Molecular pathogenesis of Salmonella enterica serotype Typhimurium-induced inflammatory responses
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Date
2009-05-15
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Abstract
We demonstrated that infection of HeLa cells, which are non-responsive to
flagellin, with wild type Salmonella enterica serotype Typhimurium
(S. typhimurium) activated chemokine expression at higher level than
S. typhimurium lacking sipAsopABDE2, indicating that the corresponding effector
proteins (SipA, SopA, SopB, SopD and SopE2) are required to induce
chemokines independent of flagellin. The S. typhimurium sipAsopABDE2 mutant
complemented with sipA activated IL-8 expression at significantly higher level
than a S. typhimurium sipAsopABDE2 mutant. However, extracellular addition of
recombinant SipA failed to induce IL-8. Phosphorylation analyses demonstrated
that S. typhimurium carrying a chromosomal copy of sipA (sopABDE2 mutant)
induced phosphorylation of CREB1, JUN and p38MAPK, which are proteins
involved in IL-8 expression.
The contribution of effector proteins to S. typhimurium-induced
intracellular Ca2+ mobilization and its role in IL-8 expression and bacterial internalization were also investigated. Our results demonstrated that wild type
S. typhimurium significantly increased the amplitude of intracellular Ca2+
beginning 30 sec after infection. However, further analyses of intracellular Ca2+
changes in HeLa cells infected with S. typhimurium mutants indicated no
correlation between increased intracellular Ca2+ and IL-8 expression or bacterial
internalization.
To analyze specific cell populations targeted by wild type S. typhimurium
or S. typhimurium carrying a chromosomal copy of sipA (sopABDE2 mutant),
laser capture microdissection was performed. Our data indicated that in wild
type S. typhimurium-infected bovine Peyer’s patches, high levels of IL-8 were
expressed in enterocytes of crypts, whereas Gro-α was expressed in enterocytes
of both crypts and absorptive villi. A strain carrying a chromosomal copy of sipA
colonized the same cell population as wild type, but induced IL8 and Gro-α in
enterocytes of both crypts and absorptive villi.
In conclusion, we demonstrated that in vitro S. typhimurium effector
proteins induce chemokine expression independent of Ca2+ changes through
phosphorylation of proteins related to IL-8 pathway. In vivo, we found higher
levels of IL-8 expression in enterocytes of crypts than enterocytes of absorptive
villi, although both cell populations contributed to Gro-α expression. These data
extend the knowledge of the molecular mechanism by which S. typhimurium
induces inflammatory genes by identifying pathogen and host molecules involved
in inflammation.
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Keywords
Salmonella, inflammation