Controlling expansion and cardiomyogenic differentiation of human pluripotent stem cells in scalable suspension culture.

To harness the potential of human pluripotent stem cells (hPSCs), an abundant supply of their progenies is required. Here, hPSC expansion as matrix-independent aggregates in suspension culture was combined with cardiomyogenic differentiation using chemical Wnt pathway modulators. A multiwell screen was scaled up to stirred Erlenmeyer flasks and subsequently to tank bioreactors, applying controlled feeding strategies (batch and cyclic perfusion). Cardiomyogenesis was sensitive to the GSK3 inhibitor CHIR99021 concentration, whereas the aggregate size was no prevailing factor across culture platforms. However, in bioreactors, the pattern of aggregate formation in the expansion phase dominated subsequent differentiation. Global profiling revealed a culture-dependent expression of BMP agonists/antagonists, suggesting their decisive role in cell-fate determination. Furthermore, metallothionein was discovered as a potentially stress-related marker in hPSCs. In 100 ml bioreactors, the production of 40 million predominantly ventricular-like cardiomyocytes (up to 85% purity) was enabled that were directly applicable to bioartificial cardiac tissue formation.

Murine and human pluripotent stem cell-derived cardiac bodies form contractile myocardial tissue in vitro.

AIMS: We explored the use of highly purified murine and human pluripotent stem cell (PSC)-derived cardiomyocytes (CMs) to generate functional bioartificial cardiac tissue (BCT) and investigated the role of fibroblasts, ascorbic acid (AA), and mechanical stimuli on tissue formation, maturation, and functionality. METHODS AND RESULTS: Murine and human embryonic/induced PSC-derived CMs were genetically enriched to generate three-dimensional CM aggregates, termed cardiac bodies (CBs). Addressing the critical limitation of major CM loss after single-cell dissociation, non-dissociated CBs were used for BCT generation, which resulted in a structurally and functionally homogenous syncytium. Continuous in situ characterization of BCTs, for 21 days, revealed that three critical factors cooperatively improve BCT formation and function: both (i) addition of fibroblasts and (ii) ascorbic acid supplementation support extracellular matrix remodelling and CB fusion, and (iii) increasing static stretch supports sarcomere alignment and CM coupling. All factors together considerably enhanced the contractility of murine and human BCTs, leading to a so far unparalleled active tension of 4.4 mN/mm(2) in human BCTs using optimized conditions. Finally, advanced protocols were implemented for the generation of human PSC-derived cardiac tissue using a defined animal-free matrix composition. CONCLUSION: BCT with contractile forces comparable with native myocardium can be generated from enriched, PSC-derived CMs, based on a novel concept of tissue formation from non-dissociated cardiac cell aggregates. In combination with the successful generation of tissue using a defined animal-free matrix, this represents a major step towards clinical applicability of stem cell-based heart tissue for myocardial repair.

Células madre hematopoyéticas, generalidades y vías implicadas en sus mecanismos de auto-renovación / Hematopoietic stem cells, overview and pathways implied on their self-renewal mechanisms

El tejido sanguíneo está compuesto en un 45% aproximadamente por células y derivados de éstas, con una vida media que oscila entre 120 días para los eritrocitos y alrededor de 3 años para ciertos tipos de linfocitos. Esta pérdida es compensada gracias a la actividad del sistema hematopoyético y a la presencia de una población de células primitivas inmaduras conocidas como Células Madre Hematopoyéticas (CMHs) encargadas del proceso de hematopoyesis, activo desde el inicio de la vida fetal y que genera cerca de 2 x 1011 eritrocitos y 1010 células blancas por día (1). Las CMHs poseen la capacidad de auto-renovarse y diferenciarse a múltiples linajes, se ubican en un nicho particular y tienen marcadores de superficie que las identifican, como por ejemplo el antígeno CD34. Recientemente se ha podido avanzar en el entendimiento de la biología básica de los procesos celulares que rigen los mecanismos de auto-renovación, diferenciación y proliferación de las CMHs, y de la participación de diferentes vías de señalización (Hedgehog, Notch y Wnt) en estos procesos, los cuales controlan el comportamiento in vivo e in vitro de las CMHs. Todo esto es de vital importancia para la implementación y generación de alternativas terapéuticas con CMHs, para diversas enfermedades entre ellas las hematológicas, como por ejemplo las leucemias.

Blood tissue is composed approximately in 45% by cells and its derivatives, with a life span of around 120 days for erythrocytes and 3 years for certain type of lymphocytes. This lost is compensated with the hematopoietic system activity and the presence of an immature primitive cell population known as Hematopoietic Stem Cells (HSCs) which perform the hematopoiesis, a process that is active from the beginning of the fetal life and produces near to 2 x 1011 eritrocytes and 1010 white blood cells per day (1). Hematopoietic Stem Cells are capable of both self-renewal and differentiation into multiple lineages, are located in a particular niche and are identified by their own cell surface markers, as the CD34 antigen. Recently it has been possible to advance in the understanding of self-renewal, differentiation and proliferation processes and in the involvement of the signaling pathways Hedgehog, Notch and Wnt. Studying the influence of these mechanisms on in vivo and in vitro behavior and the basic biology of HSCs, has given valuable tools for the generation of alternative therapies for hematologic disorders as leukemias.