Alpha-1-antitrypsin binds to the glucocorticoid receptor with anti-inflammatory and anti-mycobacterial significance in macrophages

Alpha-1-antitrypsin (AAT), a serine protease inhibitor produced mainly by the liver, is the third most abundant protein in plasma. Individuals who possess homozygous Z-AAT genotype have severe AAT deficiency and are at risk for early-onset emphysema, bronchiectasis, cirrhosis, panniculitis, and vasculitis. While a canonical receptor for AAT has not been identified, AAT can be internalized into the cytoplasm and is known to affect gene regulation. Since AAT has significant anti-inflammatory properties affecting many cell types including macrophages, we examined whether AAT binds the cytoplasmic glucocorticoid receptor (GR) in macrophages. We report the novel finding that AAT binds to GR in macrophages using several approaches, including co-immunoprecipitation, mass spectrometry, microscale thermophoresis, and in silico molecular modeling. We further demonstrate that AAT induction of angiopoietin-like 4 protein and AAT inhibition of lipopolysaccharide-induced nuclear factor-kappa B activation and interleukin-8 production are mediated, in part, through AAT–GR interaction. Furthermore, this interaction contributes to a host-protective role against Mycobacterium tuberculosis in macrophages. The interaction of AAT and GR described in this study identifies a mechanism for the anti-inflammatory and host-protective properties of AAT.

α1-抗胰蛋白酶（Alpha-1-antitrypsin, AAT）是一类主要由肝脏合成的丝氨酸蛋白酶抑制剂，亦是血浆中丰度位列第三的蛋白质。携带纯合子Z-AAT基因型的个体可出现严重的AAT缺乏症，且罹患早发性肺气肿、支气管扩张、肝硬化、脂膜炎及血管炎的风险显著升高。尽管目前尚未鉴定出AAT的经典受体，但已知AAT可被内化进入细胞质，并参与基因表达调控。鉴于AAT具有显著的抗炎活性，可作用于包括巨噬细胞在内的多种细胞类型，本研究探讨了AAT是否可结合巨噬细胞中的胞质糖皮质激素受体（glucocorticoid receptor, GR）。本研究通过免疫共沉淀、质谱分析、微量热泳动及计算机分子建模等多种实验手段，首次证实AAT可在巨噬细胞中与GR结合。进一步实验表明，AAT诱导血管生成素样4蛋白表达，以及AAT抑制脂多糖诱导的核因子-κB激活与白细胞介素-8生成的过程，部分依赖于AAT与GR的相互作用。此外，该相互作用可在巨噬细胞中发挥对抗结核分枝杆菌的宿主保护功能。本研究揭示的AAT与GR的相互作用机制，为阐明AAT的抗炎及宿主保护特性提供了分子基础。