Cardiac Function In Adult Mice Research Articles

Plakophilin 2 gene therapy prevents and rescues arrhythmogenic right ventricular cardiomyopathy in a mouse model harboring patient genetics

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a fatal genetic heart disease characterized by cardiac arrhythmias, in which fibrofatty deposition leads to heart failure, with no effective treatments. Plakophilin 2 (PKP2) is the most frequently mutated gene in ARVC, and although altered RNA splicing has been implicated, there are no models to study its effect and therapeutics. Here, we generate a mouse model harboring a PKP2 mutation (IVS10-1G>C) affecting RNA splicing, recapitulating ARVC features and sudden death starting at 4 weeks. Administering AAV-PKP2 gene therapy (adeno-associated viral therapy to drive cardiac expression of PKP2) to neonatal mice restored PKP2 protein levels, completely preventing cardiac desmosomal and pathological deficits associated with ARVC, ensuring 100% survival of mice up to 6 months. Late-stage AAV-PKP2 administration rescued desmosomal protein deficits and reduced pathological deficits including improved cardiac function in adult mice, resulting in 100% survival up to 4 months. We suggest that AAV-PKP2 gene therapy holds promise for circumventing ARVC associated with PKP2 mutations, including splice site mutations.

Loss of the Tbx5 gene in the ventricular conduction system induces spontaneous ventricular arrhythmias

The ventricular conduction system (VCS) and the working myocardium (WM) derive from the same myogenic progenitors during the embryonic development. The VCS development is regulated by numerous genes including the T-box transcription factor 5 (Tbx5). In human, Tbx5 mutations cause Holt-Oram syndrome, an autosomal dominant disease associated with heart abnormalities such as arrhythmias. In adult mice, the deletion of the Tbx5 gene provoked a slowing of ventricular conduction due to a loss of the gap junction Connexin 40 and dysfunction of cardiac channels. However, it is still unknown how Tbx5 deletion affects the development and the function of the VCS. The aim is to study the consequences of the Tbx5 deletion in embryonic progenitors of the ventricular conduction system on cardiac function in adult mice. Conditional deletion of Tbx5 alleles in mice was induced by expressing the Cre recombinase under the control of the Connexin 40 (Cx40) gene. We studied two groups of mutants: Tbx5 deletion at embryonic days E13-14 targeting both the ventricular conduction system and the working myocardium (“VCS + WM” group; n = 40) and mice deleted at E18-P2 targeting only the ventricular conduction system (“VCS” group; n = 17). Surface ECGs were achieved monthly until 3 months of age, when immunostaining was performed on the left VCS. Immunostaining showed a reduced expression of the two major connexines in the ventricle (Cx40 and Cx43) and a reduced number of conductive cells in both mutants, suggesting a defective maturation of the VCS (Fig. 1). Furthermore, the loss of Cx43 was correlated with that of Tbx5, reflecting a direct transcriptional effect. Surface ECG revealed a significant increase of the ventricular activation duration in both mutants (P < 0.01). Moreover, premature ventricular contractions (PVCs) and a left QRS axis deviation were observed in both mutants. Finally, these PVCs disappeared with age in both mutants under resting conditions, and are unmasked when the heart is challenged with a β-1 adrenergic agonist. Our results provide new insights into Tbx5 targets in the VCS. Tbx5 deletion impacts the maturation and the anatomy of the VCS as proved by the deviation of the ventricular electrical axis, which even occurs when the VCS is already formed. Tbx5 appears to have a direct impact on the Gja1 gene, encoding the gap junction Cx43, which is reduced at the junction between the VCS and the WM in both mutants and may be responsible for PVCs.

