Decoding astrocytic identity shifts post-injury: implications for neuronal reprogramming

Maddhesiya, Priya (2024): Decoding astrocytic identity shifts post-injury: implications for neuronal reprogramming. Dissertation, LMU München: Graduate School of Systemic Neurosciences (GSN)

Abstract

The regenerative capacity of the central nervous system (CNS) in the adult mammalian brain is severely limited, often leading to irreversible neuronal loss and functional decline following injury or disease. Astrocytes, the predominant glial cells in the CNS, play crucial roles in maintaining neural homeostasis, supporting the blood-brain barrier, and facilitating neuronal and synaptic functions. Upon injury or disease, these cells undergo reactive astrogliosis, significantly altering their function and phenotype. Notably, following invasive injuries, a subset of astrocytes has been observed to acquire proliferative capacity, express markers characteristic of neural stem cells (NSCs), and demonstrate the ability to self-renew and form multipotent neurospheres in vitro. This discovery adds a new dimension to our understanding of the neurogenic potential in the adult brain, which was previously thought to be limited and confined to specialized neurogenic niches such as the subventricular zone (SVZ) and the hippocampal dentate gyrus. However, the scarcity of these plastic astrocytes (occurring in low frequency) and the lack of distinct molecular markers have hindered their study and subsequent application in CNS repair strategies. Therefore, the thesis aims to 1) identify specific marker genes of this plastic astrocytic subset following stab wound injuries in the mouse cortex and 2) explore their potential in regenerative strategies, such as direct neuronal reprogramming. To identify putative markers for plastic astrocytes post-injury, a trans-species approach was adopted, leveraging regenerative insights from zebrafish ependymoglia, and integrating them with astrocyte populations in a mouse stab wound model through single-cell transcriptomic integration analysis. This method enabled the identification of key marker genes, such as Hmgb2 (High Mobility Group Box 2) and others, characterizing this distinct plastic astrocytic subset. These markers are expressed in a small subset of astrocytes emerging post-injury, demonstrating proliferation and capability of forming neurospheres in vitro. Subsequent investigation revealed that these plastic astrocytic subsets exhibit transcriptional similarities to transient amplifying progenitors (TAPs) in the SVZ. They display a partial trajectory towards neurogenic lineages while retaining gliogenic potentials due to distinct signalling pathways, compared to bonafide TAPs. The identification of Hmgb2, a chromatin-associated protein, through this comparative analysis, underscores its potential role in the reprogramming process, likely due to its involvement in chromatin remodelling—a critical step in activating neurogenic programs. Overexpressing Hmgb2 alongside the pioneer transcription factor Neurog2 in vitro, under culture conditions mimicking the in vivo injury microenvironment, significantly enhances the efficiency of neuronal conversion of astrocytes to induced neurons (iNs). This improvement is attributed to the chromatin remodelling effects of Hmgb2, which facilitate accessibility and expression of neurogenic or reprogramming relevant genes, as evidenced by analysis of chromatin (ATAC-Seq) and transcriptome (RNA-Seq) data, along with the promoting maturation of iNs. In summary, this study illuminates astrocyte plasticity following CNS injury, identifies crucial marker genes, and lays the groundwork for exploring their stem cell potential. Additionally, it underscores their significance in strategies for neuronal replacement, such as direct neuronal reprogramming. Together, these findings pave the way for advancing astrocyte research in regenerative medicine and repair approaches.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie
• Fakultäten: Graduate School of Systemic Neurosciences (GSN)
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 17. Dezember 2024
• 1. Bericht­erstatter:in: Ninkovic, Jovica