Cell contact as an independent factor modulating cardiac myocyte hypertrophy and survival in long-term primary culture

An Efficient and Reproducible Method for the Isolation and Culture of Primary Cardiomyocytes from Adult Zebrafish

Zebrafish is a popular animal model in regeneration studies due to their ability to regenerate the heart. Primary cardiomyocytes could be an alternative tool for studying the intrinsic mechanisms of cardiovascular disease in vitro. Thus, our objective is to develop an efficient protocol to isolate primary cardiomyocytes from zebrafish hearts. Low concentration of digestive enzyme (0.5 mg/mL collagenase type II) was utilized in our protocol to obtain single-cell suspension. The ventricles were fragmented, mechanically pipetted, and constantly shaken to ensure adequate contact between the tissues and the enzyme. Preplating the cell suspension onto culture plates for 2 h helped remove cardiac fibroblasts. The purity of isolated cells was validated by flow cytometry analysis of transgenic zebrafish with cardiomyocyte-specific expression of enhanced green fluorescent protein (EGFP) or endothelial cell-specific expression of mCherry. Quantitative real-time PCR analysis revealed a high level of the purity, with cardiac fibroblasts, endothelial cells, and epicardial cell markers scarcely detected in the purified cells. Altogether, this study established a reproducible protocol for isolating primary cardiomyocytes with high purity and activity from adult zebrafish hearts that can be cultured in vitro for up to 4 weeks. This protocol provides a valuable tool for studying the intrinsic mechanisms of cardiovascular disease in vitro using primary cardiomyocytes.

Electroactive biomimetic collagen-silver nanowire composite scaffolds

Electroactive biomaterials are widely explored as bioelectrodes and as scaffolds for neural and cardiac regeneration. Most electrodes and conductive scaffolds for tissue regeneration are based on synthetic materials that have limited biocompatibility and often display large discrepancies in mechanical properties with the surrounding tissue causing problems during tissue integration and regeneration. This work shows the development of a biomimetic nanocomposite material prepared from self-assembled collagen fibrils and silver nanowires (AgNW). Despite consisting of mostly type I collagen fibrils, the homogeneously embedded AgNWs provide these materials with a charge storage capacity of about 2.3 mC cm(-2) and a charge injection capacity of 0.3 mC cm(-2), which is on par with bioelectrodes used in the clinic. The mechanical properties of the materials are similar to soft tissues with a dynamic elastic modulus within the lower kPa range. The nanocomposites also support proliferation of embryonic cardiomyocytes while inhibiting the growth of both Gram-negative Escherichia coli and Gram-positive Staphylococcus epidermidis. The developed collagen/AgNW composites thus represent a highly attractive bioelectrode and scaffold material for a wide range of biomedical applications.

Effect of serial cell passaging in the retention of fiber type and mitochondrial content in primary human myotubes

OBJECTIVE

The purpose of the study was to determine the effects of passaging on retention of donor phenotypic characteristics in primary human myotubes.

METHODS

Primary muscle cultures and serial passaged myotubes from physically active, sedentary lean, and individuals with type 2 diabetes were established. Maximal ATP synthesis capacity (ATPmax) and resting ATP flux (ATPase) in vivo were measured by (31) P magnetic resonance spectroscopy, type-I fibers and intramyocelluar lipid (IMCL) in vastus lateralis tissue were determined using immunohistochemistry techniques, and oxidative phosphorylation complexes (OXPHOS) were measured by Western immunoblotting. Similar in vitro measures for lipid and type-I fibers were made in myotubes, along with mitochondrial content measured by MitoTracker.

RESULTS

Passage 4 and 5 measures for myotubes correlated positively with in vivo measurements for percent type-I fibers (P4: R(2)  = 0.39, p = 0.02; P5: R(2)  = 0.48, p = 0.01), ATPmax (P4: R(2)  = 0.30, p = 0.03; P5: R(2)  = 0.22, p = 0.05), and OXPHOS (P4: R(2)  = 0.44, p = 0.04; P5: R(2)  = 0.59, p = 0.006). No correlations were observed for IMCL. However, passage 4 measures for myotubes correlated with passage 5 measures for percent type-I fibers (R(2)  = 0.49, p = 0.01), IMCL (R(2)  = 0.80, p < 0.001), and mitochondrial content (R(2)  = 0.26, p = 0.03).