Disruption of histamine/H1R signaling pathway represses cardiac differentiation and maturation of human induced pluripotent stem cells

BackgroundThe efficiency and quality of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are crucial for regenerative medicine, disease modeling, drug screening, and the study of the development events during cardiac specification. However, their applications have been hampered by the differentiation efficiency, poor maturation, and high interline variability. Recent studies have reported that histamine plays important roles in hematopoietic stem cell proliferation and neutrophil maturation. However, its roles in cardiovascular tissue regeneration have not been thoroughly investigated. In the current study, we identified a novel physiological function of the histamine/histamine 1 receptor (H1R) signal in regulating the differentiation of hiPSC-CMs and heart development.MethodsTransgenic zebrafish model (cmlc2: mCherry) was treated with histamine and histamine receptor (HR) antagonists. Histological morphology and ultrastructure of zebrafish heart were measured. Histamine-deficient pregnant mice (HDC−/−) were treated with H1R antagonist (pyrilamine) by intragastric administration from E8.5 to E18.5. Cardiac histological morphology and ultrastructure were analyzed in neonatal mice, and cardiac function in adult mice was measured. In vitro, histamine and HR antagonists were administrated in the culture medium during hiPSC-CM differentiation at different stages. The efficiency and maturation of cardiac differentiation were evaluated. Finally, histamine-treated hiPSC-CMs were transplanted into ischemic myocardium to detect the possible therapeutic effect.ResultsAdministration of H1R antagonist during heart development induced cardiac dysplasia in zebrafish. Furthermore, using histidine decarboxylase (HDC) knockout mice, we examined abnormal swelling of myocardial mitochondria and autophagy formation under the condition of endogenous histamine deficiency. Histamine significantly promoted myocardial differentiation from human induced pluripotent stem cells (hiPSCs) with better structure and function via a H1R-dependent signal. The activation of histamine/H1R signaling pathway augmented hiPSC-derived cardiomyocyte (hiPSC-CM) differentiation through the ERK1/2-STAT3 signaling pathway. In addition, histamine-pre-treated hiPSC-CMs were transplanted into the ischemic hearts of myocardial injured mice and exhibited better survival and myocardial protection.ConclusionsThus, these findings indicated that histamine/H1R and its downstream signals were not only involved in cardiac differentiation but also provided a better survival environment for stem cell transplanted into ischemic myocardium.

Overexpression of the histidine triad nucleotide-binding protein 2 protects cardiac function in the adult mice after acute myocardial infarction.

To explore the role of the histidine triad nucleotide-binding 2 (HINT2) protein in heart failure. Neonatal mouse ventricle myocytes (NMVMs) and myocardial infarction-induced heart failure mice were used for in vitro or in vivo experiments. Adenovirus (ADV) and adeno-associated virus serum type 9 (AAV9) vectors were used to regulate HINT2 expression. The expression of HINT2 was determined by quantifying the mRNA and protein levels. Cell survival was analysed using the CCK-8 kit and TUNEL staining. Mitochondrial function was determined by the mitochondrial membrane potential and oxygen consumption rates. AAV9-HINT2 was injected 24h post-myocardial infarction following which transthoracic echocardiography and histological analyses were performed after 4weeks. Positron emission tomography tomography-computed tomography (PET/CT) and targeted metabolomics analyses were used to explore the metabolic status in vivo. NAD levels were measured using a colorimetric kit. Computer-simulated rigid body molecular docking was performed using AUTODOCK4. Molecule binding kinetics assays were performed using biolayer interferometry. HINT2 was down-regulated in NMVMs in hypoxia. ADV-HINT2-induced HINT2 overexpression improved NMVM survival after exposure to hypoxia. Mitochondrial function was preserved in the ADV-HINT2 group under hypoxic conditions. In vivo experiments showed that cardiac function and metabolic status was preserved by HINT2 overexpression. HINT2 overexpression restored mitochondrial NAD levels; this was dependent on nicotinamide mononucleotide (NMN). Using computer-simulated molecular docking analysis and biolayer interferometry, we observed that HINT2 potentially binds and associates with NMN. HINT2 overexpression protects cardiac function in adult mice after myocardial infarction by maintaining mitochondrial NAD homeostasis.

Mydgf promotes Cardiomyocyte proliferation and Neonatal Heart regeneration.

