Introduction:

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by cognitive decline and memory loss, with the accumulation of amyloid-beta (Aβ) plaques as a pathological hallmark. The ε4 allele of apolipoprotein E (APOE4) is the strongest genetic risk factor for late-onset AD, known to exacerbate Aβ aggregation and clearance deficits. While neuronal-centric models dominate, growing evidence implicates broader cellular dysfunction, including compromised white matter integrity and myelin loss, in AD progression. Myelin, produced by oligodendrocytes (OLs), is maintained by oligodendrocyte precursor cells (OPCs). Both Aβ toxicity and APOE4-related pathways have been independently linked to disrupted OPC function and myelination (1-3). It has been reported that Amyloid-β inhibits OPC proliferation and differentiation both in vitro and in vivo; factors such as BDNF rescue amyloid-β-induced OPC toxicity (1). Our lab has previously shown that iPSC-derived ECs (iPSC-EC) rescue OPC from TNF-a induced cell death and promote OPC proliferation and differentiation (2). Recent evidence of APOE4 inducing a toxic gain of function in iPSC-derived ECs, suggests they may contribute to drive a toxic milieu, alongside the Aβ toxicity (3). The present research aims to examine weather ECs carrying the APOE4 genotype exacerbate Aβ-induced deficits in OPC maturation and confirm that healthy parental controls carrying APOE3 genetoype have a positive protective effect. Building from that, the study aims to identify potential underlying molecular mechanisms.

 

Methods:

Using an in vitro co-culture system, rat primary OPCs were exposed to oligomeric Aβ1-42 and co-cultured with isogenic human induced pluripotent stem cell-derived ECs (iPSC-ECs) of either the protective APOE3/3 or the risk-associated APOE4/4 genotype. OPC differentiation was assessed by immunocytochemistry for the mature oligodendrocyte markers Olig2 and MBP (n=3 independent experiments). mTORC1 pathway activation was evaluated by quantifying phosphorylated ribosomal protein S6 (pS6) in Olig2+ cells. Data were analysed using one-way ANOVA with Kruskal-Wallis post-hoc tests.

 

Results:

We report that Aβ1-42 exposure significantly impaired OPC differentiation, reducing the proportion of Olig2+MBP+ cells compared to control conditions (p<.001). Co-culture with APOE3/3 iPSC-ECs completely rescued this deficit (p<.05 vs. Aβ alone). In contrast, co-culture with APOE4/4 iPSC-ECs failed to confer protection, with OPC maturation remaining significantly impaired (p<.01 vs. vehicle control). Mechanistically, Aβ toxicity combined with APOE4/4 EC co-culture induced a pathological hyperactivation of the mTORC1 pathway, evidenced by a significant increase in the proportion of pS6+Olig2+ cells compared to all other conditions (p<0.001). This is in line with previous reports of mTORC1 hyperactivation in ageing and offers novel context for potential disease mechanisms.

 

Conclusion:

These findings demonstrate that APOE4 confers a toxic gain-of-function in endothelial cells, transforming them from protective bystanders into active contributors to Aβ-induced OPC dysfunction. The loss of protection is associated with aberrant mTORC1 signalling in OPCs, revealing a critical disruption of the OPC-EC communication axis. Future work will focus on further elucidating this critical axis of OPC-EC communication that could be targeted to preserve white matter integrity in AD, particularly in high-risk APOE4 carriers.

 

Ethical Standards: All experiments involving primary rat cells were conducted in accordance with relevant institutional and national guidelines and UK legislation. Animals were humanely treated and where relevant humanely killed.