progenitor cell behavior in response to injury

MECHANISMS OF DEVELOPMENT

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available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/modo

Symposium – Stem cells and medicine S13-02 S13-01

In vivo visualization of hematopoietic stem cell generation

Master heart progenitor cells

Elaine Dzierzak

Kenneth Chien

Erasmus University, Rotterdam, The Netherlands

Massachusetts General Hospital, Boston, United States The aorta–gonad–mesonephros (AGM) region of the vertebrate The purification, renewal and differentiation of native car-

embryo generates the first hematopoietic stem cells (HSC). The

diac progenitors would form a mechanistic underpinning for

temporal appearance of AGM HSCs is coincident with appearance

unraveling steps for cardiac cell lineage formation, and their

of hematopoietic clusters closely associated with the ventral endo-

links to forms of congenital and adult cardiac diseases. Previ-

thelium of the embryonic aorta. These clusters and ventral endo-

ously, we have reported the identification of isl1+ cardiac pro-

thelial cells express Ly-6A GFP and Runx1. As shown by

genitors in postnatal rat, mouse and human myocardium (1).

conditional deletion experiments, all adult hematopoietic cells

The discovery of native cardioblasts represents a genetically

originate from Runx1 expressing cells that have transmitted

based system to identify steps in cardiac cell lineage formation

through a VE-cadherin positive endothelial cell stage in mouse

and maturation in development and disease. A pivotal role for

midgestation [Chen etal., 2009]. Recent invitro studies performed

isl1+ progenitors in cardiovascular lineage diversification has

with mouse cells highlight a specialized endothelial cell popula-

also recently been reported by our laboratory (2), where muscle

tion, hemogenic endothelium, as the direct HSC precursor. How-

and endothelial lineage diversification arises from a single cell-

ever, HSC emergence from hemogenic endothelium has never

level decision of a multipotent isl1(+) cardiovascular progenitor

been observed invivo because of the deep location of the aorta

cell (MICP) that lies upstream of the post-natal isl1+ post-natal

within the opaque mouse embryo. Our laboratory has developed

progenitor (2). The discovery of ES cell-derived MICPs suggests

two techniques to visualize hematopoietic clusters in whole mouse

a strategy for cardiovascular tissue regeneration via their isola-

embryos: The first technique, in which the embryo is made trans-

tion, renewal and directed differentiation into specific mature

parent, allows us to quantitate hematopoietic clusters (in normal

cardiac, pacemaker, smooth muscle and endothelial cell types.

and mutant embryos) and to localize phenotypically defined HSCs.

Toward this goal, we have recently identified the Wnt/b-cate-

The second approach allows the dynamic vital imaging of aortic

nin pathway as a major component by which cardiac mesen-

HSCs as they are generated invivo. Both 3-D and time-lapse confo-

chymal cells modulate the prespecification, renewal, and

cal imaging show that HSCs (Sca1+, c-kit+, CD41+) are budding

differentiation of isl1+ cardiovascular progenitors (3). This

directly from the aortic endothelium. Within a few hours, morpho-

microenvironment can be reconstituted by a Wnt3a-secreting

logically flat endothelial cells become round and express markers

feeder layer with ES cell-derived, embryonic, and postnatal

characteristic of HSCs. HSC function is acquired in this rapid pro-

isl1+ cardiovascular progenitors. In vivo activation of b-catenin

cess. These data will be discussed, as well as the involvement of

signaling in isl1+ progenitors of the secondary heart field leads

development signalling molecules in the induction of AGM HSCs.

to their massive accumulation, inhibition of differentiation and outflow tract (OFT) morphogenic defects. In addition, the mito-

doi:10.1016/j.mod.2009.06.1025

sis rate in OFT myocytes is significantly reduced following bcatenin deletion in isl1+ precursors. Agents that manipulate Wnt signals can markedly expand isl1+ progenitors from

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human neonatal hearts, a key advance toward the cloning of

HOX transcription factor regulation of adult stem/progenitor cell

human isl1+ heart progenitors. An update on the lineage fate

behavior in response to injury

map of islet heart progenitors into differentiated progeny

Kimberly Mace

(atrial, ventricular, smooth muscle, endothelial, SA nodal, AV nodal, etc.), including the recent characterization of a novel subset of reversible, bipotent Isl1+ atrial progenitors (4), will be provided. Challenges and opportunities in moving these discoveries towards a more therapeutic application will also be highlighted. doi:10.1016/j.mod.2009.06.1024

University of Manchester, Manchester, United Kingdom The regulated recruitment and differentiation of multipotent bone marrow-derived cells (BMDCs) to sites of injury is critical for efficient tissue repair and regeneration. BMDC are a diverse population containing adult stem/progenitor cells and more mature blood and stromal cell populations. There is increasing evidence that many of these populations are more plastic than

MECHANISMS OF DEVELOPMENT

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S41

originally thought. BMDC behavior is regulated by integrating sig-

Thymic epithelial cells exposed to a skin microenvironment exhi-

naling events that are continuously modified by environmental

bit a down-regulation or silencing of transcription factors impor-

cues. However, the details of how these processes can change cell

tant for thymic function. Hence, it is possible to reveal

fate choices are still unknown.

unsuspected potency and even to robustly reprogram stem cells

Previously, we demonstrated that sustained expression of HOXA3 both accelerated wound healing and promoted neovascularisation in diabetic mice. We have subsequently shown that in

by solely manipulating the microenvironment. doi:10.1016/j.mod.2009.06.1027

response to injury HOXA3 induces a significant increase in both mobilization and recruitment of endothelial progenitor cells. In addition, HOXA3-treated mice have significantly fewer inflamma-

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tory cells recruited to the wound compared to control mice.

