Biology subjects

Ioannou, M. S.

Publications and source records attributed to Ioannou, M. S..

8 recordsLinked to original sources

bioRxiv2026

ApoE4 impairs astrocyte lipid droplet formation via endolysosomal dysfunction

An important component of neuron-glia coupling is the transport and delivery of neuron-derived lipids to glial lipid droplets. This pathway is important as failure to store incoming lipids in glial lipid droplets exacerbates neurodegeneration. ApoE4, a risk factor for Alzheimer's disease, impairs this transport pathway. But how ApoE4 affects lipid trafficking in glia and whether these alterations can be restored is poorly understood. Here, we demonstrate that ApoE4 particles impair endolysosomal function and promote lipofuscin formation in cultured primary astrocytes, thereby disrupting the trafficking of lipids for storage into lipid droplets. Lipid droplets, however, can be recovered by preventing lysosomal impairment with PCSK9, a secreted protein that prevents LDLR recycling and reduces ApoE4 internalization. Lipid droplets are similarly recovered in the presence of ApoE4 by repairing endolysosomal function. Our findings reveal new insight into how ApoE4 dysregulates lipid storage while uncovering new mechanisms to correct these defects.

neuroscience↗

bioRxiv2025

Protective ApoE variants support neuronal function by extracting peroxidated lipids

ApoE mediates the transport of lipids from neurons to glial lipid droplets. ApoE4, a major risk factor for Alzheimer's disease, impairs this transport pathway, increasing risk for neurodegeneration. ApoE2 and ApoE3 Christchurch (ApoE3Ch) variants confer resistance to developing the disease, yet little is known regarding how these protective variants affect lipid transport. Here, we explored how lipoprotein particles containing different ApoE isoforms affect neuronal health in vitro and in intact rodent hippocampi. We demonstrate that ApoE2 and ApoE3Ch particles protect neurons from ferroptosis by preferentially extracting peroxidated unsaturated lipids through the neuronal ABCA7 transporter. ApoE4 particles, on the other hand, exacerbate the effects of these toxic lipids leading to endolysosomal dysfunction. By reducing the peroxidated lipid burden in ApoE4 neurons, ApoE2 and ApoE3Ch particles rescue endolysosomal function and restore defects in neuronal activity. Our findings reveal a new mechanism by which ApoE2 and ApoE3Ch isoforms protect neurons from neurodegenerative disease.

neuroscience↗

bioRxiv2025

Glucosylceramide induced ectosomes propagate pathogenic α-synuclein in Parkinson's disease

Intercellular transmission of -synuclein contributes to Parkinsons disease pathology. Yet, the mechanisms of -synuclein spread are not fully understood. Here, we used live-cell microscopy to examine the impact of Parkinsons disease associated lipid alterations on -synuclein release. We discovered that increased glucosylceramides induce ectosome shedding from primary neurons, and from dopaminergic neurons derived from Parkinsons disease patient iPSCs harboring mutations in GBA1 (N370S, L444P and W378G) and LRRK2 (G2019S and R1441H) compared to their isogenic control. We show that elevated glucosylceramide similarly increases vesicle release and uptake by other neurons in living mouse brains using 2-photon microscopy. Finally, we show that ectosomes are loaded with pathogenic -synuclein and lead to the transmission of -synuclein pathology to neighbouring neurons. These data reveal ectosomes as the predominant route for -synuclein transmission that can only be appreciated by live-cell imaging technologies.

cell biology↗

bioRxiv2023

DENND2B activates Rab35 at the intercellular bridge regulating cytokinetic abscission and tetraploidy

Cytokinesis is the final stage of cell division. Successful cytokinesis requires membrane trafficking pathways regulated by Rabs, molecular switches activated by guanine nucleotide exchange factors (GEFs). Late in cytokinesis, an intercellular cytokinetic bridge (ICB) connecting the two daughter cells undergoes abscission, which requires depolymerization of actin. Rab35 recruits MICAL1 to oxidate and depolymerize actin filaments. We report that DENND2B, a protein previously implicated in cancer, mental retardation and multiple congenital disorders functions as a GEF for Rab35 and recruits and activates the GTPase at the ICB. Unexpectedly, the N-terminal region of DENND2B interacts with an active mutant of Rab35, suggesting that DENND2B is both a Rab35 GEF and effector. Knockdown of DENND2B delays abscission resulting in increased multinucleated cells and overaccumulation of F-actin at the ICB. F-actin accumulation leads to formation of a chromatin bridge, a process known to activate the NoCut/abscission checkpoint, and DENND2B knockdown actives Aurora B kinase, a hallmark of checkpoint activation. This study identifies DENND2B as a crucial player in cytokinetic abscission and provides insight into the multisystem disorder associated with DENND2B mutation.

