Histone lactylation-ROS loop contributes to light exposure-exacerbated neutrophil recruitment in zebrafish.

Light serves as a crucial external zeitgeber for maintaining and restoring physiological homeostasis in most organisms. Disrupting of light rhythms often leads to abnormal immune function, characterized by excessive inflammatory responses. However, the underlying regulatory mechanisms behind this phenomenon remain unclear. To address this concern, we use in vivo imaging to establish inflammation models in zebrafish, allowing us to investigate the effects and underlying mechanisms of light disruption on neutrophil recruitment. Our findings reveal that under sustained light conditions (LL), neutrophil recruitment in response to caudal fin injury and otic vesicle inflammation is significantly increased. This is accompanied by elevated levels of histone (H3K18) lactylation and reactive oxygen species (ROS) content. Through ChIP-sequencing and ChIP‒qPCR analysis, we discover that H3K18 lactylation regulates the transcriptional activation of the duox gene, leading to ROS production. In turn, ROS further promote H3K18 lactylation, forming a positive feedback loop. This loop, driven by H3K18 lactylation-ROS, ultimately results in the over recruitment of neutrophils to inflammatory sites in LL conditions. Collectively, our study provides evidence of a mutual loop between histone lactylation and ROS, exacerbating neutrophil recruitment in light disorder conditions, emphasizing the significance of maintaining a proper light-dark cycle to optimize immune function.

Metformin Attenuates Neutrophil Recruitment through the H3K18 Lactylation/Reactive Oxygen Species Pathway in Zebrafish.

Beyond its well-established role in diabetes management, metformin has gained attention as a promising therapeutic for inflammation-related diseases, largely due to its antioxidant capabilities. However, the mechanistic underpinnings of this effect remain elusive. Using in vivo zebrafish models of inflammation, we explored the impact of metformin on neutrophil recruitment and the underlying mechanisms involved. Our data indicate that metformin reduces histone (H3K18) lactylation, leading to the decreased production of reactive oxygen species (ROS) and a muted neutrophil response to both caudal fin injury and otic vesicle inflammation. To investigate the precise mechanisms through which metformin modulates neutrophil migration via ROS and H3K18 lactylation, we meticulously established the correlation between metformin-induced suppression of H3K18 lactylation and ROS levels. Through supplementary experiments involving the restoration of lactate and ROS, our findings demonstrated that elevated levels of both lactate and ROS significantly promoted the inflammatory response in zebrafish. Collectively, our study illuminates previously unexplored avenues of metformin's antioxidant and anti-inflammatory actions through the downregulation of H3K18 lactylation and ROS production, highlighting the crucial role of epigenetic regulation in inflammation and pointing to metformin's potential in treating inflammation-associated conditions.

Effects of 0.4 T, 3.0 T and 9.4 T static magnetic fields on development, behaviour and immune response in zebrafish (Danio rerio).

Magnetic Resonance Imaging (MRI) is widely applied in medical diagnosis due to its excellent non-invasiveness. With the increasing intensity of static magnetic field (SMF), the safety assessment of MRI has been ongoing. In this study, zebrafish larvae were exposed to SMFs of 0.4, 3.0, and 9.4 T for 2 h (h), and we found that there was no significant difference in the number of spontaneous tail swings, heart rate, and body length of zebrafish larvae in the treatment groups. The expression of development-related genes shha, pygo1, mylz3 and runx2b in the three SMF groups was almost not significantly different from the control group. Behavior tests unveiled a notable reduction in both the average speed and duration of high-speed movements in zebrafish larvae across all three SMF groups. In addition, the 0.4 and 3.0 T SMFs increased the migration of neutrophils in caudal fin injury, and the expression of pro-inflammatory cytokines was also increased. To explore the mechanism of SMFs on zebrafish immune function, this study utilized aanat2-/- mutant fish to demonstrate the effect of melatonin (MT) involvement in SMFs on zebrafish immune function. This study provides experimental data for understanding the effects of SMFs on organisms, and also provides a new insight for exploring the relationship between magnetic fields and immune function.

