Reactive astrogliosis in the era of single-cell transcriptomics.

Reactive astrogliosis is a reaction of astrocytes to disturbed homeostasis in the central nervous system (CNS), accompanied by changes in astrocyte numbers, morphology, and function. Reactive astrocytes are important in the onset and progression of many neuropathologies, such as neurotrauma, stroke, and neurodegenerative diseases. Single-cell transcriptomics has revealed remarkable heterogeneity of reactive astrocytes, indicating their multifaceted functions in a whole spectrum of neuropathologies, with important temporal and spatial resolution, both in the brain and in the spinal cord. Interestingly, transcriptomic signatures of reactive astrocytes partially overlap between neurological diseases, suggesting shared and unique gene expression patterns in response to individual neuropathologies. In the era of single-cell transcriptomics, the number of new datasets steeply increases, and they often benefit from comparisons and integration with previously published work. Here, we provide an overview of reactive astrocyte populations defined by single-cell or single-nucleus transcriptomics across multiple neuropathologies, attempting to facilitate the search for relevant reference points and to improve the interpretability of new datasets containing cells with signatures of reactive astrocytes.

Corrigendum: Reactive astrogliosis in the era of single-cell transcriptomics.

[This corrects the article DOI: 10.3389/fncel.2023.1173200.].

Cortical glia in SOD1(G93A) mice are subtly affected by ALS-like pathology.

The role of glia in amyotrophic lateral sclerosis (ALS) is undeniable. Their disease-related activity has been extensively studied in the spinal cord, but only partly in the brain. We present herein a comprehensive study of glia in the cortex of SOD1(G93A) mice-a widely used model of ALS. Using single-cell RNA sequencing (scRNA-seq) and immunohistochemistry, we inspected astrocytes, microglia, and oligodendrocytes, in four stages of the disease, respecting the factor of sex. We report minimal changes of glia throughout the disease progression and regardless of sex. Pseudobulk and single-cell analyses revealed subtle disease-related transcriptional alterations at the end-stage in microglia and oligodendrocytes, which were supported by immunohistochemistry. Therefore, our data support the hypothesis that the SOD1(G93A) mouse cortex does not recapitulate the disease in patients, and we recommend the use of a different model for future studies of the cortical ALS pathology.

Glioblastoma and cerebral organoids: development and analysis of an in vitro model for glioblastoma migration.

It is currently challenging to adequately model the growth and migration of glioblastoma using two-dimensional (2D) in vitro culture systems as they quickly lose the original, patient-specific identity and heterogeneity. However, with the advent of three-dimensional (3D) cell cultures and human-induced pluripotent stem cell (iPSC)-derived cerebral organoids (COs), studies demonstrate that the glioblastoma-CO (GLICO) coculture model helps to preserve the phenotype of the patient-specific tissue. Here, we aimed to set up such a model using mature COs and develop a pipeline for subsequent analysis of cocultured glioblastoma. Our data demonstrate that the growth and migration of the glioblastoma cell line within the mature COs are significantly increased in the presence of extracellular matrix proteins, shortening the time needed for glioblastoma to initiate migration. We also describe in detail the method for the visualization and quantification of these migrating cells within the GLICO model. Lastly, we show that this coculture model (and the human brain-like microenvironment) can significantly transform the gene expression profile of the established U87 glioblastoma cell line into proneural and classical glioblastoma cell types.

Recent advances in deciphering oligodendrocyte heterogeneity with single-cell transcriptomics.

Oligodendrocytes (OL) have been for decades considered a passive, homogenous population of cells that provide support to neurons, and show a limited response to pathological stimuli. This view has been dramatically changed by the introduction of powerful transcriptomic methods that have uncovered a broad spectrum of OL populations that co-exist within the healthy central nervous system (CNS) and also across a variety of diseases. Specifically, single-cell and single-nucleus RNA-sequencing (scRNA-seq, snRNA-seq) have been used to reveal OL variations in maturation, myelination and immune status. The newly discovered immunomodulatory role suggests that OL may serve as targets for future therapies. In this review, we summarize the current understanding of OL heterogeneity in mammalian CNS as revealed by scRNA-seq and snRNA-seq. We provide a list of key studies that identify consensus marker genes defining the currently known OL populations. This resource can be used to standardize analysis of OL related datasets and improve their interpretation, ultimately leading to a better understanding of OL functions in health and disease.