CONCLUSIONS

Myotubes through the first two passages following immunopurification (referred to as passage 4 and 5) reflect the mitochondrial and type-I fiber content in vivo phenotype of the donor.

Gene transfection to spheroid culture system on micropatterned culture plate by polyplex nanomicelle: a novel platform of genetically-modified cell transplantation

Three-dimensional (3D) cellular spheroids have attracted much attention as a transplantation procedure because the increased cell-to-cell interaction in spheroids enhances cell survival and its functions after the transplantation into the body. Furthermore, the potency of spheroidal cells may be further improved by introducing transgenes to augment cellular functions as well as enhance the paracrine effects by secreting key proteins involved in the essential cellular signaling cascades. In this study, we organized a new platform for genetically-modified cell transplantation by combining a microfabricated culture system for 3D spheroid formation with a newly developed non-viral transfection system, polyplex nanomicelle. After transfection of Gaussia luciferase using the nanomicelle, the prolonged luciferase expression was obtained for more than a month with continuous albumin secretion from the hepatocyte spheroids to the level comparable with control spheroids receiving no transfection. In contrast, by the transfection using FuGENE HD, a commercially available lipid-based reagent, the luciferase expression was obtained, yet the albumin secretion was significantly decreased with disintegration of the spheroid architecture. To assess the feasibility of the hepatocyte spheroids for in vivo transplantation, the spheroids were recovered by the use of micropatterned culture plate functionalized with thermosensitive polymer and dispersed into Matrigel(TM) Matrix. The luciferase expression as well as albumin secretion was maintained for more than a month from the spheroids in the Matrix. Thus, the combination of spheroid cell culture on micropatterned plates with gene introduction using polyplex nanomicelle is a promising platform for genetically-modified cell transplantation to achieve sustained transgene expression with maintaining innate cell functions.

Characterization of functional capacity of adult ventricular myocytes in long-term culture

BACKGROUND

Functional properties of freshly isolated adult ventricular myocytes (AVMs) or those of AVMs during first few weeks in culture were well described. However, the functional capacity of these AVMs such as regenerative potential remains unknown, in part, due to the short lifespan of AVMs in culture. This study modified culture conditions that extended the lifespan of AVMs, isolated from adult rat hearts, longer than 6 months.

METHODS

Temporal changes in the morphology of individual AVMs, cell-cell interaction, formation of myofibers, self-repair capacity after injury, expression of senescence biomarkers, and contractile function of AVMs over 5 weeks (defined as long-term culture) were chronologically characterized and quantified with live-cell video and fluorescence microscopy, and immunocytochemistry.

RESULTS

Cell growth in size reached a plateau after 4 weeks in culture concomitantly with continuous increase in structural remodeling in long-term culture. Dynamic remodeling of AVMs promoted self-contact of filopodia and cell-cell contact where these contained abundant myofilaments, connexin 43 proteins, and high density and high integrity of mitochondria. Such high capacity also enabled self-repair of AVMs after injury, cytokinesis, and formation of myofibers. AVMs in long-term culture displayed spontaneous contraction and importantly were responsive to electrical stimulation. Moreover, AVMs expressed senescence-associated β-galactosidase, p16, and stress-associated atrial natriuretic peptides that resulted likely from cellular modeling.

CONCLUSIONS

Prolonged longevity of AVMs in culture with characteristics of high functional capacity of organelle regeneration and contraction makes them invaluable for further longitudinal mechanistic studies in cardiac (patho)physiology (e.g., hypertrophy and aging), single-cell analysis (e.g., function of hetero-phenotypes) and drug discovery.

