Macrophage cytotoxicity produced by adenylate cyclase toxin from Bordetella pertussis: more than just making cyclic...

Area of Science:

• Microbiology
• Cell Biology
• Toxicology

Background:

• Adenylate cyclase (AC) toxin from Bordetella pertussis is known to cause host cell cytotoxicity.
• The prevailing hypothesis attributed this effect solely to the toxin's ability to produce high levels of cyclic AMP (cAMP).

Purpose of the Study:

• To investigate the mechanisms underlying AC toxin-induced cytotoxicity.
• To determine if cAMP accumulation is the sole contributor to the toxin's cytotoxic effects.

Main Methods:

• Utilized wild-type (WT) AC toxin and various mutant forms with defects in enzymatic activity or pore-forming ability.
• Assessed cell death markers including cAMP levels, ATP depletion, caspase activation, annexin V staining, and TUNEL staining.
• Compared the cytotoxic potencies of WT toxin and mutants affecting specific mechanisms.

Main Results:

• WT AC toxin induced cell death via cAMP accumulation, ATP depletion, caspase activation, and DNA damage.
• A non-haemolytic, enzymatically active mutant showed transient ATP reduction and minimal cell death, despite increased cAMP.
• Mutants lacking enzymatic activity but capable of pore formation also induced cell death, independent of cAMP production.

Conclusions:

• AC toxin-induced cytotoxicity involves at least two distinct mechanisms: cAMP accumulation/ATP depletion and oligomerization/pore formation.
• Elevated cAMP levels alone are insufficient to fully explain the cytotoxic effects of AC toxin.
• These mechanisms may act synergistically to mediate host cell damage by Bordetella pertussis AC toxin.