A calmodulin targeted by miRNA scaffold659_26519 regulates IL-17 expression in the early immune response of oyster Crassostrea gigas

Integrated microRNA study and pathological analysis provides new insights into the immune response of Ruditapes philippinarum under Vibrio anguillarum challenge

Manila clam (Ruditapes philippenarum) is an important shellfish aquaculture product. The large-scale breeding of clams is often affected by V. anguillarum and causes large-scale death. However, the pathogenesis, immune response and metabolic pathway of V. anguillarum are still unclear. In this study, we found that the bacterial load in the hepatopancreas of R. philippinarum peaked at 48 h after V. anguillarum infection, and then gradually decreased, while the activity of lysozyme reached the peak at 12 h. Tissue section observation reveals that the infected hepatopancreas cells lost normal structure or necrosis. Additionally, six small RNA libraries were constructed using hepatopancreas of clams. A total of 15 differentially expressed (DE) microRNA (miRNA) were identified at 48 h after V. anguillarum infection, including 8 upregulated and 7 downregulated miRNAs. GO and KEGG enrichment results indicated the prediction of 48 known miRNAs and 127 new miRNAs, with functional annotation suggests that endocytosis pathway and bacterial recognition proteins may play key roles in immune response. The sequencing results were basically consistent with the qRT-PCR validation, indicating the accuracy of the data. This study provides a new idea to explore the immune regulation mechanism of shellfish after V. anguillarum infection, which brings important reference significance for modern immunological research.

Regulatory mechanism of miR-722 on C5aR1 and its functions against bacterial inflammation in half-smooth tongue sole (Cynoglossus semilaevis)

MicroRNAs (miRNAs) are small non-coding RNAs involved in various biological processes, including immunity. Previously, we investigated the miRNAs of half-smooth tongue sole (Cynoglossus semilaevis) and found that miR-722 (designated Cse-miR-722) was significantly differentially expressed after infection with Vibrio anguillarum, reflecting its importance in immune response. Our preliminary bioinformatic analysis suggested that Cse-miR-722 could target C5aR1 (designated CsC5aR1), which was known to play crucial roles in complement activation and inflammatory response, as a receptor of C5a. However, the underlying mechanisms of their interactions and specific functions in inflammatory and immune response are still enigmas. In this study, we successfully cloned the precursor sequence of Cse-miR-722 (94 bp) and the full length of CsC5aR1 (1541 bp, protein molecular weight 39 kDa). The target gene of Cse-miR-722 was verified as CsC5aR1 by a dual luciferase reporter assay, and Cse-miR-722 was confirmed to regulate CsC5aR1 at the protein level using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting. The expression of CsC5aR1 and Cse-miR-722 in liver cells and four immune tissues of half-smooth tongue sole changed significantly after LPS stimulation and infection with V. anguillarum. To explore the functional role of Cse-miR-722 in half-smooth tongue sole, we performed both in vitro and in vivo experiments. Cse-miR-722 was observed to affect phagocytosis and respiratory burst activity of macrophages by regulating CsC5aR1 in half-smooth tongue sole. Furthermore, we found that Cse-miR-722 regulated the expression of CsC5aR1, CsC5a, and the inflammatory factors CsIL1-β, CsIL6, CsIL8, and CsTNF-α both in vitro and in vivo. In addition, Cse-miR-722 reduced mortality and pathological damage. This study clarified the regulatory mechanism of Cse-miR-722 on CsC5aR1 and provided insight into the regulatory roles of Cse-miR-722 in immune responses, laying a theoretical foundation for the feasibility of using miR-722 to prevent and control bacterial diseases in teleost.

Synergistic modulation of neuroendocrine-inflammation pathway by microRNAs facilitates intertidal adaptation of molluscs

