Disease-associated capillarization of LSEC in vivo and dedifferentiation of LSEC in vitro indicate the importance of the hepatic microenvironment. To identify the LSEC-specific molecular differentiation program in the rat we used a two-sided gene expression profiling approach comparing LSEC freshly isolated ex vivo with both lung microvascular STA-9090 endothelial cells (LMEC) and with LSEC cultured for 42 hours. The LSEC

signature consisted of 48 genes both down-regulated in LMEC and in LSEC upon culture (fold change >7 in at least one comparison); quantitative reverse-transcription polymerase chain reaction confirmation of these genes included numerous family members and signaling pathway-associated molecules. The LSEC differentiation program comprised Temsirolimus cost distinct sets of growth (Wnt2, Fzd4, 5, 9, Wls, vascular endothelial growth factors [VEGFR] 1, 2, 3, Nrp2) and transcription factors (Gata4, Lmo3, Tcfec, Maf) as well as endocytosis-related (Stabilin-1/2, Lyve1, and Ehd3) and cytoskeleton-associated molecules (Rnd3/RhoE). Specific gene induction in cultured LSEC versus

freshly isolated LSEC as well as LMEC (Esm-1, Aatf) and up-regulation of gene expression to LMEC levels (CXCR4, Apelin) confirmed true transdifferentiation of LSEC in vitro. In addition, our analysis identified a novel 26-kDa single-pass transmembrane protein, liver endothelial differentiation-associated protein (Leda)-1, that was selectively expressed in all liver endothelial cells and preferentially localized to the abluminal cell surface. Upon forced overexpression in MDCK cells, Leda-1 was sorted basolaterally to E-cadherin-positive adherens junctions, suggesting functional involvement in cell adhesion and HSP90 polarity. Conclusion: Comparative microvascular analysis in rat identified a hepatic microenvironment-dependent LSEC-specific differentiation program including the novel junctional molecule Leda-1. HEPATOLOGY 2010 Endothelial cells (ECs) display marked heterogeneity in different organs and in different segments of the vascular tree. Liver sinusoidal endothelial cells

(LSECs) are a prime example of uniquely differentiated microvascular EC that exert highly specialized functions as professional endocytes1 and participate in induction of hepatic immune tolerance.2 For endocytosis, LSEC express a broad range of different scavenger receptors including Stabilin-1 and Stabilin-2, two members of a novel scavenger receptor gene family selectively expressed in sinusoidal ECs that have been identified and thoroughly characterized by us.3 Stabilin-2 is the major hyaluronan scavenger receptor of the liver, whereas Stabilin-1 mediates endocytosis of acLDL (low density lipoprotein) and SPARC. Stabilin-1 and -2 use the constitutive clathrin-mediated endocytic pathway in LSEC (4); in addition, Stabilin-1 fulfills a second role as an intracellular cargo carrier.