The role of mesenchymal stem cells in early programming of adipose tissue in the offspring of women with obesity

Maternal obesity is a well‐known risk factor for developing premature obesity, metabolic syndrome, cardiovascular disease and type 2 diabetes in the progeny. The development of white adipose tissue is a dynamic process that starts during prenatal life: fat depots laid down in utero are associated with the proportion of fat in children later on. How early this programming takes place is still unknown. However, recent evidence shows that mesenchymal stem cells (MSC), the embryonic adipocyte precursor cells, show signatures of the early setting of an adipogenic committed phenotype when exposed to maternal obesity. This review aims to present current findings on the cellular adaptations of MSCs from the offspring of women with obesity and how the metabolic environment of MSCs could affect the early commitment towards adipocytes. In conclusion, maternal obesity can induce early programming of fetal adipose tissue by conditioning MSCs. These cells have higher expression of adipogenic markers, altered insulin signalling and mitochondrial performance, compared to MSCs of neonates from lean pregnancies. Fetal MSCs imprinting by maternal obesity could help explain the increased risk of childhood obesity and development of further noncommunicable diseases.


| INTRODUCTION
The incidence of obesity is increasing worldwide. 1More than 20% of women of reproductive age in middle and high-income countries are obese. 2This results in an increasing prevalence of overweight and obesity in pregnant women worldwide. 2Maternal obesity is a risk factor for maternal complications such as gestational diabetes, hypertension, preeclampsia and Caesarean section. 3Maternal obesity also affects the foetus, leading to several adverse outcomes in the offspring: stillbirth, congenital abnormalities, macrosomia and neonatal increased adiposity. 4It has been estimated that up to 41.7% of Abbreviations: BMI, body mass index; MSC, mesenchymal stem cells; TG, triglycerides; CD36, platelet glycoprotein 4; FABP4/aP2, fatty acid binding protein 4/adipocyte protein 2; GLUT4, glucose transporter type 4; ATP, adenosine triphosphate; TNFα, tumour necrosis factor alpha; IL, interleukin; MCP1, monocyte chemoattractant protein 1; TGFβ, transforming growth factor beta; BMP, bone morphogenic protein; Wnt, wingless-related integration site; Hh, hedgehog; FGF, fibroblast growth factor; C/EBP, CCAAT enhancer binding proteins; PPAR, peroxisome proliferator activated receptor; LPL, lipoprotein lipase; NOX, NADPH oxidase; ROS, reactive oxygen species; O₂ ¯, superoxide anion; H₂O₂, hydrogen peroxide; OH, hydroxyl radical; OH ¯, hydroxyl ion; ASC, adipose-derived stem cell; FOXO, Forkhead Box O; IGF-1, insulin growth factor 1; Zfp423, zinc finger protein 423; PI3K, phosphoinositide 3-kinase; Akt, protein kinase B; MAPK, mitogen-activated protein kinases; ERK1/2, extracellular signal-regulated kinase 1 and 2; AMPK, AMP-activated protein kinase; ER, endoplasmatic reticulum; SaβG, senescence associated beta galactosidase; EP300, histone acetyltransferase p300; CREBBP, CREB binding protein gene.childhood overweight/obesity can be attributed to maternal overweight and obesity, 5 making this a transgenerational problem. 3 During maternal obesity, foetuses have increased access to nutrients, leading to fetal metabolic adaptations and increased adiposity. 68][9] Furthermore, neonates born to obese mothers are insulin resistant and prone to metabolic compromise. 7It has also been shown that excessive adipose tissue in these early stages of life results in obesity in the child. 10With this, childhood obesity is likely to extend into adulthood, which strongly predicts a lifetime of health problems, as it results in an acquired susceptibility to metabolic disease. 10 obesogenic intrauterine environment affects not only fetal adipose tissue but also adipose precursor cells, which are the mesenchymal stem cells (MSCs).MSCs are multipotent progenitor cells established during early development that commit and differentiate into mesenchymal tissue, such as adipocytes. 11In this review, we aim to evaluate how the obesogenic intrauterine environment could influence MSCs and explore the effect of maternal obesity on the metabolic state and specific adipogenic commitment of MSCs.The confirmation of a programming effect of adipose precursor cells exposed to an obesogenic intrauterine environment could be a major contribution to the current knowledge on programming the early onset obesity and chronic diseases.Understanding fetal adipogenesis in maternal obesity will increase our possibilities to prevent and intervene in infant obesity early in life.

