Key points
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For reasons not completely understood, obesogenic high‐fat, high‐sucrose (HFHS) diets and exercise training both increase free fatty acid utilization and chronic oxidative stress, yet ...the former is deleterious to cardiovascular/metabolic health, whereas the latter is beneficial.
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Here, we report that the heart shows decreased mitochondrial H2O2 (mH2O2) generation following HFHS diet, while skeletal muscle shows increased mH2O2, and uncover a novel role for thioredoxin reductase‐2 (TxnRd2) underlying these differences.
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We also show that TxnRd2 is critical to controlling mH2O2 levels during mitochondrial fatty acid oxidation, especially following exercise training in skeletal muscle.
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These findings are important in that they illustrate how the heart and skeletal muscle have contrasting adaptations in antioxidant capacity in response to HFHS diet, and uncover a new role for TxnRd2 in the overall control of mH2O2 in these organs with HFHS diet and exercise training.
Increased fatty acid availability and oxidative stress are physiological consequences of exercise (Ex) and a high‐fat, high‐sugar (HFHS) diet. Despite these similarities, the global effects of Ex are beneficial, whereas HFHS diets are largely deleterious to the cardiovascular system. The reasons for this disparity are multifactorial and incompletely understood. We hypothesized that differences in redox adaptations following HFHS diet in comparison to exercise may underlie this disparity, particularly in mitochondria. Our objective in this study was to determine mechanisms by which heart and skeletal muscle (red gastrocnemius, RG) mitochondria experience differential redox adaptations to 12 weeks of HFHS diet and/or exercise training (Ex) in rats. Surprisingly, both HFHS feeding and Ex led to contrasting effects in heart and RG, in that mitochondrial H2O2 decreased in heart but increased in RG following both HFHS diet and Ex, in comparison to sedentary animals fed a control diet. These differences were determined to be due largely to increased antioxidant/anti‐inflammatory enzymes in the heart following the HFHS diet, which did not occur in RG. Specifically, upregulation of mitochondrial thioredoxin reductase‐2 occurred with both HFHS and Ex in the heart, but only with Ex in RG, and systematic evaluation of this enzyme revealed that it is critical for suppressing mitochondrial H2O2 during fatty acid oxidation. These findings are novel and important in that they illustrate the unique ability of the heart to adapt to oxidative stress imposed by HFHS diet, in part through upregulation of thioredoxin reductase‐2. Furthermore, upregulation of thioredoxin reductase‐2 plays a critical role in preserving the mitochondrial redox status in the heart and skeletal muscle with exercise.
Abstract Objective Lipid peroxides and their reactive aldehyde derivatives (LPPs) have been linked to obesity-related pathologies, but whether they have a causal role has remained unclear. ...Glutathione peroxidase 4 (GPx4) is a selenoenzyme that selectively neutralizes lipid hydroperoxides, and human gpx4 gene variants have been associated with obesity and cardiovascular disease in epidemiological studies. This study tested the hypothesis that LPPs underlie cardio-metabolic derangements in obesity using a high fat, high sucrose (HFHS) diet in gpx4 haploinsufficient mice (GPx4+/− ) and in samples of human myocardium. Methods Wild-type (WT) and GPx4+/− mice were fed either a standard chow (CNTL) or HFHS diet for 24 weeks, with metabolic and cardiovascular parameters measured throughout. Biochemical and immuno-histological analysis was performed in heart and liver at termination of study, and mitochondrial function was analyzed in heart. Biochemical analysis was also performed on samples of human atrial myocardium from a cohort of 103 patients undergoing elective heart surgery. Results Following HFHS diet, WT mice displayed moderate increases in 4-hydroxynonenal (HNE)-adducts and carbonyl stress, and a 1.5-fold increase in GPx4 enzyme in both liver and heart, while gpx4 haploinsufficient (GPx4+/− ) mice had marked carbonyl stress in these organs accompanied by exacerbated glucose intolerance, dyslipidemia, and liver steatosis. Although normotensive, cardiac hypertrophy was evident with obesity, and cardiac fibrosis more pronounced in obese GPx4+/− mice. Mitochondrial dysfunction manifesting as decreased fat oxidation capacity and increased reactive oxygen species was also present in obese GPx4+/− but not WT hearts, along with up-regulation of pro-inflammatory and pro-fibrotic genes. Patients with diabetes and hyperglycemia exhibited significantly less GPx4 enzyme and greater HNE-adducts in their hearts, compared with age-matched non-diabetic patients. Conclusion These findings suggest LPPs are key factors underlying cardio-metabolic derangements that occur with obesity and that GPx4 serves a critical role as an adaptive countermeasure.
