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Pathophysiology of cholangiopathies
No full textThe diseases of the intrahepatic biliary tree are a large group of potentially evolutive congenital and acquired liver disorders affecting both the adult and pediatric populations. They represent a relevant cause of liver-related morbidity and mortality and an important indication for liver transplantation, particularly in children. While the practical approach to patients affected by biliary tree diseases has not significantly changed yet, the conceptual approach to the pathophysiology of cholangiopathies has witnessed important advances that will be discussed. The primary cell target of the pathogenetic sequence of these disorders is the biliary epithelium. Cholangiocytes have multifaceted functions, not limited to bile production. Their capability to secrete a range of different pro-inflammatory mediators, cytokines, and chemokines indicates a major role of cholangiocytes in the inflammatory reaction. Furthermore, paracrine secretion of growth factors and peptides mediates an extensive cross-talk with other liver cell types, including hepatocytes, stellate, and endothelial and inflammatory cells. Cholangiopathies share a number of pathogenetic mechanisms, including inflammation, cholestasis, fibrosis, apoptosis, altered development, and neoplastic transformation. These basic disease mechanisms will be discussed in detail, along with the distinct features of a number of cholangiopathies. Furthermore, an increase in the biliary cell compartment is a common response to many forms of liver injury, from cholangiopathies to viral and fulminant hepatitis. Elucidation of these pathophysiologic mechanisms will likely provide clues for future therapeutic strategies. Furthermore, understanding the role of cholangiocytes in liver regeneration/repair and the mechanisms of cholangiocyte activation and their relationship with liver progenitor cell will be of further interest
RAC1 AND CDC42 ACTIVATION REGULATES PDGF‐D MEDIATED CAF RECRUITMENT BY CANCER CELLS IN CHOLANGIOCARCINOMA
No full textACTIVATION OF STORE-OPERATED CAMP SIGNALING IS RESPONSIBLE FOR ERK 1⁄2 PHOSPHORYLATION IN POLYCYSTIN-2/TRPP2 DEFECTIVE CHOLANGIOCYTES
No full textINAPPROPRIATE STORE-OPERATED CYCLIC-AMP PRODUCTION LINKS ALTERED ENDOPLASMIC RETICULUM (ER) CA2 HOMEOSTASIS TO ERK/VEGF SIGNALING IN TRPP2-DEFECTIVE CHOLANGIOCYTES IN A MOUSE MODEL OF POLYCYSTIC LIVER DISEASE
No full textCell interactions in biliary diseases: Clues from pathophysiology and repair mechanisms to foster early assessment
Full text linkIn modern hepatology, diseases of the biliary epithelium, currently termed cholangiopathies, represent one of the main gaps in knowledge, both on experimental and clinical grounds, though they started to draw attention since the late 80s [...]
Ursodeoxycholic acid stimulates cholangiocyte fluid secretion in mice via CFTR-dependent ATP secretion.
No full textBACKGROUND and AIMS:
Cholangiopathies are characterized by impaired cholangiocyte secretion. Ursodeoxycholic acid (UDCA) is widely used for cholangiopathy treatment, but its effects on cholangiocyte secretory functions remain unclear and are the subject of this study.
METHODS:
Polarized mouse cholangiocytes in tubular (isolated bile-duct units [IBDU]) or monolayer configuration were obtained from wild-type (WT) and B6-129-Cftr(tm1Kth) and Cftr(tm1Unc) mice that are defective in CFTR, an adenosine 3',5'-cyclic monophosphate (cAMP)-stimulated Cl(-) channel expressed in cholangiocytes. Fluid secretion was assessed by video-optical planimetry, Cl(-) and Ca(2+) efflux by microfluorimetry (6-methoxy-N-ethylquinolinium chloride, fura-2, and fluo-4), adenosine triphosphate (ATP) secretion by luciferin-luciferase assay, and protein kinase C (PKC) by Western blot.
RESULTS:
UDCA stimulated fluid secretion and Cl(-) efflux in WT-IBDU but not in CFTR-KO-IBDU or in WT-IBDU exposed to CFTR inhibitors. UDCA did not affect intracellular cAMP levels but increased [Ca(2+)]i in WT and not in CFTR-KO cholangiocytes. UDCA stimulated apical ATP secretion in WT but not in CFTR-KO cholangiocytes. UDCA-stimulated [Ca(2+)]i increase was inhibited by suramin, a purinergic 2Y-receptor inhibitor. UDCA stimulated the translocation of PKC-alpha and PKC-epsilon to the plasma membrane. UDCA-stimulated secretion was inhibited by 2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid and by phospholipase C and PKC inhibitors. UDCA increased ATP output in isolated perfused livers from WT but not from CFTR-KO mice.