Structural and functional plasticity in long-term cultures of adult ventricular myocytes

Cultured heart cells have long been valuable for characterizing biological mechanism and disease pathogenesis. However, these preparations have limitations, relating to immaturity in key properties like excitation-contraction coupling and β-adrenergic stimulation. Progressive attenuation of the latter is intimately related to pathogenesis and therapy in heart failure. Highly valuable would be a long-term culture system that emulates the structural and functional changes that accompany disease and development, while concurrently permitting ready access to underlying molecular events. Accordingly, we here produce functional monolayers of adult guinea-pig ventricular myocytes (aGPVMs) that can be maintained in long-term culture for several weeks. At baseline, these monolayers exhibit considerable myofibrillar organization and a significant contribution of sarcoplasmic reticular (SR) Ca(2+) release to global Ca(2+) transients. In terms of electrical signaling, these monolayers support propagated electrical activity and manifest monophasic restitution of action-potential duration and conduction velocity. Intriguingly, β-adrenergic stimulation increases chronotropy but not inotropy, indicating selective maintenance of β-adrenergic signaling. It is interesting that this overall phenotypic profile is not fixed, but can be readily enhanced by chronic electrical stimulation of cultures. This simple environmental cue significantly enhances myofibrillar organization as well as β-adrenergic sensitivity. In particular, the chronotropic response increases, and an inotropic effect now emerges, mimicking a reversal of the progression seen in heart failure. Thus, these aGPVM monolayer cultures offer a valuable platform for clarifying long elusive features of β-adrenergic signaling and its plasticity.

Gene Mutations Resulting in the Development of ARVC/D Could Affect Cells of the Cardiac Conduction System

In contrast to epithelial cells, cardiomyocytes are connected by complex hybrid-type adhering junctions, termed composite junctions (areae compositae). Composite junctions are found to be composed of typical desmosomal as well as adherens junction proteins. Therefore, in adult mammalian cardiomyocytes desmosomal proteins are not restricted to the relatively small desmosomes but are indirectly involved in anchoring the myofibrillar actin filaments. Subsequent investigations revealed that the formation of composite junctions is a rather late event during mammalian heart development and vertebrate heart evolution. Nascent, more round shaped cardiomyocytes of early developmental stages are connected by desmosomes and separate adherens junctions quite similar to cells of epithelial origin. During progression of development both types of adhering junctions seem to gradually fuse at the two poles of the mature mammalian cardiomyocytes to establish the hybrid-type composite junctions. Recently, we demonstrated that the specialized cardiomyocytes of the cardiac conduction system exhibit high amounts of desmosomes, not fully established composite junctions and adherens junctions. This underlines the fact that cells of the cardiac conduction system are known to resemble cardiomyocytes in their nascent state and do not undergo working myocardial differentiation. However, the astonishing high amount of desmosomal protein containing adhering junctions connecting, e.g., Purkinje fibers raises the possibility that pacemaker and conductive tissue may be affected by desmosomal gene mutations in ARVC/D patients.

Modulation of alignment, elongation and contraction of cardiomyocytes through a combination of nanotopography and rigidity of substrates

The topographic and mechanical characteristics of engineered tissue constructs, simulating native tissues, should benefit tissue engineering. Previous studies reported that surface topography and substrate rigidity provide biomechanical cues to modulate cellular responses such as alignment, migration and differentiation. To fully address this issue, the present study aimed to examine the influence of nanogrooved substrates with different stiffnesses on the responses of rat cardiomyocytes. Nanogrooved substrates (450nm in groove/ridge width; 100 or 350nm in depth) made of polystyrene and polyurethane were prepared by imprinting from polydimethylsiloxane molds. The morphology and orientation of cardiomyocytes attached to the substrates were found to be influenced mainly by the nanogrooved structures, while the contractile function of the cells was regulated by the coupled effect of surface topography and substrate stiffness. The distribution of intracellular structural proteins such as vinculin and F-actin showed that the surface topography and substrate stiffness regulated the organization of the actin cytoskeleton and focal adhesion complexes, and consequently the contractile behavior of the cardiomyocytes. The beating rates of the cultured cardiomyocytes were dependent on both the surface topography and the substrate stiffness. The study provides insights into the interaction between cardiomyocytes and biomaterials, and benefits cardiac tissue engineering.

Methods in cardiomyocyte isolation, culture, and gene transfer

Since techniques for cardiomyocyte isolation were first developed 35 years ago, experiments on single myocytes have yielded great insight into their cellular and sub-cellular physiology. These studies have employed a broad range of techniques including electrophysiology, calcium imaging, cell mechanics, immunohistochemistry and protein biochemistry. More recently, techniques for cardiomyocyte culture have gained additional importance with the advent of gene transfer technology. While such studies require a high quality cardiomyocyte population, successful cell isolation and maintenance during culture remain challenging. In this review, we describe methods for the isolation of adult and neonatal ventricular myocytes from rat and mouse heart. This discussion outlines general principles for the beginner, but also provides detailed specific protocols and advice for common caveats. We additionally review methods for short-term myocyte culture, with particular attention given to the importance of substrate and media selection, and describe time-dependent alterations in myocyte physiology that should be anticipated. Gene transfer techniques for neonatal and adult cardiomyocytes are also reviewed, including methods for transfection (liposome, electroporation) and viral-based gene delivery.

