E-pub ahead of print].
AbstractThe discovery of marker proteins of human blood (BECs) and lymphatic endothelial cells (LECs) has allowed the isolation of these cells. So far, efforts to unravel their transcriptional and functional programs made use of cultured cells only. Hence, it is unknown to which extent previously identified LEC-and BEC-specific programs are representative of the in vivo situation. Here, we define the human BEC-and LEC-specific in vivo transcriptomes by comparative genome-wide expression profiling of freshly isolated cutaneous EC subsets and of non-EC skin cells (fibroblasts, mast cells, dendritic cells, epithelial cells). Interestingly, the expression of most of the newly identified EC subset-discriminating genes depends strictly on the in vivo tissue environment as revealed by comparative analyses of freshly isolated and cultured EC subsets. The identified environment-dependent, EC subset-restricted gene expression regulates lineage fidelity, fluid exchange, and MHC class II-dependent antigen presentation. As an example, for a BEC-restricted in vivo function, we show that non-activated BECs in situ, but not in vitro, assemble and display MHC class II protein complexes loaded with self peptides. Thus, our data demonstrate the key importance of using precisely defined native ECs for the global identification of in vivo relevant cell functions.This study compares, via FACS, rtPCR and microarray analyses, the characteristics of freshly isolated versus cultured blood vessel and lymphatic endothelial cells. Other skin cell types were studied to identify the distinctiveness of the endothelial cell subtypes. They found striking differences in gene expression between the freshly harvested cells and those that had undergone several passages in culture, postulating environment-dependent processes modulating protein expression and function.Blood vessel endothelial cells maintained expression of CD-146 and HOXD10 and lymphatic endothelial cells continued to express Podoplanin, LYVE-, PROX-1 and FOXC2 (thus these markers that differentiate the two cell types in vitro). A surprising finding was constitutive MHC class II-related protein expression by the normal vessel endothelial cells was lost when the cells were cultured in vitro. Further studies investigated the mechanism of MHC class II and T cell function. The authors conclude that further research may facilitate therapeutic manipulation of these cell types.