Assessing the Co-Chaperone and Synaptic Protein DNAJC5 as a Therapeutic Target in Alzheimer’s Disease
Matthew Rosene1, Niko Nykänen2, Kevin O'Dell2, Marie Nunez2, Oscar Harari2, John Cirrito2, Mark Sands2, Bruno Benitez1
1Beth Israel Deaconess Medical Center/Harvard Medical School, 2Washington University in Saint Louis
Objective:

Assess the therapeutic potential of DNAJC5 in Alzheimer’s disease (AD).

Background:
DNAJC5 encodes cysteine-string protein alpha (CSPα), whose mutations cause adult neuronal ceroid lipofuscinosis (ANCL). ANCL is characterized by endolysosomal dysfunction, synaptic loss, and protein aggregate accumulation, similar to AD. CSPα facilitates secretion of the neurodegenerative proteins tau, TDP-43, and α-synuclein and maintains synaptic integrity. Therefore, CSPα is a promising therapeutic target. 
Design/Methods:

N2A695 cells stably expressing mutant DNAJC5 or knocking down endogenous Dnajc5 were analyzed through immunoblotting and ELISA for APP processing and Aβ production. Brains of ANCL patients and Dnajc5+/-; 5xFAD mice were assessed for amyloid pathology with immunohistochemistry. Transcriptomics from ANCL, AD, and control brains was analyzed for differentially expressed genes (DEGs). The Clue.IO database was used to identify potential targets for gene therapy or pharmacological intervention.

Results:

ANCL-patient brains exhibited low soluble or insoluble Aβ levels, but intra-neuronal Aβ accumulation. They exhibited reductions in synaptic protein levels (SNAP-25, Synaptobrevin, Syntaxin 1, and Synaptophysin). Transcriptomic analysis of ANCL-patient brains showed reduced TSPAN14, which facilitates ADAM10 maturation, elevated APH1B, a γ-secretase subunit, and elevated GSAP, the γ-secretase activating protein. There were 67 upregulated and 15 downregulated transcripts associated with processes essential for synaptic function, including the MAPK cascade (FYN, SOS1), dendritic spine organization (FYN), and endosomal vesicle fusion (VPS11, VPS39). Clue.IO identified heat-shock protein inhibitors and an opioid receptor antagonist (BNTX) as potential pharmacological agents to counteract the effects of mutant DNAJC5. AD patients and 5xFAD mice exhibited reduced DNAJC5 expression. Preliminary results from Dnajc5+/-; 5xFAD mice showed increased plaques in the corpus collosum and hippocampus. N2A695 cells expressing DNAJC5 mutants showed increased Aβ while DNAJC5 knockdown decreased Aβ.

Conclusions:

Low levels of CSPα alter Ab secretion and dysregulate genes and synaptic proteins, suggesting that increasing CSPα levels could reduce Aβ and improve synaptic function.

10.1212/WNL.0000000000203350