Myocardial lipid accumulation in patients with pressure-overloaded heart and metabolic syndrome

Abstract

We evaluated the role of sterol-regulatory element binding protein (SREBP)-1c/peroxisome proliferator activated receptor-γ (PPARγ) pathway on heart lipotoxicity in patients with metabolic syndrome (MS) and aortic stenosis (AS). Echocardiographic parameters of heart function and structural alterations of LV specimens were studied in patients with (n = 56) and without (n = 61) MS undergoing aortic valve replacement. Tissues were stained with hematoxylin-eosin (H and E) and oil red O for evidence of intramyocyte lipid accumulation. The specimens were also analyzed with PCR, Western blot, and immunohistochemical analysis for SREBP-1c and PPARγ. Ejection fraction (EF) was lower in MS compared with patients without MS (P < 0.001); no difference was found in aortic orifice surface among the groups. H and E and oil red O staining of specimens from MS patients revealed several myocytes with intracellular accumulation of lipid, whereas these alterations were not detected in biopsies from patients without MS. Patients without MS have low levels and weak immunostaining of SREBP-1c and PPARγ in heart specimens. In contrast, strong immunostaining and higher levels of SREBP-1c and PPARγ were seen in biopsies from the MS patients. Moreover, we evidenced a significative correlation between both SREBP-1c and PPARγ and EF and intramyocyte lipid accumulation (P < 0.001). SREBP-1c may contribute to heart dysfunction by promoting lipid accumulation within myocytes in MS patients with AS; SREBP-1c may do it by increasing the levels of PPARγ protein. We evaluated the role of sterol-regulatory element binding protein (SREBP)-1c/peroxisome proliferator activated receptor-γ (PPARγ) pathway on heart lipotoxicity in patients with metabolic syndrome (MS) and aortic stenosis (AS). Echocardiographic parameters of heart function and structural alterations of LV specimens were studied in patients with (n = 56) and without (n = 61) MS undergoing aortic valve replacement. Tissues were stained with hematoxylin-eosin (H and E) and oil red O for evidence of intramyocyte lipid accumulation. The specimens were also analyzed with PCR, Western blot, and immunohistochemical analysis for SREBP-1c and PPARγ. Ejection fraction (EF) was lower in MS compared with patients without MS (P < 0.001); no difference was found in aortic orifice surface among the groups. H and E and oil red O staining of specimens from MS patients revealed several myocytes with intracellular accumulation of lipid, whereas these alterations were not detected in biopsies from patients without MS. Patients without MS have low levels and weak immunostaining of SREBP-1c and PPARγ in heart specimens. In contrast, strong immunostaining and higher levels of SREBP-1c and PPARγ were seen in biopsies from the MS patients. Moreover, we evidenced a significative correlation between both SREBP-1c and PPARγ and EF and intramyocyte lipid accumulation (P < 0.001). SREBP-1c may contribute to heart dysfunction by promoting lipid accumulation within myocytes in MS patients with AS; SREBP-1c may do it by increasing the levels of PPARγ protein. Metabolic syndrome (MS) is strongly associated with left ventricular (LV) hypertrophy and cardiac function derangements that lead to heart failure (HF) (1Burchfiel C.M. Skelton T.N. Andrew M.E. Garrison R.J. Arnett D.K. Jones D.W. Taylor Jr, H.A. Metabolic syndrome and echocardiographic left ventricular mass in blacks: the Atherosclerosis Risk in Communities (ARIC) Study.Circulation. 2005; 112: 819-827Crossref PubMed Scopus (77) Google Scholar). The structural basis of the progression from well-compensated hypertrophy to HF is still largely unknown in MS patients. Emerging evidence suggests that inherited and acquired cardiomyopathies, such as impaired glucose tolerance and diabetes, are associated with marked intracellular lipid accumulation in the heart (2McGavock J.M. Victor R.G. Unger R.H. Szczepaniak L.S. Adiposity of the heart, revisited.Ann. Intern. Med. 2006; 144: 517-524Crossref PubMed Scopus (311) Google Scholar, 3McGavock J.M. Lingvay I. Zib I. Tillery T. Salas N. Unger R. Levine B.D. Raskin P. Victor R.G. Szczepaniak L.S. Cardiac steatosis in diabetes mellitus: a 1H-magnetic resonance spectroscopy study.Circulation. 