Severe sepsis and septic shock are still the main causes of multiple organ failure and mortality in surgical intensive care units, its morbidity and mortality are increasing year by year [13]. Sepsis causes a systemic inflammatory response driven by the production of proinflammatory cytokines, which affects the lives of patients with sepsis [14]. Immunosuppression after inflammation is a compensatory response designed to protect the host from overproduction of cytokines and other inflammatory factors. It is currently appreciated that sepsis leads to severe immunosuppression, and most sepsis-related deaths occur during the immunosuppressive phase [15]. Therefore, the inhibition of inflammatory mediators could be considered an effective treatment of sepsis. In this study, we investigated the mechanism of miR-544 on LPS-induced septic mice, and we found that miR-544 may protect acute liver injury in septic mice mainly by inhibiting inflammatory NF-κB signaling pathway.
It is well recognized that inflammation is the main cause of sepsis, and the liver are involved in host defense and tissue repair by controlling blood coagulation and inflammation processes. Thus, the liver is a key organ failure in sepsis. In our study, a sepsis mouse models were successfully established by intraperitoneal injection of LPS, which shown a significant change of histopathology and biochemical parameters (ALT, AST, and TBIL) [16]. Studies have reported an elevated level of biochemical parameters in experimentally induced sepsis, and all enzymes measured are in concordance with in our study. Our results for all enzymes measured are consistent with other studies. In addition, the biochemical parameters were further upregulated when treatment with miR-544 inhibitor but downregulated when treatment with miR-544 mimics. Therefore, miR-544 has a protective effect on sepsis-induced liver injury.
Inflammatory activation induces expression and release of multiple chemokines, including MCP-1. which is the main chemoattractant for monocytes. The release of chemokine MCP-1 further stimulates the release of inflammatory cytokines such as interleukin-1 (IL-1). Macrophages are essential mediators of the inflammatory response, with an essential role in the initiation and maintenance of inflammation [17]. CD16/32 is a marker of macrophages, and their expression levels are important indicators of inflammatory response [12]. Our results showed that the inflammatory markers of MCP-1 and CD16/32 were significantly increased in the model group compared with the normal group, and the expressions were significantly increased in the miR-544 inhibitor group but decreased with miR-544 mimics compared with model group. Sepsis causes a systemic inflammatory response driven by the production of proinflammatory cytokines, persistent inflammation can promote secondary tissue injury through excess production of proinflammatory factors, such as TNF-α, IL-1β, and IL-6 [18]. At present, several inflammatory biomarkers have been determined as potential biomarkers for patients with sepsis [19]. Our results indicated that the expression of inflammatory cytokines IL-1β, IL-6, and TNF-α were significantly increased after miR-544 inhibitor treatment but significantly decreased after miR-544 mimics treatment compared with LPS. These data indicate that miR-544 attenuates liver inflammation induced by LPS in sepsis.
Indeed, NF-κB is a critical signaling pathway of the inflammatory cascade, and there is growing evidence that the NF-κB signaling pathway is closely related to the secretion of various inflammatory mediators during sepsis, which regulates the expression of many inflammatory genes [20]. Therefore, inhibition of NF-κB activation may be a potential treatment for sepsis [21]. Under normal physiological conditions, NF-κB is sequestered in the cytoplasm in an inactive form associated with IκB-α [22]. Once activated by external stimuli, such as LPS, pro-inflammatory cytokines, virus and other agents [23], IκB is phosphorylated by IKK which leads to the degradation of IκBα [24], and subsequently, IκB-α/NF-κB complex degradation leads to the activation and release of NF-κB [25], resulting in p65 translocated into the nucleus where it may trigger the expression of multiple inflammatory genes [26], such as IL-1β, IL-6, and TNF-α [27]. In our study, western blot analysis of NF-κB signaling pathway proteins in the liver revealed that miR-544 reduces hepatic inflammation by inhibiting NF-κB signaling in the liver of septic mice.
In conclusion, our results demonstrated the hepatoprotective effects of miR-544 against LPS-induced sepsis by inhibiting inflammation, and the anti-inflammatory activity is largely related to the regulation of the NF-κB signaling pathways. Therefore, miR-544 can be a potential therapeutic agent for liver damage caused by sepsis in the future.