Stromal catalase deficiency as the causative factor in accelerated thymic atrophy

描述（由申请人提供）：与所有血细胞一样，T淋巴细胞在生命中会不断丢失，必须不断被替换。胸腺是T淋巴产生的主要部位。然而，胸腺的特点是加速的，与年龄相关的萎缩，导致新的（na¿ve） T淋巴细胞产量随着年龄的增长而逐渐下降。虽然先前存在的T淋巴细胞的复制可以防止淋巴细胞减少的出现，但这些大多是记忆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。加速胸腺衰老的机制还没有很好地解决，但现在很清楚，它主要是一种基质表型。我们最近发表了一种表征胸腺基质基因原位表达的新方法，为基质生物学提供了前所未有的视角，并揭示了对其性质的许多见解。一个意想不到的发现是胸腺基质细胞缺乏保护免受活性氧（ROS）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，胸腺基质细胞似乎严重缺乏过氧化氢酶，过氧化氢酶是H2O2的主要清除剂。由于胸腺基质细胞寿命相对较长，并且存在于以强烈代谢活动（与淋巴母细胞祖细胞增殖有关）为特征的微环境中，因此对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，并出现萎缩。我们的中心假设是胸腺上皮间质细胞由于这些酶缺乏而对活性氧非常敏感，胸腺萎缩是代谢损伤加速积累的结果。在本应用中，我们提供了强有力的生化和遗传学数据来支持这一假设，并提出了进一步证明这一假设的实验，包括表明过氧化氢酶在上皮中特异性的遗传替代

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.