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Dual Roles of Mammalian Target of Rapamycin in Regulating Liver Injury and Tumorigenesis in Autophagy-Defective Mouse Liver.

ABSTRACT: Autophagy is a lysosomal degradation pathway that degrades cytoplasmic proteins and organelles. Absence of autophagy in hepatocytes has been linked to promoting liver injury and tumorigenesis; however, the mechanisms behind why a lack of autophagy induces these complications are not fully understood. The role of mammalian target of rapamycin (mTOR) in impaired autophagy-induced liver pathogenesis and tumorigenesis was investigated by using liver-specific autophagy related 5 knockout (L-ATG5 KO) mice, L-ATG5/mTOR, and L-ATG5/Raptor double knockout (DKO) mice. We found that deletion of mTOR or Raptor in L-ATG5 KO mice at 2 months of age attenuated hepatomegaly, cell death, and inflammation but not fibrosis. Surprisingly, at 6 months of age, L-ATG5/mTOR DKO and L-ATG5/Raptor DKO mice also had increased hepatic inflammation, fibrosis, and liver injury, similar to the L-ATG5 KO mice. Moreover, more than 50% of L-ATG5/mTOR DKO and L-ATG5/Raptor DKO mice already developed spontaneous tumors, but none of the L-ATG5 KO mice had developed any tumors at 6 months of age. At 9 months of age, all L-ATG5/mTOR DKO and L-ATG5/Raptor DKO had developed liver tumors. Mechanistically, L-ATG5/mTOR DKO and L-ATG5/Raptor DKO mice had decreased levels of hepatic ubiquitinated proteins and persistent nuclear erythroid 2 p45-related factor 2 activation but had increased Akt activation compared with L-ATG5 KO mice. Conclusion: Loss of mTOR signaling attenuates the liver pathogenesis in mice with impaired hepatic autophagy but paradoxically promotes tumorigenesis in mice at a relatively young age. Therefore, the balance of mTOR is critical in regulating the liver pathogenesis and tumorigenesis in mice with impaired hepatic autophagy.

SUBMITTER: Ni HM

PROVIDER: S-EPMC6858484 | biostudies-literature | 2019 Dec

REPOSITORIES: biostudies-literature

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Dual Roles of Mammalian Target of Rapamycin in Regulating Liver Injury and Tumorigenesis in Autophagy-Defective Mouse Liver.

Ni Hong-Min HM Chao Xiaojuan X Yang Hua H Deng Fengyan F Wang Shaogui S Bai Qingyun Q Qian Hui H Cui Yue Y Cui Wei W Shi Yinghong Y Zong Wei-Xing WX Wang Zhengtao Z Yang Li L Ding Wen-Xing WX

Hepatology (Baltimore, Md.) 20190624 6

Autophagy is a lysosomal degradation pathway that degrades cytoplasmic proteins and organelles. Absence of autophagy in hepatocytes has been linked to promoting liver injury and tumorigenesis; however, the mechanisms behind why a lack of autophagy induces these complications are not fully understood. The role of mammalian target of rapamycin (mTOR) in impaired autophagy-induced liver pathogenesis and tumorigenesis was investigated by using liver-specific autophagy related 5 knockout (L-ATG5 KO) ...[more]

PMID: 31095752

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Project description: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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Dataset Information

Dual Roles of Mammalian Target of Rapamycin in Regulating Liver Injury and Tumorigenesis in Autophagy-Defective Mouse Liver.

Publications

Dual Roles of Mammalian Target of Rapamycin in Regulating Liver Injury and Tumorigenesis in Autophagy-Defective Mouse Liver.

Similar Datasets

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