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Sarco/endoplasmic reticulum calcium ATPase activity is unchanged despite increased myofilament calcium sensitivity in Zucker type 2 diabetic fatty rat heart. Sci Rep 2022; 12:16904. [PMID: 36207382 PMCID: PMC9546843 DOI: 10.1038/s41598-022-20520-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 09/14/2022] [Indexed: 11/11/2022] Open
Abstract
Systolic and diastolic dysfunction in diabetes have frequently been associated with abnormal calcium (Ca2+) regulation. However, there is emerging evidence that Ca2+ mishandling alone is insufficient to fully explain diabetic heart dysfunction, with focus shifting to the properties of the myofilament proteins. Our aim was to examine the effects of diabetes on myofilament Ca2+ sensitivity and Ca2+ handling in left ventricular tissues isolated from the same type 2 diabetic rat hearts. We measured the force-pCa relationship in skinned left ventricular cardiomyocytes isolated from 20-week-old type 2 diabetic and non-diabetic rats. Myofilament Ca2+ sensitivity was greater in the diabetic relative to non-diabetic cardiomyocytes, and this corresponded with lower phosphorylation of cardiac troponin I (cTnI) at ser23/24 in the diabetic left ventricular tissues. Protein expression of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA), phosphorylation of phospholamban (PLB) at Ser16, and SERCA/PLB ratio were lower in the diabetic left ventricular tissues. However, the maximum SERCA Ca2+ uptake rate was not different between the diabetic and non-diabetic myocardium. Our data suggest that impaired contractility in the diabetic heart is not caused by SERCA Ca2+ mishandling. This study highlights the important role of the cardiac myofilament and provides new insight on the pathophysiology of diabetic heart dysfunction.
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Insulin Receptors and Insulin Action in the Heart: The Effects of Left Ventricular Assist Devices. Biomolecules 2022; 12:biom12040578. [PMID: 35454166 PMCID: PMC9024449 DOI: 10.3390/biom12040578] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Revised: 04/11/2022] [Accepted: 04/12/2022] [Indexed: 02/01/2023] Open
Abstract
This year, 2022, marks the 100th anniversary of the isolation of human insulin and its administration to patients suffering from diabetes mellitus (DM). Insulin exerts many effects on the human body, including the cardiac tissue. The pathways implicated include the PKB/Akt signaling pathway, the Janus kinase, and the mitogen-activated protein kinase pathway and lead to normal cardiac growth, vascular smooth muscle regulation, and cardiac contractility. This review aims to summarize the existing knowledge and provide new insights on insulin pathways of cardiac tissue, along with the role of left ventricular assist devices on insulin regulation and cardiac function.
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Voltage dependence of the Ca 2+ transient in endocardial and epicardial myocytes from the left ventricle of Goto-Kakizaki type 2 diabetic rats. Mol Cell Biochem 2018; 446:25-33. [PMID: 29318456 DOI: 10.1007/s11010-018-3269-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Accepted: 01/04/2018] [Indexed: 01/09/2023]
Abstract
Diabetes mellitus is a major global health disorder and, currently, over 450 million people have diabetes with 90% suffering from type 2 diabetes. Left untreated, diabetes may lead to cardiovascular diseases which are a leading cause of death in diabetic patients. Calcium is the trigger and regulator of cardiac muscle contraction and derangement in cellular Ca2+ homeostasis, which can result in heart failure and sudden cardiac death. It is of paramount importance to investigate the regional involvement of Ca2+ in diabetes-induced cardiomyopathy. Therefore, the aim of this study was to investigate the voltage dependence of the Ca2+ transients in endocardial (ENDO) and epicardial (EPI) myocytes from the left ventricle of the Goto-Kakizaki (GK) rats, an experimental model of type 2 diabetes mellitus. Simultaneous measurement of L-type Ca2+ currents and Ca2+ transients was performed by whole-cell patch clamp techniques. GK rats displayed significantly increased heart weight, heart weight/body weight ratio, and non-fasting and fasting blood glucose compared to controls (CON). Although the voltage dependence of L-type Ca2+ current was unaltered, the voltage dependence of the Ca2+ transients was reduced to similar extents in EPI-GK and ENDO-GK compared to EPI-CON and ENDO-CON myocytes. TPK L-type Ca2+ current and Ca2+ transient were unaltered. THALF decay of L-type Ca2+ current was unaltered; however, THALF decay of the Ca2+ transient was shortened in ENDO and EPI myocytes from GK compared to CON rat hearts. In conclusion, the amplitude of L-type Ca2+ current was unaltered; however, the voltage dependence of the Ca2+ transient was reduced to similar extents in EPI and ENDO myocytes from GK rats compared to their respective controls, suggesting the possibility of dysfunctional sarcoplasmic reticulum Ca2+ transport in the GK diabetic rat hearts.
