Significantly downregulated-gene list in RNA-seq.

Transcriptional response to changes in oxygen concentration is mainly controlled by hypoxia-inducible transcription factors (HIFs). Besides regulation of hypoxia-responsible gene expression, HIF-3α has recently been shown to be involved in lung development and in the metabolic process of fat tissue. However, the precise mechanism for such properties of HIF-3α is still largely unknown. To this end, we generated HIF3A gene-disrupted mice by means of genome editing technology to explore the pleiotropic role of HIF-3α in development and physiology. We obtained adult mice carrying homozygous HIF3A gene mutations with comparable body weight and height to wild-type mice. However, the number of litters and ratio of homozygous mutation carriers born from the mating between homozygous mutant mice was lower than expected due to sporadic deaths on postnatal day 1. HIF3A gene-disrupted mice exhibited abnormal configuration of the lung such as a reduced number of alveoli and thickened alveolar walls. Transcriptome analysis showed, as well as genes associated with lung development, an upregulation of stearoyl-Coenzyme A desaturase 1, a pivotal enzyme for fatty acid metabolism. Analysis of fatty acid composition in the lung employing gas chromatography indicated an elevation in palmitoleic acid and a reduction in oleic acid, suggesting an imbalance in distribution of fatty acid, a constituent of lung surfactant. Accordingly, administration of glucocorticoid injections during pregnancy resulted in a restoration of normal alveolar counts and a decrease in neonatal mortality. In conclusion, these observations provide novel insights into a pivotal role of HIF-3α in the preservation of critically important structure and function of alveoli beyond the regulation of hypoxia-mediated gene expression.

机体对氧浓度变化的转录应答主要由缺氧诱导转录因子（hypoxia-inducible transcription factors, HIFs）调控。除调控缺氧应答基因表达外，近期研究显示HIF-3α还参与肺发育及脂肪组织的代谢过程。然而，HIF-3α上述功能的确切机制仍未完全阐明。为此，我们借助基因组编辑技术（genome editing technology）构建了HIF3A基因敲除小鼠，以探究HIF-3α在发育及生理过程中的多效性作用。我们获得了纯合子HIF3A基因突变的成年小鼠，其体重与体高均与野生型小鼠（wild-type mice）相当。但通过纯合突变小鼠交配获得的产仔数以及纯合突变携带者的出生比例均低于预期，这是因为存在出生后第1天的散发性死亡事件。HIF3A基因敲除小鼠表现出肺结构异常，具体包括肺泡数量减少以及肺泡壁增厚。转录组分析（Transcriptome analysis）显示，除肺发育相关基因外，硬脂酰辅酶A去饱和酶1（stearoyl-Coenzyme A desaturase 1）——一种脂肪酸代谢关键酶——的表达显著上调。采用气相色谱法（gas chromatography）对肺组织脂肪酸组成进行分析，结果显示棕榈油酸（palmitoleic acid）水平升高，而油酸（oleic acid）水平降低，提示作为肺表面活性物质（lung surfactant）组成成分的脂肪酸分布失衡。据此，在妊娠期间给予糖皮质激素注射可使肺泡数量恢复至正常水平，并降低新生小鼠死亡率。综上，本研究结果为理解HIF-3α在维持肺泡关键结构与功能中的核心作用提供了新见解，该作用不限于缺氧介导的基因表达调控。