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CD24: a Novel Surface Marker for PDX1-Positive Pancreatic Progenitors Derived from Human Embryonic Stem Cells

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From the April 2011 Issue of Stem Cells

Paper Commentary by Stuart P. Atkinson

Pancreatic beta cell replacement for the treatment of type I diabetes mellitus through the directed differentiation of human embryonic stem cells (hESCs) is one of the great hopes for regenerative medicine. Great strides have been made towards this goal, although the efficient production of functionally mature functional beta cells from hESC-pancreatic progenitor cells has not yet been reported. One of the main limitations is the heterogeneity of differentiating hESC cultures in vitro. Now the group of Hongkui Deng at the School of Life Sciences at Peking University have demonstrated the potential usefulness of the cell surface marker CD24 for identification and enrichment of pancreatic progenitor cells derived from ESC. The study (Jiang et al.), published in the April Edition of Stem Cells, also shows the equivalence of in vitro differentiated pancreatic progenitor cells with those seen in vivo through the analysis of CD24 positive cells.

Building on a previous study (Zhang et al), the authors first describe the co-expression of multiple pancreatic markers (HNF6, SOX9 and PROX1) with the well-known pancreatic marker PDX1 in pancreatic progenitor cells derived from hESC. These cells were negative for CDX2, AFP and SOX17 suggesting that the cells were fully differentiated definitive endoderm cells and that these cells share similar characteristics with bona fide pancreatic progenitors during in vivo pancreatic development (Oliver-Krasinski and Stoffers). Further screening of these cells with commercially available antibodies was undertaken with an aim to discover a specific cell surface marker that could be used to purify the hESC-derived pancreatic progenitors from heterogenous cultures. Using two different hESC lines the authors demonstrated that CD24 matched the staining of PDX1, while NCAM1 was identified as a possible negative marker.

Further immunofluorescence studies showed that CD24+ cells express key transcription factors of pancreatic progenitor cells (SOX9, HNF6, HNF1B, HB9 and NKX6-1). Gene expression analysis of purified CD24+ and CD24- cells also showed the enrichment of PDX1, FOXA2, HNF6, HES1 and PROX1 gene expression in the positive population. Encouragingly, when the ESC-derived pancreatic progenitors were exposed to EGF for one week in culture, only the CD24+ population maintained CD24 expression and expressed the beta cell transcription factors PDX1, NKX6-1, NEUROD1 and, importantly - Insulin, indicative of some similarity between pancreatic cells derived in vitro with those generated following in vivo differentiation. Further analysis at different stages of differentiation, facilitated by the discovery of CD24 as a useful cell surface marker, revealed that the broad expression of CD24 in progenitors became reduced upon differentiation. At the definitive endoderm stage, CD24 was weakly expressed in FOXA2 and SOX17 positive and negative cells. Following this, at the early pancreatic specification stage, PDX1 positive cells emerge from a HNF1B-positive cell population and were also shown to express CD24. As PDX1 expression peaked, most CD24 cells were also PDX1 positive.

This study demonstrates the identification of a novel cell surface maker which has promise for the development of protocols that aim to achieve de novo beta cell production for cell replacement therapy in diabetes mellitus. The isolation and purification of hESC-pancreatic progenitor cells will facilitate research into the signals which regulate beta cell differentiation and maturation.

 

References

CD24: A Novel Surface Marker for PDX1-Positive Pancreatic Progenitors Derived from Human Embryonic Stem Cells.
Jiang W, Sui X, Zhang D, Liu M, Ding M, Shi Y, Deng H.
Stem Cells. 2011 Feb 3. doi: 10.1002/stem.608.

Highly efficient differentiation of human ES cells and iPS cells into mature pancreatic insulin-producing cells.
Zhang D, Jiang W, Liu M, Sui X, Yin X, Chen S, Shi Y, Deng H.
Cell Res. 2009 Apr;19(4):429-38.

On the origin of the beta cell.
Oliver-Krasinski JM, Stoffers DA.
Genes Dev. 2008 Aug 1;22(15):1998-2021.