| OVERVIEW OF ADIPOSE TISSUE IN NORMAL WEIGHT AND OBESITY
Adipose tissue is a crucial regulator of energy homeostasis, with a principal role in lipid storage, but responding to external signals for buffering, synthesizing and secreting a wide range of endocrine products to regulate whole-body metabolism. 12Adipose tissue consists of adipocytes, surrounded by loose connective tissue.It is highly vascularized and innervated and contains macrophages, fibroblasts and adipocyte precursor cells, amongst others. 13Adipocytes take up free fatty acids and glucose to convert them into triglycerides (TG), the optimal way for lipid storage in mammals; the process is known as lipogenesis. 14,15This process protects the body from possible lipotoxicity in other organs. 16Uptake of free fatty acids into the adipocyte occurs via both passive diffusion and a protein-mediated mechanism (fatty acid-binding and transport proteins such as CD36 and FABP4/ aP2). 17In parallel, the influx of glucose into the adipocyte is mainly regulated by the insulin receptor, the activation of which leads to translocation of glucose transporter protein 4 (GLUT4) to the cell membrane, promoting glucose uptake. 18Both fatty acids and glucose are essential substrates for cell metabolism, promoting TG synthesis and storage. 15,19The process of fat mobilization is known as lipolysis, where several neuroendocrine signals, such as norepinephrine and insulin, initiate the process of TG breakdown for body energy expenditure. 20The adipocyte machinery relies on glycolysis and mitochondrial oxidative phosphorylation as the main ATP-producing pathways to obtain energy and perform all adipocyte functions. 21together, in normal weight conditions, adipocytes respond to systemic signals to either store or mobilize nutrients as needed by the organism, and a healthy and regulated balance between nutrient uptake and metabolization contributes to the adipocyte system to work 22 (Figure 1).Adipose tissue is not only crucial for lipid storage, but this tissue also communicates with other organs through adipokines such as leptin, adiponectin, tumour necrosis factor-alpha (TNFα), interleukin-6 (IL-6), IL-8, IL-1β and monocyte chemoattractant protein 1 (MCP1). 23These molecules are known to intervene directly with metabolic balance, emphasizing the role of adipose tissue in regulating body energy homeostasis. 23ernutrition leads to increased storage of nutrients and less nutrient mobilization, insulin resistance and adipocyte dysfunction, resulting from the combination of adipocyte cellular stress, hypertrophy and hypoxia. 24This adipocyte dysfunction is associated with mitochondrial dysregulation and adipose tissue inflammation: overnutrition supplies excess of electrons to the respiratory chain, while lack of physical activity and low ATP demand favours a high proton motive force with a low respiration rate, leading to mitochondrial superoxide formation. 25,26Thus, in obesity, high levels of oxidative stress lead to cellular damage in adipocytes. 27Studies have also reported systemic oxidative stress. 28Obesity is also associated with low levels of generalized inflammation. 28This inflammation is induced by the adipocyte secretome, with increased secretion of pro-inflammatory cytokines such as TNFα, IL-6, IL-8 or MCP-1, and a decrease in the antiinflammatory adipokine adiponectin. 29Inflammation has detrimental effects on insulin secretion, sensitivity and lipid metabolism, resulting in insulin resistance, where there is no response nor translocation of GLUT4, corresponding with obesity and later metabolic syndrome 30 (Figure 1).Thus, obesity is a low-grade inflammatory state of the whole body, also referred to as meta-inflammation. 30It is now known that insulin resistance, secretion of proinflammatory adipokines and oxidative stress are hallmarks in dysfunctional adipocytes and are also found in children with obesity. 31

| MESENCHYMAL STEM CELLS AND ADIPOGENESIS