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Vasanji Z, Cantor EJF, Juric D, Moyen M, Netticadan T. Alterations in cardiac contractile performance and sarcoplasmic reticulum function in sucrose-fed rats is associated with insulin resistance. Am J Physiol Cell Physiol 2006; 291:C772-80. [PMID: 16973823 DOI: 10.1152/ajpcell.00086.2005] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Diabetes mellitus (DM) causes the development of a specific cardiomyopathy that results from the metabolic derangements present in DM and manifests as cardiac contractile dysfunction. Although myocardial dysfunction in Type 1 DM has been associated with defects in the function and regulation of the sarcoplasmic reticulum (SR), very little is known about SR function in Type 2 DM. Accordingly, this study examined whether abnormalities in cardiac contractile performance and SR function occur in the prestage of Type 2 DM (i.e., during insulin resistance). Sucrose feeding was used to induce whole body insulin resistance, whereas cardiac contractile performance was assessed by echocardiography and SR function was measured by SR calcium (Ca2+) uptake. Sucrose-fed rats exhibited hyperinsulinemia, hyperglycemia, and hyperlipidemia relative to control rats. Serial echocardiographic assessments in the sucrose-fed rats revealed early abnormalities in diastolic function followed by late systolic dysfunction and concurrent alterations in myocardial structure. The hearts of the 10-wk sucrose-fed rats showed depressed SR function demonstrated by a significant reduction in SR Ca2+uptake. The decline in SR Ca2+uptake was associated with a significant decrease in the cAMP-dependent protein kinase and Ca2+/calmodulin-dependent protein kinase II-mediated phosphorylation of phospholamban. The results show that abnormalities in cardiac contractile performance and SR function occur at an insulin-resistant stage before the manifestation of overt Type 2 DM.
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Affiliation(s)
- Zainisha Vasanji
- Institute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, Winnipeg, Manitoba, Canada
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Pereira L, Matthes J, Schuster I, Valdivia HH, Herzig S, Richard S, Gómez AM. Mechanisms of [Ca2+]i transient decrease in cardiomyopathy of db/db type 2 diabetic mice. Diabetes 2006; 55:608-15. [PMID: 16505222 DOI: 10.2337/diabetes.55.03.06.db05-1284] [Citation(s) in RCA: 197] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Cardiovascular disease is the leading cause of death in the diabetic population. However, molecular mechanisms underlying diabetic cardiomyopathy remain unclear. We analyzed Ca2+-induced Ca2+ release and excitation-contraction coupling in db/db obese type 2 diabetic mice and their control littermates. Echocardiography showed a systolic dysfunction in db/db mice. Two-photon microscopy identified intracellular calcium concentration ([Ca2+]i) transient decrease in cardiomyocytes within the whole heart, which was also found in isolated myocytes by confocal microscopy. Global [Ca2+]i transients are constituted of individual Ca2+ sparks. Ca2+ sparks in db/db cardiomyocytes were less frequent than in +/+ myocytes, partly because of a depression in sarcoplasmic reticulum Ca2+ load but also because of a reduced expression of ryanodine receptor Ca2+ channels (RyRs), revealed by [3H]ryanodine binding assay. Ca2+ efflux through Na+/Ca2+ exchanger was increased in db/db myocytes. Calcium current, I(Ca), triggers sarcoplasmic reticulum Ca2+ release and is also involved in sarcoplasmic reticulum Ca2+ refilling. Macroscopic I(Ca) was reduced in db/db cells, but single Ca2+ channel activity was similar, suggesting that diabetic myocytes express fewer functional Ca2+ channels, which was confirmed by Western blots. These results demonstrate that db/db mice show depressed cardiac function, at least in part, because of a general reduction in the membrane permeability to Ca2+. As less Ca2+ enters the cell through I(Ca), less Ca2+ is released through RyRs.
