A profound understanding of RNA binding proteins (RBPs) in the reactivation of fetal hemoglobin (HbF) may lead to novel therapeutic targets for patients with sickle cell disease (SCD), according to a study recently published in Blood Advances.

“The mechanisms controlling this fetal-to-adult switch have been under investigation for decades with the interest in this process fueled by the recognition that reversal of the switch benefits patients with β-hemoglobinopathies, such as sickle cell disease (SCD) and β-thalassemia,” the authors noted.

Researchers used fetal mouse liver cultures and peripheral blood mononuclear cells from patients previously diagnosed with SCD to later perform clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)-based analysis that revealed the role of RBPs in HbF regulation, pinpointing the RNA binding motif 12 (RBM12), an RBP, as the main antagonizing actor. 

Depleting this molecule resulted in increased HbF expression with subsequent less cell sickling in individuals with SCD.

Assays that included an enhanced crosslinking and immunoprecipitation sequencing (eCLIP-Seq) confirmed the independent activity of RBM12 on HbF and determined a strong affinity of the RNA recognition motif 1 (RRM1) portion to 5’ untranslated regions (5’UTRs) in transcripts, suggesting a possible mechanism of action, and hence a therapeutic target, Wakabayashi et al explained.

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Moreover, mass spectrometry did not show a direct interaction between RBM12 and BCL11A and ZBTB7A/LRF, the 2 main known HbF expression repressors, indicating that this RBP may produce its effect through a differing pathway not yet described. Another possibility is that RBM12 exerts post-transcriptional modulating functions. 

A modified version of RBM12 that still preserved RRM1 attached to 2 proline-rich segments did not generate the same effects. This highlights the importance of continuing research on this topic; for example, exploring a small molecule inhibitor model regarding the RRM1 domain may succeed in increasing HbF expression.

“The fact that the HbF regulatory function can be reduced to a relatively small portion of the molecule might facilitate means to perturb this function without interfering with other RBM12 functions,” the authors wrote.

Lastly, RBM12 depletion did not generate changes in either the erythroid proteome or transcriptome. This finding may translate to targeting drugs with promising results and fewer negative effects of erythroid maturation.

Reference

Wakabayashi A, Kihiu M, Sharma M, et al. Identification and characterization of RBM12 as a novel regulator of fetal hemoglobin expression. Blood Adv. Published online May 27, 2022. doi:10.1182/bloodadvances.2022007904