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Wang B, Shao Y, Wang X, Li C. Identification and functional analysis of Toll-like receptor 2 from razor clam Sinonovacula constricta. Int J Biol Macromol 2024; 265:131029. [PMID: 38518946 DOI: 10.1016/j.ijbiomac.2024.131029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2024] [Revised: 03/16/2024] [Accepted: 03/19/2024] [Indexed: 03/24/2024]
Abstract
Toll-like receptor 2 (TLR2) is a member of TLR family that plays important roles in the innate immune system, such as pathogen recognition and inflammation regulation. In this study, the TLR2 homologue was cloned from razor clam Sinonovacula constricta (denoted as ScTLR2) and its immune function was explored. The full-length cDNA of ScTLR2 comprised 2890 nucleotides with a 5'-UTR of 218 bp, an open reading frame of 2169 bp encoding 722 amino acids and a 3'-UTR of 503 bp. The deduced amino acid of ScTLR2 showed similar structure to TLR2 homologue with a conserved signal peptide, four LRR domains, one LRR-TYP domain, one LRR-CT domain, one transmembrane domain and a conserved TIR domain. ScTLR2 mRNA was detected in all examined tissues with the highest expression in the gill. After Vibrio parahaemolyticus challenge, the mRNA expression of ScTLR2 was significantly induced both in gill and haemocytes. The recombinant ScTLR2-LRR protein could bind all tested PAMPs including LPS, PGN and MAN. Bacterial agglutination assay showed that rScTLR2 could agglutinate the six tested bacteria with a calcium dependent manner. More importantly, ScTLR2 silencing by siRNA transfection could significantly depress the mRNA expression of Myd88, NF-κB, Tollip, IRF1, and IRF8. The survival rate of S. constricta was markedly decreased after V. parahaemolyticus challenge under this condition. Our current study demonstrated that ScTLR2 served as a pattern recognition receptor to induce immune response against invasive pathogen.
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Affiliation(s)
- Beibei Wang
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Ningbo University, Ningbo 315211, China
| | - Yina Shao
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Ningbo University, Ningbo 315211, China.
| | - Xuelei Wang
- Ningbo Academy of Oceanology and Fishery, Ningbo, Zhejiang, China
| | - Chenghua Li
- State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-products, Ningbo University, Ningbo 315211, China.
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Cao Z, Gao Y, Xu J, Yang N, Li T, Chang L, Si L, Yan D. Transcriptome analysis of the hepatopancreas in Penaeus vannamei under experimental infection with Enterocytozoon hepatopenaei (EHP). FISH & SHELLFISH IMMUNOLOGY 2023; 134:108605. [PMID: 36758659 DOI: 10.1016/j.fsi.2023.108605] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Revised: 10/19/2022] [Accepted: 02/06/2023] [Indexed: 06/18/2023]
Abstract
Enterocytozoon hepatopenaei (EHP) is a specialized intracellular parasite that mainly resides in the hepatopancreas of shrimp, causing significant growth retardation in shrimp. In this study, Penaeus vannamei was infected with EHP through an artificial challenge experiment, and the different genes and pathways in the hepatopancreas between EHP-infected and healthy shrimp were analyzed by transcriptome sequencing. The results showed that a total of 240 significantly differentially expressed genes were obtained, including 99 up-regulated genes and 141 down-regulated genes. Immune-related genes such as Astakine, lysozyme, NACHT, LRR, and PYD domains-containing protein 3 (NLRP3), and macrophage mannose receptor 1-like (MMR) were up-regulated, and the expression levels of lipid metabolism-related genes pancreatic lipase-related protein 2 (PLRP2), lysosomal acid lipase (LIPA), and adiponectin receptor protein (AdipoR) were also increased. However, several genes were down-regulated in carbohydrate and protein metabolism, such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH), trypsin-1, and delta-1-pyrroline-5-carboxylate synthase (ALDH18A1). The results suggested that EHP infection of shrimps could significantly activate the immune system, but the energy and material metabolism processes were disturbed. This study identified a substantial number of genes and pathways associated with EHP infection, providing a valuable resource for revealing the molecular mechanism of growth retardation in shrimp.
