Control Of Cellular Energy Metabolism

National Heart, Lung, And Blood Institute

Investigators

Linked publications & trials

Abstract

The purpose of these studies is to establish a better understanding of the energy metabolism of biological tissues using modern system biology approaches. Towards this goal, the laboratory concentrates on the use of screening approaches in proteomics, metabolomics, protein structure, post-translational modifications, minimally invasive metabolic imaging information and optical spectroscopy. One of the major hypothesizes in this program is that the activity of the multi-protein Complexes that perform Oxidative Phosphorylation are coordinated in some fashion to balance the rate of ATP production with utilization in the cell. This results in the observed metabolic homeostasis where the potential energy for doing work is maintained near constant in the cell even during major alterations in workload. The following major findings were made over the last year: 1) We have expanded our transmission optical spectroscopy investigation of the functioning of mitochondria in the intact beating heart to focus on ischemic reperfusion in the mouse heart model working with the MRC group at Cambridge University. We have also validated the use of the chromophores of Complex III of oxidative phosphorylation to provide a non-invasive determination of mitochondrial membrane potential in the beating heart. Theoretical and phenological approaches using this intrinsic chromophore have led to similar results. Using the absolute ratio of the different b hemes of Complex III has proven to be the most quantitative approach. Using this approach we have established the dynamics of the mitochondrial membrane potential and overall redox poise of the mitochondria during ischemia, contraction and reperfusion under a variety of conditions. Data demonstrates a rapid recovery of the mitochondria membrane potential at reperfusion that could contribute to both reactive oxygen species generation as well as the accumulation of Ca in the mitochondria matrix. Both of these events could contribute to mitochondria damage during the reperfusion phase and methods to differentiate these complications are being evaluated. 2) We have finalized the analysis of full 3D high resolution electron microscopy screen on hearts exposed to different degrees of ischemia before the reperfusion event. These studies demonstrate highly heterogenous morphological responses while a degradation of the mitochondria reticulum, previously described by our lab as critical in energy distribution in the heart. These data may suggest that the degradation of the mitochondria reticulum may be one of the early damage events in reperfusion injury. 3) To broaden our analysis of metabolic regulation in the mitochondria we have expanded our studies to study the ancestors of mitochondria, simple bacteria. We have recently completed our initial studies on isolated bacteria believed to be closest to the mitochondrial origins, paracoccus denitrificans (PD). The goal of these studies is to unravel acute energy conversion regulation in this bacterium and then look for similar mechanisms in mammalian mitochondria. With the growing interest in the microbiome, these studies should also provide new insight into the acute regulation of bacterial energy metabolism that has not been extensively studied. We demonstrated in this period that the previously described metabolic homeostasis described in the mammalian heart, that is constant free energy available in ATP as well as the mitochondria proton motive during increases is workload, exists in PD. That is PD can increase its metabolic rate by over 8 fold and maintain constant proton motive force as well as increase ATP content. We have recently focused on the utilization of lactate and its enzymatic pathways as a model system to simplify the analysis of this process. It is hoped that this simple system will provide insight into the molecular mechanisms involved in the regulation of oxidative phosphorylation in mammalian mitochondria. 4) Together with numerous programs at the NIH, with an in depth interaction with Dr. Campbell, and collaboration with Siemens Medical Systems, we have developed a low field 0.55T MRI system for monitoring physiological and structural function in humans. In addition to its low cost, good image quality and contrast as well as the ability to tolerate the use of interventional devices without associated radiofrequency heating, we have exploited this magnetic field to evaluate gaseous oxygen as a MRI contrast agent permitting the evaluation of lung ventilation, delivery of oxygen to the heart and potentially the relative oxygen consumption by the heart when combined with blood flow measures. Initial studies in LAM patients reveal a promising capability of monitoring both structure and oxygen tension in the lung under a variety of conditions.