Deletion of thioredoxin-interacting protein in mice impairs mitochondrial function but protects the myocardium from ischemia-reperfusion injury

Abstract

Classic therapeutics for ischemic heart disease are less effective in individuals with the metabolic syndrome. As the prevalence of the metabolic syndrome is increasing, better understanding of cardiac metabolism is needed to identify potential new targets for therapeutic intervention. Thioredoxin-interacting protein (Txnip) is a regulator of metabolism and an inhibitor of the antioxidant thioredoxins, but little is known about its roles in the myocardium. We examined hearts from Txnip-KO mice by polony multiplex analysis of gene expression and an independent proteomic approach; both methods indicated suppression of genes and proteins participating in mitochondrial metabolism. Consistently, Txnip-KO mitochondria were functionally and structurally altered, showing reduced oxygen consumption and ultrastructural derangements. Given the central role that mitochondria play during hypoxia, we hypothesized that Txnip deletion would enhance ischemia-reperfusion damage. Surprisingly, Txnip-KO hearts had greater recovery of cardiac function after an ischemia-reperfusion insult. Similarly, cardiomyocyte-specific Txnip deletion reduced infarct size after reversible coronary ligation. Coordinated with reduced mitochondrial function, deletion of Txnip enhanced anaerobic glycolysis. Whereas mitochondrial ATP synthesis was minimally decreased by Txnip deletion, cellular ATP content and lactate formation were higher in Txnip-KO hearts after ischemia-reperfusion injury. Pharmacologic inhibition of glycolytic metabolism completely abolished the protection afforded the heart by Txnip deficiency under hypoxic conditions. Thus, although Txnip deletion suppresses mitochondrial function, protection from myocardial ischemia is enhanced as a result of a coordinated shift to enhanced anaerobic metabolism, which provides an energy source outside of mitochondria. IntroductionThe clinical profile of ischemic heart disease has changed profoundly over the last decade, with a growing prevalence of systemic metabolic disorders. As the metabolic syndrome can decrease the effectiveness of classic therapeutics for ischemic heart disease (1), a better understanding of cardiac metabolism will be increasingly important for the treatment of the ischemic heart. Cellular metabolic regulation is largely dependent on mitochondrial respiration, which plays an important role in energy homeostasis by metabolizing nutrients and producing ATP and heat (2). ROS represent evanescent signaling molecules that are byproducts of the electron flux through mitochondrial oxidative phosphorylation (OXPHOS). The continuation of mitochondrial aerobic respiration in the absence of oxygen results in excessive ROS production, which can lead to cellular damage (3). The link between mitochondria-derived ROS and tissue damage is well established in ischemia-reperfusion injury of the myocardium (4).An emerging link between metabolism regulation and cellular redox balance is the ubiquitous antioxidant thioredoxin and its endogenous inhibitor, thioredoxin-interacting protein (Txnip...

Caspase 1 Activation Is Protective against Hepatocyte Cell Death by Up-regulating Beclin 1 Protein and Mitochondrial Autophagy in the Setting of Redox Stress

“…Hypoxia/Reoxygenation-One adaptive mechanism employed to protect cells from harmful ROS is through regulation of mitochondrial oxidative phosphorylation that generates ROS as a byproduct (24). We analyzed mitochondrial oxygen consumption rate (OCR) using the Seahorse extracellular flux analyzer and confirmed that the OCR in WT cells was reduced after hypoxia/reoxygenation, as expected (Fig.…”

“…The inhibition of mitochondrial respiration during hypoxia/ hemorrhagic shock and the removal of mitochondria to reduce ROS production upon reoxygenation may confer protection against mitochondrial dysfunction and subsequent cell death (10,24) and is a major cellular adaptive response to hypoxia. Although low levels of ROS may be critical to signaling in cell stress and preconditioning responses (38), our study suggests that high levels of mitochondrial ROS contribute directly to hepatocyte cell death during hypoxia/reoxygenation.…”

Thioredoxin-Interacting Protein Deficiency Protects against Diabetic Nephropathy

“…[4][5][6] We and others have implicated TxNIP in this initiating event. In cardiomyocytes 38 and mesangial cells from TxNIP-deficient mice, 15 decreased mitochondrial glucose metabolism concomitant with increased glycolysis and lactate production has been observed. Furthermore, HG did not stimulate mesangial cell mitochondrial membrane potential or ROS generation in the TxNIP-deficient state, while adenoviral mediated overexpression of TxNIP restored these responses.…”

“…15,38 Evidence for a defect in ROS generation in vivo was manifested by the lack of increase in urinary 8-OHdG in the TxNIP 2/2 diabetic mice in contrast to diabetic WT ( Figure 5B). This was supported by the reduced mitochondrial membrane potential and ROS production in TxNIP-silenced cultured podocytes exposed to HG (Figure 7, A-C).…”

Regulation of Cellular Redox Signaling by Matricellular Proteins in Vascular Biology, Immunology, and Cancer

“…The same study reported CD47-dependent expression of thioredoxin-interacting protein (TXNIP), and TXNIP was upregulated by treatment with the CD47 antibody B6H12 in triple negative breast cancer stem cells (109). In part by inhibiting the antioxidant function of thioredoxin-2 (Trx2) in the mitochondria, TXNIP limits resistance to oxidative stress, and deletion of TXNIP-protected mice from ischemia-reperfusion injury (308,309). Further studies are needed to test the hypothesis that CD47-mediated upregulation of TXNIP in cancer stem cells could sensitize them to the oxidative stress caused by radiation or anthracyclines.…”