2007; 116: 1170-1175Crossref PubMed Scopus (481) Google Scholar). In the normal body, most triglyceride is stored in adipocytes; the amount of triglyceride stored in nonadipocyte tissues (liver, and myocardium) is minimal and very tightly regulated. However, several-fold increased cardiomyocyte triglyceride stores are observed in animal models of obesity and diabetes (4Zhou Y.T. Grayburn P. Karim A. Shimabukuro M. Higa M. Baetens D. Orci L. Unger R.H. Lipotoxic heart disease in obese rats: implications for human obesity.Proc. Natl. Acad. Sci. USA. 2000; 97: 1784-1789Crossref PubMed Scopus (1077) Google Scholar).This lipid accumulation may contribute to cardiomyocyte death by nonoxidative and oxidative (5Chiu H.C. Kovacs A. Ford D.A. Hsu F.F. Garcia R. Herrero P. A novel mouse model of lipotoxic cardiomyopathy.J. Clin. Invest. 2001; 107: 813-822Crossref PubMed Scopus (617) Google Scholar) metabolic pathways and to HF. Even in humans, myocardial lipid content was recently reported to increase with the degree of adiposity and contribute to cardiac dysfunction (6Sharma S. Adrogue J.V. Golfman L. Uray I. Lemm J. Youker K. Noon G.P. Frazier O.H. Taegtmeyer H. Intramyocardial lipid accumulation in the failing human heart resembles the lipotoxic rat heart.FASEB J. 2004; 18: 1692-1700Crossref PubMed Scopus (593) Google Scholar), suggesting that myocardial lipid content may be a biomarker and putative therapeutic target for cardiac disease in patients with MS. Genes involved in lipid metabolism are nutritionally regulated at the transcriptional level in a coordinated fashion (7Rosen E.D. Walkey C.J. Puigserver P. Spiegelman B.M. Transcriptional regulation of adipogenesis.Genes Dev. 2000; 14: 1293-1307Crossref PubMed Google Scholar). Sterol-regulatory element binding protein (SREBP)-1c is a transcription factor that controls lipogenesis and is induced during overnutrition to facilitate the conversion of glucose to fatty acids and triglycerides for the storage of excess energy (8Tontonoz P. Kim J.B. Graves R.A. Spiegelman B.M. ADD1: a novel helix-loop-helix transcription factor associated with adipocyte determination and differentiation.Mol. Cell. Biol. 1993; 13: 4753-4759Crossref PubMed Scopus (534) Google Scholar). Uncontrolled activation of nuclear SREBP-1c in the liver can cause hepatosteatosis and multiple biochemical features of the MS (9Muller-Wieland D. Kotzka J. SREBP-1: gene regulatory key to syndrome X?.Ann. N. Y. Acad. Sci. 2002; 967: 19-27Crossref PubMed Scopus (30) Google Scholar). Moreover, it has been proposed that peroxisome proliferator activated receptor-γ (PPARγ) itself is a direct target gene of SREBP-1c, providing a mechanisms by which SREBP-1c and PPARγ could cooperate to enhance lipogenesis (10Fajas L. Schoonjans K. Gelman L. Kim J.B. Najib J. Martin G. Regulation of peroxisome proliferator-activated receptor gamma expression by adipocyte differentiation and determination factor 1/sterol regulatory element binding protein 1: implications for adipocyte differentiation and metabolism.Mol. Cell. Biol. 1999; 19: 5495-5503Crossref PubMed Scopus (356) Google Scholar). Thus, it is conceivable that the SREBP-1c/PPARγ pathway deregulation might be important in the pathogenesis of lipotoxic cardiomyopathy. We hypothesized that an increase in cardiac levels of both SREBP-1c and PPARγ is involved in the adaptations of the heart to myocardial metabolic derangements and that it is potentially an important stimulus of heart adiposity and HF in MS patients. To investigate this possibility, we examined myocyte lipid accumulation and cardiac levels of SREBP-1c and PPARγ protein and mRNA in patients with and without MS who underwent surgical aortic valve replacement for aortic stenosis (AS). This is a classic model of pressure-induced concentric remodelling in humans (11Opie L.H. Commerford P.J. Gersh B.J. Pfeffer M.A. Controversies in ventricular remodelling.Lancet. 