BLOC-1 deficiency causes alterations in amino acid profile and in phospholipid and adenosine metabolism in the postnatal mouse hippocampus

Abstract

Biogenesis of lysosome-related organelles complex-1 (BLOC-1) is a protein complex involved in the formation of endosomal tubular structures that mediates the sorting of protein cargoes to specialised compartments. In this study, we present insights into the metabolic consequences caused by BLOC-1 deficiency in pallid mice, which carry a null mutation in the Bloc1s6 gene encoding an essential component of this complex. The metabolome of the hippocampus of pallid mice was analysed using an untargeted, liquid chromatography-coupled mass spectrometric approach. After data pretreatment, statistical analysis and pathway enrichment, we have identified 28 metabolites that showed statistically significant changes between pallid and wild-type control. These metabolites included amino acids, nucleobase-containing compounds and lysophospholipids. Interestingly, pallid mice displayed increased hippocampal levels of the neurotransmitters glutamate and N-acetyl-aspartylglutamic acid (NAAG) and their precursor glutamine. Expression of the sodium-coupled neutral amino acid transporter 1 (SNAT1), which transports glutamine into neurons, was also upregulated. Conversely, levels of the neurotransmitter precursors phenylalanine and tryptophan were decreased. Interestingly, many of these changes could be mapped to overlapping metabolic pathways. The observed metabolic alterations are likely to affect neurotransmission and neuronal homeostasis and in turn could mediate the memory and behavioural impairments observed in BLOC-1-deficient mice.The pallid (pa) mouse, originally called pinked-eyed 2, was isolated based on abnormal coat and eye colour 1 . The defective gene was identified by positional cloning and found to encode a small, coiled-coil-forming protein, named pallidin (also known as biogenesis of lysosome-related organelles complex 1 subunit 6, BLOC1S6) 2 . Besides the pigmentation defect, the pallid mouse was found to display platelet storage pool deficiency and emphysematous lung lesions. This led to the proposal that it would serve as a model for Hermansky-Pudlak syndrome (HPS) 3 . In fact, at least two HPS patients were found to carry recessive mutations in the human pallidin-encoding gene, BLOC1S6 (formerly known as PLDN), thereby defining HPS type 9 (HPS-9) 4 .Pallidin is part of the biogenesis of lysosome-related organelles complex 1 (BLOC-1), which also includes the proteins dysbindin, muted, cappuccino, snapin, BLOS1, BLOS2 and BLOS3 5,6 . Electron microscopy revealed that the subunits of BLOC-1 are arranged in a stable elongated structure of eight globular cores 7 . There is strong evidence that all subunits are required to form a stable complex and lack of one subunit destabilizes the complex and causes a drop in levels of the other subunits, as observed in null mouse models for dysbindin (sandy, sdy), BLOS3 (reduced pigmentation, rp), muted (mu) and pallidin (pa) 6,8,9 .

Live imaging of intra-lysosome pH in cell lines and primary neuronal culture using a novel genetically encoded biosensor

“…We also found increased enrichment of lysosomal glutamine transporter SLC38A1/SNAT1 [ 45 ]. SLC38A1 expression is increased in mutants of the BLOC-1 complex [ 46 ], which controls the generation of lysosomal-related organelles, and has been recently found to modulate neuronal MTORC1-RPS6KB1/S6K signaling to stimulate macroautophagy/autophagy [ 47 ]. Other lysosomal stressors, such bafilomycin A 1 treatment, strongly reduces cellular glutamine, suggesting a role of acidic organelles [ 7 ] in amino acid flux.…”

Impaired beta-oxidation increases vulnerability to influenza A infection

“…The MS was operated in positive and negative ESI mode as described previously ( 72 ). The sampling cone voltage was set to 25 V, extraction cone voltage to 5 V, and capillary voltage to 500 V for both polarities.…”

Pallidin function in drosophila surface glia regulates sleep and is dependent on amino acid availability

“…These results indicate that the circadian clock is functional and that sleep loss in knockdown flies is largely independent from light exposure. To assess the implication of the circadian clock, flies were placed in constant light, a condition known to disrupt the cycling of the molecular clock 58 . As expected, the sleep of SG>pallidin-RNAi flies showed no 24h rhythms.…”