Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Krump, C.
Transcriptional Regulation of Human Langerhans Cell Development
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Graz Medical University; 2017. pp.
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- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Gorkiewicz Gregor
- Strobl Herbert
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- Abstract:
- Langerhans cells (LC) are a special type of dendritic cells (DCs) forming networks in stratified epithelia and play a key role in immunity and tolerance at body surfaces. LCs are established prenatally from hematopoietic progenitor cells (HPCs) and self-maintain in the adult epidermis dependent on TGF-ß1. In vitro, not only HPCs, but also blood CD14+ monocytes or CD1c+ classical dendritic cells (cDCs) can differentiate into functional LCs. Murine monocytes give rise to LCs under conditions of inflammation in vivo. However, the transcriptional mechanisms underlying the transdifferentiation of monocytes into LCs still remained to be elucidated. We performed microarray studies identifying several transcription factors that are differentially regulated during monocyte vs. TGF-ß1-mediated LC differentiation from CD34+ progenitors. Runt related transcription factor 3 (RUNX3), already described as key LC-instructive factor, was induced via TGF-ß1. The monocyte identity transcription factor Kruppel-like factor 4 (KLF4) appeared to be oppositely regulated, i.e. being repressed during LC, but induced during monocyte differentiation. We identified KLF4 to be inhibited during LC development from human blood monocytes. Conversely, KLF4 is maintained or induced during dermal DC and monocyte-derived DC (moDC) differentiation. We identified epithelial Notch signaling to repress KLF4 in monocytes undergoing LC commitment. Loss of KLF4 in monocytes transcriptionally de-represses RUNX3 in response to TGF-ß1, thereby allowing LC differentiation. Interestingly, unlike monocytes, HPCs and CD1c+KLF4- cDCs differentiate into LCs independently of exogenous Notch activation. We could show a TGF-ß1-dependent induction of the Notch signaling pathway (e.g. Notch receptor Notch-1, Notch ligand Jagged-2) in CD34+ human hematopoietic progenitors undergoing LC differentiation. Immunofluorescence staining revealed a strong activation of this pathway in CD34+-derived LCs in vitro as well as in epidermal LCs in situ in healthy adult skin; these cells appeared to be KLF4-. Also HLA-DR+ LC precursors in the prenatal epidermis lacked KLF4 expression, whereas dermal DCs strongly expressed KLF4. Retroviral gene transduction showed an inhibitory effect of KLF4 on in vitro LC differentiation in favor of monocyte development; however ectopic expression of LC-instructive RUNX3 reversed this effect. CD1c+ blood circulating cDCs do not require exogenous activation of the Notch signaling pathway due to the lack of KLF4 expression. Side-by side comparison revealed a higher potential of CD1c+ cDCs to differentiate to LCs than monocytes or CD34+ progenitors indicating a pre-commitment towards the LC lineage. However, CD1c+ cDCs showed potential to also give rise to KLF4+ moDCs and macrophages probably due to the described heterogeneity of this cell population. This indicates that CD1c+ cDCs might represent precursors of the LC as well as the monocytic DC lineage.