Quantitation and distribution of beta-tubulin in human cardiac myocytes

Raspberry polyphenols target molecular pathways of heart failure

Approximately 650,000 new cases of heart failure (HF) are diagnosed annually with a 50% five-year mortality rate. HF is characterized by reduced left ventricular (LV) ejection fraction and hypertrophy of the LV wall. The pathophysiological remodeling of the heart is mediated by increased oxidative stress and inflammation. Raspberries are rich in polyphenols which may favorably impact enzymes involved in redox homeostasis while also targeting inflammatory signaling. Thus, the objective of this study was to investigate whether raspberry polyphenols could attenuate HF. Sprague Dawley rats consumed a 10% (w/w) raspberry diet for 7 weeks. At week 3, HF was surgically induced via coronary artery ligation. Hemodynamics and morphology of the heart were assessed. Expression of cardiac proteins involved in oxidative stress, inflammation, apoptosis, and remodeling were examined, and histological analysis was conducted. Additionally, human cardiomyocytes were treated with raspberry polyphenol extract (RBPE) followed by CoCl2 to chemically induce hypoxia. Redox status, apoptosis, and mitochondrial dysfunction were measured. Raspberries attenuated reductions in cardiac function and reduced morphological changes which coincided with reduced toll-like receptor (TLR)4 signaling. Reductions in oxidative stress, apoptosis, and remodeling occurred in vivo. Incubation of cardiomyocytes with RBPE attenuated CoCl2-induced oxidative stress and apoptosis despite pronounced hypoxia-inducible factor (HIF)-1α expression. These data indicate that consumption of raspberries can reduce the underlying molecular drivers of HF; thus, leading to the observed improvements in cardiac functional capacity and morphology. This dietary strategy may be an effective alternative strategy for treating HF. However, further investigation into alternative models of HF is warranted.

Sulforaphane exposure impairs contractility and mitochondrial function in three-dimensional engineered heart tissue

Sulforaphane (SFN) is a phytochemical compound extracted from cruciferous plants, like broccoli or cauliflower. Its isothiocyanate group renders SFN reactive, thus allowing post-translational modification of cellular proteins to regulate their function with the potential for biological and therapeutic actions. SFN and stabilized variants recently received regulatory approval for clinical studies in humans for the treatment of neurological disorders and cancer. Potential unwanted side effects of SFN on heart function have not been investigated yet. The present study characterizes the impact of SFN on cardiomyocyte contractile function in cardiac preparations from neonatal rat, adult mouse and human induced-pluripotent stem cell-derived cardiomyocytes. This revealed a SFN-mediated negative inotropic effect, when administered either acutely or chronically, with an impairment of the Frank-Starling response to stretch activation. A direct effect of SFN on myofilament function was excluded in chemically permeabilized mouse trabeculae. However, SFN pretreatment increased lactate formation and enhanced the mitochondrial production of reactive oxygen species accompanied by a significant reduction in the mitochondrial membrane potential. Transmission electron microscopy revealed disturbed sarcomeric organization and inflated mitochondria with whorled membrane shape in response to SFN exposure. Interestingly, administration of the alternative energy source l-glutamine to the medium that bypasses the uptake route of pyruvate into the mitochondrial tricarboxylic acid cycle improved force development in SFN-treated EHTs, suggesting indeed mitochondrial dysfunction as a contributor of SFN-mediated contractile dysfunction. Taken together, the data from the present study suggest that SFN might impact negatively on cardiac contractility in patients with cardiovascular co-morbidities undergoing SFN supplementation therapy. Therefore, cardiac function should be monitored regularly to avoid the onset of cardiotoxic side effects.

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Sulforaphane has negative inotropic effects and increases diastolic tension.

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Sulforaphane exposure increases lactate levels and mitochondrial ROS production and reduces mitochondrial membrane potential.

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l-glutamine supplementation rescues the sulforaphane-mediated reduction in force development.

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Sulforaphane plasma levels and cardiac function should be monitored to avoid unwanted cardiac side effects in patients.

