Development of an innovative method to study in vitro the adipose function and dysfunction : precision-cut adipose tissue slices on pig

Besides its role in energy storage, adipose tissue is a major endocrine organ able to interact and communicate with our entire body. Its function and metabolism can be disrupted by various factors including environmental pollutants or diseases such as cancer. Gaining a better understanding of the mechanisms underlying such phenomenon is an essential issue, as a dysregulation of the tissue can impact the whole-body metabolism. In this regard, in vitro models offer a complementary approach to in vivo models as they can minimize the number of animals used while allowing to test various conditions in a controlled environment. Most commonly used in vitro models are rodents but differences at adipose level exist between rodents and humans. This master thesis aimed at developing an innovative model of precision-cut adipose tissue slices on pig, a relevant species for human health studies. Firstly, parameters were calibrated in order to adjust the model. We mainly focused on lipolysis to test the in vitro functionality of the tissue. Then, the model was used to study the disrupting effect of cancer cells on adipose tissue function. The porcine precision-cut adipose tissue slices were exposed to two lipolytic compounds i) isoproterenol and ii) epinephrine at different concentration ranges. Our results showed that the tissue was sensitive to 1µM of isoproterenol and that glycerol release was significantly increased in comparison with the non-induced lipolysis condition, particularly when the exposure to the lipolytic treatment occurred after a resting period of the slices in a normal culture medium. Higher concentrations of epinephrine were needed (100µM) to achieve a significant response to the lipolytic stimulus, which might result from the fact that this compound is an agonist of both of α- (inhibiting lipolysis) and β – (stimulating lipolysis) adrenergic receptors, whereas isoproterenol only binds to β-adrenergic receptors. The most appropriate type of adipose tissue seemed to be subcutaneous adipose tissue as only low response to the lipolytic stimulus was obtained with visceral adipose tissue. Visceral adipose tissue, which is much softer, also appeared more damaged than subcutaneous adipose tissue. Long term cultures pointed out that the tissue stayed functional and viable for cultures going up to five days. Latter point can be of interest for the study of the impact of chronic exposure to disruptors on adipose tissue. The disrupting effect of cancer cells on adipose precision-cut slices lipolysis was investigated by exposing precision-cut slices to tumour-conditioned medium (FaDu cells). A low release of glycerol was observed in both conditions (induced and non-induced lipolysis), as compared to the results we obtained in the other experiments. This could be due to the presence of glutamine in this medium, which is known to alter lipolysis. Nevertheless, those experiments revealed that, when the slices are incubated in presence of a tumour-conditioned medium, lipolysis is triggered even in absence of albumin, suggesting an effect of factors secreted by the tumours, on adipose metabolism. Further investigations on this topic should be conducted in order to clarify the results.