Inflammation in MERTK-dependent retinitis pigmentosa

项目总结/摘要 迄今为止，MERTK功能丧失相关性视网膜色素变性（RP）中涉及的生物学过程是 视网膜色素上皮细胞（RPE）对脱落的感光细胞外节（POS）的吞噬功能缺陷， 光感受器（PR）变性。在这里，我们提出了这种范式的转变。我们已经证明， 小鼠中Mertk的精确遗传消除（Mertk -/- V2）导致吞噬作用缺陷，但不导致PR变性。 此外，在原始Mertk敲除（Mertk -/- V1，其是Tyro 3的亚晶型）或Mertk-/- V1中的PR变性也是可能的。 -/- V2 Tyro 3-/- V2小鼠与RPE炎症相关。因此，我们假设MERTK抗- RPE中的炎性信号传导是导致RP的关键事件。为了检验这一假设，我们建议（i） 有条件地消融Tyro 3-/- RPE中的Mertk，以测试这是否重现在种系Mertk -/-中观察到的RPE炎症。 /- V1和Mertk -/- V2 Tyro 3-/- V2小鼠。另一种可能性是Mertk条件性消融时的RPE炎症 尽管在Tyro 3-/- RPE中，炎症是MERTK介导的 吞噬作用和随后的POS碎片的积累。即使在6个月内， Mertk -/- V2或Mertk -/- V3小鼠。我们还在睁眼前（p10）检测RPE炎症， 在没有MERTK的情况下，可能是主要的。为了直接测试这一点，（ii）我们已经生成了一组独特的鼠标 模型，其中MERTK的吞噬作用或抗炎信号传导功能仅被 突变了，剩下的功能完好无损。这些小鼠模型将使我们能够明确地测试结果 在PR变性中MERTK介导的吞噬作用的单独损失，以及解偶联MERTK介导的吞噬作用的损失的影响。 MERTK抗炎信号传导单独与MERTK介导的吞噬作用丧失有关。补充 在这些研究中，我们将测试分化的人类原发性RPE中的正向突变的影响， 在存在或不存在POS的情况下诱导RPE炎症。如果炎症是MERTK病因的基础 功能丧失相关的RP，它可以治疗靶向保护视力丧失？(iii)我们有 获得了有希望的初步数据，FDA批准的JAK 1/2抑制剂ruxolitinib可减少炎症反应， Mertk -/-V1小鼠中Mertk-/- V1 RPE中的基因表达和PR变性的严重程度。在此基础上 概念验证，我们将通过剂量优化ruxolitinib方案（剂量和治疗持续时间）- 递增研究，以确定对PR退化和视力丧失的最大保护。综合起来看， 这三种独立的正交方法有望揭示支持一种新的 炎症在RPE本身中的作用与MERTK功能丧失相关RP具有因果关系，以及 作为，提供了一种使用已经在临床上使用的小分子JAK 1/2抑制剂（“Jakinibs”）的治疗途径， 这种严重的早发性RP

PROJECT SUMMARY/ABSTRACT The biological process heretofore implicated in MERTK loss-of-function-associated Retinitis Pigmentosa (RP) is defective phagocytosis of shed photoreceptor outer segments (POS) by retinal pigment epithelium (RPE) leading to photoreceptor (PR) degeneration. Here we propose a shift in this paradigm. We have demonstrated that the precise genetic ablation of Mertk in mice (Mertk -/- V2) results in deficient phagocytosis, but not PR degeneration. Furthermore, PR degeneration in the original Mertk knockout (Mertk -/- V1 that is hypomorphic from Tyro3) or Mertk -/- V2 Tyro3 -/- V2 mice is associated with RPE inflammation. Therefore, we hypothesize that loss of MERTK anti- inflammatory signaling in the RPE is a critical event leading to RP. To test this hypothesis, we propose to (i) conditionally ablate Mertk in Tyro3 -/- RPE to test if this recapitulates RPE inflammation seen in germline Mertk - /- V1 and Mertk -/- V2 Tyro3 -/- V2 mice. An alternate possibility, RPE inflammation when Mertk is conditionally ablated in Tyro3 -/- RPE notwithstanding, is that inflammation is a secondary consequence of loss of MERTK-mediated phagocytosis and the consequent build-up of POS debris. We do not see POS build up even at 6 months in Mertk -/- V2 or Mertk -/- V3 mice. We also detect RPE inflammation before eye opening (at p10) and thus inflammation in the absence of MERTK is likely primary. To directly test this, (ii) we have generated a unique set of mouse models wherein either the phagocytosis or anti-inflammatory signaling function of MERTK has been exclusively mutated, leaving the remaining function intact. These mouse models will allow us to definitively test the outcome of loss of MERTK-mediated phagocytosis alone in PR degeneration, as well as uncouple the effects of loss of MERTK anti-inflammatory signaling alone from that of loss of MERTK-mediated phagocytosis. Complementing these studies, we will test the orthologous mutations in differentiated human primary RPE in terms of their effect on inducing RPE inflammation in presence or absence of POS. If inflammation underlies the etiology of MERTK loss-of-function-associated RP, can it be therapeutically targeted to protect against vision loss? (iii) We have obtained promising preliminary data that the FDA-approved JAK1/2 inhibitor ruxolitinib reduces inflammatory gene expression in the Mertk -/- V1 RPE and the severity of PR degeneration in Mertk -/- V1 mice. Building on this proof-of-concept, we will optimize the ruxolitinib regimen (dose and duration of treatment) through dose- escalation studies to determine maximum protection against PR degeneration and vision loss. Taken together, these three independent, orthogonal approaches are expected to reveal mechanistic insight supporting a novel role of inflammation within the RPE itself as causally relevant to MERTK loss-of-function-associated RP, as well as, provide a therapeutic avenue using small molecule JAK1/2 inhibitors (“Jakinibs”) already in clinical use for this severe, early-onset form of RP.