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

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.Peer reviewe

Neuron-astrocyte transmitophagy is altered in Alzheimer's disease

Under physiological conditions in vivo astrocytes internalize and degrade neuronal mitochondria in a process called transmitophagy. Mitophagy is widely reported to be impaired in neurodegeneration but it is unknown whether and how transmitophagy is altered in Alzheimer's disease (AD). Here we report that the internalization of neuronal mitochondria is significantly increased in astrocytes isolated from AD mouse brains. We also demonstrate that the degradation of neuronal mitochondria by astrocytes is increased in AD mice at the age of 6 months onwards. Furthermore, we demonstrate for the first time a similar phenomenon between human neurons and AD astrocytes, and in murine hippocampi in vivo. The results suggest the involvement of S100a4 in impaired mitochondrial transfer between neurons and AD astrocytes together with significant increases in the mitophagy regulator and reactive oxygen species in aged AD astrocytes. These findings demonstrate altered neuronsupporting functions of AD astrocytes and provide a starting point for studying the molecular mechanisms of transmitophagy in AD.Peer reviewe

Mechanisms of Neuropathic Pain Following Mild Blast Traumatic Brain Injury and Chronic Stress

The incidence of mild blast traumatic brain injury has risen due to the increased use of improvised explosive devices (IEDs) in military conflicts. Mild blast TBI (mbTBI) is especially relevant due to its lack of acutely observable symptoms, and to its association with long-term neurodegenerative and neuropsychiatric disorders. Predominantly, TBI patients often suffer from chronic stress, neuropathic pain and headaches, which greatly compromise the health and quality of life of these individuals. Treatments for neuropathic pain have been empirically found and produce little effect in lessening neuropathic pain, likely due to the lack of targeted therapies. This highlights the need for better understanding of the molecular mechanisms underlying neuropathic pain, TBI and chronic stress that could lead to mechanistic therapeutic targets. Oxidative stress is an important mechanism of the pathophysiology of neuropathic pain, TBI and chronic stress. We hypothesize that acrolein, an endogenously formed neurotoxin, is able to stay active in the body for up to 10 days, is involved in the pathophysiology of neuropathic pain in TBI and chronic stress. This study aims to correlate acrolein elevation in the body with neuropathic pain, deepen the understanding of underlying mechanisms of pain in TBI and chronic stress, and mitigate this pain with acrolein scavenging. The ultimate goal of this research is to provide therapies for TBI and chronic stress patients that can eliminate pain and significantly improve their health and quality of life