Background and objectives Hematopoietic Stem Cells (HSCs) give rise to all blood cell lineages, which have been implicated in the pathogenesis of Systemic Lupus Erythematosus (SLE). We reasoned that the fundamental immune aberrations in SLE –genetic or epigenetic- may be more facile to be traced back to the HSC population.
Materials and methods HSCs were isolated from either healthy C57/BL6 or NZBxNZW/F1 lupus prone mice bone marrow (n = 15 ± 5). The selection markers used are Lin-Sca-1+c-Kit+ for LSK compartment, including both long and short term HSCs. Flow cytometry cell sorting of the aforementioned populations was utilised for enumeration, RNA extraction and cell cultures. Finally, paired-end RNA-sequencing analysis was performed with HiSeq 2000 platform.
Results We identified significantly increased frequencies (˜3% pre-diseased vs ˜5% diseased, p < 0.05) as well as absolute numbers (80–100×103 pre-diseased vs 100–150 ×103 diseased, p < 0.05) of HSCs in the BM of lupus NZBxNZW/F1 mice with established disease as compared to young pre-diseased NZBxNZW/F1 or control C57/BL6 mice. Bone marrow populations such as hematopoietic stem progenitors cells (HSPCs), lymphoid and myeloid lineages differed in homogeneity depending upon either age or disease, suggesting alterations in HSC potential under inflammatory conditions. Accordingly, serum from F1 young mice promoted healthy HSCs to proliferation and skewed their differentiation towards to myeloid lineage. Transcriptome analysis by RNA-seq of HSCs from lupus mice revealed 294 differentially expressed genes (DEGs) (FC > 1.5, q < 0.05) in diseased lupus mice compared to pre-diseased. DEGs show enrichment in transcription factors involved in hematopoiesis (Arid3a, Runx2), regulation of immune responses during inflammation and autoimmune diseases (Irf4, Maf) and HSC function and homeostasis (Cxcl2, Vegfa, Fbxw7).
Conclusions These data provide initial insights in the fundamental changes and the molecular identity of HSCs in lupus within the inflammatory milieu of the disease, regulated by a complex transcriptional network.