A cell‐autonomous role of DNAJC5 in microglial‐mediated proteostasis in Alzheimer’s disease

Abstract Background DNAJC5 encodes co‐chaperone cysteine‐string protein alpha (CSPα), a synaptic and endolysosomal protein whose mutations cause adult‐onset neuronal ceroid lipofuscinosis (ANCL). Characterized by endolysosomal dysfunction, microgliosis, synaptic loss, and protein aggregation, ANCL shares pathological features with Alzheimer’s disease (AD). The endolysosomal role of CSPα in non‐neuronal cell types has been understudied. Here, we aimed to address this gap and hypothesized that CSPα plays a yet undefined microglial role in AD. Method Aβ levels and plaques in human tissue were assessed through ELISA and immunohistochemistry, respectively. Bulk‐RNAseq data from two independent cohorts of AD and ANCL patients with controls (GSE5281; GSE15222) were analyzed. To assess cell‐autonomous expression, single‐nuclei RNAseq (snRNA‐seq) was mined from the parietal cortex of AD patients with APP and PSEN1 mutations (n = 16) along with sporadic AD (n = 31), non‐AD (n = 9), presymptomatic (n = 3), and control patients (n = 8). An independent cohort (GSE138852) was analyzed for rigor. Using Clue.io, candidate therapeutics projected to reverse the observed transcriptomic profile from DNAJC5 mutants in myeloid cells were identified. A cohort from iPSC‐derived microglia (GSE178317) was cross‐analyzed with the ANCL RNAseq. Result In tissue from ANCL patients, soluble or insoluble Aβ levels were nearly nonexistent and synaptic protein levels were reduced, but intraneuronal Aβ accumulation was increased, suggesting altered APP processing. In two independent RNAseq cohorts (GSE5281; GSE15222), DNAJC5 was reduced in AD patients versus controls. SnRNA‐seq from parietal cortex revealed higher DNAJC5 transcript levels in microglia versus neurons. RNAseq obtained from ANCL patients was cross‐referenced with dataset obtained from iPSC‐derived microglia, revealing 35 differentially expressed genes associated with proliferative microglia and 32 genes associated with the interferon/chemokine response. Analysis of ANCL transcriptomics in myeloid cell lines using Clue.io indicate HSP inhibitors (BIIB‐021, geldanamycin), an opioid receptor antagonist (BNTX), and a proteasome inhibitor (bortezomib) suggesting convergence in proteostasis in microglial cells. ANCL‐patient transcriptomics displayed reduced TSPAN14, which facilitates ADAM10 maturation, and elevated APH1B and GSAP, enzymes that promote γ‐secretase activity suggesting a shift towards amyloidogenic pathway. Conclusion DNAJC5 is implicated in AD pathogenesis modulating APP processing and amyloidogenesis. Furthermore, endolysosomal DNAJC5 might play a novel cell‐autonomous role in microglia under altered proteostasis.