Group A Streptococcus May Suppress V‐ATPase Activity To Inhibit THP‐1 Macrophage Phagolysosomal Acidification

Abstract

Infection with Group A Streptococcus (GAS), a human‐specific bacterial pathogen, results in a multitude of diseases ranging from strep throat to toxic shock, and can lead to serious post‐infection sequelae such as rheumatic heart disease. During infection, macrophages engulf bacteria within the phagosome, which then fuses with the lysosome. Subsequent acidification of the phagolysosome allows for degradation of bacteria. Our lab and others have shown that during GAS infection, phagolysosomes are not acidified, allowing GAS to persist. The overall objective of this study was to determine how GAS inhibits phagolysosomal acidification. Our lab has previously shown that secretion of the pore‐forming toxin Streptolysin O (SLO) causes phagolysosomal leakage of relatively large proteins. In our current work, we demonstrate that during infection using a mutant strain lacking SLO or using heat‐killed bacteria that GAS‐infected phagosomes are still not acidified, indicating that lack of acidification is not due to mere leakage. Phagolysosomes undergo acidification using the enzyme complex vacuolar ATPase (VATPase), which needs to properly assemble cytosolic and membrane components to function. To assess whether V‐ATPase assembly was affected, infected cells were fractionated and recruitment of cytosolic V‐ATPase subunits to the phagosome membrane was monitored by Western blot. Our preliminary results indicate that V‐ATPase assembly is not inhibited, suggesting that GAS may instead prevent acidification by inhibiting V‐ATPase activity. We are currently conducting further research to investigate this potential inhibitory mechanism of GAS. Restoring the ability of lysosomes to become acidified and activate proteolytic enzymes may serve as a means to enhance macrophage function, both bactericidal capacity and antigen presentation capability, to elicit effective long‐lasting immunity.Support or Funding InformationAmerican Heart Association (17GRNT3410851), Occidental College Undergraduate Research Center