In a recent study published in the journal ImmunityBrazilian researchers describe the crucial function of intestinal dysbiosis during pregnancy in promoting excessive macrophage pyroptosis, which increases vulnerability to sepsis.
Study: Gut microbiota in pregnancy, please don’t change me now. Image Credit: wutzkohphoto / Shutterstock.com
Sepsis and pregnancy
Sepsis is characterized by life-threatening multi-organ dysfunction caused by a dysregulated host inflammatory response to infection. Men are more commonly affected by sepsis than women. However, certain events such as pregnancy increase the risk of severe sepsis in women, which is one of the leading causes of maternal mortality and morbidity worldwide.
Changes in the immunological response are likely responsible for the increased susceptibility and severity of infections that occur as pregnancy progresses. However, the exact mechanisms responsible for the increased risk of sepsis during pregnancy remain unclear.
About the study
In the present study, researchers explore how gut dysbiosis during pregnancy inhibits the host’s macrophage-dependent immunological response and subsequently leads to an increased risk of sepsis.
To this end, the researchers studied the vulnerability of pregnant mice to induced sepsis using two distinct experimental models of experimental sepsis. These included polymicrobial peritonitis caused by pneumonia brought on by Pseudomonas aeruginosa intratracheal inoculation and cecal ligation and puncture (CLP) surgery.
The potential role of intestinal dysbiosis during pregnancy in amplifying sepsis was assessed by transplanting faecal microbiota obtained from pregnant women or mice into non-pregnant mice. The team also performed 16S ribosomal RNA gene sequencing to determine how gut microbial dysbiosis affects susceptibility to sepsis during pregnancy. A proteomic study was also carried out.
Study results
Pregnancy has been found to worsen sepsis outcomes, characterized by an excessive inflammatory response, severe damage to multiple organs, and low bacterial clearance. Moreover, transplantation of fecal microbiota from pregnant mice increased the inflammatory response and the risk of death in non-pregnant mice with sepsis. In contrast, transplantation of faecal microbiota from non-pregnant mice reduced sepsis mortality.
Thus, changes in the intestinal flora during pregnancy increase vulnerability to sepsis. Additionally, intestinal dysbiosis was associated with immunological dysfunction, leading to greater susceptibility to sepsis in mice.
Metabolomic analysis of cecal contents obtained from pregnant mice indicated a notable alteration in the metabolic characteristics of their gut microbiota, such as reduced levels of formononetin (FMN). In addition, pregnant mice that had undergone CLP showed a reduction Parabacteroides shit levels in peritoneal fluid lavage, which correlated with lower concentrations of FMN.
These findings indicate that P.merdae may affect the endogenous bioavailability of FMNs. Intestinal microbial b-galactosidases also catalyzed the hydrolysis of bioactive substances in food, resulting in the production of isoflavone aglycones, such as FMN.
Selective macrophage depletion was observed in the peritoneal cavity of pregnant mice with sepsis. Transplantation of fecal microbiota from pregnant mice to non-pregnant mice also replicated this behavior. Depletion of macrophages with clodronate liposomes exacerbated CLP-induced sepsis, thereby negating the protective effects of FMN therapy.
Pregnancy or transplantation of fecal microbiota from pregnant mice increased peritoneal macrophage cell death rates in mice with sepsis. In contrast, FMN therapy reduced peritoneal macrophage death.
The higher frequency of peritoneal macrophages in pregnant septic mice administered with a caspase-1 inhibitor and not with other cell death inhibitors suggests that pyroptosis may be required to increase sepsis-induced macrophage death during the pregnancy.
FMN therapy inhibited gasdermin D (GSDMD) and caspase-1 p20 synthesis, as well as lipopolysaccharide (LPS)/adenosine triphosphate-mediated apoptosis-associated stain (ASC) oligomerization (ATP) in bone marrow-derived macrophages (BMDM), thus suppressing macrophage pyroptosis and the release of interleukin 18 (IL-18) and IL-1b.
Additionally, FMN reduced the messenger ribonucleic acid (mRNA) transcript Nlrp3 among LPS/ATP-activated BMDMs. This provided a new mechanism by which FMN can regulate pyroptosis.
Silencing heterogeneous nuclear ribonucleoprotein 2 (hnRNPUL2) type U protein genetically reduced macrophage pyroptosis. Moreover, extensive analyzes demonstrated that FMN could interact directly with hnRNPUL2.
This facilitated its subsequent association with chaperone protein heat shock cognate 70 (HSC70), which interacted with misfolded or denatured proteins to ultimately promote lysosomal protein degradation as a vital mechanism for cellular homeostasis. FMN also promoted the colocalization of hnRNPUL2 with lysosomes, thereby reducing its nuclear accumulation in LPS/ATP-activated BMDM.
Reporter gene and chromatin immunoprecipitation (ChIP) assays showed that hnRNPUL2 directly interacted with the promoter zone and stimulated Nlrp3 transcription in BMDMs. These results demonstrate that FMN inhibited macrophage pyroptosis by reducing Nlrp3 gene expression and nuclear hnRNPUL2 accumulation.
conclusion
Overall, the study results highlight the function of the hnRNPUL2-NLRP3 axis, which is mediated by P.merdae dysbiosis and reduced levels of FMN metabolites, in overstimulation of macrophage pyroptosis in sepsis-induced immunological dysfunction in pregnancy. Therefore, future studies should determine whether FMN drugs or supplements could be used as a therapeutic approach to treat sepsis in pregnant women.