Sex differences in the neuroinflammatory signaling pathway: Effect of miRNAs on fatty acid synthesis in microglia
Ontology highlight
ABSTRACT: Studies have shown that Alzheimer’s disease is more prevalent and severe in women than men. This could be due to the different gene and protein expression in the microglia, the brain’s primary immune cells. In this study, we analyzed microglial microRNAs from the hippocampi of adult male and female mice and identified 30 miRNAs that were expressed differently in male and female mice. The target genes of the male-enriched miRNAs belong to the fatty acid biosynthesis and metabolism pathways. As sex hormones contribute to sex differences, we investigated whether testosterone regulates the fatty acid biosynthesis pathway in the mouse microglial cell line MG6. Testosterone reduced the expression levels of fatty acid synthase, which in turn suppresses the NF-κB inflammatory signaling pathway. This suggests that testosterone, through the upregulation of specific miRNAs, plays a crucial role in suppressing inflammatory responses in male microglia, which could explain the lower susceptibility of men towards Alzheimer’s disease.
Project description:Alzheimer’s disease is associated with disrupted circadian rhythms and clock gene expression. REV-ERBα (Nr1d1) is a circadian transcriptional repressor involved in the regulation of lipid metabolism and macrophage function. While global REV-ERBα deletion increases microglial activation and mitigates amyloid plaque formation, the cell-autonomous effects of microglial REV-ERBα deletion in healthy brain and in tauopathy are unexplored. Here, we show that microglial REV-ERBα deficient enhances inflammatory signaling, disrupts lipid metabolism, and causes lipid droplet (LD) accumulation specifically in male microglia. Inflammation and LD accumulation combine to inhibit microglial tau phagocytosis, which can be partially rescued by blockage of lipid droplet formation. Microglial REV-ERBα deletion exacerbates tau aggregation and neuroinflammation in P301S and AAV-P301L tauopathy models in male, but not female mice. These data demonstrate the importance of microglial lipid droplets in tau accumulation and reveal REV-ERBα as a therapeutically accessible, sex-dependent regulator of microglial inflammatory signaling, lipid metabolism, and tauopathy.
Project description:Microglial endolysosomal dysfunction is strongly implicated in neurodegeneration. Transcriptomic studies show that a microglial state characterised by a set of genes involved in endolysosomal function is induced in both mouse Alzheimer’s Disease (AD) models and in human AD brain, and that the onset of this state is emphasised in females. Cst7 (Cystatin F) is among the most highly unregulated genes in these microglia. However, the sex-specific function of Cst7 in neurodegenerative disease is not understood. Here, we crossed Cst7 -/- mice with the App NL-G-F mouse to test the role of Cst7 in a model of amyloid-driven AD.
Project description:Sex is a key modifier of neurological disease outcomes. Microglia are implicated in neurological diseases and modulated by miRNAs, but it is unknown whether microglial miRNAs have sex-specific influences on disease. We show that microglial miRNA expression differs in males and females, and loss of miRNAs leads to sex-specific changes in the microglial transcriptome and to tau pathology. These findings suggest microglial miRNAs influence tau pathogenesis in a sex-specific manner.
Project description:Sex is a key modifier of neurological disease outcomes. Microglia are implicated in neurological diseases and modulated by miRNAs, but it is unknown whether microglial miRNAs have sex-specific influences on disease. We show that microglial miRNA expression differs in males and females, and loss of miRNAs leads to sex-specific changes in the microglial transcriptome and to tau pathology. These findings suggest microglial miRNAs influence tau pathogenesis in a sex-specific manner.
Project description:Microglia, the brain’s resident macrophages, maintain brain homeostasis and respond to injury and infection. During aging they undergo functional changes, but the underlying mechanisms and their contributions to neuroprotection versus neurodegeneration are unclear. Previous studies suggested that microglia are sex dimorphic, so we compared microglial aging in mice of both sexes. RNA-sequencing of hippocampal microglia revealed more aging-associated changes in female microglia than male microglia, and more sex differences in old microglia than young microglia. Pathway analyses and subsequent validation assays revealed a stronger AKT-mTOR-HIF1α-driven shift to glycolysis among old female microglia and indicated that C3a production and detection was elevated in old microglia, especially in females. Recombinant C3a induced AKT-mTOR-HIF1α signaling and increased the glycolytic and phagocytic activity of young microglia. Single cell analyses attributed the aging-associated sex dimorphism to more abundant disease-associated microglia (DAM) in old female mice than old male mice, and evaluation of an Alzheimer’s Disease mouse model revealed that the metabolic and complement changes are also apparent in the context of neurodegenerative disease and are strongest in the neuroprotective DAM2 subset. Collectively, our data implicate autocrine C3a-C3aR signaling in metabolic reprogramming of microglia to neuroprotective DAM during aging, especially in females, and also in Alzheimer’s Disease.
