Dihydroceramide desaturase directs the switch between exosome production and autophagy for neuronal maintenance
Exosomes are important for cell-cell communication. Deficiencies in the human dihydroceramide desaturase gene, DEGS1, increase the dihydroceramide-to-ceramide ratio and causes hypomyelinating leukodystrophy. However, the disease mechanism remains unknown. Here, we developed an in vivo assay with spatially controlled expression of exosome markers in Drosophila eye imaginal discs and showed that the level and activity of the DEGS1 ortholog, ifc, correlated with exosome production. Knocking out ifc decreased the density of the exosome precursor intraluminal vesicles (ILVs) in the multivesicular endosomes and reduced the number of exosomes released. While ifc overexpression and autophagy inhibition both enhanced exosome production, combining the two had no additive effect. Moreover, DEGS1 activity was sufficient to drive ILV formation in vitro. Together, DEGS1/Ifc controls the dihydroceramide-to-ceramide ration and enhances exosome secretion by promoting ILV formation and preventing the autophagic degradation of MVEs. These findings provide a potential cause for the neuropathy associated with DEGS1-deficient mutations. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=115 SRC="FIGDIR/small/376046v3_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@c7479corg.highwire.dtl.DTLVardef@12e7f46org.highwire.dtl.DTLVardef@1a5e7f0org.highwire.dtl.DTLVardef@11e7f08_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIAn in vivo system was developed for observing exosome production in Drosophila. C_LIO_LIDihydroceramide desaturase (DEGS1/Ifc) promotes exosome production by two means. C_LIO_LIIfc drives membrane invagination to promote the formation of intraluminal vesicles. C_LIO_LIIfc inhibits autophagic degradation of MVEs and increases exosome release. C_LI eTOC BlurbThe level and activity of dihydroceramide desaturase (human DEGS1 and Drosophila Ifc) correlate with exosome production. Wu et al. show that DEGS1 drives the formation of intraluminal vesicles in vivo and in vitro. Overexpressing Ifc inhibits autophagy and reduces the degradation of multivesicular endosomes, thus increases exosome release.