PNP deficiency and cytosolic DNA in lupus pathogenesis

摘要 I型干扰素途径信号转导是系统性红斑狼疮的主要致病因素。 尽管I型干扰素在系统性红斑狼疮中的重要性，但目前尚不清楚该途径是如何在给定的 有耐心的。虽然70%到80%的SLE患者外周血中有干扰素信号，但我们一直发现 只有40%到50%的SLE患者有高水平的功能性循环I型干扰素。因此，大约30%的 系统性红斑狼疮患者有干扰素信号，但血液中I型干扰素没有明显升高。这种脱节是 重要的是，因为I型干扰素拮抗剂的临床试验使用了干扰素信号作为生物指标 回应的问题。最近，我们发现了一种常见的嘌呤核苷酸磷酸酶基因多态性。 (PNP)基因，导致不需要I型干扰素受体信号的干扰素签名。狼疮- 相关变异结果降低了酶活性，增加了S时相阻滞。在初步研究中，我们发现 PNP变异细胞胞浆DNA包涵体增多。S可以形成胞液DNA包裹体 时相阻断或DNA损伤，这些包涵体可通过刺痛激活胞质抗病毒反应。我们 发现在携带PNP变体的培养中，纯化的B细胞增加了干扰素诱导的基因表达，但确实 而不是制造I型干扰素。我们经常使用引起S时相阻滞的药物，如霉酚酸酯和 硫唑嘌呤。在系统性红斑狼疮中观察到的某些干扰素特征可能与胞浆DNA包涵体有关。 无论有没有PNP变异体，都能对这些试剂作出反应。这种干扰素诱导的基因表达是否会 那么限制这些药物的疗效或造成副作用还不得而知。即使这种干扰素诱导的基因 表达不会加重系统性红斑狼疮的炎症，它会降低干扰素签名的临床用途。我们 PNP基因多态性相关的S时相阻滞参与系统性红斑狼疮干扰素途径激活的假说 通过胞浆DNA包涵体和胞浆受体的激活，而PNP缺乏会加重狼疮和 可能会使S相阻滞剂的治疗复杂化。在目标1中，我们将剖析PNP缺乏症和 人细胞干扰素信号上的胞浆DNA包涵体。在目标2中，我们将确定PNP的影响 小鼠狼疮表型缺陷及体内治疗。这个高风险、高回报的提案 将为系统性红斑狼疮患者的I型干扰素签名建立一种新的范式，即内源性胞浆DNA包涵体 由于低效的细胞周期导致I型干扰素途径激活，并可能提示在 在这一过程中常用的SLE药物。这些结果有助于SLE和SLE的个性化治疗 提炼我们与I型干扰素相关的生物标志物。

ABSTRACT Type I interferon (IFN) pathway signaling is a primary pathogenic factor in systemic lupus erythematosus. Despite the importance of type I IFN in SLE, it is not currently known how the pathway is activated in a given patient. While 70 to 80% of SLE patients have an IFN signature in peripheral blood, we consistently find that only 40 to 50% of SLE patients have high levels of functional circulating type I IFN. Thus approximately 30% of SLE patients have an IFN signature without a significant elevation of type I IFN in blood. This disconnect is important, because clinical trials of type I IFN antagonists have used the IFN signature as a biological indicator of response. Recently, we identified a common genetic polymorphism in the purine nucleotide phosphatase (PNP) gene that results in an IFN signature that does not require type I IFN receptor signaling. The lupus- associated variant results reduced enzyme activity, and increased S phase block. In preliminary studies, we find that PNP variant cells have increased cytosolic DNA inclusions. Cytosolic DNA inclusions can form following S phase block or DNA damage, and these inclusions can activate the cytosolic anti-viral response via STING. We find that purified B cells in culture carrying the PNP variant have increased IFN-induced gene expression, but do not make type I IFN. We frequently use drugs that induce S phase block, such as mycophenolate mofetil and azathioprine. It is possible that some of the IFN signature observed in SLE is related to cytosolic DNA inclusions in response to these agents, with or without the PNP variant. Whether this IFN-induced gene expression would then limit the efficacy of these drugs or contribute to side effects is not known. Even if this IFN-induced gene expression does not worsen inflammation in SLE, it would reduce the clinical utility of an IFN signature. We hypothesize that S phase block related to the PNP polymorphism contributes to IFN pathway activation in SLE via cytosolic DNA inclusions and activation of cytosolic receptors, and that PNP deficiency worsens lupus and may complicate treatment with S phase blockers. In Aim 1, we will dissect the influence of PNP deficiency and cytosolic DNA inclusions upon the IFN signature in human cells. In Aim 2, we will determine the impact of PNP deficiency on lupus phenotype and treatment in vivo in murine models. This high-risk, high-reward proposal would establish a new paradigm for the type I IFN signature in SLE, that endogenous cytosolic DNA inclusions resulting from inefficient cell cycle contribute to type I IFN pathway activation, and could suggest a role for commonly used SLE medications in this process. These results could help to personalize treatment in SLE and to refine our biomarkers related to type I IFN.