Role of RIG-I like receptors in hematopoietic stem cells

Abstract: In steady state conditions Hematopoietic stem cells (HSCs) are kept in a dormant state, but can be rapidly activated and mobilized in response to stress. Here, we identified the viral RNA immune receptor MDA5 as a critical regulator of HSC activation. MDA5 belongs to the RIG-I like receptor (RLR) family. We proved that Mda5 and other RLRs are expressed, at low levels, in hematopoietic precursor cell lines, but their expression is rapidly increased upon challenge such as irradiation. These data provided the first hint that RLRs play roles even in the absence of infection. In order to investigate the role of Mda5 in the hematopoietic system we used an Mda5 knockout mouse. Mda5-/- HSCs showed higher colony forming capacity in vitro and increased repopulating capacity in vivo as shown by serial CFU-C replating assays and serial transplantation experiments, respectively. Additionally, challenges such as serial irradiation or injection of the myeloablative drug 5-fluoruracil (5-FU) led to accumulation of Mda5-/- HSCs whereas their WT counterparts were exhausted. Since the quiescent status of HSCs plays a significant role in their ability to overcome challenges we reasoned that the enhanced repopulation activity of Mda5-/- HSCs may be due to their ability to retain their quiescence. Indeed, we found that Mda5-/- HSCs are remarkably more quiescent than WT HSCs at both steady-state and after chemotherapy. In addition, inhibition of TBK1, an important kinase downstream of Mda5, preserved quiescence and increased the colony forming potential of WT HSCs, thus mimicking the Mda5-/- HSC phenotype. These data suggest that MDA5 is important to control the balance between quiescence and proliferation in HSCs. To determine how MDA5 regulates HSC activation, we performed RNA-sequencing and observed that Mda5-/- HSCs show an impaired upregulation of the inflammatory response typically observed in control animals after chemotherapy. Surprisingly, our RNAseq data revealed increased transcription of transposable elements (TEs) during hematopoietic regeneration. This observation prompted us to examine whether TEs can act as potential ligands for MDA5. Indeed, by establishing a protocol for RNA immunoprecipitation after crosslinking (FLASH protocol) in our lab, we were able to prove that MDA5 is able to bind TEs such as LINEs and SINEs upon challenge.
This work reveals that during stress like chemotherapy, TE elements are upregulated and can bind and activate the innate immune receptor MDA5. Activation of MDA5 leads to the induction of an inflammatory response that is necessary for HSC activation

Object Details

• Location: Deutsche Nationalbibliothek Frankfurt am Main
• Extent: Online-Ressource
• Language: Englisch
• Notes: Universität Freiburg, Dissertation, 2019

Classification and Topics

• Keyword: Hematopoietic stem cells

Contributors, Places and Time

• Event: Veröffentlichung
• (where): Freiburg
• (who): Universität
• (when): 2020
• Creator: Prater, Pia
• Contributor: Trompouki, Eirini ; Albert-Ludwigs-Universität Freiburg. Fakultät für Biologie

Further information

• DOI: 10.6094/UNIFR/154816
• URN: urn:nbn:de:bsz:25-freidok-1548169
• Rights: Kein Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.
• Last update: 25.03.2025, 1:45 PM CET