Calcium Signals Induce Liver Stem Cells to Acquire a Cardiac Phenotype

Heart failure is a major cause of premature death and disability in the United States. Stem cell therapy has attracted great interest for the treatment of myocardial infarction and heart failure. Some tissue-specific adult-derived stem cells demonstrate plasticity in that they are multipotent, react to inductive signals provided by a new micro-environment, and acquire the phenotype of cells endogenous to the new micro-environment. The mechanism through which this phenotype is acquired is unknown. We have demonstrated that a liver-derived clonal stem cell line, WB F344, differentiate into cardiomyocytes in vivo and in vitro. Using a coculture model of neonatal heart cells and WB F344 cells, we have found that cytosolic communication between the two cell types results in calcium-induced transcription of cardiac transcription factors and appears to usher in the cardiac phenotype. Functional gap junctions and IP3 receptors appear to be required for this process. We propose that the observed low frequency of stem cell differentiation into cardiomyocytes when transplanted into the injured heart is due, in part, to their inability to establish functioning intercellular communications with healthy cardiomyocytes and receive instructive signals needed to activate a cardiac gene program.

The Fontan patient: inconsistencies in medication therapy across seven pediatric heart network centers

Patients who have undergone the Fontan procedure are at risk for thrombosis, ventricular dysfunction, and valve regurgitation, but data to guide the medical treatment and prevention of these adverse outcomes in this population are lacking. This analysis examined medication usage among Fontan patients by putative indication and by study center. The medical history and current medications of 546 Fontan subjects, ages 6-18 years, were assessed in a Pediatric Heart Network multicenter cross-sectional study. Cardiac imaging was performed within 3 months of enrollment. The majority of the subjects (64%) were taking two or more medications. Antithrombotics were taken by 86% of those with a history of stroke, thrombosis, or both and 67% of those without such a history (P = 0.01). Conversely, 14% of those with a history of stroke, thrombosis, or both were taking no antithrombotic. Angiotensin-converting enzyme inhibitor (ACEi) therapy was independently associated with moderate or severe atrioventricular valve regurgitation (P = 0.004), right ventricular morphology (P < 0.001), and shorter time since Fontan (P = 0.004) but not with ventricular systolic dysfunction. Glycoside therapy and diuretic therapy each was associated with older age at Fontan (P = 0.001 and P = 0.023, respectively) and a history of post-Fontan arrhythmia (P < 0.001 and P = 0.003, respectively) but not with ventricular systolic dysfunction. Medication use rates varied widely among the centers, even with controls for center differences in patient characteristics. Prospective therapeutic trials are needed to guide the medical treatment of Fontan patients.

Contemporary outcomes after the Fontan procedure: a Pediatric Heart Network multicenter study

OBJECTIVES

We characterized a large cohort of children who had a Fontan procedure, with measures of functional health status, ventricular size and function, exercise capacity, heart rhythm, and brain natriuretic peptide (BNP).

BACKGROUND

The characteristics of contemporary Fontan survivors are not well described.

METHODS

We enrolled 546 children (age 6 to 18 years, mean 11.9 years) and compared them within pre-specified anatomic and procedure subgroups. History and outcome measures were obtained within a 3-month period.

RESULTS

Predominant ventricular morphology was 49% left ventricular (LV), 34% right ventricular (RV), and 19% mixed. Ejection fraction (EF) was normal for 73% of subjects; diastolic function grade was normal for 28%. Child Health Questionnaire mean summary scores were lower than for control subjects; however, over 80% of subjects were in the normal range. Brain natriuretic peptide concentration ranged from <4 to 652 pg/ml (median 13 pg/ml). Mean percent predicted peak O2 consumption was 65% and decreased with age. Ejection fraction and EF Z score were lowest, and semilunar and atrioventricular (AV) valve regurgitation were more prevalent in the RV subgroup. Older age at Fontan was associated with more severe AV valve regurgitation. Most outcomes were not associated with a superior cavopulmonary connection before Fontan.

