Globoid Cell Leukodystrophy (GLD), or Krabbe disease, is a fatal inherited disease of CNS white matter affecting 1:100,000 live births worldwide. GLD results from loss of function mutations in the gene encoding galactosylceramidase (galc) which results in a pathological accumulation of the cytotoxic lipid intermediate psychosine. The “psychosine hypothesis” has been the predominant explanation for GLD pathology for over 40 years and postulates that the accumulation of psychosine is responsible for the death of myelinating oligodendrocytes, resulting in the profound demyelination observed in GLD. However, the presence of multi-nucleated abnormal microglia known as globoid cells (GCs), a neuropathological hallmark of this disease, can be identified well before overt demyelination in GLD. Our recent experimental findings have demonstrated that microglia respond to psychosine by becoming highly activated and pathogenic to oligodendrocytes. Thus while the original “psychosine hypothesis” suggested that oligodendrocyte death initiates GLD pathology and microgliosis, our new experimental evidence supports a revised sequence of events in this disease and suggests that GLD is a disease initiated by microglia.

Microglia are resident innate immune cells of the CNS that provide critical developmental and homeostatic functions. Microglia are active in demyelinating diseases and evidence for microgliosis in human GLD is present in the prenatal brain on autopsy. This information indicates that microgliosis precedes demyelination in this disease. Indeed, microgliosis is a prominent feature of GLD pathology that causes demyelination. Although is is well characterized that activated microglia and the formation of multinucleated GCs are both present in GLD, the etiology and function of microglia in this disease are poorly understood. Since microglia are known to exhibit remarkable plasticity in disease or inflammatory states, this project is interrogating microglia in GLD using single cell RNA sequencing to develop an unbiased deep sequencing library from which to identity the specific process(es) and gene targets required for the pathogenic transformation of microglia in this disease.