Obesity is a major risk factor for numerous metabolic diseases including insulin resistance (IR) and Type 2 Diabetes (T2D). During obesity, the excessive expansion of white adipose tissue (WAT) is accompanied by the accumulation of immune cells, mostly macrophages. Metabolic stress in obese adipose tissue (AT) modify the function and fate of AT macrophages (ATMs), resulting in a low-grade inflammation within the AT and in the circulation. Among others, my work has contributed to demonstrate that inflammation could impair AT functions and participate to the development of IR. However, there are major gaps in our understanding of the molecular mechanisms underlying ATMs reprogramming in response to metabolic stress during obesity. Therefore, identification of new actors and pathways modulating these responses would be of great interest for the treatment of metabolic diseases associated to obesity. My preliminary findings indicate that the transcription factor p53, which is an important cellular stress integrator, is upregulated in ATMs in obese mice. Interestingly, the upregulation of p53 is an early event, since the upregulation is detected after only three days upon high fat diet (HFD). Importantly, we found that silencing p53 specifically in ATMs improved the glucose tolerance of obese mice. Furthermore, exploration of published microarray data performed on human showed an upregulation of p53 pathway in ATMs of obese and diabetic patients, compared to obese non-diabetic patients. Based on these unpublished data, I hypothesize that p53 upregulation in ATMs during obesity could participate in the early step of the development of obesity-induced metabolic diseases such as IR. Therefore, the global objective of the MacP53 project is to explore the functional role of p53 in macrophages and to decipher the mode of action of p53 by identifying key actors of the transcriptional program induced by p53 in ATMs, and to investigate their role in obesity-associated metabolic complications. Thus, I will 1) investigate the role of p53 in ATMs in AT dysfunctions and IR in obesity. I will take advantage of a mouse model allowing a macrophage-specific invalidation of p53, to determine whether the invalidation of p53 in macrophages could prevent the development of diet-induced obesity and IR. I will also take advantage of a technology allowing to silence p53 specifically in ATMs in obese adult mice to determine whether silencing p53 in ATMs could improve the IR of obese mice; 2) identify and investigate the role of key actors of p53 transcriptomic program. I will use a sophisticated and unique methods that I have acquired during my training, and which are not accessible in many laboratories such as ChIP-seq and GRO-seq to identify the direct targets of p53 in ATMs. I will focus on micro-RNAs (miRNAs) and on a new class of non-coding RNAs (ncRNAs), the enhancer-derived RNAs (eRNAs). Indeed, miRNAs and eRNAs have been shown as crucial component of p53 mode of action in response to cellular stress by targeting multiple pathways. These ncRNAs could be very pertinent targets since they can modulate the expression of several genes at once and in a cell-type specific manner. This project will improve our understanding of the connection between p53 activation, AT dysfunctions and IR, and may identify new targets against IR.