MicroRNAs involved in innate immunity regulation in the sea cucumber: A review

Regulation of innate immunity in marine mussel Mytilus coruscus: MicroRNA Mc-novel_miR_196 targets McTLR-like1 molecule to inhibit inflammatory response and apoptosis

Toll-like receptors (TLRs) are crucial players in immune recognition and regulation, with aberrant activation leading to autoimmune, chronic inflammatory, and infectious diseases. MicroRNAs (miRNAs) have been shown to regulate gene expression at transcriptional and post-transcriptional levels. While miRNA-mediated regulation of TLR signaling has been studied in mammals, the underlying mechanisms of TLR-miRNA interactions in molluscs remain unclear. In a previous study, one of the TLR genes potentially targeted by miRNAs was identified and named McTLR-like1. McTLR-like1 was later found to be targeted by miRNA Mc-novel_miR_196 through bioinformatic prediction. In this study, we aim to experimentally determine the interaction between McTLR-like1 and Mc-novel_miR_196, as well as their functional role in the innate immune response of molluscs. The results showed that the expression of Mc-novel_miR_196 was suppressed, while the expression of McTLR-like1 was enhanced in M. coruscus hemocytes treated with lipopolysaccharide (LPS). Moreover, in vitro assays demonstrated that Mc-novel_miR_196 directly targets the 5' UTR of McTLR-like1 and leads to the down-regulation of proinflammatory cytokines in hemocytes. In addition, co-transfection experiments confirmed that Mc-novel_miR_196 inhibits McTLR-like1 and inhibits the expression of proinflammatory cytokines. The Tunel assay also showed that Mc-novel_miR_196 inhibited apoptosis in hemocytes induced by LPS. Our findings suggest that microRNA Mc-novel_miR_196 acts as a regulator of innate immunity in M. coruscus by targeting McTLR-like1 and inhibiting inflammatory response and apoptosis. These results provide further insights into the complex molecular mechanisms underlying TLR signaling in molluscs.

Exosomal microRNAs regulate the heat stress response in sea cucumber Apostichopus japonicus

Exosomes are small extracellular vesicles that contain nucleic acids such as microRNAs and may participate in important biological processes. We made the initial report of exosomes from sea cucumber Apostichopus japonicus, that were classically cup-shaped and had an average size of 74.65 nm, and identified specific exosome biomarkers (HSP70, TSG101, and CD9). We explored changes in the global expression of microRNAs in exosomes from the commercially important A. japonicus under normal conditions and heat-stressed conditions for 3 and 7 d. We found that heat stress increased exosome production and modified the expression profiles of the microRNAs that they contained. Novel_mir31, novel_mir132, novel_mir26, miR-92_1, and novel_mir27 were commonly found to be differentially expressed in three comparison groups, indicating their importance in the heat stress response. The microRNA expression levels were validated by qPCR. Function analysis of the target genes of these microRNAs indicated they were involved mainly in replication and repair in the initial response of A. japonicus to heat stress exposure. Conversely, during acclimation to the high temperature conditions, the target genes of the differentially expressed microRNAs were primarily involved in metabolism adjustments. Our results will contribute to a better understanding of the regulatory roles of exosomes in sea cucumber, and provide insights into the functions of sea cucumber exosome-shuttled microRNAs against environmental stresses exacerbated by global warming.

MiR-7 Regulates Pathogen-Induced Immune Response via PAK1 in the Sea Cucumber Apostichopus japonicus

MicroRNA-7 (miR-7) is a highly conserved short non-coding RNA involved in various bioprocesses via the regulation of multiple target genes. To enrich our knowledge of the functions of miR-7 in innate immune regulation in echinoderms, we first investigated the targeting relationship between miR-7 and PAK1 in the sea cucumber Apostichopus japonicus and then explored the functions of miR-7, the PAK1 gene, and the miR-7/PAK1 axis in the pathogen-induced immune response of A. japonicus. Our results showed that miR-7 can bind to the 3ʹUTR of PAK1 and negatively regulate the expression of PAK1 in A. japonicus. Overexpression and inhibition of miR-7 and inhibition of the expression of PAK1 can alter phagocytosis, cellular agglutination, and lysozyme contents in A. japonicus. Both miR-7 and the PAK1 gene are involved in immune defense against Vibrio splendidus infection; the miR-7/AjPAK1 axis showed immune regulatory function at 48 to 72 h post-infection (hpi) after V. splendidus infection in A. japonicus. In summary, the results of this study established that miR-7 regulates the pathogen-induced immune response by targeting PAK1 in A. japonicus.

