The many uses of autophagosomes

Hepatoprotective effect of anemoside B4 against sepsis-induced acute liver injury through modulating the mTOR/p70S6K-mediated autophagy

Sepsis triggers liver dysfunction with high morbidity and mortality. Here, we elucidated the effect of anemoside B4 on sepsis in cecal ligation and puncture (CLP)-induced mouse model and LPS-induced primary hepatocytes. Following CLP surgery, septic mice were intraperitoneally injected with anemoside B4 (50 or 100 mg/kg). Anemoside B4 improved septic mouse survival rate, decreased serum AST and ALT levels and attenuated liver histopathologic damages. Western blot analysis showed that anemoside B4 elevated the expression of Beclin-1, LC3II/LC3I, Atg3, Atg5, and Atg7, and reduced p62, suggesting the restoration of autophagy flux in liver. More autophagic vesicles were observed in liver after anemoside B4 treatment using transmission electron microscopy. Using ELISA and commercial enzyme kits, we found that anemoside B4 decreased serum TNF-α, IL-6, and IL-1β levels and increased CAT, SOD and GSH activities. TUNEL staining and western blot revealed that anemoside B4 suppressed cell apoptosis, along with decreased Bax, leaved caspase-3, cleaved PARP, but increased Bcl-2. Consistent with in vivo findings, anemoside B4 inhibited apoptosis, inflammatory response, and oxidative stress and enhanced autophagy in LPS-induced primary hepatocytes. Importantly, these cellular processes were possibly mediated by mTOR/p70S6K signaling, as reflected by the offset of 3-MA in the immunosuppression of anemoside B4.

SPIONs enhances IL-10-producing macrophages to relieve sepsis via Cav1-Notch1/HES1-mediated autophagy

Background

Sepsis is a life-threatening condition caused by dysregulated host responses to infection. Macrophages, which recognize microbial infections through identification of bacterial markers such as lipopolysaccharide (LPS), are crucial to the pathogenesis of sepsis-associated liver injury. However, the understanding of the SPIONs-mediated modulation of macrophage responses in LPS-induced sepsis and liver injury is limited.

Materials and methods

Superparamagnetic iron oxide nanoparticles (SPIONs) of γ-Fe₂O₃ nanoparticles were prepared, and their morphology and magnetic properties were characterized.

Results

Using a murine model of LPS-induced sepsis and liver injury, we found that SPIONs alleviated LPS-induced sepsis, preventing infiltration of inflammatory cells into the liver. SPIONs also increased the level of interleukin-10 (IL-10) in liver macrophages, while SPIONs’s effect on LPS-induced sepsis was abrogated in IL-10^-/- mice, indicating that the protective effect of SPIONs is dependent on IL-10⁺ macrophages. Moreover, SPIONs activated macrophage autophagy to increase IL-10 production, which was markedly attenuated by autophagy inhibition. Furthermore, SPIONs upregulated the expression of Caveolin-1 (Cav1) in macrophages, which plays a role in cellular uptake of metallic nanoparticles. Interestingly, activation of Cav1 and Notch1/HES1 signaling was involved in SPIONs-induced autophagy in both RAW 264.7 cells and bone marrow-derived macrophages (BMDMs). Our data reveal a novel mechanism for SPIONs -induced autophagy in macrophages, which occurs through activation of the Cav1-Notch1/HES1 signaling pathway, which promotes the production of IL-10 in macrophages, leading to inhibition of inflammation in LPS-induced sepsis and liver injury.

Conclusion

Our results suggest that SPIONs may represent a potential therapeutic agent for the treatment of sepsis and sepsis-induced liver injury.

Emerging Roles of Autophagy and Inflammasome in Ehrlichiosis

Human monocytic ehrlichiosis (HME) is a potentially life-threatening tick-borne rickettsial disease (TBRD) caused by the obligate intracellular Gram-negative bacteria, Ehrlichia. Fatal HME presents with acute ailments of sepsis and toxic shock-like symptoms that can evolve to multi-organ failure and death. Early clinical and laboratory diagnosis of HME are problematic due to non-specific flu-like symptoms and limitations in the current diagnostic testing. Several studies in murine models showed that cell-mediated immunity acts as a “double-edged sword” in fatal ehrlichiosis. Protective components are mainly formed by CD4 Th1 and NKT cells, in contrast to deleterious effects originated from neutrophils and TNF-α-producing CD8 T cells. Recent research has highlighted the central role of the inflammasome and autophagy as part of innate immune responses also leading to protective or pathogenic scenarios. Recognition of pathogen-associated molecular patterns (PAMPS) or damage-associated molecular patterns (DAMPS) triggers the assembly of the inflammasome complex that leads to multiple outcomes. Recognition of PAMPs or DAMPs by such complexes can result in activation of caspase-1 and -11, secretion of the pro-inflammatory cytokines IL-1β and IL-18 culminating into dysregulated inflammation, and inflammatory cell death known as pyroptosis. The precise functions of inflammasomes and autophagy remain unexplored in infections with obligate intracellular rickettsial pathogens, such as Ehrlichia. In this review, we discuss the intracellular innate immune surveillance in ehrlichiosis involving the regulation of inflammasome and autophagy, and how this response influences the innate and adaptive immune responses against Ehrlichia. Understanding such mechanisms would pave the way in research for novel diagnostic, preventative and therapeutic approaches against Ehrlichia and other rickettsial diseases.

