Impact of Diabetes and Hyperlipidemia on Host Defense

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Increased susceptibility to infections including tuberculosis (TB) is a major cause of morbidity and mortality in diabetes. Despite its clinical importance, this phenomenon has received little basic research attention. We will investigate TB resistance in mice using models of type 1 and type 2 diabetes. Diabetic and non-diabetic control mice will be challenged by low-dose aerosol infection with Mycobacterium tuberculosis (Mtb). We will characterize TB susceptibility with parameters of survival, bacterial load, and lung leukocyte recruitment. The basis of susceptibility will be evaluated by characterizing cytokine expression and by testing macrophage, dendritic cell, and T cell functions. We will investigate whether advanced glycation end products (AGE), which have been linked to diverse complications of diabetes, are responsible for impaired host defense. We will also evaluate the potential role of other biochemical mechanisms implicated in diabetes complications including polyol pathway flux, hexosamine pathway flux, and over-production of diacylglycerol with activation of protein kinase C. Hyperlipidemia is a common co-morbidity in diabetes that exacerbates diabetic vasculopathy. In preliminary studies we found that hypercholesterolemia also increases TB susceptibility. We will explore similarities and differences in the effects of diabetes and hyperlipidemia on protective immunity, and we will characterize TB susceptibility of mice with combined hyperlipidemia and diabetes. This project will identify specific deficits in protective immunity caused by hyperglycemia and hyperlipidemia, and may provide new insights to critical parameters of host defense against TB. Understanding the mechanisms of susceptibility will inform the development of treatments to reverse this diabetes-related complication. At the same time our model will be used to test the impact on protective immunity of novel treatments for diabetes co-morbidities such as statins, aminoguanidine and pyridoxamine. While our focus is on TB, the new knowledge generated by this project will have broad relevance to other infections associated with diabetes and will further basic understanding of the interplay between immunity and metabolism. This project studies how diabetes weakens the body's ability to fight tuberculosis. Learning more about the harmful effects of diabetes on the immune system will suggest new ways to prevent and treat infections that are a major problem in people with diabetes.