Effect of sea cucumber peptides on the immune response and gut microbiota composition in ovalbumin-induced allergic mice

The prevalence of food allergies has increased in Asian countries. The aim of this study was to determine the potential value of sea cucumber peptide (SCP) for anti-allergic therapeutics in terms of their effect on immune response and gut microbiota composition. Results exhibited that SCP could significantly improve the allergy symptoms caused by ovalbumin and could reduce the risk of IgE mediated allergic disorders, as well as repair the morphological damage in the colon. Flow cytometry analysis indicated that SCP could improve the ratio of CD4+/CD8+ T lymphocytes. 16S rRNA results indicated that SCP could differently impact the composition of microbiota. The relative abundances of Bacteroidetes and Firmicutes and the Bacteroidetes/Firmicutes ratio were altered in normal mice. When compared with the OVA treated group, the SCP treated groups showed an increase in the relative abundance of Lachnospiraceae, Muribaculaceae and Ruminococcaceae, and a decrease in Bacteroidaceae, Prevotellaceae, and Lactobacillaceae. These results demonstrate that SCP exhibits potential antiallergic activities in a mouse model of ovalbumin allergy by regulating intestinal microbiota diversity and upregulating the immune response of T lymphocyte subpopulations, which might provide important evidence that SCP can be developed into a novel functional food for inhibiting ovalbumin allergy.

Identification of a novel RhoA gene in the sea cucumber Apostichopus japonicus and its immune regulatory function via interacting with miR-2012-5p

RhoA (Ras homolog A) protein is a representative member of the Rho GTPase family and is involved in various cellular processes. The function of RhoA in sea cucumbers is unclear. In this study, we hypothesized that RhoA may regulate the innate immune response of Apostichopus japonicus. Our data showed that 1) the complete sequence of RhoA from A. japonicus (named AjRhoA) was 968 bp, with a high level sequence conservation across the echinoderms and other phyla; 2) tissue expression analysis showed that AjRhoA transcripts and protein exhibited higher abundance in coelomocytes, whereas the relative expression of miR-2012-5p was lower in coelomocytes; 3) interactive binding sites and a negative regulatory targeting relationship between AjRhoA and miR-2012-5p were confirmed through a dual-luciferase reporter assay and functional validation in vivo; 4) the relative expression levels of AjRhoA transcripts and protein were upregulated in coelomocytes 4- and 72-hour post infection (hpi) with Vibrio splendidus, whereas miR-2012-5p was expressed in the opposite pattern; 5) both AjRhoA silencing and miR-2012-5p overexpression suppressed the phagocytic capacity of A. japonicus compared with the control at 4 and 72 hpi. Our observations suggest that AjRhoA can regulate the pathogen-induced immune response of A. japonicus through the "AjRhoA-miR-2012-5p" module during the early infection, while miR-2012-5p plays a direct immunomodulatory role as the infection progresses.

BAG2 mediates coelomocyte apoptosis in Vibrio splendidus challenged sea cucumber Apostichopus japonicus

MicroRNAs (miRNAs) are closely related to the occurrence, development, and immune response of diseases. BCL2-associated athanogene 2 (BAG2) is a member of the BAG family that functions in diverse cellular processes, including cell death, differentiation, and cell division. In this study, we cloned the cDNA full-length of sea cucumber (Apostichopus japonicus) BAG2 (AjBAG2) and confirmed it is an anti-apoptotic protein in vitro and in vivo during Vibrio splendidus infection. Moreover, we identified a perfect complementarity between miR-375 and the 3'-untranslated region (UTR) sequence of AjBAG2. The miR-375 expression decreased the luciferase activity dose-dependently when co-transfected with the AjBAG2 3'-UTR-luciferase reporter containing the miR-375 target site in epithelioma papulosum cyprini (EPC) cells. This inhibition was partially recovered by a miR-375 specific inhibitor. The mRNA and protein levels of AjBAG2 were opposite to that of coelomocytes in challenged sea cucumber when treated with miR-375 mimics or inhibitors. Additionally, miR-375 expression induced coelomocytes apoptosis and blocked the anti-apoptotic activity of AjBAG2. Our data demonstrated that AjBAG2 is an anti-apoptotic protein during V. splendidus infection and this function can be inhibited by miR-375 in sea cucumbers.

