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Myeloid-biased HSC require Semaphorin 4A from the bone marrow niche for self-renewal under stress and life-long persistence

ABSTRACT: Tissue stem cells are hierarchically organized. Those that are most primitive serve as key drivers of regenerative response but the signals that selectively preserve their functional integrity are largely unknown. Here, we identify a secreted factor, Semaphorin 4A (Sema4A), as a specific regulator of myeloid-biased hematopoietic stem cells (myHSC), which are positioned at the top of the HSC hierarchy. Lack of Sema4A leads to exaggerated myHSC (but not downstream “balanced” HSC) proliferation after acute inflammatory stress, indicating that Sema4A enforces myHSC quiescence. Strikingly, aged Sema4A knock-out myHSC expand but almost completely lose reconstitution capacity. The effect of Sema4A is non cell-autonomous, since upon transplantation into Sema4A-deficient environment, wild-type myHSC excessively proliferate but fail to engraft long-term. Sema4A constrains inflammatory signaling in myHSC and acts via a surface receptor Plexin-D1. Our data support a model whereby the most primitive tissue stem cells critically rely on a dedicated signal from the niche for self-renewal and life-long persistence.

ORGANISM(S): Mus musculus

PROVIDER: GSE281145 | GEO | 2024/12/11

REPOSITORIES: GEO

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Project description:Background: Multiple sclerosis (MS) is a demyelinating autoimmune disease of the central nervous system and the leading cause of lasting neurological disabilities in young adults. Increasing evidence suggests that early treatment prevents the development of disability. However, there have been no reliable serum markers to assist the early diagnosis. In addition, interferon (IFN)-β, which is the major treatment for MS, is not always effective. Therefore, the development of simple serological test to help the early diagnosis and predict responsiveness to IFN-β is of clinical importance. On the other hand, a transmembrane-type semaphorin, Sema4A, has been implicated in experimental autoimmune encephalomyelitis (EAE) by regulating helper T (Th) cell differentiation. Thus, we aimed to identify the implications of Sema4A in diagnosis and pathogenesis of MS. Methods: We assayed serum Sema4A in 59 patients with relapsing-remitting MS (RRMS), 22 patients with clinically isolated syndrome (CIS) and 126 patients with other neurological diseases (OND) by developing a sandwich ELISA. To identify a source of soluble Sema4A and characteristics of MS patients with high levels of Sema4A, we analyzed peripheral blood mononuclear cells (PBMCs) from MS patients and healthy controls by flow cytometry (FACS) and gene chip analysis. The effect of Sema4A was examined in vitro and in vivo using an EAE model. Findings: Sema4A was significantly increased in sera of patients with MS and CIS compared to controls. Sema4A expression was increased on the surface of DCs in MS patients and shed from these cells in a metalloproteinase-dependent manner, affecting the Th17skewing. In addition, patients with high Sema4A levels exhibited more severe disabilities, and IFN-β treatment was not beneficial to those patients. Interpretation: Measuring Sema4A is a practical laboratory test to help diagnose MS and to predict responsiveness to IFN-β therapy. Microarray analysis showed that metalloproteinases such as ADAM 10 and MMPs 1, 3, 9, 12 and 25, which are reported to be involved in the pathogenesis of MS, were increased in PBMCs from MS patients with high Sema4A levels compared to those with low Sema4A and healthy controls. However, ADAM 17 and MMP 2 and 7 did not correlate with Sema4A levels. Taken together, these findings strongly suggest that Sema4A, abundantly expressed on monocytes and DCs in MS patients, is enzymatically cleaved and shed in a portion of the patients, which contributes to the high soluble Sema4A detected by the ELISA. Multiple sclerosis patients were classified according to Serum Sema4A levels. RNA from peripheral blood from 4 healthy controls, 3 MS patients with high serum Sema4A levels and 3 MS patients with low serum Sema4A levels was extracted and hybridized on Affymetrix microarrays. We sought to see whether there is corrlated genes with serum Sema4A levels or not, especially for genes for varions proteases.

Project description:Semaphorin 4A (Sema4A) exerts a stabilizing effect on human Treg cells in PBMC and CD4+ T cell cultures by engaging Plexin B1. Sema4A deficient mice display enhanced allergic airway inflammation accompanied by fewer Treg cells, while Sema4D deficient mice displayed reduced inflammation and increased Treg cell numbers even though both Sema4 subfamily members engage Plexin B1. The main objectives of this study were: 1. To compare the in vitro effects of Sema4A and Sema4D proteins on human Treg cells; and 2. To identify function-determining residues in Sema4A critical for binding to Plexin B1 based on Sema4D homology modeling. We report here that Sema4A and Sema4D display opposite effects on human Treg cells in in vitro PBMC cultures; Sema4D inhibited the CD4+CD25+Foxp3+ cell numbers and CD25/Foxp3 expression. Sema4A and Sema4D competitively bind to Plexin B1 in vitro and hence may be doing so in vivo as well. Bayesian Partitioning with Pattern Selection (BPPS) partitioned 4505 Sema domains from diverse organisms into subgroups based on distinguishing sequence patterns that are likely responsible for functional differences. BPPS groups Sema3 and Sema4 into one family and further separates Sema4A and Sema4D into distinct subfamilies. Residues distinctive of the Sema3,4 family and of Sema4A (and by homology of Sema4D) tend to cluster around the Plexin B1 binding site. This suggests that the residues both common to and distinctive of Sema4A and Sema4D may mediate binding to Plexin B1, with subfamily residues mediating functional specificity. We mutated the Sema4A-specific residues M198 and F223 to alanine; notably, F223 in Sema4A corresponds to alanine in Sema4D. Mutant proteins were assayed for Plexin B1-binding and Treg stimulation activities. The F223A mutant was unable to stimulate Treg stability in in vitro PBMC cultures despite binding Plexin B1 with an affinity similar to the WT protein. This research is a first step in generating potent mutant Sema4A molecules with stimulatory function for Treg cells with a view to designing immunotherapeutics for asthma.

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Myeloid-biased HSC require Semaphorin 4A from the bone marrow niche for self-renewal under stress and life-long persistence

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