Department of Medical and Surgical Neonatology, Bambino Gesù Children's Hospital IRCCS, Rome, Italy.
Respir Res. 2011 Aug 25;12(1):115. doi: 10.1186/1465-9921-12-115.
Mutations of genes affecting surfactant homeostasis, such as SFTPB, SFTPC and ABCA3, lead to diffuse lung disease in neonates and children. Haploinsufficiency of NKX2.1, the gene encoding the thyroid transcription factor-1 (TTF-1)--critical for lung, thyroid and central nervous system morphogenesis and function--causes a rare form of progressive respiratory failure designated brain-lung-thyroid syndrome. Molecular mechanisms involved in this syndrome are heterogeneous and poorly explored. We report a novel TTF-1 molecular defect causing recurrent respiratory failure episodes in an infant.
The subject was an infant with severe neonatal respiratory distress syndrome followed by recurrent respiratory failure episodes, hypopituitarism and neurological abnormalities. Lung histology and ultrastructure were assessed by surgical biopsy. Surfactant-related genes were studied by direct genomic DNA sequencing and array chromatine genomic hybridization (aCGH). Surfactant protein expression in lung tissue was analyzed by confocal immunofluorescence microscopy. For kinetics studies, surfactant protein B and disaturated phosphatidylcholine (DSPC) were isolated from serial tracheal aspirates after intravenous administration of stable isotope-labeled (2)H(2)O and (13)C-leucine; fractional synthetic rate was derived from gas chromatography/mass spectrometry (2)H and (13)C enrichment curves. Six intubated infants with no primary lung disease were used as controls.
Lung biopsy showed desquamative interstitial pneumonitis and lamellar body abnormalities suggestive of genetic surfactant deficiency. Genetic studies identified a heterozygous ABCA3 mutation, L941P, previously unreported. No SFTPB, SFTPC or NKX2.1 mutations or deletions were found. However, immunofluorescence studies showed TTF-1 prevalently expressed in type II cell cytoplasm instead of nucleus, indicating defective nuclear targeting. This pattern has not been reported in human and was not found in two healthy controls and in five ABCA3 mutation carriers. Kinetic studies demonstrated a marked reduction of SP-B synthesis (43.2 vs. 76.5 ± 24.8%/day); conversely, DSPC synthesis was higher (12.4 vs. 6.3 ± 0.5%/day) compared to controls, although there was a marked reduction of DSPC content in tracheal aspirates (29.8 vs. 56.1 ± 12.4% of total phospholipid content).
Defective TTF-1 signaling may result in profound surfactant homeostasis disruption and neonatal/pediatric diffuse lung disease. Heterozygous ABCA3 missense mutations may act as disease modifiers in other genetic surfactant defects.
影响表面活性剂动态平衡的基因（如 SFTPB、SFTPC 和 ABCA3）的突变会导致新生儿和儿童出现弥漫性肺部疾病。甲状腺转录因子-1（TTF-1）基因 NKX2.1 的单倍体不足——对肺、甲状腺和中枢神经系统的形态发生和功能至关重要——导致一种罕见的进行性呼吸衰竭，称为脑肺甲状腺综合征。这种综合征涉及的分子机制具有异质性，研究还不够深入。我们报告了一种新的 TTF-1 分子缺陷，导致婴儿反复发生呼吸衰竭。
研究对象为一名患有严重新生儿呼吸窘迫综合征的婴儿，随后出现反复呼吸衰竭、垂体功能减退和神经异常。通过外科活检评估肺组织学和超微结构。直接对基因组 DNA 进行测序和 array 染色质基因组杂交（aCGH）来研究表面活性剂相关基因。通过共聚焦免疫荧光显微镜分析肺组织中表面活性剂蛋白的表达。为了进行动力学研究，在静脉注射稳定同位素标记的（2）H（2）O 和（13）C-亮氨酸后，从连续的气管抽吸物中分离出表面活性蛋白 B 和二软脂酰磷脂酰胆碱（DSPC）；通过气相色谱/质谱法（2）H 和（13）C 丰度曲线得出分数合成率。将 6 名无原发性肺部疾病的插管婴儿作为对照组。
肺活检显示脱屑性间质性肺炎和板层小体异常，提示存在遗传表面活性剂缺陷。基因研究发现了一种以前未报道过的杂合 ABCA3 突变，L941P。未发现 SFTPB、SFTPC 或 NKX2.1 突变或缺失。然而，免疫荧光研究表明 TTF-1 主要在 II 型细胞细胞质中表达，而不是在细胞核中，表明核靶向存在缺陷。这种模式在人类中尚未有报道，在 2 名健康对照者和 5 名 ABCA3 突变携带者中也未发现。动力学研究表明 SP-B 合成显著减少（43.2 比 76.5±24.8%/天）；相反，DSPC 合成较高（12.4 比 6.3±0.5%/天），与对照组相比，尽管气管抽吸物中的 DSPC 含量明显减少（总磷脂含量的 29.8 比 56.1±12.4%）。
TTF-1 信号传导缺陷可能导致严重的表面活性剂动态平衡破坏和新生儿/儿科弥漫性肺部疾病。杂合 ABCA3 错义突变可能在其他遗传表面活性剂缺陷中作为疾病修饰因子。
