## 4 Discussion  
TGF\(\beta\) signaling has been extensively described, but there is no clear explanation of the causes that trigger massive cytokine production in cancer and several inflammatory diseases. Adipose tissue is considered a site of TGF\(\beta\) production and visceral fat is an important risk factor for the development of several cancers [12; 13; 14; 15]. Obesity in humans is associated with increased expression and release of TGF\(\beta\), although its low level of secretion by human adipose tissue has so far prevented the measurement of the active form of the cytokine and the investigation of factors influencing TGF\(\beta\) conversion of the latent form to the active one in most human studies [10]. Visceral fat accumulation can be originated by adipose tissue dysfunction, associated with changes in the cellular composition, increased lipid storage and secretion of proinflammatory, atherogenic and diabetogenic factors [63]. In fact, obese patients display hypertrophic, hypoxic and inflamed adipose tissue [53]. Interestingly, the improvement of the mitochondrial function in adipocytes can prevent adipose tissue inflammation, fibrosis and insulin resistance [1]. This suggests that adipose tissue malfunction and metabolic disorders are linked to mitochondrial impairment, defective oxidative phosphorylation (OXPHOS) and altered adipose-derived secreted factors [1]. Indeed, several studies on obese mice models reported the reduction of mitochondrial mass, high reactive oxygen species (ROS) production and low cellular ATP levels of adipose tissue [64; 65; 66]. However, it remains unclear whether the altered mitochondrial activity is a direct consequence or the cause of maladaptation in adipose tissue. A positive correlation between obesity and PDAC risk has been definitely established [15]. Preclinical studies employing PDAC mouse models have convincingly demonstrated that obesity accelerates pancreatic cancer development [15]. Many in vivo studies investigating the link between dysfunctional adipose tissue and pancreatic cancer have demonstrated that a high-fat diet, which promotes adipocyte metabolic perturbation, favors inflammation and pancreatic cancer [67; 68; 69]; however, the direct correlation between adipocyte metabolic stress and pancreatic cancer progression has not been fully investigated yet. Based on this evidence, in this proof-of-concept study we searched novel metabolic triggers of TGF\(\beta\) production in adipocytes and we investigated the link between dysmetabolism, inflammation and cancer. For this purpose, we proposed a simplified in vitro model to verify whether the deranged energy metabolism in adipocytes can trigger the secretion of the proinflammatoryTGF\(\beta\) and then we tested the effects of this production on a model of pancreatic cancer. Although human preadipocytes and adipose stem cells are excellent models for studying adipogenesis and obesity-related metabolic alterations as well as donor differences, in this study the aim of demonstrating the induction of TGF\(\beta\) secretion by metabolic stress could be achieved using the simplest model of 3T3-L1 adipocytes, which are widely used because of the highly standardized protocols of differentiation and treatments. Future studies will develop a more complex human model to confirm this initial observation and to investigate the relevance of the fat tissue microenvironment. In this study, we identified two different causes of metabolic failure that can induce TGF\(\beta\) production in our adipose cell model, namely hypoxia and a mix of concentrated fatty acids. We investigated the response to hypoxia because this known stimulus of cellular stress is associated with the hypertrophic and dysmetabolic phenotype of adipocytes. Moreover, in vitro studies have shown that experimentally induced hypoxia in adipocytes stimulates the production of inflammatory mediators and that the accumulation of hypoxia-inducible factor 1\(\alpha\) (HIF-1\(\alpha\)) leads to activation of transcription of pro-fibrotic genes [6; 35].