Constitutive Bcl-2 expression throughout the hematopoietic compartment affects multiple lineages and enhances progenitor cell survival

Abstract

Bcl-2, which can both reduce apoptosis and retard cell cycle entry, is thought to have important roles in hematopoiesis. To evaluate the impact of its ubiquitous overexpression within this system, we targeted expression of the human bcl-2 gene in mice by using the promoter of the vav gene, which is active throughout this compartment but rarely outside it. The vav-bcl-2 transgene was expressed in essentially all nucleated cells of hematopoietic tissues but not notably in nonhematopoietic tissues. Presumably because of enhanced cell survival, the mice displayed increases in myeloid cells as well as a marked elevation in B and T lymphocytes. The spleen was enlarged and the lymphoid follicles expanded. Although total thymic cellularity was normal, T cell development was altered: cells at the very immature and most mature stages were increased, whereas those at the intermediate stage were decreased. Unexpectedly, blood platelets were reduced by half, suggesting that their production from megakaryocytes is regulated by the Bcl-2 family. Colony formation by myeloid progenitor cells in vitro remained cytokine dependent, and the frequency of most progenitor and preprogenitor cells was normal. Macrophage progenitors were less frequent and yielded smaller colonies, however, perhaps reflecting inhibitory effects of Bcl-2 on cell cycling in specific lineages. After irradiation or factor deprivation, Bcl-2 markedly enhanced clonogenic survival of all tested progenitor and preprogenitor cells. Thus, Bcl-2 has multiple effects on the hematopoietic system. These mice should help to further clarify the role of apoptosis in the development and homeostasis of this compartment.apoptosis ͉ transgenic mice ͉ homeostasis

Differential effects of Vav‐promoter‐driven overexpression of BCLX and BFL1 on lymphocyte survival and B cell lymphomagenesis

“…First, thymocytes were cultured for 4, 8, 12, 20, 30, 48 and 72 h, respectively, and analysed for Annexin V and 7AAD staining by flow cytometry. As shown previously 31, 37, Vav‐BCL2 and Vav‐Mcl1 TG thymocytes were strongly protected from spontaneous apoptosis (Fig. 3A).…”

“…2B,C), unlike Vav‐BCL2 TG and Vav‐Mcl1 TG mice, which showed changes expected from previous studies 31, 37. One Vav‐BFL1 TG line (L3) displayed a trend towards an increase in immature B cells and a reduction in recirculating B cells (Fig.…”

“…1D, TG lines were pooled to simplify data presentation), while Vav‐Mcl1 and Vav‐BCL2 TG mice showed splenomegaly (Fig. 1E), as reported before 31, 37.…”

“…Granulocyte numbers were also normal in Vav‐BCLX and Vav‐Mcl1 TG mice (Fig. 2D), whereas Vav‐BCL2 TG mice had a significantly lower percentage of granulocytes in the bone marrow and spleen, as noted before 37.…”

“…In contrast to Vav‐BCL2 37 and Vav‐Mcl1 31 TG mice, the overall composition and cellularity of all major lymphoid organs was essentially normal in both Vav‐BCLX and Vav‐ BFL1 mice (Figs 1 and 2). Interestingly, while the Vav‐BCLX TG partially protected both thymocytes and pre‐B cells from spontaneous and drug‐induced apoptosis, the Vav‐BFL1 TG provided only a minor survival benefit in pre‐B cells or when thymocytes were treated with ABT‐737 (Fig.…”