<p>Neutrophils are the first cells recruited to an immune stimulus stemming from infection or sterile injuries via a mixture of chemoattractant cues. In addition to eliminating pathogens, neutrophils coordinate the overall inflammation by activating and producing inflammatory signals in the tissue while modulating the activation of other immune cells which in some cases leads to adverse tissue damage. Over amplified or chronic neutrophil recruitment directly leads to autoimmune diseases including rheumatic arthritis, diabetes, neurodegenerative diseases, and cancer. Dampening neutrophil recruitment is a strategy to intervene in neutrophil-orchestrated chronic inflammation. Despite intensive research over the past several decades, clinical studies targeting neutrophil migration have been largely unsuccessful, possibly due to the prominent redundancy of adhesion receptors and chemokines. Additional challenges lie in the balance of dampening detrimental inflammation while preserving immunity. Neutrophils are terminally differentiated cells that are hard to study in cell culture. Mouse models are often used to study hematopoiesis, migration, and chemotaxis of neutrophils but is very labor intensive. To discover novel therapeutic targets that modulate neutrophil migration, we performed a neutrophil-specific microRNA (miRNA) overexpression screen in zebrafish and identified eight miRNAs as potent suppressors of neutrophil migration. We have generated transgenic zebrafish lines that overexpresses these candidate miRNAs where we recapitulated the mitigation in neutrophil motility and chemotaxis to tissue injury or infection. Among those we further characterized two miRNAs which have not been reported to regulate neutrophil migration, namely miR-722 and miR-199.</p> <p> </p> <p>MiR-722 downregulates the transcript level of <i>rac2</i> through binding to the <i>rac2</i> 3'UTR. Furthermore, miR-722-overexpressing larvae display improved outcomes in both sterile and bacterial systemic models, which correlates with a robust upregulation of the anti-inflammatory cytokines in the whole larvae and isolated neutrophils. miR-722 protects zebrafish from lethal lipopolysaccharide challenge. In addition, overexpression of mir-722 reduced chemotaxis of human neutrophil like cells, indicating that miR-722 is a potential agent to reduce inflammation in humans. </p> <p>MiR-199<i>,</i> decreases neutrophil chemotaxis in zebrafish and human neutrophil-like cells. Intriguingly, in terminally differentiated neutrophils, miR-199 alters the cell cycle-related pathways and directly suppresses cyclin-dependent kinase 2 (<i>cdk2</i>), whose known activity is restricted to cell cycle progression and cell differentiation. Inhibiting Cdk2, but not DNA replication, disrupts cell polarity and chemotaxis of zebrafish neutrophils without inducing cell death. Human neutrophil-like cells deficient in CDK2 fail to polarize and display altered signaling downstream of the formyl peptide receptor. Chemotaxis of primary human neutrophils is also reduced upon CDK2 inhibition. Furthermore, miR-199 overexpression or CDK2 inhibition significantly improves the outcome of lethal systemic inflammation challenges in zebrafish. </p> <p> </p> <p>In summary, our results reveal previously unknown functions of these miRNAs, and provide potential avenues to modulate neutrophil migration as well as lead to discoveries of novel factors which can regulate this process. We have also discovered a non-classical role of CDK2 in regulating neutrophil migration which provides directions for alleviating systemic inflammation and a better understanding of neutrophil biology. </p>

<p dir="ltr">The aquaculture industry has experienced remarkable expansion over the past few decades, largely due to the development of modern technologies and intensive farming systems. However, as the industry continues to grow, farming-related and environmental stressors such as overcrowding, poor water conditions and handling have continued to pose major obstacles to the worldwide expansion of this sector. The presence of these stressors affect the growth potential and health of farmed animals leading to significant economic losses. Hence, efficient management of the stress response of farmed species via sustainable means is important to ensure continuous development of the aquaculture sector. This study, therefore, explores the potential of dietary tryptophan supplementation to mitigate stress and improve growth, immune response, and disease resistance in channel catfish (<i>Ictalurus punctatus</i>). The study comprised a 36-day feeding trial where juvenile catfish were fed a tryptophan-supplemented diet under stressed (cortisol-supplemented) and unstressed conditions, followed by a 72-hour disease challenge with <i>Aeromonas hydrophila </i>(vAh). At the end of the study, the results show tryptophan supplementation did not significantly enhance growth or nutrient utilization, likely due to its neuroendocrine effects on feed intake. However, tryptophan demonstrated potential in modulating stress physiology and immune responses, including upregulation of key immune-related genes post-infection and promoting survival against vAh infection. These findings suggest that while tryptophan may not directly improve growth in our specific experimental conditions, its role in stress and immune regulation warrants further investigation, particularly in optimizing its dosage and combination with other dietary additives.</p>