Critical Role for a Subset of Intestinal Macrophages in Shaping Gut Microbiota in Adult Zebrafish

The zebrafish as a model for gastrointestinal tract-microbe interactions

The zebrafish (Danio rerio) has become a widely used vertebrate model for bacterial, fungal, viral, and protozoan infections. Due to its genetic tractability, large clutch sizes, ease of manipulation, and optical transparency during early life stages, it is a particularly useful model to address questions about the cellular microbiology of host-microbe interactions. Although its use as a model for systemic infections, as well as infections localised to the hindbrain and swimbladder having been thoroughly reviewed, studies focusing on host-microbe interactions in the zebrafish gastrointestinal tract have been neglected. Here, we summarise recent findings regarding the developmental and immune biology of the gastrointestinal tract, drawing parallels to mammalian systems. We discuss the use of adult and larval zebrafish as models for gastrointestinal infections, and more generally, for studies of host-microbe interactions in the gut.

Ability of prebiotic polysaccharides to activate a HIF1α-antimicrobial peptide axis determines liver injury risk in zebrafish

Natural polysaccharides have received much attention for their ability to ameliorate hepatic steatosis induced by high-fat diet. However, the potential risks of their use have been less investigated. Here, we show that the exopolysaccharides (EPS) from Lactobacillus rhamnosus GG (LGG) and L. casei BL23 reduce hepatic steatosis in zebrafish fed a high-fat diet, while BL23 EPS, but not LGG EPS, induce liver inflammation and injury. This is due to the fact that BL23 EPS induces gut microbial dysbiosis, while LGG EPS promotes microbial homeostasis. We find that LGG EPS, but not BL23 EPS, can directly activate intestinal HIF1α, and increased HIF1α boosts local antimicrobial peptide expression to facilitate microbial homeostasis, explaining the distinct compositions of LGG EPS- and BL23 EPS-associated microbiota. Finally, we find that liver injury risk is not confined to Lactobacillus-derived EPS but extends to other types of commonly used natural polysaccharides, depending on their HIF1α activation efficiency.

An electrochemiluminescent sensing matrix for real-time probing of cell-output reactive oxygen species

Herein, a novel cell-based electrochemiluminescent (ECL) sensing matrix was developed for probing reactive oxygen species (ROSs) produced from mouse macrophage cells. Uniformly sized Au nanoparticles (AuNPs) with an average diameter of 16 nm were decorated on the surface of indium tin oxide (ITO) glass through the connection of hydrolyzed 3-aminopropyl trimethoxysilane (APTMS) serving as a sensor substrate. Then, the surface was covered with a poly-l-lysine thin film, where mouse macrophage cells were successfully cultured. The morphology of the electrodes obtained was characterized by scanning electron microscopy and atomic force microscopy, and their electrochemical properties were investigated by electrochemical impedance spectroscopy. A linear response was observed from the AuNPs/APTMS/ITO substrate with a sensitivity of 0.465 units per mg/l of H₂O₂, and a higher sensitivity of 207 units per mg/l of zymosan. Thereafter, a factor of 84 molecules of H₂O₂ produced by a single glycogen was estimated. The results demonstrated that the ECL response of this cell-based sensor quantitatively correlated with yielded ROSs during cell oxygen metabolism under the stimulation of zymosan. This work suggests that the prepared sensing matrix is efficient for monitoring the oxygen metabolism of living cells and can be applied in biological and clinical fields to provide significant information on the regular or abnormal function of cells.