Genetic analysis of Primary Pulmonary Hypertension and possible involvement of Tbx genes via BMP signaling in the pathogenesis of PPH.

1.原发性肺动脉高压(PPH)是一种潜在的致死性疾病，在这种疾病中，骨形态发生蛋白II受体基因(BMPR2)的杂合突变已被发现。我们对71例日本PPH患者进行了BMPR2基因和ALK1基因的分子研究，其中包括7例家族性PPH患者(6个家系)。我们还对继发性肺动脉高压患者进行了分子研究。我们在27例(38%)PPH患者中发现了BMPR2基因突变，其中包括所有家族性PPH患者，而仅有1例SPH患者有BMPR2突变。此外，3例(4%)PPH患者和1例SPH患者被发现有ALK1突变。预计这些突变会导致密码子提前终止或高度保守的氨基酸残基被取代。我们还根据遗传背景分析了散发性PPH患者的发病年龄。有突变的患者的平均发病年龄明显比无突变的患者年轻，这表明PPH的发病有相当大的遗传易感性。此外，对家族性PPH家系成员的遗传分析显示外显率很低(每8名患者中就有1人最终发展为PPH)。基于这些结果，PPH存在相当大的遗传异质性，需要进一步的功能研究来确定肺高压的病理生理机制。我们利用可诱导的mTbx2错误表达的小鼠证明了Tbx2对心脏形态发生的重要作用。MTbx2过表达的小鼠在E9.5和E9.75出现了NPPA、Smpx、Gja5、Myh7和Myl7小室特异性基因表达的变化。此外，我们还发现，在心脏发生过程中，透明质酸合成酶2(Has2)在脑室中的表达上调。此外，我们还观察到mTbx2错误表达胚胎的心室肌细胞过度分泌HA。

1. Primary pulmonary hypertension (PPH) is a potentially lethal disorder, in which heterozygous mutations within the bone morphogenetic protein type II receptor gene (BMPR2) have been identified. We performed the molecular study of BMPR2 gene as well as ALK1 gene in 71 Japanese patients with PPH including 7 familial PPH cases (6 families), who visited the Division of Cardiology in NCVC. We also performed the molecular study in 64 cases with secondary pulmonary hypertension (SPH). We identified mutations of BMPR2 gene in 27 cases (38%) of patients with PPH, including all familial PPH cases, while only one patient with SPH was found to have BMPR2 mutation. Furthermore, three cases (4%) of patients with PPH and one with SPH were found to have ALK1 mutations. Those mutations are predicted to result in a premature termination codon or substitution of highly conserved amino acid residues. We also analyzed the age of onset among sporadic PPH patients according to genetic background. The mean age at onset was significantly younger in those with mutations than those without mutations, suggesting a considerable genetic predisposition underlying the pathogenesis of PPH. Furthermore, genetic analysis of family members of familial PPH revealed a very low penetrance (1 in 8 affected was eventually developed PPH) Based on these results, there is considerable genetic heterogeneity of PPH, and further functional study will be needed to identify pathophysiological mechanism of pulmonary hypertension.2. We demonstrate that Tbx2 is important for cardiac morphogenesis by using inducible mTbx2-misexpression mice. The mTbx2-overexpressing mice showed the changes of chamber-specific gene expression of Nppa, Smpx, Gja5,Myh7 and Myl7 at E9.5 and E9.75. In addition, we found the expression of Hyaluronan Synthase 2 (Has2) was upregulated in the ventricles during cardiogenesis. Also, we observed excessive HA secretion in the ventricular myocytes of mTbx2-misexpressing embryos.