The vascular wall as a source of stem cells in adult organs

Microarray analyses of HOXA3-treated wounds revealed that

Bruno Pe´ault

indeed HOXA3 locally increased expression of genes that selectively promote stem/progenitor cell mobilization and recruitment

UPMC, Pittsburgh, United States

while also suppressing expression of numerous members of the

Mesenchymal stem cells (MSC) have been extracted by differ-

pro-inflammatory NF-jB pathway, attenuating the excessive

ent investigators from multiple cultured fetal and adult tissues

inflammatory response characteristic of diabetic wounds. Here

(e.g., bone marrow, brain, lung, pancreas, muscle, adipose tissue,

we examine the underlying mechanisms of HOXA3 regulation

and several others). The identity, frequency and location, within

of adult stem/progenitor cell migration and differentiation and

native tissues, of these elusive stem cells have long remained

describe a model for Hox transcription factor function in

obscure. We now suggest that these multipotent cells originate

response to injury. Enhancing our understanding of how tran-

in blood vessel walls. On the one hand, we have documented ana-

scription factors can pre/re-programme stem/progenitor cells

tomic, molecular and developmental relationships between

invivo will provide novel insights into molecular and cellular ther-

endothelial cells and myogenic cells within human skeletal mus-

apeutic medicines of the future.

cle. Cells coexpressing myogenic and endothelial cell markers (CD56, CD34, CD144) were identified by immunohistochemistry

doi:10.1016/j.mod.2009.06.1026

and flow cytometry. These myoendothelial cells regenerate myofibers in the injured skeletal muscle of immunodeficient mice ten times more effectively than customary myogenic progenitors.

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Myoendothelial cells proliferate long term, retain a normal karyo-

Harnessing epithelial stem cell potency

type, are not tumorigenic and survive better under oxidative

Yann Barrandon

stress than regular myogenic cells. Clonally derived myoendothe-

Lausanne University Medical School, Lausanne, Switzerland

lial cells differentiate into myogenic, osteogenic and chondrogenic cells in culture. Second, we have prospectively identified

Increase in potency of adult stem/progenitor cells holds great expectations for regenerative medicine; reprogramming

perivascular cells, principally pericytes, in multiple human

is

organs on CD146, NG2, and PDGF-Rbeta expression and absence

achieved by manipulating the genome or indirectly by manipulat-

of hematopoietic, endothelial, and myogenic cell markers. Peri-

ing the microenvironment. However, the genetic approach, which

vascular cells purified from skeletal muscle or nonmuscle tissues

can result in lineage conversion up to ground pluripotent embry-

were myogenic in culture and invivo. Irrespective of their tissue

onic state, will certainly face strict regulatory constraints and con-

origin, long-term cultured perivascular cells retained myogenici-

sequently translation to the clinic may be difficult. Manipulating

ty; exhibited at the clonal level osteogenic, chondrogenic, and

stem cell fate without altering the genome of adult stem cells is a

adipogenic potentials; expressed MSC markers; and migrated in

promising alternative. My laboratory has demonstrated that non

a culture model of chemotaxis. Expression of MSC markers was

hairy squamous epithelia e.g. the cornea, the oral cavity, the

also detected at the surface of native, noncultured perivascular

oesophagus, the vagina, contain clonogenic stem cells that can

cells. Thus, blood vessel walls harbor a reserve of progenitor cells

respond to skin morphogenetic signals and form epidermis,

that may be integral to the origin of the elusive MSCs and other

cycling hair follicles and sebaceous glands. This capacity is main-

related adult stem cells. Finally, both myoendothelial cells and

tained in serial transplantation, crosses primary germ line bound-

pericytes improved cardiac function after injection into the

aries and is intrinsic to the stem cells, as cells which have never

infarcted myocardium, suggesting that both qualify as therapeu-

been exposed to cell culture behave in a similar fashion. Even more

tic cells for cardiac repair. In conclusion, blood vessel walls harbor

surprising, the thymus contains a population of clonogenic epithe-

an ubiquitous stock of progenitor cells that may be integral to the

lial cells of endodermal origin that maintain a thymic identity in

origin of the elusive MSCs and other related adult stem cells.

culture and have the capacity to incorporate into a thymic network, but can acquire the functionality of bona fide multipotent stem cells of the skin when exposed to proper developmental signals.

doi:10.1016/j.mod.2009.06.1089