APOE ε4/ε4 diminishes neurotrophic function of human iPSC-derived astrocytes

Abstract

The ε4 allele of the APOE gene encoding apolipoprotein E (apoE) is a strong genetic risk factor for aging-related cognitive decline as well as late-onset Alzheimer's disease (AD) compared to the common ε3 allele. In the central nervous system, apoE is produced primarily by astrocytes and functions in transporting lipids including cholesterol to support neuronal homeostasis and synaptic integrity. Although mouse models and corresponding primary cells have provided valuable tools for studying apoE isoform-dependent functions, recent studies have shown that human astrocytes have a distinct gene expression profile compare with rodent astrocytes. Human induced pluripotent stem cells (iPSCs) derived from individuals carrying specific gene variants or mutations provide an alternative cellular model more relevant to humans upon differentiation into specific cell types. Thus, we reprogramed human skin fibroblasts from cognitively normal individuals carrying APOE ε3/ε3 or ε4/ε4 genotype to iPSC clones and further differentiated them into neural progenitor cells and then astrocytes. We found that human iPSC-derived astrocytes secreted abundant apoE with apoE4 lipoprotein particles less lipidated compared to apoE3 particles. More importantly, human iPSC-derived astrocytes were capable of promoting neuronal survival and synaptogenesis when co-cultured with iPSC-derived neurons with APOE ε4/ε4 astrocytes less effective in supporting these neurotrophic functions than those with APOE ε3/ε3 genotype. Taken together, our findings demonstrate APOE genotype-dependent effects using human iPSC-derived astrocytes and provide novel evidence that the human iPSC-based model system is a strong tool to explore how apoE isoforms contribute to neurodegenerative diseases.

Addressing variability in iPSC-derived models of human disease: guidelines to promote reproducibility

“…In pursuit of more accurate modelling of human tissue, co-culture systems consisting of multiple iPSC-derived disease-affected cell types (Zhao et al, 2017;Shi et al, 2013;Odawara et al, 2014), three-dimensional (3D) cultures (Choi et al, 2014) and 3D coculture organoids (Skardal et al, 2016) have recently been used to recapitulate tissue-level and organ-level dysfunction, whereby the pathology progresses through the interactions between different cell types. However, although these approaches can ameliorate some of the drawbacks of iPSC-based models such as reduced cell maturity, incomplete disease phenotypes and line-to-line variation (Ghaffari et al, 2018), these limitations still need to be effectively addressed to be able to work with patient-derived cells in a high-standard, reproducible and controlled environment.…”

An update on human astrocytes and their role in development and disease

“…Independently from Aβ, astrocytes derived from AD patients as well as AD mouse models have shown a variety of metabolic impairment such as: oxidative stress, reduced lactate secretion (Abramov et al, ; Oksanen et al, ), and insufficient clearance of glutamate, which contributes to enhanced glutamate signaling (Merlini, Meyer, Ulmann‐Schuler, & Nitsch, ; Talantova et al, ; Tian, Kong, Lai, Ray‐Chaudhury, & Lin, ). Furthermore, astrocytes carrying mutations in genes associated with familial AD induce defective synapse formation, resulting in reduced neuron survival when cocultured with healthy neurons (Zhao et al, ). It has also been shown that post mortem AD human brains present a higher expression of Cx43, a connexin involved in gap junction formation.…”

“…For instance, 9‐month‐old mice coexpressing ApoE4 and mutant‐tau present astrocytic activation as well as enhanced neurodegeneration compared to wild type or tau only expressing mice (Shi et al, ). Furthermore, astrocytes differentiated from hiPSCs carrying ApoE4 have been shown to be less effective in supporting neurons compared to those expressing the ApoE3 isoform (Zhao et al, ). These studies suggest that astrocytes could play a specific role in the ApoE4 dependent neurodegeneration, however, further studies are required in order to confirm this hypothesis as ApoE has also been reported to be expressed in microglia and even neurons during disease progression (Arranz & De Strooper, ).…”

Relação Entre O Polimorfismo Da Apolipoproteína E E Os Aspectos Da Obesidade, Perfil Lipídico E Atividade Física

“…Alguns outros órgãos podem produzí-la, como é o caso do baço, rins e as glândulas supra-renais (NASCIMENTO et al, 2012). A ApoE no SNC liga-se a lipídios que foram gerados pela degeneração neuronal e trabalha na redistribuição para células que necessitam de lipídios para se proliferar, reparar as membranas ou remielinizar axônios novos (NASSIF et al, 2005;ZHAO et al, 2017;BRANDON et al, 2018).…”

“…A localização do gene ApoE ocorre no cromossomo 19, no braço longo, na posição 13,2, demonstra polimorfismo alélico em três frequências principais denominadas épsilon três (ε3), épsilon quatro (ε4) e épsilon dois (ε2). Dentre esses alelos podem-se formar seis genótipos, sendo três heterozigóticos (ε2/3, ε2/4 e ε3/4) e os outros três homozigóticos (ε2/2, ε3/3 e ε4/4) (HUEBBE; RIMBACH, 2017;ZHAO et al, 2017).…”