Publications by authors named "Natasha Fillmore"

26 Publications

  • Page 1 of 1

Cardiac specific knock-down of peroxisome proliferator activated receptor α prevents fasting-induced cardiac lipid accumulation and reduces perilipin 2.

PLoS One 2022 8;17(3):e0265007. Epub 2022 Mar 8.

Laboratory of Cardiac Physiology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America.

While fatty acid metabolism is altered under physiological conditions, alterations can also be maladaptive in diseases such as diabetes and heart failure. Peroxisome Proliferator Activated Receptor α (PPARα) is a transcription factor that regulates fat metabolism but its role in regulating lipid storage in the heart is unclear. The aim of this study is to improve our understanding of how cardiac PPARα regulates cardiac health and lipid accumulation. To study the role of cardiac PPARα, tamoxifen inducible cardiac-specific PPARα knockout mouse (cPPAR-/-) were treated for 5 days with tamoxifen and then studied after 1-2 months. Under baseline conditions, cPPAR-/- mice appear healthy with normal body weight and mortality is not altered. Importantly, cardiac hypertrophy or reduced cardiac function was also not observed at baseline. Mice were fasted to elevate circulating fatty acids and induce cardiac lipid accumulation. After fasting, cPPAR-/- mice had dramatically lower cardiac triglyceride levels than control mice. Interestingly, cPPAR-/- hearts also had reduced Plin2, a key protein involved in lipid accumulation and lipid droplet regulation, which may contribute to the reduction in cardiac lipid accumulation. Overall, this suggests that a decline in cardiac PPARα may blunt cardiac lipid accumulation by decreasing Plin2 and that independent of differences in systemic metabolism a decline in cardiac PPARα does not seem to drive pathological changes in the heart.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0265007PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8903264PMC
April 2022

Human Relaxin-2 Fusion Protein Treatment Prevents and Reverses Isoproterenol-Induced Hypertrophy and Fibrosis in Mouse Heart.

J Am Heart Assoc 2019 12 10;8(24):e013465. Epub 2019 Dec 10.

Cardiac Physiology Section/Cardiovascular Branch National Heart, Lung, and Blood Institute/National Institutes of Health Bethesda MD.

Background Heart failure is one of the leading causes of death in Western countries, and there is a need for new therapeutic approaches. Relaxin-2 is a peptide hormone that mediates pleiotropic cardiovascular effects, including antifibrotic, angiogenic, vasodilatory, antiapoptotic, and anti-inflammatory effects in vitro and in vivo. Methods and Results We developed RELAX10, a fusion protein composed of human relaxin-2 hormone and the Fc of a human antibody, to test the hypothesis that extended exposure of the relaxin-2 peptide could reduce cardiac hypertrophy and fibrosis. RELAX10 demonstrated the same specificity and similar in vitro activity as the relaxin-2 peptide. The terminal half-life of RELAX10 was 7 days in mouse and 3.75 days in rat after subcutaneous administration. We evaluated whether treatment with RELAX10 could prevent and reverse isoproterenol-induced cardiac hypertrophy and fibrosis in mice. Isoproterenol administration in mice resulted in increased cardiac hypertrophy and fibrosis compared with vehicle. Coadministration with RELAX10 significantly attenuated the cardiac hypertrophy and fibrosis compared with untreated animals. Isoproterenol administration significantly increased transforming growth factor β1 (TGF-β1)-induced fibrotic signaling, which was attenuated by RELAX10. We found that RELAX10 also significantly increased protein kinase B/endothelial NO synthase signaling and protein S-nitrosylation. In the reversal study, RELAX10-treated animals showed significantly reduced cardiac hypertrophy and collagen levels. Conclusions These findings support a potential role for RELAX10 in the treatment of heart failure.
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http://dx.doi.org/10.1161/JAHA.119.013465DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6951077PMC
December 2019

A knock-in mutation at cysteine 144 of TRIM72 is cardioprotective and reduces myocardial TRIM72 release.

J Mol Cell Cardiol 2019 11 16;136:95-101. Epub 2019 Sep 16.

Laboratory of Cardiac Physiology, NHLBI, NIH, Bethesda, MD, United States of America. Electronic address:

TRIM72 is a membrane repair protein that protects against ischemia reperfusion (I/R) injury. We previously identified Cys (C144) on TRIM72 as a site of S-nitrosylation. To study the importance of C144, we generated a knock-in mouse with C144 mutated to a serine (TRIM72 C144S). We subjected ex vivo perfused mouse hearts to 20 min of ischemia followed by 90 min of reperfusion and observed less injury in TRIM72 C144S compared to WT hearts. Infarct size was smaller (54 vs 27% infarct size) and cardiac functional recovery (37 vs 62% RPP) was higher for the TRIM72 C144S mouse hearts. We also demonstrated that TRIM72 C144S hearts were protected against I/R injury using an in vivo LAD occlusion model. As TRIM72 has been reported to be released from muscle we tested whether C144 is involved in TRIM72 release. After I/R there was significantly less TRIM72 in the perfusate normalized to total released protein from the TRIM72 C144S compared to WT hearts, suggesting that C144 of TRIM72 regulates myocardial TRIM72 release during I/R injury. In addition to TRIM72's protective role in I/R injury, TRIM72 has also been implicated in cardiac hypertrophy and insulin resistance, and secreted TRIM72 has recently been shown to impair insulin sensitivity. However, insulin sensitivity (measured by glucose and insulin tolerance) of TRIM72 C144S mice was not impaired. Further, whole body metabolism, as measured using metabolic cages, was not different in WT vs TRIM72 C144S mice and we did not observe enhanced cardiac hypertrophy in the TRIM72 C144S mice. In agreement, protein levels of the TRIM72 ubiquitination targets insulin receptor β, IRS1, and focal adhesion kinase were similar between WT and TRIM72 C144S hearts. Overall, these data indicate that mutation of TRIM72 C144 is protective during I/R and reduces myocardial TRIM72 release without impairing insulin sensitivity or enhancing the development of hypertrophy.
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http://dx.doi.org/10.1016/j.yjmcc.2019.09.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7000244PMC
November 2019

Malonyl CoA Decarboxylase Inhibition Improves Cardiac Function Post-Myocardial Infarction.

