HKDC1 contributes to aberrant lysosome-mitochondria contact in Niemann-Pick disease type C

Niemann-Pick disease type C (NPC) is a neurovisceral lysosomal storage disorder comprising two clinically indistinguishable but genetically distinct subtypes caused by mutations in NPC1, or NPC2. The specific impact of each deficiency on cellular homeostasis remains poorly defined due to the phenotypic heterogeneity of patient-derived models and a lack of isogenic platforms for comparative study. Here we established isogenic ARPE19 models of NPC1 and NPC2 deficiency that faithfully recapitulate hallmark pathologies, including homogeneous lysosomal expansion and lipid sequestration. Direct comparison of these isogenic lines revealed a fundamental divergence in organelle crosstalk: while both genotypes exhibit comparable lipid accumulation, expanded mitochondria-lysosome contact sites (MLCs) are observed exclusively in NPC1 ^-/- cells. Using StARD3-targeted proximity labelling and quantitative proteomics, we identified the mitochondrial protein HKDC1 as an MLC regulator. We demonstrate that HKDC1 is markedly upregulated in NPC1 ^-/- cells and that its overexpression drives MLC expansion in wild-type cells. Thus our study uncovers a homeostatic role for HKDC1-mediated organelle remodelling and demonstrates the power of isogenic modelling for identifying novel regulators of organelle architecture and potential therapeutic targets.