Proteomic and Structural Manifestations of Cardiomyopathy in Rat Models of Obesity and Weight Loss

Obesity cardiomyopathy increases the risk of heart failure and death. Obesity is curable, leading to the restoration of the heart phenotype, but it is not clear if there are any after-effects of obesity present after weight loss. We characterize the proteomic landscape of obesity cardiomyopathy with an evaluation of whether the cardiac phenotype is still shaped after weight loss. Cardiomyopathy was validated by cardiac hypertrophy, fibrosis, oversized myocytes, and mTOR upregulation in a rat model of cafeteria diet-induced developmental obesity. By global proteomic techniques (LC-MS/MS) a plethora of molecular changes was observed in the heart and circulation of obese animals, suggesting abnormal utilization of metabolic substrates. This was confirmed by increased levels of cardiac ACSL-1, a key enzyme for fatty acid degradation and decreased GLUT-1, a glucose transporter in obese rats. Calorie restriction and weight loss led to the normalization of the heart's size, but fibrosis was still excessive. The proteomic compositions of cardiac tissue and plasma were different after weight loss as compared to control. In addition to morphological consequences, obesity cardiomyopathy involves many proteomic changes. Weight loss provides for a partial repair of the heart's architecture, but the trace of fibrotic deposition and proteomic alterations may occur.

Adenosine kinase attenuates cardiomyocyte microtubule stabilization and protects against pressure overload-induced hypertrophy and LV dysfunction

Adenosine exerts numerous protective actions in the heart, including attenuation of cardiac hypertrophy. Adenosine kinase (ADK) converts adenosine to adenosine monophosphate (AMP) and is the major route of myocardial adenosine metabolism, however, the impact of ADK activity on cardiac structure and function is unknown. To examine the role of ADK in cardiac homeostasis and adaptation to stress, conditional cardiomyocyte specific ADK knockout mice (cADK-/-) were produced using the MerCreMer-lox-P system. Within 4 weeks of ADK disruption, cADK-/- mice developed spontaneous hypertrophy and increased β-Myosin Heavy Chain expression without observable LV dysfunction. In response to 6 weeks moderate left ventricular pressure overload (transverse aortic constriction;TAC), wild type mice (WT) exhibited ~60% increase in ventricular ADK expression and developed LV hypertrophy with preserved LV function. In contrast, cADK-/- mice exhibited significantly greater LV hypertrophy and cardiac stress marker expression (atrial natrurietic peptide and β-Myosin Heavy Chain), LV dilation, reduced LV ejection fraction and increased pulmonary congestion. ADK disruption did not decrease protein methylation, inhibit AMPK, or worsen fibrosis, but was associated with persistently elevated mTORC1 and p44/42 ERK MAP kinase signaling and a striking increase in microtubule (MT) stabilization/detyrosination. In neonatal cardiomyocytes exposed to hypertrophic stress, 2-chloroadenosine (CADO) or adenosine treatment suppressed MT detyrosination, which was reversed by ADK inhibition with iodotubercidin or ABT-702. Conversely, adenoviral over-expression of ADK augmented CADO destabilization of MTs and potentiated CADO attenuation of cardiomyocyte hypertrophy. Together, these findings indicate a novel adenosine receptor-independent role for ADK-mediated adenosine metabolism in cardiomyocyte microtubule dynamics and protection against maladaptive hypertrophy.

Highly variable contractile performance correlates with myocyte content in trabeculae from failing human hearts

Heart failure (HF) is defined by compromised contractile function and is associated with changes in excitation-contraction (EC) coupling and cardiomyocyte organisation. Tissue level changes often include fibrosis, while changes within cardiomyocytes often affect structures critical to EC coupling, including the ryanodine receptor (RyR), the associated protein junctophilin-2 (JPH2) and the transverse tubular system architecture. Using a novel approach, we aimed to directly correlate the influence of structural alterations with force development in ventricular trabeculae from failing human hearts. Trabeculae were excised from explanted human hearts in end-stage failure and immediately subjected to force measurements. Following functional experiments, each trabecula was fixed, sectioned and immuno-stained for structural investigations. Peak stress was highly variable between trabeculae from both within and between failing hearts and was strongly correlated with the cross-sectional area occupied by myocytes (MCSA), rather than total trabecula cross-sectional area. At the cellular level, myocytes exhibited extensive microtubule densification which was linked via JPH2 to time-to-peak stress. Trabeculae fractional MCSA variability was much higher than that in adjacent free wall samples. Together, these findings identify several structural parameters implicated in functional impairment in human HF and highlight the structural variability of ventricular trabeculae which should be considered when interpreting functional data.

