Retinoic acid induced cytokines are selectively modulated by liver X receptor activation in zebrafish

A zebrafish model of intestinal epithelial damage reveals macrophages and igfbp1a as major modulators of mucosal healing

Promoting intestinal regeneration and enhancing mucosal healing have emerged as promising therapeutic alternatives for treating intestinal disorders that compromise epithelial barrier integrity and function. However, the cellular and molecular mechanisms underlying these processes remain poorly understood. This knowledge gap is partly due to the lack of reliable and cost-effective in vivo models for studying the mechanisms governing intestinal damage and regeneration. Here, we developed a controlled, inducible, and targeted intestinal epithelial cell (IEC) ablation transgenic zebrafish model that recapitulates features of intestinal damage and regeneration observed in humans. Single-cell RNAseq and live imaging revealed accumulation of macrophages in the recovering intestine, contributing to its regeneration. Furthermore, we observed overexpression of insulin-like growth factor binding protein 1a (igfbp1a) during intestinal damage. Morpholino-mediated knockdown of igfbp1a exacerbated intestinal damage and impaired subsequent regeneration. In summary, we introduced a novel zebrafish model of intestinal damage that enables in vivo high-throughput screening for identifying and validating novel modulators of mucosal healing and intestinal regeneration.

The Aryl Hydrocarbon Receptor (AHR): Peacekeeper of the Skin

In the last decade, the aryl hydrocarbon receptor (AHR) has emerged as a critical peacekeeper for the maintenance of healthy skin. The evolutionary conservation of AHR implied physiological functions for this receptor, beyond the detoxification of man-made compounds, a notion further supported by the existence of physiological AHR ligands, notably derivates of tryptophan by the host and host microbiome. The UV light-derived ligand, 6-formylindolo[3,2-b]carbazole (FICZ), anticipated a role for AHR in skin, a UV light-exposed organ, where physiological AHR activation promotes a healthy skin barrier and constrains inflammation. The clinical development of tapinarof, the first topical AHR modulating drug for inflammatory skin disease, approved by the FDA for mild-to-moderate psoriasis and poised for approval in atopic dermatitis, supports the therapeutic targeting of the AHR pathway to harness its beneficial effect in skin inflammation. Here, we describe how a tightly controlled, physiological activation of the AHR pathway maintains skin homeostasis, and discuss how the pathway is dysregulated in psoriasis and atopic dermatitis, identifying areas offering opportunities for alternative therapeutic approaches, for further investigation.

Tefluthrin induced toxicities in zebrafish: Focusing on enantioselectivity

Tefluthrin is one of widely used chiral pyrethroid pesticides. The potential enantioselective risk posed by tefluthrin to the aquatic ecosystem is still unclear. In this study, the toxicity differences and corresponding mechanism of tefluthrin on zebrafish were investigated at the enantiomeric level. The results indicated that two tefluthrin enantiomers showed different acute toxicity, developmental toxicity and oxidative stress to zebrafish. The acute toxicity of (1R,3R)-tefluthrin was 130-176 fold as that of (1S,3S)-tefluthrin on zebrafish embryos, larvae and adults. (1R,3R)-Tefluthrin presented approximately 10, 3 and 2 times inhibition effect on the deformity rate, hatching rate and spontaneous movements on embryos as that of (1S,3S)-tefluthrin. Meanwhile, (1R,3R)-tefluthrin caused stronger oxidative stress on zebrafish embryo than (1S,3S)-tefluthrin. The molecular docking results revealed that there were stereospecific binding affinities between tefluthrin enantimers and sodium channel protein (Nav1.6), which may lead to acute toxicity differences. Transcriptome analysis showed that the two tefluthrin enantiomers markedly disturbed differential embryonic genes expression, thereby potentially causing the chronic enantioselective toxicity. The findings of the study reveal the toxicity differences and potential mechanism of tefluthrin enantiomers on zebrafish. These results also provides a foundation for a systematic evaluation of tefluthrin at enantiomer level.

