Novel roles of matrix metalloproteinase-2 in myocardial oxidative stress injury

• Author / Creator

  Chan, Brandon Ying-How

• Matrix metalloproteinase-2 (MMP-2) is a zinc-dependent protease that proteolyzes numerous substrates both inside and outside the cell when activated during oxidative stress. However, the full gamut of MMP-2 substrates in myocardial oxidative stress injury is largely unknown. This thesis investigates novel targets of MMP-2 and the effect of MMP inhibitors in two cardiac pathologies associated with increased oxidative stress: anthracycline cardiotoxicity and ischemia-reperfusion injury.
  Oxidative stress is one of the major mechanisms of anthracycline cardiotoxicity. I showed that treating cardiomyocytes with the anthracycline doxorubicin enhanced cellular oxidative stress and concomitantly increased MMP-2 levels/activity. Doxorubicin enhanced MMP-2 activity in cardiomyocytes by two means: i) oxidative stress increased the levels and activity of 72 kDa MMP-2 and ii) oxidative stress triggers the de novo expression of N-terminal truncated MMP-2. Doxorubicin also increased the levels of MMP-2 secreted into the conditioned medium. Doxorubicin-induced cardiomyocyte injury was associated with reduced troponin I, SERCA2a, and phospholamban protein levels. However, MMP inhibitors did not prevent the loss of these proteins as doxorubicin reduced their expression at a transcriptional level.
  Anthracycline cardiotoxicity is associated with extracellular matrix remodeling and myofilament lysis. Mice treated with doxorubicin exhibited cardiac contractile dysfunction and left ventricular remodeling in vivo. Ultrastructural analysis of the left ventricle showed that doxorubicin caused significant sarcomeric degeneration including myofilament lysis, reduced sarcomere lengths, and damage to the Z-disc and M-line. Doxorubicin also caused cardiac titin proteolysis and interstitial fibrosis. This was accompanied by increased MMP-2 levels/activity in the heart and increased MMP-2 localization in the sarcomere and mitochondria. I demonstrated that mice treated with two orally available MMP inhibitors ameliorated doxorubicin-induced cardiac contractile dysfunction by attenuating titin proteolysis, interstitial fibrosis, and/or left ventricular remodeling.
  
  Junctophilin-2 is a structural protein which tethers the T-tubule to the sarcoplasmic reticulum to allow for coordinated calcium-induced calcium release in cardiomyocytes. Junctophilin-2 proteolysis and intracellular calcium overload are implicated in myocardial ischemia-reperfusion injury. I found that degradation of junctophilin-2 in isolated rat hearts subject to ischemia-reperfusion injury contributes to cardiac contractile dysfunction. Furthermore, inhibition of MMP-2 prevented junctophilin-2 proteolysis and improved the recovery of cardiac contractile function during ischemia-reperfusion. In vitro degradation assays revealed that junctophilin-2 is susceptible to proteolysis by MMP-2 and this was prevented by MMP inhibition. I showed for the first time that MMP-2 is co-localized to junctophilin-2 in the Z-disc region of the sarcomere.
  In summary, these studies show that MMP-2 plays an important role in the initiation and propagation of acute and chronic oxidative stress injury to the heart. Activation of MMP-2 by oxidative stress causes adverse remodeling of the intracellular and extracellular matrices. More importantly, these studies demonstrate the cardioprotective effects of MMP inhibitors in vivo and ex vivo against cardiac pathologies associated with increased oxidative stress. MMP inhibitors may be a potential therapeutic strategy to prevent cardiovascular disease.

• Subjects / Keywords

  • oxidative stress
  • remodeling
  • extracellular matrix
  • matrix metalloproteinase
  • sarcomere
  • cardiotoxicity

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-7xp2-2k39

• License

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