A positive feedback loop between chronic lysosomal dysfunction and circRNAs in Alzheimer’s disease mouse models
Skarleth Cardenas Romero1, Abdallah Etelee2, Niko Nikane2, Kevin O'Dell3, Marie Roberts3, Oscar Harari2, John Cirrito4, Mark Sands3, Bruno A. Benitez1
1Neurology, BIDMC/Harvard Medical School, 2Psychiatry, 3Medicine, 4Neurology, Washington University
Objective:
To test whether CLD affects circRNAs levels impacting the amyloid (Aβ) generation/accumulation in the 5xFAD mice model.
Background:
In 2019, a whole-transcriptome identified several circular RNAs (circRNAs) associated with cognitive scores and neuropathological hallmark of AD. Cerebrospinal and plasma circRNA levels has been proposed as AD biomarkers. circRNAs are highly expressed in the nervous system and enriched in synapses. The most well-established role of circRNAs is transcript regulation through microRNA (miRNA) sequestration, thus, circRNAs participate in regulation of key components of the endolysosomal pathways. Genetic studies suggest that endolysosomal dysfunction contributes to AD. However, the role of circRNAs downstream of chronic lysosomal dysfunction (CLD) and AD is poorly understood.
Design/Methods:
Five groups of transgenic mice [5xFAD, PPT1+/-, 5xFAD:PPT1+/- (P5X), Naglu+/-, 5xFAD:Naglu+/- (N5X)] were used to assess the circRNA expression profile in the brain cortex by bulk RNA sequencing. The insoluble Aβ-40 and Aβ-42 were quantified by ELISA in the hippocampal fraction. The brain Aβ plaque load was quantified using immunohistochemistry.
Results:
The P5X and N5X mice exhibit increased hippocampal amyloid plaque load, Aβ-40, and Aβ-42 insoluble levels in the hippocampus, and reduced lifespan compared to 5xFAD mice. The levels of circAdam10, circPan3, circMbtd1, circ4930402H24Rik, circSt6gal2, and circCdc14b were reduced, while circZranb1 and circMyo9a were increased in P5X and N5X compared with 5xFAD. In silico analyses show amyloidogenic-related microRNAs exhibit circRNAs binding sites. miR-361-3p has binding sites for circZranb1 and circADAM10. It has been demonstrated that miR-361-3p traps and inhibits BACE1 function and Aβ production. CircPan3 regulates the levels of autophagy-related miR-421. Experimental evidence shows that overexpression of circPan3 suppresses autophagy and alleviates apoptosis through miR-421/Pink1 pathway.
Conclusions:
CLD-induced differential changes in circRNAs levels could contribute to AD by affecting APP processing machinery or regulating autophagy. The circPAN3-miR-421-Pink1 axis and circZranb1-miR-361-3p-BACE1 as regulatory networks could be therapeutic targets for AD.