Single-Cell RNA-Seq Analysis of Olfactory Mucosal Cells of Alzheimer’s Disease Patients

Abstract

Olfaction is orchestrated by olfactory mucosal cells located in the upper nasal cavity. Olfactory dysfunction manifests early in several neurodegenerative disorders including Alzheimer’s disease, however, disease-related alterations to the olfactory mucosal cells remain poorly described. The aim of this study was to evaluate the olfactory mucosa differences between cognitively healthy individuals and Alzheimer’s disease patients. We report increased amyloid-beta secretion in Alzheimer’s disease olfactory mucosal cells and detail cell-type-specific gene expression patterns, unveiling 240 differentially expressed disease-associated genes compared to the cognitively healthy controls, and five distinct cell populations. Overall, alterations of RNA and protein metabolism, inflammatory processes, and signal transduction were observed in multiple cell populations, suggesting their role in Alzheimer’s disease-related olfactory mucosa pathophysiology. Furthermore, the single-cell RNA-sequencing proposed alterations in gene expression of mitochondrially located genes in AD OM cells, which were verified by functional assays, demonstrating altered mitochondrial respiration and a reduction of ATP production. Our results reveal disease-related changes of olfactory mucosal cells in Alzheimer’s disease and demonstrate the utility of single-cell RNA sequencing data for investigating molecular and cellular mechanisms associated with the disease.

An Alzheimer’s disease patient-derived olfactory cell model identifies gene expression changes associated with cognition

“…ONS cells were predominantly of immature cell neuro-glial lineage in keeping with previous reports (12, 14). However, this immature neuro-glial phenotype differed significantly from the original OM cultures in which neuronal and glial cell markers were reported to be (largely) absent (28). No significant marker expression differences were observed between HC, MCI and AD-derived ONS cells.…”

“…p<0.05) associated with AD and involved in pathways related to inflammatory processes, RNA and protein metabolism, and signal transduction. They also identified fibroblast/stromal-like cells, globose basal cell (GBC)-like cells at different states of differentiation, and myofibroblast-like cells as common cell types present in OM cell cultures of AD patients and cognitively healthy controls (28). Culturing of OM cells into neurospheres results in a more neuro-glial environment as described above, and this may promote the differential expression of associated neuronal or glial genes that are related to cognitive processes.…”

“…Little is known about the transcriptome of olfactory cells in AD patients. Lampinen et al (28) have recently reported single-cell transcriptomic data from AD patient-derived OM cells. They observed 240 DEGs (adj.…”

“…Voluntary study patients with AD type mild (CDR 1) dementia ( n =6) and MCI ( n =6) were diagnostically examined, recruited together with cognitively healthy control subjects ( n =6) and their nasal biopsy sample was collected and processed as previously described (28). Briefly, a piece of OM was biopsied from the nasal septum and kept on ice in Dulbecco’s Modified Eagle Medium/Ham F-12 (DMEM/F12) (#11320033)-based growth medium containing 10% heat-inactivated fetal bovine serum (FBS) (#10500064) and 1% Penicillin-Streptomycin solution (P/S) (#15140122) until processed in the laboratory (All reagents Thermo Fisher Scientific, Waltham, MA, USA).…”

“…Briefly, a piece of OM was biopsied from the nasal septum and kept on ice in Dulbecco’s Modified Eagle Medium/Ham F-12 (DMEM/F12) (#11320033)-based growth medium containing 10% heat-inactivated fetal bovine serum (FBS) (#10500064) and 1% Penicillin-Streptomycin solution (P/S) (#15140122) until processed in the laboratory (All reagents Thermo Fisher Scientific, Waltham, MA, USA). Primary OM cell cultures were established according to the published protocol (28, 92). The age of the patients with AD and cognitively healthy control subjects age averaged ∼71 years and 70 years, respectively, while the MCI group averaged 72 years.…”