Distinct responses of neurons and astrocytes to TDP-43 proteinopathy in amyotrophic lateral sclerosis

Abstract

Amyotrophic lateral sclerosis (ALS) is a fatal and incurable neurodegenerative disease caused by motor neuron loss, resulting in muscle wasting, paralysis and eventual death. A key pathological feature of ALS is cytoplasmically mislocalized and aggregated TDP-43 protein in >95% of cases, which is considered to have prion-like properties. Historical studies have predominantly focused on genetic forms of ALS, which represent ∼10% of cases, leaving the remaining 90% of sporadic ALS relatively understudied. Additionally, the role of astrocytes in ALS and their relationship with TDP-43 pathology is also not currently well understood. We have therefore used highly enriched human induced pluripotent stem cell (iPSC)-derived motor neurons and astrocytes to model early cell type-specific features of sporadic ALS. We first demonstrate seeded aggregation of TDP-43 by exposing human iPSC-derived motor neurons to serially passaged sporadic ALS post-mortem tissue (spALS) extracts. Next, we show that human iPSC-derived motor neurons are more vulnerable to TDP-43 aggregation and toxicity compared with their astrocyte counterparts. We demonstrate that these TDP-43 aggregates can more readily propagate from motor neurons into astrocytes in co-culture paradigms. We next found that astrocytes are neuroprotective to seeded aggregation within motor neurons by reducing (mislocalized) cytoplasmic TDP-43, TDP-43 aggregation and cell toxicity. Furthermore, we detected TDP-43 oligomers in these spALS spinal cord extracts, and as such demonstrated that highly purified recombinant TDP-43 oligomers can reproduce this observed cell-type specific toxicity, providing further support to a protein oligomer-mediated toxicity hypothesis in ALS. In summary, we have developed a human, clinically relevant, and cell-type specific modelling platform that recapitulates key aspects of sporadic ALS and uncovers both an initial neuroprotective role for astrocytes and the cell type-specific toxic effect of TDP-43 oligomers.

FUS is lost from nuclei and gained in neurites of motor neurons in a human stem cell model of VCP-related ALS

“…This is challenging to study in tissue sections as the arborization of processes is largely lost during sectioning. To address this issue, we used our established directed differentiation protocol to generate highly enriched spinal motor neurons from hiPSCs, which has previously been extensively validated for cellular identity and functionality ( Hall et al , 2017 ), together with its ability to faithfully recapitulate ALS phenotypes ( Luisier et al , 2018 ; Tyzack et al , 2019 ; Smethurst et al , 2020 ).…”

Rising Stars: Astrocytes as a Therapeutic Target for ALS Disease

“…In contrast, healthy astrocytes protect MNs. Recent study provides evidence for the beneficial role that astrocytes play in protecting MNs in ALS (Smethurst et al, 2020). In this study, the authors first demonstrated that iPSC-derived MNs are more vulnerable to seeded TDP-43 aggregation (extracted from sALS post-mortem spinal-cord) than iPSC-derived astrocytes, indicating a cell-type-specific difference in vulnerability.…”

“…Intriguingly, the addition of astrocyte-condition-media alone to iPSC-derived MNs, pre-exposed to TDP-43 aggregates, had similar effects on MN. Lastly, the authors demonstrated that highly purified recombinant TDP-43 oligomers reproduced the observed celltype-specific toxicity (Smethurst et al, 2020).…”

Glia in Neurodegeneration: The Housekeeper, the Defender and the Perpetrator

“…Together, these studies demonstrate the power of co-culture for gaining insight into the role of glial cells in the early cellular pathogenesis of AD. Similar effects have been unraveled for a number of neurodegenerative diseases, including ALS [109,117,118], PD [119], and HD [120]. Microglia add an additional dimension to neurodegenerative disease modeling in vitro and can be incorporated into embryoid bodies or other 3D culturing methods to create combined systems.…”

“…The ALS-associated superoxide dismutase 1 (SOD1) mutation specifically dysregulates the neuroprotective EphB1-ephrin-B1-STAT3 signaling pathway in human iPSC-derived astrocytes, while leaving the IL-6 responsive activity of STAT3 intact. This finding indicates a molecular pathway that imparts increased risk for ALS through an astrocytic cell autonomous mechanism [108,109]. Uncovering molecular mechanisms of disease pathogenesis in glial cells like this both broadens our understanding of the non-cell autonomous contributions to neural degeneration and reveals key glial vulnerable pathways that may be targeted to delay disease onset ( Figure 1C).…”