Metabolic Adaptation to a Disruption in Oxygen Supply during Myocardial Ischemia and Reperfusion Is Underpinned by Temporal and Quantitative Changes in the Cardiac Proteome

Despite decades of intensive research, there is still
no effective treatment for ischemia/reperfusion (I/R) injury, an important
corollary in the treatment of ischemic disease. I/R injury is initiated
when the altered biochemistry of cells after ischemia is no longer
compatible with oxygenated microenvironment (or reperfusion). To better
understand the molecular basis of this alteration and subsequent incompatibility,
we assessed the temporal and quantitative alterations in the cardiac
proteome of a mouse cardiac I/R model by an iTRAQ approach at 30 min
of ischemia, and at 60 or 120 min reperfusion after the ischemia using
sham-operated mouse heart as the baseline control. Of the 509 quantified
proteins identified, 121 proteins exhibited significant changes (p-value < 0.05) over time and were mostly clustered in
eight functional groups: Fatty acid oxidation, Glycolysis, TCA cycle,
ETC (electron transport chain), Redox Homeostasis, Glutathione S-transferase, Apoptosis related, and Heat Shock proteins.
The first four groups are intimately involved in ATP production and
the last four groups are known to be important in cellular antioxidant
activity. During ischemia and reperfusion, the short supply of oxygen
precipitates a pivotal metabolic switch from aerobic metabolism involving
fatty acid oxidation, TCA, and phosphorylation to anaerobic metabolism
for ATP production and this, in turn, increases reactive oxygen species
(ROS) formation. Therefore the implication of these 8 functional groups
suggested that ischemia-reperfusion injury is underpinned in part
by proteomic alterations. Reversion of these alterations to preischemia
levels took at least 60 min, suggesting a refractory period in which
the ischemic cells cannot adjust to the presence of oxygen. Therefore,
therapeutics that could compensate for these proteomic alterations
during this interim refractory period could alleviate ischemia-reperfusion
injury to enhance cellular recovery from an ischemic to a normoxic
microenvironment. Among the perturbed proteins, Park7 and Ppia were
selected for further investigation of their functions under hypoxia.
The results show that Park7 plays a key role in regulating antioxidative
stress and cell survival, and Ppia may function in coping with the
unfolded protein stress in the I/R condition.