Hypoxia induces adipocyte differentiation of adipose-derived stem cells by triggering reactive oxygen species generation

Enhancing adipose tissue functionality in obesity: senotherapeutics, autophagy and cellular senescence as a target

Obesity, a global health crisis, disrupts multiple systemic processes, contributing to a cascade of metabolic dysfunctions by promoting the pathological expansion of visceral adipose tissue (VAT). This expansion is characterized by impaired differentiation of pre-adipocytes and an increase in senescent cells, leading to a pro-inflammatory state and exacerbated oxidative stress. Particularly, the senescence-associated secretory phenotype (SASP) and adipose tissue hypoxia further impair cellular function, promoting chronic disease development. This review delves into the potential of autophagy modulation and the therapeutic application of senolytics and senomorphics as novel strategies to mitigate adipose tissue senescence. By exploring the intricate mechanisms underlying adipocyte dysfunction and the emerging role of natural compounds in senescence modulation, we underscore the promising horizon of senotherapeutics in restoring adipose health. This approach not only offers a pathway to combat the metabolic complications of obesity, but also opens new avenues for enhancing life quality and managing the global burden of obesity-related conditions. Our analysis aims to bridge the gap between current scientific progress and clinical application, offering new perspectives on preventing and treating obesity-induced adipose dysfunction.

Metallothionein 3 Inhibits 3T3-L1 Adipocyte Differentiation via Reduction of Reactive Oxygen Species

Metallothionein 3 (MT3), also known as a neuronal growth-inhibitory factor, is a member of the metallothionein family and is involved in a variety of biological functions, including protection against metal toxicity and reactive oxygen species (ROS). However, less is known about the role of MT3 in the differentiation of 3T3-L1 cells into adipocytes. In this study, we observed that MT3 levels were downregulated during 3T3-L1 adipocyte differentiation. Mt3 overexpression inhibited adipocyte differentiation and reduced the levels of the adipogenic transcription factors C/EBPα and PPARγ. Further analyses showed that MT3 also suppressed the transcriptional activity of PPARγ, and this effect was not mediated by a direct interaction between MT3 with PPARγ. In addition, Mt3 overexpression resulted in a decrease in ROS levels during early adipocyte differentiation, while treatment with antimycin A, which induces ROS generation, restored the ROS levels. Mt3 knockdown, on the other hand, elevated ROS levels, which were suppressed upon treatment with the antioxidant N-acetylcysteine. Our findings indicate a previously unknown role of MT3 in the differentiation of 3T3-L1 cells into adipocytes and provide a potential novel target that might facilitate obesity treatment.

A Wrong Fate Decision in Adipose Stem Cells upon Obesity

Progress has been made in identifying stem cell aging as a pathological manifestation of a variety of diseases, including obesity. Adipose stem cells (ASCs) play a core role in adipocyte turnover, which maintains tissue homeostasis. Given aberrant lineage determination as a feature of stem cell aging, failure in adipogenesis is a culprit of adipose hypertrophy, resulting in adiposopathy and related complications. In this review, we elucidate how ASC fails in entering adipogenic lineage, with a specific focus on extracellular signaling pathways, epigenetic drift, metabolic reprogramming, and mechanical stretch. Nonetheless, such detrimental alternations can be reversed by guiding ASCs towards adipogenesis. Considering the pathological role of ASC aging in obesity, targeting adipogenesis as an anti-obesity treatment will be a key area of future research, and a strategy to rejuvenate tissue stem cell will be capable of alleviating metabolic syndrome.

Thermal stress and selection for growth affect myogenic satellite cell lipid accumulation and adipogenic gene expression through mechanistic target of rapamycin pathway

Satellite cells (SCs) are multipotential stem cells having the plasticity to convert to an adipogenic lineage in response to thermal stress during the period of peak mitotic activity (the first week after hatch in poultry). The mechanistic target of rapamycin (mTOR) pathway, which regulates cellular function and fate of SCs, is greatly altered by thermal stress in turkey pectoralis major muscle SCs. The objective of the present study was to determine the effects of thermal stress, selection for growth, and the role of the mTOR pathway on SC intracellular lipid accumulation and expression of adipogenic regulatory genes. These effects were analyzed using SCs isolated from the pectoralis major muscle of 1-wk-old modern faster-growing commercial turkey line (NC) selected for increased growth and breast muscle yield as compared with SCs of a historic slower-growing Randombred Control Line 2 (RBC2) turkey. Heat stress (43 °C) of SCs during proliferation increased intracellular lipid accumulation (P < 0.001), whereas cold stress (33 °C) showed an inhibitory effect (P < 0.001) in both lines. Knockdown of mTOR reduced the intracellular lipid accumulation (P < 0.001) and suppressed the expression of several adipogenic regulatory genes: peroxisome proliferator-activated receptor-γ (PPARγ; P < 0.001), CCAAT/enhancer-binding protein-β (C/EBPβ; P < 0.001), and neuropeptide-Y (NPY; P < 0.001) during both proliferation and differentiation. The NC line SCs showed fewer reductions in lipid accumulation compared with the RBC2 line independent of temperature. Both intracellular lipid accumulation (P < 0.001) and PPARγ expression (P < 0.001) were greater at 72 h of proliferation than at 48 h of differentiation in both the RBC2 and NC lines independent of temperature. Thus, hot and cold thermal stress affected intracellular lipid accumulation in the pectoralis major muscle SCs, in part, through the mTOR pathway in wea growth-dependent manner. Altered intracellular lipid accumulation could eventually affect intramuscular fat deposition, resulting in a long-lasting effect on the structure and protein to fat ratio of the poultry pectoralis major muscle.

Activation of the aryl hydrocarbon receptor by clozapine induces preadipocyte differentiation and contributes to endothelial dysfunction

BACKGROUND

The superior therapeutic benefit of clozapine is often associated with metabolic disruptions as obesity, insulin resistance, tachycardia, higher blood pressure, and even hypertension.

AIMS

These adverse vascular/ metabolic events under clozapine are similar to those caused by polycyclic aromatic hydrocarbons (PAHs), and clozapine shows structural similarity to well-known ligands of the aryl hydrocarbon receptor (AhR). Therefore, we speculated that the side effects caused by clozapine might rely on AhR signaling.

METHODS

We examined clozapine-induced AhR activation by luciferase reporter assays in hepatoma HepG2 cells and we proved upregulation of the prototypical AhR target gene Cyp1A1 by realtime-PCR (RT-PCR) analysis and enzyme activity. Next we studied the physiological role of AhR in clozapine's effects on human preadipocyte differentiation and on vasodilatation by myography in wild-type and AhR-/- mice.

RESULTS

In contrast to other antipsychotic drugs (APDs), clozapine triggered AhR activation and Cyp1A1 expression in HepG2 cells and adipocytes. Clozapine induced adipogenesis via AhR signaling. After PGF2α-induced constriction of mouse aortic rings, clozapine strongly reduced the maximal vasorelaxation under acetylcholine in rings from wild-type mice, but only slightly in rings from AhR-/- mice. The reduction was also prevented by pretreatment with the AhR antagonist CH-223191.

CONCLUSION

Identification of clozapine as a ligand for the AhR opens new perspectives to explain common clozapine therapy-associated adverse effects at the molecular level.