Mechanosensitivity of microdomain calcium signalling in the heart

In cardiac myocytes, calcium (Ca²⁺) signalling is tightly controlled in dedicated microdomains. At the dyad, i.e. the narrow cleft between t-tubules and junctional sarcoplasmic reticulum (SR), many signalling pathways combine to control Ca²⁺-induced Ca²⁺ release during contraction. Local Ca²⁺ gradients also exist in regions where SR and mitochondria are in close contact to regulate energetic demands. Loss of microdomain structures, or dysregulation of local Ca²⁺ fluxes in cardiac disease, is often associated with oxidative stress, contractile dysfunction and arrhythmias. Ca²⁺ signalling at these microdomains is highly mechanosensitive. Recent work has demonstrated that increasing mechanical load triggers rapid local Ca²⁺ releases that are not reflected by changes in global Ca²⁺. Key mechanisms involve rapid mechanotransduction with reactive oxygen species or nitric oxide as primary signalling molecules targeting SR or mitochondria microdomains depending on the nature of the mechanical stimulus. This review summarizes the most recent insights in rapid Ca²⁺ microdomain mechanosensitivity and re-evaluates its (patho)physiological significance in the context of historical data on the macroscopic role of Ca²⁺ in acute force adaptation and mechanically-induced arrhythmias. We distinguish between preload and afterload mediated effects on local Ca²⁺ release, and highlight differences between atrial and ventricular myocytes. Finally, we provide an outlook for further investigation in chronic models of abnormal mechanics (eg post-myocardial infarction, atrial fibrillation), to identify the clinical significance of disturbed Ca²⁺ mechanosensitivity for arrhythmogenesis.

Docetaxel-loaded PLGA and PLGA-PEG nanoparticles for intravenous application: pharmacokinetics and biodistribution profile

Docetaxel is a highly potent anticancer agent being used in a wide spectrum of cancer types. There are important matters of concern regarding the drug’s pharmacokinetics related to the conventional formulation. Poly(lactide-co-glycolide) (PLGA) is a biocompatible/biodegradable polymer with variable physicochemical characteristics, and its application in human has been approved by the United States Food and Drug Administration. PLGA gives polymeric nanoparticles with unique drug delivery characteristics. The application of PLGA nanoparticles (NPs) as intravenous (IV) sustained-release delivery vehicles for docetaxel can favorably modify pharmacokinetics, biofate, and pharmacotherapy of the drug in cancer patients. Surface modification of PLGA NPs with poly(ethylene glycol) (PEG) can further enhance NPs’ long-circulating properties. Herein, an optimized fabrication approach has been used for the preparation of PLGA and PLGA–PEG NPs loaded with docetaxel for IV application. Both types of NP formulations demonstrated in vitro characteristics that were considered suitable for IV administration (with long-circulating sustained-release purposes). NP formulations were IV administered to an animal model, and docetaxel’s pharmacokinetic and biodistribution profiles were determined and compared between study groups. PLGA and PEGylated PLGA NPs were able to modify the pharmacokinetics and biodistribution of docetaxel. Accordingly, the mode of changes made to pharmacokinetics and biodistribution of docetaxel is attributed to the size and surface properties of NPs. NPs contributed to increased blood residence time of docetaxel fulfilling their role as long-circulating sustained-release drug delivery systems. Surface modification of NPs contributed to more pronounced docetaxel blood concentration, which confirms the role of PEG in conferring long-circulation properties to NPs.

