Abstract
Artemisinins, a group of plant-derived sesquiterpene lactones, are efficient antimalarial agents. They also share anti-inflammatory and anti-viral activities and were considered for treatment of neurodegenerative disorders like Alzheimer's disease (AD). Additionally, artemisinins bind to gephyrin, the multifunctional scaffold of GABAergic synapses, and modulate inhibitory neurotransmission in vitro. We previously reported an increased expression of gephyrin and GABAA receptors in early pre-symptomatic stages of an AD mouse model (APP-PS1) and in parallel enhanced CDK5-dependent phosphorylation of gephyrin at S270. Here, we studied the effects of artemisinin on gephyrin in the brain of young APP-PS1 mice. Wedetected an additional increase of gephyrin protein level, elevated gephyrin phosphorylation at Ser270, and anincreased amount of GABAAR-γ2 subunits after artemisinin-treatment. Interestingly, the CDK5 activator p35 was also upregulated. Moreover, we demonstrate decreased density of postsynaptic gephyrin and GABAAR-γ2 immunoreactivities in cultured hippocampal neurons expressing gephyrin with alanine mutations at two CDK5 phosphorylation sites. In addition, the activity-dependent modulation of synaptic protein density was abolished in neurons expressing gephyrin lacking one or both of these phosphorylation sites. Thus, our results reveal that artemisinin modulates expression as well as phosphorylation of gephyrin at sites that might have important impact on GABAergic synapses in AD.
Highlights
Alzheimer’s disease (AD) is the most common cause of dementia characterized by progressive loss of memory affecting an increasing number of persons worldwide
In earlier studies we detected a significant increase of gephyrin and other key inhibitory synapse proteins in the hippocampus of three-month-old amyloid precursor protein (APP)-presenilin 1 (PS1) mice (Hollnagel et al 2019; Kiss et al 2016, 2020) indicating altered GABAergic inhibition already in the early phase of AD-like pathogenesis
Based on the recently reported findings showing a direct link between gephyrin and the potentially neuroprotective artemisinins (Qiang et al 2018) with both positive (Li et al 2017) and negative (Kasaragod et al 2019) modulation of GABAergic signaling in vitro, we treated APP-PS1 mice with artemisinin to test its possible modulatory effects on the inhibitory drive in the AD-brain
Summary
Alzheimer’s disease (AD) is the most common cause of dementia characterized by progressive loss of memory affecting an increasing number of persons worldwide. Efforts to find curative treatments for AD patients mostly failed so far. This can be assigned at least partially to the still incompletely clarified pathogenesis of the disease and delayed start of therapies (Frozza et al 2018). Mutations in the amyloid precursor protein (APP) and enzymes involved in its processing, e.g., presenilin 1 (PS1) resulting in increased levels of Aβ, were identified as causes of the autosomal dominant, early-onset familial form of AD. The etiology and neurobiological processes that lead to sporadic AD (about 95% of AD cases) are still not completely understood.
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