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Regulation of synaptic connectivity in schizophrenia by mutual neuron-microglia interaction

ABSTRACT: The examination of post-mortem brain tissue suggests synaptic loss as a central pathological hallmark of schizophrenia spectrum (SCZ), which is potentially related to activated microglia and increased inflammation. Induced pluripotent stem cells serve as a source for neurons and microglia-like cells to address neuron-microglia interactions. Here, we present a co-culture model of neurons and microglia, both of human origin, to show increased susceptibility of neurons to microglia-like cells derived from SCZ patients. Analysis of IBA-1 expression, NFκB signaling, transcription of inflammasome-related genes, and caspase-1 activation shows that enhanced, intrinsic inflammasome activation in patient-derived microglia exacerbates neuronal deficits such as synaptic loss in SCZ. Anti-inflammatory pretreatment of microglia with minocycline specifically rescued aberrant synapse loss in SCZ and reduced microglial activation. These findings open up possibilities for further research in larger cohorts, focused clinical work and longitudinal studies that could facilitate earlier therapeutic intervention.

ORGANISM(S): Homo sapiens

PROVIDER: GSE213232 | GEO | 2022/09/16

REPOSITORIES: GEO

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Project description:Microglia and neuroinflammation are implicated in the development and progression of Alzheimer’s disease (AD). To better understand microglia-mediated processes in AD, we studied the function of INPP5D/SHIP1, a gene linked to AD through GWAS. Immunostaining and single nucleus RNA sequencing confirmed that INPP5D expression in the adult human brain is enriched in microglia. Examination of prefrontal cortex across a large cohort revealed reduced full-length soluble INPP5D protein levels in AD patient brains compared to cognitively normal controls. However, elevated INPP5D immunostaining in microglia in the AD brain was observed, which was driven by elevations in plaque-associated microglia suggesting that these two methods quantify different pools of INPP5D. Examination of INPP5D overexpression and bi-allelic loss-of-function in induced pluripotent stem cell derived microglia (iMGs) revealed that INPP5D LOF most closely resemble microglia in the AD brain with respect to immune signaling alterations, supporting the hypothesis that INPP5D function is reduced in AD microglia. The functional consequences of reduced INPP5D activity were evaluated in human iMGs, using both pharmacological inhibition of the phosphatase activity of INPP5D and genetic reduction in copy number. Unbiased transcriptional and proteomic profiling of these iMGs suggested an upregulation of innate immune signaling pathways, lower levels of scavenger receptors, reduced lysosomal proteins and altered inflammasome signaling with INPP5D reduction. INPP5D inhibition induced the secretion of IL-1ß and IL-18, further implicating inflammasome activation. Inflammasome activation was confirmed through visualization of inflammasome formation through ASC immunostaining in INPP5D-inhibited iMGs, increased cleaved caspase-1 and through rescue of elevated IL-1ß and IL-18 with caspase-1 and NLRP3 inhibitors. In accord, lower INPP5D is associated with higher IL-18 levels and an elevation in microglia with ASC specks in the AD brain. This work implicates INPP5D as a regulator of inflammasome signaling in human microglia.

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Regulation of synaptic connectivity in schizophrenia by mutual neuron-microglia interaction

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