Smad5 is dispensable for adult murine hematopoiesis

Abstract

Smad5 is known to transduce intracellular signals from bone morphogenetic proteins (BMPs), which belong to the transforming growth factor-beta (TGF-beta) superfamily and are involved in the regulation of hematopoiesis. Recent findings suggest that BMP4 stimulates proliferation of human primitive hematopoietic progenitors in vitro, while early progenitors from mice deficient in Smad5 display increased self-renewal capacity in murine embryonic hematopoiesis. Here, we evaluate the role of Smad5 in the regulation of hematopoietic stem cell (HSC) fate decisions in adult mice by using an inducible MxCre-mediated conditional knockout model. Surprisingly, analysis of induced animals revealed unperturbed cell numbers and lineage distribution in peripheral blood (PB), bone marrow (BM), and the spleen. Furthermore, phenotypic characterization of the stem cell compartment revealed normal numbers of primitive lin(-)Sca-1(+)c-Kit(+) (LSK) cells in Smad5(-)(/)(-) BM. When transplanted in a competitive fashion into lethally irradiated primary and secondary recipients, Smad5-deficient BM cells competed normally with wild-type (wt) cells, were able to provide long-term reconstitution for the hosts, and displayed normal lineage distribution. Taken together, Smad5-deficient HSCs from adult mice show unaltered differentiation, proliferation, and repopulating capacity. Therefore, in contrast to its role in embryonic hematopoiesis, Smad5 is dispensable for hematopoiesis in the adult mouse.

VCAM-1 ablation in nonhematopoietic cells in MxCre+ VCAM-1f/f mice is variable and dictates their phenotype

“…These findings are in agreement with those previously described for the same mice after direct interferon administration, showing no VCAM-1 mRNA in BM cells [13]. The data with BM cells are also comparable to the ones in Tie2Cre + VCAM-1 f/f mice (T2-V) we have studied previously [8], and consistent with other examples of efficient gene ablation of hematopoietic cells using the MxCre system [14][15][16][17][18][19].…”

“…Furthermore, in this model, although VCAM-1 ablation in BM cells was documented [13], the extent of VCAM-1 deletion, if any, in non-hematopoietic cells in BM was not explored in this study as well as in other studies using the interferon-induced Cremediated recombination [14][15][16][17][18][19]. In the present paper we investigate the extent of MxCremediated VCAM-1 ablation in both hematopoietic and non-hematopoietic cells and ascertain whether and to what extent such an ablation influences hemopoietic phenotype and progenitor cell biodistribution.…”

Canonical BMP signaling is dispensable for hematopoietic stem cell function in both adult and fetal liver hematopoiesis, but essential to preserve colon architecture

“…24 Surprisingly, HSCs lacking Smad5 display normal self-renewal and differentiation capacity after bone marrow (BM) transplantation, clearly indicating that Smad5 is dispensable for hematopoiesis in the adult mouse. 25 Even though Smad1 and Smad5 possess inherent specificities, demonstrated by different expression and distribution patterns [26][27][28] as well as dissimilar knockout phenotypes, 17,18,27,29,30 it is conceivable that the absence of effects in our earlier study is the result of redundancy with the related Smad1. Redundant mechanisms between Smad1 and Smad5 have recently been demonstrated as Smad1 ϩ/Ϫ ; Smad5 ϩ/Ϫ murine mutants, in contrast to Smad1 or Smad5 single heterozygotes, are embryonic lethal and display defects that closely resemble those seen in Smad1 or Smad5 homozygous mutants.…”

The role of Smad signaling in hematopoiesis and translational hematology

“…45 Although acute anemia has never been studied in the context of complete deletion of Smad5 in the mouse, these studies stand in sharp contrast to studies performed by Singbrant et al In a series of experiments, it was shown that Cre-mediated deletion of Smad1 and/or Smad5 did not impair adult hematopoiesis in the mouse and mutant HSCs displayed normal self-renewal and differentiation capacities upon transplantation. 67,68 Similarly, using a fetal liver-specific Cre-driver to induce deletion of Smad5 or Smad1/Smad5 together, hematopoiesis was shown to occur normally upon transplantation into wild-type hosts. 67 These differences are intriguing, but may suggest that Smad-mediated BMP signaling is only required under very specific stressed conditions.…”