LV Collagen Research Articles

Possible involvement of Protein Tyrosine Phosphatase in Alcoholic Cardiomyopathy

Protein tyrosine phosphatases (PTPase’s) are the enzymes that dephosphorylate survival kinase PI3K/Akt pathway this may be a key mechanism in alcohol-induced cardiomyopathy. Therefore, the present study was designed to investigate the role of PTPase in alcohol-induced cardiomyopathy. Ethanol (20%) at the dose of 7.9 g/kg P.o was given regularly for 60 days that produced Alcohol-induced Cardiomyopathy (ACM). CM (cardiomyopathy) was assessed in terms of decrease in LVDP, dp/dtmax, dp/dtmin, LV protein content, CFR and increase in LVEDP, LVW/BW, MABP, LV collagen, LV cholesterol content, TNF-α, nitrite levels and iNOS expression in alcoholic cardiomyopathic rats. Sodium Orthovanadate (SOV) (PTPase inhibitor) at the dose of 2.5, 5 and 10mg/kg significantly increased LVDP, dp/dtmax, dp/dtmin, CFR, LV protein content. Moreover, significant decrease in the elevated MABP, LVEDP, LVW/BW, LV collagen, LV cholesterol content, nitrite, TNF-α and iNOS level was observed. Furthermore, administration of SMT (S-methylisothiourea), an iNOS inhibitor (5mg/kg., i.p) with SOV (10mg/kg., p.o) significantly increased the ameliorative effect of SOV (10mg/kg., p.o). The findings suggested that PTPases may have a function in regulating alcohol-induced cardiomyopathy by interfering with Akt/Pi3k and its downstream pathways, which include TNF-alpha and iNOS.

The Anti-Inflammatory Mediator 17(R)-Resolvin D1 Attenuates Pressure Overload-Induced Cardiac Hypertrophy and Fibrosis.

Increased inflammation contributes to pressure overload-induced myocardial remodeling. 17(R)-Resolvin D1 (17(R)-RvD1), a potent lipid mediator derived from docosahexaenoic acid, possesses anti-inflammatory and pro-resolving properties. However, the association between 17(R)-RvD1 and pressure overload-induced cardiac hypertrophy remains unclear. Transverse aortic constriction (TAC) surgery was performed to establish a cardiac hypertrophy model. C57BL/6J mice were randomly assigned to the Sham, TAC and TAC+17(R)-RvD1 groups. 17(R)-RvD1 was injected (2 μg/kg, i.p.) before TAC surgery and once every other day after surgery for 4 weeks. The same volume of saline was injected into the mice in both Sham group and TAC group. Then, cardiac function was evaluated and heart tissues were collected for biological analysis. 17(R)-RvD1 treatment attenuated TAC-induced increase in left ventricular diameter and decrease in left ventricular contractility, mitigated increased cardiomyocyte cross-sectional area, and downregulated the expression of hypertrophic genes. Besides, 17(R)-RvD1 attenuated myocardial fibrosis, as indicated by the decreased LV collagen volume and expression of fibrotic genes. In addition, 17(R)-RvD1 ameliorated the inflammatory response in cardiac tissue, as illustrated by the decreased infiltration of CD68+ macrophages and reduced production of pro-inflammatory cytokines, including TNF-α, IL-1β, and IL-6. 17(R)-RvD1 treatment significantly suppressed the activation of NLRP3 inflammasome after TAC surgery, which might be responsible for the attenuation of inflammation in cardiac tissue. 17(R)-RvD1 attenuated pressure overload-induced cardiac hypertrophy and fibrosis, and the possible mechanism may be associated with the inhibition of NLRP3 inflammasome. 17(R)-RvD1 may serve as a potential drug for the treatment of cardiac hypertrophy.