Oxidative stress decreases microtubule growth and stability in ventricular myocytes

Microtubules (MTs) have many roles in ventricular myocytes, including structural stability, morphological integrity, and protein trafficking. However, despite their functional importance, dynamic MTs had never been visualized in living adult myocytes. Using adeno-associated viral vectors expressing the MT-associated protein plus end binding protein 3 (EB3) tagged with EGFP, we were able to perform live imaging and thus capture and quantify MT dynamics in ventricular myocytes in real time under physiological conditions. Super-resolution nanoscopy revealed that EB1 associated in puncta along the length of MTs in ventricular myocytes. The vast (~80%) majority of MTs grew perpendicular to T-tubules at a rate of 0.06μm∗s(-1) and growth was preferentially (82%) confined to a single sarcomere. Microtubule catastrophe rate was lower near the Z-line than M-line. Hydrogen peroxide increased the rate of catastrophe of MTs ~7-fold, suggesting that oxidative stress destabilizes these structures in ventricular myocytes. We also quantified MT dynamics after myocardial infarction (MI), a pathological condition associated with increased production of reactive oxygen species (ROS). Our data indicate that the catastrophe rate of MTs increases following MI. This contributed to decreased transient outward K(+) currents by decreasing the surface expression of Kv4.2 and Kv4.3 channels after MI. On the basis of these data, we conclude that, under physiological conditions, MT growth is directionally biased and that increased ROS production during MI disrupts MT dynamics, decreasing K(+) channel trafficking.

Dystrobrevin increases dystrophin's binding to the dystrophin-glycoprotein complex and provides protection during cardiac stress

Duchenne muscular dystrophy is a fatal progressive disease of both cardiac and skeletal muscle resulting from the mutations in the DMD gene and loss of the protein dystrophin. Alpha-dystrobrevin (α-DB) tightly associates with dystrophin but the significance of this interaction within cardiac myocytes is poorly understood. In the current study, the functional role of α-DB in cardiomyocytes and its implications for dystrophin function are examined. Cardiac stress testing demonstrated significant heart disease in α-DB null (adbn(-/-)) mice, which displayed mortality and lesion sizes that were equivalent to those seen in dystrophin-deficient mdx mice. Despite normal expression and subcellular localization of dystrophin in the adbn(-/-) heart, there is a significant decrease in the strength of dystrophin's interaction with the membrane-bound dystrophin-associated glycoprotein complex (DGC). A similar weakening of the dystrophin-membrane interface was observed in mice lacking the sarcoglycan complex. Cardiomyocytes from adbn(-/-) mice were smaller and responded less to adrenergic receptor induced hypertrophy. The basal decrease in size could not be attributed to aberrant Akt activation. In addition, the organization of the microtubule network was significantly altered in adbn(-/-) cardiac myocytes, while the total expression of tubulin was unchanged in adbn(-/-) hearts. These studies demonstrate that α-DB is a multifunctional protein that increases dystrophin's binding to the dystrophin-glycoprotein complex, and is critical for the full functionality of dystrophin.

Microtubule-mediated defects in junctophilin-2 trafficking contribute to myocyte transverse-tubule remodeling and Ca2+ handling dysfunction in heart failure

BACKGROUND

Cardiac dysfunction in failing hearts of human patients and animal models is associated with both microtubule densification and transverse-tubule (T-tubule) remodeling. Our objective was to investigate whether microtubule densification contributes to T-tubule remodeling and excitation-contraction coupling dysfunction in heart disease.

METHODS AND RESULTS

In a mouse model of pressure overload-induced cardiomyopathy by transaortic banding, colchicine, a microtubule depolymerizer, significantly ameliorated T-tubule remodeling and cardiac dysfunction. In cultured cardiomyocytes, microtubule depolymerization with nocodazole or colchicine profoundly attenuated T-tubule impairment, whereas microtubule polymerization/stabilization with taxol accelerated T-tubule remodeling. In situ immunofluorescence of heart tissue sections demonstrated significant disorganization of junctophilin-2 (JP2), a protein that bridges the T-tubule and sarcoplasmic reticulum membranes, in transaortic banded hearts as well as in human failing hearts, whereas colchicine injection significantly preserved the distribution of JP2 in transaortic banded hearts. In isolated mouse cardiomyocytes, prolonged culture or treatment with taxol resulted in pronounced redistribution of JP2 from T-tubules to the peripheral plasma membrane, without changing total JP2 expression. Nocodazole treatment antagonized JP2 redistribution. Moreover, overexpression of a dominant-negative mutant of kinesin 1, a microtubule motor protein responsible for anterograde trafficking of proteins, protected against JP2 redistribution and T-tubule remodeling in culture. Finally, nocodazole treatment improved Ca(2+) handling in cultured myocytes by increasing the amplitude of Ca(2+) transients and reducing the frequency of Ca(2+) sparks.

