Adenovirus membrane penetration activates the NLRP3 inflammasome

Area of Science:

• Immunology
• Virology
• Cell Biology

Background:

• Adenovirus type 5 (Ad5) infection in macrophages stimulates interleukin-1β (IL-1β) secretion.
• This process is known to involve inflammasome components NLRP3, ASC, and caspase-1 activity.

Purpose of the Study:

• To elucidate the specific mechanisms by which Ad5 infection activates the inflammasome and induces IL-1β release in macrophages.
• To investigate the role of Toll-like receptor 9 (TLR9) and cellular events like endosomal and lysosomal membrane integrity in Ad5-induced inflammasome activation.

Main Methods:

• Utilized lentivirus-expressed short hairpin RNA (shRNA) for gene silencing.
• Employed competitive inhibitors and a temperature-sensitive Ad5 mutant (ts1).
• Assessed IL-1β release, TLR9 sensing, endosomal and lysosomal membrane integrity, reactive oxygen species (ROS) production, and cell death.

Main Results:

• Ad5-induced IL-1β release depends on Toll-like receptor 9 (TLR9) sensing of viral double-stranded DNA (dsDNA) in human cells, but not mouse macrophages.
• Endosomal membrane penetration is essential for Ad5-induced IL-1β release, as shown by the ts1 mutant.
• Lysosomal membrane disruption, cathepsin B release, and reactive oxygen species (ROS) production are required for Ad5-induced NLRP3 activation and subsequent IL-1β secretion.
• Ad5 infection leads to necrotic cell death and release of high-mobility group box 1 (HMGB1).

Conclusions:

• Ad5 infection activates the inflammasome and induces IL-1β release through TLR9-mediated sensing of viral dsDNA.
• The pathway involves endosomal escape, lysosomal damage, ROS generation, and ultimately necrotic cell death.
• This study provides a detailed mechanistic understanding of virally induced inflammasome activation.