Long term culture of mesenchymal stem cells in hypoxia promotes a genetic program maintaining their undifferentiated and multipotent status

Abstract

In the bone marrow, hematopietic and mesenchymal stem cells form a unique niche in which the oxygen tension is low. Hypoxia may have a role in maintaining stem cell fate, self renewal and multipotency. However, whereas most studies addressed the effect of transient in vitro exposure of MSC to hypoxia, permanent culture under hypoxia should reflect the better physiological conditions.
Morphologic studies, differentiation and transcriptional profiling experiments were performed on MSC cultured in normoxia (21% O2) versus hypoxia (5% O2) for up to passage 2. Cells at passage 0 and at passage 2 were compared, and those at passage 0 in hypoxia generated fewer and smaller colonies than in normoxia. In parallel, MSC displayed (>4 fold) inhibition of genes involved in DNA metabolism, cell cycle progression and chromosome cohesion whereas transcripts involved in adhesion and metabolism (CD93, ESAM, VWF, PLVAP, ANGPT2, LEP, TCF1) were stimulated. Compared to normoxic cells, hypoxic cells were morphologically undifferentiated and contained less mitochondrias. After this lag phase, cells at passage 2 in hypoxia outgrew the cells cultured in normoxia and displayed an enhanced expression of genes (4-60 fold) involved in extracellular matrix assembly (SMOC2), neural and muscle development (NOG, GPR56, SNTG2, LAMA) and epithelial development (DMKN). This group described herein for the first time was assigned by the Gene Ontology program to "plasticity".
The duration of hypoxemia is a critical parameter in the differentiation capacity of MSC. Even in growth promoting conditions, hypoxia enhanced a genetic program that maintained the cells undifferentiated and multipotent. This condition may better reflect the in vivo gene signature of MSC, with potential implications in regenerative medicine.

Full text

RESEARCH ARTICLE Open Access
Long term culture of mesenchymal stem cells in
hypoxia promotes a genetic program maintaining
their undifferentiated and multipotent status
Leticia Basciano, Christophe Nemos, Bernard Foliguet, Natalia de Isla, Marcelo de Carvalho, Nguyen Tran and
Ali Dalloul
*
Abstract
Background: In the bone marrow, hematopietic and mesenchymal stem cells form a unique niche in which the
oxygen tension is low. Hypoxia may have a role in maintaining stem cell fate, self renewal and multipotency.
However, whereas most studies addressed the effect of transient in vitro exposure of MSC to hypoxia, permanent
culture under hypoxia should reflect the better physiological conditions.
Results: Morphologic studies, differentiation and transcriptional profiling experiments were performed on MSC
cultured in normoxia (21% O
2
) versus hypoxia (5% O
2
) for up to passage 2. Cells at passage 0 and at passage 2
were compared, and those at passage 0 in hypoxia generated fewer and smaller colonies than in normoxia. In
parallel, MSC displayed (>4 fold) inhibition of genes involved in DNA metabolism, cell cycle progression and
chromosome cohesion whereas transcripts involved in adhesion and metabolism (CD93, ESAM, VWF, PLVAP,
ANGPT2, LEP, TCF1) were stimulated. Compared to normoxic cells, hypoxic cells were morphologically
undifferentiated and contained less mitochondrias. After this lag phase, cells at passage 2 in hypoxia outgrew the
cells cultured in normoxia and displayed an enhanced expression of genes (4-60 fold) involved in extracellular
matrix assembly (SMOC2), neural and muscle development (NOG, GPR56, SNTG2, LAMA) and epithelial
development (DMKN). This group described herein for the first time was assigned by the Gene Ontology program
to “plasticity”.
Conclusion: The duration of hypoxemia is a critical parameter in the differentiation capacity of MSC. Even in
growth promoting conditions, hypoxia enhanced a genetic program that maintained the cells undifferentiated and
multipotent. This condition may better reflect the in vivo gene signature of MSC, with potential implications in
regenerative medicine.
Background
Adult bone marrow is a widely used source of mesench-
ymal stem cells (MSC) that can be isolated and
expanded in culture while keeping the ability to form
adipocytes, chondrocytes and osteoblasts [1,2] and possi-
bly other cell types including cardiomyocytes [3]. Within
the bone marrow, MSC may interact with hemopoietic
stem cells (HSC), which reside in a specific microenvir-
onment formed by various stromal precursor cells and
osteoblasts, called the niche [4-6]. Whether MSC reside
in the same niche amidst HSC or whether they dwell in
a specific niche is presently unknown. Different types of
niches for hemopoietic progenitors may exist depending
on their more or less primitive state [7] located near
bone surfaces away from blood vessels and therefore
submitted to a low O
2
tension. It is thus inferred that
stem cells are equipped to survive in a hypoxic environ-
ment and that this condition plays a role in the mainte-
nance of multipotency [8] and extension of survival [9].
ThismayholdtrueformurineandhumanMSCas
their proliferation, differentiation and survival [10-12]
are affected by culture in low O
2
tension. However the
degree and duration of hypoxia described in the litera-
ture vary greatly and may result in opposite effects on
* Correspondence: ali.dalloul@medecine.uhp-nancy.fr
Nancy University Medical School (EA 4369) and School of Surgery (NT),
54500 Vandœuvre-lès-Nancy, France
Basciano et al.BMC Cell Biology 2011, 12:12
http://www.biomedcentral.com/1471-2121/12/12
© 2011 Basciano e t al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attri bution License (http://creativecommons.org /licenses/by/2.0), which permits unrestricte d use, distribution, and
reproductio n in any medium, provided the original work is properly cited.

