Insights into Unfolded Protein Response in the Heart

• Author / Creator

  Wang, Qian

• Cellular responses to stress are an integral part of cardiovascular physiology and pathology, and endoplasmic reticulum (ER) stress is the key component in the development and progression of various heart diseases. However, the relative contribution of ER stress pathways to muscle damage and molecular mechanisms governing muscle ER stress regulation are still unclear. The objectives of this thesis were to investigate a role and regulation of IRE1α, an ER membrane associated stress sensor, in skeletal and cardiac muscle and to determine structural and function features of catecholaminergic polymorphic ventricular tachycardia (CPVT) related Casq2 mutants and their role in heart pathology.
  We identified two distinct pools of IRE1α in skeletal muscle fibers and in cardiomyocytes. One pool localized at the perinuclear ER membrane system and other at the junctional sarcoplasmic reticulum (SR). We also discovered that, at the junctional SR, calsequestrin interacts directly with the ER luminal domain of IRE1α preventing its dimerization, an initial step in activation IRE1α signaling. We generated a mouse model with cardiomyocyte specific, inducible deletion of the IRE1α gene. Heart with silenced IRE1α developed dilated cardiomyopathy and impaired cardiomyocyte Ca2+ transient indicating important role of IRE1α in the heart physiology and potential functional impact on muscle excitation-contraction coupling.
  Mutations in the gene encoding for cardiac calsequestrin, CASQ2, cause a stress-induced arrhythmia, CPVT. We carried out functional and structural analysis of six CPVT related CASQ2 mutations (R33Q, L167H, D307H, D351G, G332R, and P329S). The six mutations are distributed in diverse locations of the calsequestrin and impact on structure and function of the protein including folding, aggregation, and impaired or reduced Ca2+ binding. Remarkably these mutations are manifested in a similar phenotype in humans.
  Overall, in this thesis, we show that IRE1α is a new component of the junctional SR where it interacts with calsequestrin. This novel protein-protein interaction provides new insight into muscle specific regulatory mechanisms associated with IRE1α mediated UPR. We also provide the first direct evidence that IRE1α is required to maintain health of the heart. Finally, we provide the first evolutionary insights into the calsequestrin gene and showed that different Casq2 mutations may have distinct underlying molecular mechanisms leading to CPVT.

• Subjects / Keywords

  • UPR
  • ER stress
  • calsequestrin
  • heart

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-hs9z-jg34

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.