Species-Specific Recognition of Single-Stranded RNA via Toll-like Receptor 7 and 8

Department of Host Defense, Osaka University, Suika, Ōsaka, Japan
Science (Impact Factor: 33.61). 04/2004; 303(5663):1526-9. DOI: 10.1126/science.1093620
Source: PubMed


Double-stranded ribonucleic acid (dsRNA) serves as a danger signal associated with viral infection and leads to stimulation
of innate immune cells. In contrast, the immunostimulatory potential of single-stranded RNA (ssRNA) is poorly understood and
innate immune receptors for ssRNA are unknown. We report that guanosine (G)- and uridine (U)-rich ssRNA oligonucleotides derived
from human immunodeficiency virus–1 (HIV-1) stimulate dendritic cells (DC) and macrophages to secrete interferon-α and proinflammatory,
as well as regulatory, cytokines. By using Toll-like receptor (TLR)–deficient mice and genetic complementation, we show that
murine TLR7 and human TLR8 mediate species-specific recognition of GU-rich ssRNA. These data suggest that ssRNA represents
a physiological ligand for TLR7 and TLR8.

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    • "More recent findings show that TLR9 also responds to herpes virus DNA (Lund et al., 2003) as well as to hemozoin, a byproduct generated by Plasmodium falciparum (Coban et al., 2010). TLR7 and TLR8 were shown to detect singlestranded viral RNA (Heil et al., 2004). TLR7 also detects RNA from streptococcus B bacteria (Mancuso et al., 2009). "
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    ABSTRACT: Toll-like receptors (TLRs) are components of the innate immune system that respond to exogenous infectious ligands (pathogen-associated molecular patterns, PAMPs) and endogenous molecules that are released during host tissue injury/death (damage-associated molecular patterns, DAMPs). Interaction of TLRs with their ligands leads to activation of downstream signaling pathways that induce an immune response by producing inflammatory cytokines, type I interferons (IFN), and other inflammatory mediators. TLR activation affects vascular function and remodeling, and these molecular events prime antigen-specific adaptive immune responses. Despite the presence of TLRs in vascular cells, the exact mechanisms whereby TLR signaling affects the function of vascular tissues are largely unknown. Cardiovascular diseases are considered chronic inflammatory conditions, and accumulating data show that TLRs and the innate immune system play a determinant role in the initiation and development of cardiovascular diseases. This evidence unfolds a possibility that targeting TLRs and the innate immune system may be a novel therapeutic goal for these conditions. TLR inhibitors and agonists are already in clinical trials for inflammatory conditions such as asthma, cancer, and autoimmune diseases, but their study in the context of cardiovascular diseases is in its infancy. In this article, we review the current knowledge of TLR signaling in the cardiovascular system with an emphasis on atherosclerosis, hypertension, and cerebrovascular injury. Furthermore, we address the therapeutic potential of TLR as pharmacological targets in cardiovascular disease and consider intriguing research questions for future study.
    Preview · Article · Dec 2015 · Pharmacological reviews
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    • "Of note, mtRNA-driven activation of 3ddiTHP-1 cells was absent from Tlr8 À/À and Unc93b1 À/À -3ddiTHP-1 cells (Fig 3D). TLR7 and most likely also TLR8 preferentially bind U/G rich viral-, si-, and self-RNA [14,19,232425. Structural data imply that the RNA specificity of TLR8 might be guided by the U and G content of ssRNA [13]. "
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    ABSTRACT: Toll-like receptor (TLR) 13 and TLR2 are the major sensors of Gram-positive bacteria in mice. TLR13 recognizes Sa19, a specific 23S ribosomal (r) RNA-derived fragment and bacterial modification of Sa19 ablates binding to TLR13, and to antibiotics such as erythromycin. Similarly, RNase A-treated Staphylococcus aureus activate human peripheral blood mononuclear cells (PBMCs) only via TLR2, implying single-stranded (ss) RNA as major stimulant. Here, we identify human TLR8 as functional TLR13 equivalent that promiscuously senses ssRNA. Accordingly, Sa19 and mitochondrial (mt) 16S rRNA sequence-derived oligoribonucleotides (ORNs) stimulate PBMCs in a MyD88-dependent manner. These ORNs, as well as S. aureus-, Escherichia coli-, and mt-RNA, also activate differentiated human monocytoid THP-1 cells, provided they express TLR8. Moreover, Unc93b1(-/-)- and Tlr8(-/-)-THP-1 cells are refractory, while endogenous and ectopically expressed TLR8 confers responsiveness in a UR/URR RNA ligand consensus motif-dependent manner. If TLR8 function is inhibited by suppression of lysosomal function, antibiotic treatment efficiently blocks bacteria-driven inflammatory responses in infected human whole blood cultures. Sepsis therapy might thus benefit from interfering with TLR8 function.
    Preview · Article · Nov 2015 · EMBO Reports
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    • "Classically associated with bacterial or viral infections , nucleic acids such as DNA and RNA can elicit an innate immune response via TLR activation ( mainly TLR - 3 for double - stranded RNA ( Alexopoulou et al . , 2001 ) , TLR - 7 and 8 for single - stranded RNA ( Heil et al . , 2004 ) , and TLR - 9 for unmethylated DNA ( Hemmi et al . , 2000 ) . Typically sequestered within the cell , host DNA and RNA are normally considered as unrecognizable by these membrane bound receptors . However , nucleic acids can be released from host cell due to damage or death and can signal as DAMPs ."
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    ABSTRACT: While chemotherapeutic agents have yielded relative success in the treatment of cancer, patients are often plagued with unwanted and even debilitating side-effects from the treatment which can lead to dose reduction or even cessation of treatment. Common side effects (symptoms) of chemotherapy include (i) cognitive deficiencies such as problems with attention, memory and executive functioning; (ii) fatigue and motivational deficit; and (iii) neuropathy. These symptoms often develop during treatment but can remain even after cessation of chemotherapy, severely impacting long-term quality of life. Little is known about the underlying mechanisms responsible for the development of these behavioral toxicities, however, neuroinflammation is widely considered to be one of the major mechanisms responsible for chemotherapy-induced symptoms. Here, we critically assess what is known in regards to the role of neuroinflammation in chemotherapy-induced symptoms. We also argue that, based on the available evidence, neuroinflammation is unlikely the only mechanism involved in the pathogenesis of chemotherapy-induced behavioral toxicities. We evaluate two other putative candidate mechanisms. To this end we discuss the mediating role of damage-associated molecular patterns (DAMPs) activated in response to chemotherapy-induced cellular damage. We also review the literature with respect to possible alternative mechanisms such as a chemotherapy-induced change in the bioenergetic status of the tissue involving changes in mitochondrial function in relation to chemotherapy-induced behavioral toxicities. Understanding the mechanisms that underlie the emergence of fatigue, neuropathy, and cognitive difficulties is vital to better treatment and long-term survival of cancer patients.
    Full-text · Article · May 2015 · Frontiers in Neuroscience
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