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Affiliation(s)
- Laetitia Pereira
- Institut National de la Santé et de la Recherche Médicale U-637, University of Montpellier 1, France
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Belke DD, Swanson EA, Dillmann WH. Decreased sarcoplasmic reticulum activity and contractility in diabetic db/db mouse heart. Diabetes 2004; 53:3201-8. [PMID: 15561951 DOI: 10.2337/diabetes.53.12.3201] [Citation(s) in RCA: 198] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Although it is known that insulin-dependent (type 1) diabetes results in depressed contractile performance associated with diminished sarcoendoplasmic reticular Ca2+-ATPase (SERCA2a) activity, findings in insulin-resistant (type 2) diabetes suggest a less clear association. The db/db insulin-resistant mouse model exhibits decreased cardiac performance both in situ and in isolated ex vivo working hearts. In this study, contractile performance and calcium transients were measured in Langendorff-perfused hearts and isolated cardiac myocytes. Diabetic (db/db) mouse hearts demonstrated decreased rates of contraction, relaxation, and pressure development. Calcium transients from isolated myocytes revealed significantly lower diastolic and systolic levels of calcium in diabetic hearts. Furthermore, the decay rate of the calcium transient was significantly reduced in diabetic myocytes, suggesting a diminished capacity for cytosolic calcium removal not associated with a change in sodium-calcium exchanger activity. Calcium leakage from the sarcoplasmic reticulum (SR) measured using tetracaine was significantly increased in diabetic myocytes. Western blot analysis indicated only a small decrease in SERCA2a expression in diabetic mice, but a large increase in phospholamban expression. Expression of the ryanodine receptor did not differ between groups. In conclusion, the decreased contractile function observed in the db/db diabetic mouse model appears to be related to decreased calcium handling by the SR.
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Affiliation(s)
- Darrell D Belke
- Department of Medicine, University of California, San Diego, CA 92092-0618, USA
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Davidoff AJ, Mason MM, Davidson MB, Carmody MW, Hintz KK, Wold LE, Podolin DA, Ren J. Sucrose-induced cardiomyocyte dysfunction is both preventable and reversible with clinically relevant treatments. Am J Physiol Endocrinol Metab 2004; 286:E718-24. [PMID: 15102617 DOI: 10.1152/ajpendo.00358.2003] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We recently identified cardiomyocyte dysfunction in the early stage of type 2 diabetes (i.e., diet-induced insulin resistance). The present investigation was designed to determine whether a variety of clinically relevant interventions are sufficient to prevent and reverse cardiomyocyte dysfunction in sucrose (SU)-fed insulin-resistant rats. Subsets of animals were allowed to exercise (free access to wheel attached to cage) or were treated with bezafibrate in drinking water to determine whether these interventions would prevent the adverse effects of SU feeding on cardiomyocyte function. After 6-8 wk on diet and treatment, animals were surgically prepared to assess whole body insulin sensitivity (intravenous glucose tolerance test), and isolated ventricular myocyte mechanics were evaluated (video edge recording). SU feeding produced hyperinsulinemia and hypertriglyceridemia, with euglycemia, and induced characteristic whole body insulin resistance. Both exercise and bezafibrate treatment prevented these metabolic abnormalities. Ventricular myocyte shortening and relengthening were slower in SU-fed rats (42-63%) compared with starch (ST)-fed controls, and exercise or bezafibrate completely prevented cardiomyocyte dysfunction in SU-fed rats. In separate cohorts of animals, after 5 wk of SU feeding, animals were either switched back to an ST diet or given menhaden oil for an additional 7-9 wk to determine whether the cardiomyocyte dysfunction was reversible. Both interventions have previously been shown to have favorable metabolic effects, and both improved myocyte mechanics, but only the ST diet reversed all indications of cardiomyocyte dysfunction induced by SU feeding. Thus phenotypic changes in cardiomyocyte mechanics associated with early stages of type 2 diabetes were found to be both preventable and reversible with clinically relevant treatments, suggesting that the cellular processes contributing to this dysfunction are modifiable.
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Affiliation(s)
- Amy J Davidoff
- Univ. of New England, College of Osteopathic Medicine, 11 Hills Beach Rd., Biddeford, ME 04005, USA.
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Aasum E, Hafstad AD, Severson DL, Larsen TS. Age-dependent changes in metabolism, contractile function, and ischemic sensitivity in hearts from db/db mice. Diabetes 2003; 52:434-41. [PMID: 12540618 DOI: 10.2337/diabetes.52.2.434] [Citation(s) in RCA: 217] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Glucose and palmitate metabolism and contractile function were measured with ex vivo perfused working hearts from control (db/+) and diabetic (db/db) female mice at 6, 10-12, and 16-18 weeks of age. Palmitate oxidation was increased by 2.2-fold in 6-week-old db/db hearts and remained elevated in 10- to 12- and 16- to 18-week-old hearts. Carbohydrate oxidation was normal at 6 weeks but was reduced to 27 and 23% of control at 10-12 and 16-18 weeks, respectively. At 6 weeks, db/db hearts exhibited a slight reduction in mechanical function, whereas marked signs of dysfunction were evident at 10-12 and 16-18 weeks. Mechanical function after ischemia-reperfusion was examined in hearts from male mice; at 6 weeks, db/db hearts showed normal recovery, whereas at 12 weeks it was markedly reduced. Fatty acid oxidation was the predominant substrate used after reperfusion. Thus, diabetic db/db hearts exhibit signs of a progressive cardiomyopathy; increased fatty acid oxidation preceded reductions in carbohydrate oxidation. Postischemic recovery of function was reduced in db/db hearts, in parallel with age-dependent changes in normoxic contractile performance. Finally, peroxisome proliferator-activated receptor-alpha treatment (3 weeks) did not affect sensitivity to ischemia-reperfusion, even though carbohydrate oxidation was increased and palmitate oxidation was decreased.