Mechanotransduction: the role of mechanical stress, myocyte shape, and cytoskeletal architecture on cardiac function

Mechanotransduction refers to the conversion of mechanical forces into biochemical or electrical signals that initiate structural and functional remodeling in cells and tissues. The heart is a kinetic organ whose form changes considerably during development and disease, requiring cardiac myocytes to be mechanically durable and capable of fusing a variety of environmental signals on different time scales. During physiological growth, myocytes adaptively remodel to mechanical loads. Pathological stimuli can induce maladaptive remodeling. In both of these conditions, the cytoskeleton plays a pivotal role in both sensing mechanical stress and mediating structural remodeling and functional responses within the myocyte.

Evidence that apoptotic signalling in hypertrophic cardiomyocytes is determined by mitochondrial pathways involving protein kinase Cδ

1. Cardiomyocyte apoptosis plays an important role in the transition from cardiac hypertrophy to heart failure. Hyper-trophic cardiomyocytes show an increased susceptibility to apoptotic stimuli, but the mechanisms remain unclear. 2. We hypothesized that activated protein kinase Cδ (PKCδ) associated with cardiomyocyte hypertrophy could move from the cytoplasm to mitochondria, and subsequently trigger the apoptotic signalling pathway. 3. Hypertrophy was induced in cultured neonatal rat cardiomyocytes using endothelin-1 (ET-1), insulin-like growth factor-1 (IGF-1), thyroid hormone (T(3) ) or angiotensin-II (AngII). AngII at high concentrations (1 and 10 nmol/L) also induced apoptosis. Hypertrophic cells were then treated with AngII with or without specific inhibitors of the angiotensin receptors AT(1) and AT(2) (losartan and PD123319, respectively), endothelin receptor A (BQ-123) and PKCδ (rottlerin). ET-1 plus AngII had a threefold and significant increase in apoptosis in the hypertrophic cultures compared with AngII alone. In association with the increase in apoptosis, this treatment also promoted mitochondrial translocation of PKCδ, and increased expression of cleaved caspase 9 and activity of caspase 3. All of these increases were modulated by concurrent use of the PKCδ inhibitor, rottlerin. 4. The results suggest that apoptotic signalling in hypertrophic cardiomyocytes is determined by mitochondrial pathways involving PKCδ.

Electrical signals affect the cardiomyocyte transcriptome independently of contraction

Cardiomyocytes in vivo are continuously subjected to electrical signals that evoke contractions and instigate drastic changes in the cells' morphology and function. Studies on how electrical stimulation affects the cardiac transcriptome have remained limited to a small number of heart-specific genes. Furthermore, these studies have ignored the interplay between the electrical excitation and the subsequent contractions. We carried out a genomewide assessment of the effects of electrical signaling on gene expression, while distinguishing between the effects deriving from the electrical pulses themselves and the effects instigated by the evoked contractions. Changes in gene expression in primary cultures of neonatal ventricular cardiomyocytes from Lewis Rattus norvegicus were investigated with microarrays and RT-quantitative PCR (QPCR). A series of experiments was included in which the culture medium was supplemented with the contraction inhibitor blebbistatin to allow for electrical stimulation in the absence of contraction. Electrical stimulation was shown to directly enhance calcium handling and induce cardiomyocyte differentiation by arresting cell division and activating key cardiac transcription factors as well as additional differentiation mechanisms such as wnt signaling. Several genes involved in metabolism were also directly activated by electrical stimulation. Furthermore, our data suggest that contraction exerts negative feedback on the transcription of various genes. Together, these observations indicate that intercellular electric currents between adjacent cardiomyocytes have an important role in cardiomyocyte development. They act at least partially through a pulse-specific gene expression program that is activated independently from the evoked contractions.