Hypoxia Modulates Regenerative Potential of Fetal Stem Cells

Adult mesenchymal stem cells (MSCs) are prone to senescence, which limits the scope of their use in tissue engineering and regeneration and increases the likelihood of post-implantation failure. As a robust alternative cell source, fetal stem cells can prevent an immune reaction and senescence. However, few studies use this cell type. In this study, we sought to characterize fetal cells' regenerative potential in hypoxic conditions. Specifically, we examined whether hypoxic exposure during the expansion and differentiation phases would affect human fetal nucleus pulposus cell (NPC) and fetal synovium-derived stem cell (SDSC) plasticity and three-lineage differentiation potential. We concluded that fetal NPCs represent the most promising cell source for chondrogenic differentiation, as they are more responsive and display stronger phenotypic stability, particularly when expanded and differentiated in hypoxic conditions. Fetal SDSCs have less potential for chondrogenic differentiation compared to their adult counterpart. This study also indicated that fetal SDSCs exhibit a discrepancy in adipogenic and osteogenic differentiation in response to hypoxia.

The Phosphonate Derivative of C60 Fullerene Induces Differentiation towards the Myogenic Lineage in Human Adipose-Derived Mesenchymal Stem Cells

Inductors of myogenic stem cell differentiation attract attention, as they can be used to treat myodystrophies and post-traumatic injuries. Functionalization of fullerenes makes it possible to obtain water-soluble derivatives with targeted biochemical activity. This study examined the effects of the phosphonate C₆₀ fullerene derivatives on the expression of myogenic transcription factors and myogenic differentiation of human mesenchymal stem cells (MSCs). Uptake of the phosphonate C₆₀ fullerene derivatives in human MSCs, intracellular ROS visualization, superoxide scavenging potential, and the expression of myogenic, adipogenic, and osteogenic differentiation genes were studied. The prolonged MSC incubation (within 7–14 days) with the C₆₀ pentaphoshonate potassium salt promoted their differentiation towards the myogenic lineage. The transcription factors and gene expressions determining myogenic differentiation (MYOD1, MYOG, MYF5, and MRF4) increased, while the expression of osteogenic differentiation factors (BMP2, BMP4, RUNX2, SPP1, and OCN) and adipogenic differentiation factors (CEBPB, LPL, and AP2 (FABP4)) was reduced or did not change. The stimulation of autophagy may be one of the factors contributing to the increased expression of myogenic differentiation genes in MSCs. Autophagy may be caused by intracellular alkalosis and/or short-term intracellular oxidative stress.

NADPH Oxidases: Redox Regulators of Stem Cell Fate and Function

One of the major sources of reactive oxygen species (ROS) generated within stem cells is the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase family of enzymes (NOXs), which are critical determinants of the redox state beside antioxidant defense mechanisms. This balance is involved in another one that regulates stem cell fate: indeed, self-renewal, proliferation, and differentiation are decisive steps for stem cells during embryo development, adult tissue renovation, and cell therapy application. Ex vivo culture-expanded stem cells are being investigated for tissue repair and immune modulation, but events such as aging, senescence, and oxidative stress reduce their ex vivo proliferation, which is crucial for their clinical applications. Here, we review the role of NOX-derived ROS in stem cell biology and functions, focusing on positive and negative effects triggered by the activity of different NOX isoforms. We report recent findings on downstream molecular targets of NOX-ROS signaling that can modulate stem cell homeostasis and lineage commitment and discuss the implications in ex vivo expansion and in vivo engraftment, function, and longevity. This review highlights the role of NOX as a pivotal regulator of several stem cell populations, and we conclude that these aspects have important implications in the clinical utility of stem cells, but further studies on the effects of pharmacological modulation of NOX in human stem cells are imperative.

δ-opioid receptor activation protects against Parkinson's disease-related mitochondrial dysfunction by enhancing PINK1/Parkin-dependent mitophagy

Our previous studies have shown that the δ-opioid receptor (DOR) is an important neuroprotector via the regulation of PTEN-induced kinase 1 (PINK1), a mitochondria-related molecule, under hypoxic and MPP⁺ insults. Since mitochondrial dysfunctions are observed in both hypoxia and MPP⁺ insults, this study further investigated whether DOR is cytoprotective against these insults by targeting mitochondria. Through comparing DOR-induced responses to hypoxia versus MPP⁺-induced parkinsonian insult in PC12 cells, we found that both hypoxia and MPP⁺ caused a collapse of mitochondrial membrane potential and severe mitochondrial dysfunction. In sharp contrast to its inappreciable effect on mitochondria in hypoxic conditions, DOR activation with UFP-512, a specific agonist, significantly attenuated the MPP⁺-induced mitochondrial injury. Mechanistically, DOR activation effectively upregulated PINK1 expression and promoted Parkin's mitochondrial translocation and modification, thus enhancing the PINK1-Parkin mediated mitophagy. Either PINK1 knockdown or DOR knockdown largely interfered with the DOR-mediated mitoprotection in MPP⁺ conditions. Moreover, there was a major difference between hypoxia versus MPP⁺ in terms of the regulation of mitophagy with hypoxia-induced mitophagy being independent from DOR-PINK1 signaling. Taken together, our novel data suggest that DOR activation is neuroprotective against parkinsonian injury by specifically promoting mitophagy in a PINK1-dependent pathway and thus attenuating mitochondrial damage.

Co-transplantation with adipose-derived cells to improve parathyroid transplantation in a mice model

Background

Accidentally removed parathyroid glands are still challenging in neck surgery, leading to hypoparathyroidism characterized with abnormally low levels of parathyroid hormone. Parathyroid auto-transplantation is usually applied in compensation. To improve the efficiency of parathyroid transplantation, we introduced a method by co-transplanting with adipose-derived cells, including stromal vascular fractions (SVFs) and adipose-derived stem cells (ADSCs), and investigated the underlying molecular mechanisms involved in parathyroid transplantation survival.

Methods

Rat and human parathyroid tissues were transplanted into nude mice as parathyroid transplantation model to examine the effects of SVFs and ADSCs on grafts angiogenesis and survival rates, including blood vessel assembly and parathyroid hormone levels. Several angiogenic factors, such as vascular endothelial growth factor (VEGF)-A and fibroblast growth factor (FGF) 2, were assessed in parathyroid grafts. The effects of hypoxia were investigated on ADSCs. The modulatory roles of the eyes absent homolog 1 (EYA1), which is vital in parathyroid development, was also investigated on angiogenic factor production and secretion by ADSCs. All experimental data were statistically processed. Student’s t test was used to assess significant differences between 2 groups. For multiple comparisons with additional interventions, two-way ANOVA followed by Tukey’s post hoc test was performed. P < 0.05 was considered as significant.

Results

SVFs improve rat parathyroid transplantation survival and blood vessel assembly, as well as FGF2 and VEGF-A expression levels in parathyroid transplantation mice. Functional human parathyroid grafts have higher microvessel density and increased VEGF-A expression. The supernatant of ADSCs induced tubule formation and migration of human endothelial cells in vitro. Hypoxia had no effect on proliferation and apoptosis of human ADSCs but induced higher angiogenic factor levels of VEGF-A and FGF2, modulated by EYA1, which was confirmed by parathyroid glands transplantation in mice.

Conclusions

Adipose-derived cells, including ADSCs and SVFs, improve parathyroid transplantation survival via promoting angiogenesis through EYA1-regulating angiogenetic factors in vitro and in vivo. Our studies proved an effective method to improve the parathyroid autotransplantation, which is promising for clinical patients with hypoparathyroidism when parathyroid glands were accidentally injured, removed, or devascularized.

Negative Pressure From an Internal Spiral Tissue Expander Generates New Subcutaneous Adipose Tissue in an In Vivo Animal Model

BACKGROUND

Tissue expanders are widely utilized in plastic surgery. Traditional expanders usually are "inflatable balloons," which are planned to grow additional skin and/or to create space to be filled, for example, with an implant. In very recent years, reports suggest that negative pressure created by an external device (ie, Brava) induces both skin expansion and adipogenesis.

OBJECTIVES

The authors evaluated and assessed the adipogenetic potential of a novel internal tissue expander in an in vivo animal model.

