Neuronal A2A receptor exacerbates synapse loss and memory deficits in APP/PS1 mice

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by a progressive cognitive decline. Epidemiological studies have suggested a protective role of caffeine consumption against age-related cognitive impairments and the risk of developing AD. Effects of caffeine have been particularly ascribed to its ability to block adenosine A2A receptors (A2ARs). Early pathological upregulation of these receptors by neurons is thought to be involved in the development of synaptic and memory deficits in AD but this remains ill-defined. To tackle this question, we employed a novel transgenic mouse model allowing to promote a neuronal upregulation of A2AR in the hippocampus of APP/PS1 mice, developing AD-like amyloidogenesis. This new model was used to determine the impact of an early upregulation of A2AR on the progression of neuropathological lesions, associated behavior and underlying mechanisms in APP/PS1 mice. Our findings revealed that the early upregulation of A2AR in the presence of an ongoing amyloid pathology exacerbates memory impairments of APP/PS1 mice. These behavioral changes were not linked to major change in the development of amyloid pathology but rather associate with an increased p-tau at neuritic plaques. Moreover, proteomic and transcriptomic analysis coupled to quantitative immunofluorescence studies indicated that neuronal impairment of the receptor promoted both neuronal- and non-neuronal autonomous alterations i.e. loss of excitatory synapses and neuroinflammatory response, respectively, both presumably accounting for the detrimental effect on memory. Overall, our results provide compelling evidence that neuronal A2AR dysfunction as seen in the brain of patients contributes to AD pathogenesis, favoring synaptic deficits promoted by both amyloid (this study) and tau lesions (our previous study). In addition to provide new insights into the complex pathophysiology of AD, the present findings underscore the potential of A2AR as a relevant therapeutic target for mitigating early synaptic loss in this neurodegenerative disorder. Overall design: Heterozygous APPswe/PS1dE9 mice (herein referred to as APP/PS1, C57Bl6/J background) were crossed with an in-house developed TRE-A2A transgenic strain (in which the mouse A2AR cDNA is under the control of a Tet-responsive element). Four genotypic heterozygous groups were therefore obtained: WT, TRE-A2A (or A2A), APP/PS1 and APP/PS1 TRE-A2A (or APP/PS1 A2A). We used females in our experiments. To achieve upregulation of neuronal A2AR in TRE-A2A mice, a tTA transactivator protein needs to bind the Tet-Responsive Element (TRE) promoter. To this end, all mice were thus bi-laterally injected into the CA1 region of the dorsal hippocampus with a serotype 5 adeno-associated viral (AAV2/5) vector allowing neuronal tropism, encoding the tTA transactivator under the control of the chicken beta-actin (CBA) promoter (AVV2/5-CBA-tTA-WPRE-bGH). The tTA protein expressed in the hippocampus then binds to the TRE, driving the expression of the murine A2AR in the TRE-A2A and APP/PS1 TRE-A2A groups only. Control animals, referred as WT and APP/PS1, were injected with the same viral vector but do not express the A2AR. All mice were injected at 3 months of age and sacrificed at 6 months of age, hippocampus dissected out and frozen before RNA extraction an sequencing.