Myeloid-derived growth factor (Mydgf), a paracrine protein secreted by bone marrow-derived monocytes and macrophages, was found to protect against cardiac injury following myocardial infarction (MI) in adult mice. We speculated that Mydgf might improve heart function via myocardial regeneration, which is essential for discovering the target to reverse heart failure.Methods: Two genetic mouse lines were used: global Mydgf knockout (Mydgf-KO) and Mydgf-EGFP mice. Two models of cardiac injury, apical resection was performed in neonatal and MI was performed in adult mice. Quantitative reverse transcription-polymerase chain reaction, western blot and flow cytometry were performed to study the protein expression. Immunofluorescence was performed to detect the proliferation of cardiomyocytes. Heart regeneration and cardiac function were evaluated by Masson's staining and echocardiography, respectively. RNA sequencing was employed to identify the key involved in Mydgf-induced cardiomyocyte proliferation. Mydgf recombinant protein injection was performed as a therapy for cardiac repair post MI in adult mice.Results: Mydgf expression could be significantly induced in neonatal mouse hearts after cardiac injury. Unexpectedly, we found that Mydgf was predominantly expressed by endothelial cells rather than macrophages in injured neonatal hearts. Mydgf deficiency impeded neonatal heart regeneration and injury-induced cardiomyocyte proliferation. Mydgf recombinant protein promoted primary mouse cardiomyocyte proliferation. Employing RNA sequencing and functional verification, we demonstrated that c-Myc/FoxM1 pathway mediated Mydgf-induced cardiomyocyte expansion. Mydgf recombinant protein improved cardiac function in adult mice after MI injury with inducing cardiomyocyte proliferation.Conclusion: Mydgf promotes cardiomyocyte proliferation by activating c-Myc/FoxM1 pathway and improves heart regeneration both in neonatal and adult mice after cardiac injury, providing a potential target to reverse cardiac remodeling and heart failure.

Abstract 20958: Smyd1a Overexpression Suppresses Functional Decline in the Adult Myocardium

Heart disease is the leading cause of death in the United States. This chronic condition affects the heart so it can no longer sufficiently pump blood to vital organs in the body. While heart disease can manifest in many different ways the general pathophysiology is conserved: the heart compensates for an increased workload by undergoing hypertrophic growth, accompanied by transcriptional reprogramming, and progresses into heart failure. Although many epigenetic factors have been identified which influence these underlying changes in transcription during disease, we still know very little about how this process is regulated in the cardiomyocyte. Smyd1, a unique histone methyltransferase that regulates gene expression in the cardiomyocyte, was originally shown to play a crucial role in early cardiac development. More recently, we have shown that loss of Smyd1 in the adult mouse heart leads to pro-hypertrophic signaling resulting in cardiomyocyte growth, fibrosis and functional decline. In addition, we examined the two Smyd1 isoforms (Smyd1a and Smy1b) in isolated myocytes and showed that Smyd1a (but not Smyd1b) overexpression (OE) was capable of inhibiting phenylephrine-induced hypertrophy. To further characterize the role of Smyd1 in the myocardium and determine if Smyd1a is capable of inhibiting hypertrophic growth in adult heart we generated transgenic mice capable of inducible, cardiac-specific OE of Smyd1a using a Tet-On system. Mice were fed doxycycline-laced chow for 2 weeks to achieve Smyd1a-OE at which time we characterized their cardiac phenotype under basal conditions and after stress (permanent occlusion). Interestingly, transgenic mice showed no observable difference under basal conditions, however, 3 weeks after permanent occlusion of the LAD, the EF of wild type animals decreased to ~37%, while transgenic mice maintained an EF of ~61% . In addition, transgenic mice exhibited exacerbated growth (12% increase in HW/BW ratio) with no change in expression of the hypertrophic marker ANF, in contrast to wild type animals (4 fold increase). These exciting results suggest that Smyd1a is capable of preserving cardiac function in adult mice, however, this mechanism appears to be independent of hypertrophic signaling.