METHODS

New Zealand female rabbits were enrolled in the study. A prototype spiral inner tissue expander was employed. It consisted of a-dynamic conic expander (DCE) with a valve at the end: when empty, it is flat (Archimedean spiral), whereas when filled with a fluid, it takes a conic shape. Inside the conic spiral, a negative pressure is therefore created. DCE is implanted flat under the latissimus dorsi muscle in experimental animals (rabbit) and then filled to reach the conical shape. Animals were investigated with magnetic resonance imaging, histology, and transmission electronic microscopy at 3, 6, and 12 months.

RESULTS

Magnetic resonance imaging revealed a marked increase in newly formed adipose tissue, reaching its highest amount at 12 months after the DCE implantation. Histology confirmed the existence of new adipocytes, whereas transmission electronic microscopy ultrastructure confirmed that most of these new cells were mature adipocytes.

CONCLUSIONS

Tensile stress, associated with negative-pressure expanders, generated newly white subcutaneous adipose tissue.

Broad-Spectrum Antibacterial Effects of Human Adipose-Derived Stromal Cells

Introduction

Many pathological conditions may benefit from cell therapy using mesenchymal stromal cells, particularly from adipose tissue (ASCs). Cells may be grafted in an environment with a remnant polymicrobial component. The aim is to investigate the behavior of ASCs when brought in contact with a large panel of bacteria.

Materials and Methods

Carboxyfluorescein-labelled bacterial interaction with ASCs was followed by confocal time-lapse microscopy. Costaining with LAMP-1 was also analyzed. Viability of 4 gram-negative and 4 gram-positive bacterial strains after 6 h of coculture with ASCs was assessed by agar colony counting and by flow cytometry using SYTO-62®/propidium iodide (PI) for membrane permeabilization and DiOC6 for depolarization. A murine model of periodontitis was used to assess in vivo antibacterial capacities of ASCs.

Results

A significant increase of PI-positive events for all bacterial strains and an increase of the DiOC6 signal were obtained after contact with ASCs. The number of CFU was also significantly decreased for several bacterial strains. 0.4 μm transwell systems illustrated the necessary direct contact to induce maximal bacterial membrane damages. Some bacteria were observed into phagolysosomes, confirming macrophage-like properties of ASCs. In vivo, the bacterial load was significantly lower in the ASC-grafted side compared to the control.

Conclusion

Our results highlight for the first time a broad range of antibacterial actions of ASCs, by phagocytosis, secretion of oxygenated free radicals and antibacterial molecules. These data are in line with the development of new therapeutic strategies based on ASC transplantation, appropriated in immune-dysbiotic tissue context such as periodontitis or chronic wounds.

Crucial lncRNAs associated with adipocyte differentiation from human adipose-derived stem cells based on co-expression and ceRNA network analyses

BACKGROUND

Injection of adipose-derived stem cells (ASCs) is a promising treatment for facial contour deformities. However, its treatment mechanisms remain largely unknown. The study aimed to explain the molecular mechanisms of adipogenic differentiation from ASCs based on the roles of long noncoding RNAs (lncRNAs).

METHODS

Datasets of mRNA-lncRNA (GSE113253) and miRNA (GSE72429) expression profiling were collected from Gene Expression Omnibus database. The differentially expressed genes (DEGs), lncRNAs (DELs) and miRNAs (DEMs) between undifferentiated and adipocyte differentiated human ASCs were identified using the Linear Models for Microarray Data method. DELs related co-expression and competing endogenous RNA (ceRNA) networks were constructed. Protein-protein interaction (PPI) analysis was performed to screen crucial target genes.

RESULTS

A total of 748 DEGs, 17 DELs and 51 DEMs were identified. A total of 13 DELs and 279 DEGs with Pearson correlation coefficients > 0.9 and p-value < 0.01 were selected to construct the co-expression network. A total of 151 interaction pairs among 112 nodes (10 DEMs; eight DELs; 94 DEGs) were obtained to construct the ceRNA network. By comparing the lncRNAs and mRNAs in two networks, five lncRNAs (SNHG9, LINC02202, UBAC2-AS1, PTCSC3 and myocardial infarction associated transcript (MIAT)) and 32 genes (i.e., such as phosphoinositide-3-kinase regulatory subunit 1 (PIK3R1), protein tyrosine phosphatase receptor type B (PTPRB)) were found to be shared. PPI analysis demonstrated PIK3R1 , forkhead box O1 (FOXO1; a transcription factor) and estrogen receptor 1 (ESR1) were hub genes, which could be regulated by the miRNAs that interacted with the above five lncRNAs, such as LINC02202-miR-136-5p-PIK3R1, LINC02202-miR-381-3p-FOXO1 and MIAT-miR-18a-5p-ESR1. LINC02202 also could directly co-express with PIK3R1. Furthermore, PTPRB was predicted to be modulated by co-expression with LINC01119.

CONCLUSION

MIAT, LINC02202 and LINC01119 may be potentially important, new lncRNAs associated with adipogenic differentiation of ASCs. They may be involved in adipogenesis by acting as a ceRNA or co-expressing with their targets.

Update on the role of Sirtuin 3 in cell differentiation: A major metabolic target that can be pharmacologically controlled

Cell differentiation is a fundamental biological event in which a precursor stem cell is turning into a specialized somatic cell. It is thus crucial for the development, tissue turnover and regeneration in mammals. Among the numerous changes taking place in a cell during a differentiation programme, the biology of mitochondria, the central organelle mainly responsible for energy homeostasis and stress adaptation, is deeply modified. These modifications are now well recognized as taking an active part to the completion of the differentiation programme. Indeed, mitochondrial biogenesis and metabolic shift are observed during cell differentiation, adapting many syntheses, calcium homeostasis, ATP and reactive oxygen species production, to the needs. These mitochondrial functions are substantially regulated by the post-translational modifications of the mitochondrial proteins among which lysine acetylation is essential. This mitoacetylome is then globally controlled by the balance between spontaneous/enzymatically-catalysed protein acetylation and the NAD⁺-dependent deacetylation mediated by Sirtuin 3. This enzyme is now considered as a major regulator of the function of the organelle. Regarding the requirement of these mitochondrial adaptations, the subsequent growing interest for this enzyme recently extended to the investigation of the mechanisms driving cell differentiation. This review summarizes the currently available information about the significance of SIRT3 in cell differentiation in physio-pathological contexts. We also suggest a control of the differentiation-activated autophagy by SIRT3, a hypothesis supported by recent findings establishing a causal link between SIRT3 and autophagy. Eventually, an update on the present pharmacological modulators of SIRT3 in a context of cell differentiation is discussed.

Hypoxia Rapidly Induces the Expression of Cardiomyogenic Factors in Human Adipose-Derived Adherent Stromal Cells

BACKGROUND

The efficacy of interstitial vascular fraction (SVF) transplantation in the treatment of heart disease has been proven in a variety of in vivo studies. In a previous study, we found that bone marrow-derived mesenchymal stem cells (BM-MSCs) altered their expression of several cardiomyogenic factors under hypoxic conditions.

METHODS

We hypothesized that hypoxia may also induce obtained adipose-derived adherent stromal cells (ADASs) from SVFs and adipose-derived stem cells (ASCs) to differentiate into cardiomyocytes and/or cells with comparable phenotypes. We examined the differentiation markers of cell lineages in ADASs and ASCs according to time by hypoxic stress and found that only ADASs expressed cardiomyogenic markers within 24 h under hypoxic conditions in association with the expression of hypoxia-inducible factor 1-α (HIF-1α).

