Tropheryma whipplei, the Whipple's disease bacillus, induces macrophage apoptosis through the extrinsic pathway

Area of Science:

• Microbiology
• Immunology
• Cell Biology

Background:

• Tropheryma whipplei causes Whipple's disease, an infection primarily affecting macrophages.
• Previous studies linked T. whipplei infection to M2 macrophage polarization, apoptosis, and IL-16 secretion.
• Elevated apoptotic markers and IL-16 correlate with disease activity in patients.

Purpose of the Study:

• To elucidate the molecular mechanisms of Tropheryma whipplei-induced apoptosis in human macrophages.
• To understand the role of apoptosis in the pathophysiology of Whipple's disease.

Main Methods:

• Investigated apoptosis induction dependence on bacterial viability and protein synthesis.
• Analyzed pro- and anti-apoptotic mediator degradation.
• Utilized caspase-specific inhibitors (caspases 8, 10, 2, 9, 3, 6) to determine the apoptotic pathway.

Main Results:

• Apoptosis induction required viable bacteria and was reduced by inhibiting bacterial protein synthesis.
• Massive degradation of both pro- and anti-apoptotic mediators was observed.
• Initiator caspases 8 and 10, and effector caspases 3 and 6 were essential for apoptosis.
• Caspases 2 and 9 were not required, despite mitochondrial cytochrome-c release.

Conclusions:

• Tropheryma whipplei induces apoptosis in macrophages predominantly through the extrinsic caspase pathway.
• Apoptosis contributes to bacterial replication and serves as a virulence mechanism for T. whipplei.
• Understanding these pathways offers insights into Whipple's disease pathogenesis.