AMPK activates Parkin independent autophagy and improves post sepsis immune defense against secondary bacterial lung infections

Abstract

Metabolic and bioenergetic plasticity of immune cells is essential for optimal responses to bacterial infections. AMPK and Parkin ubiquitin ligase are known to regulate mitochondrial quality control mitophagy that prevents unwanted inflammatory responses. However, it is not known if this evolutionarily conserved mechanism has been coopted by the host immune defense to eradicate bacterial pathogens and influence post-sepsis immunosuppression. Parkin, AMPK levels, and the effects of AMPK activators were investigated in human leukocytes from sepsis survivors as well as wild type and Park2−/− murine macrophages. In vivo, the impact of AMPK and Parkin was determined in mice subjected to polymicrobial intra-abdominal sepsis and secondary lung bacterial infections. Mice were treated with metformin during established immunosuppression. We showed that bacteria and mitochondria share mechanisms of autophagic killing/clearance triggered by sentinel events that involve depolarization of mitochondria and recruitment of Parkin in macrophages. Parkin-deficient mice/macrophages fail to form phagolysosomes and kill bacteria. This impairment of host defense is seen in the context of sepsis-induced immunosuppression with decreased levels of Parkin. AMPK activators, including metformin, stimulate Parkin-independent autophagy and bacterial killing in leukocytes from post-shock patients and in lungs of sepsis-immunosuppressed mice. Our results support a dual role of Parkin and AMPK in the clearance of dysfunctional mitochondria and killing of pathogenic bacteria, and explain the immunosuppressive phenotype associated Parkin and AMPK deficiency. AMPK activation appeared to be a crucial therapeutic target for the macrophage immunosuppressive phenotype and to reduce severity of secondary bacterial lung infections and respiratory failure.

ZKSCAN3 in severe bacterial lung infection and sepsis-induced immunosuppression

“…The control group of mice (sham) underwent surgery without CLP. Post-CLP mice developed immunosuppression, including increase severity of lung infections confirmed by intratracheal instillation of P. aeruginosa , as previously described in our recent studies 19 . Mice were euthanized 7 days after surgery and lung homogenates stored in liquid nitrogen for further analyses.…”

“…Given that P. aeruginosa -induced pneumonia is associated with a robust decrease in autophagy and lysosomes in lungs of infected mice, we tested if this is relevant in the mice that survive sepsis, but developed immunosuppression. Of note, we have recently demonstrated that mice developed immunosuppression following CLP-induced intra-abdominal sepsis vs. sham 19 . This was confirmed by measurement of colony forming units (CFUs) from lung homogenates.…”

“…Phagolysosomes are a result of fusion between phagosomes and lysosomes that allows for effective degradation of many regulatory and damaged proteins, as well as neutralization of dysfunctional organelles, in processes such as mitochondrial quality control 16 – 18 . Importantly, this degradative mechanism is also utilized for pathogen neutralization 12 , 19 . Phagolysosome formation is a complex process that is initiated by LC3-I lipidation into LC3-II followed by incorporation into the phagosomal membranes 16 .…”

Aerobic exercise improves LPS-induced sepsis via regulating the Warburg effect in mice

“…Our data demonstrated that LPS injection prominently upregulated the levels of lactate and HMGB1 in serum, while AE prominently downregulated the levels of lactate and HMGB1 in serum during sepsis. It has been suggested that insulin can decrease serum HMGB1 levels in septic animals 1 , implying a possible role of glucose metabolism in the regulation of HMGB1 release. It’s well documented that exercise can improve insulin resistance.…”

“…Sepsis, which has many complications, such as MODS, hypotension, and pathoglycemia, exhibits a high mortality rate stemming from a systemic infection 1 – 3 . Sepsis is characterized by an uncontrolled inflammatory response and oxidative stress 4 , 5 .…”