An antibiotic cocktail leads to reductions in brain amyloidosis, altered morphology, and gene expression in microglia of male but not female transgenic mice that exhibit Aβ deposits. The microbiome plays a causal role in modulating Aβ burden and microglia phenotypes.
Innate immune cells destroy pathogens within a transient organelle called the phagosome. When pathogen-associated molecular patterns (PAMPs) displayed on the pathogen are recognized by Toll-like receptors (TLRs) on the host cell, it activates inducible nitric oxide synthase (NOS2) which instantly fills the phagosome with nitric oxide (NO) to clear the pathogen. Selected pathogens avoid activating NOS2 by concealing key PAMPs from their cognate TLRs. Thus, the ability to map NOS2 activity triggered by PAMPs can reveal critical mechanisms underlying pathogen susceptibility. Here, we describe DNA-based probes that ratiometrically report phagosomal and endosomal NO, and can be molecularly programmed to display precise stoichiometries of any desired PAMP. By mapping phagosomal NO produced in microglia of live zebrafish brains, we found that single-stranded RNA of bacterial origin acts as a PAMP and activates NOS2 by engaging TLR-7. This technology can be applied to study PAMP−TLR interactions in diverse organisms.
BackgroundMicroglia, the brain‐resident macrophages perform immune surveillance and engage in pathological processes by changing their phenotype and maintain homeostasis. Previously, we showed that antibiotic‐mediated changes in the gut microbiome of APPPS1‐21 transgenic mice resulted in significant decrease in amyloidosis and altered microglial phenotype that are specific to male mice. The molecular events underlying microglial phenotypic transition remain unclear due to lack of models that allow reliable in vivo proteomics. Here, we generated ‘APPPS1‐21‐CD11br’ microglia reporter mice and assessed their protein networks during their phenotypic transition in a sex‐specific manner.MethodSix groups of mice that included WT‐CD11br, antibiotic (ABX) or vehicle‐treated APPPS1‐21‐CD11br male and female were sacrificed at 7‐weeks of age (n=15/group) and used for immunoprecipitation of microglial polysomes from cortical homogenates using anti‐FLAG antibody. Liquid chromatography coupled to tandem mass spectrometry (LC‐MSMS) and label‐free quantification was used to identify newly synthesized peptides extracted from polysomesResultWe showed ABX‐treatment led to reduced Ab levels in male APPPS1‐21‐CD11br mice with no significant changes in the females. We first identified sex‐specific oxidative stress induced by Ab peptides leading to mitochondrial dysfunction and altered calcium signaling. Notably, the female mice also showed dysregulation of ribosomal machinery. Further, microglial polypeptides were associated with FcgR‐mediated phagocytosis in male mice and actin organization in female mice. Interestingly, ABX‐treatment resulted in substantial remodeling of epigenetic landscape for metabolic shift to accommodate increased bioenergetic and biosynthetic demands associated with microglial polarization in a sex‐specific manner. The male mice showed glycolytic shift for neuroprotective phenotype to promote Aβ clearance. However, the female mice showed loss of energy homeostasis due to persistent mitochondrial dysfunction associated with impaired lysosomal clearance and inflammatory phenotype.ConclusionOur studies provide first snapshot of the dynamic translational state of microglial cells in a sex‐specific manner. We identified that antibiotic‐mediated changes in gut microbiome results in metabolic reprogramming of microglial phenotypes to modulate immune responses and amyloid clearance. This microglial plasticity to support neuro‐energetic homeostasis for its function based on sex, paves the path for therapeutic modulation of immunometabolism for neurodegeneration.
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