Liver sinusoidal endothelial cells (LSECs) critically regulate liver homeostasis and diseases through angiocrine factors. Notch is critical in endothelial cells (ECs). In the current study, Notch signaling was activated by inducible EC‐specific expression of the Notch intracellular domain (NIC). We found that endothelial Notch activation damaged liver homeostasis. Notch activation resulted in decreased fenestration and increased basement membrane, and a gene expression profile with decreased LSEC‐associated genes and increased continuous EC‐associated genes, suggesting LSEC dedifferentiation. Consistently, endothelial Notch activation enhanced hepatic fibrosis (HF) induced by CCl₄. Notch activation attenuated endothelial nitric oxide synthase (eNOS)/soluble guanylate cyclase (sGC) signaling, and activation of sGC by 3‐(5′‐hydroxymethyl‐2′‐furyl)‐1‐benzylindazole (YC‐1) reversed the dedifferentiation phenotype. In addition, Notch activation subverted the hepatocyte‐supporting angiocrine profile of LSECs by down‐regulating critical hepatocyte mitogens, including Wnt2a, Wnt9b, and hepatocyte growth factor (HGF). This led to compromised hepatocyte proliferation under both quiescent and regenerating conditions. Whereas expression of Wnt2a and Wnt9b was dependent on eNOS‐sGC signaling, HGF expression was not rescued by the sGC activator, suggesting heterogeneous mechanisms of LSECs to maintain hepatocyte homeostasis. Conclusion: Endothelial Notch activation results in LSEC dedifferentiation and accelerated liver fibrogenesis through eNOS‐sGC signaling, and alters the angiocrine profile of LSECs to compromise hepatocyte proliferation and liver regeneration (LR). (Hepatology 2018).

The shortage of donors is a major challenge for transplantation; however, organs from genetically modified pigs can serve as ideal supplements^1,2. Until now, porcine hearts and kidneys have been successively transplanted into humans^3,4,5,6,7. In this study, heterotopic auxiliary transplantation was used to donate a six-gene-edited pig liver to a brain-dead recipient. The graft function, haemodynamics, and immune and inflammatory responses of the recipient were monitored over the subsequent 10 days. Two hours after portal vein reperfusion of the xenograft, goldish bile was produced, increasing to 66.5 ml by postoperative day 10. Porcine liver-derived albumin also increased after surgery. Alanine aminotransferase levels remained in the normal range, while aspartate aminotransferase levels increased on postoperative day 1 and then rapidly declined. Blood flow velocity in the porcine hepatic artery and portal and hepatic veins remained at an acceptable level. Although platelet numbers decreased early after surgery, they ultimately returned to normal levels. Histological analyses showed that the porcine liver regenerated capably with no signs of rejection. T cell activity was inhibited by anti-thymocyte globulin administration, and B cell activation increased 3 days after surgery and was then inhibited by rituximab. There were no significant peri-operative changes in immunoglobulin G or immunoglobulin M levels. C-reactive protein and procalcitonin levels were initially elevated and then quickly declined. The xenograft remained functional until study completion.

Hepatic ischemia/reperfusion (I/R) injury is initiated by reactive oxygen species (ROS) accumulated during the early reperfusion phase after ischemia, but cellular mechanisms controlling ROS production and scavenging have not been fully understood. In this study, we show that blocking Notch signal by knockout of the transcription factor RBP-J or a pharmacological inhibitor led to aggravated hepatic I/R injury, as manifested by deteriorated liver function and increased apoptosis, necrosis, and inflammation, both in vitro and in vivo. Interruption of Notch signaling resulted in increased intracellular ROS in hepatocytes, and a ROS scavenger cured exacerbated hepatic I/R injury after Notch signaling blockade, suggesting that Notch signal deficiency aggravated I/R injury through increased ROS levels. Notch signal blockade resulted in down-regulation of Hes5, leading to reduced formation of the Hes5-STAT3 complex and hypophosphorylation of STAT3, which further attenuated manganese superoxide dismutase (MnSOD) expression and increased ROS and apoptosis. Indeed, overexpression of a constitutively active STAT3 rescued MnSOD expression and I/R injury–induced apoptosis in the absence of Notch signaling. Finally, forced Notch activation by ligand stimulation or Hes5 overexpression reduced intracellular ROS and protected hepatocytes from apoptosis after I/R injury through the activation of STAT3 and MnSOD expression. Notch signal protects hepatocytes from I/R injury by Hes5-dependent activation of STAT3, which activates the expression of MnSOD, leading to the scavenging of ROS. (HEPATOLOGY 2011;).

Tumor-associated macrophages (TAM) play pivotal roles in tumor progression and metastasis, but the contribution and regulation of different macrophage populations remain unclear. Here we show that Notch signaling plays distinct roles in regulating different TAM subsets in hepatocellular carcinoma (HCC). Myeloid-specific NOTCH blockade by conditional disruption of recombination signal binding protein Jκ (RBPj cKO) significantly delayed the growth of subcutaneously inoculated Lewis lung carcinoma (LLC), but accelerated orthotopically inoculated hepatic Hepa1-6 tumors in mice. In contrast to subcutaneous LLC, RBPj cKO significantly increased the number of TAMs in hepatic Hepa1-6 tumors despite impeded differentiation of monocyte-derived TAMs (moTAM). The dominating TAMs in orthotopic HCC manifested properties of Kupffer cells (KC) and hence are tentatively named KC-like TAMs (kclTAM). The increased proliferation of RBPj cKO kclTAMs was maintained even in Ccr2−/− mice, in which moTAMs were genetically blocked. NOTCH signaling blockade accelerated proliferation of kclTAMs via enhanced β-catenin–dependent WNT signaling, which also downregulated IL12 and upregulated IL10 expression by kclTAMs likely through c-MYC. In addition, myeloid-specific RBPj cKO facilitated hepatic metastasis of colorectal cancer but suppressed lung metastasis in mice, suggesting that the phenotype of RBPj cKO in promoting tumor growth was liver-specific. In patient-derived HCC biopsies, NOTCH signaling negatively correlated with WNT activation in CD68+ macrophages, which positively correlated with advanced HCC stages. Therefore, NOTCH blockade impedes the differentiation of moTAMs, but upregulates Wnt/β-catenin signaling to promote the proliferation and protumor cytokine production of kclTAMs, facilitating HCC progression and hepatic metastasis of colorectal cancer. Significance: These findings highlight the role of NOTCH and WNT signaling in regulating TAMs in hepatocellular carcinoma.