Interleukin-10 regulates goblet cell numbers through Notch signaling in the developing zebrafish intestine

Cytokines are immunomodulatory proteins that orchestrate cellular networks in health and disease. Among these, interleukin (IL)-10 is critical for the establishment of intestinal homeostasis, as mutations in components of the IL-10 signaling pathway result in spontaneous colitis. Whether IL-10 plays other than immunomodulatory roles in the intestines is poorly understood. Here, we report that il10, il10ra, and il10rb are expressed in the zebrafish developing intestine as early as 3 days post fertilization. CRISPR/Cas9-generated il10-deficient zebrafish larvae showed an increased expression of pro-inflammatory genes and an increased number of intestinal goblet cells compared to WT larvae. Mechanistically, Il10 promotes Notch signaling in zebrafish intestinal epithelial cells, which in turn restricts goblet cell expansion. Using murine organoids, we showed that IL-10 modulates goblet cell frequencies in mammals, suggesting conservation across species. This study demonstrates a previously unappreciated IL-10-Notch axis regulating goblet cell homeostasis in the developing zebrafish intestine and may help explain the disease severity of IL-10 deficiency in the intestines of mammals.

Perfluorooctanesulfonic acid modulates barrier function and systemic T cell homeostasis during intestinal inflammation

The intestinal epithelium is continuously exposed to deleterious environmental factors which might cause aberrant immune responses leading to inflammatory disorders. However, what environmental factors might contribute to disease are yet poorly understood. Here, to overcome the lack of in vivo models suitable for screening of environmental factors we used zebrafish reporters of intestinal inflammation. Using zebrafish, we interrogated the immunomodulatory effects of polyfluoroalkyl substances (PFAS), which have been positively associated with ulcerative colitis incidence. Exposure with perfluorooctanesulfonic acid (PFOS) during TNBS-induced inflammation enhances the expression of proinflammatory cytokines as well as neutrophil recruitment to the intestine of zebrafish larvae, which was validated in TNBS-induced colitis mice models. Moreover, PFOS exposure in mice undergoing colitis resulted in neutrophil-dependent increased intestinal permeability and enhanced PFOS translocation into circulation. Finally, this was associated with a neutrophil dependent expansion of systemic CD4+ T cells. Thus, our results indicate that PFOS worsens inflammation-induced intestinal damage with disruption of T cell homeostasis beyond the gut and provides a novel in vivo toolbox to screen for pollutants affecting intestinal homeostasis.

Liver X receptor regulates Th17 and RORγt+ Treg cells by distinct mechanisms

The gastrointestinal microenvironment, dominated by dietary compounds and the commensal bacteria, is a major driver of intestinal CD4⁺ T helper (Th) cell differentiation. Dietary compounds can be sensed by nuclear receptors (NRs) that consequently exert pleiotropic effects including immune modulation. Here, we found that under homeostatic conditions the NR Liver X receptor (LXR), a sensor of cholesterol metabolites, regulates RORγt⁺ CD4 T cells in the intestine draining mesenteric lymph node (MLN). While LXR activation led to a decrease, LXR-deficiency resulted in an increase in MLN Th17 and RORγt⁺ Tregs. Mechanistically, LXR signaling in CD11c⁺ myeloid cells was required to control RORγt⁺ Treg. By contrast, modulation of MLN Th17 was independent of LXR signaling in either immune or epithelial cells. Of note, horizontal transfer of microbiota between LXRα^-/- and WT mice was sufficient to only partially increase MLN Th17 in WT mice. Despite LXRα deficiency resulted in an increased abundance of Ruminococcaceae and Lachnospiraceae bacterial families compared to littermate controls, microbiota ablation (including SFB) was not sufficient to dampen LXRα-mediated expansion of MLN Th17. Altogether, our results suggest that LXR modulates RORγt⁺ Treg and Th17 cells in the MLN through distinct mechanisms.