the proliferation and differentiation capacities of MSC
[13-15]. So far one study described the long term (one
month) effect of human MSC culture under low O
2
ten-
sion (2% O
2
) and showed improved survival and
increase in adipocytic and osteogenic differentiation
capacity [16]. In the present study we cultured human
MSC in normoxia (21% O
2
) versus hypoxia (5% O
2
)for
up to passage 3 (P3) and compared their morphology
differentiation potential and mRNA expression at early
and late passages. We observed that cells cultured under
low O
2
tension were more undifferentiated than cells
cultured in normoxia. Further, hypoxia inhibited the
expression of genes involved in DNA replication and
cell division at P0. At P2, however, Gene Ontology
(GO) analysis revealed that only one significant func-
tional group of genes was stimulated and related to
“plasticity”. We conclude that culture in hypoxia main-
tains MSC in a multipotent, undifferentiated state.
Results
The effect of hypoxia on MSC expansion and phenotype
Bone marrow mononuclear cells (MNC) were cultured
and passaged until P3. As shown in Figure 1, both the
CFU-F numbers and the mean colony size were signifi-
cantly smaller at P0 in 5% O
2
(hypoxia) versus 21% O
2
(normoxia). This diminution was however less signifi-
cant at P1 (0.05<p < 0.1), and at P2 the numbers of
CFU-F were enhanced by hypoxia. In other experiments,
cells were trypsined and counted, total cell numbers
were diminished in hypoxia versus normoxia at P0
whereas they were enhanced at P1; the overall cell dou-
bling/day was diminished by hypoxia until P1 and aug-
mented afterwards (data not shown).
In parallel, immunostaining and flow cytometry were
performed at various time points. MSC were negative for
CD45 and CD34 and positive albeit variably for several
other markers (Figure 2). In brief, cultured cells displayed
a typical MSC profile with stable phenotype overtime
and no significant phenotypic differences between
hypoxic and normoxic conditions in agreement with
others [17]. Only STRO-1 was transiently expressed on
50% of the cells at P0 under hypoxia and diminished
thereafter as expected from previous observations [18].
In brief, after a lag phase during which the hypoxic cells
grew slower than normoxic cells, the former expanded
faster in late passages. In contrast, with the exception of
STRO-1 which is dicussed in the relevant section, the
phenotype of MSC was not modified during culture
expansion irrespective of the oxygen tension. We next
looked for qualitative effects of hypoxia and investigated
the morphology of MSC by light and electron microscopy
and evaluated the numbers of mitochondria in hypoxic
versus normoxic cells.
Culture of MSC in hypoxia inhibited cell differentiation
and mitochondrial biogenesis
The number of mitochondria was evaluated by flow
cytometry, by Mitotracker staining and by transmission
electron microscopy TEM at P2, under hypoxia and
normoxia in 3 independent experiments. Cells were
Figure 1 The effect of oxygen tension on CFU-F size and numbers. Cells were plated at 1000 (plain histograms) and 10000 MNC/60 cm
2
(dotted histograms) from total BM for P0. For the next passages, 100 (plain histograms) and 1000 cells/cm
2
(dotted histograms) were seeded.
Cells were incubated under hypoxic (5% O
2
, black histograms) or normoxic conditions (21% O
2
, white histograms) respectively and colonies
were counted and their size evaluated (A & B). Mean +/- of 3 to 5 independent experiments. Numbers above the histograms (A & B) represent
the significance calculated using bilateral paired Student’s t test. A representative aspect of colonies at various passages is shown (C).
Basciano et al.BMC Cell Biology 2011, 12:12
http://www.biomedcentral.com/1471-2121/12/12
Page 2 of 12

analyzed by flow cytometry. The mean fluorescence
intensity of hypoxic cells compared to normoxic cells
was 47.7 versus 117 on histograms (Figure 3A). Thus
hypoxia did inhibit the biosynthesis of mitochondria.
The same cells were also permeabilized and stained with
Mitotracker and analysed on fluorescence microscopy.
As shown in Figure 3B, normoxic cells looked brighter
than the hypoxic ones. We observed a 50 to 75% inhibi-
tion of mitochondrial biogenesis by counting the mito-
chondria on TEM sections. Strikingly, hypoxic cells
Figure 2 Stability of MSC phenotype in culture. Flow cytometry analysis of surface markers at P0 and P2 in hypoxia and normoxia.
Histograms show the intensity of several markers within the CD34-CD45- (dot plot), MSC-enriched population from the bone marrow.
A representative experiment out of 3 from distinct donors is shown.
Basciano et al.BMC Cell Biology 2011, 12:12
http://www.biomedcentral.com/1471-2121/12/12
Page 3 of 12

looked less differentiated than normoxic ones. They dis-
played larger and less convoluted nuclei and more abun-
dant nucleoli, and a higher nuclei/cytoplasm index,
althoughthesizeofcellswasverysimilarunderboth
conditions (Figure 3C).
Long term hypoxia stimulated the differentiation of MSC
in adipocytes and osteocytes
MSC were grown from the start in normoxia versus
hypoxia until P2, then washed and cultured in osteo-
genic or adipogenic lineage-specific media. The cells
were kept in normoxia and hypoxia during the differen-
tiation process. Differentiated cells were characterized
by conventional histology staining (Figure 4A) and by
RT-PCR for the amplification of lineage-specific tran-
scripts for adipocytes (LPL, PPARg) and osteocytes
(ALPL, Runx2), respectively. The later transcripts were
investigated in MSC at P2 before they were cultured in
differentiating conditions. As shown from 2 independent
experiments in Figure 4B, the expression of ALPL was
stronger in hypoxic MSC than in normoxic cells.
Further, while Runx2 transcription was undetectable in
normoxic MSC, it was induced in hypoxic cells. This
suggested that hypoxic cells were more prone to osteo-
genic differentiation than normoxic cells. We indeed
observed that hypoxic MSC generated more (50% to
100% increase) osteogenic and adipogenic colonies, than
normoxic MSC (Figure 4C).
Figure 3 Morphological aspect of MSC. The amount of mitochondria was evaluated by flow cytometry (A) and optical microscopy (B) on MSC
stained with Mitotracker Orange. TEM was performed on MSC at P2 culture in normoxic or hypoxic conditions (C). (N = 3).
Basciano et al.BMC Cell Biology 2011, 12:12
http://www.biomedcentral.com/1471-2121/12/12
Page 4 of 12

Figure 4 Culture in hypoxia enhanced the potential of MSC to differentiate in adipocytes (A) and osteocytes (O). MSC were cultured in
hypoxia or normoxia until P2, and shifted to adipocyte- or osteocyte-specific differentiation conditions respectively for 2-4 more weeks. The
aspect of differentiated colonies under hypoxia is shown (A). In 2 independent experiments (B), MSC were harvested at P2, RNA from normoxic
(N) or hypoxic (H) cells was extracted, reverse-transcribed and amplified by PCR with primers specific for control GAPDH and the indicated
genes, representative of adipocytic (LPL, PPARg) and osteocytic (ALPL, Runx2) lineages. The same cells were grown in osteocytic and adipocytic-
specific medias and colonies were counted and compared to the numbers of CFU-F generated in MSC-specific medium (C).
Basciano et al.BMC Cell Biology 2011, 12:12
http://www.biomedcentral.com/1471-2121/12/12
Page 5 of 12

