Developmental Origin, Injury and Epigenomic Regulation of NF1-Associated Peripheral Nerve Sheath Tumors

项目摘要 患有1型神经纤维瘤病(NF1)的人患上神经纤维瘤病的风险大约增加160倍 恶性周围神经鞘瘤(MPNST)。作为NF1患者的主要死亡原因。MPNST 没有有效的治疗方法，因此迫切需要新的治疗方法。极大地增加了 MPNSTs的发生是由丛状神经纤维瘤(PNFS)引起的，丛状神经纤维瘤是主要的良性前体 NF1-MPNST病变。有观点认为，PNF是一种先天性病变，发生于 当神经脊干细胞分化为雪旺细胞(SC)谱系时，神经发育，从而产生 骨髓间充质干细胞或非髓鞘干细胞(MSCs或NMSCs)。在正常神经中，无髓鞘轴突 由NMSCs分类并包裹在单独的口袋中，形成Remak束。鉴于SC中没有缺陷 在神经发育的早期，NF1缺失(NF1-/-)会导致脑室缺失。 Remak束，以异常排列的无髓轴突为特征。这些不正常的Remak口袋 进展到轴突变性和分离的SCs异常增殖的阶段，导致 Pnf的形成。轴突变性可能通过导致神经损伤而促进PNF的形成 环境，这一概念得到了以下观察的支持：成熟干细胞中NF1的丢失不足以诱导 PNFS，除非发生神经损伤。将PNFS恶性转化为MPNSTs需要至少两个 其他基因改变：CDKN2A的顺序失活，然后是SUZ12或EED-2 多梳抑制复合体2(PRC2)的基本成分。PrC2催化组蛋白修饰 H3K27me3在整个基因组中抑制基因表达。具体观察到的PRC2丢失 MPNSTs，但在良性肿瘤中不存在，表明PRC2介导的H3K27me3通常会抑制表达 导致PNFS向MPNSTs恶变的致癌驱动因素。然而，EED/PRC2是 在正常的小鼠干细胞发育和髓鞘形成过程中是必不可少的。此外，EED/PRC2肿瘤的丧失 抑制子意外抑制损伤诱导的重编程干细胞的增殖，伴随 下调CDKN2a的表达。在这里，我们建议检验两个相关的假说：(1)发展 NF1-/-Remak袋缺陷及其相关的轴突变性(神经损伤)促使NF1-/-SCs形成PNFS 和(2)神经损伤反应诱导表观基因组开关，呈现重编程的PNF或SCs 通过CDKN2A和PRC2的顺序缺失而易发生恶变。我们将确定角色 NF1-MPNST形成中发育的Remak口袋缺陷(目标1)，研究肿瘤抑制 损伤诱导再编程干细胞的机制(目标2)，并基于 重编程干细胞中损伤诱导的表观基因组开关(目标3)。我们将识别伤害诱导和PRC2- 通过表观基因组学方法抑制MPNST形成的致癌驱动因素，开发协同治疗 使用高通量药物再利用筛选，并测试它们由GEM和患者衍生的临床前模型。

Project Abstract Individuals with neurofibromatosis type 1 (NF1) have an approximately 160-fold increased risk of developing malignant peripheral nerve sheath tumor (MPNST). As a leading cause of death for NF1 patients. MPNST has no effective therapy and thus there is an urgent need for new therapies. The dramatically increased risk of developing MPNSTs is caused by the presence of plexiform neurofibromas (PNFs), the major benign precursor lesion for NF1-MPNST. It has been proposed that PNFs are congenital lesions, arising from the early stages of nerve development when neural-crest stem cells differentiate into Schwann cell (SC) lineages, which give rise to either myelinating or nonmyelinating SCs (mSCs or nmSCs). In the normal nerve, unmyelinated axons are sorted and ensheathed by nmSCs into individual pockets, forming Remak bundles. Whereas no defect in SC precursors or mSCs was observed, Nf1 loss (Nf1-/-) during early nerve development induced a pocket defect in Remak bundles, characterized by abnormally sorted unmyelinated axons. These abnormal Remak pockets progress to a stage with axonal degeneration and abnormal proliferation of dissociated SCs, leading to the formation of PNFs. Axonal degeneration may contribute to PNF formation by inducing a nerve injury environment, a concept supported by the observation that Nf1 loss in mature SCs is not sufficient to induce PNFs unless an injury to the nerve occurs. Malignant transformation of PNFs to MPNSTs requires at least two additional genetic alterations: sequential inactivation of CDKN2A, and then either SUZ12 or EED - two essential components of Polycomb Repressive Complex 2 (PRC2). PRC2 catalyzes histone modification H3K27me3 to repress gene expression throughout the genome. Loss of PRC2 specifically observed in MPNSTs, but not in benign tumors, suggests that PRC2-mediated H3K27me3 normally represses expression of the oncogenic drivers responsible for malignant transformation of PNFs to MPNSTs. However, Eed/PRC2 is dispensable during normal mouse SC development and myelination. Further, loss of the Eed/PRC2 tumor suppressor unexpectedly inhibits proliferation of injury-induced reprogrammed SCs, accompanied by derepression of Cdkn2a expression. Here, we propose to test two related hypotheses: (1) the developmental Nf1-/- Remak pocket defect and its associated axonal degeneration (nerve injury) drive Nf1-/- SCs to form PNFs and (2) nerve injury response induces an epigenomic switch, rendering reprogrammed PNFs or SCs susceptible to malignant transformation by sequential loss of CDKN2A and PRC2. We will determine the role of the developmental Remak pocket defect in NF1-MPNST formation (Aim 1), investigate tumor suppressive mechanisms in injury-induced reprogramed SCs (Aim 2), and develop therapeutic strategies based on the injury-induced epigenomic switch in reprogrammed SCs (Aim 3). We will identify injury-induced and PRC2- repressed oncogenic drivers for MPNST formation via epigenomic approaches, develop synergistic therapies using a high-throughput drug repurposing screen, and test them GEM- and patient-derived preclinical models.