Research Projects

Project title: Metabolic shift and mitochondrial defects in the lysosomal storage disorder of saposin deficiency. Rationale: Lysosomal storage disorders (LSDs) are a group of metabolic disorders caused by lysosomal gene mutations resulting in lysosomal degradation defects. Most LSDs including saposin mutations show defects in cell growth, epilepsy, neurodegeneration, and memory defects. Recent studies on LSD diseases as NPC1 and Fabry patients reported hypometabolism and reduction in glucose utilization during PET brain scans, and metabolic switch to anaerobic metabolism by increased tissue lactate. A similar hypometabolism is observed in Alzheimer’s disease 12 years before the onset of symptoms, highlighting the chronic metabolic burden on cell function. How lysosomal degradation defects lead to metabolic shift is not clear. Objectives: Lysosomal storage disorder of saposin deficiency will be studied for 1) metabolic defects in relation to aberrant TOR activation 2) status of fatty acid synthesis and lipid stores, and 3) mitochondrial structural defects. Hypothesis and experimentation: Our recent results on saposin deficiency showed an increase in mTOR activity despite low amino acid availability due to lysosomal degradation defects. Network analysis with the parameters of abnormal TOR activation in amino acid starvation in LSD condition, in relation to autophagy inhibition and lactate production, identified three energy states related to metabolism- 1) lowering of energy state begins with aberrant activation of TOR that limits lipophagy and energy release from stores, 2) progressive drop in energy (ATP) inhibits fatty acid synthesis, activates AMP kinase (AMPK) to fragment mitochondria via mitochondrial fission factor (MFF), and 3) Still lowering of energy could induce Warburg shift where pyruvate enters anaerobic metabolism rather than oxidative phosphorylation, to meet energy demands of the cell. Mammalian cell culture and genetic modification of function and motor behaviour of Drosophila will be used to score metabolic defects of LSD-saposin mutation. Significance and application to the field: The current research evaluates metabolic and energy state of LSDs in relation to TOR activity and deciphers how chronic defects of LSDs bring about progressive sequential metabolic alterations. Moderate TOR inhibition combined with elevating intracellular levels of glucose could largely restore metabolism and energy state, and other possible therapeutic avenues based on the results will be tested. Because most LSDs show analogous transcriptional profiles indicating a similar metabolic shift and possibility of a common treatment plan for LSDs.