EBP50 induces apoptosis in macrophages by upregulating nitric oxide production to eliminate intracellular Mycobacterium tuberculosis

Enhanced cancer therapeutic efficiency of NO combined with siRNA by caspase-3 responsive polymers

The combination of nitric oxide (NO) and siRNA is highly desirable for cancer therapy. Here, the furoxans-grafted PEI polymer (FDP) with caspase-3 responsive cleavable DEVD linker was synthesized, and used to bind siRNAs via electrostatic interaction and self-assembled into FDP/siRNA nanoplexes by hydrophobic force. After cellular uptake and lysosomal escape, the FDP/siRNA nanoplexes could achieve GSH-triggered NO release, and then increase the activity of caspase-3. The activated caspase-3 could specifically cleave the DEVD peptide sequence and enhance cell apoptosis. With the cleavage of DEVD peptide sequence, the disassembly of FDP/siRNA nanoplexes was further promoted, thereby resulting in increased siRNAs of ~40% were released at 48 h compared with the caspase-3 non-responsive FDnP/siRNA nanoplexes. By this way, cell apoptosis promotion and cell proliferation inhibition was achieved by siRNA-based downregulation of EGFR protein and the upregulated activity of caspase-3, followed by the enhanced cascade release of NO from FDP/siRNA nanoplexes. Furthermore, in vivo results demonstrated the improved anti-cancer efficiency of FDP/siEGFR nanoplexes without any detectable side effects. Therefore, it is believed that the caspase-3 responsive cleavable furoxans-grafted PEI polymers could provide a potential and efficient enhancement for cancer therapeutic efficiency by the co-delivery of nitric oxide and siRNA.

Doxycycline Induces Apoptosis of Brucella Suis S2 Strain-Infected HMC3 Microglial Cells by Activating Calreticulin-Dependent JNK/p53 Signaling Pathway

Neurobrucellosis is a chronic complication of human brucellosis that is caused by the presence of Brucella spp in the central nervous system (CNS) and the inflammation play a key role on the pathogenesis. Doxycycline (Dox) is a widely used antibiotic that induces apoptosis of bacteria-infected cells. However, the mechanisms of Brucella inhibition of microglial apoptosis and Dox induction of apoptosis are still poorly understood. In this study, we found that Brucella suis S2 strain (B. suis S2) increased calreticulin (CALR) protein levels and inhbited HMC3 cell apoptosis. Hence, we constructed two HMC3 cell line variants, one with stable overexpression (HMC3-CALR) and one with low expression of CALR (HMC3-sh-CALR). CALR was found to decrease levels of p-JNK and p-p53 proteins, as well as suppress apoptosis in HMC3 cells. These findings suggest that CALR suppresses apoptosis by inhibiting the JNK/p53 signaling pathway. Next, we treated HMC3, HMC3-CALR and HMC3-sh-CALR cell lines with B. suis S2 or Dox. Our results demonstrate that B. suis S2 restrains the JNK/p53 signaling pathway to inhibit HMC3 cell apoptosis via increasing CALR protein expression, while Dox plays the opposite role. Finally, we treated B. suis S2-infected HMC3 cells with Dox. Our results confirm that Dox induces JNK/p53-dependent apoptosis in B. suis S2-infected HMC3 cells through inhibition of CALR protein expression. Taken together, these results reveal that CALR and the JNK/p53 signaling pathway may serve as novel therapeutic targets for treatment of neurobrucellosis.

Heterogeneous Strategies to Eliminate Intracellular Bacterial Pathogens

Antibiotic tolerance in bacterial pathogens that are genetically susceptible, but phenotypically tolerant to treatment, represents a growing crisis for public health. In particular, the intracellular bacteria-mediated antibiotic tolerance by acting as “Trojan horses” play a critical and underappreciated role in the disease burden of bacterial infections. Thus, more intense efforts are required to tackle this problem. In this review, we firstly provide a brief overview of modes of action of bacteria invasion and survival in macrophage or non-professional phagocytic cells. Furthermore, we summarize our current knowledge about promising strategies to eliminate these intracellular bacterial pathogens, including direct bactericidal agents, antibiotic delivery to infection sites by various carriers, and activation of host immune functions. Finally, we succinctly discuss the challenges faced by bringing them into clinical trials and our constructive perspectives.

Inorganic nitrite increases the susceptibility of tilapia (Oreochromis niloticus) leucocytes to Streptococcus agalactiae

Deteriorating water quality, especially from high concentrations of nitrite, is currently largely blamed for disease outbreaks in farmed tilapia (Oreochromis niloticus). In this study, the underlying mechanism of nitrite on the susceptibility of tilapia leucocytes to Streptococcus agalactiae (S. agalactiae) was studied. We found that a high dose of heat-killed S. agalactiae decreased tilapia leucocytes cell viability, whereas nitrite decreased the cell viability of leucocytes exposed to a low dose of bacteria. Bacterial challenge increased the production of nitric oxide (NO), whereas nitrite and bacteria coexposure caused higher NO production than nitrite or bacterial exposure alone. Cell viability increased after elimination of NO, and negative correlations existed between cell viability and the NO content, suggesting that nitrite increased the susceptibility of the leucocytes against S. agalactiae was NO-dependent. For a more comprehensive understanding of the mechanism of nitrite affecting disease resistance in tilapia leucocytes, an RNA-Seq-based transcriptome was generated. The results showed that 6173 transcripts were differently expressed, and the differentially expressed transcripts (DETs) of the bacterial group, nitrite group and bacteria-nitrite co-treatment group compared to the control group were selected for GO and KEGG analyses. The DETs in the bacterial group and bacteria-nitrite cotreatment group were highly involved with the membrane component, signal transduction, and immune responses. KEGG analysis showed that the protein processing in the endoplasmic reticulum and the AMPK signaling pathway, which are related to autophagy, were significantly enriched in the cotreatment group but not in bacterial group. In addition, the mRNA expression of ten DETs and several autophagy and apoptosis related genes validated by q-PCR showed the high reliability of the RNA-seq. Taken together, the results of this study suggest that nitrite may increase the susceptibility of tilapia leucocytes to S. agalactiae by generating excess NO to affect the autophagy and apoptosis process.

Control of Phagocytosis by Microbial Pathogens

Phagocytosis is a fundamental process of cells to capture and ingest foreign particles. Small unicellular organisms such as free-living amoeba use this process to acquire food. In pluricellular organisms, phagocytosis is a universal phenomenon that all cells are able to perform (including epithelial, endothelial, fibroblasts, etc.), but some specialized cells (such as neutrophils and macrophages) perform this very efficiently and were therefore named professional phagocytes by Rabinovitch. Cells use phagocytosis to capture and clear all particles larger than 0.5 µm, including pathogenic microorganisms and cellular debris. Phagocytosis involves a series of steps from recognition of the target particle, ingestion of it in a phagosome (phagocytic vacuole), maturation of this phagosome into a phagolysosome, to the final destruction of the ingested particle in the robust antimicrobial environment of the phagolysosome. For the most part, phagocytosis is an efficient process that eliminates invading pathogens and helps maintaining homeostasis. However, several pathogens have also evolved different strategies to prevent phagocytosis from proceeding in a normal way. These pathogens have a clear advantage to perpetuate the infection and continue their replication. Here, we present an overview of the phagocytic process with emphasis on the antimicrobial elements professional phagocytes use. We also summarize the current knowledge on the microbial strategies different pathogens use to prevent phagocytosis either at the level of ingestion, phagosome formation, and maturation, and even complete escape from phagosomes.