During early development, the first totipotent stem cell proliferates and establishes the blastocyst, from which pluripotent stem cells arise. 32Consequently, these stem cells commit to specific cell lineages to eventually differentiate and form the numerous tissues and organs of the body. 32MSCs are multipotent cells capable of renewing themselves through cell division and differentiating into mesenchymal tissue, such as adipocytes. 11 humans, adipose tissue develops by the 14th week of gestation, when aggregates of MSCs condense next to primitive blood vessels.These MSCs proliferate and differentiate into preadipocytes. 33nally, preadipocytes acquire lipid droplets and endocrine capacity upon week 19 of pregnancy, becoming adipocytes. 34,35This adipocyte differentiation involves an elaborate network of transcription factors that regulate numerous pathways responsible for developing a mature adipocyte. 22The differentiation of MSCs into adipocytes is a two-step process, a first step of lineage determination/commitment and a second step of maturation. 22During the first step, MSCs are activated by several signalling modulators for commitment towards adipocytes, including transforming growth factor-beta (TGFβ)/bone morphogenic protein (BMP), wingless-type MMTV integration site (Wnt), Hedgehogs (Hh), Notch and fibroblast growth factors (FGFs). 36,37Together, they result in the activation of transcription co-activators CCAAT/ enhancer binding protein α and β (C/EBPα and C/EBPβ), which induce lineage-specific progenitor cells: adipoblasts. 38During the second step, coordinated commitment and maturation activity, together with CCAAT-enhanced binding proteins (C/EBPs) and peroxisome proliferator-activated receptor-gamma (PPARγ) activation, leads to the expression of adipocyte-commited specific genes: glucose transporter GLUT4, lipoprotein lipase (LPL), fatty acid-binding protein 4 (FABP4/aP2), perilipin-1, adiponectin and leptin. 22At the same time, insulin participates in this process by stimulating lipogenesis 15,22 (Figure 1).
As with many differentiation processes, adipogenesis is accompanied by metabolic reprogramming of the cell, with changes in the levels of redox state and mitochondrial mass. 32,370][41][42] ROS promote essential cell functions, including proliferation, differentiation and apoptosis. 43physiological levels of ROS react readily with a variety of chemical structures such as proteins, lipids, sugars and nucleic acids, leading to oxidative damage. 44Therefore, ROS levels are regulated by antioxidant enzymes and radical scavengers, such as superoxide dismutase, peroxidases and glutathione, among others. 45ROS have been shown to be essential in adipocyte lineage commitment: increased mitochondrial biogenesis and activity, which are associated with increased levels of ROS, are a prerequisite for MSC differentiation into mature adipocytes. 39,46For instance, differentiation of adipose-derived stem cells (ASC) and mouse embryonic 10 T1/2 cells is dependent on ROS and oxidative stress status. 41,47Moreover, it has been determined that ROS generation from mitochondrial complex III is a causal factor for the adipogenic commitment of bone marrow MSC and that inhibiting mitochondrial respiration significantly suppresses adipogenic differentiation. 39,40Furthermore, exogenous application of H₂O₂ may induce and augment adipocyte differentiation and cell cycle progression of 313-L1 mouse preadipocytes. 48ROS are indeed known to trigger several pathways that set up the transcriptional machinery, including Wnt, Hg and Forkhead Box O (FoxO) signalling cascades, towards PPARγ activation and adipogenic commitment. 41I G U R E 1 Adipocyte metabolism in health and obesity.(A) Healthy adipocyte: uptake of free fatty acids into the adipocyte occurs mainly through fatty acid-binding and transport proteins (FATPs).The influx of glucose through the adipocyte is mainly regulated by insulin receptor, whose pathway activation leads to GLUT4 translocation, promoting the uptake of glucose.Both substrates go through lipogenesis to synthesize and store triglycerides (TGs).Conversely, lipolysis occurs mainly due to neuroendocrine signals, such as catecholamines and inactivated insulin receptor, for TG breakdown.Different metabolic pathways are performed in healthy mitochondria, while the adipocyte secretes higher amount of anti-inflammatory adipokines to regulate energy homeostasis.(B) Adipocyte dysfunction in obesity: Overnutrition leads to insulin resistance and no translocation of GLUT4.Mitochondrial dysfunction is a primary cause of adipose tissue inflammation: high levels of oxidative stress (ROS) and decline of antioxidant defence leads to cellular damage.A shift towards a pronounced pro-inflammatory secretome, altered lipid metabolism and hypertrophy are main characteristic in obesity.FATPs, fatty acid-binding and transport proteins.GLUT4, glucose transporter protein 4. TG, triglycerides.ROS, reactive oxygen species.

