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Projection neuron subtypes establish microglia sub-states and regulate neuroimmune interactions

ABSTRACT: Microglia are the resident immune cells of the brain, and have critical roles in circuit development and plasticity. During embryonic and postnatal development, microglia exist in multiple transcriptional states. However, it is still poorly understood how these states are established, and whether they are influenced by their cellular environment. Here we show that in the juvenile neocortex, microglia exist in multiple states whose identity and laminar distribution is instructed by the neuronal class identity of local pyramidal neurons. Using single-cell RNA sequencing, we unveil molecular signatures of distinct microglia sub-states, and show that they can be divided into layer-restricted or broadly-distributed states. Strikingly, conversion of deep-layer pyramidal neurons to an alternate class identity reconfigures both the density and molecular state of local layer-restricted microglia to correspond to the new neuronal niche, thus identifying specific populations of microglia that are sensitive to pyramidal neuron subtypes. Ligand-receptor interactomes for individual neuronal subtype-microglia pairings uncovers two categories of neuron-to-microglia communication: one associated with neuronal class identity and one associated with microglial state. Our findings highlight the fundamental role that neuronal identity and neuronal niches play in locally controlling the transcriptional status of postnatal microglia.

ORGANISM(S): Mus musculus

PROVIDER: GSE158096 | GEO | 2022/04/26

REPOSITORIES: GEO

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Project description:Neurodegenerative brain disorders become more common in the aged. Most of these disorders are associated with or caused by selective death of certain neuronal subpopulations. The mechanisms underlying the differential vulnerability of certain neuronal populations are still largely unexplored and few neuroprotective treatments are available to date. Elucidation of these mechanisms may lead to a greater understanding of the pathogenesis and treatment of neurodegenerative diseases. Moreover, preconditioning by a short seizure confers neuroprotection following a subsequent prolonged seizure. Our goal is to identify pathways that confer vulnerability and resistance to neurotoxic conditions by comparing the basal and preconditioned gene expression profiles of three differentially vulnerable hippocampal neuron populations. Hippocampal CA1 and CA3 pyramidal neurons are highly susceptible to seizures and ischemia, whereas dentate gyrus granule cells are relatively resistant. A brief preconditioning seizure confers protection to the pyramidal cells. We will first determine gene expression profiles of untreated rat CA1 and CA3 pyramidal cells, and dentate granule cells, using laser capture microscopy to obtain region-specific neuronal mRNA. We will then determine the effect of a brief preconditioning seizure, which is neuroprotective in CA1 and CA3, on these expression profiles. We hypothesize that common molecular mechanisms exist in neurons that determine their susceptibility to seizure-induced injury. Intrinsic differences in gene expression exist between hippocampal glutamatergic CA1 and CA3 pyramidal neurons, on the one hand, and dentate granule cells on the other, which contribute to the greater susceptibility of pyramidal neurons to degeneration in experimental stroke and epilepsy. We specifically hypothesize that differences in basal energy metabolism genes may confer differential susceptibility to neurodegeneration produced by seizures and ischemia. Anesthetized animals will be sacrificed by decapitation, and frozen 10 micron sections will be lightly stained with cresyl violet to identify cell layers in the hippocampus. Approximately 1000 neurons from each of the three cell layers will be isolated by LCM. Poly-A RNA will be amplified using a modified Eberwine protocol. The quality of our aRNA will be evaluated by quantitative RT-PCR of GluR6 and KA2 mRNA levels before we send the samples to the Center for labeling and hybridization to Affymetrix rat 230A arrays. We will provide a one-round amplification cDNA product to the center for labeling and hybridization. This protocol is identical to a previously approved study by Jim Greene in our laboratory.

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Projection neuron subtypes establish microglia sub-states and regulate neuroimmune interactions

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