MSC from 3 distinct donors were cultured in nor-
moxicandinhypoxicconditions.Thecellsfromeach
donor/condition were harvested at P0 and P2. RNAs
were extracted thereafter, processed and hybridization
with microarrays was performed in 6 independent
experiments. Comparative analysis of transcriptome
from MSC cultured at P0 in hypoxia versus normoxia
revealed 386 dysregulated genes (1% out of 41,000
genes), of which 174 were up regulated (45%) and 212
were down regulated (55%). GO analysis performed on
the 386 dysregulated genes revealed an over-representa-
tion of genes (122 genes, p < 0.1) involved in DNA
metabolism (cell cycle, replication, M-phase, spindle
organization and biogenesis) and/or coding for nuclear
proteins (chromosome, spindle, nucleus). Among these
122 genes, 118 (98%) had a 2-6 fold decreased expres-
sion with the range [2-5.94] corresponding to NAV2
and RRM2 genes respectively. Figure 5 and Table 1
summarize the analysis and showed the ten first down
regulated genes after short culture in hypoxia. Contrary
to down regulated genes, we showed no significant GO
over-representation for up regulated genes. Nevertheless,
we could observe a strong trend of over representation
for genes coding for membrane receptors (CD93, ZP1,
ESAM, protocadherin 17) and paracrine factors (Leptin,
angiopoietin 2, VWF) with a range of over expression
[2-6.96] corresponding to ALDOC and TCF1 genes
respectively. Table 1 depicts the ten up regulated genes
at P0 in hypoxia.
Comparative analysis of transcriptome from MSC cul-
tured at P2 in hypoxia versus normoxia revealed 519
dysregulated genes, of which 264 were up regulated
(50.9%) and 255 were down regulated (49.1%). Gene
ontology analysis performed on the 519 deregulated
genes revealed an over-representation of genes involved
in cell plasticity (48 genes, p < 0.1) and adhesion (37
genes,p<0.1).Whenweincreasedthestringencyof
analysis by selecting genes that were 4-fold differentially
expressed on 4 arrays, we eliminated genes for cell
adhesion GO term but not for plasticity. All these 48
genes characterizing plasticity GO term were up regu-
lated with a range between 4.2 and 58.3. Table 2 shows
the ten first up regulated genes after long term culture
(P2) in hypoxia. Several transcripts were validated by
quantitative, real time PCR (qPCR) (Figure 5B). The
results matched that of the gene arrays with enhanced
expression of HOXA11, KIT, WNT4, OXCT2 and
inhibited expression of CCL2, CX3CL1 under hypoxia.
Discussion
Hematopoietic and Stromal Stem Cells adapt themselves
to hypoxia in culture which probably reflects their native
hypoxic microenvironment [1-3]. Accordingly, several
teams cultured HSC and MSC in hypoxic conditions in
Figure 5 Genetic reprogramming of MSC under hypoxia. MSC from 3 donors were cultured until P0 and P2. RNA was extracted from each
culture, processed and hybridized on Agilent DNA microarrays. Diagram A shows the GO analysis of differentially expressed transcripts at P0. Six
transcripts were chosen and amplified by qPCR in order to validate gene array results obtained after long term hypoxia using the same extracts.
Mean +/- SD from 3 experiments.
Basciano et al.BMC Cell Biology 2011, 12:12
http://www.biomedcentral.com/1471-2121/12/12
Page 6 of 12

order to study their differentiation capacity [8-16,19].
Another goal of these experiments is the hope of
expanding these cells while maintaining their “stemness”
properties. Although data from various laboratories are
difficult to compare due to wide variations in oxygen
tension, ranging from 0.1 to 5%, and the duration of
culture, ranging from a few hours to 2 months, a few
studies evidenced an early growth inhibition under
hypoxia [16]. Hypoxia induces cell cycle arrest in mam-
malian cells, however stem cells are more resistant to
hypoxia than their progenies again reflecting their nat-
ural environment and their intrinsic quiescent state. We
performed MSC cultures in 5% O
2
which may be phy-
siological for bone marrow stem cells [20]. As MSC and
HSC form a single bone marrow niche [21], 5% O
2
ten-
sion is likely to be physiological for MSC as well. We
observed that MSC grew slower under 5% O
2
than
under 21% O
2
until P1, and gained a progressive growth
advantage in the next passages, which matched pre-
viously published results [16]. Meanwhile, hypoxic MSC
expressed more adhesion and extracellular matrix mole-
cules in early and late cultures, contained less mitochon-
dria and displayed undifferentiated morphological
features. In brief, early growth inhibition was somewhat
expected and strikingly, GO analysis assigned down
regulated genes to DNA metabolism and repair (POLQ,
RRM2,XRCC2,FANCD2),cellcycleprogression
(E2F8, MKI67) and chromosomal organization (CENP-
B, AURKB, KLF4) in agreement with our data on prolif-
eration and colony size. Such inhibition likely contri-
butes to the maintenance of MSC in a quiescent state,
inasmuch as the inhibition of mitochondria may protect
Table 1 Ten first down and upregulated genes at P0 in hypoxia
Gene Fold expression
H/N
Genbank
Accession
Putative Function
Down Regulated
RRM2 5.94 NM_001034 Ribonucleotide Reductase
XRCC2 5.80 CR749256 X Ray damage DNA Repair
KIF24 5.16 AK001795 Kinesin: chromatid assembly
POLQ 4.99 AF090919 DNA polymerase theta
E2F8 4.95 NM_024680 Cell cycle progression
FANCD2 4.93 NM_001018115 DNA Repair
ESCO2 4.86 NM_001017420 Sister chromatid cohesion
AURKB 4.74 NM_004217 Chromosome segregation
CENPN 4.48 AK023669 Binding to Centromeres
MKI67 4.46 NM_002417 Cell proliferation
Up Regulated
TCF1 6.96 NM_000545 Hepatic Transcription Factor
LEP 6.39 NM_000230 Metabolism, apoptosis, angiogenesis
ANGPT2 5.69 NM_001147 Antagonise vascular remodelling
ZP1 5.47 NM_207341 Sperm binding to zona pellucida
VWF 5.41 NM_000552 Platelet binding to endothelium
GIMAP4 5.37 NM_018326 T-cell development, Tumor suppressor ?
CD93 4.56 NM_012072 Intercellular adhesion, clearance apoptotic cells
PLVAP 4.25 NM_031310 Adhesion of Vascular Endothelial cells ?
ESAM 4.24 NM_138961 Adhesion of Endothelial cells
PCDH17 4.14 NM_001040429 Cell-cell connexions in the brain
Comparative analysis of transcriptome from MSC at P0 in hypox ia versus normoxia. Mean from 3 distinct samples.
Table 2 Ten first deregulated genes at P2 in hypoxia
Gene Fold
expression
H/N
Genbank
Accession
Putative Function
SMOC2 58.32 NM_022138 Promotion of Matrix assembly
PLEKHA6 13.59 NM_014935 Adhesion
DMKN 10.79 NM_033317 Epithelial cell differentiation
KIT 8.62 NM_000222 Stem cell Proliferation
LAMA1 8.49 NM_005559 Development Retina and
Myocytes
SNTG2 7.52 NM_018968 Eye development
GPR56 6.01 NM_201525 Neural development
OXCT2 5.81 NM_022120 Ketone body utilisation
NOG 5.13 NM_005450 Neural tube fusion, joint
formation
HOXA11 4.80 NM_005523 Uterine development
Stimulation of plasticity genes under hypoxia according to GO analysis.
Basciano et al.BMC Cell Biology 2011, 12:12
http://www.biomedcentral.com/1471-2121/12/12
Page 7 of 12

