Mechanisms of Transglutaminase 2 (TG2)-Mediated Gene Expression in Astrocyte

Astrocytes play an indispensable role in maintaining a healthy environment for neuronal function, and in mediating the response of the CNS to injury.

Following an injury astrocytes become ?reactive? and mediate both helpful and harmful outcomes depending on their gene expression profile.

However the molecular mechanisms that regulate gene expression in astrocytes and thus their response to injury has not been fully delineated. One protein that plays a key role in regulating the response of astrocytes to insults is transglutaminase 2 (TG2).

Deletion or depletion of TG2 results in astrocytes taking on a more ?helpful? phenotype, however the underlying molecular mechanisms are unknown.

TG2 is a multifunctional protein; it catalyzes a calcium dependent transamidation reaction, binds and hydrolyzes GTP and can function as a scaffold or linker protein.

TG2 undergoes large conformational changes mediated by calcium and GTP binding, and its conformation can dictate its function independent of its enzymatic activities. These conformational states are key a factors in determining cell survival/cell death outcomes.

There is a growing awareness that TG2 likely regulates gene expression, however the mechanisms of TG2-mediated regulation of gene expression in astrocytes has not been fully explored.

One possible mechanism may be by TG2 interacting with, and modulating the function of, a protein that plays a pivotal role in regulating gene expression.

One factor that plays a key role in regulating chromatin accessibility and the activity of specific transcription factors is Zbtb7a.

Intriguingly, preliminary data indicate that TG2 interacts with Zbtb7a, and binding sites for these transcription factors are in the majority of pro-survival genes that are upregulated in TG2-/- astrocytes.

The UNDERLYING PREMISE of this proposal is that TG2 plays a role in regulating gene expression in astrocytes, and thus how they respond to injury. However, a CRITICAL KNOWLEDGE GAP is how TG2 regulates gene expression.

The OVERALL HYPOTHESIS of this application is that TG2, in a conformational dependent manner, moderates chromatin accessibility and the gene expression landscape, which contributes to how astrocytes respond to injury.

The NOVELTY of this project is that we will be using an integrated ?omic? approach (ATAC-seq, RNA-seq, ChIP-seq) and both in vitro and in vivo models of TG2+/+ and TG2-/- astrocytes to establish the mechanisms by which TG2 in a specific conformation regulates gene expression.

The specific aims of this proposal are to test the hypothesis that: (1) the conformation of TG2 play an essential role in determining its ability to regulate chromatin accessibility and gene expression, and (2) TG2 mediates gene expression in astrocytes in part by regulating the function of Zbtb7a.

The data generated from these novel and exploratory studies will provide the basis for a future R01 grant application focused on delineating the molecular mechanisms and pathways regulated by TG2 in astrocytes to direct outcomes following CNS injury.