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Affiliation(s)
- Zheng Cao
- School of Agriculture, Ludong University, Yantai, 264025, PR China
| | - Yang Gao
- School of Agriculture, Ludong University, Yantai, 264025, PR China
| | - Jiahui Xu
- School of Agriculture, Ludong University, Yantai, 264025, PR China
| | - Ning Yang
- School of Agriculture, Ludong University, Yantai, 264025, PR China
| | - Ting Li
- School of Agriculture, Ludong University, Yantai, 264025, PR China
| | - Linrui Chang
- School of Agriculture, Ludong University, Yantai, 264025, PR China
| | - Lingjun Si
- School of Agriculture, Ludong University, Yantai, 264025, PR China.
| | - Dongchun Yan
- School of Agriculture, Ludong University, Yantai, 264025, PR China.
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Ma W, Li Y, Yang Y, Han Q, Zhang W. Cloning and functional analysis of a pacifastin-like protein from the sea cucumber, Apostichopus japonicus. FISH & SHELLFISH IMMUNOLOGY 2022; 131:736-745. [PMID: 36309323 DOI: 10.1016/j.fsi.2022.10.045] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Revised: 10/22/2022] [Accepted: 10/23/2022] [Indexed: 06/16/2023]
Abstract
Pacifastin family proteins play a crucial role in regulating innate immune responses such as phagocytosis in invertebrates. However, the function of the Ajpacifastin-like counterpart in the sea cucumber Apostichopus japonicus remains elusive. In this study, the pacifastin gene of A. japonicus was cloned, characterized and named Ajpacifastin-like. The open reading frame of Ajpacifastin-like is 1497 bp in length and encodes a polypeptide containing 498 amino acid residues. Structural analysis revealed that the protein encoded by Ajpacifastin-like contains two pacifastin light chain domains (amino acids 287-322 and amino acids 376-407). Real-time reverse transcriptase PCR showed that Ajpacifastin-like mRNA is ubiquitously expressed in all tissues examined, with the highest expression in muscle. Ajpacifastin-like mRNA expression was significantly upregulated to 3.27-fold after challenge with Vibrio splendidus for 24 h. To explore the function of the Ajpacifastin-like protein in the immune response of A. japonicus, dsRNA interference with Ajpacifastin-like expression and with the expression of its postulated target gene was performed. Flow cytometry analysis showed that the rate of phagocytosis by coelomocytes increased to 1.21-fold in individuals treated with specific Ajpacifastin-like siRNA. However, rate of phagocytosis by coelomocytes decreased to 86% in individuals treated with Ajphenoloxidase siRNA. These results show that the Ajpacifastin-like gene is ubiquitously expressed in almost all tissues and that Ajpacifastin-like protein acts as an immunomodulatory factor via phenoloxidase to mediate phagocytosis by coelomocytes in pathogen-challenged A. japonicus.
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Affiliation(s)
- Wenyang Ma
- School of Marine Sciences, Ningbo University, Ningbo, 315832, PR China; Key Laboratory of Aquacultural Biotechnology Ministry of Education, Ningbo University, Ningbo, 315832, PR China
| | - Ya Li
- School of Marine Sciences, Ningbo University, Ningbo, 315832, PR China; Key Laboratory of Aquacultural Biotechnology Ministry of Education, Ningbo University, Ningbo, 315832, PR China
| | - Yiran Yang
- School of Marine Sciences, Ningbo University, Ningbo, 315832, PR China; Key Laboratory of Aquacultural Biotechnology Ministry of Education, Ningbo University, Ningbo, 315832, PR China
| | - Qingxi Han
- School of Marine Sciences, Ningbo University, Ningbo, 315832, PR China; Key Laboratory of Aquacultural Biotechnology Ministry of Education, Ningbo University, Ningbo, 315832, PR China.
| | - Weiwei Zhang
- School of Marine Sciences, Ningbo University, Ningbo, 315832, PR China; Key Laboratory of Aquacultural Biotechnology Ministry of Education, Ningbo University, Ningbo, 315832, PR China.
