Drosophila TRPML Is Required for TORC1 Activation

Abstract

Summary Loss-of-function mutations in TRPML1 (Transient Receptor Potential Mucolipin 1) cause a lysosomal storage disorder called mucolipidosis type IV (MLIV). Previously, we established a Drosophila model for MLIV by knocking out the single TRPML1 homolog expressed in flies [1]. The mutant animals displayed impaired autophagy, and reduced viability during the pupal period—a phase when wild-type animals rely on autophagic sources for nutrients. However, the specific defect in autophagy has remained unclear. Here, we show that TRPML, which was localized to the membranes of late-endosomes and lysosomes in vivo, was required for fusion between late-endosomes with lysosomes. We report that loss of TRPML led to accumulation of vesicles of significantly larger volume, and loss of TRPML from the late-endosomes/lysosomes led to the accumulation of higher luminal Ca2+ within those vesicles. We also found that trpml1 mutant cells showed decreased TORC1 signaling, and a concomitant upregulation of autophagy induction. Both of these defects were reversed by activating TORC1 in the mutants genetically and by feeding the mutant larvae a high-protein diet. Feeding the larvae a high-protein diet also reduced both the pupal lethality, and the increased volume of acidic vesicles. Conversely, further inhibition of TORC1 activity by rapamycin exacerbated the mutant phenotypes. Finally, TORC1 exerted reciprocal control on TRPML function. A high amino acid diet enhanced cortical localization of TRPML, and this effect was blocked by rapamycin. Our findings delineate the interrelationship between TRPML- and TORC1-mediated nutrient sensing pathways, and also raise the intriguing possibility that amino acid supplementation might reduce the severity of the clinical manifestations associated with MLIV.

Carbon-Doped TiO2 and Carbon, Tungsten-Codoped TiO2 through Sol–Gel Processes in the Presence of Melamine Borate: Reflections through Photocatalysis

“…As predicted by theoretical calculations [35] and as shown by UV-vis spectroscopy here (see Figure 4 (c)), the C, W co-doped material had an absorbance significantly shifted towards the visible region. However, despite the enhanced optical properties of the W-doped and co-doped TiO 2 catalysts, these were considerably poorer photo-oxidation catalysts (see Figure 4(c)) compared to C-TiO 2 materials.…”

“…Codoping carbon and tungsten has been reported to yield such a passivation effect in comparison to singly doped tungsten or carbon TiO 2 . This reported passivation is due to the formation of a C 2p -W 5d hybridized band [35] when dopants are located near one other (as the nearest neighbour or the second nearest neighbour). This strengthens hybridization between C 2p and O 2p resulting in a fully occupied band of higher energy than the top of the valence band edge and at the same time forms a continuum-like band between the conduction band and tungsten dopant d states below.…”

Up-regulation of lysosomal TRPML1 channels is essential for lysosomal adaptation to nutrient starvation

“…Hence, nutrient-sensitive regulation of ML1 channels may link lysosome function with nutrient availability via mTORC1, PI(3,5)P 2 , and TFEB. Although our study has focused on the effect of mTORC1 inhibition on up-regulation of TRPML1, it has recently been demonstrated that the Drosophila homolog of TRPML1, TRPML, regulates the activity of TORC1 in vivo (43). Hence, TRPML1 and TORC1 may constitute a feedback loop to regulate amino acid homeostasis in vivo.…”

High susceptibility to fatty liver disease in two-pore channel 2-deficient mice

“…Bafilomycin A1 (Baf. A1)-a cell-permeant inhibitor of the vacuolar-type H þ -ATPase, results in loss of the lysosomal/late endosomal proton gradient and eventually leads to the depletion of luminal calcium 34 . By using Baf.…”