Research ArticleNEURODEGENERATIVE DISEASES

APOE genotype regulates pathology and disease progression in synucleinopathy

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Science Translational Medicine  05 Feb 2020:
Vol. 12, Issue 529, eaay3069
DOI: 10.1126/scitranslmed.aay3069

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APOE4 beyond amyloid

Although several genetic risk factors for neurodegenerative disorders have been identified, often the mechanistic aspect is not clear. Now, Zhao et al. and Davis et al. investigated whether apolipoprotein E4 (APOE4) genotype, a major risk factor for neurodegenerative diseases, affected α-synuclein pathology in mouse models and Parkinson’s disease (PD) patients. Zhao et al. generated a mouse model of α-synucleinopathy and showed that APOE4 exacerbated α-synuclein pathology independent of amyloid. Davis et al. used mouse models of α-synucleinopathy and analyzed cognition in patients with PD to demonstrate that APOE4 directly regulated α-synuclein pathology and was associated with faster cognitive decline. These results provide insight into the mechanisms linking APOE genotype to neurodegenerative disorders.

Abstract

Apolipoprotein E (APOE) ε4 genotype is associated with increased risk of dementia in Parkinson’s disease (PD), but the mechanism is not clear, because patients often have a mixture of α-synuclein (αSyn), amyloid-β (Aβ), and tau pathologies. APOE ε4 exacerbates brain Aβ pathology, as well as tau pathology, but it is not clear whether APOE genotype independently regulates αSyn pathology. In this study, we generated A53T αSyn transgenic mice (A53T) on Apoe knockout (A53T/EKO) or human APOE knockin backgrounds (A53T/E2, E3, and E4). At 12 months of age, A53T/E4 mice accumulated higher amounts of brainstem detergent-insoluble phosphorylated αSyn compared to A53T/EKO and A53T/E3; detergent-insoluble αSyn in A53T/E2 mice was undetectable. By immunohistochemistry, A53T/E4 mice displayed a higher burden of phosphorylated αSyn and reactive gliosis compared to A53T/E2 mice. A53T/E2 mice exhibited increased survival and improved motor performance compared to other APOE genotypes. In a complementary model of αSyn spreading, striatal injection of αSyn preformed fibrils induced greater accumulation of αSyn pathology in the substantia nigra of A53T/E4 mice compared to A53T/E2 and A53T/EKO mice. In two separate cohorts of human patients with PD, APOE ε4/ε4 individuals showed the fastest rate of cognitive decline over time. Our results demonstrate that APOE genotype directly regulates αSyn pathology independent of its established effects on Aβ and tau, corroborate the finding that APOE ε4 exacerbates pathology, and suggest that APOE ε2 may protect against αSyn aggregation and neurodegeneration in synucleinopathies.

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