Unique Subtype of Microglia in Degenerative Thalamus After Cortical Stroke

Abstract

Background and Purpose: Stroke disrupts neuronal functions in both local and remotely connected regions, leading to network-wide deficits that can hinder recovery. The thalamus is particularly affected, with progressive development of neurodegeneration accompanied by inflammatory responses. However, the complexity of the involved inflammatory responses is poorly understood. Herein we investigated the spatiotemporal changes in the secondary degenerative thalamus after cortical stroke, using targeted transcriptome approach in conjunction with histology and flow cytometry. Methods: Cortical ischemic stroke was generated by permanent occlusion of the left middle cerebral artery in male C57BL6J mice. Neurodegeneration, neuroinflammatory responses, and microglial activation were examined in naive and stroke mice at from poststroke days (PD) 1 to 84, in both ipsilesional somatosensory cortex and ipsilesional thalamus. NanoString neuropathology panel (780 genes) was used to examine transcriptome changes at PD7 and PD28. Fluorescence activated cell sorting was used to collect CD11c + microglia from ipsilesional thalamus, and gene expressions were validated by quantitative real-time polymerase chain reaction. Results: Neurodegeneration in the thalamus was detected at PD7 and progressively worsened by PD28. This was accompanied by rapid microglial activation detected as early as PD1, which preceded the neurodegenerative changes. Transcriptome analysis showed higher number of differentially expressed genes in ipsilesional thalamus at PD28. Notably, neuroinflammation was the top activated pathway, and microglia was the most enriched cell type. Itgax (CD11c) was the most significantly increased gene, and its expression was highly detected in microglia. Flow-sorted CD11c + microglia from degenerative thalamus indicated molecular signatures similar to neurodegenerative disease–associated microglia; these included downregulated Tmem119 and CX3CR1 and upregulated ApoE, Axl, LpL, CSF1, and Cst7. Conclusions: Our findings demonstrate the dynamic changes of microglia after stroke and highlight the importance of investigating stroke network-wide deficits. Importantly, we report the existence of a unique subtype of microglia (CD11c + ) with neurodegenerative disease–associated microglia features in the degenerative thalamus after stroke.

Neuroinflammation as a Key Driver of Secondary Neurodegeneration Following Stroke?

“…Notably, the impairment of microglial function correlated with Aβ plaque deposition, both temporally and spatially, suggesting that with further studies into the later stages of SND a relationship between non-responsive microglia and Aβ plaques may be observed [ 213 ] This is particularly detrimental given the fact that Aβ deposition plays a key role in the development of dementia [ 214 ]. In support of this, a recent study identified a unique subtype of CD11c-positive microglia in the thalamus 28 days following MCAo in mice [ 207 ]. Using flow cytometry, the group was able to indicate molecular signatures in the post-stroke microglia that are similar to neurodegenerative disease-associated microglia [ 207 ].…”

“…In support of this, a recent study identified a unique subtype of CD11c-positive microglia in the thalamus 28 days following MCAo in mice [ 207 ]. Using flow cytometry, the group was able to indicate molecular signatures in the post-stroke microglia that are similar to neurodegenerative disease-associated microglia [ 207 ].…”

The potassium channel Kv1.3 as a therapeutic target for immunocytoprotection after reperfusion

“…These findings should of course be independently reproduced by another laboratory like our findings in young male rats recently were, 38 but could suggest a bigger contribution of Kv1.3 high microglia and T cells to stroke pathophysiology in aged animals. CD11c + microglia, which express high levels of Kv1.3, 16 have recently been described to drive secondary, neurodegenerative changes in the thalamus after cortical strokes 39 . Regarding T cells, old C57BL/6 mice of both sexes recruit significantly more T cells into the brain than young and middle‐aged mice following 60‐min tMCAO 31 and CD4 T‐cell depletion has been shown to improve behavioral outcomes on day‐7 post‐MCAO in aged mice without reducing infarct size 40 .…”

“…CD11c + microglia, which express high levels of Kv1.3, 16 have recently been described to drive secondary, neurodegenerative changes in the thalamus after cortical strokes. 39 Regarding T cells, old C57BL/6 mice of both sexes recruit significantly more T cells into the brain than young and middle‐aged mice following 60‐min tMCAO 31 and CD4 T‐cell depletion has been shown to improve behavioral outcomes on day‐7 post‐MCAO in aged mice without reducing infarct size. 40 There are further reports that brain‐resident memory CD8 T cells, which appear to regulate microglia homeostasis under normal conditions, potentiate inflammation following ischemic injury by producing inflammatory cytokines and driving cytotoxic responses.…”

Acute TBK1/IKK-ε Inhibition Enhances the Generation of Disease-Associated Microglia-Like Phenotype Upon Cortical Stab-Wound Injury

“…These subpopulations were barely detected in vehicle-treated SWI samples but were substantially represented in the AMX treated mice. TMEM119 + CD11c + microglia (which may encompass more than one subset) has been recently identified as DAM, a subpopulation characteristically associated with neurodegenerative diseases ( Keren-Shaul et al, 2017 ; Krasemann et al, 2017 ; Cao et al, 2021 ) and white matter aging ( Sato-Hashimoto et al, 2019 ; Safaiyan et al, 2021 ). Expression profiling of DAM has revealed the upregulation of genes involved in lipid metabolism (most notably, ApoE) and apparently reduced capacity for engulfment, phagocytosis and degradation ( Krasemann et al, 2017 ; Ulland et al, 2017 ).…”