Knockdown of microglial iron import gene, Slc11a2, worsens cognitive function and alters microglial transcriptional landscape in a sex-specific manner in the APP/PS1 model of Alzheimer's disease.

Microglial cell iron load and inflammatory activation are significant hallmarks of late-stage Alzheimer's disease (AD). In vitro, microglia preferentially upregulate the iron importer, divalent metal transporter 1 (DMT1, gene name Slc11a2) in response to inflammatory stimuli, and excess iron can augment cellular inflammation, suggesting a feed-forward loop between iron import mechanisms and inflammatory signaling. However, it is not understood whether microglial iron import mechanisms directly contribute to inflammatory signaling and chronic disease in vivo. These studies determined the effects of microglial-specific knockdown of Slc11a2 on AD-related cognitive decline and microglial transcriptional phenotype. In vitro experiments and RT-qPCR were used to assess a role for DMT1 in amyloid-β-associated inflammation. To determine the effects of microglial Slc11a2 knockdown on AD-related phenotypes in vivo, triple-transgenic Cx3cr1Cre-ERT2;Slc11a2flfl;APP/PS1+or - mice were generated and administered corn oil or tamoxifen to induce knockdown at 5-6 months of age. Both sexes underwent behavioral analyses to assess cognition and memory (12-15 months of age). Hippocampal CD11b+ microglia were magnetically isolated from female mice (15-17 months) and bulk RNA-sequencing analysis was conducted. DMT1 inhibition in vitro robustly decreased Aβ-induced inflammatory gene expression and cellular iron levels in conditions of excess iron. In vivo, Slc11a2KD APP/PS1 female, but not male, mice displayed a significant worsening of memory function in Morris water maze and a fear conditioning assay, along with significant hyperactivity compared to control WT and APP/PS1 mice. Hippocampal microglia from Slc11a2KD APP/PS1 females displayed significant increases in Enpp2, Ttr, and the iron-export gene, Slc40a1, compared to control APP/PS1 cells. Slc11a2KD cells from APP/PS1 females also exhibited decreased expression of markers associated with subsets of disease-associated microglia (DAMs), such as Apoe, Ctsb, Ly9, Csf1, and Hif1α. This work suggests a sex-specific role for microglial iron import gene Slc11a2 in propagating behavioral and cognitive phenotypes in the APP/PS1 model of AD. These data also highlight an association between loss of a DAM-like phenotype in microglia and cognitive deficits in Slc11a2KD APP/PS1 female mice. Overall, this work illuminates an iron-related pathway in microglia that may serve a protective role during disease and offers insight into mechanisms behind disease-related sex differences.

Robertson KV ，Rodriguez AS ，Cartailler JP ，Shrestha S ，Schleh MW ，Schroeder KR ，Valenti AM ，Kramer AT ，Harrison FE ，Hasty AH ... -  《Journal of Neuroinflammation》

Knockdown of microglial iron import gene, DMT1, worsens cognitive function and alters microglial transcriptional landscape in a sex-specific manner in the APP/PS1 model of Alzheimer's disease.

Robertson KV ，Rodriguez AS ，Cartailler JP ，Shrestha S ，Schroeder KR ，Valenti AM ，Harrison FE ，Hasty AH ... -  《-》

Microglial-specific knockdown of iron import gene, Slc11a2, blunts LPS-induced neuroinflammatory responses in a sex-specific manner.

Volk Robertson K ，Schleh MW ，Harrison FE ，Hasty AH ... -  《-》

Iron accumulation in microglia triggers a cascade of events that leads to altered metabolism and compromised function in APP/PS1 mice.

Among the changes that typify Alzheimer's disease (AD) are neuroinflammation and microglial activation, amyloid deposition perhaps resulting from compromised microglial function and iron accumulation. Data from Genome Wide Association Studies (GWAS) identified a number of gene variants that endow a significant risk of developing AD and several of these encode proteins expressed in microglia and proteins that are implicated in the immune response. This suggests that neuroinflammation and the accompanying microglial activation are likely to contribute to the pathogenesis of the disease. The trigger(s) leading to these changes remain to be identified. In this study, we set out to examine the link between the inflammatory, metabolic and iron-retentive signature of microglia in vitro and in transgenic mice that overexpress the amyloid precursor protein (APP) and presenilin 1 (PS1; APP/PS1 mice), a commonly used animal model of AD. Stimulation of cultured microglia with interferon (IFN)γ and amyloid-β (Aβ) induced an inflammatory phenotype and switched the metabolic profile and iron handling of microglia so that the cells became glycolytic and iron retentive, and the phagocytic and chemotactic function of the cells was reduced. Analysis of APP/PS1 mice by magnetic resonance imaging (MRI) revealed genotype-related hypointense areas in the hippocampus consistent with iron deposition, and immunohistochemical analysis indicated that the iron accumulated in microglia, particularly in microglia that decorated Aβ deposits. Isolated microglia prepared from APP/PS1 mice were characterized by a switch to a glycolytic and iron-retentive phenotype and phagocytosis of Aβ was reduced in these cells. This evidence suggests that the switch to glycolysis in microglia may kick-start a cascade of events that ultimately leads to microglial dysfunction and Aβ accumulation.

McIntosh A ，Mela V ，Harty C ，Minogue AM ，Costello DA ，Kerskens C ，Lynch MA ... -  《-》

Dihydromyricetin inhibits microglial activation and neuroinflammation by suppressing NLRP3 inflammasome activation in APP/PS1 transgenic mice.

Activated microglia-mediated inflammation plays a key role in the pathogenesis of Alzheimer's disease (AD). In addition, chronic activation of NLRP3 inflammasomes triggered by amyloid β peptide (Aβ) in microglia contributes to persistent neuroinflammation. Here, the primary goal was to assess whether Dihydromyricetin (DHM), a plant flavonoid compound, is effective therapies for AD; it is crucial to know whether DHM will affect microglial activation and neuroinflammation in APP/PS1 transgenic mice. After DHM was intraperitoneally injected in APP/PS1 double-transgenic mice, we assessed the effect of DHM on microglial activation, the expression of NLRP3 inflammasome components, and the production of inflammatory cytokine IL-1β by immunofluorescence and Western blot. To determine whether DHM play roles in the Aβ production and deposition, amyloid β protein precursor (APP) and β-site APP cleaving enzyme1 (BACE1), as well as neprilysin (NEP), were detected by Western blot. Finally, behavior was tested by Morris Water Maze to illustrate whether DHM treatment has a significantly positive effect on ameliorating the memory and cognition deficits in AD. Dihydromyricetin treatment significantly ameliorated memory and cognition deficits and decreased the number of activated microglia in the hippocampus and cortex of APP/PS1 mice. In addition, APP/PS1 mice show reduced activation of NLRP3 inflammasomes and reduced expression of NLRP3 inflammasome components. Furthermore, DHM could promote clearance of Aβ, a trigger for NLRP3 inflammasome activation, by increasing levels of NEP and shift microglial conversion to the M2-specific agrinase-1-positive cell phenotype, which enhances microglial clearance of Aβ and its aggregates but not production of Aβ. Taken together, our findings suggest that DHM prevents progression of AD-like pathology through inhibition of NLRP3 inflammasome-based microglia-mediated neuroinflammation and may be a promising therapeutic drug for treating AD.

Feng J ，Wang JX ，Du YH ，Liu Y ，Zhang W ，Chen JF ，Liu YJ ，Zheng M ，Wang KJ ，He GQ ... -  《-》