Circadian clock1a coordinates neutrophil recruitment via nfe212a/duox-reactive oxygen species pathway in zebrafish.

Neutrophil recruitment to inflammatory sites appears to be an evolutionarily conserved strategy to fight against exogenous insults. However, the rhythmic characteristics and underlying mechanisms of neutrophil migration on a 24-h timescale are largely unknown. Using the advantage of in vivo imaging of zebrafish, this study explored how the circadian gene clock1a dynamically regulates the rhythmic recruitment of neutrophils to inflammatory challenges. We generated a clock1a mutant and found that neutrophil migration is significantly increased in caudal fin injury and lipopolysaccharide (LPS) injection. Transcriptome sequencing, chromatin immunoprecipitation (ChIP), and dual-luciferase reporting experiments suggest that the clock1a gene regulates neutrophil migration by coordinating the rhythmic expression of nfe212a and duox genes to control the reactive oxygen species (ROS) level. This study ultimately provides a visual model to expand the understanding of the rhythmic mechanisms of neutrophil recruitment on a circadian timescale in a diurnal organism from the perspective of ROS.

Fluoxetine modifies circadian rhythm by reducing melatonin content in zebrafish.

Fluoxetine (FLX), a selective serotonin reuptake inhibitor (SSRI), increases the serotonin levels in the brain to treat depression. Antidepressants have been demonstrated to modulate circadian rhythm, but the underlying mechanisms by which antidepressants regulate circadian rhythm require more research. This study aimed to investigate the role of FLX on circadian rhythm by analyzing the movement behavior and internal circadian oscillations in zebrafish. The results showed that the expression of clock genes clock1a and bmal1b was significantly down-regulated, and the amplitude reduction and phase shift were observed after FLX treatment. Furthermore, FLX exposure inhibited the expression of aanat2, which led to a decrease in nocturnal melatonin secretion. aanat2-/- larvae showed disrupted circadian rhythm. These findings may help reveal the effect of FLX exposure on the circadian rhythm and locomotor activity. It may provide theoretical data for the clinical application of FLX.

Muscarinic acetylcholine receptors regulate inflammatory responses through arginases 1/2 in zebrafish.

Muscarinic acetylcholine receptors (mAChRs) are widely expressed in various effector cells and have been proved to play vital roles in smooth muscle contraction and digestive secretion. However, there are relatively few literatures revealing the roles of mAChRs in inflammatory processes, and its underlying regulatory mechanisms have not been elucidated. Taking the advantages of live imaging of zebrafish, we found that inhibition of mAChRs resulted in increased neutrophils recruitment and proinflammatory cytokines expression, whereas activation of mAChRs led to opposite outcome. Subsequently, we found that mAChRs regulated the expression of arginases (args), and pharmacological intervention of args level could reverse the effects of mAChRs on neutrophils migration and cytokines expression, suggesting that args are important downstream proteins of mAChRs that mediate the regulation of inflammatory response. In this study, we identified args as novel downstream proteins of mAChRs in inflammatory responses, providing additional evidence for system immune regulation of cholinergic receptors.

Hypoxia regulates cytokines expression and neutrophils migration by ERK signaling in zebrafish.

Normal dissolved oxygen in water is essential for maintaining the physiological functions of fish, but environmental pollution, such as eutrophication can lead to a decrease in oxygen content in water. How this reduction of dissolved oxygen in water affects the immune functions of fish and the potential regulatory mechanisms have not been thoroughly elucidated. In this study, we made full use of the aquatic model animal zebrafish to explore this question. In a model of LPS-induced inflammation, we found that hypoxia induced by infusing nitrogen into water increased the expression of pro-inflammatory cytokines, such as il-1ß, il-6, and il-8. In vivo imaging also showed that hypoxia significantly increased neutrophil migration to the site of caudal fin injury in the transgenic line. Subsequently, we found that the phosphorylation level of ERK protein was significantly activated upon hypoxia and proved the roles of ERK signaling in the expression of pro-inflammatory cytokines and neutrophil migration in zebrafish. This study indicated that reduced water oxygen significantly increases the inflammatory response of the zebrafish.