Normal erythropoiesis but severe polyposis and bleeding anemia in Smad4-deficient mice

Abstract

The tumor suppressor Smad4 mediates signaling by the transforming growth factor beta (TGF-␤) superfamily of ligands. Previous studies showed that several TGF-␤ family members exert important functions in hematopoiesis. Here, we studied the role of Smad4 in adult murine hematopoiesis using the inducible MxCre/loxP system. Mice with homozygous Smad4 deletion (Smad4 ⌬/⌬ ) developed severe anemia 6 to 8 weeks after induction (mean hemoglobin level 70 g/L). The anemia was not transplantable, as wild-type mice reconstituted with Smad4 ⌬/⌬ bone marrow cells had normal peripheral blood counts. These mice did not develop an inflammatory disease typical for mice deficient in TGF-␤ receptors I and II, suggesting that the suppression of inflammation by TGF-␤ is Smad4 independent. The same results were obtained when Smad4 alleles were deleted selectively in hematopoietic cells using the VavCre transgenic mice. In contrast, lethally irradiated Smad4 ⌬/⌬ mice that received wild-type bone marrow cells developed anemia similar to Smad4 ⌬/⌬ mice that did not receive a transplant. Liver iron stores were decreased and blood was present in stool, indicating that the anemia was due to blood loss. Multiple polyps in stomach and colon represent a likely source of the bleeding. We conclude that Smad4 is not required for adult erythropoiesis and that anemia is solely the consequence of blood loss. IntroductionThe members of the transforming growth factor beta (TGF-␤) superfamily of ligands modulate cell proliferation, differentiation, apoptosis, adhesion, and cell migration. 1 These ligands, including TGF-␤, activins, and bone morphogenetic proteins (BMPs), bind cell-surface receptors, classified as type I and II receptors, that contain an intracellular serine/threonine protein kinase domain. Upon ligand activation, the type II and type I receptors form an active ligand-receptor complex that phosphorylates members of the Small mutants (Caenorhabditis elegans) and mothers against the decapentaplegic homolog (Smad) family of proteins. The Smad family members that directly interact with the receptors are called receptor Smads (R-Smad). The type I receptors for TGF-␤, activin, nodal, and myostatin phosphorylate R-Smad2 and 3, whereas the BMPs phosphorylate R-Smad1, 5, and 8. The R-Smads associate with Smad4, also called common partner Smad (co-Smad), and as a complex enter the nucleus to regulate transcription. Smad6 and Smad7 TGF-␤ inhibit signaling through multiple mechanisms and are called inhibitory Smads (I-Smad). 2 Hematopoiesis is a tightly balanced process consisting of cell self-renewal, differentiation, and apoptosis of hematopoietic cells. The effects of TGF-␤ signaling on hematopoiesis are cell and context specific. TGF-␤1 has an inhibitory function in early expansion of committed hematopoietic precursors, 3 and BMP4 is implicated in mesoderm induction and hematopoietic commitment during embryogenesis. 4 Mice deficient for TGF-␤1 die 3 to 4 weeks after birth due to an inflammatory syndrome, 5,6 whereas the knockouts of the TGF-␤...

Endothelial Smad4 restrains the transition to hematopoietic progenitors via suppression of ERK activation

“…The deletion of Smad4 via Vav-Cre did not affect fetal or adult viability, as previously reported. 30 No difference in the number of intravascular hematopoietic clusters could be detected between the Vav-Cre;Smad4 fl/fl and control embryos at E10.5 by whole-mount immunostaining or flow cytometry ( Figure 3B-C). The result was further confirmed at E11.5 when the efficiency of the VavCre-mediated excision was much higher, which was 61% in the CD31 1 c-Kit high intravascular cluster cells and nearly 70% in the hematopoietic progenitors ( Figure 3D-E and supplemental Figure 3A).…”

Pronounced thrombocytosis in transgenic mice expressing reduced levels of Mpl in platelets and terminally differentiated megakaryocytes

“…To address this possibility, we marked blood cells in wild-type and Yall;Mpl Ϫ/Ϫ mice with biotin and determined the fraction of labeled platelets over time by flow cytometry. 40 No significant difference in half-life was observed ( Figure 5C). …”

The DEAH-box helicase RHAU is an essential gene and critical for mouse hematopoiesis

“…Efficiency of RHAU knockout was ϳ 98% in BM and ϳ 47% in the spleen as determined by genotyping of individual clones formed in a colony-forming assay. 21 …”

“…IFN induction of MxCre recombinase activity was achieved by injecting mice with polyI:C after transplantation. 21 Complete blood analysis was performed periodically ( Figure 2B; supplemental Table 3 groups A, B, C1, and C2).…”