Poster Presentation 15th Lorne Infection and Immunity 2025

Matrikines are key regulators in smoke-related S. pneumoniae pulmonary infection (#354)

Xin Xu 1 2 3 , Sarah Robsion 1 2 3 , Jindong Li 1 2 3 , Kristopher Genschmer 1 2 , Liliana Viera 1 2 , Jeremy Foote 4 , William E Swords 2 , J. Edwin Blalock 1 2 , Amit Gaggar 1 2 3
  1. Lung Biology Program, University of Alabama at Birmingham, Birmingham, Unite States of America
  2. Department of Medicine, University of Alabama at Birmingham, Birmingham, United States of America
  3. Birmingham VA Medical Center, Birmingham, Unite States of America
  4. Department of Microbiology, University of Alabama at Birmingham, Birmingham, United States of America

Cigarette smoke is a potent inflammatory mediator that alters immunity, facilitating repeated infections. Streptococcus pneumoniae is a major pathogen of community-acquired bacterial pneumonia (CABP). Smokers are at higher risk of developing Streptococcus pneumoniae -induced lung infections and invasive pneumococcal disease, with worse outcomes compared to non-smokers. Proline-Glycine-Proline (PGP), a neutrophil chemoattractant, is an inflammatory matrikine formed from extracellular collagen breakdown by MMP-9 and further cleavage by prolyl endopeptidase (PE). Elevated PGP peptides are reported in neutrophil-driven inflammatory disorders like COPD and cystic fibrosis. To understand the connections between cigarette smoking, pulmonary bacterial infection, and protease-mediated lung injury, we developed a 2-hit murine model combining Streptococcus pneumoniae  infection with cigarette smoke exposure. Mice were exposed to cigarette smoke for 2 weeks and infected with Streptococcus pneumoniae  intranasally two days before the end of smoking. Results showed that post-infection, smoke-exposed mice had decreased body weight, increased Streptococcus pneumoniae  counts in lung tissue, and exacerbated inflammatory cell recruitment in the upper airways. Nasal coronal histology sections revealed neutrophilic infiltrate. Importantly, levels of PE, MMP-9, and PGP in the lung were elevated in smoke-exposed, infected mice. To determine the induction of PGP-generating proteases, isolated neutrophils and macrophages were treated with cigarette smoke extract (CSE) and Streptococcus pneumoniae . Significantly greater amounts of PE and MMP-9 were produced after stimulation with CSE plus Streptococcus pneumoniae  compared to controls. To further elucidate PGP's impact on lung injury, mice from the 2-week smoking and infection model were administered the PGP-specific peptide inhibitor L-arginine-threonine-arginine (RTR) intratracheally and intranasally. RTR improved bacterial burden and attenuated neutrophilic inflammation. These findings highlight the synergistic interaction of bacteria and smoke in augmenting lung inflammation and tissue injury, suggesting that PGP is a crucial matrikine in smoke-associated bacterial pneumonia.