Empagliflozin prevents angiotensin II-induced hypertension related micro and macrovascular endothelial cell activation and diastolic dysfunction in rats despite persistent hypertension: Role of endothelial SGLT1 and 2

SGLT2 inhibitors (SGLT2i) showed pronounced beneficial effects in patients with heart failure but the underlying mechanisms remain unclear. We evaluated the effect of empagliflozin, selective SGLT2i, on hypertension-induced cardiac and vascular dysfunction.Male Wistar rats received diet with or without empagliflozin (30 mg/kg/day). After 1 week, a hypertensive dose of Ang II (0.4 mg/kg/day) was administered using osmotic mini-pumps for 4 weeks. Systolic blood pressure was determined by sphygmomanometry, the cardiac function by echocardiography and ex vivo (coronary microvascular endothelial cell activation, LV remodeling and fibrosis responses), and the systemic micro and macrovascular endothelial cell activation ex vivo. Empagliflozin treatment did not affect the Ang II-induced hypertensive response. Ang II treatment increased LV mass and induced LV diastolic dysfunction, fibrosis, collagen I and ANP expression, and infiltration of macrophages. In the vasculature, it caused eNOS upregulation in the aorta and down-regulation in mesenteric microvessels associated with increased oxidative stress, ACE, AT1R, VCAM-1, MCP-1, MMP-2, and MMP-9 and collagen I expression, increased endothelial SGLT1 staining in the aorta, mesenteric and coronary microvessels, increased SGLT1 and 2 protein levels in the aorta. All Ang II-induced cardiac and vascular responses were reduced by the empagliflozin treatment.Thus, the SGLT2i effectively attenuated the deleterious impact of Ang II-induced hypertension on target organs including cardiac diastolic dysfunction and remodeling, and endothelial cell activation and pro-atherosclerotic, pro-fibrotic and pro-remodeling responses in macro and microvessels despite persistent hypertension.

Abstract P2054: Epigenetic Regulation Of TLR2 By Gut Microbial Antigens Aggravates Myocardial Fibrosis Through Activating Myd88/IRAK4/NF-kB Signaling In Type 2 Diabetes

Background: Type 2 diabetic (T2D) patients are 40% more likely to develop cardiovascular diseases compared to healthy individuals. Previously, we have shown that circulating gut peptides such as peptidoglycan (PGN) aggravate myocardial fibrosis through DNA hypomethylation-induced activation of TLR2; however, the underlying molecular mechanisms responsible remain elusive. Hypothesis: Gut microbial antigens activate MyD88/IRAK4/NF-κB signaling through TLR2 in cardiac tissue, resulting in myocardial fibrosis and cardiac dysfunction in T2D. Methods: Gut barrier integrity, cardiac inflammation, and DNA hypomethylation (5hmC) were measured in cardiac tissue via IHC, qPCR, ELISA, and western blot analysis in db/db mice, a murine model of T2D with 4 months of diabetes and age-matched controls. PGN-treated cardiac fibroblasts were analyzed via in-vitro studies with and without IRAK4 and NF-κB inhibitors. Results: db/db mice exhibited cardiac dysfunction and myocardial fibrosis as measured by reduced LVEF and LVFS with increased LV mass and collagen synthesis. These mice also exhibited higher gut permeability as observed by reduced tight junctional proteins (ZO-1, p120-catenin, and VE-cadherin, YAP, PV1) and increased levels of plasma FABP-2. The levels of PGN were higher in plasma (p<0.003) and cardiac tissue (p<0.001) of db/db mice. The expression of TLR2 (p<0.003) and pro-inflammatory cytokines IL-1β (p<0.008) and TNF-α (p<0.0004) were significantly up-regulated in diabetic hearts compared to WT. Expression of 5hmC was significantly higher (p<0.001) in the hearts of diabetic mice. Increased expression of 5hmC, ten-eleven translocation 1-3 (TET-1, 2, 3), IL-1β, IL-6, and TNF-α were also observed in PGN-treated cardiac fibroblasts. IRAK4 (PF-06650883; 10μM) and NF-κB (CAPE; 50 μM) inhibition reduced the PGN-mediated fibroblast activation, resulting in reduced inflammation. Conclusions: Increased circulating gut microbial antigens by induction of systemic and cardiac inflammatory pathways result in damage to the myocardium of db/db mice. Therapies designed to restore the gut barrier and reduce TLR2 activation may potentially minimize the risk of diabetes-induced cardiovascular complications.

Aging Impairs Reverse Remodeling and Recovery of Ventricular Function after Isoproterenol-Induced Cardiomyopathy.

