Imbalanced Activation of Wnt-/β-Catenin-Signaling in Liver Endothelium Alters Normal Sinusoidal Differentiation

Abstract

Endothelial wingless-related integration site (Wnt)-/β-catenin signaling is a key regulator of the tightly sealed blood–brain barrier. In the hepatic vascular niche angiokine-mediated Wnt signaling was recently identified as an important regulator of hepatocyte function, including the determination of final adult liver size, liver regeneration, and metabolic liver zonation. Within the hepatic vasculature, the liver sinusoidal endothelial cells (LSECs) are morphologically unique and functionally specialized microvascular endothelial cells (ECs). Pathological changes of LSECs are involved in chronic liver diseases, hepatocarcinogenesis, and liver metastasis. To comprehensively analyze the effects of endothelial Wnt-/β-catenin signaling in the liver, we used endothelial subtype-specific Clec4g-iCre mice to generate hepatic ECs with overexpression of Ctnnb1. In the resultant Clec4g-iCretg/wt;Ctnnb1(Ex3)fl/wt (Ctnnb1OE−EC) mice, activation of endothelial Wnt-/β-catenin signaling resulted in sinusoidal transdifferentiation with disturbed endothelial zonation, that is, loss of midzonal LSEC marker lymphatic vessel endothelial hyaluronic acid receptor 1 (Lyve1) and enrichment of continuous EC genes, such as cluster of differentiation (CD)34 and Apln. Notably, gene set enrichment analysis revealed overrepresentation of brain endothelial transcripts. Activation of endothelial Wnt-/β-catenin signaling did not induce liver fibrosis or alter metabolic liver zonation, but Ctnnb1OE−EC mice exhibited significantly increased plasma triglyceride concentrations, while liver lipid content was slightly reduced. Ctnnb1 overexpression in arterial ECs of the heart has been reported previously to cause cardiomyopathy. As Clec4g-iCre is active in a subset of cardiac ECs, it was not unexpected that Ctnnb1OE−EC mice showed reduced overall survival and cardiac dysfunction. Altogether, balanced endothelial Wnt-/β-catenin signaling in the liver is required for normal LSEC differentiation and for maintenance of normal plasma triglyceride levels.

A spatial atlas of Wnt and Frizzled receptor expression in adult mouse liver

“…Furthermore, we also find that many of the Fzds are robustly expressed in endothelial cells, suggesting significant autocrine Wnt/Fzd signaling locally within the hepatic vasculature. Indeed, local endothelial Wnt signaling maintains endothelial cell identity and zonation [28]. Moreover, these data are consistent with earlier work in brain demonstrating a role for Wnt/b-catenin signaling in vascular development and maintenance post-development [29].…”

Angiocrine Signaling in Sinusoidal Health and Disease

“…LSECs, macrophages, and HSCs significantly contribute in the process of liver regeneration, 5 6 9 10 12 18 22 28 32 33 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 supported by scRNAseq and spatial transcriptomics studies. 55 Regeneration is studied via acute injury models such as the two-thirds partial hepatectomy model (PHx) 10 resulting in rapid regeneration of liver mass by 96 hours postinjury or the centrilobular necrosis with acetaminophen overdose (APAP) 38 (further discussed later).…”

“…LSECs, macrophages, and HSCs significantly contribute in the process of liver regeneration, 5,6,9,10,12,18,22,28,32,33,[37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] supported by scRNAseq and spatial transcriptomics studies. 55 Regeneration is studied via acute injury models such as the two-thirds partial hepatectomy model (PHx) 10 resulting in rapid regeneration of liver mass by 96 hours postinjury or the centrilobular necrosis with acetaminophen overdose (APAP) 38 (further discussed later).…”

“…In addition to central vein-associated angiocrine Wnt signaling, endothelial tyrosine kinase with Ig-like and EGF-like domains 1/2 (Tie1/2), 10 Notch, 11,12 c-Maf, [13][14][15][16] Heg, 17 and periportal Dll4 and Esm1 16,18 also participate to hepatic and endothelial zonation. 5,6,[19][20][21][22] Briefly, paired endothelial cell/hepatocyte sequencing was originally utilized to develop a panel of pericentral to periportal endothelial functional landmark genes (70 each).…”