Tissue Repair in the Mouse Liver Following Acute Carbon Tetrachloride Depends on Injury‐Induced Wnt/β‐Catenin Signaling

Abstract

In the liver, Wnt/β‐catenin signaling is involved in regulating zonation and hepatocyte proliferation during homeostasis. We examined Wnt gene expression and signaling after injury, and we show by in situ hybridization that Wnts are activated by acute carbon tetrachloride (CCl4) toxicity. Following injury, peri‐injury hepatocytes become Wnt‐responsive, expressing the Wnt target gene axis inhibition protein 2 (Axin2). Lineage tracing of peri‐injury Axin2+ hepatocytes shows that during recovery the injured parenchyma becomes repopulated and repaired by Axin2+ descendants. Using single‐cell RNA sequencing, we show that endothelial cells are the major source of Wnts following acute CCl4 toxicity. Induced loss of β‐catenin in peri‐injury hepatocytes results in delayed repair and ultimately injury‐induced lethality, while loss of Wnt production from endothelial cells leads to a delay in the proliferative response after injury. Conclusion: Our findings highlight the importance of the Wnt/β‐catenin signaling pathway in restoring tissue integrity following acute liver toxicity and establish a role of endothelial cells as an important Wnt‐producing regulator of liver tissue repair following localized liver injury.

The Hepatic Central Vein: Anatomical and Molecular Links to Perivenous Liver Biology

“…Hence, it is proposed that some extracellular signals in the local environment/niche of the central vein interacting with perivenous hepatocytes or contacts between central vein endothelial cells and hepatocytes to trigger expression of GS. Along this line is the speculation that endothelial cells of the central vein produce Wnt proteins that activate β-catenin in adjacent perivenous hepatocytes [38,77] , which actually is consistent with the revelation that the hepatic central vein is a source of Wnt2 and Wnt9b [1,2,3,4] --mentioned above.…”

“…The endothelial residence of RSPO3 likely confers a close range of action between RSPO3 and responder hepatocytes in the perivenous area. Incidentally, Wnt2 and Wnt9b mRNA were also found to localize in the central vein endothelium [1,2,3,4] . However, expression of central vein endothelial-specific Wnt2 and Wnt9b was not affected by RSPO3, implicating that the RSPO-induced effects are not due to loss of the Wnt ligands but due to Wnt/β-catenin modulation.…”

“…In the mouse, mRNAs of Wnt2 and Wnt9b [1,2,3,4] and of RSPO3 [5] -detected by in situ hybridization--are localized in the endothelium of the central vein, which is considered to be a primary source of the angiocrines. Central vein-derived Wnt2, Wnt9b and RSPO3 participate in the cellular-molecular circuitry [3] of the Wnt/β-catenin signaling and RSPO-LGR4/5-ZNRF3/RNF43 module that direct perivenous gene expression and zonation ( Figure 4).…”

“…Deletion of WIs specifically in central vein endothelial cells resulted in a loss of Wnt signaling in perivenous hepatocytes with a concomitant decreased expression of β-catenin-responsive Axin2 and GS genes [1] . Further, the Wnt/β-catenin signaling pathway plays a role in localized liver tissue repair following acute injury by a single injection of CCl 4 in mice [4] . Acute CCl 4 injury also led to increased expression of Wnt2 and Wnt9b in central vein endothelial cells.…”

“…Recent advances have indicated that the hepatic central vein provides a source of angiocrines Wnt2, Wnt9b [1,2,3,4] and R-spondin (RSPO)3 [5] that activate ß-catenin signaling, leading to perivenous metabolic zonation and gene expression in the liver. In addition, the central vein has been considered as an anatomical niche of perivenous hepatic stem cells that subserve homeostatic hepatocyte renewal [1] .…”