Pivotal role for glycogen synthase kinase–3 in hematopoietic stem cell homeostasis in mice

Abstract

Hematopoietic stem cell (HSC) homeostasis depends on the balance between self renewal and lineage commitment, but what regulates this decision is not well understood. Using loss-of-function approaches in mice, we found that glycogen synthase kinase-3 (Gsk3) plays a pivotal role in controlling the decision between self renewal and differentiation of HSCs. Disruption of Gsk3 in BM transiently expanded phenotypic HSCs in a β-catenin-dependent manner, consistent with a role for Wnt signaling in HSC homeostasis. However, in assays of long-term HSC function, disruption of Gsk3 progressively depleted HSCs through activation of mammalian target of rapamycin (mTOR). This long-term HSC depletion was prevented by mTOR inhibition and exacerbated by β-catenin knockout. Thus, GSK-3 regulated both Wnt and mTOR signaling in mouse HSCs, with these pathways promoting HSC self renewal and lineage commitment, respectively, such that inhibition of Gsk3 in the presence of rapamycin expanded the HSC pool in vivo. These findings identify unexpected functions for GSK-3 in mouse HSC homeostasis, suggest a therapeutic approach to expand HSCs in vivo using currently available medications that target GSK-3 and mTOR, and provide a compelling explanation for the clinically prevalent hematopoietic effects observed in individuals prescribed the GSK-3 inhibitor lithium.

Genistein Protects Hematopoietic Stem Cells against G-CSF–Induced DNA Damage

“…It has been shown that the absence of GSK3b impairs long-term self-renewal capacity of HSCs, although it is not essential for myeloid development (23). While HSCs from the triple cyclin knockout mouse (cyclins D1, D2, and D3) display delayed cell-cycle entry and multilineage hematopoietic failure (46,47), single knockouts for D1 or D2 display normal granulocyte counts.…”

“…GSK-3 regulates HSC self-renewal and lineage commitment (23,24) and controls genes that are important for proliferation such as cyclin D1 (25) and D3 (26). Myeloid progenitor bone marrow cells from mice treated with G-CSF for 5 days and with genistein on the last 2 days of G-CSF treatment were sorted, lysed, and the proteins were analyzed by Western blot.…”

Adult Stem Cells in Tissue Homeostasis and Disease

“…However, there are conflicting reports on the requirement for Wnt/ -catenin signaling in basal hematopoiesis: conditional disruption of -catenin in adult HSCs does not affect their ability to self-renew and reconstitute hematopoietic lineages (Huang et al, 2009). In addition, although overexpression of stabilized -catenin increases immunophenotypic HSCs, this is associated with a loss of repopulating activity and hematopoietic failure in vivo (Kirstetter et al, 2006), findings that appear incompatible with a positive role for -catenin in hematopoiesis.…”

GSK3β regulates physiological migration of stem/progenitor cells via cytoskeletal rearrangement

“…In a steady state, low levels of HSPCs are constantly circulating as part of homeostasis, whereas in stress situations, HSPCs are recruited in high numbers from the bone marrow (BM) into the circulation as part of host defense and repair mechanisms (2). Glycogen synthase kinase-3β (GSK3β) is a well-established negative regulator of the Wnt/β-catenin pathway, implicated in self-renewal and development of human and murine HSCs (3)(4)(5)(6)(7)(8)(9)(10)(11). In addition to proliferation, GSK3β has been shown to be involved in the motility of various cells, including microglia, epidermal stem cells, human mast cells, and breast cancer cells (12)(13)(14)(15)(16), but its effect on the motility of immature hematopoietic cells has not been addressed.…”