Role of 11-beta-hydroxysteroid dehydrogenase type 1 in differentiation of 3T3-L1 cells and in rats with diet-induced obesity

How Do Glucocorticoids Regulate Lipid Metabolism?

Glucocorticoids (GCs) and their cognate, intracellular receptor, the glucocorticoid receptor (GR) have been characterized as critical checkpoints in the hormonal control of energy homeostasis in mammals. Whereas physiological levels of GCs are required for proper metabolic control, aberrant GC action has been linked to a variety of severe metabolic diseases, including type 2 diabetes and obesity. As a member of the nuclear receptor superfamily of transcription factors, the GR translocates into the cell nucleus upon GC binding where it serves as a transcriptional regulator of distinct GC-responsive target genes that are in many cases associated with lipid regulatory pathways and thereby intricately control both physiological and pathophysiological systemic lipid homeostasis. Thus, this chapter focuses on the current knowledge of GC/GR function in lipid handling and its implications for systemic metabolic dysfunction.

The alliance of mesenchymal stem cells, bone, and diabetes

Bone fragility has emerged as a new complication of diabetes. Several mechanisms in diabetes may influence bone homeostasis by impairing the action between osteoblasts, osteoclasts, and osteocytes and/or changing the structural properties of the bone tissue. Some of these mechanisms can potentially alter the fate of mesenchymal stem cells, the initial precursor of the osteoblast. In this review, we describe the main factors that impair bone health in diabetic patients and their clinical impact.

Development of a high-throughput cell-based assay for 11beta-hydroxysteroid dehydrogenase type 1 using BacMam technology

Cortisol is an important glucocorticoid in humans that regulates many physiological processes. Human 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) converts cortisone to cortisol in vivo and has emerged as an appealing therapeutic target for treating metabolic diseases. Here, we report a sensitive and robust high-throughput (HT) cell-based assay for screening 11beta-HSD1 inhibitors. This assay utilizes a HEK293 cell line transduced by a BacMam virus expressing human 11beta-HSD1. The enzyme activity in the cells was measured by quantifying cortisol levels released into the cell culture supernatant via a competitive homogenous time-resolved fluorescence (HTRF) method. We show that 11beta-HSD1 activity in supernatant of BacMam-transduced HEK293 cells increases with 11beta-HSD1 BacMam virus load in a dose-dependent manner, and is comparable to the enzyme activity detected in differentiated mouse adipocytes. In addition, we show that co-expression of hexose-6-phosphate dehydrogenase (H6PDH) is not required for the enzyme to function effectively as an oxo-reductase. This assay has been developed in low-volume 384-well format and it is sensitive, robust, and amenable to HT screening.

Suppression of 11β-hydroxysteroid dehydrogenase type 1 with RNA interference substantially attenuates 3T3-L1 adipogenesis

11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1), which regulates the local level of glucocorticoids, has been suggested to be involved in the development of obesity. A definitive functional role for 11β-HSD1 in adipogenesis, however, remains to be established. We developed 3T3-L1 cell lines stably transfected with a small hairpin RNA (shRNA) targeting 11β-HSD1. A shRNA containing two nucleotide substitutions was used as a control. Silencing of 11β-HSD1 substantially attenuated the accumulation of lipid droplets and the expression of adipogenesis marker genes, which was induced by a mixture containing either corticosterone or dexamethasone. Silencing of 11β-HSD1 increased the concentration of 11-dehydrocorticosterone in the culture supernatant but did not significantly affect the levels of corticosterone or dexamethasone. Translocation of glucocorticoid receptors to the nucleus in response to glucocorticoids was significantly attenuated by silencing 11β-HSD1. The number of cells entering the S phase of the cell cycle following the induction of adipogenesis was significantly reduced by silencing 11β-HSD1. 11β-HSD1 shRNA delivered by lentiviral vectors after the induction of differentiation, however, did not affect the progression of adipogenesis. These results indicate that 11β-HSD1 plays a significant functional role in the initiation of 3T3-L1 adipogenesis and provide new mechanistic insights into the role of 11β-HSD1 in the development of obesity and related diseases.

Correlation of obesity and osteoporosis: effect of fat mass on the determination of osteoporosis

It was previously believed that obesity and osteoporosis were two unrelated diseases, but recent studies have shown that both diseases share several common genetic and environmental factors. Body fat mass, a component of body weight, is one of the most important indices of obesity, and a substantial body of evidence indicates that fat mass may have beneficial effects on bone. Contrasting studies, however, suggest that excessive fat mass may not protect against osteoporosis or osteoporotic fracture. Differences in experimental design, sample structure, and even the selection of covariates may account for some of these inconsistent or contradictory results. Despite the lack of a clear consensus regarding the impact of effects of fat on bone, a number of mechanistic explanations have been proposed to support the observed epidemiologic and physiologic associations between fat and bone. The common precursor stem cell that leads to the differentiation of both adipocytes and osteoblasts, as well the secretion of adipocyte-derived hormones that affect bone development, may partially explain these associations. Based on our current state of knowledge, it is unclear whether fat has beneficial effects on bone. We anticipate that this will be an active and fruitful focus of research in the coming years.

Glucocorticoids, metabolism and metabolic diseases

Since the discovery of the beneficial effects of adrenocortical extracts for treating adrenal insufficiency more than 80 years ago, glucocorticoids (GC) and their cognate, intracellular receptor, the glucocorticoid receptor (GR) have been characterized as critical components of the delicate hormonal control system that determines energy homeostasis in mammals. Whereas physiological levels of GCs are required for proper metabolic control, excessive GC action has been tied to a variety of pandemic metabolic diseases, such as type II diabetes and obesity. Highlighted by its importance for human health, the investigation of molecular mechanisms of GC/GR action has become a major focus in biomedical research. In particular, the understanding of tissue-specific functions of the GC-GR pathway has been proven to be of substantial value for the identification of novel therapeutic options in the treatment of severe metabolic disorders. Therefore, this review focuses on the role of the GC-GR axis for metabolic homeostasis and dysregulation, emphasizing tissue-specific functions of GCs in the control of energy metabolism.