MiR-193a-5p as a Regulator of Intersectin1-short and Clathrin-Mediated Endocytosis in Alzheimer's Disease.

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PROJECT SUMMARY Alzheimer’s disease (AD) is the most common form of dementia and is characterized by the development of amyloid beta (Aβ) plaques and neurofibrillary tangles in the brain. Currently, the pathogenesis underlying AD is unclear and there are no reliable tools to detect early changes in the brain. Studies in the Saugstad lab revealed a specific set of microRNA (miRNA) biomarkers that are decreased in cerebrospinal fluid (CSF), and which can classify AD patients from neurologically normal controls. MiRNAs regulate post-transcriptional gene expression via complementary binding to sequences in mRNA that in turn regulate translation and expression of the resulting protein. However, there is a knowledge gap regarding which mRNAs are targeted and regulated by the AD CSF miRNAs and how these target proteins may contribute to AD pathophysiology. To address this gap, I developed a bioinformatics pipeline to predict mRNA targets of the AD CSF miRNAs, and identified Intersectin1-short (ITSN1-s) as a protein targeted by the AD CSF miRNA, miR-193a-5p. Immunoblot analysis of human post mortem hippocampus showed significant increases in ITSN1-s protein in AD relative to control. However, as ITSN1-s is expressed in multiple brain cell types, further studies that determine the specific cell type(s) with increased ITSN1-s expression in AD are needed to examine potential mechanisms underlying AD. Published studies report that ITSN-s is expressed in astrocytes and microglia, with low expression in neurons, and that ITSN1-s functions to reduce clathrin-mediated endocytosis (CME). Microglia have been shown to uptake fibrillar Aβ through a clathrin-mediated mechanism, and CME disruption in AD has been linked to reduced Aβ clearance in neurons. However, it is not known whether ITSN1-s in microglia contributes to this pathophysiology in AD. This proposal will assess the regulatory role of miR-193a-5p on ITSN1-s and its functional significance in CME and AD. In order to accomplish this, I propose the following aims: 1. establish the cellular expression of miR-193-a-5p and ITSN1-s in AD microglia and neurons; 2. investigate the interaction between miR-193a-5p and ITSN1-s mRNA and the effects on ITSN1-protein expression in vitro and in vivo; and 3. determine the role of miR-193a-5p levels on CME and Aβ uptake in AD microglia. Ultimately, these studies will provide a deeper understanding of ITSN1-s regulation in AD and how this may contribute to AD pathology. In addition, this framework can be used in future studies to evaluate the biological consequences of circulating miRNA biomarkers in AD.