Antibiotic Use in Sepsis: How and Why Less Can Really Mean More (Survival)

QKI degradation in macrophage by RNF6 protects mice from MRSA infection via enhancing PI3K p110β dependent autophagy

Background

Sepsis is a fatal condition commonly caused by Methicillin-resistant Staphylococcus aureus (MRSA) with a high death rate. Macrophages can protect the host from various microbial pathogens by recognizing and eliminating them. Earlier we found that Quaking (QKI), an RNA binding protein (RBP), was involved in differentiation and polarization of macrophages. However, the role of QKI in sepsis caused by pathogenic microbes, specifically MRSA, is unclear. This study aimed to investigate the role of QKI in regulation of host–pathogen interaction in MRSA-induced sepsis and explored the underlying mechanisms.

Methods

Transmission electron microscope and immunofluorescence were used to observe the autophagy level in macrophages. Real-time PCR and western blot were used to analyzed the expression of mRNA and protein respectively. The potential protein interaction was analyzed by iTRAQ mass spectrometry and Immunoprecipitation. RNA fluorescence in situ hybridization, dual-luciferase reporter assay and RNA immunoprecipitation were used to explore the mechanism of QKI regulating mRNA of PI3K-p110β.

Results

The mRNA level of QKI was aberrantly decreased in monocytes and PBMCs of septic patients with the increasing level of plasma procalcitonin (PCT). Then the mice with myeloid specific knockout of QKI was challenged with MRSA or Cecal Ligation and Puncture (CLP). Mice in these two models displayed higher survival rates and lower bacterial loads. Mechanistically, QKI deletion promoted phagocytosis and autophagic degradation of MRSA via activating p110β (a member of Class IA phosphoinositide 3-kinases) mediated autophagic response. QKI expression in macrophages led to the sequestration of p110β in mRNA processing (P) bodies and translational repression. Upon infection, the direct interaction of RNF6, a RING-type E3 ligase, mediated QKI ubiquitination degradation and facilitated PI3K-p110β related autophagic removal of pathogen. The administration of nanoparticles with QKI specific siRNA significantly protected mice from MRSA infection.

Conclusions

This study disclosed the novel function of QKI in the P body mRNA regulation during infection. QKI degradation in macrophage by RNF6 protects mice from MRSA infection via enhancing PI3K-p110β dependent autophagy. It suggested that QKI may serve as a potential theranostic marker in MRSA-induced sepsis.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00865-9.

Defining Clinical and Microbiological Nonresponse in Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is a severe complication of mechanical ventilation, with mortality reduced most effectively by adequate early antibiotic treatment. The clinical and microbiologic response can be assessed easily from 72 hours after starting antibiotic treatment. Evidence of nonresponse is based on several factors: (1) lack of clinical improvement, (2) radiographic progression, (3) an impaired Sequential Organ Failure Assessment (SOFA) score, (4) no improvement by days 3 to 5 on the Clinical Pulmonary Infection Score (CPIS), (5) no decreased in biomarkers on day 3, and (6) isolation of a new pathogen on day 3. Among the clinical markers of treatment failure, physicians should consider no improvement in the ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO₂/FiO₂), persistence of fever or hypothermia, persistence of purulent respiratory secretions, and new-onset septic shock or multiple-organ dysfunction syndrome. Microbiological isolation of a new pathogen on day 3 is also associated with higher mortality, but persistence of the original pathogen does not seem to be associated with a worse prognosis. The real impact of changes to treatment after diagnosing nonresponsive VAP is unknown. Physicians must evaluate whether treatments are adequate in terms of sensitivity, dose, and route. Pharmacokinetically and pharmacodynamically optimized doses are recommended in these patients. Clinical stabilization of comorbidities or underlying conditions may be of benefit.