Kv1.3 inhibition as a potential microglia-targeted therapy for Alzheimer's disease: preclinical proof of concept

Microglia significantly contribute to the pathophysiology of Alzheimer's disease but an effective microglia-targeted therapeutic approach is not yet available clinically. The potassium channels K(v)1.3 and K(ir)2.1 play important roles in regulating immune cell functions and have been implicated by in vitro studies in the 'M1-like pro-inflammatory' or 'M2-like anti-inflammatory' state of microglia, respectively. We here found that amyloid-beta oligomer-induced expression of K(v)1.3 and K(ir)2.1 in cultured primary microglia. Likewise, ex vivo microglia acutely isolated from the Alzheimer's model 5xFAD mice co-expressed K(v)1.3 and K(ir)2.1 as well as markers traditionally associated with M1 and M2 activation suggesting that amyloid-beta oligomer induces a microglial activation state that is more complex than previously thought. Using the orally available, brain penetrant small molecule K(v)1.3 blocker PAP-1 as a tool, we showed that pro-inflammatory and neurotoxic microglial responses induced by amyloid-beta oligomer required K(v)1.3 activity in vitro and in hippocampal slices. Since we further observed that K(v)1.3 was highly expressed in microglia of transgenic Alzheimer's mouse models and human Alzheimer's disease brains, we hypothesized that pharmacological K(v)1.3 inhibition could mitigate the pathology induced by amyloid-beta aggregates. Indeed, treating APP/PS1 transgenic mice with a 5-month oral regimen of PAP-1, starting at 9 months of age, when the animals already manifest cognitive deficits and amyloid pathology, reduced neuroinflammation, decreased cerebral amyloid load, enhanced hippocampal neuronal plasticity, and improved behavioural deficits. The observed decrease in cerebral amyloid deposition was consistent with the in vitro finding that PAP-1 enhanced amyloid-beta uptake by microglia. Collectively, these results provide proof-of-concept data to advance K(v)1.3 blockers to Alzheimer's disease clinical trials.