Contributions
Abstract: S247
Type: Oral Presentation
Session title: Stem cell biology and microenvironment
Background
We have previously found that a Sfrp1 knock-out environment fails to support the regeneration of hematopoetic stem cells (HSC) with the ability to repopulate secondary recipients (Renström et al., 2009).
Aims
We here aim to dissect cell specific requirements of the Sfrp1 gene in the hematopoietic microenvironment.
Methods
To study the relevance of Sfrp1 in niche cells for the maintenance of HSCs, we established the Sfrp1flox/flox mouse strain and deleted Sfrp1 gene specifically in Osterix+ (Sp7) osteolineage cells (Osx-Cre, Sfrp1Δ/Δ, shortened to OS1Δ/Δ mice).
Results
In these OS1Δ/Δ mice, the number of MSCs is reduced, but these show an increased proportion of colony forming units (CFU-F). Furthermore, stromal cells grown ex-vivo show increased senescence-associated β-galactosidase staining. In the hematopoietic compartment of these mice, we found a decrease in myeloid progenitors in the bone marrow (BM), but, the number of HSC-enriched CD34- CD48- CD150+ HSCs (CD34- SLAM cells) in the BM was unchanged, CD34- SLAM cells from OS1Δ/Δ mice show severely reduced frequency of repopulating HSCs. In single cell cultures, we found that CD34- SLAM cells from OS1Δ/Δ mice show poor proliferation with concomitant increased differentiation into mature myeloid cells. As in embryonic stem cells, differentiation is driven by a β-catenin/p300 complex (Miyabayashi et al., 2007), we hypothesized that this complex also drives HSC differentiation. Indeed, both β-catenin and p300 were expressed at higher levels in CD34- SLAM cells from OS1Δ/Δ mice. To disrupt the β-catenin/p300 complex, we inhibited complex formation by targeting p300 phosphorylation using a specific PP2A inhibitor IQ-1. In in vitro experiments, IQ-1 treatment rescued the aberrant behavior of OS1Δ/Δ CD34- SLAM cells. More importantly in vivo IQ-1 treatment also restored the serial repopulating activity of CD34- SLAM cells OS1Δ/Δ mice in vivo.
Renstroem, et al., Cell Stem Cell. 2009; 5: 157-67
Miyabayashi et al., Proc Natl Acad Sci U S A. 2007; 104: 5668-73.
Conclusion
Our results indicate that deletion of stromal Sfrp1 in niche cells diminishes the repopulating activity of HSCs by increasing their differentiation through PP2A-mediated dephosphorylation of the phospho-Ep300-binding site with β-catenin.
Keyword(s):
Abstract: S247
Type: Oral Presentation
Session title: Stem cell biology and microenvironment
Background
We have previously found that a Sfrp1 knock-out environment fails to support the regeneration of hematopoetic stem cells (HSC) with the ability to repopulate secondary recipients (Renström et al., 2009).
Aims
We here aim to dissect cell specific requirements of the Sfrp1 gene in the hematopoietic microenvironment.
Methods
To study the relevance of Sfrp1 in niche cells for the maintenance of HSCs, we established the Sfrp1flox/flox mouse strain and deleted Sfrp1 gene specifically in Osterix+ (Sp7) osteolineage cells (Osx-Cre, Sfrp1Δ/Δ, shortened to OS1Δ/Δ mice).
Results
In these OS1Δ/Δ mice, the number of MSCs is reduced, but these show an increased proportion of colony forming units (CFU-F). Furthermore, stromal cells grown ex-vivo show increased senescence-associated β-galactosidase staining. In the hematopoietic compartment of these mice, we found a decrease in myeloid progenitors in the bone marrow (BM), but, the number of HSC-enriched CD34- CD48- CD150+ HSCs (CD34- SLAM cells) in the BM was unchanged, CD34- SLAM cells from OS1Δ/Δ mice show severely reduced frequency of repopulating HSCs. In single cell cultures, we found that CD34- SLAM cells from OS1Δ/Δ mice show poor proliferation with concomitant increased differentiation into mature myeloid cells. As in embryonic stem cells, differentiation is driven by a β-catenin/p300 complex (Miyabayashi et al., 2007), we hypothesized that this complex also drives HSC differentiation. Indeed, both β-catenin and p300 were expressed at higher levels in CD34- SLAM cells from OS1Δ/Δ mice. To disrupt the β-catenin/p300 complex, we inhibited complex formation by targeting p300 phosphorylation using a specific PP2A inhibitor IQ-1. In in vitro experiments, IQ-1 treatment rescued the aberrant behavior of OS1Δ/Δ CD34- SLAM cells. More importantly in vivo IQ-1 treatment also restored the serial repopulating activity of CD34- SLAM cells OS1Δ/Δ mice in vivo.
Renstroem, et al., Cell Stem Cell. 2009; 5: 157-67
Miyabayashi et al., Proc Natl Acad Sci U S A. 2007; 104: 5668-73.
Conclusion
Our results indicate that deletion of stromal Sfrp1 in niche cells diminishes the repopulating activity of HSCs by increasing their differentiation through PP2A-mediated dephosphorylation of the phospho-Ep300-binding site with β-catenin.
Keyword(s):