STEM CELLS AND DEVELOPMENT
Volume 24, Number 4, 2015
Mary Ann Liebert, Inc.
DOI: 10.1089/scd.2014.0331
microRNAs as Regulators of Adipogenic
Differentiation of Mesenchymal Stem Cells
Dana Hamam,1,* Dalia Ali,1,* Moustapha Kassem,1,2 Abdullah Aldahmash,1,2 and Nehad M. Alajez1
microRNAs (miRNAs) constitute complex regulatory network, fine tuning the expression of a myriad of genes
involved in different biological and physiological processes, including stem cell differentiation. Mesenchymal
stem cells (MSCs) are multipotent stem cells present in the bone marrow stroma, and the stroma of many other
tissues, and can give rise to a number of mesoderm-type cells including adipocytes and osteoblasts, which form
medullary fat and bone tissues, respectively. The role of bone marrow fat in bone mass homeostasis is an area of
intensive investigation with the aim of developing novel approaches for enhancing osteoblastic bone formation
through inhibition of bone marrow fat formation. A number of recent studies have reported several miRNAs
that enhance or inhibit adipogenic differentiation of MSCs and with potential use in microRNA-based therapy
to regulate adipogenesis in the context of treating bone diseases and metabolic disorders. The current review
focuses on miRNAs and their role in regulating adipogenic differentiation of MSCs.
Introduction
R
ecent years have witnessed immense interest in
studying mesenchymal stem cells (MSCs) and harnessing
their unique differentiation capabilities for tissue engineering
and regenerative medicine applications. While there are a
myriad of molecular mechanisms that regulate stem cell
differentiation, a new class of epigenetic regulators ‘‘microRNAs’’ have emerged as key player during stem cell differentiation including MSC. The role of microRNAs (miRNAs)
in regulating MSC differentiation are currently being unraveled using integrated, experimental, and bioinformatics
approaches. Our understanding of miRNAs and how they
regulate MSC differentiation will have significant impact on
their therapeutic potential. In this review, we will provide an
overview of MSC differentiation into adipocytes and an up-todate analysis of published data implicating miRNAs in regulating the adipogenic differentiation of MSCs.
Adipocytic Differentiation of MSCs
MSCs are described as adult progenitor multipotent stromal cells found and isolated from multiple tissues, including
among others bone marrow [1], adipose tissue [2], umbilical
cord [3], and skin [4]. MSCs have been shown to differentiate
into several mesenchymal lineages including osteoblast,
chondrocytes, and adipocytes to give rise to bone, cartilage,
and adipose tissue, thus representing a possible use in cell
therapy and regenerative medicine protocols [1,5].
The process of adipogenesis includes two major phases; the
determination phase and the maturation phase. During the
phase of determination, multipotent MSCs become incapable
of differentiation into other mesenchymal lineages as they
commit only to adipocytic lineage [6]. At this point, both
adipocyte-committed MSCs (preadipocytes) and their precursors have a similar morphological phenotype. Later on, and
in the maturation phase, these preadipocytes are transformed
into mature adipocytes, which take part in synthesizing and
the transportation of lipid, secretion of adipocyte-specific
proteins and possessing the machinery that is required for
insulin sensitivity [6]. The process of adipogenesis revealed a
mark shift in the pattern of gene expression observed in undifferentiated MSC compared to mature adipocyte, which
promotes and terminates the phenotypic and molecular characteristics that identify mature adipocytes [7]. A complex and
well organized signaling cascades appear to be involved in
regulating adipogenesis, which includes the expression of several transcription factors such as peroxisome proliferator-activated receptor-g (PPARg) and members of the CCAAT/
enhancer-binding family of proteins (C/EBPs) (reviewed in
Rosen et al. [7]). Bone marrow adipocytes appear to play
significant role in bone metabolism [8], therefore, better understanding of stromal adipocyte commitment and maturation
and identifying the molecular mechanisms that regulate their
1
Stem Cell Unit, Department of Anatomy, College of Medicine, King Saud University, Riyadh, Kingdom of Saudi Arabia.
Molecular Endocrinology, KMEB, Department of Endocrinology, University of Southern Denmark, Odense, Denmark.
*These two authors contributed equally to this work.
2
Ó Dana Hamam et al. 2015; Published by Mary Ann Liebert, Inc. This Open Access article is distributed under the terms of the Creative
Commons License Attribution-Non-Commercial Share Alike ( < http://creativecommons.org/licenses/by-nc-sa/4.0/ > ).
