A Novel Lipopolysaccharide Recognition Mechanism Mediated by Internalization in Teleost Macrophages

Intestinal epithelial cells of Japanese flounder (Paralichthys olivaceus) as an in vitro model for studying intestine immune function based on transcriptome analysis

Japanese flounder (Paralichthys olivaceus) is an economically crucial marine species, but diseases like hemorrhagic septicemia caused by Edwardsiella tarda have resulted in significant economic losses. E. tarda infects various hosts, and its pathogenicity in fish is not fully understood. Lipopolysaccharides (LPS) are components of the outer membrane of Gram-negative bacteria and are representative of typical PAMP molecules that cause activation of the immune system. The PoIEC cell line is a newly established intestinal epithelial cell line from P. olivaceus. In order to investigate whether it can be used as an in vitro model for studying the pathogenesis of E. tarda and LPS stimulation, we conducted RNA-seq experiments for the PoIECs model of E. tarda infection and LPS stimulation. In this study, transcriptome sequencing was carried out in the PoIEC cell line after treatment with LPS and E. tarda. A total of 62.52G of high-quality data from transcriptome sequencing results were obtained in nine libraries, of which an average of 87.96% data could be aligned to the P. olivaceus genome. Data analysis showed that 283 and 414 differentially expressed genes (DEGs) in the LPS versus Control (LPS-vs-Con) and E. tarda versus Control groups (Et-vs-Con), respectively, of which 60 DEGs were shared in two comparation groups. The GO terms were predominantly enriched in the extracellular space, inflammatory response, and cytokine activity in the LPS-vs-Con group, whereas GO terms were predominantly enriched in nucleus and positive regulation of transcription by RNA polymerase II in the Et-vs-Con group. KEGG analysis revealed that three immune-related pathways were co-enriched in both comparison groups, including the Toll-like receptor signaling pathway, C-type lectin receptor signaling pathway, and Cytokine-cytokine receptor interaction. Five genes were randomly screened to confirm the validity and accuracy of the transcriptome data. These results suggest that PoIEC cell line can be an ideal in vitro model for studies of marine fish gut immunity and pathogenesis of Edwardsiellosis.

Phytoconstituents of Androstachys johnsonii Prain Prevent Reactive Oxygen Species Production and Regulate the Expression of Inflammatory Mediators in LPS-Stimulated RAW 264.7 Macrophages

According to a survey, the medicinal use of Androstachys johnsonii Prain is kept secret by traditional healers. Considering that inflammation and oxidative stress are major risk factors for the progression of various chronic diseases and disorders, we resolved to investigate the antioxidant and anti-inflammatory potentials of A. johnsonii using in vitro and cell-based assays. The antioxidant activity of A. johnsonii hydroethanolic leaf extract (AJHLE) was evaluated using the ABTS, DPPH, and FRAP assays. Its cytotoxic effect was assessed on RAW 264.7 macrophages using an MTT assay. Then, its anti-inflammatory effect was evaluated by measuring the NO production and 15-LOX inhibitory activities. Moreover, its preventive effect on ROS production and its regulatory effect on the expression of pro-inflammatory mediators such as IL-1β, IL-10, TNF-α, and COX-2 were determined using established methods. AJHLE strongly inhibited radicals such as ABTS•+, DPPH•, and Fe3+-TPTZ with IC50 values of 9.07 µg/mL, 8.53 µg/mL, and 79.09 µg/mL, respectively. Additionally, AJHLE induced a significant (p < 0.05) cytotoxic effect at 100 µg/mL, and when tested at non-cytotoxic concentrations, it inhibited NO and ROS production in LPS-stimulated RAW 264.7 macrophages in a concentration-dependent manner. Furthermore, AJHLE showed that its anti-inflammatory action occurs via the inhibition of 15-LOX activity, the downregulation of COX-2, TNF-α, and IL-1β expression, and the upregulation of IL-10 expression. Finally, chemical investigation showed that AJHLE contains significant amounts of procyanidin, epicatechin, rutin, and syringic acid which support its antioxidant and anti-inflammatory activities. These findings suggest that A. johnsonii is a potential source of therapeutic agents against oxidative stress and inflammatory-related diseases.

Protective Effects of Peroxiredoxin 6 in Pro-Inflammatory Response Model Using Raw 264.7 Macrophages

The aim of the work was to study effects of peroxiredoxin 6 (PRDX6), a recombinant antioxidant protein, on the level of pro-inflammatory responses of RAW 264.7 macrophages to endotoxin exposure. Addition of LPS to the RAW 264.7 cell culture medium expectedly increased production of TNF-α, and addition of PRDX6 led to a significant (15-20%) decrease in its production. The level of production of another pro-inflammatory cytokine, IL-1β, which was significantly activated by endotoxin, was completely normalized under the PRDX6 action. Moreover, addition of PRDX6 reduced production of reactive oxygen species (ROS) induced by endotoxin and also prevented overexpression of the iNos gene in the RAW 264.7 cells. The results showed that PRDX6 had a suppressive effect on the expression of Nrf-2 gene and production of the transcription factor NRF-2 during the first 6 h of cell cultivation. Addition of endotoxin caused activation of the NF-κB and SAPK/JNK signaling cascades, while in the presence of PRDX6, activity of these signaling cascades decreases. It is known that the pro-inflammatory response of cells caused by exposure to bacterial LPS leads to activation of apoptosis and elimination of the damaged cells. Our studies confirm this, since exposure to LPS led to activation of the expression of P53 gene, a marker of apoptosis. Peroxiredoxin 6 added within the first hours of the development of acute pro-inflammatory response suppressed the P53 gene expression, indicating protective effect of PRDX6 that reduced apoptosis in the RAW 264.7 macrophages.

