Enhancement of adipogenesis induction by conditioned media obtained from cancer cells

White adipose tissue is a multifunctional endocrine organ that synthesizes and secretes cytokine-like proteins termed adipokines. In the present study, the effects of cancer-derived medium on adipogenesis were examined. We prepared conditioned media from cancer cell lines, and cultured preadipocytes in the conditioned media. After 10 days of culture, intracellular lipid droplet accumulation was measured. We observed that the conditioned media significantly induced adipogenesis or enhanced the adipogenesis induced by adipogenesis inducers. Although we could not define the factors, these undefined factors derived from cancer cells may induce adipogenesis, and the resulting adipogenesis may affect cancer development.     

褪黑素对大鼠骨髓间充质干细胞成脂分化的影响

目的探讨褪黑素(MT)对骨髓间充质干细胞(BMSCs)成脂分化的影响,以及MT的作用机制。方法取大鼠骨髓分离培养BMSCs,经传代脂向分化,分组进行干预。对照组为单纯脂向分化(模型)组;实验A组用MT进行干预;实验B组用MT和其受体拮抗剂2-苯基-N-乙酰色胺(LZD)共同干预。检测脂肪细胞的比例来比较各组的脂化程度,并应用反转录聚合酶链反应(RT-PCR)技术检测各组细胞中成脂转录因子过氧化物酶体增殖体激活受体γ(PPARγ)mRNA的表达。结果实验A组脂化程度明显低于对照组和实验B组(P<0.05)。结论MT能抑制BMSCs向成脂方向分化,并通过其受体机制起作用。这可能与骨质疏松的病因学有关。     

Increased caveolin-1, a cause for the declined adipogenic potential of senescent human mesenchymal stem cells

Mesenchymal stem cell (MSC) has drawn much attention in the aspect of tissue renewal and wound healing because of its multipotency. We initially observed that bone marrow-derived human MSCs (hMSCs) divided poorly and took flat and enlarged morphology after expanded in culture over a certain number of cell passage, which resembled characteristic features of senescent cells, well-studied in human diploid fibroblasts (HDFs). More interestingly, adipogenic differentiation potential of hMSCs sharply declined as they approached the end of their proliferative life span. In this study, altered hMSCs were verified to be senescent by their senescence-associated beta-galactosidase (SA-beta-gal) activity and the increased expression of cell cycle regulating proteins (p16(INK4a), p21(Waf1) and p53). Similar as in HDFs, basal phosphorylation level of ERK was also significantly increased in senescent hMSCs, implying altered signal paths commonly shared by the senescent cells. Insulin, a major component of adipogenesis inducing medium, did not phosphorylate ERK 1/2 more in senescent hMSCs after its addition whereas it did in young cells. In senescent hMSCs, we also found a significant increase of caveolin-1 expression, previously reported as a cause for the attenuated response to growth factors in senescent HDFs. When we overexpressed caveolin-1 in young hMSC, not only insulin signaling but also adipogenic differentiation was significantly suppressed with down-regulated PPARgamma2. These data indicate that loss of adipogenic differentiation potential in senescent hMSC is mediated by the over-expression of caveolin-1.     

Microarray analysis of early adipogenesis in C3H10T1/2 cells: cooperative inhibitory effects of growth factors and 2,3,7,8-tetrachlorodibenzo-p-dioxin