Clustering genomic organization of sea cucumber miRNAs impacts their evolution and expression

Echinoderms are marine deuterostomes with fascinating adaptation features such as aestivation and organ regeneration. However, post-transcriptional gene regulation by microRNAs (miRNAs) underlying these features are largely unexplored. Here, using homology-based and de novo approaches supported by expression data, we provided a comprehensive annotation of miRNA genes in the sea cucumber Apostichopus japonicus. By linkage and phylogenic analyses, we characterized miRNA genomic organization, evolutionary history and expression regulation. The results showed that sea cucumbers evolved a large number of new miRNAs, which tended to form polycistronic clusters via tandem duplication that had been especially active in the echinoderms. Most new miRNAs were weakly expressed, but miRNA clustering increased the expression level of clustered new miRNAs. The most abundantly expressed new miRNAs were organized in a single tandem cluster (cluster n2), which was activated during aestivation and intestine regeneration. Overall, our analyses suggest that clustering of miRNAs is important for their evolutionary origin, expression control, and functional cooperation.

Integrated analysis of miRNAome and transcriptome reveals miRNA-mRNA network regulation in Vibrio alginolyticus infected thick shell mussel Mytilus coruscus

The thick shell mussel Mytilus coruscus has developed into a model species for studying the interaction between molluscs and environmental stimuli. Herein, integrated analysis of miRNAome and transcriptome was performed to reveal miRNA-mRNA network regulation in Vibrio alginolyticus infected M. coruscus. There have detected some histological abnormalities in digestive gland and gills of V. alginolyticus challenged mussels, ascertaining the effective irritation by the present bacterial strain. A total of 265 novel miRNAs were finally predicted, of which 26 were differentially expressed miRNAs (DEMs). Additionally, 667 differentially expressed genes (DEGs) were detected, which may be potentially associated with innate immune response to V. alginolyticus infection. A regulatory network linked to 22 important pathways and 16 DEMs and 34 OGs was constructed. Some traditional immune-related signaling pathways such as toll-like receptor signaling pathway (TLR) signaling pathway, transforming growth factor-beta (TGF-beta) signaling pathway, peroxisome, phagosome, lysosome, mammalian target of rapamyoin (mTOR) signaling pathway were linked to specific miRNAs and genes in this network. Further, interactional relationship between certain miRNAs and TLR pathway was dissected, which the results predicted that a number of TLRs and TLR-associated signaling genes including TLR1, TLR2, TLR4, TLR6, IRAK1, TRAF6, MAPK, and IL-17 were negatively regulated by novel_miR_11, novel_miR_145, novel_miR_196, novel_miR_5, novel_miR_163 and novel_miR_217 in the TLR pathway. Additionally, interactional relationship between novel_miR_145 and TLR2 was validated by laboratory experiment. The integrated analysis of mRNA and microRNA deep sequencing data exhibited a sophisticated miRNA-mRNA regulation network in M. coruscus in response to V. alginolyticus challenge, which shed a new light on the underlying mechanism of molluscan confronting bacterial infection.

Novel Marine Organism-Derived Extracellular Vesicles for Control of Anti-Inflammation

BACKGROUND

Extracellular vesicles (EVs) exhibit potential as functional biomolecules for tissue regeneration and immunomodulation as they play important roles in the physiological communication between cells. EV internal cargo contains miRNAs, proteins, lipids, and so on. Osteoarthritis (OA) is a common joint disease causing disability owing to impaired joint function and pain. EVs originating from animal cells and tissue matrices are also being considered for OA, in addition to research involving non-steroidal therapeutic agents. However, there are no studies on EVs from marine organisms. Hence, we focused on sea cucumber-derived EVs and conducted experiments to set up an extraction protocol and to demonstrate their efficacy to modulate the inflammatory environment.

METHODS

Sea cucumber extracellular matrices (SECMs) were prepared by a decellularization process. Lyophilized SECMs were treated with collagenase and filtered to isolate sea cucumber extracellular vesicles (SEVs). After isolation, we conducted physical characterization and cell activation studies including cytotoxicity, proliferation, and anti-inflammation effect assays.

RESULTS

The physical characterization results showed circular SEVs in the size range of 66-480 nm. These SEVs contained large amounts of protein cargo, infiltrated the synoviocyte membrane without damage, and had a suppressive effect on inflammatory cytokines.

CONCLUSION

This study established an extraction process for EVs from sea cucumber and reported the anti-inflammatory ability of SEVs. Isolated SEVs can be further utilized for tissue regeneration studies and can be compared to various marine or animal-derived EVs.