Abstract
BackgroundMycoplasma pneumoniae (M. pneumoniae) is one of the major etiological agents for community-acquired pneumonia (CAP) in all age groups. The early host response to M. pneumoniae infection relies on the concerted release of proteins with various biological activities. However, no comprehensive analysis of the secretory proteins has been conducted to date regarding the host response upon M. pneumoniae infection.ResultsWe employed the liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based label-free quantitative proteomic technology to identify and characterize the members of the human alveolar epithelial carcinoma A549 cell secretome during M. pneumoniae infection. A total of 256 proteins were identified, with 113 being differentially expressed (>1.5-fold change), among which 9 were only expressed in control cells, 10 only in M. pneumoniae-treated cells, while 55 were up-regulated and 39 down-regulated by M. pneumoniae. The changed expression of some of the identified proteins was validated by RT-PCR and immunoblot analysis. Cellular localization analysis of the secretome data revealed 59.38% of the proteins were considered as “putative secretory proteins”. Functional analysis revealed that the proteins affected upon M. pneumoniae infection were mainly related to metabolic process, stress response, and immune response. We further examined the level of one up-regulated protein, IL-33, in clinical samples. The result showed that IL-33 levels were significantly higher in the plasma and bronchoalveolar lavage fluid (BALF) of M. pneumoniae pneumonia (MPP) patients.ConclusionsThe present study provided systematic information about the changes in the expression of secretory proteins during M. pneumoniae infection, which is useful for the discovery of specific biomarkers and targets for pharmacological intervention.
Highlights
Mycoplasma pneumoniae (M. pneumoniae) is one of the major etiological agents for community-acquired pneumonia (CAP) in all age groups
The pathophysiology of M. pneumoniae infection is likely to be complex and multifactorial, and the underlying molecular mechanisms should involve a large number of genes/proteins participating in various biological pathways [3,8,9]
Western blot data showed that protein levels of six secretory proteins were significantly increased in the conditioned media (CM) and total cell lysates after M. pneumoniae-infection, which were consistent with the proteomic results (Figure 2B)
Summary
Mycoplasma pneumoniae (M. pneumoniae) is one of the major etiological agents for community-acquired pneumonia (CAP) in all age groups. Mycoplasma pnuemoniae (M. pneumoniae) belongs to the class of the Mollicutes and is one of the smallest free-living organisms. It is a major cause of communityacquired pneumonia (CAP) worldwide in all age groups, and can induce manifestations in extrapulmonary sites involving almost all organs of the human body [1,2]. The pathophysiology of M. pneumoniae infection is likely to be complex and multifactorial, and the underlying molecular mechanisms should involve a large number of genes/proteins participating in various biological pathways [3,8,9]. High-throughput technologies including genomics and proteomics can comprehensively and quantitatively decipher gene/protein expression, and are useful tools in the study of complex systems under the influence of biological perturbations, such as pathogen-host interaction [10]. As noted above, M. pneumoniae-induced immune response is important for M. pneumoniae pathogenesis, and many factors involved in the immune response, such as the cytokines, are so-called secretory proteins, which are part of the “secretome” [11]
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