Biology subjects

Fleeman, R. M.

Publications and source records attributed to Fleeman, R. M..

6 recordsLinked to original sources

bioRxiv2023

Differential responses of primary neuron-secreted MCP-1 and IL-9 to type 2 diabetes and Alzheimer's disease-associated metabolites

Type 2 diabetes (T2D) is implicated as a risk factor for Alzheimers disease (AD), the most common form of dementia. In this work, we investigated neuroinflammatory responses of primary neurons to potentially circulating, blood-brain barrier (BBB) permeable metabolites associated with AD, T2D, or both. We identified nine metabolites associated with protective or detrimental properties of AD and T2D in literature (lauric acid, asparagine, fructose, arachidonic acid, aminoadipic acid, sorbitol, retinol, tryptophan, niacinamide) and stimulated primary mouse neuron cultures with each metabolite before quantifying cytokine secretion via Luminex. We employed unsupervised clustering, inferential statistics, and partial least squares discriminant analysis to identify relationships between cytokine concentration and disease-associations of metabolites. We identified MCP-1, a cytokine associated with monocyte recruitment, as differentially abundant between neurons stimulated by metabolites associated with protective and detrimental properties of AD and T2D. We also identified IL-9, a cytokine that promotes mast cell growth, to be differentially associated with T2D. Indeed, cytokines, such as MCP-1 and IL-9, released from neurons in response to BBB-permeable metabolites associated with T2D may contribute to AD development by downstream effects of neuroinflammation.

systems biology↗

bioRxiv2023

Alzheimer's disease-specific cytokine secretion suppresses neuronal mitochondrial metabolism

IntroductionNeuroinflammation and metabolic dysfunction are early alterations in Alzheimers disease brain that are thought to contribute to disease onset and progression. Glial activation due to protein deposition results in cytokine secretion and shifts in brain metabolism, which have been observed in Alzheimers disease patients. However, the mechanism by which this immunometabolic feedback loop can injure neurons and cause neurodegeneration remains unclear. MethodsWe used Luminex XMAP technology to quantify hippocampal cytokine concentrations in the 5xFAD mouse model of Alzheimers disease at milestone timepoints in disease development. We used partial least squares regression to build cytokine signatures predictive of disease progression, as compared to healthy aging in wild-type littermates. We applied the disease-defining cytokine signature to wild-type primary neuron cultures and measured downstream changes in gene expression using the NanoString nCounter system and mitochondrial function using the Seahorse Extracellular Flux live-cell analyzer. ResultsWe identified a pattern of up-regulated IFN{gamma}, IP-10, and IL-9 as predictive of advanced disease. When healthy neurons were exposed to these cytokines in proportions found in diseased brain, gene expression of mitochondrial electron transport chain complexes, including ATP synthase, was suppressed. In live cells, basal and maximal mitochondrial respiration were impaired following cytokine stimulation. ConclusionsAn Alzheimers disease-specific pattern of cytokine secretion reduces expression of mitochondrial electron transport complexes and impairs mitochondrial respiration in healthy neurons. We establish a mechanistic link between disease-specific immune cues and impaired neuronal metabolism, potentially causing neuronal vulnerability and susceptibility to degeneration in Alzheimers disease.

neuroscience↗

bioRxiv2022

Apolipoprotein E4 modulates astrocyte neuronal support functions in the presence of amyloid-β

Apolipoprotein E (APOE) is a lipid transporter produced predominantly by astrocytes in the brain. The {varepsilon}4 variant of APOE (APOE4) is the strongest and most common genetic risk factor for Alzheimers disease (AD). Although the molecular mechanisms of this increased risk are unclear, APOE4 is known to alter immune signaling and lipid and glucose metabolism. Astrocytes provide various forms of support to neurons, including regulating neuron metabolism and immune responses through cytokine signaling. Changes in astrocyte function due to APOE4 may therefore decrease neuronal support, leaving neurons more vulnerable to stress and disease insults. To determine whether APOE4 alters astrocyte neuronal support functions, we measured glycolytic and oxidative metabolism of neurons treated with conditioned media from APOE4 or APOE3 (the common, risk-neutral variant) primary astrocyte cultures. We found that APOE4 neurons treated with conditioned media from resting APOE4 astrocytes had similar metabolism to APOE3 astrocytes, but treatment with ACM from astrocytes challenged with amyloid-{beta} (A{beta}), a key pathological protein in AD, caused APOE4 neurons to increase their basal mitochondrial and glycolytic metabolic rates more than APOE3 neurons. These changes were not due to differences in astrocytic lactate production or glucose utilization, but instead correlated with increased glycolytic ATP production and a lack of cytokine secretion response to A{beta}. Together, these findings suggest that in the presence of A{beta}, APOE4 astrocytes alter immune and metabolic functions that result in a compensatory increase in neuronal metabolic stress.