Breviscapine ameliorates hypertrophy of cardiomyocytes induced by high glucose in diabetic rats via the PKC signaling pathway

AIM

To investigate the influence of breviscapine on high glucose-induced hypertrophy of cardiomyocytes and the relevant mechanism in vitro and in vivo.

METHODS

Cultured neonatal cardiomyocytes were divided into i) control; ii) high glucose concentrations; iii) high glucose+PKC inhibitor Ro-31-8220; iv) high glucose+breviscapine; or v) high glucose+NF-kappaB inhibitor BAY11-7082. Cellular contraction frequency and volumes were measured; the expression of protein kinase C (PKC), NF-kappaB, TNF-alpha, and c-fos were assessed by Western blot or reverse transcription-polymerase chain reaction (RT-PCR). Diabetic rats were induced by a single intraperitoneal injection of streptozotocin, and randomly divided into i) control rats; ii) diabetic rats; or iii) diabetic rats administered with breviscapine (10 or 25 mg x kg(-1) x d(-1)). After treatment with breviscapine for six weeks, the echocardiographic parameters were measured. All rats were then sacrificed and heart tissue was obtained for microscopy. The expression patterns of PKC, NF-kappaB, TNF-alpha, and c-fos were measured by Western blot or RT-PCR.

RESULTS

Cardiomyocytes cultured in a high concentration of glucose showed an increased pulsatile frequency and cellular volume, as well as a higher expression of PKC, NF-kappaB, TNF-alpha, and c-fos compared with the control group. Breviscapine could partly prevent these changes. Diabetic rats showed relative cardiac hypertrophy and a higher expression of PKC, NF-kappaB, TNF-alpha, and c-fos; treatment with breviscapine could ameliorate these changes in diabetic cardiomyopathy.

CONCLUSION

Breviscapine prevented cardiac hypertrophy in diabetic rats by inhibiting the expression of PKC, which may have a protective effect in the pathogenesis of diabetic cardiomyopathy via the PKC/NF-kappaB/c-fos signal transduction pathway.

Growth and electrophysiological properties of rat embryonic cardiomyocytes on hydroxyl- and carboxyl-modified surfaces

Biodegradable scaffolds such as poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA) or poly(glycolic acid) (PGA) are commonly used materials in tissue engineering. The chemical composition of these scaffolds changes during degradation which provides a differential environment for the seeded cells. In this study we have developed a simple and relatively high-throughput method in order to test the physiological effects of this varying chemical environment on rat embryonic cardiac myocytes. In order to model the different degradation stages of the scaffold, glass coverslips were functionalized with 11-mercaptoundecanoic acid (MUA) and 11-mercapto-1-undecanol (MUL) as carboxyl- and hydroxyl-groups presenting surfaces, and with trimethoxysilylpropyldiethylenetriamine (DETA) and (3-aminopropyl)triethoxysilane (APTES) as controls. Embryonic cardiac myocytes formed beating islands on all tested surfaces, but the number of attached cells and beating patches was significantly lower on MUL compared to any of the other functionalized surfaces. Moreover, whole-cell patch-clamp experiments showed that the average length of action potentials generated by the beating-cardiac myocytes were significantly longer on MUL compared to the other surfaces. Our results, using our simple test system, are in basic agreement with earlier observations that utilized a complex 3D biodegradable scaffold. Thus, surface functionalization with self-assembled monolayers combined with histological/physiological testing could be a relatively high throughput method for biocompatibility studies and for the optimization of the material/tissue interface in tissue engineering.

The signal transduction pathway of PKC/NF-kappa B/c-fos may be involved in the influence of high glucose on the cardiomyocytes of neonatal rats

Background

High glucose could induce structure and function change in cardiomyocytes, PKC plays a core effect in the onset and progression of diabetic cardiomyopathy, but its underlying downstream signal transduction pathway is still not completely understood.

Objectives

To study the influence of high glucose on the structure, function and signal transduction pathway of PKC (Protein Kinase C)/NF-κB(Nuclear factor-κB)/c-fos in cultured cardiomyocytes.

