Biology subjects

Khakpour, M.

Publications and source records attributed to Khakpour, M..

5 recordsLinked to original sources

bioRxiv2025

Early micro and nanoscopic responses of microglia to blood-brain barrier modulation by transcranial-focused ultrasound

Modulation of the blood-brain barrier (BBB) using transcranial-focused ultrasound (FUS) has rapidly progressed to clinical trials. In combination with phospholipid microspheres, also known as microbubbles, administered in the bloodstream, ultrasound energy is guided by magnetic resonance imaging (MRI) to target specific brain regions with millimetric precision. At the targeted area, the interaction between FUS and microbubbles increases local BBB permeability for 4 to 6 hours, with an ensuing inflammation that resolves within days to weeks. Microglia, as the resident immune cells of the brain, are triggered by FUS-BBB modulation, although the time course of this response is unclear. Thus, the goal of this study was to characterize the early cellular (i.e., density, distribution, and morphology) and subcellular (i.e., ultrastructure) changes in microglial activities following FUS-BBB modulation. MethodsWe targeted the hippocampi of adult mice with FUS, in the presence of intravenous microbubbles and guided by MRI, and performed analyses 1 hour and 24 hours after FUS-BBB modulation. Microglia were investigated at the population, cellular and subcellular levels, where hippocampal BBB permeability was identified by the entry of endogenous immunoglobulin (Ig)G in the parenchyma. Respective outcome measures included i) the density and distribution of ionized calcium binding adaptor molecule-positive (Iba)1-positive (+) cells; ii) the morphology of the soma and processes of Iba1+ cells; and iii) the quantification of microglial organelles (e.g., phagosomes) and contacts with blood vessels and synapses using chip mapping scanning electron microscopy. ResultsNo significant changes in baseline density and distribution of microglia were found in IgG-positive hippocampal areas at 1 hour and 24 hours after FUS-BBB modulation. By contrast, FUS-BBB modulation was associated with more elongated microglial cell bodies at both time points. The relative distribution of morphologies at 1 hour shifted toward compact shapes with stubby processes, whereas at 24 hours, shapes were bigger, with fewer processes. At the nanoscale, microglia maintained their interactions with blood vessel elements, except vessels most affected by swollen endfeet, which occurred regardless of treatment. In the parenchyma, 24 hours after FUS-BBB modulation, microglia reduced the frequency of contacts with pre-synaptic elements and extracellular space pockets, while showing features of increased metabolic demand and reduced lysosomal activity. ConclusionAt 1 hour and 24 hours after FUS-BBB modulation, traits of microglial surveillance activity were largely maintained, with shifts in the shape of a subset of cells, which adopted a morphology associated with injury shielding. FUS-BBB modulation also appears to temporarily modify the digestive, but not the phagocytic activity, of microglia and to reduce pre-synaptic remodeling early after treatment.

neuroscience↗

bioRxiv2025

Transient, early, female-specific increase in cortical glial fibrillary acidic protein distribution in the Syrian hamster model of mild peripheral COVID-19

BackgroundMild-moderate respiratory COVID-19 is commonly associated with a range of neurological symptoms. The mechanisms linking this peripheral disease to cognitive symptoms are thought to include heightened circulating cytokines and other inflammatory mediators resulting in a leaky blood-brain barrier and increased neuroinflammation (i.e., inflammation taking place in the brain). This can lead to aberrant synaptic transmission and cognitive dysfunction. A key component of neuroinflammation is the reactivity of astrocytes, in a process termed astrogliosis, associated with altered morphology, proliferative capacity, gene expression, and function. Accumulating evidence suggests astrogliosis likely occurs in mild-moderate COVID-19; however, there has been limited investigation. In this study, we quantified changes to astrocytes in a Syrian hamster model of mild-moderate respiratory COVID-19. MethodsWe used an intranasal inoculation model to produce mild-moderate respiratory COVID-19 in 8-10-week-old male and female Syrian hamsters. We extracted brains at 1-, 3-, 5-, 7-, and 31-days post-inoculation and from uninfected controls, and immunolabelled brain sections with astrocyte- (GFAP and SOX9) and neuron-specific (NEUN) markers. We captured tiled confocal micrographs of entire brain sections and analyzed the resulting signals from five regions of interest: cortex, corpus callosum, hippocampus, third ventricle, and dorsal striatum. ResultsTo systematically quantify cell-type-specific labelling for astrogliosis markers, we first developed an unbiased pipeline. We found a transient increase in GFAP signal density in female hamster, specifically in the cortex at 3 days post-inoculation. There were no corresponding changes noted in astrocyte (SOX9), neuron (NEUN) or total cell (Hoechst) numbers. Moreover, there were no changes in male hamsters at any timepoint in any region of interest. ConclusionsOur findings provide the first spatiotemporal insight into astrogliosis in a hamster model of mild-moderate respiratory COVID-19. We identified a transient and sex-specific increase in GFAP signal density, indicative of astrogliosis. Our findings contribute to the literature surrounding sex differences in (neuro)immune responses and add to the growing body of COVID-19 literature, in which sex-specific outcomes are apparent in both human patient populations and rodent experimental models.

