Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, MD, USA.
PLoS One. 2012;7(11):e51078. doi: 10.1371/journal.pone.0051078. Epub 2012 Nov 30.
Activation state-dependent secretion of alpha-1 proteinase inhibitor (A1PI) by monocytes and macrophages was first reported in 1985. Since then, monocytes and tissue macrophages have emerged as key sentinels of infection and tissue damage via activation of self-assembling pattern recognition receptors (inflammasomes), which trigger inflammation and cell death in a caspase-1 dependent process. These studies examine the relationship between A1PI expression in primary monocytes and monocytic cell lines, and inflammatory cytokine expression in response to inflammasome directed stimuli.
IL-1 β expression was examined in lung macrophages expressing wild type A1PI (A1PI-M) or disease-associated Z isoform A1PI (A1PI-Z). Inflammatory cytokine release was evaluated in THP-1 monocytic cells or THP-1 cells lacking the inflammasome adaptor ASC, transfected with expression vectors encoding A1PI-M or A1PI-Z. A1PI-M was localized within monocytes by immunoprecipitation in hypotonic cell fractions. Cell-free titration of A1PI-M was performed against recombinant active caspase-1 in vitro.
IL-1 β expression was elevated in lung macrophages expressing A1PI-Z. Overexpression of A1PI-M in THP-1 monocytes reduced secretion of IL-1β and TNF-α. In contrast, overexpression of A1PI-Z enhanced IL-1β and TNF- α secretion in an ASC dependent manner. A1PI-Z-enhanced cytokine release was inhibited by a small molecule caspase-1 inhibitor but not by high levels of exogenous wtA1PI. Cytosolic localization of A1PI-M in monocytes was not diminished with microtubule-inhibiting agents. A1PI-M co-localized with caspase-1 in gel-filtered cytoplasmic THP-1 preparations, and was co-immunoprecipitated with caspase 1 from nigericin-stimulated THP-1 cell lysate. Plasma-derived A1PI inhibited recombinant caspase-1 mediated conversion of a peptide substrate in a dose dependent manner.
Our results suggest that monocyte/macrophage-expressed A1PI-M antagonizes IL-1β secretion possibly via caspase-1 inhibition, a function which disease-associated A1PI-Z may lack. Therapeutic approaches which limit inflammasome responses in patients with A1PI deficiency, in combination with A1PI augmentation, may provide additional respiratory tissue-sparing benefits.
1985 年首次报道了单核细胞和巨噬细胞中依赖激活状态的α-1 蛋白酶抑制剂（A1PI）分泌。此后，单核细胞和组织巨噬细胞通过自身组装的模式识别受体（炎性体）的激活而成为感染和组织损伤的关键哨兵，这些受体通过半胱天冬酶-1 依赖的过程触发炎症和细胞死亡。这些研究检查了原代单核细胞中 A1PI 表达与炎性体定向刺激反应中炎症细胞因子表达之间的关系。
检测表达野生型 A1PI（A1PI-M）或疾病相关 Z 同工型 A1PI（A1PI-Z）的肺巨噬细胞中 IL-1β 的表达。评估 THP-1 单核细胞或缺乏炎性体衔接子 ASC 的 THP-1 细胞中炎症细胞因子的释放，这些细胞转染了编码 A1PI-M 或 A1PI-Z 的表达载体。通过免疫沉淀在低渗细胞级分中定位 A1PI-M 在单核细胞内的位置。在体外，用细胞游离的 A1PI-M 对重组活性半胱天冬酶-1 进行滴定。
在表达 A1PI-Z 的肺巨噬细胞中，IL-1β 的表达升高。在 THP-1 单核细胞中过表达 A1PI-M 可减少 IL-1β 和 TNF-α 的分泌。相反，A1PI-Z 的过表达以 ASC 依赖性方式增强了 IL-1β 和 TNF-α 的分泌。小分子半胱天冬酶-1 抑制剂可抑制 A1PI-Z 增强的细胞因子释放，但不能抑制外源性 wtA1PI 的高水平。用微管抑制剂不会降低单核细胞中 A1PI-M 的细胞内定位。A1PI-M 在凝胶过滤的细胞质 THP-1 制剂中与半胱天冬酶-1 共定位，并从尼可地尔刺激的 THP-1 细胞裂解物中与半胱天冬酶 1 共免疫沉淀。血浆衍生的 A1PI 以剂量依赖的方式抑制重组半胱天冬酶-1 介导的肽底物的转化。
我们的结果表明，单核细胞/巨噬细胞表达的 A1PI-M 可能通过半胱天冬酶-1 抑制拮抗 IL-1β 分泌，而疾病相关的 A1PI-Z 可能缺乏这种功能。在 A1PI 缺乏症患者中限制炎性体反应的治疗方法，结合 A1PI 增强，可能会提供额外的呼吸组织保护益处。
