engleski

BACE1 inhibition ameliorates neuroinflammation in organotypic brain slices of Niemann-Pick type C disease murine model

Niemann-Pick type C disease (NPC) is a rare, fatal lysosomal storage disorder affecting primarily infants and children. NPC is caused by mutations in NPC1 and NPC2 genes (95% and 5% of cases, respectively) that code for cholesterol transport proteins involved in egress of free cholesterol form late endosomes and lysosomes. Mutations in these proteins disrupt intracellular trafficking of cholesterol and other lipids causing their accumulation within late endosomes and lysosomes and endolysosomal dysfunction. This leads to neurodegeneration of primarily Purkinje neurons in the cerebellum and profound neuroinflammation. Interestingly, NPC pathology shares several features with Alzheimer's disease (AD), including tau hyperphosphorylation and increased amyloid-β (Aβ) peptide levels. We have previously shown that increased levels of Aβ in NPC may be due to increased proteolysis of APP by β-site amyloid precursor protein cleaving enzyme 1 (BACE1), a key enzyme in AD pathogenesis. Thus, in this work we investigated whether inhibition of BACE1 may ameliorate/revert any of the key pathological features of NPC disease in NPC1-mouse brains. To study the effect of BACE1 inhibition on pathological features of NPC we used ogranotypic brain slice cultures of NPC murine model BALB/cNctr-Npc1m1N/J (The Jackson Laboratory, USA). Ex vivo cortico-hippocampal slice cultures of P7 wild-type, NPC1+/+ (WT) and NPC1-/- (NPC1) pups were grown in vitro for 12 days and treated with BACE1 inhibitor (β-Secretase Inhibitor IV, Sigma-Aldrich) for 96 h. Slice cultures were analysed by Western Blot and immunofluorescent confocal microscropy for BACE1 substrate cleavage/inhibition (APP and Sez6), lysosomal dysfunction (LAMP1), and neuroinflammation (activation of astrocytes - GFAP, and microglia - CD68). Western Blot analysis of BACE1 cleavage of APP and Sez6 confirmed successful inhibition of BACE1 in cortico-hippocampal slice cultures. Immunostaining of NPC1 vs. WT organotypic brain slices revealed decreased accumulation of lysosomes and reduced activation of astrocytes and microglia upon BACE1 inhibition. We found that inhibition of BACE1 ameliorates lysosomal accumulation and neuroinflammation in NPC1 mouse organotypic brain slice cultures, suggesting that enhanced BACE1-substrate proteolysis could play a role in endolysosomal dysfunction and, thus, in neuroinflammation and pathogenesis of NPC disease. We speculate that BACE1-generated APP C-terminal fragments may be involved in this process.

Niemann-Pick type C disease ; β-secretase ; endolysosomal disfunction ; neuroinflammation

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