A Step Ahead With Both Adult and Embryonic Stem Cells

[Plata]

24 June 2002. The current on-line edition of Nature features two reports on generating functional adult cells, including neurons, from stem cells.
Catherine Verfaillie and colleagues at the University of Minnesota in Minneapolis found a rare type of mesenchymal stem cell in adult mouse and rat bone marrow that retains the ability to differentiate along other mesodermal pathways, but also along endodermal and ectodermal pathways. In the presence of neural signaling molecules, these mesanchymal adult progenitor cells (MAPCs) could be induced to become neural-like cells, many of which expressed markers indicative of serotonergic, dopaminergic, or GABAergic neurons. They had polar structures with tau-containing axon-like processes and MAP2-containing somatodendritic compartments.

In a second round of experiments, Jiang et al. injected MAPCs injected into 3.5-day-old blastocysts. Most animals killed at 6-20 weeks contained the progeny of MAPCs along with their own cells. The "foreign" cells were distributed throughout many tissues, including the brain, where the authors spotted both neurons and glia derived from the injected MAPCs. Interestingly, the majority of granule cells of the hippocampal dentate gyrus were derived from the mesenchymal stem cells.

Finally, the authors injected MAPCs into the blood of adult animals. They again found evidence of incorporation in a variety of tissues, though not in brain, where the blood-brain barrier would keep out anything as large as a cell floating by.

Adult-derived stem cells like MAPCs have potential advantages over embryonic stem (ES) cells, not the least of which is the ethical storm surrounding the use of 5-day-old human embryos to derive ES cells. However, ES cells have the advantage of unlimited proliferation in culture and may offer more potential for genetic manipulations to ensure the appropriate development of particular cell types.

In the other report, Ron McKay and colleagues at the National Institute of Neurological Disorders and Stroke, in Bethesda, Maryland, sought to overcome the problem that existing generation of dopaminergic (DA) neurons ES cells is unreliable. Kim et al. increased the likelihood of producing DA cells by introducing the transcription factor nuclear receptor-related 1( Nurr1) into the genome of mouse ES cells. They further encouraged differentiation into DA cells by treating the cultures with fibroblast growth factor 8 (FGF8) and sonic hedgehog (SHH), which are essential for the differentiation of DA cells in the midbrain in vivo.

With these manipulations, they nudged about 80 percent of their ES cells into becoming fully functional dopamine-releasing cells. When the cells were grafted into a Parkinson's disease model (6-hydroxy-dopamine lesioned mice), they survived, extended axons into the host animal's striatum (the target of substantia nigra dopamine neurons lost in PD), and formed functional synapses. The grafted cells' performance under electrophysiological recording was similar to that of endogenous dopamine neurons. Finally, lesioned mice with grafts performed significantly better than lesioned, non-grafted mice on a number of motor assessments used in PD models, the authors write.

A concern with ES cell grafts is that they have shown a propensity to develop tumors. In this study, McKay's team found no evidence of continuing cell division within the grafts up to 8 weeks after surgery. -Hakon Heimer.

References:

Jiang Y, Jahagirdar BN, Reinhardt RL, Schwartz RE, Keenek CD, Ortiz-Gonzalez XR, Reyes M, Lenvik T, Lund T, Blackstad M, Du J, Aldrich S, Lisberg A, Lowk WC, Largaespada DA, Verfaillie CM. Pluripotency of mesenchymal stem cells derived from adult marrow. Nature advance online publication, 23 June 2002 (doi:10:1038/nature00870).

Kim J-H, Auerbach JM, Rodriguez-Gomez JA, Velasco I, Gavin D, Lumelsky N, Lee S-H, Nguyen J, Sanchez-Pernaute R, Bankiewicz K, McKay R. Dopamine neurons derived from embryonic stem cells function in an animal model of Parkinson's disease. Nature advance online publication, 20 June 2002 (doi:10:1038/nature00900).

Comment by Kiminobu Sugaya - Posted 24 June 2002

The Verfaillie paper reports the identification of pluripotent adult stem cells, which may serve as an alternative to embryonic stem cells as transplant material for cell replacement therapy. Although the paper's title refers to this cell as equivalent to mesenchymal stem cells, it could provide progenitors for mesenchymal and hematopoietic cells. The multipotency of mesenchymal stem cells has been discussed for a long time.

This report details a series of extensive studies from in vitro to in vivo. The characteristics and functions of a sub-population of bone marrow stem cells are quite similar to those of embryonic stem cells in that they responded to treatment with the same factors in vitro. This suggests that the "multipotent adult progenitor cells" did not differentiate to tissue-specific stem cells by responding to the environment or that adult bone marrow has environmental conditions similar to the inside of the blastocyst. Curiously, the cells did not develop a typical neural differentiation after transplantation to the postnatal animal. Since factors needed for neurogenesis may continue to be expressed in the postnatal animal, this issue needs to be explained. In summary, these cells have great potential, but I would like future studies to show their neural differentiation in the adult brain in before "multipotent adult progenitor cells" are applied to neuroreplacement strategies.