JACC Basic Transl Sci 2019 Jun 24;4(3):385-400. Epub 2019 Jun 24.

Cardiovascular Research Centre, Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada.

Alterations in cardiac energy metabolism after a myocardial infarction contribute to the severity of heart failure (HF). Although fatty acid oxidation can be impaired in HF, it is unclear if stimulating fatty acid oxidation is a desirable approach to treat HF. Both immediate and chronic malonyl coenzyme A decarboxylase inhibition, which decreases fatty acid oxidation, improved cardiac function through enhancing cardiac efficiency in a post-myocardial infarction rat that underwent permanent left anterior descending coronary artery ligation. The beneficial effects of MCD inhibition were attributed to a decrease in proton production due to an improved coupling between glycolysis and glucose oxidation.
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http://dx.doi.org/10.1016/j.jacbts.2019.02.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6609914PMC
June 2019

Uncoupling of glycolysis from glucose oxidation accompanies the development of heart failure with preserved ejection fraction.

Mol Med 2018 03 15;24(1). Epub 2018 Mar 15.

Cardiovascular Research Centre, Mazankowski Alberta Heart Institute University of Alberta, Edmonton, Canada.

Background: Alterations in cardiac energy metabolism contribute to the development and severity of heart failure (HF). In severe HF, overall mitochondrial oxidative metabolism is significantly decreased resulting in a reduced energy reserve. However, despite the high prevalence of HF with preserved ejection fraction (HFpEF) in our society, it is not clear what changes in cardiac energy metabolism occur in HFpEF, and whether alterations in energy metabolism contribute to the development of contractile dysfunction.

Methods: We directly assessed overall energy metabolism during the development of HFpEF in Dahl salt-sensitive rats fed a high salt diet (HSD) for 3, 6 and 9 weeks.

Results: Over the course of 9 weeks, the HSD caused a progressive decrease in diastolic function (assessed by echocardiography assessment of E'/A'). This was accompanied by a progressive increase in cardiac glycolysis rates (assessed in isolated working hearts obtained at 3, 6, and 9 weeks of HSD). In contrast, the subsequent oxidation of pyruvate from glycolysis (glucose oxidation) was not altered, resulting in an uncoupling of glucose metabolism and a significant increase in proton production. Increased glucose transporter (GLUT)1 expression accompanied this elevation in glycolysis. Decreases in cardiac fatty acid oxidation and overall adenosine triphosphate (ATP) production rates were not observed in early HF, but both significantly decreased as HF progressed to HF with reduced EF (i.e. 9 weeks of HSD).

Conclusions: Overall, we show that increased glycolysis is the earliest energy metabolic change that occurs during HFpEF development. The resultant increased proton production from uncoupling of glycolysis and glucose oxidation may contribute to the development of HFpEF.
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http://dx.doi.org/10.1186/s10020-018-0005-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6016884PMC
March 2018

Cardiac branched-chain amino acid oxidation is reduced during insulin resistance in the heart.

Am J Physiol Endocrinol Metab 2018 11 14;315(5):E1046-E1052. Epub 2018 Aug 14.

Cardiovascular Research Centre, Mazankowski Alberta Heart Institute, University of Alberta , Edmonton , Canada.

Recent studies have proposed that elevated branched-chain amino acids (BCAAs) may induce insulin resistance (IR) in muscle secondary to increased BCAA oxidation inhibiting glucose oxidation (GO) and fatty acid oxidation (FAO). However, BCAA oxidation rates have not been assessed in muscle IR, and cardiac FAO rates are actually already elevated in obesity-associated IR. We therefore directly examined cardiac BCAA oxidation in mice fed a high-fat diet (HFD) to induce insulin resistance to better understand the role of cardiac BCAA oxidation in cardiac IR. BCAA oxidation, GO, FAO, and glycolysis were measured in isolated working hearts from mice fed either a low-fat diet (LFD) or HFD for 10 wk. Insulin stimulation of cardiac GO and inhibition of FAO were blunted in HFD mice, resulting in a marked increase in FAO contribution to ATP production compared with LFD mice hearts (71.2% vs. 37.1%, respectively). Surprisingly, cardiac BCAA oxidation rate was reduced in HFD compared with LFD mice (33.5 ± 3.4 vs. 56.7 ± 7.1 nmol·min·g dry wt, respectively, P < 0.05, n = 9/group). In addition, BCAA oxidation contributed ~1% of the ATP production of the heart, and, as a result, alterations in BCAA oxidation could not significantly impact either GO or FAO rates. However, the decrease in BCAA oxidation was accompanied by an increase in BCAA concentration and impaired insulin signaling. These results suggest that cardiac IR is not due to an increase in BCAA oxidation and subsequent inhibition of GO and FAO. Rather, we propose that an inhibition of BCAA oxidation rate contributes to IR by leading to increased BCAA concentration, which negatively impacts insulin signaling.
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http://dx.doi.org/10.1152/ajpendo.00097.2018DOI Listing
November 2018

Cytosolic carnitine acetyltransferase as a source of cytosolic acetyl-CoA: a possible mechanism for regulation of cardiac energy metabolism.

Biochem J 2018 03 9;475(5):959-976. Epub 2018 Mar 9.