Mdm2 regulates cardiac contractility by inhibiting GRK2-mediated desensitization of β-adrenergic receptor signaling.

The oncoprotein Mdm2 is a RING domain-containing E3 ubiquitin ligase that ubiquitinates G protein-coupled receptor kinase 2 (GRK2) and β-arrestin2, thereby regulating β-adrenergic receptor (βAR) signaling and endocytosis. Previous studies showed that cardiac Mdm2 expression is critical for controlling p53-dependent apoptosis during early embryonic development, but the role of Mdm2 in the developed adult heart is unknown. We aimed to identify if Mdm2 affects βAR signaling and cardiac function in adult mice. Using Mdm2/p53-KO mice, which survive for 9-12 months, we identified a critical and potentially novel role for Mdm2 in the adult mouse heart through its regulation of cardiac β1AR signaling. While baseline cardiac function was mostly similar in both Mdm2/p53-KO and wild-type (WT) mice, isoproterenol-induced cardiac contractility in Mdm2/p53-KO was significantly blunted compared with WT mice. Isoproterenol increased cAMP in left ventricles of WT but not of Mdm2/p53-KO mice. Additionally, while basal and forskolin-induced calcium handling in isolated Mdm2/p53-KO and WT cardiomyocytes were equivalent, isoproterenol-induced calcium handling in Mdm2/p53-KO was impaired. Mdm2/p53-KO hearts expressed 2-fold more GRK2 than WT. GRK2 polyubiquitination via lysine-48 linkages was significantly reduced in Mdm2/p53-KO hearts. Tamoxifen-inducible cardiomyocyte-specific deletion of Mdm2 in adult mice also led to a significant increase in GRK2, and resulted in severely impaired cardiac function, high mortality, and no detectable βAR responsiveness. Gene delivery of either Mdm2 or GRK2-CT in vivo using adeno-associated virus 9 (AAV9) effectively rescued β1AR-induced cardiac contractility in Mdm2/p53-KO. These findings reveal a critical p53-independent physiological role of Mdm2 in adult hearts, namely, regulation of GRK2-mediated desensitization of βAR signaling.

Abstract 411: In Utero Exposure to PM2.5 Causes Adult Cardiovascular Dysfunction and Reduced Exercise Capacity

Objective: Exposure to particulate matter 2.5 μm (PM2.5) during intrauterine development is associated with adverse cardiovascular outcomes at adulthood. Deteriorations in cardiac function are observed with increased myocardial demand in PM2.5-exposed individuals. The goal of this study was to determine the effects of in utero PM2.5exposure on exercise training capacity and cardiac function in adult mice. Methods: Female FVB mice were exposed either to filtered air (FA) or PM2.5at an average concentration of 73.61μg/m 3 for 6h/day, 7days/wk throughout pregnancy. 12wk old male offspring from exposed dams were assigned to in utero FA (n=5) or PM2.5 (n=5) exposed groups which underwent exercise training for 3 weeks (housed with running wheels for 3 weeks). We measured total distance travelled and performed echocardiography at baseline, 1, 2 and 3 weeks. Results: There was a progressive decrease in total distance travelled each week in the in utero PM2.5 exposed mice (Week 1: 12.2±3.46 Km FA, 5.32±2.06 Km PM2.5; Week 2: 41.4±9.62 Km FA, 17.28±6.60 Km PM2.5; Week 3: 61.8±16.59 Km FA, 25.92.±8.62 Km PM2.5) compared to the in utero FA exposed mice. When comparing to their respective sedentary counterparts, the FA exercise group showed increased fractional shortening (%FS), left ventricular end systolic (LVESd) and diastolic (LVEDd) diameters, suggesting eccentric hypertrophy. There was a modest decrease in %FS and marked increase in posterior wall thickness during diastole (PWTd) in the PM2.5 exercise group suggesting concentric hypertrophy. Comparison of in utero FA vs PM2.5 exercise groups after 3 weeks of exercise training showed reduced %FS and marked decrease in LVEDd in the PM2.5 exercise group compared to the FA exercise group. Furthermore, a decrease in PWTs and increased PWTd was also observed in the PM2.5 group compared to FA controls. Conclusions: In utero PM2.5exposure reduced exercise capacity at adulthood and the development of both systolic and diastolic dysfunction. Thus, our study showed that individuals residing in high pollution areas are predisposed to develop cardiac dysfunction under conditions of increased myocardial demand.

