Astrogliosis

Berger, Finja (2024): Astrogliosis: regulators and pathways implicated in astrocyte reactivity and plasticity. Dissertation, LMU München: Graduate School of Systemic Neurosciences (GSN)

Abstract

Traumatic brain injury (TBI) represents one of the leading causes of death and disability worldwide and is associated with an increased risk for the development of additional pathologies including dementia. Despite the acute nature of the initial trauma, progressive secondary injuries can arise as a consequence of the multicellular response mechanisms elicited that involve the orchestrated action of glial and immune cells. Astrocytes are pivotal responders to any type of brain damage through a spectrum of sophisticated changes generally referred to as reactive astrogliosis. During my Ph.D., I focused on dichotomous astrocyte responses and tried to gain further insights into their underlying molecular regulators and pathways. To this end, my work was divided into two projects dealing with distinct aspects of astrocyte reactivity; one addressed an adaptive response with promising potential for repair strategies namely the gain of cellular plasticity whilst the other one dealt with the inhibition of a maladaptive function in the form of excessive neuroinflammation. TBI is resolved to different extent in different species. While the central nervous system (CNS) of zebrafish can for instance regenerate upon TBI, the CNS of mammals and birds by large fails to do so. Nevertheless, also the mammalian brain holds a certain capacity to react to injury via compensatory mechanisms in neurons and glia. Intriguingly, a subpopulation of reactive astrocytes with in vitro stem cell capacities has been identified in response to brain injury. This population holds great potential for regenerative strategies. To identify and then visualize this rare subpopulation in vivo, we conducted a single-cell RNA sequencing (scRNA-seq) trans-species comparison between plastic zebrafish ependymoglia and injury-induced mouse reactive astrocytes. Following candidate cluster identification, we selected suitable marker genes for in situ visualization. Employing the same mouse model of TBI as the one used for the scRNA-seq screen, namely stab wound injury within the somatosensory cortex, we could visualize the expression patterns of selected marker genes and show the upregulation of these within reactive astrocytes following injury. This strategy and the chosen set of marker genes present a promising entry point for further molecular characterization of the injury-induced, proliferative reactive astrocytes. In the second project, we investigated the role of long non-coding RNAs (lncRNAs) in the re-establishment of homeostatic state in reactive astrocytes and the concomitant resolution of neuroinflammation. LncRNAs are important regulators of gene expression at different levels and are involved in a multitude of biological processes. Changes in lncRNA expression have also been observed in the context of CNS injury and neuroinflammation, implying functional involvement and providing new opportunities for improved diagnosis and treatment. In light of this, we investigated differentially expressed lncRNAs in glial populations with respect to reactivity state changes following TBI. We identified multiple lncRNAs enriched in and thus potentially crucial to homeostatic astrocytes. Employing a CRISPR activation strategy followed by bulk RNA sequencing, we studied the effect that upregulation of a subset of these candidates has on reactive astrocytes in vitro. Intriguingly, overexpression of different lncRNA candidates was found to counteract some aspects of astrocyte reactivity with downregulation of certain innate immune responses but without entirely restoring homeostasis. Overall, the identification and investigation of lncRNAs involved in astrocytic reactivity processes could allow for fine-tuned modification of astrocyte reactivity responses and open up new avenues for therapeutic interventions in disorders involving astrogliosis, such as TBI. Although these projects had different focuses, both aimed at advancing our understanding of reactive astrogliosis following TBI and thereby gain valuable insights that could ideally contribute to the establishment of novel therapeutic strategies for brain regeneration.

• Item Type: Theses (Dissertation, LMU Munich)
• Keywords: TBI, reactive astrogliosis, scRNA-seq cross-species integration, lncRNAs, CRISPRa
• Subjects: 500 Natural sciences and mathematics > 570 Life sciences
• Faculties: Graduate School of Systemic Neurosciences (GSN)
• Language: English
• Date of oral examination: 9. September 2024
• 1. Referee: Ninkovic, Jovica
• Signature of the printed copy: 0001/UMC 32270