Debolina Ray

Functional and structural features of cholangiocytes in health and disease

Cholangiocytes are the epithelial cells that line the bile ducts. Along the biliary tree, two different kinds of cholangiocytes exist: small and large cholangiocytes. Each type has important differences in their biological role in physiologic and pathologic conditions. In response to injury, cholangiocytes become reactive and acquire a neuroendocrine-like phenotype with the secretion of a number of peptides. These molecules act in an autocrine/paracrine fashion to modulate cholangiocyte biology and determine the evolution of biliary damage. The failure of such mechanisms is believed to influence the progression of cholangiopathies, a group of diseases that selectively target biliary cells. Therefore, the understanding of mechanisms regulating cholangiocyte response to injury is expected to foster the development of new therapeutic options to treat biliary diseases. In this review, we discuss the most recent findings in the mechanisms driving cholangiocyte adaptation to damage, with particular emphasis on molecular pathways that are susceptible of therapeutic intervention. Morphogenic pathways (Hippo, Notch, Hedgehog), which have been recently shown to regulate biliary ontogenesis and response to injury, are also reviewed as well as the results of ongoing clinical trials evaluating new drugs for the treatment of cholangiopathies.

Prolonged exposure of cholestatic rats to complete dark inhibits biliary hyperplasia and liver fibrosis

Biliary hyperplasia and liver fibrosis are common features in cholestatic liver disease. Melatonin is synthesized by the pineal gland as well as the liver. Melatonin inhibits biliary hyperplasia of bile duct-ligated (BDL) rats. Since melatonin synthesis (by the enzyme serotonin N-acetyltransferase, AANAT) from the pineal gland increases after dark exposure, we hypothesized that biliary hyperplasia and liver fibrosis are diminished by continuous darkness via increased melatonin synthesis from the pineal gland. Normal or BDL rats (immediately after surgery) were housed with light-dark cycles or complete dark for 1 wk before evaluation of 1) the expression of AANAT in the pineal gland and melatonin levels in pineal gland tissue supernatants and serum; 2) biliary proliferation and intrahepatic bile duct mass, liver histology, and serum chemistry; 3) secretin-stimulated ductal secretion (functional index of biliary growth); 4) collagen deposition, liver fibrosis markers in liver sections, total liver, and cholangiocytes; and 5) expression of clock genes in cholangiocytes. In BDL rats exposed to dark there was 1) enhanced AANAT expression/melatonin secretion in pineal gland and melatonin serum levels; 2) improved liver morphology, serum chemistry and decreased biliary proliferation and secretin-stimulated choleresis; and 4) decreased fibrosis and expression of fibrosis markers in liver sections, total liver and cholangiocytes and reduced biliary expression of the clock genes PER1, BMAL1, CLOCK, and Cry1. Thus prolonged dark exposure may be a beneficial noninvasive therapeutic approach for the management of biliary disorders.

Gonadotropin-Releasing Hormone Stimulates Biliary Proliferation by Paracrine/Autocrine Mechanisms

During cholestatic liver disease, there is dysregulation in the balance between biliary growth and loss in bile duct-ligated (BDL) rats modulated by neuroendocrine peptides via autocrine/paracrine pathways. Gonadotropin-releasing hormone (GnRH) is a trophic peptide hormone that modulates reproductive function and proliferation in many cell types. We evaluated the autocrine role of GnRH in the regulation of cholangiocyte proliferation. The expression of GnRH receptors was assessed in a normal mouse cholangiocyte cell line (NMC), sham, and BDL rats. The effect of GnRH administration was evaluated in normal rats and in NMC. GnRH-induced biliary proliferation was evaluated by changes in intrahepatic bile duct mass and the expression of proliferation and function markers. The expression and secretion of GnRH in NMC and isolated cholangiocytes was assessed. GnRH receptor subtypes GnRHR1 and GnRHR2 were expressed in cholangiocytes. Treatment with GnRH increased intrahepatic bile duct mass as well as proliferation and function markers in cholangiocytes. Transient knockdown and pharmacologic inhibition of GnRHR1 in NMC decreased proliferation. BDL cholangiocytes had increased expression of GnRH compared with normal rats, accompanied by increased GnRH secretion. In vivo and in vitro knockdown of GnRH decreased intrahepatic bile duct mass/cholangiocyte proliferation and fibrosis. GnRH secreted by cholangiocytes promotes biliary proliferation via an autocrine pathway. Disruption of GnRH/GnRHR signaling may be important for the management of cholestatic liver diseases.