| EARLY PROGRAMMING OF ADIPOSE TISSUE BY MATERNAL OBESITY
Evidence shows that fetal adipogenesis can be programmed by maternal obesity.High glucose levels and lipids in the maternal circulation are transported across the placenta, inducing hyperglycemia and hyperlipidemia in the developing foetus. 49In addition, the placental function is regulated by maternal signals, such as maternal nutritional state, metabolic changes, endocrine mediators and growth factors, which will determine the placental function and, therefore, fetal development. 49Many of these signals are influenced by maternal obesity. 49Clinical studies show that neonates born from mothers with obesity have increased neonatal adiposity and adiposity markers such as higher concentrations of umbilical cord leptin, interleukin 6 (IL-6) and insulin-like growth factor 1 (IGF-1). 7,9Furthermore, epidemiological studies have shown that neonates from obese mothers are insulin resistant and prone to metabolic compromise. 9udies on fetal adipose tissue from obese pregnancies are limited to animal models and show that fetal development is vulnerable to changes in nutrition during early and late third trimester of gestation, with high fetal growth and fat deposition. 50,51Data suggested that offspring from mothers with obesity show increased fetal adiposity, with a higher fat mass and hypertrophy of adipocytes in both sheep and mice. 52,53Also, at this time, regulatory set points in the brain, neuronal-metabolic feedback loops and mitochondrial function may be impacted in rodents. 54Offspring from obese high-fat diet-induced rats and ewes accumulate excessive fat mass associated with upregulation of lipogenic genes, increased fatty acid and glucose transporters and increased expression of enzymes mediating fatty acid biosynthesis in adipose depots. 52,55Other animal studies showed upregulation of PPARγ, C/EBP, zinc finger protein 423 (Zfp423), leptin and other lipogenic gene expression 56 together with adipocyte hypertrophy in offspring of obese mothers. 57igenetic mechanisms participate in the regulation of fetal adipogenesis: a decreased methylation of C/EBP and Zfp423 promoter and enhanced adipogenesis are present in fetal adipose tissue from high-fat diet dams. 55It has also been shown that maternal obesity in animals can lead to a metabolic syndrome-like phenomenon through epigenetic modifications of the genes encoding higher expression of leptin and lower levels of adiponectin in adipose tissue of the offspring. 58The outcome of adipose tissue programming is vastly stereotypic, proposing common underlying mechanisms: offspring develops altered metabolic features such as insulin resistance, obesity, immunity disorders and endothelial dysfunction. 7,52,58How early this programming takes place is unknown.

| MESENCHYMAL STEM CELLS FROM NEONATES OF WOMEN WITH MATERNAL OBESITY
As indicated above, growing evidence indicates that increased fat mass in offspring from obese animals occurs in prenatal life, suggesting that prenatal adipocyte development may differ in foetuses of obese versus lean mothers.Studying adipocyte progenitor cells and their in vitro development into adipocytes could shed light on potential aberrant adipocyte development in the offspring of obese women.The human umbilical cord is an easily accessible and noninvasive source of MSCs, also exempt from ethical debate. 59MSCs from umbilical cords are easy to isolate and culture. 11MSCs have a multipotent differentiation potential towards the mesodermal lineage and are adipocyte precursor cells. 11Therefore MSCs obtained from umbilical sources could provide an efficient model for studying fetal adipose tissue.

| Increased adipogenesis in neonates of women with obesity
Different studies have been performed on MSCs from Wharton jelly in the umbilical cords of obese and lean pregnant women.Iaffaldano et al. (2013) showed that MSCs from neonates born from obese mothers have a higher expression of adipogenic genes, such as PPARγ and FABP4/aP2, compared to MSCs from lean mothers, 60 suggesting a higher adipogenic potential in MSCs of neonates from mothers with obesity.Recently, it has been demonstrated that during adipogenic induction, these cells have higher lipid accumulation, consistent with hypertrophy. 61A particular commitment towards adipocyte lineage in MSCs from neonates from obese women has been attributed to the downregulation of the Wnt signalling pathway.More specifically, Boyle et al. (2016) demonstrated that umbilical cord MSCs from mothers with obesity were predisposed to differentiate towards adipogenic, rather than myogenic tissue in vitro.This was due to the downregulation of the Wnt/β-catenin pathway. 62Downregulation of Wnt/β-catenin pathway is associated with lower translocation of β-catenin to the nucleus, an inhibitory signal for muscle formation.
