Shey-Shing Sheu, Ph.D.

Mitochondria play a central role in numerous fundamental cellular processes ranging from ATP generation, Ca2+ homeostasis, reactive oxygen species (ROS) generation, and apoptosis. Deregulation of the mitochondrial Ca2+ and ROS homeostasis has been implicated in the pathogenesis of ischemic heart disease, cardiac arrhythmias, neurodegenerative diseases, diabetes, and aging. Our long-term research objective is to elucidate cellular and molecular mechanism by which mitochondria control intracellular Ca2+ and ROS dynamics under both physiological and pathological conditions. Current research efforts are to focus on three projects:

(1) Mechanisms of Mitochondrial Ca2+ Transport in Heart Cells
Our immediate efforts are to characterize the mitochondrial Ca2+ influx and efflux mechanisms in cardiac muscle cells and determine how these mechanisms regulate excitation-contraction-metabolism coupling. Our working hypothesis is that cardiac mitochondria contain a Ca2+-activated, ryanodine-sensive and a Ca2+-activated cyclosporine-sensitive Ca2+ permeable channel that are responsible for the fast uptake of Ca2+ into and fast release of Ca2+ out of mitochondria, respectively. These dynamic Ca2+ transport systems participate actively in regulating cardiac excitation-contraction-metabolism coupling processes, due to their structural proximity to the junctions between sarcoplasmic reticulum and L-type Ca2+ channels.

(2) Crosstalk Signaling between Mitochondrial Ca2+ and ROS
Our long-term objective of this project is to establish a unified theory to describe the mechanisms of crosstalk signaling between Ca2+ and ROS in cardiac muscle cells, and to translate these signaling pathways to the physiology and pathology of cardiac function. Our central hypothesis is: an increased mitochondrial Ca2+ concentration tips the balance of mitochondrial dynamics towards fission that drives an increase in ROS generation. The resulting oxidized environment leads to additional mitochondrial Ca2+ increases. Eventually, this high-gain positive feedback loop is counter balanced by Ca2+ and ROS activated mitochondrial Ca2+ efflux mechanisms.

(3) Mitochondrial Modulation of Neuronal Excitotoxicity
Our immediate goal is to determine the role of mitochondrial Ca2+ overload and oxidative stress in neuronal cell death. Our working hypothesis is that Ca2+- and ROS-dependent mitochondrial permeability transition (MPT) opening is central to the process of excitotoxic cell death, and that energetically impaired cells are more susceptible to excitotoxic cell death because they have a higher likelihood of MPT occurrence in response to a given excitotoxic stimulus

We will use a multidisciplinary approach, encompassing single cell fluorescence confocal microscopy to measure cytosolic and mitochondrial Ca2+ concentrations, patch clamp to record L-type Ca2+ currents, and biochemical and molecular biological techniques to probe the mitochondrial Ca2+ transport proteins. This research will provide important information regarding the fundamental principles of mitochondrial Ca2+ transport mechanisms in heart and brain cells. This information is critical for our understanding of the participation of mitochondria in the etiology of cardiovascular diseases such as cardiac arrhythmia, cardiomyopathy, and heart failure as well as neurodegenerative diseases such as Alzheimer's disease, Huntington's disease and Parkinson's disease. Ultimately, it will provide insights to design novel targets for therapeutic intervention in these diseases.