Abeta and Tau impair retromer‐mediated cargo trafficking via distinct mechanisms

Abstract

AbstractBackgroundEvidence from neuronal pathology and experimental models suggest that endolysosomal dysfunction may contribute to Alzheimer’s Disease (AD) pathogenesis, however it is unclear how Aβ and Tau directly affect endolysosomal dynamics, partially due to a lack of reporters. The retromer, including VPS35, VPS26, and VPS29, is a conserved protein complex responsible for recycling proteins within the endolysosomal pathway. Retromer regulates Tau phosphorylation and pathogenic processing of the amyloid precursor protein. Cation‐independent Mannose 6‐phosphate receptor (CIMPR) is a well‐established retromer cargo, with a WLM motif recognized by the retromer for retrieval.MethodTo track retromer‐dependent protein trafficking in vivo, I have cloned the cytoplasmic tail of CIMPR carrying the WLM motif into a pUAST‐attb vector and generated a transgenic fly line (UAS‐CIMPR‐WLM). A transgenic line carrying CIMPR, but having WLM mutated to AAA, has also been developed as a negative control (UAS‐CIMPR‐AAA). I examined the CIMPR reporter in Vps35 and Vps29 mutants, as well as established Drosophila AD models during aging.ResultThe protein level of CIMPR‐WLM was reduced by genetic ablation of Vps35, possibly due to promoted degradation. Expressed in young Vps29 mutant brains, CIMPR‐WLM showed an increased colocalization with a late endosomal/lysosomal marker Arl8, indicating a promoted delivery of retromer cargoes into the lysosome. Further, neuronal expression of CIMPR‐WLM exhibited a punctate distribution, which was abolished when WLM was mutated to AAA. Altogether, my data suggested that CIMPR‐WLM worked as a retromer‐dependent reporter. While the reporter was broadly enriched within neuropil regions in control animals (Elav>CIMPR), neuronally expression of Aβ (Elav> Aβ+CIMPR) led to a striking redistribution of CIMPR, shifting from neuropil to enrichment in soma, and forming large perinuclear puncta. Moreover, the retromer reporter was mislocalized in brains from 1‐day‐old Elav> Aβ animals, and this result did not significantly change with aging. Interestingly, Elav>Tau+CIMPR animals showed no noticeable effects on the distribution of CIMPR‐WLM on day 1, but caused a similar redistribution of CIMPR‐WLM to the perinuclei region at day 30.ConclusionThe CIMPR‐WLM reporter requires the retromer for proper cellular localization. Our findings are consistent with the notion that Aβ and Tau affect endosomal sorting, but likely via distinct mechanisms.