Clinical cases of glucocorticoid excess are characterised by increased fat mass and obesity through the accumulation of white adipocytes. The effect of glucocorticoids on brown adipose growth and function is unknown, and may contribute to the negative energy balance observed clinically. This study aims to evaluate the effect of glucocorticoids on brown adipocyte proliferation, differentiation and metabolic function. Human brown adipocytes sourced from supraclavicular fat biopsies were grown in culture and differentiated to mature adipocytes. Human white adipocytes sourced from subcutaneous abdominal fat biopsies were cultured as controls. Dexamethasone effects on brown adipocyte growth, differentiation (Ucp1, Cidea, Pgc1? expression) and function (oxygen consumption rate, OCR) were quantified. Dexamethasone (1 ?M) significantly stimulated the proliferation of brown and reduced that of white preadipocytes. During differentiation, dexamethasone (at 0.1, 1 and 10 ?M) stimulated the expression of Ucp1, Cidea and Pgc1? in a concentration-dependent manner and enhanced by 4-6 fold the OCR of brown adipocytes. Isoprenaline (100 nM) significantly enhanced (p<0.05) Ucp1 expression and OCR of brown adipocytes. These effects were significantly reduced (p<0.05) by dexamethasone. Thus, we show that dexamethasone stimulates the proliferation, differentiation and function of human brown adipocytes but inhibits adrenergic stimulation of brown adipocyte function. We conclude that glucocorticoids exert complex effects on brown adipocyte development and function. These findings provide strong evidence for an effect of glucocorticoids on human BAT biology and for the involvement of the BAT system in the metabolic manifestation of Cushing's syndrome.
The AGEs and the receptor for AGEs (RAGE) are known contributors to diabetic complications. RAGE also has a physiological role in innate and adaptive immunity and is expressed on immune cells. The aim of this study was to determine whether deletion of RAGE from bone-marrow-derived cells influences the pathogenesis of experimental diabetic nephropathy.
Cardiovascular disease (CVD) is a leading cause of mortality in the Western World. The development and onset of disease can be attributed to many risk factors including genetic susceptibility, diabetes, obesity and atherosclerosis. Numerous studies highlight the production of advanced glycation endproducts (AGEs) and interaction with their receptor (RAGE) as playing a key pathogenic role. The AGEs-RAGE axis is thought to contribute to a proinflammatory environment inducing cellular dysfunction which cascades towards pathology. Mitochondrial dysfunction concurrently plays a role in these proinflammatory responses presenting excess reactive oxygen species (ROS) production under pathological conditions. This ROS release can exacerbate the production of AGEs fuelling the fire somewhat. However, the AGEs-RAGE axis may influence mitochondrial function independently of inflammation. Therefore instigation of the AGEs-RAGE axis may facilitate spiralling towards pathology on many fronts including CVD development.
Diabetic retinopathy is a major diabetic complication with a highly complex etiology. Although there are many pathways involved, it has become established that chronic exposure of the retina to hyperglycemia gives rise to accumulation of advanced glycation end products (AGEs) that play an important role in retinopathy. In addition, the receptor for AGEs (RAGE) is ubiquitously expressed in various retinal cells and is upregulated in the retinas of diabetic patients, resulting in activation of pro-oxidant and proinflammatory signaling pathways. This AGE-RAGE axis appears to play a central role in the sustained inflammation, neurodegeneration, and retinal microvascular dysfunction occurring during diabetic retinopathy. The nature of AGE formation and RAGE signaling bring forward possibilities for therapeutic intervention. The multiple components of the AGE-RAGE axis, including signal transduction, formation of ligands, and the end-point effectors, may be promising targets for strategies to treat diabetic retinopathy.
The receptor for advanced glycation end products (RAGE) is a pattern-recognition receptor that binds to diverse ligands and initiates a downstream proinflammatory signaling cascade. RAGE activation has been linked to diabetic complications, Alzheimer disease, infections, and cancers. RAGE is known to mediate cell signaling and downstream proinflammatory gene transcription activation, although the precise mechanism surrounding receptor-ligand interactions is still being elucidated. Recent fluorescence resonance energy transfer evidence indicates that RAGE may form oligomers on the cell surface and that this could be related to signal transduction. To investigate whether RAGE forms oligomers, protein-protein interaction assays were carried out. Here, we demonstrate the interaction between RAGE molecules via their N-terminal V domain, which is an important region involved in ligand recognition. By protein cross-linking using water-soluble and membrane-impermeable cross-linker bis(sulfosuccinimidyl) suberate and nondenaturing gels, we show that RAGE forms homodimers at the plasma membrane, a process potentiated by S100B and advanced glycation end products. Soluble RAGE, the RAGE inhibitor, is also capable of binding to RAGE, similar to V peptide, as shown by surface plasmon resonance. Incubation of cells with soluble RAGE or RAGE V domain peptide inhibits RAGE dimerization, subsequent phosphorylation of intracellular MAPK proteins, and activation of NF-kappaB pathways. Thus, the data indicate that dimerization of RAGE represents an important component of RAGE-mediated cell signaling.
Related JoVE Video
Journal of Visualized Experiments
What is Visualize?
JoVE Visualize is a tool created to match the last 5 years of PubMed publications to methods in JoVE's video library.
How does it work?
We use abstracts found on PubMed and match them to JoVE videos to create a list of 10 to 30 related methods videos.
Video X seems to be unrelated to Abstract Y...
In developing our video relationships, we compare around 5 million PubMed articles to our library of over 4,500 methods videos. In some cases the language used in the PubMed abstracts makes matching that content to a JoVE video difficult. In other cases, there happens not to be any content in our video library that is relevant to the topic of a given abstract. In these cases, our algorithms are trying their best to display videos with relevant content, which can sometimes result in matched videos with only a slight relation.