Methods

Using cultured cardiomyocytes of neonatal Sprague-Dawley rats as a model, groups were divided into: control group (glucose: 5 mmol/L); high glucose group (glucose: 10 mmol/L, 15 mmol/L, 20 mmol/L, 25.5 mmol/L); equimolar mannital group (5 mmol/L glucose + 20.5 mmol/L maninital); high glucose(25.5 mmol/L) add PKC inhibitor (Ro-31-8220, 50 nmol/L); high glucose (25.5 mmol/L) add NF-κB inhibitor (BAY11-7082, 5 μmol/L). The cellular contracting frequency and volumes were measured and the expression of PKC-α, PKC-β2, p-PKC-α, p-PKC-β2, NF-κB, p-NF-κB, TNF-α (tumor necrosis factor-α) and c-fos were measured by western blot or RT-PCR.

Results

Cardiomyocytes cultured in high glucose level, but not iso-osmotic mannital, showed an increased pulsatile frequency and higher cellular volumes consistent with the increased glucose levels, and also higher expression of PKC-α, PKC-β2, p-PKC-α, p-PKC-β2, NF-κB, p-NF-κB, TNF-α and c-fos. The addition of Ro-31-8220 and BAY11-7082 could partly reverse these changes induced by high glucose level.

Conclusion

High glucose significantly increased the pulsatile frequency and cellular volumes of cultured cardiomyocytes via PKC/NF-κB/c-fos pathway, which might lead to diabetic cardiomyopathy.

Inhibition of fibroblast proliferation in cardiac myocyte cultures by surface microtopography

Cardiac myocyte cultures usually require pharmacological intervention to prevent overproliferation of contaminating nonmyocytes. Our aim is to prevent excessive fibroblast cell proliferation without the use of cytostatins. We have produced a silicone surface with 10-microm vertical projections that we term "pegs," to which over 80% of rat neonatal cardiac fibroblasts attach within 48 h after plating. There was a 50% decrease in cell proliferation by 5 days of culture compared with flat membranes (P < 0.001) and a concomitant 60% decrease (P < 0.01) in cyclin D1 protein levels, suggesting a G1/S1 cell cycle arrest due to microtopography. Inhibition of Rho kinase with 5 or 20 microM Y-27632 reduced attachment of fibroblasts to the pegs by over 50% (P < 0.001), suggesting that this signaling pathway plays an important role in the process. Using mobile and immobile 10-microm polystyrene spheres, we show that reactive forces are important for inhibiting fibroblast cell proliferation, because mobile spheres failed to reduce cell proliferation. In primary myocyte cultures, pegs also inhibit fibroblast proliferation in the absence of cytostatins. The ratio of aminopropeptide of collagen protein from fibroblasts to myosin from myocytes was significantly reduced in cultures from pegged surfaces (P < 0.01), suggesting an increase in the proportion of myocytes on the pegged surfaces. Connexin43 protein expression was also increased, suggesting improved myocyte-myocyte interaction in the presence of pegs. We conclude that this microtextured culture system is useful for preventing proliferation of fibroblasts in myocyte cultures and may ultimately be useful for tissue engineering applications in vivo.

Regression of isoproterenol-induced cardiac hypertrophy by Na+/H+ exchanger inhibition

Cardiac hypertrophy is often associated with an increased sympathetic drive, and both in vitro and in vivo studies have demonstrated the development of cardiomyocyte hypertrophy in response to either alpha- or beta-adrenergic stimulation. Because an association between the Na+/H+ exchanger and cellular growth has been proposed, this study aimed to analyze the possible role of the antiporter in isoproterenol-induced cardiac hypertrophy. Isoproterenol alone (5 mg/kg IP once daily) or combined with a selective inhibitor of the Na+/H+ exchanger activity (3 mg x kg(-1) x d(-1) BIIB723) was given to male Wistar rats for 30 days. Sex- and age-matched rats that received 0.9% saline IP daily served as controls. Echocardiographic follow-up showed a 33% increase in left ventricular mass in the isoproterenol-treated group, whereas it did not increase in the isoproterenol+BIIB723-treated group. Heart weight-to-body weight ratio at necropsy was 2.44+/-0.11 in controls and increased to 3.35+/-0.10 (P<0.05) with isoproterenol, an effect that was markedly attenuated by BIIB723 (2.82+/-0.07). Intense cardiomyocyte enlargement and severe subendocardial fibrosis were found in isoproterenol-treated rats, and both effects were attenuated by BIIB723. Myocardial Na+/H+ exchanger activity and protein expression significantly increased in isoproterenol-treated rats compared with the control group (1.45+/-0.11 vs 0.91+/-0.05 arbitrary units, P<0.05). This effect was significantly reduced by BIIB723 (1.17+/-0.02, P<0.05). In conclusion, our results show that Na+/H+ exchanger inhibition prevented the development of isoproterenol-induced hypertrophy and fibrosis, providing strong evidence in favor of a key role played by the antiporter in this model of cardiac hypertrophy.