Cardiovascular Translational Science Institute and the Department of Pediatrics, 423 Heritage Medical Research Building, University of Alberta, Edmonton, Alberta, Canada T6G 2S2

The role of carnitine acetyltransferase (CrAT) in regulating cardiac energy metabolism is poorly understood. CrAT modulates mitochondrial acetyl-CoA/CoA (coenzyme A) ratios, thus regulating pyruvate dehydrogenase activity and glucose oxidation. Here, we propose that cardiac CrAT also provides cytosolic acetyl-CoA for the production of malonyl-CoA, a potent inhibitor of fatty acid oxidation. We show that in the murine cardiomyocyte cytosol, reverse CrAT activity (RCrAT, producing acetyl-CoA) is higher compared with the liver, which primarily uses ATP-citrate lyase to produce cytosolic acetyl-CoA for lipogenesis. The heart displayed a lower RCrAT for CoA compared with the liver. Furthermore, cytosolic RCrAT accounted for 4.6 ± 0.7% of total activity in heart tissue and 12.7 ± 0.2% in H9C2 cells, while highly purified heart cytosolic fractions showed significant CrAT protein levels. To investigate the relationship between CrAT and acetyl-CoA carboxylase (ACC), the cytosolic enzyme catalyzing malonyl-CoA production from acetyl-CoA, we studied ACC2-knockout mouse hearts which showed decreased CrAT protein levels and activity, associated with increased palmitate oxidation and acetyl-CoA/CoA ratio compared with controls. Conversely, feeding mice a high-fat diet for 10 weeks increased cardiac CrAT protein levels and activity, associated with a reduced acetyl-CoA/CoA ratio and glucose oxidation. These data support the presence of a cytosolic CrAT with a low for CoA, favoring the formation of cytosolic acetyl-CoA, providing an additional source to the classical ATP-citrate lyase pathway, and that there is an inverse relation between CrAT and the ratio of acetyl-CoA/CoA as evident in conditions affecting the regulation of cardiac energy metabolism.
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http://dx.doi.org/10.1042/BCJ20170823DOI Listing
March 2018

A Systems Biology Approach to Investigating Sex Differences in Cardiac Hypertrophy.

J Am Heart Assoc 2017 Aug 19;6(8). Epub 2017 Aug 19.

Systems Biology Center, National Heart, Lung and Blood Institute National Institutes of Health, Bethesda, MD

Background: Heart failure preceded by hypertrophy is a leading cause of death, and sex differences in hypertrophy are well known, although the basis for these sex differences is poorly understood.

Methods And Results: This study used a systems biology approach to investigate mechanisms underlying sex differences in cardiac hypertrophy. Male and female mice were treated for 2 and 3 weeks with angiotensin II to induce hypertrophy. Sex differences in cardiac hypertrophy were apparent after 3 weeks of treatment. RNA sequencing was performed on hearts, and sex differences in mRNA expression at baseline and following hypertrophy were observed, as well as within-sex differences between baseline and hypertrophy. Sex differences in mRNA were substantial at baseline and reduced somewhat with hypertrophy, as the mRNA differences induced by hypertrophy tended to overwhelm the sex differences. We performed an integrative analysis to identify mRNA networks that were differentially regulated in the 2 sexes by hypertrophy and obtained a network centered on PPARα (peroxisome proliferator-activated receptor α). Mouse experiments further showed that acute inhibition of PPARα blocked sex differences in the development of hypertrophy.

Conclusions: The data in this study suggest that PPARα is involved in the sex-dimorphic regulation of cardiac hypertrophy.
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http://dx.doi.org/10.1161/JAHA.117.005838DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5586433PMC
August 2017

Sex Differences in Metabolic Cardiomyopathy.

Cardiovasc Res 2017 03 1;113(4):370-377. Epub 2017 Feb 1.

In contrast to ischemic cardiomyopathies which are more common in men, women are over-represented in diabetic cardiomyopathies. Diabetes is a risk factor for cardiovascular disease; however, there is a sexual dimorphism in this risk factor: heart disease is five times more common in diabetic women but only two-times more common in diabetic men. Heart failure with preserved ejection fraction, which is associated with metabolic syndrome, is also more prevalent in women. This review will examine potential mechanisms for the sex differences in metabolic cardiomyopathies. Sex differences in metabolism, calcium handling, nitric oxide, and structural proteins will be evaluated. Nitric oxide synthase and PPARα exhibit sex differences and have also been proposed to mediate the development of hypertrophy and heart failure. We focused on a role for these signalling pathways in regulating sex differences in metabolic cardiomyopathies.
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http://dx.doi.org/10.1093/cvr/cvx008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5852638PMC
March 2017

Genetic and Pharmacological Inhibition of Malonyl CoA Decarboxylase Does Not Exacerbate Age-Related Insulin Resistance in Mice.

Diabetes 2016 07 13;65(7):1883-91. Epub 2016 May 13.

Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Canada Alberta Diabetes Institute, University of Alberta, Edmonton, Canada

Aging is associated with the development of chronic diseases such as insulin resistance and type 2 diabetes. A reduction in mitochondrial fat oxidation is postulated to be a key factor contributing to the progression of these diseases. Our aim was to investigate the contribution of impaired mitochondrial fat oxidation toward age-related disease. Mice deficient for malonyl CoA decarboxylase (MCD(-/-)), a mouse model of reduced fat oxidation, were allowed to age while life span and a number of physiological parameters (glucose tolerance, insulin tolerance, indirect calorimetry) were assessed. Decreased fat oxidation in MCD(-/-) mice resulted in the accumulation of lipid intermediates in peripheral tissues, but this was not associated with a worsening of age-associated insulin resistance and, conversely, improved longevity. This improvement was associated with reduced oxidative stress and reduced acetylation of the antioxidant enzyme superoxide dismutase 2 in muscle but not the liver of MCD(-/-) mice. These findings were recapitulated in aged mice treated with an MCD inhibitor (CBM-3001106), and these mice also demonstrated improvements in glucose and insulin tolerance. Therefore, our results demonstrate that in addition to decreasing fat oxidation, MCD inhibition also has novel effects on protein acetylation. These combined effects protect against age-related metabolic dysfunction, demonstrating that MCD inhibitors may have utility in the battle against chronic disease in the elderly.
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http://dx.doi.org/10.2337/db15-1145DOI Listing
July 2016

Na+/H+ exchanger isoform 1-induced osteopontin expression facilitates cardiomyocyte hypertrophy.

