Dysregulated megakaryocyte distribution associated with nestin⁺ mesenchymal stem cells in immune thrombocytopenia

Impaired megakaryocyte (MK) maturation and reduced platelet production are important causes of immune thrombocytopenia (ITP). However, MK distribution and bone marrow (BM) niche alteration in ITP are unclear. To investigate the maturation and distribution of MKs in the BM niche and examine the components of BM niche regulation of MK migration, BM and peripheral blood were obtained from 30 ITP patients and 28 healthy donors. Nestin⁺ mesenchymal stem cells (MSCs) and CD41⁺ MKs were sorted by fluorescence-activated cell sorting. The components of the BM niche and related signaling were analyzed via immunofluorescence, flow cytometry, enzyme-linked immunosorbent assay, reverse transcription polymerase chain reaction, and western blot analysis. The number of MKs in the BM vascular niche was reduced in ITP. Moreover, the concentrations of CXCL12 and CXCR4⁺ MKs in the BM were decreased in ITP. Further investigation demonstrated that nestin⁺ MSCs and CXCL12 messenger RNA (mRNA) in nestin⁺ MSCs were both reduced whereas the apoptosis of nestin⁺ MSCs was significantly increased in ITP. Sympathetic nerves, Schwann cells, the proportion of β3-adrenoreceptor (β3-AR)⁺ nestin⁺ MSCs, and β3-AR mRNA in nestin⁺ MSCs were all markedly reduced in ITP. Moreover, matrix metalloproteinase 9, vascular endothelial growth factor (VEGF), and VEGF receptor 1 were significantly reduced in ITP. Our data show that impaired MK distribution mediated by an abnormal CXCL12/CXCR4 axis is partially involved in reduced platelet production in ITP. Moreover, sympathetic neuropathy and nestin⁺ MSC apoptosis may have an effect on the alterations of BM CXCL12 in ITP.