Loss of mouse C19orf12 homolog disturbs tubular ER homeostasis and leads to neuroaxonal dystrophy

Neurodegeneration with brain iron accumulation (NBIA) is a group of rare diseases associated with genetic mutations in several genes including C19orf12. To explore the underlying mechanism of NBIA pathogenesis, we investigated a mouse homolog of human C19orf12 gene knockout mouse model. In the brains of knockout mice, an age-dependent accumulation of abundant axonal spheroids, alongside brain iron accumulation, neuroinflammation, α-synuclein and ubiquitin pathology was observed. Axonal spheroids were associated with abnormal ER and damaged mitochondria in knockout mice. These abnormal spheroids consistently contained the tubular ER protein reticulon 3 (RTN3) even at younger ages which preceded the onset of motor symptoms. The abnormal localized expansion of axonal ER underlies swollen axon terminals of dopaminergic neurons. The accumulated neuroaxonal swellings likely impair functioning of the dopaminergic system in the substantia nigra, striatum, and other brain regions, which ultimately led to motor function deficits in knockout mice. Altogether, the absence of C19orf12 in mouse brains recapitulates cardinal features of neuropathology in human NBIA, suggesting that C19orf12 is essential to maintain the tubular ER homeostasis in neuronal axon.