The McKay article pushes the envelope of embryonic stem cells in neuroreplacement strategies further. This study has overcome two hurdles: it differentiated embryonic stem cells into neural cells, and it generated from these a specific type of neuron (dopaminergic). Each experiment elegantly proceeds from in vitro differentiation to the assessment of in vivo physiological function including a behavioral test.

Transplanted cells survived for 8 weeks without changing their numbers, indicating no tumorigenesis. I like the idea of transfecting Nurr-1into embryonic stem cells, a transcription factor that induces dopaminergic differentiation in midbrain precursor cells. This approach may be useful to induce other specific types of differentiation in the stem cells.

The only down side I see with this study is that they transplanted the cell into the striatum, the projection area of the dopaminergic cells in the substantia nigra (SN). To aim at full integration of the transplanted cell into the host brain, neuroreplacement ultimately has to be done in SN. Otherwise, cells transplanted to the striatum may become uncontrolled and cause side effects, as we have seen in several fetal tissue transplant studies. I would like to see SN cell replacement and a trial with other types of stem cell using similar tactics in the future. -Kiminobu Sugaya, University of Illinois, Chicago.






Primate Stem Cells by Parthenogenesis
31 January 2002. Parthenogenesis, the development of an unfertilized egg into an embryo, has been demonstrated in mice and cows. Although such embryos have never been cultured to full-term, they could provide a valuable source of embryonic stem (ES) cells. Michael West, at Advanced Cell Technologies, and co-workers report they have successfully adopted this strategy to develop primate ES cells. Their work appears in this Friday's Science.
The researchers coaxed 77 eggs of macaque monkeys (Macaca fasicularis) to divide, 28 successfully. Four eggs reached the blastocyst stage. Inner cell masses were then extracted, plated, and a single cell line was obtained, which could be propagated for ten months without differentiation.

West et al. demonstrated the pluripotency of this cell line by its ability to differentiate into a variety of cell types including spontaneously beating cardiomyocyte-like cells, smooth muscle cells, adipocytes, ciliated epithelium, and cells of the neural lineage. HPLC analysis confirmed that some of the latter released dopamine and serotonin.

To test the developmental capability of the cells n vivo, the scientists placed them in the peritoneal cavity of SCID mice, which could not reject them. Histological analysis revealed differentiation of the ES cells into cells of all three germ layers including muscle, bone, neurons, skin, and intestinal and respiratory epithelia.

"This is very intriguing, that you can start an egg dividing parthenogenetically and get a cell line," said Curt Freed, University of Colorado Health Science Center. "It's not a common event, but on the other hand one doesn't have to do it very often if you have 10 months of continuously dividing cells."- Tom ***an

Reference: Cibelli JB et al. "Parthenogenetic Stem Cells in Nonhuman Primates." Science 1 February 2002;(295):819.





Stem Cells: From Mouse to Monkey
29 January 2002. The growth and development of transplantable neurons from embryonic stem (ES) cells could potentially have immense value for those suffering from neurodegenerative diseases. But many hurdles stand in the way, not least being the transfer of what has been learned from animal models to humans. On this score, encouraging news comes from Yoshiki Sasai and colleagues at Kyoto University, who report in today's online version of the Proceedings of the National Academy of Sciences that they have been able to generate dopaminergic primate neurons using a methodology that was developed for rodent cells.
Previously the researchers found that mouse stromal cells (PA6 cells) express on their surface a neuralizing activity that induces the differentiation of ES cells into neurons (Kawasaki et al., 2000). They have now used this stromal cell-derived inducing activity (SDIA) to generate dopaminergic neurons from Cynomolgus monkey ES cells.

This technique is simple and efficient, the authors write. ES cells grown on a layer of PA6 cells differentiate within two weeks. 45 and 25 percent of differentiated cells expressed the neural markers NCAM, and class III b-tubulin, respectively. Furthermore, 80 percent of the cell colonies contained tyrosine hydroxylase-positive (TH+) dopaminergic neurons, which released dopamine when challenged with a depolarizing stimulus. These neurons had CNS characteristics, being negative for the PNS marker peripherin. When transplanted into mouse striatum, 8 percent of the cells survived and had extended neurites two weeks later, suggesting they may be viable in vivo.

"This looks very promising that the findings in the mouse can be translated into primates," said Curt Freed, University of Colorado "That is no small feat, particularly with embryonic stem cells where the conditions for growing human cells are very different."

The Japanese group is now attempting to transplant the cells into monkey brain to evaluate long-term survival of the TH+ neurons.- Tom ***an

References: Kawasaki H et al. "Generation of dopaminergic neurons and pigmented epithelia from primate ES cells by stromal cell-derived inducing activity." PNAS. 5 February 2002;(99):1580-1585. Related News



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[Brian]

Is it just me or am I failing to see the connection between this topic and Family Ties?