2006; 367: 356-367Abstract Full Text Full Text PDF PubMed Scopus (678) Google Scholar). We selected 282 consecutive patients who underwent aortic valve replacement for isolated AS (area≤0.715 cm2) (Table 1). The WHO criteria were used to classify patients as being with or without the MS (12WHO. Definition of metabolic syndrome in definition, diagnosis and classification of diabetes and its complications. Report of a WHO consultation. Part 1: Diagnosis and classification of diabetes mellitus. WHO/NCD/NCS/99.2. 1999. Geneve, World Health Organization-Department of Noncommunicable Disease Surveillance.Google Scholar): waist circumference (WC) >102 cm for men, >88 cm for women; blood pressure elevation >130/85 mm Hg; low HDL cholesterol <40 mg/dl in men, <50 mg/dl in women; high triglycerides >150 mg/dl; hyperglycemia, fasting glucose >100 mg/dl. The MS is considered present when at least three of the five traits are present. Among the above patients, 56 presented at least three traits of MS (4 ± 0.8) and 61 without MS (MS-traits: 1.1 ± 0.6). The remaining 165 patients were excluded because of the presence of at least one of the following conditions: diabetes, unstable angina, previous myocardial infarction, coronary stenosis >70%; renal, hepatic, rheumatic, cancerous, or other severe diseases were excluded. Insulin sensitivity was estimated from the homeostasis model assessment (HOMA) [(glucose in mmol/L × insulin in µU/ml)/22.5] (13Matthews D.R. Hosker J.P. Rudenski A.S. Naylor B.A. Treacher D.F. Turner R.C. Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man.Diabetologia. 1985; 28: 412-419Crossref PubMed Scopus (25651) Google Scholar). All patients underwent coronary angiography before valve replacement. On the basis of ejection fraction (EF) determined by echocardiography at the time of admission, MS patients were subdivided into three groups: EF >50% (n = 18); EF 50% to 30% (n = 24); EF <30% (n = 14). The institutional Ethics of the the patients of the patients undergoing aortic valve replacement to the presence or of metabolic MS (n = (n = ± ± mass ± ± ± ± circumference ± ± circumference men, ± ± M. M. of in tissues by PubMed Scopus Google D. gene expression of a human J. 2002; Full Text Full Text PDF PubMed Scopus Google M. M. of in tissues by PubMed Scopus Google ± ± ± ± HDL ± ± HDL cholesterol ± ± HDL cholesterol men, ± ± ± ± ± ± ± ± ± ± disease < coronary (5Chiu H.C. Kovacs A. Ford D.A. Hsu F.F. Garcia R. Herrero P. A novel mouse model of lipotoxic cardiomyopathy.J. Clin. Invest. 2001; 107: 813-822Crossref PubMed Scopus (617) Google (9Muller-Wieland D. Kotzka J. SREBP-1: gene regulatory key to syndrome X?.Ann. N. Y. Acad. Sci. 2002; 967: 19-27Crossref PubMed Scopus (30) Google of M.E. P. Taegtmeyer H. and of the heart in Part 2002; PubMed Scopus Google G. G. M. N. M. P. H. lipid accumulation and SREBP-1c expression are to insulin resistance and in Full Text Full Text PDF PubMed Scopus Google of A. P. S. D. L.S. expression of lipogenesis in a mouse model of insulin and Biol. 2006; Full Text Full Text PDF PubMed Scopus Google B.M. lipogenesis and lipid accumulation in J. 2005; PubMed Scopus Google (9Muller-Wieland D. Kotzka J. SREBP-1: gene regulatory key to syndrome X?.Ann. N. Y. Acad. Sci. 2002; 967: 19-27Crossref PubMed Scopus (30) Google (9Muller-Wieland D. Kotzka J. SREBP-1: gene regulatory key to syndrome X?.Ann. N. Y. Acad. Sci. 2002; 967: 19-27Crossref PubMed Scopus (30) Google receptor (5Chiu H.C. Kovacs A. Ford D.A. Hsu F.F. Garcia R. Herrero P. A novel mouse model of lipotoxic cardiomyopathy.J. Clin. Invest. 2001; 107: 813-822Crossref PubMed Scopus (617) Google (4Zhou Y.T. Grayburn P. Karim A. Shimabukuro M. Higa M. Baetens D. Orci L. Unger R.H. Lipotoxic heart disease in obese rats: implications for human obesity.Proc. Natl. Acad. Sci. USA. 2000; 97: 1784-1789Crossref PubMed Scopus (1077) Google M.E. P. Taegtmeyer H. and of the heart in Part 2002; PubMed Scopus Google G. G. M. N. M. P. H. lipid accumulation and SREBP-1c expression are to insulin resistance and in Full Text Full Text PDF PubMed Scopus Google parameters valve ± ± aortic valve ± ± LV mass ± ± LV ± ± ± ± ± ± Cardiac ± ± Ejection ± ± ± ± ± ± ± ± ± ± analysis ± ± ± oil staining ± ± ± SREBP-1c ± ± PPARγ ± ± ± ± ± ± ± ± ± ± are presented as ± or MS = metabolic HDL = = = homeostasis model = = left = left = left ventricular = left ventricular = of = = SREBP-1c = regulatory = proliferator-activated proliferator-activated = = in a are presented as ± or MS = metabolic HDL = = = homeostasis model = = left = left = left ventricular = left ventricular = of = = SREBP-1c = regulatory = proliferator-activated proliferator-activated = = underwent an and were to the of the of J.M. H. for a for a from the of and and for a 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). valve was at in aortic valve was the with the and for surface The LV cardiac was as the of heart and and was for surface The myocardial which both and parameters of ventricular was as R. M. K. A. M. S. of on myocardial role of in cardiac PubMed Scopus Google Scholar). The were without of MS by the to were from the LV of was in and stored at whereas the other was in in to a of and on was analyzed for the presence of SREBP-1c, and gene of SREBP-1c and PPARγ were by by the following and SREBP-1c SREBP-1c PPARγ PPARγ of the were as was at least three SREBP-1c, and were determined by Western analysis as M. M. of in tissues by PubMed Scopus Google Scholar). The in a the SREBP-1c PPARγ and The were the with the analysis were as M. M. of in tissues by PubMed Scopus Google Scholar). Tissues were stained with and (H and The of heart were with and was determined by such as M. M. of in tissues by PubMed Scopus Google Scholar) and by the of a biomarker for an of the of by was determined by as R. K. M. M. A. S. of during coronary in human 2004; PubMed Scopus Google Scholar). were with in The were for of immunostaining = = = and = for and the was for A of was also and were stained with oil red a of heart was in and of and was into of and the was at used as the of oil red SREBP-1c, and were from the and of myocytes were determined and of myocytes were A of was to from the LV of was with of and of for the of was with a are presented as ± were compared among the with for and the for were found among the the was used to A was considered was used for correlation All were by of the are reported in MS patients not from controls in of and cholesterol coronary and The MS patients a higher of and obesity compared with patients without MS. were found for the of the mass fasting and HDL cholesterol were found in the and among the of MS patients subdivided on the basis of EF EF 50% to EF (Table of the patients with metabolic syndrome undergoing aortic valve replacement to the ejection fraction >50% (n = (n = <30% (n = ± ± ± ± ± ± ± ± ± ± ± ± HDL ± ± ± ± ± ± ± ± ± ± ± ± parameters valve ± ± ± aortic valve ± ± ± LV mass ± ± ± LV ± ± ± Ejection ± ± ± ± ± ± ± ± ± ± ± ± analysis ± ± ± ± ± ± oil staining ± ± ± SREBP-1c ± ± ± PPARγ ± ± ± are presented as ± or < compared with with ejection fraction < compared with ejection fraction between in a are presented as ± or < compared with with ejection fraction < compared with ejection fraction between All patients of LV hypertrophy (Table 1). LV function was impaired in MS MS patients lower EF and higher (P < 1). difference in the aortic orifice surface among the was found (Table 1). Moreover, MS patients EF not with aortic orifice surface = = whereas a correlation between aortic orifice surface and EF = < in patients without MS was We not in ventricular This was by of an gene that the was in ventricular biopsies from patients 1). Moreover, the staining of lipid accumulation in However, H and E staining of heart specimens from MS patients revealed with intracellular accumulation of lipid red O staining high lipid in myocytes of MS patients (Table 1). We detected myocytes and of lipid in of 56 specimens from MS patients, whereas the myocardial alterations were not detected in biopsies from patients without MS. Moreover, content was higher in specimens from MS patients in specimens of patients without MS (Table 1). Moreover, we observed that myocytes and myocytes with lipid increased with EF A correlation between and of the myocytes was observed = < analysis revealed that and triglycerides were both of myocardial lipid content = < = < whereas and were to myocardial triglyceride myocytes in specimens and The from a without