PLoS One 2015 17;10(4):e0123318. Epub 2015 Apr 17.

College of Pharmacy, Qatar University, Doha, Qatar.

Enhanced expression and activity of the Na+/H+ exchanger isoform 1 (NHE1) has been implicated in cardiomyocyte hypertrophy in various experimental models. The upregulation of NHE1 was correlated with an increase in osteopontin (OPN) expression in models of cardiac hypertrophy (CH), and the mechanism for this remains to be delineated. To determine whether the expression of active NHE1-induces OPN and contributes to the hypertrophic response in vitro, cardiomyocytes were infected with the active form of the NHE1 adenovirus or transfected with OPN silencing RNA (siRNA-OPN) and characterized for cardiomyocyte hypertrophy. Expression of NHE1 in cardiomyocytes resulted in a significant increase in cardiomyocyte hypertrophy markers: cell surface area, protein content, ANP mRNA and expression of phosphorylated-GATA4. NHE1 activity was also significantly increased in cardiomyocytes expressing active NHE1. Interestingly, transfection of cardiomyocytes with siRNA-OPN significantly abolished the NHE1-induced cardiomyocyte hypertrophy. siRNA-OPN also significantly reduced the activity of NHE1 in cardiomyocytes expressing NHE1 (68.5±0.24%; P<0.05), confirming the role of OPN in the NHE1-induced hypertrophic response. The hypertrophic response facilitated by NHE1-induced OPN occurred independent of the extracellular-signal-regulated kinases and Akt, but required p90-ribosomal S6 kinase (RSK). The ability of OPN to facilitate the NHE1-induced hypertrophic response identifies OPN as a potential therapeutic target to reverse the hypertrophic effect induced by the expression of active NHE1.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0123318PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4401699PMC
January 2016

Accumulation of ceramide in slow-twitch muscle contributes to the development of insulin resistance in the obese JCR:LA-cp rat.

Exp Physiol 2015 Jun 14;100(6):730-41. Epub 2015 May 14.

Cardiovascular Translational Science Institute, University of Alberta, Edmonton, Alberta, Canada.

New Findings: What is the central question of this study? The aim was to determine whether the accumulation of ceramide contributes to skeletal muscle insulin resistance in the JCR obese rat. What is the main finding and its importance? Our main new finding is that ceramides accumulate only in slow-twitch skeletal muscle in the JCR obese rat and that reducing ceramide content in this muscle type by inhibition of serine palmitoyl transferase-1 halts the progression of insulin resistance in this rat model predisposed to early development of type 2 diabetes. Our findings highlight the importance of assessing insulin signalling/sensitivity and lipid intermediate accumulation in different muscle fibre types. It has been postulated that insulin resistance results from the accumulation of cytosolic lipid metabolites (i.e. diacylglycerol/ceramide) that impede insulin signalling and impair glucose homeostasis. De novo ceramide synthesis is catalysed by serine palmitoyl transferase-1. Our aim was to determine whether de novo ceramide synthesis plays a role during development of insulin resistance in the JCR:LA-cp obese rat. Ten-week-old JCR:LA-cp obese rats were supplemented with either vehicle or the serine palmitoyl transferase-1 inhibitor l-cycloserine (360 mg l(-1) ) in their drinking water for a 2 week period, and glycaemia was assessed by meal tolerance testing. Treatment of JCR:LA-cp obese rats with l-cycloserine improved their plasma glucose and insulin levels during a meal tolerance test. Examination of muscle lipid metabolites and protein phosphorylation patterns revealed differential signatures in slow-twitch (soleus) versus fast-twitch muscle (gastrocnemius), in that ceramide levels were increased in soleus but not gastrocnemius muscles of JCR:LA-cp obese rats. Likewise, improved glycaemia in l-cycloserine-treated JCR:LA-cp obese rats was associated with enhanced Akt and pyruvate dehydrogenase signalling in soleus but not gastrocnemius muscles, probably as a result of l-cycloserine reducing elevated ceramides in this muscle type. Potential mechanisms of ceramide-mediated insulin resistance involve activation of atypical protein kinase Cζ/λ and protein phosphatase 2A; however, neither of these was altered in muscles of JCR:LA-cp obese rats. Our results suggest a key role for ceramide in the development of insulin resistance in the JCR:LA-cp obese rat, while supporting serine palmitoyl transferase-1 inhibition as a novel target for treatment of obesity-associated insulin resistance.
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http://dx.doi.org/10.1113/EP085052DOI Listing
June 2015

Effect of fatty acids on human bone marrow mesenchymal stem cell energy metabolism and survival.

PLoS One 2015 13;10(3):e0120257. Epub 2015 Mar 13.

Cardiovascular Research Centre, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada.

Successful stem cell therapy requires the optimal proliferation, engraftment, and differentiation of stem cells into the desired cell lineage of tissues. However, stem cell therapy clinical trials to date have had limited success, suggesting that a better understanding of stem cell biology is needed. This includes a better understanding of stem cell energy metabolism because of the importance of energy metabolism in stem cell proliferation and differentiation. We report here the first direct evidence that human bone marrow mesenchymal stem cell (BMMSC) energy metabolism is highly glycolytic with low rates of mitochondrial oxidative metabolism. The contribution of glycolysis to ATP production is greater than 97% in undifferentiated BMMSCs, while glucose and fatty acid oxidation combined only contribute 3% of ATP production. We also assessed the effect of physiological levels of fatty acids on human BMMSC survival and energy metabolism. We found that the saturated fatty acid palmitate induces BMMSC apoptosis and decreases proliferation, an effect prevented by the unsaturated fatty acid oleate. Interestingly, chronic exposure of human BMMSCs to physiological levels of palmitate (for 24 hr) reduces palmitate oxidation rates. This decrease in palmitate oxidation is prevented by chronic exposure of the BMMSCs to oleate. These results suggest that reducing saturated fatty acid oxidation can decrease human BMMSC proliferation and cause cell death. These results also suggest that saturated fatty acids may be involved in the long-term impairment of BMMSC survival in vivo.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0120257PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4358990PMC
February 2016

The link between pediatric heart failure and mitochondrial lipids.