MSC from apoptosis. How could we reconcile these data
with our observation that hypoxic MSC gained a growth
advantage over normoxic MSC at late passages? The
contradiction may be apparent. One possibility is that
these cells became more sensitive to growth factors pre-
sent in the serum. Whether growth advantage is due to
a stimulation of proliferation pathways or to the expres-
sion of receptors for cytokines and growth factors or
both, is worth investigating. Note in this respect that
CXCR4 was induced by hypoxia.
As MSC in their niche are supposed to be quiescent
and multipotent, these properties are apparently disso-
ciated in our in vitro model, with quiescence being
observed at early passages, whereas multipotency is aug-
mented at late passages. Until we understand the in vivo
signature of MSC, we cannot draw conclusions and pre-
tend that in vitro culture in hypoxia mimics the niche.
Although expected from previous studies and sug-
gested by our morphological observations, maintenance
of stem cell characteristics at early passages under
hypoxia was not inferred from GO analysis. Early
induced genes were not assigned to multipotency but
instead belonged mostly to adhesion molecules such as
Von Willebrand Endothelial Cell Adhesion molecule
and Protocadherin (Table 1). However, several genes
may clearly affect stemness. CD93 regulates the clear-
ance of apoptotic cells, a function critical to develop-
ment, maintenance of homeostasis and tissue repair
[22]. The WNT-related transcription factor TCF1 may
regulate MSC and enhance their osteogenic differentia-
tion [23]. At variance with the above genes, 8 genes
potentially involved in the control of differentiation
towards adipocytes, osteocytes and chondrocytes [1]
were not modified by hypoxia [Additional file 1]. Strong
expression of adhesion molecules may be physiologically
relevant and correlate with broader differentiation
potential of hypoxic MSC. Indeed VWF is a marker of
endothelial commitment [24] and PLVAP, reported here
for the first time in MSC is a leukocyte trafficking mole-
cule [25] which may help transendothelial migration of
MSC from the bone marrow. Stimulation of Leptin is
also meaningful as a recent work demonstrated that it
helps maintain mesenchymal progenitor cells undifferen-
tiated [26]. This result also shows that hypoxia impacts
the metabolism of MSC in agreement with a study on
rat MSC [27]. In this study however, the duration of
hypoxia was 24 hours only. Yet, several genes involved
in adhesion and extracellular matrix were stimulated.
Hypoxia generates “plasticity”.AtP2inhypoxia,only
one group of genes was stimulated and was assigned to
plasticity. SMOC2 is the first induced gene (Table 2)
and plays a role in angiogenesis and extracellular matrix
assembly [28], yet a recent article demonstrated that a
related protein increases life span and fecundity in
Drosophila [29]. Kit gene was induced thus correlating
with proliferation [30]. LAMA1/laminin [31] and
SNTG2/syntrophin gamma-2 [32,33] are both involved
in retinal and eye development whereas GPR56, a
seven-transmembrane domain protein, is involved in
brain cortical patterning [34].
We have observed that hypoxia stimulated several
genes which converge to maintain the cells in an undif-
ferentiated state, and facilitate transendothelial migra-
tion of MSC (Table 1 and 2). In parallel, hypoxia
inhibited the expression of genes involved in cell prolif-
eration (Table 1). This transcription profile probably
reflects the intrinsic genetic program of MSC in vivo as
these cells are quiescent, and endowed with migration
and multilineage differentiation capacities. With respect
to migration, note that CXCR4 was induced by hypoxia
[Additional file 1 and reference 3] with potential impli-
cations in the egress of MSC from the bone marrow.
This is in contrast with the cell surface phenotype of
MSC which was almost unaffected in our experiments
and in others [17]. Note however that STRO-1 was
expressed only transiently in cultured hypoxic but not
in normoxic cells. This is not totally surprising since
STRO-1 expression is gradually lost during culture
expansion [18,35]. Even though STRO-1 is useful to iso-
late MSC from various tissues, it is not positive on all
MSC [36]. Interestingly, STRO-1+ cells displayed
enhanced expansion and multilineage differentiation
potentialities [37,38]. Thus, the expression of STRO-1
on hypoxic MSC may not be fortuitous and reflects
multipotential status.
Our results may have physiological & medical applica-
tions. Oxygen tension is a critical parameter, possibly the
most important one, in the culture of stem cells. As nes-
tin-positive MSC and HSC form a unique bone marrow
niche [21], hypoxia is undoubtedly a physiological milieu
for MSC. In this respect it is worth mentioning that nes-
tin was induced by hypoxia in our experiments [Addi-
tional file 1]. Given the ever growing therapeutic
applications of MSC in regenerative medicine [39] and in
autoimmune diseases [40], the impact of O
2
on the func-
tions of MSC should be carefully evaluated. For instance,
intravenous injection of MSC results in their accumula-
tion in the pulmonary parenchyma. Although this was
sufficient to treat experimental septic shock [41], disse-
mination of MSC into other organs may be necessary to
treat systemic diseases; induction of molecules involved
in transendothelial migration as observed in our experi-
ments may be helpful in this setting. Conversely however,
hypoxia may be detrimental to other purposes. MSC
inhibit TH17 cells in a CCL2-dependent manner by pro-
cessing this chemokine to an antagonistic derivative, and
may be helpful in the treatment of Experimental Allergic
Enkephalitis (EAE) [42]. Note in this respect that the
Basciano et al.BMC Cell Biology 2011, 12:12
http://www.biomedcentral.com/1471-2121/12/12
Page 8 of 12