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Li X, Li S, Sun M, Yu Y, Zhang X, Xiang J, Li F. A newly identified NLR-like gene participates in bacteria and virus infection possibly through regulating hemocytes apoptosis in shrimp. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2022; 132:104395. [PMID: 35288120 DOI: 10.1016/j.dci.2022.104395] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2022] [Revised: 03/08/2022] [Accepted: 03/09/2022] [Indexed: 06/14/2023]
Abstract
The nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) play important roles in innate immunity. Previously, we identified an NLR-like gene, LvNLRPL1, and found that it participated in Vibrio infection and regulated hemocytes apoptosis in the Pacific whiteleg shrimp Litopenaeus vannamei. However, it is still unclear whether other NLR-like genes exist in shrimp and how they function during virus infection. In the present study, a novel NLR-like gene (LvNLRPL2) was identified and functionally characterized in L. vannamei. LvNLRPL2 was highly expressed in hemocytes and responsive to both Vibrio parahaemolyticus and white spot syndrome virus (WSSV) infection. Knockdown of LvNLRPL2 could markedly increase the proliferation of Vibrio and the mortality of shrimp infected with V. parahaemolyticus, whereas inhibit in vivo WSSV propagation in shrimp, indicating its distinct roles during Vibrio and WSSV infection. After LvNLRPL2 knockdown, the apoptotic rate of hemocytes increased, and the expression levels of LvCaspase 2, 3 and 5 were significantly up-regulated. In addition, LvNLRPL2 could form a hetero-dimer with LvNLRPL1 through their NACHT domains. These results suggest that LvNLRPL2 might resist bacterial infection while promote WSSV propagation by forming hetero-dimer with LvNLRPL1 and then inhibiting apoptosis of hemocytes. These data will be helpful for understanding the functions of NLR-like genes and their regulation mechanisms in crustaceans.
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Affiliation(s)
- Xuechun Li
- CAS and Shandong Province Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Shihao Li
- CAS and Shandong Province Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China.
| | - Mingzhe Sun
- CAS and Shandong Province Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
| | - Yang Yu
- CAS and Shandong Province Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China
| | - Xiaojun Zhang
- CAS and Shandong Province Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China
| | - Jianhai Xiang
- CAS and Shandong Province Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China
| | - Fuhua Li
- CAS and Shandong Province Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China; The Innovation of Seed Design, Chinese Academy of Sciences, Wuhan 430072, China.
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Dai F, Guo M, Shao Y, Li C. Vibrio splendidus flagellin C binds tropomodulin to induce p38 MAPK-mediated p53-dependent coelomocyte apoptosis in Echinodermata. J Biol Chem 2022; 298:102091. [PMID: 35654141 PMCID: PMC9249833 DOI: 10.1016/j.jbc.2022.102091] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Revised: 05/09/2022] [Accepted: 05/13/2022] [Indexed: 12/27/2022] Open
Abstract
As a typical pathogen-associated molecular pattern, bacterial flagellin can bind Toll-like receptor 5 and the intracellular NAIP5 receptor component of the NLRC4 inflammasome to induce immune responses in mammals. However, these flagellin receptors are generally poorly understood in lower animal species. In this study, we found that the isolated flagellum of Vibrio splendidus AJ01 destroyed the integrity of the tissue structure of coelomocytes and promoted apoptosis in the sea cucumber Apostichopus japonicus. To further investigate the molecular mechanism, the novel intracellular LRR domain-containing protein tropomodulin (AjTmod) was identified as a protein that interacts with flagellin C (FliC) with a dissociation constant (Kd) of 0.0086 ± 0.33 μM by microscale thermophoresis assay. We show that knockdown of AjTmod also depressed FliC-induced apoptosis of coelomocytes. Further functional analysis with different inhibitor treatments revealed that the interaction between AjTmod and FliC could specifically activate p38 MAPK, but not JNK or ERK MAP kinases. We demonstrate that the transcription factor p38 is then translocated into the nucleus, where it mediates the expression of p53 to induce coelomocyte apoptosis. Our findings provide the first evidence that intracellular AjTmod serves as a novel receptor of FliC and mediates p53-dependent coelomocyte apoptosis by activating the p38 MAPK signaling pathway in Echinodermata.
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Affiliation(s)
- Fa Dai
- State Key Laboratory for Quality and Safety of Agro-products, Ningbo University, Ningbo, China; State-Province Joint Laboratory of Marine Biotechnology and Engineering, Ningbo University, Ningbo, China
| | - Ming Guo
- State Key Laboratory for Quality and Safety of Agro-products, Ningbo University, Ningbo, China; State-Province Joint Laboratory of Marine Biotechnology and Engineering, Ningbo University, Ningbo, China
| | - Yina Shao
- State Key Laboratory for Quality and Safety of Agro-products, Ningbo University, Ningbo, China; State-Province Joint Laboratory of Marine Biotechnology and Engineering, Ningbo University, Ningbo, China
| | - Chenghua Li
- State Key Laboratory for Quality and Safety of Agro-products, Ningbo University, Ningbo, China; State-Province Joint Laboratory of Marine Biotechnology and Engineering, Ningbo University, Ningbo, China; Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao, PR China.