Production and characterization of exopolysaccharides from salinity-induced Auxenochlorella protothecoides and the analysis of anti-inflammatory activity

The set scenario of this work was to investigate the production, physicochemical characteristics, and anti-inflammatory activities of exopolysaccharides from salinity-induced Auxenochlorella protothecoides. The results demonstrated that 10 ‰ salinity manipulation endowed preferable exopolysaccharide production by A. protothecoides. Under this salinity stress, ACPEPS1A and ACPEPS2A were purified from exopolysaccharide production by anion chromatography and molecular exclusion chromatography. ACPEPS1A exhibited a molecular weight (Mw) of 132 kDa and mainly consisted of galactose. ACPEPS2A was a heteropolysaccharide with an Mw of 170 kDa and the main monosaccharides of galactose and rhamnose with separate molar percents of 42.41 % and 35.29 %, respectively. FTIR, ¹H and ¹³C NMR supported that monosaccharide components of ACPEPS1A and ACPEPS2A possessed both α- and β-configuration pyranose rings. Further evidence indicated that ACPEPS1A and ACPEPS2A could effectively inhibit the inflammatory response in lipopolysaccharide (LPS) induced RAW264.7 cells by quenching inflammatory factor levels such as ROS, iNOS, TNF-α, and IL-6. The potential anti-inflammatory possibilities were that the monosaccharides of ACPEPS1A and ACPEPS2A possessed higher affinity with receptors on the macrophage surface than LPS and hampered LPS-induced inflammation. The findings of this work would favor innovative applications of exopolysaccharides from microalgae in complementary medicines or functional foods.

Minocycline Prevents the Development of Key Features of Inflammation and Pain in DSS-induced Colitis in Mice

Abdominal pain is a common feature in inflammatory bowel disease (IBD) patients, and greatly compromises their quality of life. Therefore, the identification of new therapeutic tools to reduce visceral pain is one of the main goals for IBD therapy. Minocycline, a broad-spectrum tetracycline antibiotic, has gained attention in the scientific community because of its immunomodulatory and anti-inflammatory properties. The aim of this study was to evaluate the potential of this antibiotic as a therapy for the management of visceral pain in dextran sodium sulfate (DSS)-induced colitis in mice. Preemptive treatment with minocycline markedly reduced histological features of intestinal inflammation and the expression of inflammatory markers (Tlr4, Tnfα, Il1ß, Ptgs2, Inos, Cxcl2, and Icam1), and attenuated the decrease of markers of epithelial integrity (Tjp1, Ocln, Muc2, and Muc3). In fact, minocycline restored normal epithelial permeability in colitic mice. Treatment with the antibiotic also reversed the changes in the gut microbiota profile induced by colitis. All these ameliorative effects of minocycline on both inflammation and dysbiosis correlated with a decrease in ongoing pain and referred hyperalgesia, and with the improvement of physical activity induced by the antibiotic in colitic mice. Minocycline might constitute a new therapeutic approach for the treatment of IBD-induced pain. PERSPECTIVE: This study found that the intestinal anti-inflammatory effects of minocycline ameliorate DSS-associated pain in mice. Therefore, minocycline might constitute a novel therapeutic strategy for the treatment of IBD-induced pain.

Comparative Transcriptome Analysis of Head Kidney of Aeromonas hydrophila-infected Hypoxia-tolerant and Normal Large Yellow Croaker

The large yellow croaker (Larimichthys crocea) is one of the most economically important marine fish on the southeast coast of China and much of its yield is usually lost by hypoxia. To address this problem and lay a foundation for culturing a new strain of large yellow croaker with hypoxia tolerance, our research group screened a hypoxia-tolerant population of L. crocea. Surprisingly, we also found that hypoxia-tolerant population exhibited higher survival when infected with pathogens compared to the normal population during the farming operation. In order to understand the mechanism underlying the higher survival rate of the hypoxia-tolerant population and enrich the head kidney immune mechanism of L. crocea infected with pathogens, we compared and analyzed the head kidney transcriptome of the hypoxia-tolerant and normal individuals under Aeromonas hydrophila infection. We obtained 159.68 GB high-quality reads, of which more than 87.61% were successfully localized to the reference genome of L. crocea. KEGG analysis revealed differentially expressed genes in the signaling pathways involving immunity, cell growth and death, transport and catabolism, and metabolism. Among these, the toll-like receptor signaling pathway, Nod-like receptor signaling pathway, cytokine-cytokine receptor interaction, phagosome, apoptosis, and OXPHOS pathways were enriched in both groups after infection compared to before, and were enriched in infected tolerant individuals compared to normal individuals. In addition, we found that the expression of hif1α and its downstream genes were higher in the hypoxia-sensitive group of fish than in the normal group. In conclusion, our results showed some signaling pathways and hub genes, which may participate in A. hydrophila defense in the head kidney of two populations, and may contribute to the higher survival rate in the hypoxia-tolerant population. Overall, these findings increase our understanding of the defense mechanism within the head kidney of L. crocea under A. hydrophila infection, and suggest a preliminary hypothesis for why hypoxia-tolerant individuals may exhibit a higher survival rates after infection. Our study provides scientific evidence for the breeding of a new hypoxia-tolerant strain of L. crocea for aquaculture.