Optimization of cardiac cell seeding and distribution in 3D porous alginate scaffolds

Cardiac tissue engineering has evolved as a potential therapeutic approach to assist in cardiac regeneration. We have recently shown that tissue-engineered cardiac graft, constructed from cardiomyocytes seeded within an alginate scaffold, is capable of preventing the deterioration in cardiac function after myocardial infarction in rats. The present article addresses cell seeding within porous alginate scaffolds in an attempt to achieve 3D high-density cardiac constructs with a uniform cell distribution. Due to the hydrophilic nature of the alginate scaffold, its >90% porosity and interconnected pore structure, cell seeding onto the scaffold was efficient and short, up to 30 min. Application of a moderate centrifugal force during cell seeding resulted in a uniform cell distribution throughout the alginate scaffolds, consequently enabling the loading of a large number of cells onto the 3D scaffolds. The percent cell yield in the alginate scaffolds ranged between 60-90%, depending on cell density at seeding; it was 90% at seeding densities of up to 1 x 10(8) cells/cm(3) scaffold and decreased to 60% at higher densities. The highly dense cardiac constructs maintained high metabolic activity in culture. Scanning electron microscopy revealed that the cells aggregated within the scaffold pores. Some of the aggregates were contracting spontaneously within the matrix pores. Throughout the culture there was no indication of cardiomyocyte proliferation within the scaffolds, nor was it found in 3D cultures of cardiofibroblasts. This may enable the development of cardiac cocultures, without domination of cardiofibroblasts with time.

Tissue-Specific Patterns of Gap Junctions in Adult Rat Atrial and Ventricular Cardiomyocytes In Vivo and In Vitro

Abstract —To verify the hypothesis that tissue-specific patterns of gap junctions (GJs) are determined by intrinsic factors within myocytes forming different cardiac tissues, we have compared by quantitative transmission electron microscopy (TEM) the structural features of GJs in adult rat atrial myocytes (AMs) and ventricular myocytes (VMs) in vivo with those in developing GJs in cultured AMs and VMs in vitro. Quantitative TEM data revealed a 3-fold increase in the number of developing GJs per intercalated disk in both AMs and VMs from 6 to 15 days in culture. However, at days 12 and 15, the percentage of GJ length per intercalated disk and mean GJ length were 2-fold higher in VMs than in AMs. Measurements of connexin43 GJs by confocal microscopy confirmed TEM data and demonstrated respectively 2- and 4.5-fold greater mean values of GJ length and area in VMs than in AMs. These differences are attributable to the development of large GJs (>3 μm) in VMs, closely resembling those observed in VMs in vivo. Although large GJs in cultured VMs comprised ≈14% of the total number of GJs, their contribution to total GJ length and area constituted >60% and 85%, respectively. In marked contrast, the number of large GJs in AMs both in vitro and in vivo was <1% from the total number of GJs. These data confirm our hypothesis and provide the first evidence that tissue-specific patterns of GJs in AMs and VMs are determined primarily by intrinsic factors within cardiac myocytes and are developmentally regulated.

Endothelin-1 responsiveness of a 1.4 kb phospholamban promoter fragment in rat cardiomyocytes transfected by the gene gun