Information about heart failure with reduced ejection fraction (HFrEF) in women and the potential effects of aging in the female heart is scarce. We investigated the vulnerability to develop HFrEF in female elderly mice compared to young animals, as well as potential differences in reverse remodeling. First, HF was induced by isoproterenol infusion (30 mg/kg/day, 28 days) in young (10-week-old) and elderly (22-month-old) female mice. In a second set of animals, mice underwent isoproterenol infusion followed by no treatment during 28 additional days. Cardiac remodeling was assessed by echocardiography, histology and gene expression of collagen-I and collagen-III. Following isoproterenol infusion, elderly mice developed similar HFrEF features compared to young animals, except for greater cell hypertrophy and tissue fibrosis. After beta-adrenergic withdrawal, young female mice experienced complete reversal of the HFrEF phenotype. Conversely, reversed remodeling was impaired in elderly animals, with no significant recovery of LV ejection fraction, cardiomyocyte hypertrophy and collagen deposition. In conclusion, chronic isoproterenol infusion is a valid HF model for elderly and young female mice and induces a similar HF phenotype in both. Elderly animals, unlike young, show impaired reverse remodeling, with persistent tissue fibrosis and cardiac dysfunction even after beta-adrenergic withdrawal.

Abstract 17388: Loss of Bone Morphogenetic Protein 9 (BMP9) Limits Survival and Paradoxically Increases Collagen Abundance, but Limits Collagen Cross-Linking in a Murine Model of Acute Myocardial Infarction

Myocardial infarction (MI) is a major cause of heart failure (HF). HF is associated with adverse cardiac remodeling that is primarily driven by Transforming growth factor beta (TGFb1) mediated fibrosis and myocyte hypertrophy. We previously reported that loss of bone morphogenetic protein 9 (BMP9) promotes cardiac fibrosis in pressure-overload induced HF. No studies have explored a role for BMP9 in post MI cardiac remodeling. We hypothesize that loss of BMP9 may promote cardiac healing by stabilizing LV scar formation. To test this hypothesis, we subjected whole body BMP9 knockout (-/-) mice to left coronary artery ligation for two weeks followed by PV loop analysis and studied indices of cardiac remodeling. Compared to wild type (WT) controls BMP9-/- mice had significantly lower survival (83% vs 61%, p<0.001, respectively) with a higher rate of cardiac rupture(15% vs 90%). Compared to WT controls, surviving BMP9-/- mice had higher LVEDP, reduced LV dP/dt, and higher lung weight. Compared to WT mice, BMP9-/- mice had significantly higher levels of Type I collagen (2 fold p<0.05). Compared to WT mice, BMP9-/- mice had increased matrix metalloproteinases (MMP)-2 and MMP-9 (2.5 fold p<0.05) activity levels in the LV. Treatment of cultured primary human cardiac fibroblasts with recombinant BMP9 attenuated TGFb1-mediated Type I collagen and MMP-9 protein expression. To assess collagen content and cross-linking, two-photon excitation fluorescence imaging was performed and identified an increase in collagen abundance, but a trend towards lower collagen cross-linking in the LV of BMP9-/- mice compared to WT mice 2 weeks after MI. Our central finding is that loss of BMP9 is associated with reduced survival, increased propensity towards cardiac rupture, and increased LV collagen abundance, but reduced collagen integrity in a murine model of acute MI. These identify a potentially important functional role for BMP9 in post-infarct cardiac remodeling.

Resistance training promotes reduction in Visceral Adiposity without improvements in Cardiomyocyte Contractility and Calcium handling in Obese Rats.