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Affiliation(s)
- Ellen Aasum
- Department of Medical Physiology, Faculty of Medicine, University of Tromsoe, Norway.
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Dutta K, Podolin DA, Davidson MB, Davidoff AJ. Cardiomyocyte dysfunction in sucrose-fed rats is associated with insulin resistance. Diabetes 2001; 50:1186-92. [PMID: 11334425 DOI: 10.2337/diabetes.50.5.1186] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Diabetes is associated with impaired cardiac dysfunction in both humans and animals. Specific phenotypic changes-prolonged action potentials, slowed cytosolic Ca2+ clearing, and slowed relaxation-that contribute to this whole heart dysfunction occur in isolated ventricular myocytes. The present study was designed to determine whether cardiomyocyte abnormalities occur early in the development of type 2 diabetes (in this case, insulin resistance) and whether an insulin-sensitizing drug (metformin) is cardioprotective. In the study, high-sucrose feeding was used to induce whole-body insulin resistance. Wistar rats were maintained for 7-10 weeks on a starch (ST) diet, sucrose (SU) diet, or diet supplemented with metformin (SU + MET). Whole-body insulin resistance was measured in SU and SU + MET rats by performing euglycemic-hyperinsulinemic clamps. Mechanical properties of isolated ventricular myocytes were measured by high-speed video edge detection, and [Ca2+]i transients were evaluated with Fura-2 AM. Untreated SU rats were insulin-resistant (glucose infusion rate [GIR] = 14.5 +/- 1.1 mg.kg(-1).min(-1)); metformin treatment in SU + MET rats prevented this metabolic abnormality (GIR = 20.0 +/- 2.2 mg.kg(-1).min(-1)). Indexes of myocyte shortening and relengthening were significantly longer in SU rats (area under the relaxation phase [AR/peak] = 103 +/- 3 msec) when compared to ST and SU + MET rats (AR/peak = 73 +/- 2 and 80 +/- 1 msec, respectively). The rate of intracellular Ca2+ decay and the integral of the Ca2+ transient through the entire contractile cycle were significantly longer in myocytes from SU than from ST rats (Ca2+ signal normalized to peak amplitude = 152 +/- 8 vs. 135 +/- 5 msec, respectively). Collectively, our data showed the presence of cardiomyocyte abnormalities in an insulin-resistant stage that precedes frank type 2 diabetes. Furthermore, metformin prevented the development of sucrose-induced insulin resistance and the consequent cardiomyocyte dysfunction.
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Affiliation(s)
- K Dutta
- College of Osteopathic Medicine, University of New England, Biddeford, Maine 04005, USA
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Belke DD, Larsen TS, Gibbs EM, Severson DL. Altered metabolism causes cardiac dysfunction in perfused hearts from diabetic (db/db) mice. Am J Physiol Endocrinol Metab 2000; 279:E1104-13. [PMID: 11052966 DOI: 10.1152/ajpendo.2000.279.5.e1104] [Citation(s) in RCA: 305] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Contractile function and substrate metabolism were characterized in perfused hearts from genetically diabetic C57BL/KsJ-lepr(db)/lepr(db) (db/db) mice and their non-diabetic lean littermates. Contractility was assessed in working hearts by measuring left ventricular pressures and cardiac power. Rates of glycolysis, glucose oxidation, and fatty acid oxidation were measured using radiolabeled substrates ([5-(3)H]glucose, [U-(14)C]glucose, and [9,10-(3)H]palmitate) in the perfusate. Contractile dysfunction in db/db hearts was evident, with increased left ventricular end diastolic pressure and decreased left ventricular developed pressure, cardiac output, and cardiac power. The rate of glycolysis from exogenous glucose in diabetic hearts was 48% of control, whereas glucose oxidation was depressed to only 16% of control. In contrast, palmitate oxidation was increased twofold in db/db hearts. The hypothesis that altered metabolism plays a causative role in diabetes-induced contractile dysfunction was tested using perfused hearts from transgenic db/db mice that overexpress GLUT-4 glucose transporters. Both glucose metabolism and palmitate metabolism were normalized in hearts from db/db-human insulin-regulatable glucose transporter (hGLUT-4) hearts, as was contractile function. These findings strongly support a causative role of impaired metabolism in the cardiomyopathy observed in db/db diabetic hearts.
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Affiliation(s)
- D D Belke
- Department of Pharmacology and Therapeutics, University of Calgary, Calgary, Alberta, Canada T2N 4N1
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