RESULTS

Differentially secreted proteins in a conditioned medium (CM) from ASCs and ADASs under normoxic or hypoxic conditions were detected using an antibody assay and may be associated with a dramatic increase in the expression of cardiomyogenic markers in only ADASs. Furthermore, the cardiomyogenic factors were expressed more rapidly in ADASs than in ASCs under hypoxic conditions in association with the expression of HIF-1α, and angiogenin, fibroblast growth factor-19 (FGF-19) and/or macrophage inhibitory factor (MIF) are related.

CONCLUSIONS

These results provide new insights into the applicability of ADASs preconditioned by hypoxic stress in cardiac diseases.

Biological Morphogenetic Surgery: A Minimally Invasive Procedure to Address Different Biological Mechanisms

We present a methodology called biological morphogenetic surgery (BMS) that can recover (enlarge or reduce) the shape/volume of anatomic structures/tissues affected by congenital or acquired malformations based on a minimally invasive procedure. This emerges as a new concept in which the main task of surgery is the biological modulation of different remodeling and repair mechanisms. When applied, for example, to a tuberous breast deformity, the "enlarging BMS" expands the retracted tissue surrounding the gland through a cutting tip of a needle being inserted through small incisions percutaneously, accounting for the biological activity of the grafted fat. The obtained spaces might be spontaneously occupied and later filled with autologous grafted fat, which promotes tissue expansion by eliciting adipogenesis and preventing fibrosis. The "reducing BMS" creates an interruption of the contact between the derma and the hypoderma of the abnormally large areola and then promotes adipocytes to induce a fibrotic reaction, leading to areola reduction. Current evidence suggests that BMS might induce a bivalent mesenchymalization of the adipocyte, which promotes either new adipogenesis and angiogenesis of local fat (expanding BMS) or the granulation tissue/fibrotic response (reducing BMS), thus leading to the physiological recovery of the affected structures/tissues to normality. Level of Evidence: 4.

Phosphoinositide 3 Kinase Signaling in Human Stem Cells from Reprogramming to Differentiation: A Tale in Cytoplasmic and Nuclear Compartments

Stem cells are undifferentiated cells that can give rise to several different cell types and can self-renew. Given their ability to differentiate into different lineages, stem cells retain huge therapeutic potential for regenerative medicine. Therefore, the understanding of the signaling pathways involved in stem cell pluripotency maintenance and differentiation has a paramount importance in order to understand these biological processes and to develop therapeutic strategies. In this review, we focus on phosphoinositide 3 kinase (PI3K) since its signaling pathway regulates many cellular processes, such as cell growth, proliferation, survival, and cellular transformation. Precisely, in human stem cells, the PI3K cascade is involved in different processes from pluripotency and induced pluripotent stem cell (iPSC) reprogramming to mesenchymal and oral mesenchymal differentiation, through different and interconnected mechanisms.

Adipocyte biology: It is time to upgrade to a new model

Globally, the obesity pandemic is profoundly affecting quality of life and economic productivity, but efforts to address this, especially on a pharmacological level, have generally proven unsuccessful to date, serving as a stark demonstration that our understanding of adipocyte biology and pathophysiology is incomplete. To deliver better insight into adipocyte function and obesity, we need improved adipocyte models with a high degree of fidelity in representing the in vivo state and with a diverse range of experimental applications. Adipocyte cell lines, especially 3T3-L1 cells, have been used extensively over many years, but these are limited in terms of relevance and versatility. In this review, I propose that primary adipose-derived stromal/stem cells (ASCs) present a superior model with which to study adipocyte biology ex vivo. In particular, ASCs afford us the opportunity to study adipocytes from different, functionally distinct, adipose depots and to investigate, by means of in vivo/ex vivo studies, the effects of many different physiological and pathophysiological factors, such as age, body weight, hormonal status, diet and nutraceuticals, as well as disease and pharmacological treatments, on the biology of adipocytes and their precursors. This study will give an overview of the characteristics of ASCs and published studies utilizing ASCs, to highlight the areas where our knowledge is lacking. More comprehensive studies in primary ASCs will contribute to an improved understanding of adipose tissue, in healthy and dysfunctional states, which will enhance our efforts to more successfully manage and treat obesity.

Regulation of the mitochondrial reactive oxygen species: Strategies to control mesenchymal stem cell fates ex vivo and in vivo

Mesenchymal stem cells (MSCs) are broadly used in cell‐based regenerative medicine because of their self‐renewal and multilineage potencies in vitro and in vivo. To ensure sufficient amounts of MSCs for therapeutic purposes, cells are generally cultured in vitro for long‐term expansion or specific terminal differentiation until cell transplantation. Although physiologically up‐regulated reactive oxygen species (ROS) production is essential for maintenance of stem cell activities, abnormally high levels of ROS can harm MSCs both in vitro and in vivo. Overall, additional elucidation of the mechanisms by which physiological and pathological ROS are generated is necessary to better direct MSC fates and improve their therapeutic effects by controlling external ROS levels. In this review, we focus on the currently revealed ROS generation mechanisms and the regulatory routes for controlling their rates of proliferation, survival, senescence, apoptosis, and differentiation. A promising strategy in future regenerative medicine involves regulating ROS generation via various means to augment the therapeutic efficacy of MSCs, thus improving the prognosis of patients with terminal diseases.

Peroxiredoxin 5 regulates adipogenesis-attenuating oxidative stress in obese mouse models induced by a high-fat diet

Elevated levels of reactive oxygen species (ROS) are a hallmark of obesity. Peroxiredoxin 5 (Prx5), which is a cysteine-dependent peroxidase enzyme, has an intensive ROS scavenging activity because it is located in the cytosol and mitochondria. Therefore, we focused on the role of Prx5 in regulating mitochondrial ROS and adipogenesis. We demonstrated that Prx5 expression was upregulated during adipogenesis and Prx5 overexpression suppressed adipogenesis by regulating cytosolic and mitochondrial ROS generation. Silencing Prx5 promoted preadipocytes to differentiate into adipocytes accumulating lipids by activating adipogenic protein expression. Prx5-deletion mice fed on a high-fat diet (HFD) exhibited significant increase in body weight, enormous fat pads, and adipocyte hypertrophy in comparison to wild type mice. Prx5 deletion also remarkably induced adipogenesis-related gene expression in white adipose tissue. These phenotypic changes in Prx5-deletion mice were accompanied with lipid metabolic disorders, such as excessive lipid accumulation in the liver, severe hepatic steatosis, and high levels of triglyceride in the serum. These results demonstrated that Prx5 deletion increased the susceptibility to HFD-induced obesity and several of its associated metabolic disorders. In conclusion, we suggest that Prx5 inhibits adipogenesis by modulating ROS generation and adipogenic gene expression, implying that Prx5 may serve as a potential strategy to prevent and treat obesity.

Minoxidil Promotes Hair Growth through Stimulation of Growth Factor Release from Adipose-Derived Stem Cells

Minoxidil directly promotes hair growth via the stimulation of dermal papilla (DP) and epithelial cells. Alternatively, there is little evidence for indirect promotion of hair growth via stimulation of adipose-derived stem cells (ASCs). We investigated whether minoxidil stimulates ASCs and if increased growth factor secretion by ASCs facilitates minoxidil-induced hair growth. Telogen-to-anagen induction was examined in mice. Cultured DP cells and vibrissae hair follicle organ cultures were used to further examine the underlying mechanisms. Subcutaneous injection of minoxidil-treated ASCs accelerated telogen-to-anagen transition in mice, and increased hair weight at day 14 post-injection. Minoxidil did not alter ASC proliferation, but increased migration and tube formation. Minoxidil also increased the secretion of growth factors from ASCs, including chemokine (C-X-C motif) ligand 1 (CXCL1), platelet-derived endothelial cell growth factor (PD-ECGF), and platelet-derived growth factor-C (PDGF-C). Minoxidil increased extracellular signal–regulated kinases 1/2 (ERK1/2) phosphorylation, and concomitant upregulation of PD-ECGF and PDGF-C mRNA levels were attenuated by an ERK inhibitor. Subcutaneous injection of CXCL1, PD-ECGF, or PDGF-C enhanced anagen induction in mice, and both CXCL1 and PDGF-C increased hair length in ex vivo organ culture. Treatment with CXCL1, PD-ECGF, or PDGF-C also increased the proliferation index in DP cells. Finally, topical application of CXCL1, PD-ECGF, or PDGF-C with 2% minoxidil enhanced anagen induction when compared to minoxidil alone. Minoxidil stimulates ASC motility and increases paracrine growth factor signaling. Minoxidil-stimulated secretion of growth factors by ASCs may enhance hair growth by promoting DP proliferation. Therefore, minoxidil can be used as an ASC preconditioning agent for hair regeneration.

