MOLECULAR BIOLOGY OF THE MARFAN SYNDROME

马凡综合征(MFS)是一种主要的结缔组织疾病，患病率约为1/5000。临床表现涉及眼部、骨骼、心血管和肺部系统。编码纤维蛋白-1(FBN1)的基因突变是细胞外微纤维的主要成分，可引起MFS。普遍的观点认为，微纤维调节着胎儿晚期原弹性蛋白的沉积。基因决定的微纤维缺陷将导致弹性形成失败，从而导致主动脉壁固有的虚弱。通过靶向基因破坏建立的纤维蛋白-1缺陷小鼠品系的特征表明，尽管微纤维在数量和质量上都存在严重的异常，但在主动脉中膜中仍有完整和延伸的弹性板层。在弹性纤维断裂之前，有一个可预测的致病序列，包括强烈的血管平滑肌细胞(VSMC)纤维增殖反应和炎症介导的弹性蛋白酶的募集和激活。我们假设，正常情况下由微纤维介导的基质细胞附着的丢失会引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潜能细胞因子TGFbeta的失调来预测的。微纤维基质被认为隔离了潜在的转化生长因子β，从而通过细胞表面相关因子调节其激活。TGFβ活性的病理性上调也与我们在Fbn1(-/-)小鼠中观察到的肺泡分支形态发生的原发失败是一致的。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记来全面表征SMC的表型。我们将使用敏感和特异的转化生长因子β反应报告基因和针对活跃形式和潜伏形式的抗体来仔细研究转化生长因子β在血管和肺部疾病中的作用。对分化的VSMC和肺成纤维细胞靶向过度表达TGFβ的表型后果的分析将确定这种失调是否足以用于疾病的发病机制。我们将评估转化生长因子β中和抗体在器官培养中挽救肺分支形态发生的能力。过表达一种有效的金属蛋白酶组织抑制物(TIMP)的纤维蛋白-1缺陷系的特征将决定药理上的弹性蛋白酶抑制物是否对MFS的自然历史具有调节作用。结果将与在Fbn1显性负等位基因杂合子小鼠身上观察到的结果相关联，这是一种概括人类状况的机制。

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.