Original ArticleStereological characterization of left ventricular cardiomyocytes, capillaries, and innervation in the nondiabetic, obese mouse
Introduction
Obesity and excess weight have reached pandemic proportions in the Western world due to the high intake of calorie-dense food and a lack of exercise. Associated with obesity are metabolic disorders, such as type II diabetes and the metabolic syndrome, which are in turn linked to the accelerated development of cardiovascular diseases. However, even in the absence of traditional risk factors (e.g., diabetes, arterial hypertension), obesity is considered as an independent pathogenic factor in the development of cardiomyopathy and heart failure in humans [1]. The pathological features of the heart are thought to be characterized by the loss of cardiomyocytes as a consequence of increased apoptosis, with fibrotic tissue replacing lost cells [2], [3], hypertrophy of remaining cardiomyocytes [4], and intracellular lipid accumulation [5]. Functionally, there is evidence for obesity-associated left ventricular dysfunction, particularly in the diastole [6], [7]. The adverse effects of obesity on the structure and function and on the metabolism of the heart were explained by the concept of cardiac lipotoxicity introduced a few years ago [8]. Lipotoxicity in the heart involves the increased uptake of palmitate into cardiomyocytes, accumulation of ceramide, release of Ca2+ from the endoplasmic reticulum, generation of reactive oxygen species, release of cytochrome c from mitochondria, and initiation of apoptotic pathways [8], [9].
In addition to the cardiomyocytes, the innervation of the heart also seems to be affected in obese individuals. The left ventricle is densely innervated by adrenergic postganglionic neurons whose perikarya are located in the sympathetic ganglia [10]. In addition to noradrenalin, these postganglionic neurons contain neuropeptides, predominantly neuropeptide Y, which are packed into large dense core vesicles and released upon burst or high-frequency firing [11]. Interestingly, the regional spillover of noradrenalin in myocardium is decreased by 50% in normotensive obese compared to normotensive nonobese humans [12], whereas muscle sympathetic neural activity (measured by microneurography) is significantly increased in obese patients [13], [14]. Numerous studies have addressed the pathological changes of the heart and its innervation in obesity-related disorders, such as diabetes (e.g., Refs. [15], [16], [17], [18], [19]) or hypertension (e.g., Refs. [20], [21], [22]). Although cardiomyocyte alterations in diabetes share some similarities with those in obesity, little is known about the innervation of the myocardium in obesity. Moreover, experimentally induced diabetes is often induced by destruction of insulin-producing pancreatic beta cells and therefore does not mimic obesity-related diabetes. The pathology of the autonomic innervation of the heart in experimental diabetes can therefore not be simply transferred to the state of nondiabetic or prediabetic obesity. Although functional changes of the innervation observed in obesity are likely to alter cardiac function and suggest the presence of a dysfunctional cardiac autonomic innervation, there are currently no qualitative or quantitative studies on the effects of obesity on the morphology of the cardiac innervation.
In the present study, we tested the hypothesis that diet-induced obesity at a pre- or nondiabetic stage is associated with structural alterations of the myocardium and its autonomic innervation in the mouse. To test this hypothesis, we investigated the left ventricular innervation in relation to cardiomyocytes and capillaries by design-based stereology in diet-induced nondiabetic obese mice.
Section snippets
Animals and tissue processing
C57Bl6 mice were purchased from Charles River (Sulzfeld, Germany). Mice were housed in conditions that conform to the Guide for the Care and Use of Laboratory Animals published by the US National Institutes of Health (publication no. 85-23). Experiments were approved by governmental authorities (Regierungspräsidium Darmstadt, F28/18). Ten male C57Bl6 mice (6–8 weeks of age) were randomly assigned to a control or to an obesity group, CG and OG, respectively. Animals in CG received standard diet
Animals and heart dimensions
The animals had a mean body mass of 31.6±1.7 g (CG) and 51.2±1.9 g (OG) (P<.01) and a corresponding body mass index of 0.32±0.032 g/cm2 (CG) and 0.45±0.036 g/cm2 (OG) (P<.01). The intraperitoneal glucose tolerance test did not show significant differences between the groups (Fig. 1). The mass of the ventricles was greater in OG (162.2±12.6) than in CG (136.3±15.0) (P<.01), but only the left ventricular mass was significantly greater in OG than in CG. Dividing the left ventricular mass by body
Discussion
The present study provides the first comprehensive quantitative morphological analysis of the left ventricular myocardium in obesity-related cardiac hypertrophy. In a mouse model of advanced diet-induced obesity, the results show that this type of cardiac hypertrophy shows mild and proportional increases in total cardiomyocyte volume and capillary length without significant increases in total axon length.
