Biology subjects

Yassine, H. N.

Publications and source records attributed to Yassine, H. N..

6 recordsLinked to original sources

bioRxiv2026

TOMM40 '523' genotype induces sex- and tissue- specific differences in cholesterol and triglyceride levels in an APOE-TOMM40 humanized mouse model

IntroductionGenetic variants within the APOE-TOMM40 locus are associated with Alzheimers disease (AD). A specific role for TOMM40 is indicated by the finding that 523 poly-T variants are associated with AD risk, but the mechanism for this effect has not been established. Our studies have shown that suppression of Tomm40 in mice increased brain cholesterol content, an AD risk factor, and thus the present study sought to assess whether major 523 poly-T variants (Short [S] and Very Long [VL]) are associated with altered lipid content of brain and other tissues. MethodsWe utilized a mouse model containing the entire human APOE3-TOMM40 locus to quantify cholesterol and triglyceride levels in brain, liver, and white adipose tissue (WAT), as well as brain content of the AD biomarkers A{beta} 42 and tau, in mice carrying two homozygous TOMM40 523 poly-T genotypes (S/S and VL/VL). ResultsMale mice carrying the 523-S/S genotype, but not females, showed higher brain cholesterol and triglyceride levels than VL/VL carriers, together with greater brain A{beta} 42 content. WAT showed similar lipid differences as in the brain, while hepatic lipid content was broadly similar between 523-S/S and -VL/VL genotypes, though there was a trend for higher triglycerides in VL/VL mice in a sex- and age-dependent manner. DiscussionThese results demonstrate that TOMM40 523 poly-T variants drive tissue-specific, sex-, and age-dependent lipid differences in humanized APOE3-TOMM40 mice, with the S/S genotype linked to elevated brain cholesterol and A{beta} 42 levels, effects that link this locus to AD pathogenesis.

genetics↗

bioRxiv2025

TOMM40 suppression promotes neuronal cholesterol imbalance and molecular and behavioral phenotypes of Alzheimer's disease

INTRODUCTIONWhile the APOE4 allele is a major risk factor for Alzheimers disease (AD), the role of TOMM40--an adjacent gene involved in mitochondrial protein import--is not known. METHODSMice, human iPSC-derived neurons (iNeurons), and human brain tissue were used for study of animal cognition, cholesterol metabolism, mitochondrial function, and gene expression. RESULTSTOMM40 knockdown (KD) impaired memory in mice and increased cholesterol and A{beta} 42 in mouse brains and human iNeurons. KD disrupted mitochondria-endoplasmic reticulum contact sites (MERCs), causing mitochondrial dysfunction and promoting reactive oxygen species that led to activation of LXRB (NR1H2), upregulation of APOE and LDLR. and increased cellular cholesterol and A{beta} 42 independent of APOE4. Human brain transcriptomics showed reduced TOMM40 expression that correlated with cholesterol regulatory gene expression, amyloid burden, and clinical AD diagnosis. DISCUSSIONTOMM40 is a novel mediator of AD pathology through dual effects on MERCs that regulate cholesterol homeostasis and mitochondrial function. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=163 SRC="FIGDIR/small/685963v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@e3e3e2org.highwire.dtl.DTLVardef@1861f67org.highwire.dtl.DTLVardef@77a813org.highwire.dtl.DTLVardef@1bb9a83_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2025

Evidence for cPLA2 activation in Alzheimer's Disease Synaptic Pathology

BackgroundSynapses are essential for learning and memory, and their loss predicts cognitive decline in Alzheimers disease (AD). Synaptic loss is associated with excitotoxicity, neuroinflammation, amyloid-{beta}, and tau pathology, but the molecular mechanisms remain unclear. There is an urgent need to identify new targets to modify the disease and slow synaptic loss and cognitive decline. This study examines if calcium-dependent phospholipase A2 (cPLA2) is implicated in AD synaptic loss. cPLA2 catalyzes membrane phospholipids to release arachidonic acid, which can be metabolized into inflammatory eicosanoids. MethodscPLA2 levels were examined in synaptosomes isolated from the postmortem frontal cortex of individuals with no cognitive impairment (NCI), mild cognitive impairment (MCI), and AD dementia from the Religious Orders Study (ROS). Eicosanoids in synaptosomes were analyzed using lipidomics. Immunofluorescent staining investigated cPLA2 interactions with synaptic markers. Human iPSCs-derived neurons were used to study cPLA2 overactivation after exposure to amyloid-{beta} 42 oligomers (A{beta}42O), its relationships with synaptic markers, and the effects of cPLA2 inhibitors. ResultsWe observed elevated cPLA2 (cPLA2 and cPLA2{beta}) in AD synaptosomes and positive correlations with postsynaptic density protein 95 (PSD-95) and cognitive dysfunction. Eicosanoids were increased in AD synaptosomes and correlated with cPLA2, indicating cPLA2 activity at synapses/synaptosomes. Phosphorylated cPLA2 (p-cPLA2) colocalized with PSD-95 in synaptosomes, and with postsynaptic Ca2+/calmodulin-dependent protein kinase II (CaMKII) and dendritic microtubule-associated protein 2 (MAP2) in NCI and AD brains, where their levels were reduced in AD. P-cPLA2 colocalizes with MAP2 at the neuronal soma associated with neuritic plaques and neurodegeneration in AD. A{beta}42O activates cPLA2 in human iPSCs-derived neurons, leading to p-cPLA2 relocation from the cytosol to synaptic and dendritic sites to colocalize with CaMKII and MAP2, resulting in their reduction. P-cPLA2 also colocalized with PSD-95 in A{beta}42O-exposed neurons, accompanied with increased PSD-95 intensity at soma membrane. These processes were reversed by the cPLA2 inhibitor ASB14780. ConclusionscPLA2 overactivation at synapses, dendrites, and excitatory neuronal somas is associated with synaptic loss, neuritic plaques and neurodegeneration, potentially contributing to cognitive decline in AD. Future research needs to explore the role of cPLA2 as a disease-modifying target for AD.

