MOLECULAR BIOLOGY OF THE MARFAN SYNDROME

马凡氏综合征（MFS）是一种显性结缔组织疾病，患病率约为1/5000。 表现涉及眼、骨骼、心血管和肺系统。编码细胞外微纤维的主要成分--纤维蛋白1（FBN 1）的基因突变会导致MFS。 流行的观点是，微纤维调节胎儿后期弹性蛋白原的沉积。 遗传决定的微纤维缺乏会导致弹性纤维发生失败，从而导致主动脉壁的固有弱点。通过靶向基因破坏产生的Escherin-1缺陷小鼠系的表征显示，尽管微纤维的严重定量和定性异常，但主动脉中膜中的弹性膜完整且延伸。弹性纤维的碎片之前，一个可预测的发病顺序，包括强烈的纤维增殖反应的血管平滑肌细胞（VSMC）和炎症介导的招聘和激活的弹性蛋白酶。我们推测，通常由微纤维介导的基质细胞附着的丧失触发异常的细胞分化和行为。 或者，这种异常的细胞表型是通过多能细胞因子TGF β的失调来预测的。 微纤维基质被认为隔离潜伏的TGF β，从而通过细胞表面相关因子调节其活化。 TGF β活性的病理性上调也与我们观察到的Fbn 1（-/-）小鼠肺泡分支形态发生的原发性失败一致。 我们建议通过原位分析表达的转录本、分泌的蛋白和表面标志物来全面表征SMC表型。 我们将使用敏感和特异的TGF β反应性报告基因和对活性和潜伏形式特异的抗体来仔细检查TGF β在血管和肺部疾病中的作用。 分析TGF β在分化的VSMC和肺肌成纤维细胞中靶向过表达的表型结果将确定这种失调是否足以导致疾病的发病机制。 我们将评估TGF β中和抗体在器官培养中拯救肺分支形态发生的能力。过表达金属蛋白酶的有效组织抑制剂（TIMP）的Escherin-1缺陷系的表征将确定药理学弹性蛋白酶抑制剂是否有希望用于MFS的自然史的调节。结果将与在显性阴性Fbn 1等位基因杂合子小鼠中观察到的结果相关，这是一种重现人类状况的机制。

Marfan syndrome (MFS) is a dominant disorder of connective tissue with a prevalence of about 1 in 5,000. Manifestations involve the ocular, skeletal, cardiovascular and pulmonary systems. Mutations in the gene encoding fibrillin-1 (FBN1), the major constituent of extracellular microfibrils, cause MFS. The prevailing view has been that microfibrils regulate the deposition of tropoelastin in late fetal life. A genetically determined deficiency of microfibrils would result in failed elastogenesis and hence inherent weakness of the aortic wall. Characterization of fibrillin-1 deficient mouse lines that were created by targeted gene disruption revealed intact and extended elastic lamellae in the aortic media despite a severe quantitative and qualitative abnormality of microfibrils. Fragmentation of elastic fibers was preceded by a predictable pathogenetic sequence that included an intense fibroproliferative response of vascular smooth muscle cells (VSMC) and inflammation-mediated recruitment and activation of elastases. We hypothesize that loss of matrix-cell attachments that are normally mediated by microfibrils trigger abnormal cellular differentiation and behavior. Alternatively, this abnormal cellular phenotype is predicted by dysregulation of the multipotential cytokine TGFbeta. The microfibrillar matrix is believed to sequester latent TGFbeta, thus regulating its activation by cell surface-associated factors. A pathologic upregulation of TGFbeta activity is also consistent with our observed primary failure of alveolar branching morphogenesis in Fbn1 (-/-) mice. We propose comprehensive characterization of SMC phenotype through in situ analysis of expressed transcripts, secreted proteins and surface markers. We will scrutinize the role of TGFbeta in vascular and pulmonary disease using a sensitive and specific TGFbeta-responsive reporter transgene and antibodies specific to the active and latent forms. Analysis of the phenotypic consequences of targeted overexpression of TGFbeta in differentiated VSMC and pulmonary myofibroblasts will determine whether this dysregulation is sufficient for disease pathogenesis. We will assess the ability of TGFbeta-neutralizing Ab to rescue lung branching morphogenesis in organ culture. Characterization of a fibrillin-1 deficient line that overexpresses a potent tissue inhibitor of metalloproteinases (TIMP) will determine whether pharmacologic elastase inhibitors hold promise for the modulation of the natural history of MFS. Results will be correlated with those observed in mice heterozygous for a dominant-negative Fbn1 allele, a mechanism that recapitulates the human condition.