The Hajdu Cheney Mutation Is a Determinant of B-Cell Allocation of the Splenic Marginal Zone

Abstract

The neurogenic locus notch homolog protein (Notch)-2 receptor is a determinant of B-cell allocation, and gain-of-NOTCH2-function mutations are associated with Hajdu-Cheney syndrome (HCS), a disease presenting with osteoporosis and acro-osteolysis. We generated a mouse model reproducing the HCS mutation (Notch2HCS), and heterozygous global mutant mice displayed gain-of-Notch2 function. In the mutant spleen, the characteristic perifollicular rim marking the marginal zone (MZ), which is the interface between the nonlymphoid red pulp and the lymphoid white pulp, merged with components of the white pulp. As a consequence, the MZ of Notch2HCS mice occupied most of the splenic structure. To explore the mechanisms involved, lymphocyte populations from the bone marrow and spleen were harvested from heterozygous Notch2HCS mice and sex-matched control littermates and analyzed by flow cytometry. Notch2HCS mice had an increase in CD21/35CD23 splenic MZ B cells of approximately fivefold and a proportional decrease in splenic follicular B cells (CD21/35CD23) at 1, 2, and 12 months of age. Western blot analysis revealed that Notch2HCS mutant splenocytes had increased phospho-Akt and phospho-Jun N-terminal kinase, and gene expression analysis of splenic CD19 B cells demonstrated induction of Hes1 and Hes5 in Notch2HCS mutants. Anti-Notch2 antibodies decreased MZ B cells in control and Notch2HCS mice. In conclusion, Notch2HCS mutant mice have increased mature B cells in the MZ of the spleen.

Induction of the Hajdu-Cheney Syndrome Mutation in CD19 B Cells in Mice Alters B-Cell Allocation but Not Skeletal Homeostasis

“…In association with this increase in MZ B-cell subset, there was a modest decrease in the percentage of follicular (B220 þ IgM þ CD21/ 35 int CD23 þ ) B cells in Notch2 DPEST/WT compared with control mice. The results confirm the spleen phenotype of global Notch2 tm1.1ECan mutant mice 28 and validate the Notch2 [DPEST]COIN model for the study of B-cell phenotypic changes.…”

“…The Notch2 DPEST mutants generated by germline inversion of the COIN allele expressed the Notch2 DPEST transcript and phenocopied the spleen alterations present in global Notch2 tm1.1ECan mutants. 28 This confirms that the generalized expression of a Notch2 mutant lacking the PEST domain causes an MZ B-cell phenotype. The present study demonstrates that either the induction of a Notch2 gain-of-function mutation or activation of Notch1 signaling in CD19-expressing cells alters B-cell allocation in the MZ of the spleen, with an increase in MZ B cells and a reduction in follicular B cells.…”

“…To ensure that the effect of Notch2 on B-cell allocation in the spleen does not influence skeletal homeostasis, splenectomies or sham operations were performed in 1-montheold heterozygous Notch2 tm1.1ECan global mutant male and female mice, known to have altered B-cell allocation in the spleen and to be osteopenic. 26,28 Notch2 tm1.1ECan mice were obtained after the crossings of Notch2 tm1.1ECan heterozygous mice with wild-type mice, all in a C57BL/6J genetic background. Notch2 tm1.1ECan mutant mice were compared with sex-matched littermate controls at 2 months of age.…”

“…26 The Notch2 tm1.1ECan mutant mouse exhibits osteopenia as well as a B-cell phenotype, with reallocation of B cells to the MZ of the spleen. 28 Although B cells are presumed to affect skeletal homeostasis, it is not known whether the osteopenia of the Notch2 tm1.1ECan mutant is related to the observed alteration in B-cell lineage allocation. 29e31 Splenic as well as bone marrow B cells are considered a source of receptor activator of nuclear factor k B ligand (RANKL), and the production of RANKL by B cells contributes to the bone loss induced by estrogen deficiency and the bone erosion of rheumatoid arthritis.…”

Notch in skeletal physiology and disease

“…Notch2 is required for the development of the marginal zone of the spleen, and mouse models of HCS exhibit a reallocation of marginal zone B cells at the expense of follicular cells but do not appear to develop marginal zone lymphomas [50, 51]. The reallocation of marginal zone B cells does not influence skeletal remodeling.…”