Microglia express TMEM119 in the brains of Nasu-Hakola disease

We previously identified an evolutionarily conserved protein named transmembrane protein 119 (TMEM119) as the most reliable maker for human microglia. Recent studies showed that under homeostatic conditions, microglia intensely express TMEM119, whereas the expression levels are greatly reduced in disease-associated microglia (DAM) activated at the site of neurodegeneration. Nasu-Hakola disease (NHD) is a rare autosomal recessive disorder, pathologically characterized by leukoencephalopathy, astrogliosis, axonal spheroids, and accumulation of microglia. However, it remains unknown whether microglia are homeostatic or activated in NHD brains. In the present study, we identified TMEM119 on microglia in NHD brains by immunohistochemistry. TMEM119 was expressed on microglia in NHD brains as yell as in the brains of non-neurological controls (NC) and Alzheimer's disease (AD) patients, although TMEM119-immunolabeled areas exhibited great variability from case to case without significant differences among the study population. These results suggest that TMEM119 expression on microglia might play a key role in steady-state brain maintenance in NHD, AD and controls.