417
418
HAMAM ET AL.
formation will assist in developing novel therapeutic modalities to regulate osteogenesis and hematopoiesis.
microRNAs and Regulation of MSC
Differentiation
miRNAs are short single-stranded RNA sequences (usually
19–23 nucleotides), which are derived from *70 nucleotide
precursors, and play a critical role in the post-transcriptional
regulation of gene expression in a broad range of biological
systems varying from insects to humans [9–12], through
controlling a wide range of physiological and developmental
processes [13]. Changes in microRNAs have been associated
with many human diseases such as cancer [14–16], myocardial infarction and cardiovascular diseases [17,18], diabetes,
and obesity [19–21]. miRNAs have been identified to act in
functional networks linked to several genes as potential
targets; so far, an almost 2,578 miRNAs have been identified in human cells, which apparently can affect multiple
physiological and biological functions, such as stem cell
differentiation, neurogenesis, hematopoiesis, immune response, and skeletal and cardiac muscle development [22–
27]. While several reviews has covered the role of miRNAs
in regulating osteoblastic differentiation of MSCs [28,29],
the focus of this review is to highlight the regulation of
adipogenic differentiation of MSCs by miRNAs.
microRNAs and Regulation of Adipogenic
Differentiation of MSCs
A cascade of transcriptional events that occurs during adipocyte maturation, including the expression of PPARg and
CCAAT/enhancer-binding protein-a (C/EBPa), which are
key factors regulating a myriad of adipocyte-related enzymes
and proteins involved in generating and sustaining adipocyte
phenotype [30–32]. Furthermore, there are other factors that
can directly or indirectly interact with PPARg, such as adipocyte determination and differentiation-dependent factor 1
(ADD1/SREBP-c1), a homolog of sterol regulatory elementbinding proteins (SREBP), which was initially cloned as a
basic helix-loop-helix (bHLH) protein involved in early adipogenesis, and another binding protein, a sterol response element (SRE) [33,34]. In addition, Krox20, Krüppel-like
factors, and signal transducers and activators of transcription
have all been shown to be tightly relevant to adipocyte differentiation [35–37]. All these transcription factors share a
common characteristic as they regulate adipocyte differentiation by regulating the activity of PPARg and C/EBP family.
Adipocyte differentiation is regulated by the activity of various growth factors and hormones. Recent data suggested that
miRNAs could be involved in human adipocyte maturation
[38]. Tables 1 and 2 summarize the currently described microRNAs involved in adipocyte differentiation of MSCs derived from different sources.
microRNAs targeting cell cycle
and self-renewal-related genes
miRNAs are able to indirectly regulate adipogenic differentiation of MSCs by targeting various genes that may be
involved in balancing self-renewal and stem cell differentiation, as shown with miR-143, which was reported as the
first miRNA to regulate adipogenesis [39]. Elevated levels
of miR-143 were detected in differentiated white adipocytes
and its inhibition resulted in reduced adipocytic differentiation. miR-143 was found to target extracellular signalregulated kinase 5 (ERK5), also known as mitogen-activated
protein kinase 7 (MAPK7) gene, which is involved in promoting cell growth and proliferation in response to tyrosine
kinase signaling, where its activation resulted in boosting
adipocyte differentiation [40,41]. While the role of ERK5 in
regulating adipocyte differentiation directly has not been
confirmed, the authors suggested that it may play a role in
balancing the proliferation and differentiation of adipocytes.
