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Moderate intrinsic phenotypic alterations in C9orf72 ALS/FTD iPSC-microglia despite the presence of C9orf72
Ileana Lorenzini1, Eric Alsop2, Jennifer Levy1
1Department of Translational Neuroscience, Barrow Neurological Institute, Phoenix, AZ, United States.
Abstract:
While motor and cortical neurons are affected in C9orf72 amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD), it remains largely unknown if and how non-neuronal cells induce or exacerbate neuronal damage. We differentiated C9orf72 ALS/FTD patient-derived induced pluripotent stem cells into microglia (iPSC-MG) and examined their intrinsic phenotypes. Similar to iPSC motor neurons, C9orf72 ALS/FTD iPSC-MG mono-cultures form G4C2 repeat RNA foci, exhibit reduced C9orf72 protein levels, and generate dipeptide repeat proteins. Healthy control and C9orf72 ALS/FTD iPSC-MG equally express microglial specific genes and perform microglial functions, including inflammatory cytokine release and phagocytosis of extracellular cargos, such as synthetic amyloid beta peptides and healthy human brain synaptoneurosomes. RNA sequencing analysis revealed select transcriptional changes of genes associated with neuroinflammation or neurodegeneration in diseased microglia yet no significant differentially expressed microglial-enriched genes. Moderate molecular and functional differences were observed in C9orf72 iPSC-MG mono-cultures despite the presence of C9orf72 pathological features suggesting that a diseased microenvironment may be required to induce phenotypic changes in microglial cells and the associated neuronal dysfunction seen in C9orf72 ALS/FTD neurodegeneration.
Insights
Microglia from C9orf72 amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD) patients show some disease features but function normally in isolation. A diseased microenvironment may be necessary to trigger microglial dysfunction and neuronal damage in C9orf72 ALS/FTD.
Area of Science:
- Neuroscience
- Genetics
- Stem Cell Biology
Background:
- Amyotrophic lateral sclerosis and frontotemporal dementia (ALS/FTD) are neurodegenerative diseases linked to C9orf72 gene mutations.
- While neurons are known to be affected, the role of non-neuronal cells, like microglia, in disease pathogenesis is not fully understood.
Purpose of the Study:
- To investigate the intrinsic properties and functions of microglia derived from C9orf72 ALS/FTD patients.
- To determine if C9orf72-associated pathological features in microglia alone can induce cellular dysfunction or neuroinflammation.
Main Methods:
- Generation of induced pluripotent stem cell-derived microglia (iPSC-MG) from C9orf72 ALS/FTD patients and healthy controls.
- Analysis of C9orf72 pathological hallmarks (RNA foci, dipeptide repeats, protein levels) in iPSC-MG.
- Assessment of microglial functions including gene expression, inflammatory cytokine release, and phagocytosis.
- RNA sequencing to identify transcriptional changes in iPSC-MG.
Main Results:
- C9orf72 iPSC-MG exhibited hallmark pathological features, including G4C2 repeat RNA foci and reduced C9orf72 protein.
- Despite these features, C9orf72 iPSC-MG maintained normal microglial functions like phagocytosis and cytokine release.
- RNA sequencing revealed minor transcriptional alterations, but no significant differentially expressed microglial-enriched genes were identified.
Conclusions:
- Isolated C9orf72 iPSC-MG display intrinsic disease-related molecular changes but retain normal functional capacity.
- These findings suggest that a supportive or diseased microenvironment, rather than intrinsic microglial defects alone, may be crucial for driving neuroinflammation and neuronal dysfunction in C9orf72 ALS/FTD.
