Disruption of Bis Leads to Deterioration of Mesenchymal Stromal Cells Predominantly Affecting Vascular Compartment of Hematopoietic Stem Cell Niche.

Abstract 3627

Poster Board III-563

The stem cell niche plays an important role in the microenvironmental regulation of hematopoietic stem cells (HSCs), but the integration of niche activity remains poorly understood. In this study explored the hematopoietic defect of mice disrupted with Bis/BAG-3/CAIR-1, a protein related to apoptosis and response to cellular stress and show that functional loss of bis leads to series of hematopoietic derangements due to perturbation of vascular stem cell niche. First, mice with targeted disruption of bis (bis−/−) exhibited severe hypocellularity in the bone marrows and spleen starting from 16 days after birth. Affected mice exhibited loss of primitive neonatal HSCs (CD34+Lin-Sca-1+c-kit+) and defect in early stage B-lymphopoiesis including common lymphoid progenitors (IL-17R+LSK), pre-B and pro-B cell populations, but not for mature recycling B-lymphocytes (IgD+B220+). However, this hematological defect of bis^−/− mice was not reproduced when bis^−/− bone marrow cells were transplanted into wild-type (WT) recipients, pointing to the microenvironmental origin of the phenotypes. Subsequent analysis of bis^−/− mice bone marrow revealed a characteristic defect in the mesenchymal stromal component that included a quantitative loss of stromal cells (CD45-CD31-TER119-CD105+) in the bone marrows and rapid sensescence of stromal cells comprising colony forming unit-fibroblast (CFU-F) when re-plated in the ex-vivo culture. Moreover, mesenchymal stromal cells expressing CXCL-12 or IL-7 was lost in the affected bone marrows with lowered density of vascular development, together indicating a perturbation of peri-vascular stem cell niche in the bone marrow. In contrast, no abnormalities were observed in the growth and hematopoietic supporting activities of osteoblasts obtained from bis^−/− mice. Collectively, these results indicate that Bis functions to mediate cellular regulation of the stem cell niche activities selectively on the vascular compartment without affecting osteoblastic niche, and suggest that Bis may serve as a molecule that can bridge the microenvironment niche and cellular stress/apoptotic signals during the in-vivo orchestration of hematopoiesis.