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Li X, Li S, Yu Y, Zhang X, Xiang J, Li F. The immune function of a NLR like gene, LvNLRPL1, in the Pacific whiteleg shrimp Litopenaeus vannamei. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2022; 128:104311. [PMID: 34752843 DOI: 10.1016/j.dci.2021.104311] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Revised: 11/03/2021] [Accepted: 11/04/2021] [Indexed: 06/13/2023]
Abstract
NOD-like receptors (NLRs) are a kind of pattern recognition receptors, which are vital for detection of pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs) and then trigger downstream immune responses in vertebrates. Although many NLR like genes have been identified in invertebrates in recent years, knowledge about their immune functions is still very limited. In the present study, a NLR like gene, designated as LvNLRPL1, was identified in Litopenaeus vannamei. It was widely expressed in multiple tissues and responsive to the infection of Vibrio parahaemolyticus. Knockdown of LvNLRPL1 could accelerate the proliferation of Vibrio in hepatopancreas and increase the mortality rate of shrimp after Vibrio infection. Meanwhile, knockdown of LvNLRPL1 also up-regulated the expression of Caspase 2, 3 and 5 in hemocytes, which caused apoptosis of more hemocytes. These results indicated that LvNLRPL1 played important immune functions in shrimp during Vibrio infection through regulating the apoptosis of hemocytes in shrimp. To our knowledge, this is the first time to reveal the immune function of a NLR like gene in crustaceans.
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Affiliation(s)
- Xuechun Li
- Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Shihao Li
- Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China.
| | - Yang Yu
- Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China
| | - Xiaojun Zhang
- Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China
| | - Jianhai Xiang
- Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China
| | - Fuhua Li
- Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China; Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China; Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China; The Innovation of Seed Design, Chinese Academy of Sciences, Wuhan 430072, China.
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Shao Y, Wang Z, Chen K, Li D, Lv Z, Zhang C, Zhang W, Li C. Xenophagy of invasive bacteria is differentially activated and modulated via a TLR-TRAF6-Beclin1 axis in echinoderms. J Biol Chem 2022; 298:101667. [PMID: 35120925 PMCID: PMC8902612 DOI: 10.1016/j.jbc.2022.101667] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 01/13/2022] [Accepted: 01/18/2022] [Indexed: 11/16/2022] Open
Abstract
In marine environments, organisms are confronted with numerous microbial challenges, although the differential regulation of xenophagy in response to different pathogenic bacterial species remains relatively unknown. Here, we addressed this issue using Apostichopus japonicus as a model. We identified 39 conserved autophagy-related genes by genome-wide screening, which provided a molecular basis for autophagy regulation in sea cucumbers. Furthermore, xenophagy of two Gram-negative bacteria, Vibrio splendidus and Escherichia coli, but not a Gram-positive bacteria, Micrococcus luteus, was observed in different autophagy assays. Surprisingly, a significantly higher autophagy capacity was found in the E. coli–challenged group than in the V. splendidus–challenged group. To confirm these findings, two different lipopolysaccharides, LPSV. splendidus and LPSE. coli, were isolated; we found that these LPS species differentially activated coelomocyte xenophagy. To explore the molecular mechanism mediating differential levels of xenophagy, we used an siRNA knockdown assay and confirmed that LPSV. splendidus-mediated xenophagy was dependent on an AjTLR3-mediated pathway, whereas LPSE. coli-mediated xenophagy was dependent on AjToll. Moreover, the activation of different AjTLRs resulted in AjTRAF6 ubiquitination and subsequent activation of K63-linked ubiquitination of AjBeclin1. Inversely, the LPSV. splendidus-induced AjTLR3 pathway simultaneously activated the expression of AjA20, which reduced the extent of K63-linked ubiquitination of AjBeclin1 and impaired the induction of autophagy; however, this finding was no t evident with LPSE. coli. Our present results provide the first evidence showing that xenophagy could be differentially induced by different bacterial species to yield differential autophagy levels in echinoderms.
