Dynamic regulation of hepatic lipid metabolism by torsinA and its activators
Antonio Hernandez-Ono, Yi Peng Zhao, John W. Murray, Cecilia Östlund, Michael J. Lee, Angsi Shi, William T. Dauer, Howard J. Worman, Henry N. Ginsberg, Ji-Yeon Shin
Antonio Hernandez-Ono, Yi Peng Zhao, John W. Murray, Cecilia Östlund, Michael J. Lee, Angsi Shi, William T. Dauer, Howard J. Worman, Henry N. Ginsberg, Ji-Yeon Shin
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Research Article Hepatology Metabolism

Dynamic regulation of hepatic lipid metabolism by torsinA and its activators

Abstract

Depletion of torsinA from hepatocytes leads to reduced liver triglyceride secretion and marked hepatic steatosis. TorsinA is an atypical ATPase that lacks intrinsic activity unless it is bound to its activator, lamina-associated polypeptide 1 (LAP1) or luminal domain–like LAP1 (LULL1). We previously demonstrated that depletion of LAP1 from hepatocytes has more modest effects on liver triglyceride secretion and steatosis development than depletion of torsinA. We now show that depletion of LULL1 alone does not significantly decrease triglyceride secretion or cause steatosis. However, simultaneous depletion of both LAP1 and LULL1 leads to defective triglyceride secretion and marked steatosis similar to that observed with depletion of torsinA. Depletion of both LAP1 and torsinA from hepatocytes generated phenotypes similar to those observed with only torsinA depletion, implying that the 2 proteins act in the same pathway in liver lipid metabolism. Our results demonstrate that torsinA and its activators dynamically regulate hepatic lipid metabolism.

Authors

Antonio Hernandez-Ono, Yi Peng Zhao, John W. Murray, Cecilia Östlund, Michael J. Lee, Angsi Shi, William T. Dauer, Howard J. Worman, Henry N. Ginsberg, Ji-Yeon Shin

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Figure 3

Depletion of LAP1 and LULL1 from hepatocytes leads to liver steatosis similar to that occurring with torsinA depletion.

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Depletion of LAP1 and LULL1 from hepatocytes leads to liver steatosis si...
(A) IB of liver lysates from LUL-flox and LUL-CKO mice administered adenoviral vectors expressing either control scrambled shRNA (Ad-ctrl) or shRNA that targets LAP1 (Ad-Lap1). Lysates from liver of a LULL-flox mouse treated with saline is also included as a control. Abs against LULL1, LAP1, torsinA, and β-actin were used. *Indicates nonspecific bands often detected in whole-liver lysates using polyclonal Abs against LAP1. (B) Relative ratios of band densities of LAP1 (all isoforms) or torsinA versus β-actin in blots as shown in panel A. Band densities were measured from 2 independent IBs using protein extracts from 2 mice per group each. Values are mean ± SEM, with each circle, square, or triangle representing the value from each IB (n = 4). *P < 0.05 by unpaired, 2-tailed Student’s t test. NS, not significant. (C) Representative photographs of livers from LUL-flox and LUL-CKO mice injected with Ad-ctrl or Ad-Lap1. Photograph of a liver from an A-CKO mouse with depletion of torsinA from hepatocytes is shown for comparison. (D) Representative light photomicrographs of liver sections stained with H&E from LUL-flox and LUL-CKO mice administered Ad-Lap1 or Ad-ctrl. Section from an A-CKO mouse is shown for comparison. Scale bars: 50 μm. (E) Representative light photomicrographs of liver sections stained with Oil Red O from LUL-flox and LUL-CKO mice injected with adenoviruses expressing either Ad-ctrl or Ad-Lap1. A section from an A-CKO mouse is shown for comparison. Scale bars: 50 μm. (F) TG content in livers from LUL-flox and LUL-CKO mice administered Ad-ctrl or Ad-Lap1. Mice were fasted for 4–5 hours before isolating livers. Liver TG values from 4 A-CKO mice were included for comparison. Values are mean ± SEM, with each symbol representing the value from an individual mouse (n = 3-4). **P < 0.01; ***P < 0.001; ****P < 0.0001 by 1-way ANOVA followed by Tukey’s post hoc test.