Hexanucleotide repeat expansions in C9orf72 alter microglial responses and prevent a coordinated glial reaction in ALS
Pegah Masrori1, Baukje Bijnens2, Kristofer Davie3, Suresh Kumar Poovathingal3, Annet Storm3, Nicole Hersmus3, Laura Fumagalli2, Ludo Van Den Bosch3, Mark Fiers3, Dietmar Thal4, Renzo Mancuzo2, Philip Van Damme5
1Neurology, University Hospitals Leuven, 2Center for Molecular Neurology, 3Center for Brain & Disease Research, VIB, 4Pathology Department, UZ Leuven, 5UZ Leuven
Objective:
Neuroinflammation is an important hallmark in amyotrophic lateral sclerosis (ALS). Experimental evidence has highlighted a role of microglia in the modulation of motor neuron degeneration. However, the exact contribution of microglia to both sporadic and genetic forms of ALS is still unclear.
Background:
Single nuclei (sn) RNA sequencing is an interesting approach to study transcriptional changes at the cellular level in human tissues from patients with neurodegenerative disorders. For this study we included motor cortex and spinal cord samples from 5 patients with ALS caused by a C9orf72 hexanucleotide repeat expansion (HRE), from 5 patients with sporadic ALS (mutations in C9orf72, SOD1, TARDBP and FUS excluded) and from 5 control individuals.
Design/Methods:
We generated single nuclei profiles of spinal cord and motor cortex from sporadic and C9orf72 ALS patients, as well as controls. We particularly focused on the transcriptomic responses of both microglia and astrocytes.
Results:
We confirmed that C9orf72 is highly expressed in microglia and shows a diminished expression as a result of the HRE. This resulted in an impaired response to disease, with specific deficits in phagocytic and lysosomal transcriptional pathways. Astrocytes also displayed a dysregulated response in C9orf72 ALS patients, remaining in a homeostatic state. This suggesting that C9orf72 HRE alters a coordinated glial response, which ultimately would increase the risk for developing ALS.
Conclusions:
Our results indicate that C9orf72 HRE results in a selective microglial loss-of-function, likely impairing microglial-astrocyte communication and preventing a global glial response. This is relevant as it indicates that sporadic and familial forms of ALS may present a different cellular substrate, which is of great importance for patient stratification and selecting treatments.