Another member of ERK family was also studied as a target
for miR-375 in 3T3-L1 cells [42]. The authors demonstrated
that ERK1/2 pathway negatively regulate adipocyte differentiation, and suggested this reduction in adipogenesis is
mediated through miR-375. Wang et al. found that all
members of miR-17-92 cluster were significantly
Table 1. Mammalian microRNAs Involved in Adipogenesis in Bone Marrow-Derived
Mesenchymal Stem Cells
miRNA
miR-204
miR-637
miR-320
miR-378/378*
miR-8, miR-200c,
-141, -200b, -200a, -429
miR-199, and miR-346
miR-31
miR-24
miR-335
Cell
ST2 and C2C12
mBMSCs
hMSCs
Bone marrow-derived MSCs
Bone marrow-derived MSCs
Bone marrow-derived
ST2 cell line
Mouse ST2 marrow-derived
stromal cells (MSCs ST2)
hMSCs from bone marrow
Murine mesenchymal stem
cell line C3H10T1/2 (MSCs)
Murine mesenchymal stem
cell line C3H10T1/2 (MSCs)
Bone marrow-derived hMSCs
Target gene(s)
Related process
Reference
RUNX2
[ Adipogenesis
[63]
Osterix
RUNX2
AGO2
KLF15, FABP4, FAS,
SCD-1, and resistin
wntless (wls)
and CG32767 genes
LIF
CEBPA
[ Adipogenesis
[ Adipogenesis
[ Adipogenesis
[67]
[64]
[88]
[ Adipogenesis
[49]
[ Adipogenesis
Y Adipogenesis
[55]
[78]
Unknown
[ Adipogenesis
[78]
RUNX2
Y Adipogenesis
[66]
hMSCs, human mesenchymal stem cells; mBMSCs, mouse bone marrow-derived MSCs; [, promote; Y, inhibit.
MICRORNAS
AND REGULATION OF ADIPOGENESIS
419
Table 2. Mammalian microRNAs Involved in Adipogenesis in Adipose-Derived
Mesenchymal Stem Cells and Preadipocytes
miRNA
miR-17-92
miR-642a-3p
miR-30a and 30d
miR-21
miR-30c
miR-210
miR-143
Cell
3T3-L
hAD-MSC
hAD-MSC
hAD-MSC
3T3-l1
hAD-MSC and MEFs
3T3-L1
Human pre-ad
miR-375
miR-27b
miR-27a
miR-130
miR-138
miR-448
miR-103
and miR-107
miR-146b
miR-155
miR-221/222
3T3-L
hAD-MSC
3T3-L
Human and mouse pre-ad
hAD-MSCs
3T3-L1
Primary adipocytes and the stromalvascular
fraction from subcutaneous and visceral fat
3T3-L1
hMSC-TERT20
miR-26
hAD-MSC
Target gene(s)
Related process
Reference
Rb/p130
Unknown
RUNX2
TGF-B1
AP1
PAI-1 and ALK2
Tcf7l2
ERK5
MAPK7
ERK1/2
PPARg and C/EBPa
PPARg
PPARg
EID-1
KLF5
CAV1
[ Adipogenesis
[ Adipogenesis
[ Adipogenesis
[ Adipogenesis
[ Adipogenesis
[ Adipogenesis
[ Adipogenesis
[ Adipogenesis
[43]
[65]
[65]
[44]
[46]
[87]
[48]
[39]
[ Adipogenesis
Y Adipogenesis
Y Adipogenesis
Y Adipogenesis
Y Adipogenesis
Y Adipogenesis
Y Adipogenesis
[42]
[75]
[76]
[77]
[79]
[57]
[85]
SIRT1
CEBPB
CDKN1B
[ Adipogenesis
Y Adipogenesis
[72]
[86]
ADAM17
[ Adipogenesis
[90]
hAD-MSCs, human adipose tissue-derived mesenchymal stem cells; MEFs, mouse embryonic fibroblasts; Pre-ad, preadipocytes; TERT,
telomerase reverse transcriptase.
upregulated after hormonal induction of adipogenesis and
based on those data, they concluded that overexpression of
miR-17-92 cluster, with hormonal induction, may play a
role in the positive regulation of adipocyte differentiation
through targeting the tumor suppressor Rb/p130 gene, resulting in acceleration of adipogenic differentiation [43].
Kim et al. investigated the role of miR-21 in adipogenic
differentiation of human adipose tissue-derived mesenchymal
stem cells (hAD-MSC) and its potential targets [44]. Their data
showed that miR-21 can positively regulate adipogenic differentiation of hAD-MSC by targeting transforming growth factorbeta 1 (TGF-b1), which is known to inhibit adipogenesis in vitro
and in vivo [45]. In another study, Kang et al. showed that 3T3L1 cells that were transfected with miR-21 showed higher level
of adipogenic differentiation [46], these results were indicated
by the morphological changes in miR-21-transfected adipocytes
that expressed higher levels of adiponectin. However, their data
showed that miR-21 may regulate adipogenic commitment of
preadipocytes by directly targeting AP1 gene, activating protein-1, resulting in inducing adipocyte differentiation.
