Ion Channel Transporter Interactions

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ABSTRACT Alzheimer’s disease (AD) is a neurodegenerative disorder that is increasingly prevalent in our aging populations around the world. AD is characterized by the accumulation of Amyloid-β peptide (Aβ)-containing plaques, neurofibrillary tangles, and also worsening cognitive deficits. Compelling evidence suggests that thiamine homeostasis may also be changed in AD. Reduction in thiamine diphosphate (TDP) levels and abnormal functioning of TDP-dependent key enzymes in glucose metabolism occur in the blood and brains of AD patients. Thiamine deficiency exacerbates plaque formation and alters the metabolism of Amyloid Precursor Protein Processing (APP) and/or Aβ in mouse models of AD; many thiamine-dependent processes are diminished in the brains of AD patients. We previously discovered physical interaction of voltage-gated potassium (Kv) channels with various solute transporters. We and other groups have since reported a variety of Kv channel-transporter interactions, both in vitro and in vivo, but their potential role in AD has not been established, neither have complexes of Kv channels with thiamine transporters been reported. We believe that Kv channel-transporter complexes form crucial signaling hubs facilitating tight control over highly dynamic cellular processes, and that their disruption, as we and others have shown, is associated with neurological diseases, and potentially AD. Here, building on recent preliminary data suggestive of interactions between neuronal KCNQ channels and thiamine transporters, we aim to test the hypothesis that KCNQ and/or KCNA Kv channels form reciprocally regulating complexes with the human thiamine transporters THTR-1 and/or THTR-2, which are high-affinity transporters that concentrate thiamine in cells via a downhill proton gradient. We recently demonstrated that brains of AD patients as well as those of 5XFAD (AD model) mice express significantly reduced levels of THTR-1 – building on prior work that demonstrated that thiamine homeostasis is altered in AD, and thiamine deficiency exacerbates AD pathology. In addition, we also found that various Kv channels, including KCNQ2/3, form complexes and co-localize in nodes of Ranvier with the APP early cleavage product C99, altering channel function and in the case of KCNQ2/3 causing channel inhibition. Given these links, we hypothesize that KCNA and KCNQ channels can form physical complexes with thiamine transporters THTR-1 and/or THTR-2 and thus regulate one another’s function, and we will study how they change in AD. In two Specific Aims we will first investigate in vitro existence and functional consequences of channel-transporter complex formation between KCNA, KCNQ Kv channel α subunits and thiamine transporters THTR-1 and/or THTR-2. Next, we will investigate possible changes in expression of neuronal KCNA and KCNQ channel isoforms, and their complex formation with thiamine transporters THTR-1 and/or THTR-2 in different regions of the brains of AD patients and a mouse model of the disease. At the conclusion of this project, we will have established novel channel-transporter complexes and determined whether they are altered or have the potential for a role in the pathogenesis of AD.