Location: Boston, MassachusettsTitle: Glucocorticoids affect 24 h clock genes expression in human adipose tissue explant cultures) Author
Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2012
Publication Date: 12/10/2012
Citation: Gomez-Abellan, P., Diez-Noguera, A., Madrid, J.A., Lujan, J.A., Ordovas, J.M., Garaulet, M. 2012. Glucocorticoids affect 24 h clock genes expression in human adipose tissue explant cultures. PLoS One. DOI: 10.1371/journal.pone.0050435. Interpretive Summary: Obesity has been associated with the major causes of death and disability, including heart attack, stroke, high blood pressure, cancer, diabetes, osteoarthritis, fatty liver, and depression. The evaluation of obesity has changed over the years but body mass index (BMI), remains as the standard way to diagnose overweight and obesity. However, BMI reflects total body fat without regard to how the fat is distributed. Nowadays, we know that the risk associated to obesity depends on the different types of fat (i.e., abdominal fat, subcutaneous fat, brown fat) rather than the mere amount. Current research shows that abdominal fat is the one that may be metabolically more damaging. Moreover, adipose tissue, like all other organs follow a circadian rhythm that is important for its metabolism and that of the entire organism. Therefore, in this research we examined whether the CLOCK gene, the first gene identified as part of the human biological clock, exhibits a circadian expression in human visceral (V) and subcutaneous (S) adipose tissue (AT) in cellular studies as compared with BMAL1 and PER2 (two additional clock genes). VAT and SAT biopsies were obtained from morbidly obese women in order to investigate the rhythmic expression pattern of clock genes (CLOCK, PER2 and BMAL1). Moreover, we examined the potential modulating role of glucocorticoids on their expression. Glucocorticoids are a class of steroid hormones, which are present in almost every vertebrate animal cell. Cortisol shows a strong circadian rhythm and it is the most important human glucocorticoid. It is essential for life as it regulates or supports a variety of important cardiovascular, metabolic, immunologic, and homeostatic functions. Our results show that CLOCK, BMAL1 and PER2 expression exhibited circadian patterns in both VAT and SAT. However, the rhythm of expression was different in VAT and in SAT and was further affected by the presence of the glucocorticoid analogue dexamethasone (DEX). Therefore, we report for the first time that human adipose tissue shows 24 h expression patterns in CLOCK and BMAL1 (positive clock elements) and PER2 (negative element) and that the expression is different in different adipose tissue depots. Moreover, these patterns were altered by dexamethasone exposure, suggesting a role for cortisol in the modulation of the rhythms observed on the metabolism of adipose tissue and potentially on their potential consequences on health status.
Technical Abstract: To examine firstly whether CLOCK exhibits a circadian expression in human visceral (V) and subcutaneous (S) adipose tissue (AT) in vitro as compared with BMAL1 and PER2, and secondly to investigate the possible effect of the glucocorticoid analogue dexamethasone (DEX) on positive and negative clock genes expression. VAT and SAT biopsies were obtained from morbid obese women (body mass index greater than or equal to 40 kg/m(2)) (n = 6). In order to investigate rhythmic expression pattern of clock genes and the effect of DEX on CLOCK, PER2 and BMAL1 expression, control AT (without DEX) and AT explants treated with DEX (2 hours) were cultured during 24 h and gene expression was analyzed at the following times: 10:00 h, 14:00 h, 18:00 h, 22:00 h, 02:00 h and 06:00 h, using qRT-PCR. CLOCK, BMAL1 and PER2 expression exhibited circadian patterns in both VAT and SAT explants that were adjusted to a typical 24 h sinusoidal curve. PER2 expression (negative element) was in antiphase with respect to CLOCK and in phase with BMAL1 expression (both positive elements) in the SAT (situation not present in VAT). A marked effect of DEX exposure on both positive and negative clock genes expression patterns was observed. Indeed, DEX treatment modified the rhythmicity pattern towards altered patterns with a period lower than 24 hours in all genes and in both tissues. 24 h patterns in CLOCK and BMAL1 (positive clock elements) and PER2 (negative element) mRNA levels were observed in human adipose explants. These patterns were altered by dexamethasone exposure.