Wingless-type MMTV integration family (Wnts) has
been shown to suppress adipocyte differentiation by blocking the expression of PPARg and CEBPA, which are essential transcription factors in adipogenesis [47]. These data
were supported by different studies that were conducted to
explore the role of different miRNAs in regulating adipogenesis via modulation of the Wnt pathway [48,49]. Kennell
et al. first studied miRNA-8 in drosophila Kc167 cells and
revealed that Wnt signaling pathway is regulated by miRNA-8 at different levels via inhibition of transcription factor
(TCF) protein expression and direct targeting of wntless
(wls) and CG32767 genes, which positively regulate Wnt
signaling pathway, based on these data, they concluded that
mammalian homologues of miRNA-8, miR-200c/141, and
miR-200b/200a/429 clusters have a potential role in regulating adipocyte differentiation in ST2 marrow stromal cells
[49]. Stable expression of miR-200c/141 and/or miR-200b/
200a/429 clusters induced the differentiation of those cells
into adipocytes, which was indicated by the elevated levels
of fatty acid-binding protein 4 (FABP4), and an increase in
lipid accumulation. In a similar manner, Qin et al. performed miRNA expression profiling during adipocyte differentiation and identified 18 miRNAs, including miR-210,
miR-148a, miR-194, and miR-322, which could promote
adipocyte differentiation via inhibition of Wnt signaling
[48]. Overexpression of miR-210 in 3T3-L1 cells resulted in
enlarged cells, with distinctive lipid droplets, while its inhibition led to diminished adipogenesis. The authors identified Tcf7l2, T-cell-specific transcription factor 7 like 2, a
member of LEF/TCF family, which plays a role in triggering the downstream responsive genes of Wnt signaling [50],
as bona fide target for miR-210.
Leukemia inhibitory factor (LIF) is an inflammatory cytokine that plays a significant role in regulating multiple biological activities such as cell survival, proliferation, and cell
differentiation [51]. It was shown that LIF expression declines, in association with decreased differentiation plasticity
of hMSCs [52–54]. Oskowitz et al. identified two miRNAs,
miR-199 and miR-346, which can synergistically function by
targeting LIF during hMSC differentiation, resulting in enhanced adipocyte and osteoblast differentiation [55].
Kruppel-like factor 5 (KLF5), a transcription factor,
which function as signaling modulator for various cellular
processes including cell proliferation, cell cycle, migration,
420
apoptosis, and cell differentiation [56], was recently investigated as potential target for miR-448 [57]. The authors
demonstrated that serotonin (5-HT) is a novel autocrine/
paracrine regulator of adipocytic cell differentiation [57].
Interestingly, the authors found miR-448, which is located
in the fourth intron of 5-HT(2C)R, to suppress adipocyte
differentiation by targeting KLF5 in the 3T3-L1 model.
microRNAs targeting osteoblast-related genes
Runt-related transcription factor 2 (RUNX2) is a master
transcription factor known to regulate osteoblast and chondrocyte differentiation [58,59]. In undifferentiated cells,
RUNX2 and PPARg are expressed at low level to sustain
differentiation potential of MSC [6,60]. It has been shown
that reduction in the level of RUNX2 in chondrocytes enhanced their adipogenic commitment [61], while deficiency
in PPARg stimulates osteogenesis and enhanced bone formation [62]. Thus, Huang et al. intended to study whether
RUNX2 regulation by miR-204/211 has an effect on adipogenic differentiation [63]. Many adipogenic genes such as
AP2, adipsin, and PPARg were found to be upregulated
when miR-204 was overexpressed in ST2 cells, whereas
upregulation of RUNX2 was observed in miR-204-spongetransfected cells. As a result, it has been revealed that
miR-204 can positively regulate adipogenic commitment,
probably through downregulation of RUNX2. In an independent study, Hamam et al. performed global microRNA
and mRNA expression profiling during adipocytic differentiation of human bone marrow-derived MSCs (hBM-MSCs).
