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Blood, 15 December 2006, Vol. 108, No. 13, pp. 4246-4254.
Prepublished online as a Blood First Edition Paper on August 17, 2006; DOI 10.1182/blood-2006-02-005611.
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Submitted February 24, 2006
Accepted July 27, 2006
Smad7 promotes self-renewal of hematopoietic stem cells in vivo
Ulrika Blank, Goran Karlsson, Jennifer L Moody, Taiju Utsugisawa, Mattias Magnusson, Sofie Singbrant, Jonas Larsson, and Stefan Karlsson*
Molecular Medicine & Gene Therapy, Institute of Laboratory Medicine, Lund University, Lund, Sweden
* Corresponding author; email: stefan.karlsson{at}med.lu.se.
The Smad signaling pathway downstream of the Transforming Growth Factor- superfamily of ligands is an evolutionary conserved signaling circuitry with critical functions in a wide variety of biological processes. To investigate the role of this pathway in the regulation of hematopoietic stem cells (HSCs), we have blocked Smad signaling by retroviral gene transfer of the inhibitory Smad7 to murine HSCs. We report here, that the self-renewal capacity of HSCs is promoted in vivo upon blocking of the entire Smad pathway, as shown by both primary and secondary BM transplantations. Importantly, HSCs overexpressing Smad7 have an unperturbed differentiation capacity as evidenced by normal contribution to both lymphoid and myeloid cell lineages, suggesting that the Smad pathway regulates self-renewal independently of differentiation. Moreover, phosphorylation of Smads was inhibited in response to ligand stimulation in BM cells, thus verifying impairment of the Smad signaling cascade in Smad7 overexpressing cells. Taken together, this data reveal an important and previously unappreciated role for the Smad signaling pathway in the regulation of self-renewal of HSCs in vivo.

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