Summary
Chlamydia (C.) pneumoniae are thought to infect monocytes and use them as vectors into the vessel wall, where
they may accelerate atherosclerosis. We investigated the effects of C. pneumoniae on monocytic matrix metalloproteinase (MMP) activation with focus on the role of
the extracellular matrix metalloproteinase inducer EMMPRIN. Human monocytes or monocytic
MonoMac6 cells were infected with C. pneumoniae. Infection enhanced mRNA-and surface expression of EMMPRIN and Membrane-type-1 Matrix
Metalloproteinase (MT1-MMP), plus the secretion of MMP-7, MMP-9 and the urokinase
receptor (uPAR). Chlamydial heat shock protein 60 was identified to be partially responsible
for EMMPRIN and MMP-9 induction, while C. trachomatis-infection had no stimulatory effect, indicatinga C. pneumoniae-specific activation pathway. Suppression of EMMPRIN by gene silencing almost completely
hindered the induction of MT1-MMP and MMP-9 by C. pneumoniae, suggesting a predominant regulatory role for EMMPRIN. Moreover, C. pneumoniae-infected monocytes exhibited increased MMP-and plasmin-dependent migration through
“matrigel”. Additionally, incubation of SMCs with supernatants of C. pneumoniae-infected monocytes induced MMP-2 activation, which was inhibited by IL1-Receptor
antagonist or anti-IL-6-mAb, indicating paracrine intercellular activation pathways.
In conclusion,C. pneumoniae induce MMP activity directly in monocytes through an EMMPRINdependent pathway and
indirectly in SMCs via monocytederived cytokines.
Keywords
EMMPRIN; MMPs -
C. pneumoniae; monocytes - plaque rupture