cell biology↗

bioRxiv2022

Autolysosomal exocytosis of lipids protect neurons from ferroptosis

During oxidative stress neurons release lipids that are internalized by glia. Defects in this coordinated process play an important role in several neurodegenerative diseases. Yet, the mechanisms of lipid release and its consequences on neuronal health are unclear. Here, we demonstrate that lipid-protein particle release by autolysosome exocytosis protects neurons from ferroptosis, a form of cell death driven by lipid peroxidation. We show that during oxidative stress, peroxidated lipids and iron are released from neurons by autolysosomal exocytosis which requires the exocytic machinery; VAMP7 and syntaxin 4. We observe membrane-bound lipid-protein particles by TEM and demonstrate that these particles are released from neurons using cryoEM. Failure to release these lipid-protein particles causes lipid hydroperoxide and iron accumulation and sensitizes neurons to ferroptosis. Our results reveal how neurons protect themselves from peroxidated lipids. Given the number of brain pathologies that involve ferroptosis, defects in this pathway likely play a key role in the pathophysiology of neurodegenerative disease. SUMMARYRelease of lipid-protein particles by autolysosomal exocytosis protects neurons from ferroptosis.

cell biology↗

bioRxiv2019

Spastin tethers lipid droplets to peroxisomes and directs fatty acid trafficking through ESCRT-III

Lipid droplets (LDs) are neutral lipid storage organelles that transfer lipids to various organelles including peroxisomes. Here, we show that the hereditary spastic paraplegia protein M1 Spastin, a membrane-bound AAA ATPase found on LDs, coordinates fatty acid (FA) trafficking from LDs to peroxisomes through two inter-related mechanisms. First, M1 Spastin forms a tethering complex with peroxisomal ABCD1 to promote LD-peroxisome contact formation. Second, M1 Spastin recruits the membrane-shaping ESCRT-III proteins IST1 and CHMP1B to LDs via its MIT domain to facilitate LD-to-peroxisome FA trafficking, possibly through IST1 and CHMP1B modifying LD membrane morphology. Furthermore, M1 Spastin, IST1 and CHMP1B are all required to relieve LDs of lipid peroxidation. M1 Spastins dual roles in tethering LDs to peroxisomes and in recruiting ESCRT-components to LD-peroxisome contact sites for FA trafficking may help explain the pathogenesis of diseases associated with defective FA metabolism in LDs and peroxisomes.

cell biology↗

bioRxiv2018

Neuron-astrocyte metabolic coupling during neuronal stimulation protects against fatty acid toxicity

GRAPHICAL ABSTACT\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=165 SRC=\"FIGDIR/small/465237_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (57K):\norg.highwire.dtl.DTLVardef@1d6cbf4org.highwire.dtl.DTLVardef@e83c9corg.highwire.dtl.DTLVardef@e35b92org.highwire.dtl.DTLVardef@910303_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LIHyperactive neurons generate and release excess peroxidated fatty acids (FAs)\nC_LIO_LIAstrocytes endocytose toxic FAs as lipoprotein particles, delivering them to lipid droplets\nC_LIO_LILipid droplets trigger upregulation of genes involved in metabolism and detoxification\nC_LIO_LIAstrocytes detoxify and consume FAs by mitochondrial oxidation in response to neural activity\nC_LI\n\nSUMMARYMetabolic coordination between neurons and astrocytes is critical for the health of the brain. However, neuron-astrocyte coupling of lipid metabolism, particularly in response to neural activity, remains largely uncharacterized. Here, we demonstrate that toxic, peroxidated fatty acids (FAs) produced in hyperactive neurons are transferred to astrocytic lipid droplets by lipoprotein particles. Astrocytes consume the FAs stored in lipid droplets via mitochondrial {beta}-oxidation in response to neuronal activity and turn on a detoxification gene expression program. Together, our findings reveal that FA metabolism between neurons and astrocytes is coupled in an activity-dependent manner to protect neurons from FA toxicity. This coordinated mechanism for metabolizing FAs could underlie both homeostasis and a variety of disease states of the brain.

neuroscience↗

bioRxiv2017

Stochastic Protein Labeling Enables Long-term Single Molecule Observation In Vivo

Our ability to unambiguously image and track individual molecules in live cells is limited by packing of multiple copies of labeled molecules within the resolution limit. Here we devise a universal genetic strategy to precisely control copy number of fluorescently labeled molecules in a cell. This system has a dynamic titration range of >10,000 fold, enabling sparse labeling of proteins expressed at different abundance levels. Combined with photostable labels, this system extends the duration of automated single-molecule tracking by 2 orders of magnitude. We demonstrate long-term imaging of synaptic vesicle dynamics in cultured neurons as well as in intact zebrafish. We found axon initial segment utilizes a waterfall mechanism gating synaptic vesicle transport polarity by promoting anterograde transport processivity. Long-time observation also reveals that transcription factor hops between clustered binding sites in spatially-restricted sub-nuclear regions, suggesting that topological structures in the nucleus shape local gene activities by a sequestering mechanism. This strategy thus greatly expands the spatiotemporal length scales of live-cell single-molecule measurements, enabling new experiments to quantitatively understand complex control of molecular dynamics in vivo.

biophysics↗