Enhanced cytotoxic response of natural killer cells to interleukin-2 in Alzheimer's disease

JDSNMF: Joint Deep Semi-Non-Negative Matrix Factorization for Learning Integrative Representation of Molecular Signals in Alzheimer's Disease

High dimensional multi-omics data integration can enhance our understanding of the complex biological interactions in human diseases. However, most studies involving unsupervised integration of multi-omics data focus on linear integration methods. In this study, we propose a joint deep semi-non-negative matrix factorization (JDSNMF) model, which uses a hierarchical non-linear feature extraction approach that can capture shared latent features from the complex multi-omics data. The extracted latent features obtained from JDSNMF enabled a variety of downstream tasks, including prediction of disease and module analysis. The proposed model is applicable not only to sample-matched multiple data (e.g., multi-omics data from one cohort) but also to feature-matched multiple data (e.g., omics data from multiple cohorts), and therefore it can be flexibly applied to various cases. We demonstrate the capabilities of JDSNMF using sample-matched simulated data and feature-matched multi-omics data from Alzheimer’s disease cohorts, evaluating the feature extraction performance in the context of classification. In a test application, we identify AD- and age-related modules from the latent matrices using an explainable artificial intelligence and regression model. These results show that the JDSNMF model is effective in identifying latent features having a complex interplay of potential biological signatures.

Depletion of NK Cells Improves Cognitive Function in the Alzheimer Disease Mouse Model

Despite mounting evidence suggesting the involvement of the immune system in regulating brain function, the specific role of immune and inflammatory cells in neurodegenerative diseases remain poorly understood. In this study, we report that depletion of NK cells, a type of innate lymphocytes, alleviates neuroinflammation, stimulates neurogenesis, and improves cognitive function in a triple-transgenic Alzheimer disease (AD) mouse model. NK cells in the brains of triple-transgenic AD mouse model (3xTg-AD) mice exhibited an enhanced proinflammatory profile. Depletion of NK cells by anti-NK1.1 Abs drastically improved cognitive function of 3xTg-AD mice. NK cell depletion did not affect amyloid β concentrations but enhanced neurogenesis and reduced neuroinflammation. Notably, in 3xTg-AD mice depleted of NK cells, microglia demonstrated a homeostatic-like morphology, decreased proliferative response and reduced expression of neurodestructive proinflammatory cytokines. Together, our results suggest a proinflammatory role for NK cells in 3xTg-AD mice and indicate that targeting NK cells might unlock novel strategies to combat AD.

Immunosenescence of Natural Killer Cells, Inflammation, and Alzheimer's Disease

Alzheimer's disease (AD) represents the most common cause of dementia in the elderly. AD is a neurodegenerative disorder characterized by progressive memory loss and cognitive decline. Although the aetiology of AD is not clear, both environmental factors and heritable predisposition may contribute to disease occurrence. In addition, inflammation and immune system alterations have been linked to AD. The prevailing hypothesis as cause of AD is the deposition in the brain of amyloid beta peptides (Aβ). Although Aβ have a role in defending the brain against infections, their accumulation promotes an inflammatory response mediated by microglia and astrocytes. The production of proinflammatory cytokines and other inflammatory mediators such as prostaglandins and complement factors favours the recruitment of peripheral immune cells further promoting neuroinflammation. Age-related inflammation and chronic infection with herpes virus such as cytomegalovirus may also contribute to inflammation in AD patients. Natural killer (NK) cells are innate lymphoid cells involved in host defence against viral infections and tumours. Once activated NK cells secrete cytokines such as IFN-γ and TNF-α and chemokines and exert cytotoxic activity against target cells. In the elderly, changes in NK cell compartment have been described which may contribute to the lower capacity of elderly individuals to respond to pathogens and tumours. Recently, the role of NK cells in the immunopathogenesis of AD is discussed. Although in AD patients the frequency of NK cells is not affected, a high NK cell response to cytokines has been described together with NK cell dysregulation of signalling pathways which is in part involved in this altered behaviour.

NK cells in healthy aging and age-associated diseases

NK cells exhibit the highest cytotoxic capacity within the immune system. Alteration of their number or functionality may have a deep impact on overall immunity. This is of particular relevance in aging where the elderly population becomes more susceptible to infection, cancer, autoimmune diseases, and neurodegenerative diseases amongst others. As the fraction of elderly increases worldwide, it becomes urgent to better understand the aging of the immune system to prevent and cure the elderly population. For this, a better understanding of the function and phenotype of the different immune cells and their subsets is necessary. We review here NK cell functions and phenotype in healthy aging as well as in various age-associated diseases.

Can peripheral leukocytes be used as Alzheimer's disease biomarkers?

Alzheimer's disease (AD) is the leading cause of dementia in elderly populations throughout the world and its incidence is on the rise. Current clinical diagnosis of AD requires intensive examination that includes neuropsychological testing and costly brain imaging techniques, and a definitive diagnosis can only be made upon postmortem neuropathological examination. Additionally, antemortem clinical AD diagnosis is typically administered following onset of cognitive and behavioral symptoms. As these symptoms emerge relatively late in disease progression, therapeutic intervention occurs after significant neurodegeneration, thereby limiting efficacy. The identification of noninvasive diagnostic biomarkers of AD is becoming increasingly important to make diagnosis more widely available to clinics with limited access to neuropsychological testing or state-of-the-art brain imaging, reduce the cost of clinical diagnosis, provide a biological measure to track the course of therapeutic intervention, and most importantly, allow for earlier diagnosis--possibly even during the prodromal phase--with hopes of therapeutic intervention prior to appreciable neurodegeneration. Circulating leukocytes are attractive candidate AD biomarkers as they can be obtained in a minimally invasive manner and are easily analyzed by widely available flow cytometry techniques. In this review, we critically analyze the potential utility of peripheral leukocytes as biological markers for AD.

Peripheral markers in testing pathophysiological hypotheses and diagnosing Alzheimer's disease

Alterations in amyloid precursor protein (APP) metabolism, calcium regulation, oxidative metabolism, and transduction systems have been implicated in Alzheimer's disease (AD). Limitations to the use of postmortem brain for examining molecular mechanisms underscore the need to develop a human tissue model representative of the pathophysiological processes that characterize AD. The use of peripheral tissues, particularly of cultured skin fibroblasts derived from AD patients, could complement studies of autopsy samples and provide a useful tool with which to investigate such dynamic processes as signal transduction systems, ionic homeostasis, oxidative metabolism, and APP processing. Peripheral cells as well as body fluids (i.e., plasma and CSF) could also provide peripheral biological markers for the diagnosis of AD. The criteria required for a definite diagnosis of AD presently include clinical criteria in association with histopathologic evidence obtained from biopsy or autopsy. Thus, the use of peripheral markers as a diagnostic tool, either to predict or at least to confirm a diagnosis, may be of great importance.