Overexpression of membrane metalloendopeptidase inhibits substance P stimulation of cholangiocarcinoma growth

Substance P (SP) promotes cholangiocyte growth during cholestasis by activating its receptor, NK1R. SP is a proteolytic product of tachykinin (Tac1) and is deactivated by membrane metalloendopeptidase (MME). This study aimed to evaluate the functional role of SP in the regulation of cholangiocarcinoma (CCA) growth. NK1R, Tac1, and MME expression and SP secretion were assessed in human CCA cells and nonmalignant cholangiocytes. The proliferative effects of SP (in the absence/presence of the NK1R inhibitor, L-733,060) and of L-733,060 were evaluated. In vivo, the effect of L-733,060 treatment or MME overexpression on tumor growth was evaluated by using a xenograft model of CCA in nu/nu nude mice. The expression of Tac1, MME, NK1R, PCNA, CK-19, and VEGF-A was analyzed in the resulting tumors. Human CCA cell lines had increased expression of Tac1 and NK1R, along with reduced levels of MME compared with nonmalignant cholangiocytes, resulting in a subsequent increase in SP secretion. SP treatment increased CCA cell proliferation in vitro, which was blocked by L-733,060. Treatment with L-733,060 alone inhibited CCA proliferation in vitro and in vivo. Xenograft tumors derived from MME-overexpressed human Mz-ChA-1 CCA cells had a slower growth rate than those derived from control cells. Expression of PCNA, CK-19, and VEGF-A decreased, whereas MME expression increased in the xenograft tumors treated with L-733,060 or MME-overexpressed xenograft tumors compared with controls. The study suggests that SP secreted by CCA promotes CCA growth via autocrine pathway. Blockade of SP secretion and NK1R signaling may be important for the management of CCA.

Mouse models of liver fibrosis mimic human liver fibrosis of different etiologies

The liver has the amazing capacity to repair itself after injury; however, the same processes that are involved in liver regeneration after acute injury can cause serious consequences during chronic liver injury. In an effort to repair damage, activated hepatic stellate cells trigger a cascade of events that lead to deposition and accumulation of extracellular matrix components causing the progressive replacement of the liver parenchyma by scar tissue, thus resulting in fibrosis. Although fibrosis occurs as a result of many chronic liver diseases, the molecular mechanisms involved depend on the underlying etiology. Since studying liver fibrosis in human subjects is complicated by many factors, mouse models of liver fibrosis that mimic the human conditions fill this void. This review summarizes the general mouse models of liver fibrosis and mouse models that mimic specific human disease conditions that result in liver fibrosis. Additionally, recent progress that has been made in understanding the molecular mechanisms involved in the fibrogenic processes of each of the human disease conditions is highlighted.

Probiotic Bifidobacterium species: potential beneficial effects in diarrheal disorders. Focus on "Probiotic Bifidobacterium species stimulate human SLC26A3 gene function and expression in intestinal epithelial cells".

