Role of TGF beta and myofibroblasts in supporting the propagation of human embryonic stem cells in vitro

Abstract

The feeder layer constitutes a prerequisite for the undifferentiated proliferation of human embryonic stem (hES) cells in vitro. However, a few feeders have been reported to be nonsupportive in nature, suggesting that these feeders exhibit a different transcriptome and proteome, in comparison to their supportive counterparts. In an attempt to identify factors required for undifferentiated growth and many downstream applications of hES cells, transcriptomes of supportive (mouse fibroblasts derived from 13.5dpc embryos and human fetal fibroblasts) and non-supportive (mouse fibroblasts derived from 18.5dpc embryos) feeders were analyzed. Furthermore, the parallel correlation of data generated in the microarray study with the published proteome data of supportive feeder fibroblasts, helped us to focus on the proteins which seem to be likely candidates in supporting the undifferentiated expansion of ES cells in vitro. Our results indicated that TGFβ β β β β and its associated signaling molecules facilitate the undifferentiated proliferation of hES cells in vitro. The transient differentiation of feeder fibroblasts into myofibroblasts may be the decisive factor for a feeder layer to be supportive or non-supportive in nature. We propose that the microenvironment of feeder myofibroblasts dictates TGFβ β β β β to support proliferation and apparently plays the contradictory role of facilitating differentiation when feeder support is withdrawn, possibly by acting through different signaling mechanisms. KEY WORDS: embryonic stem cell, feeder layer, microarray, TGFβ, myofibroblastIn order to realize full clinical potential of human embryonic stem (hES) cells, a major challenge lies in its large scale production for transplantation which is restricted by the use of feeder layer. Mouse embryonic fibroblasts (MEF), although considered the ideal feeder for supporting hES cell growth, carry a potential risk of transferring animal pathogens to the hES cells and thus making them unsuitable for clinical use. Moreover, release of nonhuman sialic acid Neu5Gc from MEF make hES cells more immunogenic and thus possible rejection at the time of transplantation (Martin et al. 2005). Human feeders from various sources have also been used for hES cells derivation and culture e.g. fibroblasts obtained from fetal muscle, skin, lung of which fetal lung fibroblasts were reported to be non-supportive (Richards et al. 2003). Thus it becomes pertinent to identify the proteins/ factors that are highly expressed/ produced by feeder fibroblasts that facilitate undifferentiated proliferation, expansion and maintenance of pluripotency of embryonic stem cells in vitro, with the hope to further refine feeder free culture protocols in future.Studies are available in literature which aimed to identify the secretory factors in the conditioned medium using tools like 2-DE Int.

Embryonic Stem Cells: Introducing Exogenous Regulators into Embryonic Stem Cells

“…hES cells were first established in 1998 by Thomson and colleagues. As in primate ES cells, the feeder layer seems essential for maintaining the hES cell lines. It is suggested that TGF-beta and myofibroblasts can support the propagation of hES cells in vitro (Kumar et al, 2010). Previously, the source of hES cells was restricted to morula and blastocysts but this is no longer the case.…”