The low levels of β-catenin also indirectly promote adipogenesis of these cells by reactivating PPARγ and C/EBPα. 63Similarly, Chen et al.
(2016) suggested that umbilical cord MSCs from neonates from mothers with obesity have a lower osteogenic potential and an increased potential towards adipocyte in vitro differentiation.This was associated with an increased induction of PPARγ and adipocyte protein 2 (FABP4/aP2) gene expression. 64An impaired bone formation is associated with fat accumulation and loss of bone density, 65 and could be explained by a deficient Wnt signalling leading to decreased osteogenesis and reconstitution by adipose tissue. 37gether, these data indicate that an obesogenic environment could promote a shift in MSC commitment towards adipocyte differentiation. 62This suggests that progenitor cells can determine their lineage commitment according to external signals. 37rthermore, recent studies showed that lipid accumulation in Wharton Jelly MSCs correlates to metabolic features in neonates, suggesting that phenotypical characteristics of MSCs do translate to the clinical outcome of the child. 66This means that early metabolic dysregulations may establish the adipocyte pool and programme longterm effects: this has been associated with adiposity gain 67 (Figure 2).

| Insulin in MSC-adipocytes from neonates of women with obesity
Insulin signalling is necessary for glucose and lipid metabolic balance in cells. 68During early differentiation of MSCs, insulin is also required to activate PPARγ, C/EBPs and thus adipogenesis. 22Upon insulin binding, the insulin receptor triggers the downstream signalling cascades involving phosphoinositide 3-kinase (PI3K)/Akt, MAPK, ERK1/2 and inhibits AMPK. 69Insulin signalling works as a strictly regulated mechanism, and a minor disruptive activity of downstream pathways could lead to perturbations in metabolism. 69Disruptive signalling is often the result of inflammation, hyperglycemia, lipotoxicity and ERmitochondrial stress. 70Women with obesity often enter pregnancy with pre-existing glucose intolerance and insulin resistance, which intensifies with advancing gestation 71 and are often transferred to the foetus. 7Therefore, a state of hyperglycemia and isulin resistance is characteristic in obese mothers and their foetuses, which could also programme metabolic activity during adipocyte differentiation.There appears to be a downregulation of nutrient-sensing pathways in in vitro adipocyte-differentiated MSCs from offspring born to mothers with obesity, particularly with lower AMPK, MAPK and PI3K-AKT transcription. 67Downregulation of these pathways related to insulin signalling is known to alter insulin sensitivity, with lack of GLUT4 membrane translocation and fatty acid oxidation. 72,73MSCs from the offspring of women with obesity have no response from Akt to insulin stimulation, concluding insulin resistance. 64Moreonver, they show impaired cytoskeleton protein expression that could attempt to decrease GLUT4 transport to the membrane, in response to hyperglycemia. 74Whether this is a cause or a consequence of insulin resistance is yet to be studied.It is also reported that MSC from offspring of mothers with obesity show hypermethylation of lysophospholipases regulated by insulin. 75Together, these results suggest that umbilical cord-derived MSCs of neonates from mothers with obesity may have an altered insulin receptor signalling, related to lower insulin sensitivity and impaired glucose and lipid metabolism.
