Background: The intestinal epithelium is a vital organ that absorbs nutrients and water from luminal contents and provide protection against pathogens and chemicals through the stimulation of the immune system and secretion of antimicrobials and mucus. The development and cellular maturation of the intestinal epithelium is orchestrated by signaling factors, epigenetic regulators and transcription factors, but it is still incompletely defined. Lysinespecific demethylase 1 (LSD1) is a chromatin-modifying enzyme expressed in the intestine and acts on methyl groups connected to lysines 4 or 9 on histone H3-tails. LSD1 has been implicated in processes including embryogenesis and tissue-specific differentiation, but its function in intestinal epithelial development remains unknown.
Objectives: The Oudhoff lab group has explored the expression and function of LSD1 in the intestinal epithelium of adult mice. Unpublished data has shown that mice with an intestinal epithelial deletion of Lsd1 (Lsd1∆IEC) have abnormal quantities of stem cells and differentiated cell types when compared to wildtype (Lsd1f/f) mice. In this study, the expression pattern of the LSD1 protein in wildtype mice and the effects of its deletion on differentiated cell types in the intestinal epithelium during development were studied. The study aimed to elucidate how and when LSD1 affects intestinal epithelial cell differentiation during development.
Methods: To study the role of LSD1 in intestinal epithelial development, we used wildtypeand knockout mice from five developmental timepoints: E16.5, P0.5, P7, P14 and P21. Morphological features were visualized by hematoxylin- and eosin-staining. Staining patterns and cellular composition of the intestinal epithelium was studied by immunohistochemistry and immunofluorescence.
Results: Through two different staining methods, we retrieved two possible expression patterns of LSD1 during intestinal epithelial development. Immunofluorescent staining showed expression of LSD1 in the whole epithelium at every developmental timepoint, whereas immunohistochemical detection suggested a restriction of LSD1 towards crypts and intervillous zones in late development. When comparing Lsd1f/f with Lsd1∆IEC mice, no alterations to the proliferative compartment or to the intestinal morphology was observed. Goblet cells were significantly reduced in the Lsd1∆IEC mice from the second postnatal week in the duodenum and jejunum, whereas tuft cells were significantly increased in all small intestinal segments from P21. Enteroendocrine cells were unaffected by the tissue-specific knockout of Lsd1. Furthermore, immunohistochemical staining of H3K4me2 did not reveal any difference in staining intensity.
Conclusion: In this study, we have presented two potential expression patterns of LSD1 in the developing intestinal epithelium. The role of LSD1 in the intestinal epithelial development has been elucidated, where it regulates goblet- and tuft cell differentiation in late intestinal epithelial development and is intrinsic to Paneth cell development. Global staining of the active transcription mark H3K4me2 did not reveal any differences between the Lsd1∆IEC- and Lsd1f/f mice, suggesting that the observed phenotype is controlled by the regulation of H3K4- dimethylation at distinct sites or through other regulatory mechanisms. Further investigation is required to validate these findings and uncover the exact role of LSD1 in intestinal epithelial differentiation.