Search

Simple Summary: Controlling epigenetic signals for mediating the homeostatic immune response in skin-residing Langerhans cells (LCs) ontogeny, maintenance, and function are largely not determined. Here, we demonstrated that the epigenetic regulator miR-23a not only plays an indispensable role for LC antigen uptake but is also crucial for bone marrow-derived LC repopulation during the inflammatory condition. During this process, miR-23a may regulate LC phagocytosis by mediating efferocytosis and endocytosis-mediated targets as well as LCs repopulation via targeting Fas and Bcl-2 family proapoptotic molecules. Instead, miR-23a did not demonstrate playing any role in LC development and postnatal homeostasis. Thus, the context-dependent regulatory role of miR-23a in LCs may represent an extra-epigenetic layer for incorporating TGF-β and PU.1-mediated regulation during steady-state and inflammation-induced repopulation. Langerhans cells (LCs) are skin-resident macrophage that act similarly to dendritic cells for controlling adaptive immunity and immune tolerance in the skin, and they are key players in the development of numerous skin diseases. While TGF-β and related downstream signaling pathways are known to control numerous aspects of LC biology, little is known about the epigenetic signals that coordinate cell signaling during LC ontogeny, maintenance, and function. Our previous studies in a total miRNA deletion mouse model showed that miRNAs are critically involved in embryonic LC development and postnatal LC homeostasis; however, the specific miRNA(s) that regulate LCs remain unknown. miR-23a is the first member of the miR-23a-27a-24-2 cluster, a direct downstream target of PU.1 and TGF-b, which regulate the determination of myeloid versus lymphoid fates. Therefore, we used a myeloid-specific miR-23a deletion mouse model to explore whether and how miR-23a affects LC ontogeny and function in the skin. We observed the indispensable role of miR-23a in LC antigen uptake and inflammation-induced LC epidermal repopulation; however, embryonic LC development and postnatal homeostasis were not affected by cells lacking miR23a. Our results suggest that miR-23a controls LC phagocytosis by targeting molecules that regulate efferocytosis and endocytosis, whereas miR-23a promotes homeostasis in bone marrow-derived LCs that repopulate the skin after inflammatory insult by targeting Fas and Bcl-2 family proapoptotic molecules. Collectively, the context-dependent regulatory role of miR-23a in LCs represents an extra-epigenetic layer that incorporates TGF-b- and PU.1-mediated regulation during steady-state and inflammation-induced repopulation. [ABSTRACT FROM AUTHOR]