While several differentially expressed miRNAs were identified in that study, the authors reported proadipogenic function
for miR-320 family in hBM-MSCs via targeting multiple
genes involved in cell differentiation and cell cycle regulation. The author subsequently validated RUNX2 as bona fide
target for miR-320 family using the luciferase reporter system
[64]. Zaragosi et al. reported miR-642-3p as a highly adipospecific miRNA, and additionally studied the involvement
of miR-30 family in the regulation of adipogenesis in hADMSC [65]. Their data showed that during adipogenesis, miR642a-3p, miR-378, miR-30a, miR-30b, miR-30c, miR-30d,
miR-30e, and miR-193b were strongly upregulated. In addition, a direct link between miR-30a and miR-30d and adipogenesis by targeting the activity of the transcription factor
RUNX2, resulted in enhancing adipogenesis. RUNX2 has
also been studied as a target gene for miRNAs involved in the
regulation of adipogenesis in hMSCs derived from bone marrow, subcutaneous adipose tissue, and from articular cartilage
[66]. Tome et al. reported that all MSC populations were found
to express higher levels of miR-335 compared with dermal
fibroblasts, and in addition, BM-MSCs showed the highest
level of miR-335 expression among all examined MSC populations. Hence, miR-335 was reported to negatively regulate
both adipogenic and osteogenic differentiation of hMSCs, as
indicated by the reduction in PPARg and osteopontin, respectively. The authors’ data revealed RUNX2 as one target for
miR-355, through direct binding to its 3¢ untranslated region
(UTR) and reduced level of RUNX2 protein after miR-355
overexpression.
Balancing between adipogenic and osteogenic differentiation in MSC, Zhang et al., demonstrated a role for miR637 in maintaining the balance between these two lineages
HAMAM ET AL.
by targeting Osterix (Osx) mRNA [67]. Osx, a zinc fingercontaining transcription factor, which plays significant role
in bone and osteoblast formation and its transcription could
be induced by bone morphogenetic protein 2 (BMP2) in
hMSCs [68–71]. However, their data showed that Osterix is
a direct target for miR-637 and its inhibition can positively
regulate adipocyte differentiation, which was indicated by
the elevated levels of PPARg, C/EBPa, and SREBP-1c in de
novo adipose tissue. Furthermore, the authors went to explore the effect of miR-637 on adipogenic differentiation
in vivo using a de novo adipogenic mouse model. The authors noticed remarkable enhancement in adipose tissue
formation after injection of Lv-miR-637-transduced hMSCs.
Interestingly, the osteogenic differentiation potential of LvmiR-637-transduced cells was apparently diminished, which
was associated with lower alkaline phosphatase activity.
microRNAs targeting adipocyte-related genes
Recently, miR-146b was studied for its role in regulating
adipocytic differentiation [72], miR-146b was also revealed
to be a positive regulator of adipogenesis in 3T3-L cells, and
this effect was first indicated by the positive correlation
between the expression level of this miRNA and adipose
tissue volume in obese mice. miR-146b was reported to
positively regulate adipogenic differentiation by targeting
Sirtuin 1 (SIRT1) gene, which has been found to inhibit
PPARg and stimulates lipolysis, resulting in delaying adipogenic commitment of 3T3-L1 cells and reducing fat
production [73]. Additionally, miR-27 family was shown to
play a role in adipogenic regulation by directly targeting
adipogenic regulatory genes [74]. PPARg and C/EBPa were
reported to be key regulators of adipogenic differentiation
and targeted by miR-27b, which suppresses their expression
and negatively affect the adipogenic commitment in hADMSC cells, delaying the accumulation of triglyceride to late
stages in these cells [75]. Moreover, and in a similar manner, Kim et al. demonstrated that miR-27a, another member
of the miR-27 family, negatively regulated adipogenesis
[76]. Their data showed that miR-27a was downregulated in
mature adipocytes in the fraction of high-fat diet-fed obese
mice. Their data showed that during adipocyte differentiation, overexpression of miR-27a in 3T3-L1 cells resulted in
reduction of lipid accumulation, downregulation in PPARg
levels and reduced protein level of adiponectin. Moreover,
they revealed that miR-27a overexpression represses many
adipogenic marker genes such as adipocyte lipid-binding
protein 2 (AP2), which is also known as FABP4, adiponectin, CD36, and lipoprotein lipase (LPL). Collectively,
these results implied that miR-27a can target PPARg directly, resulting in repression of adipogenesis suggesting
that downregulation of miR-27a might be relevant to adipose tissue dysregulation in obesity.