Neuroendocrine-immune system is an evolution-conserved regulatory network in maintaining the homeostasis of animals. While knowledge on the roles of neuroendocrine-immune system in the disease and stress responses of organisms is growing, the ecological roles of neuroendocrine-immune system, especially how it shapes the unique lifestyle of organisms remain insufficiently investigated. As an endemic and dominant mollusc in intertidal region, oysters have evolved with a primitive neuroendocrine-immune system and with a sessile lifestyle. Recently, a novel neuroendocrine-immune pathway, Ca2+/calmodulin (CaM)-nitrite oxide synthase (NOS)/nitrite oxide (NO)-tumor necrosis factor (TNF) pathway, is identified in oysters and found altered dynamically during aerial exposure, one common but challenging stresses for intertidal organisms and a decisive factor shaping their habitat. Since the pathway proves fatal in prolonged aerial exposure, we hypothesized that the activation/deactivation of pathway could be strictly modulated in adaptation to the sessile lifestyle of oysters. Here, a synergistic modulation on the Ca2+/CaM-NOS/NO-TNF pathway by four members of miR-92 family and two oyster-specific miRNAs was identified, which further hallmarks the resilience and survival strategy of oysters to aerial exposure. Briefly, these six miRNAs were down-regulating CgCaM24243 post-transcriptionally and deactivating the pathway during the early-stage of stress. However, a robust recession of these miRNAs occurred at the late-stage of stress, resulting in the reactivation of pathway and overwhelming accumulation of cytokines. These results demonstrated a complicated interaction between miRNAs and ancient neuroendocrine-immune system, which facilitates the environmental adaptation of intertidal oysters and provides novel insight on the function and evolution of neuroendocrine-immune system in ecological context.

Exploring the Role of a Novel Interleukin-17 Homolog from Invertebrate Marine Mussel Mytilus coruscus in Innate Immune Response: Is Negative Regulation by Mc-Novel_miR_145 the Key?

Interleukin-17 (IL-17) represents a class of proinflammatory cytokines involved in chronic inflammatory and degenerative disorders. Prior to this study, it was predicted that an IL-17 homolog could be targeted by Mc-novel_miR_145 to participate in the immune response of Mytilus coruscus. This study employed a variety of molecular and cell biology research methods to explore the association between Mc-novel_miR_145 and IL-17 homolog and their immunomodulatory effects. The bioinformatics prediction confirmed the affiliation of the IL-17 homolog with the mussel IL-17 family, followed by quantitative real-time PCR assays (qPCR) to demonstrate that McIL-17-3 was highly expressed in immune-associated tissues and responded to bacterial challenges. Results from luciferase reporter assays confirmed the potential of McIL-17-3 to activate downstream NF-κb and its targeting by Mc-novel_miR_145 in HEK293 cells. The study also produced McIL-17-3 antiserum and found that Mc-novel_miR_145 negatively regulates McIL-17-3 via western blotting and qPCR assays. Furthermore, flow cytometry analysis indicated that Mc-novel_miR_145 negatively regulated McIL-17-3 to alleviate LPS-induced apoptosis. Collectively, the current results showed that McIL-17-3 played an important role in molluscan immune defense against bacterial attack. Furthermore, McIL-17-3 was negatively regulated by Mc-novel_miR_145 to participate in LPS-induced apoptosis. Our findings provide new insights into noncoding RNA regulation in invertebrate models.

Soluble mediators of innate immunity in annelids and bivalve mollusks: A mini-review

Annelids and mollusks, both in the superphylum of Lophotrochozoa (Bilateria), are important ecological groups, widespread in soil, freshwater, estuarine, and marine ecosystems. Like all invertebrates, they lack adaptive immunity; however, they are endowed with an effective and complex innate immune system (humoral and cellular defenses) similar to vertebrates. The lack of acquired immunity and the capacity to form antibodies does not mean a lack of specificity: invertebrates have evolved genetic mechanisms capable of producing thousands of different proteins from a small number of genes, providing high variability and diversity of immune effector molecules just like their vertebrate counterparts. This diversity allows annelids and mollusks to recognize and eliminate a wide range of pathogens and respond to environmental stressors. Effector molecules can kill invading microbes, reduce their pathogenicity, or regulate the immune response at cellular and systemic levels. Annelids and mollusks are "typical" lophotrochozoan protostome since both groups include aquatic species with trochophore larvae, which unite both taxa in a common ancestry. Moreover, despite their extensive utilization in immunological research, no model systems are available as there are with other invertebrate groups, such as Caenorhabditis elegans or Drosophila melanogaster, and thus, their immune potential is largely unexplored. In this work, we focus on two classes of key soluble mediators of immunity, i.e., antimicrobial peptides (AMPs) and cytokines, in annelids and bivalves, which are the most studied mollusks. The mediators have been of interest from their first identification to recent advances in molecular studies that clarified their role in the immune response.