Project description:Neuroinflammation and activation of innate immunity are pathological hallmarks of Alzheimer’s disease (AD). In contrast, very few studies have examined the impact of the adaptive immune system in AD pathogenesis. In this study, we find that genetic deletion of peripheral immune populations significantly accelerates amyloid pathogenesis, worsens neuroinflammation, and alters microglial activation state. We used microarray analysis to profile gene expression underlying genotype related changes at the cellular level in the context of AD .
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:Alzheimer’s disease (AD) remains one of the grand challenges facing human society. Much controversy exists around the complex and multifaceted pathogenesis of this prevalent disease. Given strong human genetic evidence, there is little doubt, however, that microglia play an important role in preventing degeneration of neurons. E.g., loss-of-function of the microglial gene Trem2 render microglia dysfunctional and causes an early-onset neurodegenerative syndrome and Trem2 variants are among the strongest genetic risk factors for AD. Thus, restoring microglial function represents a rational therapeutic approach. Here we show that systemic hematopoietic cell transplantation followed by enhancement of microglia replacement restores microglial function in a Trem2 mutant model of Alzheimer’s disease.
Project description:The gut microbiota and innate immune system play critical roles in Alzheimer’s disease (AD). Bacteroides is elevated in AD patients and correlates with cerebrospinal fluid levels of Aβ and tau. We found that increased amyloid-β (Aβ) plaques in Bacteroides fragilis treated APP/PS1-21 mice were associated with altered cortical expression Aβ processing genes. B. fragilis suppressed peripheral CD4+ T cell production of GM-CSF and IL-4 and transcriptional changes in microglia related to GM-CSF and IL-4 signaling, phagocytosis, and protein degradation. Furthermore, B. fragilis impaired the microglial uptake of intracranially injected Aβ42, whereas Erysipelotrichaceae strains increased uptake. Depleting murine Bacteroidetes with metronidazole decreased amyloid load in aged 5xFAD mice, increased CD4+ T cell GM-CSF production, and activated microglial pathways related to cytokine signaling, phagocytosis and lysosomal degradation. These data suggest that the gut microbiome may contribute to AD pathogenesis by suppressing peripheral cytokines and microglia phagocytic function, leading to impaired immune-mediated Aβ clearance.
Project description:The gut microbiota and innate immune system play critical roles in Alzheimer’s disease (AD). Bacteroides is elevated in AD patients and correlates with cerebrospinal fluid levels of Aβ and tau. We found that increased amyloid-β (Aβ) plaques in Bacteroides fragilis treated APP/PS1-21 mice were associated with altered cortical expression Aβ processing genes. B. fragilis suppressed peripheral CD4+ T cell production of GM-CSF and IL-4 and transcriptional changes in microglia related to GM-CSF and IL-4 signaling, phagocytosis, and protein degradation. Furthermore, B. fragilis impaired the microglial uptake of intracranially injected Aβ42, whereas Erysipelotrichaceae strains increased uptake. Depleting murine Bacteroidetes with metronidazole decreased amyloid load in aged 5xFAD mice, increased CD4+ T cell GM-CSF production, and activated microglial pathways related to cytokine signaling, phagocytosis and lysosomal degradation. These data suggest that the gut microbiome may contribute to AD pathogenesis by suppressing peripheral cytokines and microglia phagocytic function, leading to impaired immune-mediated Aβ clearance.
Project description:An imbalance in thyroid hormones (THs) is associated with reversible dementia and Alzheimer’s disease (AD) pathogenesis. Whether hypothyroidism occurs in AD brains and how it affects AD pathology remain largely unknown. Here, we find that reduced conversion of thyroxine (T4) to tri-iodothyronine (T3) in the brain by decreased iodothyronine deiodinase 2 (DIO2) leads to hippocampal hypothyroidism in early AD model mice prior to TH changes in the blood. A TH deficiency causes immune tolerance with decreased phagocytic activity in microglia, thereby aggravating AD pathology. We demonstrate that microglial ecto-5’-nucleotidase (CD73) is reduced in the hypothyroid state and that its inhibition contributes to immune tolerance in microglia. Thus, our data define a molecular mechanism through which decreased conversion of T4 to T3 in the early AD brain, and consequent brain hypothyroidism causes microglial dysfunction and exacerbates AD pathology.
