Deepening our understanding of G3BP1 and its paralog G3BP2 to facilitate accurate therapeutic development for ALS/FTD
While significant efforts have been made worldwide, the development of an effective therapy to significantly slow or halt ALS disease progression has remained elusive. This is due in part to our incomplete understanding of the molecular mechanisms and aberrant processes that lead to disease. TDP-43 (TAR DNA binding protein 43) is at center stage in current ALS research. While mutations in TDP-43 are causative for a small percentage of ALS cases, the mislocalization of the protein from its primarily nuclear localization to the cytoplasm is a salient feature in the vast majority of ALS cases and nearly half of FTD cases. Recent work using mouse genetics now demonstrates that nuclear TDP-43 depletion is sufficient to induce neuromuscular junction retraction and motor neuron loss, thus supporting a loss of function model1.
We have demonstrated that G3BP1 is regulated by TDP-43. While there is significant emphasis on G3BP1 function as it pertains to stress granules, there is increasing evidence that G3BP1 regulates many key cellular processes essential to neuronal survival. Indeed, G3bp1–null mice support the essentialness of G3BP1 to neuronal survival. Our proposal builds on our recently published work and will tease out stress granule-independent functions relevant to G3BP1 that are not shared by its paralog G3BP2. Furthermore, we will study how the role of G3BP1 in mRNA decay is relevant to ALS pathogenesis, an area that lacks data but is becoming increasingly important. Lastly, we will analyze how TDP-43 mutations impact a cryptic splicing event in G3BP1. These three independent specific aims will shed light on how G3BP1 and its functions are dysregulated in ALS as well as support other ongoing projects that aim to identify approaches to restore G3BP1 as a future therapeutic option.
AIM 1: Define the distinct protein interaction network of G3BP1 versus G3BP2 in neurons.
We will explore how G3BP1 and G3BP2 are functionally distinct using a proteomics-based approach in neurons. This aim will identify interactors that are common or unique to both proteins thus providing insight on their overlapping or non-overlapping functions, respectively. In addition, we will explore which domains in G3BP1 are required for specific protein-protein interactions and investigate how they mediate stress-independent functions of G3BP1.
AIM 2: Determine the role of G3BP1/2 in mRNA degradation and its implication in ALS.
We will investigate which domains and additional protein factors are required for mRNA degradation by G3BP1 and G3BP2. We will also assess whether these proteins required for G3BP1/2-mediated decay are themselves dysregulated in ALS. Moreover, we will identify mRNAs destabilized by G3BP1 in neurons and determine whether they are altered in ALS.
AIM 3: Determine the expression and impact of a TDP-43 mediated cryptic splicing event in G3BP1. We will determine if a short in-frame insertion in the N-terminal region of G3BP1 can be expressed in the context of TDP-43 pathology in ALS/FTD patients and how this modulates its cellular functions, both known roles and novel ones to be uncovered by aims 1 and 2.
Christine Vande Velde , Université de Montréal
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