Resistance training (RT) improves the cardiomyocyte calcium (Ca2+) cycling during excitation-contraction coupling. However, the role of RT in cardiomyocyte contractile function associated with Ca2+ handling in obesity is unclear. Wistar rats were distributed into four groups: control, sedentary obese, control plus RT, and obesity plus RT. The 10-wk RT protocol was used (4-5 vertical ladder climbs, 60-second interval, 3× a week, 50-100% of maximum load). Metabolic, hormonal, cardiovascular and biochemical parameters were determined. Reduced leptin levels, epididymal, retroperitoneal and visceral fat pads, lower body fat, and adiposity index were observed in RT. Obesity promoted elevation of collagen, but RT did not promote modifications of LV collagen in ObRT. RT induced elevation in maximum rates of contraction and relaxation, and reduction of time to 50% relaxation. ObRT group did not present improvement in the cardiomyocyte contractile function in comparison to Ob group. Reduced cardiac PLB serine16 phosphorylation (pPLB Ser16) and pPLB Ser16/PLB ratio with no alterations in sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) and phospholamban (PLB) expression were observed in Ob groups. Resistance training improved body composition reduced fat pads and plasma leptin levels but did not promote positive alterations in cardiomyocyte contractile function, Ca2+ handling and phospholamban phosphorylation.

MicroRNA Profile in Swimming Trained Female Rats and its Therapeutic Potential in Spontaneously Hypertensive Rats

IntroductionBoth aerobic exercise training (ET) and Hypertension (HY) induce different cardiac hypertrophy (CH) phenotypes which molecular differences and may lead to new targets for therapies in cardiovascular disease, as microRNAs (miRNAs).MethodsWe selected 15 miRNAs that were differentially expressed by ET from miRNAarray data and compared them with other from SHR (Spontaneously Hypertensive Rats) miRNAarray data. Four miRNAs were selected for qRT‐PCR confirmation: miRNA‐27a, 27b, 126 e 29c. Among then, miRNA 29c was chosen to be modulated by lentiviral vector due its role in fibrosis regulation. Intramuscular cardiac injection of the lentiviral vector particles 0.6×109 vp/was performed for two different times (7 and 14 days) (SHR7 and SHR14). The transduction efficiency was assessed by GFP expression by Western Blot. Blood pressure (BP) was measured by caudal plethysmography, CH was analyzed by ratio LVW/BW (left ventricle weight/body weight), HW/BW (heart weight/body weight) and by cardiomyocytes diameter (dCMO). qRT‐PCR was used to assess miRNA‐29c expression and its targets COLIAI and COLIIIAI gene expression. The LV collagen content was assessed by histology (Picrossirius red), by collagen volume fraction, and by hydroxiproline concentration.ResultsBoth groups that received the low doses were GFP positive in the heart and liver tissue. BP was increased to SHR7, but it was prevented by miR‐29c lentivirus treatment to SHR14. The miRNA‐29c expression increased in all treated groups versus their control (CSI). COLIAI expression decreased in treated groups, while COLIIIAI did not change. Collagen volume fraction decreased in all treated groups, which shows that the treatment was efficient to decrease the cardiac collagen. HW/BW ratio decreased 7–11% in SHR14, while the dCMO was increased in all treated groups.ConclusionsThese results suggest that miR‐29c lentivirus treatment induces beneficial cardiac remodeling in SHR, increasing dCMO and decreasing cardiac fibrosis. These results open perspective for further investigation of antifibrotic therapies for cardiovascular diseases.Support or Funding InformationFAPESP, CNPq, CAPES and NAPmirThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Sodium Butyrate Controls Cardiac Hypertrophy in Experimental Models of Rats.

The aim of the present research was to study the effect of sodium butyrate (SB) on partial abdominal aorta constriction (PAAC)-induced cardiac hypertrophy and determine its mechanism of action. Healthy Wistar rats were exposed to PAAC for eight weeks. After eight weeks, we carried out hypertrophic and hemodynamic evaluation and measured oxidative stress parameters and mitochondrial DNA concentration. PAAC control animals exhibited cardiac hypertrophy, decreased hemodynamic functions and oxidative stress. Treatment with SB reduced hypertrophic indices, LV wall thickness, LV collagen levels, cardiomyocyte diameter, serum lipid levels and serum cardiac biomarkers. Treatment with SB also improved hemodynamic functions, prevented oxidative stress and increased mitochondrial DNA concentration. Improvement in hypertrophy due to HDAC inhibition was further confirmed by HDAC mRNA expression studies which revealed that SB decreases expression of prohypertrophic HDAC, i.e., HDAC2, without altering the expression of anti-hypertrophic HDAC5. Sodium butyrate produces beneficial effect on cardiac hypertrophy as is evident, specifically from reduction in hypertrophic parameters including collagen levels, improvement in mitochondrial DNA concentration and preservation of LV systolic and diastolic dysfunction. This beneficial effect of sodium butyrate is mediated through downregulation of class I HDACs, specifically HDAC2 without any effect on class II HDAC, i.e., HDAC5. Thus, selective class I HDAC inhibition is required for controlling cardiac hypertrophy. Newer HDAC inhibitors which are class I inhibitor and class II promoter can be designed to obtain a 'pan' or 'dual' natural HDAC 'regulators.'

