Changes to Astrocyte-associated Protein Expression at Different Timepoints of Cuprizone Treatment

Abstract

Glial cells, including astrocytes, microglia, and oligodendrocytes, are brain cells that support and dynamically interact with neurons and each other. These intercellular dynamics undergo changes during stress and disease states. In response to most forms of stress, astrocytes will undergo some variation of activation, meaning upregulation in certain proteins expressed and secreted and either upregulations or downregulations to various constitutive and normal functions. While types of activation are many and contingent on the particular disturbance that triggers these changes, there are two main overarching categories that have been delineated thus far: A1 and A2. Named in the convention of microglial activation subtypes, and with the acknowledgement that the types are not completely distinct or completely comprehensive, the A1 subtype is generically associated with toxic and pro-inflammatory factors, and the A2 phenotype is broadly associated with anti-inflammatory and neurogenic factors. The present study served to measure and document dynamic changes in these subtypes at multiple timepoints using an established experimental model of cuprizone toxic demyelination. The authors found increases in proteins associated with both cell types at different timepoints, with protein increases in the A1 marker C3d and the A2 marker Emp1 in the cortex at one week and protein increases in Emp1 in the corpus callosum at three days and four weeks. There were also increases in Emp1 staining specifically colocalized with astrocyte staining in the corpus callosum at the same timepoints as the protein increases, and in the cortex weeks later at four weeks. C3d colocalization with astrocytes also increased most at four weeks. This indicates simultaneous increases of both types of activation as well as the likely existence of astrocytes expressing both markers. The authors also found the increase in two A1 associated proteins (TNF alpha and C3d) did not show a linear relationship in line with findings from other research and indicating a more complex relationship between cuprizone toxicity and astrocyte activation. The increases in TNF alpha and IFN gamma did not occur at timepoints preceding increases in C3d and Emp1, showing that other factors also precipitate the subtypes associated (A1 for C3d and A2 for Emp1). These findings add to the body of research showing the specific early timepoints at which A1 and A2 markers are most increased during the course of cuprizone treatment, including the fact that these increases can be non-linear in the case of Emp1. This provides additional information on optimal times for targeted interventions during the cuprizone model.

Astrocytes: Lessons Learned from the Cuprizone Model

“…[161] Astrocytes express C3; TIC knock-outs show reduced C3 expression [162] Aastrocyte participation in the tripartite synapse during demyelination [163] mGluR5 is expressed by astrocytes and orchestrates remyelination [164] EBI2 receptor is expressed in astrocytes and microglia [165] Astrocytes express TrkB, CTR1, ATP7A, and ATP7B; demyelination is ameliorated in mice lacking astrocytic TrkB expression [166] Fth deletion in Glast1/EAAT1-positive astrocytes inhibits remyelination [167] EAAT2 is expressed by astrocytes [168] Astrocytes express S100B, GFAP, vimentin, LCN2, and ALDH1L1 [83] LCN2 is expressed by astrocytes; oligodendrocyte loss is more severe in Lcn2 -/animals [169] Ongoing astrocytosis weeks after completion of remyelination [170] C3d, S100a10, Stat3, and Timp1 are expressed by astrocytes [171] C3d and S100a10 are expressed by astrocytes; Bu Shen Yi Sui capsules promote an A2 phenotype [172] Combined mesenchymal stem cell transplantation and astrocyte ablation support remyelination [173] Cuprizone intoxication induces astrocyte endfeet sweelings [174] Astrocytes express TRAP1; β-hydroxybutyrate downregulates the expression of this protein [71] High-resolution, single-nucleus RNA sequencing (snRNA-seq) analysis of gene expression changes across various brain cells, including astrocytes [175] Bone Marrow Mesenchymal Stem Cells reduce astrocytosis [176] Astrocytes express HNK-1-O-Man+ PTPRZ [177] A1 versus A2 astrocyte expression profiling [178] The AQP4 inhibitor TGN020 ameliorates astrocyte and microglia activation [76] Astrocytic transcriptome signature investigated via ribosomal tagging…”