Project description:An imbalance in thyroid hormones (THs) is associated with reversible dementia and Alzheimer’s disease (AD) pathogenesis. Whether hypothyroidism occurs in AD brains and how it affects AD pathology remain largely unknown. Here, we find that reduced conversion of thyroxine (T4) to tri-iodothyronine (T3) in the brain by decreased iodothyronine deiodinase 2 (DIO2) leads to hippocampal hypothyroidism in early AD model mice prior to TH changes in the blood. A TH deficiency causes immune tolerance with decreased phagocytic activity in microglia, thereby aggravating AD pathology. We demonstrate that microglial ecto-5’-nucleotidase (CD73) is reduced in the hypothyroid state and that its inhibition contributes to immune tolerance in microglia. Thus, our data define a molecular mechanism through which decreased conversion of T4 to T3 in the early AD brain, and consequent brain hypothyroidism causes microglial dysfunction and exacerbates AD pathology.
Project description:Dysregulation of microglial function contributes to Alzheimer’s disease (AD) pathogenesis. Several genetic and transcriptome studies have revealed microglia specific genetic risk factors, and changes in microglia expression profiles in AD pathogenesis, viz. the human-Alzheimer’s microglia/myeloid (HAM) profile in AD patients and the disease-associated microglia profile (DAM) in AD mouse models. The transcriptional changes involve genes in immune and inflammatory pathways, and in pathways associated with Aβ clearance. Aβ oligomers have been suggested to be the initial trigger of microglia activation in AD. To study the direct response to Aβ oligomers exposure, we assessed changes in gene expression in an in vitro model for microglia, the human monocyte-derived microglial-like (MDMi) cells. We confirmed the initiation of an inflammatory profile following LPS stimulation, based on increased expression of IL1B, IL6, and TNFα. In contrast, the Ab1-42 oligomers did not induce an inflammatory profile or a classical HAM or DAM profile. Interestingly, we observed a specific increase in the expression of metallothioneins in the Aβ1-42 oligomer treated MDMi cells. Metallothioneins are involved in metal ion regulation, protection against reactive oxygen species, and have anti-inflammatory properties. In conclusion, our data suggests that Aβ1-42 oligomers may trigger a protective response both in vitro and in vivo.
Project description:Apolipoprotein E (apoE) plays a pivotal role in the pathogenesis of Alzheimer’s disease (AD). In the brain, apoE is predominantly expressed and secreted by astrocytes, but is dramatically up-regulated in microglia under AD-associated conditions. Although the function of astrocytic apoE has been widely investigated, whether and how apoE particles derived from different types of glia differ in biological features and function remains elusive. Here, we show that apoE particles derived from astrocytes and microglia exhibit dissimilar sizes. Microglial apoE particles impaired neurite growth and synapses and promoted neuronal senescence, whereas GPNMB-deficient microglial apoE particles abolished these detrimental effects. These findings provide direct evidence supporting that microglia-derived apoE particles contribute to neuronal senescence and toxicity.
Project description:SORL1 is implicated in the pathogenesis of Alzheimer’s disease (AD) through genetic studies. To interrogate the role(s) of SORL1 in human brain cells, SORL1 null iPSCs are differentiated to neuron, astrocyte, microglial, and endothelial cell fates. Loss of SORL1 leads to alterations in both overlapping and distinct pathways across cell types, with the greatest effects in neurons and astrocytes. SORL1 loss induces a neuron-specific reduction in APOE and CLU and altered lipid profiles. Enhancement of retromer-mediated trafficking rescues tau phenotypes observed in SORL1 null neurons but does not rescue APOE levels. Pathway analyses implicate TGF-β/SMAD signaling in SORL1 function, and modulating SMAD signaling in neurons alters APOE RNA levels in a SORL1-dependent manner. Analyses of iPSCs derived from a large cohort reveal a neuron-specific association between SORL1, APOE, and CLU levels, a finding validated in post-mortem brain. These studies provide a mechanistic link between strong genetic risk factors for AD.