Streptococcus pneumoniae extracellular vesicles aggravate alveolar epithelial barrier disruption via autophagic degradation of OCLN (occludin).

ABSTRACT

Streptococcus pneumoniae (S. pneumoniae) represents a major human bacterial pathogen leading to high morbidity and mortality in children and the elderly. Recent research emphasizes the role of extracellular vesicles (EVs) in bacterial pathogenicity. However, the contribution of S. pneumoniae EVs (pEVs) to host-microbe interactions has remained unclear. Here, we observed that S. pneumoniae infections in mice led to severe lung injuries and alveolar epithelial barrier (AEB) dysfunction. Infections of S. pneumoniae reduced the protein expression of tight junction protein OCLN (occludin) and activated macroautophagy/autophagy in lung tissues of mice and A549 cells. Mechanically, S. pneumoniae induced autophagosomal degradation of OCLN leading to AEB impairment in the A549 monolayer. S. pneumoniae released the pEVs that could be internalized by alveolar epithelial cells. Through proteomics, we profiled the cargo proteins inside pEVs and found that these pEVs contained many virulence factors, among which we identified a eukaryotic-like serine-threonine kinase protein StkP. The internalized StkP could induce the phosphorylation of BECN1 (beclin 1) at Ser93 and Ser96 sites, initiating autophagy and resulting in autophagy-dependent OCLN degradation and AEB dysfunction. Finally, the deletion of stkP in S. pneumoniae completely protected infected mice from death, significantly alleviated OCLN degradation in vivo, and largely abolished the AEB disruption caused by pEVs in vitro. Overall, our results suggested that pEVs played a crucial role in the spread of S. pneumoniae virulence factors. The cargo protein StkP in pEVs could communicate with host target proteins and even hijack the BECN1 autophagy initiation pathway, contributing to AEB disruption and bacterial pathogenicity.Abbreviations AEB alveolarepithelial barrier; AECs alveolar epithelial cells; ATG16L1 autophagy related 16 like 1; ATPadenosine 5'-triphosphate; BafA1 bafilomycin A1; BBB blood-brain barrier; CFU colony-forming unit; co-IP co-immunoprecipitation; CQchloroquine; CTRL control; DiO 3,3'-dioctadecylox-acarbocyanineperchlorate; DOX doxycycline; DTT dithiothreitol; ECIS electricalcell-substrate impedance sensing; eGFP enhanced green fluorescentprotein; ermR erythromycin-resistance expression cassette; Ery erythromycin; eSTKs eukaryotic-like serine-threoninekinases; EVs extracellular vesicles; HA hemagglutinin; H&E hematoxylin and eosin; HsLC3B human LC3B; hpi hours post-infection; IP immunoprecipitation; KD knockdown; KO knockout; LAMP1 lysosomal associated membrane protein 1; LC/MS liquid chromatography-mass spectrometry; MAP1LC3/LC3 microtubule associated protein 1 light chain 3; MVs membranevesicles; NCnegative control; NETsneutrophil extracellular traps; OD optical density; OMVs outer membrane vesicles; PBS phosphate-buffered saline; pEVs S.pneumoniaeextracellular vesicles; protK proteinase K; Rapa rapamycin; RNAi RNA interference; S.aureus Staphylococcusaureus; SNFsupernatant fluid; sgRNA single guide RNA; S.pneumoniae Streptococcuspneumoniae; S.suis Streptococcussuis; TEER trans-epithelium electrical resistance; moi multiplicity ofinfection; TEMtransmission electron microscope; TJproteins tight junction proteins; TJP1/ZO-1 tight junction protein1; TSA tryptic soy agar; WB western blot; WT wild-type.