As heart failure progresses, rewiring of metabolism leads to a global decline in ATP synthesis. In studying heart failure, we focus on calcium signaling, since it is critical for cardiac contraction and metabolism. We hope to define the molecular pathways that control mitochondrial calcium signaling and target these for novel therapeutics.
In cardiomyopathies triggered by OXPHOS dysfunction, we find increased influx of mitochondrial calcium through the mitochondrial calcium uniporter (green), and diminished efflux through the sodium-calcium exchanger (purple). This leads to enhanced calcium levels in the mitochondrial matrix, potentially both boosting ATP synthesis via a compensatory mechanism, but also leading to mitochondrial dysfunction after excessive accumulation. Figure taken from Sommakia et. al. J Mol Cell Cardiol 2017
Mutations affecting mitochondrial function are among the most common forms of inborn errors of metabolism, primarily affecting infants and children. When such mitochondrial dysfunction leads to cardiac involvement, termed the mitochondrial cardiomyopathies, mortality rates increase threefold. In studying animal and cell models of these diseases, we have found that mitochondrial calcium levels are increased and are currently investigating (a) how such regulation occurs, and (b) how such changes affect cardiac function.
Far left, Brightfield image of a mitoplast, with one lobe bounded only by the mitochondrial inner membrane (IMM, white arrow) and one lobe also bounded by the outer membrane (OMM, black arrow). Matrix-targeted mCherry (middle left). GFP-tagged mitofusin-1 (an outer membrane GTPase, middle right). Far right: merged image. Figure modified from Chaudhuri et. al. eLife 2013
Because of their intracellular location, direct assessment of mitochondrial ion channels via classical electrophysiological techniques has been limited. We have overcome this barrier by studying mitoplasts, which are purified mitochondria stripped of their outer membranes. Such mitoplasts can be interrogated via voltage-clamping to allow measurement of ionic currents. Our laboratory is one of the few capable of performing this challenging technique. We use this technique to characterize the behavior of mitochondrial ion channels, including the mitochondrial calcium uniporter, the main portal for calcium entry into the mitochondrial matrix.
