Yan Wu1, Yacheng Zhang1, Jie Zhang1, Tingting Zhai1, Jingping Hu1, Hairong Luo1, Haiyan Zhou1, Qinghai Zhang1, Zhiguang Zhou2, Feng Liu3. 1. Department of Metabolism and Endocrinology, the Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, China; National Clinical Research Center for Metabolic Diseases, Key Laboratory of Diabetes Immunology, Ministry of Education, Metabolic Syndrome Research Center, the Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, China. 2. Department of Metabolism and Endocrinology, the Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, China; National Clinical Research Center for Metabolic Diseases, Key Laboratory of Diabetes Immunology, Ministry of Education, Metabolic Syndrome Research Center, the Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, China. Electronic address: zhouzhiguang@csu.edu.cn. 3. Department of Metabolism and Endocrinology, the Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, China; National Clinical Research Center for Metabolic Diseases, Key Laboratory of Diabetes Immunology, Ministry of Education, Metabolic Syndrome Research Center, the Second Xiangya Hospital, Central South University, Changsha, Hunan 410011, China; Department of Pharmacology, University of Texas at San Antonio, San Antonio, TX 78229, USA. Electronic address: liuf@uthscsa.edu.
Abstract
AIMS: The antimicrobial peptide cathelicidin (Camp) has multifunctional immunomodulatory activities. However, its roles in inflammation-related myocardial ischemia/reperfusion (MI/R) injury remain unclear. METHODS AND RESULTS: In this study, adult male C57BL/6 wild-type (WT) mice were subjected to MI/R injury by left anterior descending coronary artery ligation for 45 min followed by 3 or 24 h of reperfusion. An abundant cardiac expression of cathelicidin was observed during ischemia and reperfusion, which was mainly derived from heart-infiltrating neutrophils. Knockout of Camp in mice reduced MI/R-induced myocardial inflammation, infarct size, and circulating cTnI levels (an indicator of heart damage). CRAMP (the mature form of murine cathelicidin) administration of WT mice immediately before MI/R exerted detrimental effects on the reperfused heart. CRAMP exacerbates MI/R injury via a TLR4 and P2X7R/NLRP3 inflammasome-dependent mechanism, since I/R-induced myocardial infarction was reserved by inhibition of TLR4, P2X7R, or NLRP3 inflammasome in CRAMP-treated WT mice. Depletion of neutrophils before MI/R abrogated the amplification of infarct size in CRAMP-treated WT mice. Heart-infiltrating neutrophils were found to be one of major cellular sources of myocardial IL-1β (a "first line" pro-inflammatory cytokine) at the early stage of MI/R. At this stage, CRAMP administration just before MI/R induced pro-IL-1β protein expression in heart-infiltrating neutrophils, but not in non-neutrophils. In vitro experiments showed that LL-37 (the mature form of human cathelicidin) treatment promotes the processing and secretion of IL-1β from human neutrophils via stimulating TLR4 signaling and P2X7R/NLRP3 inflammasome. CONCLUSIONS: Our findings reveal that, at the early stage of MI/R, neutrophil-derived cathelicidin plays an injurious role in the heart. Cathelicidin aggravates MI/R injury by over-activating TLR4 signaling and P2X7R/NLRP3 inflammasome in heart-infiltrating neutrophils, which leads to the excessive secretion of IL-1β and subsequent inflammatory injury.
AIMS: The antimicrobial peptide cathelicidin (Camp) has multifunctional immunomodulatory activities. However, its roles in inflammation-related myocardial ischemia/reperfusion (MI/R) injury remain unclear. METHODS AND RESULTS: In this study, adult male C57BL/6 wild-type (WT) mice were subjected to MI/R injury by left anterior descending coronary artery ligation for 45 min followed by 3 or 24 h of reperfusion. An abundant cardiac expression of cathelicidin was observed during ischemia and reperfusion, which was mainly derived from heart-infiltrating neutrophils. Knockout of Camp in mice reduced MI/R-induced myocardial inflammation, infarct size, and circulating cTnI levels (an indicator of heart damage). CRAMP (the mature form of murine cathelicidin) administration of WT mice immediately before MI/R exerted detrimental effects on the reperfused heart. CRAMP exacerbates MI/R injury via a TLR4 and P2X7R/NLRP3 inflammasome-dependent mechanism, since I/R-induced myocardial infarction was reserved by inhibition of TLR4, P2X7R, or NLRP3 inflammasome in CRAMP-treated WT mice. Depletion of neutrophils before MI/R abrogated the amplification of infarct size in CRAMP-treated WT mice. Heart-infiltrating neutrophils were found to be one of major cellular sources of myocardial IL-1β (a "first line" pro-inflammatory cytokine) at the early stage of MI/R. At this stage, CRAMP administration just before MI/R induced pro-IL-1β protein expression in heart-infiltrating neutrophils, but not in non-neutrophils. In vitro experiments showed that LL-37 (the mature form of human cathelicidin) treatment promotes the processing and secretion of IL-1β from human neutrophils via stimulating TLR4 signaling and P2X7R/NLRP3 inflammasome. CONCLUSIONS: Our findings reveal that, at the early stage of MI/R, neutrophil-derived cathelicidin plays an injurious role in the heart. Cathelicidin aggravates MI/R injury by over-activating TLR4 signaling and P2X7R/NLRP3 inflammasome in heart-infiltrating neutrophils, which leads to the excessive secretion of IL-1β and subsequent inflammatory injury.