No abstract

Unlike some organs, the heart is unable to repair itself after injury. Human embryonic stem cells (hESCs) grow and divide indefinitely while maintaining the potential to develop into many tissues of the body. As such, they provide an unprecedented opportunity to treat human diseases characterized by tissue loss. We have identified early myocardial precursors derived from hESCs (hMPs) using an α-myosin heavy chain (αMHC)-GFP reporter line. We have demonstrated by immunocytochemistry and quantitative real-time PCR (qPCR) that reporter activation is restricted to hESC-derived cardiomyocytes (CMs) differentiated in vitro, and that hMPs give rise exclusively to muscle in an in vivo teratoma formation assay. We also demonstrate that the reporter does not interfere with hESC genomic stability. Importantly, we show that hMPs give rise to atrial, ventricular and specialized conduction CM subtypes by qPCR and microelectrode array analysis. Expression profiling of hMPs over the course of differentiation implicate Wnt and transforming growth factor-β signaling pathways in CM development. The identification of hMPs using this αMHC-GFP reporter line will provide important insight into the pathways regulating human myocardial development, and may provide a novel therapeutic reagent for the treatment of cardiac disease.

Children with single ventricle (SV) physiology have increased ventricular work and are at risk for heart failure (HF). However, HF diagnosis is especially difficult because there are few objective measures of HF validated in this cohort. We previously showed that plasma B-type natriuretic peptide (BNP) levels were sensitive and specific for detecting HF in a small, heterogeneous SV cohort. The aim of this study was to define the impact of SV morphology and stage of palliation on the correlation between BNP and HF. We also examined the utility of N-terminal pro-BNP (NT-proBNP), a more stable product of pre-BNP processing, as a biomarker of HF in these patients. A cross-sectional observational study of SV children 1 month–7 years was conducted. The presence of HF was defined as a Ross score >2. The association of BNP or NT-proBNP with HF was assessed using logistic regression and ROC curves. Twenty-two of 71 included children (31%) had clinical HF. A doubling of BNP was associated with an odds ratio for HF of 2.20 (95%CI 1.36–3.55, p=0.001) with a c-statistic >75%, yielding a detection threshold of ≥45 pg/ml. This threshold was preserved when patients were stratified by right ventricular morphology or stage of surgical palliation. Similarly, a doubling of NT-proBNP was associated with an odds ratio for HF of 1.92 (95% CI 1.17–3.14, p=0.009). In contrast with BNP, the threshold value of NT-proBNP for predicting HF decreased with stage of palliation. In conclusion, plasma BNP and NT-proBNP are reliable tests for clinical HF in young children with SV physiology, specifically those with right ventricular morphology, regardless of stage of palliation.

Directed differentiation of human embryonic stem cells (hESCs) has generated much interest in the field of regenerative medicine. While subpopulations of hESCs within pluripotent cultures have been identified based on expression of specific surface antigens, their significance and fates are not well understood. To determine whether such subpopulations indicate specific tissue fates or represent stochastic antigen distributions within proliferating cultures, we isolated CD133+ or CD135+ hESCs from proliferating cultures constitutively expressing enhanced green fluorescent protein (GFP), and co-cultured these with unselected GFP− hESCs. After passage in culture, GFP+ hESCs reanalyzed for the persistence of CD133 or CD135 expression, as well as other surface antigens (Tra-1-60, SSEA-4, FGFR-1), demonstrated that these two subpopulations continued to express CD133 or CD135 over serial passage, and that CD133+ hESCs were enriched for SSEA-4 expression as well. Upon differentiation in vitro, CD133+GFP+ hESCs gave rise solely to ectoderm, as detected by expression of nestin. Tissues representing endoderm (α-fetoprotein+) and mesoderm (smooth muscle actin+) were not seen among GFP+ tissues. In contrast, selection against CD133 gave rise almost exclusively to mesoderm and endoderm. In contrast, CD135+GFP+ hESCs gave rise to tissues representing all three embryonic germ layers, and were virtually indistinguishable from CD135−-derived tissues. Similar results were obtained by in vivo differentiation in teratomas. These data establish that subpopulations of proliferating hESCs whose tissue fate is predetermined exist, and challenge the notion that all cells within proliferating hESC cultures are truly “pluripotent.” This co-culture approach also will enable identification of other distinct hESC subpopulations, and selection for these should prove valuable in generating tissue-specific reagents for cell-based therapy.