Person:

Bhargava, Prerna

Energy metabolism plays a vital role in normal physiology, adaptive responses and host defense mechanisms. Research throughout the last decade has shown evidence that immune pathways communicate with metabolic pathways to alter the metabolic status in response to physiological or pathological signals. In this thesis, I will explore how immunomodulatory molecules affect metabolic homeostasis and conversely, how metabolic sensing pathways modulate immune responses. The first part my work utilizes an immunomodulatory sugar motif to determine mechanisms by which immune cells influence metabolism. Specifically, I show in chapter 2 that lacto-N-fucopentaose III (LNFPIII), a motif used by pathogens to attenuate inflammation, is capable of improving systemic insulin sensitivity by increasing Il-10 production in macrophages and dendritic cells and subsequently improving white adipose tissue insulin sensitivity. Chapter 3 will address the observation that this same glycan is capable of directly activating Fxra in hepatocytes. This direct effect manifests as a reduction in high-fat-diet-induced hepatic triglyceride accumulation and improvement in liver function. Lastly, in chapter 4, I will discuss the role of metabolic regulators in the macrophage and how this affects the ability of the macrophage to kill bacteria. Specifically, I will show that lipid sensing nuclear receptors, such as Ppard and Pparg, are critical regulators of phagosomal function and bacterial killing. Macrophage-specific deletion of these receptors prevents efficient killing of Streptococcus pneumoniae, the causative bacterium in many cases of respiratory pneumonia. Ligand activation improves survival, suggesting a potential therapeutic role for Ppar activation during infection. Taken together, all the data suggest a critical role for the evolutionary interaction between metabolic and immune pathways. These interactions may be important when developing new therapeutics for complex metabolic and immunological dysfunctions.

Parasitic worms express host-like glycans to attenuate the immune response of human hosts. The therapeutic potential of this immunomodulatory mechanism in controlling metabolic dysfunction associated with chronic inflammation remains unexplored. We demonstrate here that administration of Lacto-N-fucopentaose III (LNFPIII), a LewisX containing immunomodulatory glycan found in human milk and on parasitic helminths, improves glucose tolerance and insulin sensitivity in diet-induced obese mice. This effect is mediated partly through increased Il-10 production by LNFPIII activated macrophages and dendritic cells, which reduces white adipose tissue inflammation and sensitizes the insulin response of adipocytes. Concurrently, LNFPIII treatment up-regulates nuclear receptor Fxr-α (or Nr1h4) to suppress lipogenesis in the liver, conferring protection against hepatosteatosis. At the signaling level, the extracellular signal-regulated kinase (Erk)-Ap1 pathway appears to mediate the effects of LNFPIII on both inflammatory and metabolic pathways. Our results suggest that LNFPIII may provide novel therapeutic approaches to treat metabolic diseases.