DNAJC5 affects the endo‐lysosomal pathway, APP processing, and AD pathology in vitro and in vivo

Abstract

The DnaJ heat shock protein family member C5 (DNAJC5) gene encodes Cysteine String Protein-alpha (CSPα). CSPα is a key endo-lysosomal element of the misfolding-associated protein secretion (MAPS) machinery. MAPS eliminates misfolded cytosolic proteins, including alpha-synuclein, tau, TDP-43, huntingtin. Mutations in the DNAJC5 gene cause rare early-onset dementia called adult-onset Neuronal ceroid lipofuscinosis (ANCL). Data from CSPα-deficient mice and flies suggest that CSPα is critical for preventing age-dependent neurodegeneration. The endo-lysosome plays an essential role in normal and abnormal Amyloid-beta precursor protein (APP) processing and subsequent β-amyloidogenesis in Alzheimer's disease (AD). However, the role of CSPα in APP processing, trafficking, and amyloidogenesis is not well understood.We used histological staining and whole transcriptome data from ANCL, AD patients, and age-matched pathology-free controls. Differential expression (DE) analysis was performed using DESeq2 software. We performed histological analysis of 5XFAD mouse models crossed with DNAJC5 mice. We used mouse neuroblastoma (N2A) cells stably expressing wild-type human APP695 (N2A695) and human wild-type (WT) and mutant DNAJC5. We used ELISA to quantify Aβ40 and Aβ42 in cell culture media and human brain lysates.CSPα co-localizes with endo-lysosomal and synaptic markers in N2A695 cells. CSPα overexpression affects lysosomal function and SNAP29-mediated exocytosis. Overexpression and knockdown of hCSPα-WT in N2A695 cells significantly affect extracellular Aβ40, Aβ42, full-length APP, and APP C-terminal fragments (CTF). N2A-APP cells expressing a gain-of-function DNAJC5 mutant displayed a significant increase in lysosomal and autophagy (LC3-II and p62) proteins, lysosomal exocytosis, and secreted levels of Aβ40 and Aβ42. ANCL brains showed considerable neuronal Aβ accumulation. ANCL brains exhibit a significant reduction of soluble and insoluble Aβ4 and Aβ42. Transcriptome analysis from ANCL brains shows changes in the mTOR pathway. DNAJC5 transcript levels are significantly reduced in AD cases compared to controls. A mouse AD model exhibits an inverse correlation between DNAJC5 transcript levels and Aβ plaques. 5XFAD mice haploinsufficient for DNAJC5 gene significantly increased the Aβ plaque burden and decreased Aβ plaque latency.Our results provide evidence of the novel and unexpected role of CSPα in endo-lysosomal function, lysosomal exocytosis, β-amyloidogenesis both in vitro and in vivo.