Poster Presentation Australasian RNA Biology and Biotechnology Association 2025 Conference

RNA binding, but not editing, by ADAR1p150 regulates haematopoietic homeostasis. (#14)

Jacki Heraud-Farlow 1 2 , Scott Taylor 1 , Ankita Goradia 1 , Maddie Stewart 1 2 , Monique Smeets 2 , David Izon 2 , Zhen Liang 1 2 , Alistair Chalk 2 , Shi-Bin Hu 3 , Jin Billy Li 3 , Louise Purton 2 , Carl Walkley 1 2
  1. Hudson Institute of Medical Research, Clayton, VIC, Australia
  2. St. Vincent's Institute, Fitzroy, VIC, Australia
  3. Stanford University, Stanford, USA

Adenosine to inosine (A-to-I) RNA editing is mediated by ADAR1 and ADAR2, with ADAR1 the predominant ADAR expressed in haematopoiesis. ADAR1 has two isoforms, a nuclear p110 protein and a predominantly cytoplasmic p150 form. Loss of ADAR1 protein, or its editing activity, results in sensing of under-/un-edited cellular derived dsRNA by MDA5, triggering a fatal type I interferon response. Whilst editing is the primary function of ADAR1, protein dependent, editing independent functions have been suggested. We now have identified a protein dependent, RNA editing independent role for ADAR1p150 in T cell homeostasis and HSC repopulating activity in vivo.  

 

We recently established viable adult ADAR1 protein deficient (A1-/-), editing deficient (A1EA/EA) and ADAR1p150 (A1p150-/-) deficient mice by co-deleting MDA5 and PKR (Hu*, Heraud-Farlow* et al Mol Cell 2023). Peripheral blood (PB) analysis of adult A1+/+, A1-/-, A1EA/EA and A1p150-/- mice demonstrated that the A1-/- and A1p150-/- had severely reduced PB T cells. Thymic T cell development was largely normal, indicating reduced survival of the PB T cells as the likely cause. Bone marrow (BM) transplantation demonstrated that the A1-/- and A1p150-/- BM failed to regenerate T cells in the recipients, however, unexpectedly, they also have a profound defect in HSC reconstitution. A1EA/EA had normal reconstitution, demonstrating that the phenotypes are independent of RNA editing by ADAR1. The estimated HSC competitive repopulating units in the A1-/- and A1p150-/- were 200-600 fold reduced compared to A1EA/EA and A1+/+, respectively. Mechanistic studies are investigating the basis of this defect using different ADAR1p150 mutants.

 

These data demonstrate that ADAR1p150 protein, independent of both A-to-I editing and of MDA5/PKR signalling, regulates haematopoietic homeostasis.

  1. Hu SB*, Heraud-Farlow JE*, Sun T, Liang Z, Goradia A, Taylor S, Walkley CR*, Li JB*. ADAR1p150 prevents MDA5 and PKR activation via distinct mechanisms to avert fatal autoinflammation. Mol Cell. 2023 Nov 2;83(21):3869-3884.e7. doi: 10.1016/j.molcel.2023.09.018. Epub 2023 Oct 4.