CONCLUSIONS

Measures of ventricular systolic function and functional health status, although lower on average in the cohort compared with control subjects, were in the majority of subjects within 2 standard deviations of the mean for control subjects. Right ventricular morphology was associated with poorer ventricular and valvular function. Effective strategies to preserve ventricular and valvular function, particularly for patients with RV morphology, are needed.

Complement factor 1 inhibitor improves cardiopulmonary function in neonatal cardiopulmonary bypass

BACKGROUND

The inflammatory insult associated with cardiopulmonary bypass (CPB) continues to result in morbidity for neonates undergoing complex repair of congenital cardiac defects. Complement and contact activation are important mediating processes involved in this injury. Complement factor 1 esterase inhibitor (C1-inh), a natural inhibitor of complement, kallikrein, and coagulation pathways, may be decreased in children undergoing cardiac operations requiring CPB. We tested the hypothesis that C1-inh supplementation will ameliorate the cardiac and pulmonary dysfunction in a model of neonatal CPB.

METHODS

Fifty-two neonatal pigs were randomly assigned to receive 0 IU (n = 22), 500 IU (n = 15), 1,000 IU (n = 8), or 1,500 IU (n = 7) of C1-inh. Doses were delivered 5 minutes before starting 90 minutes of normothermic CPB. Pulmonary and cardiovascular measures were taken before and 5, 30, and 60 minutes after CPB.

RESULTS

Five animals did not survive CPB. The C1-inh concentration post-CPB increased monotonically with increasing dose (p < 0.001). Weight gain was significantly less in the 1,500 IU group (0.24 +/- 0.10 kg versus 0.38 +/- 0.09 kg, p = 0.001). Dynamic compliance increased with C1-inh dose from 0 to 500 IU by 23% +/- 4% (p < 0.001), but the increase leveled off at the higher doses. Alveolar-arterial O2 gradient decreased with C1-inh dose (p = 0.009). Time derivative of left ventricular pressure (dP/dt(max)) increased significantly with increasing dose (p = 0.016). At the highest dose of C1-inh, the time constant of isovolumic relaxation was increased (p = 0.018).

CONCLUSIONS

The C1-inh supplementation results in improved pulmonary and systolic cardiac function in a model of neonatal CPB. The negative effect on diastolic function requires further investigation.

Mechanisms controlling the acquisition of a cardiac phenotype by liver stem cells

The mechanisms underlying stem cell acquisition of a cardiac phenotype are unresolved. We studied early events during the acquisition of a cardiac phenotype by a cloned adult liver stem cell line (WB F344) in a cardiac microenvironment. WB F344 cells express a priori the transcription factors GATA4 and SRF, connexin 43 in the cell membrane, and myoinositol 1,4,5-triphosphate receptor in the perinuclear region. Functional cell-cell communication developed between WB F344 cells and adjacent cocultured cardiomyocytes in 24 h. De novo cytoplasmic [Ca(2+)](c) and nuclear [Ca(2+)](nu) oscillations appeared in WB F344 cells, synchronous with [Ca(2+)](i) transients in adjacent cardiomyocytes. The [Ca(2+)] oscillations in the WB F344 cells, but not those in the cardiomyocytes, were eliminated by a gap junction uncoupler and reappeared with its removal. By 24 h, WB F344 cells began expressing the cardiac transcription factors Nkx2.5, Tbx5, and cofactor myocardin; cardiac proteins 24 h later; and a sarcomeric pattern 4-6 days later. Myoinositol 1,4,5-triphosphate receptor inhibition suppressed WB F344 cell [Ca(2+)](nu) oscillations but not [Ca(2+)](c) oscillations, and L-type calcium channel inhibition eliminated [Ca(2+)] oscillations in cardiomyocytes and WB F344 cells. The use of these inhibitors was associated with a decrease in Nkx2.5, Tbx5, and myocardin expression in the WB F344 cells. Our findings suggest that signals from cardiomyocytes diffuse through shared channels, inducing [Ca(2+)] oscillations in the WB F344 cells. We hypothesize that the WB F344 cell [Ca(2+)](nu) oscillations activate the expression of a cardiac specifying gene program, ushering in a cardiac phenotype.