neuroscience↗

bioRxiv2022

Predictive link between systemic metabolism and immune signaling in the brain of APOE4 mice

The {varepsilon}4 variant of apolipoprotein E (APOE) is the strongest and most common genetic risk factor for Alzheimers disease (AD). While the mechanism of conveyed risk is incompletely understood, promotion of inflammation, dysregulated metabolism, and protein misfolding and aggregation are contributors to accelerating disease. Here we determined the concurrent effects of systemic metabolic changes and brain inflammation in young (3-month-old) and aged (18-month-old) male and female mice carrying the APOE4 gene. Using functional metabolic assays alongside multivariate modeling of hippocampal cytokine levels, we found that brain cytokine signatures are predictive of systemic metabolic outcomes, independent of AD proteinopathies. Male and female mice each produce different cytokine signatures as they age and as their systemic metabolic phenotype declines, and these signatures are APOE genotype dependent. Ours is the first study to identify a quantitative and predictive link between systemic metabolism and specific pathological cytokine signatures in the brain. Our results highlight the effects of APOE4 beyond the brain and suggest the potential for bi-directional influence of risk factors in the brain and periphery. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=123 SRC="FIGDIR/small/480074v2_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@5865d5org.highwire.dtl.DTLVardef@185a0e0org.highwire.dtl.DTLVardef@4d2e7org.highwire.dtl.DTLVardef@b27318_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2021

GM1 mediates the formation and maintenance of cytotoxic Aβ oligomers

The aggregation of amyloid beta (A{beta}) peptide is associated with Alzheimers disease (AD) pathogenesis. Cell membrane composition, especially monosialotetrahexosylganglioside (GM1), is known to promote the formation of A{beta} fibrils, yet little is known about the roles of GM1 in the early steps of A{beta} oligomer formation. Here, by using GM1-contained liposomes as a mimic of neuronal cell membrane, we demonstrate that GM1 is a critical trigger of A{beta} oligomerization and aggregation. We find that GM1 not only promotes the formation of A{beta} fibrils, but also facilitates the maintenance of A{beta} oligomers on liposome membranes. We structurally characterize the A{beta} oligomers formed on the membrane and find that GM1 captures A{beta} by binding to its arginine-5 residue. To interrogate the mechanism of A{beta} oligomer toxicity, we design a new liposome-based Ca2+-encapsulation assay and provide new evidence for the A{beta} ion channel hypothesis. Finally, we conduct cell viability assay to determine the toxicity of A{beta} oligomers formed on membranes. Overall, by uncovering the roles of GM1 in mediating early A{beta} oligomer formation and maintenance, our work provides a novel direction for pharmaceutical research for AD.

biophysics↗

bioRxiv2020

Novel microRNA multivariate biomarkers of response to immunotherapy against HPV E6 oncogene

Cervical cancer is caused by the persistent infection high-risk types of human papillomavirus (HPV) in over 99.9% of cases. To favor malignant transformation, HPV E6 and E7 oncogenes disrupt both p53 and retinoblastoma (Rb) respectively and control microRNA (miR) networks. We have previously demonstrated the therapeutic potential of anti-HPV E6 monoclonal antibodies (mAbs) in experimental models of human cervical cancer; yet the underlying mechanism remains unclear. Here, we sought to determine if anti-HPV E6 mAbs modulate the miR signatures of HPV E6 oncogenes. To this end, we performed qRT-PCR to measure the expression of thirty-four miRs and found that univariate analysis is not able to identify novel interactions characteristic of complex biological systems. Thus, we utilized partial least squares discriminant analysis (PLSDA) to identify signatures of co-varying miRs specific to mAb treatment. These miR signatures predictively discriminate between anti-HPV E6 mAb response and control mAb treatment, which may provide mechanistic insight into the action of anti-HPV E6 mAbs.Competing Interest StatementThe authors have declared no competing interest.View Full Text

systems biology↗