Discovery of novel small molecule inhibitors of cardiac hypertrophy using high throughput, high content imaging

Chronic cardiac hypertrophy is maladaptive and contributes to the pathogenesis of heart failure. The objective of this study was to identify small molecule inhibitors of pathological cardiomyocyte hypertrophy. High content screening was performed with primary neonatal rat ventricular myocytes (NRVMs) cultured on 96-well plates and treated with a library of 3241 distinct small molecules. Non-toxic hit compounds that blocked hypertrophy in response to phenylephrine (PE) and phorbol myristate acetate (PMA) were identified based on their ability to reduce cell size and inhibit expression of atrial natriuretic factor (ANF), which is a biomarker of pathological cardiac hypertrophy. Many of the hit compounds are existing drugs that have not previously been evaluated for benefit in the setting of cardiovascular disease. One such compound, the anti-malarial drug artesunate, blocked left ventricular hypertrophy (LVH) and improved cardiac function in adult mice subjected to transverse aortic constriction (TAC). These findings demonstrate that phenotypic screening with primary cardiomyocytes can be used to discover anti-hypertrophic lead compounds for heart failure drug discovery. Using annotated libraries of compounds with known selectivity profiles, this screening methodology also facilitates chemical biological dissection of signaling networks that control pathological growth of the heart.

TRPV2 is critical for the cardiac function in adult mice

TRPV2 is critical for the cardiac function in adult mice

Caffeine exposure alters cardiac gene expression in embryonic cardiomyocytes.

Previous studies demonstrated that in utero caffeine treatment at embryonic day (E) 8.5 alters DNA methylation patterns, gene expression, and cardiac function in adult mice. To provide insight into the mechanisms, we examined cardiac gene and microRNA (miRNA) expression in cardiomyocytes shortly after exposure to physiologically relevant doses of caffeine. In HL-1 and primary embryonic cardiomyocytes, caffeine treatment for 48 h significantly altered the expression of cardiac structural genes (Myh6, Myh7, Myh7b, Tnni3), hormonal genes (Anp and BnP), cardiac transcription factors (Gata4, Mef2c, Mef2d, Nfatc1), and microRNAs (miRNAs; miR208a, miR208b, miR499). In addition, expressions of these genes were significantly altered in embryonic hearts exposed to in utero caffeine. For in utero experiments, pregnant CD-1 dams were treated with 20-60 mg/kg of caffeine, which resulted in maternal circulation levels of 37.3-65.3 μM 2 h after treatment. RNA sequencing was performed on embryonic ventricles treated with vehicle or 20 mg/kg of caffeine daily from E6.5-9.5. Differential expression (DE) analysis revealed that 124 genes and 849 transcripts were significantly altered, and differential exon usage (DEU) analysis identified 597 exons that were changed in response to prenatal caffeine exposure. Among the DE genes identified by RNA sequencing were several cardiac structural genes and genes that control DNA methylation and histone modification. Pathway analysis revealed that pathways related to cardiovascular development and diseases were significantly affected by caffeine. In addition, global cardiac DNA methylation was reduced in caffeine-treated cardiomyocytes. Collectively, these data demonstrate that caffeine exposure alters gene expression and DNA methylation in embryonic cardiomyocytes.

