Page 228 - Haematologica Vol. 107 - September 2022

LETTER TO THE EDITOR AB
CDE
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Figure 1. Multiple myeloma patient samples exhibit reduced megakaryocyte–erythrocyte progenitors, elevated MAFB/GATA1 and reduced late erythroblast development that is reversed with propranolol treatment. (A) Representative contour plots of control bone marrow (CBM) and multiple myeloma (MM) sample mononuclear cells in forward vs. side scatter (left panel), from flow cytometry day 0 CBM and MM BM evaluated for common myeloid progenitors (CMP)/ granulocyte-monocyte-progenitors (GMP)/megakaryocyte–erythrocyte progenitors (MEP) frequencies (n=10) (right panel). (B) Mean fluorescence intensity (MFI) of MAFB and GATA1 expression in CMP from 10 MM patients at day 0, evaluated by flow cytometry. (C) Introduction of non-targeting and MAFB-directed small interfering RNA (siRNA) in MM BM samples (n=4). Frequencies of CMP, GMP and MEP in MM vs. MM siRNA-transfected samples are shown. (D) Evaluation of total erythroblasts (EB) (CD71+CD235a-/+) in MM vs. CBM P<0.001 (n=10) (left panel). Late erythroblasts (LEB) (CD71+CD235a+) are significantly decreased (P<0.0001) compared to early erythroblasts (EEB) (CD71+CD235a-) suggesting erythropoietic arrest in MM (right panel). (E) MEP, GMP and CMP quantified in hematopoietic stem and progenitor cell (HSPC) in phase 1 cultures treated with increasing doses of isoproterenol (ISO). (F) CMP, GMP and MEP frequencies quantified in in CBM and MM treated ex vivo with propranolol (PRO).
We first evaluated basal expression levels of the a and b AR by flow cytometry. HSPC of MM BM and CBM were found to exhibit similar expression of both a (a1, a2) and b (b1, b2, b3) AR (data not shown). Stimulation of CBM HSPC with increasing concentrations of isoproterenol, a specific agonist of b AR, increased GMP with a corresponding re- duction of MEPs (Figure 1E). Isoproterenol, importantly, in- creased MAFB expression in CMP and GMP and reduced GATA1 expression in CMP, GMP and MEP (Online Supple- mentary Figure S1C and D). Phenylephrine, an a AR spe-
cific agonist, had no effect on HSPC specification towards GMP versus MEP (n=4) or on MAFB/GATA1 expression, sug- gesting b adrenergic stimulation specifically regulates myeloid bias (Online Supplementary Figure S1E). Inhibition of b AR with propranolol suppressed MAFB expression in CMP (Online Supplementary Figure S1C). Importantly, b AR inhibition with propranolol was also able to reverse the low MEP:GMP ratio in MM BM (Figure 1F). These results, in sum, demonstrate that in MM, i) b adrenergic signaling can regulate HSPC specification; ii) propranolol reverses the
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