Page 227 - Haematologica Vol. 107 - September 2022

LETTER TO THE EDITOR
b adrenergic signaling regulates hematopoietic stem and progenitor cell commitment and therapy sensitivity
in multiple myeloma
Multiple myeloma (MM) development is dependent upon critical interactions with the bone marrow (BM) niche.1 The contribution of catecholamines and adrenergic signaling from the highly innervated BM niche2 to MM development is under-explored. MM patients demonstrate an elevated conserved transcriptional response to adversity (CTRA), in- dicative of stress that correlates with poor survival.3 A retrospective study evaluating the effects of the non-se- lective b adrenergic receptor (AR) blocker propranolol in immunomodulatory drug-treated MM found propranolol to improve progression-free survival (PFS) and overall survival (OS).4 MM patients exhibit reduced megakaryocyte–ery- throcyte progenitors (MEP) and increased monocytic mye- loid-derived suppressor cells (MDSC) (CD14+HLADRlow) in the BM, suggestive of increased myeloid bias.5 Introduction of MM precursor monoclonal gammopathy of undetermined significance (MGUS) cells into humanized IL-6 MIS(KI)TRG6 mice promotes progression to MM, suggesting the suffi- ciency of extrinsic BM niche elements in fostering MM de- velopment.6 Consistent with this, administration of propranolol in MM patients undergoing hematopoietic stem cell transplant (HSCT) demonstrates a significant reduction of not only the CTRA response, but also marked reductions in myeloid lineage bias.3 How targeting adrenergic signaling regulates hematopoietic stem and progenitor cell (HSPC) commitment in MM remains poorly understood. Our study provides mechanistic rationale for the application of pro- pranolol to resolve both microenvironmental and MM-spe- cific tumor promoting biology.
For this study, samples from MM patients, ranging from newly diagnosed to those with relapsed refractory MM were analyzed, exhibiting a range of reduced hemoglobin (Hgb) levels (characteristics in the Online Supplementary Table S1) and anemia. BM aspirates were obtained from consenting patients following an Emory University Insti- tutional Review Board-approved protocol. Research was conducted in accordance with the Declaration of Helsinki. Ficoll gradient isolated mononuclear cells were cultured for phase I expansion in serum-free expansion medium (SFEM) containing granulocyte macrophage colony-stimu- lating factor (GMCSF), stem cell factor (SCF), interleukin 3 (IL-3 – pluripotent hematopoietic colony-stimulating factor) or further expanded in phase II (day 6-16) by cul- ture in SCF, HT (holo-transferrin), EPO (erythropoietin), and SFEM for all assays involving progenitor cells as pre- viously described.7,8 Cell death/viability were assessed by
AnnexinV/DAPI flow cytometry. The CoMMpass MM trial (clinicaltrials gov. Identifier: NCT0145429) data was down- loaded from Genomic Data Commons. All other assays are as previously reported.8,9
Analysis of the proportion of granulocyte-monocyte-pro- genitors (GMP) (Linneg CD34+CD38+CD123-CD45RA+) versus MEP (Linneg CD34+CD38+CD123-CD45RA-) reconfirmed the significantly reduced number of MEP10 and importantly for the first time, identified a higher proportion of GMP in MM BM (n=10) versus control bone marrow (CBM) (Figure 1A). Myeloid-biased hematopoiesis contributes to anemia and a protumorigenic BM marrow niche in MM. Strategies tar- geting the myeloid lineage skew can potentially prevent MM progression and development of fatal refractory dis- ease. V-maf avian musculoaponeurotic fibrosarcoma on- cogene homolog B transcription factor (MAFB) and globin transcription factor 1 (GATA1) are central regulators of myeloid versus erythroid lineage commitment. We pre- viously showed that the development of anemia in human burn patients and scald burn mice is driven by high MAFB versus GATA1 expression in CMP. Similarly, we found CMP from MM BM (n=10) expressed significantly higher MAFB and reduced GATA1 expression compared to CMP from CBM (Figure 1B), which inversely correlated with the per- centage of MEP. Notably, both reduced MEP/GMP ratio and elevated MAFB/GATA1 expression in MM CMP were main- tained after phase I expansion of HSPC, suggesting that the skew in lineage specification is intrinsically driven (Online Supplementary Figure S1A and B). Genetic sup- pression of MAFB expression reduced GMP and increased MEP in the MM BM samples (n=4) (Figure 1C), suggesting that reduction of MAFB was sufficient to block the mye- loid bias detected in MM.
Concordant with reduced MM MEP specification, MM BM also exhibited significantly lower total erythroblasts com- pared to CBM (Figure 1D). Although variability in early ery- throblast (EEB) numbers were noticed, late erythroblasts (LEB) were uniformly lower in all MM BM samples (n=10), indicating erythropoietic arrest in MM (Figure 1D).
We have previously shown in human burn patients and scald burn mice that conditions resulting in high catecho- lamines instigate myelo-erythroid reprioritization and anemia.8 As stress and catecholamines are known to modulate the BM microenvironment in MM,11 we investi- gated whether adrenergic signaling regulated MEP/GMP specification in MM BM.
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