APOE4-Expressing Astrocytes Exhibit Parkinson's Disease-Related Pathology.

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Parkinson's disease (PD) is characterized by motor symptoms that are mainly attributed to the progressive loss of dopaminergic neurons of the substantia nigra (SN). It is also characterized by abnormal inclusion vesicles, termed Lewy bodies (LBs), enriched with α-synuclein aggregates that may induce inflammation and neurotoxicity. The possibility that factors involved in other neurodegenerative diseases also affect PD-related pathologies, such as α-synuclein uptake, was examined. The apoe4 allele is a major genetic risk factor for Alzheimer's disease (AD) and has also been suggested to be involved in PD. Here, we examined the effects of APOE isoform expression on α-synuclein uptake and autophagy in astrocytes expressing the apoe3 or apoe4 alleles. Using multiple autophagy manipulations (EBSS, chloroquine, and rapamycin treatments), we found that α-synuclein uptake and autophagy readouts differ between APOE3 and APOE4 astrocytes, supporting a functional link between autophagy status and α-synuclein levels. Astrocytes expressing APOE4 exhibit reduced uptake of α-synuclein and reduced autophagy. Moreover, α-synuclein treatment inhibits autophagy mainly in APOE3-expressing cells. Additional experiments showed that the autophagy inhibitor chloroquine reduced α-synuclein uptake in APOE3 astrocytes but not in APOE4 astrocytes, while the autophagy enhancer rapamycin increased α-synuclein uptake in APOE4-expressing astrocytes. In addition, we found that Toll-like receptor 2 (TLR2) levels are elevated at both the mRNA and protein levels in APOE4-expressing astrocytes, whereas α-synuclein increased only TLR2 mRNA levels in APOE3-expressing astrocytes. Using the neurotoxin 1-methyl-4-phenylpyridinium (MPP+), we found that it affects cell growth in both APOE3 and APOE4-expressing astrocytes. MPP+ treatment also reduced autophagy which was partially corrected by rapamycin. Taken together, these findings show that in astrocytes, APOE4 impairs α-synuclein uptake, which was emended by rapamycin and α-synuclein inhibits autophagy mainly in APOE3. These findings suggest that autophagy-targeting strategies can modulate astrocyte α-synuclein uptake; however, given the observed reductions in astrocyte cell number following rapamycin treatment, further optimization or examination of alternative autophagy modulators is needed.

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