Background In sepsis, circulating cytokines and lipopolysaccharide elicit mitochondrial dysfunction and cardiomyopathy, a major cause of morbidity and mortality with this condition. Emerging research ...places the PHB1 (lipid raft protein prohibitin-1) at the nexus of inflammation, metabolism, and oxidative stress. PHB1 has also been reported in circulation, though its function in this compartment is completely unknown. Methods and Results Using a wide-ranging approach across multiple in vitro and in vivo models, we interrogated the functional role of intracellular and circulating PHB1 in the heart during sepsis, and elucidated some of the mechanisms involved. Upon endotoxin challenge or sepsis induction in rodent models, PHB1 translocates from mitochondria to nucleus in cardiomyocytes and is secreted into the circulation from the liver in a manner dependent on nuclear factor (erythroid-derived 2)-like 2, a key transcriptional regulator of the antioxidant response. Overexpression or treatment with recombinant human PHB1 enhances the antioxidant/anti-inflammatory response and protects HL-1 cardiomyocytes from mitochondrial dysfunction and toxicity from cytokine stress. Importantly, administration of recombinant human PHB1 blunted inflammation and restored cardiac contractility and ATP production in mice following lipopolysaccharide challenge. This cardioprotective, anti-inflammatory effect of recombinant human PHB1 was determined to be independent of nuclear factor (erythroid-derived 2)-like 2, but partially dependent on PI3K/AKT signaling in the heart. Conclusions These findings reveal a previously unknown cardioprotective effect of PHB1 during sepsis, and illustrate a pro-survival, protective role for PHB1 in the circulation. Exploitation of circulating PHB1 as a biomarker and/or therapeutic could have widespread benefit in the clinical management of sepsis and other severe inflammatory disorders.
MuRF1 is a previously reported ubiquitin-ligase found in striated muscle that targets troponin I and myosin heavy chain for degradation. While MuRF1 has been reported to interact with mitochondrial ...substrates in yeast two-hybrid studies, no studies have identified MuRF1’s role in regulating mitochondrial function to date. In the present study, we measured cardiac mitochondrial function from isolated permeabilized muscle fibers in previously phenotyped MuRF1 transgenic and MuRF1−/− mouse models to determine the role of MuRF1 in intermediate energy metabolism and ROS production. We identified a significant decrease in reactive oxygen species production in cardiac muscle fibers from MuRF1 transgenic mice with increased α-MHC driven MuRF1 expression. Increased MuRF1 expression in ex vivo and in vitro experiments revealed no alterations in the respiratory chain complex I and II function. Working perfusion experiments on MuRF1 transgenic hearts demonstrated significant changes in glucose oxidation. This is an factual error as written; however, total oxygen consumption was decreased. This data provides evidence for MuRF1 as a novel regulator of cardiac ROS, offering another mechanism by which increased MuRF1 expression may be cardioprotective in ischemia reperfusion injury, in addition to its inhibition of apoptosis via proteasome-mediate degradation of c-Jun. The lack of mitochondrial function phenotype identified in MuRF1−/− hearts may be due to the overlapping interactions of MuRF1 and MuRF2 with energy regulating proteins found by yeast two-hybrid studies reported here, implying a duplicity in MuRF1 and MuRF2’s regulation of mitochondrial function.
