Adapting Secretory Proteostasis through Pharmacologic IRE1 Activation

不平衡的蛋白质稳态（或蛋白质稳态）涉及的发病和发病机制的病因

Imbalances in protein homeostasis (or proteostasis) are implicated in the onset and pathogenesis of etiologically- diverse diseases including diabetes, systemic amyloid disease, heart disease, and aging-related neurodegenerative disorders such as Alzheimer’s Disease (AD). There are currently no treatments for these diseases, prompting an effort to both understand disease pathogenesis and develop novel approaches to mitigate the associated pathogenic proteostasis imbalances. As the overall integrity of the cellular proteome is a central facet of viability and function, the cell evolved a proteostasis network comprised of folding and degradation factors to ensure proper folding of nascent or misfolded peptides, or to promote their degradation if folding cannot be achieved. The endoplasmic reticulum (ER) Unfolded Protein Response (UPR) plays a crucial role in maintaining both intra- and extra-cellular proteostasis, as the ER environment is a main checkpoint for the folding of secreted proteins. Importantly, many proteins implicated in proteostasis-associated diseases including AD are trafficked through the secretory pathway and therefore interface with the ER proteostasis environment. Thus, the UPR is an attractive target for manipulating the levels of destabilized, disease-relevant proteins. This response is normally activated under circumstances of increased misfolded protein load in the ER lumen (i.e., ER stress), a signal which is sensed and transduced by the ER membrane proteins Inositol Requiring Enzyme 1 (IRE1), Protein kinase-like Endoplasmic Reticulum Kinase (PERK), and Activating Transcription Factor 6 (ATF6), which in turn induce proteostatic transcriptional programs to mitigate the unfolded protein load. This research project focuses specifically on the IRE1 signaling arm of the UPR, which has been extensively studied using genetic and chemical genetic approaches to demonstrate the therapeutic potential for activation of this pathway for multiple, etiologically-diverse diseases. While these approaches have been transformative for studying IRE1 signaling, compounds currently available for pharmacologic activation of this pathway are limited by their inherent promiscuity and cellular toxicity. For this research project, I utilize a luciferase-based high-throughput screening approach in conjunction with transcriptomic and proteomic studies to identify novel small molecule activators of the IRE1 signaling axis with a defined mechanism of action (Aim 1). Through these efforts, I have prioritized compound 474 as a promising first-in-class, non-toxic and specific activator of the IRE1 signaling axis in multiple cell culture models. In an effort to characterize the therapeutic potential of pharmacologic IRE1 activation, I will apply this compound and others to cellular models of AD to study effects on destabilized Amyloid Precursor Protein (APP) and Amyloid beta (Abβ) peptide levels as well as downstream physiological readouts of cellular health in relevant cell lines (Aim 2). These efforts will demonstrate the potential for pharmacologic IRE1 activation to mitigate disease-relevant imbalances in proteostasis implicated in AD and other diseases.