C3H10T1/2 mouse embryo fibroblasts differentiate into adipocytes when stimulated by a standard hormonal mixture (IDMB). 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), via the aryl hydrocarbon receptor (AhR), inhibits induction of the key adipogenic gene peroxisome proliferator-activated receptor gamma (PPARgamma) and subsequent adipogenesis. This TCDD-mediated inhibition requires activation of the extracellular signal-regulated kinase (ERK) pathway, which can be accomplished by serum, epidermal growth factor (EGF), or fibroblast growth factor (FGF). In the absence of serum or growth factors, IDMB induced adipogenesis without mitosis. Microarray analysis identified 200 genes that exhibited expression changes of at least twofold after 24 h of IDMB treatment. This time precedes most PPARgamma stimulation but follows the period of TCDD/ERK cooperation and periods of increased cell contraction and DNA synthesis. Functionally related gene clusters include genes associated with cell structure, triglyceride and cholesterol metabolism, oxidative regulation, and secreted proteins. In the absence of growth factors TCDD inhibited 30% of these IDMB responses without inhibiting the process of differentiation. A combination of EGF and TCDD that blocks differentiation cooperatively blocked a further 44 IDMB-responsive genes, most of which have functional links to differentiation, including PPARgamma. Cell cycle regulators that are stimulated by EGF were substantially inhibited by IDMB but these responses were unaffected by TCDD. By contrast, TCDD and EGF cooperatively reversed IDMB-induced changes in cell adhesion complexes immediately prior to increases in PPARgamma1 expression. Changes in adhesion-linked signaling may play a key role in TCDD affects on differentiation.     

骨髓基质细胞定向成脂分化的实验研究

目的为了研究髓内脂肪细胞的作用,并为相关实验提供脂肪细胞来源,并观察地塞米松诱导骨髓基质细胞向脂肪细胞分化的作用。方法采用原代骨髓基质细胞体外培养技术,取大鼠双侧股骨骨髓细胞,用Ficoll-Paque淋巴细胞分离液离心分离,获取骨髓基质细胞。以地塞米松作为脂肪细胞分化诱导剂处理骨髓基质细胞,油红O染色,光镜下脂肪细胞计数。结果以递增浓度(0,1×10-8,1×10-7,1×10-6,1×10-5moL/L)地塞米松处理骨髓基质细胞,并培养21天,1×10-5moL/L组中诱导分化生成的脂肪细胞达到90%以上,对照组中脂肪细胞几乎为0。各组脂肪细胞比例随地塞米松浓度增大而增多,具有一定的浓度依赖性。结论在高浓度的地塞米松诱导下,骨髓基质细胞可分化为脂肪细胞,这可能是激素性骨质疏松的发病原因之一。     

Baicalein inhibits lipid accumulation by regulating early adipogenesis and m-TOR signaling

Baicalein is a type of flavonoid that originates from Scutellaria baicalensis. In this study, we examined how baicalein inhibits lipid accumulation during adipogenesis in 3T3-L1 cells. Our data show that baicalein inhibited lipid accumulation during adipogenesis in a dose-dependent manner. Baicalein inhibition was limited to the early adipogenic stage. Cell cycle analysis showed that baicalein induced cell cycle arrest in the G0/G1 phase through cyclin downregulation. In addition, baicalein suppressed the mRNA expression of early adipogenic factors leading to downregulation of late adipogenic factors at mRNA and protein levels. Inhibition of adipogenic factors by baicalein was correlated with downregulation of lipid synthetic enzymes. Additionally, baicalein negatively regulated the m-TOR signaling pathway involved in lipid accumulation during adipogenesis, thus inhibiting phosphorylation of m-TOR and p70S6 K. In a zebrafish study, baicalein significantly reduced lipid accumulation in Nile Red staining. Consistent with a report using cell lines, mRNA expression of adipogenic factors was decreased in a dose-dependent manner by baicalein. This result reflects a reduction in total triglyceride levels based on a triglyceride assay. Our data suggest that baicalein inhibits lipid accumulation by controlling the cell cycle and m-TOR signaling in 3T3-L1 cells, and its anti-adipogenic effect was found in a zebrafish model.     

