult flies expressing GECIs ex vivo [152] or in vivo through a cranial window [153]. AD fly models expressing mitochondria-targeted GECIs were also exploited, and mitochondrial Ca 2+ levels have been measured in dissected third instar larval brains [154].…”