RESUMEN
Cytokine-induced expansion of hematopoietic stem and progenitor cells (HSPCs) is not fully understood. In the present study, we show that whereas steady-state hematopoiesis is normal in basic fibroblast growth factor (FGF-2)-knockout mice, parathyroid hormone stimulation and myeloablative treatments failed to induce normal HSPC proliferation and recovery. In vivo FGF-2 treatment expanded stromal cells, including perivascular Nestin(+) supportive stromal cells, which may facilitate HSPC expansion by increasing SCF and reducing CXCL12 via mir-31 up-regulation. FGF-2 predominantly expanded a heterogeneous population of undifferentiated HSPCs, preserving and increasing durable short- and long-term repopulation potential. Mechanistically, these effects were mediated by c-Kit receptor activation, STAT5 phosphorylation, and reduction of reactive oxygen species levels. Mice harboring defective c-Kit signaling exhibited abrogated HSPC expansion in response to FGF-2 treatment, which was accompanied by elevated reactive oxygen species levels. The results of the present study reveal a novel mechanism underlying FGF-2-mediated in vivo expansion of both HSPCs and their supportive stromal cells, which may be used to improve stem cell engraftment after clinical transplantation.
Asunto(s)
Proliferación Celular , Quimiocina CXCL12/metabolismo , Factor 2 de Crecimiento de Fibroblastos/metabolismo , Células Madre Hematopoyéticas/metabolismo , Proteínas Proto-Oncogénicas c-kit/metabolismo , Células del Estroma/metabolismo , Animales , Secuencia de Bases , Trasplante de Médula Ósea , Ciclo Celular/efectos de los fármacos , Células Cultivadas , Quimiocina CXCL12/genética , Regulación hacia Abajo/efectos de los fármacos , Factor 2 de Crecimiento de Fibroblastos/genética , Factor 2 de Crecimiento de Fibroblastos/farmacología , Citometría de Flujo , Expresión Génica/efectos de los fármacos , Células Madre Hematopoyéticas/efectos de los fármacos , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones Transgénicos , Modelos Biológicos , Hormona Paratiroidea/farmacología , Fosforilación/efectos de los fármacos , Proteínas Proto-Oncogénicas c-kit/genética , Especies Reactivas de Oxígeno/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Factor de Transcripción STAT5/metabolismo , Células del Estroma/efectos de los fármacosRESUMEN
Fibroblast growth factor 2 (FGF2) positively modulates osteoblast differentiation and bone formation. However, the mechanism(s) is not fully understood. Because the Wnt canonical pathway is important for bone homeostasis, this study focuses on modulation of Wnt/ß-catenin signaling using Fgf2(-/-) mice (FGF2 all isoforms ablated), both in the absence of endogenous FGF2 and in the presence of exogenous FGF2. This study demonstrates a role of endogenous FGF2 in bone formation through Wnt signaling. Specifically, mRNA expression for the canonical Wnt genes Wnt10b, Lrp6, and ß-catenin was decreased significantly in Fgf2(-/-) bone marrow stromal cells during osteoblast differentiation. In addition, a marked reduction of Wnt10b and ß-catenin protein expression was observed in Fgf2(-/-) mice. Furthermore, Fgf2(-/-) osteoblasts displayed marked reduction of inactive phosphorylated glycogen synthase kinase-3ß, a negative regulator of Wnt/ß-catenin pathway as well as a significant decrease of Dkk2 mRNA, which plays a role in terminal osteoblast differentiation. Addition of exogenous FGF2 promoted ß-catenin nuclear accumulation and further partially rescued decreased mineralization in Fgf2(-/-) bone marrow stromal cell cultures. Collectively, our findings suggest that FGF2 stimulation of osteoblast differentiation and bone formation is mediated in part by modulating the Wnt pathway.