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Upregulated expression of inducible nitric oxide synthase plays a key role in early apoptosis after anterior cruciate ligament injury
Author(s) -
Murakami Hideaki,
Shinomiya Nariyoshi,
Kikuchi Toshiyuki,
Yoshihara Yasuo,
Nemoto Koichi
Publication year - 2006
Publication title -
journal of orthopaedic research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.041
H-Index - 155
eISSN - 1554-527X
pISSN - 0736-0266
DOI - 10.1002/jor.20151
Subject(s) - apoptosis , downregulation and upregulation , anterior cruciate ligament , nitric oxide synthase , p38 mitogen activated protein kinases , mapk/erk pathway , tunel assay , nitric oxide , microbiology and biotechnology , chemistry , biology , signal transduction , endocrinology , anatomy , biochemistry , gene
The reason that the anterior cruciate ligament (ACL) has a very poor healing potential after injury is not well understood. In this study, we investigated the role of nitric oxide (NO) in the apoptotic cell death of ACL cells using a rabbit model and in vitro cell culture. The apoptosis of ACL cells in vivo was analyzed by TUNEL assay and electron microscopy. NO synthase (NOS) expression was observed by immunohistochemical analysis. ACL cells were cultured and the susceptibility to NO‐induced apoptosis was tested. Inducible NOS (iNOS) expression after treatment with cytokines was examined by immunohistochemical and RT‐PCR analyses. Mitogen‐activated protein kinase (MAPK) inhibitors were used for the analysis of downstream signals. A significant number of apoptotic cells were observed on days 1 to 3 after injury; the apoptotic rate returned to the control level by day 7. Upregulation of iNOS in the ACL remnant was observed at day 1. Intraarticular injection of NOS inhibitor suppressed the apoptotic rate. Isolated ACL cells showed much higher susceptibility to NO‐induced apoptosis than did medial collateral ligament cells. IL‐1β stimulated ACL cells to upregulate iNOS mRNA and increase NO production. p38 MAPK inhibitor decreased NO‐induced apoptosis. Rapid iNOS induction after injury contributes to the high apoptotic rate of ACL cells, and this may partly account for the poor healing capacity of this ligament. iNOS and NO production is suggested to be stimulated by IL‐1β, and NO activates the p38 MAPK pathway and triggers an apoptotic signal in ACL cells. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 24:1521–1534, 2006