The Effect of APOE Genotype on Endolysosomal Dynamics in Neurons.

Background: APOE genotype is known as the most important genetic risk factor for developing AD. Understanding the cellular differences between the ApoE isoforms will be crucial for understanding the fundamental pathways that are disrupted in AD and potential pathways that can be therapeutically targeted. Accumulating evidence is suggesting that ApoE isoforms influence the endosomal system, one of the earliest sites affected in AD. However, our understanding of how the isoforms affect the endolysosomal pathway is still limited. We aim to understand how ApoE isoforms affect the endosomal pathway, but also understand the dynamics of the system in the context of ageing and activity. Method: To study cellular changes in neurons we are using primary hippocampal/cortical brain cultures, harvested from ApoE KO mice and targeted replacement mice, expressing human ApoE3 or ApoE4. Neurons in culture have accelerated maturation and with time in culture gradually show signs of age‐like stress. To study ApoE in the context of ageing, mature cultures at 18 days in vitro (DIV18) and more aged cultures at DIV25 were used. To explore how ApoE isoforms adapt to elevated activity DIV18 primary cultures were treated for 48 H with the GABA receptor antagonist bicuculline. Result: Our preliminary data suggests that especially early endosomes are affected in ApoE4 neurons. Interestingly, the appearance of the early endosomes seems to differ depending on both the intracellular localization and time in culture. However, the protein level of the early endosomal marker EEA1 remained unaltered in ApoE4. In addition, preliminary data indicate that ApoE4 has reduced capacity to adjust the endosomal system following 48 hours bicuculline treatment. When studying the trafficking of fluorescently tagged EGF (which has an established endolysosomal route), preliminary results show potential differences between both DIV18 and DIV25 but also between ApoE‐isoforms, suggesting that both time in culture and ApoE isoforms influence endolysosomal trafficking. Conclusion: The endolysosomal pathway is a highly dynamic and important system for all cells, including neurons and is increasingly linked to AD. Our preliminary findings point toward an ApoE isoform effect on endosomal trafficking and that its dynamics might be disrupted by ApoE4. [ABSTRACT FROM AUTHOR]