Download The Way to a Human`s Heart Is Through the Stomach

Editorial
The Way to a Human’s Heart Is Through the Stomach
Visceral Endoderm-Like Cells Drive Human Embryonic Stem Cells
to a Cardiac Fate
Teruya Nakamura, MD, PhD; Michael D. Schneider, MD
H
Downloaded from http://circ.ahajournals.org/ by guest on June 18, 2017
smooth muscle, and endothelium,4 albeit not all cells.6 To a
varying extent, evidence for analogous plasticity has been
adduced in just the past few years for progenitor cells from other
adult sources, including skeletal muscle,7 adipose tissue,8 and,
less accessibly, brain.9 A more nuanced or, at least, jaundiced
view of such reports has also emerged10: Claims of adult stem
cell plasticity can be deceived for many reasons—mixed starting
populations, contaminating blood-borne cells, and cell-to-cell
fusion among them.
Totipotency, the ability to generate all cell types, not just
many, has been shown best for those cells that have this task
ordinarily: embryonic stem cells (ES cells). Derived from the
blastocyst just a few days after conception, when the embryo is
just a hollow ball of cells with none of the later cell layers
(endoderm, mesoderm, ectoderm) and not of the later differentiated cell types, ES cells from mice—and the animals generated
from them— have been instrumental to the emergence of
“knockouts” lacking one gene or another as the current “gold
standard” of mammalian gene function. In addition, mouse ES
cells grown in tissue culture have been useful for gaining clues
into the very earliest steps for cardiac differentiation.11
Human ES cells evoke especially intense scientific interest,
given their unsurpassed capacity to renew themselves and
give rise to specialized human cells,5,12 thereby providing
clues into our origins and potential tools for our repair. A
suppositional linkage with abortion fuels ethical, legal, and
public debates, despite the fact that these cells are retrieved
from Fallopian tubes well before implantation and, consequently, before the stage blocked by intrauterine contraception.13 Current White House policy speaks to this issue by
permitting no new human ES cell lines to be made with
federal funds, and restricting the ones allowable for study
with National Institutes of Health support to those already in
creation as of 9 PM EDT, August 9, 2001. Despite the
potentially worrisome limitation that this compromise entails,
the crucial and innovative finding that human ES cells indeed
can form heart muscle in vitro14 has now been confirmed
independently for multiple ES cell lines.15 Cardiac myocytes
derived from human ES cells and their potential suitability for
clinical grafting in vivo have been recently reviewed.16 One
outstanding question remains, specifically what cues and
signals pass on to transcription factor networks in the nucleus,
to drive human ES cells to a cardiac destiny.
It has long been thought, on the basis of developmental
studies of amphibian and avian embryos, that cardiac progenitor cells require an instructive, inductive interaction with
anterior endoderm for their specification as cardiac myocytes
to occur.17,18 This also seems to be the case in mice19: If
explanted 7.25 days after conception, mouse mesodermal
eart failure due to myocardial infarction is the leading
cause of morbidity and mortality in developed countries.1 While that point needs no reiteration for the
Circulation audience, its corollary does: that heart failure, in
essence, is a myocyte-deficiency disease. Cell death, whether
from acute infarction alone or from sustained sporadic losses in
chronic heart failure, is not matched by sufficient cell replacement. Adult cardiac muscle cells have long lost much if not all
of their capacity for proliferative growth, and differences in
interpretation hinge on shadings between “none” and “almost
none.”2,3 What cell replacement does occur occurs by other
means, including the recruitment of undifferentiated progenitor
cells— eg, from their niche in bone marrow through the circulation to the injured myocardium.4
See p 2733
Advances in fundamental molecular and cellular biology
have paved the way for development of tissue engineering
and regenerative medicine as a new therapeutic paradigm, in
effect, the Regeneration Superhighway. Among such advances, so-called stem cells have been greeted with greatest
enthusiasm, as well as religious and political alarm. Replacing dead cardiac muscle cells with living ones to preserve
pump function is a goal of indisputable merit. But which cells
have this capacity to transform from something that isn’t a
cardiac myocyte into something that is? Among the potential
sources, why has controversy arisen for some? Which can be
propagated and expanded best in tissue culture? How faithful
is their differentiation, compared with “real” cardiac muscle
cells? And, what governs their conversion?
The concept of “stemness” embraces two properties, which
much coexist for a cell to be a stem cell. The first is long-term
self-renewal, the ability to divide indefinitely, without senescing.
The second is pluripotency, the ability to generate multiple,
disparate cell types. Clinically and historically, hematopoietic
stem cells are the most familiar of adult stem cells,5 with a
capacity to create not merely each of the various blood lineages,
but also other cell types including cardiac muscle, vascular
The opinions expressed in this editorial are not necessarily those of the
editors or of the American Heart Association.
