J Neurol Surg A Cent Eur Neurosurg 2012; 73 - P026
DOI: 10.1055/s-0032-1316228

Factors Secreted by Endothelial Progenitor Cells Promote Brain Endothelial Cell Tubulogenesis through PI3-Kinase

S. Seiler 1, C. Fontana 1, L. Andereggen 1, R. Andres 1, M. Reinert 1, A. Raabe 1, H. R. Widmer 1, S. DiSanto 1
  • 1Department of Neurosurgery, Bern University Hospital, Bern, Switzerland

Introduction: There is growing evidence that the regenerative potential of stem cells relies primarily on their secretion of soluble factors. In the present study we investigated whether paracrine factors derived from cultured endothelial progenitor cells (EPC) may support brain endothelial cell angiogenesis. Moreover we addressed the signalling pathways that may be involved.

Methods: Cultures from rat brain endothelial cells were incubated with EPC-derived conditioned medium (EPC-CM). Angiogenic response of the microvascular endothelial cells was assessed by measuring tubulogenesis and cell number after incubation with EPC-CM. Cell number in culture was measured by the MTT assay after 24 hours of incubation. The morphogenic response of endothelial cells to EPC-CM was investigated by means of tube formation assay on growth factor reduced Matrigel™ for 8 hours. The specific PI3K/AKT inhibitor LY294002 and the MAPK/ERK inhibitor PD98059 were used to analyze the involvement of these two signalling pathways in the transduction of the effects of EPC-CM.

Results: By means of an antibody array we found that EPC-CM contains a variety of growth factors and cytokines. Incubation of brain microvascular endothelial cells with EPC-CM resulted in a two- and ninefold increase of tubule and network complexity. The cell number was likewise augmented after incubation with EPC-CM. Inhibition of the PI3K/AKT signaling pathway resulted in a significant reduction of the length, the complexity of the tubule network formation as well as the cell number. Conversely the inhibition of the MAPK/ERK pathway did not affect the angiogenic response of the brain microvascular cells to EPC-CM.

Conclusion: The present study shows that EPC-derived paracrine factors substantially promote the angiogenic response of brain microvascular endothelial cells. The big variety of factors contained in the EPC-CM likely activates multiple signaling cascades; however, our findings identified the PI3K/AKT pathway to play a central role.