Description
Niemann-Pick disease type C (NPC) is a rare lysosomal storage disorder, most often caused by loss-of-function mutations in NPC1, resulting in pathological cholesterol and sphingolipid accumulation within late endosomes/lysosomes (LE/Lys). A recently-approved therapeutic, N-acetyl-L-leucine (NALL), was found to clear lysosomal lipids in NPC patient cells. NALL’s mechanism of action is not fully understood, but recent work from our lab showed that NALL normalises dysregulated inter-organelle membrane contact sites in NPC. The serine/threonine kinase Glycogen Synthase Kinase-3 Beta (GSK3β) has been implicated in contact site regulation and is recruited to the lysosome in response to leucine supplementation under starved conditions (Schwendener Frokel et al., 2024). Preliminary data suggest that NALL-mediated cholesterol clearance is GSK3β-dependent, which potentially implicates GSK3β in NALL's therapeutic effects. Here, NALL-mediated rescue of filipin-stained cholesterol accumulation in NPC patient cells is reproduced in NPC1-knockout/inhibited HeLa cells and the role for GSK3β supported. On GSK3β inhibition, NALL failed to rescue cholesterol accumulation in NPC1-knockout/inhibited cells. Current and future work aims to determine the effect of NALL on GSK3β’s subcellular localisation and if GSK3β activity is required for NALL-mediated normalisation of LE/Lys contacts with mitochondria and ER. Together, these findings will improve understanding of the molecular pathways underpinning NALL's therapeutic mechanism of action.
Lay Abstract
Niemann-Pick disease type C (NPC) is a rare inherited condition in which cholesterol becomes trapped inside a cellular compartment called the lysosome. This leads to cell damage, and neurological decline and is ultimately fatal. A recently approved NPC therapeutic called N-acetyl-L-leucine (NALL) helps cells clear this trapped cholesterol, but exactly how it does this is still not known. Recent work from our lab suggests that NALL works partly by restoring the way different compartments inside the cell communicate with each other, and that a kinase called GSK3β may be key to this process. Within the cell, GSK3β regulates many cellular processes by chemically tagging other proteins. To investigate if GSK3β activity is important for NALL to work, we used a fluorescent dye to visualise cholesterol in NPC patient cells and cellular models that mimic the disease state. NALL successfully cleared the cholesterol build-up, but when GSK3β was blocked, the cholesterol returned to disease levels, suggesting GSK3β is essential for NALL to work. We are further investigating if NALL affects GSK3β activity and if GSK3β is also needed for NALL to normalise aberrant intracellular communication in NPC, which may give us a better understanding of how NALL works.
| Lay Title | Uncovering the cellular mechanism behind an approved treatment for Niemann-Pick type C. |
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| Role | Master Student |