Division of Dermatology, Department of Medicine, David Geffen School of Medicine at University of California, Los Angeles, CA 90095.
Department of Molecular, Cell, and Developmental Biology, University of California, Los Angeles, CA 90095.
J Immunol. 2014 Mar 1;192(5):2280-2290. doi: 10.4049/jimmunol.1301686. Epub 2014 Feb 5.
A role for vitamin A in host defense against Mycobacterium tuberculosis has been suggested through epidemiological and in vitro studies; however, the mechanism is unclear. In this study, we demonstrate that vitamin A-triggered antimicrobial activity against M. tuberculosis requires expression of NPC2. Comparison of monocytes stimulated with all-trans retinoic acid (ATRA) or 1,25-dihydroxyvitamin D3 (1,25D3), the biologically active forms of vitamin A and vitamin D, respectively, indicates that ATRA and 1,25D3 induce mechanistically distinct antimicrobial activities. Stimulation of primary human monocytes with ATRA did not result in expression of the antimicrobial peptide cathelicidin, which is required for 1,25D3 antimicrobial activity. In contrast, ATRA triggered a reduction in the total cellular cholesterol concentration, whereas 1,25D3 did not. Blocking ATRA-induced cellular cholesterol reduction inhibits antimicrobial activity as well. Bioinformatic analysis of ATRA- and 1,25D3-induced gene profiles suggests that NPC2 is a key gene in ATRA-induced cholesterol regulation. Knockdown experiments demonstrate that ATRA-mediated decrease in total cellular cholesterol content and increase in lysosomal acidification are both dependent upon expression of NPC2. Expression of NPC2 was lower in caseous tuberculosis granulomas and M. tuberculosis-infected monocytes compared with normal lung and uninfected cells, respectively. Loss of NPC2 expression ablated ATRA-induced antimicrobial activity. Taken together, these results suggest that the vitamin A-mediated antimicrobial mechanism against M. tuberculosis requires NPC2-dependent expression and function, indicating a key role for cellular cholesterol regulation in the innate immune response.
维生素 A 对宿主防御结核分枝杆菌的作用已通过流行病学和体外研究得到证实；然而，其机制尚不清楚。在这项研究中，我们证明了维生素 A 触发的针对结核分枝杆菌的抗菌活性需要 NPC2 的表达。比较单核细胞用全反式视黄酸（ATRA）或 1,25-二羟维生素 D3（1,25D3）刺激，分别是维生素 A 和维生素 D 的生物活性形式，表明 ATRA 和 1,25D3 诱导了机制上不同的抗菌活性。用 ATRA 刺激原代人单核细胞不会导致抗菌肽 cathelicidin 的表达，而这是 1,25D3 抗菌活性所必需的。相反，ATRA 引发了细胞总胆固醇浓度的降低，而 1,25D3 则没有。阻断 ATRA 诱导的细胞胆固醇减少也会抑制抗菌活性。对 ATRA 和 1,25D3 诱导的基因谱的生物信息学分析表明，NPC2 是 ATRA 诱导的胆固醇调节中的关键基因。敲低实验表明，ATRA 介导的总细胞胆固醇含量降低和溶酶体酸化增加都依赖于 NPC2 的表达。与正常肺和未感染细胞相比，干酪样结核肉芽肿和结核分枝杆菌感染的单核细胞中 NPC2 的表达较低。NPC2 表达的丧失使 ATRA 诱导的抗菌活性丧失。总之，这些结果表明，维生素 A 介导的针对结核分枝杆菌的抗菌机制需要 NPC2 依赖的表达和功能，表明细胞胆固醇调节在固有免疫反应中起着关键作用。
