ODN TTAGGG (A151) - TLR9 Antagonist

Toll-like receptor 9

The Toll-like Receptor 9 (TLR9) is an endosomal receptor that triggers NF-κB- and interferon regulatory factor (IRF)-mediated pro-inflammatory responses upon the recognition of unmethylated cytosine-phosphorothioate-guanosine (CpG) forms of DNA [1-3]. Unmethylated CpG dinucleotides are a hallmark of microbial (bacterial, viral, fungal, and parasite) DNA, as well as mitochondrial self-DNA [3,4]. These TLR9 agonists can be mimicked by synthetic oligonucleotides containing CpG motifs (CpG ODNs), which have been extensively studied to improve adaptive immune responses in the context of vaccination [1,3].

AIM2 Inflammasome

AIM2 (absent in melanoma 2), a receptor for cytoplasmic DNA, forms an inflammasome with its ligand and ASC to activate caspase-1 [5-7]. AIM2 is an interferon-inducible HIN-200 family member that contains an amino-terminal pyrin domain and a carboxy-terminal oligonucleotide/oligosaccharide-binding domain. AIM2 senses cytoplasmic double-stranded DNA through its oligonucleotide/oligosaccharide-binding domain and interacts with ASC via its pyrin domain to activate caspase-1. The interaction of AIM2 with ASC also leads to the formation of the ASC pyroptosome, which induces pyroptotic cell death in cells containing caspase-1. AIM2 is necessary and sufficient for inflammasome activation in response to cytoplasmic DNA. 

cGAS

Cyclic GMP-AMP synthase (cGAS, cGAMP synthase) is a critical cytosolic DNA sensor that triggers innate immune responses through the production of type I interferons (IFNs) [8]. In response to cytosolic double‑stranded DNA (dsDNA), cGAS produces the cyclic dinucleotide (CDN) 2’3’-cGAMP.
CDNs bind directly to STING, leading to TBK1‑IRF3-mediated activation of IFN-stimulated response elements (ISRE) in the promoters of IFN-stimulated genes (ISG). The most potent agonist of human STING is 2’3’-cGAMP [9,10].

References:

1. Kumagai Y. et al., 2008. TLR9 as a key receptor of the recognition of DNA. Adv. Drug. Deliv. Rev. 60(7):795-804.
2. Heinz L.X. et al., 2021. TASL is the SLC15A4-associated adaptor for IRF5 activation by TLR7-9. Nature. 581(7808):316-322.
3. Kayraklioglu N. et al., 2021. CpG oligonucleotides as vaccine adjuvants. DNA Vaccines: Methods and Protocols. Methods in Molecular Biology. Vol. 2197. p51-77.
4. Kumar V., 2021. The trinity of cGAS, TLR9, and ALRs: guardians of the cellular galaxy against host-derived self-DNA. Front. Immunol. 11:624597.
5. Hornung V. et al., 2009. AIM2 recognizes cytosolic dsDNA and forms a caspase-1-activating inflammasome with ASC. Nature. 458(7237):514-8.
6. Fernandes-Alnemri T. et al., 2009. AIM2 activates the inflammasome and cell death in response to cytoplasmic DNA. Nature.458(7237):509-13.
7. Bürckstümmer T. et al., 2009. An orthogonal proteomic-genomic screen identifies AIM2 as a cytoplasmic DNA sensor for the inflammasome. Nat Immunol. 10(3):266-72.
8. Sun L. et al., 2013. Cyclic GMP-AMP synthase is a cytosolic DNA sensor that activates the type I interferon pathway. Science 339(6121):786-91.
9. Gao P. et al., 2013. Cyclic [G(2’,5’)pA(3’,5’)p] is the metazoan second messenger produced by DNA-activated cyclic GMP-AMP synthase. Cell. 153(5):1094-107.
10. Ablasser A. et al., 2013. cGAS produces a 2’-5’-linked cyclic dinucleotide second messenger that activates STING. Nature. 498(7454):380-4.