CRISPR/Cas9-Induced Knockout of Sting Increases Susceptibility of Zebrafish to Bacterial Infection

A review on current advancement in zebrafish models to study chronic inflammatory diseases and their therapeutic targets

Chronic inflammatory diseases are caused due to prolonged inflammation at a specific site of the body. Among other inflammatory diseases, bacterial meningitis, chronic obstructive pulmonary disease (COPD), atherosclerosis and inflammatory bowel diseases (IBD) are primarily focused on because of their adverse effects and fatality rates around the globe in recent times. In order to come up with novel strategies to eradicate these diseases, a clear understanding of the mechanisms of the diseases is needed. Similarly, detailed insight into the mechanisms of commercially available drugs and potent lead compounds from natural sources are also important to establish efficient therapeutic effects. Zebrafish is widely accepted as a model to study drug toxicity and the pharmacokinetic effects of the drug. Moreover, researchers use various inducers to trigger inflammatory cascades and stimulate physiological changes in zebrafish. The effect of these inducers contrasts with the type of zebrafish used in the investigation. Hence, a thorough analysis is required to study the current advancements in the zebrafish model for chronic inflammatory disease suppression. This review presents the most common inflammatory diseases, commercially available drugs, novel therapeutics, and their mechanisms of action for disease suppression. The review also provides a detailed description of various zebrafish models for these diseases. Finally, the future prospects and challenges for the same are described, which can help the researchers understand the potency of the zebrafish model and its further exploration for disease attenuation.

Suppressors of cGAS-STING are downregulated during fin-limb regeneration and aging in aquatic vertebrates

During the early stages of limb and fin regeneration in aquatic vertebrates (i.e., fishes and amphibians), blastema undergo transcriptional rewiring of innate immune signaling pathways to promote immune cell recruitment. In mammals, a fundamental component of innate immune signaling is the cytosolic DNA sensing pathway, cGAS-STING. However, to what extent the cGAS-STING pathway influences regeneration in aquatic anamniotes is unknown. In jawed vertebrates, negative regulation of cGAS-STING activity is accomplished by suppressors of cytosolic DNA such as Trex1, Pml, and PML-like exon 9 (Plex9) exonucleases. Here, we examine the expression of these suppressors of cGAS-STING, as well as inflammatory genes and cGAS activity during caudal fin and limb regeneration using the spotted gar (Lepisosteus oculatus) and axolotl (Ambystoma mexicanum) model species, and during age-related senescence in zebrafish (Danio rerio). In the regenerative blastema of wounded gar and axolotl, we observe increased inflammatory gene expression, including interferon genes and interleukins 6 and 8. We also observed a decrease in axolotl Trex1 and gar pml expression during the early phases of wound healing which correlates with a dramatic increase in cGAS activity. In contrast, the plex9.1 gene does not change in expression during wound healing in gar. However, we observed decreased expression of plex9.1 in the senescing cardiac tissue of aged zebrafish, where 2'3'-cGAMP levels are elevated. Finally, we demonstrate a similar pattern of Trex1, pml, and plex9.1 gene regulation across species in response to exogenous 2'3'-cGAMP. Thus, during the early stages of limb-fin regeneration, Pml, Trex1, and Plex9.1 exonucleases are downregulated, presumably to allow an evolutionarily ancient cGAS-STING activity to promote inflammation and the recruitment of immune cells.

