Shey-Shing Sheu, PhD

Mitochondria play a central role in numerous fundamental cellular processes ranging from ATP generation, Ca2+ homeostasis, reactive oxygen species (ROS) generation, and apoptosis. Disturbances in mitochondrial Ca2+ and ROS dynamics lead to the pathogenesis of ischemic heart disease, cardiac arrhythmias, heart failure, neurodegenerative diseases, diabetes, and aging. Our long-term research objective is to elucidate cellular and molecular mechanisms by which mitochondria control intracellular Ca2+ and ROS dynamics and translate these mechanisms to the function and dysfunction of the hearts. Current research efforts are to focus on two projects:

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. The hypothesis is that cardiac mitochondria contain a ryanodine-sensive and a cyclosporine-sensitive Ca2+ permeable channel that are responsible for a rapid uptake of Ca2+ into and a rapid release of Ca2+ out of mitochondria, respectively. These dynamic Ca2+ transport mechanisms regulate cardiac bioenergetics and Ca2+ signaling. Disruption of these Ca2+ transport mechanisms lead to heart failure.

Crosstalk Signaling between Mitochondrial Ca2+ and ROS

Our long-term objective of this project is to establish a unified theory to describe crosstalk signaling between Ca2+ and ROS in cardiac muscle cells. The hypothesis is: an increased mitochondrial Ca2+ concentrations tip the balance of mitochondrial dynamics towards fission that increase the probability for opening mitochondrial permeability transition pores, which enhances ROS generation. The resulting oxidized environment leads to additional mitochondrial Ca2+ increases through redox-regulated Ca2+ transport mechanisms. Eventually, this high-gain positive feedback loop is counter balanced by Ca2+ and ROS activated mitochondrial Ca2+ efflux mechanisms.

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 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. Ultimately, it will provide insights to the design of novel mitochondria-targeted therapeutic agents for treating heart diseases.

 

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