TPL2: A Central Node in Obesity-Associated Inflammation and Metabolic Disorders

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DESCRIPTION (provided by applicant): Obesity is a major independent risk factor for type 2 diabetes mellitus (T2DM), obesity promotes chronic macrophage-mediated adipose tissue inflammation, resulting in increased release of free fatty acids from adipocytes and ectopic accumulation of triglyceride. Alone and in combination, these obesity-associated increases in inflammation and altered lipid homeostasis promote insulin resistance (IR), type 2 diabetes mellitus and its comorbidities. Studies outlined in this grant application will test hypotheses concerning how the actions of Tumor Progression Locus 2 (TPL2), an 'upstream' mediator of inflammatory signaling, promote obesity-associated inflammation and IR. TPL2 is a serine/threonine kinase, located downstream of IKK-2 and reported to activate MAP Kinases (MAPK) (ERK, JNK) and upregulate pro-inflammatory cytokine (e.g., TNF-1, IL-12) production. Importantly, ERK, JNK and pro-inflammatory cytokines are directly implicated in the dysregulated lipolysis, hepatic steatosis and/or compromised insulin signaling of obesity. The role of TPL2 in obesity-associated inflammation and IR is unknown. We hypothesize that TPL2 activity in the obese state activates MAPK pathways and induces pro-inflammatory cytokine expression, thereby promoting altered glucose/insulin homeostasis and hepatic steatosis. Preliminary Studies demonstrate that relative to wild-type (WT) mice, TPL2 knockout (TPLKO) mice fed a high fat diet (HFD) were substantially protected from 1) macrophage-mediated adipose tissue inflammation, 2) adipose and hepatic induction of IR-promoting inflammatory mediators (e.g., TNF-1, IL-12), 3) dysregulated hepatic lipogenic and gluconeogenic gene expression, 4) hepatic steatosis and 5) alterations in glucose-insulin homeostasis. These observations strongly suggest that TPL2 is a novel and important protagonist in the inflammatory and metabolic complications of obesity that predispose individuals to the onset of T2DM. In this grant we will complete the following Specific Aims: 1) To conduct a detailed analysis of the inflammatory and metabolic phenotype of TPLKO mice in two separate models of obesity: 1) high fat diet (HFD) and 2) the ob/ob mouse, a genetic model of murine obesity. 2) To determine the role of TPL2 in hematopoietic (immune) and non-hematopoietic cells and tissues in mediating obesity-associated inflammation and metabolic disorders. 3) To determine the role of TPL2 in regulating TNF-1 and fatty acid-induced signaling pathways in adipocytes and macrophages. These studies will elucidate the central role of TPL2 in obesity-associated inflammation and metabolic disorders. PUBLIC HEALTH RELEVANCE: Obesity is associated with increased risk of developing diabetes and liver disease. In this grant application we will determine the specific role of a protein, called TPL2, that we hypothesize is a critical factor in obese individuals that contributes to the development of diabetes and liver disease. Understanding the role of TPL2 in obesity may lead to potential new therapies for the complications of obesity such as diabetes.