Abstract only
Peroxidation of polyunsaturated fatty acids (PUFAs) generates a number of highly reactive lipid peroxidation products (LPPs), and the seleno‐enzyme glutathione peroxidase‐4 (GPx4) is an ...antioxidant enzyme that selectively neutralizes LPPs. To determine the contribution of LPPs to the pathogenesis of cardiomyopathy precipitated by diet‐induced obesity, male WT and litter‐mate GPx4‐deficient (GPx4
+/−
) mice were placed on a n‐6 PUFA enriched high fat high sucrose (HFHS) diet for 24 weeks, along with a control group of WT mice (CTL) fed low‐fat standard chow. At termination of diet, adipose tissue mass and glucose intolerance were markedly higher in the GPx4
+/−
HFHS group compared to WT‐HFHS group, although both HFHS groups were significantly more than CTL. Blood pressure and cardiac function were not significantly different between groups, although left ventricular size and cardiomyocyte diameter was increased in WTHFHS group compared to CTL. Cardiac fibrosis was also markedly higher in both HFHS groups, but substantially more so in GPx4
+/−
compared to WT. Mitochondrial O
2
consumption was higher in WT‐HFHS but not GPx4
+/−
HFHS, compared to CTL. Surprisingly, the HFHS diet reduced mitochondrial H
2
O
2
by ~3fold in WT vs. CTL, but stayed similar between CTL and GPx4
+/−
. These findings implicate GPx4 as a critical enzyme necessary for the heart to positively adapt to the oxidative stress induced by obesity.
Abstract only
Peroxidation of n‐6 and n‐3 PUFAs generates toxic aldehydes 4‐ hydroxynonenal (HNE) and 4‐hydroxyhexenal (HHE), respectively. The high content of PUFAs and ROS in mitochondria make them ...primary sources and targets of these aldehydes, particularly in oxidative tissues such as heart. The mitochondrial enzyme aldehyde dehydrogenase‐2 (ALDH2) is responsible, in part, for neutralizing these aldehydes. To determine whether HNE and HHE differ in their effect on mitochondrial function in heart, and if activation of ALDH2 can suppress these effects, mitochondria were isolated from rat heart (N=8) and treated with vehicle (CON), HNE or HHE in the presence or absence of Alda‐1 (100 μM; ALDH2 agonist). Maximal ADP‐stimulated O
2
consumption (maxO
2
) supported by glutamate+malate (GM), pyruvate+malate and succinate was decreased ~70% by HNE in concentration (10–80 μM) and time‐dependent manner (P<0.05). maxO
2
was not affected by HHE in identical treatments. Activation of ALDH2 with Alda‐1 attenuated the HNE‐mediated inhibition of GM‐supported maxO
2
(P<0.05). Mitochondrial calcium tolerance (mCa
2+
) was reduced by HNE (−28.2 %) and HHE (−25.1 %) vs. CON (P<0.05), although much more HHE than HNE was required. Activation of ALDH2 did not restore mCa
2+
to CON levels with either aldehyde. Collectively, these findings suggest that aldehydes derived from n‐6 PUFAs are more toxic to mitochondria than aldehydes derived from n‐3 PUFAs, and that activation of ALDH2 remains a provocative therapeutic target to suppress the cytotoxic action of HNE. (Supported by NIH grant HL098780 to EJA)
Gamma delta T-cells are commonly found in response to Listeria monocytogenes infection in mice, whereas this same immunological response has only been reported a few times in vivo in humans. ...Moreover, gamma delta T-cell response in cerebral spinal fluid samples in conjunction with Listeria meningitis has never been described in medical literature to date. Thus, we describe a 64-year-old male who presented with altered mental status, fever, and neck stiffness. After lumbar puncture revealed elevated glucose, protein, lactate dehydrogenase, and white blood cell count, further cytologic analysis was indicated. The CSF showed a markedly hypercellular sample with a lymphocytic pleocytosis, including some enlarged forms with irregular nuclear contours, and rare macrophage containing intracytoplasmic bacteria. Lymphocyte immunophenotyping was performed via flow cytometric analysis, which ultimately revealed a prominent CD4/CD8 negative T-cell population, suggestive of a gamma delta T-cell population. Thus, an initial suspicion of malignancy was considered but was ruled out due to the absence of mass lesion on imaging and overall features including heterogenous lymphocyte morphology. Shortly after, gram stain and cultures were obtained revealing Listeria monocytogenes. Unfortunately, the patient rapidly succumbed to disease following the diagnosis of Listeria meningitis. Studies suggest that gamma delta T-cells are activated by the protein components of Listeria and thus have been found to be an important mediator of resistance to Listeria infection. Studies have also discovered that the level of activation for these T-cells appears to be tissue specific and dose dependent, with most cases occurring within visceral organs. Hence, we herein present the first case of gamma delta T-cell activation due to Listeria monocytogenes within the cerebral spinal fluid of a human patient.
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