Stromal catalase deficiency as the causative factor in accelerated thymic atrophy

描述（由申请人提供）：像所有的血细胞一样，T淋巴细胞在生命过程中不断丢失，必须不断补充。胸腺是T淋巴细胞生成的主要部位。然而，胸腺的特征是加速的、与年龄相关的萎缩，导致新的（幼稚的）T淋巴细胞产生随着年龄的增长而进行性下降。虽然预先存在的T淋巴细胞的复制防止淋巴细胞减少症的出现，但这些主要是记忆T细胞。因此，对新的免疫挑战（如新出现的病毒株）的反应能力随着年龄的增长而下降，对疫苗接种的反应也是如此。胸腺加速老化的机制还没有很好地解决，但现在很清楚，这主要是一个基质表型。我们最近发表了一种新的方法，胸腺基质基因表达原位表征，提供了前所未有的看法，基质生物学，并揭示了许多见解，其性质。一个意想不到的发现是，胸腺基质细胞缺乏参与保护免受活性氧（ROS）引起的损伤的关键酶，以及修复这种损伤的几种酶。最值得注意的是，胸腺基质细胞似乎是深刻缺乏过氧化氢酶，一个主要的清除剂过氧化氢。由于胸腺基质细胞的寿命相对较长，并且存在于以强烈的代谢活性为特征的微环境中（与淋巴母细胞祖细胞增殖相关），因此预计ROS损伤的保护/修复缺陷将导致功能、活力和复制能力的加速下降以及萎缩的出现。我们的中心假设是，上皮基质细胞的胸腺是非常敏感的ROS凭借这些酶的缺陷，胸腺萎缩是加速积累的代谢损伤的结果。在本申请中，我们提出了强有力的生物化学和遗传数据来支持这一假设，并提出了进一步证明这一点的实验，包括显示过氧化氢酶的遗传替代，特别是在上皮细胞中， 胸腺基质足以防止萎缩，胸腺的上皮基质细胞在体内比其它年龄和/或谱系匹配的细胞积累更多的损伤，分离的胸腺上皮细胞比其它年龄和/或谱系匹配的细胞对ROS更敏感，并且修复机制的缺陷加剧了胸腺上皮细胞中过氧化氢酶缺陷的后果。这些研究有望揭示加速胸腺萎缩的机制，并可能提出减少或预防这种病理状态的方法。

DESCRIPTION (provided by applicant): Like all blood cells, T lymphocytes are constantly lost during life, and must be continuously replaced. The thymus is the primary site of T lymphopoiesis. However, the thymus is characterized by an accelerated, age-related atrophy, leading to a progressive decline in new (na¿ve) T lymphocyte production with age. Although replication of pre-existing T lymphocytes prevents the appearance of lymphopenia, these are mostly memory T cells. Consequently, the ability to respond to new immunological challenges, such as emerging viral strains, decreases with age, as does response to vaccination. The mechanisms for accelerated thymic aging are not well resolved, but it is now clear that it is primarily a stromal phenotype. We have recently published a novel approach for the characterization of thymic stromal gene expression in situ, providing an unprecedented view of stromal biology, and revealing many insights into their nature. One unexpected finding was that thymic stromal cells are deficient in key enzymes involved in protection from damage caused by reactive oxygen species (ROS), as well as several enzymes that repair that damage. Most notably, thymic stromal cells appear to be profoundly deficient in catalase, a major scavenger of H2O2. Since thymic stromal cells are relatively long-lived, and exist in a microenvironment characterized by intense metabolic activity (associated with lymphoblastic progenitor proliferation), defects in protection from / repair of ROS damage would be expected to result in an accelerated decline in function, viability, and replicative ability, and the appearance of atrophy. Our central hypothesis is that epithelial stromal cells of the thymus are exquisitely sensitive to ROS by virtue of these enzyme deficiencies, and that thymic atrophy is a consequence of accelerated accumulation of metabolic damage. In this application, we present powerful biochemical and genetic data to support this hypothesis, and propose experiments to further prove it, including showing that genetic replacement of catalase specifically in epithelial stroma of the thymus is sufficient to prevent atrophy, that epithelial stromal cells of the thymus accumulate more damage in vivo than other age- and/or lineage-matched cells, that isolated thymic epithelial cells are more sensitive to ROS than other age- and/or lineage-matched cells, and that deficiencies in repair mechanisms exacerbate the consequences of catalase deficiency in thymic epithelial cells. These studies are expected to reveal the mechanism of accelerated thymic atrophy, and may suggest approaches to reduce or prevent this pathological state.