In another study, PPARg was also found to be targeted by
miR-130 in both human and mouse preadipocytes, and was
revealed to bind to both PPARg mRNA coding and its
3¢ UTR [77]. In the same study, the authors reported lower
levels of miR-130 in obese compared to lean women, which
was linked to increased levels of PPARg among relatively
young and healthy populations. These lower expression
levels of miR-130 in obese individuals could possibly reflect
a reduced numbers of preadipocytes due to their conversion
MICRORNAS
AND REGULATION OF ADIPOGENESIS
into mature adipocytes in the adipocyte pool. C/EBPa was
found to be targeted by miR-31 in MSCs at both the transcriptional and translational levels, resulting in negative
regulation of adipocyte differentiation [78]. The authors also
revealed proadipogenic role for miR-24, via enhanced BMP2induced commitment to adipocytes. On the other hand, a
study conducted by Yang et al. on hAD-MSCs revealed that
miR-138 overexpression in these cells suppress the expression of PPARg and C/EBPa, and other adipocyte differentiation markers, such as FABP4 and lipoprotein 4, coupled
with reduction in the accumulation of lipid droplets [79].
Furthermore, the adenovirus early region 1-A-like inhibitor of
differentiation (EID-1) was predicted to be targeted by miR138, which was previously reported to be involved in adipogenesis by promoting small heterodimer partner, an endogenous
enhancer of PPARg, and TGF-b signaling pathways. The
authors succeeded to find a link between miR-138 and
EID-1 gene and reveal that miR-138 can negatively regulate
adipogenesis by the inhibition of EID-1 gene [80–82].
Concordant with previous studies implicating miR-103
and miR-107 in adipogenesis [83], Li et al. linked miR-103
to brain development, adipogenesis, lipid metabolism, immunity, and hematopoiesis [84]. Trajkovski et al. have also
examined the effect of miR-103 and miR-107 during adipocyte differentiation of isolated stromal-vascular cells from
visceral and subcutaneous fat [85]. Their data revealed increased number of adipocyte when miR-103 was inactivated, while overexpression of miR-107 resulted in
reduced adipogenesis, which implicated miR-103 and miR107 in the negative regulation of adipocyte differentiation,
via modulation of caveolin-1. Skarn et al. identified 12
miRNAs that were differentially expressed during adipocytic differentiation of hBM-MSC line (hMSC-TERT) and
functionally validated miR-155, miR-221, and miR-222 as
negative regulators of adipocytic differentiation of hMSCs
via targeting CEBPB and CDKN1B [86].
microRNAs targeting other pathways
Karbiener et al. performed microarray on hAD-MSC and
on mouse embryonic fibroblasts and found miR-30c to be
upregulated during adipocytic differentiation [87]. Two
genes, plasminogen activator inhibitor 1 (PAI-1) and activin
receptor-like kinase 2 (ALK2), were identified as bona fide
targets for miR-30c. Although these two targeted genes are
421
so far not interconnected, the authors found that co-silencing, not single silencing of PAI-1 or ALK2 has a significant
impact on adipogenesis as measured by elevated levels of
triglycerides and lipid accumulation and the increased expression of adipogenic marker genes [PPARg, C/EBPa,
FABP4, fatty acid synthase (FASN), and glucose transporter
type 4 (GLUT4)].
Gerin et al. investigated the role of miR-378/378* in
adipocyte differentiation and metabolism, via knocking
down Argonaute2 (Ago2), which plays a key role in miRNA
processing, to study the potential role of different miRNAs
in adipocyte differentiation and/or metabolism [88,89].
Although the authors observed no remarkable differences in
adipogenesis between control and Ago2 knockdown samples of 3T3-L1 cells, incorporation of [14C] glucose or acetate into triacylglycerol showed reduced levels, which
suggests that miRNAs may play a role in adipocyte metabolism. Moreover, they focused their studies to investigate
the role of certain microRNAs in adipogenesis via screening
differentially expressed microRNAs between preadipocytes
and adipocytes in the 3T3-L1 and bone marrow-derived
stroma (ST2) cell lines. miR-378/378* were highly induced
during adipogenesis, and when they were overexpressed in
ST2 MSC precursors, an increased level of lipid droplets,
upregulation in several adipogenic markers [KLF15,
FABP4, FASN, stearoyl-Coenzyme A desaturase 1 (SCD-1),
and resistin], and increase in the incorporation of [14C] acetate into triacylglycerol was observed. In contrast, knocking down miR-378 and/or miR-378* caused reduction in the
accumulation of triacylglycerol. Interestingly, and in a traditional search for potential targets for specific miRNAs,
Gerin et al. found that none of the predicted targets of
miRNA-378 or 378* were downregulated in response to
these miRNAs. Unexpectedly, some of the suggested target
genes exhibited an increase in reporter gene expression. In
particular, C/EBPa and C/EBPb activity on the GLUT4
promoter was increased in the presence of miRNA-378/
378*, suggesting miRNAs might exert their effects in adipocytes through an atypical mechanism, such as transcriptional coactivation.