CONCLUSION

Our data identify a mechanistic link between microtubule densification and T-tubule remodeling and reveal microtubule-mediated JP2 redistribution as a novel mechanism for T-tubule disruption, loss of excitation-contraction coupling, and heart failure.

Cytoskeletal role in protection of the failing heart by β-adrenergic blockade

Formation of a dense microtubule network that impedes cardiac contraction and intracellular transport occurs in severe pressure overload hypertrophy. This process is highly dynamic, since microtubule depolymerization causes striking improvement in contractile function. A molecular etiology for this cytoskeletal alteration has been defined in terms of type 1 and type 2A phosphatase-dependent site-specific dephosphorylation of the predominant myocardial microtubule-associated protein (MAP)4, which then decorates and stabilizes microtubules. This persistent phosphatase activation is dependent upon ongoing upstream activity of p21-activated kinase-1, or Pak1. Because cardiac β-adrenergic activity is markedly and continuously increased in decompensated hypertrophy, and because β-adrenergic activation of cardiac Pak1 and phosphatases has been demonstrated, we asked here whether the highly maladaptive cardiac microtubule phenotype seen in pathological hypertrophy is based on β-adrenergic overdrive and thus could be reversed by β-adrenergic blockade. The data in this study, which were designed to answer this question, show that such is the case; that is, β(1)- (but not β(2)-) adrenergic input activates this pathway, which consists of Pak1 activation, increased phosphatase activity, MAP4 dephosphorylation, and thus the stabilization of a dense microtubule network. These data were gathered in a feline model of severe right ventricular (RV) pressure overload hypertrophy in response to tight pulmonary artery banding (PAB) in which a stable, twofold increase in RV mass is reached by 2 wk after pressure overloading. After 2 wk of hypertrophy induction, these PAB cats during the following 2 wk either had no further treatment or had β-adrenergic blockade. The pathological microtubule phenotype and the severe RV cellular contractile dysfunction otherwise seen in this model of RV hypertrophy (PAB No Treatment) was reversed in the treated (PAB β-Blockade) cats. Thus these data provide both a specific etiology and a specific remedy for the abnormal microtubule network found in some forms of pathological cardiac hypertrophy.

High sensitivity of the sheep pulmonary vein antrum to acetylcholine stimulation

Isolation of the pulmonary vein antrum can terminate atrial fibrillation, but the rationale has not been elucidated. In the present study, we show that sheep atrial effective refractory period (ERP) was heterogeneously shortened by acetylcholine administration. After perfusion with 15 μM acetylcholine, the shortest ERP occurred in the pulmonary vein antrum, which was recorded with the standard intracellular microelectrode technique (the ERP results in the pulmonary vein antrum, left atrial posterior wall, roof, free wall and appendage, and right atrial free wall were 52.0 ± 1.6, 75.1 ± 2.0, 77.2 ± 1.7, 85.6 ± 1.7, 64.3 ± 2.1, and 90.5 ± 1.3 ms, respectively; P < 0.05). Immunofluorescent staining revealed that muscarinic type 2 receptors (M2R) were also distributed heterogeneously in the atrial myocardium, with the highest density in the antrum (the relative fluorescent intensity results of the M2R in the pulmonary vein antrum, left atrial posterior wall, roof, free wall and appendage, and right atrial free wall were 62.64 ± 2.56, 53.12 ± 2.76, 51.83 ± 2.45, 47.90 ± 2.33, 55.27 ± 2.08, and 45.53 ± 2.02, respectively; P < 0.05), which was in accordance with the heterogeneity of ERP distribution. Thus the pulmonary vein antrum is a unique electrophysiological region with high sensitivity to acetylcholine, and its intensive response to acetylcholine is most likely associated with the dense M2R distribution of this region. Such an acetylcholine-induced ERP heterogeneity is possibly a substrate for atrial fibrillation and hence one of the potential electrophysiological bases for the isolation therapy.