MIF Plays a Key Role in Regulating Tissue-Specific Chondro-Osteogenic Differentiation Fate of Human Cartilage Endplate Stem Cells under Hypoxia

Degenerative cartilage endplate (CEP) shows decreased chondrification and increased ossification. Cartilage endplate stem cells (CESCs), with the capacity for chondro-osteogenic differentiation, are responsible for CEP restoration. CEP is avascular and hypoxic, while the physiological hypoxia is disrupted in the degenerated CEP. Hypoxia promoted chondrogenesis but inhibited osteogenesis in CESCs. This tissue-specific differentiation fate of CESCs in response to hypoxia was physiologically significant with regard to CEP maintaining chondrification and refusing ossification. MIF, a downstream target of HIF1A, is involved in cartilage and bone metabolisms, although little is known about its regulatory role in differentiation. In CESCs, MIF was identified as a key point through which HIF1A regulated the chondro-osteogenic differentiation. Unexpectedly, unlike the traditionally recognized mode, increased nuclear-expressed MIF under hypoxia was identified to act as a transcriptional regulator by interacting with the promoter of SOX9 and RUNX2. This mode of HIF1A/MIF function may represent a target for CEP degeneration therapy.

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The hypoxic microenvironment is disrupted in degenerative CEP

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Hypoxia promotes chondrogenesis but inhibits osteogenesis in CESCs

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Hypoxia regulates chondro-osteogenesis through HIF1A/MIF pathway

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MIF acts as a transcriptional regulator under hypoxia

Untangling the relationship between diet and visceral fat mass through blood metabolomics and gut microbiome profiling

BACKGROUND/OBJECTIVES

Higher visceral fat mass (VFM) is associated with an increased risk for developing cardio-metabolic diseases. The mechanisms by which an unhealthy diet pattern may influence visceral fat (VF) development has yet to be examined through cutting-edge multi-omic methods. Therefore, our objective was to examine the dietary influences on VFM and identify gut microbiome and metabolite profiles that link food intakes to VFM.

SUBJECTS/METHODS

In 2218 twins with VFM, food intake and metabolomics data available we identified food intakes most strongly associated with VFM in 50% of the sample, then constructed and tested the 'VFM diet score' in the remainder of the sample. Using linear regression (adjusted for covariates, including body mass index and total fat mass), we investigated associations between the VFM diet score, the blood metabolomics profile and the fecal microbiome (n=889), and confirmed these associations with VFM. We replicated top findings in monozygotic (MZ) twins discordant (⩾1 s.d. apart) for VFM, matched for age, sex and the baseline genetic sequence.

RESULTS

Four metabolites were associated with the VFM diet score and VFM: hippurate, alpha-hydroxyisovalerate, bilirubin (Z,Z) and butyrylcarnitine. We replicated associations between VFM and the diet score (beta (s.e.): 0.281 (0.091); P=0.002), butyrylcarnitine (0.199 (0.087); P=0.023) and hippurate (-0.297 (0.095); P=0.002) in VFM-discordant MZ twins. We identified a single species, Eubacterium dolichum to be associated with the VFM diet score (0.042 (0.011), P=8.47 × 10-5), VFM (0.057 (0.019), P=2.73 × 10-3) and hippurate (-0.075 (0.032), P=0.021). Moreover, higher blood hippurate was associated with elevated adipose tissue expression neuroglobin, with roles in cellular oxygen homeostasis (0.016 (0.004), P=9.82x10-6).

CONCLUSIONS

We linked a dietary VFM score and VFM to E. dolichum and four metabolites in the blood. In particular, the relationship between hippurate, a metabolite derived from microbial metabolism of dietary polyphenols, and reduced VFM, the microbiome and increased adipose tissue expression of neuroglobin provides potential mechanistic insight into the influence of diet on VFM.

Effect of hypoxia on human adipose-derived mesenchymal stem cells and its potential clinical applications

Human adipose-derived mesenchymal stem cells (hASCs) are an ideal cell source for regenerative medicine due to their capabilities of multipotency and the readily accessibility of adipose tissue. They have been found residing in a relatively low oxygen tension microenvironment in the body, but the physiological condition has been overlooked in most studies. In light of the escalating need for culturing hASCs under their physiological condition, this review summarizes the most recent advances in the hypoxia effect on hASCs. We first highlight the advantages of using hASCs in regenerative medicine and discuss the influence of hypoxia on the phenotype and functionality of hASCs in terms of viability, stemness, proliferation, differentiation, soluble factor secretion, and biosafety. We provide a glimpse of the possible cellular mechanism that involved under hypoxia and discuss the potential clinical applications. We then highlight the existing challenges and discuss the future perspective on the use of hypoxic-treated hASCs.

A genome-wide analysis of the gene expression profiles and alternative splicing events during the hypoxia-regulated osteogenic differentiation of human cartilage endplate-derived stem cells

It has been hypothesized that intervertebral disc degeneration is initiated by degeneration of the cartilage endplate (CEP), which is characterized by cartilage ossification. CEP‑derived stem cells (CESCs), with the potential for chondro‑osteogenic differentiation, may be responsible for the balance between chondrification and ossification in the CEP. The CEP remains in an avascular and hypoxic microenvironment; the present study observed that hypoxia was able to markedly inhibit the osteogenic differentiation of CESCs. This tissue‑specific CESC differentiation in response to a hypoxic microenvironment was physiologically important for the prevention of ossification in the CEP. In order to study the hypoxia‑regulated mechanisms underlying osteogenic differentiation of CESCs, a Human Transcriptome Array 2.0 was used to detect differentially expressed genes (DEGs) and alternatively spliced genes (ASGs) during the osteogenic differentiation of CESCs under hypoxia, compared with those induced under normoxia. High‑throughput analysis of DEGs and ASGs demonstrated that genes in the complement pathway were enriched, which may be a potential mechanism underlying hypoxia inhibition of CESCs osteogenesis. The results of the present study may provide a basis for future mechanistic studies regarding gene expression levels and alternative splicing events during the hypoxia‑regulated inhibition of osteogenesis, which may be helpful in identifying targets for CEP degeneration therapy.

