Myocardial tissue can remain viable, despite a prolonged period of reduced blood flow. Referred to as """"""""hibernation"""""""", the entity is observed experimentally and has important clinical implications for patients with advanced coronary artery disease and ischemic cardiomyopathy. In this proposal, we will test the hypothesis that expression of uncoupling protein (UCP)-2, as an adaptive process within mitochondria from hibernating and preconditioned heart tissue in the """"""""Second Window of Protection"""""""" (SWOP), is protective against anoxia.
In AIM #1, we hypothesize that UCP-2 protects mitochondria against anoxia-reoxygenation, by reducing superoxide generation and preventing a pathway that leads to mitochondrial permeability transition pore formation and cytochrome c loss. Our preliminary data suggest an important relationship between UCP-2 and protection, because GDP deactivates UCP-2 and inhibits stress-resistance. As part of AIM #2, we will further develop the concept by assessing the degree of mitochondrial protection in mouse hearts under basal conditions and following peroxisome proliferator activated receptor (PPAR) gamma stimulation with chronic dietary administration of pioglitazone. Our preliminary data in this resubmission show a robust increase in UCP-2 from hearts of wild type but not UCP-2 KO mice with pioglitazone, along with an increase in protection from the isolated mitochondria from the mouse hearts. Our central question is that mitochondrial adaptations against repetitive supply-demand ischemia might offset oxidant damage as a protective mitochondrial adaptation in hibernating hearts, but result in a submaximal energetic and functional response at high work states. Therefore, in AIM #3, we will test the relationship between in vivo transmural energy and function during high dose dobutamine and ex vivo expression of UCP-2. Our preliminary data from hibernating pig hearts show that the phosphorylation state, as measured by the phosphocreatine (PCr) to ATP ratio during dobutamine is reduced proportionate to the increased UCP-2 content ex vivo. To establish a more direct relationship, we will then test whether chronic stimulation of PPAR-gamma with pioglitazone will further increase the mitochondrial expression of UCP-2, leading to an additional decrement in transmural energy and function. Finally, as part of AIM #4, we will use iTRAC, to test whether mitochondrial ATP synthase, a potentially contributing factor to the observed reductions in basal regional blood flow in hibernating tissue, will be further reduced in response to chronic pioglitazone in the pig model. Potential Impact on Health Care- Mitochondria are a major source of severe oxidant damage. They have the potential for being an important therapeutic target for patients with CHF. We propose studies that address mechanisms of mitochondrial protection that may lead to novel treatments. We will also examine the effects of glitazones, a therapy for diabetes, and its potential role in UCP-2 induction on the evolution of CHF.
Progressive heart failure from coronary artery disease is the most common cause of death. Revascularization therapies and anti-tachycardia devices are available to prevent sudden death, but among the majority of patients who have received these treatments, the progressive process of cell death that leads to a debilitating disease remains of epidemic proportion. This proposal will address potential mechanisms by which mitochondria adapt to prevent apoptosis or cell death against acute reductions in blood flow, but limit maximal energy production chronically. We will focus on a pig model of heart failure that is associated with a reduction in blood flow to a viable area of the heart. The proposal will test whether the mitochondrial production of energy, as measured by state-of-the-art MRI imaging, will play a role in the sustained reductions in function. Using this model, we propose that a class of drugs used in diabetic patients that has been associated with heart failure exacerbations, alters the mitochondrial energy production in a similar way.
|Holley, Christopher T; Long, Eric K; Butterick, Tammy A et al. (2015) Mitochondrial fusion proteins in revascularized hibernating hearts. J Surg Res 195:29-36|
|Holley, Christopher T; Duffy, Cayla M; Butterick, Tammy A et al. (2015) Expression of uncoupling protein-2 remains increased within hibernating myocardium despite successful coronary artery bypass grafting at 4 wk post-revascularization. J Surg Res 193:15-21|
|Cabrera, Jesús A; Ziemba, Elizabeth A; Colbert, Robert et al. (2012) Uncoupling protein-2 expression and effects on mitochondrial membrane potential and oxidant stress in heart tissue. Transl Res 159:383-90|
|Kelly, Rosemary F; Cabrera, Jesús A; Ziemba, Elizabeth A et al. (2011) Continued depression of maximal oxygen consumption and mitochondrial proteomic expression despite successful coronary artery bypass grafting in a swine model of hibernation. J Thorac Cardiovasc Surg 141:261-8|