Humoral memory, a key feature of both adaptive immunity and some autoimmune diseases, is central to the capacity of vaccines to protect against microbes. Determinants of this process include the degrees to which germinal center (GC) and extrafollicular reactions foster the differentiation and maintenance of various classes of memory B (Bmem) cells from which recall responses are derived. Much has been learned about the potential fates of a B cell after its activation, including vital contributions of BCR affinity for Ag, but remarkably little is known about how signaling within the B cell impacts memory or recall. Accumulating evidence with in vitro manipulations as well as mouse model systems provides indications of a regulatory interplay of local physiology (e.g., nutrient supply) with signaling in cells of the immune system and their fate or functional characteristics. The unique biology of B cells suggests that they use novel mechanisms, but very little is known about metabolic regulation for the B lymphoid lineage and especially not for the persistence of classes of Bmem cells or adequate concentrations of Ab. AMP-activated kinase (AMPK), a target of anti-diabetic agents such as metformin, is central to regulation of the balance between energy generation versus utilization in bio-synthesis. We have found that the predominant isoform of AMPK in B cells, AMPKa1, promoted the capacity for a recall Ab response in a B cell- intrinsic role. We also developed evidence of a pathway parallel to AMPK, on which an ADP-ribosyl transferase, PARP14, promotes increases in glycolysis, glucose oxidation, and B cell survival. Moreover recall Ab responses of several Ab isotypes depended on PARP14. These and further findings lead us to hypothesize that AMPKa promotes the generation or maintenance of Ag-specific IgG+ memory B cells, and that this function is exerted at least in part through promotion of metabolic fitness [fatty acid oxidation (FAO), glycolysis, and glucose oxidation]. The research also will address an unresolved paradox from key studies of the central paradigm of CTL memory, in which (FAO) is associated with memory fate while glycolysis ties to effector-like phenotype. The conundrum is that the balancing act was attributed to AMPK activity, but this kinase promotes both FAO and glycolysis. We will test the hypothesis that differential regulation of these forms of energy generation is based on activity of hypoxia- induced factor(s) (HIFs - 1, 2), transcription factors that may directly repress FAO alongside its activation of glycolysis. To test the impact of AMPK activity on humoral recall, and elucidate a mechanism by which metabolic pathways can be balanced, we have three specific Aims.
The first (Aim 1) is to establish a specific B lineage- intrinsic function for the key metabolic regulaor, AMPK, in memory and identify stages at which it is required.
In Aim 2, we will test a model in which HIFs are integrated with AMPK in setting B cell metabolic balance and recall Ab responses. Finally, we will evaluate if mTOR is an effector of AMPK in B cells and humoral memory (Aim 3). The expected outcome of the proposed studies is that we will uncover novel roles for AMPK and HIF- 1 in determining the metabolic profile in B cells and functional outcomes in humoral immunity.
The ability to maintain and renew high enough concentrations of antibodies protects us against disease caused by various microbes and is central to vaccine efficacy, yet also can be part of how many immune-mediated diseases undermine our health. Long-lived antibody responses and memory are produced after one class of white blood cells is activated, interacts with other classes of cell, differentiates to new fates, and persists for year. This proposal seeks support to allow us to identify novel signaling mechanisms that regulate how well B lineage cells are directed toward long-term memory.
| Raybuck, Ariel L; Cho, Sung Hoon; Li, Jingxin et al. (2018) B Cell-Intrinsic mTORC1 Promotes Germinal Center-Defining Transcription Factor Gene Expression, Somatic Hypermutation, and Memory B Cell Generation in Humoral Immunity. J Immunol 200:2627-2639 |
| Boothby, Mark; Rickert, Robert C (2017) Metabolic Regulation of the Immune Humoral Response. Immunity 46:743-755 |
| Cho, Sung Hoon; Raybuck, Ariel L; Stengel, Kristy et al. (2016) Germinal centre hypoxia and regulation of antibody qualities by a hypoxia response system. Nature 537:234-238 |
