Search for a new therapeutic target for modulating macrophage activation during obesity: the role of Ahr signaling

• Grant number: 22/16000-9
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• Effective date (Start): July 01, 2023
• Effective date (End): June 30, 2024
• Field of knowledge: Biological Sciences - Immunology - Cellular Immunology
• Principal Investigator: Pedro Manoel Mendes de Moraes Vieira
• Grantee: Bianca Gazieri Castelucci
• Supervisor: Lev Becker
• Host Institution: Instituto de Biologia (IB). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil
• Research place: University of Chicago, United States
• Associated to the scholarship: 20/02573-1 - Effects of Aryl Hydrocarbon Receptor (AHR) modulation on the activation and metabolism of macrophages in lean and obese mice, BP.PD

Abstract

Macrophages are present in all tissues of vertebrates and play a key role in host defense and tissue homeostasis. During obesity, there is an accumulation of macrophages in adipose tissue (AT). Obesity milieu results in the production of pro-inflammatory cytokines (TNF-± and IL-1²) by AT macrophages (ATMs), leading to AT inflammation and subsequent insulin resistance. Although many proposed treatments to reduce insulin resistance focus on altering chronic AT inflammation, the therapeutic disruption of specific inflammatory signaling pathways could increase the risk for additional infections. Thus, it is necessary to understand the distinction between macrophage signaling pathways required for pathogen clearance and those related to obesity low-inflammation induction to unveil potential therapeutic targets to combat obesity progression without losing macrophage function. The aryl hydrocarbon receptor (Ahr) is one of the central regulators of immune cell fitness, directly impacting macrophage polarization. Once activated, Ahr can modulate distinct cell functions, including toll-like receptor signaling cascades, to adjust macrophage activity in response to endogenous and exogenous ligands. Although recent studies with Ahr-null mice suggested that Ahr signaling appeared to be a critical factor in obesity development, we still do not know if Ahr signaling in macrophages contributes to the development of obesity. This proposal aims to identify if Ahr signaling modulation could be a new target for reducing macrophage pro-inflammatory phenotype during obesity without changing macrophage capacity to respond to infections. Our results show a distinction in Ahr activation under obesogenic conditions or LPS stimulation. Under LPS stimulation, Ahr is activated and controls glycolytic metabolism and pro-inflammatory induction. In macrophages from AhrKO animals, there is early activation of NF-kB and p38 pathways, associated with a fast induction of glycolytic metabolism and increase production of pro-inflammatory cytokines, such as TNFa. However, Ahr signaling is downregulated under obesogenic stimuli in vitro and in vivo. Obese AhrKO mice fed a high-fat diet (HFD) have more glucose intolerance and insulin resistance than control obese mice. This phenotype was associated with higher lipid depots in the liver and increased TNFa production by splenic macrophages and also by ATMs to a lower extent. In vitro stimulation with palmitate, the most abundant FFA in the serum of obese subjects, increased the secretion of TNFa in AhrKO macrophages, which also presented elevated glycolysis. This modification combines with fast and prolonged NF-kB, p38, and JNK phosphorylation under palmitate stimulation. Treatment of macrophages with an Ahr agonist before palmitate decreased the expression of Tnfa and glycolysis compared with palmitate exposure alone, highlighting the role of Ahr for macrophage fitness upon obesogenic conditions. Therefore, our results indicate that although LPS stimulation leads to Ahr activation to control macrophage activation, the loss of Ahr signaling in macrophages exposed to an obesogenic environment affects cell metabolism and inflammatory tonus, impacting obesity-induced inflammation and subsequent insulin resistance. This proposal will allow us to understand how Ahr signaling modulation in macrophages could contribute as a new therapeutic target using proteomic and in vitro analyses. (AU)