Hypoxia induces glucose uptake and metabolism of adipose‑derived stem cells

It has previously been demonstrated that hypoxia has diverse stimulatory effects on adipose‑derived stem cells (ASCs), however, metabolic responses under hypoxia remain to be elucidated. Thus, the present study aimed to investigate the glucose uptake and metabolism of ASCs under hypoxic conditions, and to identify the underlying molecular mechanisms. ASCs were cultured in 1% oxygen, and experiments were conducted in vitro. As determined by proteomic analysis and western blotting, GAPDH and enolase 1 (ENO1) expression were upregulated under hypoxia. In addition, lactate production was significantly increased, and mRNA levels of glycolytic enzymes, including GAPDH, ENO1, hexokinase 2 (HK2), and lactate dehydrogenase α (LDHα) were upregulated. Hypoxia‑inducible factor 1‑α (HIF‑1α) expression was increased as demonstrated by western blotting, and a pharmacological inhibitor of HIF‑1α significantly attenuated hypoxia‑induced lactate production and expression of glycolytic enzymes. It was also observed that hypoxia significantly increased glucose uptake in ASCs, and glucose transporter (GLUT)1 and GLUT3 expression were upregulated under hypoxia. Pharmacological inhibition of the HIF‑1α signaling pathways also attenuated hypoxia‑induced GLUT1 and GLUT3 expression. These results collectively indicate that hypoxia increases glucose uptake via GLUT1 and GLUT3 upregulation, and induces lactate production of ASCs via GAPDH, ENO1, HK2, and LDHα. Furthermore, HIF‑1α is involved in glucose uptake and metabolism of ASCs.

Hypoxia Suppresses Spontaneous Mineralization and Osteogenic Differentiation of Mesenchymal Stem Cells via IGFBP3 Up-Regulation

Hypoxia has diverse stimulatory effects on human adipose-derived stem cells (ASCs). In the present study, we investigated whether hypoxic culture conditions (2% O₂) suppress spontaneous mineralization and osteogenic differentiation of ASCs. We also investigated signaling pathways and molecular mechanisms involved in this process. We found that hypoxia suppressed spontaneous mineralization and osteogenic differentiation of ASCs, and up-regulated mRNA and protein expression of Insulin-like growth factor binding proteins (IGFBPs) in ASCs. Although treatment with recombinant IGFBPs did not affect osteogenic differentiation of ASCs, siRNA-mediated inhibition of IGFBP3 attenuated hypoxia-suppressed osteogenic differentiation of ASCs. In contrast, overexpression of IGFBP3 via lentiviral vectors inhibited ASC osteogenic differentiation. These results indicate that hypoxia suppresses spontaneous mineralization and osteogenic differentiation of ASCs via intracellular IGFBP3 up-regulation. We determined that reactive oxygen species (ROS) generation followed by activation of the MAPK and PI3K/Akt pathways play pivotal roles in IGFBP3 expression under hypoxia. For example, ROS scavengers and inhibitors for MAPK and PI3K/Akt pathways attenuated the hypoxia-induced IGFBP3 expression. Inhibition of Elk1 and NF-κB through siRNA transfection also led to down-regulation of IGFBP3 mRNA expression. We next addressed the proliferative potential of ASCs with overexpressed IGFBP3, but IGFBP3 overexpression reduced the proliferation of ASCs. In addition, hypoxia reduced the osteogenic differentiation of bone marrow-derived clonal mesenchymal stem cells. Collectively, our results indicate that hypoxia suppresses the osteogenic differentiation of mesenchymal stem cells via IGFBP3 up-regulation.

Global profiling of the gene expression and alternative splicing events during hypoxia-regulated chondrogenic differentiation in human cartilage endplate-derived stem cells

The intervertebral disc (IVD) degeneration is initiated by cartilage endplate (CEP) degeneration and is characterised by reduced chondrification. Cartilage endplate-derived stem cells (CESCs) with chondrogenic differentiation abilities are responsible for the restoration of cartilage. CEP remains in an avascular and hypoxic microenvironment. In this study, we observed that the physiological hypoxia greatly promotes the chondrogenic differentiation of CESCs. This tissue specificity of the differentiation fate of CESCs in response to the hypoxic microenvironment was physiologically significant for the CEP to maintain the chondrification status. To investigate the mechanisms underlying the hypoxia-regulated chondrogenic differentiation of CESCs, we adopted a high-throughput scanning technology to detect the global profiling of gene expression and alternative splicing (AS) event changes during chondrogenic differentiation under hypoxia in CESCs compared to those induced under normoxia. An Affymetrix Human Transcriptome Array 2.0 was used to identify the differentially expressed genes (DEGs) and alternatively spliced genes (ASGs). After RT-PCR validation, GO and KEGG pathway analyses of both the DEGs and ASGs were performed. The enrichment of the GO functional terms and signalling pathways provided referential direction of the mechanism to study the gene expression and AS in the hypoxia-regulated chondrogenesis promotion, which could be helpful in understanding this physiological phenomenon, and it could also be instrumental in finding targets for CEP degeneration therapy.

Contribution of extracellular ATP on the cell-surface F1F0-ATP synthase-mediated intracellular triacylglycerol accumulation

Cell-surface F1F0-ATP synthase was involved in the cell signaling mediating various biological functions. Recently, we found that cell-surface F1F0-ATP synthase plays a role on intracellular triacylglycerol accumulation in adipocytes, and yet, the underlying mechanisms remained largely unknown. In this study, we investigated the role of extracellular ATP on the intracellular triacylglycerol accumulation. We demonstrated that significant amounts of ATP were produced extracellularly by cultured 3T3-L1 adipocytes and that the antibodies against α and β subunits of F1F0-ATP synthase inhibited the extracellular ATP production. Piceatannol, a F1F0-ATP synthase inhibitor, and apyrase, an enzyme which degrades extracellular ATP, suppressed triacylglycerol accumulation. The selective P2Y1 receptor antagonist MRS2500 significantly inhibited triacylglycerol accumulation, whereas the selective P2X receptor antagonist NF279 has less effect. The present results indicate that cell-surface F1F0-ATP synthase on adipocytes is functional in extracellular ATP production and that the extracellular ATP produced contributes, at least in part, to the cell-surface F1F0-ATP synthase-mediated intracellular triacylglycerol accumulation in adipocytes through P2Y1 receptor.

Vasopressin-induced Ca(2+) signals in human adipose-derived stem cells

Intracellular Ca(2+) signals are essential for stem cell differentiation due to their ability to control signaling pathways involved in this process. Arginine vasopression (AVP) is a neurohypophyseal hormone that increases intracellular Ca(2+) concentration during adipogenesis via V1a receptors, Gq-proteins and the PLC-IP3 pathway in human adipose-derived stromal/stem cells (hASCs). These Ca(2+) signals originate through calcium release from pools within the endoplasmic reticulum and the extracellular space. AVP supplementation to the adipogenic media inhibits adipogenesis and key adipocyte marker genes. This review focuses on the intersection between AVP, Ca(2+) signals and ASC differentiation.

Redox modulation of adipocyte differentiation: hypothesis of "Redox Chain" and novel insights into intervention of adipogenesis and obesity

In view of the global prevalence of obesity and obesity-associated disorders, it is important to clearly understand how adipose tissue forms. Accumulating data from various laboratories implicate that redox status is closely associated with energy metabolism. Thus, biochemical regulation of the redox system may be an attractive alternative for the treatment of obesity-related disorders. In this work, we will review the current data detailing the role of the redox system in adipocyte differentiation, as well as identifying areas for further research. The redox system affects adipogenic differentiation in an extensive way. We propose that there is a complex and interactive "redox chain," consisting of a "ROS-generating enzyme chain," "combined antioxidant chain," and "transcription factor chain," which contributes to fine-tune the regulation of ROS level and subsequent biological consequences. The roles of the redox system in adipocyte differentiation are paradoxical. The redox system exerts a "tridimensional" mechanism in the regulation of adipocyte differentiation, including transcriptional, epigenetic, and posttranslational modulations. We suggest that redoxomic techniques should be extensively applied to understand the biological effects of redox alterations in a more integrated way. A stable and standardized "redox index" is urgently needed for the evaluation of the general redox status. Therefore, more effort should be made to establish and maintain a general redox balance rather than to conduct simple prooxidant or antioxidant interventions, which have comprehensive implications.

