Heping Xu's group at Westlake University has published a research paper entitled: Neuromedin U programs eosinophils to promote mucosal immunity of the small intestine in Science.
The study reveals that intestinal nervous system signaling regulates small intestinal epithelial cell homeostasis and mucosal immunity by modulating eosinophil activity. This study provides new insights into the interactions between the neural-immune-epithelial system and opens up new ideas for understanding the new functions of eosinophils and the study of related clinical diseases.
The study reveals that intestinal nervous system signaling regulates small intestinal epithelial cell homeostasis and mucosal immunity by modulating eosinophil activity. This study provides new insights into the interactions between the neural-immune-epithelial system and opens up new ideas for understanding the new functions of eosinophils and the study of related clinical diseases.
Eosinophils are traditionally regarded as a class of terminally differentiated cells with low heterogeneity, single function, short life cycle, and pro-inflammatory function only in disease state. Therefore, compared with other immune cells such as lymphocytes and macrophages, eosinophils have always been "cold" cells in the field of immunology, and have not been the focus of immunologists' attention and research. However, eosinophils are found in large numbers in the mucosal tissues of healthy humans and animal models, including the small intestine. Earlier reports have found that eosinophils in the human small intestine release their internal granules at homeostasis; and more recently, it has been shown that these eosinophils present in tissue homeostasis can be involved in regulating the morphology of the small intestinal villi. These phenomena imply that eosinophils may have an undiscovered role in the small intestine. Therefore, since 2019, Li Yu, a PhD student in Heping Xu's group, has been working on the function of eosinophils in small intestinal homeostasis as well as cellular activity regulatory signaling.
In order to explore the molecular characteristics of small intestinal eosinophils, the authors first optimized the experimental process and methodology, overcame the difficulties posed by other intracellular mediators incompatible with transcriptional studies, such as RNA enzymes contained in eosinophils, and successfully collected transcriptomes of eosinophils from seven major tissues, including small intestine, bone marrow, and skin, in a mouse model; data analysis revealed a series of tissue-specific specific eosinophil molecular features. For example, comparing eosinophils in other tissues, it was found that the neuropeptide NMU 1-like receptor molecule (neuromedin U receptor 1, NMUR1) was specifically expressed only in small intestinal eosinophils. Further analysis by whole-tissue fluorescence confocal imaging, and scanning electron microscopy revealed that eosinophils in the small intestine are in very close contact with nerve fibers in the intestine. This specific gene expression pattern and tissue localization suggest that eosinophils may be able to directly receive neural signals from the intestine and perform specific functions.
NMU is a highly structurally conserved neuropeptide widely distributed in the hypothalamus, pituitary gland and gastrointestinal system, which has various functions such as stimulating smooth muscle contraction, inhibiting feeding, and inhibiting gastric acid secretion. More progress has been made in recent years in the study of NMU receptor NMUR1 in the immune system. For example, it was found that NMU-NMUR1 can directly promote the activity of type 2 innate lymphoid cells (group 2 innate lymphoid cells, ILC2s) . In addition a recent group report concluded that NMUR1 is a molecule characteristically expressed by ILC2 and is not expressed in any cells other than ILC2 . Obviously this conclusion is not consistent with the authors' transcriptional analysis results. In order to clarify the expression pattern of NMUR1 in different tissues and cells, the authors constructed an endogenous NMUR1-expressing reporter mouse model (Nmur1iCre-TdT mice) and analyzed and clarified that eosinophils in the small intestine do express NMUR1 in addition to ILC2. Meanwhile, the authors further analyzed and found that NMUR1 was also specifically expressed on human small intestine eosinophils.
The authors then explored the properties of NMUR1-expressing eosinophils using Nmur1iCre-TdT mice. NMUR1+ eosinophils were found to have special physicochemical properties as well as protein expression characteristics. For example, the nuclei of NMUR1+ eosinophils were mainly bilobed and elliptical, whereas the nuclei of NMUR1+ eosinophils were mainly ring-shaped; NMUR1+ eosinophils expressed higher tissue-adaptive molecules and degranulation molecules. Further combined with transmission electron microscopy results confirmed that NMUR1+ eosinophils did have stronger degranulation activity in the resting state. These differences imply that NMUR1+ eosinophils have a higher degree of activation as well as higher tissue adaptive changes.
The authors subsequently revealed that NMUR1 expression in eosinophils is regulated by the special microenvironment of the small intestine and up-regulated under inflammatory conditions by probing the development of NMUR1+ eosinophils and the dynamics of this cell population under inflammatory conditions. In order to explore the function of this special population of NMUR1+ eosinophil activity, the authors found that NMUR1 is involved in maintaining the eosinophil population in the small intestine and regulating eosinophil degranulation activity by constructing a variety of genetically engineered mouse models. Further, constitutive imaging analysis revealed that eosinophil deletion of NMUR1 reduces small intestinal epithelial cuprocyte differentiation and attenuates immunity against parasitic infections.
Finally, the authors used in vivo chemical genetics to manipulate NMU+ neuronal activity and in vitro eosinophil-small intestinal epithelial organoid co-culture system to reveal that eosinophils directly regulate small intestinal cuprocyte differentiation and that NMU-NMUR1 signaling participates in this process by regulating eosinophils.
Overall, this study reveals that NMU-NMUR1 signaling specifically drives small intestinal eosinophils to undergo adaptive changes at the transcriptional, protein, and functional levels and regulates small intestinal epithelial cell differentiation in both homeostatic and inflammatory states. This study provides new insights into the interactions between the neural-immune-epithelial system and opens up new ideas for understanding the new functions of eosinophils and the study of related clinical diseases.
Xu Heping Research Institute of Westlake University is the corresponding author of the paper, and Li Yu (Class of 2019), a PhD student in the joint training program of Westlake University-Zhejiang University, is the first author of the paper. The big data analysis work was done by Shaorui Liu; Kewen Zhou (class of 2022), a doctoral student at Westlake University, made significant contributions to the project advancement in imaging and sequencing; and the clinical sample study was done in collaboration with the team of Yan Chen, director of the Department of Gastroenterology at the Second Hospital Affiliated to the School of Medicine of Zhejiang University.