Recently, Karbiener et al. reported miR-26a family as
a positive regulator of adipogenic differentiation in hADMSC [90]. Their data showed a significant increased in
adipocytes formation assessed by oil red staining and high
expression of adipogenic markers upon overexpression of
FIG. 1. Regulation of runt-related
transcription factor 2 (RUNX2) by
miR-204/211, miR-30, and miR-320
family. During adipocytic differentiation of mesenchymal stem cells
(MSCs), members of the miR-204/
211, miR-30, and miR-320 family
are upregulated, which subsequently
repress RUNX2 and promote adipogenesis. Color images available
online at www.liebertpub.com/scd
422
miR-26a and miR-26b. Transcriptomatic analysis revealed
enriched TGF-b and Notch signaling pathways among miR26a-suppressed mRNA. Furthermore, miR-26a showed
significant effect on the expression level of various genes
involved in different cellular pathways, such as pyruvate
metabolism, tricarboxylic acid (TCA) cycle, and fatty acid
metabolism suggesting increased de novo synthesis of
lipids combined with an increase level of triglyceride accumulation upon miR-26 at the early white stage. However, In their functional studies, knocking down of several
mRNAs (SMURF2, ATPAF1, ADAM17, and PLOD2)
showed a positive effect on adipogenic differentiation as
indicated by lipid accumulation, however, induction of
UCP1 was only observed upon knocking down of ADAM
metallopeptidase domain 17 (ADAM17), which also was
shown to be the most downregulated transcriptom by miR26a. Karbiener et al. revealed the direct miR-26-ADAM17
interaction indicating that ADAM17 is a direct target for
miR-26 family with an antiadipogenic and antibrowning
effect [90].
Conclusion Remarks
The role of miRNA-mediated post-transcriptional regulation in adipogenesis has been studied particularly to
identify the schematic mechanism of microRNA and gene
regulation of adipogenic differentiation of stem cells. Thus
far, several microRNA families has been identified using
high-throughput screen, computational and experimental
approaches and were found to regulate adipogenesis by
targeting key pathways involved in stem cell differentiation
and proliferation. Of particular interest, we and others have
identified RUNX2 to be a favorite hub for microRNAmediated gene silencing during adipogenesis. RUNX2 has
been shown to be targeted by miR-204/211 and miR-30
families, and most recently we found RUNX2 to be highly
targeted by miR-320 family during adipocytic differentiation of hMSCs (Fig. 1) [64]. The findings from miRNA
investigations during adipogenesis suggest the potential
utilization of miRNA mimics/inhibitors or sponge to treat
bone diseases, metabolic disorders, and obesity. As proof of
principle, several preclinical data have shown the feasibility
of utilizing miRNA-based therapies in vivo in various disease models [17,91–93]. The only miRNA-based therapy in
clinical trials thus far is miravirsen, which is a miR-122
inhibitor previously shown to reduce HCV viral load in a
primate HCV disease model [93]. Santaris Pharma A/S has
completed phase I and phase II clinical trials using this
agent in healthy subject and patients with chronic hepatitis
C infection (http://clinicaltrials.gov). Therefore, the translation of in vitro and preclinical findings in this field into
clinical trials is just beginning to unfold. Determining biodistribution, specificity, pharmacokinetics, and safety have
to be addressed before the successful utilization of miRNAdirected therapies in the clinic.
Acknowledgment
This work was supported by the National Science Technology and Innovation Plan (NSTIP) strategic technologies
program, grant number (11-BIO-1941-02) in the Kingdom
of Saudi Arabia.
HAMAM ET AL.
Author Disclosure Statement
The authors declare no conflicts of interest.
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Address correspondence to:
Dr. Nehad M. Alajez
Stem Cell Unit
Department of Anatomy
College of Medicine
King Saud University
Riyadh 11461
Kingdom of Saudi Arabia
E-mail: nalajez@ksu.edu.sa
Received for publication July 6, 2014
Accepted after revision November 10, 2014
Prepublished on Liebert Instant Online November 18, 2014