Effect of N-Acetylcysteine on Adipose-Derived Stem Cell and Autologous Fat Graft Survival in a Mouse Model

BACKGROUND

Autologous fat grafting is a popular reconstructive technique, but is limited by inconsistent graft retention. The authors examined whether a widely available, clinically safe antioxidant, N-acetylcysteine, could improve adipose-derived stem cell survival and graft take when added to tumescent solution during fat harvest.

METHODS

Inguinal fat pads were harvested from C57BL/6 mice using tumescent solution with or without N-acetylcysteine. Flow cytometric, proliferation, and differentiation assays were performed on isolated primary adipose-derived stem cells and 3T3-L1 preadipocytes treated with or without hydrogen peroxide and/or N-acetylcysteine. N-Acetylcysteine-treated or control grafts were injected under recipient mouse scalps and assessed by serial micro-computed tomographic volumetric analysis. Explanted grafts underwent immunohistochemical analysis.

RESULTS

In culture, N-acetylcysteine protected adipose-derived stem cells from oxidative stress and improved cell survival following hydrogen peroxide treatment. Combined exposure to both N-acetylcysteine and hydrogen peroxide led to a 200-fold increase in adipose-derived stem cell proliferation, significantly higher than with either agent alone. N-Acetylcysteine decreased differentiation of adipose-derived stem cells into mature adipocytes, as evidenced by decreased transcription of adipocyte differentiation markers and reduced Oil Red-O staining. In vivo, N-acetylcysteine treatment resulted in improved graft retention at 3 months compared with control (46 versus 17 percent; p = 0.027). N-Acetylcysteine-treated grafts demonstrated less fibrosis and inflammation, and a 33 percent increase in adipocyte density compared with controls (p < 0.001) that was not associated with increased vascularity.

CONCLUSION

These findings provide proof of principle for the addition of N-acetylcysteine to tumescent harvest solution in the clinical setting to optimize fat graft yields.

Hypoxia Enhances Proliferation of Human Adipose-Derived Stem Cells via HIF-1ɑ Activation

Background

Adipose tissue-derived stem cells (ASCs) have been recently isolated from human subcutaneous adipose tissue. ASCs may be useful in regenerative medicine as an alternative to bone marrow-derived stem cells. Changes in the oxygen concentration influence physiological activities, such as stem cell proliferation. However, the effects of the oxygen concentration on ASCs remain unclear. In the present study, the effects of hypoxia on ASC proliferation were examined.

Methods

Normal human adipose tissue was collected from the lower abdomen, and ASCs were prepared with collagenase treatment. The ASCs were cultured in hypoxic (1%) or normoxic (20%) conditions. Cell proliferation was investigated in the presence or absence of inhibitors of various potentially important kinases. Hypoxia inducible factor (HIF)-1α expression and MAP kinase phosphorylation in the hypoxic culture were determined with western blotting. In addition, the mRNA expression of vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF)-2 in hypoxic or normoxic conditions were determined with real-time RT-PCR. The effects of these growth factors on ASC proliferation were investigated. Chromatin immunoprecipitation (ChIP) of the HIF–1α-binding hypoxia responsive element in FGF–2 was performed. HIF–1α was knocked down by siRNA, and FGF–2 expression was investigated.

Results

ASC proliferation was significantly enhanced in the hypoxic culture and was inhibited by ERK and Akt inhibitors. Hypoxia for 5–15 minutes stimulated the phosphorylation of ERK1/2 among MAP kinases and induced HIF–1α expression. The levels of VEGF and FGF–2 mRNA and protein in the ASCs were significantly enhanced in hypoxia, and FGF–2 increased ASC proliferation. The ChIP assay revealed an 8-fold increase in the binding of HIF–1α to FGF–2 in hypoxia. HIF–1α knockdown by siRNA partially inhibited the FGF–2 expression of ASCs induced by hypoxia.

Conclusion

ASC proliferation was enhanced by hypoxia. HIF–1α activation, FGF–2 production, and the ERK1/2 and Akt pathway were involved in this regulatory mechanism.

Xenobiotics that affect oxidative phosphorylation alter differentiation of human adipose-derived stem cells at concentrations that are found in human blood

Adipogenesis is accompanied by differentiation of adipose tissue-derived stem cells to adipocytes. As part of this differentiation, biogenesis of the oxidative phosphorylation system occurs. Many chemical compounds used in medicine, agriculture or other human activities affect oxidative phosphorylation function. Therefore, these xenobiotics could alter adipogenesis. We have analyzed the effects on adipocyte differentiation of some xenobiotics that act on the oxidative phosphorylation system. The tested concentrations have been previously reported in human blood. Our results show that pharmaceutical drugs that decrease mitochondrial DNA replication, such as nucleoside reverse transcriptase inhibitors, or inhibitors of mitochondrial protein synthesis, such as ribosomal antibiotics, diminish adipocyte differentiation and leptin secretion. By contrast, the environmental chemical pollutant tributyltin chloride, which inhibits the ATP synthase of the oxidative phosphorylation system, can promote adipocyte differentiation and leptin secretion, leading to obesity and metabolic syndrome as postulated by the obesogen hypothesis.

Summary: Some medical drugs and environmental chemical pollutants acting on the oxidative phosphorylation system can alter adipocyte differentiation and adipogenesis and, thus, have important consequences for human health.

Functional regulation of adipose-derived stem cells by PDGF-D

Platelet-derived growth factor-D (PDGF-D) was recently identified, and acts as potent mitogen for mesenchymal cells. PDGF-D also induces cellular transformation and promotes tumor growth. However, the functional role of PDGF-D in adipose-derived stem cells (ASCs) has not been identified. Therefore, we primarily investigated the autocrine and paracrine roles of PDGF-D in this study. Furthermore, we identified the signaling pathways and the molecular mechanisms involved in PDGF-D-induced stimulation of ASCs. It is of interest that PDGF-B is not expressed, but PDGF-D and PDGF receptor-β are expressed in ASCs. PDGF-D showed the strongest mitogenic effect on ASCs, and PDGF-D regulates the proliferation and migration of ASCs through the PI3K/Akt pathways. PDGF-D also increases the proliferation and migration of ASCs through generation of mitochondrial reactive oxygen species (mtROS) and mitochondrial fission. mtROS generation and fission were mediated by p66Shc phosphorylation, and BCL2-related protein A1 and Serpine peptidase inhibitor, clade E, member 1 mediated the proliferation and migration of ASCs. In addition, PDGF-D upregulated the mRNA expression of diverse growth factors such as vascular endothelial growth factor A, fibroblast growth factor 1 (FGF1), FGF5, leukemia inhibitory factor, inhibin, beta A, interleukin 11, and heparin-binding EGF-like growth factor. Therefore, the preconditioning of PDGF-D enhanced the hair-regenerative potential of ASCs. PDGF-D-induced growth factor expression was attenuated by a pharmacological inhibitor of mitogen-activated protein kinase pathway. In summary, PDGF-D is highly expressed by ASCs, where it acts as a potent mitogenic factor. PDGF-D also upregulates growth factor expression in ASCs. Therefore, PDGF-D can be considered a novel ASC stimulator, and used as a preconditioning agent before ASC transplantation.

Controlling Redox Status for Stem Cell Survival, Expansion, and Differentiation

Reactive oxygen species (ROS) have long been considered as pathological agents inducing apoptosis under adverse culture conditions. However, recent findings have challenged this dogma and physiological levels of ROS are now considered as secondary messengers, mediating numerous cellular functions in stem cells. Stem cells represent important tools for tissue engineering, drug screening, and disease modeling. However, the safe use of stem cells for clinical applications still requires culture improvements to obtain functional cells. With the examples of mesenchymal stem cells (MSCs) and pluripotent stem cells (PSCs), this review investigates the roles of ROS in the maintenance of self-renewal, proliferation, and differentiation of stem cells. In addition, this work highlights that the tight control of stem cell microenvironment, including cell organization, and metabolic and mechanical environments, may be an effective approach to regulate endogenous ROS generation. Taken together, this paper indicates the need for better quantification of ROS towards the accurate control of stem cell fate.