neuroscience↗

bioRxiv2024

Impact of prenatal delta-9-tetrahydrocannabinol exposure on mouse brain development: a fetal-to-adulthood magnetic resonance imaging study

While cannabis use during pregnancy is often perceived as harmless, little is known about its consequences on offspring neurodevelopment. There is an urgent need to map the effects of prenatal cannabis exposure on the brain through the course of the lifespan. We used magnetic resonance imaging spanning nine timepoints, behavioral assays, and electron microscopy to build a trajectory from gestation to adulthood in mice exposed prenatally to delta-9-tetrahydrocannabinol (THC). Our results demonstrate a spatio-temporal patterning, with ventriculomegaly in THC-exposed embryos followed by a deceleration of brain growth in neonates that is sustained until adulthood, especially in females. We observed consistently impacted regions in both the cortex and subcortex, aligned with sex-dependent changes to social behavior in neonates and increased anxiety-like behavior in adolescents. Our results suggest prenatal THC exposure has a sustained sex-dependent impact on neurodevelopment that may persist into early adulthood.

neuroscience↗

bioRxiv2024

Dark Microglia Are Abundant in Normal Postnatal Development, where they Remodel Synapses via Phagocytosis and Trogocytosis, and Are Dependent on TREM2

This study examined dark microglia--a state linked to central nervous system pathology and neurodegeneration--during postnatal development in the mouse ventral hippocampus, finding that dark microglia interact with blood vessels and synapses and perform trogocytosis of pre-synaptic axon terminals. Furthermore, we found that dark microglia in development notably expressed C-type lectin domain family 7 member A (CLEC7a), lipoprotein lipase (LPL) and triggering receptor expressed on myeloid cells 2 (TREM2) and required TREM2, differently from other microglia, suggesting a link between their role in remodeling during development and central nervous system pathology. Together, these results point towards a previously under-appreciated role for dark microglia in synaptic pruning and plasticity during normal postnatal development.

neuroscience↗

bioRxiv2024

Integrated stress response associated with dark microglia promotes microglial lipogenesis and contributes to neurodegeneration

Microglia, the brains primary resident immune cells, are a heterogeneous population and can assume phenotypes with diverse functional outcomes on brain homeostasis. In Alzheimers disease (AD), where microglia are a leading causal cell type, microglia subsets with protective functions have been well characterized. Yet, the identity of microglia subsets that drive neurodegeneration remains unresolved. Here, we identify a neurodegenerative microglia phenotype that is characterized by a conserved stress signaling pathway, the integrated stress response (ISR). Using mouse models to activate or inhibit ISR in microglia, we show that ISR underlies the ultrastructurally distinct "dark" microglia subset linked to pathological synapse loss. Inducing microglial ISR in murine AD models exacerbates neurodegenerative pathologies, such as Tau pathology and synaptic terminal loss. Conversely, inhibiting microglial ISR in AD models ameliorates these pathologies. Mechanistically, we present evidence that ISR promotes the secretion of toxic long-chain lipids that impair neuron and oligodendrocyte homeostasis in vitro. Accordingly, small molecule-based inhibition of lipid synthesis in AD models ameliorates synaptic terminal loss. Our results demonstrate that activation of ISR within microglia represents a novel pathway contributing to neurodegeneration and suggest that this may be sustained, at least in part, by the secretion of long-chain lipids from ISR-activated microglia.

neuroscience↗