GFAP Mutations in Astrocytes Impair Oligodendrocyte Progenitor Proliferation and Myelination in an hiPSC Model of Alexander Disease

Abstract

Alexander disease (AxD) is a leukodystrophy that primarily affects astrocytes and is caused by mutations in the astrocytic filament gene GFAP. While astrocytes are thought to have important roles in controlling myelination, AxD animal models do not recapitulate critical myelination phenotypes and it is therefore not clear how AxD astrocytes contribute to leukodystrophy. Here, we show that AxD patient iPSC-derived astrocytes recapitulate key features of AxD pathology such as GFAP aggregation. Moreover, AxD astrocytes inhibit proliferation of human iPSC-derived oligodendrocyte progenitor cells (OPCs) in co-culture and reduce their myelination potential. CRISPR/Cas9-based correction of GFAP mutations reversed these phenotypes. Transcriptomic analyses of AxD astrocytes and postmortem brains identified CHI3L1 as a key mediator of AxD astrocyte-induced inhibition of OPC activity. Thus, this iPSC-based model of AxD not only recapitulates patient phenotypes not observed in animal models, but also reveals mechanisms underlying disease pathology and provides a platform for assessing therapeutic interventions.

Stem cell derived oligodendrocytes to study myelin diseases

“…iPSC derived A and OL In vitro (Li et al, 2018) PMD: Oligodendrocytes with PLP1 missense mutation exhibit accumulation of PLP1 protein in ER, ER stress, increased apoptosis, and reduced myelinogenic capacity.…”

“…Interestingly, in co‐culture assays AD astrocytes impair oligodendroglial proliferation and myelination. Transcriptomic analyses of AD astrocytes and brain tissue samples identified CHI3L1 as one factor contributing to impaired oligodendroglial functions and thereby as a new potential drug target (Li et al, ).…”

“…Transcriptomic analyses of AD astrocytes and brain tissue samples identified CHI3L1 as one factor contributing to impaired oligodendroglial functions and thereby as a new potential drug target (Li et al, 2018).…”

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

“…The most conventional approach, 3D generation and maintenance, has become the standard method on which the majority of subsequent protocols have been based, including significant portions of direct conversion methods (Juopperi et al, 2012;Krencik & Zhang, 2011;Mormone, D'Sousa, Alexeeva, Bederson, & Germano, 2014). Finally, direct conversion through TF expression significantly decreases the induction protocols length but stands as a relatively new and unexplored approach (Caiazzo et al, 2014;Canals et al, 2018;Li, Tao, et al, 2018;Li, Tian, et al, 2018;Tchieu et al, 2019).…”

“…These mutations cause the formation of intracellular aggregates called Rosenthal fibers that are thought to cause astrocyte toxicity through toxic gain of function (Prust et al, 2011). This is sufficient to induce neurodegeneration in patients affected by AxD (Li, Tao, et al, 2018;Li, Tian, et al, 2018). Many mouse models have been developed to recapitulate this disorder (Hagemann et al, 2005;Messing et al, 1998), however none of them show a complete array of all the main characteristic of the disease.…”