Fluoxetine Decreases the Proliferation and Adipogenic Differentiation of Human Adipose-Derived Stem Cells

Fluoxetine was originally developed as an antidepressant, but it has also been used to treat obesity. Although the anti-appetite effect of fluoxetine is well-documented, its potential effects on human adipose-derived stem cells (ASCs) or mature adipocytes have not been investigated. Therefore, we investigated the mechanisms underlying the inhibitory effects of fluoxetine on the proliferation of ASCs. We also investigated its inhibitory effect on adipogenic differentiation. Fluoxetine significantly decreased ASC proliferation, and signal transduction PCR array analysis showed that it increased expression of autophagy-related genes. In addition, fluoxetine up-regulated SQSTM1 and LC3B protein expression as detected by western blotting and immunofluorescence. The autophagy inhibitor, 3-methyladenine (3-MA), significantly attenuated fluoxetine-mediated effects on ASC proliferation and SQSTM1/LC3B expression. In addition, 3-MA decreased the mRNA expression of two autophagy-related genes, beclin-1 and Atg7, in ASCs. Fluoxetine also significantly inhibited lipid accumulation and down-regulated the levels of PPAR-γ and C/EBP-α in ASCs. Collectively, these results indicate that fluoxetine decreases ASC proliferation and adipogenic differentiation. This is the first in vitro evidence that fluoxetine can reduce fat accumulation by inhibiting ASC proliferation and differentiation.

Connecting Mitochondria, Metabolism, and Stem Cell Fate

As sites of cellular respiration and energy production, mitochondria play a central role in cell metabolism. Cell differentiation is associated with an increase in mitochondrial content and activity and with a metabolic shift toward increased oxidative phosphorylation activity. The opposite occurs during reprogramming of somatic cells into induced pluripotent stem cells. Studies have provided evidence of mitochondrial and metabolic changes during the differentiation of both embryonic and somatic (or adult) stem cells (SSCs), such as hematopoietic stem cells, mesenchymal stem cells, and tissue-specific progenitor cells. We thus propose to consider those mitochondrial and metabolic changes as hallmarks of differentiation processes. We review how mitochondrial biogenesis, dynamics, and function are directly involved in embryonic and SSC differentiation and how metabolic and sensing pathways connect mitochondria and metabolism with cell fate and pluripotency. Understanding the basis of the crosstalk between mitochondria and cell fate is of critical importance, given the promising application of stem cells in regenerative medicine. In addition to the development of novel strategies to improve the in vitro lineage-directed differentiation of stem cells, understanding the molecular basis of this interplay could lead to the identification of novel targets to improve the treatment of degenerative diseases.

Megestrol Acetate Increases the Proliferation, Migration, and Adipogenic Differentiation of Adipose-Derived Stem Cells via Glucocorticoid Receptor

: Because adipose-derived stem cells (ASCs) are usually expanded to acquire large numbers of cells for therapeutic applications, it is important to increase the production yield and regenerative potential during expansion. Therefore, a tremendous need exists for alternative ASC stimuli during cultivation to increase the proliferation and adipogenic differentiation of ASCs. The present study primarily investigated the involvement of megestrol acetate (MA), a progesterone analog, in the stimulation of ASCs, and identifies the target receptors underlying stimulation. Mitogenic and adipogenic effects of MA were investigated in vitro, and pharmacological inhibition and small interfering (si) RNA techniques were used to identify the molecular mechanisms involved in the MA-induced stimulation of ASCs. MA significantly increased the proliferation, migration, and adipogenic differentiation of ASCs in a dose-dependent manner. Glucocorticoid receptor (GR) is highly expressed compared with other nuclear receptors in ASCs, and this receptor is phosphorylated after MA treatment. MA also upregulated genes downstream of GR in ASCs, including ANGPTL4, DUSP1, ERRF11, FKBP5, GLUL, and TSC22D3. RU486, a pharmacological inhibitor of GR, and transfection of siGR significantly attenuated MA-induced proliferation, migration, and adipogenic differentiation of ASCs. Although the adipogenic differentiation potential of MA was inferior to that of dexamethasone, MA had mitogenic effects in ASCs. Collectively, these results indicate that MA increases the proliferation, migration, and adipogenic differentiation of ASCs via GR phosphorylation.

SIGNIFICANCE

Magestrol acetate (MA) increases the proliferation, migration, and adipogenic differentiation of adipose-derived stem cells (ASCs) via glucocorticoid receptor phosphorylation. Therefore, MA can be applied to increase the production yield during expansion and can be used to facilitate adipogenic differentiation of ASCs.

Mitochondrial reactive oxygen species regulate adipocyte differentiation of mesenchymal stem cells in hematopoietic stress induced by arabinosylcytosine

Objective

The increase in adipocytes induced by chemotherapeutic drugs may play a negative role in hematopoietic recovery. However, the mechanism underlying adipocyte differentiation of mesenchymal stem cells (MSCs) in hematopoietic stress is still unknown. Hence, the involvement of reactive oxygen species (ROS) in adipocyte differentiation under hematopoietic stress was investigated in vitro and in vivo.

Methods

The roles of cellular ROS in adipogenesis were investigated in vivo through an adipocyte hyperplasia marrow model under hematopoietic stress induced by arabinosylcytosine (Ara-C) and in vitro via adipocyte differentiation of human MSCs. ROS levels were detected using the CM-H₂DCFDA probe and Mito-SOX dye. Adipogenesis was evaluated by histopathology and oil red O staining, whereas detection of mRNA levels of antioxidant enzymes and adipogenesis markers was performed using quantitative real-time polymerase chain reaction analysis.

Results

ROS were found to play an important role in regulating adipocyte differentiation of MSCs by activating peroxisome proliferator-activated receptor gamma (PPARγ,) while the antioxidant N-acetyl-L-cysteine acts through ROS to inhibit adipocyte differentiation. The elevated ROS levels induced by Ara-C were caused by both over-generation of mitochondrial ROS and reduction of antioxidant enzymes (Cu/Zn Superoxide dismutase and catalase). Our findings suggest that a mitochondrial-targeted antioxidant could diminish adipocyte differentiation.

Oxidative stress, redox regulation and diseases of cellular differentiation

BACKGROUND

Within cells, there is a narrow concentration threshold that governs whether reactive oxygen species (ROS) induce toxicity or act as second messengers.

SCOPE OF REVIEW

We discuss current understanding of how ROS arise, facilitate cell signaling, cause toxicities and disease related to abnormal cell differentiation and those (primarily) sulfur based pathways that provide nucleophilicity to offset these effects.

PRIMARY CONCLUSIONS

Cellular redox homeostasis mediates a plethora of cellular pathways that determine life and death events. For example, ROS intersect with GSH based enzyme pathways to influence cell differentiation, a process integral to normal hematopoiesis, but also affecting a number of diverse cell differentiation related human diseases. Recent attempts to manage such pathologies have focused on intervening in some of these pathways, with the consequence that differentiation therapy targeting redox homeostasis has provided a platform for drug discovery and development.

GENERAL SIGNIFICANCE

The balance between electrophilic oxidative stress and protective biomolecular nucleophiles predisposes the evolution of modern life forms. Imbalances of the two can produce aberrant redox homeostasis with resultant pathologies. Understanding the pathways involved provides opportunities to consider interventional strategies. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.