RNA modifications leading to pathophysiological translation of circRNAs in AD

Summary In response to “Deciphering the Impact of RNA Modifications on Brain Aging and AD/ADRD (RFA-AG-25- 022)”, we will investigate the role of RNA modifications on the translation of circular RNAs in Alzheimer’s disease (AD). Circular RNAs (circRNAs) are cytosolic and metabolically stable, allowing them to accumulate RNA modifications. We reported that during AD progression in entorhinal cortex the deamination of adenosines to inosines (A>I modification) of circular RNAs correlates with Braak stages, i.e. AD severity, which was not observed for mRNA. We also found that A>I modification result in the translation of circRNAs formed by the MAPT (microtubule associated protein tau) gene. The circRNA-encoded proteins promote aggregation of tau protein. We found a similar role of RNA modification in the translation of circRNAs from the amyloid precursor protein (APP) and presenlin1 (PSEN1) genes. We thus hypothesize that during AD progression, circRNAs undergo increasing A>I modification, resulting in their translation, generating proteins that promote tau aggregation. Other modifications, like m6A, can interfere with, or augment the translation of inosine-containing circRNAs. This central hypothesis will be tested in three specific aims where we: (#1) Determine the mechanism of inosine mediated translation of AD-relevant circular RNAs, postulating that vigilin/HDLBP is an inosine reader promoting circRNA translation. We will further test the effect of AD-relevant RNA modifications on circRNA translation. We will next (#2) Determine the pathogenetic relevance of modification-dependent circRNA translation in human brain, where we use human brain tissue, RNAseq and nanopore sequencing, polysome preparations and our circRNA- specific antisera to correlate circRNA modifications with circRNA translation and AD pathogenesis. Functionally, (#3) we will Determine the role of circRNA encoded proteins in tau aggregation and test siRNA interventions, testing the contribution of eIF4B, a protein that specifically interacts with circTau-encoded proteins and determining the contribution of circAPP and circPSEN1-encoded proteins to tau aggregation. This work is highly innovative, testing the role of A>I modification in circular RNA translation, which could unveil a new proteome in AD. The studies are significant for AD, as the circRNA encoded proteins represent new factors in AD, possibly contributing to tau pathology. The work is feasible as circRNAs were shown to be translated in human brain. This work is possible through a collaboration between an RNA biologist (Stamm, PI), a specialist for translation (Wen, Co-I) and a world-known dementia neuropathologist heading the brain bank (Nelson, Co-I), who already published together.