S100A12-Orchestrated Macrophage-ER stress crosstalk in MDS: Mechanisms and precision therapeutic targeting

Abstract Background: Myelodysplastic syndromes (MDS) are clonal hematopoietic stem cell disorders originating in the bone marrow. Current challenges include poorly defined pathogenesis, limited treatment options, and poor prognosis following disease progression, thus creating a pressing need for novel therapies targeting the underlying mechanisms. Methods and Results: This study revealed monocyte/macrophage lineage differentiation impairment in MDS patients. Single-cell analysis identified S100A12 as a master regulator of this defect. The inverse correlation between low S100A12 expression and differentiation blockade supports its role in impairing differentiation via the non-canonical ER stress-autophagy axis. Further investigations quantified S100A12 expression gradients relative to macrophage differentiation trajectories and elucidated molecular switches involving epigenetic (DNA methylation) or transcriptional (NF-κB/STAT3) regulation. Treatment of MDS patient-derived mononuclear cells (MNCs) with azacitidine induced bidirectional modulation of S100A12 expression: downregulation in cells with high pre-treatment expression and upregulation in those exhibiting low baseline expression. Integrated analysis revealed an inverse correlation between modulation extent and monocyte levels (r = -0.549, p<0.01), with positive correlation to Treg frequencies (r = 0.589, p<0.01) and IL-6 concentrations (r = 0.454, p<0.05). This heterogeneity stratified intermediate/high-risk MDS patients into distinct immunosuppressive subsets, with the upregulation group showing enhanced immunosuppression. Exogenous supplementation of recombinant S100A12 protein in the MUTZ-1–macrophage coculture system strongly activated core ER stress-sensing pathways (IRE1–XBP1 and PERK–ATF4) in Mφ, concurrently enhancing M2-like polarization and elevating immunosuppressive cytokines (IL-10, TGF-β). S100A12 functions as a molecular bridge that facilitates bidirectional ER stress propagation between cell types, transmits inhibitory signals from tumor cells to macrophages (Mφ), thus maintaining them in an immunosuppressive state. Conclusion: Our findings elucidate a pivotal role for S100A12 in MDS pathobiology: 1. Low expression at least partially promotes disease progression by inhibiting Mφ differentiation; 2. Heterogeneity of this gene dictates azacitidine-induced immune remodeling; 3. As an ER stress signaling hub, S100A12 orchestrates tumor-macrophage crosstalk to maintain an immunosuppressive microenvironment. Future work will 1) decode S100A12-regulated molecular networks controlling Mφ polarization (IL-10/TGF-β) and ER stress (IRE1-XBP1/PERK-ATF4), 2) validate the impact of S100A12 heterogeneity on azacitidine efficacy, and 3) establish its central role in MDS immunometabolic imbalance. Collectively, these insights will facilitate precise azacitidine-based combination immunotherapy development.