Bone marrow microenvironment retinoic acid receptor signaling represses multipotential progenitor dependent B cell lymphopoiesis through secretion of resistin Free

Lymphoid reconstitution following hematopoietic stem cell transplantation (HSCT) remains a significant clinical challenge. Incomplete immune recovery post-HSCT is associated with increased infection risk and non-relapse mortality. While hematopoietic stem cells (HSC) are known to respond to myelopoiesis-inducing inflammatory cues within the bone marrow (BM) microenvironment (ME), mechanisms governing lineage-specific hematopoietic regeneration remain incompletely understood. We and others have shown that the BM mesenchymal microenvironment, through retinoic acid receptor (RAR/RXR) signaling, plays a critical role in hematopoietic regeneration. Specifically, retinoid X receptor (RXR) activity supports HSC self-renewal and maintains a balance between lymphoid and myeloid hematopoiesis. However, the role of adiponectin-expressing bone marrow adipocytes (BMA), a subset of mesenchymal cells enriched in the post-transplant setting, remains largely unexplored in this context. To investigate how RXRs regulate the lymphopoietic potential of BMA, we generated tamoxifen-inducible, BMA-specific RXRα/β deficient mice (AdipoQCre-ERT2; RXRα/β^Δ/Δ). After two weeks of ending tamoxifen induction, we observed a ~70% reduction in BM adipocytes, confirming the efficacy of RXR deletion in BMA. Notably, competitive repopulation assays using AdipoQCre-ERT2; RXRα/β^Δ/Δbone marrow showed normal overall hematopoietic chimerism and T cell/myeloid reconstitution, two-fold increased B cell output and accelerated B cell recovery in serial transplants and preserved clonal diversity in regenerated B cells, as assessed by BCR profiling. This enhanced lymphopoiesis was most prominent in transplants using LT-HSC-depleted MPPs from RXR-deficient BMA mice. These MPP-derived grafts produced a 13-fold increase in B cells and 11-fold increase in T cells by 16 weeks post-transplant compared to WT MPPs or any LT-HSC-derived transplant group, indicating that BMA RXR signaling restrains MPP lymphoid potential. To determine whether this was a cell-intrinsic or microenvironment-driven effect, we reverse-transplanted WT HSCs into WT and RXR-deficient recipients. WT HSCs transplanted into AdipoQCre-ERT2; RXRα/β^Δ/Δmice exhibited a 4-fold increase in B cell regeneration, without changes in myeloid or T-lineage output, further supporting a niche-mediated mechanism. Mechanistically, single-cell RNA sequencing of LSK (Lin⁻Sca1⁺cKit⁺) cells from RXR-deficient BM revealed ~70% increase in the frequency of quiescent (CD62L-negative) lymphoid-primed multipotent progenitors (LMPPs) in BM and reduced TNFα and NF-κB transcriptional signatures in LMPP. In vivo extracellular fluid secretome analysis highlighted an ~80% reduction in Resistin, a known inflammatory adipokine, in RXR-deficient BM, Resistin supplementation in RXR-deficient mice normalized B-lymphopoiesis to WT levels. Together, these data support a model in which RXR signaling in BM adipocytes sustains local inflammatory tone via Resistin, thereby suppressing LMPP quiescence and lymphoid output. In its absence, reduced Resistin leads to enhanced B-lymphopoiesis and improved lymphoid reconstitution after HSCT. Our findings uncover a previously unrecognized role for BMA RXR signaling as a negative regulator of lymphopoietic regeneration, acting through Resistin-mediated inflammatory signaling. These results highlight the BMA RXR–Resistin axis as a modifiable niche pathway that selectively controls MPP-derived lymphopoiesis without compromising myeloid or T-cell reconstitution. Modulating this axis may offer novel therapeutic strategies to enhance immune recovery post-HSCT.