Phosphorothioate Backbone Modification of Oligodeoxynucleotides Induces TLR9-Independent Lung Epithelial Antimicrobial Responses

Pneumonias remain a leading cause of death worldwide. Seeking novel strategies to protect susceptible patients, we have reported that inhaled delivery of a diacylated lipopeptide and a synthetic CpG oligodeoxynucleotide (ODN) protects animals against a broad range of infectious pneumonias by stimulating antimicrobial responses from the lung epithelium. Toll-like receptor 9 (TLR9) is well-established as the primary cellular receptor for CpG ODNs. However, we recently reported that ODNs also stimulate TLR9-independent generation of antimicrobial mitochondrial reactive oxygen species. By testing a variety of synthetic ODN molecules, we found that ODNs containing a phosphorothioate backbone, but not those with a phosphodiester backbone, induce TLR9-independent pathogen killing in lungs and improve mouse survival. Phosphorothioate-backboned ODN binds mitochondrial protein voltage-dependent anion channel 1 (VDAC1) at its N terminus, initiating pneumonia-protective metabolic reprogramming in lung epithelial cells that yield the protective antimicrobial effect. Thus, the phosphorothioate backbone of ODN is a critical structural pattern that activates TLR9-independent, metabolically-modulated innate immune protection that may be harnessed to protect vulnerable patients against pneumonia.