Novel coenzyme Q6 variant reveals non-immune determinants of survival during pneumococcal sepsis

1 PROJECT SUMMARY 2 Sepsis caused by Streptococcus pneumoniae (Sp; the pneumococcus) causes significant morbidity and 3 mortality, despite vaccines, antimicrobials, and supportive care. Sepsis is defined as “life-threatening organ 4 damage due to a pathogen-driven, dysregulated immune response.” The immune-centric model posits that

5 imbalances between pro- and anti-inflammatory immune mediators create a perfect septic storm of hyper- 6 inflammation, tissue damage, and immuno-suppression. However, no immunomodulatory therapies have yet 7 shown efficacy in improving mortality of sepsis. Our novel model of Sp sepsis prompts us to reconsider this

8 immunocentric model. We found a novel single nucleotide variant (SNV) in the gene encoding co-enzyme Q6 9 (COQ6) to be associated with susceptibility to Sp disease in an at-risk human population. The variant converts 10 an aspartate (D) to a tyrosine (Y) residue, and so we call the variant “DY” (COQ6-DY). We created the “DY

11 mouse” line, homozygous for the homologous Coq6-DY variant, which suffer increased mortality after Sp lung 12 infection. We then made chimeric mice to separate immune from non-immune cell dysfunction. Surprisingly, 13 recipient DY mice were more susceptible to Sp sepsis, despite reconstitution with wild-type (WT) immune cells.

14 Reconstitution of WT mice with DY immune cells improved survival after Sp infection. Our data reveal that non- 15 immune factors drive mortality during Sp sepsis, prompting re-evaluation of the immunocentric model of sepsis. 16 To explore why Coq6-DY increases Sp susceptibility, we tested how Coq6-DY disrupts COQ6 function.

17 Located in the inner mitochondrial membrane, COQ6 biosynthesizes the lipid ubiquinone (Q). Q serves as an 18 electron acceptor in the electron transport chain (ETC) during oxidative phosphorylation (OXPHOS). In health, 19 most tissues rely on OXPHOS for ATP generation. Infection induces metabolic remodeling and OXPHOS

20 downregulation, necessary to generate and sustain an anti-pathogen, pro-inflammatory response. Abnormal 21 metabolic remodeling may drive sepsis. In DY tissues, Q biosynthesis was intact, but OXPHOS downregulation 22 was accelerated in DY heart muscle after Sp challenge. Our proposal tests the hypothesis that aberrant

23 metabolic remodeling in DY mice causes hyperinflammation and increases organ damage in Sp sepsis through 24 three aims. First, we define the inflammatory and physiological derangements in Sp-infected DY recipients. 25 Second, we analyze metabolomic and single cell RNASeq profiles of infected DY recipients for predicted

26 correlations between metabolic abnormalities and pro-inflammatory transcriptional profiles. Finally, we test if 27 therapies chosen to counteract metabolic abnormalities in DY recipients improve survival in Sp sepsis. As an 28 Infectious Disease physician-scientist with expertise in cellular immunology, I am uniquely qualified to lead this

29 research. Our validated mouse model and compelling preliminary data assure that proposal completion will fill 30 key knowledge gaps in current sepsis models, and will accelerate discovery of therapies for unmet clinical needs.