The use of TP10, soluble complement receptor 1, in cardiopulmonary bypass

Cardiopulmonary bypass (CPB) for cardiac surgery or lung transplantation initiates a systemic inflammatory response characterized by increased vascular permeability, generalized edema, abnormal lung function and oxygenation and impaired ventricular function. This post-CPB syndrome significantly contributes to postoperative morbidity and mortality. Activation of complement during CPB is a key component that initiates and augments this process. TP10, soluble complement receptor 1, is a novel complement inhibitor that is a potent inhibitor of C3 and C5 convertases, blocking activation of the complement cascade at the nexus of all three complement pathways. Recent controlled trials in humans have demonstrated that TP10 effectively inhibits complement activation during CPB. In high-risk adult patients, TP10 decreases the incidence of mortality and myocardial infarction in males but not in females following cardiac surgery. TP10 is also well tolerated and protects vascular function in infants undergoing CPB. In addition, TP10 leads to early extubation in adult lung transplant recipients. TP10 is currently positioned for clinical development in a male-only indication of cardiac surgery on CPB.

Development and cardiac contractility: cardiac troponin T isoforms and cytosolic calcium in rabbit

Cardiac contractility depends on calcium sensitivity of the myofilaments and cytosolic free calcium concentration ([Ca(2+)](i)) during activation. During development, the cardiac troponin T isoform cTnT(1) is replaced by shorter cTnT isoforms, including cTnT(4), and changes occur in other myofibrillar proteins and in calcium regulation. We expressed rabbit recombinant (r)cTnT(1) and rcTnT(4) in Spodoptera frugiperda cells and determined their effect on calcium binding to TnC in solution and on the calcium sensitivity of myofilaments in skinned rabbit ventricular fibers in vitro. We measured [Ca(2+)](i) and L-type calcium current (I(Ca)) in ventricular myocytes from 3-wk-old and adult rabbits. The dissociation constant (K(d)) of Ca-Tn(cTnT1) in solution was smaller than that of Ca-Tn(cTnT4) (mean +/- SE: 0.52 +/- 0.08 mumol/L versus 0.83 +/- 0.09 mumol/L). The Ca(2+) sensitivity of force development was greater in fibers reconstituted with rcTnT(1) (pCa(50) 6.07 +/- 0.04) than those reconstituted with rcTnT(4) (pCa(50) 5.75 +/- 0.07). Systolic [Ca](i) was lower in 3-wk-old than adult cells (443 +/- 35 nmol/L versus 882 +/- 88 nmol/L) as was I(Ca) (5.8 +/- 0.9 pA/pF versus 14.2 +/- 1.6 pA/pF). The higher calcium sensitivity of Tn-Ca binding and of force development conferred by rcTnT(1) suggest that higher neonatal cTnT(1) expression may partially compensate for the lower systolic [Ca(2+)](i).

The Pediatric Heart Network: a primer for the conduct of multicenter studies in children with congenital and acquired heart disease

Most contemporary diagnostic and treatment strategies for pediatric patients with cardiovascular disease are not supported by evidence from clinical trials but instead are based on expert opinion, single-institution observational studies, or extrapolated from adult cardiovascular medicine. In response to this concern, the National Heart, Lung, and Blood Institute established the Pediatric Heart Disease Clinical Research Network (PHN) in 2001. The purposes of this article are to describe the initiation, structure, and function of the PHN; to review the ongoing studies; and to address current and future challenges. To date, four randomized clinical trials and two observational studies have been launched. Design and conduct of complex, multicenter studies in children with congenital and acquired heart disease must address numerous challenges, including identification of an appropriate clinically relevant primary endpoint, lack of preliminary data on which to base sample size calculations, and recruitment of an adequate number of subjects. The infrastructure is now well developed and capable of implementing complex, multicenter protocols efficiently and recruiting subjects effectively. The PHN is uniquely positioned to contribute to providing evidence-based medicine for and improving the outcomes of pediatric patients with cardiovascular disease.