Amphiprion clarkii DDX41 modulates fish immune responses: Characterization by expression profiling, antiviral assay, and macrophage polarization analysis

DDX41, a member of the DEAD-box helicase family, serves as a vital cytosolic DNA sensor and plays a pivotal role in controlling the activation of type I interferon responses in mammals. However, the functional aspects of fish DDX41 remain relatively unexplored. In this study, we identified and characterized the DDX41 gene in Amphiprion clarkii transcriptomes and designated the gene as AcDDX41. The complete open reading frame of AcDDX41 encoded a putative protein comprising 617 amino acids. Notably, the predicted AcDDX41 protein shared several structural features that are conserved in DDX41, including DEXDc, HELICc, and zinc finger domains, as well as conserved sequence "Asp-Glu-Ala-Asp (D-E-A-D)." AcDDX41 exhibited the highest sequence homology (99.68 % similarity) with DDX41 from Acanthochromis polyacanthus. Phylogenetic analysis revealed that DDX41s from fish formed a branch distinct from that in other animals. All investigated tissues were shown to express AcDDX41 constitutively, with blood showing the highest expression levels, followed by the brain. Furthermore, AcDDX41 expression was significantly induced upon stimulation with poly I:C, lipopolysaccharide, and Vibrio harveyi, indicating its responsiveness to immune stimuli. We confirmed the antiviral function of AcDDX41 by analyzing gene expression and viral replication during viral hemorrhagic septicemia virus infection. Additionally, using a luciferase reporter assay, we validated the ability of AcDDX41 to activate the NF-κB signaling pathway upon stimulation with poly I:C. Finally, AcDDX41 influenced cytokine gene expression and played a regulatory role in macrophage M1 polarization in RAW 264.7 cells. Collectively, these results highlight the significance of AcDDX41 as an immune-related gene that contributes substantially to antiviral defense and regulation of NF-κB activity.

At the Crossroads of the cGAS-cGAMP-STING Pathway and the DNA Damage Response: Implications for Cancer Progression and Treatment

The evolutionary conserved DNA-sensing cGAS-STING innate immunity pathway represents one of the most important cytosolic DNA-sensing systems that is activated in response to viral invasion and/or damage to the integrity of the nuclear envelope. The key outcome of this pathway is the production of interferon, which subsequently stimulates the transcription of hundreds of genes. In oncology, the situation is complex because this pathway may serve either anti- or pro-oncogenic roles, depending on context. The prevailing understanding is that when the innate immune response is activated by sensing cytosolic DNA, such as DNA released from ruptured micronuclei, it results in the production of interferon, which attracts cytotoxic cells to destroy tumors. However, in tumor cells that have adjusted to significant chromosomal instability, particularly in relapsed, treatment-resistant cancers, the cGAS-STING pathway often supports cancer progression, fostering the epithelial-to-mesenchymal transition (EMT). Here, we review this intricate pathway in terms of its association with cancer progression, giving special attention to pancreatic ductal adenocarcinoma and gliomas. As the development of new cGAS-STING-modulating small molecules and immunotherapies such as oncolytic viruses involves serious challenges, we highlight several recent fundamental discoveries, such as the proton-channeling function of STING. These discoveries may serve as guiding lights for potential pharmacological advancements.

Alternative splicing variants of stimulator of interferon genes (STING) from Asian seabass (Lates calcarifer) and their immune response against red spotted grouper nervous necrosis virus (RGNNV)

The Stimulator of Interferon Genes (STING, also known as MITA/ERYS/MPYS) is an adaptor molecule that plays a crucial role in the RLR pathway and responds to DNA and RNA viruses. In the present study, we have identified two novel isoforms of STING (the canonical form named as LcSTINGa and its alternative splicing isoform named as LcSTINGb) from teleost Lates calcarifer. LcSTINGa has an ORF of 1230 bp, encoding a 409 amino acid protein, while its alternative splicing variant, LcSTINGb, features an ORF of 987 bp, encoding 328 amino acids. LcSTINGa is predicted to contain four transmembrane helices, whereas LcSTINGb has only two. The Lates STING protein showed about 86.85% identity with Perca flavescens, 86.45% with Seriola and 39.51% with Homo sapiens. The tissue distribution studies revealed that the STING variants were constitutively expressed in all the tissues examined, with the highest expression in blood. In-vivo upregulation of LcSTINGa and LcSTINGb mRNA following immune challenge with poly (I:C), Red-spotted grouper nervous necrosis virus (RGNNV) and zymosan A suggests its significance in the immune response.