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Constitutive Activation of Natural Killer Cells in Primary Biliary Cholangitis.

ABSTRACT: Natural killer (NK) cells are innate immune cells that interface with the adaptive immune system to generate a pro-inflammatory immune environment. Primary Biliary Cholangitis (PBC) is a hepatic autoimmune disorder with extrahepatic associations including systemic sclerosis, Sjogren's syndrome and thyroiditis. Immunogenetic studies have identified polymorphisms of the IL-12/STAT4 pathway as being associated with PBC. As this pathway is important for NK cell function we investigated NK cells in PBC. Circulating NK cells from individuals with PBC were constitutively activated, with higher levels of CD49a and the liver-homing marker, CXCR6, compared to participants with non-autoimmune chronic liver disease and healthy controls. Stimulation with minimal amounts of IL-12 (0.005 ng/ml) led to significant upregulation of CXCR6 (p < 0.005), and enhanced IFNγ production (p < 0.02) on NK cells from PBC patients compared to individuals with non-autoimmune chronic liver disease, indicating dysregulation of the IL-12/STAT4 axis. In RNAseq studies, resting NK cells from PBC patients had a constitutively activated transcriptional profile and upregulation of genes associated with IL-12/STAT4 signaling and metabolic reprogramming. Consistent with these findings, resting NK cells from PBC patients expressed higher levels of pSTAT4 compared to control groups (p < 0.001 vs. healthy controls and p < 0.05 vs. liver disease controls). In conclusion NK cells in PBC are sensitive to minute quantities of IL-12 and have a "primed" phenotype. We therefore propose that peripheral priming of NK cells to express tissue-homing markers may contribute to the pathophysiology of PBC.

SUBMITTER: Hydes TJ

PROVIDER: S-EPMC6874097 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Purpose of reviewPrimary biliary cholangitis (PBC) is characterized by autoimmune damage of intrahepatic bile ducts associated with a loss of tolerance to mitochondrial antigens. PBC etiopathogenesis is intriguing because of different perplexing features, namely: a) although mitochondria are present in all cell types and tissues, the damage is mainly restricted to biliary epithelial cells (BECs); b) despite being an autoimmune disorder, it does not respond to immunosuppressive drugs but rather to ursodeoxycholic acid, a bile salt that induces HCO3- rich choleresis; c) the overwhelming female preponderance of the disease remains unexplained. Here we present an etiopathogenic view of PBC which sheds light on these puzzling facts of the disease.Recent findingsPBC develops in patients with genetic predisposition to autoimmunity in whom epigenetic mechanisms silence the Cl-/HCO3- exchanger AE2 in both cholangiocytes and lymphoid cells. Defective AE2 function can produce BECs damage as a result of decreased biliary HCO3- secretion with disruption of the protective alkaline umbrella that normally prevents the penetration of toxic apolar bile salts into cholangiocytes. AE2 dysfunction also causes increased intracellular pH (pHi) in cholangiocytes, leading to the activation of soluble adenylyl cyclase, which sensitizes BECs to bile salt-induced apoptosis. Recently, mitophagy was found to be inhibited by cytosolic alkalization and stimulated by acidification. Accordingly, we propose that AE2 deficiency may disturb mitophagy in BECs, thus, promoting the accumulation of defective mitochondria, oxidative stress and presentation of mitochondrial antigens to the immune cells. As women possess a more acidic endolysosomal milieu than men, mitophagy might be more affected in women in an AE2-defective background. Apart from affecting BECs function, AE2 downregulation in lymphocytes may also contribute to alter immunoregulation facilitating autoreactive T-cell responses.SummaryPBC can be considered as a disorder of Cl-/HCO3- exchange in individuals with genetic predisposition to autoimmunity.

Project description:Primary biliary cholangitis (PBC) is a chronic cholestatic liver disease associated with autoimmune phenomena targeting intrahepatic bile duct cells (cholangiocytes). Although its etiopathogenesis remains obscure, development of antimitochondrial autoantibodies against pyruvate dehydrogenase complex E2 is a common feature. MicroRNA (miR) dysregulation occurs in liver and immune cells of PBC patients, but its functional relevance is largely unknown. We previously reported that miR-506 is overexpressed in PBC cholangiocytes and directly targets both Cl- / HCO3- anion exchanger 2 and type III inositol 1,4,5-trisphosphate receptor, leading to cholestasis. Here, the regulation of miR-506 gene expression and its role in cholangiocyte pathophysiology and immune activation was studied. Several proinflammatory cytokines overexpressed in PBC livers (such as interleukin-8 [IL8], IL12, IL17, IL18, and tumor necrosis factor alpha) stimulated miR-506 promoter activity in human cholangiocytes, as revealed by luciferase reporter assays. Experimental overexpression of miR-506 in cholangiocytes dysregulated the cell proteomic profile (by mass spectrometry), affecting proteins involved in different biological processes including mitochondrial metabolism. In cholangiocytes, miR-506 (1) induced dedifferentiation with down-regulation of biliary and epithelial markers together with up-regulation of mesenchymal, proinflammatory, and profibrotic markers; (2) impaired cell proliferation and adhesion; (3) increased oxidative and endoplasmic reticulum stress; (4) caused DNA damage; and (5) sensitized to caspase-3-dependent apoptosis induced by cytotoxic bile acids. These events were also associated with impaired energy metabolism in mitochondria (proton leak and less adenosine triphosphate production) and pyruvate dehydrogenase complex E2 overexpression. Coculture of miR-506 overexpressing cholangiocytes with PBC immunocytes induced activation and proliferation of PBC immunocytes. CONCLUSION:Different proinflammatory cytokines enhance the expression of miR-506 in biliary epithelial cells; miR-506 induces PBC-like features in cholangiocytes and promotes immune activation, representing a potential therapeutic target for PBC patients. (Hepatology 2018;67:1420-1440).

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Constitutive Activation of Natural Killer Cells in Primary Biliary Cholangitis.

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