Mature iPSC-derived astrocytes of an ALS/FTD patient carrying the TDP43A90V mutation display a mild reactive state and release polyP toxic to motoneurons

Abstract

Astrocytes play a critical role in the maintenance of a healthy central nervous system and astrocyte dysfunction has been implicated in various neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). There is compelling evidence that mouse and human ALS and ALS/FTD astrocytes can reduce the number of healthy wild-type motoneurons (MNs) in co-cultures or after treatment with astrocyte conditioned media (ACM), independently of their genotype. A growing number of studies have shown that soluble toxic factor(s) in the ACM cause non-cell autonomous MN death, including our recent identification of inorganic polyphosphate (polyP) that is excessively released from mouse primary astrocytes (SOD1, TARDBP, and C9ORF72) and human induced pluripotent stem cells (iPSC)-derived astrocytes (TARDBP) to kill MNs. However, others have reported that astrocytes carrying mutant TDP43 do not produce detectable MN toxicity. This controversy is likely to arise from the findings that human iPSC-derived astrocytes exhibit a rather immature and/or reactive phenotype in a number of studies. Here, we have succeeded in generating a highly homogenous population of functional quiescent mature astrocytes from control subject iPSCs. Using identical conditions, we also generated mature astrocytes from an ALS/FTD patient carrying the TDP43A90V mutation. These mutant TDP43 patient-derived astrocytes exhibit key pathological hallmarks, including enhanced cytoplasmic TDP-43 and polyP levels. Additionally, mutant TDP43 astrocytes displayed a mild reactive signature and an aberrant function as they were unable to promote synaptogenesis of hippocampal neurons. The polyP-dependent neurotoxic nature of the TDP43A90V mutation was further confirmed as neutralization of polyP in ACM derived from mutant TDP43 astrocytes prevented MN death. Our results establish that human astrocytes carrying the TDP43A90V mutation exhibit a cell-autonomous pathological signature, hence providing an experimental model to decipher the molecular mechanisms underlying the generation of the neurotoxic phenotype.

Skeletal myotubes expressing ALS mutant SOD1 induce pathogenic changes, impair mitochondrial axonal transport, and trigger motoneuron death

“…Non-cell autonomous toxicity to MNs induced by cultured astrocytes harboring diverse ALS-causing gene mutations, including mutations in SOD1, TDP43, and C9ORF72, has also been extensively documented (Dittlau & Bosch, 2023; Garcés et al, 2024; Harten et al, 2021). Our recent study further reveals that excessive inorganic polyphosphate (polyP) released by ALS astrocytes triggers MN death and increases neuronal excitability and Ca 2+ transients (Arredondo et al, 2022; Garcés et al, 2024; Rojas et al, 2023). Additionally, other studies have also shown that astrocyte-mediated MN degeneration is accompanied by several other pathogenic events, including oxidative stress, induction of a cell death signaling (i.e., phosphorylation of c-Abl), and impaired mitochondrial transport (Birger et al, 2019; Dittlau & Bosch, 2023; Fritz et al, 2013; Haidet-Phillips et al, 2011; Harten et al, 2021; Rojas et al, 2014, 2015).…”

The Diverse Roles of Reactive Astrocytes in the Pathogenesis of Amyotrophic Lateral Sclerosis

“…Coexistence or shared clinical, genetic (SOD1, TARDBP, and C9ORF72 et al), and pathological features (TDP-43 inclusions in astrocytes and neurons) have been observed between ALS and FTD [88]. Previous studies have demonstrated that astrocytes from postmortem patients with ALS/FTD also exert detrimental effects on motor neurons [89][90][91]. Astrocyte dysfunction specific to ALS/FTD is comparable to that seen in ALS without FTD; however, there are some distinctions [92].…”

“…Polyphosphate (polyP), an inorganic neuroactive compound that potentiates the activity of Nav and Kv channels, is synthesized by astrocytes, functioning as a glial messenger to facilitate communications between astrocytes and neurons [110]. Elevated polyP levels were observed in induced pluripotent stem cell (iPSC)-derived astrocytes from mice and postmortem patients with various ALS/FTD-associated mutations (SOD1, TARDBP, and C9ORF72) [89,90]. Similarly, spinal cord sections from patients with familial and sporadic ALS displayed abundant polyP staining signals [89].…”

“…Furthermore, polyP levels were increased in the astrocyte-conditioned media (ACM) from ALS/FTD. In contrast, motor neuron death was significantly decreased by degradation or neutralization of polyP within ALS/FTD astrocytes or ACM, suggesting that excessive astrocytic polyP could be a critical factor for non-cell autonomous MN degeneration and a potential therapeutic target for ALS/FTD [89,90]. Elevated polyP levels were also detected in the cerebrospinal fluid (CSF) of ALS patients, indicating that polyP might serve as a novel biomarker for ALS/FTD [89].…”

Microglia and Astrocytes in Amyotrophic Lateral Sclerosis: Disease-Associated States, Pathological Roles, and Therapeutic Potential

“…Studies using iPSC-derived astrocytes have provided valuable insights into their role in ALS pathogenesis. Several studies have suggested that iPSC-derived astrocytes from ALS patients are more toxic to motor neurons compared to control astrocytes [195][196][197][198][199][200]. Mechanistically, there have been several proposed mechanisms for how ALS astrocytes mediate their neurotoxicity.…”