Unraveling the transcriptional determinants of Liver Sinusoidal Endothelial Cell specialization.

Liver Sinusoidal Endothelial Cells (LSECs) are the first liver cells encountering waste macromolecules, pathogens and toxins in blood. LSECs are highly specialized to mediate the clearance of these substances via endocytic scavenger receptors and are equipped with fenestrae that mediate the passage of macromolecules towards hepatocytes.Although some transcription factors (TFs) are known to play a role in LSEC specialization, information about the specialized LSEC signature and its transcriptional determinants remains incomplete. Based on a comparison of liver, heart and brain ECs, we established a thirty-gene LSEC signature comprising both established and newly identified markers including 7 genes encoding TFs. To evaluate the LSEC TF regulatory network, we artificially increased the expression of the 7 LSEC-specific TFs in human umbilical vein ECs (HUVECs). While ZEB2, HOXB5, Cux2 and TCFEC had limited contributions, C-MAF, GATA4 and MEIS2 emerged as stronger inducers of LSEC marker expression. Furthermore, a combination of C-MAF, GATA4 and MEIS2 showed a synergistic effect on the increase of LSEC signature genes including L-SIGN (or CLEC4M ), MRC1 , LGMN, GPR182, PLXNC1 and SLCO2A1. Accordingly, L-SIGN, MRC1, pro-LGMN, GPR182, PLXNC1 and SLCO2A1 protein levels were elevated by this combined overexpression. While receptor-mediated endocytosis was not significantly induced by the triple TF combination, binding to E2, the hepatitis C virus host-binding protein, was enhanced. We conclude that C-MAF, GATA4 and MEIS2 are important transcriptional regulators of the unique LSEC fingerprint and their interaction with viruses. Additional factors are however required to fully recapitulate the molecular, morphological and functional LSEC fingerprint.