transcription of CCL2 in MSC was inhibited under
hypoxia in our experiments. Altogether our data demon-
strate that hypoxia favoured the “undifferentiation pro-
gram”of MSC, it remains to evaluate the impact of
hypoxia on each desired function of these cells in the
event of medical applications.
As the Holy Grail is to use tissue-specific cells derived
from MSC in regenerative medicine, culture of MSC in
hypoxia at least until P2 in order to induce the expres-
sion of a broad range of tissue-specific genes, may be
beneficial, inasmuch as it also enhanced the cell numbers
in parallel to their differentiating capacity. In this respect
differentiation experiments should be carried to evaluate
the potential of MSC to generate endothelial cells, myo-
cytes and neurons. Finally, the most relevant result here
is the demonstration of induction of plasticity, a major
property of MSC, at variance with HSC [43].
Conclusions
The duration of hypoxemia is a critical parameter for
the differentiation capacity of MSC. Hypoxia maintains
the cells undifferentiated and in parallel enhances the
expression of genes involved in the development of
various, mesodermal and non mesodermal, cell lineages.
In this respect hypoxia may increase both the multipo-
tency and the transdifferentiation potential of MSC.
Methods
Isolation and culture of human MSC
MSC were obtained from bone marrow samples from 6
adult donors with their informed consent following the
bylaws of the ethical committee of the Nancy University.
MNC were counted and plated at 50 × 10
3
cells/cm
2
and cultured in Minimal Eagle Medium (a-MEM; Cam-
brex) supplemented with 10% fetal bovine serum, gluta-
mine 2 mM and penicilin. They were incubated at 37°C
under an atmosphere of 5% CO
2
in either 21% O
2
(herein referred to as normoxia) or 5% O
2
(hypoxia).
Hypoxia was maintained in a dedicated incubator
(Sanyo) connected to CO
2
and N
2
injectors, in which
relative N
2
was increased to reach the desired O
2
con-
centration. Medium was changed twice weekly. MSC
were isolated by adherence to plastic. In primoculture,
cells were harvested after 21 days (passage 0 or P0) and
counted by trypan blue (Sigma-Aldrich). For the next
passages (P1, P2 or P3), cells were subcultured at differ-
ent seeding densities (100 or 1000 cells/cm
2
)for
14 days, trypsinized and counted.
For colony-forming unit fibroblast (CFU-F) assays,
1000 and 10000 MNC from total BM were seeded in
60 cm
2
dishes in duplicate. They were cultured for
14 days in normoxic and hypoxic conditions. After that,
cells were washed 3 times with PBS and stained with
Cristal Violet solution (Sigma-Aldrich). Plates were
scanned and CFU-F of more than 30 cells, were scored.
The size of the colonies was determinates thereafter
using the “Image J”software. CFU-Fs were counted at
P0, P1, P2 and P3.
To determine the population doubling (PD), cells in
P1 and P2 were seeded at 100 or 1000 cells/cm
2
in T75
flasks and trypsinized after 14 days. Cells were counted
and population doubling calculated as: PD = log
(N
f
/N
i
)/log 2, N
f
= Final cell number; N
i
= Initial cell
number.
Microscopy
For electron microscopy, cells were either trypsinized and
pelleted before processing or processed as cell mono-
layers in 12 well plates. Briefly, cells were fixed for 2 h at
4°C in 2.5% glutaraldehyde containing 0.1 M Na cacody-
late, then rinsed for 3 h in cacodylate buffer and incu-
batedfor30minatRTin1%osmiumtetroxydein
cacodylate buffer, rinsed and dehydrated in increasing
concentrations (30, 50, 70, 80, 90%) of ethanol, for 5 min
each, then in 100% ethanol for 3 × 20 min. Finally the
cells were embedded in a 50/50 volume mixture of resin
and propylene oxide. A volume of 30 ml of resin EMS
(Euromedex, France) is made by mixing 18.2 ml of
EMBED (spi-pon 812), 12.4 ml DDSA, 9.4 ml NMA, and
0.7mlDMP30for20minRTonastirringmagnet.Cell
monolayers on plastic wells were treated twice with 100%
xylene and semi thin (1.5 mm) or ultra thin sections
(70-90 nm) were performed using an ultra microtome
(Reichert-Yung). Sections were observed on a Phillips
CM12 electron microscope and photographed.
For optical microscopy and mitochondrial staining,
cells were incubated with 100 nM Mitotracker orange
CMTMRos (Invitrogen), for 45 min at 37°C, washed in
1× PBS, and photographed on an Olympus DP-70
microscope.
Flow Cytometry
For mitochondrial staining, cells were incubated as
above, enzymatically detached and resuspended in phe-
nol-red free medium before flow cytometry analysis.
For surface antigen expression on culture-expanded
MSC, cells were detached, washed, pelleted and resus-
pended in DMEM medium without phenol red and
incubated for 20 minutes at room temperature with
antibodies in a final volume of 100 μl and eventually
resuspended in 4% paraformaldehyde until analysis on
FC500 Beckman Coulter flow cytometer. We used
monoclonal antibodies listed in Table 3. Antibodies
were conjugated to fluorescein isothiocyanate (FITC),
allophycocyanin (APC) or phycoerythrin (PE). Each sam-
ple was stained with either CD34 or CD45 (negatively)
Basciano et al.BMC Cell Biology 2011, 12:12
http://www.biomedcentral.com/1471-2121/12/12
Page 9 of 12

