Abstract
Invertebrates rely solely on the innate immune system for defense against pathogens and other stimuli. Fatty acid binding proteins (FABP), members of the lipid binding proteins superfamily, play a crucial role in fatty acid transport and lipid metabolism and are also involved in gene expression induced by fatty acids. In the vertebrate immune system, FABP is involved in inflammation regulated by fatty acids through its interaction with peroxidase proliferator activate receptors (PPARs). However, the immune functions of FABP in invertebrates are not well characterized. For this reason, we investigated the immune functionality of two fatty acid binding proteins, Es-FABP9 and Es-FABP10, following lipopolysaccharide (LPS) challenge in the Chinese mitten crab (Eriocheir sinensis). An obvious variation in the expression of Es-FABP9 and Es-FABP10 mRNA in E. sinensis was observed in hepatopancreas, gills, and hemocytes post-LPS challenge. Recombinant proteins rEs-FABP9 and rEs-FABP10 exhibited distinct bacterial binding activity and bacterial agglutination activity against Escherichia coli and Staphylococcus aureus. Furthermore, bacterial growth inhibition assays demonstrated that rEs-FABP9 responds positively to the growth inhibition of Vibrio parahaemolyticuss and S. aureus, while rEs-FABP10 responds positively to the growth inhibition of Aeromonas hydrophila and Bacillus subtilis. Coating of agarose beads with recombinant rEs-FABP9 and rEs-FABP10 dramatically enhanced encapsulation of the beads by crab hemocytes in vitro. In conclusion, the data presented here demonstrate the participation of these two lipid metabolism-related proteins in the innate immune system of E. sinensis.
Highlights
Fatty acid binding proteins (FABPs) belong to a family of small proteins (14–15 kDa), which are principally located in the cytosol and characterized by the ability to bind non-covalently and with high affinity to hydrophobic ligands, such as retinol, retinoic acid, bile salts and pigments, especially long-chain fatty acids (LCFAs) [1,2]
Es-FABP9 together with Procambarus clarkia and Penaeus monodon FABPs were belong to a subbranch in branch1; Litopenaeus vannamei FABP10, Fenneropenaeus chinensis FABP and Es-FABP10 are clustered into a subbranch in branch2
In some shrimps, such as Fenneropenaeus chinensis and Litopenaeus vannamei, FABP mRNAs were upregulated in the hepatopancreas induced by white spot syndrome virus (WSSV) [11,27]
Summary
Fatty acid binding proteins (FABPs) belong to a family of small proteins (14–15 kDa), which are principally located in the cytosol and characterized by the ability to bind non-covalently and with high affinity to hydrophobic ligands, such as retinol, retinoic acid, bile salts and pigments, especially long-chain fatty acids (LCFAs) [1,2]. 12 FABP isoforms have been identified in vertebrates [4]. Isoform expression among multiple tissues and differences in tissue distribution among FABP orthologs have resulted in the implementation of a numeric nomenclature. Based on this system of nomenclature, FABP9 and FABP10 correspond to T-FABP and LFABP, respectively [5,6]. Fatty acids are thought to have a important immune function [8], especially in inflammation reactions [9]. The first FABP was reported in 1972 [10], so vertebrates have been studied in detail for about four decades up to now. Several invertebrate FABPs have been found in Crustacea and Insecta [1], some reports suggest that FABPs are associated with immunity [11]
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