The B Cell Insulin Receptor in Health and in Insulin Resistance

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PROJECT SUMMARY / ABSTRACT Obesity is a major global health concern. When people become obese, the body fails to respond well to insulin, called insulin resistance. This process can lead to high blood sugar triggering type 2 diabetes, though the underlying causes are poorly understood. We have shown that inflammation in the liver and fat are major causes of insulin resistance. Fat tissue in mice and people have increased immune cells, T and B cells, that cause inflammation. This net inflammation is one key link leading to obesity related insulin resistance. The current research proposal investigates how the B cell behaves during early and later stages of obesity. Interestingly, here we describe insulin itself as a major factor dictating the behavior of B cells in obesity. Specifically, we show that insulin binding to its receptor on B cells causes the B cells to proliferate, make inflammatory proteins and antibodies. This process contributes to establishment of insulin resistance since when mice are genetically engineered to contain B cells lacking insulin receptors, the mice show improved blood sugar levels when fed a diabetes inducing high fat diet for a limited time. However, this same pathway may also limit immune cell function during longstanding obesity. Indeed, we see insulin resistance inside immune cells with longer duration high fat diet, and compromised response to viral lung infection in mice with insulin resistant immune systems. Thus, we believe that insulin is one critical factor which primes the immune system to respond to danger signals in the environment and fuel its function. During establishment of obesity and insulin resistance, insulin boost activation and metabolism of immune cells to heighten inflammation when responding to danger signals; however, as the pathway becomes resistant, these immune cells with high basal inflammatory tone are crippled to respond to new challenge such as virus. This mechanism also likely explains in part why the obese cannot fight off viruses like influenza or SARS-2 coronaviruses. In this proposal we will use genetically engineered mouse models to map out how insulin controls B cell immunology during different durations of obesogenic diet. First, we will look at insulin’s capacity to control B cell inflammation, metabolic programming and antibody production. Next, we will understand how diet induced obesity communicates via insulin action on B cells to control blood sugar. This aim includes mapping out insulin receptor docking sites on immunological target genes. Then we will characterize the immunological consequences of immune cell insulin resistance during lung virus infection in a mouse model of influenza. Finally, we will determine the relative mechanistic roles for obesity related danger pattern signaling in contributing to the insulin resistant B cell inflammatory state. These experiments will give crucial new insights into immune cell influence on obesity, and how obesity potentially cripples immunity, which has relevance to many conditions, including lethal viruses such as our current pandemic.