Author + information
- Justin Hartupee,
- Abhinav Diwan,
- Philip Barger and
- Douglas Mann
Background: In the failing heart there is impaired protein turnover and an accumulation of ubiquitinated proteins within cardiomyocytes. This accumulation, which likely has detrimental effects on myocyte function, has been attributed to proteasome dysfunction. However, the extent to which changes in the autophagy lysosome pathway contribute remains unclear.
Methods: To explore this issue, we employed a mouse model with cardiac restricted overexpression of TNF (MHCsTNF), which we have shown mimics the heart failure phenotype. 12 week old male mice were used in all studies. Gene expression studies include 6-7 mice per group and statistical significance was determined using the unpaired Student t test. Immunofluorescence images are representative of 4-5 mice per group.
Results: There is an accumulation of ubiquitin tagged proteins in the hearts of MHCsTNF mice, similar to what has been observed in human heart failure. Interestingly, these ubiquitinated proteins are found in aggregates with p62, which is known to bind to ubiquitin tagged proteins and targets them to autophagosomes. Moreover, there is increased p62 protein expression consistent with an accumulation of autophagy substrates. We also found increased LC3-II expression indicative of increased number of autophagosomes. To determine whether the increase in autophagosomes reflected increased formation (enhanced autophagy initiation) or impaired breakdown (impaired autophagic flux) we treated the MHCsTNF mice with the lysosome inhibitor chloroquine. These studies showed that there was impaired autophagic flux in the MHCsTNF mice. As a potential mechanism to explain impaired autophagic flux in this setting we looked at mTOR activity and found increased phosphorylation of multiple targets of mTORC1 consistent with activation of this complex.
Conclusions: Collectively, these data indicate that impaired autophagy is an important mechanism that contributes to the accumulation of ubiquitinated proteins in the failing heart and may be related to enhanced mTORC1 activation.
Poster Hall, Hall C
Saturday, March 18, 2017, 3:45 p.m.-4:30 p.m.
Session Title: Cardiac Fibrosis and Heart Failure: The Next Frontier
Abstract Category: 12. Heart Failure and Cardiomyopathies: Basic
Presentation Number: 1249-258
- 2017 American College of Cardiology Foundation