Fit to remember? B cell metabolic 'fitness', AMPK & recall antibody responses

描述（由申请人提供）：体液记忆是疫苗抵抗微生物能力的核心，也是适应性免疫的关键特征。这个过程的一个主要决定因素是生发中心（GC）反应促进记忆B细胞分化和维持的能力，而记忆B细胞又是回忆反应的关键决定因素。关于B细胞激活后的潜在命运已经了解了很多， 包括BCR对Ag的亲和力和GC反应的其他全局特征的重要贡献，但是 关于B细胞内的信号传导如何影响记忆，我们知之甚少。用体外操作以及小鼠模型系统积累的证据提供了局部生理学（例如，营养供应）与免疫系统细胞中的信号传导及其命运或功能特征。B细胞和记忆的独特生物学意味着它们使用新的代谢机制。然而，对于B淋巴谱系的代谢调节知之甚少，尤其是对于B细胞记忆或足够浓度的Ab的持久性知之甚少。AMP激活激酶（AMPK）是二甲双胍等抗糖尿病药物的靶点，是调节生物合成中能量产生与利用之间平衡的关键。我们已经发现，在B细胞中AMPK的主要亚型AMPK β 1在B细胞内在作用中促进了回忆抗体应答的能力。我们还发现了与AMPK平行的途径的证据，在该途径上，ADP-核糖基转移酶PARP 14促进糖酵解、葡萄糖氧化和B细胞存活的增加。此外，几种抗体同种型的回忆抗体应答依赖于PARP 14。这些和进一步的发现使我们假设AMPK β促进Ag特异性记忆B细胞的产生或维持，并且这种功能至少部分通过促进代谢适应性[脂肪酸氧化（FAO）以及糖酵解和葡萄糖氧化]来发挥。该研究还将解决CTL记忆中心范式关键研究中一个尚未解决的悖论，其中（FAO）与记忆命运相关，而糖酵解与效应子样表型相关。难题是这种平衡作用归因于AMPK活性，但这种激酶促进FAO和糖酵解。我们将检验这一假设，即这些形式的能量产生的差异调节是基于mTOR调节的HIF-1的活性，HIF-1是一种转录因子，可以直接抑制FAO，同时激活糖酵解。为了测试AMPK活性对体液回忆的影响，并阐明AMPK驱动的代谢途径可以平衡的机制，我们有三个具体的目的。第一个（目的1）是建立一个特定的B谱系-在记忆体液免疫中的关键代谢调节因子AMPK的内在功能。此外，我们计划测试一个模型，其中HIF-1与AMPK整合在设置B细胞代谢平衡和回忆抗体反应（目标2）。最后，我们将评估mTOR是否是B细胞和体液记忆中AMPK和HIF-1的效应子（目的3）。这些研究的预期结果是，我们将发现AMPK和HIF-1在决定B细胞代谢特征和体液免疫功能结果中的新作用。

DESCRIPTION (provided by applicant): Humoral memory is central to the capacity of vaccines to protect against microbes and is a key feature of adaptive immunity. A major determinant of this process is the potency with which germinal center (GC) reactions foster the differentiation and maintenance of memory B cells, which in turn are critical determinants of recall responses. Much has been learned about the potential fates of a B cell after its activation, including vital contributions of BCR affinity for Ag and other global features of GC reactions, but remarkably little is known about how signaling within the B cell impacts memory. Accumulating evidence with in vitro manipulations as well as mouse model systems provides indications of a regulatory inter-play 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 and memory implies that they use novel metabolic mechanisms. However, very little is known about metabolic regulation for the B lymphoid lineage and especially not for B cell memory or the persistence of adequate concentrations of Ab. AMP-activated kinase (AMPK), the 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, AMPK�1, 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 AMPK� promotes the generation or maintenance of Ag-specific memory B cells, and that this function is exerted at least in part through promotion of metabolic fitness [fatty acid oxidation (FAO) as well as 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 mTOR-regulated activity of HIF-1, a transcription factor 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 AMPK-driven 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 regulator, AMPK, in memory for humoral immunity. Moreover, we plan to test a model in which HIF-1 is integrated with AMPK in setting B cell metabolic balance and recall Ab responses (Aim 2). Finally, we will evaluate if mTOR is an effector of AMPK and HIF-1 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 outcome in humoral immunity.