From the Center for Cardiovascular Development, Departments of
Medicine, Molecular and Cellular Biology, and Molecular Physiology
and Biophysics, Baylor College of Medicine, Houston, Tex.
Correspondence to Dr Michael D. Schneider, Center for Cardiovascular Development, Baylor College of Medicine, One Baylor Plaza, Rm
506D, Houston, TX 77030. E-mail [email protected]
(Circulation 2003;107:2638-2639.)
© 2003 American Heart Association, Inc.
Circulation is available at http://www.circulationaha.org
DOI: 10.1161/01.CIR.0000074240.87740.BE
2638
Nakamura and Schneider
Induction of Cardiomyocytes From Human ES Cells
Downloaded from http://circ.ahajournals.org/ by guest on June 18, 2017
tissue that lacks cardiac-specific markers (the right molecules
and beating) can turn into beating myocardium if cultured
together with an explant of visceral endoderm, the normally
subjacent tissue.19 A cardiogenic inductive effect of visceral
endoderm-like cells (VE cells) has also been shown in
coculture with mouse ES cells,20 and endogenous paracrine
factors secreted by the new parietal endoderm contribute to
cardiomyogenesis even when mouse ES cells are cultured on
their own.21 Taken together, these discoveries imply the
generalizable notion that heart formation in these many
diverse systems invariably requires some communication
from underlying endoderm, most likely in the form of a
secreted local signal. Nothing was known, though, about such
signals for cardiac muscle formation by human ES cells.
In the present issue of Circulation, Mummery et al22,23 report
dramatic and conclusive results for one such deterministic
interaction. The authors’ findings will unquestionably provoke
accelerated work on molecular mechanisms of human cardiogenesis, and likely will lead to practical benefits, as well, for the
utility of human ES cells in cardiac cell transplantation. Using a
human ES cell line that (unlike several others) does not initiate
beating spontaneously, these investigators demonstrated that
cultivation together with VE cells provided the missing trigger
for differentiation into cardiomyocytes. Within 10 days of
coculture, 35% of the surface contained beating regions. Beating
was maintained over 6 weeks, and beating clusters could be
collected individually, cultured sequentially, and even cryopreserved and thawed.
The distinguishing features of cardiomyocytes documented
in this study were unusually comprehensive: expression of
sarcomeric proteins, atrial natriuretic peptide, cardiac ion
channel genes, and phospholamban; ventricular action potentials; chronotropic responses to phenylephrine, isoproterenol,
and carbachol; dye-coupling, indicative of gap junctions; and
repetitive intracellular calcium oscillations. In addition, this
report demonstrates rational, physiologically driven ways to
surface-label (and, hence, perhaps to sort) the cardiac cells
emerging in human ES cell cultures, including antibody to the
L-type calcium channel dihydropyridine receptor.
The crux of the study, though, is its direct evidence for the
presence of paracrine factors derived from VE cells, which
function on human ES cells as extrinsic stimuli for cardiac
differentiation. The authors did not specify which molecules
are responsible for the signal but note a few candidates that
are especially well posed, such as bone morphogenetic
proteins24 and fibroblast growth factors,25 neither of which
appeared to work, and repression of signaling by a third class
of factors, Wnts, that are suspected inhibitors of cardiogenesis.26 Because of precedents for synergy among these pathways, an important experiment will be whether various
combinations of these factors can mimic the effect of visceral
endoderm, perhaps with others that have been described. Of
course, factors still unknown may play the trump card.
For human cardiac regeneration, the magnitude of the task
ahead is enormous, but the potential benefits are even greater.
Many may find it of concern that the American Heart
Association declines to support any work at all on human ES
2639
cells, even within the federally sanctioned constraints, which
constitute a prudent and responsible middle ground.
References
1. Braunwald E. Shattuck lecture– cardiovascular medicine at the turn of the
millennium: triumphs, concerns, and opportunities. N Engl J Med. 1997;
337:1360 –1369.
2. Oh H, Taffet GE, Youker KA, et al. Telomerase reverse transcriptase
promotes cardiac muscle cell proliferation, hypertrophy, and survival.
Proc Natl Acad Sci U S A. 2001;98:10308 –10313.
3. Beltrami AP, Urbanek K, Kajstura J, et al. Evidence that human cardiac
myocytes divide after myocardial infarction. N Engl J Med. 2001;344:
1750 –1757.
4. Jackson KA, Majka SM, Wang H, et al. Regeneration of ischemic cardiac
muscle and vascular endothelium by adult stem cells. J Clin Invest.
2001;107:1395–1402.
5. Smith AG. Embryo-derived stem cells: of mice and men. Annu Rev Cell
Dev Biol. 2001;17:435– 462.
6. Castro RF, Jackson KA, Goodell MA, et al. Failure of bone marrow cells
to transdifferentiate into neural cells in vivo. Science. 2002;297:1299.