J Mol Cell Cardiol 2014 Nov 12;76:71-2. Epub 2014 Aug 12.

Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada.

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http://dx.doi.org/10.1016/j.yjmcc.2014.08.002DOI Listing
November 2014

Trimetazidine therapy prevents obesity-induced cardiomyopathy in mice.

Can J Cardiol 2014 Aug 29;30(8):940-4. Epub 2014 Apr 29.

Cardiovascular Research Centre, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada. Electronic address:

Obesity is a significant risk factor for the development of cardiovascular disease. Inhibiting fatty acid oxidation has emerged as a novel approach for the treatment of ischemic heart disease. Our aim was to determine whether pharmacologic inhibition of 3-ketoacyl-coenzyme A thiolase (3-KAT), which catalyzes the final step of fatty acid oxidation, could improve obesity-induced cardiomyopathy. A 3-week treatment with the 3-KAT inhibitor trimetazidine prevented obesity-induced reduction in both systolic and diastolic function. Therefore, targeting cardiac fatty acid oxidation may be a novel therapeutic approach to alleviate the growing burden of obesity-related cardiomyopathy.
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http://dx.doi.org/10.1016/j.cjca.2014.04.023DOI Listing
August 2014

Obesity-induced lysine acetylation increases cardiac fatty acid oxidation and impairs insulin signalling.

Cardiovasc Res 2014 Sep 25;103(4):485-97. Epub 2014 Jun 25.

Mazankowski Alberta Heart Institute, University of Alberta, 423 Heritage Medical Research Building, Edmonton, AB, Canada T6G 2S2

Aims: Lysine acetylation is a novel post-translational pathway that regulates the activities of enzymes involved in both fatty acid and glucose metabolism. We examined whether lysine acetylation controls heart glucose and fatty acid oxidation in high-fat diet (HFD) obese and SIRT3 knockout (KO) mice.

Methods And Results: C57BL/6 mice were placed on either a HFD (60% fat) or a low-fat diet (LFD; 4% fat) for 16 or 18 weeks. Cardiac fatty acid oxidation rates were significantly increased in HFD vs. LFD mice (845 ± 76 vs. 551 ± 87 nmol/g dry wt min, P < 0.05). Activities of the fatty acid oxidation enzymes, long-chain acyl-CoA dehydrogenase (LCAD), and β-hydroxyacyl-CoA dehydrogenase (β-HAD) were increased in hearts from HFD vs. LFD mice, and were associated with LCAD and β-HAD hyperacetylation. Cardiac protein hyperacetylation in HFD-fed mice was associated with a decrease in SIRT3 expression, while expression of the mitochondrial acetylase, general control of amino acid synthesis 5 (GCN5)-like 1 (GCN5L1), did not change. Interestingly, SIRT3 deletion in mice also led to an increase in cardiac fatty acid oxidation compared with wild-type (WT) mice (422 ± 29 vs. 291 ± 17 nmol/g dry wt min, P < 0.05). Cardiac lysine acetylation was increased in SIRT3 KO mice compared with WT mice, including increased acetylation and activity of LCAD and β-HAD. Although the HFD and SIRT3 deletion decreased glucose oxidation, pyruvate dehydrogenase acetylation was unaltered. However, the HFD did increase Akt acetylation, while decreasing its phosphorylation and activity.

Conclusion: We conclude that increased cardiac fatty acid oxidation in response to high-fat feeding is controlled, in part, via the down-regulation of SIRT3 and concomitant increased acetylation of mitochondrial β-oxidation enzymes.
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http://dx.doi.org/10.1093/cvr/cvu156DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4155471PMC
September 2014

Treatment with the 3-ketoacyl-CoA thiolase inhibitor trimetazidine does not exacerbate whole-body insulin resistance in obese mice.

J Pharmacol Exp Ther 2014 Jun 3;349(3):487-96. Epub 2014 Apr 3.

Cardiovascular Research Centre, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada (J.R.U., W.K., N.F., J.M., L.Z., D.G.L., C.S.W., J.S.J., G.D.L.); and Sarah W. Stedman Nutrition and Metabolism Center (T.R.K., O.R.I., D.M.M.), Department of Medicine (T.R.K., O.R.I., D.M.M.), Department of Pharmacology and Cancer Biology (D.M.M.), Duke University, Durham, North Carolina.

There is a growing need to understand the underlying mechanisms involved in the progression of cardiovascular disease during obesity and diabetes. Although inhibition of fatty acid oxidation has been proposed as a novel approach to treat ischemic heart disease and heart failure, reduced muscle fatty acid oxidation rates may contribute to the development of obesity-associated insulin resistance. Our aim was to determine whether treatment with the antianginal agent trimetazidine, which inhibits fatty acid oxidation in the heart secondary to inhibition of 3-ketoacyl-CoA thiolase (3-KAT), may have off-target effects on glycemic control in obesity. We fed C57BL/6NCrl mice a high-fat diet (HFD) for 10 weeks before a 22-day treatment with the 3-KAT inhibitor trimetazidine (15 mg/kg per day). Insulin resistance was assessed via glucose/insulin tolerance testing, and lipid metabolite content was assessed in gastrocnemius muscle. Trimetazidine-treatment led to a mild shift in substrate preference toward carbohydrates as an oxidative fuel source in obese mice, evidenced by an increase in the respiratory exchange ratio. This shift in metabolism was accompanied by an accumulation of long-chain acyl-CoA and a trend to an increase in triacylglycerol content in gastrocnemius muscle, but did not exacerbate HFD-induced insulin resistance compared with control-treated mice. It is noteworthy that trimetazidine treatment reduced palmitate oxidation rates in the isolated working mouse heart and neonatal cardiomyocytes but not C2C12 skeletal myotubes. Our findings demonstrate that trimetazidine therapy does not adversely affect HFD-induced insulin resistance, suggesting that treatment with trimetazidine would not worsen glycemic control in obese patients with angina.
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http://dx.doi.org/10.1124/jpet.114.214197DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4019316PMC
June 2014

Malonyl CoA: A promising target for the treatment of cardiac disease.

