Changes in Water Channel Localization to Astrocytic Endfeet with Aging

Oregon Health & Science University, Portland OR

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Abstract

Project Summary Alzheimer's disease (AD) is an age-linked neurodegenerative disease that is the leading cause of dementia and 6th leading cause of death in the United States. It is characterized pathologically by the accumulation of amyloid ? (A?) peptides. In the healthy brain, several mechanisms facilitate clearance of A? prior to pathogenic accumulation. The function of these clearance mechanisms deteriorates as an individual ages. To develop effective therapeutic strategies for patients with AD, it is important to understand the mechanisms that drive A? clearance, and the source of their dysfunction in the aged brain. Previous research has shown that the recently described glymphatic system is one such mechanism involved in A? clearance that also demonstrates age-linked dysfunction. Proper glymphatic function relies on mixing of cerebrospinal spinal fluid (CSF) with interstitial fluid (ISF) along perivascular spaces throughout the brain. This process is mediated by water flux across astrocytes that ensheathe the brain vasculature. The water channel aquaporin-4 (AQP4) supports this water flux, and is highly localized to perivascular astrocytic endfeet in the healthy brain, but loses this localization in the aging brain and with AD status. Recent research has shown that in a transgenic mouse model of AD, deletion of the Aqp4 gene in mice increases A? plaque accumulation and worsens cognitive impairment. In aging mice and humans with AD, while overall expression of AQP4 is maintained, perivascular AQP4 localization is lost. Importantly, whether the loss of endfoot localization of AQP4 seen in the aging brain promotes accumulation of A? in a similar manner to that seen in Aqp4 knockout mice is not known. The goal of this proposal is to determine the role that loss of perivascular AQP4 localization plays in A? accumulation, and identify cellular mechanisms that contribute to the regulation of AQP4 perivascular localization and break down in the aging brain. In Aim 1, I will assess the effect of loss of perivascular localization on A? clearance using a mouse model that features both a lack of perivascular AQP4 localization and spontaneous A? plaque formation. In Aim 2 of the proposal I will investigate whether changes in dystrophin associated complex proteins regulate perivascular AQP4 localization in the aging brain, and how loss of their expression impacts A? plaque burden. In Aim 3 I will investigate a second candidate regulatory mechanism for AQP4 localization, the expression of alternate AQP4 isoforms using an astrocyte-specific viral overexpression paradigm to isolate the role of each AQP4 isoform. This study will be the first to define the consequences of age-linked loss of astrocytic perivascular AQP4 localization. Additionally it will be one of the first to examine the mechanisms underlying changes in perivascular AQP4 localization in vivo. The results of this study will provide insight into AQP4 as a potential therapeutic target for AD and other neuropathologies that demonstrate an accumulation of protein aggregates including Parkinson's and Huntington's disease.