Inflammation is a response of immune cells to microbial pathogen-associated and host damage-associated molecular patterns. Toll-like receptor 4 (TLR4) is a major immune, pattern-recognition receptor that recognizes these ligands and initiates inflammatory signaling. Previous studies have shown that binding of Apolipoprotein A-I binding protein (AIBP) to TLR4 facilitates removal of excess cholesterol from endothelial cells and macrophages, resulting in the reduction of membrane lipid rafts and inhibition of TLR4 dimerization and reduced inflammatory responses. However, the molecular basis of interaction between TLR4 and AIBP is not fully understood. Here, I investigate TLR4 binding motifs in the AIBP molecule. Using wildtype AIBP and mutated variants of AIBP expressed and purified from a baculovirus/insect cell system, I identified a TLR4 binding domain in the AIBP molecule, which plays a critical role in regulation of TLR4-dependent inflammatory responses in microglia. My findings provide important mechanistic insights into the molecular basis of interaction between TLR4 and AIBP and may contribute to the development of AIBP-based therapy for chronic inflammatory diseases, including atherosclerosis and neuropathic pain.

Despite being discovered nearly two decades ago, little is known about the in vivo function of Apolipoprotein A-I Binding Protein (AIBP). The aim of our studies was to determine this function through the use of loss-of-function knockout models and gain-of-function overexpression models. We found that AIBP plays a protective role against atherosclerosis and inflammation, by enhancing cholesterol efflux from the vessel wall and preventing inflammatory macrophage signaling. It also appears to regulate whole-body metabolism, possibly via a different mechanism. Intriguingly, while AIBP is protective against certain conditions, it may actually be detrimental to cancer survival. Tumors express AIBP, and mice lacking AIBP expression had slower sarcoma growth than wildtype mice. Taken together, these data show that AIBP has important in vivo functions in a variety of pathologies.

Chronic pain is a major problem restraining people from performing everyday tasks. Recent studies showed that cholesterol metabolism in microglia regulates neuropathic pain, however, little is known about the unique role astrocytes play during chronic pain. In this thesis paper, we focused on exploring two main cholesterol transporters in astrocytes, ABCA1 and ABCG1, and their roles in controlling neuropathic pain. Here, we used the chemotherapy-induced peripheral neuropathy (CIPN) model in male mice with conditional deletion of ABCA1 and ABCG1 cholesterol transporters in astrocytes (ABC-iaKO) and male mice with constitutive deletion of apolipoprotein E (ApoE-KO) to examine their pain behavior response and analyze their glial and neuronal lipid composition using flow cytometry. We found that ABC-iaKO mice were not affected by the CIPN model and showed higher mechanical paw-withdrawal thresholds than wild-type mice. When looking into the lipid content of neurons, both ABC-iaKO and ApoE-KO mice subjected to chemotherapy treatment displayed a trend toward lower lipid droplets and lipid rafts levels compared to wild-type mice. Our findings demonstrate that ABCA1 and ABCG1 transporters in astrocytes play essential roles in regulating neuropathic pain response and possibly altering neuronal lipid content through ApoE. Through this study, we could further understand how astrocytic cholesterol regulates neuropathic pain and contribute to creating a safe treatment for chronic pain.