Fig. 9: NPC1 dysfunction increases GRP75 and IP₃R1–VDAC1 clustering.

A Schematic diagram of the hypothesis: Enhanced IP₃R–GRP75–VDAC signaling axis in NPC neurons leads to an aberrantly increased mitochondrial Ca²⁺ and neurotoxicity. B Left, representative super-resolution Airyscan images of CTL (black) and U18-treated neurons immunolabeled for GRP75. Right, quantification of GRP75 total intensity, cluster density and cluster size of CTL (black) and U18 (red) neurons in the soma (left, yellow) and dendrite (right, orange) regions. N = 27 (CTL) and n = 25 (U18) neurons and n = 65 (CTL) and n = 54–55 (U18) dendrites were analyzed across 2 independent isolations. C Top, representative images of CTL (black) and U18 (red) neurons fixed and immunolabeled for IP₃R and VDAC1. Bottom: quantification of % soma occupied by IP₃R–VDAC1, IP₃R–VDAC1 cluster density and IP₃R–VDAC1 cluster size of CTL (black) and U18-treated (red) neurons in the soma (left, yellow) and dendrite (right, orange) regions. N = 21 (CTL) and n = 27 (U18) neurons and n = 48 (CTL) and n = 65 (U18) dendrites across 2 independent isolations. All error bars represent SEM. Statistical significance was calculated using Mann–Whitney (two-tail) and Unpaired t tests (two-tail) in (B) and (C). ns: not significant; *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001. CTL is control and U18 is U18666A.