Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, WI, 53706, USA.
Department of Neurological Surgery, University of Wisconsin-Madison, Madison, WI, USA.
Fluids Barriers CNS. 2024 Oct 11;21(1):79. doi: 10.1186/s12987-024-00580-2.
Three common isoforms of the apolipoprotein E (APOE) gene - APOE2, APOE3, and APOE4 - hold varying significance in Alzheimer's Disease (AD) risk. The APOE4 allele is the strongest known genetic risk factor for late-onset Alzheimer's Disease (AD), and its expression has been shown to correlate with increased central nervous system (CNS) amyloid deposition and accelerated neurodegeneration. Conversely, APOE2 is associated with reduced AD risk and lower CNS amyloid burden. Recent clinical data have suggested that increased blood-brain barrier (BBB) leakage is commonly observed among AD patients and APOE4 carriers. However, it remains unclear how different APOE isoforms may impact AD-related pathologies at the BBB.
To explore potential impacts of APOE genotypes on BBB properties and BBB interactions with amyloid beta, we differentiated isogenic human induced pluripotent stem cell (iPSC) lines with different APOE genotypes into both brain microvascular endothelial cell-like cells (BMEC-like cells) and brain pericyte-like cells. We then compared the effect of different APOE isoforms on BBB-related and AD-related phenotypes. Statistical significance was determined via ANOVA with Tukey's post hoc testing as appropriate.
Isogenic BMEC-like cells with different APOE genotypes had similar trans-endothelial electrical resistance, tight junction integrity and efflux transporter gene expression. However, recombinant APOE4 protein significantly impeded the "brain-to-blood" amyloid beta 1-40 (Aβ40) transport capabilities of BMEC-like cells, suggesting a role in diminished amyloid clearance. Conversely, APOE2 increased amyloid beta 1-42 (Aβ42) transport in the model. Furthermore, we demonstrated that APOE-mediated amyloid transport by BMEC-like cells is dependent on LRP1 and p-glycoprotein pathways, mirroring in vivo findings. Pericyte-like cells exhibited similar APOE secretion levels across genotypes, yet APOE4 pericyte-like cells showed heightened extracellular amyloid deposition, while APOE2 pericyte-like cells displayed the least amyloid deposition, an observation in line with vascular pathologies in AD patients.
While APOE genotype did not directly impact general BMEC or pericyte properties, APOE4 exacerbated amyloid clearance and deposition at the model BBB. Conversely, APOE2 demonstrated a potentially protective role by increasing amyloid transport and decreasing deposition. Our findings highlight that iPSC-derived BBB models can potentially capture amyloid pathologies at the BBB, motivating further development of such in vitro models in AD modeling and drug development.
载脂蛋白 E（APOE）基因的三种常见同工型 - APOE2、APOE3 和 APOE4 - 在阿尔茨海默病（AD）风险中具有不同的意义。APOE4 等位基因是已知的导致晚发性阿尔茨海默病（AD）最强的遗传风险因素，其表达与中枢神经系统（CNS）淀粉样蛋白沉积增加和神经退行性变加速相关。相反，APOE2 与 AD 风险降低和 CNS 淀粉样蛋白负担降低有关。最近的临床数据表明，AD 患者和 APOE4 携带者中常见血脑屏障（BBB）渗漏增加。然而，不同的 APOE 同工型如何影响 AD 相关的 BBB 病理学仍不清楚。
为了探讨 APOE 基因型对 BBB 特性和 BBB 与β淀粉样蛋白相互作用的潜在影响，我们将具有不同 APOE 基因型的同源人诱导多能干细胞（iPSC）系分化为脑微血管内皮细胞样细胞（BMEC 样细胞）和脑周细胞样细胞。然后，我们比较了不同 APOE 同工型对 BBB 相关和 AD 相关表型的影响。通过适当的 ANOVA 与 Tukey 事后检验确定统计学意义。
具有不同 APOE 基因型的同源 BMEC 样细胞具有相似的跨内皮电阻、紧密连接完整性和外排转运体基因表达。然而，重组 APOE4 蛋白显著阻碍了 BMEC 样细胞的“脑-血”β淀粉样蛋白 1-40（Aβ40）转运能力，表明其在减少淀粉样蛋白清除方面发挥作用。相反，APOE2 增加了模型中的β淀粉样蛋白 1-42（Aβ42）转运。此外，我们证明了 BMEC 样细胞中 APOE 介导的淀粉样蛋白转运依赖于 LRP1 和 p-糖蛋白途径，与体内发现一致。各基因型的周细胞样细胞 APOE 分泌水平相似，但 APOE4 周细胞样细胞表现出更高的细胞外淀粉样蛋白沉积，而 APOE2 周细胞样细胞显示出最少的淀粉样蛋白沉积，这与 AD 患者的血管病理学一致。
尽管 APOE 基因型并未直接影响一般的 BMEC 或周细胞特性，但 APOE4 加剧了模型 BBB 中的淀粉样蛋白清除和沉积。相反，APOE2 通过增加淀粉样蛋白转运和减少沉积显示出潜在的保护作用。我们的发现强调了 iPSC 衍生的 BBB 模型可以潜在地捕获 BBB 中的淀粉样蛋白病理学，从而促使进一步开发此类 AD 建模和药物开发中的体外模型。
