Aims: Normal lungs do not express alpha-Klotho (Klotho) protein but derive cytoprotection from circulating soluble Klotho. It is unclear whether chronic supranormal Klotho levels confer additional benefit. To address this, we tested the age-related effects of Klotho overexpression on acute lung injury (ALI) and recovery. Methods: Transgenic Klotho-overexpressing (Tg-Kl) and wild-type (WT) mice (2 and 6 months old) were exposed to hyperoxia (95% O₂; 72 h) then returned to normoxia (21% O₂; 24 h) (Hx-R). Control mice were kept in normoxia. Renal and serum Klotho, lung histology, and bronchoalveolar lavage fluid oxidative damage markers were assessed. Effects of hyperoxia were tested in human embryonic kidney cells stably expressing Klotho. A549 lung epithelial cells transfected with Klotho cDNA or vector were exposed to cigarette smoke; lactate dehydrogenase and double-strand DNA breaks were measured. Results: Serum Klotho decreased with age. Hyperoxia suppressed renal Klotho at both ages and serum Klotho at 2-months of age. Tg-Kl mice at both ages and 2-months-old WT mice survived Hx-R; 6-months-old Tg-Kl mice showed lower lung damage than age-matched WT mice. Hyperoxia directly inhibited Klotho expression and release in vitro; Klotho transfection attenuated cigarette smoke-induced cytotoxicity and DNA double-strand breaks in lung epithelial cells. Conclusions: Young animals with chronic high baseline Klotho expression are more resistant to ALI. Chronic constitutive Klotho overexpression in older Tg-Kl animals attenuates hyperoxia-induced lung damage and improves survival and short-term recovery despite an acute reduction in serum Klotho level during injury. We conclude that chronic enhancement of Klotho expression increases resilience to ALI.

中文翻译：

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组成型转基因 α-Klotho 过表达增强小鼠急性肺损伤的恢复力和恢复能力

目的：正常肺不表达 α-Klotho (Klotho) 蛋白，但从循环可溶性 Klotho 中获得细胞保护。目前尚不清楚慢性超常 Klotho 水平是否会带来额外的好处。为了解决这个问题，我们测试了 Klotho 过度表达对急性肺损伤 (ALI) 和恢复的年龄相关影响。方法：转基因 Klotho 过表达 (Tg-Kl) 和野生型 (WT) 小鼠（2 个月和 6 个月大）暴露于高氧（95% O ₂；72 小时），然后恢复到常氧（21% O ₂; 24 小时) (Hx-R)。对照小鼠保持在常氧环境中。评估了肾脏和血清 Klotho、肺组织学和支气管肺泡灌洗液氧化损伤标志物。在稳定表达 Klotho 的人胚胎肾细胞中测试了高氧的影响。转染 Klotho cDNA 或载体的 A549 肺上皮细胞暴露于香烟烟雾中；测定乳酸脱氢酶和双链 DNA 断裂。结果：血清 Klotho 随着年龄的增长而下降。高氧抑制了两个年龄的肾 Klotho 和 2 个月大的血清 Klotho。Tg-Kl 小鼠和 2 个月大的 WT 小鼠在 Hx-R 中存活；6 个月大的 Tg-K1 小鼠的肺损伤低于年龄匹配的 WT 小鼠。高氧在体外直接抑制Klotho的表达和释放；Klotho 转染减弱了香烟烟雾诱导的肺上皮细胞中的细胞毒性和 DNA 双链断裂。结论：具有慢性高基线 Klotho 表达的年轻动物对 ALI 更具抵抗力。尽管在损伤期间血清 Klotho 水平急剧下降，但老年 Tg-Kl 动物中的慢性组成型 Klotho 过表达减轻了高氧诱导的肺损伤并提高了存活率和短期恢复。我们得出结论，Klotho 表达的慢性增强增加了对 ALI 的恢复能力。