title: Liver kinase B1 regulates hepatocellular tight junction distribution and function in vivo.
abstract: Liver kinase B1 (LKB1) and its downstream effector AMP-activated protein kinase (AMPK) play critical roles in polarity establishment by regulating membrane trafficking and energy metabolism. In collagen sandwich-cultured hepatocytes, loss of LKB1 or AMPK impaired apical ABCB11 (Bsep) trafficking and bile canalicular formation. In the present study, we used liver-specific (albumin-Cre) LKB1 knockout mice (LKB1(-/-) ) to investigate the role of LKB1 in the maintenance of functional tight junction (TJ) in vivo. Transmission electron microscopy examination revealed that hepatocyte apical membrane with microvilli substantially extended into the basolateral domain of LKB1(-/-) livers. Immunofluorescence studies revealed that loss of LKB1 led to longer and wider canalicular structures correlating with mislocalization of the junctional protein, cingulin. To test junctional function, we used intravital microscopy to quantify the transport kinetics of 6-carboxyfluorescein diacetate (6-CFDA), which is processed in hepatocytes into its fluorescent derivative 6-carboxyfluorescein (6-CF) and secreted into the canaliculi. In LKB1(-/-) mice, 6-CF remained largely in hepatocytes, canalicular secretion was delayed, and 6-CF appeared in the blood. To test whether 6-CF was transported through permeable TJ, we intravenously injected low molecular weight (3 kDa) dextran in combination with 6-CFDA. In wild-type mice, 3 kDa dextran remained in the vasculature, whereas it rapidly appeared in the abnormal bile canaliculi in LKB1(-/-) mice, confirming that junctional disruption resulted in paracellular exchange between the blood stream and the bile canaliculus.
  
  
  
  LKB1 plays a critical role in regulating the maintenance of TJ and paracellular permeability, which may explain how various drugs, chemicals, and metabolic states that inhibit the LKB1/AMPK pathway result in cholestasis. (Hepatology 2016;64:1317-1329).
authors.affiliation: Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD. poratshliomn@mail.nih.gov.|Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD. poratshliomn@mail.nih.gov.
authors.forename: Natalie
authors.initials: N
authors.lastname: Porat-Shliom
authors.affiliation: Laboratory of Tight Junction Structure and Function, National Heart, Lung, and Blood Institute, Bethesda, MD.
authors.forename: Amber J
authors.initials: AJ
authors.lastname: Tietgens
authors.affiliation: Laboratory of Tight Junction Structure and Function, National Heart, Lung, and Blood Institute, Bethesda, MD.
authors.forename: Christina M
authors.initials: CM
authors.lastname: Van Itallie
authors.affiliation: Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD.
authors.forename: Lynn
authors.initials: L
authors.lastname: Vitale-Cross
authors.affiliation: Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD.
authors.forename: Michal
authors.initials: M
authors.lastname: Jarnik
authors.affiliation: Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD.
authors.forename: Olivia J
authors.initials: OJ
authors.lastname: Harding
authors.affiliation: Laboratory of Tight Junction Structure and Function, National Heart, Lung, and Blood Institute, Bethesda, MD.
authors.forename: James M
authors.initials: JM
authors.lastname: Anderson
authors.affiliation: Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD.
authors.forename: J Silvio
authors.initials: JS
authors.lastname: Gutkind
authors.affiliation: Oral and Pharyngeal Cancer Branch, National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD.|Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD.
authors.forename: Roberto
authors.initials: R
authors.lastname: Weigert
authors.affiliation: Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD.
authors.forename: Irwin M
authors.initials: IM
authors.lastname: Arias
mesh_terms: D055372:AMP-Activated Protein Kinases; D000818:Animals; D005260:Female; D022781:Hepatocytes / Q000502:physiology* / Q000648:ultrastructure*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D019108:Tight Junctions / Q000502:physiology* / Q000648:ultrastructure*
chemical_list: D017346:Protein Serine-Threonine Kinases; C491654:Stk11 protein, mouse; D055372:AMP-Activated Protein Kinases