Obesity is associated with the development of left ventricular hypertrophy, increased
Acknowledgments
The authors wish to thank Tamara Papadakis, Gerhard Kripp, and Gerd Magdowski for excellent assistance with the preparation of the microscopic samples. The authors declare that they do not have a conflict of interest.
References (54)
Obesity cardiomyopathy: pathophysiology and evolution of the clinical syndrome
Am J Med Sci
(2001)- et al.
Alterations in left ventricular structure and function in young healthy obese women
J Am Coll Cardiol
(2004) - et al.
Lipotoxicity in the heart
Biochim Biophys Acta
(2010) - et al.
Neuropeptides: opportunities for drug delivery
Lancet Neurol
(2003) - et al.
Cardiomyopathy in streptozotocin-induced diabetes involves intra-axonal accumulation of calcitonin gene-related peptide and altered expression of its receptor in rats
Neuroscience
(2005) - et al.
A review of state-of-the-art stereology for better quantitative 3D morphology in cardiac research
Cardiovasc Pathol
(2010) - et al.
The visualisation of cardiovascular innervation in the guinea pig using an antiserum to protein gene product 9.5 (PGP 9.5)
J Auton Nerv Syst
(1987) - et al.
Left atrial abnormalities indicating diastolic ventricular dysfunction in cardiopathy of obesity
Chest
(1987) - et al.
Cardiac remodeling in a rat model of diet-induced obesity
Can J Cardiol
(2010) - et al.
Scaling mitochondrial volume in heart to body mass
Respir Physiol
(1984)
Ultrastructural quantitation of mitochondria and myofilaments in cardiac muscle from 10 different animal species including man
J Mol Cell Cardiol
Effects of strenuous exercise on the quantitative morphology of left ventricular myocardium in the rat
J Mol Cell Cardiol
The total length of myocytes and capillaries, and total number of myocyte nuclei in the rat heart are time-dependently increased by growth hormone
Growth Horm IGF Res
Respiratory sinus arrhythmia and diseases of aging: obesity, diabetes mellitus and hypertension
Biol Psychol
Sympathetic nerves modify mitochondrial and capillary growth in normotensive and hypertensive rats
J Mol Cell Cardiol
Obesity and the risk of heart failure
N Engl J Med
Cardiomyocyte apoptosis in animal models of obesity
Curr Hypertens Rep
Apoptosis and fibrosis are early features of heart failure in an animal model of metabolic cardiomyopathy
Int J Exp Path
Myocardial myocyte remodelling and fibrosis in the cardiometabolic syndrome
J Cardiometab Syndr
Forgotten but not gone. The rediscovery of fatty heart, the most common unrecognized disease in America
Circ Res
Lipotoxicity in the heart
Curr Hypertens Rep
Anatomy of human extrinsic cardiac nerves and ganglia
Am J Cardiol
Regional sympathetic nervous activity and oxygen consumption in obese normotensive human subjects
Circulation
Body weight reduction, sympathetic nerve traffic, and arterial baroreflex in obese normotensive humans
Circulation
Weight loss improves neurovascular and muscle metaboreflex control in obesity
Am J Physiol Heart Circ Physiol
Cardiac ultrastructural changes in streptozotocin-induced diabetic rats: effects of insulin treatment
Can J Cardiol
Ultrastructural changes of human cardiac atrial nerve endings in diabetes mellitus
Eur J Clin Invest
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The study was partly funded by the Excellence Cluster Cardiopulmonary System.