metabolic syndrome myocytes without The specimens from a with metabolic syndrome a high of myocytes from patients with metabolic syndrome a increase in myocytes to the ejection fraction and the of the analysis of PPARγ and mRNA levels from ventricular specimens from the of patients. In patients without cardiac PPARγ and were not or were detected In contrast, higher levels of PPARγ and were seen in from the MS patients as as strong immunostaining for PPARγ was a correlation between PPARγ and SREBP-1c protein levels = < 0.001). The and plasma triglycerides were with SREBP-1c protein levels = < = < 0.001). analysis revealed that triglycerides and were both of myocardial SREBP-1c = < = < as as PPARγ = < = < whereas and were to PPARγ Moreover, was a correlation between PPARγ protein levels and EF = < = < in heart specimens from patients with MS correlation was observed between PPARγ and EF in patients without MS = = = = immunohistochemical analysis of PPARγ protein from ventricular specimens The from a without metabolic syndrome not immunostaining for PPARγ protein in The from a with metabolic syndrome a strong immunostaining for PPARγ protein in myocytes as as in myocytes in which the staining is the from patients with metabolic syndrome a increase in both myocytes and for PPARγ protein to the ejection fraction Western analysis of PPARγ protein in heart specimens from patients with metabolic syndrome to the ejection < patients with ejection fraction between 30% and < patients with ejection fraction < patients without metabolic analysis of PPARγ protein content in heart specimens from patients with metabolic syndrome to the ejection fraction PPARγ mRNA levels in ventricular biopsies from patients without metabolic syndrome and from patients with metabolic syndrome to ejection The mRNA levels were with analysis of PPARγ mRNA content in heart specimens from patients without metabolic syndrome and from patients with metabolic syndrome to the ejection fraction levels and immunostaining of and were seen in from patients with and without MS. were no among the groups. The level of protein is 30% lower in heart specimens from patients with MS compared with heart specimens from patients without MS (Table 1). Moreover, a correlation between levels and of the myocytes was observed = < of were higher in heart specimens from MS patients compared with specimens from patients without MS ± ± < 0.001). immunostaining for the was were found between tissues from patients with and without MS. immunostaining was present in from MS patients compared with tissues from patients without MS ± ± < Moreover, a correlation between levels and of the myocytes was observed = < The of was to the myocyte lipid accumulation with the expression of SREBP-1c and PPARγ in patients with MS undergoing aortic valve replacement. We evidence that MS is strongly associated with cardiac in patients with MS patients present EF and impaired compared with patients without MS. Moreover, we observed that the levels of protein are 30% lower in heart specimens from patients with MS compared with heart specimens from patients without MS. This is in with human that concentrations are D. gene expression of a human J. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). in metabolic in and in by metabolic alterations a cardiac to direct in heart function of disease M.E. P. Taegtmeyer H. and of the heart in Part 2002; PubMed Scopus Google Scholar). with into the during and of levels is an important to dysfunction in the presence of the metabolic alterations M.E. P. Taegtmeyer H. and of the heart in Part 2002; PubMed Scopus Google Scholar). In MS patients, we evidenced that a strong correlation also between the progression of cardiac dysfunction and myocytes lipid accumulation with of myocytes and oil red O and EF are and cause LV and HF in patients with AS and MS. In this the EF was to the aortic stenosis in patients, whereas a correlation between cardiac function and myocardial in patients with AS and MS because the cardiac were from the stenosis and were associated with a marked cardiomyocyte lipid accumulation. it is metabolic of MS cardiac lipid evidence suggests that excess is