IUBMB Life 2014 Mar 3;66(3):139-146. Epub 2014 Mar 3.

Cardiovascular Research Centre, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, AB, Canada.

Alterations in cardiac energy metabolism are an important contributor to the high incidence and severity of heart disease in the world. These alterations can include an impairment of the production of ATP necessary to meet the high energy demands of the heart, as well as adverse switches in energy substrate preference by the heart. With regard to this latter point, evidence suggests that a decrease in cardiac efficiency, caused by a rise in cardiac fatty acid oxidation and/or an increase in the uncoupling of glycolysis from glucose oxidation, impairs cardiac function and is a contributing factor to cardiac disease. In support of this concept, therapeutic strategies that modulate these metabolic pathways and increase cardiac efficiency produce beneficial results in the setting of heart disease. One such strategy is to increase cardiac malonyl CoA levels, an important inhibitor of mitochondrial fatty acid uptake. This includes malonyl CoA decarboxylase (MCD) inhibition that results in increased cardiac malonyl CoA levels, decreased cardiac fatty acid oxidation rates, and improved cardiac efficiency. Preclinical studies have shown that MCD inhibition can improve cardiac function in various forms of heart disease. Here, we focus on the importance of malonyl CoA in the regulation of cardiac energy metabolism and function in the normal and diseased heart and discuss the evidence that suggests that inhibition of fatty acid oxidation especially via regulation of malonyl CoA, through MCD inhibition, is a promising strategy to treat cardiac disease. © 2014 IUBMB Life, 66(3):139-146, 2014.
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http://dx.doi.org/10.1002/iub.1253DOI Listing
March 2014

The effects of chronic AMPK activation on hepatic triglyceride accumulation and glycerol 3-phosphate acyltransferase activity with high fat feeding.

Diabetol Metab Syndr 2013 31;5:29. Epub 2013 May 31.

Department of Nutrition, Dietetics, and Food Science, Brigham Young University, Provo, UT 84602, USA.

Background: High fat feeding increases hepatic fat accumulation and is associated with hepatic insulin resistance. AMP Activated Protein Kinase (AMPK) is thought to inhibit lipid synthesis by the acute inhibition of glycerol-3-phosphate acyltransferase (GPAT) activity and transcriptional regulation via sterol regulatory element binding protein-1c (SREBP-1c).

Methods: The purpose of this study was to determine if chronic activation of AMPK prevented an increase in GPAT1 activity in rats fed a high fat diet. Rats were fed a control (C), or a high fat (HF) diet (60% fat) for 6 weeks and injected with saline or a daily aminoimidazole carboxamide ribnucleotide (AICAR) dose of 0.5 mg/g body weight.

Results: Chronic AMPK activation by AICAR injections resulted in a significant reduction in hepatic triglyceride accumulation in both the C and HF fed animals (C, 5.5±0.7; C+AICAR, 2.7 ±0.3; HF, 21.8±3.3; and HF+AICAR, 8.0±1.8 mg/g liver). HF feeding caused an increase in total GPAT and GPAT1 activity, which was not affected by chronic AMPK activation (GPAT1 activity vs. C, C+AICAR, 92±19%; HF, 186±43%; HF+AICAR, 234±62%). Markers of oxidative capacity, including citrate synthase activity and cytochrome c abundance, were not affected by chronic AICAR treatment. Interestingly, HF feeding caused a significant increase in long chain acyl-CoA dehydrogenase or LCAD (up 66% from C), a marker of fatty acid oxidation capacity.

Conclusions: These results suggest that chronic AMPK activation limits hepatic triglyceride accumulation independent of a reduction in total GPAT1 activity.
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http://dx.doi.org/10.1186/1758-5996-5-29DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3679947PMC
May 2014

Inhibition of malonyl-CoA decarboxylase reduces the inflammatory response associated with insulin resistance.

Am J Physiol Endocrinol Metab 2012 Dec 16;303(12):E1459-68. Epub 2012 Oct 16.

Cardiovascular Research Centre, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada.

We previously showed that genetic inactivation of malonyl-CoA decarboxylase (MCD), which regulates fatty acid oxidation, protects mice against high-fat diet-induced insulin resistance. Development of insulin resistance has been associated with activation of the inflammatory response. Therefore, we hypothesized that the protective effect of MCD inhibition might be caused by a favorable effect on the inflammatory response. We examined if pharmacological inhibition of MCD protects neonatal cardiomyocytes and peritoneal macrophages against inflammatory-induced metabolic perturbations. Cardiomyocytes and macrophages were treated with LPS to induce an inflammatory response, in the presence or absence of an MCD inhibitor (CBM-301106, 10 μM). Inhibition of MCD attenuated the LPS-induced inflammatory response in cardiomyocytes and macrophages. MCD inhibition also prevented LPS impairment of insulin-stimulated glucose uptake in cardiomyocytes and increased phosphorylation of Akt. Additionally, inhibition of MCD strongly diminished LPS-induced activation of palmitate oxidation. We also found that treatment with an MCD inhibitor prevented LPS-induced collapse of total cellular antioxidant capacity. Interestingly, treatment with LPS or an MCD inhibitor did not alter intracellular triacylglycerol content. Furthermore, inhibition of MCD prevented LPS-induced increases in the level of ceramide in cardiomyocytes and macrophages while also ameliorating LPS-initiated decreases in PPAR binding. This suggests that the anti-inflammatory effect of MCD inhibition is mediated via accumulation of long-chain acyl-CoA, which in turn stimulates PPAR binding. Our results also demonstrate that pharmacological inhibition of MCD is a novel and promising approach to treat insulin resistance and its associated metabolic complications.
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http://dx.doi.org/10.1152/ajpendo.00018.2012DOI Listing
December 2012

Targeting mitochondrial oxidative metabolism as an approach to treat heart failure.

