The immune system has co-opted components of lipid metabolism to develop immunological responses to antigens. Our long term goal is to understand how lipoproteins and apolipoproteins influence innate and adaptive immune response, due to their ability to lay at the crossroads between systemic and cellular lipid metabolism. The objective of this proposal is to study the role of apolipoprotein E (apoE) in adaptive immunity, and specifically how apoE affects the function of cognate dendritic cell/T cell synapsis. The central hypothesis we will test is that apoE modulates cholesterol availability in lipid rafts thus influencing the localization of co-stimulatory molecules in immune cells and the activation of adaptive immune response in animal models and in humans. The rationale is based on our solid preliminary results showing that (i) the deficiency of apoE results in significantly increased effector memory CD4 T lymphocytes (TEM) and decreased naïve T cells in the circulation and in lymphoid organs, (ii) leucocytes isolated from lymphoid organs of apoE knock out (apoE KO) mice and stimulated with anti-CD3/CD28 undergo a more sustained proliferative response compared to those from wild type mice, (iii) skin graft allo-transplantation experiments in CD8 T cells depleted mice showed a significantly faster rejection in apoE KO mice compared to wild type mice, which was associated to increased numbers of CD4 TEM cells in the lymph nodes draining the graft, (iv) analysis of lymphoid organs from apoE KO mice and apoE/apoA-I double KO (impaired ability to transport cholesterol from the periphery back to the liver) showed significantly increased TEM cells numbers associated to extensive cholesterol deposition and (v) human subjects bearing three functionally distinct and genetically determined isoforms of apoE, namely apoE2, apoE3 and apoE4 showed a different proportion of TEM cells levels in the peripheral blood (apoE2apoE4). The impact of apoE-mediated cholesterol exchange in modulating cell membrane dynamics during cognate dendritic cell/T cell interactions is unknown. Addressing this basic question will allow apoE targeting for therapeutic intervention and defining genetic variants of apoE as a novel risk factor for immune disorders. On this ground, we propose to accomplish the objectives of this application by pursuing the following three specific aims: 1. To establish the role of apoE in the regulation of membrane receptors distribution (and signaling circuits) during antigen presentation using leukocytes from apoE KO mice and WT littermates and from human carriers of functionally different apoE isoforms; 2. To assess the contribution of apoE generated by either hepatic or myeloid cells on adaptive immune response during skin allograft rejection or experimental autoimmune encephalomyelitis; and 3. To evaluate the therapeutic potential of apoE reconstituted lipoproteins (r-apoE2-HDL, r-apoE3-HDL, rapoE4- HDL) in models of immune diseases described above. Upon completion of this project, we expect to determine the proteins present in lipid rafts in antigen presenting cells and T cells that are targeted by apoE/ cholesterol modulation and translate these findings in humans by taking advantage of studies in carries of different apoE isoforms. Finally we will test the therapeutic impact of fine-tuning of cholesterol levels in APCs/DCs and T cells on immunoinflammatory disease outcome. This knowledge will be seminal for the identification of the impact of apoE on the development of adaptive immunity and for devising new therapeutic strategies to prevent or ameliorate immunometabolic diseases particularly in the elderly, in which immunometabolic disorders have a high prevalence and morbidity.
