Cigarette smoke-induced lung pathology in SMP30 knockout mice

衰老标志物蛋白-30(SMP3O)最初被认为是一种新的蛋白质，其在大鼠肝脏中的表达随着年龄的增长而减少，其表达方式与雄激素无关，具有保护细胞免受凋亡的作用。逆转录-聚合酶链式反应(RT-PCR)分析发现，SMP30在小鼠肺、肝、肾、睾丸和大脑中均有转录。我们研究了衰老过程中SMP30在C57/BL6小鼠肺、肾和肝脏中的表达，发现SMP30在每个组织中的表达具有明显的时间分布。在肺组织中，SMP30基因的表达水平在出生后逐渐升高，在12月龄时达到高峰，之后下降。为了探讨SMP30在肺组织中的生理作用，对野生型(SMP30Y/+)小鼠进行了免疫组织化学研究，并对SMP30基因敲除(SMP30Y/-)小鼠进行了组织病理学检查。抗SMP30抗体免疫反应主要见于支气管上皮细胞，6~12月龄时阳性反应最强。肺的Clara细胞、肺泡巨噬细胞和浆细胞也呈阳性免疫染色。用形态计量学方法测量SMP30Y/-小鼠的平均线截距(MLI)和破坏指数(DI)，发现与SMP30Y/+小鼠相比，SMP30Y/-小鼠在1月龄、3月龄和6月龄时周围肺泡扩张而无肺泡破坏。当3月龄的野生型(SMP30Y/+)和SMP30Y/-小鼠暴露于1%香烟烟雾(IRI研究用香烟)1个月时，SMP30Y/-小鼠的MLI显著高于车辆对照组，而野生型(SMP30Y/+)小鼠的MLI无明显变化。我们的结果有力地表明SMP30Y/-小鼠可能是一种新的老年肺模型，并可能成为香烟烟雾暴露时肺气肿的模型。对SMP30Y/-小鼠的进一步检测可能为阐明老年肺部疾病的发生机制提供线索。

Senescence marker protein-30 (SMP3O) was originally identified as a novel protein of which expression decreases androgen-independent manner with aging in the rat liver and functions to protect cells from apoptosis. By reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, SMP30 mRNA transcripts were found in the mouse lung, liver, kidney, testis and cerebrum. We examined SMP30 expression in the C57/BL6 mouse lung, kidney, and liver during aging and a distinct temporal profile of SMP30 expression was found in each tissues. In the lungs, SMP30 mRNA level gradually increased after birth, peaked at 12 month old, and decreased thereafter. To investigate physiological role of SMP30 in the lung, immunohistochemical studies of wild-type (SMP30Y/+) mice and histopathological examinations of SMP30 knockout (SMP30Y/-) mice were performed. Immunoreactivity against anti-SMP30 antibody was mainly detected in bronchial epithelial cells and strongly detected at 6 to 12 months old. Positive immunostaining was also demonstrated in Clara cells, alveolar macrophages, and plasma cells in the lung. The morphometric analysis was performed to measure mean linear intercept (MLI) and destructive index (DI) and found peripheral airspace enlargement without alveolar destruction in SMP30Y/-mice at 1, 3 and 6 months old compared with that in SMP30Y/+ mice. When wild-type (SMP30Y/+) and SMP30Y/-mice at 3 months of age were exposed to 1% cigarette smoke (iRi research cigarette) for 1 month, MLI significantly increased as compared with vehicle control in SMP30Y/-mice, but not in wild-type (SMP30Y/+) mice. Our results strongly suggest that SMP30Y/-mouse could be a novel model for a senile lung and become a model for emphysema when exposed to cigarette smoke. Further examinations of SMP30Y/-mice may offer clues to elucidate the mechanisms of the development of pulmonary diseases in the elderly.