It is important to note that hyperinsulinemia and hyperglycemia from the mother to the foetus may impact many other insulin-sensitive metabolic organs, such as fetal liver, pancreas and muscle, which externally contributes to the increased neonatal adiposity and risk of metabolic disbalance in the future. 67Clinical observations show that increased maternal BMI is linked with fetal macrosomia and enhanced adiposity. 76Altogether, this strongly suggests that programming of adaptive responses to conditions such as elevated glucose, lipids and hyperinsulinemia in utero could promote higher adipose tissue formation, with the characteristic neonatal macrosomia. 77With altered insulin sensitivity it is suspected that the final mature adipocyte could be programmed to become hyperptrohic and prone to dysfunction. 64

| Mitochondrial dysfunction in MSC from neonates of women with obesity
Mitochondria are pivotal in coordinating energy production with nutritional cues. 78Glycolysis and mitochondrial oxidative F I G U R E 2 Mesenchymal stem cells and adipogenesis in lean and obese pregnancies.Lean pregnancies: fetal developmental adipogenesis is activated in mesenchymal stem cells through orchestrated extracellular signalling pathways: Wnt and insulin.These processes would activate C/EBPs (α and β) and mitochondria, leading to healthy preadipocyte that will proliferate.Final adipocytes express PPARγ, together with lipogenesis markers and adipokines.Obese pregnancies: fetal mesenchymal stem cells present a decreased insulin signalling and increased induction of adipogenesis through a stronger downregulation of Wnt.Metabolic activity is decreased.Final adipocytes show higher PPARγ expression, together with altered fatty acid metabolism, mitochondrial dysfunction and senescence markers.Wnt, wingless-type MMTV integration site.PPARγ, peroxisome proliferator-activated receptor-gamma.GLUT4, glucose transporter 4. FABP4/aP2, fatty acid-binding protein 4. LPL, lipoprotein lipase.ROS, reactive oxygen species.phosphorylation are the main ATP-producing pathways by which cells obtain energy to drive their biological functions. 32Energy demand, nutritional status and oxygen availability will determine bioenergetic pathways. 32In response to changes in energy demand and supply, the organism adapts by adjusting its capacity and ATP production efficiency. 79MSCs are characterized for being highly glycolytic, while during differentiation of MSCs towards adipocytes, oxidative phosphorylation by mitochondria is an important contributor to ATP production and metabolic reprogramming. 32In mature adipocytes, apart from ATP production, healthy mitochondria are contributors to the metabolic balance due to their role in fatty acid oxidation and energetic demand for adipokine production. 15,32In fat depots of patients with obesity, the mitochondrial membrane potential and the activities of respiratory chain complexes are reduced. 80Such mitochondrial dysfunction leads to oxidative stress, cell death, inflammation and metabolic dysfunction. 78Next to this, in fat depots of patients with obesity, the antioxidant defence mechanisms are also decreased. 31gh levels of oxidative stress and the simultaneous decline of antioxidant defence lead to cellular damage, which is a primary cause of adipose tissue inflammation. 81Cs from umbilical cords of neonates from women with obesity show less efficient mitochondrial respiration compared to MSCs of neonates from lean mothers: the electron transport chain is impaired and maximal respiration is lower in MSCs of newborns from women with obesity.82 This suggests early signatures of mitochondrial dysfunction, oxidative stress and metabolic disruption in the MSCs from umbilical cords of obese women.Baker et al. (2017) characterized mitochondrial gene expression of adipocytes differentiated from umbilical cord MSCs.This study showed upregulation of the mitochondrial respiratory chain but downregulation of mitochondrial biogenesis, mitophagy and fusion/fission in MSCs from newborns of women with obesity as compared to the MSCs from neonates of lean women.83 Altered mitochondrial electron transport machinery is considered a major ROS generator, 43 suggesting increased ROS production in MSCs from neonates from obese mothers as compared to neonates to lean mothers.
Although ROS production in MSCs from neonates of obese versus lean mothers has not been determined, oxidative stress is known to be related to premature ageing, 84 and MSCs of neonates from women with maternal obesity show higher p53, p21 and senescence associated β galactosidae (SAβG): markers of cell senescence signalling.This indicates an ageing phenotype of MSCs from offspring of mothers with obesity 64 (Figure 2).In addition, studies by Capobianco   et al. (2016) reported reduced stress response proteins in these cells, suggesting a different oxidative stress response in MSCs from neonates from mothers with obesity. 74Further studies should thus measure the levels of ROS in MSCs from neonates from mothers with obesity.It has not been determined whether the altered mitochondrial function in early precursor cells are maintained in mature adipocytes in postnatal life.Iaffaldano et al. (2018) also showed that glycolysis is less efficient in fetal MSCs isolated from the umbilical cord of women with obesity than in those isolated from control women. 82These findings suggest maternal obesity can alter the glycolytic machinery with a less efficient response to the energy demand.Furthermore, it has been established that low ATP production has been associated with increased accumulation of intracellular TGs in mouse preadipocytes. 85Whether this could be an adaptative response of the developing foetus to the excessive nutrient supply is still unknown.
