The Scaffold Protein Liprin β-1 (PPFIBP1) and the Intermediate Filament Synemin: Potential New Markers of Lymphatic Endothelial Cells.

There are a few molecules that are regularly used as markers for lymphatic endothelial cells (LECs) such as the adhesion molecule CD31/PEACAM1, the transcription factor PROX1, the Vascular Endothelial Growth Factor Receptor-3 (VEGFR3/FLT4), the glycoprotein podoplanin, and the hyaluronan receptor LYVE1. However, none of the molecules are exclusively expressed in LECs, and there is molecular and functional heterogeneity of LECs in initial lymphatics, lymphatic collectors and lymph nodes. Therefore, a combination of markers must be applied to identify lymphatics. This is particularly true for the characterization of conditions such as lymphatic malformations or cancers, in which the molecular profile of vessels may be variable or abnormal. Here we present two molecules that can help distinguish between endothelial cells of blood and lymphatic vessels: the scaffold protein liprin β-1 (PPFIBP1) and the intermediate filament synemin. We collected own data on the RNA and protein expression of the two molecules in humans, and studied publicly available databases. PPFIBP1 appears to be a suitable marker of LECs in initial lymphatics, collectors and lymph nodes, while synemin appears to be more restricted to initial lymphatics. We hope this will stimulate monoclonal antibody development and help expand the range of LEC markers in health and disease.