Efficient Differentiation of Common Marmoset Embryonic Stem Cells Into Hemangioblast-Like Cells by the Inhibition of PI3K-AKT Pathway

Abstract 2206

Recently various kinds of functional cells differentiated from embryonic stem cells and induced pluripotent stem cells (ESCs/iPSCs) are expected to be utilized for cell therapy in clinical medicine. Among the transplantable functional cells differentiated from ESCs/iPSCs, endothelial progenitor cells (EPCs) and hematopoietic stem cells (HSCs) are considered to be strong candidate cells for regenerative medicine to cure various diseases such as ischemic disease and hematopoietic malignancy. Although the transplantation of EPCs and HSCs derived from human bone marrow, mobilized peripheral blood, and umbilical cord blood is commonly conducted in clinical settings, their availability for clinical use has often been hampered by both the lack of HLA compatible donor and the insufficient number of the cells. As the in vitro expansion of EPCs and HSCs derived from above sources is very difficult using current technology, it may be easier to expand EPCs and HSCs derived from ESCs/iPSCs in vitro.

Hemangioblasts have the ability to differentiate into both EPCs and HSCs. Thus the technology to differentiate hemangioblast from ESCs/iPSCs that possess indefinite proliferative capacity is strongly expected. Differentiation of ESCs/iPSCs to hemangioblasts is best exemplified in recent studies that have used two step procedures to enhance hemangioblast differentiation with embryoid body (EB) formation and blast colony forming cell (BL-CFC) assay (Lu SJ et al., Nat Methods 4: 501–509, 2007). However the efficiency of hemangioblast differentiation by this method was quite low (approximately 0.35 ± 0.01%).

PI3K-AKT pathway is well known to regulate various cell functions. In ESCs, PI3K-AKT pathway plays an important role in maintaining the undifferentiated state (Armstrong L et al., Hum Mol Genet 15: 1894–1913, 2006), suggesting that inhibition of PI3K may promote the differentiation of ESCs/iPSCs.

Previously, we demonstrated that common marmosets (CM) are suitable laboratory animal models for preclinical studies of hematopoietic stem cell therapies (Hibino H et al., blood 1: 2839–2848, 1999). To develop the method for the more efficient generation of hemangioblasts from ESCs/iPSCs, we promoted the hemangioblast differentiation by the inhibition of PI3K-AKT pathway with the inhibitor, LY294002. CM-ESCs (Cj11 and CM40) were differentiated by EB formation in the presence of LY294002 for 4 days, and the EBs were trypsinized, and the dissociated individual cells were processed for BL-CFC assay in the methylcellulose medium containing various cytokines without LY294002 for 7 days.

The number of blast colonies found in the BL-CFC assay significantly increased (approximately 10-fold; 3.5 ± 0.3%, p < 0.001) with the treatment of LY294002 during EB formation compared with control. The colonies formed in the BL-CFC assay were homogeneous and looked like a tuft of grapes which is one of hemangioblast characters, and expressed hemagioblast markers (FLK1⁺, VE-cadherin⁺, CD31⁺ and CD45⁻), suggesting that the inhibition of PI3K during EB formation promoted the generation of hemangioblast-like cells from CM-ESCs. To determine endothelial potential of these hemangioblast-like cells derived from CM-ESCs, we grew them as adherent layers on gelatin-coated plates in EGM-2 medium. The adherent cells derived from hemangioblast-like cells expressed endothelial cell markers (CD31 and vWF). Next, we also examined hematopoietic potential of hemangioblast-like cells by colony forming unit (CFU) assay. Unexpectedly no colonies were formed regardless of whether LY294002 was added or not during EB formation, indicating that hemangioblast-like cells derived from CM-ESC might be endothelial progenitors rather than hemangioblasts.

Our novel technology is 10-fold more efficient in inducing endothelial differentiation from ESCs than previously reported methods. It should be emphasized that these endothelial progenitors are morphologically homogenous and expressed endothelial cell markers in a defined adherent cell culture condition, suggesting that our novel technology will be useful for an efficient generation of homogeneous EPCs for future regenerative medicine against ischemic diseases.