Abstract
The immunopathology of chlamydial diseases is exacerbated by a broad-spectrum of inflammatory mediators, which we reported are inhibited by IL-10 in macrophages. However, the chlamydial protein moiety that induces the inflammatory mediators and the mechanisms by which IL-10 inhibits them are unknown. We hypothesized that Chlamydia major outer membrane protein (MOMP) mediates its disease pathogenesis, and the suppressor of cytokine signaling (SOCS)1 and SOCS3 proteins are mediators of the IL-10 inhibitory actions. Our hypothesis was tested by exposing mouse J774 macrophages to chlamydial stimulants (live Chlamydia muridarum and MOMP) with and without IL-10. MOMP significantly induced several inflammatory mediators (IL-6, IL-12p40, CCL5, CXCL10), which were dose-dependently inhibited by IL-10. Chlamydial stimulants induced the mRNA gene transcripts and protein expression of SOCS1 and SOCS3, with more SOCS3 expression. Notably, IL-10 reciprocally regulated their expression by reducing SOCS1 and increasing SOCS3. Specific inhibitions of MAPK pathways revealed that p38, JNK, and MEK1/2 are required for inducing inflammatory mediators as well as SOCS1 and SOCS3. Chlamydial stimulants triggered an M1 pro-inflammatory phenotype evidently by an enhanced nos2 (M1 marker) expression, which was skewed by IL-10 towards a more M2 anti-inflammatory phenotype by the increased expression of mrc1 and arg1 (M2 markers) and the reduced SOCS1/SOCS3 ratios. Neutralization of endogenously produced IL-10 augmented the secretion of inflammatory mediators, reduced SOCS3 expression, and skewed the chlamydial M1 to an M2 phenotype. Inhibition of proteasome degradation increased TNF but decreased IL-10, CCL5, and CXCL10 secretion by suppressing SOCS1 and SOCS3 expressions and dysregulating their STAT1 and STAT3 transcription factors. Our data show that SOCS1 and SOCS3 are regulators of IL-10 inhibitory actions, and underscore SOCS proteins as therapeutic targets for IL-10 control of inflammation for Chlamydia and other bacterial inflammatory diseases.
Highlights
Chlamydia is one of the most prevalent bacterial sexually transmitted infections (STIs) worldwide, with an estimated annual incidence of 1.7 million cases in the United States [1]
We previously reported that infection of mouse J774 macrophages with live C. trachomatis induces the release of IL-6, TNF, and IL-8, which were inhibited by IL-10 [27]
We previously established that Chlamydia induces the secretion of several inflammatory cytokines and chemokines by mouse macrophages [19, 26, 27] and that IL-10 effectively inhibited the production of TNF, IL-6, and IL-8 as elicited by Chlamydia in mouse macrophages [27]
Summary
Chlamydia is one of the most prevalent bacterial sexually transmitted infections (STIs) worldwide, with an estimated annual incidence of 1.7 million cases in the United States [1]. The pathogenic agent responsible for this infection is Chlamydia trachomatis, a gram-negative and intracellular anaerobe bacterium [2] that causes mucosal infections of the genital, anorectal, and oropharyngeal surfaces in humans [3]. Genital Chlamydia is associated with significant reproductive morbidity, including tubal factor infertility, with women being more disproportionately affected than men [4, 5]. The unique developmental cycle of C. trachomatis allows for its intracellular reproduction while infecting neighboring cells, resulting in persistent disease or re-infection even after treatment [3, 6, 7]. C. trachomatis possesses diverse virulence factors including, its major outer membrane protein (MOMP) that exhibits high immunogenic potential [8, 9]
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