Formation of multinucleated globoid cells in Krabbe iPSC-derived microglia cultures: a preliminary investigation
Globoid cell leukodystrophy (Krabbe disease) is a severe demyelinating, neurodegenerative lysosomal storage disorder caused by deficiency in glycosphingolipid catabolic enzyme galactosylceramidase (GALC). Histologically, Krabbe disease is characterized by the appearance of large multinucleated globoid cells that express classical macrophage markers (both of brain-resident microglia and peripheral monocyte-derived). Globoid cells reside near areas of degeneration; however, their functional significance in disease progression remains unclear. In the current study, we differentiated microglia-like cells from iPSCs from a donor with infantile Krabbe disease and compared them to microglia generated from two healthy controls and two donors with the lysosomal storage disorder metachromatic leukodystrophy (MLD), which is genetically distinct from Krabbe disease but presents similarly in terms of severity of demyelination and neurodegeneration. We report the novel finding of prominent formation of giant multinucleated globoid cells from the microglia derived from the Krabbe donor, but not from healthy control or MLD donors. The Krabbe microglia displayed reduced IL-6 protein expression upon stimulation with lipopolysaccharide, and the multinucleated globoid cells themselves appeared deficient in phagocytosis of both disease-relevant myelin debris and E. coli, together hinting at an impairment of normal function. The formation of the globoid cells could be attenuated by fully replacing the medium following passaging, suggesting that yet-to-be determined secreted factors are influencing cell fusion in our culture system. While preliminary, our results imply that globoid cells may be detrimental in Krabbe disease by hindering the normal function of brain-residing macrophages.