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Affiliation(s)
- Yina Shao
- State Key Laboratory for Quality and Safety of Agro-products, Ningbo University, PR China
| | - Zhenhui Wang
- State Key Laboratory for Quality and Safety of Agro-products, Ningbo University, PR China
| | - Kaiyu Chen
- State Key Laboratory for Quality and Safety of Agro-products, Ningbo University, PR China
| | - Dongdong Li
- State Key Laboratory for Quality and Safety of Agro-products, Ningbo University, PR China
| | - Zhimeng Lv
- State Key Laboratory for Quality and Safety of Agro-products, Ningbo University, PR China
| | - Chundan Zhang
- State Key Laboratory for Quality and Safety of Agro-products, Ningbo University, PR China
| | - Weiwei Zhang
- State Key Laboratory for Quality and Safety of Agro-products, Ningbo University, PR China
| | - Chenghua Li
- State Key Laboratory for Quality and Safety of Agro-products, Ningbo University, PR China; Laboratory for Marine Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266071, PR China; State-Province Joint Laboratory of Marine Biotechnology and Engineering, Ningbo University, Ningbo 315211, China.
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A unique NLRC4 receptor from echinoderms mediates Vibrio phagocytosis via rearrangement of the cytoskeleton and polymerization of F-actin. PLoS Pathog 2021; 17:e1010145. [PMID: 34898657 PMCID: PMC8699970 DOI: 10.1371/journal.ppat.1010145] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Revised: 12/23/2021] [Accepted: 11/27/2021] [Indexed: 11/20/2022] Open
Abstract
Many members of the nucleotide-binding and oligomerization domain (NACHT)- and leucine-rich-repeat-containing protein (NLR) family play crucial roles in pathogen recognition and innate immune response regulation. In our previous work, a unique and Vibrio splendidus-inducible NLRC4 receptor comprising Ig and NACHT domains was identified from the sea cucumber Apostichopus japonicus, and this receptor lacked the CARD and LRR domains that are typical of common cytoplasmic NLRs. To better understand the functional role of AjNLRC4, we confirmed that AjNLRC4 was a bona fide membrane PRR with two transmembrane structures. AjNLRC4 was able to directly bind microbes and polysaccharides via its extracellular Ig domain and agglutinate a variety of microbes in a Ca2+-dependent manner. Knockdown of AjNLRC4 by RNA interference and blockade of AjNLRC4 by antibodies in coelomocytes both could significantly inhibit the phagocytic activity and elimination of V. splendidus. Conversely, overexpression of AjNLRC4 enhanced the phagocytic activity of V. splendidus, and this effect could be specifically blocked by treatment with the actin-mediated endocytosis inhibitor cytochalasin D but not other endocytosis inhibitors. Moreover, AjNLRC4-mediated phagocytic activity was dependent on the interaction between the intracellular domain of AjNLRC4 and the β-actin protein and further regulated the Arp2/3 complex to mediate the rearrangement of the cytoskeleton and the polymerization of F-actin. V. splendidus was found to be colocalized with lysosomes in coelomocytes, and the bacterial quantities were increased after injection of chloroquine, a lysosome inhibitor. Collectively, these results suggested that AjNLRC4 served as a novel membrane PRR in mediating coelomocyte phagocytosis and further clearing intracellular Vibrio through the AjNLRC4-β-actin-Arp2/3 complex-lysosome pathway. Vibrio splendidus is ubiquitously present in marine environments and in or on many aquaculture species and is considered to be an important opportunistic pathogen that has caused serious economic losses to the aquaculture industry worldwide. Phagocytosis is the first step of pathogen clearance and is triggered by specific interactions between host pattern recognition receptors (PRRs) and pathogen-associated molecular patterns (PAMPs) from invasive bacteria. However, the mechanism that underlies receptor-mediated V. splendidus phagocytosis is poorly understood. In this study, an atypical AjNLRC4 receptor without LRR and CARD domains was found to serve as the membrane receptor for V. splendidus, not the common cytoplasmic NLRs. The Ig domain of AjNLRC4 is replaced with a conventional LRR domain to bind V. splendidus, and the intracellular domain of AjNLRC4 specifically interacts with β-actin to mediate V. splendidus endocytosis in an actin-dependent manner. Endocytic V. splendidus is ultimately degraded in phagolysosomes. Our findings will contribute to the development of novel strategies for treating V. splendidus infection by modulating the actin-dependent endocytosis pathway.
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