Exosomes secreted by cardiosphere-derived cells reduce scarring, attenuate adverse remodelling, and improve function in acute and chronic porcine myocardial infarction.

Naturally secreted nanovesicles known as exosomes are required for the regenerative effects of cardiosphere-derived cells (CDCs), and exosomes mimic the benefits of CDCs in rodents. Nevertheless, exosomes have not been studied in a translationally realistic large-animal model. We sought to optimize delivery and assess the efficacy of CDC-secreted exosomes in pig models of acute (AMI) and convalescent myocardial infarction (CMI). In AMI, pigs received human CDC exosomes (or vehicle) by intracoronary (IC) or open-chest intramyocardial (IM) delivery 30 min after reperfusion. No-reflow area and infarct size (IS) were assessed histologically at 48 h. Intracoronary exosomes were ineffective, but IM exosomes decreased IS from 80 ± 5% to 61 ± 12% (P= 0.001) and preserved left ventricular ejection fraction (LVEF). In a randomized placebo-controlled study of CMI, pigs 4 weeks post-myocardial infarction (MI) underwent percutaneous IM delivery of vehicle (n = 6) or CDC exosomes (n = 6). Magnetic resonance imaging (MRI) performed before and 1 month after treatment revealed that exosomes (but not vehicle) preserved LV volumes and LVEF (−0.1 ± 2.2% vs. −5.4 ± 3.6%, P= 0.01) while decreasing scar size. Histologically, exosomes decreased LV collagen content and cardiomyocyte hypertrophy while increasing vessel density. Cardiosphere-derived cell exosomes delivered IM decrease scarring, halt adverse remodelling and improve LVEF in porcine AMI and CMI. While conceptually attractive as cell-free therapeutic agents for myocardial infarction, exosomes have the disadvantage that IM delivery is necessary.

Long-term physiological T3 supplementation in hypertensive heart disease in rats.

Animal studies suggest that hypertension leads to cardiac tissue hypothyroidism, a condition that can by itself lead to heart failure. We have previously shown that short-term thyroid hormone treatment in Spontaneously Hypertensive Heart Failure (SHHF) rats near heart failure is beneficial. This study tested the hypothesis that therapeutic, long-term T3 treatment in SHHF rats can prevent or attenuate cardiac dysfunction. Female SHHF rats were treated orally with a physiological T3 dose (0.04 μg/ml) from 12 to 24 mo of age. Age-matched female SHHF and Wistar-Kyoto rats served as hypertensive and normotensive controls, respectively. SHHF rats had reduced serum free thyroid hormone levels and cardiac tissue T3 levels, LV dysfunction, and elevated LV collagen content compared with normotensive controls. Restoration of serum and cardiac tissue thyroid hormone levels in T3-treated rats was associated with no change in heart rate, but strong trends for improvement in LV systolic function and collagen levels. For instance, end-systolic diameter, fractional shortening, systolic wall stress, and LV collagen levels were no longer significantly different from controls. In conclusion, longstanding hypertension in rats led to chronic low serum and cardiac tissue thyroid hormone levels. Long-term treatment with low-dose T3 was safe. While cardiac dysfunction could not be completely prevented in the absence of antihypertensive treatment, T3 may offer additional benefits as an adjunct therapy with possible improvement in diastolic function.