Biochim Biophys Acta 2013 Apr 31;1833(4):857-65. Epub 2012 Aug 31.

University of Alberta, Edmonton, Canada.

Heart failure is a major cause of morbidity and mortality in the world. Cardiac energy metabolism, specifically fatty acid and glucose metabolism, is altered in heart failure and has been implicated as a contributing factor in the impaired heart function observed in heart failure patients. There is emerging evidence demonstrating that correcting these changes in energy metabolism by modulating mitochondrial oxidative metabolism may be an effective treatment for heart failure. Promising strategies include the downregulation of fatty acid oxidation and an increased coupling of glycolysis to glucose oxidation. Carnitine palmitoyl transferase I (CPT1), fatty acid β-oxidation enzymes, and pyruvate dehydrogenase kinase (PDK) are examples of metabolic targets for the treatment of heart failure. While targeting mitochondrial oxidative metabolism is a promising strategy to treat heart failure, further studies are needed to confirm the potential beneficial effect of modulating these metabolic targets as an approach to treating heart failure. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.
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http://dx.doi.org/10.1016/j.bbamcr.2012.08.014DOI Listing
April 2013

Inhibition of serine palmitoyl transferase I reduces cardiac ceramide levels and increases glycolysis rates following diet-induced insulin resistance.

PLoS One 2012 22;7(5):e37703. Epub 2012 May 22.

Cardiovascular Research Centre, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Canada.

Objective: Diet-induced obesity (DIO) leads to an accumulation of intra-myocardial lipid metabolites implicated in causing cardiac insulin resistance and contractile dysfunction. One such metabolite is ceramide, and our aim was to determine the effects of inhibiting de novo ceramide synthesis on cardiac function and insulin stimulated glucose utilization in mice subjected to DIO.

Materials And Methods: C57BL/6 mice were fed a low fat diet or subjected to DIO for 12 weeks, and then treated for 4 weeks with either vehicle control or the serine palmitoyl transferase I (SPT I) inhibitor, myriocin. In vivo cardiac function was assessed via ultrasound echocardiography, while glucose metabolism was assessed in isolated working hearts.

Results: DIO was not associated with an accumulation of intra-myocardial ceramide, but rather, an accumulation of intra-myocardial DAG (2.63±0.41 vs. 4.80±0.97 nmol/g dry weight). Nonetheless, treatment of DIO mice with myriocin decreased intra-myocardial ceramide levels (50.3±7.7 vs. 26.9±2.7 nmol/g dry weight) and prevented the DIO-associated increase in intra-myocardial DAG levels. Interestingly, although DIO impaired myocardial glycolysis rates (7789±1267 vs. 2671±326 nmol/min/g dry weight), hearts from myriocin treated DIO mice exhibited an increase in glycolysis rates.

Conclusions: Our data reveal that although intra-myocardial ceramide does not accumulate following DIO, inhibition of de novo ceramide synthesis nonetheless reduces intra-myocardial ceramide levels and prevents the accumulation of intra-myocardial DAG. These effects improved the DIO-associated impairment of cardiac glycolysis rates, suggesting that SPT I inhibition increases cardiac glucose utilization.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0037703PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3358297PMC
December 2012

Reductions in RIP140 are not required for exercise- and AICAR-mediated increases in skeletal muscle mitochondrial content.

J Appl Physiol (1985) 2011 Sep 23;111(3):688-95. Epub 2011 Jun 23.

Alberta Diabetes Institute, University of Alberta, Edmonton, Alberta, Canada.

Receptor interacting protein 1 (RIP140) has recently been demonstrated to be a key player in the regulation of skeletal muscle mitochondrial content. We have shown that β-guanadinopropionic acid (β-GPA) feeding reduces RIP140 protein content and mRNA levels concomitant with increases in mitochondrial content (Williams DB, Sutherland LN, Bomhof MR, Basaraba SA, Thrush AB, Dyck DJ, Field CJ, Wright DC. Am J Physiol Endocrinol Metab 296: E1400-E1408, 2009). Since β-GPA feeding reduces high-energy phosphate levels and activates AMPK, alterations reminiscent of exercise, we hypothesized that exercise training would reduce RIP140 protein content. We further postulated that an acute bout of exercise, or interventions known to induce the expression of mitochondrial enzymes or genes involved in mitochondrial biogenesis, would result in decreases in nuclear RIP140 content. Two weeks of daily swim training increased markers of mitochondrial content in rat skeletal muscle independent of reductions in RIP140 protein. Similarly, high-intensity exercise training in humans failed to reduce RIP140 content despite increasing skeletal muscle mitochondrial enzymes. We found that 6 wk of daily 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) injections had no effect on RIP140 protein content in rat skeletal muscle while RIP140 content from LKB1 knockout mice was unaltered despite reductions in mitochondria. An acute bout of exercise, AICAR treatment, and epinephrine injections increased the mRNA levels of PGC-1α, COXIV, and lipin1 independent of decreases in nuclear RIP140 protein. Surprisingly these interventions increased RIP140 mRNA expression. In conclusion our results demonstrate that decreases in RIP140 protein content are not required for exercise and AMPK-dependent increases in skeletal muscle mitochondrial content, nor do acute perturbations alter the cellular localization of RIP140 in parallel with the induction of genes involved in mitochondrial biogenesis.
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http://dx.doi.org/10.1152/japplphysiol.00279.2011DOI Listing
September 2011

Chronic AMP-activated protein kinase activation and a high-fat diet have an additive effect on mitochondria in rat skeletal muscle.

