Hepatology : official journal of the American Association for the Study of Liver Diseases
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Polycystic liver disease may complicate autosomal dominant polycystic kidney disease (ADPKD), a disease caused by mutations in polycystins, which are proteins that regulate signaling, morphogenesis, and differentiation in epithelial cells. The cystic biliary epithelium [liver cystic epithelium (LCE)] secretes vascular endothelial growth factor (VEGF), which promotes liver cyst growth via autocrine and paracrine mechanisms. The expression of insulin-like growth factor 1 (IGF1), insulin-like growth factor 1 receptor (IGF1R), and phosphorylated mammalian target of rapamycin (p-mTOR) and the protein kinase A (PKA)-dependent phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) are also up-regulated in LCE. We have hypothesized that mammalian target of rapamycin (mTOR) represents a common pathway for the regulation of hypoxia-inducible factor 1 alpha (HIF1alpha)-dependent VEGF secretion by IGF1 and ERK1/2. Conditional polycystin-2-knockout (Pkd2KO) mice were used for in vivo studies and to isolate cystic cholangiocytes [liver cystic epithelial cells (LCECs)]. The expression of p-mTOR, VEGF, cleaved caspase 3 (CC3), proliferating cell nuclear antigen (PCNA), IGF1, IGF1R, phosphorylated extracellular signal-regulated kinase, p-P70S6K, HIF1alpha, and VEGF in LCE, LCECs, and wild-type cholangiocytes was studied with immunohistochemistry, western blotting, or enzyme-linked immunosorbent assays. The cystic area was measured by computer-assisted morphometry of pancytokeratin-stained sections. Cell proliferation in vitro was studied with 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium and bromodeoxyuridine assays. The treatment of Pkd2KO mice with the mTOR inhibitor rapamycin significantly reduced the liver cyst area, liver/body weight ratio, pericystic microvascular density, and PCNA expression while increasing expression of CC3. Rapamycin inhibited IGF1-stimulated HIF1alpha accumulation and VEGF secretion in LCECs. IGF1-stimulated LCEC proliferation was inhibited by rapamycin and SU5416 (a vascular endothelial growth factor receptor 2 inhibitor). Phosphorylation of the mTOR-dependent kinase P70S6K was significantly reduced by PKA inhibitor 14-22 amide and by the mitogen signal-regulated kinase inhibitor U1026. ⋯ These data demonstrate that PKA-dependent up-regulation of mTOR has a central role in the proliferative, antiapoptotic, and pro-angiogenic effects of IGF1 and VEGF in polycystin-2-defective mice. This study also highlights a mechanistic link between PKA, ERK, mTOR, and HIF1alpha-mediated VEGF secretion and provides a proof of concept for the potential use of mTOR inhibitors in ADPKD and conditions with aberrant cholangiocyte proliferation.
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The clinical course of alcoholic cirrhosis, a condition with a high mortality, has not been well described. We examined prevalence, risk, chronology, and mortality associated with three complications of cirrhosis: ascites, variceal bleeding, and hepatic encephalopathy. We followed a population-based cohort of 466 Danish patients diagnosed with alcoholic cirrhosis in 1993-2005, starting from the date of hospital diagnosis and ending in August 2006. Data were extracted from medical charts during the follow-up period. Risk and mortality associated with complications were calculated using competing-risks methods. At diagnosis of alcoholic cirrhosis, 24% of patients had no complications, 55% had ascites alone, 6% had variceal bleeding alone, 4% had ascites and variceal bleeding, and 11% had hepatic encephalopathy. One-year mortality was 17% among patients with no initial complications, 20% following variceal bleeding alone, 29% following ascites alone, 49% following ascites and variceal bleeding (from the onset of the later of the two complications), and 64% following hepatic encephalopathy. Five-year mortality ranged from 58% to 85%. The risk of complications was about 25% after 1 year and 50% after 5 years for all patients without hepatic encephalopathy. The complications under study did not develop in any predictable sequence. Although patients initially without complications usually developed ascites first (12% within 1 year), many developed either variceal bleeding first (6% within 1 year) or hepatic encephalopathy first (4% within 1 year). Subsequent complications occurred in an unpredictable order among patients with ascites or variceal bleeding. ⋯ Patients with alcoholic cirrhosis had a high prevalence of complications at the time of cirrhosis diagnosis. The presence and type of complications at diagnosis were predictors of mortality, but not of the risk of subsequent complications.