Acquired cell-to-cell coupling and "cardiac-like" calcium oscillations in adult stem cells in a cardiomyocyte microenvironment

Adult-derived stem cells have recently been found to respond in vivo to inductive signals from the microenvironment and to differentiate into a phenotype that is characteristic of cells in that microenvironment. We examined the differentiation potential of an adult liver stem cell line (WBF344) in a cardiac microenvironment in vitro. WBF344 cells were established from a single cloned non-parenchymal epithelial cell isolated from a normal male adult rat liver. Genetically modified, WBF344 cells that express beta-galactosidase, green fluorescent protein (GFP) or mitochondrial red fluorescent protein (DsRed) were co-cultured with rat neonatal cardiac cells. After 4-14 days, we identified WBF344-derived cardiomyocytes that were elongated, binucleated and expressed the cardiac specific proteins cardiac troponin T, cardiac troponin I and N cadherin. These WBF344-derived cardiomyocytes also exhibited myofibrils, sarcomeres, and a nascent sarcoplasmic reticulum. Furthermore, rhythmically beating WBF344-derived cardiomyocytes displayed "cardiac-like" calcium transients similar to the surrounding neonatal cardiomyocytes. Fluorescent recovery after photobleaching demonstrated that WBF344-derived cardiomyocytes were electrically coupled with adjacent neonatal cardiomyocytes through gap junctions (GJs). Collectively, these results support the conclusion that these adult-derived liver stem cells respond to signals generated in a cardiac microenvironment in vitro acquiring a cardiomyocyte phenotype and function. The identification of micro-environmental signals that appear to cross germ layer and species specificities should prove valuable in understanding the regulation of normal development and stem cell differentiation in vivo.

cTnT1, a cardiac troponin T isoform, decreases myofilament tension and affects the left ventricular pressure waveform

Four isoforms of cardiac troponin T (cTnT), a protein essential for calcium-dependent myocardial force development, are expressed in the human; they differ in charge and length. Their expression is regulated developmentally and is affected by disease states. Human cTnT (hcTnT) isoform effects have been examined in reconstituted myofilaments. In this study, we evaluated the modulatory effects of overexpressing one cTnT isoform on in vitro and in vivo myocardial function. A hcTnT isoform, hcTnT(1), expressed during development and in heart disease but not in the normal adult heart, was expressed in transgenic (TG) mice (1-30% of total cTnT). Maximal active tension measured in skinned myocardium decreased as a function of relative hcTnT(1) expression. The pCa at half-maximal force development, Hill coefficient, and rate of redevelopment of force did not change significantly with hcTnT(1) expression. In vivo maximum rates of rise and fall of left ventricular pressure decreased, and the half-time of isovolumic relaxation increased, with hcTnT(1) expression. Substituting total cTnT charge for hcTnT(1) expression resulted in similar conclusions. Morphometric analysis and electron microscopy revealed no differences between wild-type (non-TG) and TG myocardium. No differences in isoform expression of tropomyosin, myosin heavy chain, essential and regulatory myosin light chains (MLC), TnI, or in posttranslational modifications of mouse cTnT, cTnI, or regulatory MLC were observed. These results support the hypothesis that cTnT isoform amino-terminal differences affect myofilament function and suggest that hcTnT(1) expression levels present during human development and in human heart disease can affect in vivo ventricular function.

Adult-derived liver stem cells acquire a cardiomyocyte structural and functional phenotype ex vivo

We examined the differentiation potential of an adult liver stem cell line (WB F344) in a cardiac microenvironment, ex vivo. WB F344 cells were established from a single cloned nonparenchymal epithelial cell isolated from a normal male adult rat liver. Genetically modified, WB F344 cells that express beta-galactosidase and green fluorescent protein or only beta-galactosidase were co-cultured with dissociated rat or mouse neonatal cardiac cells. After 4 to 14 days, WB F344-derived cardiomyocytes expressed cardiac-specific proteins and exhibited myofibrils, sarcomeres, and a nascent sarcoplasmic reticulum. Further, rhythmically beating WB F344-derived cardiomyocytes displayed calcium transients. Fluorescent recovery after photobleaching demonstrated that WB F344-derived cardiomyocytes were coupled with adjacent neonatal cardiomyocytes and other WB F344-derived cardiomyocytes. Fluorescence in situ hybridization experiments suggested that fusion between WB F344 cells and neonatal mouse cardiomyocytes did not take place. Collectively, these results support the conclusion that these adult-derived liver stem cells respond to signals generated in a cardiac microenvironment ex vivo acquiring a cardiomyocyte phenotype and function. The identification ex vivo of microenvironmental signals that appear to cross germ layer and species specificities should prove valuable in understanding the molecular basis of adult stem cell differentiation and phenotypic plasticity.