diarrhea caused by enteric (bacterial/viral/parasitic) infections or diarrhea associated with inflammatory bowel disease represents a major health care burden worldwide (10). In addition, diarrhea associated with antibiotic administration in adults, as well as children, is a significant health care issue (1, 3). Diarrhea is also a common side effect of chemo/radiotherapy during cancer treatment (6). Antidiarrheal drugs generally have been shown to cause nausea, loss of appetite, and constipation, which often hinder treatment protocols (15). Diarrhea is a consequence of the imbalance of water and ion absorption by epithelial cells of the gastrointestinal tract, ultimately leading to enhanced secretion and/or diminished absorption of fluid and electrolytes. Aberrant ion movement across epithelia can occur through a paracellular pathway via tight junctions or a transcellular pathway via membrane transporters such as Na+-dependent glucose transporter 1, Na+/H+ exchanger isoform 3, Cl−/HCO3− exchanger, and downregulated in adenoma (DRA), which can be dysregulated in diarrhea (10). Infectious pathogens can alter ion transporters directly or may induce electrolyte imbalance via increased inflammation or reduction in the absorptive capacity of the epithelial cells (12). Several studies of the functional implication of DRA in diarrheal disorders have been published (4, 7, 13).

Liver Regeneration: The Biliary Perspective

This chapter aims to provide an overview on the contribution of cholangiocytes during liver regeneration. We begin with a brief background on the structure and function of the biliary epithelium followed by a discussion on the heterogeneity of cholangiocytes along the length of the biliary epithelium. We then discuss the three types of biliary proliferative processes into Type I (typical), Type II (atypical), and Type III (oval cell) proliferation. Specifically, we have discussed the different types of liver injuries and their effect on both large and small cholangiocytes through specific signaling mechanism. Subsequently, we discuss the various factors, such as gastrointestinal hormones, angiogenic factors, bile acids, neurotransmitters, and inflammatory cytokines that play important roles in the heterogeneous proliferative responses of cholangiocytes during liver injury. We discuss the novel molecules, such as microRNAs, that are being increasingly found essential in the regulation of biliary proliferation. Additional discussion on the contribution of the peribiliary glands on the regulation of cholangiocyte proliferation has been included to provide a comprehensive view of all the factors influencing response to liver injury. Lastly, we conclude with the relevance of biliary regeneration in human liver diseases to emphasize on the need for continuing research in this field for potential diagnostic purposes.

457 Impact of MT2 Melatonin Receptor Deletion on Cellular Senescence in Cholangiocytes Isolated From Mice After Cholestatic Liver Injury

A S L D A b st ra ct s BGJ398, a pan-FGFR inhibitor currently being employed in human trials, resulted in a significant increase in cellular apoptosis. Tumor tissue from mice sacrificed 10 weeks after biliary oncogene transduction of AKT and YAP also demonstrated increased expression of FGFR 1-4. BGJ398 treatment resulted in a significant reduction in tumor burden and increase in tumor cell apoptosis as assessed by the TUNEL assay in our mouse model of CCA. In Conclusion, YAP is a critical oncogene in CCA and promotes biliary carcinogenesis, in part, via upregulation of FGFR. In a murine genetic model of CCA, the FGFR specific inhibitor BGJ398 significantly reduces tumor burden by inducing apoptosis. Thus, inhibition of FGFR represents a promising therapeutic approach in YAP-driven human CCA.

Sa1699 Local Inhibition of Hepatic GnRH by Vivo-Morpholino Reduces Biliary Proliferation and Ameliorates the Expression of Fibrotic Markers in Cholestatic Rats

A S L D A b st ra ct s increase in circulating Galanin in the serum. Galanin immunoreactivity was observed in both cholangiocytes and hepatocytes, whereas GalR1 was found predominantly in cholangiocytes. Systemic treatment of rats with M617 increased both CK-19 expression and IBDM in both sham and BDL-treated animals. In vitro, treatment of the mouse cholangiocyte cell line with M617 increased ERK1/2 and RSK-1 activity. There was a concomitant increase in cholangiocyte proliferation after M617 treatment that could be blocked by pretreatment with inhibitors for ERK1/2 and RSK-1. Conclusions: Data presented here demonstrate a direct stimulatory role for Galanin on cholangiocyte proliferation under physiological (sham) and pathological (BDL) conditions via a mechanism involving the activation of ERK1/2 and subsequent phosphorylation of RSK-1. Targeting Galanin or GalR1 may prove a useful strategy to regulate biliary mass during cholestatic liver injury.