Cardioprotective effects of magnesium valproate in type 2 diabetes mellitus

We have evaluated the effect of magnesium valproate (210mg/kg/day, p.o.) in type 2 diabetes induced cardiovascular complications induced by streptozotocin (STZ, 90mg/kg, i.p.) in neonatal wistar rats. Various biochemical, cardiovascular and hemodynamic parameters were measured at the end of 8 weeks of treatment. STZ produced significant hyperglycaemia, hypoinsulinemia and dyslipidemia, which was prevented by magnesium valproate treatment. STZ produced increase in Creatinine Kinase, C-reactive protein and lactate dehydrogenase levels and treatment with magnesium valproate produced reduction in these levels. STZ produced increase in cardiac and LV hypertrophy index, LV/RV ratio, LV collagen deposition and LV cardiomyocyte diameter which were decreased by magnesium valproate treatment. Magnesium valproate also prevented STZ induced hemodynamic alterations and oxidative stress. These results were further supported by histopathological studies in which magnesium valproate showed marked reduction in fibrosis and cardiac fiber disarray. In conclusion, our data suggests that magnesium valproate is beneficial as an anti-diabetic agent in type-2 diabetes mellitus and also prevents its cardiac complications.

Evaluation of Buspirone on Streptozotocin Induced Type 1 Diabetes and Its Associated Complications

We have evaluated the effect of buspirone (1.5 mg/kg/day, p.o.) type 1 diabetes induced cardiovascular complications induced by streptozotocin (STZ, 45 mg/kg, i.v.) in Wistar rats. Various biochemical, cardiovascular, and hemodynamic parameters were measured at the end of 8 weeks of treatment. STZ produced significant hyperglycaemia, hypoinsulinemia, and dyslipidemia, which was prevented by buspirone treatment. STZ produced increase in serum creatinine, urea, lactate dehydrogenase, creatinine kinase, and C-reactive protein levels and treatment with buspirone produced reduction in these levels. STZ produced increase in cardiac and LV hypertrophy index, LV/RV ratio, and LV collagen, which were decreased by buspirone treatment. Buspirone also prevented STZ induced hemodynamic alterations and oxidative stress. These results were further supported by histopathological studies in which buspirone showed marked reduction in fibrosis and cardiac fiber disarray. In conclusion, our data suggests that buspirone is beneficial as an antidiabetic agent in type 1 diabetes mellitus and also prevents its cardiac complications.

Lysyl oxidase inhibition in the volume overloaded heart prevents adverse collagen remodeling, apoptosis, and cardiac dysfunction

Heart failure is the most prevalent and costly disease in the U.S. Our goal was to determine if the over‐activation of lysyl oxidase (LOX), a collagen cross‐linking enzyme, accelerates cardiac disease and failure. LOX is elevated in human failing hearts, but it is not known if LOX plays a causative role in disease. Using the aortocaval fistula (ACF) rat surgical model of volume overload, we assessed the role of LOX activity in progression of heart failure over 14 wks. LOX activity was inhibited by BAPN (100 mg/kg/d) at 2 wks post‐surgery. Echocardiography was used to evaluate cardiac function and progression of LV remodeling. LOX expression and activity, collagen content, cross‐linking, and typing were determined in LV homogenates. Fixed sections of mid‐LV were assessed for apoptosis by TUNEL. ACF surgery caused significant ventricular dilatation (43% increase) and dysfunction (26% decreased, %FS). LOX protein expression was increased (65%) with concomitant increases in LOX activity. These increases in LOX were associated with significantly elevated collagen concentration, cross‐linking, and type I/III. LOX inhibition prevented ACF‐induced changes in LV collagen, and led to maintenance of systolic function. LOX inhibition also attenuated LV dilatation and prevented apoptosis, but did not reduce LV hypertrophy. These data indicate that LOX inhibition is cardioprotective in the volume overloaded heart.

04 The Cardiac Extracellular Matrix is Remodelled Divergently with Age in Heart Failure: A Role for Altered Collagen Degradation in an Ovine Rapid Pacing Model