J Appl Physiol (1985) 2010 Aug 3;109(2):511-20. Epub 2010 Jun 3.

Department of Physiology and Developmental Biology, Birgham Young University, Provo, UT 84602, USA.

Factors that stimulate mitochondrial biogenesis in skeletal muscle include AMP-activated protein kinase (AMPK), calcium, and circulating free fatty acids (FFAs). Chronic treatment with either 5-aminoimidazole-4-carboxamide riboside (AICAR), a chemical activator of AMPK, or increasing circulating FFAs with a high-fat diet increases mitochondria in rat skeletal muscle. The purpose of this study was to determine whether the combination of chronic chemical activation of AMPK and high-fat feeding would have an additive effect on skeletal muscle mitochondria levels. We treated Wistar male rats with a high-fat diet (HF), AICAR injections (AICAR), or a high-fat diet and AICAR injections (HF + AICAR) for 6 wk. At the end of the treatment period, markers of mitochondrial content were examined in white quadriceps, red quadriceps, and soleus muscles, predominantly composed of unique muscle-fiber types. In white quadriceps, there was a cumulative effect of treatments on long-chain acyl-CoA dehydrogenase, cytochrome c, and peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) protein, as well as on citrate synthase and beta-hydroxyacyl-CoA dehydrogenase (beta-HAD) activity. In contrast, no additive effect was noted in the soleus, and in the red quadriceps only beta-HAD activity increased additively. The additive increase of mitochondrial markers observed in the white quadriceps may be explained by a combined effect of two separate mechanisms: high-fat diet-induced posttranscriptional increase in PGC-1alpha protein and AMPK-mediated increase in PGC-1alpha protein via a transcriptional mechanism. These data show that chronic chemical activation of AMPK and a high-fat diet have a muscle type specific additive effect on markers of fatty acid oxidation, the citric acid cycle, the electron transport chain, and transcriptional regulation.
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http://dx.doi.org/10.1152/japplphysiol.00126.2010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2928588PMC
August 2010

Skeletal muscle dysfunction in muscle-specific LKB1 knockout mice.

J Appl Physiol (1985) 2010 Jun 1;108(6):1775-85. Epub 2010 Apr 1.

Department of Physiology and Developmental Biology, 589 WIDB, Brigham Young University, Provo, UT 84602, USA.

Liver kinase B1 (LKB1) is a tumor-suppressing protein that is involved in the regulation of muscle metabolism and growth by phosphorylating and activating AMP-activated protein kinase (AMPK) family members. Here we report the development of a myopathic phenotype in skeletal and cardiac muscle-specific LKB1 knockout (mLKB1-KO) mice. The myopathic phenotype becomes overtly apparent at 30-50 wk of age and is characterized by decreased body weight and a proportional reduction in fast-twitch skeletal muscle weight. The ability to ambulate is compromised with an often complete loss of hindlimb function. Skeletal muscle atrophy is associated with a 50-75% reduction in mammalian target of rapamycin pathway phosphorylation, as well as lower peroxisome proliferator-activated receptor-alpha coactivator-1 content and cAMP response element binding protein phosphorylation (43 and 40% lower in mLKB1-KO mice, respectively). Maximum in situ specific force production is not affected, but fatigue is exaggerated, and relaxation kinetics are slowed in the myopathic mice. The increased fatigue is associated with a 30-78% decrease in mitochondrial protein content, a shift away from type IIA/D toward type IIB muscle fibers, and a tendency (P=0.07) for decreased capillarity in mLKB1-KO muscles. Hearts from myopathic mLKB1-KO mice exhibit grossly dilated atria, suggesting cardiac insufficiency and heart failure, which likely contributes to the phenotype. These findings indicate that LKB1 plays a critical role in the maintenance of both skeletal and cardiac function.
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http://dx.doi.org/10.1152/japplphysiol.01293.2009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2886679PMC
June 2010

Effects of excess corticosterone on LKB1 and AMPK signaling in rat skeletal muscle.

J Appl Physiol (1985) 2010 Feb 3;108(2):298-305. Epub 2009 Dec 3.

Dept. of Physiology and Developmental Biology, Brigham Young Univ., Provo, Utah 84602, USA.

Cushing's syndrome is characterized by marked central obesity and insulin insensitivity, effects opposite those seen with chronic AMP-activated protein kinase (AMPK) activation. This study was designed to determine whether chronic exposure to excess glucocorticoids influences LKB1/AMPK signaling in skeletal muscle. Corticosterone pellets were implanted subcutaneously in rats (hypercorticosteronemia, Hypercort) for 2 wk. Controls were sham operated and fed ad libitum or were sham operated and food restricted (pair-weighted group, Pair) to produce body weights similar to Hypercort rats. At the end of the 2-wk treatment period, rats were anesthetized, and the right gastrocnemius-plantaris (gastroc) and soleus muscles were removed. Left muscles were removed after electrical stimulation for 5 min. No significant differences were noted between treatment groups in ATP, creatine phosphate, or LKB1 activity. The alpha- and beta-subunit isoforms were not significantly influenced in gastroc by corticosterone treatment. Expression of the gamma3-subunit decreased, and gamma1- and gamma2-subunit expression increased. Both alpha2-AMPK and alpha1-AMPK activities were increased in the gastroc in response to electrical stimulation, but the magnitude of the increase was less for alpha2 in the Hypercort rats. Despite elevated plasma insulin and elevated plasma leptin in the Hypercort rats, phosphorylation of TBC1D1 was lower in both resting and stimulated muscle compared with controls. Malonyl-CoA content was elevated in gastroc muscles of resting Hypercort rats. These changes in response to excess glucocorticoids could be responsible, in part, for the decrease in insulin sensitivity and adiposity seen in Cushing's syndrome.
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http://dx.doi.org/10.1152/japplphysiol.00906.2009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2822674PMC
February 2010
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