Coculture of Embryonic Stem Cells with Pulmonary Mesenchyme: A Microenvironment That Promotes Differentiation of Pulmonary Epithelium

Coculture of stem/progenitor cells with mature cells or tissues can drive their differentiation toward required lineages. Thus, we hypothesized that coculture of murine embryonic stem (ES) cells with embryonic mesenchyme from distal lung promotes the differentiation of pneumocytes. Murine ES cells were differentiated to embryoid bodies (EBs) and cultured for 5 or 12 days with pulmonary mesenchyme from embryonic day 11.5 or 13.5 murine embryos, in direct contact or separated by a membrane. Controls included EBs cultured alone or with embryonic gut mesenchyme. Histology revealed epithelium-lined channels in directly cocultured EBs, whereas EBs grown alone showed little structural organization. The lining cells expressed cytokeratin and thyroid transcription factor 1, an early developmental marker in pulmonary epithelium. Differentiation of type II pneumocytes specifically was demonstrated by the presence of surfactant protein C (SP-C) in some of the epithelial cells. None of these markers was seen in EBs cultured alone or with embryonic gut mesenchyme. Indirect coculture of EBs with lung mesenchyme resulted in a 14-fold increase in SP-C gene expression. Thus, provision of an appropriate microenvironment, in the form of pulmonary mesenchyme, appears to promote the differentiation of ES cells toward lung epithelium. Our findings may have applications in regenerative medicine strategies and the engineering of lung tissue.

Initial Observations on the Effect of Medium Composition on the Differentiation of Murine Embryonic Stem Cells to Alveolar Type II Cells

The pluripotency and high proliferative index of embryonic stem (ES) cells make them a good potential source of cells for tissue engineering purposes. We have shown that ES cells can be induced to differentiate in vitro into pulmonary epithelial cells (type II pneumocytes) using a serum-free medium designed for the maintenance of mature distal lung epithelial cells in culture (SAGM). However, the resulting cell cultures were heterogeneous. Our aim in this study was to attempt to increase pneumocyte yield and differentiation state by determining which medium components enhance the differentiation of pneumocytes and modifying the medium accordingly. Quantitative RT-PCR was used to measure changes in the expression of a type II pneumocyte-specific gene, surfactant protein C (SPC), in response to alterations in the cell culture medium. Results suggested that most individual SAGM growth factors were inhibitory for type II pneumocyte differentiation, with the largest increases in SPC expression (approximately threefold) being observed upon removal of retinoic acid and triiodothryonine. However, large standard deviations occurred between replicates, illustrating the highly variable nature of ES cell differentiation. Nevertheless, these observations represent an initial step towards achieving directed differentiation of pneumocytes from stem cells that could lead to their purification for tissue engineering purposes.

Embryonic stem cells

Embryonic stem cells have huge potential in the field of tissue engineering and regenerative medicine as they hold the capacity to produce every type of cell and tissue in the body. In theory, the treatment of human disease could be revolutionized by the ability to generate any cell, tissue, or even organ, 'on demand' in the laboratory. This work reviews the history of murine and human ES cell lines, including practical and ethical aspects of ES cell isolation from pre-implantation embryos, maintenance of undifferentiated ES cell lines in the cell culture environment, and differentiation of ES cells in vitro and in vivo into mature somatic cell types. Finally, we discuss advances towards the clinical application of ES cell technology, and some of the obstacles which must be overcome before large scale clinical trials can be considered.