Met signaling in cardiomyocytes is required for normal cardiac function in adult mice

Hepatocyte growth factor (HGF) and its receptor, Met, are key determinants of distinct developmental processes. Although HGF exerts cardio-protective effects in a number of cardiac pathologies, it remains unknown whether HGF/Met signaling is essential for myocardial development and/or physiological function in adulthood. We therefore investigated the requirement of HGF/Met signaling in cardiomyocyte for embryonic and postnatal heart development and function by conditional inactivation of the Met receptor in cardiomyocytes using the Cre-α-MHC mouse line (referred to as α-MHCMet-KO). Although α-MHCMet-KO mice showed normal heart development and were viable and fertile, by 6months of age, males developed cardiomyocyte hypertrophy, associated with interstitial fibrosis. A significant upregulation in markers of myocardial damage, such as β-MHC and ANF, was also observed. By the age of 9months, α-MHCMet-KO males displayed systolic cardiac dysfunction. Mechanistically, we provide evidence of a severe imbalance in the antioxidant defenses in α-MHCMet-KO hearts involving a reduced expression and activity of catalase and superoxide dismutase, with consequent reactive oxygen species accumulation. Similar anomalies were observed in females, although with a slower kinetics. We also found that Met signaling down-regulation leads to an increase in TGF-β production and a decrease in p38MAPK activation, which may contribute to phenotypic alterations displayed in α-MHCMet-KO mice. Consistently, we show that HGF acts through p38α to upregulate antioxidant enzymes in cardiomyocytes. Our results highlight that HGF/Met signaling in cardiomyocytes plays a physiological cardio-protective role in adult mice by acting as an endogenous regulator of heart function through oxidative stress control.

BET acetyl-lysine binding proteins control pathological cardiac hypertrophy

Cardiac hypertrophy is an independent predictor of adverse outcomes in patients with heart failure, and thus represents an attractive target for novel therapeutic intervention. JQ1, a small molecule inhibitor of bromodomain and extraterminal (BET) acetyl-lysine reader proteins, was identified in a high throughput screen designed to discover novel small molecule regulators of cardiomyocyte hypertrophy. JQ1 dose-dependently blocked agonist-dependent hypertrophy of cultured neonatal rat ventricular myocytes (NRVMs) and reversed the prototypical gene program associated with pathological cardiac hypertrophy. JQ1 also blocked left ventricular hypertrophy (LVH) and improved cardiac function in adult mice subjected to transverse aortic constriction (TAC). The BET family consists of BRD2, BRD3, BRD4 and BRDT. BRD4 protein expression was increased during cardiac hypertrophy, and hypertrophic stimuli promoted recruitment of BRD4 to the transcriptional start site (TSS) of the gene encoding atrial natriuretic factor (ANF). Binding of BRD4 to the ANF TSS was associated with increased phosphorylation of local RNA polymerase II. These findings define a novel function for BET proteins as signal-responsive regulators of cardiac hypertrophy, and suggest that small molecule inhibitors of these epigenetic reader proteins have potential as therapeutics for heart failure.

Endogenous regulation of cardiovascular function by apelin-APJ

Studies have shown significant cardiovascular effects of exogenous apelin administration, including the potent activation of cardiac contraction. However, the role of the endogenous apelin-APJ pathway is less clear. To study the loss of endogenous apelin-APJ signaling, we generated mice lacking either the ligand (apelin) or the receptor (APJ). Apelin-deficient mice were viable, fertile, and showed normal development. In contrast, APJ-deficient mice were not born in the expected Mendelian ratio, and many showed cardiovascular developmental defects. Under basal conditions, both apelin and APJ null mice that survived to adulthood manifested modest decrements in contractile function. However, with exercise stress both mutant lines demonstrated consistent and striking decreases in exercise capacity. To explain these findings, we explored the role of autocrine signaling in vitro using field stimulation of isolated left ventricular cardiomyocytes lacking either apelin or APJ. Both groups manifested less sarcomeric shortening and impaired velocity of contraction and relaxation with no difference in calcium transient. Taken together, these results demonstrate that endogenous apelin-APJ signaling plays a modest role in maintaining basal cardiac function in adult mice with a more substantive role during conditions of stress. In addition, an autocrine pathway seems to exist in myocardial cells, the ablation of which reduces cellular contraction without change in calcium transient. Finally, differences in the developmental phenotype between apelin and APJ null mice suggest the possibility of undiscovered APJ ligands or ligand-independent effects of APJ.