The transcriptional regulation of an isolated rat phospholamban (PL) promoter fragment in rat cardiomyocytes was analyzed by applying a new method to reach substantially higher transfection efficiencies: gene gun biolistics. The gene gun transfection method was optimized for application to primary cultures of rat neonatal cardiomyocytes. Cells, cultured at different densities (0.75-1.50x10(5)cells/cm(2)) in serum-free medium, were transfected with DNA coated gold particles. A transfection efficiency of up to 10% could be achieved (compared to <1% with other methods) by the gene gun as checked using a RSV- beta-Gal construct. Cardiomyocytes were stimulated by endothelin-1 (ET-1) (10(-8)M) to induce hypertrophy, thereby yielding the characteristic changes in gene expression (upregulation of Atrial Natriuretic Factor (ANF) and downregulation of PL). The basal activity of an ANF promoter fragment (increasing from the lowest to highest density 2.6-fold) and its ET-1 inducibility (only significant upregulation of 2.6-fold, at lowest density) appeared to be dependent on the plating density of the cardiomyocytes. A PL promoter fragment was isolated, sequenced and 1.4 kb was subcloned in a luciferase reporter vector. The basal activity of the PL promoter fragment was not dependent on the plating density. ET-1 did not downregulate the PL promoter, rather a significant upregulation (1.4-fold) was found at the highest plating density. In conclusion, plating density of the cardiomyocytes can influence promoter activity as shown with an ANF promoter fragment. A newly isolated and sequenced rat PL promoter fragment did not direct gene expression as expected on basis of downregulation of the PL gene by ET-1 observed in this model.

Cardiac tissue engineering: cell seeding, cultivation parameters, and tissue construct characterization

Cardiac tissue engineering has been motivated by the need to create functional tissue equivalents for scientific studies and cardiac tissue repair. We previously demonstrated that contractile cardiac cell-polymer constructs can be cultivated using isolated cells, 3-dimensional scaffolds, and bioreactors. In the present work, we examined the effects of (1) cell source (neonatal rat or embryonic chick), (2) initial cell seeding density, (3) cell seeding vessel, and (4) tissue culture vessel on the structure and composition of engineered cardiac muscle. Constructs seeded under well-mixed conditions with rat heart cells at a high initial density ((6-8) x 10(6) cells/polymer scaffold) maintained structural integrity and contained macroscopic contractile areas (approximately 20 mm(2)). Seeding in rotating vessels (laminar flow) rather than mixed flasks (turbulent flow) resulted in 23% higher seeding efficiency and 20% less cell damage as assessed by medium lactate dehydrogenase levels (p < 0.05). Advantages of culturing constructs under mixed rather than static conditions included the maintenance of metabolic parameters in physiological ranges, 2-4 times higher construct cellularity (p &le 0.0001), more aerobic cell metabolism, and a more physiological, elongated cell shape. Cultivations in rotating bioreactors, in which flow patterns are laminar and dynamic, yielded constructs with a more active, aerobic metabolism as compared to constructs cultured in mixed or static flasks. After 1-2 weeks of cultivation, tissue constructs expressed cardiac specific proteins and ultrastructural features and had approximately 2-6 times lower cellularity (p < 0.05) but similar metabolic activity per unit cell when compared to native cardiac tissue.

Spatiotemporal development and distribution of intercellular junctions in adult rat cardiomyocytes in culture

The mode of development of the intercalated disk (ID) is largely unknown, and the hypothesis was tested that the assembly of cell adhesion junctions may precede the formation of gap junctions (GJ) in developing ID in adult rat cardiomyocyte (ARC) in long-term culture. Immunostaining for connexin 43 (Cx43) and for cell adhesion junction proteins (N-cadherin, catenins, and desmoplakin) in single- and double-label techniques was analyzed and quantified by confocal and electron microscopy. All proteins investigated disappeared 48 hours after ARC isolation and reappeared parallel to redifferentiation of ARC. The newly formed ID, observed after 5 days, showed the presence of N-cadherin, catenins, and desmoplakin, low levels of Cx43, and absence of ultrastructurally discernible gap junctions. A progressive incorporation of Cx43 within ID was observed after 6 days, when cell adhesion junction proteins were already organized as zipper-like structures. Quantitative confocal analysis revealed a progressive augmentation of the fluorescence intensity of Cx43, associated with an increase in both the number and size of GJ, resulting in a substantial increase in the percentage of total GJ length per reassembled ID from 1.67% (day 6) to 15.58% (day 12). In the present study, we show that (1) the formation of the ID can be followed in ARC in culture and (2) the assembly of the adhering type of junction is the prerequisite for subsequent GJ formation within the ID. These findings may have clinical relevance in elaborating strategies for using myocardial grafts and for the potential restoration of GJ communication in cardiac diseases.