Intracellular regulation of matrix metalloproteinase-2 activity: the roles of caveolin-1 and troponin I phosphorylation

• Author / Creator

  Chow, Ava Kalyca

• Matrix metalloproteinase‐2 (MMP‐2) was recently revealed to have targets and actions within the cardiac myocyte. In ischemia/reperfusion (I/R) injury, MMP‐2 is activated and degrades troponin I (TnI) and α‐actinin. The regulation of intracellular MMP‐2 activity is relatively unknown and is thus the subject of this thesis. The localization of MMP‐2 in caveolae of endothelial cells suggests that caveolin‐1 (Cav‐1) may play a role in regulating MMP‐2. Whether Cav‐1 is responsible for regulating MMP‐2 in the heart is unknown. A Cav‐1 knockout mouse model was used to explore the role Cav‐1 may play in the regulation of MMP‐2 activity. The initial studies found that MMP‐2 and Cav‐1 were co‐localized in cardiomyocytes and that MMP‐2 activity in Cav‐1‐/‐ hearts was markedly enhanced. Additionally, the caveolin scaffolding domain inhibited MMP‐2 activity in a concentration‐dependent manner. To explore whether increased MMP‐2 in Cav‐1‐/‐ hearts translates to impaired cardiac function, Cav‐1+/+ and Cav‐1‐/‐ isolated working hearts were physiologically challenged with increasing increments of left atrial preload followed by increasing concentrations of isoproterenol. Cav‐1‐/‐ hearts show similar or better cardiac function compared to Cav‐1+/+ hearts following preload challenge or β‐adrenergic stimulation in vitro, and this appears unrelated to changes in MMP‐2. Though the function of Cav‐1‐/‐ hearts appears similar to that of Cav‐1+/+ hearts during physiological situations, whether this is the case during I/R injury is not known. Cav‐1+/+ and Cav‐1‐/‐ isolated working mouse hearts exposed to global, no‐flow ischemia showed no functional differences. However, Cav‐1‐/‐ hearts had significantly higher levels of both TnI and α‐actinin following I/R than Cav‐1+/+ hearts. Post‐translational modifications of the intracellular MMP‐2 substrates could alter susceptibility to MMP‐2 proteolysis. Isolated working mouse hearts were exposed to isoproterenol and/or I/R injury to examine the phosphorylation status of TnI. Isoproterenol and I/R both result in the phosphorylation of TnI, however, isoproterenol lead to a more highly phosphorylated form of TnI than that observed in hearts exposed I/R alone. These and subsequent studies will further reveal the molecular mechanisms that underlie the complex interactions between Cav‐1 and MMP‐2. This may eventually lead to a novel avenue of therapeutic intervention for heart diseases.

• Subjects / Keywords

  • Heart
  • Ischemia-reperfusion
  • Troponin I
  • Matrix metalloproteinase
  • Caveolin

• Graduation date

  Fall 2010

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3BW2P

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.