Insulin resistance, diabetes and many kinds of cancers are common in overweight and obese individuals. The tumor suppressor p53 is important in securing genetic stability, but its role in the regulation of metabolic processes and cell differentiation remains unclear. We have investigated the role of p53 in adipocyte differentiation. Using 3T3-L1 cells, a mouse embryonic fibroblast preadipocyte model and DIO rat model, p53 expression and function during adipocyte differentiation were investigated. p53 expression increased on the second and fourth day of adipocyte differentiation and decreased thereafter. Its overexpression in 3T3-L1 preadipocytes markedly reduced adipogenesis and marker gene expression. p53 activity was weakened in DIO rat abdominal adipose tissue because of an decreased expression of its activated phosphorylated form. In contrast, p53 knockout enhanced adipogenesis and the expression of marker genes, but significantly reduced insulin-stimulated Akt phosphorylation. These results indicate that p53 partly suppresses preadipocyte differentiation and adipogenesis by regulating adipocyte gene expression and Akt signaling.
The aim of this study is to determine the effects of E2 on metabolic syndrome and the molecular mechanisms involving S100A16. Ovariectomized (OVX) rat models and mouse embryonic fibroblasts cell models were used. E2 loss in OVX rats induced body weight gain and central abdominal fat accumulation, which were ameliorated by E2 treatment under chow and high-fat diet (HFD) conditions. E2 decreased the expression of the adipocyte marker genes PPAR?, aP2, C/EBP?, and S100A16. E2 inhibited adipogenesis. Overexpression of S100A16 reversed the E2-induced adipogenesis effect. A luciferase assay showed that E2 inhibited the expression of S100A16. E2 treatment decreased body weight gain and central abdominal fat accumulation under both chow and HFD conditions. Also, E2 suppressed adipogenesis by inhibiting S100A16 expression.
Bone marrow-derived mesenchymal stem cells (BM-MSCs) have the capacity to differentiate into osteoblasts and adipocytes. Bone marrow adipogenesis exerts an inhibitory effect on osteogenesis, which leads to osteoporosis. S100A16, a novel member of the S100 family, is ubiquitously expressed, and markedly enhances adipogenesis. The aim of this study was to demonstrate, in the mouse BM-MSC model, whether S100A16 significantly stimulates adipogenic, rather than osteogenic differentiation. The overexpression of S100A16 led to a significant increase in Oil Red O staining (a marker of adipocyte differentiation) but a decrease in Alizarin Red S staining (a marker of osteoblast differentiation). In contrast, reducing the expression of S100A16 resulted in minimal Oil Red O staining but increased Alizarin Red S staining. During differentiation into osteoblasts, RUNX2 expression increased fourfold in the S100A16(KO+/-) BM-MSCs, but only increased by approximately 1.5-fold in the S100A16(TG+/+) BM-MSCs. And BMP2 occurred in the same changes. Upon induction of BM-MSC differentiation into adipocytes, peroxisome proliferator-activated receptor-? (PPAR?) and CCAAT/enhancer binding protein-? expression were significantly higher in the cells overexpressing S100A16 protein but lower in the cells with reduced expression of S100A16 protein, compared with the control cells, which were BM-MSCs derived from C57/BL6. S100A16 increased PPAR? promoter luciferase activity and decreased RUNX2 promoter luciferase activity. ERK1/2 phosphorylation was stimulated during osteogenesis, whereas p-JNK phosphorylation was increased by stimulation of adipogenesis. Our results suggest that S100A16 inhibits osteogenesis but stimulates adipogenesis by increasing the transcription of PPAR? and decreasing the transcription of RUNX2. The ERK1/2 pathway is involved in the regulation of osteogenesis whereas the JNK pathway is involved in adipogenesis.
Dietary calcium influences the regulation of energy metabolism, and weight gain is attenuated by a high-calcium diet. S100A16 is a novel calcium-binding signaling protein of the EF-hand superfamily that promotes adipogenesis. This study aimed to investigate the effect of S100A16 on weight gain attenuation with a calcium-rich diet. An obese rat model was produced after feeding with a high-fat diet. Animals were randomly divided into 4 groups according to the diet provided over 8 weeks: normal diet group; high-fat, normal-calcium diet group; high-fat, high-calcium diet (HH) group; and high-fat, low-calcium diet group. Serum biochemistry was analyzed, and body weight and visceral fat pads were measured. Expression of S100A16 was assayed by Western blotting. Adipogenesis was detected by oil red O staining. Increases in body weight and visceral fat weight were attenuated in the HH group. High-calcium diets decreased the concentrations of serum total cholesterol and triglyceride. Expression of S100A16 decreased in the HH group. Using the 3T3-L1 preadipocyte model, it was observed that elevation of intracellular Ca(2+) via calcium ionophores led to the exclusion of S100A16 from the nucleus. Overexpression of S100A16 in 3T3-L1 preadipocytes enhanced adipogenesis, although a significant reduction in Akt phosphorylation was also detected. High-calcium diets were associated with a significant reduction in body weight gain. High-calcium diets may lead to nuclear exclusion of S100A16, which results in the inhibition of adipogenesis and enhanced insulin sensitivity.
