Niemann Pick C1 mistargeting disrupts lysosomal cholesterol homeostasis contributing to neurodegeneration in a Batten disease model.

Abstract

Neurodegeneration is a devastating manifestation in most lysosomal storage disorders (LSDs). Loss-of-function mutations in <i>CLN1</i>, encoding palmitoyl-protein thioesterase-1 (PPT1), cause CLN1 disease, a devastating neurodegenerative LSD that has no curative treatment. Numerous proteins in the brain require dynamic S-palmitoylation (palmitoylation-depalmitoylation) for trafficking to their destination. Although PPT1 depalmitoylates S-palmitoylated proteins and its deficiency causes CLN1 disease, the underlying pathogenic mechanism has remained elusive. We report that Niemann-Pick C1 (NPC1), a polytopic membrane protein mediating lysosomal cholesterol egress, requires dynamic S-palmitoylation for trafficking to the lysosome. In <i>Cln1^-/-</i> mice, Ppt1 deficiency misroutes NPC1-dysregulating lysosomal cholesterol homeostasis. Along with this defect, increased oxysterol-binding protein (OSBP) promotes cholesterol-mediated activation of mechanistic target of rapamycin C1 (mTORC1), which inhibits autophagy contributing to neurodegeneration. Pharmacological inhibition of OSBP suppresses mTORC1 activation, rescues autophagy, and ameliorates neuropathology in <i>Cln1^-/-</i> mice. Our findings reveal a previously unrecognized role of <i>CLN1</i>/PPT1 in lysosomal cholesterol homeostasis and suggest that suppression of mTORC1 activation may be beneficial for CLN1 disease.