Translational profiling identifies sex-specific metabolic and epigenetic reprogramming of cortical microglia/macrophages in APPPS1-21 mice with an antibiotic-perturbed-microbiome
Authors: Shaik Shabana M , Cao Yajun , Dodiya Hemraj B. , Zhang Xulun , Boutej Hejer , Gogola Joseph V. , Han Weinong , Kriz Jasna , Sisodia Sangram S 
Published: May 2023

Background:
Microglia, the brain-resident macrophages perform immune surveillance and engage with pathological processes resulting in phenotype changes necessary for maintaining homeostasis. In preceding studies, we showed that antibiotic-induced perturbations of the gut microbiome of APPPS1-21 mice resulted in significant attenuation in Ab amyloidosis and altered microglial phenotypes that are specific to male mice. The molecular events underlying microglial phenotypic transitions remain unclear due to lack of models that allow reliable in vivo proteomics. Here, by generating ‘APPPS1-21-CD11br’reporter mice, we investigated the translational state of microglial/macrophage ribosomes during their phenotypic transition and in a sex-specific manner.
Methods:
Six groups of mice that included WT-CD11br, antibiotic (ABX) or vehicle-treated APPPS1-21-CD11br males and females were sacrificed at 7-weeks of age (n=15/group) and used for immunoprecipitation of microglial/macrophage polysomes from cortical homogenates using anti-FLAG antibody. Liquid chromatography coupled to tandem mass spectrometry and label-free quantification was used to identify newly synthesized peptides isolated from polysomes.
Results:
We show that ABX-treatment leads to decreased Ablevelsin male APPPS1-21-CD11br mice with no significant changes in females. We identified microglial/macrophage polypeptides involved in mitochondrial dysfunction and altered calcium signaling that are associated with Ab-induced oxidative stress. Notably, female mice also showed downregulation of newly-synthesized ribosomal proteins. Furthermore, male mice showed an increase in newly-synthesized polypeptides involved in FcgR-mediated phagocytosis, while females showed an increase in newly-synthesized polypeptides responsible for actin organization associated with microglial activation. Next, we show that ABX-treatment resulted in substantial remodeling of the epigenetic landscape, leading to a metabolic shift that accommodates the increased bioenergetic and biosynthetic demands associated with microglial polarization in a sex-specific manner. While microglia in ABX-treated male mice exhibited a metabolic shift towards a neuroprotective phenotype that promotes Aβ clearance, microglia in ABX-treated female mice exhibited loss of energy homeostasis due to persistent mitochondrial dysfunction and impaired lysosomal clearance that was associated with inflammatory phenotypes.
Conclusions:
Our studies provide the first snapshot of the translational state of microglial/macrophage cells in a mouse model of Ab amyloidosis that was subject to ABX treatment. ABX-mediated changes resulted in metabolic reprogramming of microglial phenotypes to modulate immune responses and amyloid clearance in a sex-specific manner. This microglial plasticity to support neuro-energetic homeostasis for its function based on sex paves the path for therapeutic modulation of immunometabolism for neurodegeneration.