Autotaxin (ATX) possesses lysophospholipase D (lyso PLD) activity, which converts lysophosphatidylcholine (LPC) into lysophosphatidic acid (LPA). The ATX-LPA signaling axis has been implicated in angiogenesis, chronic inflammation and tumor progression. Osteopontin (OPN) is an important chemokine involved in the survival, proliferation, migration, invasion and metastasis of gastric cancer cells. The focus of the present study was to investigate the relationship between the ATX-LPA axis and OPN.
Osteopontin, SDF-1?, and MMP-2 are important secreted molecules involved in the pathophysiology of human hepatocellular carcinoma (HCC). This study investigates the effect of the SDF-1?/CXCR4 axis on expression and activity of MMP-2 induced by osteopontin.
Osteopontin (OPN) and autotaxin (ATX) are important chemokines involved in the survival, proliferation, migration, invasion, and metastasis of many cancer cells. The focus of the study was to investigate the relationship between OPN and ATX-lysophosphatidic acid (LPA) axis. The expression of OPN and its cellular cascades were determined by western blot and real-time quantitative transcription polymerase chain reaction (real-time PCR) analyses. Cell migration activity was determined by a Transwell-migration assay. In comparison with nontreated cells, we found that the ATX-LPA axis upregulated OPN expression by 2.91-fold in protein levels and 2.52-fold in mRNA levels. The ATX-LPA axis activates Akt and ATX/LPC-induced OPN expression in SMMC7721 cells was largely reduced by the inhibitors of phosphatidylinositol 3-kinase (PI3K)/Akt or LPA receptor. This study provides the first evidence that the induction of the OPN expression by ATX-LPA axis was mediated by the activation of Akt through LPA receptors and OPN was required for migration of SMMC7721 cells induced by ATX-LPA axis.
S100A16 is a member of S100 protein super family that carries calcium-binding EF-hand motifs. Its expression is ubiquitous and elevated in various types of tumors. The functions of S100 proteins are still being defined, although many members of S100 protein family are traditionally considered as markers of tumor tissues. Using 3T3-L1 preadipocyte model, we investigated the expression and function of S100A16 during differentiation into adipocytes as well as the potential roles of S100A16 in the regulation of insulin sensitivity. We found that the expression of S100A16 was increased during differentiation and that elevation of intracellular Ca(2+) via calcium ionophores led to its nucleus exclusion. Overexpression of S100A16 in 3T3-L1 preadipocytes increased their proliferation and markedly enhanced adipogenesis but resulted in significant reduction of insulin-stimulated glucose uptake and phosphorylation of AKT. In contrast, suppression of S100A16 expression with two different types of RNA interference significantly inhibited adipogenesis and preadipocyte proliferation. Immunoprecipitation analysis revealed that S100A16 could physically interact with tumor suppressor protein p53, also a known inhibitor of adipogenesis. Overexpression or RNA interference-initiated reduction of S100A16 led to the inhibition or activation of the expression of p53-responsive genes, respectively. Interestingly, Western blot assays showed that S100A16 protein levels were markedly higher in the adipose tissues of diet-induced obese mice and the ob/ob mice than that in control lean mice. Thus, we reveal for the first time that S100A16 protein is a novel adipogenesis-promoting factor and that increased expression of S100A16 in 3T3-L1 adipocytes can have a negative impact on insulin sensitivity.
Forkhead Box O1 (FoxO1) is a key transcription regulator of insulin/IGF-I signaling pathway, and its activity can be increased by dexamethasone (DEX) in several cell types. However, the role of FoxO1 in DEX-induced pancreatic beta-cell dysfunction has not been fully understood. Therefore, in this study, we investigated whether FoxO1 could mediate DEX-induced beta-cell dysfunction and the possible underlying mechanisms in pancreatic beta-cell line RINm5F cells and primary rat islet. We found that DEX markedly increased FoxO1 mRNA and protein expression and decreased FoxO1 phosphorylation through the Akt pathway, which resulted in an increase in active FoxO1 in RINm5F cells and isolated rat islets. Activated FoxO1 subsequently inhibited pancreatic duodenal homeobox-1 expression and induced nuclear exclusion of pancreatic duodenal homeobox-1. Knockdown of FoxO1 by RNA interference restored the expression of pancreatic duodenal homeobox-1 and prevented DEX-induced dysfunction of glucose-stimulated insulin secretion in rat islets. Together, the results of present study demonstrate that FoxO1 is integrally involved in DEX-induced inhibition of pancreatic duodenal homeobox-1 and glucose-stimulated insulin secretion dysfunction in pancreatic islet beta-cells. Inhibition of FoxO1 can effectively protect beta-cells against DEX-induced dysfunction.
Recently, more and more attention has been drawn on the long-term effects of insulin glargine. Here we strived to estimate the association of cancer occurrence with the use of insulin glargine.
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