Biology subjects

Dorman, L. C.

Publications and source records attributed to Dorman, L. C..

3 recordsLinked to original sources

bioRxiv2021

Interleukin-33 coordinates a microglial phagocytic response and limits corticothalamic excitability and seizure susceptibility

Microglia are key remodelers of neuronal synapses during brain development, but the mechanisms that regulate this process and its ultimate impact on neural circuit function are not well defined. We previously identified the IL-1 family cytokine Interleukin-33 (IL-33) as a novel mediator of microglial synapse remodeling. Here we define the phagocytic program induced in microglia in response to IL-33. We find that IL-33 markedly alters the microglial enhancer landscape and exposes AP-1 transcription factor sites that promote target gene expression. We identify the scavenger receptor MARCO and the pattern recognition receptor TLR2 as downstream mediators of IL-33 dependent synapse engulfment. Conditional deletion of IL-33 in the CNS or its receptor on microglia results in increased numbers of excitatory synapses in the corticothalamic circuit and spontaneous epileptiform activity as well as increased seizure susceptibility by early adulthood. These findings define novel mechanisms through which IL-33 coordinates experience-dependent synaptic refinement to restrict hyperexcitability in the developing brain.

neuroscience↗

bioRxiv2021

In situ and transcriptomic identification of synapse-associated microglia in the developing zebrafish brain

Microglia are brain resident macrophages that play vital roles in central nervous system (CNS) development, homeostasis, and pathology. Microglia both remodel synapses and engulf apoptotic cell corpses during development, but whether unique molecular programs regulate these distinct phagocytic functions is unknown. Here we identify a molecularly distinct synapse-associated microglial subset in the zebrafish (Danio rerio). We found that ramified microglia populated synapse-rich regions of the midbrain and hindbrain between 7 and 28 days post fertilization. In contrast, microglia in the optic tectum were ameboid and clustered around neurogenic zones. Using single-cell mRNA sequencing combined with metadata from regional bulk sequencing, we identified synapse-associated microglia (SAMs) that were highly enriched in the hindbrain, expressed known synapse modulating genes as well as novel candidates, and engulfed synaptic proteins. In contrast, neurogenic-associated microglia (NAMs) were enriched in optic tectum, had active cathepsin activity, and preferentially engulfed neuronal corpses. These data yielded a functionally annotated atlas of zebrafish microglia (https://www.annamolofskylab.org/microglia-sequencing). Furthermore, they reveal that molecularly distinct phagocytic programs mediate synaptic remodeling and cell engulfment, and establish zebrafish hindbrain as a model circuit for investigating microglial-synapse interactions.

neuroscience↗

bioRxiv2021

A type I interferon response defines a conserved microglial state required for effective phagocytosis

Microglia are brain resident phagocytes that can engulf synaptic components and extracellular matrix as well as whole neurons. However, whether there are unique molecular mechanisms that regulate these distinct phagocytic states is unknown. Here we define a molecularly distinct microglial subset whose function is to engulf neurons in the developing brain. We transcriptomically identified a cluster of Type I interferon (IFN-I) responsive microglia that expanded 20-fold in the postnatal day 5 somatosensory cortex after partial whisker deprivation, a stressor that accelerates neural circuit remodeling. In situ, IFN-I responsive microglia were highly phagocytic and actively engulfed whole neurons. Conditional deletion of IFN-I signaling (Ifnar1fl/fl) in microglia but not neurons resulted in dysmorphic microglia with stalled phagocytosis and an accumulation of neurons with double strand DNA breaks, a marker of cell stress. Conversely, exogenous IFN-I was sufficient to drive neuronal engulfment by microglia and restrict the accumulation of damaged neurons. IFN-I deficient mice had excess excitatory neurons in the developing somatosensory cortex as well as tactile hypersensitivity to whisker stimulation. These data define a molecular mechanism through which microglia engulf neurons during a critical window of brain development. More broadly, they reveal key homeostatic roles of a canonical antiviral signaling pathway in brain development.

neuroscience↗