Genomic studies in adipocytes differentiated from umbilical cord MSCs show that maternal free fatty acids (FFA) and neonatal adiposity are associated with upregulation of mitochondrial electron transport genes, but downregulation of mitochondrial biogenesis genes, including EP300, CREBBP and PPARA. 83This is consistent with lower mitochondrial abundance. 82In similar studies, epigenetic analysis show hypermethylation of genes of the fatty acid oxidation machinery 67 and differently expressed miR-138-5p and miR-222-3p, which upregulate genes engaged with lipid metabolism and stress response. 86Overexpression of miR-138-5p and miR-222-3p has been found in subcutaneous and visceral adipose tissues from obese adults associated with the chronic inflammatory environment. 87These results suggest that energetic adaptation during gestation may enable the foetus to survive in an aversive energetic environmental condition by reprogramming mitochondrial function for adaptative responses (Figure 2).

| CONCLUDING REMARKS
Maternal obesity is known to create an adverse intrauterine environment that can lead to fetal adaptation.Maternal obesity programmes several developmental pathways, including fetal adipogenesis.The potentiation of adipogenesis in early life may trigger the later development of obesity.During a lean pregnancy, adipocyte precursor cells in the foetus express high mesenchymal stem cell markers, maintained in a committed but undifferentiated state, limiting the differentiation towards adipocytes.In an obese pregnancy, however, MSCs have an increased differentiation potential towards adipocytes, which may help to explain the progressive increase in fat mass of the offspring of women with obesity.It is still unclear if this is a protective mechanism from the foetus to the mother's nutritional overload.
The increased adipogenic potential of MSCs from umbilical cords of neonates from mothers with obesity raises several questions: could maternal obesity lead to increased adipogenesis in other mesodermal tissues, such as bone and muscle?Could this result in a decreased differentiation towards muscle, bone and cartrilage cells?In this respect, it is important to note that obesity is a condition associated to a disturbed muscle and bone physiology, together with higher intramuscular fat deposition and osteoporosis. 88,89This suggests that proper development of these tissues may also be disturbed in utero.Also, this raises the question of whether other stem cell lineages could be compromised: are ectodermal and endodermal lineages altered by maternal obesity?These questions remain unclear and are necessary to answer in future research of early embryonic cell programming.
It appears that the insulin pathway as well as mitochondrial activity are different in MSCs from neonates born to mothers with obesity, and this could contribute to the early commitment towards adipocytes and, with this, increased adipogenesis of its precursor pool.Whether it would lead to dysfunctional adipocytes in the neonate is a question that remains, and more follow-up studies are needed.However, these progenitor cells can determine their lineage commitment according to external signals.Premature signatures in early progenitor cells from neonates exposed to maternal obesity may indicate that the problem starts with the early first totipotent cell exposed to this adverse intrauterine environment.This could be the main reason why interventions, such as nutrition and exercise during mid and late gestation, have concluded no beneficial effects over the altered anthropometric and metabolic parameters in these neonates-it may be too late. 90em cells are abundant during early life and carry specific prenatal signatures.We suggest that they may be proposed as potential performers of the developmental programming of obesity and metabolic diseases.Although studies on maternal obesity and fetal outcomes have been performed for many decades, the current knowledge of the altered phenotype of this progenitor cells can be an interesting instrument to understand the mechanisms by which the high nutrient supply in early progenitor cells may lead to adipocyte imprinting.The knowledge on this early imprinting of precursor cells shows that there is an urgent need to focus on preventive strategies targeted to preconceptional and early days of pregnancy.This may provide an opportunity to break the rising cycle of obesity and the concomitant noncommunicable diseases.

AUTHOR CONTRIBUTIONS
SB contributed to the investigation, conceptualization, analysis of the information and writing this manuscript.PC, MF and TP contributed to conceptualization and editing.SB prepared figures.All authors read and approved the final manuscript.