Nonylphenol-induced hyperadrenalism can be reversed/alleviated by inhibiting of 11-β hydroxysteroid dehydrogenase type 1

We previously observed that nonylphenol (NP) exposure during development resulted in increases in body weight and hyperadrenalism in adult male offspring. The mechanism of hyperadrenalism includes the primary activation of the adrenal gland and the conversion of inactive glucocorticoids to active glucocorticoids by 11β-HSD1. The inhibition of 11β-HSD1 is investigated as a new therapeutic approach. This study examined the effect of PF915275 (a selective 11β-HSD1 inhibitor) on hyperadrenalism and adipogenesis in male rats exposed to NP during development. The results showed that treatment with the 11β-HSD1 inhibitor PF915275 reversed/alleviated NP-induced hyperadrenalism via the following mechanisms: (1) decreasing serum corticosterone, 11β-hydroxylase, and aldosterone synthase levels; (2) significantly increasing PPARα protein and mRNA expression. In adipose tissue, NP significantly increased PPARγ mRNA expression, whereas PF915275 significantly decreased the level of mRNA expression; and (3) the expression of key regulators/enzymes in the adipogenesis metabolic pathway was also modulated.     

Leucine signaling in the pathogenesis of type 2 diabetes and obesity

Epidemiological evidence points to increased dairy and meat consumption,staples of the Western diet,as major risk factors for the development of type 2 diabetes(T2D).This paper presents a new concept and comprehensive review of leucine-mediated cell signaling explaining the pathogenesis of T2D and obesity by leucine-induced over-stimulation of mammalian target of rapamycin complex 1(mTORC1).mTORC1,a pivotal nutrient-sensitive kinase,promotes growth and cell proliferation in response to glucose,energy,growth factors and amino acids.Dairy proteins and meat stimulate insulin/insulin-like growth factor 1 signaling and provide high amounts of leucine,a primary and independent stimulator for mTORC1 activation.The downstream target of mTORC1,the kinase S6K1,induces insulin resistance by phosphorylation of insulin receptor substrate-1,thereby increasing the metabolic burden of β-cells.Moreover,leucine-mediated mTORC1-S6K1-signaling plays an important role in adipogenesis,thus increasing the risk of obesity-mediated insulin resistance. High consumption of leucine-rich proteins explains exaggerated mTORC1-dependent insulin secretion, increased β-cell growth and β-cell proliferation promoting an early onset of replicative β-cell senescence with subsequent β-cell apoptosis.Disturbances of β-cell mass regulation with increased β-cell proliferation and apoptosis as well as insulin resistance are hallmarks of T2D,which are all associated with hyperactivation of mTORC1.In contrast,the anti-diabetic drug metformin antagonizes leucine-mediated mTORC1 signaling.Plant-derived polyphenols and flavonoids are identified as natural inhibitors of mTORC1 and exert anti-diabetic and anti-obesity effects.Furthermore,bariatric surgery in obesity reduces increased plasma levels of leucine and other branched-chain amino acids.Attenuation of leucine-mediated mTORC1 signaling by defining appropriate upper limits of the daily intake of leucine-rich animal and dairy proteins may offer a great chance for the prevention of T2D and obesity,as well as other epidemic diseases of civilization with increased mTORC1 signaling,especially cancer and neurodegenerative diseases,which are frequently associated with T2D.     

Spatial control of adult stem cell fate using nanotopographic cues

Adult stem cells hold great promise as a source of diverse terminally differentiated cell types for tissue engineering applications. However, due to the complexity of chemical and mechanical cues specifying differentiation outcomes, development of arbitrarily complex geometric and structural arrangements of cells, adopting multiple fates from the same initial stem cell population, has been difficult. Here, we show that the topography of the cell adhesion substratum can be an instructive cue to adult stem cells and topographical variations can strongly bias the differentiation outcome of the cells towards adipocyte or osteocyte fates. Switches in cell fate decision from adipogenic to osteogenic lineages were accompanied by changes in cytoskeletal stiffness, spanning a considerable range in the cell softness/rigidity spectrum. Our findings suggest that human mesenchymal stem cells (hMSC) can respond to the varying density of nanotopographical cues by regulating their internal cytoskeletal network and use these mechanical changes to guide them toward making cell fate decisions. We used this finding to design a complex two-dimensional pattern of co-localized cells preferentially adopting two alternative fates, thus paving the road for designing and building more complex tissue constructs with diverse biomedical applications.