and with one of the other MAbs from Becton Dickinson
(BD, USA), Beckman Coulter (BC, Canada) or Santa
Cruz (SC, USA).
MSC Differentiation Assays
The potential of MSC to differentiate into the adipo-
genic and osteogenic lineages was verified. MSC were
enzymatically detached from the culture flasks at nearly
confluence and replated in 60 cm
2
dishes at different
densities and with specialized culture mediums accord-
ing to the desired differentiation:
Adipogenic differentiation
MSC cells were seeded at 500 cells/cm
2
and cultured for
14 days with standard culture medium. After that we
induced differentiation by supplementing standard cul-
ture medium with dexamethasone 1 μM, indomethacin
60 μMandinsulin5μg/ml for 21 days. Cells were then
washed with PBS, fixed in 10% formaldehyde, washed
with 60% isopropanol and stained with Oil red O Solu-
tion (Sigma-Aldrich) to detect lipid droplets within the
cells.
Osteogenic differentiation
MSC cells were seeded at 100 cells/cm
2
and cultured for
14 days with standard culture medium. After that we
induced differentiation by supplementing standard cul-
ture medium with ascorbic acid 60 μM, b-glycerol phos-
phate 10 mM and dexamethasone 0.1 μMfor21days.
Cells were washed with PBS and fixed in ice-cold 70%
ethanol and stained with Alizarin Red S (pH: 4.1;
Sigma-Aldrich) to detect Ca
2+
deposits.
Differentiation was further assessed by PCR amplifica-
tion of lineage-specific transcripts and GAPDH as con-
trol using primers listed in Table 4.
Lineage specific transcript analyses
Microarrays
Total RNA was extracted and purified from MSC trea-
ted in normoxic or hypoxic conditions (P0-P2) accord-
ing to the RNeasy Mini Kit protocol (Qiagen, Valencia,
CA, USA). To perform whole Human Genome Oligo
(60-mer) array gene expression analysis, total RNA was
extracted from MSC treated on normoxic or hypoxic
condition (n = 4) each, including technological and
biological replicates). For each sample, 350 ng of total
RNA was reverse transcribed, linear amplified, and
labelled with Cy3 (one colour protocol) using Agilent’s
Low RNA Input Linear Amplification Kit PLUS,
according to manufacturer’s instructions. After label-
ling, samples were measured on a Nanodrop microar-
ray module for labelling efficiency and quantification.
Samples were then hybridized on Agilent 4 × 44 K
whole human genome GE arrays (Agilent Design
#014850) at 65°C for 17 h. After washing in GE wash-
ing buffers, the slide was scanned with Agilent Micro-
array Scanner G2565CA. Feature extraction software
(Version 9.5.3.1, Agilent technologies Inc., CA, USA)
was used to convert the image into gene expression
data. Genespring GX10 software (Agilent technologies
Inc., CA, USA) was used to compile and analyse data.
First normalized data (background substracted) were
filtered on expression (lower and upper cut-off 20 and
100 respectively for 100% of signal), then on error (CV
< 50% for 100% of signal). Only genes that were 2-fold
differentially expressed on 4 arrays were scored as sig-
nificant and used for analysis. Biological process and
cellular component of genes were classified according
to Gene Ontology (p < 0.1).
Table 3 List of monoclonal antibodies
Antibody Conjugated Isotype Reference
Anti-CD34 FITC IgG1 Mouse IM1870, BC
Anti-CD45 FITC IgG1 Mouse A07782, BC
Anti-CD90 PE IgG1 Mouse IM3600U, BC
Anti-CD105 PE IgG3,k Mouse A07414, BC
Anti-CD271 PE IgG1, k Mouse 557196, BD
Anti-CD106 PE IgG1, k Mouse 555647, BD
Anti- CD166 PE IgG1, k Mouse 559263, BD
Anti-CD73 PE IgG1, k Mouse 550257, BD
Anti-CD29 APC IgG1, k Mouse 559883, BD
Anti-CD44 APC IgG2b, k Mouse 559942, BD
Anti-STRO-1 PE IgM Mouse sc-47733, SC
Isotype control APC IgG2b, k Mouse 555745, BD
Isotype control PE IgG1, k Mouse 555749, BD
Isotype control PE IgM Mouse sc-2870, SC
Isotype control APC IgG1, k Mouse 555751, BD
Isotype control FITC IgG1, Mouse A07795, BC
Isotype control PE IgG1, Mouse A07796, BC
Table 4 List of primers for amplification of lineage-
specifics transcripts (GAPDH is used as control)
Gene Product Primers Product
Size (bp)
GAPDH
(NM_002046.3)
Fw: 5’-AATCCCATCACCATCTTCCAGG-3’
Rv: 5’-
AGAGGCAGGGATGATGTTCTGG-3’
417
ALPL
(NM_000478)
Fw: 5’-CTGGACCTCGTTGACACCTG-3’
Rv: 5’-GCGGTGAACGAGAGAATGTC-3’
546
LPL
(NM_000237.2)
Fw: 5’-AAAGCCCTGCTCGTGCTGAC-3’
Rv: 5’-ACAGGATGTGGCCCGGTTTA-3’
406
PPARG
(NM_005037.5)
Fw: 5’-GGAGAAGCTGTTGGCGGAGA-3’
Rv: 5’-CACAATGCTGGCCTCCTTGA-3’
431
RUNX-2
(NM_001015051.2)
Fw: 5’-AACTTCCTGTGCTCGGTGCTG-3’
Rv: 5’-GGGGAGGATTTGTGAAGACGG-3’
268
Basciano et al.BMC Cell Biology 2011, 12:12
http://www.biomedcentral.com/1471-2121/12/12
Page 10 of 12