7. Seale P, Asakura A, Rudnicki MA. The potential of muscle stem cells.
Dev Cell. 2001;1:333–342.
8. Zuk PA, Zhu M, Ashjian P, et al. Human adipose tissue is a source of
multipotent stem cells. Mol Biol Cell. 2002;13:4279 – 4295.
9. Clarke DL, Johansson CB, Wilbertz J, et al. Generalized potential of adult
neural stem cells. Science. 2000;288:1660 –1663.
10. Anderson DJ, Gage FH, Weissman IL. Can stem cells cross lineage
boundaries? Nat Med. 2001;7:393–395.
11. Jackson M, Baird JW, Cambray N, et al. Cloning and characterization of
Ehox, a novel homeobox gene essential for embryonic stem cell differentiation. J Biol Chem. 2002;277:38683–38692.
12. Odorico JS, Kaufman DS, Thomson JA. Multilineage differentiation from
human embryonic stem cell lines. Stem Cells. 2001;19:193–204.
13. Robertson JA. Human embryonic stem cell research: ethical and legal
issues. Nat Rev Genet. 2001;2:74 –78.
14. Kehat I, Kenyagin-Karsenti D, Snir M, et al. Human embryonic stem cells
can differentiate into myocytes with structural and functional properties
of cardiomyocytes. J Clin Invest. 2001;108:407– 414.
15. Xu C, Police S, Rao N, et al. Characterization and enrichment of cardiomyocytes derived from human embryonic stem cells. Circ Res. 2002;91:
501–508.
16. Gepstein L. Derivation and potential applications of human embryonic
stem cells. Circ Res. 2002;91:866 – 876.
17. Nascone N, Mercola M. An inductive role for the endoderm in Xenopus
cardiogenesis. Development. 1995;121:515–523.
18. Schultheiss TM, Xydas S, Lassar AB. Induction of avian cardiac myogenesis by anterior endoderm. Development. 1995;121:4203– 4214.
19. Arai A, Yamamoto K, Toyama J. Murine cardiac progenitor cells require
visceral embryonic endoderm and primitive streak for terminal differentiation. Dev Dyn. 1997;210:344 –353.
20. Rohwedel J, Maltsev V, Bober E, et al. Muscle cell differentiation of
embryonic stem cells reflects myogenesis in vivo: developmentally regulated expression of myogenic determination genes and functional
expression of ionic currents. Dev Biol. 1994;164:87–101.
21. Bader A, Gruss A, Hollrigl A, et al. Paracrine promotion of cardiomyogenesis in embryoid bodies by LIF modulated endoderm. Differentiation.
2001;68:31– 43.
22. Mummery C, Ward D, van den Brink CE, et al. Cardiomyocyte differentiation of mouse and human embryonic stem cells. J Anat. 2002;200:
233–242.
23. Mummery C, Ward-van Oostwaard D, Doevendans P, et al. Differentiation of human embryonic stem cells to cardiomyocytes: role of
coculture with visceral endoderm-like cells. Circulation. 2003;107:
2733–2740.
24. Schneider MD, Gaussin V, Lyons KM. Tempting fate: BMP signals for
cardiac morphogenesis. Cytokine Growth Factor Rev. 2003;14:1– 4.
25. Alsan BH, Schultheiss TM. Regulation of avian cardiogenesis by Fgf8
signaling. Development. 2002;129:1935–1943.
26. Marvin MJ, Di Rocco G, Gardiner A, et al. Inhibition of Wnt activity
induces heart formation from posterior mesoderm. Genes Dev. 2001;15:
316 –327.
KEY WORDS: Editorials
䡲
stem cells
䡲
cells, visceral
䡲
myocytes
The Way to a Human's Heart Is Through the Stomach: Visceral Endoderm-Like Cells
Drive Human Embryonic Stem Cells to a Cardiac Fate
Teruya Nakamura and Michael D. Schneider
Downloaded from http://circ.ahajournals.org/ by guest on June 18, 2017
Circulation. 2003;107:2638-2639
doi: 10.1161/01.CIR.0000074240.87740.BE
Circulation is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231
Copyright © 2003 American Heart Association, Inc. All rights reserved.
Print ISSN: 0009-7322. Online ISSN: 1524-4539
The online version of this article, along with updated information and services, is located on the
World Wide Web at:
http://circ.ahajournals.org/content/107/21/2638
Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published
in Circulation can be obtained via RightsLink, a service of the Copyright Clearance Center, not the Editorial
Office. Once the online version of the published article for which permission is being requested is located,
click Request Permissions in the middle column of the Web page under Services. Further information about
this process is available in the Permissions and Rights Question and Answer document.
Reprints: Information about reprints can be found online at:
http://www.lww.com/reprints
Subscriptions: Information about subscribing to Circulation is online at:
http://circ.ahajournals.org//subscriptions/