Effects of miR-7 on Tau Expression

Student: Erika Beyrent
Mentor: Suren Ambegaokar (OWU Department of Botany & Microbiology, Neuroscience Program)

In patients with Alzheimer’s disease, the protein tau is overly abundant, is modified differently than normal tau proteins, and forms clumps with other tau proteins. This project may uncover a gene that could play a role in controlling the levels of tau, which may help in understanding or even mitigating Alzheimer disease.

Abnormal expression of the microtubule-associated protein tau (MAPT) has been shown to play a role in neurodegenerative disorders. In individuals with neurodegenerative disorders, including Alzheimer’s disease and Parkinson’s disease, aggregates of MAPT have commonly been identified. Previous research in our lab has shown that co-expression of tau with microRNA-7 (miR-7) in transgenic fruit flies (Drosophila) results in repression of tau protein expression. Thus, we wished to investigate if there was a direct interaction between miR-7 and MAPT. Human embryonic kidney (HEK) cells were transfected with plasmids containing MAPT, and co-transfected with plasmids containing miR-7 or a control microRNA. All MAPT plasmids were tagged with a red-fluorescent protein (mCherry or DsRed), and all miR-7 or control microRNA plasmids co-expressed a green fluorescent protein (GFP). This allowed evaluation of MAPT expression by measuring levels of red fluorescence in cells double-labeled for red and green fluorescence. MAPT expression was reduced by 29% when co-expressed with miR-7, as compared to control microRNA co-expression or MAPT expression without co-transfection, indicating a possible direct interaction between miR-7 and MAPT transcript. MAPT plasmids were then mutated via site-directed mutagenesis at 1 of the predicted 8 binding sites for miR-7. Expression of the mutated tau plasmid was reduced by 27%-43% when co-expressed with miR-7, compared to expression of the mutated tau plasmid alone. These results suggest that miR-7 specifically binds to the MAPT transcript to inhibit expression, but not at the binding site we tested. Our future studies will focus on testing the remaining 7 binding sites for miR-7 on the MAPT transcript.