PNP deficiency and cytosolic DNA in lupus pathogenesis

摘要 I型干扰素（IFN）信号通路是系统性红斑狼疮的主要致病因素。 尽管I型IFN在SLE中的重要性，但目前尚不清楚该途径在给定的SLE患者中是如何被激活的。 病人虽然70 - 80%的SLE患者外周血中存在IFN信号，但我们始终发现， 只有40 - 50%的SLE患者具有高水平的功能性循环I型IFN。约30%的 SLE患者具有IFN特征，而血液中I型IFN没有显著升高。与这种脱节 重要的是，因为I型IFN拮抗剂的临床试验已经使用IFN信号作为生物指示剂 的回应。最近，我们在嘌呤核苷酸磷酸酶中发现了一种常见的遗传多态性， (PNP)产生不需要I型IFN受体信号传导的IFN特征的基因。狼疮- 相关的变体结果降低了酶活性，并增加了S期阻滞。在初步研究中，我们发现 PNP变异细胞具有增加的胞质DNA内含物。细胞溶质DNA包涵体可在S 相阻断或DNA损伤，并且这些内含物可以通过STING激活胞质抗病毒应答。我们 发现携带PNP变体的培养物中纯化的B细胞增加了IFN诱导的基因表达，但确实如此 而不是产生I型干扰素我们经常使用诱导S期阻滞的药物，如吗替麦考酚酯和 硫唑嘌呤。在SLE中观察到的一些IFN信号可能与胞浆DNA包涵体有关 对这些药剂的反应，有或没有PNP变体。IFN诱导的基因表达是否 然后限制这些药物的疗效或有助于副作用是未知的。即使这个干扰素诱导的基因 如果IFN的表达不恶化SLE中的炎症，则它将降低IFN标签的临床效用。我们 假设与PNP多态性相关S期阻滞有助于SLE中IFN途径的激活 通过胞质DNA内含物和胞质受体的激活，PNP缺陷导致狼疮， 可能使S期阻滞剂治疗复杂化。在目标1中，我们将剖析PNP缺陷的影响， 细胞溶质DNA内含物对人细胞中IFN特征的影响。在目标2中，我们将确定PNP的影响 在小鼠模型中对狼疮表型和体内治疗的缺陷。这个高风险高回报的求婚 将建立一个新的范例，I型干扰素签名在系统性红斑狼疮，内源性细胞溶质DNA夹杂物 导致低效的细胞周期有助于I型IFN途径的激活，并可能表明 在这个过程中常用的SLE药物。这些结果可能有助于SLE的个性化治疗， 来完善我们与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.