Aeromonas hydrophila infection induces Toll-like receptor 2 (tlr2) and associated downstream signaling in Indian catfish, Clarias magur (Hamilton, 1822)

Abstract

Motile Aeromonas septicaemia (MAS), caused by Aeromonas hydrophila, is one of the most significant bacterial disease responsible for mortality in Indian catfish, Clarias magur, a potential aquaculture species in the Indian subcontinent. In fish, innate immunity elicited by pathogen recognition receptors (PRRs) plays an important role in providing protection against bacterial infection. Information on PRRs including Toll-like receptors (tlrs) and their response to bacterial pathogens remains unexplored in magur. Toll-like receptor 2 (tlr2), a phylogenetically conserved germ-line encoded PRR recognizes specific microbial structure and trigger MyD88-dependent signaling pathway to induce release of various cytokines responsible for innate immune response. In the present study, tlr2 gene of magur was characterized and downstream signaling was studied following challenge with A. hydrophila. The full-length cDNA of magur tlr2 (mtlr2) comprised of 3,066 bp with a single open reading frame of 2,373 bp encoding 790 amino acids having a theoretical pI value of 6.11 and molecular weight of 90 kDa. Structurally, it comprised of signal peptide (1–42aa), one leucine-rich repeat region (LRR) at N-terminal (LRR1-NT: 50–73 aa) and C-terminal (LRR-CT: 588–608 aa), twenty LRRs in between, one trans-membrane (Tm) domain (609–631aa) followed by cytoplasmic TIR domain (670–783aa). Phylogenetically, mtlr2 is closely related to pangasius and channel catfish. Highest basal expression of mtlr2, myd88 and il-1β in spleen, nf-kb in anterior kidney was observed. Lowest basal expression of mtlr2 in skin and myd88, nf-kb and il-1β in muscle was detected. Significant up-regulation of mtlr2 and downstream expression occurred at 3, 8, 24 h post infection to A. hydrophila in important immune organs such as liver, spleen, intestine and kidney. These findings highlight the vital role of tlr2 in eliciting innate immune defence against A. hydrophila infection.

Comparative Transcriptomic Analyses Revealed the Effects of Poly (I:C) on the Liver and Spleen of Argyrosomus japonicus

“…The genes TNF , TLR2 , IL8 and MHCII in these pathways were also downregulated. They are associated with the body function of the natural cell-killing ability and T-cell immunity, and their downregulation demonstrated that poly (I:C) would regulate these genes, and then enhance the natural cell-killing ability, affect the T-cell immunity and decrease apoptosis induced by endogenesis [ 1 , 45 , 46 , 47 ]. At 48 h, poly (I:C) injection might, on the one hand, enhance the spleen energy metabolism, while, on the other hand, induce some injury, such as virus infection, which is a finding that could be supported by the results that found that the disease-related pathways were significantly enriched, the damaged presentation gene TXNRD was upregulated [ 36 ] and HBA was downregulated [ 38 ].…”

Identification of reference genes for quantitative expression analysis in Indian catfish,Clarias magur, under physiological and pathological conditions

“…EF‐1α was found to be the best candidate gene for analysis of Toll‐like receptor 3 and melanoma differentiation associated gene in CIK ( Ctenopharyngodon idella kidney) cell culture post Grass carp reovirus infection (Su et al, 2011). EF‐1α was used as RG for relative expression quantification of TLR2 and its downstream signalling molecule (Muduli, Paria, et al, 2021; Muduli, Rathore, et al, 2021). Paria et al (2016) also suggested EF‐1α and 18S to be the best RG in Asian seabass following V. alginolyticus infection.…”

“…Each sub‐group was maintained in three experimental tanks containing 10 fish each. Our previously isolated and characterized A. hydrophila strain 9C (Muduli et al, 2020, 2021b; Muduli, Rathore, et al, 2021) was used in this study. In A. hydrophila injected sub‐group, fish were injected with A. hydrophila at a concentration of 1 × 105 cfu/ fish in 100 µl PBS by intra‐peritoneal route.…”

Riding the wave of innovation: immunoinformatics in fish disease control

“…TLR13, TLR22, TLR25, and TLR26 in Walking catfish ( Clarias batrachus ) ( Priyam et al, 2020 ). Furthermore, researchers have also examined what occurs when a pathogenic bacterium, virus, or ligand is used as a stimulator, with regard to expression profiles and signalling cascade genes ( Jiang et al, 2020 ; Muduli et al, 2021 ; Wang et al, 2021 ). TLR ligands remain substantially unknown, especially in cartilaginous fish and lobe-finned fish ( Nie et al, 2018 ; Smith, Rise & Christian, 2019 ).…”