Introduction:
Exosomes, a group of nano-vesicles secreted from living cells, are documented to increase in the circulation and are believed to promote cardiac dysfunction in sepsis patients and animal models. However, whether inhibition of exosome release could exert a cardio-protective effect in polymicrobial sepsis remains unexplored.
Methods and Results:
C57BL/6 mice (male, 8-week old) were pre-treated with GW4869 (dissolved in DMSO, injection i.p. at a dose of 2.5μg/g body weight), a known inhibitor of exosome secretion. Same volume of DMSO was used as controls. One hour later, cecal ligation and puncture (CLP) surgery was performed to induce polymicrobial sepsis. We found that the concentration of serum exosomes, measured by membrane markers CD63 and CD81with detection ELISA kits, was increased by 3.5-fold in DMSO-CLP mice, but no increase was detected in GW4869-CLP mice or in sham operated mice (n=4-6, p<0.01). Myocardial contractile function, assessed at 12h post-CLP using a SONOS-7500 echocardiography system, revealed that pre-injection of GW4869 significantly attenuated CLP-associated cardiac dysfunction, evidenced by an improved left ventricular ejection fraction (LVEF) and minor axis fractional shortening (LVFS), compared to DMSO controls (n=8-10, p<0.01). Myeloperoxidase (MPO) activity, a marker of myocardial inflammation, measured with a [[Unable to Display Character: fl]]uorometric assay kit, also showed a significant reduction in GW4869-pre-treated mice, compared to DMSO-controls (n=5, p<0.01). Similarly, serum levels of inflammatory cytokines TNF-α and IL-1β triggered by CLP were reduced by 72% and 61%, respectively in GW4869-treated mice, compared with controls (n=6). Furthermore, we observed that 67% (n=9) of the DMSO controls, but only 20% in GW4869-treated mice (n=10) had died by 48h post-CLP. In vitro study confirmed that GW4869 limited the production of TNF-α and IL-1β in RAW 264.7 cells (a mouse macrophage cell line) challenged with endotoxin (LPS, 1μg/ml, 24 h).
Conclusions:
Together, this study indicates that blockade of exosome secretion could attenuate the inflammatory cytokine response as well as the consequent cardiac dysfunction and mortality in polymicrobial sepsis. Thus, our study may provide a new approach to the treatment of sepsis.
Toll-like receptor 2 plays a critical role in cardiac dysfunction during polymicrobial sepsis*
