Liver-specific β-catenin knockout (β-Catenin-LKO) mice have revealed an essential role of β-catenin in metabolic zonation where it regulates pericentral gene expression and in initiating liver regeneration (LR) after partial hepatectomy (PH), by regulating expression of Cyclin-D1. However what regulates β-catenin activity in these events remains an enigma. Here, we investigate to what extent β-catenin activation is Wnt-signaling dependent and the potential cell source of Wnts. We studied liver-specific Lrp5/6 KO (Lrp-LKO) mice where Wnt-signaling was abolished in hepatocytes while the β-catenin gene remained intact. Intriguingly, like β-catenin-LKO mice, Lrp-LKO exhibited a defect in metabolic zonation observed as lack of glutamine synthetase (GS), Cyp1a2 and Cyp2e1. Lrp-LKO also displayed a significant delay in initiation of LR due to absence of β-catenin-TCF4 association and lack of Cyclin-D1. To address the source of Wnt proteins in liver, we investigated conditional Wntless (Wls) KO mice, which lacked ability to secrete Wnts from either liver epithelial cells (Wls-LKO), or macrophages including Kupffer cells (Wls-MKO), or endothelial cells (Wls-EKO). While Wls-EKO was embryonic lethal precluding further analysis in adult hepatic homeostasis and growth, Wls-LKO and Wls-MKO were viable but did not show any defect in hepatic zonation. Wls-LKO showed normal initiation of LR, however Wls-MKO showed a significant but temporal deficit in LR that was associated with decreased β-catenin-TCF4 association and diminished Cyclin-D1 expression. Conclusion Wnt-signaling is the major upstream effector of β-catenin activity in pericentral hepatocytes and during LR. Hepatocytes, cholangiocytes or macrophages are not the source of Wnts in regulating hepatic zonation. However, Kupffer cells are a major contributing source of Wnt secretion necessary for β-catenin activation during LR.

Mesenchymal stem cell (MSC)-derived exosomes have diverse functions in regulating wound healing and inflammation; however, the molecular mechanism of human umbilical cord MSC (hUCMSC)-derived exosomes in regulating burn-induced inflammation is not well understood. We found that burn injury significantly increased the inflammatory reaction of rats or macrophages exposed to lipopolysaccharide (LPS), increased tumor necrosis factor α (TNF-α) and interleukin-1β (IL-1β) levels and decreased IL-10 levels. hUCMSC-exosome administration successfully reversed this reaction. Further studies showed that miR-181c in the exosomes played a pivotal role in regulating inflammation. Compared to control hUCMSC-exosomes, hUCMSC-exosomes overexpressing miR-181c more effectively suppressed the TLR4 signaling pathway and alleviated inflammation in burned rats. Administration of miR-181c-expressing hUCMSC-exosomes or TLR4 knockdown significantly reduced LPS-induced TLR4 expression by macrophages and the inflammatory reaction. In summary, miR-181c expression in hUCMSC-exosomes reduces burn-induced inflammation by downregulating the TLR4 signaling pathway.

Hepatic repair is directed chiefly by the proliferation of resident mature epithelial cells. Further if predominant injury is to cholangiocytes, the hepatocytes can transdifferentiate to cholangiocytes to assist in the repair and vice versa as shown by various fate-tracing studies. However, the molecular bases of reprograming remain elusive. Using two models of biliary injury where repair occurs via cholangiocyte proliferation and hepatocyte transdifferentiation to cholangiocytes, we identify an important role of Wnt signaling. First we identify upregulation of specific Wnt proteins in the cholangiocytes. Next, using conditional knockouts of Wntless and Wnt co-receptors LRP5/6, transgenic mice expressing stable β-catenin, and in vitro studies, we show a role of Wnt signaling through β-catenin in hepatocyte to biliary transdifferentiation. Lastly, we show that specific Wnts regulate cholangiocyte proliferation but in a β-catenin-independent manner. Conclusion: Wnt signaling regulates hepatobiliary repair after cholestatic injury in both β-catenin dependent and independent manners.

To understand the physiological functions of exogenous hepatocyte growth factor (HGF) on normal adult animals, we delivered human HGF gene into mice by a hydrodynamics-based in vivo gene transfection approach using a naked plasmid vector. Systemic administration of naked plasmid containing HGF cDNA driven under cytomegalovirus promoter (pCMV-HGF) by rapid injection via the tail vein produced a remarkable level of human HGF protein in the circulation, beginning to appear at 4 hours and peaking at 12 hours following injection. Tissue distribution studies identified the liver as the organ with the highest level of transgene expression. Through weekly repeated injections of plasmid vector, we achieved sustained, long-term, high levels of exogenous HGF expression in mice for 8 weeks. Increases of more than 31% and 16% in liver and body weights were found, respectively, in the mice that received pCMV-HGF plasmid compared with that given the control vector for 8 weeks. Expression of exogenous HGF in vivo activated mitogen-activated protein kinases and induced proliferating cell nuclear antigen expression in normal adult liver and kidneys. These data suggest that systemic administration of naked plasmid vector is a convenient, safe, and highly efficient approach to introduce and maintain exogenous HGF gene expression in vivo in a controllable fashion. Our results also indicate that long-term expression of human HGF in mice markedly activates growth-related signal transduction events, promotes cell proliferation, and leads to liver and overall body growth in whole adult animals. (HEPATOLOGY 2001;33:848-859.)

Emerging evidence has shown that miRNA-mediated gene expression modulation contributes to chronic pain, but its functional regulatory mechanism remains unknown. Here, we found that complete