Mouse Models of Cerebral Arteriovenous Malformation.
Mouse Models of Cerebral Arteriovenous Malformation.
复制标题
小鼠脑动静脉畸形模型。
DOI：
10.1161/strokeaha.115.002869
复制
发表时间：
2016
期刊：
影响因子：
8.3
通讯作者：
Wang,RongA
中科院分区：
文献类型：
--
作者：
Nielsen,CorinneM;Huang,Lawrence;Murphy,PatrickA;Lawton,MichaelT;Wang,RongA
这些致病突变的鉴定为今后发现AVM的分子途径提供了希望。用Eng（HHT 1）和Alk 1（HHT 2）基因中的靶向突变改造实验小鼠模型。Eng或Alk 1基因敲除表现出胚胎血管缺陷，包括扩张和融合的动脉-静脉对，并在子宫内死亡。42，43 Eng+/−或Alk 1 +/−杂合子小鼠存活，并在成年期出现HHT特征; 10-13然而，BAVM的特征，包括AV分流、扩张血管的病灶和圆形、错位的EC核，发生在30%的25 - 40周龄Eng+/−小鼠中，与HHT 1患者的BAVM发生率相似。12因此，Eng或Alk 1的1个等位基因的缺失足以在成年小鼠中诱导BAVM，但具有不完全的迁移率。Eng+/−和Alk 1 +/−小鼠中的不完全突变和局灶性BAVM发展导致以下假设：这些遗传扰动需要AVM形成中的第二次打击-一个确证过程或遗传病变。来自人类BAVM患者的数据支持二次命中假说：（1）BAVM通常出现在青春期或成年期，即使患者携带生殖系突变44;（2）人类AVM附近的高水平血管生成信号表明AVM可能由血管生成触发45;（3）在RASA 1介导的AVM中观察到杂合性的体细胞丢失。46基因干扰导致未成熟/重塑但不成熟/静止小鼠大脑中的BAVM的发现提供了第一个实验证据，即血管生成重塑可能是AVM形成的许可因素。26，28两类二次命中候选者都已探索，导致BAVM形成的更稳健和更易处理的模型。血管内皮生长因子（VEGF）的局部递送导致Eng+/−或Alk 1 +/−小鼠的局部血管发育不良。将重组人VEGF注射到Eng+/−脑中会导致微血管异常，包括血管扩大、迂曲和聚集，潜伏期为2- 4周，潜伏期为89%。14类似地，将局灶性腺病毒VEGF递送到Eng+/−和Alk 1 +/−成年小鼠的大脑皮层中，导致毛细血管异常增大和毛细血管密度增加，潜伏期为6周。[15]值得注意的是，Eng+/−小鼠的血管缺陷比Alk 1 +/−小鼠更严重。15总之，这些研究支持VEGF诱导的血管生成刺激可能是Eng+/−和Alk 1 +/−小鼠血管发育不良的第二次打击。体细胞杂合性缺失增加AVM形成的假设已经通过使用组织特异性、时间基因缺失的遗传工具进行了实验测试。在表达Alk 1的细胞亚群中，胚胎中Alk 1的两个等位基因缺失导致妊娠晚期或出生后脑（图2A）、肺和肠中AVM致死（图17、18、20）。16，17然而，使用R26-CreERT 2从成年小鼠中缺失Alk 1的他莫昔芬依赖性导致肺和肠AVM，但不足以诱导BAVM。17总之，这些研究表明，两个Alk 1等位基因的缺失足以在发育期间诱导BAVM，但在成年期不会。局部血管生成刺激和Alk 1或Eng缺失的组合促进成年小鼠BAVM的形成（参见表）。Alk 1或Eng缺失，加上VEGF给药，导致AVM体征，包括扩大和发育不良的血管（图2B和2C），18-21 AV分流，18，20不规则血管聚集，18，20和微出血。20，23这些研究表明，Alk 1或Eng等位基因的缺失，与血管生成刺激相结合，可能导致AVM形成。
Identification of these causal mutations holds promise for future discovery of molecular pathways attributable to AVMs. Experimental mouse models were engineered with targeted mutations in the Eng (HHT1) and Alk1 (HHT2) genes. Eng or Alk1 knockouts exhibit embryonic vascular defects, including dilated and fused artery–vein pairs and die in utero. 42, 43 Eng+/− or Alk1+/− heterozygous mice are viable and develop characteristics of HHT during adulthood; 10–13 however, features of BAVM, including AV shunts, niduses of dilated vessels, and rounded, misaligned EC nuclei, occur in 30% of Eng+/− mice aged 25 to 40 weeks, similar to BAVM incidence in HHT1 patients. 12 Thus, loss of 1 allele of Eng or Alk1 is sufficient to induce BAVM in adult mice, but with incomplete penetrance. The incomplete penetrance and focal BAVM development in Eng+/− and Alk1+/− mice led to the hypothesis that these genetic perturbations require a second hit—a corroborating process or genetic lesion—in AVM formation. Data from human BAVM patients support the second hit hypothesis:(1) BAVM typically presents in adolescence or adulthood, even though patients harbor germline mutations44;(2) a high level of angiogenic signaling near human AVM suggests that AVM may be triggered by angiogenesis45;(3) somatic loss of heterozygosity has been observed in RASA1-mediated AVMs. 46 The finding that a genetic perturbation leads to BAVM in immature/remodeling but not mature/quiescent mouse brains provides the first experimental evidence that angiogenic remodeling may be a permissive factor for AVM formation. 26, 28 Both classes of second hit candidates have been explored, resulting in more robust and tractable models of BAVM formation. Local delivery of vascular endothelial growth factor (VEGF) results in local vascular dysplasia in Eng+/− or Alk1+/− mice. Recombinant human VEGF injection into Eng+/− brains leads to microvascular abnormalities, including enlarged, tortuous, and clustered vessels, with 89% penetrance and 2-to 4-week latency. 14 Similarly, focal adenoviral VEGF delivery into the cerebral cortex of Eng+/− and Alk1+/− adult mice results in abnormally enlarged capillaries and increased capillary density, with 6-week latency. 15 Notably, vascular defects are more profound in Eng+/− mice than in the Alk1+/− mice. 15 Together, these studies support the possibility that VEGF-induced angiogenic stimulus can be a second hit for vascular dysplasia in Eng+/− and Alk1+/− mice. The hypothesis that a somatic loss of heterozygosity increases AVM formation has been experimentally tested using genetic tools for tissue-specific, temporal gene deletion. Deletion of both alleles of Alk1 from embryos in a subset of Alk1 expressing cells results in late gestational or postnatal lethality with AVMs in the brain (Figure 2A), 17, 18, 20 lung, and intestine. 16, 17 However, tamoxifen-dependent deletion of Alk1 from adult mice using R26-CreERT2 results in lung and intestinal AVMs, but is insufficient to induce BAVMs. 17 Together, these studies suggest that deletion of both Alk1 alleles is sufficient to induce BAVM during development, but not during adulthood.Combination of local angiogenic stimulus and Alk1 or Eng deletion promotes BAVM formation in adult mice (refer to Table). Deletion of Alk1 or Eng, coupled with VEGF administration, results in signs of AVM, including enlarged and dysplastic vessels (Figure 2B and 2C), 18–21 AV shunting, 18, 20 irregular vessel aggregates, 18, 20 and microhemorrhage. 20, 23 These studies show that the loss of either Alk1 or Eng alleles, in conjunction with angiogenic stimulation, may lead to AVM formation.