A Novel Aminosaccharide Compound Blocks Immune Responses by Toll-like Receptors and Nucleotide-binding Domain, Leucine-rich Repeat Proteins

Abstract

Toll-like receptors (TLRs) and nucleotide-binding domain, leucine-rich repeat (NLR) proteins are two major forms of innate immune receptors that trigger inflammatory responses by various biological mechanisms such as cytokine production, recruitment of inflammatory cells, or activation of adaptive immunity. Although the innate immune system is designed to fight against infectious pathogens, excessive activation of TLR or NLR signaling pathways may lead to unwarranted inflammation with hazardous outcomes, including septic shock or inflammatory diseases. As part of the search for effective therapeutics to regulate these responses, here we show that a novel aminosaccharide compound, named DFK1012, inhibits immune responses caused by TLR and NLR activation. Treatment with DFK1012, but not its derivatives DFK845 or DFK846, strongly inhibited pro-inflammatory cytokine production upon stimulation via either TLR or NLR proteins in macrophages. Importantly, we have not observed cytotoxicity in any range of its working concentration. Treatment with DFK1012 did not interfere with TLR-or NLR-induced activation of p38 and JNK, phosphorylation/degradation of IB, and subsequent nuclear translocation of NF-B subunit p65, suggesting that the inhibitory activity of DFK1012 is not due to the suppression of downstream signaling. Indeed, DFK1012 did not impair transcription of pro-inflammatory cytokine genes but rather promoted post-translational degradation of pro-inflammatory cytokines. Therefore, DFK1012 is a novel anti-inflammatory compound that drives proteolysis of proinflammatory cytokines induced by TLR and NLR stimulation. DFK1012 may represent a novel class of potential therapeutic agents aimed at the treatment of inflammatory disorders.The innate immune system serves as the first line of host defense against infectious agents by detecting the presence of microbial infection through germ line-encoded pattern recognition receptors (1). Membrane-bound Toll-like receptors (TLRs) 2 as well as cytoplasmic nucleotide-binding domain and leucine-rich repeat (NBD-LRRs or NLRs) protein families are important groups of pattern recognition receptors that provide immediate immune responses by recognizing different but overlapping microbial components, frequently referred to as pathogen-associated molecular patterns (PAMPs) (2). Mammalian TLRs detect components from various microorganisms, including bacteria, viruses, and protozoa (3-18). Signaling of TLRs utilizes an adaptor MyD88, except for TLR3, which requires an adaptor TIR-domain-containing adapter-inducing interferon-␤ (TRIF), leading to the activation of signaling cascades such as MAP kinases and NF-B. These events result in the transcriptional activation of immune response genes and lead to the up-regulation of surface co-stimulatory molecules on antigen-presenting cells and the secretion of pro-inflammatory cytokines such as IL-6, IL-8, .Similar to TLRs, NLR proteins have been shown to play an important role in the recognition and control of bacterial infection (23,24). For ex...

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