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Transcriptomic Response and Survival of Iodine-Pretreated Zebrafish Larvae to Bacterial Endotoxin

ABSTRACT: Iodine is an essential micronutrient with recognised endocrine and immunomodulatory roles, but its concentration‑dependent effects on innate immune responses remain poorly defined in whole‑organism models. This study examined how aqueous molecular iodine influenced the survival and transcriptional response of zebrafish (Danio rerio) larvae challenged with bacterial lipopolysaccharide (LPS) endotoxin derived from Pseudomonas aeruginosa. Larvae were first exposed to a range of iodine concentrations (0-50 µg/mL) to determine a tolerated window, then pre‑treated with relevant iodine doses (0-4 µg/mL) prior to LPS challenge (0-100 µg/mL). A separate cohort was pre‑exposed to 4 µg/mL iodine and subjected to 60 or 80 µg/mL of LPS for RNA‑sequencing and pathway analysis. Iodine exposure produced a dose-dependent survival relationship with maximal survival between 0.1 and 4 µg/mL and a LD₅₀ of approximately 9 µg/mL. Pre‑exposure to 2 and 4 µg/mL iodine improved survival at LPS doses of 50-90 µg/mL, significantly at 80 and 90 µg/mL. RNA‑sequencing further showed that 4 µg/mL of iodine selectively downregulated glycosylation and leukocyte‑migration pathways, and that 60 and 80 µg/mL of LPS induced distinct innate immune, metabolic, and protein and chromosome‑associated pathways. Iodine treatment before 60 µg/mL of LPS exposure shifted responses toward lymphocyte and immunoglobulin (Ig)‑mediated pathways, while responses at 80 µg/mL of LPS were shifted toward chemosensory and G protein‑coupled receptor (GPCR) signalling. Overall, these findings define a narrow functional window in which molecular iodine supports innate immune competence in zebrafish larvae, reshaping endotoxin‑driven transcriptional responses, and demonstrate that exceeding this window compromises larval survival.

ORGANISM(S): Danio rerio

PROVIDER: GSE347950 | GEO | 2026/10/01

REPOSITORIES: GEO

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Project description:Vitamin D3 (VD3) plays a complex role in immunoregulation, but can be deleterious at high doses. In fish, VD3 metabolism and its immunological impact remain poorly understood. Our prior study demonstrated that high VD3 levels sensitize zebrafish (Danio rerio) to bacterial lipopolysaccharide (LPS) endotoxin; however, the molecular mechanisms underlying this chemosensitization remain unclear. The aim of this study was to investigate the transcriptomic responses of zebrafish larvae acutely exposed to high sublethal doses of VD3, bacterial endotoxin, or a combination thereof, to elucidate the molecular basis of VD3-induced sensitivity to immune challenge. Zebrafish larvae were exposed to egg water (control, EWC), 5 µg/mL VD3 (VD5) or 10 µg/mL VD3 (VD10) for 24 hours followed by a 2-hour exposure to either EWC, 90 µg/mL endotoxin (positive control, PC), VD5+endotoxin or VD10+endotoxin for 24 hours. Total RNA was extracted and subjected to RNA sequencing. Differentially expressed genes (DEGs) were identified and analyzed using gene ontology (GO) and KEGG pathway enrichment tools. The PC, VD5 and VD10 groups exhibited 383, 100 and 133 DEGs, respectively, compared to the EWC, while VD5+endotoxin and VD10+endotoxin exhibited 319 and 220 DEGs, respectively, compared to the PC. Combined exposure to VD3 and endotoxin up- and downregulated the expression of hundreds of genes, with notable enrichments in pathways related to steroid biosynthesis, p53 signalling, and MAPK signalling compared to control groups. Several immune- and stress-related GO terms were significantly enriched by excessive concentrations of VD3 including inflammatory response and immune effector processes. Additionally, excessive VD3 pre-exposure led to downregulation of key stress response genes and upregulation of genes associated with chemical and xenobiotic responses, potentially exacerbating endotoxin-induced toxicity. Our findings suggest that acute exposure to high concentrations of VD3 alter the immune landscape of zebrafish larvae, sensitizing them to endotoxin challenge. This study provides novel insights into the gene regulatory pathways influenced by VD3 in zebrafish and underscores the potential risks of excessive vitamin D supplementation for fish that should be considered when determining feed formulations and recommendations to avoid excessive inflammation and increased morbidity and mortality.

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Transcriptomic Response and Survival of Iodine-Pretreated Zebrafish Larvae to Bacterial Endotoxin

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