Tuesday, March 21, 2023
3/21/2023
Summary Approximately one person dies from heart disease every 30 seconds in the United States. About 1.5 million Americans die from myocardial infarction each year. Clinically, genetic disorders (e.g. hereditary hemochromatosis) and repeated blood transfusions (as required for sickle cell anemia and beta thalassemia) are known to cause Fe accumulation in the heart with iron overload cardiomyopathy being a major cause of death. It has been recently reported that dilated cardiomyopathy occurs in up to 95% of patients with Duchenne muscular dystrophy and that iron levels are elevated in mouse models. Furthermore, iron levels are known to be elevated in the heart after ischemia followed by reperfusion. Nevertheless, the underlying mechanism(s) involved in Fe associated cardiotoxicity remain unclear. Calcium and iron are both known to play vital cellular roles in the heart. Cells exhibit a remarkable dependence on keen regulation of calcium and iron concentrations. Cellular dysregulation of either ion can result in systolic and diastolic dysfunction and ultimately cardiomyopathy. Loss or disruption of normal homeostasis of cellular calcium and/or cellular iron concentrations can not only cause direct myocardial cardiotoxicity, but can also result in loss of myocardial excitability and abnormal excitation contraction coupling. We propose that a cross talk between calcium and iron combined results in a highly cardiotoxic cellular environment. We posit that the presence of iron can result in cell death via an underappreciated pathway, i.e. ferroptosis in the heart resulting in cardiomyopathy as well as ischemia reperfusion injury. Furthermore, we propose a similar link between myocardial stunning seen after brief periods of ischemia reperfusion to be in part due to the same cross talk resulting in a partially reversible reduction in myocardial systolic function. Linking the transport of calcium and iron signaling is the mitochondria Ca uniporter (mCU) and the activation of transient receptor potential canonical channels. We show that iron can regulate TRPC ion channel function. Our preliminary data have shown that TRPC channels are directly activated by iron. Importantly, activation of TRPCs has been implicated in calcium paradox injury and post- myocardial infarction remodeling. We aim to demonstrate that neither calcium nor iron are simply passive participants in cellular processes, but when forces are joined result in systolic and diastolic failure of the heart, cardiotoxcity, and together are predictive of a reduced lifespan in humans. We will demonstrate that it is cellular diastolic calcium and mitochondrial calcium that defines cell death and myocardial function with iron loading. We hypothesize that mCU accounts for mitochondrial iron overload and that an interaction (or crosstalk) between elevated diastolic calcium and increased mitochondrial iron results in a highly volatile and cardiotoxic environment that causes cardiac cell death via ferroptosis resulting in cardiomyopathy and ischemia reperfusion injury. The field of ferroptosis is nascent in many regards when it comes to the heart. The key drivers and pathways of ferroptosis in the heart differ depending on biological context. In summary, there is a wealth of foreseeable opportunities to elucidate both the trigger(s) and pathways activated that can result in ferroptosis and its role in various forms of cardiac cardiomyopathy and ischemia-reperfusion injury. Our preliminary studies have demonstrated ferroptosis in iron induced cardiomyopathy and Duchenne Muscular Dystrophy cardiomyopathy. We will use woodchucks that have been shown by us to be protected from ischemia reperfusion injury as a tool to identify novel anti-ferroptosis pathways that can be targeted for treatment and/or preventative therapies. We will pursue the following aims. Aim 1: Determine the role of mCU and TRPCs in Fe induced cardiac dysfunction at the level of the isolated myocyte and in vivo. Sub-aim 1-1: We will demonstrate in vitro and in vivo whether mCU mediated Fe uptake and Ca dysregulation are associated with Fe induced cardiac toxicity. We will confirm mito Fe loading is mediated by mCU. The effects of Fe treatment on mito function, oxidative stress and the role of mCU will be defined. Sub-aim 1-2: We will demonstrate Fe induced activation of TRPCs and the relationship to cardiac dysfunction in vitro (acute) and in vivo (Fe-CM). Sub-aim 1-3: Data derived from Sub-aims 1-1 and 1-2 will be used to populate a computer model of E-C-M coupling and simulations run with incorporation of Fe effects. Aim 2: To determine pathways involved in ferroptosis in Fe-CM, DMD-CM, and Woodchucks during I/R injury. Sub-aim 2-1: We will determine whether mito Fe uptake via mCU plays a role in ferroptosis with Fe loading and test other known inducers of ferroptosis. We will determine the role of ROS and TRPC in vitro and in vivo with Fe loading and I/R. Sub-aim 2-2: In DMD-CM hearts, we will determine remodeling of ferroptosis-related genes and proteins, evaluate biomarkers, and test the susceptibility to ferroptosis inducers in vitro. We will test various ferroptosis pathways and attempt to mitigate DMD-CM by inhibiting ferroptosis in vivo. Sub-aim 2-3: We will obtain novel insights into protective mechanism(s) in woodchucks during I/R (in vitro and in vivo).
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