A direct test of the hypothesis that increased microtubule network density contributes to contractile dysfunction of the hypertrophied heart

Contractile dysfunction in pressure overload-hypertrophied myocardium has been attributed in part to the increased density of a stabilized cardiocyte microtubule network. The present study, the first to employ wild-type and mutant tubulin transgenes in a living animal, directly addresses this microtubule hypothesis by defining the contractile mechanics of the normal and hypertrophied left ventricle (LV) and its constituent cardiocytes from transgenic mice having cardiac-restricted replacement of native β4-tubulin with β1-tubulin mutants that had been selected for their effects on microtubule stability and thus microtubule network density. In each case, the replacement of cardiac β4-tubulin with mutant hemagglutinin-tagged β1-tubulin was well tolerated in vivo. When LVs in intact mice and cardiocytes from these same LVs were examined in terms of contractile mechanics, baseline function was reduced in mice with genetically hyperstabilized microtubules, and hypertrophy-related contractile dysfunction was exacerbated. However, in mice with genetically hypostabilized cardiac microtubules, hypertrophy-related contractile dysfunction was ameliorated. Thus, in direct support of the microtubule hypothesis, we show here that cardiocyte microtubule network density, as an isolated variable, is inversely related to contractile function in vivo and in vitro, and microtubule instability rescues most of the contractile dysfunction seen in pressure overload-hypertrophied myocardium.

Effects of chronic therapy with cardiac contractility modulation electrical signals on cytoskeletal proteins and matrix metalloproteinases in dogs with heart failure

OBJECTIVES

Therapy with cardiac contractility modulation (CCM) electrical signals delivered to left ventricular (LV) muscle during the absolute refractory period improves LV systolic and diastolic function in dogs with heart failure (HF). This study examined the effects of CCM therapy on mRNA and protein expression of cytoskeletal proteins, matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) in the LV myocardium of dogs with HF.

METHODS

HF was produced in 14 dogs by coronary microembolizations. Dogs were randomized to 3 months of CCM therapy (n = 7) or to sham-operated controls (n = 7). LV tissue from 6 normal (NL) dogs was used for comparison. mRNA expression was measured using reverse-transcriptase polymerase chain reaction and protein expression using Western blots.

RESULTS

Compared with NL dogs, controls showed upregulation of mRNA and protein expression of the cytoskeletal proteins tubulin and fibronectin and MMP-1, MMP-2 and MMP-9, and downregulation of the cytoskeletal protein titin. Normalized expression of all these genes and proteins was seen after CCM therapy. No differences in expression of TIMP-1 and TIMP-2 were observed among groups.

CONCLUSIONS

CCM therapy normalizes expression of key cytoskeletal proteins and MMPs and may partly explain the improvement in LV function seen in HF following CCM therapy.

Concurrent opposite effects of trichostatin A, an inhibitor of histone deacetylases, on expression of alpha-MHC and cardiac tubulins: implication for gain in cardiac muscle contractility

Histone deacetylases (HDACs) are a family of enzymes that catalyze the removal of acetyl groups from core histones, resulting in change of chromatin structure and gene transcription activity. In the heart, HDACs are targets of hypertrophic signaling, and their nonspecific inhibition by trichostatin A (TSA) attenuates hypertrophy of cultured cardiac myocytes. In this study, we examined the effect of TSA on two major determinants of cardiac contractility: alpha-myosin heavy chain (MHC) expression and microtubular composition and organization. TSA upregulated the expression of alpha-MHC in cultured cardiac myocytes, as well as in an in vivo model of hypothyroid rats. Studies designed to delineate mechanisms of alpha-MHC induction by TSA revealed an obligatory role of early growth response factor-1 on activation of the alpha-MHC promoter. Concurrently, TSA downregulated the expression of alpha- and beta-tubulins and prevented the induction of tubulins by a hypertrophy agonist, ANG II. The ANG II-mediated increased proportion of alpha- and beta-tubulins associated with polymerized microtubules was also markedly reduced after treatment of cells by TSA. Results obtained from immunofluorescent microscopy indicated that TSA had no noticeable effect on the organization of cardiac microtubules in control cells, whereas it prevented the ANG II-induced dense parallel linear arrays of microtubules to a profile similar to that of controls. Together, these results demonstrate that inhibition of HDACs by TSA regulates the cardiac alpha-MHC and tubulins in a manner predictive of improved cardiac contractile function. These studies improve our understanding of the role of HDACs on cardiac hypertrophy with implications in development of new therapeutic agents for treatment of cardiac abnormalities.

