C9orf72 is required for proper macrophage and microglial function in mice

Linking neurodegeneration and immune cells The expansion of a repetitive DNA sequence in the C9orf72 gene is the major genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia. Although the expansion decreases C9orf72 expression, most research has focused on the toxic RNA and protein products it creates in neurons. O'Rourke et al. found that C9orf72 unexpectedly plays a key role in innate immune cells. Loss of C9orf72 in mice led to macrophage and microglial dysfunction and age-related neuroinflammation. This raises the possibility of a “dual-effect” disease mechanism, in which toxic byproducts in neurons are combined with microglial dysfunction from decreased C9orf72 expression, together promoting neurodegeneration. Science, this issue p. 1324 Loss of C9orf72 disrupts microglial function and may contribute to neurodegeneration in C9orf72 expansion patients. Expansions of a hexanucleotide repeat (GGGGCC) in the noncoding region of the C9orf72 gene are the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia. Decreased expression of C9orf72 is seen in expansion carriers, suggesting that loss of function may play a role in disease. We found that two independent mouse lines lacking the C9orf72 ortholog (3110043O21Rik) in all tissues developed normally and aged without motor neuron disease. Instead, C9orf72 null mice developed progressive splenomegaly and lymphadenopathy with accumulation of engorged macrophage-like cells. C9orf72 expression was highest in myeloid cells, and the loss of C9orf72 led to lysosomal accumulation and altered immune responses in macrophages and microglia, with age-related neuroinflammation similar to C9orf72 ALS but not sporadic ALS human patient tissue. Thus, C9orf72 is required for the normal function of myeloid cells, and altered microglial function may contribute to neurodegeneration in C9orf72 expansion carriers.