<p>Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are neurodegenerative disorders which overlap in their clinical presentation, pathology, and genetic origin. An over-representation of autoimmune disorders exists in both ALS and FTD, but this remains an unexplained epidemiologic observation. Expansions of a hexanucleotide repeat (GGGGCC) in the C9orf72 gene (<a href="https://www.ncbi.nlm.nih.gov/gene/?term=203228">GeneID:203228</a>) are the most common cause of familial ALS and FTD (C9-ALS/FTD), leading to both repeat containing RNA and dipeptide accumulation coupled with decreased C9orf72 protein expression in brain and peripheral blood cells. Here we show that loss of C9orf72 in myeloid cells is sufficient to recapitulate the age dependent lymphoid hypertrophy and autoinflammation seen in complete C9orf72-/- mice. Dendritic cells isolated from C9orf72-/- mice showed marked early activation of the type I interferon response, and C9orf72-/- myeloid cells were primarily hyperresponsive to activators of stimulator of interferon gene (STING1 <a href="https://www.ncbi.nlm.nih.gov/gene/340061">GeneID:340061</a>), a key regulator of the innate immune response to cytosolic DNA. STING degradation through the autolysosomal pathway was diminished in C9orf72-/- mice myeloid cells, and blocking STING suppressed hyperactive type I interferon responses in C9orf72-/- myeloid cells and splenomegaly and inflammation in C9orf72-/- mice. Additionally, mice lacking one or both copies of C9orf72 were more susceptible to experimental autoimmune encephalitis, mirroring the susceptibility to autoimmune diseases seen in C9-ALS/FTD patients. Finally, we found that blood derived macrophages, peripheral blood monocytes, and brain tissue from C9-ALS/FTD patients all showed a hyperactive type I interferon signature compared to sporadic ALS/FTD subjects. Collectively, our results indicate that C9-ALS/FTD patients have an altered immunophenotype due to loss of C9orf72 regulation of STING mediated type I interferon activation.</p>

Peripheral Blood Transcriptome Analysis of ALS Patients