The Effect Of SDF-1α On Inducing Vascular Endothelial Cells Expressing Lymphatic Phenotype

Background The lymphatic system complements functions of the blood vascular system by regulating tissue fluid balance, facilitating interstitial protein transport, and serving immunological functions.It was proposed that during the first stage of the organism development, the lymphatic vessel system is represented by a more or less regular series of small and blind-ending outgrowths of the major embryonic veins. While in adult, the lymphangiogenesis was predominantly related to a critical protein which was named as vascular endothelial growth factor receptor3, a tyrosine kinase receptor expressed primarily in lymphatic endothelial cells (LECs), enhancing lymphangiogenesis through binding vascular endothelial growth factor-C (VEGF-C) or the related factor, VEGF-D. Meanwhile, as is indicated in several articles, some proinflammatory factors contributed to the differentiation from vascular endothelial cells to the lymphatic endothelial cells via a well-known signal pathway, nuclear factor-kappa B, NF-κB, which was a critical factor in inflammatory reaction.Although both vascular and lymphatic endothelium maintained expression of VEGFR2, VE-cadherin, and vWF, these biomarkers were more expressed in vascular endothelial cells than in lymphatic endothelial cells. However, the hyaluronate receptor LYVE-1and podoplanin was selectively expressed by LECs, but not by BECs. And also the lymphatic endothelial cells can be distinguished from vascular endothelial cells by their expression of Prox-1, a key transcription factor in converting the transcriptional program of cultured microvascular endothelium towards the lymphatic endothelial phenotype, which control the expression of the other lymphatic biomarker directly.Several published research articles have shown that there are two types of the formation of new lymphatic vessels. For one thing, bone marrow-derived circulating progenitor endothelial cells migrate to the local tissue and then differentiate into lymphatic endothelial cells. For another, the newly formed lymphatic vessels sprout from the existed lymphatic vessels. But the mechanism of the bone marrow-derived circulating progenitor endothelial cells differentiate into lymphatic endothelial phenotype has not been figured out. Interestingly, recent studies demonstrated the progenesis effect of inflammatory environment on the lymphatic vessels.Chemokines are a superfamily of small, cytokine-like proteins that induce, through their interaction with G-protein-coupled receptors, cytoskeletal rearrangement, firm adhesion to endothelial cells and directional migration. And stromal cell-derived factor-1α(SDF-1α), for example, which is a member of the CXC chemokine family, was secreted by bone marrow stromal cell, and other related mesothelium or epithelium, and has been found to recruit CD34+hematopoietic progenitor cells, megakaryocytes, B cells, and T cells, by binding to CXC chemokine receptor4(CXCR4). Thus SDF-la plays an essential role in inflammatory reaction. And stromal fibroblasts present in cancer microenvironment promote tumor growth through elevated SDF-la/CXCL12a secretion. Also it is said that SDF-la plays an important role in cancer cells’ metastasis. However few reports about it effect on the generation of lymphatic vessels in tumor or inflammatory environment were found.Objective We planned to investigate the effects of stromal cell-derived factor-la on inducing vascular endothelial cells expressing lymphatic phenotype in vitro at the protein level and gene expression levels after stimulating the umbilical vein endothelial cell with different concentrations of SDF-la. And illustrate the mechanism of the lymphangiogenesis and provide the basis for the treatment of the related disease, lymphedema and tumor metastasis, for example. Materials and methods The CRL-1730cell line (blood endothelial cell line) was cultured in DMEM containing10%FBS and different amount of SDF-la was introduced into the culture medium when the cells grew to cover60to70percent of the culture dish. Then the cells were collected, and the expression of blood endothelial cell (BEC) markers and lymphatic endothelial cell (LEC) markers were investigated with Realtime-PCR, western blotting and immunocytochemistry. The statistics were analyzed by Statistical analysis software (SPSS17.0).Result In CRL-1730cell line, endothelial cell markers such as vWF, VE-cadherin and VEGFR2were down-regulated after SDF-la stimulation, dose dependently. While lymphatic phenotype such as Prox-1, podoplanin, and LYVE-1were up-regulated after SDF-la stimulation, dose dependently.Conclusion We elucidated the effect of SDF-la on converting the transcriptional program of cultured vascular endothelium towards the lymphatic endothelial phenotype for the first time. And we proposed that SDF-la may induce transdifferentiation of blood vessel endothelial cells to lymphatic endothelial cells.