Project description:Microglia, the resident macrophage of the brain, are derived from the yolk sac and colonize the brain before the blood-brain barrier forms. Once established, they expand locally and require Colony-stimulating factor 1 receptor (CSF1R) signaling for their development and maintenance. CSF1R inhibitors have been used extensively to deplete microglia in the healthy and diseased brain. In this study, we demonstrated sex-dependent differences in the microglial response to the CSF1R inhibitor PLX3397. Male mice exhibited greater microglial depletion compared to females. Transcriptomic and flow cytometry analysis revealed sex-specific differences in the remaining microglia population, with female microglia upregulating autophagy and proteostasis pathways while male microglia increased mitobiogenesis. Furthermore, manipulating key microglial receptors by using different transgenic mouse lines resulted in changes in depletion efficacies that were also sex-dependent. These findings suggest sex-dependent microglial survival mechanisms, which might contribute to the well-documented sex differences in various neurological disorders.
Project description:Type I interferons (IFN-I) are important mediators of antiviral immunity and autoimmune diseases. Plasmacytoid dendritic cells (pDCs) from females exert an elevated capacity to produce IFN-I in response to activation of toll-like receptor 7 (TLR7) compared to male pDCs, and both hormones and genes encoded by the X chromosome have been implicated in these sex-specific differences. Using longitudinal samples collected from a cohort of trans men receiving testosterone injections as gender-affirming hormone therapy (GAHT), the impact of testosterone on TLR7-mediated IFN-I production by pDCs was assessed. GAHT induced testosterone and estradiol levels within male reference ranges and increased hemoglobin and hematocrit levels, demonstrating biological activity of testosterone. scRNA seq of pDCs showed downregulation of IFN-I-related gene expression signatures, but also revealed inter-donor heterogeneity on the transcriptional level. Longitudinal quantification of IFN-I protein production by pDCs following TLR7-stimulation showed significant and continuous reduction of IFN-I production in trans men, and reduced expression of IFN-I-stimulated genes. These longitudinal studies in trans men demonstrate that testosterone can reduce IFN-I production by pDCs, and provide novel insights into the immune-modulatory role of testosterone in sex differential IFN-I-mediated immune responses.
Project description:Alzheimer’s disease is associated with disrupted circadian rhythms and clock gene expression. REV-ERBα (Nr1d1) is a circadian transcriptional repressor involved in the regulation of lipid metabolism and macrophage function. While global REV-ERBα deletion increases microglial activation and mitigates amyloid plaque formation, the cell-autonomous effects of microglial REV-ERBα on tau pathology are unexplored. Here, we show that microglial REV-ERBα deletion enhances inflammatory signaling, disrupts lipid metabolic processes, and causes lipid droplet (LD) accumulation specifically in male microglia. Inflammation and LD accumulation combine to inhibit microglial tau phagocytosis, which can be partially rescued by blockage of lipid droplet formation. Microglial REV-ERBα deletion exacerbates tau aggregation and neuroinflammation in P301S and AAV-P301L tauopathy models in male, but not female mice. These data demonstrate the importance of microglial lipid droplets in tau accumulation and reveal REV-ERBα as a therapeutically accessible, sex-dependent regulator of microglial inflammatory signaling, lipid metabolism, and tauopathy.
Project description:Neuroprotective, anti-inflammatory and remyelinating properties of androgens are well-characterized in demyelinated male mice and men suffering from multiple sclerosis. However, androgen effects mediated by the androgen receptor AR, have been only poorly studied in females who make low androgen levels. Here, we show a predominant microglial AR expression in demyelinated lesions from female mice and women with multiple sclerosis, but virtually undetectable AR expression in lesions from male animals and men with multiple sclerosis. In female mice, androgens and estrogens act in a synergistic way while androgens drive microglia response towards regeneration. Transcriptomic comparisons of demyelinated mouse spinal cords indicate that, regardless of the sex, androgens up-regulate genes related to neuronal function integrity and myelin production. Depending on the sex, androgens down-regulate genes related to the immune system in females and lipid catabolism in males. Thus, androgens are required for proper myelin regeneration in females and therapeutic approaches of demyelinating diseases need to consider male-female differences.
Project description:Neuroligin-4 (NL4) loss-of-function mutations are strongly associated with monogenic heritable abnormalities linked with Autism Spectrum Disorder (ASD). NL4 mutation in mice causes ASD related alterations in both, the synaptic and behavioral phenotype. Since microglia closely regulate synaptic development and are implicated as key players in ASD development and progression, we here studied microglial properties in the NL4-/- mouse model. We show that loss of NL4 caused altered behavior and impaired hippocampal gamma oscillations predominantly in male mice. In parallel, microglial density, morphology, and response to injury specifically in the CA3 region of the hippocampus were altered in NL4-deficient males only. A transcriptomic and proteomic analysis revealed a strong impact of sexual dimorphism on molecular alterations in microglia of NL4-deficient compared to wildtype mice. Estrogen application in male NL4-/- animals partially restored the impaired social behavior and the altered microglial phenotype. Together, these results indicate that loss of NL4 affects not only neuronal network activity and behavior, but changes in addition the phenotype of microglia in a sex-specific manner that could be targeted by estrogen treatment.