Role of Brain Macrophages in the Pathogenesis and Treatment of Globoid Cell Leukodystrophy

Globoid cell leukodystrophy (GLD), or Krabbe, is a fatal pediatric neurodegenerative disease caused by
mutations in GALC. It is so-named due to the appearance of globoid cell macrophages. The major hurdle to
curing GLD is treatment of central nervous system (CNS) pathology. Hematopoietic stem cell transplant (HSCT)
is the only treatment, but is not curative, and must be administered presymptomatically in early infancy. HSCT
is thought to work by therapeutic engraftment of donor macrophages and replacement of globoid cells, but in the
brain, does so inefficiently. Despite being pathognomonic for GLD, little is known about globoid cells in the brain
- their function, origin, and formation. It is unknown if globoid cells arise from embryonically-derived tissue
resident microglia or HSC-derived infiltrating macrophages, the degree to which they are pathogenic, and if their
replacement is key to GLD treatment. This is a critical knowledge gap that has limited the advancement of more
effective GLD therapies and is the focus of this proposal. Our central hypothesis is that globoid cells are
unique reactive microglia and that robust replacement by “true” microglia is sufficient to treat GLD CNS
neuropathology. We are experts in the study of brain macrophages by direct CNS transplantation in mice. The
twitcher (GALCKO) mouse is a widely accepted model of GLD. We created new methods to 1) distinguish
microglia, infiltrating macrophages, and transplanted donor macrophages from each other and 2) replace host
brain macrophages with directly injected cells at high efficiency without HSCT, including by engineering the first
small molecule inhibitor-resistant variant of CSF1R, a survival receptor for brain macrophages. In this proposal,
we will apply these new methods in the GALCKO model to determine the role of brain macrophages in GLD
pathogenesis and treatment. In Aim 1, we will define the origin and transcriptomic identity of all reactive brain
macrophages, including globoid cells, in GALCKO, including after HSCT. This knowledge promises to reveal new
therapeutic targets for GLD. In Aim 2, we will test the hypothesis that direct replacement of GALCKO microglia
with healthy surrogates eliminates globoid cells and drives the neurotherapeutic effects of HSCT. If true, this
approach has great translational potential to maximize engraftment efficiency and broaden the therapeutic
window for cell therapy. Finally in Aim 3, we will determine if HSC-derived cells are effective microglial
surrogates, given the distinct functions of non-microglial macrophages in the CNS. This will guide future work to
enhance the efficacy of cell therapies for brain diseases. Completion of these aims will fill longstanding
knowledge gaps about the role of microglia and other macrophages in the pathogenesis and treatment of
pediatric neurodegenerative diseases.

Grant Number: 5R01NS120960-05
NIH Institute/Center: NIH
Principal Investigator: Frederick Bennett