Hexanucleotide repeat expansions in C9orf72 alter microglial responses and prevent a coordinated glial reaction in ALS (P1-6.002)

Abstract

<h3>Objective:</h3> 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. <h3>Background:</h3> 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. <h3>Design/Methods:</h3> We generated single nuclei profiles of spinal cord and motor cortex from sporadic and <i>C9orf72</i> ALS patients, as well as controls. We particularly focused on the transcriptomic responses of both microglia and astrocytes. <h3>Results:</h3> We confirmed that <i>C9orf72</i> 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 <i>C9orf72</i> ALS patients, remaining in a homeostatic state. This suggesting that <i>C9orf72</i> HRE alters a coordinated glial response, which ultimately would increase the risk for developing ALS. <h3>Conclusions:</h3> Our results indicate that <i>C9orf72</i> 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. <b>Disclosure:</b> Dr. Masrori has received research support from European Academy of Neurology. An immediate family member of Miss Bijnens has received personal compensation in the range of $0-$499 for serving as a Consultant for Lundbeck . The institution of Miss Bijnens has received research support from University of Antwerp . Dr. Davie has nothing to disclose. Suresh Kumar Poovathingal has nothing to disclose. Miss Storm has nothing to disclose. Nicole Hersmus has nothing to disclose. Laura Fumagalli has nothing to disclose. The institution of Ludo Van Den Bosch has received research support from FWO-Vlaanderen. The institution of Ludo Van Den Bosch has received research support from Muscular Dystrophy Association (MDA). The institution of Ludo Van Den Bosch has received research support from American ALS Association (ALSA). The institution of Ludo Van Den Bosch has received research support from Thierry Latran Foundation. The institution of Ludo Van Den Bosch has received research support from Target ALS. The institution of Ludo Van Den Bosch has received research support from ABMM. Mark Fiers has nothing to disclose. Dietmar Thal has nothing to disclose. Prof. Mancuso has received personal compensation in the range of $500-$4,999 for serving as a Consultant for Sanofi. The institution of Dr. Van Damme has received research support from CSL Behring.