Sullivan, K. D. | bioRxiv Science

bioRxiv2018

Trisomy 21 drives production of neurotoxic tryptophan catabolites via the interferon-inducible kynurenine pathway

Trisomy 21 (T21) causes Down syndrome (DS), affecting immune and neurological function by unknown mechanisms. We report here the results of a large metabolomics study showing that people with DS produce elevated levels of kynurenine and quinolinic acid, two tryptophan catabolites with potent immunosuppressive and neurotoxic properties, respectively. We found that immune cells of people with DS overexpress IDO1, the rate-limiting enzyme in the kynurenine pathway (KP) and a known interferon (IFN)-stimulated gene. Furthermore, we found a positive correlation between levels of specific inflammatory cytokines and KP dysregulation. Using metabolic flux assays, we found that IFN stimulation causes IDO1 overexpression and kynurenine overproduction in cells with T21, dependent on overexpression of IFN receptors encoded on chromosome 21. Finally, KP dysregulation is conserved in a mouse model of DS carrying triplication of the IFN receptors. Altogether, these results reveal a mechanism by which T21 could drive immunosuppression and neurotoxicity in DS.

physiology↗

bioRxiv2018

Phosphatidylinositol 3,5-Bisphosphate Regulates Yeast Vacuole Fusion at the Transition between trans-SNARE Complex Formation and Hemifusion

Phosphoinositides (PIs) regulate myriad cellular functions including membrane fusion, as exemplified by the yeast vacuole, which uses various PIs at different stages of fusion. In light of this, the effect of phos-phatidylinositol 3,5-bisphosphate [PI(3,5)P2] on vacuole fusion remains unknown. PI(3,5)P2 is made by the PI3P 5-kinase Fab1/PIKfyve and has been characterized as a regulator of vacuole fission during hyperosmotic shock where it interacts with the TRP family Ca2+ channel Yvc1. Here we demonstrate that exogenously added dioctanoyl (C8) PI(3,5)P2 abolishes homotypic vacuole fusion. This effect was not linked to interactions with Yvc1, as fusion was equally affected using yvc1{Delta} vacuoles. Thus, the effects of C8-PI(3,5)P2 on fusion versus fission operate through distinct mechanisms. Further testing showed that C8-PI(3,5)P2 inhibited vacuole fusion after the formation of trans-SNARE pairs. Although SNARE complex formation was unaffected we found that C8-PI(3,5)P2 strongly inhibited hemifusion. Overproduction of endogenous PI(3,5)P2 by the fab1T2250A hyperactive kinase mutant also inhibited at the hemifusion stage, bolstering the model in which PI(3,5)P2 inhibits fusion when present elevated levels. Taken together, this work identifies a novel function for PI(3,5)P2 as a negative regulator of vacuolar fusion. Moreover, it suggests that this lipid acts as a molecular switch between fission and fusion.

biochemistry↗