A Novel Peptide as a Specific and Selective Probe for Klebsiella pneumoniae Detection

Klebsiella pneumoniae is infamous for generating hospital-acquired infections, many of which are difficult to treat due to the bacterium’s multidrug resistance. A sensitive and robust detection method of K. pneumoniae can help prevent a disease outbreak. Herein, we used K. pneumoniae cells as bait to screen a commercially available phage-displayed random peptide library for peptides that could be used to detect K. pneumoniae. The biopanning-derived peptide TSATKFMMNLSP, named KP peptide, displayed a high selectivity for the K. pneumoniae with low cross-reactivity to related Gram-negative bacteria. The specific interaction between KP peptide and K. pneumoniae lipopolysaccharide resulted in the peptide’s selectivity against K. pneumoniae. Quantitative analysis of this interaction by enzyme-linked immunosorbent assay revealed that the KP peptide possessed higher specificity and sensitivity toward K. pneumoniae than commercially available anti-Klebsiella spp. antibodies and could detect K. pneumoniae at a detection limit of 10⁴ CFU/mL. These results suggest that KP peptide can be a promising alternative to antibodies in developing a biosensor system for K. pneumoniae detection.

Variation in selection constraints on teleost TLRs with emphasis on their repertoire in the Walking catfish, Clarias batrachus

The high degree of conservation of toll-like receptors (TLRs), and yet their subtle variations for better adaptation of species in the host–pathogen arms race make them worthy candidates for understanding evolution. We have attempted to track the trend of TLR evolution in the most diverse vertebrate group—teleosts, where Clarias batrachus was given emphasis, considering its traits for terrestrial adaptation. Eleven C. batrachus TLRs (TLR1, 2, 3, 5, 7, 8 9, 13, 22, 25, 26) were identified in this study which clustered in proximity to its Siluriformes relative orthologues in the phylogenetic analysis of 228 TLRs from 25 teleosts. Ten TLRs (TLR1, 2, 3, 5, 7, 8 9, 13, 21, 22) with at least 15 member orthologues for each alignment were processed for selection pressure and coevolutionary analysis. TLR1, 7, 8 and 9 were found to be under positive selection in the alignment-wide test. TLR1 also showed maximum episodic diversification in its clades while the teleost group Eupercaria showed the maximum divergence in their TLR repertoire. Episodic diversification was evident in C. batrachus TLR1 and 7 alignments. These results present a strong evidence of a divergent TLR repertoire in teleosts which may be contributing towards species-specific variation in TLR functions.

Paralogues From the Expanded Tlr11 Gene Family in Mudskipper (Boleophthalmus pectinirostris) Are Under Positive Selection and Respond Differently to LPS/Poly(I:C) Challenge

Toll-like receptors (TLRs) are major molecular pattern recognition receptors, which are essential for triggering a series of innate immune responses against invading pathogens by recognizing their evolutionary conserved molecular patterns. The mudskipper, Boleophthalmus pectinirostris is exceptional among fishes due to its amphibious lifestyle and adaptation to living on mudflats. The whole-genome sequencing of B. pectinirostris has revealed that this species possesses an expansion of Tlr11 family [12 Tlr11 family genes (one tlr21, 4 tlr22, and 7 tlr23)] that we focused on in the present study. The full-length cDNA sequences of the 12 tlrs in B. pectinirostris were cloned and their deduced amino acid sequences possessed a typical TLR domain arrangement. Likelihood tests of selection revealed that these 12 Tlr11 family genes are under diversifying selection. A total of 13 sites were found to be positively selected by more than one evolution model, of which 11 were located in the ligand-binding ectodomain. The observed non-synonymous substitutions may have functional implications in antigen and pathogen recognition specificity. These 12 tlrs were highly expressed in immune-related tissues, i.e. spleen and kidney. Tlr21 and tlr22b transcripts were significantly up-regulated by LPS, whereas tlr22a, tlr22d, tlr23b, tlr23e, tlr23g were significantly up-regulated by poly(I:C) in the spleen or/and kidney, which implies that the expanded Tlr11 family genes may play roles in protecting the fish from the invasion of gram-negative bacteria and double-stranded RNA viruses. The results from the present study suggested that the expansion of Tlr11 family genes in B. pectinirostris may recognize ligands from various pathogens found in the intertidal zone.