Pharmacokinetics and safety of TP10, soluble complement receptor 1, in infants undergoing cardiopulmonary bypass

BACKGROUND

Increase in vascular permeability and multiorgan dysfunction after cardiopulmonary bypass (CPB) are barriers to successful cardiac surgery in infants. Complement inhibition with TP10, a C3/C5 convertase inhibitor (AVANT Immunotherapeutics, Needham, Mass), blunts post-CPB organ dysfunction in the neonatal pig. Methods and results The pharmacokinetics and safety of TP10 in infants (age <1 year, n = 15) undergoing CPB were examined in a phase I/II open-label prospective trial. TP10 (10 mg/kg) was given intravenously before CPB and also added (10 mg/100 mL prime volume) to the CPB circuit. TP10 plasma levels correlated with C3a levels and measures of clinical course. All infants survived. No adverse events were attributed to TP10. TP10 plasma concentration fell to < or =60 microg/mL 12 hours after CPB. A 2-compartment model was fit to the TP10 blood levels as a function of time. Based on this model, an initial dose of 10 mg/kg over 0.5 hours followed by 10 mg/kg over 23.5 hours is the most appropriate for maintaining TP10 concentration between 100 microg/mL and 160 microg/mL for 24 hours after CPB. C3a was lower 12 hours after CPB than before CPB and still lower 24 hours after CPB. TP10 concentration was inversely correlated with the 12-hour post-CPB to pre-CPB ratio of C3a (Spearman rho -0.76, P = -.016), and with total (rho -0.56, P =.047) and net (rho -0.85, P =.0016) fluid and blood product administration/kg >24 hours after CPB.

CONCLUSIONS

TP10 administration to infants appears safe. Pharmacokinetic analysis generated an optimal dosing strategy to achieve effective TP10 levels for 24 hours after CPB. In the infant, TP10 appears to decrease CPB-induced complement activation and protect vascular function. These results support a phase III trial of TP10 in infants requiring CPB.

Cardiac troponin T isoforms expressed in renal diseased skeletal muscle will not cause false-positive results by the second generation cardiac troponin T assay by Boehringer Mannheim

The purpose of this study was to determine whether the two monoclonal anti-cardiac troponin T (cTnT) antibodies (MAbs) used in the second generation cTnT assay by Boehringer Mannheim (BM, capture Ab, M11.7; detection Ab, M7) would detect cTnT isoforms expressed in human skeletal muscle in response to chronic renal disease (CRD). cTnT expression was examined in skeletal muscle biopsies obtained from 45 CRD patients, as well as nondiseased human heart (n = 3) and skeletal muscle (n = 3). cTnT proteins were resolved by modified 7.5% sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transferred to nitrocellulose, and probed with the following anti-cTnT MAbs: M11.7; M7; JS-2, Lakeland Biomedical; and 13–11, Duke University. All four antibodies detected the cTnT isoforms (Ta, Te) expressed in human myocardium. In 20 of 45 skeletal muscle biopsies, MAb M11.7 recognized its epitope in one to three proteins, molecular mass 34–36 kDa, designated Te, Td, and Tc; the strongest signal was that of Te. The same proteins were recognized by MAbs JS-2 and 13–11. The BM M7 antibody did not detect the cTnT isoforms in the molecular mass range of 34–36 kDa. However, MAb M7 did detect a cTnT isoform, molecular mass 39 kDa, in 2 of 45 biopsies. This isoform had an electrophoretic mobility similar to the predominant heart cTnT isoform, Ta. We conclude that cTnT isoforms are expressed in the skeletal muscle of CRD patients. However, given the epitopes recognized by the BM MAbs M7 and M11.7 and the variable presence of these cTnT isoforms in skeletal muscle, the second generation BM cTnT assay will not detect these isoforms if they are released from skeletal muscle into the circulation.