ABSTRACT
AIMS/HYPOTHESIS: Adipose tissue-derived tumour necrosis factor-alpha (TNF-alpha) has been implicated in the insulin resistance observed in animal models of obesity. Moreover, TNF-alpha has inhibitory effects on adipocyte differentiation. Glucocorticoids play important roles in the regulation of insulin sensitivity and adipose tissue distribution. We therefore studied the effect of dexamethasone on TNF-alpha expression and adipocyte differentiation in human PAZ6 cells. METHODS: The expression of TNF-alpha and adipocyte differentiation markers was assessed by reverse-transcription polymerase chain reaction in PAZ6 cells. RESULTS: In cells cultured for 15 days in the presence of dexamethasone, adipocyte differentiation marker expression was higher and TNF-alpha expression was lower than in cells cultured in the absence of dexamethasone. The presence of dexamethasone was necessary during the whole period of differentiation because removal of dexamethasone during the second week resulted in poorly differentiated adipocytes that express higher levels of TNF-alpha. Dexamethasone also reduced TNF-alpha expression during early stages of differentiation. The use of a TNF-alpha-neutralising antibody showed, however, that endogenously-produced TNF-alpha did not play an important part in the control of PAZ6 cell differentiation. During early stages of adipocyte differentiation, dexamethasone induced the expression of the transcription factors PPAR gamma (peroxisome proliferator activated receptor gamma) and C/EBP alpha (CCAAT/enhancer binding protein alpha) while inhibiting the expression of the inhibitor of DNA binding Id2. CONCLUSION/INTERPRETATION: The effect of dexamethasone on human adipocyte differentiation is not mediated by reduction of TNF-alpha expression but more likely by regulation of the expression of nuclear factors such as PPAR gamma, CEBP alpha and Id2.
Subject(s)
Adipocytes/drug effects , Dexamethasone/pharmacology , Gene Expression Regulation/physiology , Neoplasm Proteins , Tumor Necrosis Factor-alpha/genetics , Adipocytes/cytology , Adipocytes/physiology , Biomarkers , CCAAT-Enhancer-Binding Protein-alpha/genetics , Cell Differentiation/drug effects , Cell Differentiation/physiology , Gene Expression Regulation/drug effects , Humans , Inhibitor of Differentiation Proteins , Receptors, Cytoplasmic and Nuclear/genetics , Reverse Transcriptase Polymerase Chain Reaction , Transcription Factors/genetics , Tumor Necrosis Factor-alpha/analysisABSTRACT
AIMS/HYPOTHESIS: Thiazolidinediones, a new class of insulin sensitizers, up-regulate the expression of uncoupling protein 2 in rodent adipocytes. It is not known, however, whether thiazolidinediones influence uncoupling protein 2 expression in human adipocytes. We therefore investigated the effect of these drugs on uncoupling protein 2 expression in the recently immortalized human PAZ6 adipocyte cell line. METHODS: Immortalized human PAZ6 preadipocytes were differentiated into adipocytes in the presence or absence of thiazolidinediones. The effect of the drugs on uncoupling protein 2 expression and adipocyte differentiation was measured by reverse transcription-polymerase chain reaction of mRNA of uncoupling protein 2 and of five adipocyte differentiation markers. RESULTS: When cells were differentiated 15 days in the presence of thiazolidinediones, uncoupling protein 2 expression was 2.1-fold higher than in the absence of the drugs. The expression of five adipocyte differentiation markers was, however, also increased by thiazolidinediones. Short-term incubation for 4 and 24 h with thiazolidinediones increased uncoupling protein 2 expression 1.35-fold and 2.3-fold, respectively. The expression of adipocyte markers studied in parallel was also augmented. CONCLUSION/INTERPRETATION: Thiazolidinediones rapidly increase the expression of uncoupling protein 2 in human PAZ6 adipocytes but the increase of uncoupling protein 2 expression is always associated with an augmentation of the expression of all adipocyte markers studied in parallel. This indicates that the effect of thiazolidinediones on uncoupling protein 2 mRNA reflects a general increase in adipocyte differentiation rather than a specific augmentation of uncoupling protein 2 gene expression.