Alterations to the amount, quality and/or distribution of the cardiac extracellular matrix (ECM) are defining features of the structural remodelling which occurs in heart failure (HF). However, whether the ECM remodelling which occurs in the aged failing heart occurs to the same extent as in the young remains to be determined. HF was instigated in sheep aged either 18 months (young) or >8 years (aged) by rapid ventricular pacing (210 bpm). HF increased LV diameter and reduced fractional shortening (measured by echocardiography) in both young and aged animals (all P<0.001), although these changes were more pronounced in the aged (P<0.05). LV collagen content measured from picro-sirius red-stained LV sections was altered with HF in an age-dependent manner - with collagen accumulation in young HF (P<0.001) and depletion in aged HF (P<0.05). Matrix metalloproteinase-2 (MMP-2) activity determined from gelatin zymograms was enhanced with both ageing and in young HF (both P<0.05). Protein levels of tissue inhibitor of metalloproteinases (TIMPs) 3 & 4 quantified by immunoblotting were reduced in aged HF only (P<0.05). Levels of secreted protein acidic and rich in cysteine (SPARC) were increased in aged hearts compared to young controls (P<0.05) whilst serum procollagen type I C-peptide (PICP) was increased in both young failing (P<0.05) and aged failing (P<0.01) animals, as measured using specific ELISA. In conclusion, remodelling of the cardiac ECM in HF is age-dependent. Diminished TIMP levels only in aged HF alongside enhanced collagen synthesis in HF provide a potential mechanism for this age-dependent response.

Effects of biglycan deficiency on myocardial infarct structure and mechanics.

Biglycan, a small leucine-rich proteoglycan, has been shown to interact with extracellular matrix (ECM) collagen and may influence fibrillogenesis. We hypothesized that biglycan contributes to post-myocardial infarction (MI) scar development and that the absence of biglycan would result in altered scar structure and mechanics. Anterior MI was induced in biglycan hemizygous null and wild-type mice by permanent ligation of the left coronary artery. The initial extent of ischemic injury was similar in the two groups, as was the infarct size after 30 days, although there was some tendency toward reduced expansion in the biglycan-null. Electron microscopy revealed that collagen fibrils had a smaller average diameter and a narrower range in the biglycan-null scar, as well as appearing more densely packed. In vivo strain analysis showed that biglycan-null scars were stiffer than the wild-type. Remote LV collagen concentration tended to be reduced in biglycan-null hearts, but the difference was not statistically significant. Null-expression of biglycan may alter collagen fibril ultrastructure, and thereby influence scar mechanics and remodeling.

Extensive Downregulation of Matrix Scaffolding Genes and TGF‐beta in Isolated Mitral Regurgitation in the Dog

The volume overload of isolated mitral regurgitation (MR) in the dog is characterized by LV dilatation and loss of extracellular matrix. We hypothesize that the MR heart is not only marked by increased matrix metalloproteinase (MMP) expression but also by downregulation of collagen synthesis. Gene arrays were compared from biopsy specimens obtained in 4 dogs prior to MR and 4 months after MR induction. There was a 50% increase in LV end‐diastolic volume by magnetic resonance imaging. MMP‐1 and ‐9 increased 5‐ and 10‐fold, in the face of no change in collagen I, a 1.5‐fold increase in collagen III, but a 35% decrease in LV hydroxyproline levels. Genes associated with cell‐matrix scaffolding including decorin, fibulin, fibrillin, were significantly downregulated. Genes regulating collagen synthesis including thrombospondin, TGF‐beta binding protein, TGF‐beta receptor, connective tissue growth factor, and plasminogen activator inhibitor were also significantly downregulated. LV TGF‐beta activity decreased 30% in MR compared to normal LV. These results indicate that LV collagen loss in MR is chiefly due to post‐translational processing and degradation of collagen I and III. In addition, there is an extensive downregulation of cell‐matrix scaffolding genes controlled by TGF‐beta pathway which is also downregulated. Taken together, this could explain why RAS blockade does not improve LV remodeling in isolated MR.

Abstract 964: Effect of Volume Overload on Left Ventricular Torsion and Extra Cellular Matrix

