Abstract:

Objective To discuss the effect of triggering receptor expressed on myeloid cells-1 （TREM-1） inhibitory peptide LR12 on myocardial injury in the septic mice， and to clarify its possible mechanism. Methods The mouse model of sepsis was established by cecal ligation and puncture （CLP）. Forty male mice were randomly divided into sham operation group， model group， CLP+LR12 control peptide （LR12-scr） group， CLP+LR12 group， and CLP+DNase Ⅰ group， and there were 8 mice in each group. Except for sham operation group， the mice in the other groups underwent CLP to establish the sepsis models， and were intraperitoneally injected with LR12-scr， LR12， and DNase Ⅰ at 1 h after operation， respectively. At 24 h after operation， the status and behavior of the mice in various groups were observed. A small animal ultrasound system was used to detect the cardiac function of the mice in various groups； enzyme-linked immunosorbent assay （ELISA） method was used to detect the levels of creatine kinase isoenzyme-MB （CK-MB）， cardiac troponin I （cTnI）， and inflammatory indicators interleukin-1β （IL-1β）， interleukin-6 （IL-6）， and tumor necrosis factor-α （TNF-α） in serum， as well as the levels of myeloperoxidase （MPO）-DNA and neutrophil elastase （NE）-DNA in myocardium tissue of the mice in various groups； HE staining was used to observe the pathomorphology of myocardium tissue of the mice in various groups； immunofluorescence staining was used to detect the co-expression of lymphocyte antigen 6G （Ly6G） and citrullinated histone H3 （cit-H3） proteins in myocardium tissue of the mice in various groups； Western blotting method was used to detect the expression levels of TREM-1， MPO， NE， and cit-H3 proteins in myocardium tissue of the mice in various groups. Results Compared with sham operation group， the mice in model group were listless， with disordered arrangement of myocardium tissue， and atrophy and deformation of cardiomyocytes； compared with model group， the mental state and myocardium tissue injury of the mice in CLP+LR12 group and CLP+DNase Ⅰ group were significantly improved， while no significant change was observed in CLP+LR12-scr group. The cardiac function detection results showed that compared with sham operation group， the left ventricular ejection fraction （LVEF） and left ventricular fractional shortening （LVFS） of the mice in model group were significantly decreased （P<0.01）； compared with model group， the LVEF and LVFS of the mice in CLP+LR12 group and CLP+DNase Ⅰ group were significantly increased （P<0.01）. The ELISA results showed that compared with sham operation group， the levels of CK-MB， cTnI， IL-1β， IL-6， and TNF-α in serum and the levels of MPO-DNA and NE-DNA in myocardium tissue of the mice in model group were significantly increased （P<0.01）； compared with model group， the levels of CK-MB， cTnI， IL-1β， IL-6， and TNF-α in serum and the levels of MPO-DNA and NE-DNA in myocardium tissue of the mice in CLP+LR12 group and CLP+DNase Ⅰ group were significantly decreased （P<0.01）； no significant changes in the above indicators were observed in CLP+LR12-scr group （P>0.05）. The immunofluorescence staining results showed that compared with sham operation group， the co-expression of Ly6G and cit-H3 proteins in myocardium tissue of the mice in model group was increased； compared with model group， the co-expression of Ly6G and cit-H3 proteins in myocardium tissue of the mice in CLP+LR12 group and CLP+DNase Ⅰ group was decreased. The Western blotting method results showed that compared with sham operation group， the expression levels of TREM-1， MPO， NE， and cit-H3 proteins in myocardium tissue of the mice in model group were significantly increased （P<0.01）； compared with model group， the expression levels of TREM-1， MPO， NE， and cit-H3 proteins in myocardium tissue of the mice in CLP+LR12 group were significantly decreased （P<0.01）， while the expression levels of MPO， NE， and cit-H3 proteins in myocardium tissue of the mice in CLP+DNase Ⅰ group were significantly decreased （P<0.01）， and there was no significant difference in the expression level of TREM-1 protein （P>0.05）. Conclusion TREM-1 inhibitory peptide LR12 can improve the cardiac function and alleviate myocardial inflammation and injury in the septic mice， and its mechanism may be related to inhibiting the formation of neutrophil extracellular traps （NETs）.

Key words: Sepsis, Myocardial injury, Triggering receptor expressed on myeloid cells-1, Neutrophil extracellular trap, LR12