associated with gene expression G. G. M. N. M. P. H. lipid accumulation and SREBP-1c expression are to insulin resistance and in Full Text Full Text PDF PubMed Scopus Google Scholar). Regulation of gene expression by in is an important to to the The metabolic the of and 2005; PubMed Scopus Google Scholar). models have that the transcription of for and in liver is by SREBP-1c is a transcription factor that controls lipogenesis and is induced during overnutrition to facilitate the conversion of glucose to fatty acids and triglycerides for the storage of the excess energy (8Tontonoz P. Kim J.B. Graves R.A. Spiegelman B.M. ADD1: a novel helix-loop-helix transcription factor associated with adipocyte determination and differentiation.Mol. Cell. Biol. 1993; 13: 4753-4759Crossref PubMed Scopus (534) Google Scholar). Uncontrolled activation of nuclear SREBP-1c that hepatosteatosis and MS K. M. J.M. of and on regulatory and the of the metabolic 2005; PubMed Scopus Google Scholar, I. S. Y. of regulatory in mouse adipocyte increased fatty and fatty Biol. Full Text Full Text PDF PubMed Scopus Google Scholar) may have a role in the intramyocyte lipid accumulation observed in heart specimens from MS. we detected strong to SREBP-1c in both and the in specimens of the human heart by MS. that SREBP-1c could a role in the regulation of intracellular lipid stores in the human heart, as it has been observed in liver I. S. Y. of regulatory in mouse adipocyte increased fatty and fatty Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). The by which SREBP-1c its unknown and not by several have been that to a with PPARγ. PPARγ to be a direct target gene of SREBP-1c (10Fajas L. Schoonjans K. Gelman L. Kim J.B. Najib J. Martin G. Regulation of peroxisome proliferator-activated receptor gamma expression by adipocyte differentiation and determination factor 1/sterol regulatory element binding protein 1: implications for adipocyte differentiation and metabolism.Mol. Cell. Biol. 1999; 19: 5495-5503Crossref PubMed Scopus (356) Google Scholar). The of PPARγ by SREBP-1c to a role in the regulation of intracellular lipid stores in human heart, as it has been observed in B.M. lipogenesis and lipid accumulation in J. 2005; PubMed Scopus Google Scholar, A. P. S. D. L.S. expression of lipogenesis in a mouse model of insulin and Biol. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar). of PPARγ was to strongly in and when with SREBP-1c (7Rosen E.D. Walkey C.J. Puigserver P. Spiegelman B.M. Transcriptional regulation of adipogenesis.Genes Dev. 2000; 14: 1293-1307Crossref PubMed Google Scholar, A. P. S. D. L.S. expression of lipogenesis in a mouse model of insulin and Biol. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar, H. M. K. S. L.S. expression of PPARγ to cardiac dysfunction in Clin. Invest. 2007; PubMed Scopus Google Scholar). In with is that myocardial metabolic derangements in MS may be associated with SREBP-1c and PPARγ that in the storage of the lipid excess in the induced by increased expression of the transcription factor increased expression of increased lipid in nonoxidative oxidative cardiomyocyte heart This may be with the of the excess in the on the of as in J.B. of human as by and peroxisome proliferator activated Biol. 2007; Full Text Full Text PDF PubMed Scopus Google Scholar, R.H. diabetes and PubMed Scopus Google Scholar), as in such as myocytes R. M. G. Insulin and lipid in PubMed Scopus Google Scholar). is a on and not to a role for this these we have not of the most to SREBP-1c such as fatty has been to be by SREBP-1c and to in J. N. M. Kovacs A. M. lipotoxic 2007; PubMed Scopus Google Scholar) and we may that may a role in the heart metabolic of patients with MS. are potentially important from a because a by which MS may the of heart are also potentially important from a because the that of the SREBP-1c/PPARγ pathway might a novel of for cardiac dysfunction of patients with MS. gene aortic stenosis mass ejection fraction hematoxylin-eosin heart failure homeostasis model assessment left ventricular myocardial metabolic syndrome peroxisome proliferator activated receptor sterol-regulatory element binding protein waist circumference