neuroscience↗

bioRxiv2025

Development of Potent, Selective cPLA2 Inhibitors for Targeting Neuroinflammation in Alzheimer's Disease and Other Neurodegenerative Disorders

Chronic neuroinflammation plays a key role in the progression of Alzheimers disease (AD), and the cytosolic calcium-dependent phospholipase A2 (cPLA2) enzyme is a critical mediator of inflammatory lipid signaling pathways. Here we investigate the therapeutic potential of novel cPLA2 inhibitors in modulating neuroinflammation in AD. By leveraging the giga-scale V-SYNTHES 2.0 virtual screening in on-demand chemical space and conducting two rounds of optimization for potency and selectivity, we have identified BRI-50460, achieving an IC50 of 0.88 nM in cellular assays of cPLA2 activity. In vivo studies revealed favorable brain-to-plasma ratios, highlighting the ability of BRI-50460 to penetrate the central nervous system, potentially modulating neuroinflammatory pathways and restoring lipid homeostasis. In cultured astrocytes and neurons derived from human induced pluripotent stem cells, BRI-50460 mitigates the effects of amyloid beta 42 oligomers on cPLA2 activation, tau hyperphosphorylation, and synaptic and dendritic reduction. Our results suggest that small molecule inhibitors of the cPLA2 enzyme can modulate the downstream inflammatory lipid signaling pathways, offering a promising therapeutic strategy for AD and other neurodegenerative diseases.

neuroscience↗

bioRxiv2024

Increased cerebrospinal fluid and plasma apoE glycosylation is associated with reduced levels of Alzheimer's disease biomarkers

The apolipoprotein E (APOE) {varepsilon}4 allele is the strongest genetic risk factor for Alzheimers disease (AD). ApoE is glycosylated with an O-linked Core-1 sialylated glycan at several sites, yet the impact and function of this glycosylation on AD biomarkers remains unclear. We examined apoE glycosylation in a cohort of cerebrospinal fluid (CSF, n=181) and plasma (n= 178) samples from the Alzheimers Disease Neuroimaging Initiative (ADNI) stratified into 4 groups: cognitively normal (CN), Mild Cognitive Impairment (MCI), progressors and non-progressors based on delayed word recall performance over 4 years. We observed decreasing glycosylation from apoE2 > apoE3 > apoE4 in CSF, and in plasma (apoE3 > apoE4). ApoE glycosylation was reduced in the MCI compared with CN groups, and in progressors compared to non-progressors. In CSF, higher apoE glycosylation associated cross-sectionally with lower total tau (t-tau), p-tau181, and with higher A{beta}1-42. Similar associations of apoE glycosylation with higher A{beta}1-42 were observed in plasma. In CSF, greater apoE4 glycosylation was associated with lower t-tau and p-tau181. Over a 6-year period, higher baseline levels of CSF apoE glycosylation predicted lower rates of increase in CSF t-tau and p-tau181 and lower rates of decrease in CSF A{beta}1-42. These results indicate strong associations of apoE glycosylation with biomarkers of AD pathology independent of apoE genotype, warranting a deeper understanding of the functional role of apoE glycosylation on AD tau pathology.

neuroscience↗

bioRxiv2024

Microglia States are Susceptible to Senescence and Cholesterol Dysregulation in Alzheimer's Disease

Cellular senescence is a major contributor to aging-related degenerative diseases, including Alzheimers disease (AD) but much less is known on the key cell types and pathways driving mechanisms of senescence in the brain. We hypothesized that dysregulated cholesterol metabolism is central to cellular senescence in AD. We analyzed whole transcriptomic data and utilized single-cell RNA seq integration techniques to unveil the convoluted cell-type-specific and sub-cell-type-state-specific senescence pathologies in AD using both ROSMAP and Sea-AD datasets. We identified that microglia are central components to AD associated senescence phenotypes in ROSMAP snRNA-seq data (982,384 nuclei from postmortem prefrontal cortex of 239 AD and 188 non-AD) among non-neuron cell types. We identified that homeostatic, inflammatory, phagocytic, lipid processing and neuronal surveillance microglia states were associated with AD associated senescence in ROSMAP (152,459 microglia nuclei from six regions of brain tissue of 138 early AD, 79 late AD and 226 control subject) and in Sea-AD (82,486 microglia nuclei of 42 dementia, 42 no dementia and 5 reference subjects) via integrative analysis, which preserves the meaningful biological information of microglia cell states across the datasets. We assessed top senescence associated bioprocesses including mitochondrial, apoptosis, oxidative stress, ER stress, endosomes, and lysosomes systems. Specifically, we found that senescent microglia have altered cholesterol related bioprocesses and dysregulated cholesterol. We discovered three gene co-expression modules, which represent the specific cholesterol related senescence transcriptomic signatures in postmortem brains. To validate these findings, the activation of specific cholesterol associated senescence transcriptomic signatures was assessed using integrative analysis of snRNA-seq data from iMGs (microglia induced from iPSCs) exposed to myelin, Abeta, and synaptosomes (56,454 microglia across two replicates of untreated and four treated groups). In vivo cholesterol associated senescence transcriptomic signatures were preserved and altered after treatment with AD pathological substrates in iMGs. This study provides the first evidence that dysregulation of cholesterol metabolism in microglia is a major driver of senescence pathologies in AD. Targeting cholesterol pathways in senescent microglia is an attractive strategy to slow down AD progression.

neuroscience↗