(A-33) Profiling Neuron Inflammation Driven by Alzheimer’s Disease and Type 2 Diabetes Associated Metabolites

Introduction:: Alzheimer’s disease (AD) is the most common form of dementia and is the seventh leading cause of death in the United States. Studies have shown that the progression of AD is not due to a single risk factor, but likely to a combination of age, genetics, family history, and environment. Evidence also suggests that people with type 2 diabetes (T2D) experience a higher prevalence of AD than the general population. In fact, the number of people with AD who also have T2D, or impaired glucose levels, may be as high as 81%. While studies point to possible impairment of insulin receptors, dysregulation of brain glucose metabolism, or chronic inflammatory processes, the exact state of how T2D exacerbates AD pathology is not well-understood. Our objective is to profile neuroinflammatory responses to metabolites associated with AD and T2D that is able to cross the blood brain barrier.

Materials and Methods:: Through literature review, we identified nine candidate metabolites associated with neuroprotective or neurodegenerative properties, which include lauric acid, asparagine, fructose, arachidonic acid, aminoadipic acid, sorbitol, retinol, tryptophan, and niacinamide. The nine metabolites associated with the potential development of AD or T2D were used to individually stimulate cultures of primary neurons collected from embryonic CD1 mice (Figure 1A). All neuron cultures were inspected after cell plating, and before metabolite stimulation (Figure 1B). After stimulating the neurons, the cell media was sampled and analyzed using a Luminex assay. The quantified in-range concentrations for each cytokine were normalized in respect to its vehicle by applying a log2 fold change calculation. The results were analyzed using RStudio (version 1.4.1717).

Results, Conclusions, and Discussions:: The stimulated neurons exhibited distinct cytokine signatures based on disease-association of the metabolite, which was supported by principal component analysis (PCA) and hierarchical clustering analysis. With PCA, we found that seven of the nine metabolites, excluding retinol and arachidonic acid, clustered together regardless of disease association, indicating that the neuroinflammatory response to these seven metabolites is similar (Figure 1C). When comparing the fold changes of each cytokine, we found that MCP-1 was upregulated by retinol, L-tryptophan, and niacinamide, all which are metabolites associated with protection from AD (Figure 1D). Metabolites associated with T2D and AD effects downregulated MCP-1. From this data and relevant literature on mouse model studies, we hypothesize the existence of a pathway involving neuron-secreted MCP-1 in response to the protective metabolite retinol. (Figure 1E). However, we acknowledge that there be conflicting findings in human AD studies, which may indicate other implicit signaling dysregulations during AD development.

Using an in vitro primary neuron model, we have identified MCP-1 to serve an important role in the neuroprotective properties of AD and T2D at the early-stages, with a hypothesized signaling pathway between neurons and microglia that is supported by a literature review. Our work has shown that there is neuron inflammation that is mediated by metabolites associated with AD and T2D pathology. Despite these findings, our limitation is that these cytokine profiles are a result of early-stage stimulation and may not represent the signaling process of later stage of AD pathology. However, these results encourage future studies to expand the investigation to include other neural cell types, other metabolites, and longer time frames associated with T2D or AD pathology.

Acknowledgements (Optional): :

References (Optional): :