| Summary: |
As overweight and obesity have reached pandemic dimensions, the demand for treatments which effectively promote weight loss is higher than ever. To date, therapeutic strategies have focused on energy intake (either intestinal absorption of nutrients or central regulation of appetite) but have continuously failed to efficiently reduce body fat. However, the other side of the energy balance equation, energy expenditure, remains relatively unexplored. Recently, the alternative concept of promoting energy expenditure via activation and recruitment of thermogenic brown and beige adipocytes has been revitalized as several studies have demonstrated the presence of brown adipose tissue (BAT) in healthy adults (Lichtenbelt 2009). The development of pharmacological compounds able to activate pre-existing thermogenic adipocytes or their de novo recruitment, is therefore heavily pursued due to interesting therapeutic perspectives.
In this context, the role of the anorexigenic neuropeptides melanocortins on adipose tissue has emerged. Administration of melanocortins induces lipolysis and impairs fatty acid re-esterification in white adipocytes (Rodrigues 2013) and potentiates thermogenesis in BAT (Voss-Andreae 2007). However, data on the melanocortins ability to induce white adipose tissue (WAT) browning is scarce. Our preliminary results indicate that they are able to reprogram isolated murine energy-storing fat cells to a beige/brown pattern of gene expression, which is followed by an increase on mitochondrial biogenesis, also a typical feature of the brown adipocytes (Figure 1). Departing from these assumptions, this project addresses the hypothesis that the peripheral melanocortin system increases energy expenditure and weight loss also by inducing structural, transcriptional and functional changes on white adipocytes promoting their differentiation into beige/brown adipocytes. This will be accomplished using as experimental models the C57BL/J6 diet-induced obese (DIO) m  |
Summary
As overweight and obesity have reached pandemic dimensions, the demand for treatments which effectively promote weight loss is higher than ever. To date, therapeutic strategies have focused on energy intake (either intestinal absorption of nutrients or central regulation of appetite) but have continuously failed to efficiently reduce body fat. However, the other side of the energy balance equation, energy expenditure, remains relatively unexplored. Recently, the alternative concept of promoting energy expenditure via activation and recruitment of thermogenic brown and beige adipocytes has been revitalized as several studies have demonstrated the presence of brown adipose tissue (BAT) in healthy adults (Lichtenbelt 2009). The development of pharmacological compounds able to activate pre-existing thermogenic adipocytes or their de novo recruitment, is therefore heavily pursued due to interesting therapeutic perspectives.
In this context, the role of the anorexigenic neuropeptides melanocortins on adipose tissue has emerged. Administration of melanocortins induces lipolysis and impairs fatty acid re-esterification in white adipocytes (Rodrigues 2013) and potentiates thermogenesis in BAT (Voss-Andreae 2007). However, data on the melanocortins ability to induce white adipose tissue (WAT) browning is scarce. Our preliminary results indicate that they are able to reprogram isolated murine energy-storing fat cells to a beige/brown pattern of gene expression, which is followed by an increase on mitochondrial biogenesis, also a typical feature of the brown adipocytes (Figure 1). Departing from these assumptions, this project addresses the hypothesis that the peripheral melanocortin system increases energy expenditure and weight loss also by inducing structural, transcriptional and functional changes on white adipocytes promoting their differentiation into beige/brown adipocytes. This will be accomplished using as experimental models the C57BL/J6 diet-induced obese (DIO) mice, human primary cell and explant cultures established from visceral and subcutaneous adipocytes collected from normoponderal and obese subjects and the human Simpson-Golabi-Behmel syndrome (SGBS) cell line. The availability of samples from control and obese subjects and mice will allow the correlation between the melanocortins "browning" capacity and the weight status and adiposity. Melanocortin-mediated adipocytes morphological and metabolic changes will be assessed by analysis of mitochondrial biogenesis, structure (monitored by electron microscopy) and function (measured by indirect calorimetry). Real-time PCR studies will allow the quantification of the expression of beige hallmark genes, and these results will be confirmed at protein level by western-blotting. The importance of specific microRNAs in the melanocortin-mediated browning effect will also be assessed. The melanocortins protection against obesity-associated oxidative damage of biomolecules, inflammation and cellular endoplasmic reticulum (ER) stress will also be evaluated at the adipose samples.
The mechanism of action of melanocortins at the WAT and BAT is still a matter of debate. Relevant data suggests that the brain controls many of the functions of WAT and BAT via MC4R present at the sympathetic nervous system (SNS) innervation of these tissues (Nogueiras 2007, Bartness 2010 and Voss-Andreae 2007). Although less explored, melanocortins action directly on the adipose tissue is also considered. Probably these two pathways co-exist and co-regulate the physiology of the adipocyte. To clarify this, the effect of peripherally administered melanocortins will be evaluated in animals subjected to surgical or chemical denervation of WAT and BAT pads and in the MC4R knockout mice, animals with no MC4R function on SNS innervation of adipose tissue.
This project comprises a team of researchers (Adriana Rodrigues, Henrique Almeida and Alexandra Gouveia) with a large experience in molecular biology techniques, adipocyte cell culture and oxidative and ER stress, approaches that are routinely performed in our laboratory. The human adipose tissue arises from an already established important collaboration with Mariana Monteiro. The human SGBS cell line was kindly offered by Martin Wabitsch, a consultant that will certainly add to the success of this project. Experiments that involve animal manipulation, specifically the establishment of the DIO model and adipose tissue denervation, will benefit from the large experience of Delminda Neves and Célia Cruz, respectively.
With this project we expect to establish a research line that will contribute to a better understanding of the capability of melanocortins to promote differentiation of human white adipocytes into beige/brown adipocytes. Since BAT is specialized for energy expenditure, in contrast to WAT, the aims of this project are highly pertinent to the physiopathology of obesity and constitute a promise to therapeutic strategies. |