Background: Muscle fibers are arranged in a spiral network and are connected by extracellular matrix (ECM). LV torsion is increased in the pressure overloaded heart where there is an increase in ECM. However, torsion and its relation to ECM have not been systematically studied in the volume overloaded heart. Hypothesis: The volume overloaded heart has a decrease in LV torsion due a loss of ECM. Methods: Primary mitral regurgitation (MR) (n=29), resistant hypertension (HTN) (n=77) and normal volunteers (NL) (n±37) were studied. Comprehensive cardiac magnetic resonance imaging (MRI) with tissue tagging was performed and analyzed using three-dimensional data set. Torsion was computed by fitting a B-spline deformation model in prolate-spheroidal coordinates to the tag line data. A subset of MR subjects had LV collagen assessed by picric acid Sirius red from biopsy samples taken at the time of surgery. Results: LV ejection fraction was 65% in MR and 70% in HTN. MR demonstrated eccentric remodeling and HTN demonstrated concentric remodeling. HTN had significantly higher torsion angle and systolic twist compared to NL and MR. This was associated with a simultaneous decrease in longitudinal strain. In contrast, MR patients had similar torsion indices, circumferential and longitudinal strains compared to NL. LV biopsy in MR demonstrated a decrease in interstitial collagen compared to NL. Conclusions: As opposed to the pure volume overloaded heart, LV torsional forces are increased in the pressure overloaded heart. This difference may be related to a rearrangement of the laminar structure due to a differential effect on ECM in the volume overloaded versus the pressure overloaded heart.

MAST CELL BLOCKADE ATTENUATES THE COLLAGEN LOSS AND VENTRICULAR DILATION ASSOCIATED WITH MITRAL REGURGITATION IN DOGS

In a canine model of mitral regurgitation (MR) induced by chordal rupture, we have shown infiltration of LV by mast cells and increased matrix metalloproteinase (MMP) activity, resulting in extracellular matrix (ECM) loss, myocyte and myofiber slippage, LV dilatation and failure. Mast cells release mediators that can affect LV ECM. We hypothesized that mast cell blockade with ketotofen (K, n=6) would result in improved LV remodeling compared to untreated dogs with four weeks of MR (n=6). Mean pulmonary artery pressures (13¡À1 vs. 20¡À3 mmHg, p<0.05) and SVR (1684¡À132 vs. 2151¡À147, p<0.05) were significantly decreased in K-MR vs. MR dogs. K-MR dogs had significantly smaller LV end-diastolic dimensions, left atrium/aortic root ratio, and wall thinning (LVfw) vs. untreated MR dogs. K-MR dogs had significantly less LV hypertrophy vs. MR dogs. LV collagen volume % was significantly higher in K-MR dogs vs. MR dogs (0.50¡À0.033 vs. 0.34¡À0.017, p<0.05). The relative transcript abundance of collagen I ¦Á1 and fibronectin were significantly decreased in MR dogs compared to normal dogs (n=6) while in K-MR these levels did not differ from normal (n=6) (p<0.05). K- MR dogs also had higher collagen III transcript levels vs. MR dogs. Thus, Ketotofen treatment restored synthesis of collagen matrix components and improved LV function and remodeling in MR. This may provide a new form of therapy for pure MR since renin-angiotensin system blockade, which is anti-fibrotic, does not improve LV remodeling and function in the pure volume overload of MR.

Remodelação miocárdica na sobrecarga crônica de pressão ou de volume no coração de ratos

To compare cardiac structural changes in experimental pressure and volume overload models. The study analysis included renovascular hypertensive rats (RVH, n = 8), normotensive rats with volume overload caused by an aortocaval fistula (ACF, n = 10) and control rats (CONT, n = 8). After four weeks, tail cuff blood pressure (SBP) was recorded. Rats were killed, the hearts were excised and the right and left ventricles (RV&LV) were weighed (RVW&LVW). Using histological sections, myocyte cross sectional areas (MA). LV wall thickness (LVWT) LV cavity diameter (LVD), normalized LVWT (LVWT/LVD) and collagen volume fraction (CVF) were measured. The comparisons were made using the ANOVA and Tukey test for a significance level of 5%. Tail cuff blood pressure (mmHg) was higher in the RVH group (RVH = 187 +/- 22; CONT = 125 +/- 10; ACF = 122 +/- 6, p < 0.05). LV hypertrophy was observed in the RVH and ACF groups. The ACF group presented a significant increase in size of LVD, compared to CONT and RVH. The absolute and normalized ventricular wall thickness were similar among the groups. The RVH group presented a significant increase in CVF compared to CONT group and ACF group. Cardiac remodeling patterns following volume or pressure overload are distinct, suggesting that their implications on ventricular dysfunction are not interchangeable.