Bone Marrow Adipocyte Secreted Resistin Is a Positive Regulator of Long-Term Hematopoietic Stem Cell Engraftment and Myelopoiesis
Authors: Prasad Parash , D'Alessandro Angelo , Oh Grace , Wellendorf Ashley , Ricote Mercedes , Salomonis Nathan , Cancelas Jose 
Published: December 2024

Myeloablative hematopoietic stem cell transplant (HSCT) can cure cancer, bone marrow failure, hemoglobinopathies or immunodeficiencies. The aim of HSC transplant is to restore the endogenous hematopoiesis by long-term, multi-lineage hematopoiesis derived from a healthy donor or genetically corrected patient's HSC. In the bone marrow (BM), HSCs are responsive to the BM microenvironment (ME) to engraft and regenerate hematopoiesis. HSC and ME-dependent retinoic acid signaling is crucial to regenerate hematopoiesis. Bone marrow adipocytes (BMA) are a crucial cellular component of the BM ME that can occupy up to 70% of the BM volume. BMA and their precursor leptin-receptor expressing stromal cells express adiponectin. Differentiation and activity of adiponectin-expressing cells are largely dependent on RXR signaling. To understand how RXRs regulate the activity of BM ME adiponectin-expressing (BMA) cells and its effect on hematopoiesis, we generated tamoxifen (TAM)-inducible, BMA-specific RXR α/β deficient (AdipoQCre-ERTi2-RXRα/βΔ/Δ or AdipoQ-RXRα/βΔ/Δ) mice. We found ~70% reduction in BMA cells in AdipoQ-RXRα/βΔ/Δ BM. Competitive hematopoietic repopulation after transplantation of AdipoQ-RXRα/βΔ/Δ BM generated comparable levels of hematopoietic chimerism. However, the HSC, multipotential progenitor and myelopoietic recovery after 5-FU treatment or after HSC transplantation of myeloablated animals were significantly impaired. Competitive transplantation of purified HSC (Lin-Sca1-cKit-CD48-CD150+) confirmed the results of non-purified BM transplantation indicating that BM HSC from AdipoQ-RXRα/βΔ/Δ are significantly less efficient in hematopoietic regeneration. To understand the effects of RXR deficient BMA ME on HSC/Ps, we compared the single-cell RNAseq transcriptome of Lin-Sca1+c-Kit+ (LSK) BM cells from WT and AdipoQ-RXRα/βΔ/Δ mice. Pathway enrichment analysis suggested a significant reduction in mitochondrial oxidative phosphorylation and expression of electron transfer chain (ETC) complex genes and reduced expression of TNFa/NF-kB signaling pathway genes. Metabolomic analysis and adipokine profiling from the extracellular BM fluid indicated a significant decrease in the levels of triglycerides and a ~80% reduction in the levels of Resistin, a secreted pro-inflammatory cytokine, in BMA-RXR deficient BM. In vivo Resistin neutralization hampered the normal blood cell production, bone marrow cellularity and myeloid cell production. To test efficacy of Resistin towards HCS maintenance during ex-vivo HSC culture, we treated isolated WT LSK with Resistin. Short-term Resistin treatment induced transient NF-kB activation in HSC, increased the levels of myeloid progenitors and the capacity of treated HSC to support long-term hematopoiesis as assessed in serial, competitive repopulation assays. Together, our data indicate that BMA-RXR dependent Resistin is a positive regulator of long-term hematopoiesis under stress conditions and can be used during ex vivo manipulation of HSCs destined to transplantation and myeloid cell reconstitution.