Real time PCR
For quantitative PCR, the cDNA used for DNA chip ana-
lysis were amplified using the primers listed in Table 5.
The reactions were carried out in 25 μLvolumecon-
taining cDNA and Master mix (Power SYBR Green PCR
Master Mix kit). Thermocycling conditions were 40
cycles of two steps: 15 sec at 95°C plus 1 min at 60°C.
Detection was performed using a Mastercycler
®
ep real-
plex real-time PCR system (Eppendorf). The relative
RNA level and fold change in hypoxia/normoxia condi-
tion were calculated using the 2
-ΔCt
using GAPDH as a
calibrator.
Statistics
All statistics were carried using the bilateral Student’st
test on Excel program, in order to compare the data in
normoxia versus hypoxia.
Additional material
Additional file 1: HN-fold change 4.
Acknowledgements
We thank Pr JP Frippiat for carefully reading the manuscript and Mrs J
Chanel for help in processing MSC for TEM. This work is supported by grants
from the “Communauté Urbaine du Grand Nancy”and “Ligue Grand Est
contre le Cancer”.
Authors’contributions
LB did the cultures and PCRs and participated in Microscopy and FACS
analysis, CN did the gene arrays, BF did the microscopy, N de I did the
cultures, M de C helped in FACS, NT participated in the experiments and
culture, AD designed the experiments, wrote the article and participated in
microscopy, gene array and FACS analysis.
All authors read and approved the final manuscript.
Received: 15 December 2010 Accepted: 30 March 2011
Published: 30 March 2011
References
1. Baksh D, Song L, Tuan RS: Adult mesenchymal stem cells:
characterization, differentiation, and application in cell and gene
therapy. J Cell Mol Med 2004, 8:301-316.
2. Delorme B, Chateauvieux S, Charbord P: The concept of mesenchymal
stem cells. Regen Med 2006, 1:497-509.
3. Zhang M, Mal N, Kiedrowski M, Chacko M, Askari AT, Popovic ZB, Koc ON,
Penn MS: SDF-1 expression by mesenchymal stem cells results in trophic
support of cardiac myocytes after myocardial infarction. FASEB J 2007,
21:3197-3207.
4. McCulloch EA, Siminovitch L, Till JE, Russell ES, Bernstein SE: The cellular
basis of the genetically determined hemopoietic defect in anemic mice
of genotype Sl-Sld. Blood 1965, 26:399-410.
5. Schofield R: The relationship between the spleen colony-forming cell
and the haemopoietic stem cell. Blood Cells 1978, 4:7-25.
6. Taichman RS: Blood and bone: two tissues whose fates are intertwined
to create the hematopoietic stem-cell niche. Blood 2005, 105:2631-2639.
7. Wilson A, Trumpp A: Bone-marrow haematopoietic-stem-cell niches. Nat
Rev Immunol 2006, 6:93-106.
8. Cipolleschi MG, Dello Sbarba P, Olivotto M: The role of hypoxia in the
maintenance of hematopoietic stem cells. Blood 1993, 82:2031-2037.
9. Packer L, Fuehr K: Low oxygen concentration extends the lifespan of
cultured human diploid cells. Nature 1977, 267:423-425.
10. Martin-Rendon E, Hale SJM, Ryan D, Baban D, Forde SP, Roubelakis M,
Sweeney D, Moukayed M, Harris AL, Davies K, Watt SM: Transcriptional profiling
of human cord blood CD133+ and cultured bone marrow mesenchymal
stem cells in response to hypoxia. Stem Cells 2007, 25:1003-1012.
11. Sekiya I, Larson BL, Smith JR, Pochampally R, Cui J, Prockop DJ: Expansion
of human adult stem cells from bone marrow stroma: conditions that
maximize the yields of early progenitors and evaluate their quality. Stem
Cells 2002, 20:530-541.
12. Annabi B, Lee Y, Turcotte S, Naud E, Desrosiers RR, Champagne M,
Eliopoulos N, Galipeau J, Béliveau R: Hypoxia promotes murine bone-
marrow-derived stromal cell migration and tube formation. Stem Cells
2003, 21:337-347.
13. Salim A, Nacamuli RP, Morgan EF, Giaccia AJ, Longaker MT: Transient
changes in oxygen tension inhibit osteogenic differentiation and Runx2
expression in osteoblasts. J Biol Chem 2004, 279:40007-40016.
14. Lennon DP, Edmison JM, Caplan AI: Cultivation of rat marrow-derived
mesenchymal stem cells in reduced oxygen tension: effects on in vitro
and in vivo osteochondrogenesis. J Cell Physiol 2001, 187:345-355.
15. Malladi P, Xu Y, Chiou M, Giaccia AJ, Longaker MT: Effect of reduced
oxygen tension on chondrogenesis and osteogenesis in adipose-derived
mesenchymal cells. Am J Physiol Cell Physiol 2006, 290:C1139-46.
16. Grayson WL, Zhao F, Izadpanah R, Bunnell B, Ma T: Effects of hypoxia on
human mesenchymal stem cell expansion and plasticity in 3 D
constructs. J Cell Physiol 2006, 207:331-339.
17. Holzwarth C, Vaegler M, Gieseke F, Pfister SM, Handgretinger R, Kerst G,
Müller I: Low physiologic oxygen tensions reduce proliferation and
differentiation of human multipotent mesenchymal stromal cells. BMC
Cell Biol 2010, 11:11.
18. Simmons PJ, Torok-Storb B: Identification of stromal cell precursors in
human bone marrow by a novel monoclonal antibody, STRO-1. Blood
1991, 78:55-62.
19. Carrancio S, López-Holgado N, Sánchez-Guijo FM, Villarón E, Barbado V,
Tabera S, Díez-Campelo M, Blanco J, San Miguel JF, Del Cañizo MC:
Optimization of mesenchymal stem cell expansion procedures by cell
separation and culture conditions modification. Exp Hematol 2008,
36:1014-1021.
20. Mostafa SS, Miller WM, Papoutsakis ET: Oxygen tension influences the
differentiation, maturation and apoptosis of human megakaryocytes. Br J
Haematol 2000, 111:879-889.
21. Méndez-Ferrer S, Michurina TV, Ferraro F, Mazloom AR, Macarthur BD,
Lira SA, Scadden DT, Ma’ayan A, Enikolopov GN, Frenette PS: Mesenchymal
and haematopoietic stem cells form a unique bone marrow niche.
Nature 2010, 466:829-834.
22. Greenlee MC, Sullivan SA, Bohlson SS: CD93 and related family members:
their role in innate immunity. Curr Drug Targets 2008, 9:130-138.
23. Wang Y, Volloch V, Pindrus MA, Blasioli DJ, Chen J, Kaplan DL: Murine
osteoblasts regulate mesenchymal stem cells via WNT and cadherin
Table 5 List of primers used for qPCR (GAPDH is used as
a calibrator)
Gene Product Primers Product
Size (bp)
HoxA11
(NM_005523.5)
Fw: 5’-TTGAGCATGCGGGACAGTT-3’
Rv: 5’-GTACCAGATCCGAGAGCTGGAA-3’
87
OxCT2
(NM_022120.1)
Fw: 5’-GAGTTCAACGGCGACCACTT-3’
Rv:5’-GCGCTTCTCCTGAAGACCA-3’
110
V-KIT
(NM_000222.2)
Fw: 5’-GGCGACGAGATTAGGCTGTT-3’
Rv: 5’-CATTCGTTTCATCCAGGATCTCA-3’
77
CCL2
(NM_002982.3)
Fw: 5’-ACTCTCGCCTCCAGCATGAA-3’
Rv: 5’-GGGAATGAAGGTGGCTGCTA-3’
72
CX3CL1
(NM_002996.3)
Fw: 5’-TGACATCAAAGATACCTGTAGC-3’
Rv: 5’-CTCGTCTCCAAGATGATTGC-3’
88
WNT4
(NM_030761.4)
Fw: 5’-AGCAACTGGCTGTACCTG-3’
Rv: 5’-CTGGATCAGGCCCTTGAG-3’
87
GAPDH
(NM_002046.3)
Fw: 5’-CGCTCTCTGCTCCTCCTGTT-3’
Rv: 5’-CCATGGTGTCTGAGCGATGT-3’
81
Basciano et al.BMC Cell Biology 2011, 12:12
http://www.biomedcentral.com/1471-2121/12/12
Page 11 of 12

