Related Experiment Videos
Pathogenic mycobacteria disrupt the macrophage actin filament network
1INSERM U411, UFR de Médecine Necker, 75730 Paris Cedex 15, France.
Abstract:
Phagosomes with pathogenic mycobacteria retain fusion and intermingling characteristics of early endosomes indefinitely. The time course of acquisition of newly endocytosed tracers becomes, however, atypical (lag instead of immediate acquisition) starting from day 1 postinfection (p.i.), thereby suggesting that additional factors affect this process. Disruption of the actin filament (F-actin) network by cytochalasin D perturbs the movement of early endosomes and probably fusion events among early endosomes and phagosomes. Here we compare, by immunofluorescence microscopy, the morphology and distribution of F-actin in macrophages infected with virulent Mycobacterium avium, in uninfected macrophages, or in macrophages after phagocytosis of nonpathogenic bacteria (Mycobacterium smegmatis or Bacillus subtilis) or hydrophobic latex particles. In uninfected cells, F-actin appeared as a network of small filaments distributed throughout the cell; about 80% of the cells also displayed one or two small patches of F-actin at the cell periphery. Virulent M. avium caused a marked disorganization of the F-actin network starting from day 1 p.i. The most salient features were the formation of several large patches, the progressive disappearance of the small filaments, and the appearance of large numbers of tiny punctate structures starting from day 2 p.i. With the three other particles, the F-actin network was unmodified compared to that in uninfected cells. The atypical lag in acquisition of newly endocytosed tracers by M. avium-containing phagosomes, therefore, seems to coincide with the disorganization of the F-actin network.
Insights
Virulent Mycobacterium avium infection disrupts macrophage actin filaments, causing atypical phagosome function. This actin disorganization correlates with delayed tracer uptake in M. avium-containing phagosomes.
Area of Science:
- Cell Biology
- Immunology
- Microbiology
Background:
- Phagosomes containing pathogenic mycobacteria exhibit altered fusion dynamics.
- Mycobacterium avium infection leads to atypical phagosome maturation.
- Actin filament (F-actin) disruption affects endosome and phagosome trafficking.
Purpose of the Study:
- To investigate the impact of virulent Mycobacterium avium infection on the macrophage F-actin network.
- To compare F-actin organization in macrophages infected with M. avium versus nonpathogenic bacteria or particles.
- To correlate F-actin disorganization with altered phagosome function during M. avium infection.
Main Methods:
- Immunofluorescence microscopy was used to visualize F-actin distribution.
- Macrophages were infected with virulent Mycobacterium avium, nonpathogenic bacteria (M. smegmatis, B. subtilis), or latex particles.
- F-actin morphology and distribution were compared between infected and uninfected macrophages.
Main Results:
- Virulent M. avium infection caused significant F-actin network disorganization starting day 1 postinfection.
- Observed changes included large F-actin patches, loss of small filaments, and punctate structures.
- Nonpathogenic bacteria and latex particles did not alter the F-actin network.
- F-actin disorganization coincided with a lag in tracer acquisition by M. avium-containing phagosomes.
Conclusions:
- Virulent Mycobacterium avium infection disrupts the macrophage F-actin cytoskeleton.
- This F-actin disorganization is linked to the atypical functional behavior of M. avium-containing phagosomes.
- The actin cytoskeleton plays a crucial role in phagosome maturation and trafficking during mycobacterial infections.