CONCLUSIONS:
Our data indicate that UDCA stimulates a CFTR-dependent apical ATP release in cholangiocytes. Secreted ATP activates purinergic 2Y receptors, and, through [Ca(2+)]i increase and PKC activation stimulates Cl(-) efflux and fluid secretion. These data support the concept that CFTR plays a role in modulating purinergic signaling in secretory epithelia and suggest a novel mechanism explaining the choleretic effect of UDCA
Loss of CFTR affects biliary epithelium innate immunity and causes TLR4-NF-kB-mediated inflammatory response in mice.
No full textBACKGROUND and AIMS:
Loss of function of the cystic fibrosis transmembrane conductance regulator (CFTR) in the biliary epithelium reduces bile flow and alkalinization in patients with cystic fibrosis (CF). Liver damage is believed to result from ductal cholestasis, but only 30% of patients with CF develop liver defects, indicating that another factor is involved. We studied the effects of CFTR deficiency on Toll-like receptor 4 (TLR4)-mediated responses of the biliary epithelium to endotoxins.
METHODS:
Dextran sodium sulfate (DSS) was used to induce colitis in C57BL/6J-Cftrtm1Unc (Cftr-KO) mice and their wild-type littermates. Ductular reaction and portal inflammation were quantified by keratin-19 and CD45 immunolabeling. Cholangiocytes isolated from wild-type and Cftr-KO mice were challenged with lipopolysaccharide (LPS); cytokine secretion was quantified. Activation of nuclear factor κB (NF-κB), phosphorylation of TLR4, and activity of Src were determined. HEK-293 that expressed the secreted alkaline phosphatase reporter and human TLR4 were transfected with CFTR complementary DNAs.
RESULTS:
DSS-induced colitis caused biliary damage and portal inflammation only in Cftr-KO mice. Biliary damage and inflammation were not attenuated by restoring biliary secretion with 24-nor-ursodeoxycholic acid but were significantly reduced by oral neomycin and polymyxin B, indicating a pathogenetic role of gut-derived bacterial products. Cftr-KO cholangiocytes incubated with LPS secreted significantly higher levels of cytokines regulated by TLR4 and NF-κB. LPS-mediated activation of NF-κB was blocked by the TLR4 inhibitor TAK-242. TLR4 phosphorylation by Src was significantly increased in Cftr-KO cholangiocytes. Expression of wild-type CFTR in the HEK293 cells stimulated with LPS reduced activation of NF-κB.
CONCLUSIONS:
CFTR deficiency alters the innate immunity of the biliary epithelium and reduces its tolerance to endotoxin, resulting in an Src-dependent inflammatory response mediated by TLR4 and NF-κB. These findings might be used to develop therapies for CF-associated cholangiopathy
PKA dependent p-Ser-675β-catenin, a novel signaling defect in a mouse model of Congenital Hepatic Fibrosis
No full textBackground and Aims: Genetically-determined loss of fibrocystin function causes Congenital Hepatic Fibrosis (CHF), Caroli Disease (CD) and Autosomal Recessive Polycystic Kidney Disease (ARPKD). Cystic dysplasia of the intrahepatic bile ducts and progressive portal fibrosis characterize liver pathology in CHF/CD. At a cellular level, several functional morphological
and signaling changes have been reported including increased levels of 3'-5'-cyclic adenosine monophosphate (cAMP). In this study, we have addressed the relationships between increased cAMP and β-catenin.
Methods and Results: In cholangiocytes isolated ad cultured from Pkhd1del4/del4 mice, stimulation of cAMP/PKA signaling (forskolin 10 μM) stimulated Ser-675-phosphorylation of β-catenin, its nuclear localization and its transcriptional activity (Western blot and TOP Flash assay, respectively) along with a downregulation of E-cadherin expression (Immunocytochemistry and Western blot); these changes were inhibited by the PKA blocker, PKI (1 μM). The Rho-GTPase, Rac-1, was also significantly activated by cAMP in Pkhd1del4/del4 cholangiocytes. Rac-1 inhibition blocked cAMP-dependent nuclear translocation and transcriptional activity of pSer-675β-catenin. Cell migration (Boyden chambers) was significantly higher in cholangiocytes obtained from Pkhd1del4/del4 and was inhibited by: 1) PKI, 2) silencing β-catenin (siRNA) and 3) the Rac-1 inhibitor, NSC 23766. Conclusions: These data show that in fibrocystin-defective cholangiocytes, cAMP stimulates pSer-675phosphorylation of β-catenin and Rac-1 activity. In the presence of activated Rac-1, pSer-675-β-catenin is translocated to the nucleus, becomes transcriptionally active, and is responsible for increased motility of Pkhd1del4/del4 cholangiocytes. β-catenin dependent changes in cell motility may be central to the pathogenesis of the disease and represent a potential therapeutic target
PKA-DEPENDENT P-SER-675-CATENIN PHOSPHORYLATION INCREASES CHOLANGIOCYTE MOTILITY IN A MOUSE MODEL OF FIBROPOLYCYSTIC LIVER DISEASES
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