MyD88-dependent inflammasome activation and autophagy inhibition contributes to Ehrlichia-induced liver injury and toxic shock

Severe hepatic inflammation is a common cause of acute liver injury following systemic infection with Ehrlichia, obligate Gram-negative intracellular bacteria that lack lipopolysaccharide (LPS). We have previously shown that type I IFN (IFN-I) and inflammasome activation are key host-pathogenic mediators that promote excessive inflammation and liver damage following fatal Ehrlichia infection. However, the underlying signals and mechanisms that regulate protective immunity and immunopathology during Ehrlichia infection are not well understood. To address this issue, we compared susceptibility to lethal Ixodes ovatus Ehrlichia (IOE) infection between wild type (WT) and MyD88-deficient (MyD88^-/-) mice. We show here that MyD88^-/- mice exhibited decreased inflammasome activation, attenuated liver injury, and were more resistant to lethal infection than WT mice, despite suppressed protective immunity and increased bacterial burden in the liver. MyD88-dependent inflammasome activation was also dependent on activation of the metabolic checkpoint kinase mammalian target of rapamycin complex 1 (mTORC1), inhibition of autophagic flux, and defective mitophagy in macrophages. Blocking mTORC1 signaling in infected WT mice and primary macrophages enhanced bacterial replication and attenuated inflammasome activation, suggesting autophagy promotes bacterial replication while inhibiting inflammasome activation. Finally, our data suggest TLR9 and IFN-I are upstream signaling mechanisms triggering MyD88-mediated mTORC1 and inflammasome activation in macrophages following Ehrlichia infection. This study reveals that Ehrlichia-induced liver injury and toxic shock are mediated by MyD88-dependent inflammasome activation and autophagy inhibition.

Human monocytic ehrlichiosis (HME) is the most prevalent emerging infectious disease in the United States. Ehrlichia chaffeensis, etiologic agent of HME, is a Gram negative obligate intracellular bacterium transmitted by infected tick bites and can infect different cell type. Although Ehrlichia lack lipopolysaccharide (LPS), they induce potentially life threatening HME that mimic sepsis or toxic shock associated with multi-organ failure. The clinical diagnosis of HME is difficult, and definitive diagnosis is most often retrospective. Late antibiotic treatment is frequently ineffective in preventing disease progression to fatal multi-organ failure. Liver failure is one of the most serious complications and the most frequent cause of death in patients with HME, however we only have a limited understanding of how this liver failure is caused during fatal Ehrlichia infection. The objective of this study is to determine how LPS-negative Ehrlichia activates inflammatory responses in macrophages during Ehrlichia infection to promote liver damage. We show here that MyD88-signaling causes detrimental derangement of the immune system and subsequent liver damage by regulating two key innate immune events in macrophages: autophagy and inflammasome activation. Targeting host-pathogenic pathways in ehrlichiosis can be incorporated into future design of novel therapeutic approaches for HME.

An ERp57-mediated disulphide exchange promotes the interaction between Burkholderia cenocepacia and epithelial respiratory cells

Previous studies have demonstrated that extracellular glutathione reduces the ability of the Cystic Fibrosis pathogen Burkholderia cenocepacia to infect primary or immortalized epithelial respiratory cells. We report here that the adhesion and invasion ability of B. cenocepacia is limited also by thiol-oxidizing and disulphide-reducing agents and by protein disulfide isomerase (PDI) inhibitors. PDI inhibitors also reduce the proinflammatory response elicited by cells in response to Burkholderia. These findings indicate that a membrane-associated PDI catalyzes thiol/disulphide exchange reactions which favor bacterial infection. The combined use of selective PDI inhibitors, RNA silencing and specific antibodies identified ERp57 as a major PDI involved in the interaction between B. cenocepacia and epithelial cells. This study contributes to the elucidation of the Burkholderia pathogenic mechanisms by showing that this microorganism exploits a membrane-associated host protein to infect epithelial cells and identifies ERp57 as a putative pharmacological target for the treatment of Burkholderia lung infections.

At the Center of Autophagy: Autophagosomes

Autophagosomes are double-membrane sequestering vesicles that are the hallmark of the intracellular catabolic process called macroautophagy. They are formed by the orchestrated interplay of the AuTophaGy-related (ATG) proteins. The cargo molecules targeted by autophagosomes ranges from long-lived proteins and superfluous or excess organelles to invading pathogens. Autophagosomes finally fuse with lysosomes delivering the sequestered material in the interior of these organelles where it is degraded by resident hydrolases. Autophagy represents a key survival mechanism because it clears the cytoplasm from unwanted and potentially toxic structures, and the autophagosomes are the central stage of it.

Francisella tularensis intracellular survival: to eat or to die

Francisella tularensis is a highly infectious facultative intracellular bacterium causing the zoonotic disease tularemia. Numerous attributes required for F. tularensis intracellular multiplication have been identified recently. However, the mechanisms by which the majority of them interfere with the infected host are still poorly understood. The following review summarizes our current knowledge on the different steps of Francisella intramacrophagic life cycle and expands on the importance of nutrient acquisition.

Autophagic clearance of bacterial pathogens: molecular recognition of intracellular microorganisms

Autophagy is involved in several physiological and pathological processes. One of the key roles of the autophagic pathway is to participate in the first line of defense against the invasion of pathogens, as part of the innate immune response. Targeting of intracellular bacteria by the autophagic machinery, either in the cytoplasm or within vacuolar compartments, helps to control bacterial proliferation in the host cell, controlling also the spreading of the infection. In this review we will describe the means used by diverse bacterial pathogens to survive intracellularly and how they are recognized by the autophagic molecular machinery, as well as the mechanisms used to avoid autophagic clearance.