Unraveling lysosomal acidification defect in a lysosomal storage disorder model

Authors

• MB Bagh
• S Peng
• G Chandra
• Z Zhang
• SP Singh
• N Pattabiraman
• A Liu
• AB Mukherjee

Abstract

Lysosome, the major organelle for intracellular digestion, contains ~50 hydrolases, which require acidic pH for optimal function. Dysregulation of lysosomal acidification contributes to pathogenesis of virtually all lysosomal storage disorders (LSD) and common neurodegenerative diseases like Alzheimer’s and Parkinson’s. Lysosomal acidification is regulated by v-ATPase, a multi-subunit protein complex, consisting of a cytosolic V1 sector and lysosomal membrane-anchored V0 sector. Despite intense studies the mechanism(s) underlying defective lysosomal acidification in these disorders remains obscure. Neuronal-ceroid-lipofuscinoses (NCLs) constitute the most common neurodegenerative LSDs caused by mutations in 13 different genes (CLNs). The infantile-NCL (INCL) is the most lethal neurodegenerative disease caused by mutations in the CLN1 gene encoding palmitoyl-protein-thioesterase-1 (PPT1). Palmitoylation is the only reversible posttranslational lipid-modification. Dynamic palmitoylation (palmitoylation-depalmitoylation) facilitates steady-state membrane localization required for function of many important proteins. Using Cln1-/- mice, which mimic INCL, we uncovered that subunit a1 of the V0 sector (V0a1) of v-ATPase requires dynamic palmitoylation for its interaction with adaptor protein-2 (AP-2) and AP-3, respectively, essential for trafficking to lysosomal membrane. Ppt1-deficiency in Cln1-/- mice disrupted V0a1 dynamic palmitoylation, which suppressed dissociation of V0a1-AP2 complex preventing V0a1-AP3 interaction leading to its mistargeting to plasma membrane, dysregulating lysosomal acidification. Importantly, treatment of Cln1-/- mice with a thioesterase (Ppt1)-mimetic small molecule, NtBuHA, ameliorated this defect, which restored lysosomal acidic pH. Our findings reveal an unanticipated role of Cln1/Ppt1 in lysosomal acidification and suggest that varying factors adversely affecting v-ATPase activity may underlie pathogenesis of other LSDs and common neurodegenerative diseases.

Scientific Focus Area: Cell Biology

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