Abstract
Galectin-8 is a member of the galectin family that is involved in immune response against pathogens. However, the roles of fish galectin-8 during pathogen infection require comprehensive studies. In this study, a galectin-8 homolog (OnGal8-like, OnGal8-L) was characterized from Nile tilapia (Oreochromis niloticus), and its roles in response to bacterial infection were analyzed. The OnGal8-L contains an open reading frame of 891 bp, encoding a peptide of 296 amino acids with two CRD regions of tandem-repeat galectin and two carbohydrate recognition sites. The OnGal8-L protein shares 46.42% identities with reported Oreochromis niloticus galectin-8 protein. Transcriptional expression analysis revealed that OnGal8-L was constitutively expressed in all examined tissues and was highly expressed in spleen. The transcript levels of OnGal8-L were up-regulated in the spleen, head kidney, and brain, following Streptococcus agalactiae (S. agalactiae) challenge. Further in vitro analysis indicated that the recombinant protein of OnGal8-L (rOnGal8L) could agglutinate erythrocyte, S. agalactiae, and A. hydrophila and bind S. agalactiae, A. hydrophila, and various PAMPs (lipopolysaccharides, lipoteichoic acid, poly I:C, peptidoglycan, galactose, mannose, and maltose). Also, rOnGal8L could regulate inflammatory-related gene expression, phagocytosis, and a respiratory burst of monocytes/macrophages. Moreover, in vivo analysis showed that OnGal8-L overexpression could protect O. niloticus from S. agalactiae infection through modulating serum antibacterial activity (AKP, ACP, and LZM), antioxidant capacity (CAT, POD, and SOD), and monocyte/macrophage proliferation and cytokine expression, as well as reducing bacterial burden and decreasing tissue damage. Our results collectively indicate that OnGal8-L plays important regulatory roles in immune response against bacterial infection.
Highlights
Galectins are a family of proteins that possess high affinity for β-galactosides, which play a variety of roles in cell–cell adhesion, cell–matrix interaction, and transmembrane signaling [1, 2]
Phylogenetic analysis showed that OnGal8-L located within fish galectin-8 subgroup and was clustered close to Oreochromis niloticus galectin-8 and Maylandia zebra galectin-8 (Figure 1B)
Further comparison of OnGal8-L with reported galectin-8 revealed that OnGal8L protein has two characteristic carbohydrate recognition domain (CRD) with different linker length
Summary
Galectins are a family of proteins that possess high affinity for β-galactosides, which play a variety of roles in cell–cell adhesion, cell–matrix interaction, and transmembrane signaling [1, 2]. Galectins serve as pattern recognition receptors (PRR) that regulate the innate immune processes triggered by pathogen-associated molecular patterns [4, 5]. The intracellular galectins are involved in cellular functional processes including pre-mRNA splicing, cell growth regulation, and cell cycle processes [6, 7]. 15 galectins have been discovered in mammals, which are subdivided into three subfamilies based on their conserved carbohydrate recognition domain (CRD): “prototype,” “chimera,” and “tandem repeat” [8]. The immobilized galectin-8 can promote cell adhesion via attaching and aggregating integrin receptors on the cell surface, which subsequently trigger integrin-mediated signaling cascades [10]. The involvement of galectin-8 in host defenses against bacterial infection has been well-described in mammals. The mammalian galectin-8 can detect the bacterial invasion by monitoring the integrity of endosomes and lysosomes, and activate antibacterial autophagy to protect cells from bacterial infection [11]
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