Abstract 791: A Critical Role for Bmper (BMP-binding Endothelial cell precursor-derived Regulator) in Cardiac Muscle Mass Regulation during Development and Pressure Overload Induced Hypertrophy

Bone morphogenetic proteins (BMPs) of the TGF-beta superfamily, have been implicated in multiple processes during cardiac development. Our laboratory recently described an unprecedented role for Bmper in antagonizing BMP-2, BMP-4, and BMP-6. To determine the role of Bmper on cardiac development in vivo, we created Bmper null (Bmper −/−) mice by replacing exons 1 and 2 with GFP. Since Bmper −/− mice are perinatally lethal, we determined pre-natal cardiac function of Bmper −/− mice in utero just before birth. By echocardiography, E18.5 Bmper −/− embryos had decreased cardiac function (24.2 +/− 8.1% fractional shortening) compared to Bmper +/− and Bmper +/+ siblings (52.2 +/− 1.6% fractional shortening) (N=4/group). To further characterize the role of Bmper on cardiac function in adult mice, we performed echocardiography on 8-week old male and female Bmper +/− and littermate control Bmper +/+. Bmper +/− mice had an approximately 15% decrease in anterior and posterior wall thickness compared to sibling Bmper +/+ mice at baseline (n=10/group). Cross-sectional areas of Bmper +/− cardiomyocytes were approximately 20% less than wild type controls, indicating cardiomyocyte hypoplasia in adult Bmper +/− mice at baseline. Histologically, no significant differences were identified in representative H&amp;E and trichrome stained adult Bmper +/− and Bmper +/+ cardiac sections at baseline. To determine the effects of Bmper expression on the development of cardiac hypertrophy, both Bmper +/− and Bmper +/+ sibling controls underwent transaortic constriction (TAC), followed by weekly echocardiography. While a deficit was identified in Bmper +/− mice at baseline, both anterior and posterior wall thicknesses increased after TAC, such that identical wall thicknesses were identified in Bmper +/− and Bmper +/+ mice 1–4 weeks after TAC. Notably, cardiac function (fractional shortening %) and histological evaluation revealed no differences between Bmper +/− and Bmper +/+ any time after TAC. These studies identify for the first time that Bmper expression plays a critical role in regulating cardiac muscle mass during development, and that Bmper regulates the development of hypertrophy in response to pressure overload in vivo.

Assessment of cardiac function with the pressure-volume conductance system following myocardial infarction in mice

Myocardial infarction (MI) is a major cause of heart failure (HF) with the progressive worsening of cardiac performance due to structural and functional alterations. Therefore, we studied cardiac function in adult mice following MI using the Millar pressure-volume (P-V) conductance catheter system in vivo during the later phase of compensatory remodeling and decompensation to HF. We evaluated load-dependent and -independent parameters in control and 2-, 4-, 6-, and 10-wk post-MI mice and integrated changes in function with changes in gene expression. Our results indicated a significant deterioration of cardiac function in post-MI mice over time, reflected first by systolic dysfunction, followed by a transient improvement before further decline in both systolic and diastolic function. Associated with the function and adaptive remodeling were transient changes in fetal gene and extracellular matrix gene expression. However, undermining the compensatory remodeling response was a continual decline in cardiac contractility, which promoted the transition into failure. Our study provided a scheme of integrated cardiac function and gene expression changes occurring during the adaptive and maladaptive response of the heart independent of systemic vascular properties during the transition to HF following MI in mice. P-V loop analysis was used to quantitatively evaluate the gradual deterioration in cardiac function post-MI. P-V loop analysis was found to be an appropriate method for assessment of global cardiac function under varying load-dependent and -independent conditions in the murine model with many similarities to data obtained from larger animals and humans.