Poster Presentation 20th Lancefield International Symposium on Streptococci and Streptococcal Diseases 2017

The NAD-glycohydrolase mediates the multiplication of Group A Streptococcus in endothelial cells (#206)

Cheng Lu Hsieh 1 , Shu Ying Hsieh 1 , Hsuan Min Huang 1 , Jiunn Jong Wu 1 2
  1. National Cheng Kung University, Tainan, TAIWAN, Taiwan
  2. National Yang-Ming University, Taipei, TAIWAN, Taiwan

Group A Streptococcus (GAS) is a human pathogen causing wide spectrum of diseases from mid pharyngitis to life-threatening necrotizing fasciitis. Although GAS is considered as an extracellular pathogen, increased evidences indicated that GAS could efficiently invade into host cells to evade the host immune defense and antibiotics-mediated killing. GAS secrete several virulence factors to enhance intracellular survival, but the exact role is still unclear. In present study, we found significantly greater intracellular multiplication of invasive strains NZ131 and A20 than non-invasive strain SF370 in human endothelial cells (HMEC-1). Using genetic manipulation, we demonstrated that nga-knockout and ifs (an endogenous inhibitor of NADase) overexpression strains dramatically decrease NADase activity and growth capacity in HMEC-1 cells, indicating that enzymatic activity of nga is required for GAS multiplication in endothelial cells. NADase hydrolyzed NAD+ to nicotinamide and ADP-ribose. The wild type NZ131-infected HMEC-1 cells showed lower intracellular NAD+ level than in nga mutant-infected cells, implying that intracellular energy imbalance may cause impaired intracellular bacterial clearance of endothelial cells. Confocal microscopic images further demonstrated that intracellular GAS was encapsulated into LC3-positive vacuoles, but prevented co-localization with lysosome and acidification in wild type NZ131 compared with its nga mutant. Moreover, immunoblotting images also revealed that a signal decrease in LC3-II conversion and autophagic adaptor protein p62/SQSTM1 in the nga mutant relative to wild-type strain at the late stage of infection. These results indicated that intracellular GAS secretes NADase to alter intracellular NAD+ content, leading to escape autophagic killing and efficiently multiply in infected cells.