Cytoskeletal structure and recovery in single human cardiac myocytes

BACKGROUND

Mechanical support of the failing human heart with a left ventricular assist device (LVAD) normalizes many components of myocyte structure and function. We hypothesized that recovery of the cytoskeleton, a major site of mechanotransduction in cardiac myocytes, is crucial for sustained improvement of myocardial function. We therefore measured the effects of LVAD support on 4 cytoskeletal proteins in single human heart cells.

METHODS

Myocytes were isolated from non-failing (NF), hypertrophied (H), failing (F) and LVAD-supported failing (L) human hearts. Protein quantitation was performed using Western blot analysis and cellular distribution was determined by immunolabeling and confocal microscopy.

RESULTS

alpha-actinin did not differ in cells from H or F as compared with NF, and L had no effect. Vinculin was not quantitatively different in H or F vs NF, but localization at the intercalated disks was significantly decreased in H and absent in F, and this pattern was consistently reversed in L. Desmin protein was significantly increased in F vs NF, both in quantity and distribution, and these increases were reversed in L. beta-tubulin was increasingly polymerized in H and F, and the hyperpolymerization was reversed in L.

CONCLUSIONS

On the level of the single cardiomyocyte, major proteins of the cytoskeleton are significantly altered in hypertrophied and failing human hearts. These alterations are reversed by mechanical unloading with an LVAD, suggesting that the cytoskeleton is not the limiting factor in determining full cardiac recovery.

Effects of prenatal glucocorticoid exposure on cardiac calreticulin and calsequestrin protein expression during early development and in adulthood

Overexpression of the conserved Ca(2+)-binding proteins calreticulin and calsequestrin impairs cardiac function, leading to premature death. Calreticulin is vital for embryonic development, but also impairs glucocorticoid action. Glucocorticoid overexposure during late fetal life causes intra-uterine growth retardation and programmed hypertension in adulthood. To determine whether intra-uterine growth retardation or programmed hypertension was associated with altered calreticulin or calsequestrin expression, effects of prenatal glucocorticoid overexposure (maternal dexamethasone treatment on days 15-21 of pregnancy) were examined during fetal life and postnatal development until adulthood (24 weeks). Dexamethasone (100 or 200 microg/kg of maternal body weight) was administered via osmotic pump. Calreticulin was detected as a 55 kDa band and calsequestrin as 55 and 63 kDa bands in 21 day fetal hearts. Only the 55 kDa calsequestrin band was detected postnatally. Prenatal glucocorticoid overexposure at the higher dose decreased calreticulin protein expression (26%; P <0.05) but increased calsequestrin protein expression, both 55 and 63 kDa bands, by 87% ( P <0.01) and 78% ( P <0.01); only the 55 kDa calsequestrin band was increased at the lower dose (66%; P <0.05). Offspring of dams treated at the lower dexamethasone dose were studied further. In control offspring, cardiac calreticulin protein expression declined between 2 and 3 weeks of age, and remained suppressed until adulthood. Cardiac calsequestrin protein expression increased 2-fold between fetal day 21 and postnatal day 1 and continued to increase until adulthood, at which time it was 3.4-fold higher ( P <0.001). Prenatal dexamethasone exposure minimally affected postnatal calsequestrin protein expression, but the postnatal decline in calreticulin protein expression was abrogated and calreticulin protein expression in adulthood was 2.2-fold increased ( P <0.001) compared with adult controls. In view of the known associations between cardiac calreticulin overexpression and impaired cardiac function, targeted up-regulation of calreticulin may contribute to the increased risk of adult heart disease introduced as a result of prenatal overexposure to glucocorticoids.