pathways: mechanism depends on cell-cell contact mode. J Tissue Eng
Regen Med 2007, 1:39-50.
24. Bruno S, Bussolati B, Grange C, Collino F, di Cantogno LV, Herrera MB,
Biancone L, Tetta C, Segoloni G, Camussi G: Isolation and characterization
of resident mesenchymal stem cells in human glomeruli. Stem Cells Dev
2009, 18:867-880.
25. Keuschnigg J, Henttinen T, Auvinen K, Karikoski M, Salmi M, Jalkanen S: The
prototype endothelial marker PAL-E is a leukocyte trafficking molecule.
Blood 2009, 114:478-484.
26. Scheller EL, Song J, Dishowitz MI, Soki FN, Hankenson KD, Krebsbach PH:
Leptin functions peripherally to regulate differentiation of mesenchymal
progenitor cells. Stem Cells 2010, 28:1071-1080.
27. Ohnishi S, Yasuda T, Kitamura S, Nagaya N: Effect of hypoxia on gene
expression of bone marrow-derived mesenchymal stem cells and
mononuclear cells. Stem Cells 2007, 25:1166-1177.
28. Rocnik EF, Liu P, Sato K, Walsh K, Vaziri C: The novel SPARC family
member SMOC-2 potentiates angiogenic growth factor activity. J Biol
Chem 2006, 281:22855-22864.
29. Li Y, Tower J: Adult-specific over-expression of the Drosophila genes
magu and hebe increases life span and modulates late-age female
fecundity. Mol Genet Genomics 2009, 281:147-162.
30. Ohnishi S, Sumiyoshi H, Kitamura S, Nagaya N: Mesenchymal stem cells
attenuate cardiac fibroblast proliferation and collagen synthesis through
paracrine actions. FEBS Lett 2007, 581:3961-3966.
31. Edwards MM, Mammadova-Bach E, Alpy F, Klein A, Hicks WL, Roux M,
Simon-Assmann P, Smith RS, Orend G, Wu J, Peachey NS, Naggert JK,
Lefebvre O, Nishina PM: Mutations in Lama1 disrupt retinal vascular
development and inner limiting membrane formation. J Biol Chem 2010,
285:7697-7711.
32. Nagai R, Hashimoto R, Tanaka Y, Taguchi O, Sato M, Matsukage A,
Yamaguchi M: Syntrophin-2 is required for eye development in
Drosophila. Exp Cell Res 2010, 316:272-285.
33. Piluso G, Mirabella M, Ricci E, Belsito A, Abbondanza C, Servidei S, Puca AA,
Tonali P, Puca GA, Nigro V: Gamma1- and gamma2-syntrophins, two
novel dystrophin-binding proteins localized in neuronal cells. J Biol Chem
2000, 275:15851-15860.
34. Koirala S, Jin Z, Piao X, Corfas G: GPR56-regulated granule cell adhesion is
essential for rostral cerebellar development. J Neurosci 2009,
29:7439-7449.
35. Gronthos S, Zanettino AC, Hay SJ, Shi S, Graves SE, Kortesidis A,
Simmons PJ: Molecular and cellular characterization of highly purified
stromal stem cells derived from human bone marrow. J Cell Sci 2003,
116:1827-1835.
36. Kolf CM, Cho E, Tuan RS: Biology of adult mesenchymal stem cells:
regulation of niche, self-renewal and differentiation. Arthritis research &
therapy 2007, 9:204-213.
37. Bensidhoum M, Chapel A, Francois S, Demarquay C, MAzurier C, Fouillard L,
Bouchet S, Bertho JM, Gourmelon P, Aigueperse J, Charbord P, Gorin NC,
Thierry D, Lopez M: Homing of in vitro expanded Stro1- or Stro-1+
human mesenchymal stem cells into the NOD/CSID mouse and their
role in supporting human CD34 cell engraftment. Blood 2004,
103:3313-3319.
38. Psaltis PJ, Paton S, See F, Arthur A, Martin S, Itescu S, Worthley SG,
Gronthos S, Zannettino AC: Enrichment for STRO-1 expression enhaces
the cardiovascular paracrine activity of human bone marrow-derived
mesenchymal cell populations. J Cell Physiol 2010, 223:530-540.
39. Charbord P: Bone marrow mesenchymal stem cells: historical overview
and concepts. Hum Gene Ther 2010, 21:1045-1056.
40. Pistoia V, Raffaghello L: Potential of mesenchymal stem cells for the
therapy of autoimmune diseases. Expert Rev Clin Immunol 2010, 6:211-218.
41. Németh K, Leelahavanichkul A, Yuen PST, Mayer B, Parmelee A, Doi K,
Robey PG, Leelahavanichkul K, Koller BH, Brown JM, Hu X, Jelinek I, Star RA,
Mezey E: Bone marrow stromal cells attenuate sepsis via prostaglandin E
(2)-dependent reprogramming of host macrophages to increase their
interleukin-10 production. Nat Med 2009, 15:42-49.
42. Rafei M, Campeau PM, Aguilar-Mahecha A, Buchanan M, Williams P,
Birman E, Yuan S, Young YK, Boivin M, Forner K, Basik M, Galipeau J:
Mesenchymal stromal cells ameliorate experimental autoimmune
encephalomyelitis by inhibiting CD4 Th17 T cells in a CC chemokine
ligand 2-dependent manner. J Immunol 2009, 182:5994-6002.
43. Zipori D: The stem state: plasticity is essential, whereas self-renewal and
hierarchy are optional. Stem Cells 2005, 23:719-726.
doi:10.1186/1471-2121-12-12
Cite this article as: Basciano et al.: Long term culture of mesenchymal
stem cells in hypoxia promotes a genetic program maintaining their
undifferentiated and multipotent status. BMC Cell Biology 2011 12:12.
Submit your next manuscript to BioMed Central
and take full advantage of:
• Convenient online submission
• Thorough peer review
• No space constraints or color figure charges
• Immediate publication on acceptance
• Inclusion in PubMed, CAS, Scopus and Google Scholar
• Research which is freely available for redistribution
Submit your manuscript at
www.biomedcentral.com/submit
Basciano et al.BMC Cell Biology 2011, 12:12
http://www.biomedcentral.com/1471-2121/12/12
Page 12 of 12