Activation of Toll-Like Receptor 9 Impairs Blood Flow Recovery After Hind-Limb Ischemia

• Published in: Frontiers in cardiovascular medicine 2018-10, Vol.5, p.144-144
• Main Authors: Nishimoto, Sachiko, Aini, Kunduziayi, Fukuda, Daiju, Higashikuni, Yasutomi, Tanaka, Kimie, Hirata, Yoichiro, Yagi, Shusuke, Kusunose, Kenya, Yamada, Hirotsugu, Soeki, Takeshi, Shimabukuro, Michio, Sata, Masataka
• Format: Article
• Language: English
• Subjects: blood flow recovery; Cardiovascular Medicine; hind-limb ischemia; inflammation; macrophage; Toll-like receptor 9
• ISSN: 2297-055X; 2297-055X
• DOI: 10.3389/fcvm.2018.00144

Peripheral artery disease causes significant functional disability and results in impaired quality of life. Ischemic tissue injury releases various endogenous ligands for Toll-like receptors (TLRs), suggesting the involvement of TLRs in blood flow recovery. However, the role of TLR9, which was originally known as a sensor for bacterial DNA, remains unknown. This study investigated the role of TLR9 in blood flow recovery in the ischemic limb using a mouse hind-limb ischemia model. Unilateral femoral artery ligation was performed in TLR9-deficient ( ) mice and wild-type mice. In wild-type mice, femoral artery ligation significantly increased mRNA expression of TLR9 in the ischemic limb ( < 0.001) and plasma levels of cell-free DNA (cfDNA) as determined by single-stranded DNA (ssDNA) ( < 0.05) and double-stranded DNA (dsDNA) ( < 0.01), which are endogenous ligands for TLR9, compared with the sham-operated group. Laser Doppler perfusion imaging demonstrated significantly improved ratio of blood flow in the ischemic to non-ischemic limb in mice compared with wild-type mice at 2 weeks after ligation ( < 0.05). mice showed increased capillary density and reduced macrophage infiltration in ischemic limb. Genetic deletion of TLR9 reduced the expression of TNF-α, and attenuated NF-κB activation in ischemic muscle compared with wild-type mice ( < 0.05, respectively) at 3 days after the surgery. ODN1826, a synthetic agonistic oligonucleotide for TLR9, or plasma obtained from mice with ischemic muscle promoted the expression of TNF-α in wild-type macrophages ( < 0.05), but not in macrophages. ODN1826 also activated NF-κB signaling as determined by the degradation of IκBα in wild-type macrophages ( < 0.05), but not in macrophages. In vitro experiments using human umbilical vein endothelial cells demonstrated that TNF-α, or conditioned medium obtained from wild-type macrophages treated with ODN1826 accelerated cell death as determined by MTS assay ( < 0.05 and < 0.01, respectively). Our results suggest that ischemic muscle releases cfDNA, which activates TLR9 and enhances inflammation, leading to impairment of blood flow recovery in the ischemic limb. cfDNA-TLR9 signaling may serve as a potential therapeutic target in ischemic limb disease.